Thin-walled aluminum die-cast member and its manufacturing method

Abstract

To provide an aluminum thin die-casting member made of pure aluminum having high heat conductivity or an aluminum alloy including a little amount of chemical elements other than aluminum, and having a thin shape with little inclination and great height, so that it is lightweight and has excellent heat radiation performance and is suitably used for heat sinks and the like, and a manufacturing method therefor.SOLUTION: A die-casting member is made of pure aluminum or an aluminum alloy containing 97 mass% or more of aluminum and has a fin shape, wherein a tip thickness of the thin shape is 1 mm or less, its height is 20 mm or more to 70 mm or less, and its inclination is 1° or less. There is also provided a manufacturing method therefor.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a thin-walled die-cast aluminum member made of pure aluminum or an aluminum alloy containing 97% by mass or more of aluminum, and suitable for use as a heat sink or the like, and to a method for manufacturing the thin-walled die-cast aluminum member by die casting. [Background technology]

[0002] Heat sinks with heat dissipation fins are installed in contact with electrical and electronic appliances, such as automotive laser headlamps, high-power LEDs, and electrical equipment, to dissipate heat generated from the appliances. In recent years, heat sinks have become larger to accommodate the increased heat generated by the higher performance of the appliances. However, to prevent the increased weight and cost of the heat sinks due to the larger size, there is a strong demand for lighter and more compact heat sinks with improved heat dissipation performance.

[0003] Therefore, efforts are being made to reduce the weight of heat sinks and improve their heat dissipation performance by using lightweight materials with good thermal conductivity, increasing the fin area (fin height), thinning the fins, etc. Furthermore, because manufacturing heat sinks using cutting or casting methods results in high manufacturing costs, efforts are being made to use die casting, which is a relatively easy way to reduce manufacturing costs.

[0004] Aluminum and its alloys are lightweight materials with good thermal conductivity and are widely known as materials for forming heat sinks. However, pure aluminum has poor fluidity and is prone to severe seizure on molds, making its application to die casting technically difficult. Therefore, aluminum alloys containing silicon and copper have been proposed as materials that solve these problems, and are disclosed in Japanese Patent No. 5301750 (Patent Document 2) and Japanese Patent No. 5937223 (Patent Document 1), among others. Among these, the ADC12 alloy, an Al-Si-Cu alloy containing approximately 10% Si, is widely used due to its excellent fluidity in die casting.

[0005] However, even with ADC12 alloy, it is difficult to produce thin-walled die-cast components with a thickness of 1 mm or less, and there are limitations to the production of heat sinks that have a fin tip thickness of 1 mm or less and that combine lightweight and high heat dissipation performance using die-casting with existing aluminum alloys. Furthermore, aluminum alloys such as ADC12 have a lower thermal conductivity than pure aluminum. For example, the thermal conductivity of ADC12 is 96 W / (m·k), while that of pure aluminum is 230 W / (m·k), which is approximately 2.5 times higher. Therefore, in order to achieve both lightweight and high heat dissipation performance, there was a demand for a thin-walled die-cast component (heat sink) made of pure aluminum with a fin tip thickness of 1 mm or less.

[0006] As a result of the inventor's investigation into die-casting of pure aluminum, Non-Patent Document 1 discloses a heat sink with thin fins with a tip thickness of 0.5 mm, but does not describe the fin draft angle (hereinafter simply referred to as "gradient"). The industry standard for fin gradient is 1.5° or greater. Therefore, there has been a need to develop a method for manufacturing thin-walled die-cast components made of pure aluminum with a tip thickness of 1 mm or less, a gradient of preferably 1° or less, and a thin shape (such as fins) that is tall (and therefore has a large heat dissipation area), and that can be easily released from the mold. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5937223 [Patent Document 2] Patent No. 5301750 [Non-patent literature]

[0008] [Non-Patent Document 1] Shinjiro Imamura, Hiroshi Fuse, Toshio Haga, "Pure Aluminum Die Casting", Proceedings of the 27th Japan Society of Mechanical Engineers Conference on Machine Materials and Materials Processing Technology, p. 10, (November 20, 2019) Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a thin-walled aluminum die-cast member that is made of pure aluminum having high thermal conductivity or an aluminum alloy containing only small amounts of elements other than aluminum, has a thin-walled shape with a small surface gradient and a high height, such as a heat sink fin, and is therefore lightweight and has excellent heat dissipation performance, making it suitable for use in heat sinks and the like.

[0010] Another object of the present invention is to provide a method for producing thin-walled die-cast aluminum parts, which can stably produce the above-mentioned thin-walled die-cast aluminum parts and which also allows the produced die-cast parts to be easily released from the mold. [Means for solving the problem]

[0011] As a result of extensive investigations to solve the above problems, the present inventors have found that If a molten metal of pure aluminum or an aluminum alloy containing 97% by mass or more of aluminum is injected and pressurized into a mold while maintaining the mold at a temperature of 0°C or more and 100°C or less, and if the temperature of the molten metal poured into the injection sleeve (hereinafter referred to as the "pouring temperature") is adjusted so that the temperature of the molten metal at the start of injection into the mold (hereinafter referred to as the "injection temperature") is equal to or higher than the liquidus temperature of the pure aluminum or aluminum alloy and equal to or lower than the liquidus temperature + 100°C, then: It was found that the die-cast material fills well into the mold, and can be used to mold thin-walled shapes, such as heat sink fins, with a tip thickness of 1 mm or less, a height of 20 mm to 70 mm, and a slope of 1° or less.It was also found that the molded die-cast material does not stick to the mold and is easy to release from the mold.

[0012] Conventionally, it was believed that a mold temperature of 150°C or higher, specifically the mold cavity surface temperature, was required for good filling of thin-walled shapes by die casting. However, the inventors discovered that, in the case of pure aluminum, lowering the mold temperature to 100°C or lower actually improves filling. Furthermore, the inventors discovered that by adjusting the pouring temperature within a predetermined range and the injection temperature within a predetermined range, the molten metal can be sufficiently filled into the mold cavity, even in molds that can accommodate thin-walled shapes with a tip thickness of 1 mm or less, a height of 20 mm to 70 mm, and a slope of 1° or less, and the molded product can be easily released from the mold. This finding led to the completion of the present invention. The inventors have now obtained a die-cast component made of pure aluminum or an aluminum alloy containing 97% or more by mass of aluminum with only traces of elements other than aluminum, i.e., a lightweight, highly thermally conductive material, having the above-mentioned thin-walled shape, which is lightweight and has excellent heat dissipation performance when used as a heat sink. That is, the above-mentioned problems of the present invention are solved by the configurations disclosed below.

[0013] The first disclosure is a die-cast aluminum component made of pure aluminum or an aluminum alloy containing 97% or more by mass of aluminum, and having a thin-walled shape, characterized in that the thin-walled shape has a tip thickness of 1 mm or less, a height of 20 mm or more and 70 mm or less, and a slope of 1° or less.

[0014] As a preferred embodiment of the first disclosure, there is provided a thin-walled aluminum die-cast member having the following features in addition to the features of the first disclosure. The height of the thin-walled shape is 40 mm or more. Pure aluminum or aluminum alloy containing 97% or more by mass of aluminum is pure aluminum or aluminum alloy containing 99% or more by mass of aluminum. A heat sink, wherein the thin-walled shapes are fins of the heat sink.

[0015] The second disclosure is a method for manufacturing the thin-walled die-cast aluminum member of the first disclosure. The thin-walled die-cast aluminum member of the first disclosure can be manufactured by the method of the second disclosure. That is, This is a method for producing a thin-walled die-cast member made of pure aluminum or an aluminum alloy containing 97% or more by mass of aluminum, the method comprising the steps of: pouring molten pure aluminum or aluminum alloy into the injection sleeve of an injection device provided outside a melting furnace or within the molten metal in the melting furnace; injecting and filling the molten metal by the injection device into a mold for forming the thin-walled shape while maintaining the temperature of the mold at 0°C or higher and 100°C or lower; and pressurizing the mold after filling is complete; and adjusting the temperature of the molten metal when poured into the injection sleeve so that the temperature of the molten metal when injected into the mold is above the liquidus temperature of the pure aluminum or aluminum alloy but not higher than the liquidus temperature + 100°C.

[0016] As a preferred embodiment of the second disclosure, there is provided a method for manufacturing a thin-walled die-cast aluminum member having the following features in addition to the features of the second disclosure. The die for molding the thin-walled shape has a tip thickness of 1 mm or less, a height of 20 mm or more and 70 mm or less, and a slope of 1° or less. The pressure applied after the completion of filling (hereinafter referred to as "casting pressure") is 25 MPa or more and 75 MPa or less. The speed of the injection plunger used by the injection device to inject and fill the molten metal into the mold (hereinafter referred to as "injection speed") is 0.1 m / s or more and 2.5 m / s or less. [Effects of the Invention]

[0017] According to the configuration of the first disclosure, a thin-walled die-cast aluminum member is provided that is lightweight and exhibits excellent heat dissipation performance when used as a heat sink or the like. According to the configuration of the second disclosure, a method is provided for stably and easily manufacturing the thin-walled aluminum die-cast member of the first disclosure. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a perspective view showing an example of a heat sink that is a thin-walled aluminum die-cast member according to the first disclosure. FIG. [Figure 2] 1 is a cross-sectional view showing an example of a heat sink that is a thin-walled aluminum die-cast member according to the first disclosure. [Figure 3] FIG. 1 is a schematic cross-sectional view showing an injection device and a mold in cold chamber die casting. [Figure 4] FIG. 1 is a schematic cross-sectional view showing an injection device and a mold in hot chamber die casting. [Figure 5] 1 shows photographs of molded bodies obtained in Examples 2, 4, 5 and 6 and Comparative Examples 1, 4 and 7. [Figure 6] 1 is a graph showing the relationship between pouring temperature and injection temperature. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments for carrying out the present invention will be described in more detail, but the scope of the present invention is not limited to the following embodiments.

[0020] The thin-walled aluminum die-cast member of the first disclosure is The material forming the member is made of pure aluminum or an aluminum alloy containing 97% by mass or more of aluminum; A die-cast member having a thin wall shape; The thin-walled shape has a tip thickness of 1 mm or less, a height of 20 mm or more and 70 mm or less, and a slope of 1° or less. It is characterized by:

[0021] Fig. 1 is a perspective view showing an example of a heat sink, which is an example of the thin-walled aluminum die-cast member of the first disclosure, and Fig. 2 is a cross-sectional view taken along the line AA in Fig. 1. In Figs. 1 and 2, 1 represents the heat sink, 2 represents the fins, and 3 represents the base. 4 represents the tip of the fin, and S (mm) represents its thickness. T (mm) represents the height of the fin (the length from the bottom of the fin 2, i.e., the joint with the base 3, to the tip 4), and V (°) represents the angle of the slope of the surface of the fin 2 (the angle between the surface of the fin 2 and a plane perpendicular to the base 3: i.e., the slope; hereinafter, this may be referred to simply as "slope").

[0022] (Materials that form the components) The material for forming the thin-walled die-cast aluminum component of the first disclosure is characterized by containing 97 to 100 mass% aluminum. That is, the material contains 3 mass% or less of components other than aluminum, and pure aluminum made from inexpensive recycled materials can also be used as this material. Therefore, it is a lightweight material with high thermal conductivity, and can be used to form thin-walled die-cast aluminum components, such as heat sinks, that are lightweight and have excellent heat dissipation performance. Pure aluminum containing nearly 100% aluminum by mass and aluminum alloys containing high-purity aluminum have traditionally been thought to be difficult to produce thin-walled die-cast components from, due to their poor fluidity and severe seizure to dies. However, the present inventors have discovered that thin-walled die-cast components can also be produced from these materials under the conditions described below.

[0023] More preferably, the material contains 99% or more by mass of aluminum, i.e., the material contains 1% or less by mass of components other than aluminum. Using these materials can further reduce the weight of the part and / or improve its heat dissipation performance. Furthermore, the higher the purity of the aluminum, the shorter the contact time with the mold, which reduces heat transfer to the mold due to the peeling phenomenon and improves the flow of the molten metal. Therefore, it is preferable for achieving thinner walls. Components other than aluminum that may be contained in the material forming the aluminum thin-walled die-cast part of the first disclosure include impurities that are inevitably contained in aluminum, such as silicon (Si), copper (Cu), magnesium (Mg), nickel (Ni), zinc (Zn), iron (Fe), manganese (Mn), beryllium (Be), phosphorus (P), sodium (Na), and strontium (Sr). One or more elements selected from the group consisting of these elements may be contained as impurities in the material forming the aluminum thin-walled die-cast part of the first disclosure, for example, to improve the properties of the part, provided that the total content is within the range of the content of the components other than aluminum and does not impair the spirit of the present invention.

[0024] Examples of components other than aluminum that may be contained in the material forming the thin-walled aluminum die-cast member of the first disclosure are shown below. Iron (Fe): If the Fe content exceeds 1.0 mass%, it may form intermetallic compounds such as Al-Fe and Al-Fe-Si, and may also cause metallic hard spots. Therefore, the content should preferably be 1.0 mass% or less. Silicon (Si): May cause the anodic oxide film to become non-uniform. The Si content should preferably be 1.0 mass% or less. Copper (Cu): If the Cu content exceeds 1.0 mass %, problems such as a decrease in corrosion resistance may occur, so it is preferable that the Cu content be 1.0 mass % or less. Magnesium (Mg): Mg may have the effect of improving the corrosion resistance of thin-walled die-cast aluminum components after molding. However, the content should preferably be 1.0 mass% or less. Even if trace amounts of zinc (Zn), manganese (Mn), nickel (Ni), titanium (Ti), and other impurities are contained, the intended effect of the present invention can be obtained. However, as the number and content of these elements, known as impurities, increases, there is a possibility that the heat dissipation performance will decrease in applications such as heat sinks. Therefore, it is preferable that the content of each element be 0.2 mass% or less.

[0025] (shape of components, etc.) The thin-walled die-cast aluminum component of the first disclosure is a component formed by die-casting, and is characterized by having a plurality of thin-walled shapes. In Figures 1 and 2, if the thin-walled die-cast aluminum component is a heat sink, the thin-walled shapes represented by 2 are its fins, which serve as the main heat dissipation portion.

[0026] (Thin-walled shape size) When the component is a heat sink, its heat dissipation performance is almost proportional to the total surface area of ​​the thin-walled fins, which are the heat dissipation parts. Therefore, when the component is a heat sink, it is desirable to have a large number of fins, and for each fin to have a large surface area, i.e., a high fin. Furthermore, to reduce the weight of thin-walled aluminum die-cast components (e.g., heat sinks), it is desirable for the thin-walled shape (e.g., fins) to be thin and have a small gradient. If the thin-walled shape is thin and has a small gradient, the thickness of the part that is connected to the thin-walled base becomes small, making it possible to thin the fins and reduce their weight.

[0027] In the thin-walled aluminum die-cast member of the first disclosure, the tip thickness of the thin-walled shape is 1 mm or less, and the slope of the thin-walled shape is 1° or less. As a result, the thickness of the part of the thin-walled shape that is connected to the base can also be reduced. Because the thickness of each thin-walled shape is reduced, it also contributes to weight reduction, and the heat dissipation performance (heat dissipation amount) relative to the weight of the thin-walled shape can be improved. The height of the thin-walled shape is 20 mm or more. As a result, the surface area of ​​the thin-walled shape is increased, improving heat dissipation performance. To obtain even better heat dissipation performance, the height of the thin-walled shape is preferably 40 mm or more. On the other hand, the height of the thin-walled shape is 70 mm or less. When using the above material to form a thin-walled shape with a tip thickness of 1 mm or less and a gradient of 1° or less by die casting, making the height of the thin-walled shape greater than 70 mm (when the gradient is 1° or less) makes it difficult to manufacture by die casting from the standpoint of fluidity, because the temperature difference between the liquidus temperature and solidus temperature of pure aluminum or molten metal mainly composed of aluminum is 5°C or less and the time it takes for the temperature to drop from the molten state to the solid state is short.

[0028] The thin-walled aluminum die-cast member of the first disclosure is made of a lightweight material with high thermal conductivity and has a thin shape with a large surface area, making it suitable for use in components where excellent heat dissipation performance is desired, particularly as a heat sink for removing heat from heat-generating electrical appliances and electronic and electrical equipment.

[0029] The second disclosure is a method for manufacturing a die-cast member having a thin wall shape and made of pure aluminum or an aluminum alloy containing 97% by mass or more of aluminum. Its features are as follows: - Die casting is performed by injecting and pressurizing molten aluminum or aluminum alloy containing 97% or more by mass of aluminum. The injection is performed by an injection device into a cavity in a mold for molding a thin-walled shape, the cavity having a shape corresponding to the thin-walled shape; - adjusting the pouring temperature so that the temperature when the molten metal is injected into the mold, i.e., the injection temperature, is equal to or higher than the liquidus temperature of the pure aluminum or aluminum alloy and equal to or lower than the liquidus temperature + 100°C; The injection molding of the molten metal is carried out while the mold is kept at a temperature of 0°C or higher and 100°C or lower; is.

[0030] These features enable the molten metal of pure aluminum or aluminum alloy containing 97% by mass or more of aluminum to flow sufficiently to the portion of the cavity corresponding to the tip of the thin-walled shape (i.e., to the portion of the narrow cavity farthest from the molten metal inlet), even if the mold has a cavity corresponding to a thin-walled shape with a tip thickness of 1 mm or less, a height of 20 mm to 70 mm, and a slope of 1° or less. Therefore, the manufacturing method of the second disclosure enables the stable production of the thin-walled aluminum die-cast member of the first disclosure.

[0031] It was previously thought that it would be difficult to fill the entire narrow cavity of a mold with pure aluminum or aluminum-based molten metal, even when high-speed, high-pressure injection was used. However, the inventors have discovered that, as will be described later, by adjusting the temperature of the molten metal during injection and the temperature of the mold within a predetermined range, it is possible to sufficiently fill the entire narrow cavity (from the molten metal inlet to the furthest tip) with molten metal, and form a thin-walled shape with a tip thickness of 1.0 mm or less, made of pure aluminum or an aluminum-based alloy with high thermal conductivity.

[0032] Furthermore, conventional die-casting processes tend to cause mold release problems for compacts made of aluminum or its alloys, making them difficult to remove from the mold after molding. To improve mold release, expensive powder release agents, oil-based release agents, or emulsion-type high-temperature special release agents must be applied to the mold cavity surface. Because demolding and removal are particularly difficult when the gradient of the surface of the thin-walled part being molded is small, it was considered difficult to achieve a gradient of less than 1.5°, the guideline established by the Japan Die Casting Association. In particular, pure aluminum, which has good contact (wettability) between the mold and the compact, adheres strongly to the mold, making demolding difficult. Therefore, a gradient of at least 2° was considered necessary. However, the inventors have discovered that, as will be described later, by adjusting the injection temperature (pouring temperature) and mold temperature within a predetermined range, a molded body made of pure aluminum or an aluminum-based alloy obtained by die casting can be easily released from the mold, even when the gradient of the thin-walled shape is 1° or less. As a result, it is possible to use an inexpensive emulsion-type water-soluble mold release agent as the mold release agent to be applied to the inner surface of the cavity, or it is no longer necessary to apply a mold release agent, thereby achieving the effect of reducing manufacturing costs.

[0033] (injection material) In the manufacturing method disclosed in the second disclosure, the material injected into the mold is molten pure aluminum or aluminum alloy containing 97% or more by mass of aluminum. As mentioned above, this material has previously been considered difficult to apply to the production of thin-walled components by die casting because of problems such as the small difference between its liquidus and solidus temperatures, the rapid temperature drop from the molten state to the solid state, poor fluidity, and severe seizure to the mold. However, the manufacturing method disclosed in the second disclosure makes this application possible. As a result, it is now possible to manufacture thin-walled die-cast components made of a material with high thermal conductivity, like the thin-walled die-cast components disclosed in the first disclosure.

[0034] (Mold) The mold into which the molten metal is injected is a mold for molding a thin-walled shape. That is, a mold having a plurality of narrowly spaced cavities corresponding to the respective thin-walled shapes within the cavity is used. In particular, the manufacturing method of the second disclosure can be applied even when the mold has cavities corresponding to the thin-walled shapes with a tip thickness of 1 mm or less, a height of 20 mm to 70 mm, and a slope of 1° or less, and this mold can be used to manufacture the thin-walled aluminum die-cast member of the first disclosure.

[0035] (Pouring temperature, injection temperature) In the manufacturing method disclosed in the second aspect, the pouring temperature is adjusted so that the injection temperature is equal to or higher than the liquidus temperature of pure aluminum or an aluminum alloy containing 97% or more by mass of aluminum, and equal to or lower than the liquidus temperature + 100°C. In the case of pure aluminum, the liquidus temperature is 660°C, the melting point of aluminum, so the injection temperature is in the range of 660°C or higher and 760°C or lower. In the case of cold chamber die casting, in which the injection unit is installed outside the melting furnace, the temperature of the molten metal poured into the injection sleeve of the injection unit drops before being injected into the mold, as is clear from the relationship shown in Figure 6 (Reference Example), so the pouring temperature is adjusted to a temperature range higher than the injection temperature. In the injection unit used in the cold chamber die casting of the Examples described below, the temperature drops by 35 to 70°C, so the pouring temperature is in the range of 695 to 830°C.

[0036] If the injection temperature is below the liquidus temperature, the molten metal will begin to solidify, reducing its fluidity and making it difficult to fully fill the cavity of the mold that can accommodate tall fins. On the other hand, if the injection temperature exceeds the liquidus temperature + 100°C, and the fin slope is small, the molded body will have good contact with the mold (wettability) and will be difficult to release from the mold, making it difficult to produce thin-walled aluminum die-cast parts with a fin slope of 1° or less. The injection temperature is preferably the liquidus temperature of pure aluminum or an aluminum alloy containing 97% by mass or more of aluminum + 20°C or more and the liquidus temperature + 80°C or less. Within this range, it is possible to sufficiently fill the cavity of a mold that can accommodate taller fins, and the molded body can be easily released from the mold.

[0037] (mold temperature) The manufacturing method disclosed in the second embodiment is characterized in that injection molding is carried out while maintaining the mold cavity surface temperature (hereinafter sometimes referred to as "mold temperature") at a temperature between 0°C and 100°C (the mold is cooled if necessary). This characteristic makes it possible to sufficiently fill even mold cavities that accommodate tall fins, and also makes it easy to release the molded product from the mold.

[0038] If the mold temperature exceeds 100°C, it becomes difficult to sufficiently fill the cavity of a mold that accommodates tall fins. Furthermore, the molded body's releasability from the mold decreases, making demolding difficult. Conventionally, a higher mold temperature was considered preferable for filling the cavity because it prevented the molten metal in the mold from dropping, maintained its molten state, and improved its fluidity. However, the inventors discovered that, in the case of pure aluminum, cooling the mold temperature to below 100°C improved the fluidity of the molten metal. When the mold temperature is cooled, the surface of the molten metal that comes into contact with the cavity interior (the inner surface of the cavity) cools and shrinks, creating a gap between the cavity interior and the molten metal. This suppresses heat transfer from the molten metal to the mold, maintaining the temperature of the interior of the molten metal (parts other than the surface), thereby maintaining high fluidity. Furthermore, the creation of a gap between the cavity interior and the molten metal (between the molded body) is thought to prevent seizure between the molded body and the mold, making it easier to demold the molded body. Furthermore, pure aluminum has a larger solidification shrinkage rate (6.6% for pure aluminum, 3.7% for ADC12) than aluminum such as ADC12, which is commonly used in conventional die casting. As a result, shrinkage due to cooling makes it more likely that gaps will form between the inner surface of the cavity and the molten metal. This suppresses the transfer of heat from the molten metal to the mold and seizure between the molded body and the mold more than in the case of ADC12, etc., and is thought to be why the unexpected effects described above were achieved.

[0039] During injection molding, the mold is usually cooled by water. Therefore, the mold temperature is 0°C or higher. The mold temperature is preferably 20°C or higher and 100°C or lower. By keeping the mold temperature within this range, the molten metal can be more reliably filled into the cavity, and the molded body can be more easily released from the mold.

[0040] (Casting pressure) In the second disclosed manufacturing method, the casting pressure, i.e., the pressure applied to the molten metal after it has been filled into the mold, is preferably 25 MPa or more and 75 MPa or less. A pressure within this range allows sufficient filling even in mold cavities designed for tall, thin shapes. If the pressure is less than 25 MPa, the molten metal is not pressurized enough, making it difficult to sufficiently fill mold cavities designed for tall, thin shapes, resulting in an underfilled state and the occurrence of casting defects such as cold shuts and creases. The casting pressure applied to the molten metal after the molten metal has been completely filled into the mold is preferably 30 MPa or more and 75 MPa or less. By setting the pressure within this range, the molten metal can be more reliably filled into the cavity and the mold can be more easily released from the mold.

[0041] (molten metal injection speed) The speed of the injection plunger that fills the mold with molten metal, i.e., the injection speed, is preferably 0.1 m / s or more and 2.5 m / s or less. By keeping the injection speed within this range, it is possible to produce the thin-walled aluminum die-cast member of the first disclosure at a casting pressure of 25 MPa or more and 75 MPa or less. Furthermore, with injection speeds and casting pressures within this range, it is not necessary to use a special mold filling method known as a short-time filling method using expensive equipment, such as a high-speed injection type ultra-high-speed servo machine or an equivalent device capable of achieving an injection speed of 5 m / s or more. Instead, the thin-walled aluminum die-cast member of the first disclosure can be produced using currently widely used injection equipment. The speed of the injection plunger that fills the molten metal into the mold, i.e., the injection speed, is more preferably 0.2 m / s or more and 2.0 m / s or less.

[0042] (injection device) The injection device used in the manufacturing method of the second disclosure may be provided outside the melting furnace (cold chamber type) or may be provided in the molten metal of the melting furnace (hot chamber type). Figure 3 is a schematic cross-sectional view showing the injection device and mold in cold chamber type die casting, and Figure 4 is a schematic cross-sectional view showing the injection device and mold in hot chamber type die casting.

[0043] (1) In cold chamber die casting, molten metal at a temperature higher than the liquidus temperature of the material (pure aluminum or aluminum alloy containing 97% or more by mass of aluminum) forming the part is prepared in a melting furnace or the like, and the molten metal is poured into an injection sleeve by a molten metal supply means such as a ladle as shown in Figure 3. The molten metal in the injection sleeve is then injected into a mold by a pressure means such as an injection plunger. The mold is equipped with mold cooling means, and the mold cavity surface is cooled during the molding process so that it falls within the aforementioned "mold temperature" range. As the die casting machine having the injection sleeve, pressure means, mold, etc., die casting machines manufactured by, for example, Shibaura Machinery, Toyo Machinery & Metals, Ube Machinery, Hishinuma Machinery, etc. can be used.

[0044] (2) In hot chamber die casting, an injection device is installed adjacent to a melting furnace, and the molten metal in an injection section (a device for injecting the molten metal into a mold) that is submerged and heated in the molten metal melted by the melting furnace is pressurized by a pressurizing means and injected into the mold. For example, in the injection device shown schematically in Figure 4, the molten metal extruded from the injection section passes through a gooseneck (inlet pipe) and is injected into the mold. An injection device in which injection into the mold is performed within the molten metal may also be used. In both cold chamber die casting and hot chamber die casting, the temperature of the molten metal prepared in a melting furnace or the like is adjusted so that the temperature of the molten metal when it is poured into the injection machine and then injected into the mold, i.e., the injection temperature, is equal to or higher than the liquidus temperature of the material of the molten metal and equal to or lower than the liquidus temperature + 100°C.

[0045] (mold release agent) To facilitate release of the molded body from the mold after molding, a release agent may be applied to the inner surface of the mold cavity. According to the manufacturing method of the second disclosure, adhesion of the molded body to the mold during molding is suppressed, making application of a release agent unnecessary in many cases. Even when a release agent is applied, it is not necessary to use expensive release agents used in conventional technology (e.g., citrus oil-based release agents or powder release agents such as Astrolube manufactured by MORESCO Corporation) or release agents diluted with kerosene or other volatile oils, which are conventionally used in thick-walled pure aluminum die-castings such as motor rotors. Instead, inexpensive water-soluble release agents can be used. Examples of such inexpensive water-soluble release agents include Graface NS-660, Graface GL-1000, and Graface TX-5700 manufactured by MORESCO Corporation. Such release agents can be used, for example, by diluting an emulsion with water, forming a fine mist, and spraying it onto the mold surface before each injection.

[0046] In the manufacturing method of the second disclosure, conditions other than those mentioned above, such as the injection pressure time, are the same as those normally used in die casting of aluminum alloys. [Example]

[0047] The present invention will be described below with reference to examples, but the scope of the present invention is not limited to these examples.

[0048] Examples 1 to 12, Comparative Examples 1 to 12 (Experimental Method) The aluminum material under investigation and the composition shown in Tables 2-3 were melted in a melting furnace to produce molten metal. The molten metal was then poured into the sleeve of a cold-chamber die-casting machine (Hishinuma Machinery Co., Ltd., product name HC-50F) as shown in Figure 3 at a temperature adjusted to the temperature shown in the "Pouring Temperature" column in Tables 2-3. The molten metal was then injected into a mold with a cavity (molding portion) of the shape and size shown in the "Mold Type" column in Tables 2-3 using an injection device such as a plunger. The pressure shown in the "Casting Pressure" column in Tables 2-3 was applied to the molten metal in the mold to perform molding (die casting). During molding, the mold was cooled as necessary to adjust the mold surface temperature to the temperature shown in the "Mold Temperature" column in Tables 2-3. The injection speed of the molten metal during injection is shown in the "Injection Speed" column in Tables 2-3.

[0049] (Estimated injection temperature) The relationship between the pouring temperature (temperature of the molten metal when poured into the sleeve) and the injection temperature (temperature at the mold inlet) when molding (die casting) was performed in the same manner using the cold chamber die casting machine used in the above (experimental method) was measured at pouring temperatures of 790°C and 720°C. The relationship between the pouring temperature and the injection temperature obtained from the measurements is shown in Figure 6. The injection temperature estimated based on the pouring temperatures of each example and each comparative example and the graph in Figure 6 is shown in the column "(Assumed) Injection Temperature °C" in Tables 2 and 3.

[0050] (Materials to be considered) The materials shown in 1) to 4) below were used as materials to be examined in the above "Experimental Method." 1) Pure aluminum containing 99.7% by mass of aluminum (the amount of components other than Al is shown in Table 1. In the "Material" column of Table 2, this is listed as "Pure Aluminum 1.") 2) Pure aluminum containing 99.9% by mass of aluminum (the amount of components other than Al is shown in Table 1. In the "Material" column of Tables 2 and 3, this is listed as "Pure Aluminum 2.") 3) An aluminum alloy containing 97.7% by mass of aluminum obtained by adding 2.0% by mass of iron (Fe) to the pure aluminum of 1) above (referred to as "Aluminum Alloy 1" in the "Materials" column of Table 2). 4) Aluminum alloy with the composition shown as "4" ADC12" in Table 1 (in the "Materials" column of Table 3, it is listed as "ADC12").

[0051] [Table 1]

[0052] (Mold type: Cavity shape and size) The shape and size of the cavity corresponding to the fin formation of the mold used in the experiment are shown below. Mold 1 T: 50mm, S: 0.5mm, V: 0.5°, Number of fins: 6 Mold 2 T: 50mm, S: 0.5mm, V: 0.5°, Number of fins: 4 Mold 3 T: 35mm, S: 0.5mm, V: 0.5°, Number of fins: 4

[0053] [Evaluation method] After molding (die casting) according to the "experimental method," the molded body was removed from the mold, and the filling property (whether the molten metal filled the entire cavity) and the demolding property (whether there was a problem with demolding the molded body and whether part of the molded body remained in the cavity after removal) were evaluated according to the following criteria. Photographs of the molded bodies obtained in Examples 2, 4, 5, and 6 and Comparative Examples 1, 4, and 7 are shown in Figure 5. The "Photograph of molded body" column in Tables 2 and 3 indicates which of (a) to (g) in Figure 5 the photograph of the molded body obtained in each Example and Comparative Example corresponds to.

[0054] (Evaluation criteria for filling ability) Good: The molten metal filled the entire cavity, and a fin was obtained that matched the shape of the cavity. Defective: The molten metal does not fill the entire cavity, and the tip of the fin of the molded body is not formed, resulting in insufficient filling or poor flow of the molten metal, or casting defects such as creases, cold shuts, or blisters are found on the tip of the fin.

[0055] (Evaluation criteria for releasability) Good: The entire molded body is removed, and no adhesion (of any part of the molded body) is observed within the cavity. Defective: After removal, some of the molded body is found to be stuck inside the cavity. Also, there are cases where the aluminum has adhered to the mold due to burning, or where some of the formed fins remain in the mold cavity.

[0056] [Table 2]

[0057] [Table 3]

[0058] As is clear from the results shown in Table 2, in Examples 1 to 6, in which die casting was performed using pure aluminum or an aluminum alloy containing 97% by mass or more of aluminum and in which the injection temperature and mold temperature satisfied the characteristics of the manufacturing method of the second disclosure, both filling and demolding properties were evaluated as good. Furthermore, as shown in the photographs of Figures 5(a), (b), (c), and (g), no missing portions were observed on the tip side of the fins of the obtained molded body, and no casting defects such as molten iron wrinkles, cold shuts, or blisters were observed, resulting in a good molded body.

[0059] On the other hand, in Comparative Examples 1 to 4, which used pure aluminum but had a mold temperature that did not satisfy the characteristics of the manufacturing method of the second disclosure, both the filling property and the demolding property were poor. As shown in the photographs of Figures 5(d) and (f), in Comparative Examples 1 and 4, where the mold temperature was high, there were areas on the tip side of the fins of the obtained molded body where no molded body was formed (areas not filled with molten metal), and further, as shown in the photograph of Figure 5(f), in Comparative Example 4, the gate part was also found to be stuck to the mold. Furthermore, in Comparative Examples 5 to 7, which used aluminum alloy ADC12, a material other than aluminum containing 97% by mass or more of aluminum, both the filling property and the demolding property were poor (even though the injection temperature and mold temperature satisfied the characteristics of the manufacturing method of the second disclosure, as in Comparative Example 5). In Comparative Example 7, which used ADC12, a mold with a low fin height of 35 mm was used, but as shown in the photograph in Figure 5(e), there were areas on the tip side of the fins of the molded body where the molded body was not formed (areas not filled with molten metal), and a good molded body was not obtained.

[0060] From the results of the above examples and comparative examples, it is clear that in order to obtain the effects aimed at by the present invention, the mold temperature must be 100°C or less (since poor results were obtained in examples where the temperature exceeded 100°C). It is also shown that if the mold temperature is 100°C or less, the effects aimed at by the present invention can be obtained at an injection temperature of liquidus + 100°C or less. Furthermore, good results were obtained in Example 6, which used aluminum alloy 1 with an aluminum content of 97.7% by mass, so it is clear that good results can be obtained with any aluminum alloy with an aluminum content of 99.0% by mass or more.

[0061] In the examples and comparative examples, the casting pressure was 72 MPa and the injection speed was 1.6 m / s, which is lower than the casting pressure of 100 MPa to 150 MPa or more of a typical die-casting machine, and the high injection speed is low, and the mold fin height was only 50 mm.However, from the results under these conditions, it is fully predictable that good results will also be obtained with a casting pressure of 25 to 72 MPa, an injection speed of 0.1 to 2.5 m / s, and a mold fin height of 20 to 70 mm (especially 40 to 70 mm). Therefore, it can be said that the manufacturing method disclosed in the second disclosure can stably produce thin-walled aluminum die-cast components characterized by a thin-walled shape with a tip thickness of 1 mm or less, a height of 20 mm to 70 mm, and a slope of 1° or less. [Explanation of symbols]

[0062] 1 heat sink 2 Fins 3. Bass 4 Fin tip S Fin tip thickness (mm) T-fin height (mm) V-fin surface gradient (°)

Claims

1. 1. A method for producing a thin-walled die-cast member made of pure aluminum or an aluminum alloy containing 97% or more by mass of aluminum, the method comprising the steps of: pouring molten metal of the pure aluminum or aluminum alloy into an injection sleeve of an injection device provided outside a melting furnace or provided within the molten metal in the melting furnace; injecting and filling the molten metal by the injection device into a mold for molding a thin-walled shape having a tip thickness of 1 mm or less, a height of 20 mm to 70 mm and a gradient of 1° or less, while maintaining a temperature of the mold at 20°C to 100°C; and pressurizing the mold after completion of filling; and adjusting the temperature of the molten metal when poured into the injection sleeve so that the temperature of the molten metal when injected into the mold is equal to or higher than the liquidus temperature of the pure aluminum or aluminum alloy but not higher than the liquidus temperature + 100°C.

2. 2. The method for manufacturing a thin-walled aluminum die-cast member according to claim 1, wherein the pressure applied after the completion of filling is 25 MPa or more and 75 MPa or less.

3. 3. The method for manufacturing a thin-walled aluminum die-cast member according to claim 1, wherein the speed of the injection plunger that fills the molten metal from the injection device into the mold is 0.1 m / s or more and 2.5 m / s or less.

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