Supplementary Information for submission to resource, conservation and
recycling
Component- and alloy-specific modeling for evaluating aluminum
recycling strategies for vehicles
Authors:
Roja Modaresi1)*, Amund N. Løvik1), Daniel B. Müller 1)
1) Industrial Ecology Programme (IndEcol), Department of Energy and Process
Engineering - EPT, NTNU, NO-7491 Trondheim
Roja Modaresi
Phone: +47 -735 93194
E-mail: roja.modaresi@ntnu.no
Industrial Ecology Programme and Department of Energy and Process Engineering - EPT
Norwegian University of Science and Technology (NTNU)
NO-7491 Trondheim
Norway
Amund N. Løvik
Phone: +47 -735 93194
E-mail: amund.lovik@ntnu.no
Industrial Ecology Programme and Department of Energy and Process Engineering - EPT
Norwegian University of Science and Technology (NTNU)
NO-7491 Trondheim
Norway
Daniel B.Müller
Phone: +47 -735 94754
Fax: +47 -73591298
E-mail: daniel.mueller@ntnu.no
Industrial Ecology Programme and Department of Energy and Process Engineering - EPT
Norwegian University of Science and Technology (NTNU)
NO-7491 Trondheim
Norway
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1. Model formulation
Determining the vehicle stock and flow: The basic principle of the global dynamic MFA
model is described in a previous paper (Modaresi and Müller, 2012) and here the SI explains
the aspects specific to this application. Figure S1 shows the dynamic model for aluminium in
passenger cars. There are two steps in the model calculation. First, vehicle stocks and flows
are calculated for the five car segments. Subsequently, aluminium stocks and flows are
determined, in 14 different components. The parameters are population (Pop), lifestyle as
vehicle per capita (Vp), vehicle lifetime (L), penetration of car segments, and aluminium
content for the distinguished component and segments. All these parameters are functions of
time. For each of these 14 component groups, the content of various alloy classes (1xxx,
3xxx, 5xxx, 6xxx, 2xxx/7xxx/6xxx with Cu content >1%, 4xxx + low impurity cast alloys,
and cast high Si (high impurity cast alloys) are defined, and assumed that alloy content is
valid for the whole period of time.
Reliable information for the lifetime distribution is essential for determining current and
future ELV flows, and for designing ELV management strategies. Result of evaluation of
different distribution functions such as weibull distribution, and lognormal compared to
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normal distribution in a study for service lifetimes of minerals end uses from U.S.G.S shows
that passenger cars tend to follow normal distributions function(Müller et al. , 2007)
Figure S1: Dynamic model for aluminium in passenger car stock
Mathematical illustration for stock, inflow and outflow calculation is shown in figure S2 and
equations (S1) and (S2). S0 denotes the initial stock in the year 0 and stock change (∆St) for
each year is St+1 – St. input of new and output of retired passenger cars is determined by a
given stock development and lifetime. The lifetime is estimated assuming a normal
distribution with mean τ and standard deviation σ:
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St  I t  Ot
For t  1 then Ot  0
(S1)
 S1  I1
t
Ot 
 L(t ', t ) * I *d t '
(S2)
t
t '0
Figure S2: System of in-use stocks. I is the input into use, O the output from use, and ∆S is the rate of change in
stock. t’ is the vintage year (year of manufacturing), t the actual time of the system state.
2. Parameter estimation
Population (Pop): Population data are estimated using UN national population statistics and
the UN Population Projection is used for the scenarios (UN, 2003, 2010). Base scenario is the
medium growth assumption with a thick line in figure 2.
Vehicle ownership (Vp): Passenger car stock data were compiled and used to estimate
weighted-average vehicle ownership on a global scale (Mitchell, 2007a, b, c, UN, 2010).
Future scenarios for car ownership are estimated based on regional IEA projections (IEA,
2010) and other studies(Joyce Dargay, 2007). All scenarios assume a logistic growth in car
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ownership with saturation around 2100. The saturation levels were chosen to be 450cars per
1000 capita in this study.
Life time (L): Based on previous studies on the lifetime from the US, Norway and Japan
(Kagawa et al. , 2011, Müller, Cao, 2007, Scacchetti, 2009), we assume for the global level a
constant lifetime approximated using a distribution function with a mean (τ) of 16 years and
a standard deviation (σ) of 3 years. We further assume that the lifetime of aluminium
components in cars is the same as the lifetime of the cars. A lifetime analysis for passenger
cars in the U.S. using combined vintage output approach showed 15.9 years (Müller, Cao,
2007). In a case study from Norway by analysing stock dynamics of car vintages, the result
shows that the lifetime of a car in Norway is between 15 to 19 years. The average age of
ELVs has been variously estimated at 15.3 years (Netherlands, 2004), 12.1 years (UK) and
more than 11 years (Hungary). In the UK, TRL (2003) estimated the average age of ELVs as
a whole at 12.1 years, with the average age of natural end of life vehicles at 12.8
years(Kagawa et al. , 2011).
Alloy composition for vehicle groups: Each of the 14 component groups is produced using
different alloys (see figure 2). It is assumed that the share of an alloy in a component does not
differ between years, and is valid for the entire time series. The following alloys categories
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are differentiated: 1xxx, 3xxx, 5xxx, 6xxx, 2xxx/7xxx/6xxx with Cu>1%, 4xxx + cast alloys
(AlSi, AlMg) with low alloying/impurity content (<0.5% each), and cast alloys with high
silicon content and higher alloying/impurity contents. Table S1 shows the alloy composition
for vehicles components.
Table S1: Alloy composition for vehicle components.
Alloys
categories
Components
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
1xxx
0%
0%
0%
75 %
45 %
0%
0%
0%
0%
0%
0%
0%
0%
30 %
3xxx
0%
0%
0%
25 %
25 %
0%
0%
0%
0%
0%
0%
0%
0%
5%
5xxx
40 %
35 %
5%
0%
5%
0%
40 %
5%
0%
0%
10 %
5%
10 %
10 %
6xxx
45 %
65 %
80 %
0%
5%
0%
20 %
80 %
10 %
10 %
30 %
10 %
25 %
40 %
2xxx/7xxx/
6xxx
0%
0%
15 %
0%
0%
0%
0%
0%
0%
0%
0%
5%
0%
0%
4xxx + cast
alloys with
low impurity
15 %
0%
0%
0%
20 %
45 %
40 %
15 %
90 %
10 %
60 %
0%
25 %
15 %
High Si
cast alloys
0%
0%
0%
0%
0%
55 %
0%
0%
0%
80 %
0%
80 %
40 %
0%
ELV index: ELV indexes are based on experts assumptions considering economical
feasibilities with the current available technology (EAA, 2012). The following three ELV
indexes are assigned to the parts (see figure 2):
ELV1 = Components which are easy to dismantle and to separate into alloy groups. For
instance, wheels (C9) has ELV1= 100%, which means they are easily dismantled. While
ELV1 is equal to zero for BIW (C1), and components C10:14.
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ELV2 = Components which are possible to dismantle, but present some difficulties. A
fraction of closures, engine blocks and cylinder head, and other engine components are
among these components.
ELV3 = Components which are difficult to dismantle and separate into alloy groups, and
therefore have to be shredded. For instance, brake components (C11), and other steering
components (C13) are among those that end up in shredders.
Based on the ELV indexes, the sum of ELV1 and ELV2 is considered as a high dismantling
strategy.
3. Source-sink diagram
The calculation of the alloy-recycling matrix: The alloy recycling matrix (fig. 1) illustrates
the maximum recycled content for combinations of two alloys, one as the produced alloy
(sink) and the other as scrap (source). The calculations are based on the chemical composition
limits given by industry standards (ASTM International, 2011, The Aluminum Association,
2009) and includes 9 elements as potential limiting factors: Al, Si, Fe, Cu, Mn, Cr, Zn, Ni and
Ti. Magnesium was not considered because it is partially lost in the remelting process and
may be removed further by chlorination if necessary. Composition limits are given as ranges
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with a lower and an upper level for each element. The chemical composition limits are given
in table S2.The maximum recycled content can be calculated as:
RCmax 
Here,
max
csink
nom
csource
max
csink
(2)
is the upper limit of the limiting element in the produced alloy, and
nom
csource
is the
nominal concentration in the source alloy. In reality, producers will use narrower ranges than
what is given in specifications, and therefore, the figure is slightly on the optimistic side.
Aluminum itself can also be considered as a limiting element in cases where the sink alloy
requires high concentrations of alloying elements. The chemical composition limits are given
in table S2.
Table S2 Composition limits for 10 typical automotive alloys (ASTM International, 2011, The Aluminum Association,
2009)
Si
1070A 0-0.2
Fe
Cu
Mn
Mg
Cr
Ni
Zn
Ti
0-0.25
0-0.03
0-0.03
0-0.03
0-0.03
0-0.03
0-0.07
0-0.03
3103
0-0.5
0-0.7
0-0.1
0.9-1.5
0-0.3
0-0.1
0-0.05
0-0.2
0-0.1
5182
0-0.2
0-0.35
0-0.15
0.2-0.5
4.0-5.0
0-0.1
0-0.05
0-0.25
0-0.1
5754
0-0.4
0-0.4
0-0.1
0-0.5
2.6-3.6
0-0.3
0-0.05
0-0.2
0-0.15
6061
0.4-0.8
0-0.7
0.15-0.4
0-0.15
0.8-1.2
0.04-0.35
0-0.05
0-0.25
0-0.15
6082
0.7-1.3
0-0.5
0-0.1
0.4-1.0
0.6-1.2
0-0.25
0-0.05
0-0.2
0-0.1
A356
6.5-7.5
0-0.2
0-0.2
0-0.1
0.25-0.45
0-0.05
0-0.05
0-0.1
0-0.2
301
9.5-10.5
0.8-1.5
3-3.5
0.5-0.8
0.25-0.5
0-0.03
1.0-1.5
0-0.05
0-0.2
319
5.5-6.5
0-1.0
3.0-4.0
0-0.5
0-0.1
0-0.5
0-0.35
0-1.0
0-0.25
A380
7.5-9.5
0-1.3
3.0-4.0
0-0.5
0-0.1
0-0.5
0-0.5
0-3.0
0-0.5
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Alloys selection
1070A: The 1xxx-series alloys are essentially unalloyed aluminium, with a minimum
aluminium content of 99%. Formability, good corrosion resistance and high heat conductivity
are characteristics that grant these alloys application in components such as heat exchangers
and heat shields (EAA, 2011). The alloy 1070A was chosen as an example with intermediate
impurity levels between those of 1050 and 1100. For the purpose of the calculations, it does
not make a significant difference, as their capacity to absorb scrap is close to zero, and it will
be unproblematic to use 1xxx alloys as source material for any of the other alloys shown.
3103: The 3xxx-series alloys are little used in vehicles compared to 6xxx or 5xxx, but might
be important from a recycling perspective because manganese, the main alloying element, is
undesirable in many of the other alloys. Main applications are fins and tubes in heat
exchangers, due to high formability and corrosion resistance, and medium strength (Kaufman,
2002). Typical alloys are 3003 and 3103 (EAA, 2011, Rossel, 1998), which have similar
concentration ranges for all elements.
5182 and 5754: Alloys with magnesium as the main alloying element (typically 2-5%) have
excellent corrosion resistance, toughness and weldability, and can be strain hardened for
improved strength (Kaufman, 2002). In passenger cars they may be used in sheet form in for
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example axle subframes, structural BIW components and inner panels of doors and hoods.
doors or hoods. Alloy 5754 is a typical choice where temperatures might exceed 80°C; in
other cases 5182 may be used for increased strength (Benedyk, 2010, EAA, 2011, Fridlyander
et al. , 2002, Koganti and Weishaar, 2008).
6061 and 6082: The 6xxx-series alloys are alloyed mainly with silicon and magnesium, and
may be strengthened by heat treatment. They are used in both sheet and extruded form, and in
many different parts of the vehicle. Alloys 6061 and 6082 are typical selections where a
higher strength is required, for example in bumpers, suspension arms or wheels (EAA, 2011,
Koganti and Weishaar, 2008, Yotsuya G and Yamauchi R, 2013), 6061 being more common
in the U.S. and 6082 in Europe (Benedyk, 2010, EAA, 2011).
A356, 301, 319 and A380: Cast alloys with silicon and copper or silicon and magnesium
belong to the 3xx-series and are the most widely used of cast alloys. Silicon levels may reach
up to 20%, and there is often a high concentration of other alloying elements (ASTM
International, 2011). Alloy A356 was chosen as an example of a primary cast alloy, being
widely used in wheels, as well as other structural components such as suspension frames or
body-in-white (Benedyk, 2010, EAA, 2011, Tirelli et al. , 2011). Alloy 301, commonly used
in pistons, contains around 1% Ni, and was included in the figure mainly to illustrate how the
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diversity of cast alloys may further complicate recycling. Alloys 319, A380 and variations,
used in cylinder heads and engine blocks (Bendyk 2010; European Aluminium Association
2011), are the most important secondary alloys in terms of production volume (Bray, 2012)
and currently the main sinks for scrap.
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