Microstructure and Mechanical Properties of Al-Mg-Sc-Zr Alloy Variable Polarity Plasma Arc Welding Joint

Al-Mg-Sc-Zr alloy plates were welded by variable polarity plasma arc welding (VPPAW) with Sc-containing filler wire. The microstructure and mechanical properties were investigated. Results show that the weld zone and heat-affected zone (HAZ) are narrow due to the high concentrated heat input of VPPAW. Primary Al₃(Sc,Zr) particles are nice nucleating sites for α-Al, which can significantly refine the grains of α-Al, helping the weld zone maintain an outstanding strength. The unmelted Al₃(Sc,Zr) precipitates of the base metal aggregated near the fusion boundary result in the formation of a fine equiaxed grains zone, which improves the bonding degree between the weld zone and the base metal. The Al₃(Sc,Zr) precipitates in the HAZ have excellent inhibition effect on recrystallization. According to the observed microhardness distribution and microstructure characteristics, the microstructure model of welded joint is obtained. The fractured position of welded joint locates in the weld zone. The tensile strength of the welded joint without reinforcing rib is 330 MPa. The welding coefficient reaches 74%.