In-situ alloying arc additive manufacturing of magnesium alloys and methods of making the same

Abstract

This invention provides an in-situ alloying arc additive manufacturing method for magnesium alloys, belonging to the field of arc additive manufacturing and welding. The method includes: under argon protection, alternating 20-40 layers of arc additive manufacturing and metal powder solution coating on a pretreated magnesium alloy substrate using magnesium alloy welding wire. Each layer is prepared with the following parameters: a vertical distance of 8-20 mm between the welding wire and the substrate; a welding current of 70-130 A; a welding voltage of 10 V-22 V; a wire feed speed of 8-15 m / min; and a welding torch travel speed of 10-20 mm / s. The resulting magnesium alloy has a fully equiaxed crystal structure with an average grain size ≤25 μm; no anisotropy; a texture strength ≤1.6 mrd; a tensile strength ≥210 MPa; and an elongation ≥20%, meeting the requirements of high-end equipment manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of arc additive manufacturing and welding, and specifically relates to an in-situ alloying arc additive manufacturing method for magnesium alloys and its preparation method. Background Technology

[0002] Magnesium alloys are among the lightest metallic structural materials, possessing advantages such as low density, high specific strength, and good stability, and are currently widely used in aerospace, automotive, electronics and communications, and medical fields. However, compared with traditional non-ferrous metal structural materials such as aluminum alloys and titanium alloys, magnesium alloys have relatively lower strength and poorer ductility, which limits their application areas and scope. Strength can be improved by increasing the content of alloying elements (generally >6 wt.%). In actual production, the addition of large amounts of alloying elements not only increases production costs but also forms coarse eutectic phases in the matrix, resulting in a loss of ductility while increasing strength. Therefore, there is an urgent need to develop low-alloy, high-strength, and ductile magnesium alloys to reduce costs and promote the large-scale application of magnesium alloys.

[0003] Currently, the main manufacturing processes for magnesium alloy components include casting and plastic forming. Casting is suitable for producing integrally molded components; however, it is prone to defects such as hot cracking, porosity, and looseness, resulting in poor dimensional accuracy and surface quality, leading to lower performance of the magnesium alloy. Furthermore, limitations in production conditions, such as molds, make it difficult to produce complex-shaped components. Plastic forming processes include rolling, extrusion, and forging, but the hexagonal close-packed structure of magnesium makes the production process complex and costly, hindering the production of complex-shaped components at room temperature. In addition, casting and extrusion technologies require complex machining and post-processing for large components, and the extrusion speed is low, limiting the production of simple structural components and making it difficult to achieve complex structures. These problems lead to material waste and reduced production efficiency. Therefore, how to reduce costs, simplify processes, avoid cracking and anisotropy, achieve both simple and complex structures, develop rapid prototyping technology for magnesium alloys, and produce low-alloy high-performance magnesium alloys with a good balance of strength and plasticity are urgent technical challenges that need to be addressed. Summary of the Invention

[0004] To address the aforementioned technical challenges, this invention provides an in-situ alloying arc additive manufacturing method for magnesium alloys, comprising the following steps: The magnesium alloy substrate surface was sanded to remove oxide scale, and then rinsed and dried with anhydrous ethanol to obtain a pretreated magnesium alloy substrate. Under a high-purity argon gas shielding gas with a purity ≥99.99% and a flow rate of 12-20 L / min, the pretreated magnesium alloy substrate underwent alternating treatment with magnesium alloy welding wire arc additive manufacturing and metal powder solution coating. The alternating arc additive manufacturing and metal powder solution coating process involved a first layer of cold metal transition arc additive manufacturing to obtain the component. The cold metal transition arc additive manufacturing process was characterized by a vertical distance of 8-20 mm between the magnesium alloy welding wire and the magnesium alloy substrate, a welding current of 70-130 A, a welding voltage of 10 V-22 V, and a wire feed speed of 8 m / min-15 m / min. The welding torch travel speed is 10mm / s-20mm / s. Metal powder solution coating is applied to the component surface. After evaporation, drying, and cooling to 25-40℃ for 5-10 minutes, the next layer of arc additive manufacturing and metal powder solution coating are alternated. This process is repeated until 20-40 layers of in-situ alloyed arc additive manufacturing magnesium alloy are obtained. The process parameters for each layer of alternating arc additive manufacturing and metal powder solution coating are different. The obtained in-situ alloyed arc additive manufacturing magnesium alloy has a completely equiaxed crystal structure with an average grain size ≤25μm; it is free from cracking and anisotropy, has a weak texture structure with a texture strength ≤1.6mrd; the alloy has a good balance of strength and plasticity, with a tensile strength ≥210MPa and an elongation ≥20%. The magnesium alloy welding wire, by mass percentage, comprises: Gd: 0.3-0.7 wt.%, Zn: 0.2-0.6 wt.%, Zr: 0.1-0.3 wt.%, Ca: 0.05-0.2 wt.%, Sm: 0.03-0.15 wt.%, wherein the mass ratio of Gd+Sm to Zn+Ca is 0.6~1.2, and the balance is magnesium and unavoidable impurities, the content of unavoidable impurities being ≤0.05 wt.%; the magnesium alloy substrate is one of AZ31, AZ51, and ZK60; The metal powder solution is prepared by mixing metal powder with anhydrous ethanol, stirring and ultrasonically vibrating for 5-10 minutes to obtain the metal powder solution. The metal powder is one or a combination of Al powder and Zn powder, and the mass fraction of the metal powder in the metal powder solution is 2wt.%-8wt.%.

[0005] Furthermore, the welding current is 75-120A, the welding voltage is 12V-18V, the wire feed speed is 9.5m / min-13.5m / min, and the welding torch travel speed is 12mm / s-17mm / s.

[0006] Furthermore, the flow rate of the protective gas is 13-18 L / min.

[0007] Furthermore, this process is repeated until 25-35 layers of in-situ alloyed arc additive manufacturing magnesium alloy are obtained.

[0008] Furthermore, the average grain size is 20.76-24.55 μm, and the texture intensity is 1.31-1.50 mrd.

[0009] Furthermore, the tensile strength is 215.8-226.5 MPa, and the elongation is 22.3%-25.6%.

[0010] Compared with the prior art, the present invention has the following characteristics:

[0011] Compared with existing technologies, this invention achieves excellent comprehensive mechanical properties through the synergistic control of alloy component interactions, proportions, processes, and process parameters. For example, the process parameters for each layer are different, and the synergistic control of components, proportions, processes, and process parameters is crucial. The resulting in-situ alloyed arc additive manufacturing magnesium alloy exhibits good comprehensive mechanical properties and is of great significance in the field of magnesium alloy arc additive manufacturing technology.

[0012] (1) Existing technologies for manufacturing magnesium alloys employ casting or complex deformation processes, which not only result in high production costs but also require heat treatment processes such as homogenization, making the manufacturing process complex. Due to limitations in molds and technology, only simple single-layer structures can be manufactured, making it difficult to achieve complex structures. Even if complex structures are formed, cracking and anisotropy will occur. Compared with existing technologies, this invention can achieve integrated rapid prototyping of simple or complex components, increasing the material manufacturing rate and shortening the manufacturing cycle. At the same time, it avoids cracking and anisotropy, saving manufacturing time and costs, which is beneficial for large-scale industrial production.

[0013] (2) Existing technologies improve the mechanical properties of alloys by increasing the content of alloying elements (generally >6wt.%). As the content of alloying elements increases, the strength of magnesium alloys increases, but the plasticity decreases, which not only makes the preparation cost high, but also results in a mismatch between strength and plasticity in the final magnesium alloy. The present invention uses low-alloy magnesium alloy welding wire with a total alloying element addition of <2wt.%, and simultaneously improves the strength and plasticity of the alloy, greatly reducing the production cost.

[0014] (3) This invention enables metal particles to serve as heterogeneous nucleation sites, thereby increasing the nucleation rate and inhibiting grain growth. This results in the complete transformation of columnar crystals into equiaxed crystals and significant grain refinement, achieving an average grain size of <25μm for magnesium alloys. It also achieves continuous and stable additive manufacturing processes, with tight bonding between layers and good overall component morphology. The magnesium alloy components have fine and uniform microstructure, avoiding cracking, lacking anisotropy, and achieving a weak texture structure with a texture strength ≤1.6mrd. The prepared alloy exhibits good strength-plasticity matching, with a tensile strength ≥210MPa and an elongation ≥20%. Detailed Implementation Example 1

[0015] In-situ alloying arc additive manufacturing of magnesium alloy components, the preparation method includes the following steps: The magnesium alloy substrate surface was sanded to remove oxide scale, rinsed with anhydrous ethanol, and dried to obtain a pretreated magnesium alloy substrate. Under a high-purity argon gas shielding gas with a purity ≥99.99% and a flow rate of 16 L / min, the pretreated magnesium alloy substrate underwent alternating treatment with arc additive manufacturing and metal powder solution coating using magnesium alloy welding wire. The alternating arc additive manufacturing and metal powder solution coating process was as follows: a first layer of additive manufacturing was performed using cold metal transition arc additive manufacturing to obtain the component. The cold metal transition arc additive manufacturing process was characterized by a vertical distance of 9 mm between the magnesium alloy welding wire and the magnesium alloy substrate, a welding current of 100 A, a welding voltage of 14 V, a wire feed speed of 11.5 m / min, and a welding torch travel speed of 15 mm / s. Metal powder solution coating was then applied to the component surface. After evaporation, drying, and cooling to 30°C for 6 minutes, the next layer of arc additive manufacturing and metal powder solution coating was performed. The process involves alternating powder coating and solution coating, repeated cyclically until 28 layers of in-situ alloyed arc additive manufacturing magnesium alloy are obtained. Each layer has different process parameters: the vertical distance between the magnesium alloy welding wire and the magnesium alloy substrate is 8-20 mm; the welding current is 70-130 A; the welding voltage is 10 V-22 V; the wire feed speed is 8 m / min-15 m / min; and the welding torch travel speed is 10 mm / s-20 mm / s. The component is then coated with a metal powder solution, which is evaporated, dried, and cooled to 25-40℃ after 5-10 minutes. The resulting in-situ alloyed arc additive manufacturing magnesium alloy exhibits a fully equiaxed crystal structure with an average grain size of 24.55 μm; it is free of cracks and anisotropy; the texture is significantly weakened, with a texture strength of 1.45 mrd; and the alloy shows good strength-ductility matching. The alloy tensile properties were tested under the following conditions: loading speed 0.6-1 mm / min, strain rate 3 × 10⁻⁶. -4 s -1 - 1×10 -3s -1 The alloy has a tensile strength of 217.3±0.3MPa and an elongation of 25.6±0.2%.

[0016] The magnesium alloy welding wire, by mass percentage, has the following composition: Gd: 0.41 wt.%, Zn: 0.43 wt.%, Zr: 0.17 wt.%, Ca: 0.07 wt.%, Sm: 0.05 wt%, wherein the mass ratio of Gd+Sm to Zn+Ca is 0.92, and the balance is magnesium and unavoidable impurities, with the content of unavoidable impurities ≤0.05 wt.%; the magnesium alloy substrate is an AZ31 magnesium alloy substrate. The metal powder solution is prepared by mixing metal powder with anhydrous ethanol, stirring and ultrasonically vibrating for 8 minutes to obtain the metal powder solution. The metal powder is Al powder, and the mass fraction of the metal powder in the metal powder solution is 6 wt.%. Example 2

[0017] In-situ alloying arc additive manufacturing of magnesium alloy component 2, its preparation method includes the following steps: The magnesium alloy substrate surface was sanded to remove oxide scale, and then rinsed and dried with anhydrous ethanol to obtain a pretreated magnesium alloy substrate. Under a high-purity argon gas shielding gas with a purity ≥99.99% and a flow rate of 15 L / min, the pretreated magnesium alloy substrate underwent alternating treatment with arc additive manufacturing and metal powder solution coating using magnesium alloy welding wire. The alternating arc additive manufacturing and metal powder solution coating process was as follows: a first layer of additive manufacturing using cold metal transition arc additive manufacturing was performed to obtain the component. The cold metal transition arc additive manufacturing process involved a vertical distance of 10 mm between the magnesium alloy welding wire and the magnesium alloy substrate, a welding current of 110 A, a welding voltage of 15 V, a wire feed speed of 13 m / min, and a welding torch travel speed of 14 mm / s. Metal powder solution coating was then applied to the component surface. After 8 minutes of evaporation, drying, and cooling to 30°C, the next layer of arc additive manufacturing and metal powder solution coating were performed. The process involves alternating powder coating and solution coating, repeated cyclically until 31 layers of in-situ alloyed arc additive manufacturing magnesium alloy are obtained. The process parameters for each layer are different: the vertical distance between the magnesium alloy welding wire and the magnesium alloy substrate is 8-20 mm; the welding current is 70-130 A; the welding voltage is 10 V-22 V; the wire feed speed is 8 m / min-15 m / min; and the welding torch travel speed is 10 mm / s-20 mm / s. A metal powder coating process is then performed on the component surface, followed by evaporation, drying, and cooling to 25-40℃ for 5-10 minutes. The resulting in-situ alloyed arc additive manufacturing magnesium alloy exhibits a fully equiaxed crystal structure with an average grain size of 23.73 μm; it is free from cracking and anisotropy; the texture is significantly weakened, with a texture strength of 1.50 mrd; and the prepared alloy shows good strength-ductility matching. The alloy tensile properties were tested under the following conditions: loading speed 0.6-1 mm / min, strain rate 3 × 10⁻⁶. -4 s -1 - 1×10 -3 s -1 The alloy has a tensile strength of 215.8±0.5MPa and an elongation of 26.8±0.1%.

[0018] The magnesium alloy welding wire, by mass percentage, comprises: Gd: 0.35 wt.%, Zn: 0.52 wt.%, Zr: 0.13 wt.%, Ca: 0.11 wt.%, Sm: 0.08 wt.%, wherein the mass ratio of Gd+Sm to Zn+Ca is 0.68, and the balance is magnesium and unavoidable impurities, the content of unavoidable impurities being ≤0.05 wt.%; the magnesium alloy substrate is AZ51 magnesium alloy substrate; The metal powder solution is prepared by mixing metal powder with anhydrous ethanol, stirring and ultrasonically vibrating for 5 minutes to obtain the metal powder solution. The metal powder is Zn powder, and the mass fraction of the metal powder in the metal powder solution is 2 wt.%. Example 3

[0019] In-situ alloying arc additive manufacturing of magnesium alloy component 3, its preparation method includes the following steps: The magnesium alloy substrate surface was sanded to remove oxide scale, rinsed with anhydrous ethanol, and dried to obtain a pretreated magnesium alloy substrate. Under a high-purity argon gas shielding gas with a purity ≥99.99% and a flow rate of 15 L / min, the pretreated magnesium alloy substrate underwent alternating treatment with arc additive manufacturing and metal powder solution coating using magnesium alloy welding wire. The alternating arc additive manufacturing and metal powder solution coating process was as follows: a first layer of additive manufacturing was performed using cold metal transition arc additive manufacturing to obtain the component. The cold metal transition arc additive manufacturing process was characterized by a vertical distance of 13 mm between the magnesium alloy welding wire and the magnesium alloy substrate, a welding current of 115 A, a welding voltage of 17 V, a wire feed speed of 12 m / min, and a welding torch travel speed of 16 mm / s. Metal powder solution coating was then applied to the component surface. After evaporation, drying, and cooling to 25°C for 7 minutes, the next layer of arc additive manufacturing and metal powder solution coating was performed. The process involves alternating powder coating and solution coating, repeated cyclically until 30 layers of in-situ alloyed arc additive manufacturing magnesium alloy are obtained. Each layer has different process parameters: the vertical distance between the magnesium alloy welding wire and the magnesium alloy substrate is 8-20 mm; the welding current is 70-130 A; the welding voltage is 10 V-22 V; the wire feed speed is 8 m / min-15 m / min; and the welding torch travel speed is 10 mm / s-20 mm / s. The component is then coated with a metal powder solution, which is evaporated, dried, and cooled to 25-40 °C for 5-10 minutes. The resulting in-situ alloyed arc additive manufacturing magnesium alloy exhibits a fully equiaxed crystal structure with an average grain size of 21.62 μm; it is free of cracks and anisotropy; the texture is significantly weakened, with a texture strength of 1.48 mrd; the prepared alloy shows good strength-ductility matching; and the alloy tensile properties are tested under the following conditions: loading speed 0.6-1 mm / min, strain rate 3 × 10⁻⁶. -4 s -1 - 1×10 -3 s -1 The alloy has a tensile strength of 216.3±0.2MPa and an elongation of 24.6±0.4%.

[0020] The magnesium alloy welding wire, by mass percentage, has the following composition: Gd: 0.48 wt.%, Zn: 0.37 wt.%, Zr: 0.22 wt.%, Ca: 0.17 wt.%, Sm: 0.12 wt.%, wherein the mass ratio of Gd+Sm to Zn+Ca is 1.11, and the balance is magnesium and unavoidable impurities, with the content of unavoidable impurities ≤0.05 wt.%; the magnesium alloy substrate is AZ31 magnesium alloy substrate; The metal powder solution is prepared by mixing metal powder with anhydrous ethanol, stirring and ultrasonically vibrating for 8 minutes to obtain the metal powder solution. The metal powder is Zn powder, and the mass fraction of the metal powder in the metal powder solution is 7 wt.%. Example 4

[0021] In-situ alloying arc additive manufacturing of magnesium alloy component 4, its preparation method includes the following steps: The magnesium alloy substrate surface was sanded to remove oxide scale, rinsed with anhydrous ethanol, and dried to obtain a pretreated magnesium alloy substrate. Under a high-purity argon gas shielding gas with a purity ≥99.99% and a flow rate of 18 L / min, the pretreated magnesium alloy substrate underwent alternating treatment with arc additive manufacturing and metal powder solution coating using magnesium alloy welding wire. The alternating arc additive manufacturing and metal powder solution coating process was as follows: a first layer of additive manufacturing was performed using cold metal transition arc additive manufacturing to obtain the component. The cold metal transition arc additive manufacturing process was characterized by a vertical distance of 13 mm between the magnesium alloy welding wire and the magnesium alloy substrate, a welding current of 120 A, a welding voltage of 18 V, a wire feed speed of 13 m / min, and a welding torch travel speed of 17 mm / s. Metal powder solution coating was then applied to the component surface. After 8 minutes of evaporation, drying, and cooling to 35°C, the next layer of arc additive manufacturing was performed. The process involved alternating treatments of metal powder solution coating until a 29-layer in-situ alloyed arc additive manufacturing magnesium alloy was obtained. The process parameters for each layer were different: the vertical distance between the magnesium alloy welding wire and the magnesium alloy substrate was 8-20 mm; the welding current was 70-130 A; the welding voltage was 10 V-22 V; the wire feed speed was 8 m / min-15 m / min; and the welding torch travel speed was 10 mm / s-20 mm / s. Metal powder solution coating was then applied to the component surface, followed by evaporation, drying, and cooling to 25-40 °C for 5-10 minutes. The resulting in-situ alloyed arc additive manufacturing magnesium alloy exhibited a fully equiaxed crystal structure with an average grain size of 20.76 μm; it was free of cracks and anisotropy; the texture was significantly weakened, with a texture strength of 1.31 mrd; the prepared alloy showed good strength-ductility matching; and the alloy tensile properties were tested under the following conditions: loading speed 0.6-1 mm / min, strain rate 3 × 10⁻⁶.-4 s -1 - 1×10 -3 s -1 The alloy has a tensile strength of 226.5±0.3MPa and an elongation of 22.3±0.4%.

[0022] The magnesium alloy welding wire, by mass percentage, has the following composition: Gd: 0.55 wt.%, Zn: 0.59 wt.%, Zr: 0.26 wt.%, Ca: 0.11 wt.%, Sm: 0.15 wt.%, wherein the mass ratio of Gd+Sm to Zn+Ca is 1, and the balance is magnesium and unavoidable impurities, with the content of unavoidable impurities ≤0.05 wt.%; the magnesium alloy substrate is a ZK60 magnesium alloy substrate; The metal powder solution is prepared by mixing metal powder with anhydrous ethanol, stirring and ultrasonically vibrating for 10 minutes to obtain the metal powder solution. The metal powder is a mixture of Al powder and Zn powder in a 1:1 ratio, and the mass fraction of the metal powder in the metal powder solution is 8 wt.%. Comparative Example 1

[0023] The additive manufacturing method for magnesium alloy component 5 includes the following steps: The magnesium alloy substrate surface was sanded to remove oxide scale, and then rinsed and dried with anhydrous ethanol to obtain a pretreated magnesium alloy substrate. Under a high-purity argon gas shielding gas with a purity ≥99.99% and a flow rate of 10 L / min, the pretreated magnesium alloy substrate underwent alternating treatment using magnesium alloy welding wire and metal powder solution coating. The alternating treatment of arc additive manufacturing and metal powder solution coating involved a first layer of additive manufacturing using cold metal transition arc additive manufacturing to obtain the component. The cold metal transition arc additive manufacturing was performed with a vertical distance of 6 mm between the magnesium alloy welding wire and the magnesium alloy substrate, a welding current of 65 A, a welding voltage of 9 V, a wire feed speed of 7 m / min, and a welding torch travel speed of 7 mm / s. Metal powder solution coating treatment is performed on the component: a metal powder solution is coated on the component surface, evaporated and dried for 3 minutes, and then cooled to 55°C. This process is repeated with the next layer of arc additive manufacturing and metal powder solution coating, until 15 layers of in-situ alloyed arc additive manufactured magnesium alloy are obtained. The obtained in-situ alloyed arc additive manufactured magnesium alloy has a fully equiaxed crystal structure, an average grain size of 38.72 μm, a texture strength of 2.67 mrd, a loading rate of 0.6-1 mm / min, and a strain rate of 3 × 10⁻⁶. -4 s -1 - 1×10 -3 s -1The alloy has a tensile strength of 190.4±0.2MPa and an elongation of 18.5±0.1%.

[0024] The magnesium alloy welding wire, by mass percentage, comprises: Gd 0.75 wt.%, Zn 0.17 wt.%, Zr 0.34 wt.%, Ca 0.26 wt.%, Sm 0.19 wt.%, wherein the mass ratio of Gd+Sm to Zn+Ca is 2.19, and the balance is magnesium and unavoidable impurities, the content of unavoidable impurities being ≤0.05 wt.%; the magnesium alloy substrate is AZ31 magnesium alloy substrate; The metal powder solution is prepared by mixing metal powder with anhydrous ethanol, stirring and ultrasonically vibrating for 3 minutes to obtain the metal powder solution. The metal powder is Zn powder, and the mass fraction of the metal powder in the metal powder solution is 10 wt.%.

[0025] Comparative Example 1 uses the same magnesium alloy substrate and magnesium alloy welding wire as the present invention, but the composition ratio of the magnesium alloy welding wire is not within the scope of the claims of the present invention. Both the present invention and the comparative example employ alternating processes of arc additive manufacturing and metal powder solution coating, but the process parameters of the arc additive manufacturing and metal powder solution coating processes in the comparative example are not within the scope of protection of the claims of the present invention. Compared with the present invention, Comparative Example 1 has a larger grain size, higher texture strength, and the alloy's strength and plasticity are both lower than the lowest values ​​of the embodiments of the present invention. This demonstrates that the optimal mechanical properties of the component obtained by the present invention are not determined by a certain component, process, or process parameter, but are achieved by the synergistic control of components, proportions, processes, and process parameters, and the optimal performance of the material can only be achieved within the scope of protection of the claims of the present invention. Comparative Example 2

[0026] A publicly published journal article entitled "A new die-cast magnesium alloy for applications at higher elevated temperatures of 200–300℃" (authors: Xixi Dong et al., journal: Journal of Magnesium and Alloys, volume: 9, publication date: November 2020) mentions a magnesium alloy in the experiment, with the composition by mass percentage as follows: La: 1.62 wt.%, Ce: 0.89 wt.%, Nd: 0.91 wt.%, Gd: 1.38 wt.%, Al: 0.52 wt.%, Zn: 0.32 wt.%, Mn: 0.24 wt.%, Y: 0.09 wt.%, with the balance being Mg. The alloy preparation includes the following steps: First, melting is carried out in an electric resistance furnace. During the melting process, a mixed gas of N2 (6 L / min) and SF6 (0.025 L / min) is used for protection. Pure Mg ingots and intermediate alloys are added sequentially to ensure that all alloying elements are fully dissolved and uniformly distributed in the melt. The melt temperature is controlled at 720℃ and held for 30 minutes, followed by high-pressure die casting. The high-pressure die casting process is as follows: The magnesium alloy melt is injected into the injection barrel of a 4500 kN cold chamber high-pressure die casting machine using manual feeding. During high-pressure die casting, the mold is preheated at 225℃, the melt pouring temperature is 715℃, the pressure is increased to 320 bar, and the injection barrel diameter is 70 mm. After high-pressure die casting, the alloy is obtained. The room temperature tensile strength of this alloy is 197 ± 2.8 MPa, and the elongation is 2.3 ± 0.3%. Table 1. Comparison of mechanical properties of alloys obtained in Examples 1-4 and Comparative Examples 1-2

[0027] Compared to the present invention, Comparative Example 2 requires first using a resistance furnace for melting, heating to a high temperature and holding for a long time to ensure that the alloying elements are fully dissolved and uniformly distributed in the melt; at the same time, it uses a high-pressure die casting process to prepare the alloy, and the melt is poured under high temperature and high pressure conditions. Furthermore, due to the limitations of the mold, it is impossible to process complex structures, which consumes more energy and time. The present invention uses alternating treatments of electric arc additive manufacturing and metal powder solution coating to achieve integrated rapid prototyping of simple or complex components, which significantly reduces manufacturing costs, simplifies the preparation process, increases material manufacturing speed, and shortens the manufacturing cycle. The total alloy content of Comparative Example 2 reaches 5.97 wt.%, of which the rare earth content is 4.89 wt.%, while the alloy and rare earth contents of the present invention are ≤2 wt.% and ≤0.85 wt.%, respectively. Therefore, the alloy and rare earth contents of Comparative Example 2 are much higher than the highest alloy and rare earth element contents of the present invention. The alloy prepared by Comparative Example 2 has a mismatch between strength and plasticity, with low elongation (only 2.3 ± 0.3%) and tensile strength <200 MPa. The magnesium alloy obtained by this invention has a low total amount of alloy and rare earth added, a simple preparation process, and low energy consumption. It can form both simple structures and complex components. The strength and plasticity of the prepared alloy are higher than those of the alloy obtained in Comparative Example 2, achieving a good match between strength and plasticity.

[0028] Compared with existing technologies, this invention significantly reduces the raw material addition cost for alloy preparation, lowering the total alloy addition to below 2 wt.%, simplifying the production process of magnesium alloy components, and achieving integrated rapid prototyping. It can prepare both simple and complex structures, avoiding cracking and anisotropy, while simultaneously improving the strength and plasticity of the material. The obtained in-situ alloyed arc additive manufacturing magnesium alloy has a completely equiaxed crystal structure with an average grain size <25 μm; it exhibits no anisotropy, forming a weak textured structure with a texture strength ≤1.6 mrd; the prepared alloy has good strength-plasticity matching, with a tensile strength ≥210 MPa and an elongation ≥20%. Each embodiment of this invention uses different welding wire composition ratios, additive manufacturing process parameters, etc., resulting in different mechanical properties and microstructures of the final obtained magnesium alloys. Although Comparative Example 1 uses a similar process to this invention, the welding wire composition ratio and process parameters used are not within the scope of protection of the claims of this invention, and the mechanical properties of the magnesium alloy obtained in Comparative Example 1 are all lower than the minimum values ​​of this invention. This demonstrates that the superior performance achieved by this invention is not determined by a specific component, ratio, or process parameter, but rather by the synergistic regulation of component interactions, ratios, processes, and process parameters. Furthermore, the superior material performance can only be achieved within the scope of the claims of this invention. For example, the process parameters for each layer of additive manufacturing in this invention are different, and the synergistic regulation of components, ratios, and the processes and parameters for each layer is crucial for improving the final material performance. Comparative Example 2 uses die casting to prepare magnesium alloys, which is not only complex in its preparation process but also difficult to prepare complex structures due to mold limitations. Its alloy content reaches 5.97 wt.%, with alloy and rare earth content far exceeding the maximum addition amount of this invention. However, the prepared alloy exhibits lower strength and ductility than the lowest values ​​obtained by this invention, with an elongation of only 2.3 ± 0.3% and a strength < 200 MPa. Addressing the problems of high preparation costs and complex processes in existing technologies, this invention develops a rapid prototyping technology for magnesium alloys and prepares low-alloy high-performance magnesium alloys with matched strength and ductility, enabling integrated rapid prototyping of simple or complex components. This significantly reduces manufacturing costs, simplifies the preparation process, increases material manufacturing speed, and shortens the manufacturing cycle. To address the issue of coarse columnar crystal formation caused by high cooling rates, high temperature gradients, and thermal cycling during arc additive manufacturing, this invention effectively improves stress concentration and cracking problems, achieves a fully equiaxed crystal structure, strengthens grain boundary reinforcement, and weakens texture. This effectively suppresses defects in additively manufactured magnesium alloys such as premature fracture, insufficient mechanical properties, significant mechanical anisotropy, and uneven local and overall mechanical properties. Ultimately, it achieves a simultaneous improvement in the strength and plasticity of magnesium alloy components, enabling both simple and complex structures to be realized. Furthermore, it significantly optimizes the comprehensive mechanical properties of additively manufactured magnesium alloys, meeting the needs of high-end equipment manufacturing.

Claims

1. An in-situ alloyed electric arc additive manufacturing of magnesium alloys, characterized in that, Its preparation method includes the following steps: The magnesium alloy substrate surface was sanded to remove oxide scale, and then rinsed and dried with anhydrous ethanol to obtain a pretreated magnesium alloy substrate. Under a high-purity argon gas shielding gas with a purity ≥99.99% and a flow rate of 12-20 L / min, the pretreated magnesium alloy substrate underwent alternating treatment with magnesium alloy welding wire arc additive manufacturing and metal powder solution coating. The alternating arc additive manufacturing and metal powder solution coating process involved a first layer of cold metal transition arc additive manufacturing to obtain the component. The cold metal transition arc additive manufacturing process was characterized by a vertical distance of 8-20 mm between the magnesium alloy welding wire and the magnesium alloy substrate, a welding current of 70-130 A, a welding voltage of 10 V-22 V, and a wire feed speed of 8 m / min-15 m / min. The welding torch travel speed is 10mm / s-20mm / s. Metal powder solution coating is applied to the component surface. After evaporation, drying, and cooling to 25-40℃ for 5-10 minutes, the next layer of arc additive manufacturing and metal powder solution coating are alternated. This process is repeated until 20-40 layers of in-situ alloyed arc additive manufacturing magnesium alloy are obtained. The process parameters for each layer of alternating arc additive manufacturing and metal powder solution coating are different. The obtained in-situ alloyed arc additive manufacturing magnesium alloy has a completely equiaxed crystal structure with an average grain size ≤25μm; it is free from cracking and anisotropy, has a weak texture structure with a texture strength ≤1.6mrd; the alloy has a good balance of strength and plasticity, with a tensile strength ≥210MPa and an elongation ≥20%. The magnesium alloy welding wire, by mass percentage, comprises: Gd: 0.3-0.7 wt.%, Zn: 0.2-0.6 wt.%, Zr: 0.1-0.3 wt.%, Ca: 0.05-0.2 wt.%, Sm: 0.03-0.15 wt.%, wherein the mass ratio of Gd+Sm to Zn+Ca is 0.6~1.2, and the balance is magnesium and unavoidable impurities, the content of unavoidable impurities being ≤0.05 wt.%; the magnesium alloy substrate is one of AZ31, AZ51, and ZK60; The metal powder solution is prepared by mixing metal powder with anhydrous ethanol, stirring and ultrasonically vibrating for 5-10 minutes to obtain the metal powder solution. The metal powder is one or a combination of Al powder and Zn powder, and the mass fraction of the metal powder in the metal powder solution is 2wt.%-8wt.%.

2. The in-situ alloying arc additive manufacturing of magnesium alloy according to claim 1, characterized in that, The welding current is 75-120A, the welding voltage is 12V-18V, the wire feed speed is 9.5m / min-13.5m / min, and the welding torch travel speed is 12mm / s-17mm / s.

3. The in-situ alloying arc additive manufacturing of magnesium alloy according to claim 1, wherein, The flow rate of the protective gas is 13-18 L / min.

4. The in-situ alloying arc additive manufacturing of magnesium alloy according to claim 1, wherein, This process is repeated until 25-35 layers of in-situ alloyed arc additive manufacturing magnesium alloy are obtained.

5. The in-situ alloying arc additive manufacturing of magnesium alloy according to claim 1, wherein, The average grain size is 20.76-24.55 μm, and the texture intensity is 1.31-1.50 mrd.

6. The in-situ alloying arc additive manufacturing method for magnesium alloys according to claim 1, characterized in that, The tensile strength is 215.8-226.5 MPa, and the elongation is 22.3%-25.6%.

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