U.S. patent application number 11/670880 was filed with the patent office on 2007-08-16 for aluminum alloy containing copper and zinc.
This patent application is currently assigned to AJOU UNIVERSITY INDUSTRY COOPERATION FOUNDATION. Invention is credited to JAE HWAN AHN, JUNG HO CHOI, HYUNG SIK CHUNG, MOON TAE KIM, SUNG KYU LEE.
Application Number | 20070187006 11/670880 |
Document ID | / |
Family ID | 38367113 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070187006 |
Kind Code |
A1 |
CHUNG; HYUNG SIK ; et
al. |
August 16, 2007 |
ALUMINUM ALLOY CONTAINING COPPER AND ZINC
Abstract
Disclosed is an elementally mixed Al--Cu--Zn base powder blend
for a sintered Al base alloy. The powder blend includes more than
5.6 wt % and less than 9 wt % Cu, 1.about.5 wt % Zn, and a balance
Al. With the powder blend, an article of a sintered Al base alloy
having higher wear resistance as well as higher tensile strength
can be fabricated.
Inventors: |
CHUNG; HYUNG SIK;
(YONGIN-SI, GYEONGGI-DO, KR) ; AHN; JAE HWAN;
(SEOUL, KR) ; LEE; SUNG KYU; (SUWON-SI,
GYEONGGI-DO, KR) ; KIM; MOON TAE; (SUWON-SI,
GYEONGGI-DO, KR) ; CHOI; JUNG HO; (SEOUL,
KR) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Assignee: |
AJOU UNIVERSITY INDUSTRY
COOPERATION FOUNDATION
SAN5, WONCHEON-DONG, YEONGTONG-GU
SUWON-SI
KR
443-749
|
Family ID: |
38367113 |
Appl. No.: |
11/670880 |
Filed: |
February 2, 2007 |
Current U.S.
Class: |
148/438 ;
420/531 |
Current CPC
Class: |
C22C 21/18 20130101;
C22F 1/057 20130101; B22F 3/1035 20130101; C22C 1/0416
20130101 |
Class at
Publication: |
148/438 ;
420/531 |
International
Class: |
C22C 21/18 20060101
C22C021/18 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 4, 2006 |
KR |
10-2006-0010896 |
Claims
1. An aluminum alloy comprising Al, Cu and Zn, wherein a portion of
the alloy comprises: Cu in an amount over 5.6 wt % and less than
about 9 wt % with reference to the weight of the portion; and Zn in
an amount from about 1 wt % to about 5 wt % with reference to the
weight of the portion.
2. The alloy of claim 1, wherein the portion comprises
Al-containing grains and an intergrain material disposed between
and interconnecting neighboring grains, wherein a substantial
amount of Cu is present in the intergrain material, and wherein a
substantial amount of Zn is present in central areas of the
Al-containing grains.
3. The alloy of claim 2, wherein a substantial amount of Cu present
in the intergrain material is in the form of CuAl.sub.2.
4. The alloy of claim 3, wherein substantially the entire amount of
Cu present in the intergrain material is in the form of
CuAl.sub.2.
5. The alloy of claim 2, wherein the intergrain material comprises
a portion which comprises Cu in an amount from about 20 wt % to
about 60 wt % with reference to the weight of the portion of the
intergrain material.
6. The alloy of claim 2, wherein substantially the entire amount of
Zn is present in the Al-containing grains.
7. The alloy of claim 1, wherein the portion of the alloy comprises
Cu in an amount from about 6 wt % to about 8 wt % with reference to
the weight of the portion.
8. The alloy of claim 1, wherein the portion of the alloy contains
Sn in an amount from about 0.01 wt % to about 0.05 wt % with
reference to the weight of the portion.
9. The alloy of claim 1, wherein the portion of the alloy contains
Mg in an amount less than about 0.03 wt % with reference to the
weight of the portion.
10. The alloy of claim 1, wherein the alloy is produced by a
method, which comprises: providing a powder mixture comprising Al,
Cu and Zn; and heating the powder mixture to a temperature
sufficient to melt at least part of the powder mixture.
11. A method of making an aluminum alloy, comprising: providing a
powder mixture comprising Al, Cu and Zn, wherein Cu is in an amount
over 5.6 wt % and less than about 9 wt % with reference to the
weight of the powder mixture, and wherein Zn is in an amount from
about I wt % to about 5 wt % with reference to the weight of the
powder mixture; and heating the powder mixture to a temperature
sufficient to melt at least part of the powder mixture.
12. The method of claim 11, wherein the powder mixture comprises
Al-containing particles, and wherein a substantial amount of Zn is
dissolved into at least part of the Al-containing particles.
13. The method of claim 11, wherein upon heating at least part of
the powder mixture is melt to form a liquefied state, and wherein a
substantial amount of Cu is present in the liquefied state.
14. The method of claim 11, further comprising cooling the heated
powder mixture thereby forming an alloy comprising a portion which
comprises Al-containing grains and an intergrain material disposed
between and interconnecting neighboring grains, wherein a
substantial amount of Cu is present in the intergrain material.
15. An aluminum alloy produced by the method of claim 11, wherein a
portion of the alloy comprises Al-containing grains and an
intergrain material disposed between and interconnecting
neighboring grains, wherein a substantial amount of Cu is present
in the intergrain material, and wherein a substantial amount of Zn
is present in central areas of the Al-containing grains.
16. The alloy of claim 15, wherein a substantial amount of Cu in
the intergrain material is present in the form of CuAl.sub.2.
17. The alloy of claim 16, wherein substantially the entire amount
of Cu in the intergrain material is present in the form of
CuAl.sub.2.
18. The alloy of claim 15, wherein a substantial amount of Zn is
present in the Al-containing grains.
19. The alloy of claim 18, wherein substantially the entire portion
of Zn is present in the Al-containing grains.
20. A powder blend for use in making an aluminum alloy, the powder
blend comprising Al, Cu and Zn, wherein the powder blend comprises:
Cu in an amount over 5.6 wt % and less than about 9 wt % with
reference to the weight of the powder blend; and Zn in an amount
from about 1 wt % to about 5 wt % with reference to the weight of
the powder blend.
21. The powder blend of claim 20, wherein the powder blend
comprises Cu in an amount from about 6 wt % to about 8 wt % with
reference to the weight of the powder blend.
22. The powder blend of claim 20, wherein the powder blend
comprises Sn in an amount from about 0.01 wt % to about 0.05 wt %
with reference to the weight of the powder blend.
23. The powder blend of claim 20, wherein the powder blend
comprises Mg in an amount less than about 0.03 wt % with reference
to the weight of the powder blend.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application claims priority to and the benefit
of Korean Patent Application No. 10-2006-0010896, filed Feb. 4,
2006, the disclosure of which is incorporated by reference in its
entirety.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates to an aluminum alloy, and more
particularly, to a sintered aluminum base alloy.
[0004] 2. Discussion of Related Technology
[0005] Recently, Al-base alloys have been actively replacing
various ferrous components in automobiles to reduce the weight and
improve the performance. (See The International Journal of Powder
Metallurgy, 36, 2002, p 41 by F. V. Beaumont, and p 45 by C. Lall
et al.) Most of aluminum alloys can be easily processed to final
shapes via casting, forging, forming or machining, and also
heat-treated to improve desired final properties. Many automotive
components, such as space frames, an engine blocks, wheel frames,
housings, etc, are currently utilizing aluminum castings or
forgings. For ferrous or copper-base components in automobiles,
powder metallurgy products are widely used because of their easy
net-shaping capability, cost competitiveness and acceptable
properties. Aluminum base powder products, however, have found very
limited applications in automobiles despite many potential merits.
(See The International Journal of Powder Metallurgy, 36, p 51, 2002
by W. H. Hunt) One of the main obstacles limiting the use of
aluminum sintered products is the poor sintering behavior of
aluminum-base powders which cause relatively low sintered
properties. (See Nature, 181, p 833, 1958 by R. F. Smart et al.,
and Journal of Metals, 37, p 27, 1985 by Y. Kim et al.)
[0006] In general, aluminum-base powder mixtures for sintered
products are prepared by mixing air atomized aluminum powder with
secondary alloying powders such as copper, magnesium, silicon, zinc
or others. The air atomized aluminum powder, though least
expensive, contains a relatively thick aluminum oxide layer around
each particle surface due to the oxidation during the atomization.
Since the aluminum oxide is very stable and the sintering
temperature for aluminum is relatively low, it is very difficult to
reduce the oxide layer during sintering at around 600.degree. C.
The oxide layers between particles in a compact block the
inter-diffusion between aluminum particles, thus severely limiting
the sintering process. Compaction of a powder mixture at a
relatively high pressure in order to break the surface oxide layers
is known to improve the sintering to some extent.
[0007] However, forming a liquid phase during the sintering is
considered as the most effective way of improving the sintering of
elementally mixed aluminum powder compacts. (See "Properties and
design guidelines for aluminum parts" in Proceeding 2000
International Conference on P/M Aluminum & Light Alloys for
Automotive Applications, pp 51-58 by Antonio Romero, Acta
Materialia, 35, p 589, 1996 by R. N. Lumley et al., and Material
Chemistry and Physics, 67, p 85, 2001 by G. B. Schaffer et al.)
Such liquid phases can be formed easily during the heating period
of sintering by eutectic reaction between the aluminum powder and
additive elemental powders such as copper, zinc, magnesium,
silicon, etc. When a powder compact is heated to sintering
temperature, localized alloying occurs at the contacts between
aluminum and the additive powders to form a liquid phase during the
heating cycle or sintering. The liquid phase, if persistently
present during the sintering, can spread through particle
boundaries, pulling particles and filling pores, so that higher
sintered density and better bonding between particles can be
obtained. On the other hand, if the liquid phase is transient, that
is, formed at a relatively low temperature but disappeared by
solutionizing in the matrix during heating or in the early stage of
sintering, the dissolved liquid phase leaves pores behind and
little persistent liquid phase in the matrix to assist particle
bonding during the sintering. Therefore, controlling the
characteristics and the amount of the liquid phase are most
critical to improve the sintering of mixed elemental aluminum
powders.
[0008] Most of commercially available mixed elemental aluminum
powder blends, however, have the compositions based on those of
wrought aluminum-base alloy systems, i.e., 201AB of Alcoa Inc. and
AMB2712 of Ampal Inc. from AA2014, 601AB of Alcoa Inc. and AMB6712
of Ampal Inc. from AA6061, and AMB 7775 of Ampal Inc. from AA7075,
rather than being optimized for sintering. The sintered properties
obtainable from these powder mixtures are relatively low when
compared to those of the wrought counterparts. For example,
sintered Alcoa 201AB at 95% theoretical density was reported to
have the tensile strength of .about.330 MPa after T6 condition,
which is about only 70% of that of AA2014, despite the only 5% of
porosity level. (See above "Properties and design guidelines for
aluminum parts" in Proceeding 2000 International Conference on P/M
Aluminum & Light Alloys for Automotive Applications, pp 51-58
by Antonio Romero) AMB7775 was reported to have the highest tensile
strength over 400 MPa, but exhibits a relatively poor wear
resistance. AMB7775 contains 6-8 wt % Zn, 3-5 wt % Mg and 1-3 wt %
Cu with a small amount of Si and Pb, and also forms a liquid phase
during the sintering. The liquid phase, however, is mainly
transient, that is, disappeared by dissolving in the aluminum
matrix during the sintering because of relatively large solubility
of these elements in aluminum at or below the sintering
temperature. The blend thus can be well strengthened by solid
solution hardening and also by precipitation hardening, but
dimensional control could be rather difficult because of the pores
left by the solutionized liquid phase.
[0009] U.S. Pat. No.5,902,943 describes about Al--Zn-Mg--Cu base
mixed elemental aluminum alloy powder blends and sintered aluminum
alloys. The blends described in the patent are basically 7xxx type
alloys and contain a relatively large amount of Zn as the principal
alloying addition and other elements to enhance the sintering.
Depending on the relative quantities of the alloying additions and
heat treatment conditions, the blends can exhibit tensile strengths
over 400 MPa but require a precise control of processing variables.
The patent does not describe any results on the wear properties of
the blends. Wear is also a big concern for most of potential
aluminum powder metallurgy (PM) parts which will replace steel
parts. Aluminum alloys generally have a relatively poor wear
resistance than steels and thus require methods to improve the wear
resistance. Hypereutectic Al--Si alloys which contain over 20% Si
possess excellent wear resistance when they are produced in a
pre-alloyed powder form and consolidated to full density at
elevated temperatures. The pre-alloyed powders, however, are not
well suited for the press and sinter processing, and thus are not
very economical. (See above Material Chemistry and Physics, 67, p
85, 2001 by G. B. Schaffer et al.) Aluminum alloy composites
reinforced with hard ceramic particles are alternatives but they
are generally not well sinter-able and thus possess very poor
strength and ductility in as-sintered condition.
[0010] Therefore, new mixed elemental aluminum base powder blends
which can provide a better combination of strength and wear
resistance are needed for wider range of applications than has been
possible with existing blends.
[0011] The discussion in this section is to provide general
background information, and does not constitute an admission of
prior art.
SUMMARY
[0012] One aspect of the invention provides an aluminum alloy
comprising Al, Cu and Zn, wherein a portion of the alloy comprises:
Cu in an amount over 5.6 wt % and less than about 9 wt % with
reference to the weight of the portion; and Zn in an amount from
about 1 wt % to about 5 wt % with reference to the weight of the
portion.
[0013] In the foregoing alloy, the portion may comprise
Al-containing grains and an intergrain material disposed between
and interconnecting neighboring grains, wherein a substantial
amount of Cu may be present in the intergrain material, and wherein
a substantial amount of Zn is present in central areas of the
Al-containing grains. In one embodiment, the substantial amount of
Cu present in the intergrain material is about 2.5% to about 95% of
the total amount of Cu. In certain embodiments, Cu present in the
intergrain material may be about 2.5, 5, 7.5, 10, 15, 20, 25, 30,
35, 40, 50, 65, 80 or 95% of its total amount in the alloy portion.
In some embodiments, Cu present in the intergrain material may be
within a range defined by two of the foregoing amounts. In one
embodiment, the substantial amount of Zn present in the
Al-containing grain is about 5% to 100% of the total amount of Zn.
In certain embodiments, Zn present in the Al-containing grain may
be about 5, 20, 35, 50, 60, 70, 80, 85, 90, 95, 97, 98, 99, 99.5 or
100% of its total amount in the alloy portion. In some embodiments,
Zn present in the Al-containing grain may be within a range defined
by two of the foregoing amounts. Substantially the entire amount of
Zn may be present in the Al-containing grains.
[0014] Still in the foregoing alloy, a substantial amount of Cu
present in the intergrain material is in the form of CuAl.sub.2.
Substantially the entire amount of Cu present in the intergrain
material may be in the form of CuAl.sub.2. In one embodiment, the
substantial amount of Cu which is present in the intergrain
material in the form of CuAl.sub.2 is about 5% to 100% of the total
amount of Cu present in the intergrain material. In certain
embodiments, Cu present in the intergrain material in the form of
CuAl.sub.2 may be about 5, 20, 35, 50, 60, 70, 80, 85, 90, 95, 97,
98, 99, 99.5 or 100% of its total amount in the intergrain
material. In some embodiments, Cu present in the intergrain
material in the form of CuAl.sub.2 may be within a range defined by
two of the foregoing amounts. The intergrain material may comprise
a portion which comprises Cu in an amount from about 20 wt % to
about 60 wt % with reference to the weight of the portion of the
intergrain material.
[0015] Further in the foregoing alloy, the portion of the alloy may
comprise Cu in an amount from about 6 wt % to about 8 wt % with
reference to the weight of the portion. The portion of the alloy
may contain Sn in an amount from about 0.01 wt % to about 0.05 wt %
with reference to the weight of the portion. The portion of the
alloy may contain Mg in an amount less than about 0.03 wt % with
reference to the weight of the portion. The alloy may be produced
by a method, which comprises: providing a powder mixture comprising
Al, Cu and Zn; and heating the powder mixture to a temperature
sufficient to melt at least part of the powder mixture.
[0016] Another aspect of the invention provides a method of making
an aluminum alloy, comprising: providing a powder mixture
comprising Al, Cu and Zn, wherein Cu is in an amount over 5.6 wt %
and less than about 9 wt % with reference to the weight of the
powder mixture, and wherein Zn is in an amount from about 1 wt % to
about 5 wt % with reference to the weight of the powder mixture;
and heating the powder mixture to a temperature sufficient to melt
at least part of the powder mixture.
[0017] In the foregoing method, the powder mixture may comprise
Al-containing particles, and wherein a substantial amount of Zn may
be dissolved into at least part of the Al-containing particles.
Upon heating at least part of the powder mixture is melt to form a
liquefied state, and wherein a substantial amount of Cu may be
present in the liquefied state. The method may further comprise
cooling the heated powder mixture thereby forming an alloy
comprising a portion which comprises Al-containing grains and an
intergrain material disposed between and interconnecting
neighboring grains, wherein a substantial amount of Cu is present
in the intergrain material.
[0018] Yet another aspect of the invention provides an aluminum
alloy produced by the foregoing method, wherein a portion of the
alloy comprises Al-containing grains and an intergrain material
disposed between and interconnecting neighboring grains, wherein a
substantial amount of Cu is present in the intergrain material, and
wherein a substantial amount of Zn is present in central areas of
the Al-containing grains.
[0019] A further aspect of the invention provides a powder blend
for use in making an aluminum alloy, the powder blend comprising
Al, Cu and Zn, wherein the powder blend comprises: Cu in an amount
over 5.6 wt % and less than about 9 wt % with reference to the
weight of the powder blend; and Zn in an amount from about 1 wt %
to about 5 wt % with reference to the weight of the powder
blend.
[0020] In the foregoing powder blend, wherein the powder blend may
comprise Cu in an amount from about 6 wt % to about 8 wt % with
reference to the weight of the powder blend. The powder blend may
comprise Sn in an amount from about 0.01 wt % to about 0.05 wt %
with reference to the weight of the powder blend. The powder blend
may comprises Mg in an amount less than about 0.03 wt % with
reference to the weight of the powder blend.
[0021] One or more embodiments of the present invention provide an
elementally mixed Al--Cu--Zn base powder blend, a method of
fabricating an article of a sintered alloy using the powder blend,
and an article fabricated using the powder blend.
[0022] An aspect of the present invention provides a powder blend
comprising more than 5.6 wt % Cu added to a balance Al to form a
mixed powder blend. Thus, considerable amount of a liquid phase,
which is formed over the eutectic temperature of Al--Cu, i.e.
548.degree. C., persistently presents at a sintering temperature
(about 600.degree. C.), though a portion of the liquid phase is
solutionized into a matrix. The persistent liquid phase fills
boundaries and pores between powders as well as accelerates the
sintering of the solid powders. Thus densification of the sintered
alloy is improved.
[0023] Maximal solid solubility of Cu in an Al matrix is about
5.5.about.5.6 wt % at the eutectic temperature 548.degree. C. Thus,
when more than 5.6 wt % Cu powder is added to Al powder, the
persistent liquid phase always presents during the sintering,
without relation to a temperature elevation rate, etc. The liquid
phase which persistently presents during the sintering is
solidified into a mixed phase of .alpha.-Al and CuAl.sub.2
(.theta.) phase, as the liquid phase is cooled to the room
temperature, and the solidified liquid phase incorporates Al and 35
wt % Cu. (See Journal of Materials Science, 40, p 441, 2005 by Sang
Chul et al.) The CuAl.sub.2 phase has vickers hardness (HV) of 980
higher than that of .alpha.-Al. (See Intermetallics, 7 p 1001, 1999
by D. Moreno et al.) The CuAl.sub.2 phase contributes to improve
both of the strength and the wear resistance of the sintered alloy.
However, increment of the amount of the CuAl.sub.2 phase may result
in decrease of ductility of the sintered alloy. Thus, the amount of
Cu may be decided by way of considering the strength, ductility,
productivity of a sintered article, required shape of the article,
required dimensions and tolerance of the article and deformation of
a product shape during sintering. It is preferable to limit the
amount of Cu to less than 9 wt %.
[0024] Meanwhile, since the solid solubility of Cu at a temperature
of about 600.degree. C. for sintering Al base powder blends is less
than 3 wt %, the effect of solid solution strengthening is limited.
Thus, Zn powder which has a higher solid solubility is added to
improve the solid solution strengthening effect. Zn reacts with Al
during a heating period of sintering, and forms a eutectic liquid
phase over 382.degree. C., and then is all solutionized into the Al
matrix to enhance the strength of the matrix. In addition, Zn
together with Cu can improve a hardening effect resulting from an
age-hardening treatment after a solution-treatment, thus enhancing
the strength of a sintered alloy. Increment of addition of Zn
increases the strength of a sintered alloy and a thermal treated
sintered alloy. However, an excessive transient liquid phase formed
due to the surplus increment of Zn makes it difficult to maintain
the shape of a compact. Therefore, it is preferable to limit the
addition of Zn to not more than 5 wt %.
[0025] An aspect of the present invention provides a method of
fabricating an article of a sintered Al--Cu--Zn base alloy. The
method comprises mixing more than 5.6 wt % and less than 9 wt % Cu,
1.about.5 wt % Zn, and a balance Al to form a mixed powder blend.
The mixed powder blend is compacted, and then the compacted powder
is sintered to form a sintered alloy. As a result, an article of a
sintered Al--Cu--Zn base alloy can be fabricated.
[0026] The sintered alloy may be easily re-pressed because it has
low yield strength (YS). With the re-pressing, a sintered alloy
having a theoretical density of over 95% can be obtained, and the
increase of the density improves the strength of the article of the
sintered alloy. Also, deformation occurred during the sintering can
be corrected using the re-pressing. Thus, the article having
precise dimensions can be fabricated. In addition, the re-pressed
alloy can be heat-treated to fabricate an article of a sintered
alloy having a better combination of strength and wear resistance.
The heat treatment may comprise solution-treating the re-pressed
alloy, and heat-treating the solution-treated alloy for an
age-hardening. Usually, the solution-treated alloy is
water-quenched before the heat treating for an age-hardening. With
the solution treatment, Cu in the liquid phase is solutionized into
an Al matrix, and then CuAl.sub.2-x (.theta.'', .theta.', or
.theta.) phases are precipitated by the age-hardening treatment. As
a result, the strength and hardness of the sintered alloy are
improved.
[0027] An aspect of the present invention provides an article of a
sintered Al--Cu--Zn base alloy. The article includes more than 5.6
wt % and less than 9 wt % Cu, 1.about.5 wt % Zn, and a balance Al.
The article of the sintered Al--Cu--Zn base alloy may be fabricated
using the fabricating method described above. Meanwhile, the
article of the sintered Al--Cu--Zn base alloy comprises an Al
matrix (.alpha.-Al) and a CuAl.sub.2 phase. The CuAl.sub.2 phase
may present at boundaries of .alpha.-Al and/or in the Al matrix.
The CuAl.sub.2 phase serves as a reinforcing phase and improves
both of the strength and the wear resistance of the article of the
sintered Al--Cu--Zn base alloy. In several embodiments of the
present invention, additive powders may be incorporated in the
Al--Cu--Zn base powder blends. Mg added to the Al--Cu--Zn powder
blends decreases the strength and ductility of its sintered alloy,
whereas a small amount of Sn added to the Al--Cu--Zn powder blends
increases the ductility of its sintered alloy. Preferably, 0.010.05
wt % Sn may be added to the powder blends, and less than 0.01 wt %
Mg may be incorporated in the powder blends.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The above features and advantages of the present invention
will become more apparent by describing the embodiment thereof with
reference to the accompanying drawings, in which:
[0029] FIG. 1 is a schematic diagram depicting a method of
measuring transverse rupture strength (TRS) and an amount of
deflection at rupture of a sintered sample.
[0030] FIG. 2 is a graph for describing TRSs and amounts of
deflection of sintered samples of Al base alloys incorporating
different Cu contents.
[0031] FIG. 3 shows SEM images of sintered Al--Cu base alloys
incorporating different Cu contents according to certain
embodiments and a sintered Alcoa 201AB.
[0032] FIG. 4 is a graph depicting TRSs and amounts of deflection
of sintered samples of Al-6 wt % Cu powder mixtures with sintering
temperatures.
[0033] FIG. 5 is a graph depicting TRSs and amounts of deflection
of sintered samples with different Zn contents in Al--Cu--Zn powder
blends.
[0034] FIG. 6 shows optical images of sintered samples with
different Zn contents in Al--Cu--Zn powder blends.
[0035] FIG. 7 shows a SEM image for describing a solidified liquid
phase (A) and a matrix (B) of a sintered Al--Cu--Zn base alloy.
[0036] FIG. 8 is a graph depicting TRSs and amounts of deflection
of sintered samples with different Mg contents in Al--Cu powder
blends.
[0037] FIG. 9 shows optical images of sintered samples with
different Mg contents in Al--Cu powder blends.
[0038] FIG. 10 is a graph depicting TRSs and amounts of deflection
of sintered samples with different Mg contents in Al--Cu--Zn powder
blends.
[0039] FIG. 11 is a graph depicting TRSs and amounts of deflection
of sintered samples with different Sn contents in Al--Cu--Zn powder
blends.
[0040] FIG. 12 is a graph depicting age-hardening behaviors of
sintered Al--Cu--Zn base alloys with aging temperature and
time.
[0041] FIG. 13 shows a SEM image of a heat-treated sintered
Al--Cu--Zn base alloy
[0042] FIG. 14 shows XRD results of sintered alloys of an
Al--Cu--Zn base powder blend and a commercially available powder
blend.
DETAILED DESCRIPTION OF EMBODIMENTS
[0043] Hereinafter, embodiments of the invention will be described
in detail with reference to the accompanying drawings.
[0044] Table 1 lists typical compositions and tensile properties of
commercially available aluminum base mixed elemental powder blends.
2xxx blends contain Cu as a main additive element, however, Cu is
less than 5 wt %, and 7xxx blends contain Zn as a main additive
element. All of the commercially available aluminum base powder
blends show a transient liquid phase sintering behavior, that is,
the liquid phase formed during the sintering is almost solutionized
or absorbed into a matrix. Among these powder blends, 7xxx series
possess the highest tensile strength at both as-sintered and
heat-treated conditions. Wherein, T1 indicates the as-sintered
condition, and T6 indicates the heat-treated condition, that is,
aged to peak hardness condition. TABLE-US-00001 TABLE 1 Tensile
properties Composition(wt %) Elongation wrought Cu Mg Si Zn Al
YS(MPa) TS(MPa) (%) equivalent 6xxx: 0.2 1.0 0.5 -- Bal. 135(T1) 5
6061 Al--Mg--Si 240(T6) 3 2xxx: 4.4 0.5 0.7 -- Bal. 180(T1) 205(T1)
5 2014 Al--Cu--Mg 327(T6) 330(T6) 1 7xxx: 1.5 2.5 -- 5.5 Bal.
230(T1) 270(T1) 4 7075 Al--Zn--Mg--Cu 370(T6) 413(T6) 2
[0045] FIG. 1 shows how to measure transverse rupture strength
(TRS) and an amount of deflection at rupture of a sintered sample
in accordance with ASTM B312. The TRS and the amount of deflection
are utilized as the measure of mechanical strength and ductility of
the sintered sample, respectively. Thickness, length and width of
sample for this test was 6.35 mm, 31.8 mm and 12.7 mm,
respectively.
[0046] FIG. 2 is a graph for describing TRSs and amounts of
deflection of sintered samples of Al base alloys incorporating
different Cu contents. Each sample is provided by sintering a mixed
powder blend of Al and Cu powders at 600.degree. C. for 1 hour in a
dry nitrogen atmosphere, and then slowly cooling the sintered alloy
to room temperature. For comparison, two commercial powder blends,
201AB and 601AB of Alcoa Inc., were processed via same procedure
and their TRSs and deflections were also measured. Referring to
FIG. 2, it is noticeable that with increasing the Cu content, TRS
increases but ductility decreases. In addition, all the samples
incorporating 6, 8 and 10 wt % Cu showed much higher strength than
the samples of the commercial powder blends, and showed ductility
almost similar to the samples of the commercial powder blends.
[0047] FIG. 3 shows SEM images of sintered alloys incorporating
different Cu amount and a sintered Alcoa 201AB, where (a) is for
Al-6 wt % Cu, (b) is for Al-8 wt % Cu, (c) is for Al-10 wt % Cu,
and (d) is for Alcoa 201AB. Referring to FIG. 3, a liquid phase is
observed in the samples of (a), (b) and (c). The solidified liquid
phase fills boundaries and pores between powders, and increases
with increasing the Cu content. The solidified liquid phase can be
an evidence of a persistent liquid phase during the sintering.
However, (d) for the sintered Aloca 201AB shows some coarse pores
with no evidence of the persistent liquid phase despite of about
4.5 wt % of Cu content. In certain embodiments, the amount of Cu
may be about 5.6, 5.7, 5.8, 6, 6.2, 6.5, 7, 7.5, 8, 8.5, 9 or 9.5
wt % of the sintered alloy. In some embodiments, the amount of Cu
may be within a range defined by two of the foregoing amounts.
[0048] FIG. 4 is a graph depicting TRSs and amounts of deflection
of sintered samples of Al-6 wt %Cu (Al-6Cu) powder mixtures with
sintering temperatures. Each power blend is sintered for 1 hour in
a dry nitrogen atmosphere, and then slowly cooled to room
temperature. Referring to FIG. 4, the strength and the amount of
deflection at rupture increased with the increase of the sintering
temperature. And, for both of the strength and deflection, marked
differences were observed between 590.degree. C. and 600.degree. C.
This is attributed to the significant improvement of sintering due
to an extensive liquid phase formation at temperatures of or above
600.degree. C.
[0049] FIG. 5 is a graph depicting TRSs and amounts of deflection
of sintered samples with different Zn contents in Al--Cu--Zn powder
blends. All samples contained 6 wt % Cu, and were sintered at
625.degree. C. for 1 hour in a dry nitrogen atmosphere. Referring
to FIG. 5, even 1 wt % of Zn addition showed a quite significant
effect for increasing the strength. The strength also increased
with the increase of Zn, while the ductility decreased slightly.
This is a result of solid solution strengthening effect due to the
solid solution of Zn in Al matrix or grains.
[0050] FIG. 6 shows optical images of sintered samples with
different Zn contents in Al--Cu--Zn powder blends. Where, (a) is
for Al-6Cu-1Zn, (b) is for Al-6Cu-3Zn, and (c) is for Al-6Cu-5Zn.
All samples were sintered at 625.degree. C. for 1 hour in a dry
nitrogen atmosphere. Referring to FIG. 6, with increasing the Zn
content, the amount of pore decreased and grains became larger. In
certain embodiments, the amount of Zn may be about 0.5, 1, 2, 3, 4,
4.5, 5 or 5.5 wt % of the sintered alloy. In some embodiments, the
amount of Zn may be within a range defined by two of the foregoing
amounts.
[0051] FIG. 7 shows a SEM image for describing an intergrain
material or solidified liquid phase (A) and a Al matrix or grains
(B) of a sintered Al--Cu--Zn base alloy. Compositional variations
of liquid phase (A) and the Al matrix (B) were analyzed using an
EDAX, and the results are listed in Table 2. The sintered alloy was
provided by sintering an Al-6Cu-3Zn powder blend at 625.degree. C.
for 1 hour in a dry nitrogen atmosphere. TABLE-US-00002 TABLE 2 A B
Element wt % at % wt % at % O 1.05 2.36 1.3 2.28 Al 54 72.14 90.46
94.12 Cu 44.95 25.5 4.49 1.98 Zn 0 0 3.75 1.61 Totals 100 100 100
100
[0052] Referring to Table 2, the solidified liquid phase (A)
includes Al and Cu and does not incorporate Zn. The solidified
liquid phase was identified to consist of .alpha.-Al and CuAl.sub.2
(.theta.) phase by XRD analysis of FIG. 14, and their relative
fractions were calculated with lever rule as about 15 wt % and
about 85 wt %, respectively. All of the Zn along with considerable
amounts of Cu was solutionized in the matrix, thus improving a
solid solution strengthening effect. Therefore, the observed
microstructure of FIG. 7 can be regarded as a composite material
where Al--Cu--Zn solid solutionized matrix is strengthened by the
reinforcing CuAl.sub.2 phase which contributes to increased
strength and wear resistance of the alloy. (B) shows a contents of
Al matrix or grains.
[0053] FIG. 8 is a graph depicting TRSs and amounts of deflection
of sintered samples with different Mg contents in Al-6Cu powder
blends. And, FIG. 9 shows optical images of sintered samples with
different Mg contents in Al-6Cu powder blends. Where, (a) is for
Al-6Cu-0.1Mg, (b) is for Al-6Cu-0.3Mg, and (c) is for Al-6Cu-0.5Mg.
Referring to FIG. 8, even 0.1 wt % Mg in Al--Cu powder blends
lowered the TRS and ductility. The TRSs and ductility decreased
with increase of the Mg contents in Al-6Cu. Referring to FIG. 9, it
is noticeable that the addition of Mg to the Al--Cu powder blends
altered the sintered microstructures significantly to have many
isolated pores. Increase of Mg in the powder blend resulted in more
porosity and coarse pores.
[0054] FIG. 10 is a graph depicting TRSs and amounts of deflection
of sintered samples with different Mg contents in Al-6Cu-3Zn powder
blends. In Al--Cu--Zn systems, even 0.03 wt % Mg lowered the TRS
and ductility of a sintered alloy. Thus, addition of Mg in
Al--Cu--Zn powder blends is preferable to be limited below 0.03 wt
%.
[0055] FIG. 11 is a graph depicting TRSs and amounts of deflection
of sintered samples with different Sn contents in Al-6Cu-3Zn powder
blends. In Al--Cu--Zn systems, 0.01 wt % Sn increased ductility of
a sintered alloy, however, 0.05 wt % Sn decreased the TRS and
ductility. Thus, 0.01.about.0.05 wt % Sn may be utilized as a minor
addition in the Al--Cu--Zn powder blends to control ductility of
sintered alloys.
[0056] FIG. 12 is a graph depicting age-hardening behaviors of
sintered Al--Cu--Zn base alloys with aging temperature and time.
Sintered samples of Al-6Cu-3Zn were used, and the sintered samples
were re-pressed and solution-treated at 540.degree. C. and
water-quenched, and then aging-treated at various temperatures and
times. Vickers hardness (HV) and Rockwell hardness (HRB) were
together shown.
[0057] Referring to FIG. 12, with increase of the aging time after
the solution treatment, the hardness of the samples increased.
Also, with increase of the aging temperature, the hardness of the
samples increased much more. This implies that the sintered
Al--Cu--Zn base alloy according to embodiments of the present
invention can be effectively strengthened by heat treatments such
as the solution treatment and age-hardening treatment.
[0058] FIG. 13 shows a SEM image of a heat-treated sintered
Al--Cu--Zn base alloy. A sintered sample of Al-6Cu-3Zn was used,
and the sintered sample was re-pressed and heat-treated.
Compositional variations of liquid phase (A) and the Al matrix (B)
were analyzed using an EDAX, as described above referring to FIG.
7, and the results are listed in Table 3. TABLE-US-00003 TABLE 3 A
B Element wt % at % wt % at % Al 65.97 82.03 89.99 95.53 Cu 34.03
17.97 7.01 3.16 Zn 0 0 3 1.31 Totals 100 100 100 100
[0059] In certain embodiments, the Cu content of the Al matrix can
be slightly increased after the heat treatment, but Zn content was
almost unchanged. Referring to Table 3, the solidified liquid phase
was found to contain about 34 wt % Cu. Therefore, the Al matrix is
strengthened by fine precipitates after aging and also by the
presence of a Cu-rich hard phase in. The Cu-rich hard phase
consists of about 40 wt % of a-Al and 60 wt % of CuAl.sub.2
(.theta.) phase. The CuAl.sub.2 phase functions as a reinforcing
phase, thus improving the strength and wear resistance of the
sintered alloy.
[0060] FIG. 14 shows XRD graphs of a sintered alloys after
sintering, solution-treatment and water-quenching, and then
artificial aging. Where, (a) shows the XRD graphs of commercial
7xxx and (b) shows the XRD graphs of Al-6Cu-3Zn according to one
embodiment of the present invention. XRD datum were obtained after
sintering, after solution treatment, and after aging treatment,
respectively. The XRD data after solution treatment was obtained
from a sample which was solution-treated at 540.degree. C. for 1
hour and then water-quenched. The XRD data after aging treatment
was obtained from a sample which was aging-treated after the
solution treatment and water-quenching.
[0061] Referring to FIG. 14, for the Al-6Cu-3Zn, main constituents
of the as-sintered sample are .alpha.-Al and CuAl.sub.2 (.theta.)
phase. The CuAl.sub.2 (.theta.) phase disappeared after the
solution treatment. This is attributed to super-saturation of Cu
atoms in the Al matrix after the solution-treatment at 540.degree.
C. and subsequent water-quenching. During natural or artificial
aging, CuAl.sub.2-x (.theta.', or .theta.'') and CuAl.sub.2
(.theta.) phases precipitate in the Al matrix (B) and the
solidified liquid phase (A), respectively, effectively improving
the strength and wear resistance. In the meantime, for the
commercial 7xxx, the CuAl.sub.2 (.theta.) phase did not appear
after the aging treatment.
[0062] Table 4 lists hardness, transverse rupture and tensile
properties of Al-6Cu-3Zn and Al-6Cu-5Zn mixed elemental powder
alloys compacted to 90% theoretical density (T.D.) at room
temperature using double action die, sintered at 610.degree. C. for
1 hour under flowing N2 atmosphere to about 96% T.D., further
re-pressed to 98% T.D., and finally heat-treated for age-hardening.
All samples were maintained at 540.degree. C. for 1 hour and then
water-quenched before aging. TABLE-US-00004 TABLE 4 Transverse
Rupture Properties Tensile Properties Deflection Yield Tensile
Alloy Heat Hardness Strength at Rupture Strength Strength
Elongation System Treatment (HV) (MPa) (mm) (MPa) (MPa) (%)
Al--6Cu--3Zn As-sintered 64 371 1.9 60 197 10.9 150.degree. C./19
hrs 152 673 0.69 287 410 6.9 170.degree. C./13 hrs 152 667 0.54 317
419 5.1 Al--6Cu--5Zn As-sintered 65 374 1.7 75 204 10.2 150.degree.
C./22 hrs 152 636 0.64 314 396 4.0 170.degree. C./10 hrs 154 642
0.55 320 399 4.1
[0063] Referring to Table 4, as-sintered samples usually show very
low hardness and yield strength (YS) values and significant
ductility, facilitating further plastic working process such as
re-pressing and other cold working processes. Heat-treated samples
usually show significant increases in hardness and strength with
accompanying decrease in ductility. This is caused by precipitation
of fine .theta.' phase in the .alpha.-Al matrix. Strength and
ductility slightly decreased by increasing Zn contents from 3 to 5
wt %. Thus, it is preferable to limit the Zn contents within 5 wt
%.
[0064] Table 5 details wear resistance characteristics of various
Al-base alloy systems, commercial and developed ones alike,
compacted to 90% T.D., sintered for 1 hour at 610.degree. C. under
flowing N.sub.2 atmosphere to about 96% T.D., further re-pressed to
98% T.D., and finally heat-treated for age-hardening. For
age-hardening, sintered samples were solution-treated for 1 hour at
540.degree. C. and water-quenched immediately afterward, followed
by artificial ageing for 22 hours at 150.degree. C. Wear resistance
was characterized by weight loss of pins after sliding 2000 m
against rotating disk at 100.degree. C. in a commercial engine oil.
The pins were pressed against the rotating disk with the force of
500 N. Both the pin and disk were made with same blend.
TABLE-US-00005 TABLE 5 Weight Coefficient Loss of Weight Loss of
Total Weight of Alloy Systems Disk Pin Loss Friction AMB7775 0.0220
0.1595 0.1815 0.6601 AMB7777- 0.0580 0.2590 0.3170 1.2515 10v/oSiC
Al--4Cu--5Zn 0.1145 0.1685 0.2830 0.1289 Al--4Cu--7Zn 0.0420 0.1013
0.1433 0.1442 Al--6Cu--5Zn 0.0254 0.0325 0.0579 0.1425 Al--8Cu--5Zn
0.0365 0.0205 0.0570 0.0994
[0065] Referring to Table 5, Very high coefficients of friction
were observed for commercially available 7xxx series alloys and the
7xxx alloys with reinforcing SiC particles, resulting in
significant amounts of wear. Al-4Cu alloy system shows still
significant amount of wear, although somewhat reduced compared to
commercially available 7xxx series alloys. Al-6Cu alloy system, on
the other hand, caused marked reduction in both coefficient of
friction and amount of wear. This is attributed to the solidified
liquid phase which acted as reinforcing phase upon solidification
as illustrated in FIG. 9. Although Al-4Cu alloys show somewhat
reduced coefficient of friction by the liquid phase, the
contribution is regarded as minimal at best due to small amount of
liquid formation in the Al-4Cu alloy. However, significant increase
in wear resistance observed for Al-6Cu alloy is attributed to the
ample amount of liquid phase formed during sintering.
[0066] It will be appreciated that many changes and modifications
can be made to the discussed embodiments without departing from the
scope of the present invention, which is defined in the following
claims.
* * * * *