U.S. patent application number 10/674811 was filed with the patent office on 2004-08-05 for cast aluminum alloy for forging, and aluminum cast-forged product and method of manufacturing the same.
This patent application is currently assigned to Asahi Tec Corporation. Invention is credited to Kotani, Kohji, Machino, Daisuke, Watanabe, Masatoshi.
Application Number | 20040151615 10/674811 |
Document ID | / |
Family ID | 32063674 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040151615 |
Kind Code |
A1 |
Kotani, Kohji ; et
al. |
August 5, 2004 |
Cast aluminum alloy for forging, and aluminum cast-forged product
and method of manufacturing the same
Abstract
There is disclosed a cast-forged product of an aluminum alloy
consisting essentially of: 0.6 to 1.8 wt % of silicon; 0.6 to 1.8
wt % of magnesium; 0.8 wt % or less of copper; 0.2 to 1.0 wt % of
manganese; 0.25 wt % or less of chromium; 0.0 to 0.15 wt % of
titanium; and unavoidably contained impurities. When the product is
used as various parts for automobiles formed of aluminum, such as
suspension parts, frames, and parts for engines, the product is
more superior in mechanical properties such as a tensile strength,
proof stress, and elongation, and can be manufactured with a low
cost.
Inventors: |
Kotani, Kohji; (Ogasa-gun,
JP) ; Watanabe, Masatoshi; (Inabe-gun, JP) ;
Machino, Daisuke; (Inabe-gun, JP) |
Correspondence
Address: |
PARKHURST & WENDEL, L.L.P.
1421 PRINCE STREET
SUITE 210
ALEXANDRIA
VA
22314-2805
US
|
Assignee: |
Asahi Tec Corporation
Ogasa-gun
JP
Hoei Industries Co., Ltd.
Inabe-gun
JP
|
Family ID: |
32063674 |
Appl. No.: |
10/674811 |
Filed: |
October 1, 2003 |
Current U.S.
Class: |
420/544 ;
148/552; 420/546 |
Current CPC
Class: |
B22D 21/007 20130101;
C22F 1/05 20130101; B21J 5/00 20130101; B21K 3/00 20130101; C22C
21/02 20130101; C22C 21/08 20130101; B21J 5/002 20130101; B21K 1/26
20130101; B21J 1/06 20130101 |
Class at
Publication: |
420/544 ;
420/546; 148/552 |
International
Class: |
C22C 021/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2002 |
JP |
2002-288455 |
Claims
What is claimed is:
1. An aluminum alloy consisting essentially of: 0.6 to 1.8 wt % of
silicon; 0.6 to 1.8 wt % of magnesium; 0.8 wt % or less of copper;
0.2 to 1.0 wt % of manganese; 0.25 wt % or less of chromium; 0.0 to
0.15 wt % of titanium; and unavoidably contained impurities.
2. A use of an aluminum alloy in manufacturing an aluminum
cast-forged product, wherein a preformed material is cast from the
aluminum alloy consisting essentially of 0.6 to 1.8 wt % of
silicon, 0.6 to 1.8 wt % of magnesium, 0.8 wt % or less of copper,
0.2 to 1.0 wt % of manganese, 0.25 wt % or less of chromium, 0.0 to
0.15 wt % of titanium, and unavoidably contained impurities, and
the preformed material is forged to manufacture an aluminum
cast-forged product.
3. The use in manufacturing an aluminum cast-forged product
according to claim 2, wherein the preformed material has a shape
indicating a forging ratio of 18 to 60%, assuming that the shape of
a final product is 100%.
4. The use in manufacturing an aluminum cast-forged product
according to claim 2, wherein the aluminum cast-forged product is a
suspension part for a vehicle, a frame for the vehicle, or a part
for an engine.
5. The use in manufacturing an aluminum cast-forged product
according to claim 3, wherein an aluminum cast-forged product is a
suspension part for a vehicle, a frame for the vehicle, or a part
for an engine.
6. A method of manufacturing an aluminum cast-forged product
consisting essentially of 0.6 to 1.8 wt % of silicon, 0.6 to 1.8 wt
% of magnesium, 0.8 wt % or less of copper, 0.2 to 1.0 wt % of
manganese, 0.25 wt % or less of chromium, 0.0 to 0.15 wt % of
titanium, and unavoidable impurities, the method including: a
melting step of melting an aluminum alloy consisting essentially of
0.6 to 1.8 wt % of silicon, 0.6 to 1.8 wt % of magnesium, 0.8 wt %
or less of copper, 0.2 to 1.0 wt % of manganese, 0.25 wt % or less
of chromium, 0.0 to 0.15 wt % of titanium, and the unavoidable
impurities at about 680 to 780.degree. C. to obtain a molten metal;
a casting step of casting the obtained molten metal at a mold
temperature of about 60 to 150.degree. C. to obtain a preformed
material which is a raw material for forging; a rough forging step
of heating the raw material for forging to a surface temperature at
about 380.degree. C. to a melting point or less and forging the raw
material to obtain a roughly forged material; a finish forging step
of heating the roughly forged material to a surface temperature at
about 380.degree. C. to the melting point or less and forging the
roughly forged material to obtain a finish forged material; and a
clipping flash step of removing flash from the finish forged
material to obtain a final product.
7. The method according to claim 6, wherein the aluminum alloy
includes the flash generated at the time of the forging as a
portion of a raw material.
8. The method according to claim 7, wherein a forging ratio of the
shape of a preformed material is in a range of 18 to 60%, assuming
that the shape of a final product is 100%.
9. A suspension part for a vehicle, a frame for the vehicle, or a
part for an engine prepared by a method of manufacturing an
aluminum cast-forged product consisting essentially of 0.6 to 1.8
wt % of silicon, 0.6 to 1.8 wt % of magnesium, 0.8 wt % or less of
copper, 0.2 to 1.0 wt % of manganese, 0.25 wt % or less of
chromium, 0.0 to 0.15 wt % of titanium, and unavoidable impurities,
the method including: a melting step of melting an aluminum alloy
consisting essentially of 0.6 to 1.8 wt % of silicon, 0.6 to 1.8 wt
% of magnesium, 0.8 wt % or less of copper, 0.2 to 1.0 wt % of
manganese, 0.25 wt % or less of chromium, 0.0 to 0.15 wt % of
titanium, and the unavoidable impurities at about 680 to
780.degree. C. to obtain a molten metal; a casting step of casting
the obtained molten metal at a mold temperature of about 60 to
150.degree. C. to obtain a preformed material which is a raw
material for forging; a rough forging step of heating the raw
material for forging to a surface temperature at about 380.degree.
C. to a melting point or less and forging the raw material to
obtain a roughly forged material; a finish forging step of heating
the roughly forged material to a surface temperature at about
380.degree. C. to the melting point or less and forging the roughly
forged material to obtain a finish forged material; and a clipping
flash step of removing flash from the finish forged material to
obtain a final product.
10. The suspension part for the vehicle, the frame for the vehicle,
or the part for the engine according to claim 9, wherein the
aluminum alloy includes flash generated at the time of the forging
as a portion of a raw material.
11. The suspension part for the vehicle, the frame for the vehicle,
or the part for the engine according to claim 9, wherein a forging
ratio of the shape of the preformed material is in a range of 18 to
60%, assuming that the shape of the final product is 100%.
12. The suspension part for the vehicle, the frame for the vehicle,
or the part for the engine according to claim 9, having mechanical
properties such as a tensile strength of 320 MPa or more, a proof
stress of 280 MPa or more, and an elongation of 10% or more.
13. The suspension part for the vehicle, the frame for the vehicle,
or the part for the engine according to claim 10, having mechanical
properties such as a tensile strength of 320 MPa or more, a proof
stress of 280 MPa or more, and an elongation of 10% or more.
14. The suspension part for the vehicle, the frame for the vehicle,
or the part for the engine according to claim 11, having mechanical
properties such as a tensile strength of 320 MPa or more, a proof
stress of 280 MPa or more, and an elongation of 10% or more.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a cast aluminum alloy for
forging and an aluminum cast-forged product that is used for a
vehicular part or the like and is less costly, and a method of
manufacturing an aluminum cast-forged product. More particularly,
it relates to a cast aluminum alloy for forging that is used to
manufacture vehicular suspension parts which are required to be
light in weight to improve fuel consumption of an automobile and
can use useless forging materials such as flash generated in a
forging process, an aluminum cast-forged product that has high
mechanical properties and contains particular amounts of silicon,
magnesium, copper, and manganese, and a method of manufacturing an
aluminum cast-forged product.
[0003] 2. Description of the Related Art
[0004] It is said that global warming, which is one of global
environmental problems, is greatly affected by carbon dioxide
produced by all human activities, and a reduction in carbon dioxide
discharged from factories and electric power plants and a reduction
in fuel consumption of automobiles are strongly required all over
the world. At the third conference of the United Nations Framework
Convention on Climate Change, so-called Global Warming Prevention
Conference COP3, held in Kyoto in 1997, Japan promised that the
emission of gas causing greenhouse effect which mainly contains
carbon dioxide will be decreased by 6% on average of values in 2008
through 2012 as compared with 1990. Based on this promise,
regarding the fuel consumption rate of automobiles, the target
reference value of fuel consumption rate under vehicle weight
classification was determined with the target fiscal year being
fiscal 2010 for gasoline engine and fiscal year 2005 for diesel
engine. Also, in the taxation system, measures were taken to treat
low-pollution cars favorably. Hereafter, auto manufacturers will
strongly be pressed to promote technology development to improve
fuel consumption and to develop an automobile having improved fuel
consumption, with further progress of understanding towards
environmental problems by automobile purchasers and users. Such
development will be needed to win competition among the auto
manufactures.
[0005] The measures for improving the fuel consumption of the
automobile include the use of new power sources such as a fuel
cell, natural gas, and electricity, or the hybrid use thereof, the
technical improvement in a motor system such as a lean fuel engine
and a direct injection engine, and the decrease of running
resistance due to improvement in loss of a power transmission
system and improvement in vehicle body contours. Among these
measures, a measure that is most effective and capable of being
taken together with any other technology is the reduction in weight
of the automobile. If the automobile itself is made light in the
weight, the load on the power source is lessened, and the amount of
power to be consumed can be saved irrespective of power sources. As
one measure for the reduction in weight of the automobile, the
reduction in weight of the suspension parts of the automobile is an
object having a higher priority, because this reduction contributes
to the improvement in drivability and riding quality of the
automobile. In recent years, frame parts or some parts of the
engine have also been regarded as the objects of the reduction in
weight, and attempts have been made to use light metal materials
therefor.
[0006] Incidentally, when the lightening in the weight of
automobile is intended, the up in the cost remains as a theme to be
solved. The weight lightening technology is broadly divided into a
structure design technology and a material technology. In
comparison with the drastic improvement in vehicle body structure
and construction elements, the change of material used is an easily
employable measure for lightening the weight. However, such a
material for lightening the weight is generally expensive. Examples
of the material for lightening the weight include resin materials
such as FRP, thinned iron sheets using high tensile strength steel
sheets, aluminum alloys, magnesium alloys, titanium alloys,
ceramics, metallic compound materials, and the like. Among these
materials, aluminum alloys have fewest drawbacks such as corrosion
resistance and the like, and are lowest in cost in the materials
for lightening the weight although being higher in cost than iron,
and can easily be applied as alternatives without requiring any
large change in the basic design of the automobile.
[0007] The aluminum alloys, having a density about one-third that
of iron, have already been used for many easy-to-manufacture
castings such as engine cylinder heads and engine cylinder blocks.
These castings are manufactured by high-speed injection molding, a
so-called high pressure die casting method, and thus can be
manufactured at a relatively low cost with high production
efficiency. However, castings having large thickness and high
strength cannot be produced. There is a problem that the
application of cast parts to suspensions as a part light in weight
since a failure of such a part due to insufficient strength
directly leads to the safety problem.
[0008] Referring to the suspension parts which have advanced in
studies of the weight reduction technology as examples, the present
status of the technology will be described. Materials used for the
suspension parts such as a steering knuckle and a suspension arm
are required to have high corrosion resistance, sufficient
properties such as strength and elongation, and few defects, and an
A6061 alloy forged product, an AC4CH alloy squeeze cast product
(low-speed injection molded product), and the like that meet the
requirements have already been used. However, these materials still
have an unsolved problem of high cost, so that the application
thereof is extremely limited at present.
[0009] Reasons why so-called aluminum products formed only by
forging, such as the conventional A6061 alloy forged product are
high in cost lie in that the number of manufacturing processes is
large and that the raw material for forging itself is expensive and
that wastes such as flash are caused during the manufacturing
process and that useless materials such as the flash cannot be
recycled as the raw material for forging. Also, for a squeeze
casting, because of a large number of processes and a low injection
speed, the productivity is low and the cost reduction cannot be
attained.
[0010] Thus, in particular, in order to reduce the weight of the
vehicular part, an aluminum product having superior corrosion
resistance, strength, and elongation, no defects, and a low cost
has been demanded. To meet this demand, various improved aluminum
alloys have heretofore been proposed as a material for
manufacturing an aluminum product.
[0011] According to JP-A-5-59477, an aluminum alloy for forging in
which the coarseness of crystal grains is restrained by controlling
a composition, whereby high mechanical properties are attained has
been proposed. It is stated that a tensile strength of 40
kgf/mm.sup.2 has been attained because of the improvement in
strength of matrix, and the restraint in not coarsening crystal
grains by adjusting the composition so as to contain 1.0 to 1.5 wt
% of silicon, 0.8 to 1.5 wt % of magnesium, 0.4 to 0.9 wt % of
copper, 0.2 to 0.6 wt % of manganese, 0.3 to 0.9 wt % of chromium,
and the like.
[0012] Although the strength is increased, there arises a new
problem that a low cost cannot be attained, and the corrosion
resistance is deteriorated because a larger amount of copper is
contained than the conventional raw material for forging (A6061
alloy), and also the fluidity decreases so that the castability is
poor because much magnesium is contained.
[0013] Also, an aluminum alloy material for forging having superior
castability and high strength has been proposed in JP-A-7-258784.
According to this document, the formation of crack during casting,
which has been formed in the case where the conventional A6061
alloy is used as the raw material, does not occur, in the case of
aluminum alloy forged product obtained by casting continuously a
molten metal of an aluminum alloy material in which the composition
is adjusted so as to contain 0.8 to 2.0 wt % of silicon, 0.5 to 1.5
wt % of magnesium, 0.5 to 1.0 wt % of copper, 0.4 to 1.5 wt % of
manganese, 0.1 to 0.3 wt % of chromium, and the like with
controlling a cooling rate in a solidification process, thereafter
soaking the resultant, subsequently hot-forging aluminum alloy,
thereafter subjecting to a solution heat treatment, and further an
aging treatment, when the aluminum alloy forged product is cast
into a shape close to a final product.
[0014] In this proposal, although castability is improved, the low
cost cannot be attained yet as compared with the conventional raw
material for forging (A6061 alloy), also the corrosion resistance
is deteriorated because much copper is contained, and there remains
anxiety when this material is used for the suspension part. Also,
there arises a problem that the fluidity decreases because much
magnesium is contained, and the above-described rigorous control is
needed in the casting process, and the manufacturing cost rather
increases.
[0015] Furthermore, according to JP-A-8-3675, an aluminum alloy for
forging having superior mechanical properties and involving the low
cost has been proposed. It is stated that the formation of the hot
crack does not occur at the time of casting, and that the strength
after the forging can be improved by forging, with an upsetting
ratio of 10 to 50%, an aluminum alloy whose components have been
adjusted so as to contain 0.6 to 3.0 wt % of silicon, 0.2 to 2.0 wt
% of magnesium, 0.3 to 1.0 wt % of copper, 0.1 to 0.5 wt % of
manganese, 0.1 to 0.5 wt % of chromium, and the like, and also 1.5
wt % or more of Mg.sub.2Si.
[0016] In this proposal, although a shape close to that of the
final product can be formed at the time of the casting, and the
manufacturing cost can be reduced because the forging can be
performed by omitting an extrusion process, there arises a problem
in that the strength decreases because an excessive amount of
manganese is contained. Manganese is an element capable of
restraining the growth of aluminum crystal grains, keeping the gain
structure to be refined, and improving the strength. If the content
thereof is high, however, intermetallic compounds are liable to be
formed, and the strength is rather decreased.
[0017] In JP-A-2002-302728, the present inventors also have
proposed a thick-wall aluminum processed product which is an
aluminum cast-forged product having high tensile strength, proof
stress, and elongation and having improved mechanical properties as
compared with the conventional cast-forged product, and having
superior corrosion resistance and high quality without any defects
and involving the low cost, and a method of manufacturing the
product. In this proposal, there is proposed, as a cast aluminum
alloy for forging which is the raw material for the forging, an
aluminum alloy, characterized in that the alloy contains 0.2 to 2.0
wt % of silicon, 0.35 to 1.2 wt % of magnesium, 0.1 to 0.4 wt % of
copper, and 0.01 to 0.08 wt % of manganese.
[0018] When the above-described material is used, a desired effect
can be attained. However, in respect of the mechanical strength, it
cannot be said that the material can sufficiently satisfy needs of
the market, depending on use conditions. It is the present
situation that there still exists a demand for a material more
superior in the mechanical strength.
[0019] There has been a demand for a low-cost aluminum product
which is more superior in mechanical properties such as the tensile
strength, proof stress, and elongation and which can be applied as
various components for automobiles such as the suspension
components, frames, and engine parts and which involves the low
cost, but it is the present situation that an appropriate aluminum
product has not been proposed yet.
SUMMARY OF THE INVENTION
[0020] The present invention has been developed in view of the
above-described conventional problems, and an object thereof is to
solve the problems with the conventional art and, more
particularly, to provide an aluminum cast-forged product capable of
satisfying needs of the market as an aluminum thick-wall processed
product and having high tensile strength, proof stress, and
elongation; and a method of manufacturing an aluminum cast-forged
product. That is, the object is to provide an aluminum alloy
material which can be cast/processed like high-concentration
products such as AC4CH containing 3 wt % or more of silicon and
which can be processed in a final shape of a desired component like
AC4CH without requiring low-speed casting, an aluminum cast-forged
product cast/forged by the material, and a method of manufacturing
an aluminum cast-forged product. Another object of the present
invention is to provide various lightweight parts for vehicles
brought about by the above-described aluminum cast-forged product
and the method of manufacturing the product, and accordingly to
save fuel consumption of automobiles and to reduce the amount of
emitted carbon dioxide and to contribute to environmental measures
such as the prevention of global warming.
[0021] As a result of various studies on raw materials and
manufacturing method for the thick-wall aluminum product to solve
the above problems, the present inventors have found that an
aluminum cast-forged product having a sufficient strength capable
of meeting needs of market can be obtained by making predetermined
amounts of silicon, magnesium, copper, manganese, and chromium, and
optionally titanium contain therein, with improving fluidity and
castability. Thus, the present invention has been completed.
[0022] That is, according to the present invention, there is
provided a cast aluminum alloy for forging which is usable for a
material for forging, consisting essentially of: 0.6 to 1.8 wt % of
silicon; 0.6.degree. to 1.8 wt % of magnesium; 0.8 wt % or less of
copper; 0.2 to 1.0 wt % of manganese; 0.25 wt % or less of
chromium; 0.0 to 0.15 wt % of titanium; and unavoidable impurities.
It is possible to use the present cast aluminum alloy for forging
in manufacturing various parts for vehicles including suspension
parts having mechanical properties capable of satisfying needs of
the market such as a tensile strength of 320 MPa or more, a proof
stress of 280 MPa or more, and an elongation of 10% or more.
[0023] To use the material in manufacturing a desired final
product, assuming that a shape of the final product is 100%, the
aluminum alloy is used to cast a preformed product having a forging
ratio of 18 to 60%, and subsequently the preformed product may be
cast and formed in the shape of the final product. Accordingly, it
is possible to manufacture the parts for vehicles with a lower cost
and higher productivity as compared with low-speed casting using
AC4CH.
[0024] Moreover, according to the present invention, there is also
provided an aluminum cast-forged product which is manufactured by
forging a preformed product cast from the above-described aluminum
alloy consisting essentially of 0.6 to 1.8 wt % of silicon, 0.6 to
1.8 wt % of magnesium, 0.8 wt % or less of copper, 0.2 to 1.0 wt %
of manganese, 0.25 wt % or less of chromium, 0.0 to 0.15 wt % of
titanium, and unavoidable impurities, the aluminum cast-forged
product consisting essentially of: 0.6 to 1.8 wt % of silicon; 0.6
to 1.8 wt % of magnesium; 0.8 wt % or less of copper; 0.2 to 1.0 wt
% of manganese; 0.25 wt % or less of chromium; 0.0 to 0.15 wt % of
titanium; and unavoidable impurities. Therefore, the manufactured
aluminum cast-forged product has a sufficient mechanical properties
such that the product is usable as the suspension parts for the
vehicles, the frames for the vehicles, and the parts for the
engines.
[0025] Furthermore, according to the present invention, there is
provided a method of manufacturing an aluminum cast-forged product
consisting essentially of 0.6 to 1.8 wt % of silicon, 0.6 to 1.8 wt
% of magnesium, 0.8 wt % or less of copper, 0.2 to 1.0 wt % of
manganese, 0.25 wt % or less of chromium, 0.0 to 0.15 wt % of
titanium, and unavoidable impurities, the method including: a
melting step of melting a material for forging which is an aluminum
alloy consisting essentially of 0.6 to 1.8 wt % of silicon, 0.6 to
1.8 wt % of magnesium, 0.8 wt % or less of copper, 0.2 to 1.0 wt %
of manganese, 0.25 wt % or less of chromium, 0.0 to 0.15 wt % of
titanium, and unavoidable impurities at about 680 to 780.degree. C.
to obtain a molten metal; a casting step of casting the obtained
molten metal at a mold temperature of about 60 to 150.degree. C. to
obtain a raw material for forging; a rough forging step of heating
the raw material for forging to a surface temperature at about
380.degree. C. to a melting point or less and forging the raw
material to obtain a roughly forged material; a finish forging step
of heating the roughly forged material to a surface temperature at
about 380.degree. C. to the melting point or less and forging the
roughly forged material to obtain a finish forged material; and a
clipping flash step of removing flash from the finish forged
material to obtain a final product.
[0026] For the material for forging, while the respective
components are adjusted so as to obtain the composition of the
aluminum alloy according to the present invention, the flash
generated at the time of the forging may be reused as the raw
material. It is to be noted that assuming that the shape of the
final product is 100%, a shape forging ratio of the raw material
for forging, that is, the preformed material is preferably 18 to
60%. Therefore, it is possible to preferably manufacture the
suspension parts for the vehicles, the frames for the vehicles, and
the parts for engine by the method of manufacturing an aluminum
cast-forged product according to the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a side view showing one example of an aluminum
cast-forged product in accordance with the present invention;
[0028] FIGS. 2(a), (b), and (c) are views showing one example of a
method of manufacturing an aluminum cast-forged product of the
present invention, FIG. 2(a) is a schematic explanatory view
showing a difference in shape of a preformed material for each
forging ratio at the time of casting, FIG. 2(b) is an enlarged side
view showing one example of a cast body in which an internal defect
is generated at the time of the casting, and FIG. 2(c) is an
enlarged side view showing one example of a cast body in which no
internal defect is generated at the time of the casting; and
[0029] FIGS. 3(a) and (b) are sectional views of the preformed
material showing the forging ratio.
[0030] The numerical references used in the drawings denote
respectively a part, an apparatus, a portion or the like as
specified below:
[0031] 21, 22 . . . columnar test piece, 40 . . . steering knuckle,
41, 42, 43, 44 . . . position from which test piece was taken, and
50 . . . internal defect.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0032] Hereunder, embodiments of a cast aluminum alloy for forging,
an aluminum cast-forged product, and a method of manufacturing an
aluminum cast-forged product in accordance with the present
invention will be described in detail. The present invention is not
construed by being limited to these embodiments, and various
changes, modifications, and improvements can be made based on the
knowledge of those skilled in the art as far as such changes,
modifications, or improvements are within the scope of the
invention.
[0033] In the present invention, an aluminum alloy consisting
essentially of 0.6 to 1.8 wt % of silicon, 0.6 to 1.8 wt % of
magnesium, 0.8 wt % or less of copper, 0.2 to 1.0 wt % of
manganese, 0.25 wt % or less of chromium, 0.0 to 0.15 wt % of
titanium, and unavoidable impurities is used to first cast a
preformed material, and next the preformed material is forged to
manufacture a cast-forged product having a desired shape. When the
aluminum alloy constituted of the above-described composition is
used, it is possible to prepare an aluminum cast-forged product of
the present invention, having mechanical properties meeting
marketing needs. It is possible to preferably use the product in
parts for vehicles in rugged environments, especially suspension
parts for automobiles, frames for vehicles, and parts for
engines.
[0034] The cast aluminum alloy for forging and the aluminum
cast-forged product of the present invention will hereinafter
concretely be described.
[0035] The cast aluminum alloy for forging of the present invention
is an aluminum alloy consisting essentially of 0.6 to 1.8 wt % of
silicon, 0.6 to 1.8 wt % of magnesium, 0.8 wt % or less of copper,
0.2 to 1.0 wt % of manganese, 0.25 wt % or less of chromium, 0.0 to
0.15 wt % of titanium, and unavoidable impurities.
[0036] Silicon serves to enhance fluidity and to improve a casting
shrinkage when contained in the aluminum alloy. Also, this element
precipitates Mg.sub.2Si when coexisting with magnesium, and
contributes to the improvement in mechanical properties such as
elongation, tensile strength, and proof stress. When the content of
silicon is less than 0.6 wt %, a sufficient mechanical property is
not secured. On the other hand, when the content of silicon exceeds
1.8 wt %, the elongation decreases, it is not possible to
manufacture the product in accordance with marketing needs, and
therefore this is not preferable. It is to be noted that the
content of silicon is preferably 0.8 to 1.3 wt %, further
preferably 0.8 to 1.1 wt %.
[0037] Magnesium precipitates Mg.sub.2Si in a matrix, when
coexisting with silicon, and improves the mechanical properties
such as the elongation, tensile strength, and proof stress when
contained in the aluminum alloy. Since the present invention
provides an aluminum cast-forged product substituted for the
conventional forged product although being low in cost, the
strength higher than that of the conventional product is
indispensable, and magnesium needs to be contained. However, even
if much magnesium is contained, there is no increase in strength.
With too much content, since magnesium is an element liable to be
oxidized, oxidation of molten metal is accelerated, the fluidity
decreases, and the casting defect is liable to be generated. Also,
the corrosion resistance is deteriorated, so that the product
cannot withstand harsh service environments. Therefore, a rather
low content is preferable.
[0038] It is preferable that 0.6 to 1.8 wt % of magnesium be
contained in the cast aluminum alloy for forging. If the content of
magnesium is less than 0.6 wt %, the amount of precipitation of
Mg.sub.2Si is undesirably insufficient, and the strength is
insufficient. If the content is more than 1.8 wt %, in addition to
the insufficient strength, quenching sensitivity decreases, and
thus the forging defect is liable to be generated. As a result, the
quality of the forged material decreases, and the mechanical
property also unfavorably decreases. The content is preferably 0.6
to 1.2 wt %, further preferably 0.7 to 1.1 wt %.
[0039] Copper is an element that can improve the strength, when
contained in the aluminum alloy. For a copper-containing forged
material, an Al--Cu or Al--Cu--Mg based precipitate yielded by a
so-called aging treatment, in which the forged material is left to
stand at ordinary temperature after cooled and crystals are
precipitated for a long period of time, can be obtained.
Accordingly, a strength improving function by Mg.sub.2Si
precipitated as described above is promoted to enhance the
strength. In the present invention, since the strength higher than
that of the conventional forged material is indispensable, it is
preferable that copper be contained. However, in consideration of
an application to products in which corrosion resistance is
regarded as most important, such as an automobile suspension part,
if too much copper, liable to be oxidized, is contained, the forged
material is easily corroded, and it is therefore preferable that
the content of copper be controlled to be as low as possible.
[0040] It is preferable that 0.8 wt % or less of copper be
contained in the cast aluminum alloy for forging. If the content of
copper is more than 0.8 wt %, the corrosion resistance is
deteriorated, the alloy is liable to rust, and the strength cannot
unfavorably be maintained over a long period. The content is
preferably 0.005 wt % or more, less than 0.3 wt %, further
preferably more than 0.1 wt %, and less than 0.2 wt %.
[0041] Manganese is an element that restrains the recrystallization
of the aluminum alloy and the growth of crystal grains, when
contained in the aluminum alloy. As a result, the grain structure
in the aluminum alloy is kept to be refined, and the strength is
maintained. In the present invention, since it is necessary to
maintain the mechanical properties such as the elongation, tensile
strength, and proof stress over the long period, a minute amount of
manganese needs to be contained. However, if too much manganese is
contained, workability decreases at the time of the forging, also
intermetallic compounds are formed, and a decrease in the
mechanical properties, especially the elongation, is found.
[0042] It is preferable that 0.2 to 1.0 wt % of manganese be
contained in the cast aluminum alloy for forging. If the content of
manganese is less than 0.2 wt %, a desired strength cannot
sometimes be obtained. If the content is more than 1.0 wt %,
formability undesirably decreases, and defects are liable to be
generated. The content is more preferably more than 0.5 wt %, and
0.7 wt % or less.
[0043] Chromium forms dispersed particles, and it has an effect of
inhibiting a grain boundary from moving after recrystallization,
when contained in the aluminum alloy. Therefore, refined crystal
grains and sub-crystal grains can be obtained. It is preferable
that 0.25 wt % or less of chromium be contained in the cast
aluminum alloy for forging. Even when the content of chromium
exceeds 0.25 wt %, the desired effect cannot sometimes unfavorably
be attained. The content is more preferably 0.04 to 0.25 wt %.
[0044] Titanium refines the crystal grains of a casting, and
enhances workability at the time of the forging, when contained in
the aluminum alloy. It is preferable that 0.0 to 0.15 wt % of
titanium be contained in the cast aluminum alloy for forging. It is
to be noted that even when titanium is not contained, a
considerably large trouble is not caused.
[0045] The metals contained in minute amounts in the cast aluminum
alloy for forging and the aluminum cast-forged product in
accordance with the present invention are as described above, and
the balance is unavoidably contained impurities and aluminum. It is
preferable that the unavoidably contained impurities be contained
by an amount as small as possible. The content is less than 0.1 wt
%, preferably 0.05 wt % or less.
[0046] It is to be noted that in a casting/forging method according
to the present invention, flash generated in the forging process
and accounting for about 30% of the generally used raw material can
be recovered and reused as the raw material of the aluminum alloy
according to the present invention. Therefore, in the present
invention, the cost of raw materials can be reduced.
[0047] Next, the method of manufacturing an aluminum cast-forged
product of the present invention will be described.
[0048] As described above, it is preferable that the flash
generated at the time of the forging be used as the raw material.
This raw material is adjusted so as to allow the resulting
composition to form the intended aluminum alloy consisting
essentially of 0.6 to 1.8 wt % of silicon, 0.6 to 1.8 wt % of
magnesium, 0.8 wt % or less of copper, 0.2 to 1.0 wt % of
manganese, 0.25 wt % or less of chromium, 0.0 to 0.15 wt % of
titanium, and unavoidably contained impurities by measures such as
preparing of metals that are insufficient using pure metals, and
mixing with another aluminum alloy. At this time, it is preferable
that the unavoidable impurities be not contained in the aluminum
alloy by 0.1 wt % or more in total.
[0049] These raw materials are charged in a melting furnace and is
heated to a temperature at about 680 to 780.degree. C. to be
melted, and next is charged into a holding furnace where a
degassing treatment and deoxidizing treatment are done to obtain a
molten metal. In this case, the temperature of a mold is preferably
adjusted at about 60 to 150.degree. C. Also, the mold preferably
has a shape such that a forging ratio is about 18 to 60%, assuming
that the shape of the final forged product is 100%, because the
strength is enhanced by the subsequent forging and the forging
process can further be simplified. That is, when the forging ratio
is set to about 18 to 60%, the strength improving effect due to the
forging and the cost reduction due to a simplified forging process
are balanced.
[0050] Herein, the forging ratio means a value representing the
degree of forming. For example, as shown in FIG. 3(a), when a
material A with an initial thickness D1 is formed by a load F and
the thickness is changed to D2 after forming as shown in FIG. 3(b),
a forging ratio R is represented by the following equation.
R[%]=(D1-D2)/D1.times.100(D1>D2)
[0051] However, when the thickness D2 after the forming is larger
than the initial thickness, the forging ratio is represented by the
following equation.
R[%]=(D2-D1)/D1.times.100(D2>D1)
[0052] That is, in the present invention, the fact that the
so-called preformed material having a shape such that the forging
ratio is about 18 to 60% assuming that the shape of the final
forged product is 100% is obtained by the casting means that the
preformed material having a shape such that the forging ratio
determined using the thickness of each portion of the raw material
for forging and the thickness of each corresponding portion in the
final product obtained by forging the raw material for forging is
about 18 to 60% in each portion is obtained by the casting.
[0053] Next, the cast material obtained/molded using a casting
apparatus, that is, the raw material for forging is heated to a
surface temperature at about 380.degree. C. to a melting point or
less and is stamped by a forging press to obtain a roughly forged
material. The roughly forged material is cooled, thereafter heated
again to the surface temperature at about 380.degree. C. to the
melting point or less, and is finished/stamped by the forging press
to obtain a finish forged material. The finish forged material is
subjected to clipping flash and heat treatment such as T6 treatment
to obtain a forged product. For example, to manufacture a steering
knuckle which is one of the suspension parts for the automobiles,
the load of the forging press is about 2600 to 2800 tons for rough
forging and about 3200 to 3800 tons for finish forging. By this
manufacturing process, the aluminum cast-forged product in
accordance with the present invention can be obtained.
[0054] In the present invention, the flash generated by the
forge-pressing and clipping flash in the manufacturing process of
the present invention is collected by a flash removing machine, and
can be reused as the raw material for the aluminum cast-forged
product of the present invention. Therefore, all of the raw
materials for forging are recycled, and are not disposed of as
wastes or are not used as an inexpensive raw material for
forging.
[0055] In the method of manufacturing an aluminum cast-forged
product of the present invention, after the raw material is melted
to obtain the molten metal, the mold for the casting is brought
closer to the shape of the product as compared with the
conventional raw material for forging so that the forging ratio is
about 18 to 60% assuming that the shape of the final forged product
is 100% while achieving the strength improving effect by the
forging, by which the pressing is facilitated. Therefore, unlike
the conventional forging process, steps of extruding, cutting,
heating, rough forging, finish forging, and clipping flash are not
observed, thus the manufacturing process can be simplified, and the
manufacturing cost can be reduced.
EXAMPLES
[0056] Examples of the present invention will hereinafter be
described, but the present invention is not limited to these
examples.
Examples 1 and 2
[0057] FIG. 1 is a diagram showing one example of the aluminum
cast-forged product of the present invention. A steering knuckle 40
which is the part for the automobile is shown. A small amount of
copper was added to scraps of A6082 alloy to prepare a raw material
forming the aluminum alloy consisting essentially of 0.6 to 1.8 wt
% of silicon, 0.6 to 1.8 wt % of magnesium, 0.8 wt % or less of
copper, 0.2 to 1.0 wt % of manganese, 0.25 wt % or less of
chromium, 0.0 to 0.15 wt % of titanium, and unavoidably contained
impurities. Using this raw material, the steering knuckle 40 having
a shape shown in FIG. 1 was manufactured in accordance with the
following steps.
[0058] After the raw material was melted at a molten metal
temperature of 728.degree. C. to obtain the molten metal, the raw
material for forging having a shape with a forging ratio of 30%
assuming that the shape of the final steering knuckle 40 was 100%
was cast at a mold temperature of 100.degree. C. Next, die forging
was performed using a forging press at a rough forging temperature
of 395.degree. C. (surface temperature) by applying a rough forging
load of 2770 tons to obtain a roughly forged material. Then, the
roughly forged material was subjected to the die forging again
using the forging press at a finish forging temperature of
460.degree. C. (surface temperature) by applying a finish forging
load of 3260 tons. Finally, the finish forged material was trimmed.
After a solution heat treatment which was a T4 treatment by heating
the finish forged material at 530.degree. C. for three hours, the
finish forged material was cooled. Then, an aging treatment was
done as T6 treatment by heating the finish forged material at
180.degree. C. for six hours. Thus, the steering knuckle 40 was
obtained as a product. In Example 2, operations similar to those of
Example 1 were repeated to obtain the steering knuckle 40, except
that the molten metal temperature was set to 720.degree. C. and the
mold temperature was set to 125.degree. C. Temperature conditions
and load conditions are given in Tables 1 and 2, respectively.
1 TABLE 1 Molten metal temperature Mold temperature (.degree. C.)
(.degree. C.) Example 1 728 100 Example 2 720 125
[0059]
2 TABLE 2 Rough forging Finish forging Surface Surface temperature
temperature Load (ton) (.degree. C.) Load (ton) (.degree. C.)
Example 1 2770 395 3260 460 Example 2 2730 400 3780 445
[0060] The test pieces were cut out from thus obtained steering
knuckle 40, and tensile strength, proof stress, and elongation were
measured as mechanical properties. The results are shown in Table
3.
3 TABLE 3 Tensile Proof strength stress Elongation (MPa) (MPa) [%]
Example 1 358 323 14.7 Example 2 378.6 335.8 14.3 Required value
320 280 10 from market
[0061] The results of Examples 1 and 2 reveal that the mechanical
properties of the aluminum cast-forged product in accordance with
the present invention were capable of clearing the standards as
needs of market in all of the tensile strength, proof stress, and
elongation.
[0062] As described above, in accordance with the present
invention, there is provided an aluminum cast-forged product
further satisfying needs of market in mechanical properties such as
a tensile strength, proof stress, and elongation with a simpler
manufacturing process with good productivity and at low cost.
Moreover, by this aluminum cast-forged product, various lightweight
and inexpensive vehicular parts such as suspension parts for
vehicles, frames for the vehicles, and parts for engines are
provided. Through lightening of weights of the vehicles, fuel
consumption of automobiles is saved. As a result, emitted carbon
dioxide is reduced, and an effect of contribution to prevention of
global warming is also attained.
* * * * *