U.S. patent application number 10/520358 was filed with the patent office on 2005-10-27 for as-magnesium pressure die cast alloy and method for producing a subassembly part from an as-magnesium pressure die cast alloy of this type.
Invention is credited to Barth, Andreas.
Application Number | 20050238524 10/520358 |
Document ID | / |
Family ID | 29761667 |
Filed Date | 2005-10-27 |
United States Patent
Application |
20050238524 |
Kind Code |
A1 |
Barth, Andreas |
October 27, 2005 |
As-magnesium pressure die cast alloy and method for producing a
subassembly part from an as-magnesium pressure die cast alloy of
this type
Abstract
A water quenched magnesium/aluminum die casting alloy, includes
Al between 2.8 and 3% by weight; Si between 0.7, and 1.5% by
weight; Mn greater than 0.20% by weight; Zn less than 0.20% by
weight; Cu less than 100 ppm; Ni less than 20 ppm; and Fe less than
50 ppm. in addition, a method for manufacturing the
magnesium/aluminum die casting alloy wherein the water quenching
takes place within a predetermined time period after casting or
after the die casting mold is opened.
Inventors: |
Barth, Andreas;
(Leinfelden-Echterdingen, DE) |
Correspondence
Address: |
DAVIDSON, DAVIDSON & KAPPEL, LLC
485 SEVENTH AVENUE, 14TH FLOOR
NEW YORK
NY
10018
US
|
Family ID: |
29761667 |
Appl. No.: |
10/520358 |
Filed: |
June 23, 2005 |
PCT Filed: |
June 26, 2003 |
PCT NO: |
PCT/EP03/06727 |
Current U.S.
Class: |
420/408 |
Current CPC
Class: |
C22C 23/02 20130101 |
Class at
Publication: |
420/408 |
International
Class: |
C22C 023/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 5, 2002 |
DE |
102302766 |
Claims
1-13. (canceled)
14. A water quenched magnesium/aluminum die casting alloy,
comprising: Al between 2.8 and 3% by weight; Si between 0.7, and
1.5% by weight; Mn greater than 0.20% by weight; Zn less than 0.20%
by weight; Cu less than 100 ppm; Ni less than 20 ppm; and Fe less
than 50 ppm.
15. The magnesium/aluminum die casting alloy as recited in claim
14, wherein the alloy is water quenched after casting or after a
die casting mold is opened.
16. The magnesium/aluminum die casting alloy as recited in claim
14, wherein the magnesium/aluminum die casting alloy is part of a
thermally stressable component.
17. The magnesium/aluminum die casting alloy as recited in claim
16, wherein the component is part of an automobile.
18. The magnesium/aluminum die casting alloy as recited in claim
14, wherein the magnesium/aluminum die casting alloy is a MgAl 3 Si
1 alloy.
19. The magnesium/aluminum die casting alloy as recited in claim
14, wherein a large amount of aluminum is dissolved in a magnesium
matrix.
20. A method for manufacturing the magnesium/aluminum die casting
alloy as recited in claim 14, wherein the water quenching takes
place within a time period after casting or after the die casting
mold is opened, the time period being 60 seconds.
21. The method as recited in claim 20, wherein the time period is
40 seconds.
22. The method as recited in claim 20, wherein the time period is
30 seconds.
Description
[0001] The present invention relates to an AS die casting alloy, in
particular for automotive components susceptible to thermal
stress.
[0002] If magnesium alloys are used in components susceptible to
high thermal stresses, they must have a low aluminum content to be
creep-resistant, so that when the unit operates at a high
temperature, the connecting screws do not come loose. MgAl2Si1 die
casting alloys, also known as AS21 alloys and MgAl4Si1 alloys, also
known as AS41 alloys, are known to be creep-resistant alloys. With
decreasing aluminum content in the magnesium alloy, fewer
Mg.sub.17Al.sub.12 grain boundary separations, susceptible to
creep, occur under thermal stress at temperatures over 120.degree.
C.; therefore, AS21 alloys are more creep-resistant than AS41
alloys. Due to its lower aluminum content, an AS21 alloy, however,
has a lower strength, is more susceptible to corrosion, and,
mainly, is difficult to cast. Casting errors such as adhesion to
the casting mold and hot cracks do not allow large components to be
reliably mass produced.
[0003] An AS41 alloy, however, does not have these disadvantages.
It is, however, more susceptible to creep and less ductile due to
the high Mg.sub.17Al.sub.12 grain boundary separations. A lower
toughness reduces the dynamic strength of the alloy in the case of
the notch effect, caused, for example, by stone impact, corrosion,
etc. In the case of a thermal load, ductility drops as a result of
the separation of additional, brittle Mg.sub.17Al.sub.12 phases at
the grain boundaries. Therefore, the allowable dynamic load on
components made of AS41 alloys decreases during drive operation. WO
A-01 02 614 describes alloys of this type.
[0004] The object of the present invention is therefore to provide
an AS alloy which is thermally stable regarding creep and
ductility, while being satisfactorily castable.
[0005] This object is achieved according to the present invention
by an AS die casting alloy of the type recited in the preamble by
the fact that its aluminum content is between the aluminum content
of AS21 and AS41 alloys.
[0006] According to the present invention, a metallurgical
compromise has been found between castability, strength, and
corrosion resistance on the one hand, which are achieved by a
higher aluminum content, and creep-resistance and ductility on the
other hand, which are achieved by a lower aluminum content. In the
AS die casting alloy according to the present invention, the
aluminum content is between those of the standard alloys AS21 and
AS41.
[0007] Casting tests on transmission housings have shown that AS
alloys above an aluminum content of 2.5 wt. % are easily cast. No
adhesion of castings to the die casting mold was found. In
addition, the castings exhibited no hot cracks. Furthermore, a
higher aluminum content compared to an AS21 alloy results in the
desired increase in strength. Because the aluminum content of the
AS die casting alloy according to the present invention does not
reach that of an AS41 alloy, there is no danger of the die cast
part to embrittle.
[0008] According to the present invention, the aluminum content is
between 2.5 wt. % and 4 wt. %, in particular between 2.8 wt. % and
3.5 wt. %, preferably 3 wt. %. Castability, strength,
corrosion-resistance, creep-resistance, and ductility may be
adjusted within certain limits by selecting the aluminum
content.
[0009] According to the present invention, the AS die casting alloy
is an MgAl3Si1 alloy (AS31). This alloy has an aluminum content and
in particular additional alloy components which are between those
of AS21 and AS41 alloys.
[0010] In particular, the AS die casting alloy according to the
present invention has an Mn content which is greater than 0.20 wt.
%. The Cu content is <100 ppm. The Ni content is <20 ppm. The
Fe content is also <50 ppm. The Si content is between 0.7 wt. %
and 1.5 wt. %. In addition, the Zn content is less than 0.20 wt.
%.
[0011] Finally, a relatively high amount of Al is dissolved in the
Mg matrix. This results in high ductility, which is described in
more detail below. This is achieved in particular by water
quenching the AS die casting alloy according to the present
invention.
[0012] The above object is furthermore achieved in a method for
manufacturing a thermally stressable component made of the AS die
casting alloy recited in the preamble by water quenching after
casting or after the casting mold is opened.
[0013] As mentioned above, high ductility is hereby achieved.
Compared to slow cooling in air, more aluminum is dissolved in the
Mg matrix in the case of water quenching, so that a favorable mixed
crystal hardening occurs, which, contrary to Mg.sub.17Al.sub.12
separation hardening, barely embrittles the microstructure.
Furthermore, contrary to air cooling according to the related art,
the aluminum which is not dissolved in the Mg matrix separates in
the form of very fine Mg.sub.17Al.sub.12 phases.
[0014] Also, in the case of water quenching, separation occurs not
only at the grain boundaries, but also in the Mg matrix. The
tensile strength and the permanent elongation limit of the AS die
casting alloy according to the present invention are thereby
considerably increased in comparison to air cooling, without the
elevated Al content compared to the known AS21 alloy causing
deterioration in toughness, because only a small amount of coarse
Mg.sub.17Al.sub.12 grain boundary phases appear.
[0015] Finally, thermal stability of the microstructure in the case
of long-term stress at 150.degree. C. is noticeably improved. In
the case of air cooling according to the related art, the separated
coarse Mg.sub.17Al.sub.12 grain boundary separations function as
nuclei for forming further Mg.sub.17A.sub.12 phases, so that after
thermal aging the grain boundaries are fully occupied, i.e.,
anchored with Mg.sub.17Al.sub.12 phases. This results in total
material embrittlement.
[0016] When water quenching is used according to the present
invention, the new AS die casting alloy has fewer and finer
Mg.sub.17Al.sub.12 grain boundary separations and thus fewer
nuclei, so that the grain boundaries barely embrittle upon thermal
aging.
[0017] The water-quenched AS31 die casting according to the present
invention suffers only a slight loss of elongation at rupture after
thermal aging for 2000 hours at 150.degree. C., although the
tensile strength and the permanent elongation limit advantageously
increase due to the separation of further fine Mg.sub.17Al.sub.12
phases. This results in excellent dynamic strength properties
overall, even in the case of thermal stress at 150.degree. C.
[0018] The creep resistance of the alloy according to the present
invention is improved due to water quenching. Thus, as mentioned
before, more aluminum is dissolved in the Mg matrix from the
beginning. This improves creep resistance to the point where the
loosening tendency of aluminum screws corresponds to that of the
known AS21 alloy despite the higher Al content of the alloy
according to the present invention.
[0019] It has been found that, for a water-quenched AS41 alloy, the
relaxation properties of Al screws at 150.degree. C. are poorer
than for the AS31 alloy according to the present invention. The
reason therefor is the higher aluminum content in the AS41 alloy,
i.e., the higher proportion of non-creep resistant
Mg.sub.17Al.sub.12 grain boundary phases in the original
microstructure.
[0020] The AS31 alloy according to the present invention, in
particular a transmission housing manufactured therefrom, has a
minimum tensile strength of 180 MPa, a minimum permanent elongation
limit of 110 MPa, and the minimum elongation at rupture in the area
of the casting notch is 6%.
[0021] The component manufactured from the alloy according to the
present invention is preferably water quenched within 60 s, in
particular within 40 s, preferably within 30 s after casting or
after the die casting mold is opened. This temperature drop
immediately after casting prevents, as mentioned above, the
formation of an excessive amount of coarse Mg.sub.17A.sub.12 grain
boundary phases.
* * * * *