U.S. patent application number 12/376044 was filed with the patent office on 2010-01-14 for method for producing aluminum-alloy shaped product, aluminum-alloy shaped product and production system.
This patent application is currently assigned to SHOWA DENKO K.K.. Invention is credited to Yasuo Okamoto.
Application Number | 20100006192 12/376044 |
Document ID | / |
Family ID | 38997339 |
Filed Date | 2010-01-14 |
United States Patent
Application |
20100006192 |
Kind Code |
A1 |
Okamoto; Yasuo |
January 14, 2010 |
METHOD FOR PRODUCING ALUMINUM-ALLOY SHAPED PRODUCT, ALUMINUM-ALLOY
SHAPED PRODUCT AND PRODUCTION SYSTEM
Abstract
The present invention are to provide a method for producing an
aluminum-alloy shaped product that exhibits high-temperature
mechanical strength superior to that of a conventional
aluminum-alloy forged product. The present invention provides a
method for producing an aluminum-alloy shaped product, comprising a
step of forging a continuously cast rod of aluminum-alloy serving
as a forging material, in which the aluminum-alloy contains Si in
an amount of 10.5 to 13.5 mass %, Cu in an amount of 2.5 to 6 mass
%, Mg in an amount of 0.3 to 1.5 mass % and Ni in an amount of 0.8
to 4%, and satisfies a relational expression of "Ni(%
bymass).gtoreq.(-0.68.times.Cu(% by mass)+4.2(% by mass)),and heat
treatment and heating steps including a step of subjecting the
forging material to pre-heat treatment (82), a step (87) of heating
the forging material during a course of forging of the forging
material and a step of subjecting an aluminum-alloy shaped product
to post-heat treatment (89), said pre-heat treatment (82) including
treatment of maintaining the forging material at a temperature of
-10 to 480.degree. C. for two to six hours.
Inventors: |
Okamoto; Yasuo;
(Kitakata-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SHOWA DENKO K.K.
Minato-ku, Tokyo
JP
|
Family ID: |
38997339 |
Appl. No.: |
12/376044 |
Filed: |
July 31, 2007 |
PCT Filed: |
July 31, 2007 |
PCT NO: |
PCT/JP2007/065331 |
371 Date: |
March 13, 2009 |
Current U.S.
Class: |
148/691 ;
148/439; 148/695; 266/249 |
Current CPC
Class: |
B22D 21/007 20130101;
B21K 1/18 20130101; F05C 2201/021 20130101; F02F 3/0084 20130101;
B22D 11/045 20130101; B22D 11/003 20130101; C22F 1/043 20130101;
C22F 1/00 20130101; B21J 1/02 20130101; C22C 21/02 20130101; B21J
5/00 20130101 |
Class at
Publication: |
148/691 ;
148/695; 148/439; 266/249 |
International
Class: |
C22F 1/043 20060101
C22F001/043; C22C 21/02 20060101 C22C021/02; C21D 1/00 20060101
C21D001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 1, 2006 |
JP |
2006-209898 |
Claims
1. A method for producing an aluminum-alloy shaped product,
comprising: a step of forging a continuously cast rod of
aluminum-alloy serving as a forging material, in which the
aluminum-alloy contains Si in an amount of 10.5 to 13.5 mass %, Cu
in an amount of 2.5 to 6 mass %, Mg in an amount of 0.3 to 1.5 mass
% and Ni in an amount of 0.8 to 4%, and satisfies a relational
expression of "Ni(% by mass).gtoreq.(-0.68.times.Cu(% by
mass)+4.2(% by mass)), and heat treatment and heating steps
including a step of subjecting the forging material to pre-heat
treatment, a step of preliminary heating the forging material
before a course of forging of the forging material and a step of
subjecting a shaped product to post-heat treatment, said pre-heat
treatment including treatment of maintaining the forging material
at a temperature of -10 to 480.degree. C. for two to six hours.
2. The method according to claim 1, wherein the pre-heat treatment
is performed at a temperature of at least 200.degree. C. and
370.degree. C. or lower.
3. The method according to claim 1, wherein the pre-heat treatment
is performed at a temperature of at least -10.degree. C. and less
than 200.degree. C.
4. The method according to claim 1, wherein the pre-heat treatment
is performed at a temperature of at least 370.degree. C. and
480.degree. C. or lower.
5. The method according to claim 1, wherein the post-heat treatment
is performed at 170 to 230.degree. C. for one to 10 hours without
performing solid solution treatment.
6. The method according to claim 1, wherein, the aluminum-alloy
further contains Fe in an amount of 0.15 to 0.65 mass %.
7. The method according to claim 1, wherein the aluminum-alloy
further contains P in an amount of 0.003 to 0.02 mass %.
8. The method according to claim 1, wherein the aluminum-alloy
further contains at least one species selected from among Sr in an
amount of 0.003 to 0.03 mass %, Sb in an amount of 0.1 to 0.35 mass
%, Na in an amount of 0.0005 to 0.015 mass % and Ca in an amount of
0.001 to 0.02 mass %.
9. The method according to claim 1, wherein the aluminum-alloy
further contains at least one species selected from among Mn in an
amount of 0.1 to 1.0 mass %, Cr in an amount of 0.05 to 0.5 mass %,
Zr in an amount of 0.04 to 0.3 mass %, V in an amount of 0.01 to
0.15 mass % and Ti in an amount of 0.01 to 0.2 mass %.
10. The method according to claim 1, wherein during the forging
step, a percent reduction of a portion of the forging material that
requires high-temperature fatigue strength resistance is regulated
to 90% or less.
11. The method according to claim 1, wherein in the forging step,
the preliminary heating step is performed at a temperature of 380
to 480.degree. C.
12. The method according to claim 1, wherein the continuously cast
rod is produced through continuous casting of a molten
aluminum-alloy having an average temperature which falls within a
range of a liquidus temperature +40.degree. C. to the liquidus
temperature +230.degree. C. at a casting speed of 80 to 2,000
mm/minute.
13. An aluminum-alloy shaped product produced through the method
according to claim 1 and having a metallographic structure in which
crystallization product networks, acicular crystallization products
or crystallization product aggregates that have been formed during
a course of continuous casting remain partially even after forging
and heat treatment steps.
14. An aluminum-alloy shaped product produced through the method
according to claim 1 and having a eutectic Si area share of 8% or
more, an average eutectic Si particle diameter of 5 .mu.m or less,
25% or more of eutectic Si having an acicular eutectic Si ratio of
1.4 or more, an intermetallic compound area share of 1.2% or more,
an average intermetallic compound particle diameter of 1.5 .mu.m or
more and 30% or more of intermetallic compounds or intermetallic
compound aggregates having an intermetallic compound length or
intermetallic compound aggregate length of 3 .mu.m or more.
15. An aluminum-alloy shaped product produced through the method
according to claim 13, wherein an engine piston is made of the
aluminum-alloy and includes a top surface portion and a skirt
portion and the high-temperature fatigue strength of the top
surface portion is 50 MPa or more.
16. A production system comprising a continuous line for performing
a series of steps for producing an aluminum-alloy shaped product
from a molten aluminum-alloy, wherein the series of steps includes
at least the steps of the method of claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing an
aluminum-alloy shaped product, which method includes a step of
forging a continuously cast aluminum-alloy rod serving as a forging
material, to an aluminum-alloy shaped product and to a production
system for the shaped product.
BACKGROUND ART
[0002] In recent years, in vehicles such as four-wheel-drive
automobiles and two-wheel-drive automobiles (hereinafter such a
vehicle will be referred to simply as an "automobile"), attempts
have been made to employ an aluminum-alloy forged product in an
internal combustion engine piston in order to attain high
performance or to cope with environmental regulations. This is
because, when such an aluminum-alloy forged product is employed,
the weight of driving parts (e.g., a piston) for an internal
combustion engine can be reduced, leading to reduction of a load
upon operation of the internal combustion engine, enhancement of
output, or reduction of fuel consumption. Conventionally, most
internal combustion engine pistons have been produced from an
aluminum-alloy cast product. However, in the case of such a cast
product, difficulty is encountered in reducing internal defects
generated during the course of casting, and excess material must be
provided on the cast product so as to ensure safety design in terms
of strength. Therefore, when such a cast product is employed in an
internal combustion engine piston, reducing the weight of the
piston is difficult.
[0003] In view of the foregoing, attempts have been made to reduce
the weight of such a piston by producing the piston from an
aluminum-alloy forged product, in which generation of internal
defects can be suppressed.
[0004] A conventional method for producing an aluminum-alloy
forging material includes a step of preparing molten aluminum-alloy
by means of a typical smelting technique, a step of subjecting the
molten aluminum-alloy to any continuous casting technique, such as
continuous casting, semi-continuous casting (DC casting) or hot top
casting, to thereby produce an aluminum-alloy cast ingot and a step
of subjecting the cast ingot to homogenization heat treatment to
thereby homogenize aluminum-alloy crystals. The thus produced
aluminum-alloy forging material (cast ingot) is subjected to
forging and then to a T6 treatment of JIS (Japanese Industrial
Standard) to thereby produce an aluminum-alloy forged product.
[0005] JP-A 2002-294383 (Patent Document 1) discloses a method for
producing a 6000-series-alloy cast product, in which the
homogenization treatment temperature is lowered or the
homogenization treatment is omitted.
[0006] However, high-temperature mechanical characteristics of the
cast product are not examined in Patent Document 1.
[0007] Meanwhile, the following Japanese Patent Application
Publication No. 2005-290545 (Patent Document 2), which is objected
to produce an aluminum-alloy shaped product that exhibits
high-temperature mechanical strength superior to that of a
conventional aluminum-alloy forged product, discloses a method for
producing an aluminum-alloy shaped product, comprising a step of
forging a continuously cast rod of aluminum-alloy serving as a
forging material, in which the aluminum-alloy contains Si in an
amount of 10.5 to 13.5 mass %, Fe in an amount of 0.15 to 0.65 mass
%, Cu in an amount of 2.5 to 5.5 mass % and Mg in an amount of 0.3
to 1.5 mass %, and heat treatment and heating steps including a
step of subjecting the forging material to pre-heat treatment, a
step of heating the forging material during a course of forging of
the forging material and a step of subjecting a shaped product to
post-heat treatment, the pre-heat treatment including treatment of
maintaining the forging material at a temperature of -10 to
480.degree. C. for two to six hours.
[0008] In recent years, there has been increasing demand for an
internal combustion engine of high efficiency and high output, and
accordingly, parts employed in the engine have been further
required to exhibit high-temperature mechanical strength.
[0009] Therefore, in view of the tact that an aluminum-alloy forged
product enables further reduction of the weight, demand has arisen
for a method for producing an aluminum-alloy shaped product
exhibiting high-temperature (for example, fatigue strength at a
temperature of 350.degree. C.) mechanical strength superior to that
of a conventional aluminum-alloy forged product.
[0010] In view of the foregoing, objects of the present invention
are to provide a method for producing an aluminum-alloy shaped
product that exhibits high-temperature mechanical strength superior
to that of a conventional aluminum-alloy forged product, to provide
an aluminum-alloy shaped product and to provide a production system
for the shaped product.
DISCLOSURE OF THE INVENTION
[0011] (1) In order to achieve the object, according to a first
invention of the present invention, the present invention provides
a method for producing an aluminum-alloy shaped product, comprising
a step of forging a continuously cast rod of aluminum-alloy serving
as a forging material, in which the aluminum-alloy contains Si in
an amount of 10.5 to 13.5 mass %, Cu in an amount of 2.5 to 6 mass
%, Mg in an amount of 0.3 to 1.5 mass % and Ni in an amount of 0.8
to 4%, and satisfies a relational expression of "Ni(% by
mass).gtoreq.(-0.68.times.Cu(% by mass)+4.2(% by mass)), and heat
treatment and heating steps including a step of subjecting the
forging material to pre-heat treatment, a step of preliminary
heating the forging material before a course of forging of the
forging material and a step of subjecting a shaped product to
post-heat treatment, said pre-heat treatment including treatment of
maintaining the forging material at a temperature of -10 to
480.degree. C. for two to six hours.
[0012] (2) According to a second invention of the present
invention, in the first mentioned method, the pre-heat treatment is
performed at a temperature of at least 200.degree. C. and
370.degree. C. or lower.
[0013] (3) According to a third invention of the present invention,
in the first mentioned method, the pre-heat treatment is performed
at a temperature of at least -10.degree. C. to and less than
200.degree. C.
[0014] (4) According to a fourth invention of the present
invention, in the first mentioned method, the pre-heat treatment is
performed at a temperature of at least 370.degree. C. and
480.degree. C. or lower.
[0015] (5) According to a fifth invention of the present invention,
in the method according to any one of the first to fourth mentioned
methods, wherein the post-heat treatment is performed at 170 to
230.degree. C. for one to 10 hours without performing solid
solution treatment.
[0016] (6) According to a sixth invention of the present invention,
in the method according to any one of the first to fifth mentioned
methods, the aluminum-alloy further contains Fe in an amount of
0.15 to 0.65 mass %.
[0017] (7) According to a seventh invention of the present
invention, in the method according to any one of the first to sixth
mentioned methods, the aluminum-alloy further contains P in an
amount of 0.003 to 0.02 mass %.
[0018] (8) According to an eighth invention of the present
invention, in the method according to any one of the first to
seventh mentioned methods, the aluminum-alloy further contains at
least one species selected from among Sr in an amount of 0.003 to
0.03 mass %, Sb in an amount of 0.1 to 0.35 mass %, Na in an amount
of 0.0005 to 0.015 mass % and Ca in an amount of 0.001 to 0.02 mass
%.
[0019] (9) According to a ninth invention of the present invention,
in the method according to any one of the first to eighth mentioned
methods, the aluminum-alloy further contains at least one species
selected from among Mn in an amount of 0.1 to 1.0 mass %, Cr in an
amount of 0.05 to 0.5 mass %, Zr in an amount of 0.04 to 0.3 mass
%, V in an amount of 0.01 to 0.15 mass % and Ti in an amount of
0.01 to 0.2 mass %.
[0020] (10) According to a tenth invention of the present
invention, in the method according to any one of the first to ninth
mentioned methods, during the forging step, a percent reduction of
a portion of the forging material that requires high-temperature
fatigue strength resistance is regulated to 90% or less.
[0021] (11) According to an eleventh invention of the present
invention, in the method according to any one of the first to tenth
mentioned methods, the preliminary heating step is performed at a
temperature of 380 to 480.degree. C.
[0022] (12) According to a twelfth invention of the present
invention, in the method according to any one of the first to
eleventh mentioned methods, the continuously cast rod is produced
through continuous casting of a molten alloy having an average
temperature which falls within a range of a liquidus temperature
+40.degree. C. to the liquidus temperature +230.degree. C. at a
casting speed of 80 to 2,000 mm/minute.
[0023] (13) According to a thirteenth invention of the present
invention, the present invention further provides an aluminum-alloy
shaped product produced through the method according to any one of
claims 1 to 12 and having a metallographic structure in which
crystallization product networks, acicular crystallization products
or crystallization product aggregates that have been formed during
a course of continuous casting remain partially even after forging
and heat treatment steps.
[0024] (14) According to a fourteenth invention of the present
invention, the present invention also provides an aluminum-alloy
shaped product produced through the method according to any one of
claims 1 to 12 and having a eutectic Si area share of 8% or more,
an average eutectic Si particle diameter of 5 .mu.m or less, 25%
ormore of eutectic Si having an acicular eutectic Si ratio of 1.4
or more, an intermetallic compound area share of 1.2% or more, an
average intermetallic compound particle diameter of 1.5 .mu.m or
more and 30% or more of intermetallic compounds or intermetallic
compound aggregates having an intermetallic compound length or
intermetallic compound aggregate length of 3 .mu.m or more.
[0025] (15) According to a fifteenth invention of the present
invention, in the aluminum-alloy shaped product produced through
the method according to the thirteenth or fourteenth, an engine
piston is made of the aluminum-alloy and includes a top surface
portion and a skirt portion and the high-temperature fatigue
strength of the top surface portion is 50 MPa or more.
[0026] (16) According to a sixteenth invention of the present
invention, The present invention also provides a production system
comprising a continuous line for performing a series of steps for
producing an aluminum-alloy shaped product from a molten
aluminum-alloy, wherein the series of steps includes at least the
steps of the method of any one of the first to thirteenth mentioned
methods.
[0027] According to the first invention described in (1), since the
aluminum-alloy includes Si, Cu, Mg, and Ni, it is possible to
obtain shaped products that have excellent high-temperature fatigue
strength, forgeability, ductility, and toughness. Further, since
the composition of Ni and Cu satisfies a relational expression of
Ni(% by mass).gtoreq.[-0.68.times.Cu(% by mass)+4.2(% by mass)], it
is possible to improve fatigue strength characteristics at higher
temperature.
[0028] Meanwhile, conventionally, shaped products made of
multilevel alloys should be experimentally produced by changing the
alloy composition, or complicated facilities and much time were
required for the evaluation of the high-temperature fatigue
strength. Accordingly, it was particularly difficult to design an
alloy that has fatigue strength at high temperature.
[0029] However, it is possible to easily obtain an alloy, which has
fatigue strength characteristics at higher temperature by designing
alloy composition through using the aforementioned relational
expression of the present invention as an index. Further, even
though temperature is higher than 350.degree. C., it is possible to
obtain aluminum-alloy shaped products that have excellent
mechanical strength.
[0030] More specifically, for example, after aluminum-alloy shaped
products are retained at a temperature of 350.degree. C. for 100
hours, the fatigue strength thereof at a temperature of 350.degree.
C. becomes 33 MPa or more. These characteristics are
characteristics required for a top surface portion of a piston of
an internal combustion engine that comes in contact with a high
temperature atmosphere. Accordingly, it is possible to further
reduce the thickness of a piston of a conventional internal
combustion engine by using the aluminum-alloy shaped product
according to the present invention and to reduce the weight of a
piston of an internal combustion engine. Further, it is possible to
realize to satisfy weight reduction required from the market, to
reduce fuel consumption of an internal combustion engine, and to
improve output.
[0031] According to the second invention described in (2), since
the heat treatment temperature of the pre-heat treatment step is in
the range of 200.degree. C. to 370.degree. C., high-temperature
fatigue strength, forgeability, ductility, and toughness further
become excellent, so that it is possible to obtain better shaped
products.
[0032] According to the third invention described in (3), since the
heat treatment temperature of the pre-heat treatment step is in the
range of -10.degree. C. to 200.degree. C., it is possible to obtain
a shaped product having more excellent high-temperature fatigue
strength. However, forgeability, ductility, and toughness
deteriorate as compared to when the heat treatment temperature is
in the range of 200.degree. C. to 370.degree. C.
[0033] According to the fourth invention described in (4), since
the heat treatment temperature of the pre-heat treatment step is in
the range of 370.degree. C. to 480.degree. C., it is possible to
obtain a shaped product having more excellent forgeability,
ductility, and toughness. However, high-temperature fatigue
strength deteriorates as compared to when the heat treatment
temperature is in the range of 200.degree. C. to 370.degree. C.
[0034] According to the fifth invention described in (5), the
forging material is retained at a temperature of 170.degree. C. to
230.degree. C. for 1 to 10 hours, without performing a solid
solution treatment at a post-heat treatment step. Accordingly, it
is possible to obtain a shaped product having more excellent
high-temperature fatigue strength. However, ductility and toughness
deteriorate as compared to when a solution treatment is performed
and the forging material is retained at a temperature of
170.degree. C. to 230.degree. C. for 1 to 10 hours.
[0035] According to the sixth invention described in (6), since the
aluminum-alloy includes 0.15 to 0.65% by mass of Fe, Al--Fe,
Al--Fe--Si, or Al--Ni--Fe based particles are crystallized, thereby
improving high-temperature mechanical strength. Further, the
content of 0.15 to 0.65% by mass of Fe suppresses the increase of
the large crystallization products and improves forgeability,
high-temperature fatigue strength, and toughness.
[0036] According to the seventh invention described in (7), the
aluminum-alloy includes 0.003 to 0.02% by mass of P. Since
generating primary Si crystals, P is preferable when wear
resistance is a priority. In addition, P has an effect of
micronizing primary Si crystals, and acts by suppressing the
decrease of forgeability, ductility, or high-temperature fatigue
strength that is caused by primary Si crystals generated. Further,
the content of 0.003 to 0.02% by mass of P suppresses the increase
of large primary Si crystals, thereby improving forgeability,
high-temperature fatigue strength, and toughness.
[0037] According to the eighth invention described in (8), the
aluminum-alloy may include one or the combination of two or more of
0.003 to 0.03% by mass of Sr, 0.1 to 0.35% by mass of Sb, 0.0005 to
0.015% bymass of Na, and 0.001 to 0.02% bymass of Ca. Accordingly,
it is possible to suppress the generation of primary Si crystals
and this is preferable when forgeability, ductility, and toughness
are priorities. Further, the contents of Sr, Sb, Na, and Ca in this
range suppress the generation of primary Si crystals, and improve
forgeability, toughness, and high-temperature fatigue strength.
[0038] According to the ninth invention described in (9), the
aluminum-alloy may include one or the combination of two or more of
0.1 to 1.0% by mass of Mn, 0.05 to 0.5% by mass of Cr, 0.04 to 0.3%
by mass of Zr, 0,01 to 0.15% by mass of V, and 0.01 to 0.2% by mass
of Ti. Accordingly, Al--Mn, Al--Fe--Mn--Si, Al--Cr, Al--Fe--Cr--Si,
Al--Zr, Al--V, and Al--Ti based compounds are crystallized or
precipitated, thereby improving high-temperature mechanical
strength of the aluminum-alloy. Further, the contents of Mn, Cr,
Zr, V, and Ti in this range suppress the increase of large
crystallization products, and improve forgeability,
high-temperature fatigue strength, and toughness.
[0039] According to the tenth invention described in (10), since a
percent reduction of a portion requiring high-temperature fatigue
resistant strength is 90% or less in the forging step, the
networks, acicular crystallization products, or aggregates of the
crystallization products are appropriately divided and remain.
Therefore, it is possible to obtain shaped products that have
excellent ductility, toughness, and high-temperature fatigue
strength.
[0040] According to the eleventh invention described in (11), since
a preliminary heating temperature before processing is in the range
of 380.degree. C. to 480.degree. C. in the forging step, it is
possible to obtain shaped products that have excellent
high-temperature fatigue strength, forgeability, ductility, and
toughness.
[0041] According to the twelfth invention described in (12), the
continuously cast rod is obtained by casting an aluminum-alloy, of
which an average temperature of the molten alloy corresponds to a
liquidus line of +40.degree. C. to +230.degree. C., at a casting
speed of 80 (mm/min) to 2000 (mm/min) by a continuous casting
methods Accordingly, it is possible to obtain the networks,
acicular crystallization products, or aggregates of the uniform and
fine crystallization products, and to obtain shaped products that
have excellent high-temperature fatigue strength, forgeability,
ductility, and toughness.
[0042] According to the thirteenth invention described in (13),
networks of crystallization products, acicular crystallization
products, or aggregates of crystallization products formed during
continuous casting partially remain in the structure even after
forming and a heat treatment. Accordingly, it is possible to obtain
shaped products that have excellent high-temperature fatigue
strength, forgeability, ductility, and toughness.
[0043] According to the fourteenth invention described in (14), a
sample having an area occupation ratio of eutectic Si of 8% or
more, an average grain size of eutectic Si of 5 .mu.m or less, and
an acicular eutectic Si ratio of eutectic Si of 1.4 or more
corresponds to 25% or more; and a sample having an area occupation
ratio of an intermetallic compound of 1.2% or more, an average
grain size of an intermetallic compound of 1.5 .mu.m or more, and a
length of an intermetallic compound or a length of an aggregate of
a contacted intermetallic compound is 3 .mu.m or more corresponds
30% or more. Accordingly, it is possible to reliably obtain shaped
products that have excellent high-temperature fatigue strength,
forgeability, ductility, and toughness.
[0044] According to the fifteenth invention disclosed in (15),
since the high-temperature fatigue strength of the top surface
portion is 50 MPa or more, the shaped products have sufficient
high-temperature fatigue strength and may be suitably used for a
top surface portion, and the like, of a piston of an internal
combustion engine.
[0045] According to the sixteenth invention described in (16), a
series of steps between molten metal and the aluminum-alloy shaped
product are built up as a continuous line, and any one of the
above-mentioned methods for production of aluminum-alloy shaped
product is necessarily included in the series of steps.
Accordingly, it is possible to improve fatigue strength
characteristics at higher temperature.
[0046] Meanwhile, conventionally, shaped products made of
multilevel alloys should be experimentally produced by changing the
alloy composition, or complicated facilities and much time were
required for the evaluation of the high-temperature fatigue
strength. Accordingly, it was difficult to design an alloy that has
fatigue strength at particularly high temperature.
[0047] However, it is possible to easily obtain an alloy, which has
fatigue strength characteristics at higher temperature by designing
alloy composition by using the relational expression of the present
invention as an index. Further, even though temperature is higher
than 350.degree. C., it is possible to obtain aluminum-alloy shaped
products that have excellent mechanical strength.
[0048] More specifically, for example, after aluminum-alloy shaped
products are retained at a temperature of 350.degree. C. for 100
hours, the fatigue strength thereof at a temperature of 350.degree.
C. becomes 33 MPa or more. These characteristics are, for example,
characteristics required for a top surface portion of a piston of
an internal combustion engine that comes in contact with a high
temperature atmosphere. Accordingly, it is possible to further
reduce the thickness of a piston of a conventional internal
combustion engine by using the aluminum-alloy shaped product
according to the present invention and to reduce the weight of a
piston of an internal combustion engine. Further, it is possible to
satisfy weight reduction required from the market, and realize to
reduce fuel consumption of an internal combustion engine, and to
improve output.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] FIG. 1 is a view showing a forging production system that is
an example of a production line for realizing production method
according to the present invention;
[0050] FIG. 2 is a view showing an example of a portion near a mold
of a continuous casting apparatus that is used in the present
invention;
[0051] FIG. 3 is a view showing another example of the portion near
the mold of the continuous casting apparatus that is used in the
present invention;
[0052] FIG. 4 is a view showing the effective mold length of the
continuous casting apparatus that is used in the present
invention;
[0053] FIG. 5 is a view showing another example of the continuous
casting apparatus that is used in the present invention;
[0054] FIG. 6 is a view illustrating a relationship between
contents of Ni and Cu that are in an aluminum-alloy;
[0055] FIG. 7A is a plan view of a piston having the shape of
Examples 17 and 18 of the present invention and Comparative
Examples 11 to 13;
[0056] FIG. 7B is a front view of the piston shown in FIG. 7A;
and
[0057] FIG. 8 is a cross-sectional view taken along line VIII-VIII
of FIG. 7A.
BEST MODE FOR CARRYING OUT THE INVENTION
[0058] The alloy composition of the shaped product according to the
present invention will be described.
[0059] A molten aluminum-alloy used in the present invention
includes 10.5 to 13.5% by mass (preferably, 11.5 to 13% by mass) of
Si, 2.5 to 6% by mass (preferably, 3.5 to 5.5% by mass) of Cu, 0.3
to 1.5% by mass (preferably, 0.5 to 1.3% by mass) of Mg, and 0.8 to
4% by mass (preferably, 1.8 to 3.5% by mass) of Ni, and is adjusted
to have composition that satisfies a relational expression of Ni(%
by mass).gtoreq.[-0.68.times.Cu(% by mass)+AA(% by mass)] (wherein,
AA is a constant and AA.gtoreq.4.2 preferably AA.gtoreq.4.7).
[0060] Si increases high-temperature mechanical strength and wear
resistance by the distribution of eutectic Si, and coexists with Mg
and precipitates Mg.sub.2Si particles, thereby improving
high-temperature mechanical strength. If Si content is less than
10.5% bymass, the above-mentioned effects are small. If Si content
exceeds 13.5% by mass, a large amount of primary Si crystals is
crystallized, so that high-temperature fatigue strength, ductility,
and toughness are decreased.
[0061] Ni generates Al--Ni based and Al--Ni--Cu based
crystallization products, and improves high-temperature mechanical
strength by using the crystallization products. If Ni content is
less than 0.8% bymass, the above-mentionedeffects are small. If Ni
content exceeds 4% by mass, the amount of large crystallization
products is increased, so that forgeability or high-temperature
fatigue strength, ductility, and toughness are decreased.
[0062] Cu precipitates CuAl.sub.2 particles, and generates Al--Cu
based and Al--Ni--Cu based crystallization products, thereby
improving high-temperature mechanical strength. If Cu content is
less than 2.5% bymass, the above-mentionedeffects are small. If Cu
content exceeds 6% bymass, the amount of large Al--Cu
basedcrystallization products is increased, so that forgeability or
high-temperature fatigue strength, ductility, and toughness are
decreased.
[0063] Mg coexists with Si and precipitates Mg.sub.2Si particles,
thereby improving high-temperature mechanical strength. If Mg
content is less than 0.3% by mass, the above-mentioned effects are
small. If Mg content exceeds 1.5% by mass, the amount of large
Mg.sub.2Si crystallization products is increased, so that
forgeability or high-temperature fatigue strength, ductility, and
toughness are decreased.
[0064] Further, in the present invention, the composition of Ni and
Cu needs to satisfy a relational expression of Ni(% by
mass).gtoreq.[-0.68.times.Cu(% bymass)+AA(% by mass)] (wherein, AA
is aconstant and AA.gtoreq.4.2 preferably AA.gtoreq.4.7). The
reason for this is that a fatigue strength characteristic at higher
temperature is improved if Ni and Cu satisfy this relational
expression. Meanwhile, since having a large amount of a generated
network-like or acicular intermetallic compounds that contribute to
high-temperature strength, the aluminum-alloy shaped product that
are prepared to have a constant AA equal to or larger than 4.7 are
preferable.
[0065] The mechanism of the improvement of the fatigue strength
characteristic is not clear, but may be estimated as follows. It is
considered that Al--Ni based crystallization products, Al--Ni--Cu
based crystallization products, Al--Cu based crystallization
products, and Co dissolved in an aluminum matrix under
high-temperature environment contribute most to the improvement of
high-temperature mechanical strength. A relationship between Cu
content and Ni content where high-temperature mechanical strength
is effectively improved by these crystallization products and the
solid solution of Cu has been deduced from the above-mentioned
relational expression.
[0066] The fatigue strength of the shaped product using the
aluminum-alloy at a temperature of 350.degree. C. is equal to or
higher than 33 MPa that is a preferable value, more preferably, 43
MPa.
[0067] Further, the fatigue strength of the shaped product using
the aluminum-alloy at a temperature of 300.degree. C. is equal to
or higher than 55 MPa.
[0068] It is preferable that the molten alloy contain one or two or
more of 0.1 to 1% by mass (preferably, 0.2 to 0.5% by mass). of Mn,
0.05 to 0.5% by mass (preferably, 0.1 to 0.3% by mass) of Cr, 0.04
to 0.3% by mass (preferably, 0.1 to 0.2% by mass) of Zr, and 0.01
to 0.15% by mass (preferably, 0.05 to 0.1% by mass) of V, and 0.01
to 0.2% by mass (preferably, 0.02% to 0.1% by mass) of Ti. The
reason why Mn, Cr, Zr, V, and Ti is contained is to crystallize or
precipitate Al--Mn or Al--Fe--Mn--Si based compounds, Al--Cr or
Al--Fe--Cr--Si based compounds, Al--Zr based compounds, Al--V based
compounds, and Al--Ti based compounds, and to improve the
high-temperature mechanical strength of the aluminum-alloy. If Mn
content is less than 0.1% by mass, Cr content is less than 0.05% by
mass, Zr content is less than 0.04% by mass, V content is less than
0.01% by mass, and Ti content is less than 0.01% by mass,
theabove-mentioned effects aresmall. If Mn content exceeds 1.0% by
mass, Cr content exceeds 0.5% by mass, Zr content exceeds 0.3% by
mass, V content exceeds 0.15% by mass, and Ti content exceeds 0.2%
by mass, the amount of large crystallization products is increased,
so that forgeability, high-temperature fatiguestrength, and
toughness are decreased.
[0069] Further, it ispreferable that the molten alloy include 0.15
to 0.65% bymass (preferably, 0.3 to 0.5% bymass) of Fe, and Al--Fe,
Al--Fe--Si, or Al--Ni--Fe based particles are crystallized, thereby
improving high-temperature mechanical strength. If Fe content is
less than 0.15% by mass, the above-mentioned effects are small. If
Fe content exceeds 0.65% by mass, the amount of Al--Fe, Al--Fe--Si,
or Al--Ni--Fe based large crystallization products is increased, so
that forgeability or high-temperature fatigue strength, ductility,
and toughness are decreased.
[0070] Furthermore, it is preferable that the molten alloy includes
0.003 to 0.02% by mass (preferably, 0.007 to 0.016% by mass) of P.
Since generating primary Si crystals, P is preferable when wear
resistance is a priority. In addition, P has an effect of
micronizing primary Si crystals, and suppresses the decrease of
forgeability, ductility, or high-temperature fatigue strength that
is caused by primary Si crystals generated. If P content is less
than 0.003% by mass, the effect of micronizing primary Si crystals
is small, large primary Si crystals is generated at the center of
an ingot, and forgeability or high-temperature fatigue strength,
ductility, and toughness are decreased. If P content exceeds 0.02%
by mass, the amount of generated primary Si crystals is increased,
and forgeability or high-temperature fatigue strength, ductility,
and toughness are decreased.
[0071] In addition, the molten alloy contains one or two or more of
0.003 to 0.03% by mass (preferably, 0.01 to 0.02% by mass) of Sr,
0.1 to 0.35% by mass (preferably, 0.15 to 0.25% by mass) of Sb,
0.0005 to 0.015% by mass (preferably, 0.001 to 0.01% by mass) of
Na, and 0.001 to 0.02% by mass (preferably, 0.005 to 0.01% by mass)
of Ca, which is preferable because there is an effect of
micronizingprimary Si crystals. If Sr content is less than 0.003%
by mass, Sb content is less than 0.1% by mass, Na content is less
than 0.0005% by mass, and Ca content is less than 0.001% by mass,
theabove-mentioned effects aresmall. If Sr contentexceeds 0.03% by
mass, Sb content exceeds 0.35% by mass, Na content exceeds 0.015%
by mass, and Ca content exceeds 0.02% by mass, the amount of large
crystallization products is increased or casting defects are
generated, so that forgeability, high-temperature fatigue strength,
and toughness are decreased.
[0072] The composition ratios of the aluminum-alloy shaped product
and an alloy ingredient of an ingot can be confirmed by a method
using, for example, an optical emission spectrometer (e g.,
PDA-5500, product of Shimadzu Corporation), which is based on
photoelectric that is disclosed in JIS H1305.
[0073] An embodiment of the present invention will be described in
detail below with reference to drawings.
[0074] FIG. 1 is a view showing a production system that is an
example of a production line for realizing production method
according to the present invention. In FIG. 1, a forging production
system configures a continuous casting apparatus 81 that
horizontally casts a continuously cast rod from molten metal and
cuts the continuously cast rod to a predetermined length; a
pre-heat treatment apparatus 82 for performing a heat treatment on
the continuously cast rod that is cast by the continuous casting
apparatus 81; a correction apparatus 83 for correcting the bend of
the continuously cast rod if the continuously cast rod heat-treated
by the pre-heat treatment apparatus 82 is bent; a peeling apparatus
84 for removing the outer peripheral portion of the continuously
cast rod of which the bent is corrected by the correction apparatus
83; a cutting apparatus 85 for cutting the continuously cast rod of
which the outer peripheral portion is removed by the peeling
apparatus 84 into cut pieces that have a length required for the
forging of the shaped product; an upsetting apparatus (not shown)
that preliminarily heats the cut pieces cut by the cutting
apparatus 85 and upsets the cut pieces; lubrication apparatuses 86A
and 86B for applying a graphite lubricant to the preliminarily
heated forging material, for immersing the preliminarily heated
forging material in a graphite lubricant, or for coating the
preliminarily heated forging material with a graphite lubricant in
order to coat the forging material which is upset by the upsetting
apparatus with a lubricant; a forging apparatus 88 for forging the
product (preform) from the forging material that is further heated
by the preliminary heating apparatus 87 and coated with a
lubricant; and a post-heat treatment apparatus 89 for performing a
post-heat treatment on the forged products (product) that are
forged by the forging apparatus 88
[0075] For example, the post-heat treatment apparatus 89 may
configure a solid solution treatment apparatus 90 that performs a
solution treatment on the forged products, a quenching apparatus 91
that quenches the product heated by the solid solution treatment
apparatus 90, and an aging treatment apparatus 92 that performs an
aging treatment on the product quenched by the quenching apparatus
91. If the solution treatment is omitted, it is preferable that the
aging treatment apparatus 92 be provided behind the forging
apparatus 88 without providing the solid solution treatment
apparatus 90 and the quenching apparatus 91.
[0076] Meanwhile, the peeling apparatus 84 and the upsetting
apparatus may be omitted. Further, the conveyance between the
apparatus may be achieved by automatic conveying apparatuses.
Further, a lubricant coating treatment of the lubrication
apparatuses 86A and 86B may be substituted with an apparatus 86C
for bonde treatment (phosphoric-acid-salt coating treatment).
[0077] In this case, the pre-heat treatment apparatus 82 has a
function to retain the temperature of the forging material in the
range of -10.degree. C. to 480.degree. C. for 2 to 6 hours. The
preliminary heating apparatus 87 has a function to make the
temperature of the forging material in the range of 380.degree. C.
to 480.degree. C. The solid solution treatment apparatus 90 and the
quenching apparatus 91 of the post-heat treatment apparatus 89 have
functions to make the temperature of the forged products (shaped
products) for the solution be in the range of 480.degree. C. to
520.degree. C. and then to quench the forged products. The aging
treatment apparatus 92 of the post-heat treatment apparatus 89 has
a function to retain the temperature of the forged products (shaped
products) in the range of 170.degree. C. to 230.degree. C.
[0078] A method for production used in the production system
according to the present invention includes a step of performing a
pre-heat treatment on the round rod that is obtained by casting an
aluminum-alloy by a continuous casting method, a step of forming
the preform from pre-heat treated materials as forging material by
hot plastic forming, and a step of performing a post-heat treatment
after the plastic forming. The temperature of the pre-heat
treatment is in the range of -10.degree. C. to 480.degree. C., and
the temperature of the forging material during the hot plastic
forming is in the range of 380.degree. to 480.degree. C. In the
post-heat treatment step, solution heating is performed so that the
temperature of the preform is in the range of 480.degree. C. to
520.degree. C., or temperature is directly managed so as to satisfy
a temperature condition of 170.degree. C. to 230.degree. C. without
performing the solution treatment. Accordingly, shaped products are
consistently produced by performing steps that include from the
casting step to each of all heat treatment steps. As a result, it
is possible to stably produce shaped products having preferred
mechanical strength.
[0079] Forging may be mentioned to be used as the above-mentioned
plastic forming. However, as long as the temperature of the
pre-heat treatment, the conditions of the temperature of the
forging material during the hot plastic forming, and the
temperature of the post-heat treatment are satisfied, the
combination of rolling working and extruding working may be used as
the method for production according to the present invention. The
reason for this is that it is possible to obtain an effect of the
present invention in controlling the network of the structure or
crystallization products in either case.
[0080] The aluminum-alloy shaped product according to the present
invention may be suitably used as parts that require mechanical
strength at high temperature. Accordingly, the shaped product
having the shapes of, for example, an engine piston, a valve
litter, a valve retainer, a cylinder liner, and the like, may be
produced according to the present invention; and the shaped product
may be formed in desired shapes by further performing machining on
the shaped product with a lathe, a machining center, and the like,
if necessary, so as to be used as parts for various products.
[0081] Any one of a known hot top continuous casting, a known
vertical continuous casting, a known horizontal continuous casting,
and a known DC casting may be used in a part of a basic
solidification method of the method for production that is used in
the present invention. For example, the method may be a horizontal
continuous casting that supplies one or two or more fluids, which
are selected from a gas lubricant and a liquid lubricant, and the
gas obtained through thermal decomposition of the liquid thereof,
onto the inner wall surfaces of a tubular mold that has forced
cooling and is held so as to have a central axis parallel to a
horizontal direction; supplies a molten aluminum-alloy containing
Si to one end of the tubular mold so as to form columnar molten
alloy; and draws an ingot which is formed by solidifying the
columnar molten alloy in the tubular mold from the other end of the
tubular mold. A case where the present invention is applied to a
horizontal continuous casting will be described below.
[0082] FIG. 2 is a view showing an example of a portion near the
mold of the continuous casting apparatus that is used in the
present invention. A tundish 250, a refractory plate-like body 210,
and a tubular mold 201 are disposed so that an molten alloy 255
stored in the tundish 250 is supplied to the tubular mold 201
through the refractory plate-like body 210. The tubular mold 201 is
held so that a center axis 220 of the mold is substantially
parallel to a horizontal direction. A means for forcedly cooling
the mold is disposed in the tubular mold 201 and a means for
forcedly cooling the mold for a cast ingot 216 is disposed at an
outlet of the tubular mold 201 so that the molten alloy 255 becomes
the cast ingot 216. In FIG. 2, a cooling water showering apparatus
205 is provided as an example of a means for forcedly cooling the
cast ingot 216. A drive apparatus (not shown) is disposed near the
outlet of the tubular mold 201 so that the forcedly cooled and cast
ingot 216 is drawn at a constant speed and continuously cast.
Further, a synchronized cutting machine (not shown), which cuts the
drawn and cast rod to a predetermined length, is provided.
[0083] Another example of the portion near the mold of the
continuous casting apparatus, which is used in the present
invention, will be described with reference to FIG. 3. FIG. 3 is a
schematic cross-sectional view of an example of a DC casting
apparatus. In the DC casting apparatus, a molten aluminum-alloy 1
is introduced into a stationary water-cooling mold 5, which is made
of an aluminum-alloy or copper, through a trough 2, a dip tube 3,
and a floating distributor 4. The water-cooling mold 5 is cooled by
cooling water 5A. A molten aluminum-alloy 6 introduced into the
water-cooling mold 5 forms a solidification shell 7 at a portion
thereof, which comes in contact with the water-cooling mold 5, and
is constructed. A solidified aluminum-alloy ingot 7A is drawn
downward from the water-cooling mold 5 by a lower mold 9. In this
case, the aluminum-alloy ingot 7A is further cooled by cooling
water jet 8 that is supplied from the water-cooling mold 5, thereby
being completely solidified. If the lower mold 9 reaches a lower
end where the lower mold 9 can be moved, the aluminum-alloy ingot
7A is cut at a predetermined position and withdrawn.
[0084] Referring to FIG. 2, the tubular mold 201 is held so that
the center axis 220 of the mold is substantially parallel to a
horizontal direction. The tubular mold 201 includes a means for
forcedly cooling the tubular mold 201. This means for forcedly
cooling the mold 201 cools the wall surfaces of the mold by cooling
water 202 that is stored in a mold's cooling water cavity 204;
removes the heat of the columnar molten alloy 215, which is tilled
in the tubular mold 201, from the surfaces of the molten metal that
comes in contact with the inner wall of the mold 201; and forms a
solidification shell on the surface of the molten metal. The
tubular mold 201 further includes a means for forcedly cooling the
mold. This means for forcedly cooling the mold discharges cooling
water from the cooling water showering apparatus 205 so that
cooling water comes in direct contact with the cast ingot 216 at
the end of the outlet of the tubular mold 201, thereby solidifying
the columnar molten alloy 215 stored in the tubular mold 210. In
addition, an end of the tubular mold 201, which is positioned
opposite to nozzles of the cooling water showering apparatus 205,
is connected to the tundish 250 through the refractory plate-like
body 210.
[0085] In FIG. 2, cooling water that is used to forcedly cool the
tubular mold 201, and cooling water that is used to forcedly cool
the cast ingot 216 are supplied through a cooling water feed tube
203. However, the cooling water may be separately supplied.
[0086] A distance from a position, where the extension line of the
central axis of the nozzle of the cooling water showering apparatus
205 intersects the surface of the cast ingot 216, to the contact
surface between the tubular mold 201 and the refractory plate-like
body 210 is referred to as an effective mold length (see reference
numeral L of FIG. 4). It is preferable that the effective mold
length be in the range of 15 to70 mm. If the effective mold length
is less than 15 mm, such as a good film is not formed, so that
casting cannot be performed. If the effective mold length exceeds
70 mm, forced cooling is ineffective and the solidification caused
by the inner wall of the mold is dominant. Accordingly, the contact
resistance between the tubular mold 201 and the columnar molten
alloy 215 or the solidification shell is increased, so that cracks
are generated on the casting surface or the tubular mold 201 is
torn off therein, and the like. Therefore, this is not preferable
due to unstable casting.
[0087] It is preferable that a material of the tubular mold 201 be
one or the combination of two or more selected from aluminum,
copper, or alloys thereof. The combination of materials may be
selected in consideration of thermal conductivity, heat resistance,
and mechanical strength.
[0088] Further, it is preferable in the mold that a permeable
porous member 222 having a self-lubricity be provided in a ring
shape on the surface of the tubular mold 201 coming in contact with
the columnar molten alloy 215. The ring shape means that the
permeable porous member is provided on the entire inner wall 221 of
the tubular mold 201 in a circumferential direction. The air
permeability of the permeable porous member 222 may be in the range
of 0.005 to 0.03 [L(liter)/(cm.sup.2/min)], more preferably, 0.07
to 0.02 [L/(cm.sup.2/min)]. The thickness of the permeable porous
member 222 to be provided is not particularly limited, but is
preferably in the range of 2 to 10 mm, more preferably, 3 to 8 mm.
For example, graphite of which air permeability is in the range of
0.008 to 0.012 ]L/(cm.sup.2/min)] may be used as the permeable
porous member 222. In this case, the air permeability is obtained
by measuring the amount of air, which has a pressure of 2
kg/cm.sup.2 and is ventilated through a test piece having a
thickness of 5 mm, per minute under.
[0089] It is preferable to use a tubular mold 201 in which a
permeable porous member 222 is provided in the range of 5 to 15 mm
within the range of the effective mold length. It is preferable
that an O-ring 213 is provided on the matching surface of the
tubular mold 201, the refractory plate-like body 210, and the
permeable porous member 222.
[0090] The shape of the inner wall 221 of the radial cross-section
of the tubular mold 201 may have a triangular shape, a rectangular
shape, or an irregular shape having no symmetry axis nor symmetry
plane, in addition to a circular shape. Alternatively, a core may
be provided in the mold in order to form a hollow cast ingot.
Further, the tubular mold 201 is a tubular mold of which both ends
are opened. The molten alloy 255 is supplied into the tubular mold
201 from one end of the tubular mold 201 through a molten alloy
inlet 211 that is formed through the refractory plate-like body
210, and the cast ingot 216 is extruded or drawn from the other end
of the tubular mold 201.
[0091] The inner wall 221 of the tubular mold 201 is formed to have
an elevation angle in the range of 0 to 3.degree., more preferably,
0 to 1.degree. with respect to the center axis 220 of the mold in a
direction where the cast ingot 216 is drawn. If the elevation angle
is less than 0.degree., resistance is applied to the outlet of the
tubular mold 201 when the cast ingot 216 is drawn from the tubular
mold 201. For this reason, casting cannot be performed. Meanwhile,
if the elevation angle exceeds 3.degree., the inner wall 221 of the
tubular mold 201 comes in insufficient contact with the columnar
molten alloy 215. Accordingly, an effect of removing heat that heat
is removed from the columnar molten alloy 215 or the solidification
shell to the tubular mold 201 deteriorates, so that solidification
becomes insufficient. As a result, this is not preferable due to
the increase of the possibility of casting troubles that re-melted
surface is formed on the surface of the cast ingot 216 or the
molten alloy 255, which is unsolidified, is discharged from the end
of the tubular mold 201, and the like.
[0092] The tundish 250 configures a molten alloy receiving inlet
251 for receiving a molten aluminum-alloy that is adjusted to have
prescribed alloy ingredients by an external melting furnace or the
like, a molten alloy reservoir 252, and an outlet 253 that makes
the molten metal to flow into the tubular mold 201. The tundish 250
maintains the level 254 of the molten alloy 255 at a position that
is higher than the upper surface of the tubular mold 201, and
stably distributes the molten alloy 255 to each tubular mold 201 in
the case of multiple casting. The molten alloy 255 held in the
molten alloy reservoir 252 of the tundish 250 is poured in the
tubular mold 201 from the molten alloy inlet 211 that is provided
through the refractory plate-like body 210.
[0093] The refractory plate-like body 210 is used to isolate the
tundish 250 from the tubular mold 201, and can be produced from a
material having refractory heat-insulating properties. For example,
Lumiboard manufactured by NICHIAS Corporation, INSURAL manufactured
by FOSECO JAPAN, Ltd., or Fiber Blanket Board manufactured by
IBIDEN CO., LTD. may be used as the refractory plate-like body. The
refractory plate-like body 210 has the shape that can form the
molten alloy inlet 211. One or more pouring ports 211 may be formed
at a portion of which the refractory plate-like body 210 protrudes
inward from the inner wall 221 of the tubular mold 201.
[0094] Reference numeral 208 denotes a fluid feed-tube through a
fluid is supplied. A lubrication fluid may be used as the fluid.
The fluid may be one kind or two kinds or more selected from
gaseous lubricants and liquid lubricants. It is preferable that
supply pipes for a gaseous lubricant and a liquid lubricant be
separately provided.
[0095] The fluid, which is pressurized and supplied from the fluid
feed-tube 208, is supplied to a gap, which is formed between the
tubular mold 201 and the refractory plate-like body 210, through a
circular path 224. It is preferable that a gap of 200 .mu.m or less
be formed to the portion between the tubular mold 201 and the
refractory plate-like body 210. The gap has a size so that the
molten alloy 255 can not permeate through the gap and the fluid can
flow to the inner wall 221 of the tubular mold 201. In the mode
shown in FIG. 2, the circular path 224 is formed on the outer
peripheral surface of the permeable porous member 222 that is
provided on the tubular mold 201. The fluid permeates into the
permeable porous member 222 due to applied pressure, is fed onto
the entire surface of the permeable porous member 222 that comes in
contact with the columnar molten alloy 215, and is supplied onto
the inner wall 221 of the tubular mold 201. The liquid lubricant
may be heated and changed into decomposed gas, and may be supplied
onto the inner wall 221 of the tubular mold 201.
[0096] As a result, it is possible to improve the lubrication
between the permeable porous surfaces of the tubular mold 201, and
the periphery of the columnar molten alloy 215 and the periphery of
the solidification shell. The permeable porous member 222 is
provided in a ring shape, so that it is possible to obtain a better
lubrication effect and to easily cast a continuously cast rod made
of an aluminum-alloy.
[0097] A corner space 230 is formed by one or two or more selected
from the supplied gases, the supplied liquid lubricant, and the
gases decomposed from the liquid lubricant.
[0098] A casting step included in the method for production
according to the present invention will be described.
[0099] In FIG. 2, the molten alloy 255 stored in the tundish 250 is
supplied to the tubular mold 201, which is held so as to have a
center axis 220 of the mold substantially parallel to a horizontal
direction, through the refractory plate-like body 210. The molten
alloy is forcedly cooled at the outlet of the tubular mold 201, and
becomes the cast ingot 216. Since the cast ingot 216 is drawn at a
constant speed by a drive apparatus that is provided near the
outlet of the tubular mold 201, the molten alloy is continuously
cast into a cast rod. The drawn cast rod is cut to a predetermined
length by a synchronized cutting machine. That is, an
aluminum-alloy, of which the average temperature of a molten alloy
255 corresponds to a liquidus line of +40.degree. C. to +230 C. can
be cast into the continuously cast rod at a casting speed of 300
(mm/min) to 2000 (mm/min) by a continuous casting method. Under
this condition, it is possible to obtain shaped products where
crystallization products are finely dispersed and forgeability and
high-temperature mechanical strength are excellent. It is
preferable that a casting speed be in the range of 80 (mm/min) to
400 (mm/min) in case of a hot top continuous casting, a vertical
continuous casting, and a DC casting. Accordingly, it is preferable
that a casting speed be in the range of 80 (mm/min) to 2000
(mm/min).
[0100] The composition of the molten aluminum-alloy 255 stored in
the tundish 250 will be described.
[0101] The molten alloy 255 includes 10.5 to 13.5% by mass
(preferably, 11.5 to 13% by mass) of Si, 2.5 to 6% by mass
(preferably, 3.5 to 5.5% by mass) of Cu, 0.3 to 1.5% by mass
(preferably, 0.5 to 1.3% by mass) of Mg, and 0.8 to 4% by mass
(preferably, 1.8 to 3.5% by mass) of Ni, and is an aluminum-alloy
that satisfies a relational expression of Ni(% by
mass).gtoreq.[-0.68.times.Cu(% by mass)+AA(% by mass)] (wherein, AA
is a constant and AA.gtoreq.4.2 preferably AA.gtoreq.4.7 is
satisfied.).
[0102] It is preferable that the molten alloy 255 contain one or
two or more of 0.1 to 1% by mass (preferably, 0.2 to 0.5% by mass)
of Mn, 0.05 to 0.5% by mass (preferably, 0.1 to 0.3% by mass) of
Cr, 0.04 to 0.3% by mass (preferably, 0.1 to 0.2% by mass) of Zr,
and 0.01 to 0.15% by mass (preferably, 0.05 to 0.1% by mass) of V,
and 0.01 to 0.2% by mass (preferably, 0.02% to 0.1% by mass) of
Ti.
[0103] Further, it is preferable that the molten alloy includes
0.15 to 0.65% by mass (preferably, 0.3 to 0.5% by mass) of Fe.
[0104] Furthermore, it is preferable that the molten alloy includes
0.003 to 0.02% by mass (preferably, 0.007 to 0.016% by mass) of
P.
[0105] In addition, the molten alloy contains one or two or more of
0.003 to 0.03% by mass (preferably, 0.01 to 0.02% by mass) of Sr,
0.1 to 0.35% by mass (preferably, 0.15 to 0.25% by mass) of Sb,
0.0005 to 0.015% by mass (preferably, 0.001 to 0.01% by mass) of
Na, and 0.001 to 0.02% by mass (preferably, 0.005 to 0.01% by mass)
of Ca, which is preferable because there is an effect of
micronizing eutectic Si crystals.
[0106] A difference between the height of the level 254 of the
molten alloy 255 that is stored in the tundish 250, and the height
of the upper surface of the inner wall 221 of the tubular mold 201
is set in the range of 0 to 250 mm, more preferably, 50 to 170 mm.
If the difference is provided to both, the pressure of the molten
alloy 255 supplied inside the tubular mold 201, liquid lubricant,
and gas obtained from the vaporization of the liquid lubricant are
suitably balanced with each other. The reason for this is that the
castability is stabilized and it is possible to easily produce a
continuously cast rod made of an aluminum-alloy. If level sensors,
which are used to measure and monitor the height of the level 254
of the molten alloy 255, are provided to the tundish 250, it is
possible to accurately manage the difference and maintain the
difference at a predetermined value.
[0107] Vegetable oil, which is liquid lubricant, may be used as the
liquid lubricant. For example, rape seed oil, castor oil, and salad
oil maybe used as the liquid lubricant. Since hardly having an
adverse effect on environment, these are preferable.
[0108] It is preferable that the amount of supplied liquid
lubricant be in the range of 0.05 (mL/min) to 5 (mL/min) [more
preferably, 0.1 (mL/min) to 1 (mL/min)]. If the amount of supplied
liquid lubricant is excessively small, the breakout of an ingot is
generated due to the lack of lubrication. If the amount of supplied
liquid lubricant is excessively large, surplus oil will be mixed to
the ingot. For this reason, there is a concern that the formation
of crystal grains having a uniform size will deteriorate.
[0109] It is preferable that the casting speed, that is, a speed
where the cast ingot 216 is drawn from the tubular mold 201, be in
the range of 300 (mm/min) to 2000 (mm/min) [more preferably, 600
(mm/min) to 2000 (mm/min)]. This is preferable because the networks
of the crystallization products formed by casting become uniform
and fine and resistance against the deformation of an aluminum
matrix at high temperature is increased, and high-temperature
mechanical strength is improved. Of course, the effect of the
present invention is not limited by the casting speed. However, if
the casting speed is increased, the effect thereof becomes
significant.
[0110] It is preferable that the amount of the cooling water
discharged from the cooling water showering apparatus 205 be in the
range of 5 (L/min) to 30 (L/min) [more preferably, 25 (L/min) to 30
(L/min)] per mold. If the amount of cooling water is excessively
small, the breakout will be generated or the surface of the cast
ingot 216 will be re-melted, so that non-uniform structure will be
formed. For this reason, there is a concern that the formation of
crystal grains having a uniform size will deteriorate. Meanwhile,
if the amount of cooling water is excessively large, a very large
amount of heat will be removed from the tubular mold 201, so that
casting cannot be performed. Of course, the effect of the present
invention is not limited by the amount of cooling water. However,
if the cooling capacity is increased to increase a temperature
gradient from a solidification interface to the interior of the
tubular mold 201, the effect thereof becomes significant.
[0111] It is preferable that the average temperature of the molten
alloy 255, which flows into the tubular mold 201 from the tundish
250, correspond to aliquidus line of +40.degree. C. to +230.degree.
C. (more preferably, a liquidus line of +60 to +200.degree. C.). If
the temperature of the molten alloy 255 is excessively low, large
crystallization products will be formed in the tubular mold 201 and
before that. For this reason, there is a concern that the formation
of crystal grains having a uniform size deteriorates. Meanwhile, if
the temperature of the molten alloy 255 is high, a large amount of
hydrogen gas will be included in the molten alloy 255 and also
include porosities in the cast ingot 216. For this reason, there is
a concern that the formation of crystal grains having a uniform
size will deteriorate.
[0112] In the present invention, these casting conditions are
controlled so that eutectic Si of the structure of the castings or
intermetallic compounds become the networks of the crystallization
products, acicular crystallization products, or aggregates of
crystallization products formed during the continuous casting, with
few spherical aggregates. Accordingly, the effect of each of
subsequent heat treatments becomes effective, which is
preferable.
[0113] In the present invention, as a pre-heat treatment, it is
important that a cast rod after having been cast is retained in the
temperature range of -10.degree. C. to 480.degree. C. (preferably,
-10.degree. C. to 370.degree. C.) for 2 to 6 hours before being
provided to a forging step as forging material. It is more
preferable that the temperature condition corresponds to room
temperature. However, even though the temperature is equal to or
lower than the room temperature, it is possible to obtain the
effect thereof.
[0114] If a pre-heat treatment is performed as described above, the
aluminum shaped product where the networks of the crystallization
products, acicular crystallization products, or the aggregates of
crystallization products formed during the continuous casting
partially remain in the structure even after forming and a heat
treatment. The crystallization products having these shapes resist
against the deformation of an aluminum matrix under high
temperature. As a result, mechanical strength is obtained under
high temperature in the range of 250.degree. C. to 400.degree. C.
That is, since the networks of the crystallization products,
acicular crystallization products, or the aggregates of
crystallization products resist against deformation under high
temperature where the aluminum matrix is softened, aluminum shaped
products have excellent high-temperature mechanical strength.
Meanwhile, if a pre-heat treatment temperature is high and a
percent reduction of the forging material is high, the networks of
the crystallization products, acicular crystallization products, or
the aggregates of crystallization products are divided and
aggregated in a granular shape, and the aggregates in a granular
shape are uniformly dispersed state in the aluminum matrix
softening under high temperature. For this reason, the resistance
of the crystallization products against the deformation of the
aluminum matrix under high temperature deteriorates, and
high-temperature mechanical strength is also not increased.
[0115] According to the present invention, under the
above-mentioned alloy composition, the aluminum matrix is softened,
and the network or acicular crystallization products of
crystallization products, or aggregates, which resist against the
deformation of the aluminum matrix, partially remain in a
high-temperature range higher than the range of 250.degree. C. to
400.degree. C. where deformation occurs very easily, thereby
increasing high-temperature mechanical strength.
[0116] When a homogenization treatment is suppressed or omitted on
a 6000 series alloy or the like that is a dilute alloy where the
amount of crystallization products is relatively small and the
network or acicular crystallization products of the crystallization
products do not so appear, the suppression or omission of the
homogenization treatment facilitates the suppression of
recrystallization or the simplification of steps, This is different
from the present invention that facilitates high-temperature
improvement by maintaining preferably the network or acicular
crystallization products contained in a high-Si-content alloy
forging material where the amount of crystallization products is
large and the network or acicular crystallization products appears
during casting.
[0117] As described in the Background Art, the disclosure of Patent
Document 1 (Japanese Patent Application Publication No.
2002-294383) relates to a 6000 series alloy, and the suppression or
omission of the temperature of the homogenization treatment is
performed not to obtain high-temperature characteristics of the
alloy but to improve mechanical characteristics at normal
temperature by suppressing recrystallization. The network or
acicular crystallization products of the crystallization products
does not so appear in the dilute alloy where the alloy system is
also different and the amount of crystallization products is
relatively small. Al--Mn and Al--Cr based compounds, which suppress
the recrystallization, are finely precipitated by lowering and
suppressing the temperature of the homogenization treatment. This
is different from the present invention that facilitates
high-temperature improvement by maintaining preferably the network
or acicular crystallization products in a high-Si-content alloy
forging material where the amount of crystallization products is
large and the network and acicular crystallization products appear
during casting.
[0118] In particular, in order to increase the high-temperature
mechanical strength and improve the forgeability of the forging
material, it is preferable that the retention temperature of the
pre-heat treatment be in the range of 200.degree. C. to 370.degree.
C. If the retention temperature is set in this temperature range,
it is possible to form an aluminum shaped product where the
eutectic Si or intermetallic compounds at the time of the pre-heat
treatment are hardly aggregated in a spherical shape, and the
networks of the crystallization products, acicular crystallization
products, or the aggregates of crystallization products formed
during the continuous casting partially remain even after forging
and a post-heat treatment, so that the aluminum shaped product has
excellent high-temperature mechanical strength excellent.
[0119] In particular, in order to further increase the
high-temperature mechanical strength of the forging material, it is
preferable that the retention temperature of the pre-heat treatment
is in the range of -10.degree. C. to 200.degree. C. If the
retention temperature is set in this temperature range, it is
possible to form an aluminum shaped product where the eutectic Si
or intermetallic compounds at the time of the pre-heat treatment
are not almost aggregated in a spherical shape, and the networks of
the crystallization products, acicular crystallization products, or
the aggregates of crystallization products formed during the
continuous casting partially remain even after forging and a
post-heat treatment, so that the aluminum shaped product has
excellent high-temperature mechanical strength.
[0120] Further, in order to further increase the forgeability of
the forging material, it is preferable that the retention
temperature of the pre-heat treatment be in the range of the
370.degree. C. to 480.degree. C. If the retention temperature is
set in this temperature range, it is possible to form an aluminum
shaped product where some entectic Si or intermetallic compounds at
the time of the pre-heat treatment are aggregated in a spherical
shape and the resistance against the deformation is decreased
during the casting, so that the aluminum shaped product has
excellent forgeability. Furthermore, in this temperature range, it
is possible to form an aluminum shaped product where the networks
of the crystallization products, acicular crystallization products,
or the aggregates of crystallization products formed during the
continuous forging partially remain even after the forging and a
post-heat treatment, so that the aluminum shaped product has
excellent high-temperature mechanical characteristics.
[0121] The pre-heat treatment step may be provided between after
the casting and the forging step. For example, the pre-heat
treatment step may be performed within one day after the casting,
or the forging material may be provided to the forging step within
one week after the pre-heat treatment step. Correction treatment
and peeling treatment may be performed during this period.
[0122] Next, an example of the forging step included in the present
invention will be described. A method for production includes 1) a
step of cutting the continuously cast round rod to a predetermined
length, 2) a step of preliminarily heating and upsetting the cut
forging material, 3) a step of lubricating the upset forging
material, 4) a step of providing the forging material into a mold
so as to forge the forging material, and 5) a step of extracting
product from the mold by a knock-out mechanism.
[0123] A lubricant may be applied to the forging material to be
forged, and may be heated before being provided to the upsetting
treatment. Meanwhile, the upsetting step may be omitted.
[0124] A lubricant treatment may be the application of a
water-soluble lubricant or a bonde treatment. For example, it is
preferable that the forging material be preliminarily heated at a
temperature of 380.degree. C. to 480.degree. C. and provided to a
forging apparatus after the bonde treatment is performed on the
forging material. If the forging material is preliminarily heated
at a temperature of 380.degree. C. to 480.degree. C., the
deformability of the forging material is improved and easily formed
in a complicated shape.
[0125] It is preferable that an aqueous lubricant be used as the
lubricant, and it is more preferable that a water-soluble graphite
lubricant is used as the lubricant. The reason for this is that
graphite is easily seized on the forging material. In this case,
for example, it is preferable that the forging material is heated
at a temperature of 380.degree. C. to 480.degree. C. and provided
to a forging apparatus after a lubricant is applied to the forging
material corresponding to a temperature of 70.degree. C. to
350.degree. C. and then the forging material is cooled at normal
temperature (for example, the forging material is retained for 2 to
4 hours). It is preferable that an aqueous lubricant be used as the
lubricant, and it is more preferable that a water-soluble graphite
lubricant be used as the lubricant. The reason for this is that
graphite is easily seized on the forging material.
[0126] Before the forging material is provided, a lubricant is
applied to the surface of the mold. The amount of the lubricant may
be further appropriately set in a state so as to correspond to the
combination of an upper mold and dies by adjusting a spraying time.
It is preferable that an oil-based lubricant be used as the
lubricant. For example, mineral oil maybe used as the lubricant.
The reason for this is that the temperature of the mold may be
lowered in the case of aqueous liquid lubricant but the lowering of
the temperature can be suppressed. Since a lubrication effect is
improved if an oil-based lubricant is a mixture of graphite and
mineral oil, it is more preferable that the oil-based lubricant be
used.
[0127] It is preferable that the heating temperature of the mold be
in the range of 150.degree. C. to 250.degree. C. The reason for
this is that a sufficient plastic flow can be obtained.
[0128] In the present invention, a percent reduction of a portion
requiring high-temperature fatigue resistant strength is preferably
90% or less (preferably 70% or less) in the forging. Ifa
percentreduction isequal toor lessthan this percentreduction, it is
possible to form a shaped product where the division of the
networks of the crystallization products, acicular crystallization
products, or the aggregates of crystallization products is
suppressed, so that the aluminum shaped product has excellent
high-temperature mechanical strength.
[0129] Meanwhile, the portions of the shaped product, which
requires high-temperature mechanical strength, may satisfy this
percent reduction.
[0130] Meanwhile, if plastic forming step such as an upsetting step
is performed before forging, it is preferable that a percent
reduction be considered as a total of the percent reductions of
those plastic forming stops. For example, in case of the shaped
product that have complicated shapes, a percent reduction per
processing is preferably in the range of 10 to 80% (more preferably
10 to 50%) and processing is preferably performed several times
(more preferably twice). For example, a percent reduction of the
first processing is preferably in the range of 10 to 50% (more
preferably 10 to 30%).
[0131] Herein, a percent reduction is defined as follows.
Percent reduction=(thickness before plastic forming-thickness after
plastic forming)/(thickness before plastic forming).times.100%
[0132] A post-heat treatment is performed on the resultant forged
products. The combination of a solution treatment and an aging
treatment may be used as the post-heat treatment. The post-heat
treatment may be performed within one week after the forging
treatment.
[0133] Specifically, it is possible to perform a solution treatment
on the forged products under conditions where the forged products
are retained at a temperature of, for example, 480.degree. C. to
520.degree. C. (preferably 490.degree. C. to 510.degree. C.) for 3
hours.
[0134] A T5 treatment or a T6 treatment of JIS standards may be
performed on the forged products as the post-heat treatment other
than the above-mentioned post-heat treatment.
[0135] In the present invention, it is preferable that the product
taken out of the forging apparatus is retained at a temperature of
170.degree. C. to 230.degree. C. (more preferably 190.degree. C. to
220.degree. C.) for 1 to 10 hours as an aging treatment without the
solution treatment or quenching. It is possible to form a shaped
product where the division and aggregation of the networks of the
crystallization products, acicular crystallization products, or the
aggregates of crystallization products can be suppressed, which
makes high-temperature mechanical strength excellent. Therefore,
this is preferable.
[0136] The alloy structure of the shaped product produced by the
above-mentioned method corresponds to aluminum the shaped product
where the eutectic Si or intermetallic compounds are hardly
aggregated in a spherical shape, and the networks of the
crystallization products, acicular crystallization products, or the
aggregates of crystallization products formed during the continuous
casting partially remain even after the forging and a post-heat
treatment, so that the shaped products has excellent
high-temperature mechanical strength.
[0137] Further, the alloy composition contains 10.5 to 13.5% by
mass (preferably, 11.5 to 13% by mass) of Si, 2.5 to 6% by mass
(preferably, 3.5 to 5.5% by mass) of Cu, 0.3 to 1.5% by mass
(preferably, 0.5 to 1.3% by mass) of Mg, and 0.8 to 4% by mass
(preferably, 1.8 to 3.5% by mass) of Ni, and corresponds to an
aluminum-alloy that satisfies a relational expression of Ni (% by
mass).gtoreq.[-0.68.times.Cu(% by mass)+AA(% by mass)] (wherein, AA
is a constant and AA.gtoreq.4.2 preferably AA.gtoreq.4.7).
[0138] It is preferable that the alloy composition contain one or
two or more of 0.1 to 1% by mass (preferably, 0.2 to 0.5% by mass)
of Mn, 0.05 to 0.5% by mass (preferably, 0.1 to 0.3% by mass) of
Cr, 0.04 to 0.3% by mass (preferably, 0.1 to 0.2% by mass) of Zr,
0.01 to 0.15% by mass (preferably, 0.05 to 0.1% by mass) of V, and
0.01 to 0.2% by mass (preferably, 0.02% to 0.1% by mass) of Ti.
[0139] Further, itis preferablethat thealloy compositionincludes
0.15 to 0.65% by mass (preferably, 0.3 to 0.5% by mass) of Fe.
[0140] Furthermore, -it is preferable that the alloy composition
includes 0.003 to 0.02% by mass (preferably, 0.007 to 0.016% by
mass) of P.
[0141] In addition, the alloy composition contains one or two or
more of 0.003 to 0.03% by mass (preferably, 0.01 to 0.02% by mass)
of Sr, 0.1 to 0.35% by mass (preferably, 0.15 to 0.25% by mass) of
Sb, 0.0005 to 0.015% by mass (preferably, 0.001 to 0.01% by mass)
ofNa, and 0.001 to 0.02% bymass (preferably, 0.005 to 0.01% by
mass) of Ca, which is preferable because there is an effect of
micronizing primary Si crystals.
Examples
[0142] The present invention will be specifically described below
by using examples. However, the present invention is not limited to
these examples.
Examples 1 to 16
[Manufacturing Conditions]
[0143] The aluminum-alloy shaped product of Examples 1 to 16 shown
in Table 1 and Comparative Examples 1 to 10 shown in Table 2 were
produced by a production system shown in FIG. 1.
TABLE-US-00001 TABLE 1 Temperature Percent Post- Fatigur Strength
Stress of Homoge- reduction Heat (Unit: MPa) nization during the
Treat- Temperature Temperature Value Treatment course of ment
Composition of Aluminum-alloy (% by mass) Condition Condition of
(.degree. C.) upsetting (T6, T5) Si Fe Cu Mn Mg Ni Ti P Sr
300.degree. C. 350.degree. C. AA Example 1 370 50% T6 10.5 0.25 2.7
-- 0.95 3.8 -- -- 0.015 60 45 5.64 Example 2 370 50% T6 10.5 0.25
2.7 -- 0.95 3.8 -- 0.015 -- 59 44 5.64 Example 3 370 50% T6 12.8
0.48 3.0 0.23 0.95 3.0 0.075 0.018 -- 59 43 5.04 Example 4 370 50%
T5 12.8 0.48 3.0 0.23 0.95 3.0 0.075 0.018 -- 62 44 5.04 Example 5
370 50% T6 11.8 0.33 3.2 -- 0.72 2.2 -- 0.005 -- 54 39 4.38 Example
6 370 50% T6 12.8 0.25 3.8 -- 0.95 1.8 -- 0.018 -- 53 38 4.38
Example 7 370 50% T6 13.4 0.25 4.1 -- 1.10 2.2 -- 0.018 -- 57 43
4.99 Example 8 370 50% T6 13.4 0.61 4.1 0.32 1.21 2.2 -- 0.010 --
58 43 4.99 Example 9 not over 200 50% T6 13.4 0.61 4.1 0.32 1.21
2.2 -- 0.010 -- 59 44 4.99 Example 10 370 50% T6 12.8 0.48 4.5 0.23
0.95 1.5 0.075 0.018 -- 55 40 4.56 Example 11 370 50% T6 12.5 0.28
5.1 0.21 1.14 1.1 -- 0.007 -- 55 39 4.57 Example 12 370 50% T6 12.8
0.25 5.5 -- 0.95 1.0 -- 0.018 -- 57 43 4.74 Example 13 370 50% T6
12.8 0.48 5.5 0.23 0.95 1.0 0.075 0.018 -- 58 44 4.74 Example 14
370 50% T6 10.5 0.25 5.7 -- 0.95 3.5 -- 0.010 -- 62 47 7.38 Example
15 370 88% T6 12.8 0.48 3.0 0.23 0.95 3.0 0.075 0.018 -- 58 41 5.04
Example 16 470 50% T6 12.8 0.48 3.0 0.23 0.95 3.0 0.075 0.018 -- 58
41 5.04
TABLE-US-00002 TABLE 2 Temperature Percent Post- Fatigur Strength
Stress of Homoge- reduction Heat (Unit: MPa) nization during the
Treat- Temperature Temperature Value Treatment course of ment
Composition of Aluminum-alloy (% by mass) Condition Condition of
(.degree. C.) upsetting (T6, T5) Si Fe Cu Mn Mg Ni Ti P Sr
300.degree. C. 350.degree. C. AA Comparative 370 50% T6 11.0 0.25
3.0 0.10 0.40 1.8 -- 0.010 -- 45 30 3.84 Example 1 Comparative 370
50% T6 12.3 0.3 3.3 0.15 0.85 1.8 0.05 0.005 -- 47 32 4.04 Example
2 Comparative 470 50% T6 12.3 0.3 3.3 0.15 0.85 1.8 0.05 0.005 --
45 30 4.04 Example 3 Comparative 370 50% T6 12.8 0.48 4.0 -- 0.95
1.2 -- 0.010 -- 46 31 3.92 Example 4 Comparative 370 50% T6 12.8
0.48 5.0 -- 0.95 0.5 -- 0.010 -- 46 32 3.90 Example 5 Comparative
500 50% T6 13.4 0.61 4.1 0.32 1.21 2.2 -- 0.010 -- 48 35 4.99
Example 6 Comparative 370 50% T6 12.3 0.3 5.7 0.16 0.98 0.5 --
0.010 -- 49 36 4.38 Example 7 Comparative 370 50% T6 12.4 0.3 6.3
0.17 0.97 0.6 -- 0.010 -- *1 *1 4.88 Example 8 Comparative 370 50%
T6 12.3 0.32 2.3 0.16 0.94 3.7 0.05 0.010 -- 49 35 5.26 Example 9
Comparative 370 50% T6 12.4 0.36 2.3 0.15 0.99 4.3 -- 0.010 -- *1
*1 5.86 Example 10
[0144] Continuously cast round rods, which each have a diameter of
.phi.85 (mm) and are made of aluminum-alloys of Examples 1 to 16
having a composition shown in Table 1 and Comparative Examples 1 to
10 shown in Table 2, were cast by using a hot top continuous
casting apparatus shown in FIG. 5 as the continuous casting
apparatus 81 configuring the production system. The hot top
continuous casting apparatus is a caster using a gas pressurization
hot top casting method, and is configured so that gas and liquid
lubricant are introduced into a clearance between a header and a
mold and the pressure of the molten alloy supplied to the mold,
liquid lubricant, and gas obtained from the vaporization of the
liquid lubricant are preferably balanced with each other. Since an
area where the molten aluminum comes in contact with the mold is
small due to this configuration, it is possible to rapidly cool and
solidify a molten alloy by cooling water and to stably cast a
continuously cast rod made of an aluminum-alloy.
[0145] After that, as the pre-heat treatment step, a homogenization
treatment was performed on each of the continuously cast round rods
at temperatures shown in Tables 1 and 2. Each of the continuously
cast round rods was cut at a thickness of 20 or 80 mm and was used
as a forging material to be forged. Then, after forging materials
to be forged were preliminarily heated at a temperature of
420.degree. C., each upsetting step was performed at predetermined
percent reductions during the course of upsetting shown in Tables 1
and 2 and plastic forming was performed in a predetermined
shape.
[0146] Meanwhile, when an upsetting step was performed at a percent
reduction during the course of upsetting of 55% on Examples 5 to 7
and 10 to 13, a crack rate was evaluated. The evaluation results
are shown in Table 3. In Table 3, an .largecircle. mark indicated
that a crack rate caused by an upsetting step was less than 1%, and
a .DELTA. mark indicated that a crack rate caused by an upsetting
step was equal to or larger than 1%.
TABLE-US-00003 TABLE 3 Temperature of Percent reduction
Homogenization during the Treatment course of Content in
Aluminum-alloy (wt %) Value of Crack (.degree. C.) upsetting Cu Ni
AA Rate Example 5 370 55% 3.2 2.2 4.38 .DELTA. Example 6 370 55%
3.8 1.8 4.38 .largecircle. Example 7 370 55% 4.1 2.2 4.99 .DELTA.
Example 10 370 55% 4.5 1.5 4.56 .largecircle. Example 11 370 55%
5.1 1.1 4.57 .largecircle. Example 12 370 55% 5.5 1.0 4.74
.largecircle. Example 13 370 55% 5.5 1.0 4.74 .largecircle.
[0147] After that, each of Examples and Comparative Examples was
produced by performing a predetermined post-heat treatment step
shown in Tables 1 and 2 on the forging material on which plastic
forming was has been performed.
[0148] Meanwhile, the post-heat treatment step was performed by any
one of a T5 treatment that quenched plastic worked articles with
water and retained the plastic worked articles at a temperature of
210.degree. C. for 6 hours; and a T6 treatment that retained
plastic worked articles at a temperature of 500.degree. C. for 2.5
hours, quenched the plastic worked articles with water, and
retained the plastic worked articles at a temperature of
210.degree. C. for 6 hours.
[Evaluation of Fatigue Strength]
[0149] The fatigue strength of each of Examples and Comparative
Examples was evaluated by the following method.
[0150] Test pieces were fabricated from each of Examples and
Comparative Examples, and the fatigue strength of each of the test
pieces was evaluated under environment of 300.degree. C. and
350.degree. C. by an Ono-type rotary bending fatigue testing
machine after the test pieces were preliminarily heated at a
temperature of 300.degree. C. or 350.degree. C. for 100 hours.
Repeated stress was applied 10,000,000 times, and stress where the
test piece was not broken was measured.
[0151] Tables 1 and 2 show the composition, the heat treatment
condition, the percent reduction during the course of upsetting,
and the evaluation result of fatigue strength of each of Examples
and Comparative Examples, and a constant AA that satisfies a
relational expression defined by Ni(% by mass)=[-0.68.times.Cu(% by
mass)+AA(% by mass)]. Further, FIG. 6 shows a relationship between
the percentage contents of Ni and Cu in the composition of each of
Examples and Comparative Examples. Meanwhile, in FIG. 6, the
respective values of AA of Examples 1 to 14 were represented by
reference characters S1 to S14, respectively, and the respective
values of AA of Comparative Examples 1 to 10 (excluding Comparative
Example 6) were represented by reference characters C1 to C10,
respectively.
[0152] All Examples 1 to 16 were produced by the method for
production according to the present invention, and have fatigue
strength of 33 MPa or more at a temperature of 350.degree. C. as
appreciated from Table 1. Since having target fatigue strength as
described above, Examples 1 to 16 produced by the method for
production according to the present invention may be preferably
used for-parts that require mechanical strength at high
temperature.
[0153] It is essential for the aluminum-alloy, which is used in S
the method for production according to the present invention, to
have the composition where Ni content and Cu content are included
in a region surrounded by A-B-C-D-E-A of FIG. 6.
[0154] All Examples 10 to 13 and Example 6, of which Ni content and
Cu content are included in a region surrounded by D-E-H-I-D, can be
processed over an percent reduction during the course of upsetting
of 55% asshown inTable 3. Thus, inthe presentinvention, it is more
preferable to use an aluminum-alloy containing Cu content so that
Ni content is equal to or less than 2.0 wt % and AA.gtoreq.4.2 is
satisfied.
[0155] In contrast, Comparative Examples 1-to 5 and 7 to 10, which
have composition out of the range of the alloy composition defined
in the method for production according to the present invention,
did not have target fatigue strength as shown in Table 2.
Comparative Examples 8 and 10 had poor plastic workability and
generated cracks during upsetting. "*1" shown in Table2 indicates a
case that a test piece of Comparative Example cannot have been
sampled. Meanwhile, the values of AA of Comparative Examples 1 to 4
were less than 4.2. Further, Comparative Example 6, on which a
pre-heat treatment step was performed at a temperature out of the
temperature range defined in the method for production according to
the present invention, also did not have target fatigue
strength.
[Evaluation of Metal Structure]
[0156] Samples of which structure to be observed were cut out from
a center portion of a vertical cross section of each of Examples of
Table 1 and Comparative Examples of Table 2, and the samples were
micro-polished. Then, the networks of the crystallization products
of the samples were observed from microphotographs of the samples
in order to evaluate the metal structure of each of Examples and
Comparative Examples.
[0157] It could be confirmed that the networks of the
crystallization products, acicular crystallization products, or the
aggregates of crystallization products formed during the continuous
casting partially remain in the structure of Examples even after
forming and a heat treatment.
[0158] Further, as for each of the Examples, an area occupation
ratio of eutectic Si is 8% or more, an average grain size of the
eutectic Si is 5 .mu.m or less, and the eutectic Si of an acicular
ratio of 1.4 or more is 25% or more; and an area occupation ratio
of an intermetallic compound is 1.2% or more, an average grain size
of an intermetallic compound of 1.5 .mu.m or more. And a length of
an intermetallic compound or a length of an aggregate of a
contacted intermetallic compound of 30% or more is 3 .mu.m or
more.
[0159] In particular, as shown in Table 4, all Examples 10 and 13,
which contain Ni and Co at preferred concentration, have average
grain sizes of eatectic Si of 2.5 .mu.m or less. It is appreciated
that both Examples 10 and 13 have about 80% eutectic Si of which
acicular ratios are 1.4 or more, and have about 90% ormore
aggregates of intermetallic compounds of which length is 3 .mu.m or
more.
[0160] Further, according to the results of Tables 1 and 4, it is
appreciated that Example 13 having a constant AA larger than 4.7
has a larger amount of network-like or acicular intermetallic
compounds contributing to high-temperature strength, and higher
fatigue strength as compared to Example 10 having a constant AA
less than 4.7. As described above, in the present invention, the
aluminum-alloy shaped product prepared a constant AA of 4.7 or more
are preferable.
[0161] In contrast, each of comparative Examples had a smaller
percentage content of eutectic Si having an acicular ratio of 1.4
or more, and a smaller length of an intermetallic compound or a
smaller length of an aggregate of a contacted intermetallic
compound, as compared to Examples. For example, as shown in Table
4, Comparative Example 6 included only about 22% eutectic Si of
which acicular ratio is 1.4 or more. And an intermetallic compound
or an aggregate of a contacted intermetallic compound of which
length is 3 .mu.m or more is only about 28% in Comparative Example
6.
TABLE-US-00004 TABLE 4 Eutectic Si Intermetallic Compound Area
Average Acicular Area Average Acicular Occupation Grain Ratio of
Occupation Grain Ratio of Ratio (%) Size 1.4 or More Ratio (%) Size
1.4 or More Example 10 8.6% 2.4 .mu.m 78% 7.4% 2.6 .mu.m 88%
Example 13 8.5% 2.5 .mu.m 80% 7.8% 2.7 .mu.m 89% Comparative 8.5%
2.0 .mu.m 22% 7.2% 1.9 .mu.m 28% Example 6
Examples 17 and 18
[Manufacturing Conditions]
[0162] Examples 17 and 18 and Comparative Examples 11 and 12,
respectively, were produced under the composition and manufacturing
conditions shown in Table 5 by the same method for production as
Examples 1 to 16 and Comparative Examples 1 to 10.
[0163] Meanwhile, Comparative Example 13 was made of a powdery
extruded-cast material, and was produced by the same method for
production as Comparative Examples 11 and 12 except that
Comparative Example 13 was not formed from a continuously cast
round rod made of an aluminum-alloy and a homogenization treatment
was not performed. All Examples 17 and 18 and Comparative Examples
11 to 13 were formed as the aluminum-alloy shaped product having
the shape of a piston 1 that had a diameter of 80 mm and a top
surface 10 having a thickness of 8 mm as shown in FIGS. 7A to
7C.
[Evaluation of Fatigue Strength]
[0164] The fatigue strength of each of Examples 17 and 18 and
Comparative Examples 11 to 13 was evaluated by the following
method.
[0165] First, after the piston 1 of each of Examples and
Comparative Examples was preliminarily heated at a temperature of
300.degree. C. or 350.degree. C. for 100 hours, a test piece 11 was
cut out from a center portion of the top surface 10 of each of
Examples and Comparative Examples. The fatigue strength of each of
the test pieces 11 was evaluated by a pulsating tensile fatigue
test under temperature environment corresponding to the preliminary
heating temperature. In the fatigue test, a stress ratio R was
-0.1, and the maximum stress where the test piece was not broken
against the application of stress 10,000,000 times was referred to
as fatigue strength. Table 5 shows the evaluation results of the
fatigue strength of Examples 17 and 18 and Comparative Examples 11
to 13.
[0166] As appreciated from Table 5, the fatigue strength of
Examples 17 and 18 at a temperature of 350.degree. C. exceeds 43
MPa that is preferable for a part requiring mechanical strength at
high temperature, and the fatigue strength thereof at a temperature
of 300.degree. C. exceeds 55 MPa. Further, since Examples 17 and 18
correspond to Examples 10 and 13 where the same manufacturing
conditions as Examples 17 and 18 except for shapes are used, it is
appreciated that Examples 17 and 18 have stable mechanical strength
a thigh temperature despite an evaluation method.
TABLE-US-00005 TABLE 5 Temperature Post- Fatigur Strength Stress of
Homoge- Heat (Unit: MPa) nization Treat- Temperature Temperature
Value Treatment ment Composition of Aluminum-alloy (% by mass)
Condition Condition of Forging material (.degree. C.) (T6, T5) Si
Fe Cu Mn Mg Ni Ti P 300.degree. C. 350.degree. C. AA Comparative
Continuously 370 T6 12.3 0.3 3.3 0.15 0.85 1.8 0.05 0.005 64 45
4.04 Example 11 Cast Rod Comparative Continuously 370 T6 12.4 0.3
1.0 -- 1.04 1.0 -- 0.010 45 33 1.66 Example 12 Cast Rod Comparative
Powdery -- T6 11.7 5.3 2.5 -- 1.1 -- -- -- 80 59 1.70 Example 13
Extruded-Cast Material Example 17 Continuously 370 T6 12.8 0.48 4.5
0.23 0.95 1.5 0.075 0.018 70 52 4.56 Cast Rod Example 18
Continuously 370 T6 12.8 0.48 5.5 0.23 0.95 1.0 0.075 0.018 73 54
4.74 Cast Rod
[0167] In contrast, a value of AA of Comparative Example 11 is less
than 4.2, and corresponds to Comparative Example 2 where the same
manufacturing conditions as Comparative Example 11 except for
shapes are used. From the evaluation results of the fatigue
strength of Comparative Example 2 of Table 2 and Comparative
Example 11 of Table 5, it is considered that the reliability of the
mechanical strength of Comparative Example 11 lacks at high
temperature.
[0168] Further, AA of Comparative Example 12 is 1.68, and the
fatigue strength thereof at a temperature of 350.degree. C. is
significantly lower than 43 MPa.
[0169] Meanwhile, Comparative Example 13 made of a powdery
extruded-cast material has fatigue strength higher than the fatigue
strength of Examples 17 and 18, regardless of a fact that AA is
1.7. However, there is a drawback in that a fine portion, for
example, a skirt portion 12 of a sample formed by packing is apt to
become brittle. Thus, the shaped product using the powdery
extruded-cast material have poorer ductility and toughness as
compared to the aluminum-alloy shaped products that include a
forging step using a continuously cast rod made of an
aluminum-alloy as forging material.
[0170] Since having excellent ductility, toughness, and fatigue
strength, the aluminum-alloy shaped product, which are produced by
the method for production according to the present invention, may
be preferably used for top surfaces or the like of a piston of an
internal combustion engine.
INDUSTRIAL APPLICABILITY
[0171] As described above, the present invention provides a method
for production of aluminum-alloy shaped product that includes a
forging step using a continuously cast rod made of an
aluminum-alloy as forging material. The aluminum-alloy contains Si,
Cu, Mg, and Ni. Accordingly, according to the present invention, it
is possible to obtain a shaped product that has excellent
high-temperature fatigue strength, forgeability, ductility, and
toughness, Further, in Ni and Cu, since a relational expression of
"Ni(% by mass).gtoreq.[-0.68.times.Cu(% by mass)+4.2(% by mass)] is
satisfied, it is possible to further improve fatigue strength
characteristics at high temperature.
[0172] It is possible to further reduce the thickness of a piston
of a conventional internal combustion engine by using the
aluminum-alloy shaped product according to the present invention
and to reduce the weight of a piston of an internal combustion
engine. Further, it is possible to satisfy weight reduction
required from the market, to reduce fuel consumption of an internal
combustion engine, and to improve output.
* * * * *