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.

Description

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

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

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

However, care must be taken when handling the aluminum alloy composition of the prior art because it contains toxic Be.

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.

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”.

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.

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.

In addition, another object of the present invention is to provide an aluminum alloy for die castings that has superior strength.

In addition, another object of the present invention is to provide an aluminum alloy for die castings capable of lowering material hardness.

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.

Namely, it was determined that in the case of JIS-ADC12, together with the generation of β-AlFeSi particles, which compose a cathode pole (noble in potential) that is detrimental to corrosion resistance, α-Al(Fe.Mn)Si particles are also generated, which although have a weaker action than β-AlFeSi particles, also similarly compose a cathode pole, thereby lowering corrosion resistance.

It was found that the generation of these β-AlFeSi particles and α-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 β-AlFeSi particles, the other cause of poor corrosion resistance attributable to α-Al(Fe.Mn)Si particles could also be removed.

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 Al₂Cu phases, and the solid solubilization of Cu into α-Al(Fe.Mn)Si particles is promoted, thereby making the potential of the α-Al(Fe.Mn)Si particles even nobler and causing a decrease in corrosion resistance.

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,

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.

According to experimental research conducted by the inventors of the present invention, it was found that the generation of β-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 α-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.

In addition, by controlling the added amount of Cu to 0.5% by weight or less, noble Al₂Cu phases can be reduced, the solid solubilization of Cu into α-Al(Fe.Mn)Si particles can be inhibited, and the potential of α-Al(Fe.Mn)Si particles can be lowered.

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).

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.

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.

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.

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.

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).

In addition, handling of the aluminum alloy is easy since it does not contain a toxic component such as Be.

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 α-Al phase and reformation of eutectic Si particles, making it possible to provide an aluminum alloy in which castability and strength are further improved.

More specifically, Ti, B and Zr have the effect of increasing the fineness of the primary crystal α-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.

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).

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:

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

a melt filling step, in which a melt of the aluminum alloy is filled into the mold (10,11) after the decompression step.

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.

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:

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

a melt filling step, in which a melt of the aluminum alloy is filled into the mold (10,11) after the atmospheric adjustment step.

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.

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.

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.

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.

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.

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

FIG. 1 is a table of the material components of Examples 1 to 5 of the present invention and Comparative Examples 1 to 3.

FIG. 2 is a graph of the results of evaluating fluidity of the various aluminum alloy materials of FIG. 1.

FIG. 3A and FIG. 3B are tables of the material components of aluminum alloy materials defined in JIS.

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.

FIG. 5 is a graph of the results of evaluating the corrosion resistance of the various aluminum alloy materials of FIG. 4.

FIG. 6 is a graph of the relationship between the amount of Cu added to aluminum alloy materials and material hardness.

FIG. 7 is a table of the material components of Examples 6 to 8 of the present invention and Comparative Example 4.

FIG. 8 is a graph of the relationship between the amount of Mg added to aluminum alloy materials and material strength.

FIG. 9 is a schematic cross-sectional view of an example of a die castings apparatus in an embodiment of the present invention.

FIG. 10 is a schematic cross-sectional view of another example of a die castings apparatus in an embodiment of the present invention.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

While in this state, a melt of the aluminum alloy is injected into injection sleeve 16 from melt supply port 16a by ladle 18.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.