Semi-solid aluminum alloy suitable for friction stir welding and preparation method and machining method of semi-solid aluminum alloy

Abstract

The invention relates to the technical field of aluminum alloys, in particular to a semi-solid aluminum alloy suitable for friction stir welding and a preparation method and a machining method of the semi-solid aluminum alloy. The semi-solid aluminum alloy suitable for friction stir welding comprises, by weight, 6.5%-8.0% of Si, 1.0%-1.5% of Cu, 0.2%-0.8% of Mg, 0.01%-0.05% of Sr, 0.01%-0.1% of RE and the balance Al and inevitable impurities, and the total content of the inevitable impurities is smaller than or equal to 0.2%. The semi-solid aluminum alloy can be formed through a semi-solid rheo-die-casting process and can be welded through a friction stir welding process, the mechanical property of the semi-solid aluminum alloy is excellent, and the mechanical property of a welded joint obtained through welding is excellent.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, and in particular to a semi-solid aluminum alloy suitable for friction stir welding, and its preparation and processing methods. Background Technology

[0002] Aluminum alloy die casting technology is a highly efficient and precise liquid forming technology, and one of the main forming and manufacturing methods for aluminum alloys. Aluminum alloy die casting products are mainly used in the automotive, communications, and other fields. However, with the increasing dimensional requirements of aluminum alloy die castings, their joining technology has become a major problem for the industry. Due to the inherent high-speed filling characteristics of the die casting process, the high gas content in the die castings makes them unsuitable for fusion welding. This is because the high temperature of fusion welding causes surface blistering in the heat-affected zone, and the weld and fusion zone suffer from severe porosity defects due to gas release and expansion, resulting in poor weld performance. Friction stir welding is a solid-state joining method that effectively avoids a series of defects that occur in fusion welding. It has a wider process window when welding aluminum alloy materials, and the mechanical properties of the joints are much higher than those of fusion welding, making it an important technology for expanding the application fields of aluminum alloy materials. Chinese patent CN114941092A uses friction stir welding to join die-cast aluminum alloys and obtains welded joints with good performance, but the problem caused by gas entrapment in the die castings themselves has not been fundamentally solved. Furthermore, existing technologies have not yet developed an aluminum alloy composition system suitable for semi-solid rheo-die casting in friction stir welding. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a semi-solid aluminum alloy suitable for friction stir welding and its preparation method, which can be formed by semi-solid die casting process and welded by friction stir welding process, and the resulting welded joint has excellent mechanical properties.

[0004] Another technical problem that this invention aims to solve is to provide a method for processing semi-solid aluminum alloys.

[0005] To address the aforementioned technical problems, the present invention provides a semi-solid aluminum alloy suitable for friction stir welding, comprising the following components by weight percentage: Si 6.5%~8.0%, Cu 1.0%~1.5%, Mg 0.2%~0.8%, Sr 0.01%~0.05%, RE 0.01%~0.1%, with the remainder being Al and unavoidable impurities, the total content of which is ≤0.2%.

[0006] As an improvement to the above technical solution, the RE can be selected from one or more of La, Ce, Sm, Y, Gd, Pr, and Sc.

[0007] As an improvement to the above technical solution, the RE is made of La and Ce, and the weight ratio of La to Ce is 1:(0.5~1.5).

[0008] As an improvement to the above technical solution, the following components by weight percentage are included: Si 7.0%~8.0%, Cu 1.0%~1.2%, Mg 0.2%~0.4%, Sr 0.02%~0.05%, RE 0.01%~0.05%, with the remainder being Al and unavoidable impurities, the total content of which is ≤0.2%.

[0009] Accordingly, the present invention also discloses a method for preparing a semi-solid aluminum alloy suitable for friction stir welding, which includes the following steps: (1) Prepare raw materials according to the proportions and melt them to obtain a melt; (2) The melt is cooled to a first preset temperature and then prepared into a semi-solid slurry; (3) The semi-solid slurry is subjected to rheological die casting to obtain a die-cast billet; (4) The die-cast billet is subjected to solution treatment to obtain a semi-solid aluminum alloy suitable for friction stir welding; Among them, the solution treatment temperature is ≥450℃.

[0010] As an improvement to the above technical solution, in step (2), the first preset temperature is 650℃~680℃, and the cooling rate is 5℃ / s~20℃ / s; a semi-solid slurry is prepared by electromagnetic stirring; the solid phase of the semi-solid slurry is 45wt%~60wt%; and / or In step (3), the mold temperature is 150℃~250℃, the slow injection speed is 0.05m / s~0.25m / s, the fast injection speed is 0.5m / s~3m / s, the injection pressure is 50MPa~100MPa, and the holding time is 10s~30s. In step (4), the solution treatment temperature is 450℃~500℃ and the solution treatment time is 4h~12h.

[0011] As an improvement to the above technical solution, in step (4), after the die-casting billet is subjected to solution treatment, it is cooled to a second preset temperature at a first cooling rate. The first cooling rate is 200℃ / min to 400℃ / min, and the second preset temperature is 10℃ to 30℃.

[0012] Accordingly, the present invention also discloses a method for processing semi-solid aluminum alloys, which includes the following steps: (1) Prepare raw materials according to the proportion and melt them to obtain a melt; wherein, the semi-solid aluminum alloy comprises the following components by weight percentage: Si 6.5%~8.0%, Cu 1.0%~1.5%, Mg 0.2%~0.8%, Sr 0.01%~0.05%, RE 0.01%~0.1%, and the remainder is Al and unavoidable impurities, wherein the total content of the unavoidable impurities is ≤0.2%; (2) The melt is cooled to a first preset temperature and then prepared into a semi-solid slurry; (3) The semi-solid slurry is subjected to rheological die casting to obtain a die-cast billet; (4) The die-casting billet is subjected to solution treatment to obtain a die-casting part; wherein the solution treatment temperature is ≥450℃; (5) The die-cast part is subjected to friction stir welding to obtain a welded blank; wherein the rotation speed of the stirring head is ≤1000rpm and the welding speed is ≥60mm / min; (6) Cool the welding blank to a third preset temperature and keep it at that temperature for a preset time; wherein the third preset temperature is ≥120℃ and the preset time is ≥5h.

[0013] As an improvement to the above technical solution, in step (2), the first preset temperature is 650℃~680℃, and the cooling rate is 5℃ / s~20℃ / s; a semi-solid slurry is prepared by electromagnetic stirring; the solid fraction of the semi-solid slurry is 10wt%~50wt%; and / or In step (3), the mold temperature is 150℃~250℃, the slow injection speed is 0.05m / s~0.25m / s, the fast injection speed is 0.5m / s~3m / s, the injection pressure is 50MPa~100MPa, and the holding time is 10s~30s. In step (4), the solution treatment temperature is 450℃~500℃, and the solution treatment time is 4h~12h; and / or In step (5), the stirring head rotates at 600 rpm to 800 rpm, and the welding speed is 80 mm / min to 100 mm / min; and / or In step (6), the third preset temperature is 150℃~180℃ and the preset time is 6h~18h.

[0014] As an improvement to the above technical solution, step (6) includes: (6.1) Cool the welding blank to a third preset temperature at a second cooling rate and hold it at that temperature for a preset time; (6.2) The welding blank, after being held at the third preset temperature, is cooled to the fourth preset temperature at the third cooling rate; The second cooling rate is 30℃ / min to 80℃ / min, and the third cooling rate is 30℃ / min to 50℃ / min. The fourth preset temperature is 15℃~40℃.

[0015] Implementing this invention has the following beneficial effects: 1. The semi-solid aluminum alloy suitable for friction stir welding in one embodiment of the present invention comprises the following components by weight percentage: Si 6.5%~8.0%, Cu 1.0%~1.5%, Mg 0.2%~0.8%, Sr 0.01%~0.05%, RE 0.01%~0.1%, with the remainder being Al and unavoidable impurities, the total content of which is ≤0.2%. This semi-solid aluminum alloy can be formed using a semi-solid rheo-die casting process and can also be welded using a friction stir welding process. Furthermore, the semi-solid aluminum alloy exhibits excellent mechanical properties, and the resulting welded joint also possesses excellent mechanical properties.

[0016] 2. A method for preparing a semi-solid aluminum alloy suitable for friction stir welding according to an embodiment of the present invention includes: melting to obtain a melt, preparing a semi-solid slurry, semi-solid rheo-die casting, and solution treatment at a temperature ≥450℃. Based on the above preparation method, firstly, by performing solution treatment at a temperature ≥450℃ after semi-solid rheo-die casting, the Cu-containing phase can be fully integrated into the matrix, reducing the hardness of the matrix and improving the weldability of the material, laying a good foundation for subsequent friction stir welding. Secondly, no aging treatment is performed on the die-cast billet to prevent excessive coarsening of the precipitated phase, which could lead to defects such as voids and cracks in the weld, thereby improving the overall mechanical properties of the welded joint.

[0017] 3. In one embodiment of the present invention, the processing method of a semi-solid aluminum alloy includes: melting to obtain a melt, preparing a semi-solid slurry, semi-solid rheostat casting, solution treatment at a temperature ≥450℃, friction stir welding, and cooling. Based on the above processing method, firstly, by performing solution treatment at a temperature ≥450℃ after semi-solid rheostat casting, the Cu-containing phase can be fully integrated into the matrix, reducing the hardness of the matrix and improving the weldability of the material, laying a good foundation for subsequent friction stir welding. Secondly, no aging treatment is performed on the die-cast billet to prevent excessive coarsening of the precipitated phase, which could lead to defects such as voids and cracks in the weld, thereby improving the overall mechanical properties of the weld joint. Thirdly, by performing friction stir welding with a lower stirring head speed, the heat input can be reduced without affecting the welding, reducing the impact of excessively high temperature in the weld area on the precipitated phase. Fourth, friction stir welding at a low stirring speed is equivalent to a high-temperature aging of the die casting. After cooling to a certain temperature and then holding it at that temperature, it is equivalent to a second low-temperature aging. This two-stage aging can effectively strengthen the mechanical properties of the weld zone, thereby improving the overall mechanical properties of the joint. Detailed Implementation

[0018] To facilitate understanding of this application, it will be described in more detail below. However, it should be understood that this application can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular implementations or embodiments only and is not intended to be limiting of the application. The optional range of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0020] The following embodiments are provided for the purpose of illustrating various implementations of this application and are not intended to limit this application in any way. Those skilled in the art will understand that variations and other uses thereof, as defined in the claims, are included within the spirit and scope of this application. Unless otherwise specified, the materials, reagents, etc., used in the following embodiments are commercially available.

[0021] In this application, terms such as "first aspect" and "second aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0022] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0023] Unless otherwise specified, the percentage content mentioned in this application refers to solid-liquid mixtures and solid phases. Solid-phase mixing refers to mass percentage; for liquid phases... Liquid phase mixing refers to volume percentage.

[0024] Unless otherwise specified, all percentage concentrations mentioned in this application refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0025] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0026] As a first aspect of the present invention, the present invention provides a semi-solid aluminum alloy for friction stir welding, characterized in that it comprises the following components in weight percentages: Si 6.5%~8.0%, Cu 1.0%~1.5%, Mg 0.2%~0.8%, Sr 0.01%~0.05%, RE 0.01%~0.1%, with the remainder being Al and unavoidable impurities, the total content of which is ≤0.2%.

[0027] Silicon enhances the fluidity of the alloy and reduces solidification shrinkage, which is beneficial for the semi-solid die-casting process. Simultaneously, Si forms reinforcing phases such as Mg2Si during friction stir welding, optimizing the weld joint performance and the mechanical properties of the aluminum alloy. However, excessive Si content can lead to brittle phases in the weld joint, reducing its fatigue resistance. Therefore, this invention controls the Si content to be 6.5wt%~8.0wt%, exemplarily 6.7wt%, 6.9wt%, 7.1wt%, 7.3wt%, 7.5wt%, 7.7wt%, or 7.9wt%, but is not limited thereto. Preferably, it is 6.5wt%~7wt%, 6.8wt%~7.5wt%, or 7.2wt%~8.0wt%, but is not limited thereto.

[0028] Cu can form strengthening phases such as Al₂Cu, improving the strength of semi-solid aluminum alloys, but it also reduces corrosion resistance. Furthermore, Cu significantly affects recrystallization behavior during friction stir welding, leading to a more complex process of dissolution and re-precipitation of precipitated phases and the formation of more brittle intermetallic compounds. Therefore, this invention controls the Cu content to be 1.0wt%~1.5wt%, exemplarily 1.05wt%, 1.1wt%, 1.15wt%, 1.2wt%, 1.25wt%, 1.3wt%, 1.35wt%, 1.4wt%, or 1.45wt%, but is not limited thereto. Preferably, it is 1.0wt%~1.3wt%, 1.1wt%~1.4wt%, or 1.2wt%~1.5wt%, but is not limited thereto.

[0029] Mg can form the Mg2Si phase with Si, which can improve the mechanical properties of semi-solid die-cast aluminum alloys and welded joints. Furthermore, Mg can refine grains, improving the strength and toughness of welded joints. In this invention, the Mg content is controlled at 0.2wt% to 0.8wt%, exemplarily 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, 0.55wt%, 0.6wt%, 0.65wt%, 0.7wt%, or 0.75wt%, but is not limited thereto. Preferably, it is 0.2wt% to 0.3wt%, 0.25wt% to 0.4wt%, 0.3wt% to 0.5wt%, 0.4wt% to 0.7wt%, or 0.45wt% to 0.8wt%, but is not limited thereto.

[0030] Sr can effectively refine eutectic silicon, thereby improving the mechanical properties of semi-solid aluminum alloys. However, Sr also leads to increased porosity, which is detrimental to the friction stir welding process. Therefore, this invention controls the Sr content to be 0.01wt%~0.05wt%, exemplarily 0.015wt%, 0.02wt%, 0.025wt%, 0.03wt%, 0.035wt%, 0.04wt%, or 0.045wt%, but is not limited thereto. Preferably, it is 0.01wt%~0.02wt%, 0.02wt%~0.04wt%, or 0.03wt%~0.05wt%, but is not limited thereto.

[0031] Rare earth elements (RE) can refine grains, purify the melt, improve the overall performance of aluminum alloys, and optimize friction stir welding performance. However, excessive rare earth elements can also have adverse effects. Therefore, this invention controls the RE content to be 0.01wt%~0.1wt%, exemplarily 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, or 0.09wt%, but is not limited thereto. Preferably, it is 0.01wt%~0.03wt%, 0.02wt%~0.05wt%, 0.04wt%~0.06wt%, or 0.05wt%~0.08wt%, but is not limited thereto.

[0032] In addition, the semi-solid aluminum alloy of the present invention also contains some unavoidable impurity elements, the total content of which is ≤0.2wt% and the content of a single impurity is ≤0.1wt%.

[0033] The aluminum alloy based on the above formula is not only suitable for semi-solid rheo-die casting process, but can also be post-processed by friction stir welding process.

[0034] Specifically, in this invention, the rare earth element (RE) can be one or more of La, Ce, Y, Er, Nd, Gd, Pr, Sm, Tb, and Sc, but is not limited thereto. Preferably, it is one or more of La, Ce, Sm, Y, Gd, Pr, and Sc. More preferably, it is La and Ce, and the weight ratio of La to Ce is 1:(0.5~1.5). The combination of these two rare earth elements can further improve the strength of the welded joint.

[0035] Preferably, in some embodiments, the semi-solid aluminum alloy is characterized by comprising the following components in weight percentages: Si 7.0%~8.0%, Cu 1.0%~1.2%, Mg 0.2%~0.4%, Sr 0.02%~0.05%, RE 0.01%~0.05%, with the remainder being Al and unavoidable impurities, the total content of which is ≤0.2%.

[0036] Accordingly, as a second aspect of the present invention, a method for preparing a semi-solid aluminum alloy suitable for friction stir welding is also disclosed, comprising the following steps: S110: Prepare raw materials according to the proportions and melt them to obtain a melt; S120: The melt is cooled to a first preset temperature to prepare a semi-solid slurry; S130: The semi-solid slurry is subjected to rheological die casting to obtain a die-cast billet; S140: The die-cast billet is subjected to solution treatment to obtain a semi-solid aluminum alloy suitable for friction stir welding. Based on the above preparation method, firstly, by performing solution treatment at 450°C or higher after semi-solid rheological die casting, the Cu-containing phase can be fully integrated into the matrix, reducing the hardness of the matrix and improving the weldability of the material, thus laying a good foundation for subsequent friction stir welding. Secondly, no aging treatment is performed on the die-cast billet to prevent excessive coarsening of the precipitated phase, which could lead to defects such as voids and cracks in the weld, thereby improving the overall mechanical properties of the welded joint.

[0037] Specifically, in step S110, the semi-solid aluminum alloy comprises the following components by weight percentage: Si 6.5%~8.0%, Cu 1.0%~1.5%, Mg 0.2%~0.8%, Sr 0.01%~0.05%, RE 0.01%~0.1%, with the remainder being Al and unavoidable impurities, the total content of which is ≤0.2%.

[0038] Specifically, in step S110, raw materials are prepared according to the above formula and smelted in a melting furnace. The raw materials can be pure metals (such as pure aluminum ingots) or alloys (such as Al-Cu alloys), but are not limited to these. The smelting process also includes common operations in the art for purifying the melt, such as refining, settling, and slag removal, but is not limited to these.

[0039] Specifically, in step S120, the temperature of the melt is first reduced to 650℃~680℃ at a cooling rate of 5℃ / s~20℃ / s, and then a semi-solid slurry is prepared by stirring. The solid fraction in the prepared semi-solid slurry is 10wt%~60wt%. Preferably, the semi-solid slurry is prepared by electromagnetic stirring, which is more suitable for large-scale operations, and the solid fraction of the prepared semi-solid slurry is 45wt%~60wt%. The die-casting billet formed at this solid fraction has a more uniform microstructure, which provides a good foundation for subsequent friction stir welding and improves the mechanical properties of the welded joint.

[0040] Specifically, in step S130, the mold temperature is 150℃~300℃. The mold temperature affects the rheological properties and solidification process of the semi-solid slurry, and thus affects the microstructure of the die-cast billet. Therefore, it is quite important for the friction stir welding process. Preferably, the mold temperature is 150℃~250℃.

[0041] Specifically, in step S130, the slow injection speed is 0.05m / s to 0.25m / s, the fast injection speed is 0.5m / s to 3m / s, the injection pressure is 50MPa to 100MPa, and the holding time is 10s to 30s. The injection speed and injection pressure ensure that the semi-solid slurry fills the mold in a stable flow, reduces gas entrapment, lowers porosity, and optimizes the welding performance of the aluminum alloy.

[0042] Specifically, in step S140, the solution treatment temperature is ≥450℃. It should be noted that while the introduction of Cu is beneficial for improving the mechanical properties of semi-solid aluminum alloys, it easily forms brittle intermetallic compounds during welding, significantly weakening the mechanical properties of the weld joint. Therefore, solution treatment is performed in this invention to allow the Cu-containing phase to enter the matrix, ensuring weldability. However, if the solution treatment temperature is too low, the Cu-containing phase will have difficulty effectively entering the matrix. Therefore, the solution treatment temperature is controlled to be ≥450℃. Preferably, the solution treatment temperature is 450℃~500℃. Furthermore, to achieve sufficient solution of the Cu-containing phase, the solution treatment time should also be controlled. If the solution treatment time is too long, the Cu-containing phase will precipitate at the grain boundaries, weakening the weldability. If the solution treatment time is too short, the Cu-containing phase will not be fully dissolved. Specifically, the solution treatment time is 4h~12h, preferably 4h~6h.

[0043] Specifically, in step S140, the die-cast part is cooled after solution treatment. Cooling can be achieved through forced air cooling, water spray cooling, or water mist cooling, but is not limited to these methods. Preferably, in some embodiments, after solution treatment, the die-cast billet is cooled to a second preset temperature at a first cooling rate; wherein the first cooling rate is 200℃ / min~400℃ / min, and the second preset temperature is 10℃~30℃. It should be noted that when the cooling rate is slow, the Al2Cu phase will accumulate at the grain boundaries, easily causing fracture during subsequent welding; moreover, other strengthening phases are also prone to grain enlargement, reducing the strength of the matrix. However, an excessively fast cooling rate will also increase residual stress, which is detrimental to die-cast parts with more complex configurations.

[0044] Accordingly, as a third aspect, the present invention also discloses a method for processing semi-solid aluminum alloys, which includes the following steps: S210: Prepare raw materials according to the proportion and melt them to obtain a melt; S220: The melt is cooled to a first preset temperature to prepare a semi-solid slurry; S230: The semi-solid slurry is subjected to rheological die casting to obtain a die casting billet; S240: The die-casting billet is subjected to solution treatment to obtain a die-casting part; S250: The die-cast part is subjected to friction stir welding to obtain a welded blank; S260: Cool the welding blank to a third preset temperature and hold it at that temperature for a preset time; Based on the above processing methods, firstly, by performing solution treatment at 450°C or higher after semi-solid rheological die casting, the Cu-containing phase can be fully integrated into the matrix, reducing the matrix hardness and improving the weldability of the material, laying a good foundation for subsequent friction stir welding. Secondly, aging treatment is not performed on the die-cast billet to prevent excessive coarsening of the precipitated phase, which could lead to defects such as porosity and cracks in the weld, thereby improving the overall mechanical properties of the welded joint. Thirdly, by performing friction stir welding with a lower stirring head speed, the heat input can be reduced without affecting the welding process, minimizing the impact of excessively high temperatures in the weld area on the precipitated phase. Fourthly, performing friction stir welding with a lower stirring speed is equivalent to performing a high-temperature aging of the die-cast part, followed by cooling to a certain temperature and then holding it at that temperature, which is equivalent to performing a second low-temperature aging. This two-stage aging effectively strengthens the mechanical properties of the weld area, thereby improving the overall mechanical properties of the joint.

[0045] Specifically, in step S210, the semi-solid aluminum alloy comprises the following components by weight percentage: Si 6.5%~8.0%, Cu 1.0%~1.5%, Mg 0.2%~0.8%, Sr 0.01%~0.05%, RE 0.01%~0.1%, with the remainder being Al and unavoidable impurities, the total content of which is ≤0.2%.

[0046] Specifically, in step 210, raw materials are prepared according to the above formula and smelted in a melting furnace. The raw materials can be pure metals (such as pure aluminum ingots) or alloys (such as Al-Cu alloys), but are not limited to these. The smelting process also includes common operations in the art for purifying the melt, such as refining, settling, and slag removal, but is not limited to these.

[0047] Specifically, in step S220, the temperature of the melt is first reduced to 650℃~680℃ at a cooling rate of 5℃ / s~20℃ / s, and then a semi-solid slurry is prepared by stirring. The solid fraction in the prepared semi-solid slurry is 10wt%~60wt%. Preferably, the semi-solid slurry is prepared by electromagnetic stirring, which is more suitable for large-scale operations, and the solid fraction of the prepared semi-solid slurry is 45wt%~60wt%. The die-casting billet formed at this solid fraction has a more uniform microstructure, which provides a good foundation for subsequent friction stir welding and improves the mechanical properties of the welded joint.

[0048] Specifically, in step S230, the mold temperature is 150℃~300℃. The mold temperature affects the rheological properties and solidification process of the semi-solid slurry, and thus affects the microstructure of the die-cast billet. Therefore, it is quite important for the friction stir welding process. Preferably, the mold temperature is 150℃~250℃.

[0049] Specifically, in step S230, the slow injection speed is 0.05m / s to 0.25m / s, the fast injection speed is 0.5m / s to 3m / s, the injection pressure is 50MPa to 100MPa, and the holding time is 10s to 30s. The injection speed and injection pressure ensure that the semi-solid slurry fills the mold in a stable flow, reducing gas entrapment, lowering porosity, and optimizing the welding performance of the aluminum alloy.

[0050] Specifically, in step S240, the solution treatment temperature is ≥450℃. It should be noted that while the introduction of Cu is beneficial for improving the mechanical properties of semi-solid aluminum alloys, it easily forms brittle intermetallic compounds during welding, significantly weakening the mechanical properties of the weld joint. Therefore, solution treatment is performed in this invention to allow the Cu-containing phase to enter the matrix, ensuring weldability. However, if the solution treatment temperature is too low, the Cu-containing phase will have difficulty effectively entering the matrix. Therefore, the solution treatment temperature is controlled to be ≥450℃. Preferably, the solution treatment temperature is 450℃~500℃. Furthermore, to achieve sufficient solution of the Cu-containing phase, the solution treatment time should also be controlled. If the solution treatment time is too long, the Cu-containing phase will precipitate at the grain boundaries, weakening the weldability. If the solution treatment time is too short, the Cu-containing phase will not be fully dissolved. Specifically, the solution treatment time is 4h~12h, preferably 4h~6h.

[0051] Specifically, in step S240, the die-cast part is cooled after solution treatment. Cooling can be achieved through forced air cooling, water spray cooling, or water mist cooling, but is not limited to these methods. Preferably, in some embodiments, after solution treatment, the die-cast billet is cooled to a second preset temperature at a first cooling rate; wherein the first cooling rate is 200℃ / min~400℃ / min, and the second preset temperature is 10℃~30℃. It should be noted that when the cooling rate is slow, the Al2Cu phase will accumulate at the grain boundaries, easily causing fracture during subsequent welding; moreover, other strengthening phases are also prone to grain enlargement, reducing the strength of the matrix. However, an excessively fast cooling rate will also increase residual stress, which is detrimental to die-cast parts with more complex configurations.

[0052] Specifically, in step S250, the stirring head speed is ≤1000 rpm. If the stirring head speed is too fast, too much heat will be introduced, weakening the mechanical properties of the joint. However, if the speed is too low, it will also lead to poor weld surface formation, reducing the joint density and tensile strength. Therefore, the stirring head speed is controlled to be ≥550 rpm.

[0053] Specifically, in step S250, the welding speed is ≥60mm / min. A higher welding speed can reduce heat input and increase the cooling rate, preventing rapid grain growth and improving the mechanical properties of the welded joint. However, if the welding speed is too fast, it may inhibit plastic flow, leading to defects such as incomplete penetration and poor joint. Therefore, the welding speed should be controlled to ≤120mm / min.

[0054] Preferably, in some embodiments, in step S250, the rotation speed of the stirring head is 600 rpm to 800 rpm, and the welding speed is 80 mm / min to 100 mm / min.

[0055] Specifically, in step S260, the third preset temperature is ≥120℃ and the preset time is ≥5h to effectively improve the mechanical properties of the welded joint. Preferably, in some embodiments, the third preset temperature is 150℃~180℃ and the preset time is 6h~18h.

[0056] Preferably, in some embodiments, step S260 includes: S261: Cool the welding blank to a third preset temperature at a second cooling rate and hold it at that temperature for a preset time; Specifically, the second cooling rate is 30℃ / min to 80℃ / min. By adopting a higher cooling rate, the adverse effects of heat input in friction stir welding can be further reduced.

[0057] S262: The welding blank, after being held at the third preset temperature, will be cooled to the fourth preset temperature at the third cooling rate; The third cooling rate is 30℃ / min to 50℃ / min; the fourth preset temperature is 15℃ to 40℃.

[0058] The present invention is further illustrated below with specific embodiments: Example 1 This embodiment provides a semi-solid aluminum alloy and its preparation and processing method, the specific processing method of which is as follows: (1) Prepare raw materials according to the following alloy composition by mass percentage: silicon 7.5%, copper 1.0%, magnesium 0.25%, strontium 0.03%, LaCe mixed rare earth (La:Ce=1:1) 0.02%, and the balance is aluminum.

[0059] (2) The raw materials are smelted at 750°C. After the raw materials are smelted, the temperature of the smelting furnace is adjusted to 690°C and then refined for degassing and impurity removal.

[0060] (3) First, the temperature of the melt is reduced to 650℃~660℃ at a cooling rate of 5℃ / s~7℃ / s, and then a semi-solid slurry is prepared by electromagnetic stirring. The solid content in the semi-solid slurry is 55wt%~57wt%. (4) The semi-solid slurry is subjected to rheological die casting to obtain a die casting billet; wherein the mold temperature is 210℃~220℃, the slow injection speed is 0.12m / s~0.15m / s, the fast injection speed is 1m / s~1.5m / s, the injection specific pressure is 85MPa, and the holding time is 15s.

[0061] (5) The die-casting billet is subjected to solution treatment to obtain the die-casting part; wherein the solution temperature is 470℃, the solution time is 4h, and after solution treatment, it is cooled to room temperature at a cooling rate of 250℃ / min.

[0062] (6) The die-cast part is subjected to friction stir welding to obtain a welded blank; wherein the rotation speed of the stirring head is 800 rpm and the welding speed is 80 mm / min; (7) Cool the welding blank to 165°C at a cooling rate of 50°C / min and hold for 12 hours; then cool to room temperature at a cooling rate of 40°C / min.

[0063] Example 2 This embodiment provides a semi-solid aluminum alloy and its preparation and processing method, the specific processing method of which is as follows: (1) Prepare raw materials according to the following alloy composition by mass percentage: silicon 8.0%, copper 1.5%, magnesium 0.8%, strontium 0.05%, LaCe mixed rare earth (La:Ce=1:1) 0.01%, and the balance is aluminum.

[0064] (2) The raw materials are smelted at 750°C. After the raw materials are smelted, the temperature of the smelting furnace is adjusted to 690°C and then refined for degassing and impurity removal.

[0065] (3) First, the temperature of the melt is reduced to 670℃~680℃ at a cooling rate of 8℃ / s~10℃ / s, and then a semi-solid slurry is prepared by electromagnetic stirring. The solid content in the semi-solid slurry is 57wt%~60wt%; (4) The semi-solid slurry is subjected to rheological die casting to obtain a die casting blank; wherein the mold temperature is 220℃~230℃, the slow injection speed is 0.18m / s~0.22m / s, the fast injection speed is 1.5m / s~2m / s, the injection specific pressure is 80MPa, and the holding time is 20s.

[0066] (5) The die casting billet is subjected to solution treatment to obtain the die casting part; wherein the solution temperature is 490℃, the solution time is 8h, and after solution treatment, it is cooled to room temperature at a cooling rate of 350℃ / min.

[0067] (6) The die-cast part is subjected to friction stir welding to obtain a welded blank; wherein the rotation speed of the stirring head is 700 rpm and the welding speed is 85 mm / min; (7) Cool the welding blank to 160°C at a cooling rate of 60°C / min and hold for 14 hours; then cool to room temperature at a cooling rate of 40°C / min.

[0068] Example 3 This embodiment provides a semi-solid aluminum alloy and its preparation and processing method, the specific processing method of which is as follows: (1) Prepare raw materials according to the following alloy composition by mass percentage: silicon 6.5%, copper 1%, magnesium 0.2%, strontium 0.01%, LaCe mixed rare earth (La:Ce=1:1) 0.1%, and the balance is aluminum.

[0069] (2) The raw materials are smelted at 750°C. After the raw materials are smelted, the temperature of the smelting furnace is adjusted to 690°C and then refined for degassing and impurity removal.

[0070] (3) First, the temperature of the melt is reduced to 650℃~660℃ at a cooling rate of 10℃ / s~13℃ / s, and then a semi-solid slurry is prepared by electromagnetic stirring. The solid content in the semi-solid slurry is 48wt%~55wt%. (4) The semi-solid slurry is subjected to rheological die casting to obtain a die casting billet; wherein the mold temperature is 180℃~200℃, the slow injection speed is 0.06m / s~0.1m / s, the fast injection speed is 0.8m / s~1.5m / s, the injection specific pressure is 90MPa, and the holding time is 25s.

[0071] (5) The die casting billet is subjected to solution treatment to obtain the die casting part; wherein the solution temperature is 470℃, the solution time is 5h, and after solution treatment, it is cooled to room temperature at a cooling rate of 320℃ / min.

[0072] (6) The die-cast part is subjected to friction stir welding to obtain a welded blank; wherein the rotation speed of the stirring head is 650 rpm and the welding speed is 80 mm / min; (7) Cool the welding blank to 170°C at a cooling rate of 50°C / min and hold for 14 hours; then cool to room temperature at a cooling rate of 40°C / min.

[0073] Comparative Example 1 This comparative example provides an aluminum alloy and its processing method, which differs from Example 1 in that the aluminum alloy formulation does not include rare earth elements (LaCe mixed rare earth elements).

[0074] Everything else is the same as in Example 1.

[0075] Comparative Example 2 This comparative example provides an aluminum alloy and its processing method, which differs from Example 1 in that the aluminum alloy formulation does not include strontium.

[0076] Everything else is the same as in Example 1.

[0077] Comparative Example 3 This comparative example provides an aluminum alloy and its processing method, which differs from Example 1 in that: Cold chamber high-pressure die casting replaces semi-solid rheological die casting, and no heat treatment is performed after die casting; instead, friction stir welding is performed directly.

[0078] Comparative Example 4 This comparative example provides an aluminum alloy and its processing method, which differs from Example 1 in that: In step (5), the solution temperature is 430℃.

[0079] Everything else is the same as in Example 1.

[0080] Comparative Example 5 This comparative example provides an aluminum alloy and its processing method, which differs from Example 1 in that: In step (5), the solution treatment time is 24 hours.

[0081] Everything else is the same as in Example 1.

[0082] Comparative Example 6 This comparative example provides an aluminum alloy and its processing method, which differs from Example 1 in that: In step (6), the stirring head rotates at 1200 rpm.

[0083] Everything else is the same as in Example 1.

[0084] Comparative Example 7 This comparative example provides an aluminum alloy and its processing method, which differs from Example 1 in that: In step (6), the welding speed is 40 mm / min.

[0085] Everything else is the same as in Example 1.

[0086] Comparative Example 8 This comparative example provides an aluminum alloy and its processing method, which differs from Example 1 in that: In step (7), the temperature is directly cooled to room temperature.

[0087] Everything else is the same as in Example 1.

[0088] The aluminum alloys provided in Example 1 and Comparative Examples 1-8 were used to test the tensile mechanical properties of their base materials and welded joints. The results are shown in the table below:

[0089] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of the present invention to facilitate a specific and detailed understanding of the technical solution of the present invention, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

[0090] It should be understood that any technical solutions obtained by those skilled in the art based on the technical solutions provided in this invention through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A semi-solid aluminum alloy suitable for friction stir welding, characterized in that, Comprise the following weight percentage of components: Si 6.5%~8.0%, Cu 1.0%~1.5%, Mg 0.2%~0.8%, Sr 0.01%~0.05%, RE 0.01%~0.1%, the rest is Al and inevitable impurities, the total content of the inevitable impurities ≤0.2%.

2. The semi-solid aluminum alloy for friction stir welding according to claim 1, wherein The RE can be selected from one or more of La, Ce, Sm, Y, Gd, Pr, Sc.

3. The semi-solid aluminum alloy suitable for friction stir welding according to claim 1, wherein The RE is selected from La and Ce, and the weight ratio of La to Ce is 1:(0.5~1.5).

4. The semi-solid aluminum alloy for friction stir welding according to any one of claims 1 to 3, wherein Comprise the following weight percentage of components: Si 7.0%~8.0%, Cu 1.0%~1.2%, Mg 0.2%~0.4%, Sr 0.02%~0.05%, RE 0.01%~0.05%, the rest is Al and inevitable impurities, the total content of the inevitable impurities ≤0.2%.

5. A method for producing a semi-solid aluminum alloy for friction stir welding, for producing the semi-solid aluminum alloy for friction stir welding according to any one of claims 1 to 4, characterized by, Comprise the following steps: (1) prepare raw materials according to the proportion, and melt to obtain a melt; (2) prepare a semi-solid slurry after the melt is cooled to a first preset temperature; (3) rheo-die casting the semi-solid slurry to obtain a die casting blank; (4) solid solution treatment of the die casting blank, to obtain a semi-solid aluminum alloy suitable for friction stir welding; Wherein, the solid solution temperature is ≥450℃.

6. The method of producing a semi-solid aluminum alloy for friction stir welding according to claim 5, wherein In step (2), the first preset temperature is 650℃~680℃, and the cooling rate is 5℃ / s~20℃ / s; the semi-solid slurry is prepared by electromagnetic stirring method; the solid phase rate of the semi-solid slurry is 45wt%~60wt%; and / or In step (3), the mold temperature is 150℃~250℃, the slow injection speed is 0.05m / s~0.25m / s, the fast injection speed is 0.5m / s~3m / s, the injection specific pressure is 50MPa~100MPa, and the holding time is 10s~30s; In step (4), the solid solution treatment temperature is 450℃~500℃, and the solid solution treatment time is 4h~12h.

7. The method of producing a semi-solid aluminum alloy for friction stir welding according to claim 5, wherein In step (4), after the solid solution treatment of the die casting blank, cool to a second preset temperature at a first cooling rate; Wherein, the first cooling rate is 200℃ / min~400℃ / min, and the second preset temperature is 10℃~30℃.

8. A method of processing a semi-solid aluminum alloy characterized by, Comprise the following steps: (1) prepare raw materials according to the proportion, and melt to obtain a melt; wherein, the semi-solid aluminum alloy comprises the following weight percentage of components: Si 6.5%~8.0%, Cu 1.0%~1.5%, Mg 0.2%~0.8%, Sr 0.01%~0.05%, RE 0.01%~0.1%, the rest is Al and inevitable impurities, the total content of the inevitable impurities ≤0.2%; (2) prepare a semi-solid slurry after the melt is cooled to a first preset temperature; (3) rheo-die casting the semi-solid slurry to obtain a die casting blank; (4) solid solution treatment of the die casting blank, to obtain a semi-solid aluminum alloy suitable for friction stir welding; wherein, the solid solution temperature is ≥450℃; (5) friction stir welding is performed on the die casting to obtain a welded blank; wherein the rotation speed of the stir head is ≤1000 rpm, and the welding speed is ≥60 mm / min; (6) the welded blank is cooled to a third preset temperature and held for a preset time; wherein the third preset temperature is ≥120℃, and the preset time is ≥5 h.

9. The method of processing a semi-solid aluminum alloy of claim 8 wherein, In step (2), the first preset temperature is 650℃-680℃, and the cooling rate is 5℃ / s-20℃ / s; the semi-solid slurry is prepared by electromagnetic stirring; the solid phase rate of the semi-solid slurry is 10wt%-50wt%; and / or In step (3), the mold temperature is 150℃-250℃, the slow injection speed is 0.05 m / s-0.25 m / s, the fast injection speed is 0.5 m / s-3 m / s, the injection specific pressure is 50 MPa-100 MPa, and the holding pressure time is 10 s-30 s; In step (4), the temperature of the solid solution treatment is 450℃-500℃, and the solid solution treatment time is 4 h-12 h; and / or In step (5), the rotation speed of the stir head is 600 rpm-800 rpm, and the welding speed is 80 mm / min-100 mm / min; and / or In step (6), the third preset temperature is 150℃-180℃, and the preset time is 6 h-18 h.

10. The method of processing a semi-solid aluminum alloy of claim 8 wherein, Step (6) comprises: (6.1) the welded blank is cooled to a third preset temperature at a second cooling rate and held for a preset time; (6.2) the welded blank held at the third preset temperature is cooled to a fourth preset temperature at a third cooling rate; wherein the second cooling rate is 30℃ / min-80℃ / min, and the third cooling rate is 30℃ / min-50℃ / min; the fourth preset temperature is 15℃-40℃.

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