Grain structure in ultrasonic vibration assisted friction stir weld nugget zones of 2A12/AZ31B dissimilar alloys

Abstract

The comparative experiments of 2A12/AZ31B dissimilar materials friction stir welding (FSW) and ultrasonic vibration assisted FSW (UVaFSW) were carried out. The grain structures of different parts in the weld nugget zone were characterized, and the influence of ultrasonic vibration on the grain structure evolution was analyzed. The results show that compared with the base materials, the grain sizes in the weld nugget zone (WNZ) of 2A12/AZ31B joints are obviously refined. The mode of dynamic recrystallization of grains in 2A12 Al side WNZ is the combined action of continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX) mechanisms. The dynamic recrystallization of grains in AZ31B Mg side WNZ is the combined action of CDRX, GDRX and discontinuous dynamic recrystallization (DDRX) mechanisms. Applying ultrasonic vibration can promote the recrystallization degree of grains, especially in the middle and lower parts of Al side and the bottom of Mg side. The texture evolution results show that the strain of the material in Al side WNZ increases when ultrasonic vibration is applied, which indicates that ultrasonic vibration can promote the material flow in the WNZ. The texture strength of different areas on the Mg side decreases, which is due to the more complete recrystallization behavior of magnesium alloy grains when ultrasonic is applied, thus weakening the grain orientation.

Keywords

• friction stir welding
• ultrasonic vibration
• 2a12
• az31b
• grain structure
• weld nugget zone