Method for producing Al alloy for casting

Abstract

Provided is an Al alloy for casting, which can achieve both high mechanical properties and cost reduction. An Al alloy for casting according to the present invention contains 8.0 to 10.0 mass% of Si, 0.25 to 0.40 mass% of Mg, 0.30 to 0.50 mass% of Fe, 0.28 to 0.52 mass% of Mn, 0.08 to 0.22 mass% of Cu, 0.04 to 0.15 mass% of Ti, and 0.0075 to 0.028 mass% of Sr, with the balance being Al. The sum of the Fe content and the Mn content is limited to 1.0 mass% or less. Sr is not added in the dissolution step, but is added in a molten metal treatment step in which the Al oxide and H2 gas in the Al alloy molten metal obtained in the dissolution step are removed.

Description

Technical Field

[0001] The present invention relates to a method for producing an Al alloy for casting. Background Art

[0002] In the past, aluminum alloys (hereinafter referred to as Al alloys) have been widely used as raw materials for structural parts in automobiles, industrial machinery, aircraft, home appliances and other fields because they are lightweight and excellent in formability and mass production. For example, large castings such as suspension towers, side beams, and battery housings in the automotive field are generally made by die-casting AlSi10Mg (Al-Si-Mg alloys) and then T7 treatment (solution treatment and stabilization treatment (overaging treatment) by heating and quenching. Large castings made in this way have an elongation of more than 8%, a tensile strength of 200 to 230 MPa, and a yield strength of 120 to 140 MPa (also known as 2% yield strength). By the way, as structural parts in the automotive field, if it is a giga-die casting (large die-casting casting), it is required to have an elongation of more than 8%, a tensile strength of more than 180 MPa, and a yield strength of more than 120 MPa.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent document 1: Japanese Patent Application Publication No. 11-12673. Summary of the invention

[0006] However, in this Al alloy casting, while requiring high mechanical properties as an important safety component, strict cost reduction is also required. As one of the measures to reduce costs, for example, the heat treatment after casting can be omitted. However, when the Al-Si-Mg alloy classified as a heat-treated alloy is subjected to non-heat treatment (no heat treatment), the mechanical properties such as elongation, tensile strength and yield strength do not reach the required level, so there is a problem that it is difficult to take into account both high mechanical properties and cost reduction.

[0007] For example, Patent Document 1 discloses a method for manufacturing an Al alloy casting having high mechanical properties even in the cast state (no heat treatment after casting), wherein the Al alloy contains Si: 4 to 8 wt%, Cu: 0.4 to 1.0 wt%, Mg: 0.2 to 0.4 wt%, Fe: 0.05 to 0.3 wt%, Sr: 0.002 to 0.02 wt%, Zr: 0.0005 to 0.1 wt%, and the remainder substantially has the composition of Al, satisfying the condition of Cu+2.5Mg≥1.25 wt%.

[0008] However, the Al alloy casting obtained by the production method of Patent Document 1 has a high Cu content of 0.4 wt % or more and therefore has a disadvantage of being poor in corrosion resistance.

[0009] Means for solving problems

[0010] The technical problem of the present invention is to provide a method for producing an Al alloy for casting, which is obtained by studying the above-mentioned current situation and implementing improvements.

[0011] The present invention relates to a method for producing an Al alloy for casting, which contains 8.0 to 10.0 mass % Si, 0.25 to 0.40 mass % Mg, 0.30 to 0.50 mass % Fe, 0.28 to 0.52 mass % Mn, 0.08 to 0.22 mass % Cu, 0.04 to 0.15 mass % Ti and 0.0075 to 0.028 mass % Sr, and the remainder contains Al.

[0012] Furthermore, the sum of the contents of Fe and Mn is limited to 1.0 mass % or less. Sr is not added in the melting step but is added in the molten metal treatment step of removing Al oxides and H2 gas from the Al alloy molten metal obtained in the melting step.

[0013] In the method for producing the Al alloy for casting of the present invention, the Mg may be added in the molten metal treatment step instead of in the dissolution step.

[0014] Effects of the Invention

[0015] According to the invention of the present application, for example, even if giga-die casting (large die casting) or large low-pressure casting parts are set to the as-cast state (no heat treatment after casting), it is possible to obtain an Al alloy for casting or even an Al alloy casting showing good castability and mechanical properties (elongation, tensile strength and yield strength, etc.), and the high-cost heat treatment can be omitted, and the Al alloy for casting and the Al alloy casting can be provided at low cost. In particular, in the invention of the present application, since Sr is not added in the dissolution process, but is added during the molten metal treatment process of removing Al oxides and H2 gas in the Al alloy molten metal obtained in the dissolution process, it is possible to suppress Sr from being burned by the heat of the Al alloy molten metal, and the addition effect of Sr can be reliably exerted in the Al alloy for casting or the Al alloy casting. Therefore, the quality and yield rate of the Al alloy for casting or the Al alloy casting can be improved.

[0016] Furthermore, if Mg is not added in the melting process, but is added in the molten metal treatment process of removing Al oxides and H2 gas in the Al alloy molten metal obtained in the dissolution process, it is possible to suppress Mg from being burned by the heat of the Al alloy molten metal, and the addition effect of Mg can be reliably exerted in the Al alloy for casting or Al alloy casting. Therefore, the quality and yield rate of the Al alloy for casting or Al alloy casting can be improved. In addition, the present invention does not completely exclude heat treatment after casting. In applications requiring higher mechanical properties, for example, heat treatment performance of large low-pressure cast parts will be higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a flow chart showing the manufacturing process of the present invention;

[0018] Figure 2 It is a diagram showing the composition range of alloys of other companies and the alloy of the present application and the composition of the components of Examples and Comparative Examples;

[0019] Figure 3 It is a graph showing the results of measuring the tensile strength, yield strength and elongation of a casting obtained by a die casting method;

[0020] Figure 4 It is a graph showing the relationship between the Al alloy molten metal temperature during die casting and the tensile strength and yield strength of the casting;

[0021] Figure 5 It is a graph showing the relationship between the Al alloy molten metal temperature and the elongation of the casting during die casting;

[0022] Figure 6 It is a graph showing the relationship between the mold temperature during die casting and the tensile strength and yield strength of the casting;

[0023] Figure 7 It is a graph showing the relationship between the mold temperature during die casting and the elongation of the casting;

[0024] Figure 8 It is a graph showing the relationship between the mold vacuum degree during die casting and the tensile strength and yield strength of the casting;

[0025] Fig. 9 It is a graph showing the relationship between the mold vacuum degree and the elongation of the casting during die casting;

[0026] Fig.10 is a diagram showing the composition of a casting obtained by low pressure casting without heat treatment and a casting after T6 treatment;

[0027] Fig.11This is a graph showing the results of measuring the tensile strength, yield strength and elongation of a casting without heat treatment and a casting subjected to T6 treatment obtained by a low pressure casting method. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present invention will be described based on the drawings.

[0029] like Figure 2 As shown, the composition of the Al alloy for casting and the Al alloy casting involved in the invention of the present application contains, on a mass basis, 8.0 mass % to 10.0 mass % of Si (silicon), 0.25 mass % to 0.40 mass % of Mg (magnesium), 0.30 mass % to 0.50 mass % of Fe (iron), 0.28 mass % to 0.52 mass % of Mn (manganese), 0.08 mass % to 0.22 mass % of Cu (copper), 0.04 mass % to 0.15 mass % of Ti (titanium) and 0.0075 mass % to 0.028 mass % of Sr (strontium), and the remainder contains Al (aluminum) and inevitable impurities.

[0030] Si is an important alloy component (element) that helps improve castability, especially the fluidity of the melt. As mentioned above, the content of Si relative to the entire Al alloy for casting is preferably in the range of 8.0 mass % or more and 10.0 mass % or less. When the Si content is too low (less than 8.0 mass %), the fluidity of the melt cannot be ensured due to insufficient fluidity, and casting cracks are also prone to occur. On the contrary, if it contains more than 10.0 mass % of excess Si, the elongation of the Al alloy casting will be reduced.

[0031] Mg is mainly in the state of solid solution in the Al matrix of the Al alloy for casting, or exists as Mg2Si, and is an alloy component that effectively improves the tensile strength and yield strength. The content of Mg relative to the overall Al alloy for casting is preferably 0.25 mass % or more and 0.40 mass % or less. If Mg is contained within the above range, it will not have a significant effect on the castability or the elongation of the Al alloy casting, but can improve the mechanical properties such as the tensile strength and yield strength of the Al alloy casting. When the Mg content is too little (less than 0.25 mass %), it is easy to cause sintering of the mold. When the Mg content is too much (more than 0.40 mass %), there will be a tendency to reduce the elongation of the Al alloy casting.

[0032] Fe is an alloy component that has the effect of preventing sintering of the mold during casting. The content of Fe relative to the entire Al alloy for casting is preferably in the range of 0.30 mass % or more and 0.50 mass % or less. When the Fe content is too much (more than 0.50 mass %), Al-Si-Fe needle-shaped crystals (ternary compounds) will be generated, which significantly reduces the elongation of the Al alloy casting. If the Fe content is less than 0.50 mass %, the formation of needle-shaped crystals is suppressed, and the adverse effect on the elongation of the Al alloy casting can be controlled.

[0033] Mn is an alloy component added to prevent sintering of the mold during casting, and to suppress the generation of needle-shaped crystals consisting of Al-Si-Fe, to ensure the elongation of Al alloy castings. The content of Mn relative to the entire Al alloy for casting is preferably in the range of 0.28 mass % or more and 0.52 mass % or less. If the Mn content is set to 0.39 mass % or less, the demoulding property for the mold will be improved. In addition, when the Mn content exceeds 0.52 mass %, the Al grains will be coarsened so that the elongation is reduced. Therefore, if Mn is contained in the range of 0.39 mass % or less, the reduction of the elongation of the Al alloy casting can be suppressed, and the demoulding property is improved.

[0034] As described above, Mn has an inhibitory effect on the formation of Al-Si-Fe needle-shaped crystals in relation to Fe. According to the investigation and research conducted by the present inventors, if the sum of the contents of Fe and Mn is 1.0 (mass %) or less (Fe+Mn≤1.0), the inhibitory effect on the formation of needle-shaped crystals is extremely high.

[0035] Cu is dissolved in Al matrix, and is an effective alloy component for improving the mechanical properties of Al alloy castings, especially tensile strength and yield strength. The content of Cu relative to the overall content of Al alloy for casting is preferably in the range of 0.08 mass % or more and 0.22 mass % or less. If Cu is contained within the above range, corrosion resistance will not be impaired, and the solid solution strengthening effect in Al alloy can be effectively exerted. When Cu content is too much (exceeding 0.22 mass %), the reduction of corrosion resistance and elongation of Al alloy castings will be caused.

[0036] Ti is an effective alloy component for refining Al grains. When the Ti content is too low (less than 0.04 mass%), the Al grains are coarsened and the elongation, tensile strength and yield strength are reduced. On the contrary, when the Ti content is too high (more than 0.15 mass%), the Si grains (eutectic Si) are too concentrated at the grain boundaries and become defects. In this case, the elongation, tensile strength and yield strength are also reduced. Therefore, the Ti content relative to the entire Al alloy for casting is preferably in the range of 0.04 mass% to 0.15 mass%. In this way, the degree of Al grain refinement is adjusted to the extent that the dendrite shape remains in the Al grains, and the Si grains are finely dispersed in the entire casting structure, so that a stable and uniform casting structure is obtained.

[0037] Sr is an alloy component that can refine Si grains and effectively improve elongation, tensile strength and yield strength even in the cast state (no heat treatment after casting). The effect is significantly exerted when 0.0075% by mass or more of Sr is added. In contrast, when more than 0.028% by weight of excess Sr is added, Al-Si-Sr system ternary compounds are generated, which become over-modified, and casting defects are easily generated, thereby leading to a reduction in mechanical properties such as elongation, tensile strength and yield strength. The addition of Sr in the cast state will show the effect of spheroidizing and refining Si grains. If Si grains are spheroidized, stress concentration is suppressed. Therefore, if Sr is included in the composition of the Al alloy for casting, heat treatments such as solution treatment can be omitted due to its effect. Although there is no heat treatment in the cast state, Al alloy castings that fully ensure mechanical properties such as elongation, tensile strength and yield strength can be obtained. Therefore, the Sr content relative to the entire Al alloy for casting is preferably in the range of 0.0075 mass % to 0.028 mass %.

[0038] In the present invention, alloy components such as Zn, Ni, Sn, Pb, Ca, Cr, and Cd are treated as inevitable impurities. For Zn, if the content is too high, it will damage the corrosion resistance like Cu, so the content is limited to 0.15% by mass or less. Ca is a harmful alloy component that makes the casting structure unstable and deteriorates the flow of the molten metal, so the content is limited to 0.005% by mass or less. The content of other inevitable impurities is preferably controlled to be less than 0.1% by mass.

[0039] In addition, there is no particular limitation on the purity (quality) of the Al raw material used. If it is fully refined, it is easy to obtain an Al alloy casting with good mechanical properties. However, since refining requires a high cost, it may also contain other unavoidable impurities. For example, blocks (ingots) of high-purity Al and recycled materials may be mixed in an appropriate ratio.

[0040] In addition, when manufacturing the Al alloy for casting or Al alloy casting of the present invention, first, raw materials of each alloy component other than Mg and Sr among Al, Si, Mg, Fe, Mn, Cu, Ti, and Sr as main alloy components are put into a melting and holding furnace to dissolve these raw materials (dissolving step, see Figure 1 ). Here, a flux for slag removal is added to perform slag removal. The temperature of the Al alloy molten metal in the dissolution process is controlled within the range of 730°C ± 10°C. Raw materials containing Mg and Sr are not put into the dissolution holding furnace.

[0041] Next, the Al alloy molten metal dissolved in the dissolution holding furnace is transferred to a ladle preheated within the range of 750°C±50°C, and Al oxides and H2 gas in the Al alloy molten metal are removed by using rotary bubbling of N2 gas (molten metal treatment process). The molten metal treatment process varies depending on the amount of Al alloy molten metal, and takes about 10 to 15 minutes to perform. Moreover, during the molten metal treatment process, the raw materials (secondary alloy substrate) containing Mg and Sr are put into the ladle in such a way that the composition of the Al alloy for casting becomes the above-mentioned specified proportion (secondary alloy feeding treatment). Flux is added 5 minutes after the start of the molten metal treatment process, and Al oxides and H2 gas in the Al alloy molten metal are removed by performing rotary bubbling of N2 gas.

[0042] When the treatment time of the molten metal treatment process is, for example, 12 minutes, it is necessary to ensure the time for stirring Mg and Sr in the Al alloy molten metal as evenly as possible. In addition, the management of the molten metal temperature is extremely important, and the temperature of the Al alloy molten metal after the molten metal treatment process is controlled within the range of 680°C ± 10°C. Since alloy components such as Mg and Sr are easily burned by the heat of the Al alloy molten metal, in the present invention, they are added in the molten metal treatment process rather than the dissolution process to prevent the burning of Mg and Sr.

[0043] As secondary alloy substrates, for example, AlMn20 (containing Mn: 20 mass%) and AlSr10 (containing Sr: 10 mass%) can be used. Of course, in order to adjust the alloy composition, AlSi50 (containing Si: 50 mass%), AlCu50 (containing Cu: 50 mass%), Mg99.9%, AlTi5B1 (containing Ti: 5 mass%, B: 1 mass%), etc. can also be added to the ladle. In addition, slag removal can also be performed in the molten metal processing step. It is also possible to add only raw materials containing Sr in the molten metal processing step, and add raw materials containing Mg in the dissolution step, but both are preferably added in the molten metal processing step.

[0044] Next, the Al alloy molten metal refined by the molten metal treatment process is transferred from the ladle to the hand-held furnace (hand-held process). The temperature of the Al alloy molten metal in the hand-held furnace is controlled within the range of 665°C ± 5°C. Then, the refined Al alloy molten metal is cast from the hand-held furnace into a specified mold (casting mold) by a casting machine or a low-pressure casting machine under pressure and solidified, thereby forming an Al alloy for casting or an Al alloy casting (casting process). Here, the mold temperature is set in the range of 180°C to 220°C so that the temperature of the Al alloy molten metal cast into the mold from the hand-held furnace is maintained at about 665°C ± 5°C. When the die casting method is used, the vacuum degree of the mold is set in the range of 50mbar to 100mbar.

[0045] The Al alloy casting of the present invention can be manufactured by the conventionally known die casting method, low pressure casting method or gravity casting method. Therefore, the present invention is specifically described in each embodiment. In addition, the present invention is not limited to the contents of the following embodiments, and various changes can be made within the scope of the main purpose of the present invention.

[0046] exist Figure 2 The composition ranges of other companies' casting Al alloys (hereinafter referred to as other companies' alloys) and the casting Al alloy of the present invention (hereinafter referred to as the present alloy) are shown in the table, as well as the component compositions of the examples and comparative examples. Figure 3 The figure shows the results of measuring the tensile strength, yield strength and elongation as accurate values ​​by cutting test pieces from large castings (giga die casting) obtained by die casting using the same mold for alloys of other companies, examples and comparative examples. Figure 3 The value is an average value measured using 5 test pieces respectively.

[0047] In addition, Figure 3 The results of evaluating the molten metal fluidity during die casting, the sintering of the mold, and the cracking of the casting are also shown. Figure 2 and Figure 3 The other company alloy shown is an Al alloy for casting called C370 manufactured by Alcoa, which is considered to be equivalent to AlSi10MnMg. Comparative Example 1 is a case where the Sr content is near the lower limit of the alloy of the present application, and Comparative Example 2 is a case where the Sr content is near the upper limit of the alloy of the present application. All the other company alloys, examples and comparative examples are in the as-cast state without heat treatment.

[0048] from Figure 3It can be seen that Examples 1 and 2 of the present invention both show a tensile strength of about 280 MPa, a yield strength of about 140 MPa, and an elongation of about 14% in the cast state, and their mechanical properties are much better than those of other companies' alloys and Comparative Examples 1 and 2. It was found that the mechanical properties of Examples 1 and 2 greatly exceed the requirements for structural parts in the automotive field, for example, and therefore, they can fully withstand use even without heat treatment in the cast state. In addition, Examples 1 and 2 have good molten fluidity during casting and do not produce sintering. Moreover, no cracks can be seen in large castings, and the overall castability is extremely good. In addition, in Comparative Examples 1 and 2, cracks in large castings can be seen everywhere.

[0049] exist Figure 4 The relationship between the Al alloy molten metal temperature during die casting and the tensile strength and yield strength of the Al alloy casting in the present invention is shown in FIG. Figure 4 It can be seen that if the Al alloy molten metal temperature is within the range of 665℃~±5℃, the Al alloy casting can obtain extremely high tensile strength and yield strength. Figure 5 The relationship between the Al alloy molten metal temperature and the elongation of the Al alloy casting during die casting in the present invention is shown in FIG. At this time, if the Al alloy molten metal temperature is also within the range of 660° C. to 670° C., the Al alloy casting can obtain extremely high elongation.

[0050] exist Figure 6 The relationship between the mold temperature during die casting and the tensile strength and yield strength of the Al alloy casting in the present invention is shown in FIG. Figure 6 It can be seen that if the mold temperature is within the range of 180°C to 220°C, the Al alloy casting can obtain extremely high tensile strength and yield strength. Figure 7 The relationship between the mold temperature during die casting and the elongation of the Al alloy casting in the present invention is shown in FIG. At this time, if the mold temperature is in the range of 180°C to 220°C, the Al alloy casting can also obtain extremely high elongation. Although the details are not clear, it is believed that if the mold temperature is in the range of 180°C to 220°C, it is easy to maintain the Al alloy molten metal temperature in the die casting in the range of 660°C to 670°C. Due to the mold temperature, the Al alloy molten metal temperature is difficult to decrease. The Al alloy molten metal temperature is in the range of 660°C to 670°C, and thus the Al alloy casting is understood to have good mechanical properties.

[0051] exist Figure 8 The relationship between the mold vacuum degree during die casting and the tensile strength and yield strength of the Al alloy casting in the present invention is shown in FIG. Figure 8It can be seen that if the mold vacuum is within the range of 50mbar to 100mbar, the Al alloy casting can obtain extremely high tensile strength and yield strength. Fig. 9 The relationship between the mold vacuum degree during die casting and the elongation of the Al alloy casting in the present invention is shown in FIG. At this time, if the mold vacuum degree is within the range of 50 mbar to 100 mbar, the Al alloy casting can also obtain extremely high elongation.

[0052] As can be seen from the above description, according to the invention of the present application, even in the as-cast state (no heat treatment after casting), it is possible to obtain an Al alloy for casting and even an Al alloy casting that exhibits castability equivalent to that of an Al-Si-Mg alloy and exhibits good mechanical properties (elongation, tensile strength, yield strength, etc.), thereby being able to omit costly heat treatment and providing an Al alloy for casting and an Al alloy casting at low cost.

[0053] In particular, in the present invention, since the raw material (secondary alloy base material) containing Mg and Sr is added in the molten metal processing step so that the composition of the Al alloy for casting becomes the above-mentioned specified ratio, it is possible to suppress the burning of alloy components such as Mg and Sr due to the heat of the Al alloy molten metal, and the addition effect of Mg and Sr can be reliably exerted in the Al alloy for casting or Al alloy casting. Therefore, the quality and yield rate of the Al alloy for casting and the Al alloy casting can be improved.

[0054] The present invention does not intend to completely exclude heat treatment after casting. For example, in low-pressure casting applications requiring higher mechanical properties (particularly tensile strength and yield strength), T4 treatment (natural aging after solution treatment), T5 treatment (artificial aging and curing treatment after cooling from high temperature processing), T6 treatment (artificial aging and curing treatment after solution treatment) or T7 treatment may also be implemented.

[0055] exist Fig.10 The composition of Example 3 (no heat treatment) and Example 4 (T6 treatment) of the alloy of the present application are shown in FIG. In addition, the composition of Examples 3 and 4 is completely the same. Fig.11 2 shows the results of measuring the tensile strength, yield strength and elongation as accurate values ​​for Examples 3 and 4, by cutting test pieces from a non-heat-treated casting (Example 3) and a T6-treated casting (Example 4) obtained by low-pressure casting using the same mold. Fig.11 The value is the average value measured using 5 test pieces. Fig.11 The results of evaluating the molten metal fluidity during die casting, sintering of the mold, and cracking of the casting are also shown.

[0056] from Fig.11It can be seen that Example 3 of the present invention has obtained a tensile strength of more than 180 MPa and a yield strength of more than 120 MPa even in the as-cast state during low-pressure casting. However, the elongation is only 5%, which shows a slightly lower value. The melt fluidity of Example 3 during casting is good, no sintering occurs, and no cracks in the casting are observed. Example 3 shows very good castability as a whole. It can be seen that the results of Example 3 are roughly the same as the performance (mechanical properties) of AC4C after heat treatment specified in Japanese Industrial Standard JIS H5302.

[0057] In contrast, in Example 4, in which a large low-pressure casting component was subjected to T6 treatment, the tensile strength of 300 MPa, the yield strength of 242 MPa, and the elongation of 8.0% greatly exceeded the mechanical properties of Example 3. The mechanical properties of Example 4 far exceeded the performance (mechanical properties) after the heat treatment of AC4C, and greatly exceeded the required level of structural parts in the automotive field, for example. It can be seen that the heat treatment can be sufficiently durable depending on the application. In addition, even in Example 4, the melt fluidity during casting was good, no sintering occurred, and no cracks in the casting were observed.

Claims

1. A method for producing an Al alloy for casting, characterized in that: Contains 8.0-10.0 mass% of Si, 0.25-0.40 mass% of Mg, 0.30-0.50 mass% of Fe, 0.28-0.52 mass% of Mn, 0.08-0.22 mass% of Cu, 0.04-0.15 mass% of Ti and 0.0075-0.028 mass% of Sr, and the remainder contains Al, The sum of the contents of Fe and Mn is limited to 1.0 mass % or less. The Sr is not added in the dissolution step, but is added in the molten metal treatment step of removing Al oxides and H 2 gas in the Al alloy molten metal obtained in the dissolution step.

2. The method for producing an Al alloy for casting according to claim 1, wherein: The Mg is not added in the dissolving step but is added in the molten metal treating step.

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