2.1. Materials and FSW parameters
The 7085 with trace Sc alloy (hereinafter referred to as 7085Sc alloy) used in this study was supplied as 4.5 mm-thick rolled plates. The chemical composition is listed in Table 1. A solid solution treatment (480°C/1h, quenching in water) and aging annealing treatment (120°C/24h, cooling in air) were applied to obtain T6 plate samples for welding. Before FSW process, the surfaces of plates were polished to remove the oxide layer for the purpose of minimizing welding defects in welding joint. The friction stir pin tool had a 15 mm concave shoulder, and a taper threaded probe whose diameter was 3.5 mm and long was 4 mm. The welding direction was parallel to the rolling direction of the plates. The weld travelling speed was 100 mm/min and ration rate of pin tool was 900 RPM.
Table 1. Chemical compositions (in wt.%) of the 7085Sc alloy