Patent Application
20060137774
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.
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.
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.
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
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
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
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.
The following provides an explanation of embodiments of the present invention based on specific examples.
Furthermore, a “-” indicated for the material components of
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
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,
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.
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,
As shown in
Next,
As can be understood from
Furthermore, the trend observed for changes in strength of aluminum alloy caused by changes in the added amount of Mg shown in
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
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
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
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
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
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
After the melt has solidified, movable platen 11 is moved in the direction of separation from stationary platen 10 (to the left in
Next, another example of a die castings apparatus of the present embodiment is explained with reference to
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
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
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
According to the example of
Next, an explanation of a specific example of a product of aluminum alloy castings of the present invention is provided with reference to
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
In the die castings apparatuses shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-380757 | Dec 2004 | JP | national |
