Aluminum alloy for casting and aluminum alloy casting

Abstract

The present invention provides: an Al-Mg-Si-based alloy that enables an aluminum alloy casting to exhibit excellent mechanical properties and good corrosion resistance without performing a heat treatment; and an aluminum alloy casting comprising said Al-Mg-Si-based alloy. More specifically, the present invention is characterized by comprising 2.0-8.5 wt% Mg, 0.02-5.0 wt% Si, and 0.01-1.5 wt% Cu, with the remainder being Al and unavoidable impurities, wherein the content of Zn contained as an unavoidable impurity is not more than 0.5 wt%, and the expressions "Mg content - 1.73 × Si content > 0" and "(Mg content - 1.73 × Si content) / Cu content > 0.2" are satisfied.

Description

Aluminum alloys for casting and aluminum alloy castings

[0001] The present invention relates to aluminum alloys for casting and aluminum alloy castings made from said aluminum alloys, and more particularly to aluminum alloy castings suitable for structural materials for automobiles.

[0002] Efforts to reduce the weight of structures are progressing in various fields, including transportation equipment, and aluminum alloys, which are lighter than iron, are attracting attention. There are various methods for manufacturing structural materials from aluminum alloys, but casting can be cited as a method that can efficiently produce complex shapes at low cost and is suitable for mass production. In particular, the die-casting method, in which molten aluminum alloy is injected into a mold to form cast components, is extremely productive.

[0003] Here, an example of an aluminum alloy that can produce components with high strength and ductility by casting is the Al-Mg-Si alloy. The Al-Mg-Si alloy also has the advantage of being able to obtain high strength without heat treatment.

[0004] For example, Patent Document 1 (Japanese Patent Publication No. 9-41060) proposes a non-heat-treatable aluminum alloy for high-pressure casting that can be used for automobile parts and the like, and states that it contains, "10-14% Si, 0.8-2.0% Cu, over 0.5-1.5% Mg, 0.005-0.05% Sr, and 0.001-0.01% Be by weight, with the remainder being Al and unavoidable impurities."

[0005] In the non-heat-treatable aluminum alloy for high-pressure casting described in Patent Document 1 above, it is stated that "by including appropriate amounts of trace amounts of Cu, Mg, and Sr in the composition near the Al-eutectic Si, high strength and good elongation can be obtained in the as-cast state without heat treatment, and it can be used as a component material without heat treatment."

[0006] Furthermore, Patent Document 2 (Japanese Unexamined Patent Publication No. 2008-127630) proposes, with the objective of providing an aluminum alloy for casting with excellent casting characteristics and productivity, an aluminum die-cast product using the same alloy, and a method for manufacturing the same product, "an aluminum alloy for casting characterized by containing Si: 9.0 to 11.0 mass%, Mg: 0.05 to 0.35 mass%, Cu: 0.1 mass% or less, Fe: 0.05 to 0.40 mass%, Mn: 0.3 to 0.5 mass%, and Li: 0.0020 to 0.0600 mass%, with the remainder being aluminum and unavoidable impurities."

[0007] In the aluminum alloy described in Patent Document 2 above, "the permissible range for the content of Li as an improving element is 0.0020 to 0.0600 mass%, which is significantly wider than the permissible range for the content of Sr as an improving element in the conventional invention. Therefore, in the aluminum alloy for casting of the present invention, productivity can be improved while the refinement effect of eutectic Si is sufficiently maintained." Furthermore, in die casting, "it has excellent casting properties and mold adhesion resistance, i.e., mold release properties, and the resulting die-cast products have high mechanical strength, i.e., tensile strength, yield strength and hardness, and high elongation, i.e., high ductility, as well as excellent productivity."

[0008] Japanese Patent Publication No. 9-41060 Japanese Patent Publication No. 2008-127630

[0009] However, the non-heat-treatable aluminum alloy for high-pressure casting described in Patent Document 1 contains 0.8 to 2.0% Cu to improve the tensile strength of the aluminum alloy casting. It is known that the addition of Cu reduces the corrosion resistance of aluminum alloy castings, and if the corrosion resistance of the aluminum alloy casting is insufficient, it is difficult to use it as a structural material for automobiles.

[0010] Furthermore, in recent years, in order to achieve carbon neutrality, there has been a growing demand to reduce the proportion of new aluminum ingots in the raw materials of aluminum products and increase the proportion of aluminum scrap. Since copper (Cu) improves the yield strength of aluminum materials when added to aluminum alloys, it is added to many aluminum alloys and is often found in aluminum scrap. Therefore, Cu is an element that is easily mixed in when the proportion of scrap is increased.

[0011] Against this backdrop, increasing the proportion of aluminum scrap in the raw materials inevitably increases the amount of copper (Cu) mixed in, which is problematic because it negatively affects the corrosion resistance of the final aluminum material.

[0012] On the other hand, the aluminum alloy for casting described in Patent Document 2 has a Cu content of 0.1 mass% or less, and although productivity is improved while maintaining the refinement effect of eutectic Si by adding Li, it is difficult to say that the mechanical properties are sufficient when aluminum alloy castings are used as structural materials for automobiles.

[0013] In recent years, in order to improve fuel efficiency, there has been a growing demand for lighter automobiles (especially hybrid and electric vehicles), and Al-Mg-Si alloys with excellent mechanical properties such as strength and toughness, as well as corrosion resistance, are in high demand. However, currently, there are no aluminum alloys for casting that adequately achieve both high mechanical properties and good corrosion resistance while allowing for the inclusion of Cu as an impurity.

[0014] In view of the problems of the prior art described above, the object of the present invention is to provide an Al-Mg-Si alloy that can exhibit high mechanical properties and good corrosion resistance in aluminum alloy castings without heat treatment, and an aluminum alloy casting made from the Al-Mg-Si alloy.

[0015] To achieve the above objective, the inventors diligently researched the relationship between the composition of aluminum alloys for castings and the microstructure and various properties of aluminum alloy castings. As a result, they found that the main reason for the decrease in corrosion resistance when Cu is added to aluminum alloys is Al ２This is due to the formation of Cu, and in Al-Mg-Si-Cu alloys, by optimizing the balance between excess Mg and Cu, Al ２ We discovered that it is possible to preferentially form Al-Mg-Cu compounds (such as the T phase) that are more stable than Cu. In addition, we confirmed that Al-Mg-Cu compounds do not reduce the corrosion resistance of aluminum alloy castings, leading to the present invention.

[0016] In other words, the present invention provides an aluminum alloy for casting characterized by containing Mg: 2.0 to 8.5 wt%, Si: 0.02 to 5.0 wt%, Cu: 0.01 to 1.5 wt%, with the remainder being Al and unavoidable impurities, wherein the content of Zn mixed in as the unavoidable impurities is 0.5 wt% or less, and satisfying the following relationships (1) and (2): (1) Mg content - 1.73 × Si content > 0 (2) (Mg content - 1.73 × Si content) / Cu content > 0.2

[0017] In relation (1), "Mg content - 1.73 × Si content" is the amount of excess Mg, and excess Mg refers to Si and Mg ２ This refers to the Mg remaining after the formation of Mg-Si precipitates such as Si. In the aluminum alloy for casting of the present invention, the excess Mg has a value greater than 0. The presence of excess Mg allows for the formation of Al-Mg-Cu compounds preferentially over Al-Cu compounds. Since Al-Mg-Cu compounds have a lower potential and are more stable than Al-Cu compounds, the corrosion resistance of aluminum alloy castings can be improved.

[0018] Furthermore, relation (2) defines the relationship between the amount of excess Mg and the Cu content. When the value of excess Mg / Cu content is greater than 0.2, a sufficient amount of excess Mg is present relative to the Cu content, and Al-Mg-Cu compounds can be reliably formed preferentially over Al-Cu compounds.

[0019] Furthermore, in the aluminum alloy for castings of the present invention, the content of Zn, which is an unavoidable impurity, is restricted to 0.5 wt% or less. By strictly restricting the Zn content, it is possible to suppress a decrease in the corrosion resistance of the aluminum alloy casting. The Zn content is preferably 0.3 wt% or less, and more preferably 0.1 wt% or less.

[0020] Furthermore, the aluminum alloy for casting according to the present invention preferably contains one or more of the following: Fe: 0.2 to 1.2 wt%, and Mn: 0.2 to 1.2 wt%. Fe and Mn have the effect of improving the mechanical properties of the aluminum alloy casting, as well as preventing seizing to the mold during casting.

[0021] Furthermore, the aluminum alloy for casting according to the present invention preferably contains one or more of the following: Ca: 0.004 to 0.04 wt%, Sr: 0.004 to 0.04 wt%, Be: 0.0005 to 0.005 wt%, Ti: greater than 0 wt% and less than or equal to 0.5 wt%, and B: greater than 0 wt% and less than or equal to 0.2 wt%. Ca and Sr have the effect of refining Mg-Si precipitates, Be has the effect of suppressing the blackening of the casting surface due to the oxidation of Mg, and Ti and B have the effect of refining the casting structure.

[0022] Furthermore, the aluminum alloy for casting according to the present invention is preferably a non-heat-treatable alloy. Since the aluminum alloy for casting according to the present invention can exhibit high mechanical properties and good corrosion resistance without heat treatment after casting, various aluminum alloy castings can be manufactured simply and inexpensively.

[0023] Furthermore, the present invention also provides an aluminum alloy casting characterized by being made of the aluminum alloy for casting of the present invention. By using the aluminum alloy for casting of the present invention, the aluminum alloy casting of the present invention combines high mechanical properties and good corrosion resistance.

[0024] Furthermore, it is preferable that the aluminum alloy casting of the present invention contains an Al-Mg-Cu compound. In aluminum alloy castings containing a large amount of Cu, Al-Cu compounds tend to form easily, but by optimizing the amount of excess Mg and the Cu content, the formation of Al-Mg-Cu compounds can be promoted, and by forming an Al-Mg-Cu compound that is more stable than Al-Cu compounds, the corrosion resistance of the aluminum alloy casting can be improved.

[0025] Furthermore, in the aluminum alloy casting of the present invention, it is preferable that the volume proportion of the Al-Mg-Cu compound is greater than that of the Al-Cu compound. By making the volume proportion of the Al-Mg-Cu compound greater than that of the Al-Cu compound, the corrosion resistance of the aluminum alloy casting can be further improved.

[0026] According to the present invention, it is possible to provide an Al-Mg-Si alloy that can exhibit high mechanical properties and good corrosion resistance in aluminum alloy castings without heat treatment, and an aluminum alloy casting made from said Al-Mg-Si alloy.

[0027] This is a backscattered electron image of an aluminum alloy plate having the composition of Example 2. This is a backscattered electron image of an aluminum alloy plate having the composition of Example 3. This is a backscattered electron image of an aluminum alloy plate having the composition of Example 4. This is a backscattered electron image of an aluminum alloy plate having the composition of Example 5. This is a backscattered electron image of an aluminum alloy plate having the composition of Example 6. This is a backscattered electron image of an aluminum alloy plate having the composition of Example 7. This is a backscattered electron image of an aluminum alloy plate having the composition of Example 12. This is a backscattered electron image of an aluminum alloy plate having the composition of Comparative Example 2.

[0028] The aluminum alloy for casting and aluminum alloy castings of the present invention will be described in detail below, but the present invention is not limited to these.

[0029] 1. Aluminum Alloy for Castings The aluminum alloy for castings of the present invention imparts high mechanical properties to aluminum alloy castings without heat treatment, while the additive elements and their content are optimized so that Al-Mg-Cu compounds are formed preferentially to Al-Cu compounds. Each component will be described in detail below.

[0030] (1) Essential additive elements Mg: 2.0-8.5 wt% Mg, even in its pure form, contributes to improving the mechanical properties of aluminum alloys, but Si and Mg ２ It forms Mg-Si precipitates such as Si, contributing to improved strength of aluminum alloy castings. By adding 2.0 wt% or more (preferably 3.5 wt% or more) of Mg, sufficient tensile strength, yield strength, and ductility can be obtained even in the as-cast state after casting. Conversely, if the amount of Mg exceeds 8.5 wt%, the fluidity of the molten metal decreases, and castability decreases. Ductility also tends to decrease. Furthermore, if the aluminum alloy casting of the present invention is subjected to aging treatment, Mg-Si compounds precipitate, further improving the mechanical properties.

[0031] Si: 0.02 to 5.0wt% Si is Mg and Mg ２ Si forms Mg-Si precipitates, such as Si, contributing to improved strength of aluminum alloy castings. Furthermore, Si improves molten metal flowability and enhances castability. This effect becomes significant at content levels of 0.02 wt% or higher. Conversely, at content levels exceeding 5.0 wt%, the Mg-Si precipitates tend to become coarser. The preferred Si content is 1.5 to 4.0 wt%, and a more preferred content is 1.5 to 3.0 wt%.

[0032] Cu: 0.01 to 1.5 wt% Cu has the effect of improving the mechanical properties of aluminum alloy castings through solid solution strengthening or crystallization as an intermetallic compound. This effect becomes significant with the addition of 0.01% (preferably 0.2 wt% or more, more preferably 0.5 wt% or more), while conversely, if added at levels exceeding 1.5 wt%, Al-Cu compounds are more likely to form, reducing corrosion resistance. In addition, Al-Mg-Cu compounds and Al-Cu compounds tend to coarseen, reducing elongation.

[0033] Furthermore, the Mg content and Si content must satisfy the relationship (1): Mg content - 1.73 × Si content > 0. In relationship (1), "Mg content - 1.73 × Si content" is the amount of excess Mg, and excess Mg refers to Si and Mg ２ This refers to the Mg remaining after the formation of Mg-Si precipitates such as Si. In the aluminum alloy for casting of the present invention, the excess Mg is greater than 0. The presence of excess Mg allows for the formation of Al-Mg-Cu compounds preferentially over Al-Cu compounds. Since Al-Mg-Cu compounds have a lower potential and are more stable than Al-Cu compounds, the corrosion resistance of the aluminum alloy casting can be improved. On the other hand, the amount of excess Mg is preferably 2.5 wt% or less, and more preferably 2.0 wt% or less. By setting the upper limit of excess Mg to such a value, the decrease in the ductility of the aluminum alloy casting can be suppressed.

[0034] In addition, the amount of excess Mg and the Cu content must satisfy the relationship (2): (Mg content - 1.73 × Si content) / Cu content > 0.2. When the value of excess Mg amount / Cu content is greater than 0.2, a sufficient amount of excess Mg is present relative to the Cu content, and Al-Mg-Cu compounds can be reliably formed in preference to Al-Cu compounds. On the other hand, the upper limit of excess Mg amount / Cu content is not particularly limited as long as it does not impair the effects of the present invention, but it is preferably 10 or less.

[0035] (2) Optional additive elements Fe: 0.2 to 1.2 wt% Fe has the effect of improving the mechanical properties of aluminum alloy castings and preventing seizing to the mold during casting. This effect becomes significant when the content is 0.2 wt% or more. Conversely, if added in amounts exceeding 1.2 wt%, coarse compounds such as Al-Fe and Al-Si-Fe precipitates are formed, which tends to reduce the ductility of the casting material. Corrosion resistance also decreases.

[0036] Mn: 0.2 to 1.2 wt% Mn has the effect of improving the mechanical properties of aluminum alloy castings and preventing sticking to the mold during casting. This effect becomes significant when the content is 0.2 wt% or more. Conversely, when added in excess of 1.2 wt%, coarse compounds such as Al-Mn-based precipitates are formed, and the ductility of the casting material tends to decrease. Also, the corrosion resistance decreases.

[0037] Ca: 0.004 to 0.04 wt% Ca has the effect of refining Mg-Si-based precipitates, and this effect becomes significant when the content is 0.004 wt% or more. Conversely, when added in excess of 0.04 wt%, the fluidity of the molten metal decreases and the casting property deteriorates.

[0038] Sr: 0.004 to 0.04 wt% Sr has the effect of refining Mg-Si-based precipitates, and this effect becomes significant when the content is 0.004 wt% or more. Conversely, when added in excess of 0.04 wt%, the fluidity of the molten metal decreases and the casting property deteriorates.

[0039] Be: 0.0005 to 0.005 wt% Be has the effect of suppressing the oxidation depletion of Mg during melting. This effect becomes significant when it is 0.0005 wt% or more. On the other hand, even if added in excess of 0.005 wt%, no improvement in the effect is observed. Also, Be is a poisonous substance, and it is preferably suppressed to 0.005 wt% or less.

[0040] Ti: More than 0 wt% and 0.5 wt% or less Ti has the effect of refining the casting structure (α phase). This effect is exhibited by adding a small amount, but no improvement in the effect is observed even if added in excess of 0.5 wt%.

[0041] B: More than 0 wt% and 0.2 wt% or less B has the effect of refining the casting structure of aluminum alloy castings, and by containing B in the range of more than 0 wt% and 0.2 wt% or less, this effect can be surely exhibited.

[0042] (3) Inevitable impurities: The content of Zn as an inevitable impurity is regulated to be 0.5 wt% or less. By setting the content of Zn to 0.5 wt% or less, it is possible to suppress a decrease in the corrosion resistance of the aluminum alloy casting. The content of Zn is preferably 0.3 wt% or less, and more preferably 0.1 wt% or less.

[0043] In addition, inevitable impurities such as Cr and Ni are regulated to be 0.2 wt% or less.

[0044] 2. Aluminum alloy casting The aluminum alloy casting of the present invention is an aluminum alloy casting made of the aluminum alloy for casting of the present invention. Hereinafter, the microstructure, mechanical properties, and corrosion resistance of the aluminum alloy casting will be described in detail.

[0045] (1) Metallographic structure The greatest feature of the metallographic structure of the aluminum alloy casting of the present invention is that it has an Al-Mg-Cu-based compound (T phase or S phase). By using the aluminum alloy for casting of the present invention, an Al-Mg-Cu-based compound (T phase or S phase) is formed due to the presence of an appropriate amount of excess Mg and Cu. On the other hand, when excess Mg does not exist, an Al-Cu-based compound (Al ２ Cu) crystallizes.

[0046] Here, even when an Al-Cu-based compound is formed in the aluminum alloy casting, the volume ratio of the Al-Mg-Cu-based compound is preferably larger than that of the Al-Cu-based compound. By making the volume ratio of the Al-Mg-Cu-based compound larger than that of the Al-Cu-based compound, the corrosion resistance of the aluminum alloy casting can be further improved.

[0047] The method for evaluating the volume ratio of the Al-Mg-Cu-based compound and the Al-Cu-based compound is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known methods can be used. For example, the cross-section of the mirror-polished aluminum alloy casting may be observed by SEM-EDS or EPMA, or may be evaluated from the peak intensity ratio of the XRD diffraction pattern.

[0048] (2) Mechanical properties The aluminum alloy casting of the present invention has high yield strength and excellent elongation after fracture in a state where no heat treatment is performed after casting.

[0049] More specifically, the 0.2% yield strength of the aluminum alloy casting of the present invention is preferably 150 MPa or more, more preferably 160 MPa or more. Also, the elongation after fracture is preferably 7% or more, more preferably 9% or more, and most preferably 13% or more.

[0050] (3) Corrosion resistance While the aluminum alloy casting of the present invention contains a sufficient amount of Cu for improving mechanical properties, the formation of an Al-Cu-based compound (Al ２ Cu) that reduces corrosion resistance is suppressed. Also, since an Al-Mg-Cu-based compound (T phase or S phase), which is more chemically stable than the Al-Cu-based compound, is formed, it has good corrosion resistance.

[0051] For the evaluation of the corrosion resistance of the aluminum alloy casting of the present invention, various conventionally known methods can be used. For example, it can be evaluated by the degree of weight loss due to salt spray. More specifically, it can be confirmed that the degree of weight loss of the aluminum alloy casting of the present invention is clearly smaller compared to an aluminum alloy casting in which an Al-Cu-based compound (Al ２ Cu) has formed after salt spray for 1000 hours or more.

[0052] 3. Method for manufacturing an aluminum alloy casting An aluminum alloy casting can be obtained by casting an aluminum alloy molten metal made of the aluminum alloy for casting of the present invention. The casting method in the casting process is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known casting methods (sand casting, die casting, gravity casting, low-pressure casting, die casting, etc.) can be used. That is, the aluminum alloy casting of the present invention is not limited to those cast by a specific casting method.

[0053] Also, heat treatment after casting is not necessary, but appropriate heat treatment may be performed if necessary. The casting conditions are not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known casting conditions can be used.

[0054] 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.

[0055] 《Examples》 Raw materials were mixed to have the compositions (wt%) shown in Table 1 as Examples 1 to 15, melted at 770 to 790°C, deslag treatment with molten metal cleaning flux, and degassing treatment by Ar gas injection. Then, an aluminum alloy sheet material, which is an embodiment of the present invention, was obtained by PF die casting under the following conditions: high injection speed: 2.0 m / s, casting pressure: 80 MPa, casting temperature: 720 to 740°C, and mold temperature: 120 to 160°C. The size of the aluminum alloy sheet material is 110 x 110 x 3 mm.

[0056]

[0057] Table 1 also shows the value of "Mg content - 1.73 × Si content" indicating excess Mg, as well as the excess Mg / Cu value. In the compositions of Examples 1 to 7, it can be seen that excess Mg was present in all cases, and the excess Mg / Cu value was greater than 0.2. In addition, in all cases, the content of Zn, which was introduced as an unavoidable impurity, was 0.5 wt% or less.

[0058] <Comparative Examples> An aluminum alloy sheet material, which is a comparative aluminum 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 (wt%) shown as Comparative Examples 1 to 3 in Table 1.

[0059] Comparative Example 1 has a low Cu content, which reduces the corrosion resistance of aluminum alloy castings. On the other hand, it has a low Mg content, and the composition is free of excess Mg. The composition of Comparative Example 2 contains 1.1 wt% Cu and is free of excess Mg. Comparative Example 3 has a composition that does not contain Cu, which reduces the corrosion resistance of aluminum alloy castings.

[0060] [Evaluation] The microstructure, corrosion resistance, and tensile properties of each aluminum alloy sheet obtained as examples and comparative examples were evaluated.

[0061] (1) Samples for cross-sectional observation were cut from each aluminum alloy plate from which the microstructure was obtained, and these were mirror-polished to prepare samples for microstructure observation. For observation, a scanning electron microscope (JSM7200F, JEOL Ltd.) equipped with an EDS (JED2300, JEOL Ltd.) was used to perform SEM-EDS point analysis on the aluminum alloy matrix and compounds. The obtained results are shown in Table 2. Table 2 also lists the generated phases at the measurement points identified from the EDS point analysis results. Furthermore, backscattered electron images of the aluminum alloy plates in Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 12 and Comparative Example 2 are shown in Figures 1, 2, 3, 4, 5, 6, 7, and 8, respectively. The measurement points (1 to 18) for the EDS point analysis are shown in each backscattered electron image.

[0062]

[0063] EDS point analysis was performed on each aluminum alloy sheet in regions corresponding to the Al alloy matrix and regions corresponding to the compounds. Compounds containing more Mg than the Al alloy matrix are Al-Mg-Cu compounds, and compounds containing less Mg than the Al alloy matrix are Al-Cu compounds. From Table 2, it can be seen that Al-Mg-Cu compounds are formed in the aluminum alloy sheet material, which is an embodiment of the present invention. In contrast, Al-Cu compounds, which cause a decrease in corrosion resistance, are formed in the aluminum alloy material having the composition of Comparative Example 2.

[0064] (2) Corrosion Resistance (Corrosion Test) A salt spray test was conducted on each aluminum alloy plate. Specifically, an aluminum alloy plate, which had been surface-machined to a depth of 1 mm, was immersed in acetone, cleaned in an ultrasonic cleaner for 2 minutes, and then the weight of the test piece was measured before the corrosion test. Next, all parts of the test piece except the evaluation surface (100 x 100 mm) were masked with masking tape, and corrosion tests were conducted in a salt spray test apparatus for 100 hours, 500 hours, and 1000 hours. Three test pieces were used for each test time, for a total of nine test pieces.

[0065] Next, the test specimens were removed from the salt spray test apparatus, the masking tape was removed, and they were washed with pure water and dried in a drying oven at 40°C. Then, the lincro solution (phosphoric acid (JIS K 9005), chromium(VI) oxide (CrO2) was used. ３ A solution (20 g of [the substance] mixed with distilled water to make 1000 mL) was boiled, and the test specimen was immersed in the Linncro solution for 10 minutes to remove corrosion products.

[0066] Next, the test specimens removed from the Wrinkro solution were immersed in tap water, washed in an ultrasonic cleaner for 2 minutes, then rinsed with pure water, and dried in a drying oven at 40°C. The weight of the dried test specimens was measured, and the change in weight of the test specimens before and after the corrosion test was defined as the corrosion loss. The degree of corrosion loss was calculated by dividing this by the evaluation area. The results are shown in Table 3.

[0067]

[0068] Table 3 shows that all of the aluminum alloy plates, which are the aluminum alloy castings of the present invention, exhibit excellent corrosion resistance. In particular, the aluminum alloy plate having the composition of Example 2 shows little corrosion weight loss even after 1000 hours of salt spraying. Furthermore, even the aluminum alloy plate having the composition of Example 15, which contains 1.0 wt% Fe, shows no change in corrosion weight loss after 500 hours of salt spraying. In contrast, the aluminum alloy plate, which is a comparative aluminum alloy casting, shows a large corrosion weight loss due to salt spraying, with the corrosion weight loss after 1000 hours of salt spraying being approximately five times that of Example 2. In addition, the aluminum alloy plate having the composition of Comparative Example 3, which does not contain Cu, shows good corrosion resistance, but it cannot be made from aluminum scrap material.

[0069] (3) Tensile properties Tensile test specimens of JIS Z 2241 14B were cut from each aluminum alloy plate and tensile tests were performed under the condition of a tensile speed of 5 mm / min. The obtained 0.2% yield strength and elongation at break are shown in Table 4.

[0070]

[0071] As shown in Table 4, the aluminum alloy plates, which are the aluminum alloy castings of the present invention, all have excellent tensile properties, with a 0.2% yield strength of 150 MPa or more and an elongation at break of 7% or more.

[0072] Furthermore, comparing the aluminum alloy plate in Example 8, which differs only in its Fe and Mn content, with the aluminum alloy plate in Example 9, it can be seen that increasing the Fe and Mn content improves the 0.2% yield strength without reducing the corrosion resistance and elongation at break of the aluminum alloy plate.

[0073] Furthermore, comparing the aluminum alloy plate in Example 9, which differs only in its Zn content, with the aluminum alloy plate in Example 10, it can be seen that the effect of Zn content on the corrosion resistance of the aluminum alloy plate is extremely small up to approximately 0.5 wt%.

[0074] Furthermore, comparing the corrosion resistance of the aluminum alloy plate in Example 12 with that of the aluminum alloy plate in Comparative Example 2, it can be seen that the aluminum alloy plate, which is an embodiment of the present invention and an aluminum alloy casting, has better corrosion resistance than the aluminum alloy plate in Comparative Example 2, even when the Cu content is increased to 1.4 wt%.

[0075] Furthermore, from the elongation at break of the aluminum alloy sheet in Comparative Example 2, it can be seen that when the excess Mg content / Cu content value is less than 0, the ductility of the aluminum alloy sheet decreases significantly.

Claims

1. An aluminum alloy for casting characterized by containing Mg: 2.0 to 8.5 wt%, Si: 0.02 to 5.0 wt%, Cu: 0.01 to 1.5 wt%, with the remainder being Al and unavoidable impurities, wherein the content of Zn, which is mixed in as an unavoidable impurity, is 0.5 wt% or less, and satisfying the following relationships (1) and (2): (Mg content - 1.73 × Si content) > 0 (1) (Mg content - 1.73 × Si content) / Cu content > 0.2 (2) 2. The aluminum alloy for casting according to claim 1, characterized in that it contains one or more of the following: Fe: 0.2 to 1.2 wt%, and Mn: 0.2 to 1.2 wt%.

3. The aluminum alloy for casting according to claim 1 or 2, characterized by containing one or more of the following: Ca: 0.004 to 0.04 wt%, Sr: 0.004 to 0.04 wt%, Be: 0.0005 to 0.005 wt%, Ti: greater than 0 wt% and less than or equal to 0.5 wt%, and B: greater than 0 wt% and less than or equal to 0.2 wt%.

4. The aluminum alloy for casting according to claim 1 or 2, characterized in that it is a non-heat-treatable alloy.

5. An aluminum alloy casting characterized by being made of the aluminum alloy for casting described in claim 1 or 2.

6. The aluminum alloy casting according to claim 5, characterized by having an Al-Mg-Cu compound.

7. The aluminum alloy casting according to claim 5, characterized in that the volume proportion of the Al-Mg-Cu compound is greater than that of the Al-Cu compound.

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