U.S. patent application number 15/934342 was filed with the patent office on 2019-09-26 for aluminum alloy powders for powder bed fusion additive manufacturing processes.
The applicant listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Andrew C. Bobel, Tyson W. Brown, Anil K. Sachdev.
Application Number | 20190291182 15/934342 |
Document ID | / |
Family ID | 67848475 |
Filed Date | 2019-09-26 |
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United States Patent
Application |
20190291182 |
Kind Code |
A1 |
Bobel; Andrew C. ; et
al. |
September 26, 2019 |
ALUMINUM ALLOY POWDERS FOR POWDER BED FUSION ADDITIVE MANUFACTURING
PROCESSES
Abstract
A three-dimensional aluminum alloy part may be manufactured by a
process in which a layer of aluminum alloy powder feed material is
distributed over a substrate and scanned with a high-energy laser
or electron beam in selective regions corresponding to a
cross-section of the aluminum alloy part being formed. During the
manufacturing process, the selective regions may melt and form a
pool of molten aluminum alloy material. Thereafter, the pool of
molten aluminum alloy material may cool and solidify into a solid
layer of fused aluminum alloy material. During solidification of
the pool of molten aluminum alloy material, solid phase particles
may form within a solution of liquid phase aluminum prior to
formation of solid phase aluminum dendrites. The resulting aluminum
alloy part may exhibit a polycrystalline structure that
predominantly includes a plurality of equiaxed grains, instead of
columnar grains.
Inventors: |
Bobel; Andrew C.; (Clinton
Township, MI) ; Brown; Tyson W.; (Royal Oak, MI)
; Sachdev; Anil K.; (Rochester Hills, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
DETROIT |
MI |
US |
|
|
Family ID: |
67848475 |
Appl. No.: |
15/934342 |
Filed: |
March 23, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 2999/00 20130101;
B33Y 70/00 20141201; B22F 2301/052 20130101; B33Y 10/00 20141201;
C22C 21/02 20130101; C22C 1/0425 20130101; B22F 3/1055 20130101;
B22F 2999/00 20130101; B22F 1/0003 20130101; B22F 3/1055 20130101;
B22F 1/0003 20130101; C22C 1/0416 20130101; C22F 1/043 20130101;
C22C 1/0416 20130101; C22C 1/0425 20130101 |
International
Class: |
B22F 3/105 20060101
B22F003/105; B22F 1/00 20060101 B22F001/00; C22C 21/02 20060101
C22C021/02 |
Claims
1. An aluminum alloy powder for manufacturing a three-dimensional
high-strength aluminum alloy part by a powder bed fusion additive
manufacturing process, each particle of the aluminum alloy powder
comprising: an aluminum alloy including, by weight, 13-25% silicon,
0.1-10% copper, and 0-2% magnesium, wherein, when the aluminum
alloy is heated to a first temperature greater than a liquidus
temperature of the aluminum alloy and subsequently cooled to a
second temperature less than the liquidus temperature of the
aluminum alloy and greater than a solidus temperature of the
aluminum alloy, the aluminum alloy transitions from a liquid phase
to a multiphase system, and wherein the multiphase system includes
a solution of liquid phase aluminum and a solid phase of silicon
particles dispersed throughout the liquid phase aluminum.
2. The aluminum alloy powder of claim 1 wherein the aluminum alloy
comprises, by weight, 15-22% silicon, 2-5.1% copper, and 0.6-0.8%
magnesium.
3. The aluminum alloy powder of claim 1 wherein the aluminum alloy
comprises, by weight, 19-21% silicon, 3.5-4.1% copper, and aluminum
as balance.
4. The aluminum alloy powder of claim 1 wherein the aluminum alloy
comprises, by weight: greater than 0% iron and less than 9% iron,
and greater than 0% manganese and less than 5% manganese, and
wherein the multiphase system includes the solution of liquid phase
aluminum, the solid phase of silicon particles, and another solid
phase of iron-containing intermetallic particles dispersed
throughout the liquid phase aluminum.
5. An aluminum alloy powder for manufacturing a three-dimensional
high thermal conductivity aluminum alloy part by a powder bed
fusion additive manufacturing process, each particle of the
aluminum alloy powder comprising: an aluminum alloy including, by
weight: greater than 95% aluminum, and greater than 0% and less
than 5% of at least one nucleating agent, and wherein the at least
one nucleating agent comprises an element or compound having a
solid solubility in aluminum of, by weight, less than 0.5% at
temperatures less than 530 degrees Celsius, wherein, when the
aluminum alloy is heated to a first temperature greater than a
liquidus temperature of the aluminum alloy and subsequently cooled
to a second temperature less than the liquidus temperature of the
aluminum alloy and greater than a solidus temperature of the
aluminum alloy, the alloy transitions from a liquid phase to a
multiphase system, and wherein the multiphase system includes a
solution of liquid phase aluminum and a solid phase of particles of
the at least one nucleating agent dispersed throughout the liquid
phase aluminum.
6. The aluminum alloy powder of claim 5 wherein the at least one
nucleating agent comprises an element or compound having a solid
solubility in aluminum of, by weight, less than or equal to 2.0% at
the second temperature.
7. A method of manufacturing a three-dimensional aluminum alloy
part, the method comprising: (a) providing an aluminum alloy powder
feed material; (b) distributing a layer of the powder feed material
over a substrate; (c) scanning selective regions of the layer of
the powder feed material with a high-energy laser or electron beam
to form a pool of molten aluminum alloy material therein, the
selective regions of the layer of the powder feed material
corresponding to a cross-section of an aluminum alloy part being
formed; (d) terminating the laser or electron beam to cool and
solidify the pool of molten aluminum alloy material into a solid
layer of fused aluminum alloy material; and (e) sequentially
repeating steps (b) through (d) to form an aluminum alloy part made
up of a plurality of solid layers of fused aluminum alloy material,
wherein, during solidification of the pool of molten aluminum alloy
material, solid phase particles form within a solution of liquid
phase aluminum prior to formation of solid phase aluminum
dendrites, and wherein, each of the solid layers of fused aluminum
alloy material in the aluminum alloy part includes a continuous
aluminum matrix phase that exhibits a polycrystalline structure and
predominantly includes a plurality of equiaxed grains.
8. The method of claim 7 wherein, after termination of the laser or
electron beam, the pool of molten aluminum alloy material is cooled
at a rate in the range of 10.sup.4 Kelvin per second to 10.sup.6
Kelvin per second.
9. The method of claim 7 wherein, during solidification of the pool
of molten aluminum alloy material, the molten aluminum alloy
material transitions from an entirely liquid phase to a multiphase
system in which the solid phase particles are dispersed throughout
the solution of liquid phase aluminum.
10. The method of claim 7 wherein the solid phase particles serve
as nuclei for the subsequent formation of the solid phase aluminum
dendrites, and wherein, after the solid phase particles form within
the solution of liquid phase aluminum, the solid phase aluminum
dendrites nucleate and grow in multiple directions on the solid
phase particles.
11. The method of claim 10 wherein growth of the solid phase
aluminum dendrites is arrested when neighboring aluminum dendrites
impinge upon one another and form grain boundaries.
12. The method of claim 7 wherein each particle of the aluminum
alloy powder feed material comprises, by weight, 13-25% silicon,
and wherein the solid phase particles comprise particles of
silicon.
13. The method of claim 12 wherein each particle of the aluminum
alloy powder feed material also comprises, by weight: greater than
0% iron and less than 9% iron, and greater than 0% manganese and
less than 5% manganese, and wherein the solid phase particles
comprise the particles of silicon and iron-containing intermetallic
particles.
14. The method of claim 12 wherein each particle of the aluminum
alloy powder feed material also comprises, by weight, 0.1-10%
copper and 0-2% magnesium.
15. The method of claim 14 including: heating the aluminum alloy
part at a temperature in the range of 180.degree. C. to 210.degree.
C. for a duration of 0.5 hours to 7 hours to form at least one
copper-containing precipitate phase within the aluminum matrix
phase of each of the solid layers of fused aluminum alloy material
in the aluminum alloy part.
16. The method of claim 7 wherein each particle of the aluminum
alloy powder feed material comprises, by weight: greater than 95%
aluminum, and greater than 0% and less than 5% of at least one
nucleating agent, and wherein the at least one nucleating agent
comprises an element or compound having a solid solubility in
aluminum of, by weight, less than 0.5% at temperatures less than
530 degrees Celsius.
17. The method of claim 16 wherein each particle of the aluminum
alloy powder feed material comprises, by weight, greater than 98%
aluminum and less than 2% of the at least one nucleating agent.
18. The method of claim 16 wherein the at least one nucleating
agent comprises at least one element or compound of titanium (Ti),
boron (B), beryllium (Be), cobalt (Co), chromium (Cr), cesium (Cs),
iron (Fe), hafnium (Hf), manganese (Mn), molybdenum (Mo), niobium
(Nb), lead (Pb), sulfur (S), zirconium (Zr), antimony (Sb),
scandium (Sc), selenium (Se), strontium (Sr), tantalum (Ta),
vanadium (V), or tungsten (W).
19. The method of claim 18 wherein each particle of the aluminum
alloy powder feed material comprises, by weight, at least one of
greater than 0% B and less than 5% B, greater than or equal to 0.7%
Be and less than 5% Be, greater than or equal to 0.9% Co and less
than 5% Co, greater than or equal to 0.3% Cr and less than 5% Cr,
greater than 0% Cs and less than 5% Cs, greater than or equal to
1.7% Fe and less than 5% Fe, greater than or equal to 0.4% Hf and
less than 5% Hf, greater than or equal to 1.8% Mn and less than 5%
Mn, greater than 0% Mo and less than 5% Mo, greater than 0% Nb and
less than 5% Nb, greater than or equal to 1.4% Pb and less than 5%
Pb, greater than 0% S and less than 5% S, greater than or equal to
0.9% Sb and less than 5% Sb, greater than or equal to 0.4% Sc and
less than 5% Sc, greater than 0% Se and less than 5% Se, greater
than or equal to 0.5% Sr and less than 5% Sr, greater than 0% Ta
and less than 5% Ta, greater than or equal to 0.12% Ti and less
than 5% Ti, greater than 0% V and less than 5% V, greater than 0% W
and less than 5% W, or greater than 0% Zr and less than 5% Zr.
20. The method of claim 18 wherein each particle of the aluminum
alloy powder feed material comprises, by weight, greater than 0.12%
Ti, less than 5% Ti, and aluminum as balance.
Description
INTRODUCTION
[0001] A variety of aluminum alloy compositions have been developed
for use in the manufacture of three-dimensional aluminum alloy
parts via casting and/or hot forming operations to impart certain
desirable chemical and mechanical properties to the resulting
parts. However, it has been found that when such aluminum alloy
compositions are employed as a powder feed material in a powder bed
fusion additive manufacturing process, the resulting aluminum alloy
parts oftentimes exhibit a columnar grain structure, and thus are
relatively susceptible to cracking along grain boundaries between
adjacent columnar grains. Therefore, there is a need in the art for
an aluminum alloy composition that can be employed in a powder bed
fusion additive manufacturing process to form three-dimensional
aluminum alloy parts that predominantly exhibit an equiaxed grain
structure and thus are relatively resistant or impervious to
solidification cracking.
SUMMARY
[0002] In accordance with one aspect of the present disclosure, an
aluminum alloy powder for manufacturing a three-dimensional
high-strength aluminum alloy part by a powder bed fusion additive
manufacturing process is provided. Each particle of the aluminum
alloy powder may comprise an aluminum alloy that includes, by
weight, 13-25% silicon, 0.1-10% copper, and 0-2% magnesium. When
the aluminum alloy is heated to a first temperature greater than a
liquidus temperature of the aluminum alloy and subsequently cooled
to a second temperature less than the liquidus temperature of the
aluminum alloy and greater than a solidus temperature of the
aluminum alloy, the aluminum alloy may transition from a liquid
phase to a multiphase system. The multiphase system may include a
solution of liquid phase aluminum and a solid phase of silicon
particles dispersed throughout the liquid phase aluminum.
[0003] In one form, the aluminum alloy may comprise, by weight,
15-22% silicon, 2-5.1% copper, and 0.6-0.8% magnesium. In another
form, the aluminum alloy powder may comprise, by weight, 19-21%
silicon, 3.5-4.1% copper, and aluminum as balance.
[0004] The aluminum also may comprise, by weight: greater than 0%
iron and less than 9% iron, and greater than 0% manganese and less
than 5% manganese. In such case, the multiphase system may include
the solution of liquid phase aluminum, the solid phase of silicon
particles, and another solid phase of iron-containing intermetallic
particles dispersed throughout the liquid phase aluminum.
[0005] In accordance with another aspect of the present disclosure,
an aluminum alloy powder for manufacturing a three-dimensional high
thermal conductivity aluminum alloy part by a powder bed fusion
additive manufacturing process is provided. Each particle of the
aluminum alloy powder may comprise an aluminum alloy that includes,
by weight: greater than 95% aluminum, and greater than 0% and less
than 5% of at least one nucleating agent. The at least one
nucleating agent may comprise an element or compound having a solid
solubility in aluminum of, by weight, less than 0.5% at
temperatures less than 530 degrees Celsius. When the aluminum alloy
is heated to a first temperature greater than a liquidus
temperature of the aluminum alloy and subsequently cooled to a
second temperature less than the liquidus temperature of the
aluminum alloy and greater than a solidus temperature of the
aluminum alloy, the aluminum alloy may transition from a liquid
phase to a multiphase system. The multiphase system may include a
solution of liquid phase aluminum and a solid phase of particles of
the at least one nucleating agent dispersed throughout the liquid
phase aluminum. In one form, the at least one nucleating agent may
comprise an element or compound having a solid solubility in
aluminum of, by weight, less than or equal to 2.0% at the second
temperature.
[0006] A method of manufacturing a three-dimensional aluminum alloy
part may comprise the following step. In step (a), an aluminum
alloy powder feed material may be provided. In step (b), a layer of
the powder feed material may be distributed over a substrate. In
step (c), selective regions of the layer of the powder feed
material may be scanned with a high-energy laser or electron beam
to form a pool of molten aluminum alloy material therein. The
selective regions of the layer of the powder feed material may
correspond to a cross-section of an aluminum alloy part being
formed. In step (d), the laser or electron beam may be terminated
to cool and solidify the pool of molten aluminum alloy material
into a solid layer of fused aluminum alloy material. Steps (b)
through (d) may be sequentially repeated to form an aluminum alloy
part made up of a plurality of solid layers of fused aluminum alloy
material. During solidification of the pool of molten aluminum
alloy material, solid phase particles may form within a solution of
liquid phase aluminum prior to formation of solid phase aluminum
dendrites. Each of the solid layers of fused aluminum alloy
material in the aluminum alloy part may include a continuous
aluminum matrix phase that exhibits a polycrystalline structure and
predominantly includes a plurality of equiaxed grains.
[0007] After termination of the laser or electron beam, the pool of
molten aluminum alloy material may be cooled at a rate in the range
of 10.sup.4 Kelvin per second to 10.sup.6 Kelvin per second.
[0008] During solidification of the pool of molten aluminum alloy
material, the molten aluminum alloy material may transition from an
entirely liquid phase to a multiphase system. In the multiphase
system, the solid phase particles may be dispersed throughout the
solution of liquid phase aluminum.
[0009] The solid phase particles may serve as nuclei for the
subsequent formation of the solid phase aluminum dendrites. In such
case, after the solid phase particles form within the solution of
liquid phase aluminum, the solid phase aluminum dendrites may
nucleate and grow in multiple directions on the solid phase
particles. Growth of the solid phase aluminum dendrites may be
arrested when neighboring aluminum dendrites impinge upon one
another and form grain boundaries.
[0010] In one form, each particle of the aluminum alloy powder feed
material may comprise, by weight, 13-25% silicon. In such case, the
solid phase particles may comprise particles of silicon.
[0011] Each particle of the aluminum alloy powder feed material
also may comprise, by weight: greater than 0% iron and less than 9%
iron, and greater than 0% manganese and less than 5% manganese. In
such case, the solid phase particles may comprise the particles of
silicon and iron-containing intermetallic particles.
[0012] Each particle of the aluminum alloy powder feed material
also may comprise, by weight, 0.1-10% copper and 0-2% magnesium. In
such case, the aluminum alloy part may be heated at a temperature
in the range of 180.degree. C. to 210.degree. C. for a duration of
0.5 hours to 7 hours to form at least one copper-containing
precipitate phase within the aluminum matrix phase of each of the
solid layers of fused aluminum alloy material in the aluminum alloy
part.
[0013] In another form, each particle of the aluminum alloy powder
feed material may comprise, by weight: greater than 95% aluminum,
and greater than 0% and less than 5% of at least one nucleating
agent. The at least one nucleating agent may comprise an element or
compound having a solid solubility in aluminum of, by weight, less
than 0.5% at temperatures less than 530 degrees Celsius.
[0014] In one specific example, each particle of the aluminum alloy
powder feed material may comprise, by weight, greater than 98%
aluminum and less than 2% of the at least one nucleating agent.
[0015] The at least one nucleating agent may comprise at least one
element or compound of titanium (Ti), boron (B), beryllium (Be),
cobalt (Co), chromium (Cr), cesium (Cs), iron (Fe), hafnium (Hf),
manganese (Mn), molybdenum (Mo), niobium (Nb), lead (Pb), sulfur
(S), zirconium (Zr), antimony (Sb), scandium (Sc), selenium (Se),
strontium (Sr), tantalum (Ta), vanadium (V), or tungsten (W).
[0016] In one form, each particle of the aluminum alloy powder feed
material may comprise, by weight, at least one of greater than 0% B
and less than 5% B, greater than or equal to 0.7% Be and less than
5% Be, greater than or equal to 0.9% Co and less than 5% Co,
greater than or equal to 0.3% Cr and less than 5% Cr, greater than
0% Cs and less than 5% Cs, greater than or equal to 1.7% Fe and
less than 5% Fe, greater than or equal to 0.4% Hf and less than 5%
Hf, greater than or equal to 1.8% Mn and less than 5% Mn, greater
than 0% Mo and less than 5% Mo, greater than 0% Nb and less than 5%
Nb, greater than or equal to 1.4% Pb and less than 5% Pb, greater
than 0% S and less than 5% S, greater than or equal to 0.9% Sb and
less than 5% Sb, greater than or equal to 0.4% Sc and less than 5%
Sc, greater than 0% Se and less than 5% Se, greater than or equal
to 0.5% Sr and less than 5% Sr, greater than 0% Ta and less than 5%
Ta, greater than or equal to 0.12% Ti and less than 5% Ti, greater
than 0% V and less than 5% V, greater than 0% W and less than 5% W,
or greater than 0% Zr and less than 5% Zr.
[0017] In one specific form, each particle of the aluminum alloy
powder feed material may comprise, by weight, greater than 0.12%
Ti, less than 5% Ti, and aluminum as balance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a temperature (.degree. C.) vs. composition
equilibrium phase diagram of a binary Al--Si alloy system;
[0019] FIG. 2 is a schematic perspective view of an apparatus for
manufacturing aluminum alloy parts via a powder bed fusion additive
manufacturing process using an aluminum alloy powder feed material,
in accordance with one embodiment of the present disclosure;
[0020] FIG. 3 is a magnified view of a layer of the aluminum alloy
powder feed material distributed over a previously solidified layer
of aluminum alloy material on a building platform of the apparatus
of FIG. 2;
[0021] FIG. 4 is a magnified view of a laser beam impinging upon
and melting the layer of the aluminum alloy powder feed material of
FIG. 3;
[0022] FIG. 5 is a schematic illustration of a plurality of
columnar-shaped aluminum dendrites growing in epitaxy with a
surface of a substrate during solidification of a conventional
aluminum alloy;
[0023] FIG. 6 is a schematic illustration of a plurality of
unidirectionally solidified columnar grains formed within the
conventional aluminum alloy of FIG. 5 after solidification
thereof;
[0024] FIG. 7 is a schematic illustration of a plurality of solid
phase particles serving as nuclei for the subsequent nucleation and
growth of aluminum dendrites during solidification of the presently
disclosed aluminum alloys; and
[0025] FIG. 8 is a schematic illustration of a plurality of
equiaxed grains formed within the aluminum alloy of FIG. 7 after
solidification thereof.
DETAILED DESCRIPTION
[0026] The presently disclosed aluminum alloys can be prepared in
powder form and used in various powder bed fusion additive
manufacturing processes to produce three-dimensional aluminum alloy
parts that predominantly exhibit an equiaxed grain structure and
relatively high resistance to solidification cracking, as compared
to aluminum alloy parts that predominantly exhibit a columnar grain
structure. To inhibit the formation of columnar grains within the
aluminum alloy parts during the powder bed fusion process, the
aluminum alloys include at least one element or compound that,
during solidification of the aluminum alloys, nucleates within a
solution of liquid phase aluminum and serves as nuclei for the
subsequent nucleation and growth of aluminum dendrites. As the
aluminum dendrites grow outward in all directions from their
respective nuclei, the aluminum dendrites eventually impinge upon
neighboring dendrites and form grain boundaries. Because the
nucleation and growth of the aluminum dendrites occurs throughout
the solidifying aluminum alloy, instead of along a single plane
(e.g., on a substrate or on a layer of previously solidified
aluminum alloy material), the formation of columnar grains within
the solidifying alloy is prevented or inhibited.
[0027] As used herein, the term "aluminum alloy" refers to a
material that comprises, by weight, greater than or equal to 50%
aluminum (Al) and one or more other elements selected to impart
certain desirable properties to the material that are not exhibited
by pure aluminum.
[0028] In one form, an aluminum alloy composition for manufacturing
a three-dimensional high-strength aluminum alloy part by an
additive manufacturing process may comprise, in addition to
aluminum, alloying elements of silicon (Si) and copper (Cu), and
thus may be referred to herein as an "Al--Si--Cu alloy." More
specifically, the Al--Si--Cu alloy may comprise, by weight, greater
than or equal to 13%, 15%, or 19% silicon; less than 25%, 22%, or
21% silicon; or between 13-25%, 15-22%, or 19-21% silicon. In
addition, the Al--Si--Cu alloy may comprise, by weight, greater
than or equal to 0.1%, 2%, or 3.5% copper; less than 10%, 5.1%, or
4.1%, copper; or between 0.1-10%, 2-5.1%, or 3.5-4.1% copper.
[0029] FIG. 1 depicts an equilibrium phase diagram 10 for a binary
Al--Si alloy. As shown, a binary Al--Si alloy that includes, by
weight, about 12.6% Si and the balance Al is a eutectic
composition, as indicated by the presence of a eutectic-type
invariant point 12 at such composition on the binary Al--Si
equilibrium phase diagram 10. At the eutectic point 12, the
liquidus lines 14 and the solidus line 16 intersect and, at
equilibrium, a liquid phase (L) and two solid phases, i.e.,
Al.sub.(s) and solid Si.sub.(s), coexist. Binary Al--Si alloys that
include, by weight, greater than 12.6% Si and the balance Al (such
as the presently disclosed Al--Si--Cu alloy) contain more Si than
the Al--Si eutectic composition and thus are referred to as
hypereutectic compositions. As shown in FIG. 1, when a binary
Al--Si alloy having a eutectic composition is cooled through the
eutectic point 12, from a first temperature above the solidus line
16 (and above the eutectic temperature (T.sub.E) of the alloy
(i.e., about 577.degree. C.)) to a second temperature below the
solidus line 16 and below the T.sub.E of the alloy, the Al--Si
alloy undergoes a eutectic transformation and transitions from an
entirely liquid phase (L) to an entirely solid phase
(Al.sub.(s)+Si.sub.(s)). On the other hand, when an Al--Si alloy
having a hypereutectic composition is melted to form an entirely
liquid phase (L) and is subsequently cooled from a first
temperature above the liquidus line 14 to a second temperature
below the liquidus line 14, the Al--Si alloy does not directly
transition from the liquid phase (L) to an entirely solid phase.
Instead, as this hypereutectic Al--Si alloy is cooled to a
temperature below the liquidus line 14, the Al--Si alloy
transitions to a two-phase system, including a liquid phase (L) of
aluminum and a solid phase (Si.sub.(s)) of substantially pure
silicon particles. If the hypereutectic Al--Si alloy is further
cooled to a third temperature below the solidus line 16, the Al--Si
alloy will eventually transition to an entirely solid phase
including an aluminum matrix phase and a dispersed phase of silicon
(Al.sub.(s)+Si.sub.(s)). Without intending to be bound by theory,
it is believed that the solidification behavior of a binary Al--Si
alloy having a eutectic or hypereutectic composition may be due, at
least in part, to the exceptionally low solubility of silicon in
aluminum and the relatively high melting point of silicon
(m.p..about.1414.degree. C.) as compared to that of aluminum
(m.p..about.660.degree. C.).
[0030] The amount of silicon in the Al--Si--Cu alloy described
herein is selected so that the Al--Si--Cu alloy exhibits a
hypereutectic composition and can be heated to a temperature above
a liquidus temperature of the Al--Si--Cu alloy and subsequently
cooled to a temperature below a solidus temperature of the
Al--Si--Cu alloy to produce an entirely solid polycrystalline
Al--Si--Cu alloy that predominantly exhibits an equiaxed grain
structure, instead of a columnar grain structure. Without intending
to be bound by theory, it is believed that the equiaxed grain
structure of the resulting polycrystalline Al--Si--Cu alloy is due,
at least in part, to the solidification behavior of the Al--Si--Cu
alloy. In particular, it is believed that, when the hypereutectic
Al--Si--Cu alloy is heated to a temperature above the liquidus
temperature of the Al--Si--Cu alloy and subsequently cooled to a
temperature below the liquidus temperature of the Al--Si--Cu alloy,
the Al--Si--Cu alloy will transition from an entirely liquid phase
to a multiphase system. During this transition, particles of solid
phase silicon will nucleate throughout a solution of liquid phase
aluminum to produce a multiphase system that includes a solution of
liquid phase aluminum and a solid phase of silicon particles
dispersed throughout the liquid phase aluminum. Nucleation of the
particles of solid phase silicon may occur simultaneously
throughout multiple horizontally and vertically spaced-apart
regions of the solution of liquid phase aluminum, and may occur
generally homogeneously throughout the solution of liquid phase
aluminum. Thereafter, when the hypereutectic Al--Si--Cu alloy is
further cooled to a temperature at or below the solidus temperature
of the Al--Si--Cu alloy, solid phase aluminum dendrites will
nucleate and grow in multiple directions on the previously formed
silicon particles. Growth of these aluminum dendrites will
eventually be arrested when neighboring aluminum dendrites impinge
upon one another and form grain boundaries. After the hypereutectic
Al--Si--Cu alloy has completely solidified, the Al--Si--Cu alloy
will exhibit a polycrystalline structure including a continuous
aluminum matrix phase and a dispersed phase of silicon. In
addition, the resulting hypereutectic Al--Si--Cu alloy will
predominantly include a plurality of randomly oriented equiaxed
grains, instead of columnar grains. The equiaxed grains may have a
mean grain diameter in the range of 0.1 .mu.m to 50 .mu.m.
[0031] The Al--Si--Cu alloy may have a liquidus temperature in the
range of 570.degree. C. to 850.degree. C., and a solidus
temperature in the range of 500.degree. C. to 540.degree. C. As
such, the Al--Si--Cu alloy may exhibit a multiphase system of
liquid phase aluminum and solid phase silicon at a temperature in
the range of 500.degree. C. to 850.degree. C.
[0032] As used herein, the term "predominantly" means something,
for example, a grain structure, that is present in the greatest
amount by volume, as compared to other similar things, for example,
as compared to other grain structures.
[0033] The amount of copper in the Al--Si--Cu alloy is selected to
provide the alloy with the ability to develop one or more
Cu-containing precipitate phases within the aluminum matrix phase
when the Al--Si--Cu alloy is subjected to a heat treatment process.
For example, the amount of copper in the Al--Si--Cu alloy may be
selected to provide the alloy with the ability to develop an Al-
and Cu-based precipitate (referred to herein as an "AlCu
precipitate") phase within the aluminum matrix phase when the
Al--Si--Cu alloy is subjected to a heat treatment process that
includes an aging heat treatment stage and optionally a solution
heat treatment stage. The AlCu precipitate phase is Al- and
Cu-based, meaning that Al and Cu constitute the largest
constituents of the precipitate phase by weight. Formation of the
AlCu precipitate phase within the aluminum matrix phase may provide
the Al--Si--Cu alloy with high strength at relatively low
temperatures, e.g., at ambient temperature (e.g., 25.degree. C.)
and at temperatures up to about 200.degree. C.
[0034] In some embodiments, the Al--Si--Cu alloy also may comprise
alloying elements of magnesium (Mg), iron (Fe), and/or manganese
(Mn). When present, the Al--Si--Cu alloy may comprise, by weight,
greater than or equal to 0%, 0.5%, or 0.6% magnesium; less than 2%,
1.5%, or 0.8% magnesium; or between 0-2%, 0.5-1.5%, or 0.6-0.8%
magnesium. The Al--Si--Cu alloy may comprise, by weight, greater
than or equal to 0% or 7% iron; less than 10% or 9% iron; or
between 0-10% or 7-9% iron. The Al--Si--Cu alloy may comprise, by
weight, greater than or equal to 0% or 3% manganese; less than 6%
or 5% manganese; or between 0-6% or 3-5% manganese.
[0035] The amount of magnesium in the Al--Si--Cu alloy may be
selected to provide the alloy with the ability to develop an Al-,
Cu-, Mg-, and Si-based precipitate (referred to herein as an
"AlCuMgSi precipitate") phase within the aluminum matrix phase when
the Al--Si--Cu alloy is subjected to a heat treatment process that
includes an aging heat treatment stage and optionally a solution
heat treatment stage. The AlCuMgSi precipitate phase is Al-, Cu-,
Mg-, and Si-based, meaning that Al, Cu, Mg, and Si constitute the
largest constituents of the precipitate phase by weight. Formation
of the AlCuMgSi precipitate phase within the aluminum matrix phase
may provide the Al--Si--Cu alloy with high strength at ambient
temperature and at elevated temperatures (e.g., up to about
300.degree. C.).
[0036] The amount of iron and manganese in the Al--Si--Cu alloy may
be selected to promote the formation of at least one intermetallic
phase within the Al--Si--Cu alloy during solidification thereof. In
particular, the amount of iron and/or manganese in the Al--Si--Cu
alloy may be selected so that at least one intermetallic phase
nucleates within the liquid phase aluminum during solidification of
the Al--Si--Cu alloy and provides additional nucleation sites (in
addition to the nucleation sites provided by the silicon particles)
for the subsequent nucleation and equiaxed growth of aluminum
dendrites. For example, the at least one intermetallic phase may
comprise an Fe-containing intermetallic phase and/or a
Mn-containing intermetallic phase. In one specific example, the
amount of iron in the Al--Si--Cu alloy may be selected to promote
the formation of solid particles of an Al-, Fe-, and Si-based
intermetallic (referred to herein as an "AlFeSi intermetallic")
phase within the liquid phase aluminum during solidification of the
Al--Si--Cu alloy. The AlFeSi intermetallic phase is Al-, Fe-, and
Si-based, meaning that Al, Fe, and Si are the largest constituents
of the intermetallic phase. For example, the combined amounts of
Al, Fe, and Si in the AlFeSi intermetallic phase may account for,
by weight, greater than 50% of the AlFeSi intermetallic phase and,
in some cases, greater than 90% of the AlFeSi intermetallic
phase.
[0037] In embodiments where the Al--Si--Cu alloy comprises iron,
the amount of manganese in the Al--Si--Cu alloy may be selected to
promote the formation of an Al-, Fe-, Mn-, and Si-based
intermetallic (referred to herein as an "AlFeMnSi intermetallic")
phase within the liquid phase aluminum during solidification of the
Al--Si--Cu alloy and to inhibit the formation of an Al-, Fe-, and
Si-based intermetallic (referred to herein as an "AlFeSi
intermetallic") phase.
[0038] The hypereutectic Al--Si--Cu alloy does not require addition
of scandium (Sc) to achieve an equiaxed grain structure during
solidification thereof. As such, the amount of Sc in the Al--Si--Cu
alloy may be less than 0.2%, preferably less than 0.05%, and more
preferably less than 0.01% by weight of the Al--Si--Cu alloy.
[0039] Additional elements not intentionally introduced into the
composition of the Al--Si--Cu alloy nonetheless may be inherently
present in the alloy in relatively small amounts, for example, less
than 0.2%, preferably less than 0.05%, and more preferably less
than 0.01% by weight of the Al--Si--Cu alloy. Such elements may be
present, for example, as impurities in the raw materials used to
prepare the Al--Si--Cu alloy composition. In embodiments were the
Al--Si--Cu alloy is referred to as comprising one or more alloying
elements (e.g., one or more of Si, Cu, Mg, Fe, and Mn) and aluminum
as balance, the term "as balance" does not exclude the presence of
additional elements not intentionally introduced into the
composition of the Al--Si--Cu alloy but nonetheless inherently
present in the alloy in relatively small amounts, e.g., as
impurities.
[0040] In another form, an aluminum alloy composition for
manufacturing a three-dimensional high thermal conductivity
aluminum alloy part by an additive manufacturing process may
comprise, by weight, greater than or equal to 95% aluminum and less
than 5% of at least one nucleating agent, and thus may be referred
to as a "high-purity Al alloy." In one specific example, the
high-purity Al alloy may comprise, by weight, greater than or equal
to 98% aluminum and less than 2% of at least one nucleating
agent.
[0041] The at least one nucleating agent included in the
high-purity Al alloy may comprise an element or compound that
exhibits relatively low solid solubility (e.g., less than 1 wt %
or, more preferably, less than 0.5 wt %) in aluminum at
temperatures less than 530.degree. C. The composition and amount of
the at least one nucleating agent included in the high-purity Al
alloy may be selected so that the high-purity Al alloy can be
heated to a temperature above a liquidus temperature of the
high-purity Al alloy and subsequently cooled to a temperature below
a solidus temperature of the high-purity Al alloy to produce an
entirely solid polycrystalline high-purity Al alloy that
predominantly exhibits an equiaxed grain structure, instead of a
columnar grain structure.
[0042] In particular, the composition and amount of the at least
one nucleating agent in the high-purity Al alloy may be selected so
that, when the high-purity Al alloy is melted and subsequently
cooled from an entirely liquid phase to an entirely solid phase,
particles of the at least one nucleating agent will form within a
solution of liquid phase aluminum prior to formation of a solid
aluminum matrix phase. More specifically, when the high-purity Al
alloy is heated to a temperature above the liquidus temperature of
the high-purity Al alloy and subsequently cooled to a temperature
below the liquidus temperature of the high-purity Al alloy, the
high-purity Al alloy will transition from an entirely liquid phase
to a multiphase system. During this transition, solid particles of
the at least one nucleating agent will nucleate throughout a
solution of liquid phase aluminum to produce a multiphase system
that includes a solution of liquid phase aluminum and a solid phase
of particles of the at least one nucleating agent dispersed
throughout the liquid phase aluminum. In the multiphase system, the
solid particles of the at least one nucleating agent may exhibit a
solubility in liquid aluminum of, by weight, less than or equal to
2%, which may help maximize the number if solid particles within
the liquid phase aluminum. Nucleation of the solid particles of the
at least one nucleating agent may occur simultaneously throughout
multiple horizontally and vertically spaced-apart regions of the
solution of liquid phase aluminum, and may occur generally
homogeneously throughout the solution of liquid phase aluminum.
Thereafter, as the high-purity Al alloy continues to cool, solid
phase aluminum dendrites will nucleate and grown in multiple
directions on the previously formed nuclei (i.e., on the solid
particles of the at least one nucleating agent). Growth of these
aluminum dendrites within the solidifying high-purity Al alloy will
eventually be arrested when neighboring aluminum dendrites impinge
upon one another and form grain boundaries. After the high-purity
Al alloy has been cooled to a temperature below the solidus
temperature of the high-purity Al alloy and is completely
solidified, the high-purity Al alloy will exhibit a polycrystalline
structure including a continuous aluminum matrix phase and a
dispersed phase of particles of the at least one nucleating agent.
In addition, the resulting high-purity Al alloy will predominantly
include a plurality of randomly oriented equiaxed grains, instead
of columnar grains. The equiaxed grains may have a mean diameter in
the range of 0.1 .mu.m to 50 .mu.m.
[0043] The high-purity Al alloy may have a liquidus temperature in
the range of 660.degree. and 1300.degree. C. and a solidus
temperature in the range of 650.degree. and 680.degree. C. As such,
the high-purity Al alloy may exhibit a multiphase system of liquid
phase aluminum and solid particles of the at least one nucleating
agent at a temperature in the range of 650.degree. and 1300.degree.
C.
[0044] Due to the relatively low solubility of the at least one
nucleating agent in solid aluminum, limited amounts of the at least
one nucleating agent will be present in solid solution in the
aluminum matrix phase after complete solidification of the
high-purity Al alloy. As such, inclusion of the at least one
nucleating agent in the high-purity Al alloy will have little to no
adverse effect on the thermal conductivity of the high-purity Al
alloy. For example, after complete solidification, the high-purity
Al alloy may exhibit a thermal conductivity in the range of 120
watts per meter-Kelvin (W/(mK)) to 220 W/(mK).
[0045] In some embodiments, the at least one nucleating agent may
comprise an element that, when present in the high-purity Al alloy,
exhibits a eutectic point or a peritectic point at a concentration
of, by weight, less than 5% of the high-purity Al alloy. In such
case, the element may be present in the high-purity Al alloy in an
amount that is greater than the amount of the same element in the
eutectic or peritectic composition of the Al alloy.
[0046] For example, in one form, the at least one nucleating agent
may comprise titanium (Ti). A binary Al--Ti alloy exhibits a
peritectic point at a composition of, by weight, about 0.12% Ti and
a temperature of about 665.degree. C. Therefore, in one form, the
high-purity Al alloy may comprise a high-purity Al--Ti alloy
including, by weight, greater than or equal to 95% aluminum,
greater than 0.12% titanium, and less than 5% titanium. In such
case, when this high-purity Al--Ti alloy is melted and subsequently
cooled from an entirely liquid phase to an entirely solid phase,
solid particles of Al.sub.3Ti will nucleate within a solution of
liquid phase aluminum at the liquidus temperature of the alloy.
Thereafter, aluminum dendrites will nucleate and grown in all
directions on the previously formed Al.sub.3Ti particles, resulting
in the formation of a polycrystalline structure that predominantly
includes a plurality of randomly oriented equiaxed grains, instead
of columnar grains.
[0047] Some examples of elements (in addition to Ti) that can be
used as the at least one nucleating agent in the high-purity Al
alloy include boron (B), beryllium (Be), cobalt (Co), chromium
(Cr), cesium (Cs), iron (Fe), hafnium (Hf), manganese (Mn),
molybdenum (Mo), niobium (Nb), lead (Pb), sulfur (S), zirconium
(Zr), antimony (Sb), scandium (Sc), selenium (Se), strontium (Sr),
tantalum (Ta), vanadium (V), tungsten (W), and combinations
thereof. For example, the high-purity Al alloy may include, by
weight, equal to or greater than 0% B to 5% B, 0.7-5% Be, 0.9-5%
Co, 0.3-5% Cr, equal to or greater than 0% Cs to 5% Cs, 1.7-5% Fe,
0.4-5% Hf, 1.8-5% Mn, equal to or greater than 0% Mo to 5% Mo,
equal to or greater than 0% Nb to 5% Nb, 1.4-5% Pb, equal to or
greater than 0% S to 5% S, 0.9-5% Sb, 0.4-5% Sc, equal to or
greater than 0% Se to 5% Se, 0.5-5% Sr, equal to or greater than 0%
Ta to 5% Ta, 0.12-5% Ti, equal to or greater than 0% V to 5% V,
equal to or greater than 0% W to 5% W, and/or equal to or greater
than 0% Zr to 5% Zr, and the balance Al.
[0048] The high-purity Al alloy may include one or more additional
elements that may or may not be intentionally introduced into the
composition of the high-purity Al alloy, with such additional
elements being present in the high-purity Al alloy in amounts less
than 0.2%, preferably less than 0.05%, and more preferably less
than 0.01% by weight of the high-purity Al alloy. Additional
elements not intentionally introduced into the composition of the
high-purity Al alloy may be present, for example, as impurities in
the raw materials used to prepare the high-purity Al alloy
composition. In embodiments were the high-purity Al alloy is
referred to as comprising at least one nucleating agent (e.g., at
least one element or compound of Ti, B, Be, Co, Cr, Cs, Fe, Hf, Mn,
Mo, Nb, Pb, S, Zr, Sb, Sc, Se, Sr, Ta, V, or W) and aluminum as
balance, the term "as balance" does not exclude the presence of
additional elements not intentionally introduced into the
composition of the high-purity Al alloy but nonetheless inherently
present in the alloy in relatively small amounts, e.g., as
impurities.
[0049] FIG. 2 depicts an apparatus 100 that can be used to
manufacture a three-dimensional aluminum alloy part 108 from an
aluminum alloy powder feed material 110, which may comprise or
consist of the Al--Si--Cu alloy and/or the high-purity Al alloy.
The three-dimensional aluminum alloy part 108 may be formed via a
powder bed fusion additive manufacturing process, in which digital
design data is used to build up the part 108 layer by layer. For
example, the apparatus 100 may be configured to manufacture the
aluminum alloy part 108 by a powder bed fusion process, which may
be carried out using a selective laser melting or an electron beam
melting technique. In such case, the apparatus 100 may comprise a
building chamber 112 including a building platform 114, a powder
feed material reservoir 116 separated from the building chamber 112
by a weir 118, and a high-power energy beam source 120.
[0050] A volume of the aluminum alloy powder feed material 110 may
be distributed over a surface of the building platform 114, for
example, by a blade 122 to form a layer 124 of aluminum alloy
powder feed material 110. In one form, the aluminum alloy powder
feed material 110 may have a mean particle diameter in the range of
5 micrometers to 100 micrometers and the layer 124 of aluminum
alloy powder feed material 110 may have a thickness in the range of
20 micrometers to 100 micrometers. In FIG. 2, the layer 124 of
powder feed material 110 is distributed over a surface of the
building platform 114 and also over a surface of one or more
previously melted, fused, and solidified aluminum alloy layers 126
(FIG. 3). Then, selective regions 128 of the layer 124 are scanned
by a high-energy laser or electron beam 130. As shown, the
selective regions 128 of the layer 124 scanned by the beam 130
correspond to a cross-section of the three-dimensional aluminum
alloy part 108 being formed.
[0051] Referring now to FIG. 4, as the high-energy beam 130 scans
the selective regions 128 of the layer 124, the beam 130 impinges
the layer 124 and heat generated by absorption of energy from the
beam 130 initiates melting of the layer 124 within the selective
regions 128. As a result, a pool of molten aluminum alloy material
132 is created that fully penetrates the layer 124 and extends
through the layer 124 in a direction substantially perpendicular to
the surface of the building platform 114 (i.e., along the z-axis).
In one form, the pool of molten aluminum alloy material 132 may
extend into the layer 124 and partially into the underlying layers
126 at a depth in the range of 10 .mu.m to 300 .mu.m. After
termination of the high-energy beam 130, the pool of molten
aluminum alloy material 132 rapidly cools and solidifies to form
another solidified aluminum alloy layer that bonds with the
previously solidified layers 126. For example, after termination of
the high-energy beam 130, the pool of molten aluminum alloy
material 132 may cool at a rate in the range of 10.sup.4 Kelvin per
second to 10.sup.6 Kelvin per second. Thereafter, the reservoir 116
may be raised in a build direction (i.e., along the z-axis), or the
building platform 114 may be lowered, by a thickness of the newly
solidified layer, for example, by a piston 134. Then, a further
layer of powder feed material 110 may be distributed over the
surface of the building platform 114 and over the previously
solidified aluminum alloy layers 126, scanned with the high-energy
beam 130 in regions corresponding to another cross-section of the
three-dimensional aluminum alloy part 108, and solidified to form
yet another solidified aluminum alloy layer that bonds with the
previously solidified layers 126. This process is repeated until
the entire alloy part 108 is built up layer-by-layer.
[0052] In embodiments where the aluminum alloy powder feed material
110 comprises the Al--Si--Cu alloy, the resulting alloy part 108
may be heat treated to dissolve into solid solution any coarse
intermetallic phases that may have formed during solidification
and/or to promote the formation of one or more Cu-containing
precipitate phases (e.g., an AlCu precipitate phase and/or AlCuMgSi
precipitate phase) within the aluminum matrix phase. The heat
treatment process may include an aging heat treatment stage and
optionally a solution heat treatment stage. If performed, the
solution heat treatment stage may be performed prior to the aging
heat treatment stage. During the optional solution heat treatment
stage, the alloy part 108 may be heated to a temperature in the
range of 490.degree. C. to 550.degree. C. for a duration of 10
minutes to 10 hours. In one form, the alloy part 108 may be heated
during the solution heat treatment stage to a temperature in the
range of 490.degree. C. to 550.degree. C. for a duration of 3 hours
to 10 hours. In another form, the alloy part 108 may be heated
during the solution heat treatment stage to a temperature in the
range of 490.degree. C. to 550.degree. C. for a duration of less
than 1 hours, for example, for a duration of 10 minutes to 30
minutes. After the optional solution heat treatment stage, the
alloy part 108 may be cooled or quenched to a temperature less than
100.degree. C., e.g., ambient temperature, at a cooling rate
sufficient to prevent diffusion and precipitation of alloying
elements dissolved in into solid solution during the solution heat
treatment stage. In the aging heat treatment stage, the alloy part
108 may be heated to a temperature in the range of 180.degree. C.
to 210.degree. C. for a duration of 0.5 hours to 7 hours. After the
aging heat treatment stage, the alloy part 108 may be cooled or
quenched to a temperature less than 100.degree. C., e.g., ambient
temperature.
[0053] As described in further detail above, the Al--Si--Cu alloy
and the high-purity Al alloy each include at least one element or
compound that, during solidification of the alloy, nucleates within
a solution of liquid phase aluminum and provides sites for the
subsequent nucleation and growth of aluminum dendrites. However,
referring now to FIGS. 5 and 6, it has been found that, when
aluminum alloys that do not include such elements and/or compounds
(or do not include appropriate amounts of such elements and/or
compounds) are melted and subsequently solidified, columnar-shaped
aluminum dendrites 236 tend to grow unidirectionally within the
solidifying aluminum alloys and in epitaxy with a surface of an
adjacent solid substrate 238 (FIG. 5). As shown in FIG. 6, after
solidification, the resulting aluminum alloys exhibit a columnar
grain structure including a plurality of unidirectional columnar
grains 240. Likewise, it has been found that, when such aluminum
alloys are used as a powder feed material in an additive
manufacturing process, such as the process described above with
respect to FIGS. 2-4, columnar-shaped aluminum dendrites tend to
grow unidirectionally in the build direction (i.e., along the
z-axis) and in epitaxy with the surface of the building platform
114 or with the surface of one or more previously solidified
aluminum alloy layers 126. In addition, this unidirectional
epitaxial aluminum dendrite growth tends to persist through each of
the subsequently melted and solidified layers of the aluminum alloy
part being formed, with the resulting aluminum alloy part being
readily susceptible to the formation of cracks along the grain
boundaries between the adjacent elongated columnar grains 240.
[0054] As shown in FIGS. 7 and 8, when the Al--Si--Cu alloy and the
high-purity Al alloy are melted and subsequently cooled,
solidification of the alloys begins with the nucleation of solid
particles 342 throughout a solution of liquid phase aluminum 344.
In the Al--Si--Cu alloy, the solid particles 342 may comprise
particles of substantially pure silicon and optionally particles of
an Fe- and/or Mn-containing intermetallic phase. Alternatively, in
the high-purity Al alloy, the solid particles 342 may comprise an
element or compound of Ti, B, Be, Co, Cr, Cs, Fe, Hf, Mn, Mo, Nb,
Pb, S, Zr, Sb, Sc, Se, Sr, Ta, and/or V, as described above in
further detail. As these alloys continue to solidify, solid phase
aluminum dendrites 346 will nucleate and grown in all directions on
the solid particles 342, as shown in FIG. 7. Additional aluminum
dendrites 347 also may grow in epitaxy with a surface of an
adjacent substrate 338. Growth of the aluminum dendrites 346, 347
within the solidifying liquid phase aluminum 344 will eventually be
arrested when neighboring aluminum dendrites 346, 347 impinge upon
one another and form grain boundaries 348, as shown in FIG. 8. The
resulting aluminum alloys will exhibit an equiaxed grain structure
including a plurality of randomly oriented equiaxed grains 350.
Likewise, when the Al--Si--Cu alloy and/or the high-purity Al alloy
are prepared in powder form and used as a powder feed material in
an additive manufacturing process, such as the process described
above with respect to FIGS. 2-4, aluminum dendrite 346 growth has
been found to occur heterogeneously throughout each layer of
solidifying aluminum alloy material. In addition, any
columnar-shaped aluminum dendrites 347 originating on (e.g.,
growing in epitaxy with) the surface of the building platform 114
or on the surface of one or more previously solidified aluminum
alloy layers 126 are stopped by the aluminum dendrites 346 growing
in multiple random directions from the solid particles 342
distributed throughout the bulk of each layer of solidifying
aluminum alloy material.
[0055] The above description of preferred exemplary embodiments,
aspects, and specific examples are merely descriptive in nature;
they are not intended to limit the scope of the claims that follow.
Each of the terms used in the appended claims should be given its
ordinary and customary meaning unless specifically and
unambiguously stated otherwise in the specification.
* * * * *