Xiangchen Meng

Enhancing Friction Stir Weldability of 6061-T6 Al and AZ31B Mg Alloys Assisted by External Non-rotational Shoulder

In order to increase cooling rate and then reduce the amounts of intermetallic compounds, external non-rotational shoulder tool system derived from traditional tool in friction stir welding was used to join dissimilar Al and Mg alloys. In this study, based on the external non-rotational shoulder, the weldability of Al and Mg alloys was significantly improved. The non-rotational shoulder tool is propitious to make more materials into weld, increase cooling rate and then reduce material adhesion of rotational pin, obtaining sound joint with smaller flashes and smooth surface. Importantly, the thickness of intermetallic compounds layer is reduced compared with traditional tool. Meanwhile, hardness values of dissimilar joint present uneven distribution, resulting from complex intercalated structures in nugget zone (NZ) featured by intermetallic compound layers and fine recrystallized Mg and Al grains. Compared with traditional tool, non-rotational shoulder is beneficial to higher tensile properties of joint. Due to the intermetallic compound layer formed in the interface of Al-Mg, the welding joint easily fractures at the NZ, presenting the typical brittle fracture mode.

A practical strategy for improving the weldability of ultra-thin Al/Mg sheets by ultrasonic-assisted friction stir welding

ABSTRACT In order to enhance the weldable thickness and tensile properties of dissimilar ultra-thin Al/Mg alloy sheets, ultrasonic-assisted friction stir welding (UaFSW) was performed. The addition of ultrasonic produces three benefits. First, a sound joint with smooth surface appearance was achieved. Next, weldable thickness and mixing degree of Al/Mg alloys were improved based on better material flow. Finally, continuous intermetallic compound (IMC) layer in the conventional joint was broken into small pieces, delaying crack propagation. Maximum tensile strength of the UaFSW joint reached 130 MPa, which was much more higher than 102 MPa of the conventional joint. It is concluded that UaFSW has a huge potential to join dissimilar alloys, especially those with the formation of IMCs.