Note: Descriptions are shown in the official language in which they were submitted.
CA 03011631 2018-07-17
- 1 -
Hardenable Al-Mq-Si-based aluminum alloy
Field of the invention
The invention relates to a hardenable Al-Mg-Si-based aluminum alloy.
Description of the prior art
In order to improve the thermosetting capability of A6061 Al-Mg-Si-based
aluminum
alloy which is age-hardened at room temperature, W02013/124472A1 suggests
adding to the solid solution of the aluminum alloy a vacancy-active trace
element,
namely tin (Sn) and/or indium (In).
In addition, it is known ("Statistical and thermodynamic optimization of trace-
element
modified Al-Mg-Si-Cu Alloys", Stefan Pogatscher et al.) that certain main and
minor
alloying elements of the A6061 aluminum alloy reduce the solubility of tin or
indium
in aluminum alloy, which negatively affects the storage stability at room
temperature
of the 6xxx aluminum alloys. For example, an increased content of Mg, Si, Cu
or Zn
in the 6xxx aluminum alloy should reduce the solubility, whereas an increased
con-
tent of Fe, Ti and Mn increases the solubility. In addition, interaction
effects, e.g.
between Si and Mg and/or between Cu and Mg, also play an important role in the
solubility of Sn in the aluminum alloy.
However, the main and minor alloying elements can not be arbitrarily varied in
their
content in the aluminum alloy, because in addition to a desirable high
thermosetting
capability other mechanical and/or chemical requirements - such as
formability,
strength, ductility and/or corrosion resistance ¨ need to be met. This
requires, for
example, high concentrations of main alloying elements in the aluminum alloy
in
order to form certain hot precipitations.
CA 03011631 2018-07-17
- 2 -
In the setting of the composition of an Al-Mg-Si-based aluminum alloy,
countercur-
rent proportions are therefore usually required for the main and secondary
alloying
elements - on the one hand, those quantity proportions which are beneficial
for the
solubility of Sn in the aluminum alloy in order to ensure high storage
stability at room
temperature, and on the other hand those quantity proportions which ensure
high
mechanical and/or chemical characteristics or properties of the aluminum
alloy, but
which usually adversely affect the solubility of Sn.
Summary of the invention
It is therefore the object of the invention to modify a hardenable Al-Mg-Si-
based
aluminum alloy with Sn as a trace element in the composition such that a high
me-
chanical and chemical property of the aluminum alloy can be combined after hot
age-hardening with high storage stability at room temperature. In addition,
the alu-
minum alloy should be particularly suitable for the use of secondary aluminum.
The invention solves this problem in that the aluminum alloy comprises from
0.6 to
1% by weight of magnesium (Mg), from 0.2 to 0.7% by weight of silicon (Si),
from
0.16 to 0.7% by weight of iron (Fe), from 0.05 to 0.4% by weight of copper
(Cu), a
maximum of 0.15% by weight (or from 0 to 0.15% by weight) of manganese (Mn), a
maximum of 0.35% by weight (or from 0 to 0.35% by weight) of chromium (Cr), a
maximum of 0.2% by weight (or from 0 to 0.2% by weight) of zirconium (Zr), a
max-
imum of 0.25% by weight (or from 0 to 0.25% by weight) of zinc (Zn), a maximum
of
0.15% by weight (or from 0 to 0.15% by weight) of titanium (Ti), 0.005 to
0.075% by
weight of tin (Sn) and/or indium (In), and the remainder aluminum and
production-
related unavoidable impurities, wherein the ratio of the weight percentages of
Si/Fe
is less than 2.5 and the content of Si is determined according to the equation
wt.%
Si = A + [0.3 * (wt.% Fe)], with the parameter A being in the range of 0.17 to
0.4%
by weight.
CA 03011631 2018-07-17
,
. ,
. .
- 3 -
As a result of the rule of restricting the Si content to 0.2 to 0.7% by weight
and the
Fe content to 0.16 to 0.7% by weight and adjusting the Si content to the Fe
content,
the storage stability and the thermosetting capability of the Al-Mg-Si-
aluminum alloy
can be particularly favorably influenced if this adjustment meets both the
ratio of the
weight percentages of Si/Fe less than 2.5 and the equation wt.% Si = A + [0.3
*
(wt.% Fe)], with the parameter A being in the range of 0.17 to 0.4% by weight.
An aluminum alloy tuned so closely in Si and Fe content, which tuning can be
rec-
ognized, for example, in the hatched area in Fig. 1, can, because of the upper
limit
of said provision, ensure sufficient solubility of tin and/or indium in the
solid solution
of the aluminum alloy, which slows down the precipitation behavior during cold
age-
hardening and thus promotes the storage stability of the aluminum alloy. In
addition,
due to the lower limit in the tuning, adequate precipitation behavior during
hot age-
hardening is to be expected, whereby high strength values can be achieved in
the
hot age-hardening and the aluminum alloy itself can achieve or improve those
me-
chanical and chemical properties which are known from 6xxx aluminum alloy with
a
higher content of main and secondary alloy elements.
Surprisingly, however, it has been found that, compared with known 6xxx
aluminum
alloys, comprising Sn to suppress cold age-hardening, this method can be used
to
observe a much slower precipitation behavior at room temperature. Although it
is
known that a comparatively low Si content may be responsible for delayed cold
age-
hardening, the tuning of the Si content according to the invention, however,
leads far
beyond these known effects and shows an unusually high storage stability of
the
aluminum alloys.
According to the invention, therefore, the advantages of a particularly high
storage
stability at room temperature as well as good thermosetting capability of the
alumi-
num alloy can be combined.
In addition, this composition according to the invention may also be
particularly suit-
able for the use of secondary aluminum for this purpose due to the
comparatively
high Fe content.
CA 03011631 2018-07-17
- 4 -
In general, it is mentioned that the Al-Mg-Si-aluminum alloy can comprise
impurities
each having a maximum of 0.05% by weight and a total of at most 0.15% by
weight.
In addition, it is generally mentioned that maximum weight percentages, such
as
those found with Mn, Cr, Zr, Zn or titanium, for example, can be considered as
start-
ing from 0.
For the sake of completeness, it is further mentioned that aluminum or an
aluminum
alloy, obtained from aluminum scrap, can be understood as the secondary alumi-
num.
The storage stability and the thermosetting capability of the aluminum alloy
can be
further improved when the parameter A is in the range of 0.26 to 0.34% by
weight.
As a result of this rule, the solubility of Sn can thus become relatively high
and Si
has only a low impact on cold age-hardening. This allows an unexpectedly high
sta-
bility at room temperature. In addition, it can be seen that this alloy set in
this way
can achieve surprisingly high strength after hot age-hardening, for example by
means of heat aging, although this alloy has a comparatively low Si content.
An optimum of storage stability and thermosetting capability may be exhibited
when
the parameter A is 0.3% by weight.
If the content of Si is determined by the equation wt.% Si = A + [0.3 * (wt.%
Fe)] -
wt.% Ti, the components affecting the solubility of Sn can be matched to each
other
in a further improved manner. In particular, Ti can form phases with Si, which
can
have a positive influence on the solubility of Sn. The storage stability of
the alumi-
num alloy is thus further improved.
If the ratio of the weight percentages of Si/Fe is less than 2, by increasing
the set-
ting of Si by Fe, the content of dissolved Si in the aluminum alloy can be
significantly
reduced. Thus, the solubility of tin and/or indium in the solid solution of
the Al-Mg-Si-
aluminum alloy can be improved, which can further increase the storage
stability.
CA 03011631 2018-07-17
. . ,
- 5 -
A comparatively high solubility of tin and/or indium in the solid solution of
the Al-Mg-
Si-aluminum alloy can be achieved when the ratio of the weight percentages of
Si/Mg is in the range of 0.3 to 0.9.
If the aluminum alloy has at least 0.25% by weight of copper (Cu), based on
this
comparatively high Cu content, it is possible to intervene in a compensatory
manner
with respect to the adverse effects of Mg and Si on the solubility of Sn in
the solid
solution of Al-Mg-Si-aluminum alloy.
An excellent storage stability of the aluminum alloy can be achieved if it has
tin (Sn)
in the range of 0.005 to 0.05% by weight in solid solution in the aluminum
mixed
crystal. In general, it is mentioned that the term "solid solution" may denote
a state
in which an alloying element is dispersed in a solid matrix.
Preferably, the aluminum alloy belongs to the 6xxx series. Preferably, the
aluminum
alloy is an EN AW-6061 aluminum alloy.
If the aluminum alloy has at most 0.05% by weight of chromium (Cr) and more
than
0.05% by weight of zirconium (Zr), the quenching sensitivity for Sn can be
reduced
and Sn can also be retained in solid solution in the aluminum mixed crystal at
com-
paratively low quenching rates. In addition, it is thus possible, even with
heavy
plates, to achieve optimum storage stability and thermosetting capability.
The aluminum alloy may contain at least 0.02% by weight of chromium (Cr) in
order
to possibly improve the corrosion behavior.
Detailed description of the preferred embodiments
CA 03011631 2018-07-17
- 6 -
To demonstrate the effects achieved, thin sheets of various Al-Mg-Si-based
alumi-
num alloys (6xxx series) were produced. The compositions of the alloys
investigated
are listed in Table 1.
Alloys Sn Mg Si Cu Fe Mn Cr Zn Ti
1 0.04 0.8
0.64 0.22 0.47 0.11 0.16 0.05 0.05
2 0.04 0.78
0.43 0.36 0.46 0.11 0.14 0.05 0.06
Table 1: Overview of the investigated alloys in weight percent
The aluminum alloy 1 of Table 1 essentially corresponds to a standard alloy
AA6061
after addition of the trace element Sn, wherein it is conceivable to use
indium or a
combination of Sn and In instead of tin. Alloy 2 represents the composition
accord-
ing to the invention of the 6xxx series and is comparatively recycling-
friendly due to
the comparatively high Fe content.
The aluminum alloy 1 is well outside the Si/Fe content tuned according to the
inven-
tion, which is shown by way of example in Fig. 1. The aluminum alloy 2 is
placed
substantially centrally in this tuned Si/Fe content.
Both aluminum alloys 1 and 2 were solution-annealed in solid solution,
quenched,
and cold-hardened by aging at room temperature, and then hot-hardened.
Solution
annealing was carried out at a temperature greater than 530 degrees Celsius -
quenching at a quench rate greater than 20 degrees Celsius/second. Both alloys
1
and 2 were subjected to a storage time or cold age-hardening of 180 days jdj
and
30-minute hot age-hardening at different temperatures. Brinell hardness [HBW]
was
determined during cold aging and after hot aging.
With regard to the storage stability, it can be seen from Fig. 2 that the
alloy 1 under-
goes a comparatively rapidly increasing cold hardening during storage at room
tem-
perature after only 14 days - which leads disadvantageously to a comparatively
high
CA 03011631 2018-07-17
4 =
- 7 -
and increasing Brinell hardness over a longer storage time and has a
disadvanta-
geous effect on forming before hot age-hardening.
In contrast, alloy 2 shows an onset of cold age-hardening only after
approx.180
days, whereby the alloy 2 according to the invention is considered to be
particularly
resistant to storage. Such a surprisingly high storage stability has not yet
been ob-
served with any 6xxx alloy. This leads to an unexpected, enormous gain in the
ma-
nipulation time of the alloy after quenching in a soft state.
In the subsequent hot age-hardening, it can be seen in the comparison of the
two
alloys according to Fig. 3 that the alloy 2 initially lags behind the alloy 1
at lower ag-
ing temperatures in the Brinell hardness. At higher aging temperatures, the
Brinell
hardness of the alloy 1 can be significantly exceeded.
