A new energy vehicle recycled aluminum die casting easy to rivet and a preparation method thereof

Abstract

The application relates to the technical field of aluminum alloy, in particular to a new energy automobile recycled aluminum die casting easy to rivet and a preparation method thereof. The aluminum die casting comprises the following components in percentage by mass: Si 7.0-9.5%, Mg<=0.25%, Cu<=0.5%, Fe 0.2-0.4%, Cr 0.1-0.3%, Mn 0.05-0.15%, Zn 1.0-2.0%, Sr 0.01-0.1%, other single element content <=0.05%, total content of other elements <=0.15%, the rest being Al, and the proportion of recycled waste aluminum in raw materials is not less than 75%. The die casting is formed by die casting after over-recycled aluminum ingot smelting and refining, and then solid solution and aging treatment are carried out, riveting assembly and coating baking are carried out with other parts of the vehicle body. Compared with the prior art, the prepared large die casting has high strength and good ductility when the casting flow distance exceeds 500 mm, the preparation process of the application is simple, the cost is low, and the industrialized scale production is easy to realize, and the prepared die casting has good ductility and excellent riveting performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of manufacturing of aluminum alloy die castings for automobiles, and relates to a new energy automobile recycled aluminum die casting easy to rivet and a preparation method thereof. BACKGROUND

[0002] Automobile lightening is an effective method for reducing the overall vehicle weight, improving the automobile power performance, reducing energy consumption and reducing environmental pollution. Research shows that if the automobile weight is reduced by half, the corresponding energy consumption will also be reduced by nearly half. Increasing the use amount of aluminum alloy in the overall vehicle is one of important measures for realizing automobile lightening. As for the commonly used cast aluminum alloy for automobiles, the aluminum-silicon cast alloy accounts for about 80% of the cast aluminum alloy, and the aluminum-silicon cast alloy has good casting performance, corrosion resistance and mechanical properties, and can be used for producing large castings with complex shapes, high corrosion resistance and high ductility requirements. However, in the aluminum-silicon cast alloy without any treatment under the traditional casting process, the eutectic Si presents as a coarse needle with sharp corners, which is extremely easy to cut the matrix and cause stress concentration during the alloy stress process, resulting in the decrease of the mechanical properties of the alloy. The traditional aluminum alloy uses electrolytic primary aluminum as a raw material to prepare the aluminum alloy, and the carbon emission amount is high. With the requirement of low-carbon environmental protection, the world is accelerating the use amount of green low-carbon aluminum alloy in the automobile industry. It is of great significance to develop and research green low-carbon environmental protection recycled aluminum alloy automobile parts.

[0003] Using the riveting method to replace the traditional welding process can promote the realization of the heterogeneous material connection of the automobile hybrid body, further reduce the weight and energy consumption of the automobile body, and reduce carbon emission. Riveting refers to the rivet, under the extrusion of the rivet rod, penetrating the materials of the surface layer and the intermediate layer, flowing and extending in the lowermost layer of materials, and undergoing a permanent plastic deformation of the rivet linking process. The ductility of the existing large-scale die-cast aluminum alloy is very sensitive to the flow distance during die casting. Generally, when the flow distance exceeds 500 mm, the elongation will decrease sharply, and even decrease by more than 60% compared with the position close to the gate, resulting in the fluctuation of the mechanical properties of the large-scale die-cast parts at different positions, and increasing the difficulty of product design.

[0004] Patent document CN 112779444 A introduces an aluminum alloy for riveting, the chemical composition of which is as follows: Mg: 0.2-0.3%, Si: 1.4-1.6%, Mn: 0.05-0.2%, Cr: 0.1-0.5%, Zn: 0.1-0.4%, Ti: 0.1-0.2%, Sr: 0.2-0.3%, and the balance of Al and inevitable impurities. The yield strength of the final casting is between 80-100 MPa, and the elongation is about 17%. The influence of flow distance on the ductility of the alloy is not considered in the sampling process of performance testing of the alloy, and the yield strength of the alloy is low. In addition, the content of Sr in the alloy is too high at 0.2-0.3%, which greatly increases the degassing pressure during alloy smelting, and also increases the production cost.

[0005] Patent document CN 113909448 A introduces a preparation method of an aluminum alloy die casting for riveting of new energy vehicles and the die casting. The chemical composition of the aluminum alloy is as follows: Si: 9.0-11.5%, Fe: ≤0.2%, Cu: ≤0.05%, Mn: 0.4-0.8%, Mg: 0.1-0.6%, Zn: ≤0.07%, Ti: 0.1-0.2%, Sr: 0.01-0.027%, and the balance of Al and inevitable impurities. The yield strength of the alloy is between 110 MPa and 125 MPa, and the elongation is between 3.55-4.36%. The influence of flow distance on the ductility of the alloy is not considered in the sampling process of performance testing of the alloy, the yield strength of the alloy is good, but the elongation is low. At the same time, the maximum tolerance of impurity element Fe is 0.2%, which limits the amount of waste aluminum used in the preparation process.

[0006] Patent document CN 110195175 B introduces a corrosion-resistant die casting alloy for automobiles. The chemical composition of the aluminum alloy is as follows: Si 6.5-7.6%, Mg 1.4-2.1%, Cu 0.8-1.3%, Sr 0.05-0.11%, Zn 0.4-0.9%, Mn 0.4-0.8%, Fe 0.2-0.6%, Y 0.2-0.5%, Er 0.03-0.05%, and the balance of Al and inevitable impurities. The Mg content of the alloy is relatively high, between 1.4-2.1%, and Y element is used for modification treatment of the aluminum alloy, so that the alloy has certain strength and excellent corrosion resistance. Y element is a rare earth element, and in this invention, Y is used as a modifier with an addition amount of 0.2-0.5%, which makes the manufacturing cost of the alloy material relatively high, and is not conducive to mass production. SUMMARY

[0007] The present application aims at overcoming the defects of the prior art and provides a new energy automobile recycled aluminum die casting easy to rivet and a preparation method thereof.

[0008] The present application can be achieved by the following technical scheme: a new energy automobile recycled aluminum die casting easy to rivet, in addition to Al element, comprising the following mass percentages of chemical components: Si 7.0-9.5%, Mg≤0.25%, Cu≤0.5%, Fe 0.2-0.4%, Cr 0.1-0.3%, Mn 0.05-0.15%, Zn 1.0-2.0%, Sr 0.01-0.1%, other elements≤0.05% in single content, other elements≤0.15% in total content, and the use proportion of waste aluminum in raw materials is not less than 75%. The other elements are unavoidable impurities.

[0009] Preferably, in addition to Al element, comprising the following mass percentages of chemical components: Si 7.0-8.0%, Mg 0.05-0.15%, Cu 0.1-0.2%, Fe 0.25-0.35%, Cr 0.1-0.2%, Mn 0.05-0.15%, Zn 1.0-1.5%, Sr 0.01-0.05%, other elements≤0.05% in single content, other elements≤0.15% in total content, and the use proportion of waste aluminum in raw materials is not less than 80%.

[0010] Preferably, the alloy structure of the aluminum die casting is hypoeutectic structure, and the eutectic intermetallic compound is not greater than 2.0 μm and is dispersedly distributed.

[0011] The present application also provides a preparation method of the new energy automobile recycled aluminum die casting easy to rivet, comprising:

[0012] Step one: recycled aluminum ingot smelting: according to the main alloy element composition, the waste aluminum not less than 75% is used to cooperate with pure aluminum ingot and intermediate alloy to smelt and cast the casting blank; wherein the waste aluminum is preferably recycled pop can, and further preferably the amount of recycled pop can in the recycled aluminum alloy is not less than 50%;

[0013] Step 2: Ingot refining: The ingot from step 1 is remelted and refined and degassed, and the composition is fine-tuned to the target composition. The refining temperature is controlled at 700-780°C, preferably 720-780°C, and the degassing temperature is controlled at 740-760°C, preferably 745-755°C. After degassing, the ingot is allowed to stand for 5.0-20.0 minutes, preferably 10.0-15.0 minutes. Then, a crystal-controlling modifier and a refiner are added to the melt, and the ingot is fully stirred for 2.0-10.0 minutes (preferably 5.0-10.0 minutes) under the action of an electromagnetic field before die casting.

[0014] Step 3: Die casting: Before die casting, preheat the mold to 220-250℃. Apply a layer of release agent on the mold surface during the preheating process. After preheating, die casting is carried out. The temperature of the aluminum melt is controlled between 680-720℃.

[0015] Step 4: Riveting assembly: After the die-cast parts are water-cooled or mist-cooled, they are cleaned and riveted within 2 to 90 days, preferably after 10 to 20 days of natural aging.

[0016] Step 5: Painting, baking, packaging and warehousing.

[0017] Preferably, the modifier added in step 2 is a crystal-controlling mixture with Sr and Zn as main elements (i.e., a mixture of the aforementioned modifier and refiner) that can significantly improve the morphology and distribution of the eutectic alloy, and its chemical composition by mass percentage is: Sr 1.1-1.2, Zn 3.0-4.0, Cu ≤ 0.02%, and the rest is Al.

[0018] Preferably, the die castings can be directly riveted after die casting, or can be riveted after solution aging treatment. The solution aging treatment is to heat the die castings to 530-550°C, keep them at this temperature for 1.0-2.0 hours, then water quench them. After water quenching, they are heated to 100-180°C and aged for 1.0-4.0 hours.

[0019] Preferably, after the coating in step five, a baking hardening treatment is performed, the baking temperature is 140-160° C., and the baking time is 0.5-1.0 h.

[0020] The present invention provides a method for preparing a recycled aluminum die-casting for new energy vehicles that is easy to rivet. The prepared recycled aluminum die-casting has a thickness of ≤3.5 mm, and the body is sampled at a casting flow distance of ≤500 mm starting from the inner gate. The yield strength is ≥120 MPa and the elongation after fracture is ≥8.0%.

[0021] Preferably, the prepared thickness≤3.5mm recycled aluminum die casting, from the ingate, through the casting flow distance≥500mm and≤1000mm, the body sampling, the yield strength≥120MPa, the elongation after breaking≥5.0%.

[0022] The application utilizes waste aluminum to produce the easy-to-rivet recycled aluminum die casting, from the perspective of material formula and preparation method, adopts the morphology regulation of eutectic microstructure, and invents an easy-to-rivet recycled aluminum die casting for new energy vehicles, which can meet the performance requirements of new energy vehicle structural part manufacturing and application.

[0023] The die casting adopts traditional aluminum-silicon alloy, the Si content is controlled in 7.0-9.5%, the Si content is relatively high in the hypoeutectic system, close to eutectic structure, and the high Si content makes the alloy system have good casting performance, and the high volume fraction of Si also helps to enhance the wear resistance of the alloy. Under the traditional casting process, the eutectic Si in the aluminum-silicon casting alloy without any treatment presents as coarse needle-shaped, sharp corners, and is easy to cut the matrix and cause stress concentration during the alloy stress process, causing the mechanical properties of the alloy to decrease. In the application, Sr modification treatment is added to the melt during alloy smelting, and in the alloy solidification process, Sr can selectively adsorb on the specific growth surface of Si, inhibit the growth of eutectic Si, and improve the morphology of eutectic Si and the mechanical properties.

[0024] In the present invention, the Zn content is controlled between 1.0 and 2.0%. The inventors have found that adding Zn above 1.0%, in addition to promoting the uniform distribution of the precipitated phase, can also significantly improve the fracture resistance of the eutectic structure. For cast Al-Si alloys, the fracture toughness of the eutectic region is much lower than that of the aluminum matrix. Therefore, the main factor affecting its riveting performance and fracture toughness is the ability of its eutectic structure to resist crack initiation and propagation. The cracking of the eutectic structure is mainly the cracking of the Si particles themselves and the destruction of the bond between the Si particles and the aluminum matrix. The inventors have found that after adding Zn above 1.0% into the aluminum-silicon alloy, under the pressure and cooling rate conditions of high-pressure casting, the Zn element will be segregated at the interface between the Al matrix and Si particles of the eutectic structure during solidification, which can improve the interfacial bonding strength between the aluminum matrix and the Si particles, thereby preventing the interface cracking between the Si particles and the matrix during riveting and significantly improving the macroscopic resistance of the casting to riveting cracking. Furthermore, the inventors discovered that the addition of Zn can lower the eutectic reaction temperature and appropriately increase the solidification range, thus improving the fluidity of the alloy melt during casting. Furthermore, Zn can segregate at the melt front, hindering oxidation reactions between oxygen in the mold cavity and the melt front, forming oxide inclusions. This facilitates the production of products with low oxide inclusion content and casting defects even at long casting flow distances, thereby improving the stability of mechanical properties.

[0025] Products produced using this method are water quenched after die-casting and then cleaned. After cleaning, the parts are riveted and assembled with other vehicle body parts within 2 to 90 days. After riveting and assembly, the die-cast parts, along with the entire body-in-white, are then sent to the paint shop for painting and baking. The cleaned parts are left to stand for natural aging, while painting and baking in the paint shop produce an effect equivalent to artificial aging. If die-cast parts are riveted and assembled earlier than 2 days or later than 90 days, the alloy's riveting performance and mechanical properties after painting and baking will be degraded.

[0026] Compared with the prior art, the beneficial effects of the above technical solution of the present invention are as follows:

[0027] 1. The present invention utilizes waste aluminum to produce the recycled aluminum die-casting for new energy vehicles that is easy to rivet, and invents a recycled aluminum die-casting for new energy vehicles that is easy to rivet. The preparation method conforms to the development concept of green environmental protection, energy conservation and emission reduction.

[0028] 2. This method targets low-cost aluminum-silicon casting alloys. After being processed by this technical means, it obtains excellent comprehensive performance and the ability to resist riveting cracking on a macro scale, which can meet the performance requirements of the manufacturing and application of new energy vehicle structural parts.

[0029] 3. The preparation method is simple in process, easy to implement in mass production, and can be used for the production of large die castings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 1 is a process flow chart of the preparation method of the present invention;

[0031] Figure 2 This is the rivet morphology of the die-cast part in Example 3. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, those skilled in the art will be able to make several changes and improvements without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention.

[0033] Example 1

[0034] A recycled aluminum die-casting for new energy vehicles that is easy to rivet has the following chemical components by mass: Si 7.0%, Mg 0.25%, Cu 0.5%, Fe 0.4%, Cr 0.1%, Mn 0.15%, Zn 1.0%, Sr 0.01%, and the remainder being Al and unavoidable impurities.

[0035] The preparation method of the above alloy is as follows Figure 1 As shown, the following steps are included:

[0036] Step 1: Prepare the materials according to the main alloying elements, use no less than 75% of scrap aluminum, pure aluminum ingots and master alloys to melt and cast the ingots;

[0037] Step 2: The ingot from step 1 is remelted and refined and degassed, and the composition is fine-tuned to the target composition. The refining temperature is controlled at 780° C., and the degassing temperature is controlled at 740° C. After degassing, the ingot is allowed to stand for 20.0 min. A crystal-controlling modifier and a refiner are added to the solution (in this embodiment, a crystal-controlling mixture is used as the modifier and refiner, and the composition of the crystal-controlling mixture is Sr 1.15%, Zn 3.5%, and the remainder is Al). The ingot is fully stirred under the action of an electromagnetic field for 2.0 min.

[0038] Step 3: Before die casting, preheat the mold to 220°C. Apply a layer of mold release agent on the mold surface during the preheating process. After preheating, perform die casting. The temperature of the aluminum melt is controlled between 720°C.

[0039] Step 4: The die-cast parts are cleaned after water cooling or mist cooling, and riveted and assembled on the second day.

[0040] Step 5: Paint and bake. The baking temperature is 140℃ and the time is 1 hour. After painting and baking, the products are packaged and put into storage.

[0041] The obtained aluminum alloy is subjected to a tensile property test, wherein the tensile property is tested on a universal tensile testing machine at room temperature.

[0042] Example 2

[0043] A new energy vehicle recycled aluminum die casting easy to rivet, each chemical component mass percent is: Si 9.5 %, Mg 0.2 %, Cu 0.4 %, Fe 0.2 %, Cr 0.3 %, Mn 0.05 %, Zn 2.0 %, Sr 0.1 %, the rest is Al and inevitable impurities. The preparation method of the alloy is carried out according to the process steps of example 1. The difference lies in that the refining temperature in step two is 700℃, the degassing temperature is 760℃, and after degassing, it is placed for 5.0 min, after modification and refinement treatment, electromagnetic stirring for 10.0 min; In step three, the mold preheating temperature is 250℃, and the temperature of the aluminum melt during pressure casting is 680℃; In step 4, after the part cleaning is completed, riveting assembly and coating baking are carried out on the 90th day, the baking temperature is 160℃, and the time is 0.5h.

[0044] Tensile property test is carried out according to the test method of example 1.

[0045] Example 3

[0046] A new energy vehicle recycled aluminum die casting easy to rivet, each chemical component mass percent is: Si 8.25 %, Mg 0.15 %, Cu 0.3 %, Fe 0.3 %, Cr 0.2 %, Mn 0.1 %, Zn 1.5 %, Sr 0.05 %, the rest is Al and inevitable impurities. The preparation method of the alloy is carried out according to the process steps of example 1. The difference lies in that the refining temperature in step two is 740℃, the degassing temperature is 750℃, and after degassing, it is placed for 10.0 min, after modification and refinement treatment, electromagnetic stirring for 5.0 min; In step three, the mold preheating temperature is 235℃, and the temperature of the aluminum melt during pressure casting is 700℃; In step 4, after the part cleaning is completed, riveting assembly and coating baking are carried out on the 45th day, the baking temperature is 150℃, and the time is 0.6h.

[0047] Tensile property test is carried out according to the test method of example 1.

[0048] Example 4

[0049] A new energy vehicle recycled aluminum die casting easy to rivet, each chemical component mass percentage is: Si 8.5%, Mg 0.1%, Cu 0.2%, Fe 0.35%, Cr 0.25%, Mn 0.125%, Zn 1.75%, Sr 0.03%, the rest is Al and inevitable impurities. The difference lies in that the refining temperature in step two is 730 DEG C, the degassing temperature is 745 DEG C, and the standing time after degassing is 15.0 min, after modification and refinement treatment, electromagnetic stirring for 6.0 min; in step three, the mold preheating temperature is 230 DEG C, and the temperature of aluminum melt during die casting is 710 DEG C; in step 4, riveting assembly and coating baking are carried out on the 20th day after the completion of part cleaning, the baking temperature is 150 DEG C, and the time is 0.7 h.

[0050] Tensile property test is carried out according to the test method of example 1.

[0051] Example 5

[0052] A new energy vehicle recycled aluminum die casting easy to rivet, each chemical component mass percentage is: Si 8.5%, Mg 0.1%, Cu 0.2%, Fe 0.35%, Cr 0.25%, Mn 0.125%, Zn 1.75%, Sr 0.03%, the rest is Al and inevitable impurities. The difference lies in that the refining temperature in step two is 730 DEG C, the degassing temperature is 745 DEG C, and the standing time after degassing is 15.0 min, after modification and refinement treatment, electromagnetic stirring for 6.0 min; in step three, the mold preheating temperature is 230 DEG C, and the temperature of aluminum melt during die casting is 710 DEG C; in step 4, riveting assembly and coating baking are carried out on the 20th day after the completion of part cleaning, the baking temperature is 150 DEG C, and the time is 0.7 h.

[0053] Tensile property test is carried out according to the test method of example 1.

[0054] Example 6

[0055] A recycled aluminum die-casting for new energy vehicles that is easily riveted has the following chemical composition by weight: Si 9.5%, Mg 0.07%, Cu 0.25%, Fe 0.2%, Cr 0.3%, Mn 0.05%, Zn 1.3%, Sr 0.09%, with the remainder being Al and unavoidable impurities. The alloy was prepared according to the process steps of Example 1. The difference is that the refining temperature in step 2 is 733°C, the degassing temperature is 744°C, the degassing is allowed to stand for 13.0 minutes, and after modification and refinement treatment, electromagnetic stirring is performed for 9.0 minutes; the mold preheating temperature in step 3 is 222°C, and the temperature of the aluminum melt during die casting is 720°C; the die casting is heated to 530°C, kept warm for 2.0 hours, and then water quenched. After water quenching, it is heated to 100°C for aging treatment for 4.0 hours; after the parts are cleaned in step 4, riveted assembly and paint baking are carried out on the 60th day, and the baking temperature is 155°C for 0.9 hours.

[0056] The tensile properties test was performed according to the test method of Example 1.

[0057] Example 7

[0058] A recycled aluminum die-casting for new energy vehicles that is easily riveted has the following chemical composition by weight: Si 8.25%, Mg 0.21%, Cu 0.35%, Fe 0.33%, Cr 0.2%, Mn 0.06%, Zn 1.6%, Sr 0.06%, with the remainder being Al and unavoidable impurities. The alloy was prepared according to the process steps of Example 1. The difference is that the refining temperature in step 2 is 730℃, the degassing temperature is 750℃, the degassing is allowed to stand for 17.0min, and after modification and refinement treatment, electromagnetic stirring is performed for 8.0min; the mold preheating temperature in step 3 is 230℃, and the temperature of the aluminum melt during die casting is 710℃; the die casting is heated to 550℃, kept warm for 1.0h, and then water quenched. After water quenching, it is heated to 180℃ for aging treatment for 1.0h; after the parts are cleaned in step 4, riveted assembly and paint baking are carried out on the 10th day, and the baking temperature is 144℃ for 0.55h.

[0059] The tensile properties test was performed according to the test method of Example 1.

[0060] Example 8

[0061] A recycled aluminum die-casting for new energy vehicles that is easily riveted has the following chemical composition by weight: Si 8.5%, Mg 0.18%, Cu 0.5%, Fe 0.36%, Cr 0.25%, Mn 0.12%, Zn 1.7%, Sr 0.04%, with the remainder being Al and unavoidable impurities. The alloy was prepared according to the process steps of Example 1. The difference is that the refining temperature in step 2 is 770℃, the degassing temperature is 760℃, the degassing is allowed to stand for 13.0min, and after modification and refinement treatment, electromagnetic stirring is performed for 8.0min; the mold preheating temperature in step 3 is 235℃, and the temperature of the aluminum melt during die casting is 705℃; the die casting is heated to 545℃, kept warm for 1.5h, and then water quenched. After water quenching, it is heated to 170℃ for aging treatment for 1.5h; after the parts are cleaned in step 4, riveted assembly and paint baking are carried out on the 20th day, and the baking temperature is 147℃ for 0.65h.

[0062] The tensile properties test was performed according to the test method of Example 1.

[0063] Example 9

[0064] A recycled aluminum die-casting for new energy vehicles that is easily riveted has the following chemical composition by weight: Si 8%, Mg 0.14%, Cu 0.15%, Fe 0.22%, Cr 0.15%, Mn 0.07%, Zn 1.55%, Sr 0.02%, with the remainder being Al and unavoidable impurities. The alloy was prepared according to the process steps of Example 1. The difference is that the refining temperature in step 2 is 710℃, the degassing temperature is 755℃, the degassing is allowed to stand for 8.0min, and after modification and refinement treatment, electromagnetic stirring is performed for 3.0min; the mold preheating temperature in step 3 is 220℃, and the temperature of the aluminum melt during die casting is 700℃; the die casting is heated to 550℃, kept warm for 1.0h, and then water quenched. After water quenching, it is heated to 170℃ for aging treatment for 1.25h; after the parts are cleaned in step 4, riveted assembly and paint baking are carried out on the 35th day, and the baking temperature is 152℃ for 0.85h.

[0065] Comparative Example 1

[0066] The composition ratio and preparation method of the alloy are carried out according to the process steps of Example 3. The difference from Example 3 is that the alloy composition does not contain Zn element.

[0067] The rivet morphology of the die casting obtained in Example 3 is as follows Figure 2 As shown in the figure, the rivet morphology of the die casting obtained in Example 1 shows that the die casting prepared by using the crystal-controlled mixture containing Sr and Zn as the main elements (Example 3) has a smooth and flat surface morphology after riveting ( Figure 2); while in the casting prepared by the crystal-controlling mixture containing Sr and Zn as main elements (Comparative Example 1), cracks were found on the surface of the rivet buckle after riveting assembly.

[0068] The tensile properties test was performed according to the test method of Example 1.

[0069] Table 1: Tensile properties of Example 3

[0070] Casting flow distance (mm) Yield strength (MPa) Elongation after break (%) 100 125 13.1 300 129 12.3 500 123 12.1 700 124 6.6 900 120 6.2 1100 123 5.5

[0071] Table 2: Tensile properties of comparative example 1

[0072] Casting flow distance (mm) Yield strength (MPa) Elongation after break (%) 100 119 11.6 300 122 10.8 500 125 12.3 700 120 3.6 900 122 2.8 1100 118 2.3

[0073] As can be seen from the above table, the die-castings prepared using a crystal-controlling mixture with Sr and Zn as main elements (Example 3) and the samples sampled at different casting flow distances have better elongation after fracture than the castings prepared without using a crystal-controlling mixture with Sr and Zn as main elements (Comparative Example 1), especially the elongation after fracture of the samples sampled after the casting flow distance is greater than 500 mm.

[0074] The yield strength of the body at a distance of ≤500mm from the ingate through the casting is ≥120MPa and the elongation after fracture is ≥8.0%;

[0075] All the above embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

Claims

1. A method for preparing recycled aluminum die castings for new energy vehicles that are easy to rivet, characterized in that: The preparation method comprises the following steps: (1) Recycled aluminum ingot smelting: the ingredients are prepared according to the main alloying elements, and the recycled aluminum scrap added is recycled cans; the ingot is smelted and cast; the aluminum die-casting includes the following components by mass percentage: Si 7.0~9.5%, Mg≤0.25%, Cu≤0.5%, Fe0.2~0.4%, Cr0.1~0.3%, Mn0.05~0.15%, Zn 1.0~2.0%, Sr 0.01~0.1%, the content of other single elements is ≤0.05%, the total content of other elements is ≤0.15%, and the rest is Al, and the proportion of recycled aluminum scrap in the raw materials is not less than 75%; (2) Ingot refining: The ingot obtained in step (1) is remelted and refined and degassed, and the composition is fine-tuned to the target composition. The refining temperature is controlled at 720-780°C, and the degassing temperature is controlled at 745-755°C. After degassing, the ingot is allowed to stand for 10.0-15.0 min, and then a crystal control modifier and a refiner are added to the melt. The ingot is fully stirred under the action of an electromagnetic field for 5.0-10.0 min and then die-casted. The added modifier is a crystal-controlling mixture composed mainly of Sr and Zn, which can significantly improve the morphology and distribution of the eutectic alloy. The weight percentage of the chemical composition is: Sr 1.1-1.2, Zn 3.0-4.0, Cu≤0.02%, and the rest is Al; (3) Die casting: Before die casting, preheat the mold to 220~250℃. Apply a layer of release agent on the mold surface during the preheating process. After preheating, die casting is carried out. The temperature of the aluminum melt is controlled between 680~720℃. (4) Riveting assembly: After water cooling or mist cooling, the die-cast parts are cleaned and riveted and assembled within 2 to 90 days; the die-cast parts after die-casting are directly riveted or riveted after solid solution aging treatment. The solid solution aging treatment is to heat the die-cast parts to 530-550℃, keep them warm for 1.0-2.0 hours, and then water quench them. After water quenching, they are heated to 100-180℃ and aged for 1.0-4.0 hours. (5) After painting, the product is baked and hardened at a temperature of 140-160°C for 0.5-1.0 h, and then packaged and stored.

2. The method for preparing a recycled aluminum die casting for new energy vehicles that is easy to rivet according to claim 1, characterized in that: The aluminum die casting includes the following components in mass percentage: Si 7.0-8.0%, Mg 0.05-0.15%, Cu 0.1-0.2%, Fe 0.25-0.35%, Cr 0.1-0.2%, Mn 0.05-0.15%, Zn 1.0-1.5%, Sr 0.01-0.05%, the content of other single elements is ≤0.05%, the total content of other elements is ≤0.15%, the rest is Al, and the proportion of recycled scrap aluminum in the raw materials is not less than 80%.

3. The method for preparing a recycled aluminum die casting for new energy vehicles that is easy to rivet according to claim 1 or 2, characterized in that: The alloy structure of the aluminum die casting is a hypoeutectic structure, and the intermetallic compounds in the eutectic region are no larger than 2.0 μm and are dispersed.

4. The method for preparing a recycled aluminum die-casting for new energy vehicles that is easy to rivet according to claim 1, characterized in that: After the die-cast parts are riveted and assembled, they are brought into the paint shop together with the entire body-in-white for painting and baking.

5. The method for preparing a recycled aluminum die-casting for new energy vehicles that is easy to rivet according to claim 1, characterized in that: The prepared recycled aluminum die casting with a thickness of ≤3.5 mm has a yield strength of ≥120 MPa and an elongation after fracture of ≥8.0% at a flow distance of ≤500 mm from the ingate. The prepared recycled aluminum die-casting with a thickness of ≤3.5 mm has a yield strength of ≥120 MPa and an elongation after fracture of ≥5.0% at a flow distance ≥500 mm and ≤1000 mm from the ingate.

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