U.S. patent application number 13/634358 was filed with the patent office on 2013-08-08 for aluminum die casting alloy.
This patent application is currently assigned to RHEINFELDEN ALLOYS GMBH & CO. KG. The applicant listed for this patent is Diran Apelian, Makhlouf M. Makhlouf. Invention is credited to Diran Apelian, Makhlouf M. Makhlouf.
Application Number | 20130199680 13/634358 |
Document ID | / |
Family ID | 42978206 |
Filed Date | 2013-08-08 |
United States Patent
Application |
20130199680 |
Kind Code |
A1 |
Apelian; Diran ; et
al. |
August 8, 2013 |
Aluminum Die Casting Alloy
Abstract
Aluminum die casting alloy comprising 2 to 6% by weight nickel,
0.1 to 0.4% by weight zirconium, 0.1 to 0.4% by weight vanadium,
optionally up to 5% by weight manganese, optionally up to 2% by
weight iron, optionally up to 1% by weight titanium, optionally
total max. 5% by weight transition elements including scandium,
lanthanum, yttrium, hafnium, niobium, tantalum, chromium and/or
molybdenum, and aluminum as the remainder with further elements and
impurities due to production total max. 1% by weight.
Inventors: |
Apelian; Diran; (West
Boylston, MA) ; Makhlouf; Makhlouf M.; (Shrewsbury,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Apelian; Diran
Makhlouf; Makhlouf M. |
West Boylston
Shrewsbury |
MA
MA |
US
US |
|
|
Assignee: |
RHEINFELDEN ALLOYS GMBH & CO.
KG
Rheinfelden
DE
|
Family ID: |
42978206 |
Appl. No.: |
13/634358 |
Filed: |
April 6, 2011 |
PCT Filed: |
April 6, 2011 |
PCT NO: |
PCT/EP2011/055318 |
371 Date: |
November 13, 2012 |
Current U.S.
Class: |
148/698 ;
148/415; 420/543; 420/544; 420/545; 420/551 |
Current CPC
Class: |
C22C 21/00 20130101;
C22F 1/04 20130101; B22D 17/20 20130101 |
Class at
Publication: |
148/698 ;
420/551; 420/543; 420/545; 420/544; 148/415 |
International
Class: |
C22C 21/00 20060101
C22C021/00; B22D 17/20 20060101 B22D017/20; C22F 1/04 20060101
C22F001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 2010 |
EP |
10159192.3 |
Claims
1-11. (canceled)
12. An aluminum die casting alloy comprising: 2 to 6% by weight
nickel, 0.1 to 0.4% by weight zirconium, 0.1 to 0.4% by weight
vanadium, optionally up to 5% by weight manganese, optionally up to
2% by weight iron, optionally up to 1% by weight titanium, and and
aluminum as the remainder with impurities due to production total
max 1% by weight.
13. The aluminum die casting alloy according to claim 12,
comprising 4 to 6% by weight nickel.
14. The aluminum die casting alloy according to claim 12,
comprising 0.1 to 0.3% by weight zirconium.
15. The aluminum die casting alloy according to claim 12,
comprising 0.3 to 0.4% by weight vanadium.
16. The aluminum die casting alloy according to claim 12, further
comprising: up to 2% by weight hafnium, up to 2% by weight
magnesium, up to 1% by weight chromium, up to 1% by weight
molybdenum, up to 0.5% by weight silicon, up to 0.5% by weight
copper, and up to 0.5% by weight zinc.
17. The aluminum die casting alloy according to claim 12, including
substantially uniformly dispersed particles of
Al.sub.3Zr.sub.xV.sub.1-x, where x is a fraction of unity that
depends on the ratio of Zr:V in the alloy, the particles having an
equivalent diameter of less than about 50 nm.
18. The aluminum die casting of Al.sub.3Zr.sub.xV.sub.1-x alloy
according to claim 17, where the particles have an equivalent
diameter of less than about 30 nm.
19. The aluminum die casting alloy according to claim 12, including
particles of Al.sub.3Ni having an equivalent diameter of less than
about 500 nm.
20. The aluminum die casting of Al.sub.3Zr.sub.xV.sub.1-x alloy
according to claim 19, wherein the particles of Al.sub.3Ni have an
equivalent diameter of less than 300 nm.
21. The aluminum die casting of Al.sub.3Zr.sub.xV.sub.1-x alloy
according to claim 19, wherein the particles of Al.sub.3Ni have an
equivalent diameter of less than 100 nm.
22. The aluminum die casting alloy according to claim 12, including
substantially uniformly dispersed particles of manganese aluminide
having an equivalent diameter of less than about 50 nm.
23. The aluminum die casting alloy according to claim 12, including
substantially uniformly dispersed particles of manganese aluminide
having an equivalent diameter of less than about 30 nm.
24. The aluminum die casting alloy according to claim 12, including
substantially uniformly dispersed particles of iron aluminide
having an equivalent diameter of less than about 50 nm.
25. The aluminum die casting alloy according to claim 12, including
substantially uniformly dispersed particles of iron aluminide
having an equivalent diameter of less than about 30 nm.
26. A die-cast component made from the aluminum alloy according to
claim 12.
27. A method of producing a die-cast component made from the
aluminum alloy according to claim 12, wherein the alloy is
age-hardened by holding the solidified die-cast component at a
temperature of 250.degree. C. to 350.degree. C. for 2 to 6 hours
followed by holding it at a temperature of 350.degree. C. to
450.degree. C. for 2 to 6 hours.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to aluminum alloys that can be
processed by conventional high pressure die casting and are
dispersion-strengthened, age-hardenable, and have useful mechanical
properties at temperatures up to at least 300.degree. C.
BACKGROUND OF THE INVENTION
[0002] Aluminum alloys are one of the most important groups of
light materials employed in the automotive industry, mainly because
of their high specific strength. Most of the traditional aluminum
casting alloys are based on the aluminum-silicon eutectic system
because of its excellent casting characteristics. Unfortunately the
solidus in this system does not exceed 550.degree. C., and
consequently the maximum working temperature of aluminum-silicon
alloys is limited to about 200.degree. C. In addition, the major
alloying elements in traditional aluminum-based alloys (i.e., zinc,
magnesium, and copper) have high diffusivity in the aluminum solid
solution. Therefore, while these elements enhance the room
temperature strength of the alloy, they compromise the alloy's
thermal stability. For example, aluminum alloys based on the
Al--Zn--Mg, the Al--Cu--Mg, and the Al--Li systems are able to
achieve very high tensile strength (up to about 700 MPa); however
their mechanical properties rapidly degrade when they are used at
high temperature. In many applications, stability of mechanical
properties at high temperature--not high strength--is the primary
need. Therefore traditional aluminum alloys are not useful in such
applications, and there is a need for a light-weight,
thermally-stable material.
PRIOR ART
[0003] Attempts have been made in the prior art to provide aluminum
casting alloys with enhanced thermal stability. Notable among these
attempts are those that utilize the aluminum-nickel system with
minor additions of zirconium. The following journal articles
represent these attempts: [0004] N. A. Belov, "Structure and
Strength of Cast Alloys of the System Aluminum-Nickel-Zirconium,"
Metallov., No. 10, pp. 19-22, 1993. [0005] N. A. Belov, "Principles
of Optimizing the Structure of Creep-Resisting Casting Aluminum
Alloys using Transition Metals," Journal of Advanced Materials,
Vol. 1, No. 4, pp. 321-329, 1994. [0006] N. A. Belov, V. S.
Zolotorevsky, S. Goto, A. N. Alabin, V. V. Istomin-Kastrovsky, and
V. I. Mishin, "Effect of Zirconium on Liquidus and Hardening of
Al-6% Ni Casting Alloy," Metals Forum, Vol. 28, pp. 533-538,
2004.
[0007] The preceding journal articles teach that an optimum
structure for an aluminum alloy that exhibits stability at high
temperature can be produced on the basis of a eutectic composition
consisting of an aluminum solid solution (.alpha.-aluminum) phase
that is alloyed with at least 0.6.degree. A) by weight zirconium;
and a second phase that has high creep strength, namely nickel
tri-aluminide (Al.sub.3Ni).
[0008] The preceding journal articles also teach that objects made
from these alloys are obtained by melting the carefully weighed
solid alloy ingredients (aluminum, aluminum nickel master alloy,
and aluminum zirconium master alloy) at about 900.degree. C. This
relatively high melting temperature is necessary in order to
dissolve the high zirconium content (.gtoreq.0.6% by weight
zirconium) into aluminum and obtain a homogeneous
aluminum-nickel-zirconium melt. In addition, the preceding journal
articles teach that the aluminum-nickel-zirconium melt must be
cooled at a cooling rate that is faster than 10.degree. C./second
in order to solidify it and retain a homogeneous super saturated
solid solution of zirconium in .alpha.-aluminum at room
temperature. Furthermore, the preceding journal articles teach that
as the material cools from the melt temperature, it may be shaped
into the desired object form by casting it in a mold. Said mold
must permit the material to cool from the melt temperature to room
temperature at a rate that exceeds 10.degree. C./second. Finally,
the preceding journal articles teach that the cast solid object may
be aged at a temperature between 350.degree. C. and 450.degree. C.
in order to precipitate fine zirconium tri-aluminide (Al.sub.3Zr)
particles that harden the alloy.
[0009] When properly processed, the alloys represented in the
preceding journal articles have better mechanical properties at
elevated temperature than traditional aluminum casting alloys.
However, hardening will not occur in the alloys represented in the
preceding journal articles unless the zirconium content of the
alloy is in excess of 0.4% by weight, and significant hardening
will not occur unless the zirconium content of the alloy is at
least 0.6% by weight. Smaller amounts of zirconium will not result
in a volume of second phase particles (in this case Al.sub.3Zr)
that is sufficient to induce significant hardening of the
.alpha.-aluminum solid solution. FIG. 1 depicts the amount of solid
present in the melt as a function of temperature for an alloy of
the prior art. The Figure shows that the alloy is completely molten
only at temperatures above 850.degree. C. Such high melt
temperature does not allow the alloys represented in the preceding
journal articles to be processed into shaped objects by
conventional high pressure die casting since the temperature of the
melt that may be introduced into the shot sleeve of a traditional
high pressure die casting machine should not exceed 750.degree.
C.
[0010] A high cooling rate--in excess of 10.degree. C./second--is
necessary for retaining 0.6% by weight zirconium in solid solution
in .alpha.-aluminum at room temperature. With the exception of high
pressure die casting, such a fast cooling rate cannot be attained
in most objects that are cast by conventional casting processes.
Accordingly, with the exception of casting very small objects in
graphite or copper molds, the alloys represented in the preceding
journal articles cannot be processed into shaped objects by
conventional casting processes.
DISCLOSURE OF THE INVENTION
[0011] This invention relates to a class of aluminum alloys which
(i) are dispersion-strengthened, (ii) can be age-hardened for
improved mechanical properties, and (iii) can be processed by
conventional high pressure die casting to produce shaped articles
that have useful mechanical properties at temperatures up to at
least 300.degree. C.
[0012] It is an object of the present invention to provide
light-weight, wear-resistant, and corrosion-resistant materials
that are castable via the conventional high pressure die casting
process and that are thermally-stable up to at least 300.degree.
C.
[0013] The foregoing object is achieved according to the invention
by an aluminum die casting alloy comprising
[0014] 2 to 6% by weight nickel,
[0015] 0.1 to 0.4% by weight zirconium,
[0016] 0.1 to 0.4% by weight vanadium,
[0017] optionally up to 5% by weight manganese,
[0018] optionally up to 2% by weight iron,
[0019] optionally up to 1% by weight titanium,
[0020] and aluminum as the remainder with impurities due to
production total max. 1% by weight.
[0021] A preferred nickel range is 4 to 6% by weight, a preferred
zirconium range is 0.1 to 0.3% by weight, and a preferred vanadium
range is 0.3 to 0.4% by weight.
[0022] The alloys of the present invention have the general
chemical composition: aluminum-nickel-zirconium-vanadium and their
chemical composition is optimized such that their liquidus
temperature is less than 750.degree. C.
[0023] Upon solidification from the melt, nickel and aluminum form
a eutectic structure comprised of a solid solution of nickel in
aluminum (referred to as the .alpha.-aluminum phase) and a second
phase comprised of nickel tri-aluminide (Al.sub.3Ni). Alloys with a
eutectic component in their microstructure have a narrower
solidification range, and therefore are less prone to hot tearing,
than alloys without a eutectic component in their microstructure.
The Al.sub.3Ni phase is in the form of thin rods whose diameter is
in the range of 300 to 500 nanometers. If cooling from the melt
temperature to room temperature is performed fast enough (i.e., at
a rate that exceeds 10.degree. C./second), then also dissolved in
the .alpha.-aluminum phase will be zirconium and vanadium. Upon
subsequent controlled thermal aging of the solid alloy, zirconium
and vanadium combine with aluminum via a solid-state reaction to
form a strengthening precipitate phase of the chemical composition
Al.sub.3Zr.sub.xV.sub.1-x. The sub-micron size meta-stable
Al.sub.3Zr.sub.xV.sub.1-x particles have the L1.sub.2 cubic crystal
structure and are uniformly distributed in the .alpha.-aluminum
solid solution.
[0024] The alloys of the present invention may also include up to
5% by weight manganese and up to 2% by weight iron. In addition to
forming metal aluminides, which can further strengthen the alloy,
iron and manganese are useful ingredients in high pressure die
casting alloys as they tend to mitigate soldering of the alloy to
the die components.
[0025] The alloys of the present invention may also include up to
2% by weight magnesium, up to 2% by weight hafnium, up to 1% by
weight titanium, up to 1% by weight molybdenum, up to 1% by weight
chromium, up to 0.5% by weight silicon, up to 0.5% by weight copper
and up to 0.5% by weight zinc.
[0026] The alloys of the present invention preferably include
substantially uniformly dispersed particles of
Al.sub.3Zr.sub.xV.sub.1-x, where x is a fraction of unity that
depends on the ratio of Zr:V in the alloy, the particles having an
equivalent diameter of less than about 50 nm and preferably less
than about 30 nm.
[0027] The alloys of the present invention preferably include
particles of Al.sub.3Ni having an equivalent diameter of less than
about 500 nm, preferably less than about 300 nm, particularly less
than about 100 nm.
[0028] The alloys of the present invention may include
substantially uniformly dispersed particles of manganese aluminide
having an equivalent diameter of less than about 50 nm and
preferably less than about 30 nm.
[0029] The alloys of the present invention may include
substantially uniformly dispersed particles of iron aluminide
having an equivalent diameter of less than about 50 nm and
preferably less than about 30 nm.
[0030] A feature of the alloys of the present invention which
distinguishes them from prior art aluminum alloys which contain
nickel and zirconium but without vanadium (described in the journal
articles by N. A. Belov) is that the alloys of the present
invention have a much lower liquidus temperature (typically less
than 750.degree. C. as opposed to more than 850.degree. C. for the
prior art alloys). The lower liquidus temperature permits the
alloys of the present invention to be processed into shaped objects
by conventional high pressure die casting whereas the alloys of the
prior art cannot be processed into shaped objects by conventional
high pressure die casting and are thus limited to the casting of
small objects in graphite molds.
[0031] Another feature of the alloys of the present invention which
distinguishes them from the prior art aluminum alloys containing
nickel and zirconium but without vanadium is that the precipitation
hardening particles in the alloys of the present invention are
Al.sub.3Zr.sub.xV.sub.1-x particles (compared to Al.sub.3Zr
particles in the alloys of the prior art). Because of the smaller
size of the vanadium atom (0.132 nm) compared to the zirconium atom
(0.159 nm), the Al.sub.3Zr.sub.xV.sub.1-x lattice has a lattice
parameter that is smaller than that of the Al.sub.3Zr lattice and
which more closely matches the lattice parameter of the
.alpha.-aluminum matrix. For this reason, aluminum-nickel alloys
that are hardened with Al.sub.3Zr.sub.xV.sub.1-x precipitates are
more thermally stable than aluminum-nickel alloys that are hardened
with Al.sub.3Zr precipitates.
[0032] The foregoing and other features and advantages of the
present invention will become more apparent from the following
detailed description and accompanying drawings.
DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a computer-generated solidification path for
aluminum--6% by weight nickel--0.6% by weight zirconium alloy;
[0034] FIG. 2 is a computer-generated solidification path for
aluminum--6% by weight nickel--0.1% by weight zirconium--0.4% by
weight vanadium alloy.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Dispersion strengthening of aluminum alloys relies on the
creation of dispersed particles in the alloy's matrix. This
strengthening mechanism is typified by alloys based on the
aluminum-nickel system. Hypo-eutectic and eutectic aluminum-nickel
alloys solidify in a structure that contains a fine dispersion of
nickel tri-aluminide (Al.sub.3Ni) particles in a matrix comprised
of a solid solution of nickel in aluminum (.alpha.-aluminum). Since
nickel tri-aluminide is essentially insoluble in aluminum up to
about 855.degree. C., aluminum-nickel alloys are more stable at
elevated temperatures than aluminum-silicon alloys. However,
aluminum-nickel binary alloys do not posses adequate mechanical
properties for most automotive applications as their room
temperature tensile yield strength does not exceed 80 MPa; and
therefore additional strengthening of these alloys is
necessary.
[0036] Precipitation strengthening is a well-known mechanism of
strengthening aluminum alloys as typified by alloys based on the
aluminum-copper system. In these alloys precipitation of copper
aluminide particles in an .alpha.-aluminum matrix is thermally
controlled in order to produce effective strengthening of the alloy
matrix.
[0037] The present invention combines characteristics of both types
of the hardening mechanisms previously described in order to obtain
aluminum alloys with sufficient elevated temperature mechanical
strength for most automotive applications. The alloys of the
present invention contain a fine dispersion of creep-resistant
nickel tri-aluminide particles and a strengthening precipitate that
is based on zirconium and vanadium, namely
Al.sub.3Zr.sub.xV.sub.1-x.
[0038] In the prior art alloys, which contain nickel and zirconium
but without vanadium (described in the journal articles by N. A.
Belov), a strengthening phase with the chemical composition
Al.sub.3Zr is formed. In the invention alloy, the strengthening
phase is also based on the Al.sub.3Zr structure but with vanadium
atoms substituting for some of the zirconium atoms. The accurate
representation of the strengthening phase in the invention alloy is
thus Al.sub.3Zr.sub.xV.sub.1-x with x being a fraction of unity
whose magnitude depends on the ratio of zirconium to vanadium. The
role that vanadium plays in the invention alloy is important in
allowing the alloy to be processed into articles by high pressure
die casting. The extent of strengthening induced by a precipitate
is related to both the volume fraction of the precipitate and the
size of the precipitate particles. A large volume fraction of small
size particles is essential for strengthening. The prior art alloys
employ a minimum 0.6% by weight zirconium in order to create about
0.83% by volume of the Al.sub.3Zr strengthening phase. This amount
is shown to be sufficient for significant strengthening of the
alloy. However, examination of FIG. 1 shows that the liquidus
temperature of an alloy with 0.6% zirconium is over 850.degree. C.
This relatively high melt temperature is prohibitive for
conventional high pressure die casting, and therefore alloys of the
prior art cannot be mass produced by high pressure die casting
operations. A preferred version of the invention alloy employs only
0.1% by weight zirconium and 0.4% by weight vanadium. This mixture
creates about 0.84% by volume of the Al.sub.3Zr.sub.xV.sub.1-x
strengthening phase. The main benefit of employing vanadium in the
invention alloy is that the liquidus temperature of the invention
alloy is only about 730.degree. C.--see FIG. 2, which permits the
use of conventional high pressure die casting in manufacturing
shaped articles with the invention alloy.
[0039] A broad description of the invention material after optimum
processing is that it is an .alpha.-aluminum (a very dilute solid
solution of nickel in aluminum) matrix which contains about
0.8-1.0% by volume of a uniformly distributed strengthening phase
that is based on zirconium and vanadium and that has a structure
represented by the chemical formula Al.sub.3Zr.sub.xV.sub.1-x, and
about 1-10% by volume nickel tri-aluminide particles uniformly
dispersed in the alloy matrix. In a material of this invention that
has been processed to have maximum strength, the
Al.sub.3Zr.sub.xV.sub.1-x strengthening particles are meta-stable,
have the L1.sub.2 cubic structure, are coherent with the
.alpha.-aluminum matrix, and have an average diameter of less than
about 25 nm.
[0040] The production of such a structure requires: (1) fast
cooling from the melt temperature, and (2) controlled thermal aging
of the solidified article.
[0041] Fast cooling from the melt temperature is necessary to
ensure that zirconium and vanadium are retained in solution in the
.alpha.-aluminum matrix at room temperature; i.e., at room
temperature the alloy contains the Al.sub.3Ni eutectic phase and a
second phase that is a super saturated solid solution of zirconium
and vanadium in .alpha.-aluminum. For the invention alloy, a
cooling rate that exceeds 10.degree. C./second is necessary to
obtain a super saturated solid solution of zirconium and vanadium
in .alpha.-aluminum. One of the advantages of the invention alloy
over prior art alloys is that it is designed so that it can be
processed into shaped articles by conventional high pressure die
casting wherein the molten alloy at about 750.degree. C. is
introduced directly into the shot sleeve of the die casting
machine. It is then injected under high pressure into a steel die;
the pressure is maintained on the alloy until solidification is
complete, and then the solidified article is ejected. It is known
that cooling rates in conventional high pressure die casting
operations typically exceed 10.degree. C./second. Therefore the
casting process which shapes the article also provides the
quenching that is necessary for obtaining a homogeneous super
saturated solid solution of the strengthening elements (zirconium
and vanadium) in .alpha.-aluminum.
[0042] Controlled thermal aging of solidified cast articles made
with the invention alloy is necessary in order to precipitate the
meta-stable L1.sub.2 cubic Al.sub.3Zr.sub.xV.sub.1-x strengthening
particles in the .alpha.-aluminum solid solution. This may be
accomplished by an optimized thermal aging schedule. One such
schedule includes holding the solidified cast article at a
temperature between 250.degree. C. and 350.degree. C. for between
two and six hours followed by holding it at a temperature between
350.degree. C. and 450.degree. C. for between two and six hours. A
preferred thermal aging schedule includes holding the solidified
cast article at 350.degree. C. for three hours followed by holding
it at 450.degree. C. for an additional 3 hours. Simultaneous with
precipitating the Al.sub.3Zr.sub.xV.sub.1-x strengthening particles
in the .alpha.-aluminum solid solution, the prescribed thermal
aging schedule fragments and changes the shape of the Al.sub.3Ni
eutectic rods into submicron size particles. This fragmentation and
globularization of the Al.sub.3Ni eutectic rods enhances the
overall ductility of the cast article.
[0043] Although this invention has been shown and described with
respect to detailed embodiments thereof, it will be understood by
those skilled in the art that various changes in form and detail
thereof may be made without departing from the spirit and scope of
the claimed invention.
* * * * *