Friction stir welding of novel T-phase strengthened Zn-modified Al–Mg alloy

Friction stir welding is extensively used in aluminum alloys for advanced engineering applications. A current challenge for 5 × × × series alloys is their poor welding strength due to the lack of hardening precipitates. Here we report Zn-modified novel Al–Mg alloys with Zn/Mg ratio below 1.0. Compared with 5 × × × series alloys, the strength of the welded alloy can be increased by 100 MPa owing to the distribution of T-Mg₃₂(AlZn)₄₉ hardening precipitates during friction stir welding and the subsequent heat treatment after welding. Fine spherical T″ precipitates and coarsening polygonal T′ precipitates are both observed at the thermo-mechanically affected zone. The bimodal distribution of the precipitates and the widest precipitate-free zone weakened the strength of this region, and thus the welded alloys are fractured at this area. The novel alloy with T precipitates is expected to further stimulate the researchers to improve the properties of traditional 5 × × × series alloy.