Achieving ultra-fine grains and high strength of Mg–9Li alloy via room-temperature ECAP and post rolling

Abstract

Ultra-fine grains (UFG’s) and high strength was successfully achieved in Mg–9Li alloy via room temperature (RT) equal channel angular pressing (ECAP) and post rolling. The solid solution (SS) treatment of the alloy was performed before ECAP to achieve the refined needle-like α-Mg phase and excellent RT plastic deformation ability. The SS-treated alloy was ECAP processed continuously for 8 passes at room temperature without any cracks. Low temperature effectively inhibits dynamic recovery and recrystallization during the multi-pass ECAP process, reaching ultra-fine grains of about 1 μm and ultimate tensile strength (UTS) values of 187 MPa of the alloy. Post RT rolling of the ECAP-processed alloy further refines the grains into ultra-fine grains ranging between 500 and 700 nm, which endows the alloy with an excellent UTS value of 206 MPa and decent elongation to failure (Ef) of 21%. The ultra-fine grains with certain intragranular dislocation, leading to grain boundary and dislocation strengthening was a major contributory factor to the obtained high strength. Texture strengthening from the formation of strong basal textures of the α-Mg phase also improved the strength.