Abstract: Friction stir welding (FSW)is a new,solid state plastically joining process developed in the beginning of the 1990's.In this paper,an extensive investigation was carried out on the FSW of aviation structural material LD10 aluminum alloy with a thickness of 6 mm.An excellent weld appearance,without void,cracking,or distortion was obtained when the welding parameters were carefully chosen.The joint consists of the weld nugget,the thermal mechanically affected zone,the heating affected zone,the shoulder deformation zone and the pin pressing zone.Within each zone,the microstructure is very different.The mechanical property results shown that maximum joint tensile strength can reach 357Mpa,which is 87% of the parent materials (410 MPa).This is stronger than that of fusion joints,and the failure locations are almost at the heating affected zone.