Microstructural evolution and mechanical properties of friction stir welded Mg-Zn-Y-Zr alloy

Six millimetre thick Mg-Zn-Y-Zr plate was friction stir welded (FSW). Under a tool rotation rate of 800 rpm and a traverse speed of 100 mm/min, the defect-free weld was obtained. After FSW, coarse strip-like microstructure in forged Mg-Zn-Y-Zr alloy changed into fine equiaxed recrystallized grains in the nugget zone. Furthermore, bulky I-phase particles were broken up and dispersed with some of them being transformed to W-phase, and most of MgZn precipitates were dissolved. Micro-hardness measurement indicated that the hardness of the nugget zone was higher than that of the parent material and the lowest value of hardness was found in the heat-affected zone (HAZ). Transverse tensile tests showed that the strengths and elongation of the weld was only slightly lower than those of parent material with ultimate tensile strength of the weld reaching 95% of the parent material.