Core-shell microstructure magnesium alloy wire and preparation method thereof

Abstract

The application discloses a kind of core-shell microstructure magnesium alloy wire and preparation method thereof, it is related to magnesium alloy electric arc additive manufacturing and welding wire technical field.The application is with high-purity hot extrusion pure magnesium wire as substrate, after surface pretreatment, zinc transition layer and aluminum protective layer are prepared in turn, then heat treatment and drawing treatment are carried out, obtain the core-shell microstructure magnesium alloy wire from inside to outside in turn pure magnesium core layer, zinc transition layer and aluminum protective layer.The method bypasses the traditional casting-extrusion-drawing long process technology, with coating thickness accurate control wire composition, fundamentally eliminates the segregation defects of ingot;Zinc transition layer effectively eliminates interface potential difference and significantly improves coating adhesion, aluminum protective layer surface forms dense passivation film to realize long-acting corrosion protection, product wire composition is uniform, interface adhesion is strong, can be widely applied to electric arc additive manufacturing and various welding processes.

Description

Technical Field

[0001] This invention belongs to the technical field of wires for arc additive manufacturing and welding of magnesium alloys, specifically relating to a core-shell microstructure magnesium alloy wire and its preparation method. Background Technology

[0002] With the continuous upgrading of demand for lightweight and weight reduction in aerospace, rail transportation, and new energy vehicles, magnesium alloys, with their outstanding advantages such as low density, high specific strength, excellent damping and vibration reduction properties, and complete recyclability, have become a core candidate material for lightweight structural components. Electrical arc additive manufacturing (WAAM) technology uses wire as raw material and achieves near-net-shape forming of large and complex components through layer-by-layer deposition via electric arc cladding. It features high material utilization, short forming cycle, and low manufacturing cost, and has become one of the mainstream technical routes for the efficient manufacturing of high-performance magnesium alloy complex components.

[0003] As a core consumable in arc additive manufacturing, the uniformity of its composition, surface quality, and batch stability directly determine the final microstructure and mechanical properties of the additive components. Compared with ordinary welding wire, additive manufacturing wire has more stringent performance requirements: on the one hand, the WAAM process involves multi-layer, multi-pass continuous stacking, and minute fluctuations in the composition of the wire accumulate layer by layer during the forming process, ultimately leading to significant dispersion in the microstructure and mechanical properties of different locations in the component, severely restricting the service reliability of the component; on the other hand, high-performance magnesium alloys often require high alloying design, but the addition of alloying elements significantly reduces the room temperature plasticity of magnesium alloys, resulting in a sharp increase in the difficulty of wire drawing, low yield, and even some composition systems that cannot be processed into wire using traditional processes.

[0004] Currently, magnesium alloy wire generally adopts the traditional process route of alloy smelting - casting into ingots - hot extrusion - multi-pass cold drawing. This technical route has the following three major shortcomings: First, the challenges of plastic processing and the limitations imposed by alloy composition design are significant. High-alloy magnesium alloys (such as AZ61 and AZ91) exhibit poor room-temperature plasticity, resulting in severe work hardening during drawing and requiring frequent intermediate annealing. This leads to a long process flow, low production efficiency, and a yield rate of less than 30%. For high-strength magnesium alloys with higher aluminum content and those with special composition ratios, conventional casting-extrusion-drawing processes are often completely incapable of producing usable wires. Furthermore, alloy composition design must simultaneously consider both casting performance and plastic processing properties. Many high-alloy systems with excellent service performance cannot be processed into wires and therefore cannot be used in additive manufacturing, severely restricting the freedom of composition design.

[0005] Secondly, ingot segregation is difficult to eliminate, resulting in poor uniformity of wire composition. Dendritic segregation and regional segregation are unavoidable during the solidification process of magnesium alloy ingots. Even after subsequent hot extrusion deformation, the segregation scale can only be improved but not completely eliminated. Ultimately, the axial and circumferential compositional deviation of the wire can reach more than 0.5wt%, directly leading to compositional stratification and uneven performance in additive parts. This is a key bottleneck restricting the engineering application of magnesium alloy additive components.

[0006] Third, magnesium alloy wire is prone to oxidation and corrosion under atmospheric conditions, posing high barriers to storage and transportation. Magnesium metal is highly chemically reactive and can oxidize and corrode within 24 hours in humid environments. Corrosion products entering the additive manufacturing molten pool can cause fatal defects such as inclusions, porosity, and hot cracks. Among existing surface protection solutions, rare earth coatings have extremely weak adhesion to the substrate, only achieving micro-alloying and failing to meet long-term protection requirements; direct aluminum plating results in a loose oxide film easily forming on the magnesium substrate surface, with a coating adhesion of only 2-3 MPa, making it extremely prone to peeling and failure during drawing and wire feeding; while single zinc coatings have better adhesion, zinc has a low boiling point and volatilizes violently under the high temperature of the electric arc, exacerbating molten pool spatter and porosity defects, and cannot achieve precise control of the molten pool composition.

[0007] Furthermore, existing magnesium alloy surface aluminizing technologies are mostly focused on surface modification of cast magnesium alloy sheets. Their pretreatment and electroplating processes are difficult to adapt to the continuous production of wires, and cannot guarantee the uniformity and bonding stability of the circumferential coating on the wires. At the same time, existing coated wires are all developed around welding scenarios and have not been designed for the special requirements of arc additive manufacturing for wire composition uniformity and batch consistency. They also have not fundamentally solved the inherent defects of traditional cast wires, such as difficult processing and large segregation. Summary of the Invention

[0008] In order to overcome the shortcomings of the prior art, the present invention aims to provide a core-shell microstructured magnesium alloy wire and its preparation method, so as to solve the technical problems in the prior art of magnesium alloy wire, which are difficult to plastically process due to reliance on casting process, uneven composition caused by ingot segregation, poor coating adhesion and serious element burn-off during additive manufacturing process.

[0009] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for preparing a core-shell microstructured magnesium alloy wire, comprising the following steps: S1, perform surface pretreatment on pure magnesium wire, and prepare a zinc transition layer on the surface of the pretreated pure magnesium wire; S2, an aluminum protective layer is prepared on the surface of the zinc transition layer to obtain a coated wire blank with the pure magnesium wire as the core layer and the zinc transition layer and the aluminum protective layer in sequence. S3, the coated wire blank is heat-treated to obtain the heat-treated coated wire; S4, the heat-treated coated wire is drawn to obtain a core-shell microstructure magnesium alloy wire of the target diameter.

[0010] A further improvement of the present invention is that the surface pretreatment includes grinding and polishing, alkaline washing and degreasing, and surface activation treatment performed sequentially.

[0011] A further improvement of the present invention is that the alkaline washing solution used for the alkaline washing and degreasing includes sodium hydroxide, sodium carbonate and sodium phosphate; and the surface activation solution used includes phosphoric acid and ammonium bifluoride.

[0012] A further improvement of the present invention is that the zinc transition layer is prepared by a zincate immersion zinc process, wherein the immersion zinc solution includes zinc sulfate, potassium pyrophosphate, sodium carbonate and potassium fluoride; and the aluminum protective layer is prepared by an ionic liquid bipolar pulse electroplating process.

[0013] A further improvement of the present invention is that the electroplating system of the ionic liquid bipolar pulse electroplating is an aluminum chloride-1-methyl-3-ethylimidazoline chloride system, wherein the molar ratio of aluminum chloride to the 1-methyl-3-ethylimidazoline chloride is (2~3):1.

[0014] A further improvement of the present invention is that the process conditions for the bipolar pulse electroplating are: a cathode peak current density of -15 to -25 mA / cm². 2 The anode current density is 0.4~0.6 mA / cm². 2 The cathode duty cycle is 0.2~0.5, and the pulse frequency is 2 Hz.

[0015] A further improvement of the present invention is that the heat treatment temperature is 150~250℃ and the holding time is 10~14 h; the drawing process is 1~4 passes of cold drawing, the drawing speed is 4~5 m / min, the single pass cross-sectional deformation is 6%~25%, and the cumulative cross-sectional deformation is 6%~40%.

[0016] A further improvement of the present invention is that, after S4, a step of cleaning and purifying the drawn filament is included, wherein the cleaning and purification includes degreasing with organic solvents and ultrasonic water washing.

[0017] A further improvement of the present invention is that the thickness of the zinc transition layer is 1~7 μm, the thickness of the aluminum protective layer is 6~20 μm, and the target diameter of the core shell microstructure magnesium alloy wire is 1.2~2.0 mm.

[0018] Secondly, the present invention also provides a core-shell microstructured magnesium alloy wire, which is prepared by the above-mentioned preparation method. The core-shell microstructured magnesium alloy wire comprises, from the inside to the outside, a pure magnesium core layer, a zinc transition layer and an aluminum protective layer.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing core-shell microstructured magnesium alloy wire. This method bypasses the traditional long process route, which involves alloy melting and casting, ingot homogenization, hot extrusion, multi-pass drawing, and intermediate annealing. In contrast, this invention uses pure magnesium wire with excellent plasticity as the processing substrate. The finished wire can be obtained by only performing surface pretreatment, preparing a zinc transition layer and an aluminum protective layer, heat treatment, and drawing. The process is shortened by more than 40%, and the intermediate annealing process is eliminated. This completely solves the industry pain point of severe work hardening and low yield caused by the poor plasticity of high alloy magnesium alloys during drawing, and significantly reduces the manufacturing difficulty and preparation cost of high alloy wire.

[0020] Furthermore, in this method, the alloy composition of the wire is precisely controlled by the thickness of the zinc transition layer and the aluminum protective layer, eliminating the need for smelting and adjusting the alloy composition. This completely avoids the unavoidable dendritic segregation and regional segregation problems during the solidification process of traditional ingots. The axial and circumferential compositional deviations of the finished wire can be controlled to below 0.1wt%, significantly improving batch stability. This solves the bottleneck problem of compositional dispersion and performance fluctuations in additive manufacturing parts caused by uneven wire composition, and can improve the consistency of mechanical properties of additive components by more than 20%.

[0021] Furthermore, this method employs a gradient coating process involving surface pretreatment, preparation of a zinc transition layer, and preparation of an aluminum protective layer. This process eliminates the interfacial oxidation and potential difference issues between the pure magnesium substrate and the aluminum coating, significantly improving the adhesion between the coating and the pure magnesium substrate. No coating peeling occurs during subsequent drawing and additive wire feeding processes. The outer aluminum protective layer forms a dense alumina passivation film at room temperature, completely isolating the wire from corrosive media. This ensures no significant corrosion even after 30 days of exposure to humid environments, greatly improving the storage and transportation convenience of the wire. Simultaneously, the entire process parameters are stable and controllable, making it suitable for continuous wire production. The diameter tolerance of the finished wire is ≤±0.02mm, demonstrating promising industrialization prospects.

[0022] This invention also provides a core-shell microstructured magnesium alloy wire, which comprises, from the inside out, a pure magnesium core layer, a zinc transition layer, and an aluminum protective layer, forming a three-layer gradient composite structure. The zinc transition layer, as the intermediate layer, effectively eliminates the tendency for galvanic corrosion caused by the potential difference between the pure magnesium core layer and the aluminum protective layer, while significantly improving the interlayer interface bonding state and greatly enhancing the interfacial bonding strength. The outer aluminum protective layer utilizes its spontaneously formed dense alumina passivation film to physically block corrosive media, thus enabling the wire to possess both excellent room-temperature corrosion resistance and structural integrity, making it stably compatible with WAAM arc additive manufacturing and mainstream welding processes such as GTAW, GMAW, and CMT. Attached Figure Description

[0023] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components of the invention.

[0024] Figure 1 This is a process flow diagram of the preparation method of the core-shell microstructure magnesium alloy wire of the present invention; Figure 2 This is a schematic diagram of the magnesium alloy wire core-shell microstructure of the present invention; Figure 3 The images show actual wire materials, where (a) is a single-layer galvanized wire and (b) is a double-layer galvanized wire. Figure 4 SEM-EDS characterization of galvanized single-coated wire, where (a) is the surface morphology of the coating on the longitudinal section of the wire, and (b) is the line scan EDS analysis result along the direction of the arrow shown in (a). Figure 5 SEM-EDS characterization of galvanized and aluminized wires, where (a) is the surface morphology of the coating on the longitudinal section of the wire, and (b) is the line scan EDS analysis result along the direction of the arrow shown in (a). Figure 6 The SEM-EDS characterization of the wire cladding test sample is shown in (a), where (b) is the surface morphology of the cladding test sample between two passes, (c) is the distribution of Mg element in the surface scan corresponding to (a), and (d) is the distribution of Zn element in the surface scan corresponding to (a). Detailed Implementation

[0025] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0026] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0027] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0028] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0029] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0030] like Figure 1As shown, this invention provides a method for preparing a core-shell microstructured magnesium alloy wire, comprising the following steps: S1, pretreating the surface of pure magnesium wire and preparing a zinc transition layer on the surface of the pretreated pure magnesium wire; S2, preparing an aluminum protective layer on the surface of the zinc transition layer to obtain a coated wire blank with the pure magnesium wire as the core layer and sequentially coated with the zinc transition layer and the aluminum protective layer; S3, heat-treating the coated wire blank to obtain a heat-treated coated wire; S4, drawing the heat-treated coated wire to obtain a core-shell microstructured magnesium alloy wire of the target diameter. The pure magnesium wire is prepared by using high-purity magnesium ingots with a purity ≥99.95% as raw material, and hot-extruded at a temperature of 150~400℃, resulting in a pure magnesium core material with a diameter of 1.5~2.5mm. This method uses pure magnesium wire as the processing substrate, leveraging its excellent plasticity to ensure the processing performance of the wire during drawing. It fundamentally solves the problem of severe work hardening and low yield caused by the poor room-temperature plasticity of high-alloy magnesium alloys during drawing. Simultaneously, by precisely controlling the thickness of the zinc transition layer and aluminum protective layer, the overall composition of the wire is controlled, eliminating the need for alloy casting and completely avoiding the unavoidable dendritic and regional segregation problems during traditional ingot solidification. The axial and circumferential compositional deviations of the finished wire can be controlled below 0.1 wt%, significantly improving batch stability. This method also breaks through the processing limits of traditional processes for high-alloy wires, enabling the preparation of magnesium alloy wires with high alloy content and special compositional ratios that cannot be formed by conventional extrusion drawing.

[0031] In the above preparation method, the surface pretreatment includes sequential grinding and polishing, alkaline washing and degreasing, and surface activation treatment. Grinding and polishing involves sequentially grinding and polishing the pure magnesium core material with 320#, 800#, and 1800# abrasive belts to remove oxide scale and processing scratches from the surface of the pure magnesium wire, ensuring a uniform and dense subsequent coating. The alkaline washing and degreasing solution includes 10 g / L NaOH, 25 g / L Na2CO3, and 15 g / L Na3PO4, and is treated at 65-75°C for 5-6 minutes, effectively removing grease contaminants from the wire surface. After alkaline washing, the material must be immediately rinsed 2-3 times with distilled water and dried with airflow to avoid alkaline residue. The surface activation solution used includes 50~60g / L H3PO4 (wt=85%) and 100~120g / L NH4HF2, with deionized water as the solvent. The treatment is carried out at 25℃ for 8~15min, which can remove the residual oxide film after alkaline washing and put the wire surface in an active state, providing good interfacial bonding conditions for subsequent coating. After activation, it must be rinsed with distilled water 2~3 times immediately and blown dry with airflow to avoid the residue of acid pickling etching solution.

[0032] In the above preparation method, the zinc transition layer is prepared using a zincate immersion zinc process. The immersion solution comprises 0.16 mol / L ZnSO4·7H2O, 0.42 mol / L K4P2O7, 0.047 mol / L Na2CO3, and 0.103 mol / L KF, with deionized water as the solvent and a pH value of 10.0~10.5. The zinc is immersed at room temperature for 1000~2000 seconds, forming a uniform and dense zinc layer on the surface of pure magnesium wire through a chemical displacement reaction. This zinc transition layer can, on the one hand, eliminate the interfacial potential difference between the magnesium substrate and the subsequent aluminum protective layer, significantly improving the coating adhesion; on the other hand, it can control the solidification behavior of the molten pool during additive manufacturing. The aluminum protective layer is prepared using an ionic liquid bipolar pulse electroplating process. The electroplating system is an aluminum chloride-1-methyl-3-ethylimidazoline chloride (AlCl3-EMIC) system, wherein the molar ratio of aluminum chloride to 1-methyl-3-ethylimidazoline chloride is (2~3):1, preferably 2:1. Electroplating is performed at room temperature. The process conditions for bipolar pulse electroplating are: cathode peak current density of -15~-25 mA / cm². 2 The anode current density is 0.4~0.6 mA / cm². 2 The cathode duty cycle is 0.2~0.5, the pulse frequency is 2Hz, and the total cathode charge is 15~60C / cm. 2 The use of ionic liquid electroplating system avoids the technical problem of aluminum not being able to be deposited in aqueous solution system, while bipolar pulse electroplating process effectively suppresses dendrite tendency during coating growth by periodically changing the current direction, thus obtaining a dense and smooth aluminum protective layer.

[0033] In the above preparation method, the coated wire blank is heat-treated under argon protection at a temperature of 150-250℃ for 10-14 hours, preferably at 200℃ for 12 hours. This heat treatment process promotes the interfacial element diffusion between the zinc transition layer and the pure magnesium substrate, and between the aluminum protective layer and the zinc transition layer, forming a metallurgical bonding transition region, thereby further improving the corrosion resistance and interfacial bonding strength of the coating. The drawing process consists of 1-4 passes of cold drawing at a speed of 4-5 m / min, with a single pass cross-sectional deformation of 6%-25% and a cumulative cross-sectional deformation of 6%-40%. Because pure magnesium wire has excellent plasticity, and both the zinc transition layer and the aluminum protective layer are pure metal layers with good deformation coordination, the coated wire blank only requires a few passes of precision cold drawing to obtain the finished wire of the target diameter, eliminating the need for an intermediate annealing process and significantly shortening the process flow. Following step S4, the process includes cleaning and purifying the drawn wire. Specifically, the cleaning and purification involves: first, removing drawing oil stains from the surface of the coated wire using an organic solvent; then, ultrasonically rinsing the wire with deionized water for 10-20 minutes; after rinsing, drying in a vacuum environment at 60°C for 1 hour; and finally, vacuum sealing and packaging to obtain the finished wire. The thickness of the zinc transition layer is 1-7 μm, the thickness of the aluminum protective layer is 6-20 μm, the total thickness of the zinc transition layer and the aluminum protective layer is 7-27 μm, and the target diameter of the core-shell microstructure magnesium alloy wire is 1.2-2.0 mm.

[0034] like Figure 2As shown, this invention also provides a core-shell microstructured magnesium alloy wire, prepared using the above-described method. The core-shell microstructured magnesium alloy wire comprises, from the inside out, a pure magnesium core layer, a zinc transition layer, and an aluminum protective layer. The interfacial bonding strength between the zinc transition layer and the pure magnesium core layer and the aluminum protective layer is significantly improved. Specifically, the thickness of the zinc transition layer is 1-7 μm. This thickness range eliminates the interfacial potential difference between the magnesium substrate and the aluminum protective layer, significantly improving the coating adhesion. Furthermore, it allows for control of the molten pool solidification behavior during the additive manufacturing process. The thickness of the aluminum protective layer is 6-20 μm. This thickness range allows for the formation of a dense alumina passivation film at room temperature, achieving long-term corrosion resistance. Additionally, during the arc additive manufacturing process, after melting and alloying with the pure magnesium core layer, the aluminum content matches the composition design range of the AZ series magnesium alloys, preventing excessive formation of brittle phases in the additive layer. This wire uses pure magnesium as its core layer, fundamentally eliminating the unavoidable segregation defects in traditional cast magnesium alloy wires. Its compositional uniformity is far superior to traditional products. The outer aluminum protective layer effectively isolates corrosive media at room temperature, while the inner zinc transition layer provides cathodic protection to the magnesium substrate at damaged areas, preventing pitting corrosion. This results in a wire that possesses both excellent room-temperature corrosion resistance and compatibility with additive manufacturing processes. The wire has a diameter tolerance of ≤±0.02mm, provides smooth and stable wire feeding, and can be directly applied to mainstream welding processes such as WaaAAM (Wafer Electric Arc Additive Manufacturing), Gas Tungsten Inert Gas Welding (GTAW), Gas Metal Arc Welding (GMAW), and Cold Metal Transfer (CMT).

[0035] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0036] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0037] Example 1 This embodiment describes the preparation of an AZ31 composition core-shell microstructured magnesium alloy wire suitable for WAAM arc additive manufacturing, with a finished diameter of 1.6 mm. The specific steps include: S1, Preparation of pure magnesium core material: Using high-purity magnesium ingots with a purity of ≥99.95% as raw material, pure magnesium wire is prepared by hot extrusion method. The extrusion temperature is 300℃, and the diameter of the extruded pure magnesium core material is 2.0mm.

[0038] S2, Surface pretreatment and zinc immersion: The pure magnesium core material is subjected to grinding and polishing, alkaline washing and degreasing, surface activation and zincate immersion treatment in sequence.

[0039] Grinding and polishing: The pure magnesium core material is continuously ground and polished with 320#, 800# and 1800# abrasive belts in sequence to remove surface oxide scale and processing scratches.

[0040] Alkaline washing for degreasing: The polished pure magnesium wire is degreased using an alkaline washing solution at 70℃ for 5 minutes. The alkaline washing solution consists of 10 g / L NaOH, 25 g / L Na2CO3, and 15 g / L Na3PO4, with deionized water as the solvent. Immediately after alkaline washing, the wire is rinsed twice with distilled water and then dried with an airflow to prevent alkaline residue.

[0041] Surface activation: The alkaline-washed pure magnesium wire was activated using an acid pickling and etching solution at 25°C for 12 minutes. The acid pickling and etching solution consisted of 55 g / L H3PO4 (wt=85%) and 110 g / L NH4HF2, with deionized water as the solvent. Immediately after activation, the wire was rinsed three times with distilled water and dried with an airflow to prevent any residue of the acid pickling and etching solution.

[0042] Zincate immersion: Surface-activated pure magnesium wire was immersed in a zinc immersion solution. The solution composition was: 0.16 mol / L ZnSO4·7H2O, 0.42 mol / L K4P2O7, 0.047 mol / L Na2CO3, 0.103 mol / L KF, with a pH of 10. Immersion was carried out at room temperature for 2000 s, resulting in a zinc transition layer approximately 6 μm thick. After removal, the wire was rinsed and dried to obtain the finished product. Figure 3 As shown in (a), the obtained finished filament was characterized by SEM-EDS, as follows: Figure 4 As shown, the coating interface is well bonded, and the composition is continuous without voids.

[0043] S3, Aluminum Plating: Using zinc-immersed pure magnesium wire as the cathode and a pure aluminum plate as the anode, an aluminum protective layer is prepared using a bipolar pulse electroplating process in an ionic liquid system with a molar ratio of AlCl3 to EMIC of 2:1; the process conditions are: cathode peak current density IC = -15 mA / cm². 2 Anode current density IA = 0.4 mA / cm² 2 The cathode duty cycle rC = 0.2, the pulse frequency f = 2 Hz, and the total cathode charge is 46 C / cm.2 After electroplating at room temperature, an aluminum protective layer with a thickness of about 15 μm is obtained, and the total coating thickness is about 24 μm, forming a gradient core-shell microstructure.

[0044] S4, Post-plating heat strengthening treatment: The coated wire is placed in an argon protective atmosphere and kept at 150 ℃ for 14 h, and then cooled with the furnace.

[0045] S5, Precision drawing and sizing: The heat-treated coated wire was subjected to two passes of precision cold drawing using 1.8 mm and 1.6 mm drawing dies, respectively. The drawing speed was 4.5 m / min, with a single-pass cross-sectional deformation of approximately 20% and a cumulative deformation of approximately 36%, yielding a semi-finished wire with a diameter of 1.6 mm. The resulting finished wire was characterized by SEM-EDS, such as... Figure 5 As shown in (a), the thickness decreases after drawing, with the final zinc coating thickness being approximately 3 μm and the aluminum coating thickness being approximately 6 μm. Figure 5 As shown in (b), based on its EDS characterization results, its coating composition is continuous without voids and has good surface bonding.

[0046] S6, Cleaning and Packaging: The semi-finished filament material is degreased, ultrasonically cleaned, and dried, then vacuum-sealed to obtain the finished filament material, such as... Figure 3 As shown in (b), its surface is smooth and burr-free, which meets the requirements for the surface quality of finished wire materials in GB / T 41112-2021.

[0047] Example 2 This embodiment prepares a high-aluminum-content core-shell microstructure magnesium alloy wire, using electroplating to prepare a zinc transition layer, with a finished diameter of 1.2 mm. The specific steps include: S1, Preparation of pure magnesium core material: Using high-purity magnesium ingots with a purity of ≥99.95% as raw material, pure magnesium wire is prepared by hot extrusion method. The extrusion temperature is 350℃, and the diameter of the extruded pure magnesium core material is 1.5mm.

[0048] S2, Surface pretreatment and zinc immersion: The pure magnesium core material is subjected to grinding and polishing, alkaline washing and degreasing, surface activation and zincate immersion treatment in sequence.

[0049] Grinding and polishing: The pure magnesium core material is continuously ground and polished with 320#, 800# and 1800# abrasive belts in sequence to remove surface oxide scale and processing scratches.

[0050] Alkaline washing for degreasing: The polished pure magnesium wire is degreased using an alkaline washing solution at 70℃ for 5 minutes. The alkaline washing solution consists of 10 g / L NaOH, 25 g / L Na2CO3, and 15 g / L Na3PO4, with deionized water as the solvent. Immediately after alkaline washing, the wire is rinsed three times with distilled water and then dried with an airflow to prevent alkaline residue.

[0051] Surface activation: The alkaline-washed pure magnesium wire was activated using an acid pickling and etching solution at 25°C for 12 minutes. The acid pickling and etching solution consisted of 55 g / L H3PO4 (wt=85%) and 110 g / L NH4HF2, with deionized water as the solvent. Immediately after activation, the wire was rinsed three times with distilled water and dried with an airflow to prevent any residue of the acid pickling and etching solution.

[0052] Zincate immersion: The surface-activated pure magnesium wire was immersed in zinc using a zinc immersion solution with the following composition: 0.16 mol / L ZnSO4·7H2O, 0.42 mol / L K4P2O7, 0.047 mol / L Na2CO3, 0.103 mol / L KF, and pH 10.2. The immersion was carried out at room temperature for 1000 s, resulting in a zinc transition layer with a thickness of approximately 2 μm. The wire was then removed, rinsed, and dried.

[0053] S3, Aluminum Plating: Using a pure magnesium wire pre-plated with zinc as the cathode and a pure aluminum plate as the anode, an aluminum protective layer is prepared in an ionic liquid system with a molar ratio of AlCl3 to EMIC of 2.5:1 using a bipolar pulse electroplating process; the process conditions are: cathode peak current density IC = -25 mA / cm². 2 Anode current density IA = 0.5 mA / cm² 2 The cathode duty cycle rC = 0.5, the pulse frequency f = 2Hz, and the total cathode charge is 56 C / cm. 2 After electroplating at room temperature, an aluminum protective layer with a thickness of about 20 μm is obtained, forming a gradient core-shell microstructure.

[0054] S4, Post-plating heat strengthening treatment: The coated wire is placed in an argon protective atmosphere and kept at 200 ℃ for 12 h, and then cooled with the furnace.

[0055] S5, Precision drawing and sizing: The heat-treated coated wire is subjected to three precision cold drawing passes using drawing dies of 1.4 mm, 1.3 mm and 1.2 mm respectively, with a drawing speed of 5 m / min. The cross-sectional deformation per pass is about 14%, and the cumulative deformation is about 36%, resulting in a semi-finished wire with a diameter of 1.2 mm.

[0056] S6, Cleaning and Packaging: After degreasing with organic solvent, ultrasonically clean with deionized water for 10 min, then dry in a vacuum environment at 60 ℃ for 1 h, and finally vacuum seal and package to obtain the finished filament.

[0057] Example 3 This embodiment prepares an AZ31 composition core-shell microstructured magnesium alloy wire suitable for WAAM arc additive manufacturing, with a finished diameter of 1.2 mm. The specific steps include: S1, Preparation of pure magnesium core material: Using high-purity magnesium ingots with a purity of ≥99.95% as raw material, pure magnesium wire is prepared by hot extrusion method. The extrusion temperature is 350℃, and the diameter of the extruded pure magnesium core material is 1.2mm.

[0058] S2, Surface pretreatment and zinc immersion: The pure magnesium core material is subjected to grinding and polishing, alkaline washing and degreasing, surface activation and zincate immersion treatment in sequence.

[0059] Grinding and polishing: The pure magnesium core material is continuously ground and polished with 320#, 800# and 1800# abrasive belts in sequence to remove surface oxide scale and processing scratches.

[0060] Alkaline washing for degreasing: The polished pure magnesium wire is degreased using an alkaline washing solution at 70℃ for 5 minutes. The alkaline washing solution consists of 10 g / L NaOH, 25 g / L Na2CO3, and 15 g / L Na3PO4, with deionized water as the solvent. Immediately after alkaline washing, the wire is rinsed three times with distilled water and then dried with an airflow to prevent alkaline residue.

[0061] Surface activation: The alkaline-washed pure magnesium wire was activated using an acid pickling and etching solution at 25°C for 12 minutes. The acid pickling and etching solution consisted of 55 g / L H3PO4 (wt=85%) and 110 g / L NH4HF2, with deionized water as the solvent. Immediately after activation, the wire was rinsed three times with distilled water and dried with an airflow to prevent any residue of the acid pickling and etching solution.

[0062] Zincate immersion: The surface-activated pure magnesium wire was immersed in zinc using a zinc immersion solution with the following composition: 0.16 mol / L ZnSO4·7H2O, 0.42 mol / L K4P2O7, 0.047 mol / L Na2CO3, 0.103 mol / L KF, and pH 10.5. The immersion was carried out at room temperature for 1500 s, resulting in a zinc transition layer with a thickness of approximately 4 μm. The wire was then removed, rinsed, and dried.

[0063] S3, Aluminum Plating: Using a pure magnesium wire pre-plated with zinc as the cathode and a pure aluminum plate as the anode, an aluminum protective layer is prepared in an ionic liquid system with a molar ratio of AlCl3 to EMIC of 3:1 using a bipolar pulse electroplating process; the process conditions are: cathode peak current density IC = -20 mA / cm². 2 Anode current density IA = 0.5 mA / cm² 2 The cathode duty cycle rC = 0.4, the pulse frequency f = 2 Hz, and the total cathode charge is 45 C / cm. 2 After electroplating at room temperature, an aluminum protective layer with a thickness of about 10 μm is obtained, forming a gradient core-shell microstructure.

[0064] S4, Post-plating heat strengthening treatment: The coated wire is placed in an argon protective atmosphere and kept at 250℃ for 10 hours, then cooled with the furnace.

[0065] S5, Precision drawing and sizing: The heat-treated coated wire is subjected to one pass of precision cold drawing using a 1.2 mm drawing die and a drawing speed of 4 m / min. The cross-sectional deformation in a single pass is about 6%, and the cumulative deformation is about 6%, resulting in a semi-finished wire with a diameter of 1.2 mm.

[0066] S6, Cleaning and Packaging: After degreasing with organic solvent, ultrasonically clean with deionized water for 10 minutes, then dry in a vacuum environment at 60℃ for 1 hour, and finally vacuum seal and package to obtain the finished filament.

[0067] After obtaining the finished filament, a cladding test is performed. The positions between the two cladding passes in the cladding structure are characterized by SEM-EDS, such as... Figure 6 As shown, the elements in the wire are well dispersed during the additive manufacturing process, and the composition distribution is consistent between passes, achieving a good alloying effect.

[0068] Comparative Example 1 This comparative example represents the conventional preparation method of traditional homogeneous AZ31 magnesium alloy welding wire, serving as a control group for the coated magnesium alloy welding wire of this application. The specific preparation process is as follows: S1, Raw material preparation: By weight, weigh 96.2 parts of pure magnesium ingot with a purity of 99.95wt%, 3.0 parts of pure aluminum ingot with a purity of 99.90wt%, 0.8 parts of pure zinc ingot with a purity of 99.995wt%, and 2.0 parts of Al-10wt%Mn master alloy; also prepare 1.8 parts of RJ-2 magnesium alloy covering agent and 0.6 parts of RJ-5 magnesium alloy refining agent.

[0069] S2, alloy melting and semi-continuous casting: Raw materials are added to a resistance-heated crucible furnace, and a mixed protective atmosphere of SF6 + CO2 (SF6 volume percentage 0.3%) is introduced. The temperature is raised to 710℃ and held for 35 minutes until the raw materials are completely melted. The temperature is then raised to 730℃, argon gas is introduced for bottom blowing, and a refining agent is added for refining for 12 minutes. After refining, the mixture is allowed to stand for 25 minutes, surface slag is skimmed off, and the melt temperature is adjusted to 700℃ for semi-continuous water-cooled casting to obtain 80mm AZ31 magnesium alloy ingots. The casting speed is 100mm / min, and the cooling water flow rate is 2.0m³ / min. 3 / h.

[0070] S3, homogenization annealing: the cast rod is placed in a vacuum annealing furnace, heated to 420℃ and held for 16 hours, then cooled in the furnace to below 200℃ and air-cooled to eliminate casting dendrite segregation.

[0071] S4, hot extrusion billet preparation: the annealed cast rod is preheated to 380℃ and hot extruded on a horizontal extrusion press; the extrusion barrel temperature is 350℃, the extrusion die temperature is 330℃, the extrusion ratio is 25:1, the extrusion speed is 2m / min, and the extrusion is air-cooled to obtain φ2mm AZ31 magnesium alloy extruded wire.

[0072] S5, multi-pass cold drawing, processes extruded bars into φ1.2mm finished welding wire through multiple cold drawing passes; the deformation amount per pass is controlled at 12%~18%, and intermediate annealing is performed every 2~3 passes, with the intermediate annealing process being 300℃ and held for 2 hours; polycrystalline diamond molds are used for drawing, with matching calcium-based special lubricant, and the drawing speed is 30m / min; the entire process consists of 9 drawing passes and 5 intermediate annealing passes.

[0073] S6. Finished product heat treatment and post-treatment: The drawn finished welding wire is placed in an argon-protected annealing furnace, heated to 280℃ and held for 1.5 hours. After furnace cooling, it is taken out of the furnace. The surface lubricant is removed by alkaline washing, and after drying, it is vacuum sealed and packaged to obtain the traditional homogeneous AZ31 magnesium alloy welding wire.

[0074] Performance test results of Comparative Example 1 Chemical composition: Al 3.02wt%, Zn 0.78wt%, Mn 0.21wt%, conforming to the AZ31 magnesium alloy composition standard; Salt spray corrosion: The wire obtained in Comparative Example 1 and the wire obtained in Example 3 were compared and tested. During the first 24 hours of the test, under the same surface area exposed to the corrosive medium of simulated seawater, the corrosion rate of the coated wire obtained in Example 3 was 3.85 mm / a, while that of the conventional alloy wire obtained in Comparative Example 1 was 11.23 mm / a. The corrosion rate of the coated wire was only about 34% of that of the conventional AZ31 alloy wire, and the corrosion resistance was significantly improved.

[0075] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a core-shell microstructured magnesium alloy wire, characterized in that, Includes the following steps: S1, perform surface pretreatment on pure magnesium wire, and prepare a zinc transition layer on the surface of the pretreated pure magnesium wire; S2, an aluminum protective layer is prepared on the surface of the zinc transition layer to obtain a coated wire blank with the pure magnesium wire as the core layer and the zinc transition layer and the aluminum protective layer in sequence. S3, the coated wire blank is heat-treated to obtain the heat-treated coated wire; S4, the heat-treated coated wire is drawn to obtain a core-shell microstructure magnesium alloy wire of the target diameter.

2. The method for preparing a core-shell microstructured magnesium alloy wire according to claim 1, characterized in that, The surface pretreatment includes sequential grinding and polishing, alkaline washing and degreasing, and surface activation treatment.

3. The method for preparing a core-shell microstructured magnesium alloy wire according to claim 2, characterized in that, The alkaline washing solution used for degreasing includes sodium hydroxide, sodium carbonate, and sodium phosphate; the surface activation solution used includes phosphoric acid and ammonium bifluoride.

4. The method for preparing a core-shell microstructured magnesium alloy wire according to claim 1, characterized in that, The zinc transition layer is prepared using a zincate immersion zinc process, and the immersion zinc solution includes zinc sulfate, potassium pyrophosphate, sodium carbonate and potassium fluoride; the aluminum protective layer is prepared using an ionic liquid bipolar pulse electroplating process.

5. The method for preparing a core-shell microstructured magnesium alloy wire according to claim 4, characterized in that, The electroplating system of the ionic liquid bipolar pulse electroplating is an aluminum chloride-1-methyl-3-ethylimidazoline chloride system, wherein the molar ratio of aluminum chloride to the 1-methyl-3-ethylimidazoline chloride is (2~3):

1.

6. The method for preparing a core-shell microstructured magnesium alloy wire according to claim 4, characterized in that, The process conditions for the bipolar pulse electroplating are as follows: cathode peak current density is -15 to -25 mA / cm². 2 The anode current density is 0.4~0.6 mA / cm². 2 The cathode duty cycle is 0.2~0.5, and the pulse frequency is 2 Hz.

7. The method for preparing a core-shell microstructured magnesium alloy wire according to claim 1, characterized in that, The heat treatment temperature is 150~250℃, and the holding time is 10~14 h; the drawing process is 1~4 passes of cold drawing, the drawing speed is 4~5 m / min, the single pass cross-sectional deformation is 6%~25%, and the cumulative cross-sectional deformation is 6%~40%.

8. The method for preparing a core-shell microstructured magnesium alloy wire according to claim 1, characterized in that, Following step S4, the process further includes a step of cleaning and purifying the drawn filament, which includes degreasing with organic solvents and ultrasonic water washing.

9. The method for preparing a core-shell microstructured magnesium alloy wire according to claim 1, characterized in that, The zinc transition layer has a thickness of 1~7 μm, the aluminum protective layer has a thickness of 6~20 μm, and the target diameter of the core shell microstructure magnesium alloy wire is 1.2~2.0 mm.

10. A core-shell microstructured magnesium alloy wire, characterized in that, The magnesium alloy wire with core and shell microstructure is prepared by any one of claims 1 to 9, and comprises, from the inside out, a pure magnesium core layer, a zinc transition layer and an aluminum protective layer.

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