Enhancing metallurgical bonding of thick plate friction stir welded Al/Mg joints by changing the friction interface

Abstract

For the thick plate friction stir welded Al/Mg joint, there exists poor metallurgical bonding at the bottom of the weld due to the lack of heat. In this work, a method for enhancing metallurgical bonding of thick plate Al/Mg FSW joint is proposed by controlling the friction interface between the shoulder and the base material. The results show that the upper at the weld under the friction interface and without friction interface is composed of massive eutectics (Mg + Al12Mg17) and thin Al3Mg2 phase. The bottom at the weld without friction interface exists a 4.7 μm wide unwelded zone, while a dense reaction layer is formed under the friction interface. The formation of this dense reaction layer is related to the high friction coefficient under the friction interface, which provides high peak temperature and long elevated temperature residence time along the thickness direction.