JP2025021981A - Manufacturing method of aluminum alloy castings - Google Patents

Abstract

The present invention provides a method for producing an aluminum alloy casting in which the decrease in ductility is suppressed and mechanical properties are excellent.
[Solution] A manufacturing method for aluminum alloy castings includes a casting process in which a molten Al-Si-Mg alloy material is solidified in a mold to obtain a casting material, a crystallization process in which the casting temperature of the casting material is lowered to 400°C or lower after solidification of the molten metal is complete, a solution treatment process in which the casting temperature of the casting material after the crystallization process is maintained at 450 to 550°C for 10 minutes or more, and a cooling process in which the casting material after the solution treatment process is cooled.
[Selected Figure] Figure 1

Description

The present invention relates to a method for manufacturing aluminum alloy castings.

In order to reduce the weight of automobiles, the body parts of automobiles are being replaced from iron-based materials to aluminum materials. Body parts using aluminum materials can be manufactured by various manufacturing methods, such as pressing, forging, and casting. These manufacturing methods are used according to the required product characteristics and product shape. Body parts are required to have high mechanical properties (e.g., strength and ductility) from the standpoint of safety and productivity. In order to obtain high mechanical properties, for example, aluminum alloy castings (Al alloy castings) using Al-Si-Mg alloys have been proposed.

Patent Document 1 discloses an aluminum alloy (Al alloy) for casting and an aluminum alloy casting (Al alloy casting) that contains, based on the total being 100 mass% (simply referred to as "%"), the remainder being Al, 5-8.5% Si, 0.35-0.7% Mg, 0.05-0.3% Ti, 0.05-0.4% Zr, and the sum of Ti and Zr: 0.2% or more, and further contains at least one of Sr: 0.003-0.05%, Na: 0.001-0.03%, and Sb: 0.001-0.2%. Patent Document 1 describes that when this Al alloy is used, even by gravity casting or low-pressure casting, a casting made of a cast structure in which primary crystals Al and eutectic Si are finely dispersed can be obtained, and that this casting has excellent strength as well as ductility and toughness, making it suitable for use in, for example, vehicle tire wheels.

JP 2017-171960 A

When manufacturing Al alloy castings, in order to achieve both strength and ductility, it is preferable to perform solution treatment after casting an Al-Si-Mg alloy, for example. However, depending on the conditions of the solution treatment, compounds containing alloying elements may crystallize at the grain boundaries in the cast structure. As a result of extensive research into the relationship between the compounds containing alloying elements crystallized at the grain boundaries and the ductility of Al alloy castings, the inventors have found that by reducing the Mg-based compounds crystallized at the grain boundaries, the decrease in ductility is suppressed and an Al alloy casting with excellent mechanical properties can be obtained.

The present invention was made to solve these problems, and aims to provide a method for manufacturing aluminum alloy castings that suppresses the decline in ductility and has excellent mechanical properties.

The manufacturing method of an aluminum alloy casting according to one embodiment includes a casting process in which a molten Al-Si-Mg alloy material is solidified in a mold to obtain a casting material, a crystallization process in which the temperature of the casting material is lowered to 400°C or lower after the molten metal has completely solidified, a solution treatment process in which the temperature of the casting material after the crystallization process is kept at 450 to 550°C for 10 minutes or more, and a cooling process in which the casting material after the solution treatment process is cooled.

The present invention provides a method for producing aluminum alloy castings that suppresses the decrease in ductility and has excellent mechanical properties.

1 is a flowchart showing a method for manufacturing an aluminum alloy casting according to a first embodiment. 2 is a graph showing the change in casting temperature over time in the method for producing the aluminum alloy casting shown in FIG. 1 . 1 shows an optical microscope image of the cast structure and an EPMA image of Mg element.

First embodiment
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiment. In addition, in order to clarify the description, the following description and drawings are appropriately simplified. In the following description, the same or equivalent elements are given the same reference numerals, and duplicate descriptions are omitted.

The manufacturing method of an aluminum alloy casting (Al alloy casting) according to this embodiment will be described with reference to Figures 1 and 2. The manufacturing method of an Al alloy casting according to this embodiment is a method for manufacturing an Al alloy casting from an Al-Si-Mg alloy material. Figure 1 is a flow chart showing the manufacturing method of an aluminum alloy casting according to the first embodiment. Figure 2 is a graph showing the change in casting temperature over time in the manufacturing method of an aluminum alloy casting shown in Figure 1.

As shown in FIG. 1, the method for producing an Al alloy casting according to this embodiment includes a casting process (step S1), a crystallization process (step S2), a solution treatment process (step S3), and a cooling process (step S4).

The casting process (step S1) is a casting process in which molten Al-Si-Mg alloy material is solidified in a mold to obtain a casting material. The casting process includes, for example, a filling process in which molten Al-Si-Mg alloy material is filled into a mold, and a solidification process in which the molten metal is solidified in the mold. As shown in FIG. 2, in the filling process, at time T0, molten metal heated to, for example, about 680°C is filled into the mold. In the solidification process, solidification of the molten metal is completed at time T1, when the casting temperature reaches, for example, about 560°C.

In this embodiment, the alloy composition of the Al-Si-Mg alloy is the mass ratio of each element when the entire Al-Si-Mg alloy is 100% by mass. In addition to Al, Si, and Mg, the Al-Si-Mg alloy material may optionally contain at least one element of, for example, Cu, Zn, Fe, and Mn. Since it has excellent mechanical properties such as strength and ductility (elongation), corrosion resistance, heat resistance, etc., the Al-Si-Mg alloy material is preferably AC4CH (JIS) or ADC3 (JIS). AC4CH is an Al-Si-Mg alloy containing Cu: ≦0.1% by mass, Si: 6.5 to 7.5% by mass, Mg: 0.25 to 0.45% by mass, Zn: ≦0.1% by mass, Fe: ≦0.2% by mass, Mn: ≦0.1% by mass, and the remainder being Al and unavoidable impurities. ADC3 is an Al-Si-Mg alloy containing Cu: ≦0.6 mass%, Si: 9.0-11.0 mass%, Mg: 0.4-0.6 mass%, Zn: ≦0.5 mass%, Fe: ≦1.3 mass%, Mn ≦0.3 mass%, and the remainder being Al and unavoidable impurities.

The casting method is not particularly limited, but examples include gravity casting, sand casting, and die casting. When AC4CH is used as the Al-Si-Mg alloy material, the Al alloy casting is preferably produced by gravity casting or sand casting. When ADC3 is used as the Al-Si-Mg alloy material, the Al alloy casting is preferably produced by die casting.

Si can improve the flow (running) of molten metal during casting. Mg can form Mg-Si compounds together with Si, which can increase mechanical strength and fatigue strength. Fe can improve mold releasability, preventing the material from sticking to the mold. Optional elements such as Cu, Zn, Fe, and Mn can contribute to making crystal grains finer and improving strength.

Here, when cooling after casting, the alloying elements contained in the Al alloy, such as Si, Mg, and Fe, crystallize as compounds mainly at the grain boundaries in the cast structure. The distribution of compounds containing alloying elements crystallized at the grain boundaries can be confirmed, for example, from the element distribution (EPMA image) obtained by analyzing the cast structure with an EPMA (Electron Probe Micro Analyzer). However, compounds containing alloying elements crystallized at the grain boundaries may cause defects such as breakage and corrosion at the grain boundaries.

The inventors have therefore conducted extensive research into the relationship between compounds containing alloying elements crystallized at grain boundaries and the ductility of Al alloy castings, and have found that compounds containing Mg (Mg-based compounds) crystallized at grain boundaries drastically reduce ductility. Specifically, by casting AC4CH as an Al-Si-Mg-based alloy material using gravity casting, two types of casting samples were produced: one in which compounds containing Si (Si-based compounds) were crystallized at grain boundaries, and the other in which compounds containing Mg together with Si (Mg-Si-based compounds) were crystallized at grain boundaries. When the fracture elongations of these two types of casting samples were compared, the fracture elongation of the casting sample in which the Si-based compounds were crystallized was 27%, and the fracture elongation of the casting sample in which the Mg-Si-based compounds were crystallized was 6%.

Therefore, in the manufacturing method of the Al alloy casting according to the present embodiment, the Mg-based compounds such as Mg-Si-based compounds in the Al alloy casting can be reduced by the crystallization process and the solution treatment process after casting. In the crystallization process (step S2), the casting temperature of the casting material is lowered to 400°C or less after the solidification of the molten metal is completed. As shown in FIG. 2, in the crystallization process, the casting temperature of the casting material is lowered to 400°C or less, so that compounds containing at least Mg among the alloy elements contained in the casting material are crystallized at the grain boundaries. In the crystallization process, the time (times T2 to T3) for the casting temperature to be 400°C or less is not particularly limited as long as the entire casting material is 400°C or less after the solidification is completed (time T1). From the viewpoint of productivity, the shorter the time for the casting temperature to be 400°C or less, the more preferable. In the crystallization process, if the casting temperature does not reach 400°C or less after the solidification is completed, the crystallization of the Mg-based compounds may be insufficient. If the crystallization of Mg-based compounds is insufficient, the ductility of the Al alloy casting may decrease.

Next, in the solution treatment process (step S3), the casting temperature of the casting material after the crystallization process is held at 450 to 550°C for 10 minutes or more. As shown in FIG. 2, in the solution treatment process, the holding time (times T4 to T5) for holding the casting temperature at 450 to 550°C is not particularly limited as long as it is 10 minutes or more. From the viewpoint of productivity, the shorter the holding time is within the range of 10 minutes or more, the more preferable it is. By such solution treatment, the Mg-based compounds crystallized during the crystallization process can be suitably dissolved in the crystal grains. In the solution treatment process, if the casting temperature is less than 450°C, the solid solution of the Mg-based compounds may be insufficient. Also, if the holding time is less than 10 minutes, the solid solution of the Mg-based compounds may be insufficient. If the solid solution of the Mg-based compounds is insufficient, the ductility of the Al alloy casting may decrease. On the other hand, in the solution treatment process, if the casting temperature exceeds 550°C, a part of the material may dissolve.

Next, in the cooling step (step S4), the casting material after the solution treatment step is cooled. In the cooling step, the cooling of the casting material is completed at time T6 when the casting temperature reaches, for example, about 100°C. Here, the fracture elongation was measured for a total of four types of casting materials, including the casting material immediately after casting (as cast) and three types of casting materials cooled after casting at a cooling rate of 2°C/min (ultra-slow cooling), 20°C/min (natural cooling), and 20,000°C/min (water cooling). The fracture elongation was higher after cooling than immediately after casting, but there was no change due to the cooling rate. Specifically, the fracture elongation of the casting material immediately after casting was 7%, and the fracture elongation of each of the three types of casting materials cooled at any of the above cooling rates was 16%. Therefore, in the cooling step, the cooling rate at which the casting material is cooled is not particularly limited. However, from the viewpoint of material strength, the faster the cooling rate, the better.

The above-mentioned casting process, crystallization process, solution treatment process, and cooling process can produce an Al alloy casting. Furthermore, it is preferable to perform an aging treatment or the like on the Al alloy casting after the cooling process. This strengthens the primary crystal Al, which is the first phase of the Al alloy casting, by aging precipitation.

Next, Figure 3 shows an optical microscope image of the cast structure and an EPMA image of Mg element. The example in Figure 3 shows the cast structure of an Al alloy casting produced from ADC3, an Al-Si-Mg alloy material, using a die casting method according to the manufacturing method of an Al alloy casting according to this embodiment. The comparative example in Figure 3 shows the cast structure of an Al alloy casting that, unlike the example, was not subjected to solution treatment after the casting process.

As is clear from Figure 3, the Al alloy casting of the comparative example has a cast structure in which Mg-based compounds are crystallized at the grain boundaries. On the other hand, the Al alloy casting of the example has a cast structure in which Mg-based compounds are suitably dissolved in the grains, compared to the Al alloy casting of the comparative example.

In addition, the behavior of the Si-based compounds and Fe-containing compounds (Fe-based compounds) crystallized at the grain boundaries was confirmed using EPMA images (not shown) of the Si element and the Fe element. Specifically, in the examples, EPMA images (Si element and Fe element) of the cast structure were obtained for the cast material before and after the solution treatment process, and the presence of the Si-based compounds and Fe-based compounds was confirmed using the obtained EPMA images. As a result, the Si-based compounds and Fe-based compounds crystallized at the grain boundaries were present in the same distribution both before and after the solution treatment process.

In this way, the manufacturing method of the Al alloy casting according to this embodiment allows Mg-based compounds to be sufficiently crystallized at the grain boundaries in the crystallization process after casting, and then the Mg-based compounds are suitably dissolved within the grains in the solution treatment process, thereby reducing the Mg-based compounds that can reduce the ductility of the Al alloy casting. Therefore, according to the manufacturing method of the Al alloy casting according to this embodiment, it is possible to manufacture an Al alloy casting with excellent mechanical properties by suppressing the decrease in ductility. The Al alloy casting manufactured by the manufacturing method of the Al alloy casting according to this embodiment can be suitably used, for example, for automobile body parts that require high strength and high ductility.

The present invention is not limited to the above embodiment, and can be modified as appropriate without departing from the spirit and scope of the invention.

Claims (1)

A casting process in which a molten Al-Si-Mg alloy material is solidified in a mold to obtain a casting material;
a crystallization step of lowering the casting temperature of the casting material to 400° C. or less after the solidification of the molten metal is completed;
a solution treatment step of maintaining the casting temperature of the casting material after the crystallization step at 450 to 550°C for 10 minutes or more;
a cooling step of cooling the casting material after the solution treatment step;
The present invention relates to a method for producing an aluminum alloy casting having the above structure.

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