Effect of welding parameters on microstructure and mechanical properties of friction stir welded Al–Mg–Er alloy

3.7 mm thick cold-rolled Al–Mg–Er alloy plates were friction stir welded (FSW) under rotation rates of 400–1200 rpm and welding speeds of 100–400 mm/min. The influence of tool rotation rate and welding speed on the microstructure and mechanical properties were investigated by means of the optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), and hardness and tensile tests. Experimental results revealed that defect-free joints could be obtained under a wide range of parameters except for 800 rpm–400 mm/min. The nugget zones (NZs) exhibited equiaxed recrystallized grains and the grain size increased with increasing the tool rotation rate or decreasing the welding speed. For all FSW joints, the NZs exhibited the lowest hardness due to the annealing softening. All the FSW joints fractured in the NZs. The joint welded at 400 rpm–100 mm/min had the greatest ultimate tensile strength (UTS) of 346 MPa and yield strength (YS) of 218 MPa with a joint efficiency of 73%. In general, increasing the tool rotation rate reduced both UTS and YS of the FSW joints, while increasing the welding speed increased UTS and YS.