Progress in the stationary shoulder friction stir welding

The progress in stationary shoulder friction stir welding(SSFSW) is reviewed in this paper,mainly involving the basic principle of SSFSW,the high rotational speed SSFSW,the SSFSW operated at conventional rotational speeds and the SSFSW for corner welds of T-joints.The high rotational speed SSFSW can reduce the process load applied on the tool,and reduce or even eliminate welding defects such as the weld flash and cavity.As for the SSFSW operated at conventional rotational speeds,the existence of the non-rotational shoulder is beneficial to obtain uniform microstructures in the thickness direction of the weld,and thus it is very suitable to weld titanium alloys characterized of a low thermal conductivity.Additionally,the SSFSW for corner welds of T-joints can also be accomplished by means of a non-rotational shoulder shaped to the internal corner of the T-type joints.Therefore,the application range of FSW is further widened.No matter be which kinds of SSFSW mentioned above,the wear and overheating of the tool system are the key problems which need to be studied in detail.