Compared with steels, Al alloys possess lots of advantages, such as light specific gravity, good plasticity, excellent thermal conductivity, corrosion resistant, etc. Nowadays, more and more products are designed by welding structure of Al alloys and used in the shipbuilding, automobile manufacturing, aerospace and petrochemical industry, presenting unique advantages and significant economic benefits. The welding problems of Al alloys have always been a focus of attention, such as cracks, pores, overburning, etc. As a result, the safety problems severely restrict the industrial application of Al alloys. Friction stir welding (FSW) is a solid-state bonding process. FSW achieves the joining between materials through the generation of frictional heat and strong plastic deformation. At the same time, the stirring head shoulder applies a certain compressive stress to the material to ensure a high-density and defect-free weld. Compared with the traditional fusion welding process, it has the advantages of good joint quality, refined microstructure, excellent fatigue performance, low peak temperature, energy saving, etc. Therefore, FSW is exactly suitable for the welding of Al alloys.