Effect of microstructural evolution on mechanical properties of friction stir welded ZK60 alloy

Six millimeters thick extruded ZK60 plate was successfully friction stir welded at a rotation rate of 800 rpm and a traverse speed of 100 mm/min. Friction stir welding (FSW) resulted in breakup and dissolution of MgZn2 phase and remarkable grain refinement in the nugget zone. Relatively weak basal texture on the transverse plane of the nugget zone was not the dominant factor for determining the mechanical properties of the ZK60 weld. As-welded joints failed on the nugget zone with ultimate tensile strength (UTS) reaching 87% of the parent material. After aging, the precipitation of the fine MgZn2 particles increased the mechanical properties of the weld significantly with the UTS reaching 94% of the parent material and the fracture occurring in the heat-affected zone. The fracture locations under both as-welded and aged conditions were consistent with the lowest hardness distribution of the welds.