U.S. patent application number 11/085086 was filed with the patent office on 2005-07-28 for aluminum alloy.
Invention is credited to DasGupta, Rathindra.
Application Number | 20050161128 11/085086 |
Document ID | / |
Family ID | 37024653 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050161128 |
Kind Code |
A1 |
DasGupta, Rathindra |
July 28, 2005 |
Aluminum alloy
Abstract
All aluminum alloy is disclosed that includes 6.5 to 8.5 percent
silicon, 0.6 to 1.0 percent iron, 0.3 to 0.5 percent manganese,
0.35 to 0.65 percent magnesium, 0.01 to 1.0 percent zinc, 0.11 to
0.2 percent titanium, 2.0 to 2.5 percent copper, and aluminum as
the remainder with further one or more other elements that are
0.001 to 0.15 percent of the weight of the aluminum alloy. An
aluminum alloy of the above composition is high in strength and
suitable for use with SSM methods of casting, such as Rheocasting
and Thixocasting.
Inventors: |
DasGupta, Rathindra;
(Portage, MI) |
Correspondence
Address: |
BAKER & HOSTETLER LLP
WASHINGTON SQUARE, SUITE 1100
1050 CONNECTICUT AVE. N.W.
WASHINGTON
DC
20036-5304
US
|
Family ID: |
37024653 |
Appl. No.: |
11/085086 |
Filed: |
March 22, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11085086 |
Mar 22, 2005 |
|
|
|
10100053 |
Mar 19, 2002 |
|
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Current U.S.
Class: |
148/549 ;
164/113; 164/900; 420/532; 420/534; 420/537 |
Current CPC
Class: |
B22D 17/007 20130101;
B22D 21/007 20130101; C22C 1/005 20130101; C22C 21/02 20130101 |
Class at
Publication: |
148/549 ;
164/113; 164/900; 420/532; 420/534; 420/537 |
International
Class: |
B22D 017/08; B22D
023/00; B22D 025/00; C22C 021/04 |
Claims
What is claimed is:
1. An aluminum alloy, consisting essentially of the following
constituents by percentage of weight:
3 6.5 to 8.5 percent silicon; 0.6 to 1.0 percent iron; 0.3 to 0.5
percent manganese; 0.35 to 0.65 percent magnesium; 0.01 to 1.0
percent zinc; 0.11 to 0.2 percent titanium; 2.0 to 2.5 percent
copper; 0.001 to 0.15 percent one or more other elements; and
aluminum as the remainder.
2. The aluminum alloy of claim 1, wherein the aluminum alloy
comprises 7.2 to 8 percent silicon.
3. The aluminum alloy of claim 1, wherein the aluminum alloy
comprises to 0.6 to 0.8 percent iron.
4. The aluminum alloy of claim 1, wherein the aluminum alloy
comprises 0.45 to 0.6 percent magnesium.
5. The aluminum alloy of claim 1, wherein the one or more other
elements is lead.
6. The aluminum alloy of claim 1, wherein the one or more other
elements is chromium.
7. The aluminum alloy of claim 1, wherein the one or more other
elements are lead and chromium.
8. A die cast product, comprising by percentage of weight:
4 6.5 to 8.5 percent silicon; 0.6 to 1.0 percent iron; 0.3 to 0.5
percent manganese; 0.35 to 0.65 percent magnesium; 0.01 to 1.0
percent zinc; 0.11 to 0.2 percent titanium; 2.0 to 2.5 percent
copper; 0.001 to 0.15 percent one or more other elements; and
aluminum as the remainder.
9. The die cast product, of claim 8, wherein the die cast product
comprises 7.2 to 8 percent silicon.
10. The die cast product of claim 8, wherein the die cast product
comprises 0.6 to 0.8 percent iron.
11. The die cast product of claim 8, wherein the die cast product
comprises 0.45 to 0.6 percent magnesium.
12. The die cast product of claim 8, wherein the one or more other
elements is lead.
13. The die cast product of claim 8, wherein the one or more other
elements is chromium.
14. The die cast product of claim 8, wherein the one or more other
elements are lead and chromium.
15. A method of making a die cast product by an SSM method of
casting, comprising: forming a semi-solid aluminum alloy, wherein
the semi-solid aluminum alloy comprises by percentage of
weight:
5 6.5 to 8.5 percent silicon; 0.6 to 1.0 percent iron; 0.3 to 0.5
percent manganese; 0.35 to 0.65 percent magnesium; 0.01 to 1.0
percent zinc; 0.11 to 0.2 percent titanium; 2.0 to 2.5 percent
copper; 0.001 to 0.15 percent one or more other elements; and
aluminum as the remainder.
placing the aluminum alloy in a die cavity.
16. The method of making the die cast product of claim 15, wherein
the one or more other element is lead.
17. The method of making the die cast product of claim 15, wherein
the one or more other element is chromium.
18. The method of making the die cast product of claim 17, wherein
the one or more other elements are lead and chromium.
19. The method of making the die cast product of claim 15, wherein
the SSM method of casting is Rheocasting.
20. The method of making the die cast product of claim 15, wherein
the SSM method of casting is Thixocasting.
Description
PRIORITY
[0001] The present application claims priority from United States
Patent Application entitled, Aluminum Alloy, filed Mar. 19, 2002,
having Ser. No. 10/100,053, the disclosure of which is hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to casting alloys.
More particularly, the present invention is directed to an aluminum
alloy for semi-solid metal (SSM) casting processes.
BACKGROUND OF THE INVENTION
[0003] SSM aluminum alloy castings outperform, in both cost and
performance, other casting techniques, such as conventional die
casting, which is performed under high pressure, gravity permanent
mold casting and squeeze casting. SSM casting methods, when
utilized for the manufacturing of aluminum alloy products/castings,
have proven advantageous over other casting techniques because SSM
castings tend to exhibit higher mechanical properties in the areas
of strength and ductility and reduced porosity than castings
produced by the above-listed other methods.
[0004] Microstructures of SSM aluminum alloy castings reveal the
primary phase particles as round crystals that are often referred
to as rosettes or globules. The primary phase particles in SSM
aluminum alloy castings that contain less than twelve percent
silicon are comprised of essentially aluminum. Because solid
primary phase particles are part of the semi-solid metal being
injected into a mold/die cavity, the microstructure of the primary
phase of an aluminum alloy prior to injection into a mold/die is
indicative of the microstructure of the primary phase of the
resulting aluminum alloy casting. Thus, when SSM methods of casting
are utilized, the mechanical properties of a casting can be
predicted before a casting is even produced. Accordingly, the
production of castings with defects can be avoided.
[0005] Unlike SSM methods of casting, non-SSM casting processes
involve injection/pouring of a molten metal directly into the die.
Thus, because the metal is molten, with no parts of the metal being
solid, the microstructure of the resulting casting cannot be
ascertained until after the molten metal has solidified in the
mold/die cavity. Thus, with non-SSM casting processes the
microstructure of the primary phase of a casting cannot be
predicted before the casting is formed.
[0006] Typically, the microstructures of castings prepared by
non-SSM casting processes have dendrites. Dendrites are "tree-like"
structures, and castings with dendrites are prone to microporosity
and have inferior mechanical properties than those that exhibit
round crystals.
[0007] Thixocasting and Rheocasting are SSM methods of casting.
Thixocasting involves the electromagnetic stirring of metal during
solidification/freezing to provide aluminum SSM feedstock billets
up to approximately 4" in diameter. The stirring action due to the
movement of liquid fragments the aluminum dendrites as they form
during solidification and results in the formation of small
equiaxed grains in the billets. The billets are subsequently cut
into slugs, and re-heated to a semi-solid state before being
injected into the cavity. It is during the billet re-heating stage
that the equiaxed aluminum grains undergo globularization.
Chemically grain-refined billets are often used in lieu of
electromagnetically stirred billets. Heating of grain-refined
billets in the semi-solid temperature regime also helps yield
globular primary phase particles prior to injection into die
cavity.
[0008] Rheocasting, which is also known as "slurry" or
"slurry-on-demand" casting, involves heating a metal to a liquid
state, cooling the molten metal to a semi-solid state, and then
injecting the semi-solid metal into the die cavity. Rheocasting is
more efficient than Thixocasting because Rheocasting involves fewer
steps than Thixocasting.
[0009] Rheocasting has also proven to be more economically feasible
than Thixocasting because any unused scrap metal can be easily
re-melted and reprocessed by an SSM component manufacturer. With
Thixocasting, the scrap metal has to be reformed into billets by
the billet manufacturer via the use of electromagnetic stirring or
chemical grain refining before being used again. However, unlike
Thixocasting, Rheocasting requires only that the scrap metal is
re-melted and cooled to a semi-solid state before it is injected
into a die cavity. As a result, scrap metal can easily be reused
with the Rheocasting method of SSM casting and the expense
associated with recycling scrap metal is less.
[0010] In recent years, SSM casting methods utilizing aluminum
alloys have been used for manufacturing brake cylinders, fuel
rails, engine brackets steering knuckles, suspension links and auto
seat backs because, in addition to the above-discussed advantages
over non-SSM casting techniques, SSM casting methods offer
non-turbulent filling (ie., less air entrapment), require lower die
temperatures, reduce cycle time, reduce shrinkage, and provide the
option of heat treatment (i.e., solution treatment).
[0011] Among the various casting alloys in use, A356.2 and 357 are
the primary aluminum alloys used for SSM castings, including
castings of automotive components. The chemistries of A356.2 and
357 are as follows:
1 A356.2 357 Percent of Percent of Element Weight Element Weight
Silicon 6.5-7.5 Silicon 6.5-7.5 Iron 0.12 max Iron 0.12 max
Manganese 0.05 max Manganese 0.03 max Magnesium 0.30-0.45 Magnesium
0.45-0.6 Zinc 0.50 max Zinc 0.05 max Titanium 0.20 max Titanium
0.20 max Copper 0.10 max Copper 0.03 max Others 0.15 total Others
0.15 total Aluminum Balance Aluminum Balance
[0012] A356.2 and 357, when used with SSM casting methods, generate
castings of essentially high toughness, i.e., ability to absorb
energy before failure, and thus, have been found suitable for
automotive components, such as steering knuckles and suspension
links.
[0013] However, the A356.2 and 357 alloys, when used with SSM
casting methods, have not been found suitable for automotive
components that require essentially high strength, i.e., high load
bearing ability, such as axle carriers, rack and pinion housings,
and steering column housings.
[0014] There are, however, problems associated with the use of
A356.2 and 357 aluminum alloys. Maintaining low percentages of
iron, copper and zinc increases the cost of the A356.2 and 357
aluminum alloys. By keeping the iron content low, there is also the
potential that soldering will occur during the casting process.
Soldering refers to the phenomenon that takes place when aluminum
adheres to the die cavity during the die casting process. Soldering
occurrences often lead to defective castings.
[0015] Accordingly, it is desirable to provide an aluminum alloy
that can be utilized with SSM methods of castings, especially with
the increasingly popular Rheocasting method of SSM casting, that
can produce high integrity, high-strength automotive components,
such as axle carriers, rack and pinion housings, and steering
column housings.
[0016] Further, it is desirable to provide an aluminum alloy that
is less prone to the soldering phenomenon.
[0017] It is also desirable to provide an alloy that is less
expensive to produce than other alloys such as A 356.2 and 357.
SUMMARY OF THE INVENTION
[0018] In an exemplary embodiment of the present invention, an
alloy in accordance with the present invention is provided that
includes 6.5 to 8.5 percent silicon, 0.60 to 1.0 percent iron, 0.3
to 0.5 percent manganese, 0.35 to 0.65 percent magnesium, 0.01 to
1.0 percent of zinc, 0.11 to 0.2 percent titanium, 2.0 to 2.5
percent copper, and aluminum as the remainder with further one or
more other elements 0.001 to 0.15 percent of the weight.
[0019] In another exemplary embodiment of the present invention a
die cast product is provided that includes 6.5 to 8.5 percent
silicon, 0.60 to 1.0 percent iron, 0.3 to 0.5 percent manganese,
0.35 to 0.65 percent magnesium, 0.01 to 1.0 percent of zinc, 0.11
to 0.2 percent titanium, 2.0 to 2.5 percent copper, and aluminum as
the remainder with further one or more other elements 0.001 to 0.15
percent of the weight.
[0020] In yet another exemplary embodiment of the present invention
a method of making a die cast product is provided that includes
forming a semi-solid aluminum alloy, wherein the semi-solid
aluminum alloy contains 6.5 to 8.5 percent silicon, 0.60 to 1.0
percent iron, 0.3 to 0.5 percent manganese, 0.35 to 0.65 percent
magnesium, 0.01 to 1.0 percent of zinc, 0.1 to 0.2 percent
titanium, 2.0 to 2.5 percent copper, and aluminum as the remainder
with further one or more other elements 0.001 to 0.15 percent of
the weight, and placing the semi-solid aluminum alloy in a die
cavity.
[0021] 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.
[0022] 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.
[0023] 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
[0024] FIG. 1 illustrates microstructures of an exemplary
embodiment an aluminum alloy in accordance with the present
invention.
[0025] FIG. 2 illustrates microstructures of an exemplary
embodiment of an aluminum alloy in accordance with the present
invention.
[0026] FIG. 3 illustrates microstructures of an exemplary
embodiment of an aluminum alloy in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0027] An aluminum alloy in accordance with the present invention
is a high copper, manganese and iron (HiCMF) aluminum alloy. In an
exemplary embodiment of the present invention, an aluminum alloy in
accordance with the present invention, is composed of the
below-listed elements, by percentage of weight, as follows:
2 Element % of Weight Silicon 6.5 to 8.5 Iron 0.6 to 1.0 Manganese
0.01 to 0.5 Magnesium 0.35 to 0.65 Zinc 0.001-1.0 Titanium
0.001-0.2 Copper 2.0-2.5 Tin 0.001-0.3 Others 0.001-0.15 Aluminum
Balance
[0028] In a preferred embodiment of the present invention, the
"others" are lead and/or chromium.
[0029] In addition, the amount of manganese is more preferably 0.30
to 0.50 percent by weight. The ranges of manganese as described
herein facilitate a reduction in the amount of solder when adhering
the aluminum alloy to die steel. Furthermore, the ranges described
herein contribute to the formation of `Chinese-script`
intermetallics and are therefore less detrimental to ductility of
the aluminum alloy. Particular examples of preferred amounts of
manganese include 0.30, 0.35, and 0.45 percent by weight.
[0030] Preferred amounts of zinc include 0.01 to 1.00 percent by
weight. The range of zinc described herein facilitates minimizing
or substantially eliminating `hot cracking` of the aluminum alloy
during solidification. Particular examples of preferred amounts of
zinc include 0.01, 0.03, 0.05, and 0.08 percent by weight.
[0031] Preferred amounts of titanium include 0.11 to 0.20 percent
by weight. The range of titanium described herein promotes
effective grain refinement and thereby generally contributes to
increased mechanical properties. More particularly, toughness is
increased by effective grain refinement. Particular examples of
preferred amounts of titanium include 0.11, 0.15, 0.18, 0.19, and
0.20 percent by weight.
[0032] It is a benefit of the aluminum alloy having 0.001 to 0.10
percent tin by weight that the response to artificial aging is
unexpectedly improved. In particular, the response to artificial
aging following solution treatment is unexpectedly improved by
including 0.001 to 0.10 percent tin by weight. Particular examples
of preferred amounts of tin include 0.003, 0.045, and 0.09 percent
by weight.
[0033] Preferred amounts of chromium include 0.001 to 0.10 percent
by weight. The range of chromium described herein facilitates a
reduction or substantially eliminates sludge formation in the
aluminum alloy. The term, `sludge` as used herein refers to a
complex of essentially iron, chromium and manganese. Particular
examples of preferred amounts of chromium include 0.003, 0.04, and
0.09 percent by weight.
[0034] It is an unexpected benefit of the aluminum alloy having
0.001 to 0.10 percent lead by weight that machinability is improved
while essentially eliminating "hot shortness" e.g., brittleness at
elevated temperatures. In this regard, higher lead content
generally increases machinability. On the other hand, increased
lead content also contributes to segregation of the element during
casting and cause hot shortness. Particular examples of preferred
amounts of lead include 0.003, 0.06, and 0.09 percent by
weight.
[0035] An aluminum alloy in accordance with the present invention
is suitable for SSM methods of casting because the microstructure
of the primary aluminum phase of the metal slurry prior to its
injection into a die cavity is comprised of globular and/or rosette
crystals.
[0036] An alloy in accordance with the present invention is
hypoeutectic because its silicon content is less than 12 percent.
The primary phase metal of an alloy in accordance with the present
invention is aluminum.
[0037] Alloys with silicon composing less than twelve percent of
their weight are hypoeutectic and alloys with silicon composing
more than twelve percent of their weight are hypereutectic.
[0038] Referring to FIG. 1 and FIG. 2, shown are microstructures of
the primary phase from various locations of an aluminum alloy in
accordance with the present invention prior to its injection into a
die cavity. The illustrations of FIG. 1 and FIG. 2 were ascertained
in accordance with the conventional evaluation method of
"water-quenching," which "locks in" the microstructure. The
microstructures of FIG. 1, from top to bottom, are from the middle
edge 10, middle 12 and center 14 of a water-quenched slug. It can
be seen from FIG. 1 that the primary aluminum phase particles
consist of round crystal/globular 16, and/or rosette 18
formations.
[0039] FIG. 2 depicts microstructures of the primary phase of an
aluminum alloy in accordance with the present invention prior to
its injection into a die cavity. The microstructures of FIG. 2,
from top to bottom, are from the bottom edge 20, middle 22 and
center 24 of a water-quenched slug. It can be seen from FIG. 2 that
the primary aluminum phase particles of an aluminum alloy in
accordance with the present invention consist of round
crystal/globular 26 and/or rosette 28 formations.
[0040] FIG. 3 depicts microstructures of the primary phase of an
aluminum alloy in accordance with the present invention after it
has been injected into a die cavity. It can be seen from FIG. 3
that the primary aluminum phase particles of an aluminum alloy in
accordance with the present invention consist of round
crystals/globular 32 and/or rosette 34 formations. Thus, when FIG.
1 and FIG. 2 are compared with FIG. 3, it can be seen that the
morphology of the primary aluminum phase prior to injection into a
die cavity is similar to that of the aluminum alloy in the
resulting casting. Accordingly, the microstructure of the primary
phase of an alloy in accordance with the present invention can be
determined before it is utilized to form a casting. Thus, the
number of casts with microstructures unsuitable for their purpose
can be reduced.
[0041] In an exemplary embodiment of the present invention silicon
is restricted to 7.2 percent to 8 percent of the weight to
efficiently achieve formation of the primary aluminum phase during
the cooling of the molten metal to the semi-solid state.
[0042] Additionally, the amount of silicon present in an aluminum
alloy may be directly related to the strength of the aluminum
alloy. Typically, the higher the content of silicon, the higher the
strength of the aluminum alloy. In exemplary embodiments of the
present invention, the average silicon content of the alloy is
higher than other alloys, such as the A356.2 and 357 aluminum
alloys. Accordingly, the strength of an aluminum alloy in
accordance with the present invention is higher than other alloys,
such as A 3562.2 and 357.
[0043] Further, as shown in FIG. 3, an aluminum alloy in accordance
with the present invention reveals the presence of fine
aluminum-silicon eutectic and entrapped intermetallic particles 30
within the round crystals, globular and/or rosette primary aluminum
phase. The entrapped intermetallic particles 30 essentially consist
of iron, silicon and manganese.
[0044] Typically, the formation of the intermetallic particles 30,
such as those shown in FIG. 3, lead to fractures that travel along
a path (fracture path) within the structure of the casting.
However, because the intermetallic particles 30 are entrapped
within the round crystal/globular 32 and/or rosette 34 structures,
the fracture path is now restricted. Accordingly, fractures occur
with less frequency, especially when an aluminum alloy in
accordance with the present invention is compared to the A356.2 and
357 aluminum alloys that do not reveal entrapped particles in their
microstructures in the primary aluminum phase.
[0045] The formation of the intermetallic particles in an aluminum
alloy in accordance with the present invention can be attributed to
the high content of iron in the aluminum alloy. In an exemplary
embodiment of the present invention, iron is 0.6 to 1.0 percent of
the weight. In another exemplary embodiment of the present
invention iron is 0.6 to 0.8 percent of the weight. The iron
content of an aluminum alloy in accordance with the present
invention is higher than other alloys, such as A 356.2 and 357
which are, at a maximum, 0.12 percent of the weight. Accordingly,
an alloy in accordance with the present invention is less expensive
than A 356.2 and 357 because the iron content does not have to be
maintained low. Additionally, because the iron content is not low,
the potential of soldering is reduced.
[0046] In an exemplary embodiment of the present invention,
magnesium is approximately 0.35 to 0.65 percent of the weight. The
magnesium content of an aluminum alloy in accordance with the
present invention is higher than the magnesium content of other
aluminum alloys, such as the A 356.2 and 357, which is 0.30 to 0.45
and 0.45 to 0.6 percent of the weight, respectively. The strength
of a casting made from an aluminum alloy in accordance with the
present invention will be even greater after the alloy has been
heat treated, i.e., subjected to a solution treatment and
artificially aged. In a preferred embodiment of an aluminum alloy
in accordance with the present invention, the magnesium content is
approximately 0.45 to 0.6 percent of the weight.
[0047] As a result of its high strength, an aluminum alloy in
accordance with the present invention is suitable for the
manufacturing of products that require high strength, such as axle
carriers, rack and pinion housings and steering column housings by
both Rheocasting and Thixocasting.
[0048] 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 spirit 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 as falling within
the scope of the invention.
* * * * *