Microstructure and Mechanical Properties of Cross Weld for Ultrasonic-Frequency-Pulsed GMAW and FSW 1561 Aluminum Alloy

Due to the complexity of fixture installation for FSW (friction stir welding), the cross joint between FSW and the fusion weld is usually inevitable in the fabrication process of aluminum alloy hull. Nevertheless, in the actual hull fabrication, cross joint between FSW and the gas metal arc welding (GMAW) is prone to porosity defects and the mechanical properties are seriously degraded compared with the base metal. In this study, a novel ultrasonic-frequency pulsed gas metal arc welding (UFP-GMAW) was applied to replace the conventional gas metal arc welding (GMAW) after the FSW process. The microstructure and mechanical properties of both FSW-(UFP-GMAW) and FSW-GMAW cross weld joints were studied. The results indicated that the number and the size of the pores in FSW-(UFP-GMAW) weld joint obviously decreased compared with that in the FSW-GMAW weld joint. Moreover, the grain size was refined and the microstructure was more uniform after applied with the ultrasonic-frequency current in the FSW-(UFP-GMAW) weld joint. Compared with the cross joint of FSW-GMAW, the mechanical properties for the FSW-(UFP-GMAW) cross joint were improved.