A method of fusing filament additive manufacturing of heat stable magnesium alloys

Abstract

The present application relates to the field of magnesium alloy design and processing technology, in particular to a method for preparing a heat-stable magnesium alloy by fused wire additive manufacturing, comprising magnesium alloy substrate pretreatment; performing additive manufacturing on the pretreated magnesium alloy substrate, each layer using main path magnesium alloy wire and bypass alloy wire for additive manufacturing, using a cold metal transfer welding arc as a power source and laser as an auxiliary heat source; obtaining an atom replacement magnesium alloy by sequentially performing solid solution and aging treatment on the additive manufactured magnesium alloy substrate, and realizing the precipitation of rare earth solute atom doped microstructure. Through the synergistic regulation of the welding wire and the process, the present application realizes the regulation of the rare earth solute atom doped microstructure, actively regulates the thermal stability of the nanometer precipitate in the magnesium alloy, thereby widening the aging window and improving the performance persistence of the material in a high temperature environment, and provides a new way for the high reliability manufacturing of large magnesium alloy components in the fields of aerospace and the like.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy design and processing technology, and in particular to a method for preparing thermally stable magnesium alloys by fused wire additive manufacturing. Background Technology

[0002] Magnesium alloys are currently the lowest density metallic structural materials used in industrial applications (approximately 1.8 g / cm³). 3 While magnesium alloys are only 1 / 4 the weight of steel and 2 / 3 the weight of aluminum, they face a prominent common problem when used at temperatures of 100°C and above: due to the rapid coarsening and phase transformation of their metastable precipitates during high-temperature aging, the peak aging window of the alloy is very narrow. This phenomenon severely restricts the material's performance uniformity and long-term service reliability, often accompanied by a significant decrease in strength. Therefore, existing technologies struggle to simultaneously improve the room temperature strength of the alloy and its strength under long-term heat exposure (i.e., reduce the strength degradation rate). The root cause of this problem lies in the insufficient thermal stability of the precipitates themselves. Under prolonged heat exposure, the precipitates coarsen, their density decreases, leading to a significant decrease in alloy strength. Obtaining magnesium alloys with high thermal stability is crucial, as it helps magnesium alloys replace aluminum / steel in high-temperature scenarios, significantly reducing component weight. For example, in high-temperature components such as cylinder head covers and gearbox housings of automobile engines, the use of magnesium alloys with high thermal stability can reduce weight by 20%-30%, directly improving fuel efficiency or the range of electric vehicles; in the aerospace field, they can be used for engine peripheral brackets and drone structural components to reduce the overall weight and ensure structural reliability in high-temperature environments.

[0003] Arc-wire additive manufacturing, as a near-net-shape forming technology, has shown significant advantages in the fabrication of large, lightweight, and complex magnesium alloy components for aerospace and weapon systems. The mechanical properties of these alloys typically rely on the strengthening effect of high-density nano-precipitates formed during post-heat treatment. These precipitates enhance material strength by hindering dislocation movement. To achieve ideal performance, precise control of the morphology, size, and distribution of precipitates is often required through aging treatment. This aims to form numerous coherent or semi-coherent nanostructures, such as atomic clusters, Geneiève-Preston (GP) zones, and fine precipitates, thereby achieving a synergistic improvement in alloy strength and plasticity. However, these precipitates are prone to coarsening. In the aging heat treatment of large and complex components, short-time heat treatment cannot adequately heat the core, while long-time treatment can lead to over-aging of the outer layer. Furthermore, coarsened precipitates can cause performance degradation during long-term thermal exposure. Additionally, magnesium alloys have limited slip systems, and complex alloy composition design makes wire fabrication difficult. Therefore, new methods are needed, and achieving the design of thermally stable precipitates has become a pressing technological bottleneck.

[0004] Current technologies primarily improve the thermal stability of magnesium alloys and suppress issues such as coarsening of precipitated phases at high temperatures by adding a large amount of various alloying components (alloy mass percentage ≥ 6%). While this approach can reduce the strength degradation rate of high-temperature alloys, the high alloy content not only increases production costs but also reduces forming efficiency. Therefore, reducing the alloy content, avoiding cracking, simplifying the process, ensuring high room temperature strength and low strength degradation rate at high temperatures, and achieving industrial production of complex and large components are pressing technical challenges that need to be addressed. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method for preparing thermally stable magnesium alloys using fused wire additive manufacturing. Through the synergistic regulation of the welding wire, process, and process parameters, a rare earth solute atom doped microstructure is formed, enabling active regulation of the thermal stability of nano-precipitates in magnesium alloys. This broadens the aging window, improves the performance durability of materials under high-temperature environments, and provides a new approach for the high-reliability manufacturing of large magnesium alloy components in aerospace and other fields.

[0006] The technical solution adopted in this invention is as follows: The present invention proposes a method for preparing heat-stabilized magnesium alloys by fused wire additive manufacturing, which specifically includes the following steps: S1: Pretreatment of magnesium alloy substrate; S2: Additive manufacturing of 5 or more layers is carried out on the pretreated magnesium alloy substrate. Each layer is manufactured using main magnesium alloy wire and bypass alloy wire. Cold metal transfer welding arc is used as the power source and laser is used as the auxiliary heat source. The angle between the cold metal transfer welding arc and the laser is 20°-60°. Main magnesium alloy wire: The magnesium alloy wire is coaxial with the cold metal transfer welding arc power source and perpendicular to the magnesium alloy substrate. The distance between the wire and the magnesium alloy substrate is 8-20mm. S3: After the magnesium alloy substrate is produced by additive manufacturing, solid solution treatment and aging treatment are performed in sequence to obtain magnesium alloy with precipitated phase atomic substitution, so as to realize the precipitation control of rare earth solute atom doped microstructure.

[0007] Furthermore, in step S1, the pretreatment includes: removing the oxide layer and contaminants on the surface of the magnesium alloy substrate by physical polishing, then ultrasonically cleaning it in anhydrous ethanol, and finally preheating it at 50-200℃ for 10-60 minutes.

[0008] Furthermore, in step S2, the angle between the bypass alloy wire and the main magnesium alloy wire is 25-70°, and the distance between the bypass alloy wire and the magnesium alloy substrate is 14-18mm; the welding voltage is 9-24V, the welding current is 70-200A, and the welding speed is 3-8mm / s; the laser power is 200-1800W; the wire feeding speed of the main magnesium alloy wire is 2-10m / min, the wire feeding speed of the bypass alloy wire is 5-30cm / min, and the temperature of the additive manufacturing layer is controlled at 25-200℃ before starting the next layer of additive manufacturing.

[0009] Furthermore, the magnesium alloy substrate is pure magnesium or Mg-Al extruded sheet; the Mg-Al system is AZ31 or AZ61.

[0010] Furthermore, the main magnesium alloy wire is a Mg-Ca, Mg-Al, or Mg-Zn magnesium alloy.

[0011] Furthermore, the bypass alloy wire is a pure Al or Al-RE or Mg-Ca magnesium alloy with a diameter of 0.8-2.0 mm.

[0012] Furthermore, when the main magnesium alloy wire and the bypass alloy wire are made of Mg-Ca system magnesium alloy, the Ca content of the Mg-Ca system is 0.3-2 wt.%; when the main magnesium alloy wire is made of Mg-Zn system magnesium alloy, the Zn content of the Mg-Zn system is 0.5-2 wt.%; when the bypass alloy wire is made of Al-RE system, RE includes one or more of Gd, Y, Nd, and Sc, and the RE content is 0.03-2 wt.%.

[0013] Furthermore, the width of the rare-earth solute atom-doped microstructure is three atomic layers, with the middle atomic layer being Al or Zn, and the two outer atomic layers being Ca and rare-earth atoms; the rare-earth atoms are Gd, Y, Nd, or Sc; the length of the three-atom-layer microstructure is ≤10 nm, and the density is ≥1.0 × 10⁻⁶. 23 m -3 .

[0014] Furthermore, step S3 includes: Solution treatment: Place the additively manufactured magnesium alloy at 350-500℃ for 2-4 hours; Aging treatment: Place the solution-treated magnesium alloy at 180-200℃ for 2-15 hours; The treated alloy has a yield strength ≥120MPa and an elongation ≥10%; after being exposed to heat at 150-220℃ for 50-300h, the room temperature yield strength retention rate is ≥92%, the yield strength is ≥110MPa, and the elongation is ≥10%.

[0015] Compared with the prior art, the present invention has the following advantages: 1. This invention proposes a novel in-situ alloying method based on dual-wire arc additive manufacturing, through the synergistic control of welding wire, process, and process parameters. This method enables the control of rare-earth solute atom-doped microstructures, achieving active regulation of the thermal stability of nano-precipitates in magnesium alloys. This broadens the aging window and improves the material's performance durability under high-temperature environments, providing a new approach for the high-reliability manufacturing of large magnesium alloy components in aerospace and other fields. Compared with existing technologies, this invention achieves the following significant advantages: First, it overcomes the limitations of existing technologies where the alloy composition is entirely determined by the chemical composition of the deposited layer, which is predetermined by a single wire. The manufacturing process is merely an accumulation of physical shapes, making it impossible to redesign the material system. Second, through synchronous dual-wire delivery and in-situ alloying reaction within the molten pool, this invention dynamically introduces additional alloying elements during additive manufacturing, achieving real-time and precise "re-control" of the molten pool's chemical composition. This expands the achievable composition range of a single-wire system and makes it possible to design gradient compositions based on regional performance requirements during manufacturing, thereby elevating additive manufacturing from "shape manufacturing" to a new level of "material and shape integrated manufacturing."

[0016] 2. This invention simplifies the process and avoids cracking and anisotropy; it overcomes the technical bottlenecks faced by existing technologies. However, in practical applications, to improve the coarsening resistance of precipitates, existing technologies often employ extensive microalloying strategies. However, magnesium alloys themselves have limited slip systems, and complex alloying designs often exacerbate the difficulty in preparing high-quality welding wires, limiting the practical application of multi-component compositions in additive manufacturing. Due to the difficulty in preparing high-strength magnesium alloy wires, poor plasticity, and the difficulty in achieving strength, plasticity, and thermal stability with a single-component system, components manufactured by traditional methods often suffer from problems such as coarse grains and difficulty in controlling precipitates, resulting in insufficient room temperature strength, high-temperature creep resistance, and over-aging resistance, making it difficult to simultaneously improve the room temperature and long-term heat exposure strength of the alloy. This invention utilizes additive manufacturing with sub-rapid solidification and high cooling rates, combined with elemental interactions and synergistic control of processes and parameters. Besides refining grains, it also increases matrix solid solubility, promoting the formation of high-density, nanoscale coherent precipitates during aging. Due to its high solid solubility, only trace amounts of rare earth alloying are needed to achieve rare earth solute atom doping into the precipitated microstructure. This generates a strong orbital hybridization effect between microstructure atoms, significantly reducing the microstructure free energy and improving the coarsening resistance of the nanoscale coherent strengthening precipitates at high temperatures. Simultaneously, the extremely low intrinsic diffusion rate of rare earth elements in the magnesium matrix effectively suppresses the Ostwald ripening process and inhibits precipitate growth from a kinetic perspective. After heat exposure at 180-200℃ for 100-250 hours, the room temperature yield strength retention rate is ≥92%, the yield strength is ≥110MPa, and the elongation is ≥10%. This fundamentally improves upon the technical bottleneck of simultaneously improving the comprehensive mechanical properties and long-term thermal stability of magnesium alloy components, providing a highly flexible and precise means of composition control. By independently controlling the types (different alloy systems), diameters, wire feed speeds, and related processes and parameters of the two wires, the rate and proportion of each alloying element entering the molten pool can be precisely controlled. This enables effective control of continuous or stepwise changes in alloy composition from the macroscopic component scale to the microscopic melt channel scale during a single manufacturing process. It allows for fine-tuning of trace element composition within the same matrix alloy, as well as the composite material and functionally graded material preparation of two different alloy systems, greatly expanding the diversity of material composition in additive manufacturing of magnesium alloys.

[0017] 3. This invention enables the introduction of homo- or hetero-component welding wires into the magnesium alloy matrix during additive manufacturing, resulting in a wider range of control over the magnesium alloy composition and proportions, and allowing for the microstructure control of key precipitated phases in the magnesium alloy. This microstructure control of precipitated phases produces a dual positive effect: thermodynamically, it reduces the formation energy and enhances the stability of the precipitated phases themselves; kinetically, it forms a barrier to element diffusion, inhibiting the coarsening process of the precipitated phases under prolonged exposure to high temperatures. Therefore, it can significantly improve the retention rate of mechanical properties and dimensional stability of materials under high-temperature service environments, providing a practical and feasible technical approach for the direct manufacturing of large, lightweight magnesium alloy load-bearing components with extreme reliability requirements in aerospace and other fields. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the three-atom-layer microstructure with Sc occupancy prepared in Example 1 of the present invention. Detailed Implementation

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] The method for preparing heat-stabilized magnesium alloys by fused wire additive manufacturing proposed in this invention specifically includes the following steps: S1: Pre-treat the magnesium alloy substrate; remove the oxide layer and contaminants on the surface of the magnesium alloy substrate by physical polishing, then place it in anhydrous ethanol for ultrasonic cleaning, and finally preheat it at 50-200℃ for 10-60 minutes.

[0021] The magnesium alloy substrate is pure magnesium or Mg-Al extruded sheet; the Mg-Al system is AZ31 or AZ61.

[0022] S2: Additive manufacturing of 5 or more layers is carried out on the pretreated magnesium alloy substrate. Each layer is manufactured using main magnesium alloy wire and bypass alloy wire. Cold metal transfer welding arc is used as the power source and laser is used as the auxiliary heat source. The angle between the cold metal transfer welding arc and the laser is 20°-60°. Main magnesium alloy wire: The magnesium alloy wire is coaxial with the cold metal transfer welding arc power source and perpendicular to the magnesium alloy substrate. The distance between the wire and the magnesium alloy substrate is 8-20mm.

[0023] The angle between the bypass alloy wire and the main magnesium alloy wire is 25-70°, and the distance between the bypass alloy wire and the magnesium alloy substrate is 14-18mm; the welding voltage is 9-24V, the welding current is 70-200A, and the welding speed is 3-8mm / s; the laser power is 200-1800W; the wire feeding speed of the main magnesium alloy wire is 2-10m / min, and the wire feeding speed of the bypass alloy wire is 5-30cm / min. After controlling the temperature of the additive manufacturing layer at 25-200℃, the next layer of additive manufacturing is started.

[0024] The main magnesium alloy wire is a Mg-Ca, Mg-Al, or Mg-Zn magnesium alloy; the bypass alloy wire is a pure Al, Al-RE, or Mg-Ca magnesium alloy with a diameter of 0.8-2.0 mm.

[0025] When the main magnesium alloy wire is of the Mg-Al system, the Al content of the Mg-Al system is 1-3 wt.%; when the main magnesium alloy wire and the bypass alloy wire are of the Mg-Ca system, the Ca content of the Mg-Ca system is 0.3-2 wt.%; when the main magnesium alloy wire is of the Mg-Zn system, the Zn content of the Mg-Zn system is 0.5-2 wt.%; when the bypass alloy wire is of the Al-RE system, RE includes one or more of Gd, Y, Nd, and Sc, and the RE content is 0.03-2 wt.%.

[0026] S3: After sequentially performing solution treatment and aging treatment on the additively manufactured magnesium alloy substrate, a magnesium alloy with precipitated phase atomic substitution is obtained, achieving precipitation control of rare earth solute atom-doped microstructures; specifically including: Solution treatment: Place the additively manufactured magnesium alloy at 350-500℃ for 2-4 hours; Aging treatment: Place the solution-treated magnesium alloy at 180-200℃ for 2-15 hours; The treated alloy has a yield strength ≥120MPa and an elongation ≥10%; after being exposed to heat at 150-220℃ for 50-300h, the room temperature yield strength retention rate is ≥92%, the yield strength is ≥110MPa, and the elongation is ≥10%.

[0027] The rare-earth solute atom-doped microstructure has a width of three atomic layers, with the middle atomic layer being Al or Zn, and the two outer atomic layers being Ca and rare-earth atoms; the rare-earth atoms are Gd, Y, Nd, or Sc, with a length ≤10 nm and a density ≥1.0 × 10⁻⁶. 23 m -3 .

[0028] The present invention will be further illustrated below through specific embodiments and comparative examples: Example 1 In this embodiment, the main wire is a Mg-Ca alloy, with the following composition by mass percentage: Mg 99.0%, Ca 1.0%, trace impurity elements ≤0.02%, and a diameter of 1.2 mm; the bypass wire is an Al-Sc alloy, with the following composition by mass percentage: Al 98.0%, Sc 2.0%, trace impurity elements ≤0.02%, and a diameter of 1.2 mm.

[0029] The processing procedure is as follows: Select a magnesium alloy substrate, grind the magnesium alloy substrate clean, remove the surface oxide scale, clean it with anhydrous ethanol and dry it for later use. Substrate preheating: Heat the magnesium alloy substrate to 100°C, and fix the preheated substrate on the worktable with a clamp; Adjust the position of the robotic arm so that the main wire is perpendicular to the magnesium alloy substrate and the distance between them is 8mm; the angle between the cold metal transfer welding arc and the laser is 60°; and the angle between the bypass wire and the main wire is 70°. Ten layers of additive manufacturing were performed using a cold metal transfer welding power-coupled fiber laser. The welding current was 180A, the welding voltage was 22V, the main wire speed was 4.4m / min, the bypass wire speed was 20cm / min, and the welding speed was 4mm / s. The laser power was 1500W, the frequency was 2000Hz, and the wavelength was 1080nm. The temperature of each layer of additive manufacturing was controlled at 100℃. After additive manufacturing was completed, a Mg-2.9Al-0.9Ca-0.1Sc sample was obtained and subjected to solution treatment and aging treatment in sequence. The solution treatment was carried out at 450℃ for 1 hour and then at 500℃ for 1 hour. The aging treatment was carried out at 200℃ for 12 hours. The precipitated phase atomic substitution magnesium alloy had a yield strength of approximately 120 MPa and an elongation of 15%. After being exposed to heat at 200℃ for 200 hours, the room temperature yield strength retention rate was 98%, the yield strength was approximately 118 MPa, and the elongation was still 15%.

[0030] The rare earth solute-doped microstructure has a width of three atomic layers, with Al in the middle layer and Ca and Sc on both sides; the three-atom-layer microstructure is as follows: Figure 1 As shown, the length is approximately 5 nm, and the density is approximately 4.6 × 10⁻⁶. 23 m -3 .

[0031] Example 2 The main wire used in this embodiment is a Mg-Al magnesium alloy, with the following composition by mass percentage: Mg 96.0%, Al 3.0%, Ca 1.0%, trace impurity elements ≤0.02%, and a diameter of 1.6 mm; The bypass wire is an Al-RE alloy, with the following composition by mass percentage: Al 99.0%, Nd 1.0%, and trace impurity elements ≤0.02%, and a diameter of 1.2 mm; The processing procedure is as follows: Select a magnesium alloy substrate, grind the magnesium alloy substrate clean, remove the surface oxide scale, clean it with anhydrous ethanol and dry it for later use. Substrate preheating: Heat the magnesium alloy substrate to 200°C, and fix the preheated substrate on the worktable with a clamp; Adjust the position of the robotic arm so that the main wire is perpendicular to the substrate and the distance between it and the magnesium alloy substrate is 20mm; the angle between the cold metal transfer welding arc and the laser is 20°; and the angle between the bypass wire and the main wire is 10°. Five layers of additive manufacturing were performed using a cold metal transfer welding power-coupled fiber laser. The welding current was 70A, the welding voltage was 10V, the main wire speed was 7m / min, the bypass wire speed was 30cm / min, and the welding speed was 8mm / s. The laser power was 1000W, the frequency was 2000Hz, and the wavelength was 1080nm. The temperature of each layer of additive manufacturing was controlled at 200℃. After additive manufacturing was completed, a Mg-3.0Al-0.7Ca-0.051Nd sample was obtained, and it was subjected to solution treatment and aging treatment in sequence. The solution treatment was carried out at 500℃ for 3 hours, and the aging treatment was carried out at 190℃ for 15 hours. The precipitated phase atomic substitution magnesium alloy had a yield strength of about 150 MPa and an elongation of 13%. After being exposed to heat at 200℃ for 300 hours, the room temperature yield strength retention rate was 97%, the yield strength was about 146 MPa, and the elongation was 12%.

[0032] The rare-earth solute atom-doped microstructure has a width of three atomic layers, with Al in the middle layer and Ca and Nd on both sides; the three-atom-layer microstructure has a length of approximately 4 nm and a density of approximately 5.6 × 10⁻⁶. 23 m -3 .

[0033] Example 3 The main wire used in this embodiment is a Mg-Zn magnesium alloy, with the following composition by mass percentage: Mg 97.0%, Zn 2.0%, Ca 1.0%, trace impurity elements ≤0.02%, and a diameter of 1.2 mm; The bypass wire is an Al-RE alloy, with the following composition by mass percentage: Al 98.0%, Gd 1.0%, Y 1.0%, trace impurity elements ≤0.02%, and a diameter of 1.2 mm; The processing procedure is as follows: Select a magnesium alloy substrate, grind the magnesium alloy substrate clean, remove the surface oxide scale, clean it with anhydrous ethanol and dry it for later use. Substrate preheating: Heat the magnesium alloy substrate to 50°C and fix the preheated substrate on the worktable with a clamp. Adjust the position of the robotic arm so that the main wire is perpendicular to the substrate and the distance between it and the magnesium alloy substrate is 20mm; the angle between the cold metal transfer welding arc and the laser is 45°; the angle between the bypass wire and the main wire is 55°. A cold metal transfer welding power supply coupled with a fiber laser was used to perform arc-initiated additive manufacturing of 15 layers. The welding current was 150A, the welding voltage was 18V, the main wire speed was 5m / min, the bypass wire speed was 15cm / min, and the welding speed was 6mm / s. The laser power was 500W, the frequency was 2000Hz, the wavelength was 1080nm, and the temperature of each arc-initiated additive manufacturing layer was controlled at 50℃. After additive manufacturing is completed, a Mg-1.9Zn-0.9Ca-0.05Gd-0.05Y sample is obtained, and it is subjected to solution treatment and aging treatment in sequence. The solution treatment is carried out at 350℃ for 1 hour and then at 450℃ for 1 hour. The aging treatment is carried out at 180℃ for 13 hours. The precipitated phase atomic substitution magnesium alloy has a yield strength of about 143 MPa and an elongation of 16%. After being exposed to heat at 220℃ for 300 hours, the room temperature yield strength retention rate is 95%, the yield strength is about 137 MPa, and the elongation is 14%.

[0034] The rare-earth solute atom-doped microstructure has a width of three atomic layers, with the middle atomic layer being Zn and the two outer atomic layers being Ca and Gd or Y; the three-atom-layer microstructure has a length of approximately 6 nm and a density of approximately 5.0 × 10⁻⁶. 23 m -3 .

[0035] Comparative Example The paper "Revisited precipitation process in dilute mg-Ca-Zn alloys" published by ZH Li et al. prepared as-cast Mg-0.5Ca-1.6Zn magnesium alloys, which were then solution-treated at 520℃ for 2 hours and quenched in water. Peak aging was achieved by aging at 200℃ for 0.3 hours, resulting in a Vickers hardness of approximately 63.6 HV. After heat exposure at 200℃ for 100 hours, the Vickers hardness was approximately 48.3 HV, with a retention rate of approximately 76%. It is evident that the mechanical property retention rate of this alloy is significantly lower than that of the embodiments described in this invention.

[0036] As can be seen, compared with the prior art, this invention has achieved a breakthrough, especially in promoting the thermal stability of magnesium alloys, through the synergistic control of material composition, ratio, and key process parameters, which can significantly improve the overall performance of the material, as specifically reflected in the following: This invention optimizes the process to promote alloy solidification into fine equiaxed crystals during additive manufacturing, achieving a uniform distribution of composition and grains within and between layers. This effectively suppresses defects such as compositional segregation, coarse grains, surface roughness, porosity, and microcracks caused by edge effects in traditional processes. This uniform, fine-grained microstructure exhibits excellent resistance to coarsening under prolonged heat exposure, with grains not easily growing and the microstructure remaining stable. Simultaneously, the yield strength retention rate is ≥92%, far superior to existing levels, and the strength does not significantly degrade during long-term high-temperature service. Furthermore, this invention supports multi-path synergistic additive manufacturing of the same or different alloys (same or different diameter wires). The equiaxed crystal structure and its thermal stability can be flexibly controlled through the process, enabling highly reliable manufacturing of large-size, irregularly shaped components. Ultimately, the additively manufactured alloy maintains high thermal stability of its mechanical properties even after prolonged heat exposure.

[0037] In summary, the core advantage of this invention lies in the active cultivation of microstructures during additive manufacturing through process innovation, thereby achieving significant progress in improving material strength and thermal stability, and overcoming the limitations of existing technologies in controlling the thermal stability of medium- and high-strength magnesium alloys.

[0038] All matters not covered in this invention are common knowledge.

[0039] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing thermally stable magnesium alloys using fused wire additive manufacturing, characterized in that, The method includes the following steps: S1: Pretreatment of magnesium alloy substrate; S2: Additive manufacturing of 5 or more layers is carried out on the pretreated magnesium alloy substrate. Each layer is manufactured using main magnesium alloy wire and bypass alloy wire. Cold metal transfer welding arc is used as the power source and laser is used as the auxiliary heat source. The angle between the cold metal transfer welding arc and the laser is 20°-60°. Main magnesium alloy wire: The magnesium alloy wire is coaxial with the cold metal transfer welding arc power source and perpendicular to the magnesium alloy substrate. The distance between the wire and the magnesium alloy substrate is 8-20mm. S3: After the magnesium alloy substrate is produced by additive manufacturing, solid solution treatment and aging treatment are performed in sequence to obtain magnesium alloy with precipitated phase atomic substitution, so as to realize the precipitation control of rare earth solute atom doped microstructure.

2. The method for preparing thermally stable magnesium alloys by fused wire additive manufacturing according to claim 1, characterized in that: In step S1, the pretreatment includes: removing the oxide layer and contaminants on the surface of the magnesium alloy substrate by physical polishing, then ultrasonically cleaning it in anhydrous ethanol, and finally preheating it at 50-200℃ for 10-60 minutes.

3. The method for preparing thermally stable magnesium alloys by fused wire additive manufacturing according to claim 1, characterized in that: In step S2, the angle between the bypass alloy wire and the main magnesium alloy wire is 25-70°, and the distance between the bypass alloy wire and the magnesium alloy substrate is 14-18mm; the welding voltage is 9-24V, the welding current is 70-200A, and the welding speed is 3-8mm / s; the laser power is 200-1800W; the wire feeding speed of the main magnesium alloy wire is 2-10m / min, and the wire feeding speed of the bypass alloy wire is 5-30cm / min. After controlling the temperature of the additive manufacturing layer at 25-200℃, the next layer of additive manufacturing is started.

4. The method for preparing thermally stable magnesium alloys by fused wire additive manufacturing according to claim 1, characterized in that: The magnesium alloy substrate is pure magnesium or Mg-Al extruded sheet; the Mg-Al system is AZ31 or AZ61.

5. The method for preparing thermally stable magnesium alloys by fused wire additive manufacturing according to claim 1, characterized in that: The main magnesium alloy wire is a Mg-Ca, Mg-Al, or Mg-Zn magnesium alloy.

6. The method for preparing thermally stable magnesium alloys by fused wire additive manufacturing according to claim 5, characterized in that: The bypass alloy wire is a pure Al or Al-RE or Mg-Ca magnesium alloy with a diameter of 0.8-2.0 mm.

7. The method for preparing thermally stable magnesium alloys by fused wire additive manufacturing according to claim 6, characterized in that: When the main magnesium alloy wire and the bypass alloy wire are made of Mg-Ca system magnesium alloy, the Ca content of Mg-Ca system is 0.3-2 wt.%; when the main magnesium alloy wire is made of Mg-Zn system magnesium alloy, the Zn content of Mg-Zn system is 0.5-2 wt.%; when the bypass alloy wire is made of Al-RE system, RE includes one or more of Gd, Y, Nd, and Sc, and the RE content is 0.03-2 wt.%.

8. The method for preparing thermally stable magnesium alloys by fused wire additive manufacturing according to claim 7, characterized in that: The rare-earth solute atom-doped microstructure has a width of three atomic layers, with the middle atomic layer being Al or Zn, and the two outer atomic layers being Ca and rare-earth atoms; the rare-earth atoms are Gd, Y, Nd, or Sc; the length of the three-atom-layer microstructure is ≤10 nm, and the density is ≥1.0 × 10⁻⁶. 23 m -3 .

9. The method for preparing thermally stable magnesium alloys by fused wire additive manufacturing according to claim 7, characterized in that: Step S3 includes: Solution treatment: Place the additively manufactured magnesium alloy at 350-500℃ for 2-4 hours; Aging treatment: Place the solution-treated magnesium alloy at 180-200℃ for 2-15 hours; The treated alloy has a yield strength ≥120MPa and an elongation ≥10%; after being exposed to heat at 150-220℃ for 50-300h, the room temperature yield strength retention rate is ≥92%, the yield strength is ≥110MPa, and the elongation is ≥10%.

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