High-bending-performance heat-treatment-free die-casting aluminum alloy and preparation method thereof

Abstract

This invention discloses a high-bending-performance heat-free die-cast aluminum alloy and its preparation method, comprising Si 6.2~7.5%, Mn 0.35~0.60%, Fe 0.08~0.15%, Mg 0.08~0.15%, Cu The alloy contains 0.12~0.20% Sr, 0.10~0.25% Mo, 0.05~0.15% Cr, 0.01~0.03% Sr, 0.01~0.05% Ba, with the remainder being Al and unavoidable impurity elements, the total amount of unavoidable impurity elements being ≤0.5%. The synergistic modification effect of Sr and Ba elements in this invention significantly improves the Si modification effect, transforming the coarse, lamellar eutectic Si phase into a dispersed granular or short rod-shaped Si phase, greatly enhancing the alloy's impact toughness and bending performance. The composite solid solution strengthening effect of Mg and Cu elements significantly reduces the solid solubility of a single element in the matrix, making the solid solution strengthening effect of the casting more uniform, thereby improving the alloy's strength, toughness, and impact toughness. The synergistic effect of Mn, Cr, and Mo elements significantly improves the Fe phase morphology, transforming acicular and bulk Fe phases into fine-sized bulk Fe phases, improving the alloy's toughness.

Description

Technical Field

[0001] This invention relates to the field of metal materials technology, specifically to a high-bending-performance, heat-treatable die-cast aluminum.

[0002] Alloys and their preparation methods. Background Technology

[0003] In the past two years, the new energy vehicle industry has developed rapidly, with domestic sales accounting for an increasingly large proportion. To improve driving range and handling performance, new energy vehicles have higher requirements for lightweighting. The car body accounts for about 30% of the total vehicle weight, making it the largest part of the vehicle and the area with the greatest potential for lightweighting. Integrated die casting has become a key focus of the automotive industry's lightweighting technology layout. However, the integration of multiple parts leads to the large size of die castings, which greatly increases the difficulty of subsequent straightening after heat treatment and the scrap rate. Therefore, the development of heat-treatment-free aluminum alloy materials suitable for large, thin-walled die castings has become an inevitable choice for integrated die casting.

[0004] Integrated die casting of large components has ended the traditional automotive manufacturing method of stamping followed by welding, significantly reducing process complexity and offering the following advantages: 1) Lightweighting: Fully utilizing the low-density characteristics of aluminum alloys in large structural parts, the weight of the car body is significantly reduced. 2) Efficiency improvement and cost reduction: One-time die casting greatly reduces the number of production lines for parts, reduces welding processes, and shortens the production cycle. 3) Increased part strength: Integrated die casting avoids the strength reduction caused by welding, eliminates elements such as mounting holes, and improves the strength of structural parts. As the integration of components increases, the connection methods with surrounding components become more diverse, among which bending performance is an important evaluation indicator. Currently, the bending performance of alloys is often below 30°, while OEMs often require this indicator to exceed 45°. Therefore, there is an urgent need to develop high-bending-performance, heat-treatable die-cast aluminum alloys for thin-walled car body structural parts.

[0005] The shortcomings of existing technology:

[0006] CN117947319 discloses an aluminum alloy, its preparation method, and an aluminum alloy die-casting part. The aluminum alloy comprises the following components: Si content 6.5~8.5%; Fe content ≤0.3%; Cu content ≤0.3%; Mn content ≤0.5%; Mg content ≤0.5%; Cr content ≤0.2%; V content 0.002~0.02%; Nb content 10~100ppm; Sr content 0.01~0.03%; rare earth element content 10~100ppm, wherein the rare earth element is La and / or Ce; the balance is Al and unavoidable impurities. The patent adds appropriate amounts of V, rare earth element La, and / or C. The aluminum alloy obtained by adding e and Nb elements possesses high strength along with excellent ductility, toughness, corrosion resistance, and flowability. The alloy exhibits a tensile strength exceeding 240 MPa, a yield strength exceeding 120 MPa, an elongation exceeding 10%, and a bending angle reaching 38°. However, the bending angle achieved by this patent does not yet meet the requirements. The Sr-modified silicon phase is prone to burn-out during recycling, necessitating additional addition, increasing process costs, and also leading to insufficient weldability. Furthermore, the high prices of V and Nb elements significantly reduce the alloy's cost competitiveness.

[0007] WO2021 / 150604A1 discloses a method for preparing a heat-free integrated die-cast aluminum alloy using recycled aluminum as raw material. The alloy has the following composition by mass percentage: Si 6.5-7.5%, Cu 0.4-0.8%, Mg 0.2-0.4%, Fe <0.4%, V 0.05-0.15%, Sr 0.01-0.03%, Ti <0.15%, Cr <0.03%. This patent, by adding Cu and controlling the Cu / Mg and α-Al volume fractions, achieves an alloy yield strength exceeding 130 MPa and a bending angle approaching 40°. However, excessive Cu content significantly reduces the alloy's corrosion resistance, thus affecting the application range of the castings. Summary of the Invention

[0008] The purpose of this invention is to provide a high-bending-performance heat-free die-cast aluminum alloy and its preparation method, so as to solve the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a high-bending-performance heat-free die-cast aluminum alloy, comprising Si 6.2~7.5%, Mn 0.35~0.60%, Fe 0.08~0.15%, Mg 0.08~0.15%, Cu 0.12~0.20%, Mo 0.10~0.25%, Cr 0.05~0.15%, Sr 0.01~0.03%, Ba 0.01~0.05%, with the remainder being Al and unavoidable impurity elements, the total amount of unavoidable impurity elements being ≤0.3%.

[0010] Preferably, the mass relationship between Cu and Mg is as follows:

[0011] Cu:Mg≤2.5

[0012] The mass relationship between Fe, Mn and Cr is as follows:

[0013] (Fe+2Mn+3Cr)≤1.65.

[0014] Preferably, the unavoidable impurity elements include Ni, V, P, Ca and Ti, wherein the sum of Ni and Ca is <0.09% and the sum of V, P and Ti is <0.21%.

[0015] This invention also provides a method for preparing a high-bending-performance heat-free die-cast aluminum alloy, which specifically includes the following steps:

[0016] S1. Obtain the alloy melt;

[0017] S2. Obtain a high-strength and tough die-cast aluminum alloy that does not require heat treatment;

[0018] S3, die casting.

[0019] Preferably, step S1 specifically includes the following steps:

[0020] a1. Preheat the raw materials of aluminum, silicon, molybdenum, manganese, strontium, chromium, copper, magnesium and barium to 150~200°C;

[0021] a2. Put the preheated aluminum raw material from step a1 into an industrial smelting furnace and heat it to 760~820℃;

[0022] a3. Add silicon, molybdenum, manganese, strontium, chromium and copper raw materials to a melting furnace and dissolve them at a temperature of 760~800℃. Then add magnesium raw materials and stir, setting the reduction rate to 30~40 cycles / min and the stirring time to 2~5min. The alloy melt is obtained after complete melting.

[0023] Preferably, step S2 specifically includes the following steps:

[0024] b1. Add a slag remover to the alloy melt. The weight of the slag remover accounts for 0.1~0.3 wt.% of the total alloy melt. The added slag remover is a sodium-free refining agent. The temperature of the alloy melt is controlled at 730~750℃.

[0025] b2. Perform direct-reading spectral analysis on the alloy composition;

[0026] b3. After passing the test, add Sr and Ba raw materials, control the alloy melt temperature at 720~740°C, stir and let stand for 5-10 minutes, the stirring rate is 30~40 revolutions / min, the stirring time is 2~5 minutes, and the alloy melt temperature is controlled at 720~740°C.

[0027] b4. After adding a covering agent to the alloy melt obtained in b3 within 0-2 min, directly refine and degas the mixture. The covering agent is a sodium-free covering agent, and the amount added is 0.05-0.1 wt.%. Argon or nitrogen with a purity of 5N or higher is introduced during the refining and degassing process at a pressure of 0.18-0.25 MPa for 5-20 minutes and at a temperature of 720-730℃.

[0028] b5. The refined alloy melt is subjected to composition testing, density testing, and slag content testing. After passing the tests, it is allowed to stand and cool down to 690~720℃ to obtain a high-strength and tough die-cast aluminum alloy that does not require heat treatment.

[0029] Preferably, in step S3, the die-casting temperature is set to 670~705℃, the casting pressure is set to 1200-1600 bar, the slow injection speed is set to 0.18~0.55 m / s, the fast injection speed is set to 3.5~6.0 m / s, the mold temperature and barrel temperature are set to 150-250℃, and the mold cavity vacuum degree is set to 80~95 Pa.

[0030] Preferably, in step a1, the aluminum raw material is pure aluminum with a mass fraction purity of more than 99.7%, the silicon raw material is industrial silicon of 441 or higher, the copper raw material is pure copper, the manganese raw material is aluminum-manganese master alloy or manganese agent, the strontium raw material is Al-10Sr master alloy, the chromium raw material is aluminum-chromium master alloy, the molybdenum raw material is aluminum-molybdenum master alloy, the magnesium raw material is pure magnesium, and the barium raw material is aluminum-barium master alloy.

[0031] Preferably, in step b3, the weight of the Sr raw material accounts for 0.1 to 0.3% of the total alloy melt.

[0032] Preferably, in step b5, the component detection is performed using direct-reading spectroscopy, the density detection is performed using a vacuum solidification apparatus, and the slag content detection is performed using the K-mode or PoDFA method. The standard for qualified components is a density value of not less than 2.62 g / cm³. 3 The K-modulus value is no higher than 1 / 20.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] This invention discloses a high-bending-performance heat-free die-cast aluminum alloy and its preparation method. The synergistic modification effect of Sr and Ba elements significantly enhances the Si modification effect, transforming the coarse, lamellar eutectic Si phase into a dispersed granular or short rod-shaped Si phase, greatly improving the alloy's impact toughness and bending performance. The combined solid solution strengthening effect of Mg and Cu elements significantly reduces the solid solubility of any single element in the matrix, resulting in a more uniform solid solution strengthening effect in the casting, thereby improving the alloy's strength, toughness, and impact toughness. The synergistic effect of Mn, Cr, and Mo elements significantly improves the Fe phase morphology, transforming acicular and bulky Fe... The phase transformation into a fine-sized blocky Fe phase improves the toughness of the alloy. High-bending-performance heat-free aluminum alloy materials are mainly used in the production of large structural parts with large size, complex structure, high connection performance requirements, and difficult heat treatment. Without heat treatment, it can meet the production requirements of automotive structural parts with tensile strength ≥250MPa, yield strength ≥120MPa, and elongation ≥10%. This alloy has high casting strength, toughness, and bending performance, which is conducive to improving the subsequent connection qualification rate and connection strength, reducing product qualification rate and cost, and has significant technical significance and broad application prospects.

[0035] In this invention, the sum of Ni and Ca is less than 0.09%, which avoids the easy formation and enrichment of calcium at the grain boundaries to form a low-temperature brittle phase. The brittle phase is prone to forming microcracks during casting ejection and deformation, which can lead to premature cracking and fracture of the casting during stretching and bending. Ni is also prone to forming coarse-sized high-temperature brittle phases with Fe, Mn, etc., which can affect bending performance and elongation. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the second phase particle morphology of the heat-free die-cast aluminum alloy for the thin-walled vehicle body structural component of the present invention, which has high bending performance. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0039] In the description of this patent, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integrated connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this patent according to the specific circumstances.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a number" means two or more, unless otherwise explicitly specified.

[0041] Example

[0042] Please see Figure 1 As shown, the present invention provides a high-bending-performance heat-free die-cast aluminum alloy solution comprising: Si 6.2~7.5%, Mn 0.35~0.60%, Fe 0.08~0.15%, Mg 0.08~0.15%, Cu 0.12~0.20%, Mo 0.10~0.25%, Cr 0.05~0.15%, Sr 0.01~0.03%, Ba 0.01~0.05%, the remainder being Al and unavoidable impurity elements, the total amount of unavoidable impurity elements ≤0.5%, unavoidable impurity elements include Ni, V, P, Ca and Ti; the mass relationship between Cu and Mg is Cu:Mg≤2.5, the mass relationship between Fe, Mn and Cr is (Fe+2Mn+3Cr)≤1.65%, the sum of Ni and Ca <0.09%, the sum of V, P and Ti <0.21%, the ultimate tensile strength of the alloy is 250~300MPa, the yield strength is 120~140MPa, the elongation after fracture is 10~16%, and the bending angle is ≥50°.

[0043] This invention also provides a method for preparing a high-bending-performance heat-free die-cast aluminum alloy, specifically including the following steps:

[0044] S1. Obtain the alloy melt;

[0045] a1. Preheat the raw materials of aluminum, silicon, molybdenum, manganese, strontium, chromium, copper, magnesium and barium to 150~200°C. The aluminum raw material is pure aluminum with a mass fraction purity of more than 99.7%. The silicon raw material is industrial silicon of 441 or above. The copper raw material is pure copper. The manganese raw material is aluminum-manganese master alloy or manganese agent. The strontium raw material is Al-10Sr master alloy. The chromium raw material is aluminum-chromium master alloy. The molybdenum raw material is aluminum-molybdenum master alloy. The magnesium raw material is pure magnesium. The barium raw material is aluminum-barium master alloy.

[0046] a2. Put the preheated aluminum raw material from step a1 into an industrial smelting furnace and heat it to 760~820℃;

[0047] a3. Add silicon, molybdenum, manganese, strontium, chromium and copper raw materials to a melting furnace and dissolve them at a temperature of 760~800℃. Then add magnesium raw materials and stir. Set the halving rate to 30~40 cycles / min and the stirring time to 2~5min. The alloy melt is obtained after complete melting.

[0048] S2. Obtain a high-strength and tough die-cast aluminum alloy that does not require heat treatment;

[0049] b1. Add a slag remover to the alloy melt. The weight of the slag remover accounts for 0.1~0.3 wt.% of the total alloy melt. The added slag remover is a sodium-free refining agent. The temperature of the alloy melt is controlled at 730~750℃.

[0050] b2. Perform direct-reading spectral analysis on the alloy composition;

[0051] b3. After passing the test, add Sr and Ba raw materials. The weight of Sr raw materials accounts for 0.1~0.3% of the total alloy melt. The alloy melt temperature is controlled at 720~740°C. After stirring, let it stand for 5-10 minutes. The stirring rate is 30~40 revolutions / min and the stirring time is 2~5 minutes. The alloy melt temperature is controlled at 720~740°C.

[0052] b4. After adding a covering agent to the alloy melt obtained in b3 within 0-2 min, directly refine and degas the mixture. The covering agent is a sodium-free covering agent, and the amount added is 0.05-0.1 wt.%. Argon or nitrogen with a purity of 5N or higher is introduced during the refining and degassing process at a pressure of 0.18-0.25 MPa for 5-20 minutes and at a temperature of 720-730℃.

[0053] b5. The refined alloy melt is subjected to composition analysis, density analysis, and slag content analysis. Composition analysis is performed using direct-reading spectroscopy; density analysis is performed using a reduced-pressure solidification apparatus; and slag content analysis is performed using the K-mold or PoDFA method. The standard for acceptable composition is a density value of not less than 2.62 g / cm³. 3The K-modulus value is not higher than 1 / 20. After passing the test, it is allowed to stand and cool down to 690~720℃ to obtain a heat-free high-strength and tough die-cast aluminum alloy.

[0054] S3. Die casting: Die casting temperature is set to 670~705℃, casting pressure is set to 1200-1600 bar, slow injection speed is set to 0.18~0.55 m / s, fast injection speed is set to 3.5~6.0 m / s, mold temperature and barrel temperature are set to 150-250℃, and mold cavity vacuum degree is set to 80~95 Pa.

[0055] The following are specific examples of Examples 1-6 and Comparative Examples 1-3:

[0056]

[0057] Table 1 shows the specific data for Examples 1-6 and Comparative Examples 1-3.

[0058]

[0059] Table 2 shows the mechanical properties and bending angle test data of Examples 1-6 and Comparative Examples 1-3 after vacuum die casting.

[0060] Therefore, the synergistic modification effect of Sr and Ba elements can significantly improve the modification effect of Si, transforming the coarse and lamellar eutectic Si phase into a dispersed granular or short rod-shaped Si phase, greatly improving the impact toughness and bending performance of the alloy. The composite solid solution strengthening effect of Mg and Cu elements significantly reduces the solid solubility of a single element in the matrix, making the solid solution strengthening effect of the casting more uniform, thereby improving the strength, toughness and impact toughness of the alloy. The synergistic effect of Mn, Cr and Mo elements can significantly improve the morphology of the Fe phase, transforming the acicular and bulk Fe phase into a fine-sized bulk Fe phase, improving the toughness of the alloy.

[0061] Furthermore, high-bending-performance heat-free aluminum alloy materials are mainly used in the production of large structural components that are large in size, complex in structure, have high requirements for connection performance, and are difficult to heat treat. Without the need for heat treatment, they can meet the production requirements of automotive structural components with tensile strength ≥250MPa, yield strength ≥120MPa, and elongation ≥10%. This alloy has high casting strength, toughness, and bending performance, which is beneficial to improving the subsequent connection qualification rate and connection strength, reducing product qualification rate and cost, and has significant technical significance and broad application prospects.

[0062] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-bending-performance heat-free die-cast aluminum alloy, characterized in that: It includes Si 6.2~7.5%, Mn 0.35~0.60%, Fe 0.08~0.15%, Mg 0.08~0.15%, Cu 0.12~0.20%, Mo 0.10~0.25%, Cr 0.05~0.15%, Sr 0.01~0.03%, Ba 0.01~0.05%, with the remainder being Al and unavoidable impurity elements, the total amount of unavoidable impurity elements being ≤0.3%; The mass relationship between Cu and Mg is as follows: Cu:Mg≤2.5 The mass relationship between Fe, Mn and Cr is as follows: (Fe + 2Mn + 3Cr) ≤ 1.65; The unavoidable impurity elements include Ni, V, P, Ca, and Ti, wherein the sum of Ni and Ca is <0.09%, and the sum of V, P, and Ti is <0.21%. The specific steps in the aluminum alloy preparation method are as follows: S1. Obtain the alloy melt; S2. Obtain a high-strength and tough die-cast aluminum alloy that does not require heat treatment; S3, die casting.

2. The high bending performance heat-free die-cast aluminum alloy according to claim 1, characterized in that: Step S1 specifically includes the following steps: a1. Preheat the raw materials of aluminum, silicon, molybdenum, manganese, strontium, chromium, copper, magnesium and barium to 150~200°C; a2. Put the preheated aluminum raw material from step a1 into an industrial smelting furnace and heat it to 760~820℃; a3. Add silicon, molybdenum, manganese, strontium, chromium and copper raw materials to a melting furnace and dissolve them at a temperature of 760~800℃. Then add magnesium raw materials and stir, setting the reduction rate to 30~40 cycles / min and the stirring time to 2~5min. The alloy melt is obtained after complete melting.

3. The high bending performance heat-free die-cast aluminum alloy according to claim 1, characterized in that: Step S2 specifically includes the following steps: b1. Add a slag remover to the alloy melt. The weight of the slag remover accounts for 0.1~0.3 wt.% of the total alloy melt. The added slag remover is a sodium-free refining agent. The temperature of the alloy melt is controlled at 730~750℃. b2. Perform direct-reading spectral analysis on the alloy composition; b3. After passing the test, add Sr and Ba raw materials, control the alloy melt temperature at 720~740°C, stir and let stand for 5-10 minutes, the stirring rate is 30~40 revolutions / min, the stirring time is 2~5 minutes, and the alloy melt temperature is controlled at 720~740°C. b4. After adding a covering agent to the alloy melt obtained in b3 within 0-2 min, directly refine and degas the mixture. The covering agent is a sodium-free covering agent, and the amount added is 0.05-0.1 wt.%. Argon or nitrogen with a purity of 5N or higher is introduced during the refining and degassing process at a pressure of 0.18-0.25 MPa for 5-20 minutes and at a temperature of 720-730℃. b5. The refined alloy melt is subjected to composition testing, density testing, and slag content testing. After passing the tests, it is allowed to stand and cool down to 690~720℃ to obtain a high-strength and tough die-cast aluminum alloy that does not require heat treatment.

4. The high bending performance heat-free die-cast aluminum alloy according to claim 1, characterized in that: In step S3, the die-casting temperature is set to 670~705℃, the casting pressure is set to 1200-1600 bar, the slow injection speed is set to 0.18~0.55 m / s, the fast injection speed is set to 3.5~6.0 m / s, the mold temperature and barrel temperature are set to 150-250℃, and the mold cavity vacuum degree is set to 80~95 Pa.

5. The high bending performance heat-free die-cast aluminum alloy according to claim 2, characterized in that: In step a1, the aluminum raw material is pure aluminum with a mass fraction purity of over 99.7%, the silicon raw material is industrial silicon of 441 or higher, the copper raw material is pure copper, the manganese raw material is aluminum-manganese master alloy or manganese agent, the strontium raw material is Al-10Sr master alloy, the chromium raw material is aluminum-chromium master alloy, the molybdenum raw material is aluminum-molybdenum master alloy, the magnesium raw material is pure magnesium, and the barium raw material is aluminum-barium master alloy.

6. The high bending performance heat-free die-cast aluminum alloy according to claim 3, characterized in that: In step b3, the weight of Sr raw material accounts for 0.1~0.3% of the total alloy melt.

7. The high bending performance heat-free die-cast aluminum alloy according to claim 3, characterized in that: In step b5, direct-reading spectroscopy is used for component detection, vacuum solidification equipment is used for density detection, and K-mode or PoDFA method is used for slag content detection. The standard for acceptable composition is a density value of not less than 2.62 g / cm³. 3 The K-modulus value is no higher than 1 / 20.

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