Microstructure and mechanical properties of ZK60 magnesium alloy fabricated by high strain rate multiple forging

Abstract

High strain rate multiple forging (HSRMF) was successfully carried out on ZK60 magnesium alloy to an accumulated strain of ∑Δϵ = 2·64 at temperature of 573 K, and the microstructure and mechanical properties of the high strain rate multiple forged samples were investigated. The results show that the initial grains were extensively refined after HSRMF due to dynamic recrystallisation (DRX). However, the DRX mechanism at initial grain boundaries was different from that at grain core. Rotation DRX and twin induced DRX were responsible for the DRX at initial grain boundaries and original grain core respectively. A novel mixed structure of honeycomb-like coarse DRX grains with average grain size of 10 μm and island-like ultrafine grains with average grain size of 1 μm formed at ∑Δϵ = 2·64. This novel mixed structure showed substantial improvements in mechanical properties. Mechanical testing gave an ultimate tensile strength of 330 MPa and an elongation of 25·7%. Therefore, HSRMF was identified as a potential technique for stronger and more ductile wrought ZK60 alloy.