Change of LPSO Phases Morphology in Extruded Mg₉₆Zn₂Y₂ Alloy Joints during Ultrasonic Spot Welding Process

Abstract

Mg and the alloys are materials with highly anisotropic and an extruded Mg₉₆Zn₂Y₂ alloy used in this study also has strong anisotropy. One of the factors originates in LPSO phases extending along the extrusion direction which the Mg₉₆Zn₂Y₂ alloys have. In this study, a change of the LPSO phases morphology during ultrasonic spot welding process was evaluated, and the relationship between the microstructure evolution and crack propagation after the lap shear tensile test was discussed. Ultrasonic vibration was applied in a direction orthogonal to the LPSO phases extending along the extrusion direction and was applied in a direction parallel to the weld interface of specimens. As a result, the LPSO phases orthogonal to the vibration direction formed curved LPSO phases and rearranged in the direction parallel to the weld interface during the welding process. And, it was revealed that the rearranged LPSO phases extended in the radial direction of the spot welds. The severe plastic deformation during the welding process effected a drastic change of the LPSO phases. In addition, plug fracture was exhibited in the region where the severe plastic deformation occurred.