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

Abstract

Provided is an Al-Si alloy for casting which is capable of imparting high yield strength to an Al-Si alloy casting in addition to being capable of effectively suppressing the occurrence of cracking when press-fitting a self-piercing rivet into an aluminum alloy casting. In addition, provided are: an Al-Si alloy casting which has high yield strength and effectively suppresses the occurrence of cracking when press-fitting a self-piercing rivet therein; and an Al-Si alloy casting joint in which said Al-Si alloy casting is the material to be joined. The Al-Si alloy for casting in the present invention is characterized by comprising Si in the amount of 5.0-12.0 mass%, Mn in the amount of 0.4-1.5 mass%, Mg in the amount of 0.05-0.6 mass%, Cr in the amount of 0.1-0.5 mass%, and Fe in an amount greater than 0 and no greater than 0.6 mass%, with the remainder constituting Al and inevitable 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, and Al-Si alloy castings cast from this Al-Si alloy are suitable for mechanical joining using rivets (particularly self-piercing rivets) and the like. [Background technology]

[0002] Aluminum materials are joined by brazing, adhesive bonding, welding, friction stir welding, friction welding, etc. In recent years, mechanical joining using self-piercing rivets and the like has attracted attention as a simpler joining method.

[0003] Self-piercing riveting is a joining method in which two materials to be joined are stacked on top of each other, a receiving mold is placed on the underside of the lower material, and a self-piercing rivet is driven from above into the upper material; the shank of the self-piercing rivet expands when driven into the materials, achieving a join.

[0004] For example, Patent Document 1 (JP 2020-66751 A) describes a plastically worked aluminum alloy material to be used for self-pierce riveting, containing 0.95 to 1.25 mass% Si, 0.80 to 1.05 mass% Mg, 0.30 to 0.50 mass% Cu, 0.40 to 0.60 mass% Mn, 0.15 to 0.30 mass% Fe, 0.09 to 0.21 mass% Cr, and 0.0001 to 0.03 mass% B, with a Zn content of 0.25 mass% or less, a Zr content of 0.05 mass% or less, a Ti content of 0.10 mass% or less, and the balance being Al and unavoidable impurities. JIS The document discloses an Al-Mg-Si based aluminum alloy plastically worked material characterized in that the maximum shear tensile load measured in accordance with Z3136-1999 is 8.5 kN or more.

[0005] The plastically worked Al-Mg-Si aluminum alloy material described in Patent Document 1 is said to be able to provide an Al-Mg-Si aluminum alloy plastically worked material with excellent joining strength in self-pierce riveting by optimizing the composition.

[0006] Patent Document 2 (Japanese Patent Laid-Open Publication No. 2002-121635) describes an extruded Al-Mg-Si aluminum alloy containing 0.30 to 0.70% (mass%, the same applies hereinafter) Mg, 0.40 to 0.80% Si, 0.05 to 0.40% Cu, 0.05 to 0.30% Mn, 0.05 to 0.20% Zr, and the balance being Al and unavoidable impurities. The extruded Al-Mg-Si aluminum alloy is press-quenched by air cooling and then aged to a strength of 200 N / mm 2 The present invention discloses an aluminum alloy extrusion material for automobile frames having excellent self-pierce rivet joinability, characterized by having a proof stress of 3.5% or more and a local elongation of 3.5% or more.

[0007] In the aluminum alloy extrusion material for automobile frames described in Patent Document 2, it is said that by performing aging treatment on an Al-Mg-Si aluminum alloy extrusion material after press-quenching by air cooling, which is advantageous in terms of dimensional accuracy and cost, it is possible to obtain an aluminum alloy extrusion material that has the strength (yield strength) required for automobile frames and excellent self-pierce rivet joinability. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-66751 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-121635 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the subject of Patent Document 1 is a plastically processed Al-Mg-Si aluminum alloy material, and the subject of Patent Document 2 is an extruded aluminum alloy material, and in both cases, the subject is an aluminum alloy material whose microstructure and mechanical properties are controlled by plastic processing.

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

[0011] In view of the above-mentioned problems in the prior art, an object of the present invention is to provide an Al-Si alloy for casting that can effectively suppress the occurrence of cracks when a self-piercing rivet is pressed into an aluminum alloy casting and can impart high yield strength to the Al-Si alloy casting. Another object of the present invention is to provide an Al-Si alloy casting that effectively suppresses the occurrence of cracks when a self-piercing rivet is pressed into the aluminum alloy casting and has high yield strength, as well as a joined Al-Si alloy casting body that uses the Al-Si alloy casting as a joined material. [Means for solving the problem]

[0012] In order to achieve the above object, the inventors conducted extensive research into the relationship between the composition, microstructure, and mechanical properties of Al-Si alloy castings and cracking that occurs when self-pierce rivets are pressed in. As a result, they discovered that the occurrence of cracking can be suppressed by controlling the amounts of Mg and Mn added, in particular, and that the occurrence of cracking is strongly correlated with the limiting bending angle in a VDA bending test, leading to the present invention.

[0013] That is, the present invention provides: 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: more than 0 and 0.6% by mass or less; The balance consists of Al and unavoidable impurities. The present invention provides an Al-Si alloy for casting, characterized by:

[0014] In the Al-Si alloy for casting of the present invention, the addition of 0.4% by mass or more of Mn can prevent seizure to the mold, suppress the formation of acicular Al-Si-Fe crystals, and suppress the decrease in elongation of the Al-Si alloy casting. Furthermore, the addition of 1.5% by mass or less of Mn can suppress the decrease in elongation of the Al-Si alloy casting due to the coarsening of Al-Si-(Fe,Mn) crystals.

[0015] In addition, adding 0.05% or more by mass of Mg improves the mechanical properties of Al-Si alloy castings through solid solution strengthening of Mg and precipitation strengthening of Mg-Si compounds. Furthermore, by limiting the amount of Mg to 0.6% or less by mass, an excessive increase in deformation resistance is suppressed, and cracking during self-pierce rivet insertion can be suppressed extremely effectively.

[0016] In addition, 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, Na: 0.002 to 0.02 mass%, is preferred.

[0017] By further adding these elements, the microstructure and mechanical properties of the Al-Si alloy casting can be adjusted, and the effect of suppressing cracking during self-pierce rivet insertion can be further enhanced. In addition, the Al-Si alloy casting can be given the desired yield strength.

[0018] The addition of Cu can increase the strength and yield strength of Al-Si alloy castings, and the addition of 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, thereby improving the elongation of Al-Si alloy castings.

[0019] The present invention also provides an Al-Si alloy casting comprising the Al-Si alloy for casting of the present invention. The Al-Si alloy casting of the present invention effectively suppresses the occurrence of cracks when a self-piercing rivet is pressed into the casting, and has high yield strength.

[0020] In the Al-Si alloy casting of the present invention, the limiting bending angle in the VDA bending test specified in VDA238-100 is preferably 28° or more, more preferably 30° or more, and most preferably 33° or more.

[0021] Here, VDA stands for the German Association of the Automobile Industry (Verband der Automobilindustrie) standard, and VDA238-100 is prescribed as a plate bending test for the purpose of evaluating crack behavior when a component is crushed.

[0022] In addition, the Al-Si alloy casting of the present invention preferably has a 0.2% yield strength of 100 MPa or more, more preferably 105 MPa or more, and most preferably 110 MPa or more.

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

[0024] The self-pierce riveted joint of the present invention is an Al-Si alloy casting with excellent mechanical properties that has been given a variety of shapes and is firmly mechanically fastened to other metal components, and the occurrence of cracks at the joint is suppressed, making it suitable for 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 a self-piercing rivet is pressed into an aluminum alloy casting and can impart high yield strength to the Al-Si alloy casting.It is also possible to provide an Al-Si alloy casting that effectively suppresses the occurrence of cracks when a self-piercing rivet is pressed into the aluminum alloy casting and has high yield strength, as well as a joined Al-Si alloy casting body that uses the Al-Si alloy casting as the joined material. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a photograph showing the appearance of a self-pierce rivet joint (Example 2). [Figure 2] 1 is a photograph showing the appearance of an Al—Si alloy sheet material after a VDA bending test (Example 2). [Figure 3] 1 is a photograph showing the appearance of a self-pierce rivet joint (Comparative Example 1). DETAILED DESCRIPTION OF THE INVENTION

[0027] The Al-Si alloy for casting, the Al-Si alloy cast product, and the joined Al-Si alloy cast product 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 casting of the present invention is characterized by the composite 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 and also the effect of improving mechanical properties such as tensile strength. This effect is significant when the content is 5.0% by mass or more, but when added in excess of 12.0% by mass, eutectic Si and primary Si crystals tend to coarsen, reducing elongation and making cracks more likely to occur when a self-pierce rivet is pressed into the alloy. The amount of Si added is preferably 6.0 to 9.0% by mass.

[0030] Mn:0.4~1.5% by mass Mn has the effect of preventing seizure to the mold and suppressing the formation of acicular Al-Si-Fe crystals, thereby suppressing a decrease in elongation. This effect becomes significant at 0.4 mass% or more, but conversely, at more than 1.5 mass%, Al-Si-(Fe,Mn) crystals tend to become coarse, which causes a decrease in elongation. The Mn content is preferably 0.5 to 0.7 mass%.

[0031] Mg:0.05~0.6% by mass Mg dissolves in Al to improve mechanical properties, and when aging is performed, it precipitates with Si as an Mg-Si compound, improving mechanical properties. This effect is significant at 0.05% by mass or more, but conversely, at more than 0.6% by mass, deformation resistance increases, making cracks more likely to occur when a self-piercing rivet is driven. 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 prevents seizure on the mold and improves corrosion resistance. This effect becomes significant at 0.1% by mass or more. Conversely, at more than 0.5% by mass, coarse compounds are more likely to form, leading to reduced elongation.

[0033] Fe: More than 0 and 0.6% by mass or less Fe improves mechanical properties such as tensile strength and prevents mold seizure, but if it exceeds 0.6 mass%, elongation decreases and cracks are more likely to occur when a self-piercing rivet is driven in.

[0034] (2) Optional additive elements Cu:0.05~0.5% by mass Cu has the effect of improving mechanical properties, and this effect becomes significant at 0.05% by mass or more. Conversely, if it exceeds 0.5% by mass, corrosion resistance decreases. 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 improves self-pierce rivet joinability. This effect is significant at 0.001% by mass or more. Conversely, if it exceeds 0.02% by mass, it will increase production costs.

[0036] Ca:0.005~0.03% by mass Adding 0.005 to 0.03 mass% of Ca can make the eutectic silicon fine and granular. When the eutectic silicon is fine and granular, elongation improves and cracks that occur when a self-pierce rivet is pressed in can be suppressed.

[0037] Sr:0.005~0.03 mass% Adding 0.005 to 0.03 mass% of Sr can make the eutectic silicon fine and granular. When the eutectic silicon is fine and granular, elongation improves and cracks that occur when a self-pierce rivet is pressed in can be suppressed.

[0038] Sb:0.01~0.2% by mass Adding 0.01 to 0.2 mass% of Sb can make the eutectic silicon fine and granular. When the eutectic silicon is fine and granular, elongation is improved and cracks that occur when a self-pierce rivet is pressed in can be suppressed.

[0039] Na:0.002~0.02% by mass Adding 0.002 to 0.02 mass% of Na can make the eutectic silicon fine and granular. When the eutectic silicon is fine and granular, elongation improves and cracks that occur when a self-pierce rivet is pressed in can be suppressed.

[0040] Ti:0.005~0.2% by mass Ti has the effect of refining the cast structure and improving castability and elongation. This effect is significant at 0.005% by mass or more. Conversely, at more than 0.2% by mass, coarse crystals are likely to form and elongation is likely to decrease.

[0041] 2. Al-Si alloy castings The Al-Si alloy casting of the present invention is made of the Al-Si alloy for casting of the present invention, and is characterized by having high yield strength and suppressing the occurrence of cracks when a self-pierce rivet is pressed in. The microstructure and mechanical properties are described in detail below.

[0042] (1) Metal structure The metallurgical reasons why the Al-Si alloy casting of the present invention has excellent self-pierce riveting weldability are not entirely clear, but it is thought that this is due to the fact that the various crystallized particles are prevented from becoming acicular and coarsening, as well as the formation of eutectic Si aggregates is prevented.

[0043] When brittle eutectic Si aggregates are formed, cracks tend to propagate along the aggregates, making cracks more likely to occur when a self-pierce rivet is pressed in. In the Al-Si alloy casting of the present invention, the formation of eutectic Si aggregates tends to be suppressed, and cracks are effectively suppressed when a self-pierce rivet is pressed in.

[0044] The method for confirming the presence or absence of eutectic Si aggregates is not particularly limited, and various conventionally known microstructural observation methods may be used. For example, when a mirror-polished cross section of an Al-Si alloy casting is observed with an optical microscope or a scanning electron microscope (SEM), if eutectic Si is formed continuously to a thickness of 50 μm or more, it can be determined that eutectic Si aggregates that promote the initiation and propagation of cracks have been formed.

[0045] (2) Mechanical properties The Al-Si alloy casting of the present invention has excellent tensile properties, including high strength, proof stress, and ductility. In addition, the occurrence of cracks during press-fitting of a self-piercing rivet is effectively suppressed.

[0046] The mechanism by which cracks occur when a self-pierce rivet is pressed into place is complex, and it is difficult to evaluate this solely from measurements of the mechanical properties of the Al-Si alloy casting, such as tensile properties and hardness.However, as a result of extensive research by the inventors, it has become clear that there is a strong correlation between the limit bend angle in the VDA bend test specified in VDA238-100 and the presence or absence of cracks when a self-pierce rivet is pressed into place.

[0047] More specifically, to prevent cracking when a self-piercing rivet is pressed into place, it is preferable to set the limit bend angle in the VDA bend test specified in VDA238-100 to 28° or greater. A more preferable limit bend angle is 30° or greater, and the most preferable limit bend angle is 33° or greater. For example, when an Al-Si alloy casting having tensile properties of 0.2% proof stress of 100 to 120 MPa and fracture elongation of approximately 10 to 14% is used, setting the limit bend angle in the VDA bend test to 28° or greater can almost completely prevent 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 more, more preferably 105 MPa or more, and most preferably 110 MPa or more. The fracture elongation is preferably 10%, more preferably 12% or more, and most preferably 14% or more.

[0049] The Al-Si alloy casting of the present invention can be produced by adjusting raw materials so as to have the composition of the Al-Si alloy casting for casting of the present invention, and casting them by various conventionally known casting methods (sand casting, metal mold casting, gravity casting, low-pressure casting, 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 casting joints (self-pierce riveted joints) The self-pierce riveted joint of the present invention is characterized in that at least one of the members joined with the self-pierce rivet is the Al—Si alloy casting of the present invention.

[0052] Self-pierce riveted joints are made by firmly mechanically fastening Al-Si alloy castings with excellent mechanical properties that have been given various shapes to other metal components, and because the occurrence of cracks 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-pierce rivet are not particularly limited as long as they do not impair the effects of the present invention, and various conventionally known self-pierce rivets can be used. Furthermore, the press-fit area of ​​the self-pierce rivet is also not particularly limited as long as they do not impair the effects of the present invention, and may be determined appropriately depending on the desired joined body.

[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-pierce rivet are not particularly limited as long as they do not impair the effects of the present invention, and may be adjusted appropriately depending on the material, shape, size, etc. of the self-pierce rivet and the workpieces to be joined.

[0056] Representative embodiments of the present invention have been described above, but the present invention is not limited to these, and various design modifications are possible, all of which are included in the technical scope of the present invention. [Example]

[0057] Example Raw materials blended to give the compositions (mass%) shown in Table 1 for Examples 1 to 8 were melted at 750°C, deslag-removal treatment was performed using a molten metal cleaning flux, and degassing treatment was performed by blowing Ar gas. PF die-casting was then performed 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, to obtain Al-Si alloy plates, which are embodied Al-Si alloy castings of the present invention. The dimensions of the Al-Si alloy plates were 110 × 110 × 3 mm.

[0058] [Table 1]

[0059] An Al-Si alloy sheet was cut to a size of 100 × 30 × 3 mm, and a 100 × 30 × 1 mm steel plate (SPCC) was placed on top of it. A rivet with a body diameter of 5.2 mm and a length of 4.4 mm was driven into three locations from the steel plate side to perform self-piercing riveting. The joining test was performed five times for each composition, and a total of 15 self-piercing riveted joints were checked for cracks and evaluated for the crack occurrence rate. More specifically, the crack occurrence rate was calculated as "crack occurrence rate = (number of joints with cracks / 15) × 100." The obtained crack occurrence rates are shown in Table 1. A photograph of the appearance of a self-piercing riveted joint in an Al-Si alloy sheet having the composition of Example 2 is shown in Figure 1. The self-piercing riveted joint shown in Figure 1 was completely free of cracks.

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

[0061] Furthermore, the tensile properties of the Al-Si alloy sheets were evaluated. JIS Z 2241 14B tensile test pieces were cut out from the Al-Si alloy sheets and subjected to tensile tests at a tension speed of 5 mm / min. The tensile strength, 0.2% yield strength, and fracture elongation obtained are shown in Table 1.

[0062] Comparative Example Al-Si alloy plates, which are comparative Al-Si alloy castings of the present invention, were obtained in the same manner as in the Examples, except that raw materials were used that were blended to obtain the compositions (mass%) shown in Table 1 as Comparative Examples 1 to 3.

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

[0064] The results shown in Table 1 confirm that the Al-Si alloy sheets, which are the embodied Al-Si alloy castings of the present invention, have excellent self-pierce riveting weldability. Furthermore, a strong correlation was observed between the cracking rate and the critical bending angle in the VDA bending test, and it was found that cracking can be effectively suppressed by setting the critical bending angle to 28° or more.

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

[0066] In contrast, in the compositions of Comparative Examples 1 and 2, which have a low Mg content, and Comparative Example 3, which has a high Mn and Mg content, the limit bending angle in the VDA bending test is small, and the crack occurrence rate of the self-pierce rivet joint is high.

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: more than 0 and 0.6 mass% or less; Ca: 0.005 to 0.03% by mass, Sr: 0.005 to 0.03% by mass, Sb: 0.01 to 0.2% by mass, Na: 0.002 to 0.02 mass%, The balance is an Al-Si alloy for casting, which is composed of Al and inevitable impurities; The limit bending angle of the VDA bending test specified in VDA238-100 is 28° or more. An Al-Si alloy casting characterized by:

2. 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: more than 0 and not more than 0.6% by mass, Ti: 0.005 to 0.2 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, Na: 0.002 to 0.02 mass%, The balance is an Al-Si alloy for casting, which is composed of Al and inevitable impurities; The limit bending angle of the VDA bending test specified in VDA238-100 is 28° or more. An Al-Si alloy casting characterized by:

3. The Al-Si alloy for casting Cu: 0.05 to 0.5% by mass, B: 0.001 to 0.02 mass % The Al-Si alloy casting according to claim 1, characterized in that

4. The Al-Si alloy for casting Cu: 0.05 to 0.5% by mass, B: 0.001 to 0.02 mass % The Al-Si alloy casting according to claim 2, characterized in that:

5. 0.2% yield strength is 100 MPa or more, The Al-Si alloy casting according to any one of claims 1 to 4, characterized in that:

6. A joined body joined using a self-piercing rivet, At least one of the joined members is an Al-Si alloy casting according to any one of claims 1 to 4. A self-pierce riveted joint comprising:

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