U.S. patent application number 11/097158 was filed with the patent office on 2005-09-29 for semi-solid metal casting process of hypoeutectic aluminum alloys.
This patent application is currently assigned to SPX Corporation. Invention is credited to Apelian, Diran, Brown, Zach, Killingsworth, Dayne, Musser, Mark A., Saha, Deepak.
Application Number | 20050211407 11/097158 |
Document ID | / |
Family ID | 33309962 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050211407 |
Kind Code |
A1 |
Saha, Deepak ; et
al. |
September 29, 2005 |
Semi-solid metal casting process of hypoeutectic aluminum
alloys
Abstract
A method for the refining of primary aluminum in hypoeutectic
alloys by mixing at least two hypoeutectic alloys into a
solid/semi-solid hypoeutectic slurry is described. The method
provides control of the morphology, size, and distribution of
primary Al in a hypoeutectic Al--Si casting by mixing a
hypoeutectic Al--Si liquid with solid hypoeutectic Al--Si particles
to impart desirable mechanical properties. The invention enables
SSM molding of hypoeutiectic alloys without the need for secondary
processing steps associated with other rheocasting processes.
Inventors: |
Saha, Deepak; (Worcester,
MA) ; Apelian, Diran; (West Boylston, MA) ;
Musser, Mark A.; (Osceola, IN) ; Brown, Zach;
(Kalamazoo, MI) ; Killingsworth, Dayne; (South
Bend, IN) |
Correspondence
Address: |
Baker & Hostetler LLP
Washington Square, Suite 1100
1050 Connecticut Avenue, N.W.
Washington
DC
20036
US
|
Assignee: |
SPX Corporation
|
Family ID: |
33309962 |
Appl. No.: |
11/097158 |
Filed: |
April 4, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11097158 |
Apr 4, 2005 |
|
|
|
10426799 |
May 1, 2003 |
|
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|
6880613 |
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Current U.S.
Class: |
164/113 ;
164/900 |
Current CPC
Class: |
B22D 17/007 20130101;
C22C 21/02 20130101; C22C 1/005 20130101; Y10S 164/90 20130101 |
Class at
Publication: |
164/113 ;
164/900 |
International
Class: |
B22D 023/00; B22D
025/00 |
Claims
1-17. (canceled)
18. A semi-solid metal product, comprising: the product made by
heating a first aluminum-silicon hypoeutectic alloy to a liquid
state, combining the first alloy and a second aluminum-silicon
hypoeutectic alloy at different temperatures to form a semi-solid
metal, cooling the semi-solid metal for a length of time effective
to increase nucleation of primary aluminum particles therein, and
casting the semi-solid metal.
19. The product of claim 18, wherein the product is also made by
choosing the length of time to be effective in restricting growth
of a primary aluminum phase in the semi-solid metal.
20. The product of claim 18, wherein the product is also made by
combining a third aluminum-silicon hypoeutectic alloy with the
first and second alloys.
21. The product of claim 18, wherein at least one of the first and
second alloys comprises from about 6 to about 8 percent
silicon.
22. The product of claim 21, wherein at least one of the first and
second alloys comprises about 7 percent silicon.
23. The product of claim 18, wherein the product is also made by
heating the second alloy before combining it with the first
alloy.
24. The product of claim 23, wherein the product is also made by
heating the first alloy to a higher temperature than the heated
second alloy.
25. The product of claim 23, wherein the product is also made by
heating the second alloy to a temperature from about 22.degree. C.
to about 660.degree. C.
26. The product of claim 18, wherein the product comprises aluminum
particles having an average diameter from about 40 microns to about
60 microns.
27. The product of claim 18, wherein the product is also made by
heating the first alloy to a temperature from about 577.degree. C.
to about 715.degree. C.
28. The product of claim 27, wherein the product is also made by
heating the first alloy to a temperature from about 577.degree. C.
to about 580.degree. C.
29. The product of claim 27, wherein the product is also made by
heating the first alloy to a temperature from about 690.degree. C.
to about 715.degree. C.
30. The product of claim 27, wherein the product is also made by
heating the first alloy to a temperature of about 640.degree. C.
and squeeze casting.
31. The product of claim 18, wherein the product comprises aluminum
particles having a compaction ratio from about 1.6 to about
3.0.
32. The product of claim 31, wherein the product comprises aluminum
particles having a compaction ratio from about 1.6 to about
1.8.
33. The product of claim 18, wherein the product is also made by
choosing the difference in temperature between the first alloy and
the second alloy to be effective in producing the product
comprising more homogeneous distribution of aluminum particles as
compared to aluminum particles in a cast product made by
traditional casting methods.
34. A cast product, comprising: an alloy comprising: a first
aluminum-silicon hypoeutectic alloy heated to a liquid state; and a
second aluminum-silicon hypoeutectic alloy mixed with the first
alloy; wherein the first alloy and the second alloy are allowed to
cool for a length of time effective to increase nucleation of
primary aluminum particles.
35. The cast product of claim 34, wherein the length of time is
effective to restrict growth of a primary aluminum phase.
36. The cast product of claim 34, where in the aluminum particles
have an average diameter from about 40 microns to about 60
microns.
37. The cast product of claim 34, wherein the aluminum particles
have a compaction ratio from about 1.6 to about 3.0.
38. The product of claim 37, wherein the aluminum particles have a
compaction ratio from about 1.6 to about 1.8.
39. The product of claim 34, where in the method is effective to
produce a cast product comprising more homogeneous distribution of
aluminum particles as compared to aluminum particles in a cast
product made by traditional casting methods.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a process of
casting metal alloys. More particularly, the present invention
relates to a method of semi-solid metal casting of aluminum-silicon
alloys.
BACKGROUND OF THE INVENTION
[0002] Conventional casting methods such as die casting, gravity
permanent mold casting, and squeeze casting have long been used for
Aluminum-Silicon (Al--Si) alloys. However, where semi-solid metal
(SSM) casting of Al--Si alloy materials has been involved, the
conventional methods have not been employed successfully to date.
Rheocasting and thixocasting are casting methods that were
developed in an attempt to convert conventional casting means to
SSM casting. However, these SSM methods require additional
retrofitting to conventional casting machinery and challenges
remain in the ability to manipulate the microstructures of primary
Al and/or Si in the cast part for improving cast performance.
[0003] Accordingly, it is desirable to provide a method of casting
SSM Al--Si alloys utilizing both conventional and rheocasting means
that can impart desirable mechanical properties. In particular,
there is a need for a process to control the nucleation of primary
Al particles in hypoeutectic Al--Si alloys to limit the formation
of large primary Al particles. Further still, it is desirable to
provide a method of producing products with Al--Si alloy castings
by conventional or rheocasting techniques wherein the temperature
of the semi-solid slurry can be controlled.
SUMMARY OF THE INVENTION
[0004] The foregoing needs are met, to an extent, by the present
invention, wherein according to one embodiment, an SSM casting
process is provided that generates products with Al--Si alloy
castings by conventional or rheocasting techniques wherein the
temperature and the final morphology of the primary Al of the
product can be controlled.
[0005] In accordance with one embodiment of the present invention
an SSM casting process is provided comprising heating a first
Al--Si hypoeutectic alloy to a first temperature, combining the
heated alloy with a second Al--Si hypoeutectic alloy having a
second temperature to form a semi-solid metal, cooling the combined
first and second Al--Si hypoeutectic alloys for a determined length
of time, and then casting the semi-solid metal. The length of
cooling time can be zero. The alloys may be of the same or
different chemical composition. The alloys may also be heated to
the same or different temperatures.
[0006] In accordance with another embodiment of the present
invention an SSM casting process is provided wherein the
temperature of a first Al--Si hypoeutectic alloy is higher than the
temperature of a second Al--Si hypoeutectic alloy such that there
is a difference in temperature between the first and second Al--Si
hypoeutectic alloys. The difference in temperature may be chosen to
achieve a determined rate of cooling which may allow control of
primary Al particle size in the final cast product. In some
embodiments, hypoeutectic Al--Si cast products may have Al
particles with an average diameter ranging from about 40 microns to
about 60 microns. The difference in temperature may also be chosen
to achieve a faster rate of cooling of the hotter alloy as compared
to heating the hotter Al--Si hypoeutectic alloy and allowing the
hotter alloy to cool independently at room temperature.
[0007] There has thus been outlined, rather broadly, the more
important features of the invention in order that the detailed
description thereof that follows may be better understood, and in
order that the present contribution to the art may be better
appreciated. There are, of course, additional features of the
invention that will be described below and which will form the
subject matter of the claims appended hereto.
[0008] In this respect, before explaining at least one embodiment
of the invention in detail, it is to be understood that the
invention is not limited in its application to the details of
construction and to the arrangements of the components set forth in
the following description or illustrated in the drawings. The
invention is capable of other embodiments and of being practiced
and carried out in various ways. Also, it is to be understood that
the phraseology and terminology employed herein, as well as the
abstract, are for the purpose of description and should not be
regarded as limiting.
[0009] As such, those skilled in the art will appreciate that the
conception upon which this disclosure is based may readily be
utilized as a basis for the designing of other structures, methods
and systems for carrying out the several purposes of the present
invention. It is important, therefore, that the claims be regarded
as including such equivalent constructions insofar as they do not
depart from the spirit and scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a graphic representation of one embodiment of how
the inventive process can be performed.
[0011] FIG. 2 shows the representative microstructure from
different locations within a castings produced by the process of
FIG. 1.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0012] The present invention provides a method for controlling the
composition, temperature and microstructure of Al--Si alloys prior
to SSM casting in an attempt to control the mechanical properties
of the final cast product. Generally, this is accomplished by
mixing at least two hypoeutectic Al--Si alloys. By definition,
aluminum alloys with up to but less than about 11.7 weight percent
Si are defined "hypoeutectic", whereas those with greater than
about 11.7 weight percent Si are defined "hypereutectic". In all
instances, the term "about" has been incorporated in this
disclosure to account for the inherent inaccuracies associated with
chemical weights and measurements known and present in the art.
[0013] The metallic composition of alloys used in current methods
for SSM casting is limited to the availability and composition of
the starting materials. In contrast, according to the present
invention, a broad range of metallic compositions are achievable
from the same starting materials because the combination of
hypoeutectic alloys into a singular hypoeutectic alloy allows for
the manipulation of the final concentration of Si in the Al--Si
alloy by controlling the composition and mass of the starting
materials or semi-solid slurries.
[0014] Mixed hypoeutectic alloy compositions can be formed by
combining two or more aluminum alloys comprising up to but less
than about 11.7 percent Si in aluminum. In one embodiment, two
Al--Si alloys are combined to form a mixed hypoeutiectic alloy. It
will be noted that one of the starting materials need not be an
Al--Si alloy, but alternatively, purely Aluminum. In yet other
embodiments, combinations of two or more hypoeutectic alloys with
the same Al--Si chemistry (i.e., same weight percent Si) are
disclosed herein. One example of a hypoeutectic alloy with about 7%
Si is developed by Elkem (under the trademark of SIBLOY.RTM.).
[0015] In addition to imparting unique physical properties to the
end product, the concentration of Si in aluminum has consequences
in the phase profile of any given alloy at any given temperature.
For example, hypoeutectic Al--Si alloys begin to develop large Al
particles as they begin to cool below the liquidus and into the SSM
range. In a preferred embodiment, the instant invention teaches a
method of mixing two Al--Si alloys at different temperatures
together so that the amount of time the mixture spends in the
transitional semi-solid phase is minimized.
[0016] Temperature control of the alloys can be achieved by mixing
two or more hypoeutectic alloys as in the present invention.
Generally, one alloy is heated to a liquid state and then mixed
with an alloy of cooler temperature to bring the combined melt
within the SSM range. The cooler alloy may serve as a heat sink
when the hotter alloy is combined therewith, thus bringing the
combined alloy mixture into the semi-solid regime more rapidly than
using conventional coolers or air cooling. In some embodiments, one
or more of the hypoeutectic alloys is maintained in a solid state.
Preferably, the hotter or liquid alloy is generally poured into the
cooler or solid hypoeutectic alloy; however, it is also possible to
add the cooler alloy to the hotter alloy. Solid phase alloys may be
presented in any form known in the art, which include, but are not
limited to, grains, chips, and/or pellets.
[0017] In one embodiment, when squeeze casting is involved, the
alloys may be heated to a range of from about 690.degree. C. to
about 715.degree. C. In another embodiment, when the SSM is refined
(e.g., grain refined or electromagnetically-stirred), the alloys
may be heated typically to a range of from about 577.degree. C. to
about 580.degree. C. In yet other embodiments, one of the alloys to
be combined may not be heated at all, i.e., it may be used at
ambient room temperature.
[0018] In a preferred embodiment of the invention, a hotter alloy
is combined with a cooler alloy, and preferably, the hotter alloy
is raised to about 640.degree. C. and the cooler alloy is left at
ambient or room temperature. This large temperature gradient allows
for a quicker extraction of heat from the hotter parent alloy than
with conventional coolers and decreases the time necessary for the
liquid alloy to drop in temperature to a semi-solid/slurry
processing temperature. Such rapid nucleation of the primary Al
phase is thought to result in a more homogeneous microstructure
throughout the material.
[0019] In this manner, the current invention can enable SSM casting
of hypoeutectic alloys via the rheocast method without secondary
processing equipment such as external cooling mechanisms, or
induction heating apparatuses. For example, in one embodiment,
current squeeze casting processes can now be converted to an SSM
casting process at significantly reduced retrofitting costs by
using the teachings described herein to cool hypoeutectic Al--Si
alloys to the SSM range rather than with additional abovementioned
apparatuses.
[0020] FIG. 1 is a graphic representation of a squeeze casting
process in accordance with one embodiment of the invention used for
squeeze casting. Persons of ordinary skill will recognize that
alternate embodiments are also possible within the scope and spirit
of the present invention, and that therefore, the invention should
not limited to the details of the construction or the arrangement
of the components described herein. According to the embodiment in
FIG. 1, a shot sleeve on a casting device first reaches a pour
position thereupon initiating a pour cycle. The shot sleeve is a
receptacle to contain measured amounts of liquid/slurry material to
be later transferred into a die cavity. Solid chunks of the cooler
hypoeutectic alloy are added to the shot sleeve. Thereafter, molten
metal of the hotter hypoeutectic alloy is poured into the shot
sleeve and mixed with the solid chunks. The combination in this
embodiment leads to rapid dissolution of the solid material into
the molten metal and in so doing, drops the initial temperature of
the molten metal. Once in the SSM range, the slurry is then
injected, by any one of a variety of methods known in the art, into
the die cavity and proceeds to be cast.
[0021] As mentioned above, the growth of Al particles in the
semi-solid phase is directly correlated to the initial temperature
and the time of cooling of the alloy before casting. The longer an
alloy remains in the semi-solid phase, the likelihood for
undesirable growth of large Al particles is increased.
Alternatively, shortening the time an alloy spends in the SSM phase
before casting minimizes the growth of large Al particles by
maximizing the number of nucleating events, producing more Al
particles of smaller size. FIG. 2 is representative of the
microstructure of products cast by the inventive steps
described.
[0022] FIG. 2 shows the microstructure of cast alloys after they
have been quenched. In the particular embodiment presented, a 357
alloy (commercially available alloy of approximately 7% Si) was
heated to 640.degree. C. and then combined with 357 alloy chips at
room temperature. The 357 alloy chips were about 0.25 in.sup.3 in
average size. The combined liquid mixture cooled to 587.degree. C.
by virtue of mixing of the two alloys of different temperature,
before it was finally quenched. Three separate cross sections of
the cast product were taken: the edge, mid-radius, and center.
Microanalysis of the various sections of the casting demonstrates
that the primary Al particles are relatively evenly distributed
with minimal aggregate formation. The Al particles are seen as the
light colored particles in the microstructure, and the background
is the eutectic (i.e., a mixture of Al--Si). The Al particles shown
range in size from about 40 microns to about 60 microns in diameter
from the center of the cast though to the edge of the cast. The
compactness of the Al particles can be assessed relative to a
perfectly spherical particle and expressed as a ratio of
(2.pi.r).sup.2/4.pi.r.sup.- 2. Accordingly, a perfectly spherical
Al particle would have a ratio of 1 and would appear as a circle on
a micrograph, and larger ratios would indicate deviations
therefrom. The compactness ratio of the center of the cast ranged
from about 1.6 to 1.8 while the edge of the casting ranged from
about 2.2 to about 3.0.
[0023] Analysis of the edge cross sections of FIG. 2 shows the
morphology of primary Al to be less uniform and slightly radiating
from a given point (star-shaped). This is generally observed at the
outer edges of a casting where the molten liquid or slurry comes in
direct contact with the cold surface of the die cast.
[0024] A more rapid drop in temperature results in greater
nucleating events than if the temperature is dropped gradually.
This has the desirable effect of generating multiple Al particles
that are smaller in size (width and length), but also generally
uniformly distributed through out the alloy. The even distribution
of the Al particles, as seen in FIG. 2, allows for better
prediction ofinechanical properties with less likelihood of
mechanical failure which in effect limit the average growth of the
Al particles and diminished the likelihood of globular
aggregates.
[0025] The many features and advantages of the invention are
apparent from the detailed specification, and thus, it is intended
by the appended claims to cover all such features and advantages of
the invention which fall within the true spirits and scope of the
invention. Further, since numerous modifications and variations
will readily occur to those skilled in the art, it is not desired
to limit the invention to the exact construction and operation
illustrated and described, and accordingly, all suitable
modifications and equivalents may be resorted to, falling within
the scope of the invention.
* * * * *