电弧熔丝增材制造 Mg/Mg 双金属的组织与力学性能

Mg/Mg bimetallic components, especially Mg-Al-Si/Mg-Gd-Y-Zn bimetals, hold promise for applications in the aerospace and automotive industries as structural materials because of their potential advantages of low cost, lightweight, high strength, and high plasticity. At present, Mg/Mg bimetallic components are primarily fabricated via extrusion and compound casting. However, these conventional processes are complex and have low forming efficiency. Recently, rapid advancements in additive manufacturing have enabled the real-time manufacturing of bimetallic structural components. In particular, wire arc additive manufacturing (WAAM) offers technical advantages for improving the forming efficiency of large-sized bimetallic components. Herein, to enhance the forming efficiency and interfacial performance of large-sized Mg/Mg bimetallic components, a thin-walled Mg-Al-Si/Mg-Gd-Y-Zn bimetallic component was fabricated using WAAM technology. Specifically, a Mg-Al-Si alloy thin wall was first deposited and then cooled to room temperature over a period of time. Subsequently, the top layer of the Mg-Al-Si alloy thin wall was remelted, followed by the deposition of the Mg-Gd-Y-Zn alloy. Further, the macroscopic morphology, microstructure, microhardness, and mechanical properties of the bimetallic component were examined. Based on the macroscopic morphology, bimetallic components exhibited good interface bonding through WAAM. OM images demonstrated a transition zone near the bimetallic interface with a thickness of approximately 1.4 mm. The line scanning results and EPMA mappings revealed the formation of a composition gradient in the transition zone due to element diffusion. From the Mg-Al-Si alloy side to the Mg-Gd-Y-Zn alloy side, the Al and Si contents gradually decreased, while the Gd, Y, and Zn contents gradually increased. Based on the nonequilibrium solidification phase diagram and microstructure analysis, the bimetallic component comprised three regions: the Mg-Al-Si region with the Chinese-script Mg₂Si phase; transition region comprising granular Mg₂Si, the Mg₃(Gd, Y) phase, and the Mg₅(Gd, Y) phase; and Mg-Gd-Y-Zn alloy region with the Mg₁₂Zn(Gd, Y) phase as the primary component. After microhardness testing, the hardness of the bimetallic component continuously increased from 57 HV_0.5 (Mg-Al-Si alloy side) to 90 HV_0.5 (Mg-Gd-Y-Zn alloy side) due to the composition gradient and small second phases in the transition zone. The results of tensile testing at room temperature (20 ^oC) showed that the strength of the bimetallic component was close to that of the Mg-Al-Si alloy, with an ultimate tensile strength of 236.8 MPa and a yield strength of 102.2 MPa. Meanwhile, the elongation and hardening index of the bimetallic component were close to those of the Mg-Gd-Y-Zn alloy, reaching 11.0% and 0.323, respectively. The fracture position of the WAAM Mg-Al-Si/Mg-Gd-Y-Zn bimetal was located in the transition zone. The fracture mechanism of the Mg-Al-Si alloy was primarily ductile, while those of the bimetal and Mg-Gd-Y-Zn alloy were quasi-cleavage.