An attempt at friction-stir-welding of α-Mg/long-period stacking ordered two-phase Mg–Zn–Y–Al–La alloys: Effect of texture weakening on their mechanical properties

Abstract

Friction-stir (FS) welding was used for the first time to successfully join Mg–Zn–Y–Al–La alloy extrusions containing the long-period stacking ordered (LPSO) phase. Plastic flow produced fine α-Mg grains of sizes 2.0–2.5 μm with random orientation in the stir zone (SZ) and stir-affected zone (SAZ), as well as fine fragmentation of the LPSO phase. No strong (10$\overline{1}$0) textures were observed in the SZ and the SAZ of the FS-welded Mg–Zn–Y–Al–La alloys. The tensile deformation behavior and texture evolution were evaluated via mechanical testing using digital image correlation and electron backscatter diffraction measurements. The FS-welded Mg–Zn–Y–Al–La alloy exhibited a tensile yield strength of 248 MPa, a joint efficiency of 1.12, and sufficient ductility owing to texture weakening caused by rare-earth texture formation, which suppressed geometric softening. However, no damage was observed at the incompatible boundary between the SZ and SAZ, which is typically a fracture point. The FS-welded Mg–Zn–Y–Al–La alloy fractured in the heat-affected zone on the advancing side, where the temperature was higher than on the retreating side, owing to recrystallization promotion.