Ultrasonic effects on microstructures and mechanical properties of friction stir weld joints of dissimilar AA2024/AZ31B alloys

Friction stir welding (FSW) and ultrasonic vibration-assisted FSW (UVaFSW) experiments of AA2024 aluminum alloy and AZ31B magnesium alloy plates with thickness of 3 mm were carried out. The effects of ultrasonic vibration on the microstructures and mechanical properties of dissimilar joints were investigated. The test results show that with application of ultrasonic vibration, the mechanical interlocking degree of AA2024/AZ31B dissimilar materials in the weld nugget zone (WNZ) was enhanced, and the thickness of intermetallic compounds at top and lower parts of WNZ was reduced. Therefore, the joint tensile strength was improved in UVaFSW. The exerted ultrasonic vibration caused only about 5-10 & DEG;C variation of the peak temperature in welding, indicating that the acoustic softening effect plays more important roles than the thermal effect of ultrasonic vibration. It lays foundation for the process optimization and joint quality control in welding of dissimilar AA2024 and AZ31B alloys which are of great application prospects in aircraft and space craft industries.