Al-Si alloy for casting, Al-Si alloy castings, and Al-Si alloy casting joints

Abstract

The present invention provides an Al-Si alloy for castings that can effectively suppress the occurrence of cracks when self-piercing rivets are press-fitted into aluminum alloy castings, and that can impart high yield strength to Al-Si alloy castings. Furthermore, the present invention provides an Al-Si alloy casting that effectively suppresses the occurrence of cracks when self-piercing rivets are press-fitted and has high yield strength, as well as an Al-Si alloy casting joint in which the Al-Si alloy casting is used as the joined material. [Solution] An Al-Si alloy for casting, characterized by containing Si: 5.0~12.0 mass%, Mn: 0.4~1.5 mass%, Mg: 0.05~0.6 mass%, Cr: 0.1~0.5 mass%, Fe: greater than 0 and 0.6 mass% or less, with the remainder consisting of Al and unavoidable impurities.

Description

Technical Field

[0001] The present invention relates to an Al-Si alloy that can be suitably used for casting, particularly for die casting. An Al-Si alloy casting cast from the Al-Si alloy is suitable for mechanical joining using rivets (particularly self-piercing rivets) and the like.

Background Art

[0002] For joining aluminum materials, brazing, adhesion, welding, friction stir welding, friction pressure welding, etc. are used. Here, in recent years, as a more convenient joining method, mechanical joining using self-piercing rivets and the like has attracted attention.

[0003] Self-piercing rivet joining is a joining method in which the joined materials are overlapped, a receiving die is placed on the lower surface of the lower joined material, and a self-piercing rivet is driven in from above the upper joined material. When the self-piercing rivet is driven into the material, the shaft portion of the self-piercing rivet expands, thereby achieving the joining.

[0004] For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2020-66751) discloses a plastic working material used for self-piercing rivet joining, which contains Si: 0.95% by mass to 1.25% by mass, Mg: 0.80% by mass to 1.05% by mass, Cu: 0.30% by mass to 0.50% by mass, Mn: 0.40% by mass to 0.60% by mass, Fe: 0.15% by mass to 0.30% by mass, Cr: 0.09% by mass to 0.21% by mass, B: 0.0001% by mass to 0.03% by mass, the content of Zn is 0.25% by mass or less, the content of Zr is 0.05% by mass or less, the content of Ti is 0.10% by mass or less, and the balance is composed of Al and unavoidable impurities. The self-piercing rivet joined body of the aluminum alloy plastic working materials has a maximum shear tensile load of 8.5 kN or more measured in accordance with JIS Z3136-1999. An Al-Mg-Si-based aluminum alloy plastic working material is disclosed.

[0005] In the Al-Mg-Si aluminum alloy plastic deformation material described in Patent Document 1 above, it is stated that by optimizing the composition, an Al-Mg-Si aluminum alloy plastic deformation material with excellent bonding strength for self-piercing rivet joints can be provided.

[0006] Furthermore, Patent Document 2 (Japanese Unexamined Patent Publication No. 2002-121635) describes an Al-Mg-Si aluminum alloy extruded material containing Mg: 0.30~0.70% (mass%, the same applies hereinafter), Si: 0.40~0.80%, Cu: 0.05~0.40%, Mn: 0.05~0.30%, Zr: 0.05~0.20%, with the remainder being Al and unavoidable impurities. After press quenching by air cooling, it is subjected to aging treatment to 200 N / mm². 2 Disclosed is an aluminum alloy extruded material for automobile frames that has the above yield strength and local elongation of 3.5% or more, and is excellent in self-piercing rivet bonding.

[0007] In the aluminum alloy extruded material for automobile frames described in Patent Document 2 above, it is stated that by applying an aging treatment after press quenching by air cooling, which is advantageous in terms of dimensional accuracy and cost, an aluminum alloy extruded material with the strength (yield strength) and self-piercing rivet jointability required for automobile frames can be obtained. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-66751 [Patent Document 2] Japanese Patent Publication No. 2002-121635 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, the subject of Patent Document 1 is an Al-Mg-Si aluminum alloy plastically deformed material, and the subject of Patent Document 2 is an aluminum alloy extruded material. In both cases, the patents relate to aluminum alloy materials in which the microstructure and mechanical properties are controlled by plastic deformation.

[0010] In contrast, it is often necessary to join aluminum alloy castings, such as die-cast materials, to other structural members using mechanical fastening methods such as self-piercing rivets. When mechanical fastening is applied to aluminum alloy castings, suppressing cracks that occur during the joining process becomes a more serious challenge.

[0011] In view of the problems of the prior art described above, the object of the present invention is to provide an Al-Si alloy for casting that can effectively suppress the occurrence of cracks when self-piercing rivets are pressed into aluminum alloy castings, and that can impart high yield strength to Al-Si alloy castings. Furthermore, the present invention also aims to provide an Al-Si alloy casting that effectively suppresses the occurrence of cracks when self-piercing rivets are pressed into them and has high yield strength, as well as an Al-Si alloy casting joint in which the Al-Si alloy casting is used as the joined material. [Means for solving the problem]

[0012] To achieve the above objective, the inventors diligently researched the relationship between the composition, microstructure, and mechanical properties of Al-Si alloy castings and cracking during self-piercing rivet press-fitting. As a result, they discovered that cracking can be suppressed by controlling the amount of Mg and Mn added, and that the occurrence of such cracking is strongly correlated with the limiting bending angle of the VDA bending test, leading to the present invention.

[0013] In other words, the present invention is Si: 5.0~12.0% by mass, Mn: 0.4~1.5% by mass, Mg: 0.05~0.6% by mass, Cr:0.1~0.5% by mass, Fe: Contains more than 0% by mass and less than or equal to 0.6% by mass, The remainder consists of Al and unavoidable impurities. We provide an Al-Si alloy for castings characterized by the following.

[0014] In the Al-Si alloy for casting of the present invention, by adding 0.4 mass% or more of Mn, it is possible to prevent sticking to the mold, suppress the needle-like formation of Al-Si-Fe precipitates, and suppress the decrease in elongation of the Al-Si alloy casting. Furthermore, by limiting the amount of Mn added to 1.5 mass% or less, it is possible to suppress the decrease in elongation of the Al-Si alloy casting due to the coarsening of Al-Si-(Fe,Mn) precipitates.

[0015] In addition, by adding 0.05% by mass or more of Mg, the mechanical properties of Al-Si alloy castings can be improved through solid solution strengthening by Mg and precipitation strengthening of Mg-Si compounds. Furthermore, by limiting the amount of Mg added to 0.6% by mass or less, an excessive increase in deformation resistance can be suppressed, and the occurrence of cracks during self-piercing rivet press-fitting can be suppressed very effectively.

[0016] Furthermore, in the Al-Si alloy for casting of the present invention, Cu:0.05~0.5% by mass, Ca:0.005~0.03% by mass, B:0.001~0.02% by mass, Sr:0.005~0.03% by mass, Sb:0.01~0.2% by mass, Contains one or more of the following: Na: 0.002 to 0.02% by mass. It is preferable.

[0017] By further adding these elements, the microstructure and mechanical properties of the Al-Si alloy casting can be adjusted, further enhancing the crack suppression effect during self-piercing rivet press-fitting. Additionally, the desired yield strength can be imparted to the Al-Si alloy casting.

[0018] Adding Cu can increase the strength and yield strength of Al-Si alloy castings, and adding B can improve the local elongation of Al-Si alloy castings. In addition, Ca, Sr, Sb, and Na have the effect of refining and granulating eutectic Si, and can improve the elongation of Al-Si alloy castings.

[0019] The present invention also provides an Al-Si alloy casting characterized by being made of the Al-Si alloy for castings of the present invention. The Al-Si alloy casting of the present invention effectively suppresses the occurrence of cracks when press-fitting self-piercing rivets and has high yield strength.

[0020] In the Al-Si alloy casting of the present invention, it is preferable that the limit bending angle in the VDA bending test defined by VDA238-100 is 28° or more. A more preferable limit bending angle is 30° or more, and the most preferable limit bending angle is 33° or more.

[0021] Here, VDA is the standard of the German Automobile Industry Association (Verband der Automobilindustrie), and VDA238-100 is defined as a sheet bending test for the purpose of evaluating the cracking behavior at the time of member crushing.

[0022] In the Al-Si alloy casting of the present invention, it is preferable that the 0.2% yield strength is 100 MPa or more. The 0.2% yield strength is more preferably 105 MPa or more, and most preferably 110 MPa or more.

[0023] Furthermore, the present invention also provides a self-piercing rivet joint, which is a joint joined using a self-piercing rivet, and at least one of the joined members is the Al-Si alloy casting of the present invention.

[0024] The self-piercing rivet joint of the present invention is made of Al-Si alloy castings with excellent mechanical properties and various shapes, which are firmly mechanically fastened to other metal members. Because the occurrence of cracks at the joint is suppressed, it can be suitably applied to a wide variety of uses. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide an Al-Si alloy for casting that can effectively suppress the occurrence of cracks when self-piercing rivets are press-fitted into aluminum alloy castings, and that can impart high yield strength to Al-Si alloy castings. Furthermore, it is possible to provide an Al-Si alloy casting that effectively suppresses the occurrence of cracks when self-piercing rivets are press-fitted and has high yield strength, as well as an Al-Si alloy casting joint using the Al-Si alloy casting as the joined material. [Brief explanation of the drawing]

[0026] [Figure 1] This is a photograph of the external appearance of the self-piercing rivet joint (Example 2). [Figure 2] This is a photograph of the appearance of the Al-Si alloy sheet material after the VDA bending test (Example 2). [Figure 3] This is a photograph of the external appearance of the self-piercing rivet joint (Comparative Example 1). [Modes for carrying out the invention]

[0027] The Al-Si alloy for casting, Al-Si alloy castings, and Al-Si alloy casting joints of the present invention will be described in detail below, but the present invention is not limited to these.

[0028] 1. Al-Si alloy for casting The Al-Si alloy for castings of the present invention is characterized by the compound addition of Mn, Mg, Cr, and Fe to a hypoeutectic Al-Si alloy. Each component will be described in detail below.

[0029] (1) Essential additive elements Si:5.0~12.0% by mass Si has the effect of improving the castability of aluminum alloys, as well as improving mechanical properties such as tensile strength. This effect becomes significant at 5.0 mass% or more, but if added above 12.0 mass%, eutectic Si and primary Si tend to coarseen, reducing elongation and making cracking more likely when self-piercing rivets are pressed in. The amount of Si added is preferably 6.0 to 9.0 mass%.

[0030] Mn:0.4~1.5% by mass Mn has the effect of preventing sticking to the mold and suppressing the needle-like formation of Al-Si-Fe precipitates, thereby suppressing the decrease in elongation. This effect becomes significant at 0.4 mass% or higher, and conversely, above 1.5 mass%, Al-Si-(Fe,Mn) precipitates tend to coarseen, which becomes a factor in the decrease in elongation. The Mn content is preferably 0.5 to 0.7 mass%.

[0031] Mg:0.05~0.6% by mass Mg has the effect of improving mechanical properties by solid dissolving in Al, and when subjected to aging treatment, it precipitates together with Si as a Mg-Si compound, further improving mechanical properties. This effect becomes significant at 0.05% by mass or higher, but conversely, if it exceeds 0.6% by mass, the deformation resistance increases, making it more prone to cracking when self-piercing rivets are driven in. The amount of Mg added is preferably 0.05 to 0.3% by mass, and more preferably 0.05 to 0.14% by mass.

[0032] Cr:0.1~0.5% by mass Cr has the effect of preventing seizing on molds and improving corrosion resistance. This effect becomes significant at 0.1% by mass or higher. Conversely, above 0.5% by mass, it tends to form coarse compounds, and the elongation tends to decrease.

[0033] Fe: More than 0 and 0.6% by mass or less Fe improves mechanical properties such as tensile strength and prevents mold seizing, but when its content exceeds 0.6% by mass, elongation decreases, making cracking more likely when self-piercing rivets are driven in.

[0034] (2) Any additive element Cu:0.05~0.5% by mass Cu has the effect of improving mechanical properties, and this effect becomes significant at a concentration of 0.05% by mass or higher. Conversely, corrosion resistance decreases when the concentration exceeds 0.5% by mass. The Cu content is preferably 0.2 to 0.4% by mass.

[0035] B:0.001~0.02% by mass B improves local elongation and enhances self-piercing rivet bonding properties. This effect becomes significant at concentrations of 0.001% by mass or higher. Conversely, concentrations exceeding 0.02% by mass increase production costs.

[0036] Ca:0.005~0.03% by mass By adding 0.005 to 0.03 mass% of Ca, the eutectic Si can be made finer and more granular. When the eutectic Si is made finer and more granular, the elongation improves, which can suppress cracking that occurs during self-piercing rivet press-fitting.

[0037] Sr:0.005~0.03 mass% By adding 0.005 to 0.03 mass% of Sr, the eutectic Si can be made finer and more granular. When the eutectic Si is made finer and more granular, the elongation improves, and cracking that occurs during self-piercing rivet press-fitting can be suppressed.

[0038] Sb:0.01~0.2% by mass Adding 0.01-0.2 mass% of Sb allows for the eutectic Si to be refined and granulated. This refinement and granulation of the eutectic Si improves elongation and suppresses cracking that occurs during self-piercing rivet press-fitting.

[0039] Na:0.002~0.02% by mass By adding 0.002 to 0.02 mass% of Na, the eutectic Si can be made finer and more granular. When the eutectic Si is made finer and more granular, the elongation improves, which can suppress cracking that occurs during self-piercing rivet press-fitting.

[0040] Ti:0.005~0.2% by mass Ti has the effect of refining the microstructure of castings, improving castability and elongation. This effect becomes significant at concentrations of 0.005 mass% or higher. Conversely, above 0.2 mass%, coarse crystals tend to form, and elongation tends to decrease.

[0041] 2. Al-Si alloy castings The Al-Si alloy casting of the present invention is made from the Al-Si alloy for casting of the present invention and is characterized by having high yield strength and suppressing the occurrence of cracks during self-piercing rivet press-fitting. The microstructure and mechanical properties will be described in detail below.

[0042] (1) Metal structure The metallic reasons why the Al-Si alloy casting of the present invention has excellent self-piercing rivet bonding properties are not entirely clear, but it is thought that this is due to the suppression of needle-like and coarsening of various precipitates, as well as the suppression of the formation of eutectic Si aggregates.

[0043] When brittle eutectic Si aggregates form, cracks propagate along these aggregates, making cracks more likely to occur during self-piercing rivet press-fitting. In the Al-Si alloy casting of the present invention, the formation of eutectic Si aggregates tends to be suppressed, effectively suppressing crack occurrence during self-piercing rivet press-fitting.

[0044] Furthermore, there are no particular limitations on the method for confirming the presence or absence of eutectic Si aggregates; various conventionally known microstructural observation techniques can be used. For example, if a cross-section of a mirror-polished Al-Si alloy casting is observed with an optical microscope or scanning electron microscope (SEM) and eutectic Si is continuously formed to a thickness of 50 μm or more, it can be determined that eutectic Si aggregates that promote crack initiation and propagation have been formed.

[0045] (2) Mechanical properties The Al-Si alloy casting of the present invention possesses excellent tensile properties, combining high strength, yield strength, and ductility. In addition, it effectively suppresses the occurrence of cracks when self-piercing rivets are press-fitted.

[0046] The mechanism of crack formation during press-fitting of self-piercing rivets is complex, making it difficult to evaluate solely based on measured values ​​related to the mechanical properties of Al-Si alloy castings, such as tensile properties and hardness. In response to this, the inventors conducted diligent research and found a strong correlation between the limit bending angle of the VDA bending test specified in VDA238-100 and the presence or absence of cracking during press-fitting of self-piercing rivets.

[0047] More specifically, to suppress cracking during press-fitting of self-piercing rivets, it is preferable to set the limit bending angle of the VDA bending test specified in VDA238-100 to 28° or higher. A more preferable limit bending angle is 30° or higher, and the most preferable limit bending angle is 33° or higher. For example, when dealing with Al-Si alloy castings having tensile properties of approximately 100-120 MPa for 0.2% yield strength and 10-14% for elongation at break, setting the limit bending angle of the VDA bending test to 28° or higher can almost completely suppress cracking under typical joining conditions.

[0048] In the Al-Si alloy casting of the present invention, the 0.2% yield strength is preferably 100 MPa or higher. More preferably, the 0.2% yield strength is 105 MPa or higher, and most preferably, 110 MPa or higher. Furthermore, the elongation at break is preferably 10%, more preferably 12% or higher, and most preferably 14% or higher.

[0049] The Al-Si alloy casting of the present invention can be manufactured by adjusting the raw materials to achieve the composition of the Al-Si alloy casting for casting of the present invention and casting it using various conventionally known casting methods (sand casting, metal casting, gravity casting, low-pressure casting, and die casting, etc.). In other words, the aluminum alloy casting of the present invention is not limited to those cast by a specific casting method.

[0050] Furthermore, the casting conditions are not particularly limited as long as they do not impair the effects of the present invention, and various conventionally known casting conditions can be used.

[0051] 3. Al-Si alloy cast joint (self-piercing rivet joint) The self-piercing rivet joint of the present invention is characterized in that at least one of the members joined using self-piercing rivets is the Al-Si alloy casting of the present invention.

[0052] Self-piercing rivet joints are constructed by firmly mechanically fastening Al-Si alloy castings, which have excellent mechanical properties and are given various shapes, to other metal components. Because crack formation at the joint is suppressed, they can be suitably applied to a wide variety of uses.

[0053] The material, shape, and size of the self-piercing rivet are not particularly limited as long as they do not impair the effects of the present invention, and various conventionally known self-piercing rivets can be used. Furthermore, the press-fitting area of ​​the self-piercing rivet is not particularly limited as long as it does not impair the effects of the present invention, and can be appropriately determined according to the desired joint.

[0054] Furthermore, the other material to be joined to the Al-Si alloy casting of the present invention is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known materials to which self-piercing rivets can be applied can be used.

[0055] Furthermore, the conditions for press-fitting the self-piercing rivet are not particularly limited, as long as they do not impair the effects of the present invention, and can be appropriately adjusted according to the material, shape, and size of the self-piercing rivet and the materials to be joined.

[0056] Although typical embodiments of the present invention have been described above, the present invention is not limited to these, and various design modifications are possible, all of which fall within the technical scope of the present invention. [Examples]

[0057] Examples Raw materials were mixed to have the compositions (mass%) shown in Table 1 as Examples 1 to 8, melted at 750°C, deslag treatment with molten metal cleaning flux, and degassing treatment with Ar gas injection. Then, Al-Si alloy sheets, which are Al-Si alloy castings embodying the present invention, were obtained by PF die casting under the following conditions: high injection speed: 2.0 mm / s, casting pressure: 80 ± 5 MPa, casting temperature: 730 ± 10°C (Examples 1 to 8, Comparative Example 3), 700 ± 10°C (Comparative Examples 1 and 2), and mold temperature: 100 to 150°C. The size of the Al-Si alloy sheets is 110 × 110 × 3 mm.

[0058] [Table 1]

[0059] Al-Si alloy sheets were cut to a size of 100 x 30 x 3 mm, and a 100 x 30 x 1 mm steel plate (SPCC) was placed on top of them. Self-piercing rivet joints were then constructed by driving rivets with an outer diameter of 5.2 mm and a length of 4.4 mm into three locations on the steel plate side. The joint test was performed five times for each composition, and the presence or absence of cracks was checked for a total of 15 self-piercing rivet joints, and the crack occurrence rate was evaluated. More specifically, the crack occurrence rate was calculated as "crack occurrence rate = (number of joints where cracks were observed / 15) × 100". The obtained crack occurrence rates are shown in Table 1. Figure 1 shows a photograph of the appearance of the self-piercing rivet joint in the Al-Si alloy sheet with the composition of Example 2. No cracks occurred in the self-piercing rivet joint shown in Figure 1.

[0060] Furthermore, a VDA bending test, as specified in VDA238-100, was performed on the Al-Si alloy sheet material to evaluate the limit bending angle. The obtained limit bending angles are shown in Table 1. Figure 2 shows a photograph of the appearance of the Al-Si alloy sheet material having the composition of Example 2 after the VDA bending test.

[0061] Furthermore, the tensile properties of the Al-Si alloy sheet were evaluated. Tensile test specimens conforming to JIS Z 2241 (14B) were cut from the Al-Si alloy sheet, and tensile tests were performed at a tensile speed of 5 mm / min. The obtained tensile strength, 0.2% proof stress, and elongation at break are shown in Table 1.

[0062] Comparative Example An Al-Si alloy sheet material, which is a comparative Al-Si alloy casting of the present invention, was obtained in the same manner as in the examples, except that raw materials were used that were formulated to have the compositions (mass%) shown as Comparative Examples 1 to 3 in Table 1.

[0063] Furthermore, the crack occurrence rate of the self-piercing rivet joint and the limit bending angle of the VDA bending test were evaluated in the same manner as in the examples. The obtained crack occurrence rate and limit bending angle are shown in Table 1. In addition, Figure 3 shows a photograph of the appearance of the self-piercing rivet joint of the Al-Si alloy sheet material having the composition of Comparative Example 1. Significant crack occurrence was observed in the self-piercing rivet joint.

[0064] The results shown in Table 1 confirm that the Al-Si alloy sheet material, which is an Al-Si alloy casting embodying the present invention, has excellent self-piercing rivet bonding properties. Furthermore, a strong correlation was observed between the crack occurrence rate and the limit bending angle of the VDA bending test, indicating that crack occurrence can be effectively suppressed by setting the limit bending angle to 28° or higher.

[0065] Furthermore, the results of the tensile tests show that the Al-Si alloy sheet material, which is an Al-Si alloy casting embodying the present invention, has a low cracking rate and excellent tensile properties.

[0066] In contrast, when the compositions of Comparative Examples 1 and 2, which have a low Mg content, and when the composition of Comparative Example 3, which has a high Mn and Mg content, are used, the limiting bending angle in the VDA bending test is smaller, and the crack occurrence rate of the self-piercing rivet joint is higher.

Claims

1. Si: 5.0 to 12.0% by mass, Mn: 0.4 to 1.5% by mass, Mg: 0.05 to 0.3% by mass, Cr: 0.1 to 0.5% by mass, Fe: Contains more than 0% by mass and less than or equal to 0.6% by mass, Ca: 0.005 to 0.03% by mass, Sr: 0.005 to 0.03% by mass, Sb: 0.01 to 0.2% by mass, Contains one or more of the following: Na: 0.002 to 0.02% by mass, The Al-Si alloy for casting consists of Al and unavoidable impurities, The limit bending angle of the Al-Si alloy casting obtained from the aforementioned Al-Si alloy for castings, as defined in VDA238-100, is 28° or greater. An Al-Si alloy for casting characterized by the following features.

2. It contains Ti: 0.005 to 0.2% by mass. The Al-Si alloy for casting according to claim 1, characterized by the above.

3. Cu: 0.05 to 0.5% by mass, B: Contains one or more of the following: 0.001 to 0.02% by mass. The Al-Si alloy for casting according to claim 1 or 2, characterized by the above.

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