JP7804313B2 - Thin-walled aluminum die-cast member and its manufacturing method - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies. Website address: https://www.jst.go.jp/tt/fair/ij2020/exhibitor/un20200074.html Website posting date: September 28, 2020 Website address: https://us02web.zoom.us/j/87533946777 Conference name: "The 28th Mechanical Materials and Materials Processing Technology Symposium" (sponsored by: The Japan Society of Mechanical Engineers) Website posting date and time: November 19, 2020, 4:45 PM - 5:00 PM Website address: https://ynuacjpoffice365-my.sharepoint. com/:f:/g/personal/oikawa-risa-zm_ynu_ac_jp/El_r2itQs15Os34QBpB0lSMBInArQavGQ5h7VRrfSHffgw? e=5%3an9AhDu&at=9 Website posting date: November 18, 2020 Website posting address: https://doi.org/10.1299/jsmemp.2020.28.222 Website posting date: July 7, 2021 Website posting address: https://jfs.or. jp/tokusetsu1/ Meeting name: "The 177th National Conference of the Japan Foundry Engineering Society" (Organizer: Japan Foundry Engineering Society, Public Interest Incorporated Association) Website posting date and time: May 22, 2021, 11:25-11:45 Website posting address: https://jfs.or.jp/tokusetsu1/ Website posting date: May 7, 2021 Website posting address: https://www.mdpi.com/1996-1944/14/18/5372 (Publication name: Materials 2021, Vol. 14, No. 18, pp. 5372-15: Publisher: MDPI) Website posting date: September 17, 2021

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

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 by the appliance. In recent years, heat sinks have become larger to accommodate the increased heat generated by these appliances' higher performance. However, to prevent the increased weight and cost of larger heat sinks, there is a strong demand for lighter, more compact heat sinks with improved heat dissipation performance.

Therefore, methods are being considered to reduce the weight of heat sinks and improve heat dissipation performance by using lightweight materials with good thermal conductivity, increasing the fin area (fin height), and thinning the fins. Furthermore, because manufacturing heat sinks using cutting or casting methods is expensive, consideration is being given to using die-casting, which allows for relatively easy reductions in manufacturing costs.

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 it technically difficult to use in die casting. Therefore, aluminum alloys containing silicon and copper have been proposed as materials that solve these problems, and are disclosed in Patent No. 5301750 (Patent Document 2) and Patent No. 5937223 (Patent Document 1), among others. Among these, the ADC12 alloy, an Al-Si-Cu alloy containing around 10% Si, is widely used due to its excellent fluidity in die casting.

However, even with the 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 design with 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 has been 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.

As a result of the inventor's research 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 makes no mention of the fin draft angle (hereinafter simply referred to as "gradient"). The industry standard for fin gradient is 1.5° or greater. Therefore, there was 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 high, thin-walled shape (fins, etc.) with a large height (and therefore a large heat dissipation area), which also allows for easy release from the mold.

Patent No. 5937223 Patent No. 5301750

Shinjiro Imamura, Hiroshi Fuse, Toshio Haga, "Pure Aluminum Die Casting", Proceedings of the 27th JSME Conference on Machine Materials and Materials Processing Technology, p. 10, (November 20, 2019)

The objective of the present invention is to provide a thin-walled aluminum die-cast component made of pure aluminum with high thermal conductivity or an aluminum alloy containing only traces of elements other than aluminum, with a thin, high profile with a small surface gradient, such as a heat sink fin, that is lightweight and has excellent heat dissipation performance, making it suitable for use in heat sinks and the like.

An additional objective of the present invention is to provide a method for manufacturing thin-walled aluminum die-cast parts that can stably produce the above-mentioned thin-walled aluminum die-cast parts and that allows the manufactured die-cast parts to be easily released from the mold.

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 a 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 gradient of 1° or less. It was also found that the molded die-cast material did not stick to the mold and was easy to release from the mold.

Conventionally, when filling a thin-walled shape by die casting, it was thought that a mold temperature, specifically a mold cavity surface temperature of 150°C or higher, was necessary to ensure good filling. However, the present inventors discovered that, in the case of pure aluminum, lowering the mold temperature to 100°C or lower actually improves filling. Furthermore, 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 a mold that can accommodate 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, and the molded product can be easily released from the mold. This finding led to the completion of the present invention. Furthermore, a die-cast component was obtained that has the above-mentioned thin-walled shape, is lightweight, and has excellent heat dissipation performance when used as a heat sink, and is 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.
That is, the above-mentioned problems of the present invention are solved by the configurations disclosed below.

The first disclosure is a thin-walled die-cast aluminum component made of pure aluminum or an aluminum alloy containing 97% or more by mass of aluminum, characterized in that the thin-walled component 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.

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.
The 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, and the thin-walled features are fins of the heat sink.

The second disclosure relates to 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 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 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 equal to or higher than the liquidus temperature of the pure aluminum or aluminum alloy but not higher than the liquidus temperature + 100°C.

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 mold for molding the thin-walled shape is a mold for molding a thin-walled shape having 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.

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.

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

The following describes in more detail the embodiments of the present invention, but the scope of the present invention is not limited to the following embodiments.

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

Figure 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 Figure 2 is a cross-sectional view taken along the line A-A in Figure 1. In Figures 1 and 2, 1 represents the heat sink, 2 represents the fin, 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, sometimes simply referred to as "slope").

(Materials forming 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. In other words, 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% by mass of aluminum 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.

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. The use of these materials can further reduce the weight of the component 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, this 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 other 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, for the purpose of improving the properties of the part, as long as the total content is within the range of the content of the components other than aluminum and within a range that does not impair the spirit of the present invention.

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 is preferably 1.0 mass% or less.
Silicon (Si): Silicon may cause the anodized film to become non-uniform. The Si content is preferably 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 the Cu content is preferably 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 of Mg is preferably 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 types and contents of these elements, which are called impurities, increase, there is a possibility that heat dissipation performance will decrease in applications such as heat sinks. Therefore, it is preferable that the contents of these elements be 0.2 mass% or less.

(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.

(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.

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 portion 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 improves the heat dissipation performance (heat dissipation amount) relative to the weight of the thin-walled shape.
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. In order 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, if the height of the thin-walled shape exceeds 70 mm (if the gradient is 1° or less), pure aluminum or molten metal mainly composed of aluminum has a temperature difference between the liquidus temperature and solidus temperature of 5° C. or less and therefore the time required for the temperature to drop from the molten state to the solid state is short, making it difficult to manufacture by die casting from the standpoint of fluidity.

The thin-walled aluminum die-cast component of the first disclosure is formed from 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. In particular, it is suitable for use as a heat sink for removing heat from heat-generating electrical appliances, electronic devices, and electrical equipment.

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. The features of the method 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 the 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.

And because of these features, 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, the molten metal of pure aluminum or aluminum alloy containing 97% or more by mass of aluminum can be sufficiently flowed and filled up to the part of the cavity corresponding to the tip of the thin-walled shape (i.e., to the part of the narrow cavity farthest from the molten metal entrance). Therefore, the manufacturing method disclosed in the second disclosure enables the stable production of the thin-walled aluminum die-cast parts disclosed in the first disclosure.

Conventionally, it was 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 described below, by adjusting the temperature of the molten metal and the mold temperature during injection within a specified range, it is possible to sufficiently fill even a 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 from pure aluminum or an aluminum-based alloy with high thermal conductivity.

Furthermore, conventionally, molded articles made of aluminum or its alloys tend to stick to the mold during die casting, making them difficult to release and remove from the mold after molding. To improve mold releasability, it has been necessary to apply expensive powder release agents, oil-based release agents, or emulsion-type high-temperature special release agents to the mold cavity surface. In particular, when the surface gradient of the thin-walled shape being molded is small, mold release and removal become difficult. Therefore, it has been thought that it is difficult to make the gradient of the thin-walled shape smaller than the 1.5° guideline established by the Japan Die Casting Association. In particular, with pure aluminum, the contact (wettability) between the mold and the molded article is good, but adhesion to the mold is severe, resulting in poor mold releasability. Therefore, it has been thought that a gradient of at least 2° is 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.

(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 a short temperature drop from the molten state to the solid state due to the small difference between its liquidus and solidus temperatures, 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 produce 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.

(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 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.

(Pouring temperature, injection temperature)
In the manufacturing method disclosed in the second embodiment, 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 mass% or more 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, which is 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 located outside the melting furnace, the temperature of the molten metal poured into the injection sleeve of the injection unit drops before it is injected into the mold, as is clear from the relationship shown in Figure 6 (Reference Example), so the pouring temperature is adjusted to a 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.

If the injection temperature is below the liquidus temperature, the molten metal begins to solidify, reducing fluidity and making it difficult to fully fill the cavity of a mold that accommodates taller fins. On the other hand, if the injection temperature exceeds the liquidus temperature + 100°C, if the fin gradient is small, the molded body will have good contact with the mold (wettability) but will be difficult to release from the mold, making it difficult to produce thin-walled aluminum die-cast parts with fin gradients of 1° or less. The injection temperature is preferably between + 20°C and + 80°C, both inclusive, of the liquidus temperature of pure aluminum or an aluminum alloy containing 97% or more by mass of aluminum. Within this range, it is possible to fully fill the cavity of a mold that accommodates taller fins, and the molded body will have good releasability from the mold, making demolding easier.

(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 of 0° C. or higher and 100° C. or lower (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.

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 present 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 (surface) of the molten metal that contacts 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 than aluminum such as ADC12, which has been widely used in conventional die casting (6.6% for pure aluminum, 3.7% for ADC12). As a result, gaps are more likely to form between the inner surface of the cavity and the molten metal due to shrinkage caused by cooling, and heat transfer from the molten metal to the mold and seizure between the molded body and the mold are more suppressed than in the case of ADC12, etc., which is thought to be why the unexpected effect described above was achieved.

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. Keeping the mold temperature within this range ensures that the molten metal can be filled into the cavity more reliably, and also makes it easier to release the molded body from the mold.

(Casting pressure)
In the manufacturing method disclosed in the second disclosure, the casting pressure, i.e., the pressure applied to the molten metal after the molten metal has been completely 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 that accommodate tall, thin shapes. If the pressure is less than 25 MPa, the molten metal is pressurized too little, making it difficult to sufficiently fill mold cavities that accommodate tall, thin shapes, resulting in an unfilled 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 to 75 MPa. By setting the pressure within this range, the molten metal can be more reliably filled into the cavity and the mold release properties can be improved.

(molten metal injection speed)
The speed of the injection plunger that fills the molten metal into the mold, i.e., the injection speed, is preferably 0.1 m/s or more and 2.5 m/s or less. By setting 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 called a short-time filling method using expensive equipment, such as a high-speed injection type ultra-high-speed servo machine or an equivalent device that can achieve 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.

(injection device)
The injection device used in the manufacturing method disclosed in the second embodiment may be provided outside the melting furnace (cold chamber type) or 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.

(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 shown in Figure 3. The molten metal in the injection sleeve is then injected into a mold by a pressurizing means such as an injection plunger. The mold is provided with mold cooling means, and the surface of the mold cavity 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.

(2) In hot chamber die casting, an injection device is provided 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 either cold chamber die casting or 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 an injection machine and then injected into a 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.

(Release agent)
A release agent may be applied to the inner surface of the mold cavity to facilitate release of the molded body from the mold after molding. 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.

In the manufacturing method disclosed in 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.

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

Examples 1 to 12, Comparative Examples 1 to 12
(Experimental Method)
The aluminum material below (the aluminum material under investigation) and the material with the composition shown in Tables 2-3 were melted in a melting furnace to produce a molten metal. The molten metal was then poured into the sleeve of a cold chamber die-casting machine (manufactured by 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 of Tables 2-3. The molten metal was then injected into a mold having a cavity (molding portion) with the shape and size shown in the "Mold Type" column of Tables 2-3 using an injection device such as a plunger. The pressure shown in the "Casting Pressure" column of 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 of Tables 2-3. The injection speed of the molten metal during injection is shown in the "Injection Speed" column of Tables 2-3.

(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 as a result of the measurements is shown in Figure 6. The injection temperature estimated based on the pouring temperatures of each Example and Comparative Example and the graph in Figure 6 is shown in the column "(Assumed) Injection Temperature °C" in Tables 2 and 3.

(Materials to be considered)
The materials shown in 1) to 4) below were used as materials to be investigated 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 referred to 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 having a composition shown as "4"ADC12" in Table 1 (described as "ADC12" in the "Material" column of Table 3).

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

[Evaluation method]
After molding (die casting) according to the "experimental method," the molded body was removed from the mold, and the filling property (evaluation of whether the molten metal filled the entire cavity) and the demolding property (evaluation of 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.

(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 molten metal flow, or casting defects such as molten metal wrinkles, cold shuts, and blisters are found on the tip of the fin.

(Evaluation criteria for releasability)
Good: The entire molded body is removed, and no adhesion (of any part of the molded body) is observed inside 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 some of the formed fins remain in the mold cavity.

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% or more by mass of aluminum and in which the injection temperature and mold temperature satisfied the characteristics of the manufacturing method described in the second disclosure, both filling and demolding properties were evaluated as good. Furthermore, as shown in the photographs in Figures 5(a), (b), (c), and (g), no missing portions were observed on the tip side of the fins of the resulting molded body, and no casting defects such as molten metal wrinkles, cold shuts, or blisters were observed, resulting in a good molded body.

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 described in the second disclosure, both the filling property and the demolding property were poor. As shown in the photographs in Figures 5(d) and (f), in Comparative Examples 1 and 4, in which the mold temperature was high, portions where no molded body was formed (portions not filled with molten metal) were observed on the tip side of the fins of the obtained molded body. Furthermore, as shown in the photograph in Figure 5(f), in Comparative Example 4, the gate portion was also observed to stick to the mold.
Furthermore, in Comparative Examples 5 to 7, which used aluminum alloy ADC12, a material other than an aluminum material 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 no molded body was formed (areas not filled with molten metal), and a good molded body was not obtained.

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, since good results were obtained in Example 6 using aluminum alloy 1 with an aluminum content of 97.7% by mass, it is clear that good results can be obtained with aluminum alloys with an aluminum content of 99.0% by mass or more.

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 a typical die-casting machine, which is 100 MPa to 150 MPa or more, 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 (particularly 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.

1 Heat sink 2 Fin 3 Base 4 Fin tip S Thickness of fin tip (mm)
T Fin height (mm)
V Fin surface gradient (°)

Claims (3)

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. 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. 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.