2015 年 79 巻 4 号 p. 176-182
Extruded Mg96Zn2Y2 alloys have excellent mechanical properties and are two-phase alloys consisting of an Mg-matrix and a long-period stacking ordered (LPSO) structure phase extended along the extrusion direction. Developing the welding process of the advanced Mg/LPSO alloys is indispensable for expanding applications. This study evaluated microstructure evolution of the extruded Mg96Zn2Y2 alloy joints which were welded by ultrasonic welding.
Specimens were welded so that extrusion directions could be orthogonal to each other. The extrusion direction and the direction in which the LPSO phases extended are parallel, thus the extrusion direction of the top plate is 90° orientation to the ultrasonic vibration. The bottom plate is 0° orientation.
A band with fine grains around the weld interface was generated and the grain growth occurred outside of the band. Inside of the band indicated the basal texture and outside of the band kept the extruded texture. The width of the band with fine grains expanded in the top plate side with increasing the welding energy. The grown grains outside of the band were also large in the top plate side. In addition, the grown grains of Mg matrix were estimated to be morphology that extended to the extrusion direction. In ultrasonic welding process, the expansion of the band width and the grain size of the grown grains in the top plate side were found that the direction of ultrasonic vibration and the orientation of the extruded texture were contributed.