Microstructure and mechanical properties of electrically assisted friction stir welded AZ31B alloy joints

The electrically assisted friction stir welding (EFSW) of 5 mm thick AZ31B magnesium alloy with DC current ranged 0-200 A has been investigated. The effect of current on microstructure and mechanical properties of the EFSW joint was studied. EFSW increased the heat input by resistance heat, and minimized the weakly welded area at the root of the joints. With the increase of current, the stir zone (SZ) become gradually larger, and there is no obvious boundary line between the shoulder affected zone (SAZ) and the pin affected zone (PAZ), microstructure along the thickness direction of the SZ centre is much more uniform; the difference in grain size between the SZ and the thermo-mechanically affected zone (TMAZ) at the advancing side (AS) changed from abrupt to smooth. All the joints fractured in regions with the lowest hardness. The tensile strength of the joint increased with increasing current, the tensile strength of the EFSW joint with a current of 200 A is the highest, but the hardness of the weld is hardly affected by the current.