Enhanced mechanical properties and corrosion resistance of friction-stir processed ultralight LA141 magnesium-lithium-aluminum alloy

Abstract

This study focuses on conducting friction-stir processing (FSP) on 3 mm thick LA141 alloy using different tools. Under low heat input conditions of 600 rpm and 200 mm/min, the use of the WC-Co cemented carbide tool successfully produced a defect-free stir zone. This stir zone exhibited an ultrafine grain structure resulting from continuous dynamic recrystallization. Additionally, the stir zone introduced massive grain boundaries, nanoscale MgAlLi2 particles, and stacking faults. The stir zone displayed a favorable balance of strength and ductility. The enhanced strength is attributed to the inhibitory effect of nanoscale MgAlLi2 particles, grain boundaries, and Lomer-Cottrell locks on dislocation movement. The improved work hardening ability and ductility can be attributed to the increase in stacking faults, Lomer-Cottrell locks, and deformation twins during deformation. Furthermore, the stir zone showed improved corrosion resistance, characterized by lower corrosion current density and larger polarization resistance. This improvement in corrosion resistance can be attributed to multiple factors. These include the reduced defect density, refined and evenly distributed MgLiAl2 particles that weakened galvanic corrosion effects, and the presence of more stable Li2CO3 and Al2O3 compounds that resulted in a compact and protective film.