U.S. patent application number 11/319094 was filed with the patent office on 2006-06-29 for aluminum alloy for die castings and production process of aluminum alloy castings.
This patent application is currently assigned to DENSO Corporation. Invention is credited to Tomoyuki Hatano, Hiroshi Horikawa, Masatoshi Koumura, Takeshi Nagasaka, Hiromi Takagi, Yoshiki Tan.
Application Number | 20060137774 11/319094 |
Document ID | / |
Family ID | 35841250 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060137774 |
Kind Code |
A1 |
Nagasaka; Takeshi ; et
al. |
June 29, 2006 |
Aluminum alloy for die castings and production process of aluminum
alloy castings
Abstract
The present invention provides an aluminum alloy for die
castings that has superior castability and corrosion resistance.
The amounts of Mn, Fe and Cu contained in the aluminum alloy
components for die castings were determined to have a considerable
effect on the corrosion resistance of the aluminum alloy.
Therefore, the aluminum alloy for die castings of the present
invention contains 9.0 to 12.0% by weight of Si, 0.20 to 0.80% by
weight of Mg, and 0.7 to 1.1% by weight of Mn+Fe, the Mn/Fe ratio
is 1.5 or more, the amount of Cu as impurity is controlled to 0.5%
by weight or less, and the remainder is composed of aluminum and
unavoidable impurities.
Inventors: |
Nagasaka; Takeshi;
(Obu-city, JP) ; Hatano; Tomoyuki; (Nagoya-city,
JP) ; Takagi; Hiromi; (Nagoya-city, JP) ; Tan;
Yoshiki; (Anjo-city, JP) ; Koumura; Masatoshi;
(Okazaki-city, JP) ; Horikawa; Hiroshi;
(Shizuoka-shi, JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Assignee: |
DENSO Corporation
Kariya-city
JP
Nippon Light Metal Co., Ltd.
Tokyo
JP
|
Family ID: |
35841250 |
Appl. No.: |
11/319094 |
Filed: |
December 27, 2005 |
Current U.S.
Class: |
148/440 ;
148/549; 420/546; 420/547 |
Current CPC
Class: |
B22D 17/14 20130101;
C22C 21/08 20130101 |
Class at
Publication: |
148/440 ;
148/549; 420/546; 420/547 |
International
Class: |
C22C 21/04 20060101
C22C021/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2004 |
JP |
2004-380757 |
Claims
1. An aluminum alloy for die castings comprising 9.0 to 12.0% by
weight of Si, 0.20 to 0.80% by weight of Mg, and 0.7 to 1.1% by
weight of Mn+Fe; wherein, the Mn/Fe ratio is 1.5 or more, and the
amount of Cu as impurity is controlled to 0.5% by weight or less,
and the remainder is composed of aluminum and unavoidable
impurities.
2. An aluminum alloy for die castings according to claim 1, wherein
one or more types of Ti, B, Zr, Sr, Ca, Na or Sb is contained as
impurity.
3. An aluminum alloy for die castings according to claim 1, wherein
the upper limit of the Mn/Fe ratio is 5.0 or less.
4. A production process for producing aluminum alloy castings using
the aluminum alloy for die castings according to claim 1
comprising: a decompression step, in which the mold is closed and
the inside of the mold is decompressed to at least a predetermined
pressure that is lower than atmospheric pressure, and a melt
filling step, in which a melt of the aluminum alloy is filled into
the mold after the decompression step.
5. A production process for producing aluminum alloy castings using
the aluminum alloy for die castings according to claim 1
comprising: a venting step, in which the mold is closed and air
inside the mold is vented, an atmospheric adjustment step, in which
oxygen is supplied to the mold after the venting step to replace
the inside of the mold with an oxygen atmosphere, and a melt
filling step, in which a melt of the aluminum alloy is filled into
the mold after the atmospheric adjustment step.
6. Aluminum alloy castings produced using the aluminum alloy for
die castings according to claim 1, the castings having thin-walled
fins in which the plate thickness of the portion having the minimum
plate thickness is 0.5 to 1.5 mm.
7. Aluminum alloy castings produced using the aluminum alloy for
die castings according to claim 1, the castings having a coupling
that is coupled to another part by press-fitting or caulking.
Description
[0001] This application is a new U.S. patent application that
claims benefit of JP 2004-380757, filed Dec. 28, 2004, the entire
contents of each of which are hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an aluminum alloy for die
castings having superior castability and corrosion resistance, a
production process of aluminum alloy castings, and aluminum alloy
castings.
BACKGROUND OF THE INVENTION
[0003] Japanese Unexamined Patent Publication No. 2-232331
describes an aluminum alloy for die castings of the prior art in
which the Cu content is 0.02% by weight or less, contains 4 to 13%
by weight of Si, and is used by providing a transparent film,
wherein filiform corrosion resistance is improved by adding 0.05 to
0.3% by weight of Ti and/or 0.05 to 0.15% by weight of Be.
SUMMARY OF THE INVENTION
[0004] However, care must be taken when handling the aluminum alloy
composition of the prior art because it contains toxic Be.
[0005] Although JIS-ADC12 (JIS-H-5302-2000) alloy has typically
been used in the prior art for aluminum die cast automobile parts
due to its superior castability, this JIS-ADC12 has low corrosion
resistance. Consequently, in products used in environments where
corrosion proceeds rapidly such as environments where the product
is subjected to moisture, corrosion occurs on the material surface
in a short period of time and, as this results in a decrease in
strength, JIS-ADC12 is difficult to use.
[0006] In addition, although JIS-ADC5 and JIS-ADC6 alloys have
satisfactory corrosion resistance, as the melt is susceptible to
solidification as a result of being cooled by the surface of the
mold due to the high melting point of aluminum alloy, the melt has
poor fluidity resulting in poor castability. In this connection,
the term "castability" used in the present description refers to
overall moldability including evaluation parameters such as "melt
fluidity", "shrinkage cavity formation following melt
solidification", "castings breakage following melt solidification"
and "mold seizure resistance".
[0007] In consideration of these matters, an object of the present
invention is to provide an aluminum alloy for die castings that has
superior castability and corrosion resistance.
[0008] In addition, another object of the present invention is to
provide an aluminum alloy for die castings that does not contain
toxic components such as Be.
[0009] In addition, another object of the present invention is to
provide an aluminum alloy for die castings that has superior
strength.
[0010] In addition, another object of the present invention is to
provide an aluminum alloy for die castings capable of lowering
material hardness.
[0011] As a result of conducting extensive studies on the causes of
decreased corrosion resistance of JIS-ADC12, the inventors of the
present invention determined that the amounts of Mn, Fe and Cu
contained in aluminum alloy for die castings have a considerable
effect on the corrosion resistance of the aluminum alloy.
[0012] Namely, it was determined that in the case of JIS-ADC12,
together with the generation of .beta.-AlFeSi particles, which
compose a cathode pole (noble in potential) that is detrimental to
corrosion resistance, .alpha.-Al(Fe.Mn)Si particles are also
generated, which although have a weaker action than .beta.-AlFeSi
particles, also similarly compose a cathode pole, thereby lowering
corrosion resistance.
[0013] It was found that the generation of these .beta.-AlFeSi
particles and .alpha.-Al(Fe.Mn)Si particles is because the ratio of
the added amounts of Mn and Fe in JIS-ADC12 (Mn/Fe ratio) is as low
as about 0.34, and if this ratio of the added amounts of Mn and Fe
(Mn/Fe ratio) was controlled, then together with being able to
inhibit the generation of .beta.-AlFeSi particles, the other cause
of poor corrosion resistance attributable to .alpha.-Al(Fe.Mn)Si
particles could also be removed.
[0014] In addition, the amount of Cu added in JIS-ADC12 is
comparatively high at 1.5 to 3.5% by weight. Consequently, there
are many noble Al.sub.2Cu phases, and the solid solubilization of
Cu into .alpha.-Al(Fe.Mn)Si particles is promoted, thereby making
the potential of the .alpha.-Al(Fe.Mn)Si particles even nobler and
causing a decrease in corrosion resistance.
[0015] The present invention was conceived on the basis of the
aforementioned findings, and the invention according to claim 1 is
an aluminum alloy for die castings comprising 9.0 to 12.0% by
weight of Si, 0.20 to 0.80% by weight of Mg, and 0.7 to 1.1% by
weight of Mn+Fe; wherein,
[0016] the Mn/Fe ratio is 1.5 or more, and
[0017] the amount of Cu as impurity is controlled to 0.5% by weight
or less, and the remainder is composed of aluminum and unavoidable
impurities.
[0018] According to experimental research conducted by the
inventors of the present invention, it was found that the
generation of .beta.-AlFeSi particles that compose a cathode pole
(noble component of the electrical potential) detrimental to
corrosion resistance can be inhibited by setting the Mn/Fe ratio to
1.5 or more, while at the same time, the potential of
.alpha.-Al(Fe.Mn)Si particles that similarly compose a cathode pole
can be lowered by holding the Fe/Mn ratio in the particles to 1 or
less, thereby making it possible to remove the causes of poor
corrosion resistance.
[0019] In addition, by controlling the added amount of Cu to 0.5%
by weight or less, noble Al.sub.2Cu phases can be reduced, the
solid solubilization of Cu into .alpha.-Al(Fe.Mn)Si particles can
be inhibited, and the potential of .alpha.-Al(Fe.Mn)Si particles
can be lowered.
[0020] In combination with the above features, the invention
according to claim 1 was confirmed to be able to considerably
improve corrosion resistance as compared with JIS-ADC12 (see FIG. 5
to be described later).
[0021] Fluidity equivalent to JIS-ADC12 can be obtained by setting
the added amount of Si to within the range of 9.0 to 12.0% by
weight. Accordingly, both castability and corrosion resistance of
an aluminum alloy for die castings can be realized.
[0022] Moreover, in addition to improving corrosion resistance, the
material hardness can be lowered considerably as compared with
JIS-ADC12 by controlling the added amount of Cu to 0.5% by weight
or less (see FIG. 6 to be described later). As a result, as the
processability such as press-fitting and caulking of aluminum alloy
castings becomes satisfactory, the aluminum alloy castings can be
easily coupled to other parts.
[0023] Moreover, inhibiting the aforementioned Cu solid
solubilization by controlling the added amount of Cu to 0.5% by
weight or less improves the electrical conductivity (thermal
conductivity) of the aluminum alloy, thus improving heat
dissipation.
[0024] In addition, Mn and Fe have the effect of inhibiting seizure
of the aluminum alloy to the mold. Here, if the amount of Mn+Fe
(total added amount of Mn and Fe) is reduced to less than 0.7% by
weight, the effect of inhibiting seizure becomes inadequate. On the
other hand, if the amount of Mn+Fe exceeds 1.1% by weight, in
addition to both corrosion resistance, strength and elongation
decreasing, massive Al--Si--Fe-based intermetallic compounds form
in the furnace holding the melt, which increases the possibility of
causing poor cutting and other machining properties. Accordingly,
the amount of Mn+Fe should be within the range of 0.7 to 1.1% by
weight.
[0025] On the other hand, Mg is added to improve mechanical
strength, and if the added amount of Mg is less than 0.20% by
weight, the effect of improving strength is inadequate, while if
the added amount of Mg exceeds 0.80% by weight, the effect of
improving strength decreases. Accordingly, the added amount of Mg
should be within the range of 0.20 to 0.80% by weight (see FIG. 8
to be described later).
[0026] In addition, handling of the aluminum alloy is easy since it
does not contain a toxic component such as Be.
[0027] The invention according to claim 2 additionally contains one
or more types of Ti, B, Zr, Sr, Ca, Na or Sb as impurity in the
aluminum alloy of claim 1. This results in increased fineness of
the primary crystal .alpha.-Al phase and reformation of eutectic Si
particles, making it possible to provide an aluminum alloy in which
castability and strength are further improved.
[0028] More specifically, Ti, B and Zr have the effect of
increasing the fineness of the primary crystal .alpha.-Al phase.
Sr, Ca, Na and Sb have the effect of reforming eutectic Si
particles while also having the effect of improving castability and
strength.
[0029] In the invention according to claim 3, the upper limit of
the Mn/Fe ratio in the aluminum alloy for die castings according to
claim 1 or 2 is defined to be 5.0 or less. As a result, the minimum
required amount of Fe can be secured, and the effect can be secured
of preventing seizure of the aluminum alloy to the mold (seizure
resistance).
[0030] The invention according to claim 4 is a production process
for producing aluminum alloy castings using the aluminum alloy for
die castings according to any one of claims 1 to 3 comprising:
[0031] a decompression step, in which the mold (10,11) is closed
and the inside of the mold (10,11) is decompressed to at least a
predetermined pressure that is lower than atmospheric pressure,
and
[0032] a melt filling step, in which a melt of the aluminum alloy
is filled into the mold (10,11) after the decompression step.
[0033] According to this invention, as a melt of the aluminum alloy
is filled into the mold (10,11) after having decompressed the
inside of the mold (10,11) to at least a predetermined pressure
that is lower than atmospheric pressure, making it possible to
prevent phenomena wherein the mold internal pressure (back
pressure) rises during melt filling so as to impede the flow of the
melt. Thus, the fluidity of the melt can be further improved.
[0034] The invention according to claim 5 is a production process
for producing aluminum alloy castings using the aluminum alloy for
die castings according to any one of claims 1 to 3 comprising:
[0035] a venting step, in which the mold (10,11) is closed and air
inside the mold (10,11) is vented, an atmospheric adjustment step,
in which oxygen is supplied to the mold (10,11) after the venting
step to replace the inside of the mold (10,11) with an oxygen
atmosphere, and
[0036] a melt filling step, in which a melt of the aluminum alloy
is filled into the mold (10,11) after the atmospheric adjustment
step.
[0037] According to this invention, as a melt of the aluminum alloy
is filled into the mold (10,11) after having replaced the inside of
the mold (10,11) with an oxygen atmosphere, oxidation of the
aluminum alloy can be promoted and the structure of the alloy
material can be made more dense, thereby improving the material
strength.
[0038] The invention according to claim 6 is aluminum alloy
castings produced using the aluminum alloy for die castings
according to any of claims 1 to 3, the castings having thin-walled
fins (31b) in which the plate thickness of the portion having the
minimum plate thickness is 0.5 to 1.5 mm.
[0039] As the fluidity of an aluminum alloy according to the
present invention can be increased to a high level in proportion to
JIS-ADC12 by setting the added amount of Si to the previously
described range, even a product shape having thin-walled fins (31b)
as in claim 6 can be cast easily.
[0040] The invention according to claim 7 is aluminum alloy
castings produced using the aluminum alloy for die castings
according to any of claims 1 to 3, the castings having a coupling
(31c) that is coupled to another part by press-fitting or
caulking.
[0041] In an aluminum alloy according to the present invention,
since material hardness can be lowered considerably as compared
with JIS-ADC12 by controlling the added amount of Cu to 0.5% by
weight or less as previously described, even a product structure
having a coupling (31c) that is coupled to another part by
press-fitting or caulking as in claim 7 can be easily coupled
mechanically by either press-fitting or caulking.
[0042] Furthermore, the reference symbols indicated in parentheses
in each of the above paragraphs indicate the correlation with
specific constituents described in the embodiments to be described
later.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 is a table of the material components of Examples 1
to 5 of the present invention and Comparative Examples 1 to 3.
[0044] FIG. 2 is a graph of the results of evaluating fluidity of
the various aluminum alloy materials of FIG. 1.
[0045] FIG. 3A and FIG. 3B are tables of the material components of
aluminum alloy materials defined in JIS.
[0046] FIG. 4 is a table of the material components of Examples 1
to 5 of the present invention and Comparative Examples 2 and 3, in
which Mn/Fe ratios and the amounts of Mn+Fe have been added to FIG.
1.
[0047] FIG. 5 is a graph of the results of evaluating the corrosion
resistance of the various aluminum alloy materials of FIG. 4.
[0048] FIG. 6 is a graph of the relationship between the amount of
Cu added to aluminum alloy materials and material hardness.
[0049] FIG. 7 is a table of the material components of Examples 6
to 8 of the present invention and Comparative Example 4.
[0050] FIG. 8 is a graph of the relationship between the amount of
Mg added to aluminum alloy materials and material strength.
[0051] FIG. 9 is a schematic cross-sectional view of an example of
a die castings apparatus in an embodiment of the present
invention.
[0052] FIG. 10 is a schematic cross-sectional view of another
example of a die castings apparatus in an embodiment of the present
invention.
[0053] FIG. 11 is a perspective view of a specific example of an
aluminum alloy castings product according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0054] The following provides an explanation of embodiments of the
present invention based on specific examples. FIG. 1 shows the
material components of aluminum alloys for die castings of Examples
1 to 5 of the present invention and Comparative Examples 1 to 3.
FIG. 2 shows the results of evaluating the fluidity of each of the
material components of FIG. 1. Comparative Example 2 is JIS-ADC12,
while Comparative Example 3 is JIS-AC4C.
[0055] Furthermore, a "-" indicated for the material components of
FIG. 1 and FIG. 4 to be described later means that the added amount
of each component is a trace amount of less than 0.01% by weight.
The material components of JIS-ADC12, JIS-ADC5, JIS-ADC6 and
JIS-AC4C are shown in FIGS. 3A and 3B.
[0056] In Examples 1 to 5, the added amount of Si is set to 9.1 to
10.8% by weight, which is within the range of the added amount of
Si of the present invention.
[0057] The results of evaluating fluidity of FIG. 2 represent the
flow length ratio based on a value of 1 for the flow length of
JIS-ADC12 of Comparative Example 2. Here, flow length is defined as
the flow length in the direction in which the aluminum alloy melt
advances until it solidifies and stops advancing when various types
of aluminum alloy melts are poured into a castings mold having a
predetermined cross-sectional shape.
[0058] According to Examples 1 to 5, a flow length ratio of 0.8 or
more can be obtained based on the flow length of JIS-ADC12 of
Comparative Example 2, thus demonstrating that a high level of
fluidity can be secured in proportion to JIS-ADC12.
[0059] In contrast, in Comparative Examples 1 and 3, the added
amounts of Si were low at 6.7% by weight and 7.0% by weight,
respectively. As a result, a flow length ratio of only around 0.7
was obtained based on the flow length of JIS-ADC12 of Comparative
Example 2, thus demonstrating that fluidity decreases more than in
Comparative Example 2 and Examples 1 to 5.
[0060] Next, FIG. 4 indicates the Mn/Fe ratios and amounts of Mn+Fe
in Examples 1 to 5 and Comparative Examples 2 and 3. The Mn/Fe
ratios of Examples 1 to 5 were within the range of 2.2 to 4.8, and
the amounts of Mn+Fe were within the range of 0.92 to 1.04% by
weight.
[0061] In contrast, the Mn/Fe ratio of Comparative Example 2 was
0.34, thus demonstrating a value that was much lower than the range
of the present invention. In addition, both the Mn/Fe ratio and
amount of Mn+Fe of Comparative Example 3 deviated considerably from
their respective ranges of the present invention.
[0062] FIG. 5 shows the results of evaluating the corrosion
resistance of each material, and represents the corrosion weight
loss ratio of each material based on a value of 1 for the corrosion
weight loss of JIS-ADC12 of Comparative Example 2. Here, the most
commonly used method for evaluating corrosion resistance in the
form of Methods of Salt Spray Testing (see JIS Z 2371 (2000)) was
used to evaluation corrosion resistance.
[0063] More specifically, test pieces fabricated from each of the
alloy materials of Examples 1 to 5 and Comparative Examples 2 to 5
were placed in a tank that enabled them to be sprayed with salt
water, the test pieces were taken out of the tank after a
predetermined amount of time had elapsed, and the amount of
corrosion of the test pieces (corrosion weight loss) was measured
to evaluate corrosion resistance such that greater corrosion weight
loss was evaluated as constituting lower corrosion resistance.
[0064] According to Examples 1 to 5, their corrosion weight loss
ratios were reduced considerably to 0.4 or less of JIS-ADC12 of
Comparative Example 2, and corrosion resistance was improved
remarkably.
[0065] Incidentally, JIS-ADC12 of Comparative Example 2 has a low
value of 0.34 for its Mn/Fe ratio, while the added amount of Cu is
high at 3.08% by weight, and both of these factors contribute to
lowering corrosion resistance.
[0066] In addition, although the added amount of Cu of JIS-AC4C of
Comparative Example 3 is reduced to 0.09% by weight, as its Mn/Fe
ratio is low at 0.33, its corrosion weight loss ratio was about
0.5, and the corrosion resistance of Comparative Example 3 was
lower than that of Examples 1 to 5.
[0067] Furthermore, as the amount of Mn+Fe of JIS-AC4C of
Comparative Example 3 is low at 0.24% by weight, its effect of
inhibiting seizure of the aluminum alloy to the mold is also
inadequate.
[0068] Next, FIG. 6 shows changes in material hardness versus the
added amount of Cu based on relative hardness as determined by
assigning of value of 1 to the material hardness of JIS-ADC12. In
the example of FIG. 6, the added amount of Cu of JIS-ADC12 is
defined to be 2.5% by weight. On the other hand, the added amounts
of Cu of Examples 6, 7 and 8 and Comparative Example 4 are defined
to be 1.0% by weight or less. Furthermore, the material
compositions of Examples 6, 7 and 8 and Comparative Example 4 were
as shown in FIG. 7.
[0069] As shown in FIG. 6, as the added amounts of Cu decreased in
the order of Comparative Example 4, Example 8, Example 7 and
Example 6, material hardness can be seen to have decreased. By
controlling the added amount of Cu to 0.5% by weight or less in
particular, the relative hardness based on JIS-ADC12 was greatly
reduced to around 0.8. As a result, this enables parts to be
press-fit or caulked to die-cast aluminum alloy castings.
[0070] Next, FIG. 8 shows changes in material strength versus the
added amount of Mg based on relative strength as determined by
assigning a value of 1 to the resulting strength (specifically,
tensile strength) when the added amount of Mg is zero.
[0071] As can be understood from FIG. 8, tensile strength of the
aluminum alloy can be effectively improved by making the added
amount of Mg to be within the range of 0.20 to 0.80% by weight (and
preferably within the range of 0.35 to 0.60% by weight).
[0072] Furthermore, the trend observed for changes in strength of
aluminum alloy caused by changes in the added amount of Mg shown in
FIG. 8 also appeared in Examples 1 to 8.
[0073] Furthermore, the contents of other unavoidable impurities of
aluminum alloys such as Zn, Ni, Sn, Pb and Bi, which lower
corrosion resistance in particular, were controlled in Examples 1
to 8. The amounts of Zn, Ni and Sn are preferably 0.05% by weight
or less, while the amounts of Pb and Bi are preferably 0.005% by
weight or less.
[0074] Next, a production process (die castings process) for
aluminum alloy castings that uses an aluminum alloy according to
the present embodiment is explained. To begin with, an explanation
is provided of a die castings apparatus of the present embodiment
with reference to FIG. 9. This die castings apparatus has a mold
consisting of a stationary platen 10, and a movable platen 11 that
is disposed in opposition to this stationary platen 10.
[0075] Movable platen 11 is composed of a movable block 12, a
spacer 13 and a die base 14. A hydraulic-powered mechanism and so
forth, not shown, is coupled to die base 14 of movable platen 11 so
that movable platen 11 can be moved to the left and right in FIG.
9.
[0076] FIG. 9 shows the state in which the mold is closed as a
result of movable block 12 of movable platen 11 moving to the
location where it contacts stationary platen 10, and a cavity 15 is
formed between movable block 12 and stationary platen 10 where a
product shape of aluminum alloy castings is made.
[0077] A cylindrical injection sleeve 16 is disposed on the outside
of stationary platen 10, and one end of the space inside this
injection sleeve 16 is continuous with cavity 15 through a spool
bushing 10a that penetrates through stationary platen 10. A melt
supply port 16a is opened in the upper surface of injection sleeve
16.
[0078] An injection plunger 17 fits inside injection sleeve 16.
This injection plunger 17 is coupled to a hydraulic-powered
mechanism and so forth not shown, and injection plunger 17 is able
to move in the axial direction (to the left and right in FIG. 9) of
injection sleeve 16.
[0079] FIG. 9 shows injection plunger 17 retracted to the opening
of melt supply port 16a. A ladle 18 fulfills the role of a melt
injector that injects the aluminum alloy melt into injection sleeve
16, and the aluminum alloy melt retained in a furnace not shown is
injected into injection sleeve 16 from melt supply port 16a by
ladle 18.
[0080] A motorized or other type of vacuum pump 19 and a vacuum
tank 20 compose a decompression apparatus for decompressing the
space inside the mold that includes cavity 15 to at least a
predetermined pressure that is lower than atmospheric pressure, and
vacuum tank 20 is continuous with cavity 15 through a hose 21 and
connecting path 22 inside movable block 12.
[0081] Here, a motorized or other type of shutoff valve 21a is
disposed at an intermediate location of hose 21. More specifically,
connecting path 22 is connected to cavity 15 at a site on the
opposite side of the site where injection sleeve 16 is connected.
In addition, a pressure gauge (vacuum gauge) 23 is connected to
connecting path 22, and the pressure inside the mold (degree of
decompression) can be measured with this pressure gauge 23.
[0082] Moreover, a cutoff pin 25, which serves as a shutoff device
capable of opening and closing connecting path 22, extrusion pins
26 and an extrusion plate 27 and so forth are installed on movable
platen 11.
[0083] Next, an explanation is provided of a production process of
aluminum alloy castings (die castings process) using the
aforementioned die castings apparatus. First, movable block 12 of
movable platen 11 is contacted with stationary platen 10 as shown
in FIG. 9, and together with being in the state in which the mold
is closed (mold clamped state), injection plunger 17 is retracted
to the maximum retraction position indicated with solid lines in
FIG. 9 to open melt supply port 16a.
[0084] While in this state, a melt of the aluminum alloy is
injected into injection sleeve 16 from melt supply port 16a by
ladle 18.
[0085] Following completion of melt injection into injection sleeve
16, injection plunger 17 is advanced to the intermediate stopping
position indicated with broken line 17a in FIG. 9. At this time,
melt supply port 16a does not have to be completely closed, but
what is important is that the inside of the mold is sealed by the
advancement of injection plunger 17 so that the atmosphere inside
the mold is isolated from the air (outside atmosphere).
[0086] Next, a decompression step is carried out in which the space
inside the mold that includes cavity 15 is decompressed to at least
a predetermined pressure that is lower than atmospheric pressure.
More specifically, the motorized or other type of shutoff valve 21a
and cutoff pin 25 are operated to the open state, and the air in
the space inside the mold is suctioned towards vacuum tank 20
through connecting path 22 and hose 21 due to the high vacuum
inside vacuum tank 20 to decompress the space inside the mold.
[0087] When the mold internal pressure has decreased at least to a
predetermined pressure (for example, 13.3 kPa) that has been set in
advance by measuring the pressure of the space inside the mold with
pressure gauge 23, shutoff valve 21a and cutoff pin 25 are returned
to the closed state based on the measurement signal from pressure
gauge 23.
[0088] Next, injection plunger 17 begins to advance based on the
measurement signal of pressure gauge 23, and melt inside injection
sleeve 16 is injected into cavity 15. During this filling step, as
the inside of the mold has been decompressed in advance to at least
the aforementioned predetermined pressure, there is no increase in
back pressure (pressure in the space in front in the direction of
melt flow) accompanying melt filling. Consequently, the melt can be
filled smoothly into cavity 15.
[0089] Broken line 17b in FIG. 9 indicates the injection forward
limit position of injection plunger 17, and melt filling into
cavity 15 is completed when injection plunger 17 reaches this
injection forward limit position 17b. Following completion of
filling, injection plunger 17 is held at injection forward limit
position 17b until the melt inside cavity 15 solidifies.
[0090] After the melt has solidified, movable platen 11 is moved in
the direction of separation from stationary platen 10 (to the left
in FIG. 9) to open the mold, extrusion plate 27 and extrusion pins
26 are advanced to the right in FIG. 9, and the product (castings)
that has solidified inside cavity 15 is taken out of the mold.
[0091] Next, another example of a die castings apparatus of the
present embodiment is explained with reference to FIG. 10. In the
example of FIG. 10, an oxygen supply apparatus 24 is added to the
die castings apparatus of FIG. 9. This oxygen supply apparatus 24
is for supplying oxygen to the space inside the mold that includes
cavity 15, and more specifically, is provided with an oxygen tank
24a that stores oxygen at a predetermined pressure, a supply tube
24b, and a motorized or other type of shutoff valve 24c that opens
and closes the pathway of supply tube 24b.
[0092] The end of supply tube 24b opens at a location in the
internal space composed by injection sleeve 16 and spool bushing
10a that is farther to the advancing side than intermediate
stopping position 17a of injection plunger 17, and supplies oxygen
to the space inside the mold through the internal space of spool
bushing 10a.
[0093] Next, an explanation is provided of a production process of
aluminum alloy castings (die castings process) that uses the die
castings apparatus of FIG. 10. First, a melt of the aluminum alloy
is injected into injection sleeve 16 from melt supply port 16a.
This melt injection step is the same as that of the example shown
in FIG. 9, and following completion of melt injection into
injection sleeve 16, injection plunger 17 is advanced to
intermediate stopping position 17a.
[0094] Next, a venting step (or vacuum drawing step) is carried out
in which the atmospheric component of the space inside the mold
that includes cavity 15 is vented from the mold. Although this
venting step is equivalent to the decompression step of the example
shown in FIG. 9, its objective is not to decompress the inside of
the mold, but rather vent the atmospheric component inside the
mold.
[0095] Following this venting step, an atmospheric adjustment step,
in which the inside of the mold is replaced with an oxygen
atmosphere, is carried out. Namely, in this atmospheric adjustment
step, shutoff valve 24c of supply tube 24b is opened, and oxygen
inside oxygen tank 24a of oxygen supply apparatus 24 is supplied to
cavity 15 through supply tube 24b, injection sleeve 16 and spool
bushing 10a.
[0096] When the pressure of the oxygen atmosphere within the mold
is determined to have risen to a predetermined pressure that
exceeds atmospheric pressure according to pressure gauge 23,
shutoff valve 24c of supply tube 24b is closed automatically to
complete the atmospheric adjustment step.
[0097] Next, the product (castings) is taken out following a melt
filling step, retaining the melt in the filled state and the
opening the mold, in the same manner as the aforementioned example
of FIG. 9.
[0098] According to the example of FIG. 10, as the melt of an
aluminum alloy is filled into the mold after replacing the inside
of the mold with an oxygen atmosphere, oxidation of the aluminum
alloy can be aggressively promoted, and the structure of the alloy
material can be made denser by this oxidation, thereby improving
material strength.
[0099] Next, an explanation of a specific example of a product of
aluminum alloy castings of the present invention is provided with
reference to FIG. 11. FIG. 11 shows an example of composing a
radiator fin 31 of an electrical heat-generating part 30 from
aluminum alloy castings of the present invention. More
specifically, electrical heat-generating part 30 is a diode.
[0100] Radiator fin 31 has a plurality of thin-walled fins 31b
integrally molded on the top and bottom surfaces of a plate-like
substrate 31a. A circular mounting hole 31c is opened in the flat
portion of substrate 31a where thin-walled fins 31 are not molded,
and electrical heat-generating part 30, which is formed to have a
roughly cylindrical outer diameter, is fixed in this circular
mounting hole 31c by press-fitting.
[0101] The plate thickness t of the portions having the minimum
plate thickness (tips) of thin-walled fins 31b is about 0.5 to 1.5
mm. A product having a thin-walled plate-like shape such as this
can be molded during die-castings of an aluminum alloy castings due
to its improved fluidity.
[0102] In addition, according to aluminum alloy castings of the
present invention, press-fitting to fix electrical heat-generating
part 30 in mounting hole 31c of substrate 31a of radiator fin 31
can be carried out efficiently and with satisfactory quality as the
material hardness of the aluminum alloy is decreased.
[0103] Furthermore, although electrical heat-generating part 30 is
fixed in substrate 31a of radiator fin 31 by press-fitting in FIG.
11, even in the case of fixing electrical heat-generating part 30
in substrate 31a of radiator fin 31 by caulking, caulking of
substrate 31a of radiator fin 31 can be carried out efficiently and
with satisfactory quality due to the decreased material hardness of
the aluminum alloy.
[0104] In the die castings apparatuses shown in FIGS. 9 and 10, the
drive mechanism of movable platen 11 is not limited to a
hydraulic-powered mechanism, but rather a drive mechanism that uses
various types of power sources such as an electric motor, water
pressure or air pressure can also be used. Similarly, various power
sources such as oil pressure, water pressure and air pressure can
be used for the power source that drives the vacuum pump 19, in
addition to an electric motor.
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