Achieving ultrahigh specific strength of an ultrafine grained Mg–9Li–1Al alloy via the combined processing of ECAP with repeated annealing and rolling

Abstract

A super-high strength Mg–9Li–1Al (LA91) alloy with ultimate tensile strength (UTS) of 312 MPa and specific strength of ∼215 kNmkg−1 was successfully achieved via a combined processing of multi-pass equal-channel angular pressing (ECAP) with repeated annealing and room temperature (RT) rolling. Significant grain refinement after ECAP led to the formation of ultrafine-grain (UFG) α-Mg phase with grain size of ∼350 nm. Further refinement of the α-Mg grains reaching ∼200 nm was achieved by further repeated annealing and RT-rolling with high dislocation density. The formation of strong basal texture of the α-Mg phase of the combined-processed alloy also contributed to the achieved excellent strength-ductility synergy. The 1 wt% Al (aluminum) in the Mg–Li dual-phase matrix acted as a high-efficient strengthening element, and was the major contributory factor to the 48% improved specific strength of the alloy compared to the UFG Mg–9Li binary alloy in our former study. The Al element distributing throughout the alloy phases without segregation contributed to the enhanced refinement of the α-Mg grains during the combined processing and improved strain-hardening rate during the tension plastic deformation, allowing for the achievement of a high strength of the LA91 alloy.

Keywords

• Mg–9Li–1Al alloy
• RD-ECAP
• Rolling
• Ultrafine grains
• High specific strength
• Al