The organization and performance of LD31-LF6 aluminium alloy friction stir welding

Dissimilar materials,LD31 and LF6 aluminium alloy were joined by friction stir welding,and the effects of the position for the pin to be inserted on the weld appearance,microstructure and mechanical properties of joint were analyzed.The results show that a defect-free joint with good weld surface appearance can be obtained with suitable welding conditions for lock joint of the dissimilar materials.Optical microscopy reveals the stir zone presents particularly fine equiaxed grains,resulting in dynamic recrystallization.In the stir zone,the microstructure presents lamella alternately on the lower part.The maximum tensile strength of the joint was about 100% of that of the LF6 aluminium alloy base metal.The tensile failure happened at the boundary between the nugget and thermomechanically affected zone of the LD31 aluminium alloy,indicating that the weld has a higher joining strength.