Final Report
Mg Science & Technology Workshop - Fundamental Research Issues
Held May 19-20, 2011
Arlington, VA
by
Sean R. Agnew, Organizer
Heinz and Doris Wilsdorf Research Chair and
Associate Professor of Materials Science and Engineering
University of Virginia
395 McCormick Rd
Charlottesville, VA 22904-4745
Ph: 434-924-0605
FAX: 434-982-5660
e-mail: agnew@virginia.edu
in consultation with the Workshop Steering Committee
Eric Nyberg, Pacific Northwest National Lab (Co-Organizer)
Tresa Pollock, UC Santa Barbara
Robert Wagoner, the Ohio State University
Bob Powell, General Motors
Ray Decker, Thixomat, Nanomag LLC
Donald Shih, The Boeing Company
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Executive Summary
Workshop Overview: A 2-day workshop held on May 19 and 20 in Arlington, Virginia brought
together a diverse group of 52 scientists and engineers from academia, government laboratories,
industry, and funding agencies to i) identify the outstanding fundamental science issues which
inhibit broader application of Magnesium (Mg) alloys in structural (including biomedical)
applications and ii) to recommend research directions to address the outstanding issues. Notably,
fellowships to attend the workshop were issued to four graduate students, who are interested in
academic or research-intensive careers, providing them with a unique perspective of a part of the
research process that students rarely see. Two other local graduate students were also able to
attend and participate in all aspects of the workshop. This final report summarizes the
deliberations and recommendations of the participants.
Workshop Commission: The current renaissance in Mg application and R&D was initiated by
interest from the automotive industry, with the primary driver being vehicle mass reduction for
improved vehicle efficiency and performance. Interest has expanded into the consumer goods
sector with a large number of manufacturers selecting to die cast or semi-solid molding of Mg
alloys for the cases of handheld tools and portable electronic goods. Now, the aerospace,
defense, and biomedical sectors are all developing interest in strategies to exploit the lightest
structural metal in the periodic table of elements. However, there are a variety of application
areas which require either better alloy properties or better understanding of how to process
and/or design with Mg alloys before broader application will be possible.
Workshop Agenda: 12 invited speakers presented 11 lectures designed to set the tone for the
smaller group discussions (see Appendix A for a detailed schedule). The invited speakers
represented a broad cross-section of industry, academia and national laboratories from across the
globe. They described recent advances and highlighted remaining gaps in our understanding of
Mg alloys as well as their personal perspectives regarding opportunities for scientific impact,
given new advanced experimental techniques and computational methods. The subsequent
break-out discussion sessions addressed 13 topical areas of research (see Appendix B).
The results of those discussions are synthesized into recommendations in eight sections of this
final report: Casting and Solidification, Alloy Development, Coatings and Corrosion,
Mechanical Performance, Deformation Processing, Joining and Fastening, Flammability and
Aerospace Concerns, and Integrated Computational Materials Engineering (ICME). This
document should help research sponsors and researchers alike to focus future efforts on those
areas that are considered most important and/or appear to have the greatest promise. A short
summary of the recommendations follows on the next page.
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Summary of Recommendations
Mg alloys play an increasingly important role in structural applications, which demand the light
weighting potential of the lowest density structural metal. This is most obvious in the recent,
marked increase in the use of Mg alloy die castings for automotive interior parts and consumer
products. More aggressive application of Mg alloys in situations demanding greater corrosion
resistance, strength, workability, and tolerance for dynamic loading will require active
research and development to overcome outstanding scientific and technical barriers.
The following list highlights the areas in greatest need of fundamental research:
1. The poor corrosion resistance of Mg alloys demands a focus on slowing the kinetics of
dissolution. Improved fundamental understanding of the mechanisms of corrosion will
enable the development of game-changing alloy compositions/surface modifications
designed to promote better surface film properties and/or improved barriers (coatings) at the
interface with the environment. These approaches should be pursued in parallel, in order to
overcome what many view as the critical obstacle to broader application of Mg.
2. There is a need to enhance the mechanical behavior (formability, strength, fatigue, fracture,
creep) relevant to deformation processing and application. The unifying theme is a need to
improve the understanding of the fundamentals of anisotropic plasticity of hexagonal close
packed crystals, including the roles of deformation twinning, shear localization, and the
effects of alloying (solute and precipitates) on various deformation mechanisms. Without this
understanding, alloy and microstructure design efforts will proceed in an empirical, datadriven manner at a pace too slow for incorporation into modern engineering applications.
3. The knowledge base of Mg alloy thermodynamics is developing quickly, yet that pertaining
to kinetics lags. There is a need for more diffusion data and understanding of nonequilibrium phase transformations relevant to solidification, precipitation, and creep.
Models of structure evolution during thermal processing and under service conditions are
poorly developed, due to inadequate knowledge of system kinetics.
4. Finally, because there are more gaps in the fundamental scientific understanding of Mg based
alloys, as compared to more heavily studied ferrous, aluminum, and nickel based alloy
systems, they are considered ripe to benefit from increased computational modeling,
including that relevant to corrosion, deformation mechanisms, alloy and microstructure
design, processing (casting and forming), and performance (failure prediction & mitigation).
Integrated approaches which span this entire spectrum and permit new design paradigms are
viewed as optimal.
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Contents
Executive Summary ...................................................................................................................................... 2
Summary of Recommendations .................................................................................................................... 3
Workshop Recommendations ....................................................................................................................... 5
Introduction ............................................................................................................................................... 5
Invited Presentations ............................................................................................................................. 5
Breakout Discussions ............................................................................................................................ 5
1.
Casting and Solidification ................................................................................................................. 6
2.
Alloy Development ........................................................................................................................... 8
3.
Coatings and Corrosion..................................................................................................................... 9
4.
Mechanical Performance................................................................................................................. 11
Deformation Mechanisms ................................................................................................................... 11
Dynamic Loading................................................................................................................................ 13
Creep ................................................................................................................................................... 13
Fatigue and Fracture ........................................................................................................................... 14
5.
Deformation Processing (including Rolling, Extrusion, and Sheet Forming) ................................ 15
Extrusion ............................................................................................................................................. 16
Plate and Sheet Rolling ....................................................................................................................... 16
Sheet Formability ................................................................................................................................ 17
6.
Joining and Fastening ..................................................................................................................... 18
7.
Flammability and Aerospace Issues ................................................................................................ 20
8.
Integrated Computational Materials Engineering (ICME).............................................................. 21
Acknowledgements ..................................................................................................................................... 23
Appendix A: Workshop Schedule............................................................................................................... 24
Appendix B: Discussion Group Assignments ............................................................................................. 26
Appendix C: List of Participants and E-mails ............................................................................................ 28
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Workshop Recommendations
Introduction
The recommendations expressed in this report are the collective opinions of the workshop
participants. The participants were not required to provide citation or attribution for the work
upon which the opinions are based. Nevertheless, experts in the respective fields were present to
refute unsubstantiated claims or ideas that have limited merit.
Invited Presentations
12 invited speakers presented 11 lectures designed to set the tone for the smaller group
discussions whose deliberations are summarized below. Full *.ppt or *.pdf presentation files
containing their individual recommendations are available on-line via a password protected
website: https://collab.itc.virginia.edu/portal/
1.
2.
Integrated Computational Materials Engineering (ICME) (John Allison, U. of Michigan)
Casting, extrusion, rolling and international collaboration (Karl Kainer, Helmholz Center,
Geestacht, Germany)
3. Alloy design & Applications of modern hi-res probes (J.F. Nie, Monash U., Melbourne,
Australia)
4. Coatings and Corrosion (Guangling Song, GM, and Robert McCune, retired Ford)
5. High strain rate performance (G.T. “Rusty” Gray, Los Alamos National Laboratory)
6. Biomedical applications (Wim Sillekens, TNO, Netherlands)
7. DoD perspective on Mg Applications: Past, Present & Future (Suveen Mathaudhu, Army
Research Office)
8. Formability (Paul Krajewski, General Motors)
9. Crystal plasticity modeling and formability (Surya Kalidindi, Drexel Univeristy)
10. Ab initio modeling (Dallas Trinkle, University of Illinois, Urbana-Champaign)
11. Alloy Design - CALPHAD, texture (Alan Lou, General Motors)
The key quote of the workshop: “Al alloys of incredible strength were developed by Edisonian
trial and error, over the course of 80 years. The science and engineering community will only
permit us 5-10 years to make similar improvements to Mg alloys.” --- J.F. Nie. There was a
consensus that the necessary theoretical, computational, and characterization tools are now
available to make this dream a reality.
Breakout Discussions
Workshop attendees were broken up into a number of discussion groups on Thursday and Friday
afternoons (see Appendix B). The results of those discussions are synthesized in the following
eight sections: Casting and Solidification, Alloy Development, Coatings and Corrosion,
Mechanical Performance, Deformation Processing, Joining and Fastening, Flammability and
Aerospace Concerns, and Integrated Computational Materials Engineering (ICME). The
following sections provide detailed recommendations in each of these eight areas.
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Noteworthy absences in the list of topics are those of which explicitly deal with the price of Mg
or life cycle analysis. It is true that Mg alloys can be expensive relative to competing alloys and
polymers. Thus, their use must be justified in terms of lowered manufacturing cost (e.g. via part
integration), lowered life cycle cost (e.g. lowered fuel consumption of a lighter vehicle), or a
specific performance enhancement. During the workshop planning stages, it was decided that an
explicit focus on these issues was outside the scope of the workshop objectives. For example, it
is clear that political factors (including tariffs and other import controls) have a strong influence
on the price of Mg alloy products, which can positively or negatively affect the prospects for
more widespread application of Mg alloys. However, policy issues are not the immediate
purview of the materials scientists and mechanical engineers who comprised the list of workshop
participants. Two technical areas that have direct cost implications, which were not addressed,
are magnesium extraction and recycling. On the other hand, we did address a number of
technical barriers that have direct implications for the cost of using Mg alloys. For example:

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
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Developing a better ability to predict macro/microstructure which results from the die
casting processes would improve properties and foundry yields. This would enable the
foundries to improve their margins or to lower the price for the end-user.
Exploring low cost methods of primary conversion, e.g. strip casting of Mg alloy sheet is
also fruitful, particularly if it can be partnered with low-cost methods of sheet forming,
such as a lower temperature forming.
Some of the alloy development strategies highlighted below target improving extrusion
rates, which could affect the price of extrusions.
Finally, the entire subjects of coatings, corrosion, fatigue, and fracture all have a strong
impact upon the longer term cost of use.
The details of these, and many other, strategies are more fully described in each of the breakout
discussion summaries below.
1. Casting and Solidification
It was noted that all magnesium products begin as liquid, whether die-cast, wrought, or even
advanced composites and powder metallurgical concepts that have been proposed recently. It
was further noted that the vast majority of current magnesium alloy products are die cast. The
need to understand solidification effects on microstructure and properties, in that case, are
obvious.
It was celebrated that the thermodynamics (free energies, phase diagrams, etc.) of many of the
alloy systems of interest are in reasonable shape and are continuing to develop. Accordingly, we
do not view this as an area of desperate need for increased support, but the present level should
continue, since one may expect the continuing emergence of new alloy systems which will need
further exploration. On the other hand, there are large gaps in our understanding of fundamental
diffusion kinetics in both solids and liquids – more complete diffusion databases are needed and
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new simulation capabilities needed – first principles, cluster variation, and kinetic Monte Carlo
techniques were mentioned. Additionally, we need to develop a better quantitative understanding
of the properties of Mg alloy liquids (viscosity, thermal conductivity, diffusivity, and solution
type, e.g. regular or other, etc.) With these properties in hand, simulations of liquid metal flow as
well as solidification itself, will improve. Details of the nucleation of the solid within the liquid
are still viewed as an area requiring further research. Finally, better models of porosity formation
are needed for many metal systems and Mg alloys are no exception.
More broadly speaking, higher fidelity simulations of the entire casting process are required. For
example, most casting simulations employ Scheil solidification models, which are inadequate to
describe solidification during the typically high rates of cooling employed during most casting
operations. New simulation models to more accurately simulate non-equilibrium cooling
response are required. These models need to provide a means to link solidification paths to the
final microstructure formation (e.g. solute distribution is critical for predicting subsequent age
hardening response). It is also important to consider that as new casting and solidification
processes develop, their needs will put further stress on the fidelity of existing simulation
methodologies.
Producing fine grain microstructures is a goal of many metallurgical processes, and the
properties of magnesium alloys appear to respond particularly favorably to grain size reduction.
For instance, grain size reduction has been shown to improve the creep resistance of some
magnesium alloys, which is unusual. (It is wondered if this result is restricted to alloys based
upon the Mg-Al system.) The tremendous grain refining potential of Zr in Al-free Mg alloys is
well-known. However, research into other inoculation strategies is still viewed as worthy of
research. The potential of adding small (nano-sized) particles to improve the properties of cast
Mg should be further explored. Questions arise concerning the grain refining possibilities
associated with semisolid processing. In fact, there is a need for models for flow of semisolid
material over the range conditions encountered in die casting, thixomolding, etc. Additionally,
the possibility of hybrid cast-wrought processes (such as nanoMAG and twin roll casting) should
not be overlooked. The grain sizes that are produced by these processes can be quite small and
the potential of these processes has not been fully explored.
The potential of twin roll casting has been trumpeted for some years in the Mg community,
based upon laboratory-scale results, but the process appears to be very technologically
challenging during scale-up. Holistic engineering and simulation strategies are needed. The U.S.
research community has played essentially no role in this area, which is dominated by Korean,
Australian, Chinese, German, Turkish, and Canadian companies and research institutes.
Furthermore, it has yet to be demonstrated that the investment costs for such sheet products has a
reasonable return on investment.
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The final area explored within the context of casting and solidification was the development of
Mg-based metal matrix composites. A more rigorous microstructure design framework is
needed: micro- and nano-composites do show promise, but less Edisonian approaches are
needed. What is needed is modeling of in-situ phenomena (solid/liquid interfacial phenomena)
and property prediction before making the composite. Use of new 3D characterization methods,
such as synchrotron facilities to uncover a better understanding of liquid-solid phenomena should
be encouraged. Dispersion control seriously inhibits the potential of many composite processing
strategies, and techniques to prevent agglomeration, ranging from colloid-type approaches to
agitation (ultrasonics) should be evaluated. Lower cost approaches aimed at selective
reinforcement (e.g. for wear resistance) via local compositing should also be explored.
2. Alloy Development
The workshop participants agreed that new Mg alloys are needed which target specific property
combinations, both to address existing limitations of Mg (susceptibility to corrosion), and to
further enhance the advantages of Mg. Currently, there are a very limited number of Mg alloys
commercially available from which design engineers must choose. Furthermore, there was a
consensus that today’s pace of technology is such that non-Edisonian alloy development efforts
need to take place within five-year periods, rather than the 80 years it took to develop the current
suite of ultra-high strength aluminum alloys. Rapidly solidified Mg-Y-Zn alloys with tensile
yield strengths of 600 MPa and elongation ~ 5% already exist. Developing compositions and
processing strategies that make these such property achievements cost-competitive is a real goal.
Mg-Zn is viewed as perhaps the most promising binary system for developing high strength
casting or wrought alloys because of the strong precipitation hardening response in this system.
In addition, this system meets the need for low-cost alloys. To advance this and other promising
alloy systems, principles or rules need to be established for selecting appropriate alloying
additions and including micro-alloying additions; e.g., to further enhance age hardening response
and mechanical properties. Some published work has already illustrated the great potential of
micro-alloying strategies in the Mg-Zn system. There is a balancing point of view, however,
since there are ranges of Zn content which suffer from poor hot cracking and corrosion
resistance. These facts have historically limited the applicability to die casting and they have
limited the application of high strength commercial alloys like ZK60.
Despite the fears surrounding the current high price of rare earth (RE) metals and the nearly solesupplier status of China, it is suggested that Mg-rare earth systems still deserve more research.
Rare earth additions to Mg have proven very potent for improving strength (numerous alloys),
creep resistance (numerous alloys), resistance to flammability (e.g. WE43), and reduction in the
texture strength of wrought products and subsequent improvement in formability. For one thing,
developing alloys which retain these advantages at lower RE content could improve the weight
and price competitiveness of Mg alloys. For another thing, the scientific knowledge which is
developed through the study of RE alloys may be translated into alloy development strategies
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applicable to non-RE-containing systems. As an example, RE-containing AE44 was developed
to enable the production of a lightweight engine cradle for the Corvette. Later, the AX alloys
were developed on the basis that Ca was a low cost alternative to RE which forms similar
precipitate phases.
At the risk of redundancy, it is again observed that the development of thermodynamic databases
has progressed at a good pace in recent years. However, there continues to be a need for more
accurate binary and multi-component phase diagrams. For example, the Mg-Nd binary is
controversial. Perhaps more urgently, there is a great need for diffusivity data for alloy
development. Interfacial energies are also important. This will take a combination of
experimental measurements (e.g., using three dimensional EBSD measurements) and some
calculations. Interfacial energy of precipitates is also needed for developing precipitation
hardenable alloys. More modeling work is needed to support science-based alloy development,
including first-principles calculations, molecular dynamics, monte carlo, phase-field, etc, to
cover major issues on thermodynamics, kinetics, precipitation, crystal plasticity, strengthening,
etc. The lecture by Dallas Trinkle illustrated the potential of first-principles atomistic
calculations within a concurrent multiscale framework for predicting bulk alloy properties.
Finally, while many emphasized the need to develop alloys with high strength (in combination
with various other properties such as corrosion resistance), some participants expressed the view
that not all applications demand high strength. This contingent suggested an equally important
focus should be placed on the development of high formability alloys through enhancements in:
i) work hardening and ii) resistance to damage initiation. Some suggested that damage initiation,
especially at high strain rates, is linked to one of the deformation twinning modes. They suggest
that twinning should be suppressed by alloying or grain size reduction. Evidence that such an
approach will work is still lacking. In fact, some researchers point out the possibility of
enhancing certain types of twinning in ultrafine grained Mg alloys. It would be beneficial if hard
answers to these implied questions could be provided by the scientific community.
3. Coatings and Corrosion
Many view corrosion as THE issue which prevents broader application of Mg alloys. The
intrinsic problem is that elemental Mg is not thermodynamically stable. In fact,
thermodynamically speaking, it is the most active structural metal, and unfortunately, it does not
have a good inherent kinetic barrier to corrosion. What we can do to improve its corrosion
resistance is try to slow down the kinetics of the dissolution reactions by applying a barrier
(coating) at the interface with the environment, adding alloying additions which promote better
surface film properties, or altering the environment (where possible).
The basic corrosion mechanisms for Mg are well established, and the common Mg alloys (AZ91,
AM60, AZ31, etc.) have been extensively studied. However, there still are some phenomena that
cannot be explained. Further studies are urgently required, since these will affect future
developments and applications of Mg alloys. In short, there is still opportunity to develop high
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quality, quantitative corrosion data with correlation to microstructure and processing, even in
commercial alloys. Given the commercial significance of these alloys, such research is valued by
industry. Similarly, there is interest in developing standardized testing schemes that focus on
standard environments, relevant to the applications. For example, existing ASTM standards
often do not reflect the in-service environments encountered. Thus, there is also interest in
developing better qualitative (corrosion damage morphology) and quantitative (corrosion
damage evolution) correlations between laboratory tests and service experience.
The detailed roles of all possible alloying/coating elements are not established and must be.
Further understanding of precise roles of major and minor alloying elements of passivity and on
the details of anodic dissolution must be developed. Further, the role of major and minor alloying
elements, intermetallic compounds, and microstructural heterogeneity on cathodic reactions must
be better understood. The role of species in complex solutions in aiding in passivation, beyond
mere oxides, should be determined. Examples include the possible formation of complex mineral
scales.
Given the priority of improving the corrosion resistance of Mg alloys, all possible strategies
should be pursued including the development of “game changing,” passivated “stainless” alloys,
alloys with more resistant surface "skins,” traditional purification approaches that have proven
successful in improving the corrosion resistance of AZ91C  AZ91D  AZ91E, and coating
strategies based upon metals, oxides, and polymers. Concerning metallic coatings, some feel that
amorphous coatings or surface modification may have a role to play in corrosion protection of
Mg.
In parallel with alloy/coating development and in support of it, the development of a predictive
Mg alloy corrosion modeling capability is viewed as critical. Although thermodynamic modeling
(including first-principles modeling of Pourbaix diagrams) has some potential, due to the
thermodynamic limitations mentioned above, we really need a broader modeling approach
including gathering kinetic data and applying it to modeling. This kind of holistic,
experimentally validated modeling is expensive, requires a team of investigators, and needs a
long-term financial commitment, but the workshop participants view it as important. A roadmap
for this modeling work can likely be gained from the recent corrosion modeling work on
Al alloys (e.g., the work of Rob Kelly and John Scully at UVa, and Farrel Marin at NRL).
Macro-galvanic corrosion due to joining of dissimilar metals is understood and viewed as an
engineering design problem, not requiring deeper mechanistic understanding. Micro-galvanic
coupling between phases within an alloy is a significant issue in Mg alloys that deserves
significant research attention. Further, coatings should be designed to optimize protection against
galvanic corrosion.
Beyond corrosion, other environmental effects, such as stress corrosion cracking and
environmentally affected fatigue cracking should be investigated as these are often life-limiting
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in practical applications in which the uniform and localized corrosion damage accumulation rates
in the absence of stress would be acceptable. There does not appear to be nearly as much
quantitative data available regarding the effect of the environment on the mechanical properties
of Mg alloys, relative to Al alloys, steels, etc. Along these lines, alloying and surface treatment
designed to minimize hydriding and ways of suppressing/poisoning the hydrogen evolution
reaction should be explored.
A final issue related to the corrosion resistance of magnesium alloys is the possible application
of bioabsorbable stents and orthopedic implants. In this case, the controlled, but reasonably
rapid, corrosion of the implant is actually the goal. There are many issues to be addressed,
including processing strategies, drug coatings, and possible unintended health effects of locally
high Mg concentrations. Significant research in this area is being done in Europe, with new
programs being proposed in Canada, and limited research on-going within U.S. institutions.
4. Mechanical Performance
Deformation Mechanisms
A great deal about the deformation mechanisms of magnesium and its alloys has been learned in
the past decade. The basic roles of dislocation-based mechanisms of plasticity, including basal
and non-basal slip of <a> type dislocations, and the significance of <c+a> non-basal dislocations
are established. The basic role of mechanical twinning is understood as well, including {10.2}
“extension” twinning, {10.1} “contraction” twinning and {10.1}-{10.2} double-twinning. EBSD
has proven very effective in answering many of the previously unanswered questions. The plastic
anisotropies (and asymmetries) that result from the operation of these mechanisms are basically
understood and can be accounted for by existing crystal plasticity modeling approaches. The
same can be said about the effect of crystallographic texture on macroscopic deformation. There
are some inconsistencies in the literature, but consensus appears to be emerging on many of these
aspects.
That said, there are many basic phenomena which require much more careful consideration of
the various individual deformation mechanisms and of the crystallographic texture than is
required for traditional cubic metals. For example, there currently is no widely accepted rule for
grain size strengthening of Mg alloys, which can accurately account for all these factors, let
alone the effect of grain size distribution. It is suggested by some that only crystal plasticity
based approaches will suffice to accurately capture these details relevant to materials design,
although this approach may not immediately solve the problems of component and process
design. There are many other outstanding questions for which only vague answers exist today.
There has been a great deal of confusion about the basal stacking fault energy. Experimental
estimates published in the literature vary tremendously. Some very long stacking faults have
been observed, but recent experiments reveal solute segregated at such faults. (In fact, some
argue these are precipitates.) If there is no solute, then the faults tend to be very short. The
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interrelation between chemistry and stacking fault energy should be clarified. Atomistic
modeling may be helpful in such cases. Atomistic modeling is also demonstrating promise in the
area of mechanical twinning. However, we still have a very incomplete understanding of the
nucleation of twins. The effects of twinning are challenging to implement in continuum models,
which are important for forming prediction. Existing continuum models are highly suspect.
It is generally observed that our understanding of the strain hardening behavior of Mg alloys is
much less developed that that for fcc metals, for example. What are the interactions between
various dislocation and twin types? Additionally, the effect of strain path changes on strain
hardening behavior is much stronger than that in cubic metals, and must be accounted for in
order to develop robust constitutive models. The effect of temperature (and strain rate) on the
strength and activity of various deformation mechanisms has been heavily studied and a number
of issues have become clear. The main twinning mode, {10.2} extension twinning, appears to be
essentially athermal, while the {10.1} mode is thermally activated. Atomistic modeling has
helped to explain distinctions like this, and the details of the twinning dislocation structure are
becoming clearer.
Alloy designers, in particular, want to know the quantitative effects of alloy solute and
precipitates on the individual deformation mechanisms. In this context, there is a need for control
and characterization of tramp impurities. Commercially available material is not of very high
purity. The role of Zr, for example, is not clear. Atomistic modeling is beginning to augment
single crystal experiments in the area of solute effects on dislocation mobilities and stacking fault
energies. There are good ideas about the relative impacts of particles: size, shape, and orientation
on yield strength and various deformation mechanisms, but these are not well-tested and our
ability to predict microstructure effects on strain hardening behavior are still at a relatively
nascent state. Finally, there is great interest in better understanding the mechanism(s) of shear
localization, which impacts plastic anisotropy, fracture during quasistatic and dynamic loading,
and dynamic recrystallization during hot deformation processing. Our basic ability to predict
shear banding in Mg is rudimentary.
Some researchers have proposed explanations for the poor multi-axial ductility, fracture
toughness, and resistance to shear instability based upon mechanical twinning. Images of shear
bands, cracking, and cavitation associated with twins have caused scientists to suggest that
minimizing the occurrence of mechanical twinning would promote improved formability and
improved dynamic loading response. However, hard evidence that this strategy would work is
lacking. Current strategies for minimizing twinning are limited to grain size refinement. Even
that notion has been challenged by some recent observations of twinning in a nano-grained MgTi alloy. Our knowledge of the impact of solutes on mechanical twinning is limited. There have
been some investigations of the effects of various precipitates on twinning, but this area is still
considered open to investigation. The notion that twinning is detrimental to ductility must be
tempered by the knowledge that pure Ti is ductile despite prolific twinning and Ti-alloys in
which twinning is suppressed have much poorer ductility. Further, one study of the Mg-Cd solid
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solution alloys revealed that the ductility plummeted in the alloy in which the c/a ratio caused the
{10.2} twinning mode to switch from an “extension” to a “contraction” twin, i.e. at that
condition extension twinning did not occur.
There are various new characterization methods that have been successfully brought to bear on
the problem of deformation mechanisms and these ought to be further exploited. These include,
but are not limited to: neutron diffraction, 3D synchotron methods, nanoindentation, micro-pillar
compression, X-ray tomography, high angle annular dark field imaging in the TEM. There is a
need for mesoscale characterization, including grain size, grain orientation and grain boundary
character distribution effects on mechanical response and on corrosion resistance. There also
opportunities for efficient, statistical quantification of the details of the microstructure using a
more rigorous framework such as the n-point statistics, since this approach has not been applied
to Mg alloys. There was a discussion of FIB damage. Mg is easily damaged by Ga. This is a
problem in preparing micro-compression samples, TEM specimens, and atom probe specimens.
Dynamic Loading
Mg alloys generally exhibit poor dynamic loading response. As suggested above, they have
lower resistance to shear instability than many competing Al alloys and steels. Fundamental
explanations and possible solutions must be sought. An explanation rooted in texture-based
plastic anisotropy has been offered, however, this is countered by the fact that even randomly
textured die castings suffer from this problem. There is still the possibility of a texture-softening
effect during shear localization; this should be further explored. The poor resistance to shear
instability may be connected with a low strain hardening rate, beyond an initial period of high
strain hardening. Strategies to improve the strain hardening response should be explored.
Similarly, higher strain rate hardening behavior is cited as beneficial. Finally, it would be very
useful if there were models which could explain the relationships between strength/ductility and
energy absorption/fragmentation.
Creep
Clarity has emerged in the area of creep deformation under service conditions, whereas there
were significant inconsistencies in the recent past. For example, the role of grain boundary
sliding has been disputed. Recent work has suggested that creep is dislocation accommodated in
most of the alloys and stress/temperature regimes of interest for application. Emphasis has now
been placed upon alloy systems which offer significant solid solution strengthening or stable
precipitation strengthening, the two major avenues employed to achieve creep resistance in other
alloy systems. Nevertheless, there is continued interest in understanding the role of grain
boundary sliding type deformation at low temperatures and during high temperature forming. A
few years ago, creep and bolt-load retention were the principal mechanical properties of interest,
as researchers sought to develop new alloys for automotive powertrain applications. The
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successes achieved with the Mg-Al-RE and Mg-Al-Sr alloys within the engine cradle and engine
block applications have demonstrated the feasibility of Mg alloys for powertrain applications.
Fatigue and Fracture
Discussion revealed that the understanding of Mg fatigue and fracture behavior is more nascent
than our basic understanding of plastic anisotropy of textured alloys and creep behavior, for
instance. The existing studies have been largely empirical and the models phenomenological,
rather than mechanism based. Connections between microstructure and fatigue properties are not
clear. One thing that is clear is that Mg alloys exhibit a very strong Bauschinger effect, at least
part of which is due to the intrinsic plastic anisotropy of Mg single crystals and a phenomenon
known as twinning-detwinning. The significance of the latter effect on the fatigue properties is
only vaguely understood.
The state-of-the-art fatigue models are empirical and are not Mg-alloy specific, which does not
provide sufficient information for modeling a broad class of cast and wrought Mg alloy
developments. Cyclic plasticity modeling of pure HCP Mg and Mg alloys and understanding the
interaction between the slip and twin during unloading should be viewed as a priority. Recent
work on deformation and role of microstructure and texture, both experimental and modeling,
needs to be extended to cyclic behavior and fatigue crack propagation. In order to achieve this
goal, we would need to develop a physics-based understanding of the mechanisms of fatigue
damage formation and small-crack growth. Toward this end, 3D microstructure data bases are
needed for the modeling of fatigue in magnesium alloys. Such data bases have been developed
for aluminum alloys of interest to the aerospace industry. Emerging physics based models for
fatigue and fracture, based on 3D microstructure datasets are ready to be developed and applied
for Mg-alloys. The computational, analytical, and characterization tools required to advance our
understanding of Mg fatigue mechanisms and modeling are available. Applying such tools to
Mg will in-turn contribute to improved Mg alloy design and optimization. In short, if we could
develop sound, physics-based models for cyclic deformation, damage development and small
crack propagation, more rapid alloy design and materials insertion into commercial applications
would become a reality.
There is a similar need to educate the Mg research community regarding fracture mechanics and
failure models/modes. While our collective knowledge of Mg fracture behavior is relatively
limited, we do understand that Mg alloys do not fail by cleavage, despite the fact that many
authors frequently misapply that term in their fractographic analyses. Things as basic as the
impact of triaxiality, given the strong anisotropy, appear to be open questions. Some materials
are more sensitive to imposed hydrostatic pressures than others. This ought to be further
explored for Mg alloys. Quantitative understanding and modeling of the nucleation of cracks is
needed. For example, are Gurson-type models applicable? Do they need to be modified to
account for the greater tendency to localize? There have been very few systematic studies of
14
environmental effects, such as the possibility of hydrogen embrittlement, stress corrosion
cracking (which may become a bigger concern if higher strength alloys are developed), and
environmentally enhanced fatigue.
5. Deformation Processing (including Rolling, Extrusion, and Sheet Forming)
There is a need to develop improved constitutive laws (e.g., yield surface models) that take into
account the effects of temperature, strain rate, and the various deformation mechanisms. These
new constitutive laws are necessary for the construction of accurate models of deformation
processes. Issues of anisotropy and tension/compression asymmetry and how to model them,
reduce them, or take advantage of them were all discussed. In fact, there is significant overlap in
the needs for Deformation Processing and those of the Alloy Development and Mechanical
Performance; see these previous sections. It is emphasized that there is a difference between
fundamental understanding of the deformation mechanism behavior and a constitutive model that
can be employed for predicting the forming behavior or performance of an actual component.
While the fundamental understanding of deformation mechanisms has been developing through
the use of crystal plasticity modeling, the need remains for constitutive models which are
relevant to engineering problems. Combined methods have been developed in other alloy classes,
and these should be further explored for Mg alloys.
There is a need to better understand the interactions between the deformed state and that which
evolves during recovery/recrystallization. Such issues have been heavily studied, in ferrous and
aluminum alloys, but much less detail is available for Mg alloys. There is significant interest in
developing a more quantitative understanding of dynamic recrystallization in Mg alloys, as this
process may be the key to sustaining the large strains imparted during hot deformation processes,
such as hot rolling and extraction. An improved general understanding of microstructure
evolution during hot, and warm, deformation and its relation to recrystallization and grain
growth is needed for the principal Mg alloy types. The purpose of this understanding is to apply
it to the control of product microstructure, e.g., control the recrystallized grain size. The effects
of Zr and rare-earth elements, particularly, must be understood. The need to understand the “rare
earth effect” was noted specifically and emphatically, as well as our collective ignorance as to
the specific mechanisms behind this effect. Other schemes of microstructure control based upon
Hornbogen’s concept of “combined reactions,” e.g. recrystallization and phase transformation
seem worthy of exploration.
Before moving on to the details individual deformation processing methods, it is mentioned that
almost all metal forming processes, involve significant “friction.” The metal has a surface
morphology and chemistry, which is distinct from the bulk, and interfacial mediation is applied
in the form of liquids, solid particulate, films, etc. The tool/workpiece interface evolves (and
hence can be described with suitable state variables) just like the bulk. It is suggested that we
have put so much emphasis on modeling the bulk material, that when it comes time to actually
simulate a forming process, it is absurd to appeal to an eighteenth century “Law” and use a single
15
"friction coefficient." New research should be conducted to develop "interfacial constitutive
models." This recommendation applies far beyond the present scope of Mg alloy processing, but
is certainly relevant since the frictional behavior of Mg appears to be largely unknown,
particularly at forming temperatures and conditions.
Extrusion
Extrusion offers the potential to be a high volume source of wrought magnesium products. The
hydrostatic state of stress and elevated temperature present in deformation zone during extrusion
allows achieving much higher strain than in many other technological processes. However, they
have historically been plagued by low production rates due to limited workability and problems
of hot-shortness (depending upon the alloy.) In any event the process window for Mg alloys
tends to be smaller than for Al alloys. There is a need for better understanding of the required
degree of homogenization of billet material. This is usually achieved by deformation processing.
There is continued interest in developing alloys, which can be extruded at higher speeds, but
have the desired physical properties in the finished product. Some felt that the Mg-Zn-RE alloy
systems merit further investigation. Additionally, it was mentioned that the RE effect on texture
was not fully understood, though there has been significant progress over the past five years. On
the finished product side, there are problems associated with non-uniform grain size and textureinduced anisotropy.
Plate and Sheet Rolling
Final product should be fine grained, isotropic, and possess microstructural stability necessary
for warm forming. There is also interest in developing age hardenable sheets, since the present
mass-produced sheet alloy, AZ31, does not respond to heat treatment. Higher strength, heat
treatable Mg alloy sheets would open up new application opportunities and are already under
development by both US and Korean producers. The “Achilles heel” of many of the sheet/plate
alloys applications, relative to die cast alloys, is corrosion. While the base corrosion rate of AZ31
is not significantly higher than AZ91D, thin sheets are much more sensitive to localized
(particularly galvanic) corrosion than presently used die-castings, which are thick and most
frequently employed in dry or oily environments.
There is interest in developing alternative rolling processes, such as asymmetric and high speed
rolling, both of which have demonstrated potential in preliminary trials. In a more conventional
sense, there is interest in comparisons of microstructures and sheet properties developed on
reversing coil mills vs. unidirectional (e.g. tandem) rolling mills. As has been mentioned in many
of the discussions above, there is a sense that fine grained materials may be part of the answer. In
this regard, Mg grain refinement in casting, such as that provided by twin-roll casting (TRC)
possibly combined with severe shear is of interest. An extreme angle endorsed by some
participants was the exploration of rapidly solidified, powder metallurgical routes.
16
Sheet Formability
Because of very limited cold formability, Mg alloys have not historically been used in sheet form
to produce components with complex shapes. The hot formability of Mg alloys, however, can be
outstanding, e.g., superplastic. This excellent hot formability is often attributed to the fine grain
structure (relative to many Al alloys and steels) that can be readily developed during
conventional wrought magnesium production. Plate applications are, for all practical purposes,
presently limited to photo-engraving plate, which benefits from ease of machining and etching
and tooling applications which benefit from stiffness combined with low inertia. There is current
military interest in broadening the applications of plate, but concerns do exist regarding the
mechanical properties at high strain rates.
There was a sense that novel hot- and warm-forming processes (non-isothermal, press quench,
etc.), which overcome the difficulties of current technologies or take advantage of particular
opportunities specific to Mg alloys, should be explored. There is interest in leveraging the
significant current research into alloy and process development, as well as constitutive modeling
relevant to warm and hot forming. A specific need to develop new and innovative “joining”
processes, such as warm hemming, that take advantage of local heating was recognized. Friction
and tribological issues influence all sorts of sheet forming operations, but there is very little
knowledge of these phenomena with respect to Mg alloy sheet materials. The success of future
forming technologies for Mg alloys will rely upon improved understanding of tribological
interactions as a function of alloy, surface condition, temperature and surface deformation (strain
rate of surface deformation, surface morphology changes, oxide breakage/formation, etc.)
A clearer answer regarding the optimal grain size for forming of various alloys needs to be
provided. Many researchers are suggesting that a finer grain size may produce better forming
behaviors (e.g., down to 1 or 2 um), but others suggest that a larger grain size can promote higher
greater strain hardening to delay plastic instability. Additionally, questions concerning failure
mechanisms abound. What are the failure initiation sites (are they inclusions, twins, shear bands,
etc.?) Does void nucleation and growth or necking control ultimate failure during sheet forming?
Is there a relationship between alloy content and the role of grain boundary sliding? As
mentioned in the deformation processing section, there is a great need to develop our
understanding of recrystallization, both static and dynamic. There is a need to better understand
how to appropriately suppress or enhance recrystallization for different applications. Finally, an
alloy which can be formed and subsequently aged to increase strength is viewed as desirable;
perhaps a press-quenching process and an applicable alloy should be developed in parallel. The
group feels that answers to these and many other questions about optimal microstructure and
alloying may be specific to the target forming temperature and strain rate conditions. Hence, this
section is divided into three sections: high temperature (frequently superplastic), warm, and room
temperature.
High-temperature forming: Microstructure evolution during hot forming is still poorly
understood. It has not been adequately quantified or modeled, for the purpose of prediction. The
optimal alloy composition for hot forming is not known. It is known that texture plays a primary
role in determining the behavior at low homologous temperatures. However, it is not known
what role texture plays during hot deformation.
17
Warm Forming (< 250ºC): The basics physics of warm deformation in Mg alloys is not well
understood. For example, solute-drag creep in Mg is not understood, but solute-drag creep is
recognized as critical for developing warm formability in Al alloys. The idea of press quenching
merits further exploration. Multi-physics modeling to enable exploration of novel non-isothermal
conditions is viewed as essential. For example, if one were to develop a press-quench process,
questions arise concerning the relevant constitutive model to use when the temperature range in
the material could span hundreds of degrees Kelvin. Understanding tribological effects and
determination of the optimal lubricants for forming in this temperature regime are needed.
Room-temperature forming: All of the aforementioned issues relating to grain size, texture,
etc. are pertinent here. A form-anneal-form, multi-step process may be a viable solution to
forming somewhat complex shapes. However, limitations of such an approach, such as
production speed, must be explored. It is emphasized that determining the stress exponent
describing the hardening rate during uniaxial tension testing is not a standalone answer to the
question of multiaxial formability. Multiaxial experiments and modeling are required, and this is
also true for warm- and hot-forming applications. There is strong evidence that the “RE effect”
can improve low-temperature formability. A better understanding of this effect is required. Can it
be induced by alloying with other elements? Spring back is anticipated to be complicated in a
magnesium alloy which can be formed at low temperatures, due to the low modulus and
relatively high strength these alloys exhibit, in combination with the effects of twinning.
6. Joining and Fastening
The overall conclusion of this group is that joining and fastening should not be an afterthought.
Rather, consideration of possible options and complications should be a part of initial material
selection, manufacturing, and part design strategies. There are a variety of joining processes and
options, including mechanical fastening that can be potentially applied to join Mg alloys. Multimaterial solutions have great promise from a mechanical design perspective. However, in
addition to concerns over galvanic corrosion, mentioned earlier, there are also significant
challenges associated with joining Mg to other metals and/or polymer composites in a cost
effective manner. The cost penalty associated with joining potentially challenging material
combinations needs to be considered up front. Joint efficiency (i.e. the ratio of joint strength to
the base-metal strength) also needs to be considered, as it can exceed 100% or be significantly
lowered by a variety of metallurgical effects discussed below.
Fusion welding processes, such as gas metal arc welding (GMAW), resistance spot welding
(RSW), and laser welding are attractive because of all the existing industrial knowhow and
infrastructure. However, Mg weld quality can be poor. GMAW is a widely used mass production
process for Al alloys, steels and stainless steels. It could also be widely useful for Mg alloys if
the following fundamental issues can be solved: (1) spattering caused by high Mg vapor
pressure, (2) gas porosity caused mainly by hydrogen dissolved into the weld pool, and (3)
cracking caused by liquation (liquid formation and hence weakening along grain boundaries),
which can occur easily because of the very low eutectic temperature (e.g., ~435 oC) of many Mg
alloys. Liquation cracking has been reported in fusion welding, resistance spot welding and even
18
friction stir welding of Mg alloys. High vapor pressure, hydrogen porosity and liquation are
problems that potentially can be solved by welding metallurgy approaches.
Dissimilar material joining between Mg alloys and other metals or polymer composites presents
the greatest challenge. Solid state/cold processes such as friction stir welding (FSW), ultrasonic
welding (UW), friction bit joining (FBJ), self-piecing riveting (SPR) are attractive, but require
considerable research and development before they can be applied by the industry. For example,
friction stir welding is not presently widely practiced in the automotive industry and it is difficult
for certain applications. Most Mg alloys do not have sufficient high-strain rate ductility at
ambient temperature required for SPR. Adhesive bonding does not appear to have been
significantly investigated, but does have interest for multi-material joining where it may provide
some electrical isolation to protect against galvanic corrosion.
There is also interest in developing hybrid solutions such as weld bonding and friction bit
joining. There are questions regarding the compatibility of FSW with adhesives in weld bonding,
and friction bit joining is only in its infancy of research and development. Different processes
have different advantages and disadvantages depending on the application and materials. The
optimal joining process for large-scale application of Mg is unknown. Current applications rely
exclusively on mechanical fastening (bolting) coupled with galvanic isolation techniques.
Science-based, systematic development and fundamental understanding of materials behavior
before/during/after joining is critically needed to evaluate the other options. Although research
publications on Mg joining have increased sharply recently, the main focus has been on the
evaluation of various joining processes on Mg alloys. Much less has been done to understand and
overcome the fundamental metallurgical issues. A widely useful process for joining Mg alloys is
still not available, and this will hinder more widespread use of Mg alloys.
The effect of heat/deformation from joining processes on defects, microstructure evolution far
from equilibrium, and related degradation of weld properties relative to base metal properties
need to be determined. The sensitivity of the weld performance to base metal and weld
crystallographic texture must be determined. There are indications that the strong texture
developed during friction stir welding could render the weld vulnerable to shear loads. Finally,
the interest in novel alloys, such as those containing rare earth elements raises questions
regarding the effect these additions may have on alloy weldability and weld performance.
Finally, there are not established protocols for inspection of Mg weld quality.
In the spirit of Integrated Computational Materials Science (other ICME topics are detailed
below), it is suggested that advanced computer aided engineering (CAE) model tools must be
developed and matured to accelerate the use of Mg alloys for automobile light-weighting. Such
modeling tools are essential for body structure performance prediction (durability,
crashworthiness, and rigidity), and body structure assembly dimensional tolerance control. These
modeling tools must be able to capture the microstructure changes and inhomogeneity in the
19
joints caused by different joining processes. Linking the desired joint properties with the
underlying microstructure features by integration of joining process models with the structure
performance CAE models would allow for intelligent design and optimization of the joint and
joining processes for light-weighting, performance and cost-effectiveness. It is recommended
that ICME needs to include material joining as an essential manufacturing technology in its
future development.
7. Flammability and Aerospace Issues
The drive for light weighting is even greater in aerospace than in automotive. Fuel accounts for
35-40% of the cost in aerospace applications. A 20% weight reduction saves 10% fuel. A 30%
weight reduction would save 10% of the entire operating cost. Aircraft manufacturers currently
employ Mg castings in helicopter transmission housings, jet engine auxiliary gearboxes, thrust
reversers, and a number of cockpit and cabin door fittings. However, other applications are
currently under consideration, including fuselage interior, particularly seat applications, which
have been considered banned by the FAA under Paragraph 3.3.3 of SAE Standard AS8049. At
this point, Mg alloys meet Federal Aviation Regulations (FAR) requirements as well as Joint
Aviation Authorities Europe Regulations (JAR). There has been NO known case of aircraft or
helicopter accident due to Mg ignition. Nevertheless, flammability is clearly a general concern
for all of the payload materials and structures, e.g. polymers, composites, Al, and (potentially)
Mg alloys.
Recent full-scale flammability tests of aircraft seat structures (leg assemblies, cross tubes,
spreaders, seat back frames and baggage bars) by the FAA Technical Center reveal that Mg alloy
WE43 performs better than Mg alloy AZ31, but even the latter performs similarly to Al alloy
2024. Other recently introduced Mg-based materials, such as the Korean ECO-Mg (which
contains CaO), also appear to have good flammability resistance. Outstanding gaps are
quantitative explanations for alloy chemistry effects on flammability resistance, including rare
earth element and CaO effects. Standardized seat frame testing methodologies for the FAA to
use in the qualification of materials are being developed. A report describing a new test method
will be submitted by the FAA project researchers to the Transport Airplane Directorate by March
2012. The review process will take several months, but it is conceivable that a path to
certification of magnesium in aircraft seats could be available by the middle of 2012.
The aerospace industry is also interested in formable wrought products (sheet and extrusion)
which could compete with current Al alloys in an effort to reduce weight. A goal of any such
alloy design strategy must be to remain cost competitive. Due to currently escalating costs of rare
earths (RE) from China, minimizing RE alloying elements could be an important approach for
future applications. Of course, the interplay with the new RE mining undertakings in the U.S.,
Malaysia and the newly discovered undersea RE resources near Hawaii has the potential to
stabilize RE pricing at lower levels than today. Moreover, there may be applications where the
20
improvement in creep strength, texture modification, and increased flammability resistance
would merit the increased cost associated with rare earth alloying.
8. Integrated Computational Materials Engineering (ICME)
Many of the individual topics above mentioned the need for a more developed modeling
capability. The following recommendations reiterate some of those, but also include the implicit
recommendation that an integrated approach, which has come to be known as ICME is
meritorious. The ICME approach, as described in a recent National Research Council document
has a number of ingredients which distinguish it, for example, from a stand-alone structureproperty modeling effort. The approach seeks to promote competitiveness through the rapid
insertion of materials innovations into industrial product design. Because there is not a great deal
of experience-based empirical knowledge in industry, Mg is viewed as ripe to benefit from an
ICME-based approach.
The ICME paradigm involves integration of “materials information” – whether digital data or
computational models – into product performance analysis and manufacturing process simulation
tools with the goal of promoting more rapid conversion of science-based information into viable
engineering tools. Product design, process optimization, and material selection all need to be
more closely married in order to develop the optimal product. It is generally recognized that the
success of the ICME approach will required coordinated and sustained funding.
While the ICME approach offers a compelling framework, its application still requires a great
deal of development work. Isolated researchers (in both academia and industry) will not quickly
address these issues. Some feel that advancing the ICME approach will require focused, small
team efforts targeting individual tough problems. Enlightened leadership will be required at the
research team level as well as from the funding agencies. There are a number of successful
demonstrations of modeling a property (in the spirit of the ICME approach) available in the
literature. The development of a more comprehensive ICME capability would offer an important
outlet and end use for the scientific understanding developed in traditional fundamental projects.
In addition to the uses of ICME tools for engineering and alloy design, there are important
scientific synergies to be gained by integrating fundamental research projects into an ICME
framework.
A high-risk, high-payoff goal would be to develop an integrated composition-processingmicrostructure-property modeling approach that would enable alloy optimization for a range of
properties, within the next 5-10 years. If we could develop sound, physics-based models for the
various properties of interest, more rapid alloy design and materials insertion into commercial
applications would become a reality. The potential of Mg alloys to contribute substantially to the
light weighting of a variety of transportation systems is great. However, the present knowledge
base in the target application industries is limited. Providing them with ICME tools would
greatly reduce reluctance on the part of design engineers to employ “unknown” solutions.
21
The development of an ICME framework and capability for magnesium alloys would provide a
means to conduct computationally the quantitative tradeoffs (between processing routes, alloying
additions and properties) required to accelerate alloy design for complex engineering
applications. In the context of an NSF program on Mg that explicitly includes ICME, there was
discussion that novel funding mechanisms would be required to ensure that integration of the
efforts of multiple PIs is accomplished. This could take the form of a call for one or more
Focused Research Groups or proposals that explicitly linked PIs to efforts within industrial firms
developing ICME capabilities (i.e. ICME GOALI proposals).
As the workshop proceeded, it became clear that many of the participants were not aware of
what ICME meant as the acronym was frequently used as a placeholder for computational
modeling. In fact, there was significant discussion over the terms “multi-scale” and “multitemporal” modeling and some dispute over whether it was appropriate to use these terms as
synonymous with ICME. Despite individual opinions, there was agreement that the following
modeling needs and approaches merit further investigation.
More predictive capability for precipitation in Mg systems: For example, ab initio combined
with phase field has been demonstrated as useful in modeling the processing of Al alloys and
should be applied to Mg-based systems. However, there were cautionary notes expressed about
the ability of the models to predict certain important quantities and one should expect to have to
measure certain aspects and impose them on the meso-scale models. One example concerns
atomistic models, we do not have a single Mg embedded atom method (EAM) potential that is
accepted by the community for predicting the structure and kinetics of both dislocations and
twinning.
Thermomechanical process (TMP) modeling: There is plenty of evidence that microstructure
(including texture, microtexture) is critical such that controlling it requires modeling of
thermomechanical processing (TMP). We need to understand how the various deformation
mechanisms compete and especially how recrystallization nucleates and grows; again nucleation
of damage (voiding, cracking) will probably have to be imposed on the models. We need to
model both the processing and the deformation involved in properties such as fatigue. Such
modeling may well have to include multiple scales such as continuum mechanics and dislocation
dynamics. Particles affect many of these processes (e.g. recrystallization). Even before one can
start a TMP model, one needs to model the solidification process so that, for example, one can
quantify segregation of solutes. Obviously, these issues were mentioned in great detail earlier in
the report. However, repetition should serve to emphasize their importance. In the context of
development of an ICME capability for Mg, an important element of such developments is
ensuring that the individual research activities are sufficient to provide a continuous stream of
information in the form of constitutive and microstructural evolution models going from casting
through wrought processing and heat treating and leading to models for predicting properties.
22
Experimental Validation: Validation of modeling is,an important issue. Some aspects of this
are currently accessible. Some, however, require 3D characterization, such as synchrotron-based
methods, e.g. for solidification models or for plastic deformation models. Also, there are only
some aspects of microstructure that we know how to quantify (e.g. grain size) and plenty that we
do not have robust tools for (e.g. grain shape). The ICME paradigm admits that models with
sufficient fidelity do not exist to describe all the phenomena that must be described for complete
process modeling. Therefore, implementation of an ICME capability requires state-of-the-art
experimental capabilities to fill outstanding gaps with empirical relationships as well as
providing validation of existing models.
Acknowledgements
The organizers would like to thank the NSF Grant #1121133, with primary support from the
Division of Civil, Mechanical, and Manufacturing Innovation (CMMI); Materials and Surface
Engineering (MSE) Program; Clark Cooper, Program Manager; and the Division of Materials
Research (DMR); Metals and Metallic Nanostructures (MMN); Alan Ardell, Program Manager,
for sponsoring this event, the participants (listed in Appendix C) for their active engagement, and
the steering committee for fielding an unending list of questions. We would specifically like to
thank the many participants and committee members who read and re-read the proposal and this
report during the editing phase.
23
Appendix A: Workshop Schedule
May 19, 2011
Holiday Inn Arlington-Ballston, Arlington, VA
7:45 – 8:15
Ballston Room - Gathering and registration, light breakfast
8:15 – 8:30



Short Opening Remarks
Sean Agnew (Overview, Schedule)
Clark Cooper (NSF perspective)
Will Joost (DOE perspective)
8:30-12:15
State of the Art in Mg Alloy Science and Technology
8:30
9:20
ICME (John Allison, U Mich)
Casting, extrusion, rolling and international collaboration (Karl Kainer,
Helmholz Center, Geestacht, Germany)
10:10
Coffee Break
10:20
Alloy design & Applications of modern hi-res probes (J.F. Nie, Monash U,
Melbourne, Australia)
Coatings and Corrosion (McCune, retired Ford and Song , GM)
11:10
12:15 – 13:30
Lunch break
13:30 – 15:10
State of the Art in Mg Alloy Science and Technology
13:30
14:20
High strain rate performance (G.T. “Rusty” Gray, LANL)
Biomedical applications (Wim Sillekens, TNO, Netherlands)
15:15
Coffee Break
15:30 – 18:00
17:30
19:00 – 20:30

Breakout Session 1: commission (Eric Nyberg)
Breakout 1 group reports
Dinner and Stakeholder presentation, Arlington-Clarendon Room
Suveen Mathaudhu (Army Research Office, DoD perspective)
24
May 20, 2011 – Holiday Inn Arlington-Ballston, Arlington, VA
8:00 – 8:30
Ballston Room, Gathering and registration, light breakfast
8:30 - 12:00
Focus Topics in Mg Alloys
8:30
9:20
Formability (Paul Krajewski, GM)
Crystal plasticity modeling and formability (Surya Kalidindi, Drexel)
10:10
Coffee Break
10:20
11:10
Ab initio modeling (Dallas Trinkle, UIUC)
Alloy Design - CALPHAD, texture (Alan Lou, GM)
12:00 – 13:15
Lunch
13:15 – 15:00
Breakout session 2: commission (Eric Nyberg)
14:45
Breakout 2 reports
15:15
Participant Coffee Break
(Steering committee to quickly meet to discuss wrap-up)
15:30 – 16:00
Closing remarks
16:00
Adjourn
25
Appendix B: Discussion Group Assignments
Thursday
1. Integrated Computational Materials Engineering 1 (ICME1) (6)
a. Leader – Tony Rollett
b. Secretary – Dongwon Shin
c. Participants –Ibrahim Karaman, Dallas Trinkle, Surya Kalidindi
2. Characterization (8)
a. Leader – J.F. Nie
b. Secretary – Greg Rohrer
c. Participants – Jim Fitz-Gerald, Yong-ho Sohn, Bin Li, Donald Stone, Cindy Byer,
Benjamin Anglin
3. High stain rate deformation (8)
a. Leader – K.T. Ramesh
b. Secretary – Suveen Mathaudhu
c. Participants – Will Joost, Jian Wang, Bob McCune, Rusty Gray, Paul Krajewski,
Neha Dixit
4. Fatigue and fracture (8)
a. Leader – Wayne Jones
b. Secretary – Anna Xue
c. Participants – John Allison, Mark Weaver, Somnath Ghosh, Rupalee Mulay,
Donald Shih, Dean Paxton
5. Casting (8)
a. Leader - Tresa Pollock
b. Secretary – Mike Dierks
c. Participants – Karl Kainer, Anand Raghunathan, Eric Nyberg, Zhili Feng, Alan
Luo, Vince Hammond
6. Deformation processing – rolling and extrusion (8)
a. Leader – Martyn Alderman
b. Secretary – Warren Poole
c. Participants – Wojtek Misiolek, Rad Radhakrishnan, Eric Taleff, Yuri Hovanski,
Amanda Levinson, David Foley, Keith Wang
7. Biomedical applications (6)
a. Leader – Michelle Manuel
b. Secretary – Wim Sillekens
c. Participants – Guangling Song, Barb Shaw, Clark Cooper, Ray Decker
26
Friday
1.
2.
3.
4.
5.
6.
7.
Integrated Computational Materials Engineering 2 (ICME2) (8)
a. Leader – John Allison
b. Secretary – Rad Radhakrishnan
c. Participants – Dallas Trinkle, Bin Li, Jian Wang, Somnath Ghosh, Yong-Ho
Sohn, Ben Anglin
Alloy development (8)
a. Leader – Alan Luo
b. Secretary – J.F. Nie
c. Participants - Michelle Manuel, Tresa Pollock, Rupalee Mulay, Dongwon Shin,
Anna Xue
Formability (8)
a. Leader – Eric Taleff
b. Secretary – Eric Nyberg
c. Participants – Paul Krajewski, Amanda Levinson, Warren Poole, Mark Weaver,
Ibrahim Karaman
Flammability, Aerospace, and Composites (8)
a. Leader - Donald Shih
b. Secretary – Martyn Alderman
c. Participants - Ray Decker, Suveen Mathaudhu, Mike Dierks, David Foley, Karl
Kainer, Wayne Jones
Joining and Fastening and Multi-material Solutions (6)
a. Leader – Dean Paxton
b. Secretary – Zhili Feng
c. Participants – Jim Fitz-Gerald, Vince Hammond, Yuri Hovanski, Keith Wang
Corrosion and Coatings and Multi-material solutions (7)
a. Leader – Barb Shaw
b. Secretary – Robert McCune
c. Participants – Guangling Song, Wim Sillekens, Clark Cooper, Karl Kainer, Will
Joost
Deformation and Fracture Mechanism (7)
a. Leader – Surya Kalidindi
b. Secretary – Bin Li
c. Participants – Rusty Gray, Neha Dixit, Tony Rollett, Donald Stone, Cindy Byer
27
Appendix C: List of Participants and E-mails
Speakers
John Allison johnea@umich.edu
Jian-Feng Nie Jianfeng.Nie@monash.edu
Karl Kainer karl.kainer@hzg.de
Guangling Song Guangling.song@gm.com
Bob McCune robert.mccune@sbcglobal.net
“Rusty” Gray rusty@lanl.gov
Wim Sillekens wim.sillekens@tno.nl
Suveen Mathaudhu suveen.n.mathaudhu.civ@mail.mil
Paul Krajewski paul.e.krajewski@gm.com
Surya Kalidindi skalidin@coe.drexel.edu
Dallas Trinkle dtrinkle@illinois.edu
Alan Luo alan.luo@gm.com
Participants
Anna Xue anna.xue@usu.edu
Anand Raghunathan araghunathan@energetics.com
Bin Li binli@cavs.msstate.edu
Barbara Shaw bas13@psu.edu
Dean Paxton dean.paxton@pnl.gov
Zhili Feng fengz@ornl.gov
Greg Rohrer gr20@andrew.cmu.edu
Ibrahim Karaman ikaraman@tamu.edu
Wayne Jones jonesjwa@umich.edu
Jim Fitz-Gerald jmf8h@virginia.edu
Martyn Aldreman martyn.alderman@magnesium-elektron.com
Mike Dierks mdierks@spartanlmp.com
Michelle Manuel mmanuel@mse.ufl.edu
Mark Weaver mweaver@eng.ua.edu
“Rad” Radhakrishnan radhakrishnb@ornl.gov
Tony Rollett rollett@andrew.cmu.edu
Dongwon Shin shind@ornl.gov
Eric Taleff taleff@mail.utexas.edu
Vince Hammond vincent.h.hammond@us.army.mil
Warren Poole warren.poole@ubc.ca
“Wojtek” Misiolek wzm2@Lehigh.edu
Yongho Sohn ysohn@mail.ucf.edu
Yuri Hovanski yuri.hovanski@pnl.gov
Jian Wang wangj6@lanl.gov
Clark Cooper ccooper@nsf.gov
Will Joost William.Joost@ee.doe.gov
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Donald Stone dsstone@wisc.edu
Somnath Ghosh sghosh20@jhu.edu
Qi Yang Qi.Yang@hap.com
Steering Committee
Sean Agnew sra4p@virginia.edu
Eric Nyberg eric.nyberg@pnl.gov
Tresa Pollock pollock@engineering.ucsb.edu
Ray Decker RDecker@Nanomag.us
Donald Shih donald.s.shih@boeing.com
*Bob Powell bob.r.powell@gm.com
*Rob Wagoner wagoner@matsceng.ohio-state.edu
* unable to attend workshop
Graduate Students:
Rupalee Mulay rpm8g@virginia.edu
Ben Anglin anglin.ben@gmail.com
David Foley tdfoley@tamu.edu
Amanda Levinson amanda.j.levinson@gmail.com
Neha Dixit dixitnehar@gmail.com
Cindy Byer cbyer1@jhu.edu
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