2011 International Conference on Advanced Materials Engineering
IPCSIT vol.15 (2011) © (2011) IACSIT Press, Singapore
Alloying Elements and DIMOX Induced High Performance
Structural Foam Composite
Bakr Mohamed Rabeeh+
Engineering and Materials Science, German University in Cairo
Abstract. Direct metal oxidation (DIMOX) and semisolid (rheocsting) processing are applied for the
development of structural composite materials. Non traditional technique for foam processing is introduced.
The effect of alloying elements as well as parametric study are being utilized for metal matrix composite
reinforced with either whiskers of alumina or nano-intermetallic fibers. Aluminum alloy 6xxx is applied for
the objectives of Al- metal matrix composite at different temperatures (950, 1000, and 1050oC), and holding
time of 20 minute. The process is also followed by semisolid reaction, rheocasting, at 750oC for 20 minutes.
The addition of α-Fe powder and Mg powder established separately. Synergetic effect of alloying elements
as well as DIMOX process with semisolid reaction induced delocalized zone of interest. Alumina whiskers
or intermetallic fibers introduced with the control of bulk matrix porosity. Porosity as well as reinforcement
controlled and delocalized through rheocsting aiming at high performance materials. Scanning electron
microscopy with energy dispersive X-ray spectroscopy EDX is also utilized. Modulus of rupture is also
obtained through 3-point test on another group of samples. The inter-mutual effects of alloying elements as
well as the introduction of DIMOX established with Al-Si-Mg alloy (recycled). Rheocsting has dominant
effects on the control of porosity size and shape for the enhancement of mechanical properties.
Keywords: DIMOX, Rheocasting, foam, nanofibers, intermetallic, alumina, FGM.
1. Introduction
For the objective of minimizing cost and maximizing performance, aluminum scrap [classified] is
applied. In addition , direct Al-metal oxidized at three levels of temperatures, 950, 1000, and 1050 oC for 20
minutes holding time then cast in a metallic mould [1]. Other samples are prepared with semisolid work
rheocasting followed direct metal oxidation. Rheocasting is applied at 750oC for 20 minutes. Alloying
element effect on DIMOX and rheocasting is also investigated by applying 3 % of -Fe and Mg separately.
The segregation, of alloying elements, commencement of -alumina whiskers with of intermetallic fibers
introduced with residual aluminum. Porosity is also delocalized and controlled through semisolid reaction in
crucible for 20 minutes. The effect of addition -Fe powder as well as Mg powder resolved with different
functions [1-4]. Addition of -Fe powder has a powerful effect of nucleating intermetallic fibers as well as
alumina fibers homogeneously distributed along residual aluminum. Synergetic effects of -Fe with DIMOX
as well as rheocasting have a dominant effect on the morphology of composite constituents. Nucleation and
growth of reinforcement has an implicit effect of alloying element segregation in bulk aluminum [5-6].
Different delocalized zone of microstructures resolve bulk aluminum and porous aluminum matrix [7]. The
porosity shape and size controlled via rheocasting induced aluminum foam. Scanning electron microscopy
and energy dispersive X-ray spectroscopy (EDS) is utilized. In addition to, mechanical characterization is
introduced through 3-point test with rupture stress. Modulus of rupture is calculated for square cross section
sample and compared. However, the addition of -Fe introduced a new hybrid material; aluminum alloy
reinforced with ceramic alumina as well as intermetallic fibers, in residual porous aluminum is also
introduced. The control of porosity is dominated by rheocasting process which tends to reduce stress raisers
of flake porosity to a controlled shape and size. Magnesium addition has another new functional hybrid
+
Corresponding author. Tel.: Mobile: (202)-0101268145
E-mail address: bakr.rabeeh@guc.edu.eg
85
material. Ceramic alumina whiskers, instead of fibers with less percentage of intermetallic fibers are
introduced. A clear porosity obtained with DIMOX is now being controlled in shape and size for better
mechanical properties as well as a new emerging process for producing aluminum foam. The addition of
alloying elements with both DIMOX and rheocasting process induced different morphology of ceramic
reinforcement with intermetallic whiskers in a residual aluminum metal matrix composite. Alloying element
segregation has its synergetic effect for introducing new composite foam. The control of porosity as well as
the control of reinforcement established for the assessment of high performance aluminum foam with
intermetallic whiskers and fibers. Mechanical characterization is also introduced through 3-point testing of
metallic mold casted samples of 10x10x55 mm. Modulus of rupture [MOR] is applied on different samples
through DIMOX only or DIMOX and rheocasting. Rheocasting has a clear evidence of controlling porosity
shape and size that leading to a great evidence of increasing flexural strength [MOR].
2. Experimental Results and Discussion
The effect of alloying elements addition in directly oxidized aluminium is introduced through Fig. 1 to
Fig. 8. Fig. 1 and 2 present the addition of α-Fe induced α-alumina with intermetallic fibres [Fig. 1] and
micro-cracking in a residual aluminium matrix [Fig. 2]. The increase of α-Fe percent to 3% induced
dendritic growth of inermetallic fibres [Fig. 3]. Rheocasting at 750oC for 20 minutes after DIMOX at 1000oC
induced the control of shape and size of porosity [Fig. 4]. Kinetic of DIMOX reaction as well as rheocasting
reaction, in addition to alloying elements segregation induced the formation of semisolid inoculants in
liquidus residual aluminium. Mg addition with DIMOX induced the formation of alumina whiskers as well
as clear porosity [Fig. 5]. The control of shape and size of porosity is obtained by rheocasting at 750oC for 20
min. [Fig. 6]. Alloying elements segregation as well as reaction kinetics induced functionally-graded
materials [Fig. 7] where alumina phase delocalized with metallic aluminium matrix reinforced with
intermetallic whiskers at 1000oC. Aluminum foam introduced and illustrated in Figure 8 at 1050oC. Alumina
whiskers, intermetallic phase [Fig. 4] introduced with chemical analysis using EDS and presented in Figure 9
and 10 respectively. Fig. 11 and 12 introduce EDX of residual aluminium matrix chemical composition for
both α-Fe and Mg addition.
Table 1 introduces chemical composition of aluminium alloy 6xxx as received scrap materials. Table 2
presents chemical composition of alumina whiskers, intermetallic fibres as well as residual aluminium. It
resolves the effect of addition of -Fe or Mg that induced hybrid composite with clear evidence of alloying
elements segregation. 3-point test introduced for all samples resolving the effect of rheocasting after DIMOX
for the enhancement of mechanical properties [Table 3]. Clear evidence of an increase of MOR related to
rheocasting with DIMOX. Shape and size of porosity are controlled with rheocasting that induced the
dominant increase of MOR as presented in Table 3. Alloying element addition induced the formation of
intermetallic fibres or whiskers due to addition of -Fe or Mg in porous matrix. DIMOX has a great effect on
the segregation of alloying elements that induce delocalized zone of alumina or residual aluminum with
intermetallic that presented with chemical composition of different constituents [Table 2].
The addition of both -Fe and Mg induced a clear evidence of alumina phase at DIMOX temperatures in a
porous matrix. However a clear difference introduced that resolve intermetallic fibres via steel addition. In
addition the effect of rheocasting introduced with the control of porosity shape and size. Kinetic of DIMOX
reaction as well as semisolid reaction introduced with the segregation of alloying elements along with
intermetallic and residual aluminium matrix. Semisolid reaction not only introduced for the control of foam
formation but also for mechanical characterization and the enhancement of materials properties. The
formation of new phase in residual aluminum due to the addition of both -Fe or Mg induced an increase of
MOR [Table 3]
Table 1: Chemical composition of as received used raw materials
Elements
Si
Mg
Fe
Ni
Cu
Mn
Ti
Zr
V
Zn
Sr
Al
Balance
Wt%
From
11.0
0.5
0.0
0.05
0.06
0.0
0.05
0.12
0.05
0.05
0.001
To
14.0
1.5
0.8
0.9
0.8
1.0
1.2
1.2
1.2
0.9
0.1
86
Fig. 1: A-Fe induced a-alumina, intermetallic,in residual Aluminum Fig. 2: Steel additions induced micro-cracking
Fig. 3: A-Fe induced, intermetallic fibres in residual Aluminum Fig. 4: A-Fe induced, intermetallic fibres in
porous Aluminum
Fig. 5: Mg induced, intermetallic whiskerss in porous Aluminum
Fig. 6: Rheocasting control shape and size of
porous Aluminum
Fig. 7: Segregation induced localized zone of interest Fig. 8: Aluminium foam with uniformly distributed porosity
87
Fig. 9: EDS resolve alumina [gray spot in Fig. 4] Fig. 10: EDS resolve intermetallic fibres [white spot in Fig. 4]
Fig. 11: EDS resolve residual aluminium [white spot in Fig. 4]
Fig. 12: EDS resolve residual aluminium [white
spot in Fig. 6]
Table 2: Chemical composition of DIMOX samples segregation of alloying elements.
DIMOX
Al(%) Mg(%) Si(%) Fe(%) Cu(%)
950Al Fe (Gray)
Alumina Whiskers
100
0
0
0
0
0
1000 Al Fe(white)
Intermetallic Fibers
74.3
0
0
7.72
0
17.98
1050Al Fe(White)
68.35
0
0
0
14.27
17.37
950 Al Mg(Gray)
Intermetallic Fibers
54.24
17.75
22.82
5.20
0
0
1000Al Mg(White)
Residual aluminum
48.46
8.37
2.14
0
20.62
20.41
1050Al Mg
Residual aluminum
46.71
18.50
26.93
5.06
0
2.79
Table 3: Modulus of Rupture resolves the effect of DIMOX and Rheocasting samples.
DIMOX
Sample Classification
Rheocasting
950Al
1000Al
1050Al
1000Al Fe
1050Al Fe
Force
[N]
2683
2592
2900
4963
5314
Deflection
[mm]
0.66
0.51
0.53
1.00
0.60
MOR
[MPa]
201.225
194.4
217.5
372.225
398.55
Force
[N]
3368
3358
5283
5572
7146
Deflection
[mm]
0.69
0.6
1.05
1.07
0.75
MOR
[MPa]
252.6
251.85
396.225
417.9
643.21
1050Al Mg
5169
0.63
387.675
6253
0.58
562.78
88
3. Conclusions
The effect of addition -Fe powder as well as Mg powder resolved with different functions. Addition of Fe powder has a powerful effect of nucleating intermetallic fibers as well as alumina fibers homogeneously
distributed along residual aluminum. Synergetic effects of -Fe with DIMOX as well as rheocasting have a
dominant effect on the morphology of composite constituents. Clear intermetallic fibers as well as alumina
fibers are introduced as commenced at 950oC to 1050oC with scanning electron microscopy. However, the
addition of -Fe introduced a new functional hybrid material, aluminum alloy reinforced with ceramic
alumina as well as intermetallic fibers, in residual porous aluminum. The control of porosity is dominated by
rheocasting process which tends to reduce stress raisers of flake porosity to a controlled shape and size.
Magnesium addition has another new functional hybrid material. Ceramic alumina whiskers, instead of fibers
with less percentage of intermetallic fibers are introduced. The clear porosity obtained with DIMOX is now
being controlled in shape and size for better mechanical properties as well as a new emerging process for
producing not aluminum foam but also hybrid aluminum foam reinforced with ceramic alumina or
intermetallic fibers.
Non traditional method for hybrid aluminum foam is now being introduced via DIMOX and rheocasting.
The addition of alloying elements with the non traditional processes [DIMOX and rheocasting] clearly
dominates two functional materials. The first established with -Fe addition leading to the third generation
metal matrix composite with both alumina and intermetallic fibers reinforcements. The second dominated by
the addition of Mg that induced whiskers with new foaming matrix materials. This may lead to more
mechanical properties as well as high performance materials. The addition of semisolid process after
DIMOX has a clear enhancement not only at micro-structural evidence, but also at mechanical
characterization. There is some evidence of mechanical enhancement as increase of modulus of rupture for
different samples. Synergetic effects of alloying elements as well as DIMOX parametric induced different
intermetallic kinetics as well as delocalized zone of interests. DIMOX processing induced engineering of
new materials with different functions. A hybrid composite of aluminum metal matrix foam reinforced with
alumina particulate as well as intermetallic whiskers and/or fibers are introduced. In addition delocalized
zone of interests are also introduced with a new porous material (metallic foam) in a functionally-gradedMaterials [FGM].
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