Enhanced strength and ductility of rapid cooling friction stir welded ultralight Mg–14Li–1Al alloy joint

Abstract

Ultralight Mg–14Li–1Al alloy sheets were subjected to conventional friction stir welding (FSW) and rapid cooling FSW (RCFSW) for comparative study. Compared with decreasing the rotation rate, the use of coolant significantly improved the thermal cycle and inhibited the grain coarsening. The RCFSW600 joint had an ultrafine grain structure with its average grain size of 2.1 μm. The yield strength was mainly determined by the synergic influences of grain boundaries, dislocations, and nanoscale MgLiAl2 precipitations. The ultimate tensile strength was 181 MPa and the welding efficiency reached 94.3%. A relatively good fracture elongation of 9.6% was also obtained. Finally, the improved strength-ductility synergy was regarded as the interaction among dislocations, deformation twins, and stacking faults.

Keywords

• Ultralight Mg–Li alloy
• Friction stir welding
• Rapid cooling
• Microstructure
• Mechanical properties
• Strengthening mechanism