The aim of this work is to investigate the influence of ultrasonic vibration on the microstructure and texture evolution in ultrasonic-assisted friction stir welding (UaFSW) of AZ91 Mg alloy. Ultrasonic vibration with an amplitude of 15 µm induced to the weld line perpendicularly to the welding direction. A scanning electron microscopy equipped with electron backscattered diffraction (EBSD) was used to investigate the microstructure and texture changes of the joints. A high fraction of low-angle grain boundaries (LAGBs) was observed during the occurrence of dynamic recovery (DRV) in thermomechanically affected zones (TMAZs) of welded specimens. Statistical analysis from the grain boundaries of the stir zone (SZ) revealed that the fraction of high-angle grain boundaries (HAGBs) in the SZ of UaFSW joint is higher than that of the FSW joint. The results along with the formation of simple shear texture components in the SZ of welds imply that continuous dynamic recrystallization (CDRX) is responsible for grain refinement in the SZs. Moreover, vibration associated with UaFSW assisted the DRV and CDRX mechanisms and increases the intensity of the developed texture in the SZ of the UaFSW joint.

本工作的目的是研究超声振动对 AZ91 镁合金超声辅助搅拌摩擦焊 (UaFSW) 组织和织构演变的影响。与焊接方向垂直的焊缝感应振幅为 15 µm 的超声波振动。配备电子背散射衍射 (EBSD) 的扫描电子显微镜用于研究接头的微观结构和织构变化。在焊接试样的热机械影响区 (TMAZ) 中发生动态恢复 (DRV) 期间，观察到大量低角度晶界 (LAGB)。搅拌区 (SZ) 晶界的统计分析表明，UaFSW 接头 SZ 中大角度晶界 (HAGB) 的比例高于 FSW 接头。结果以及在焊缝的 SZ 中形成简单的剪切织构分量意味着连续动态再结晶 (CDRX) 是 SZ 中晶粒细化的原因。此外，与 UaFSW 相关的振动有助于 DRV 和 CDRX 机制，并增加了 UaFSW 关节 SZ 中发展纹理的强度。