Constitutive modelling of LZ91 magnesium-lithium alloy sheet by uniaxial tension loading tests

Abstract

Magnesium-lithium (Mg-Li) alloy is a kind of ultra-lightweight metallic materials with much lower density than those of conventional magnesium alloy or aluminum alloy. Here, the mechanical behavior of LZ91 Mg-Li alloy sheet was investigated by uniaxial tension loading tests, including standardized uniaxial tension tests and plane strain tests, in which the strain field was measured by 2D digital image correlation (DIC). Firstly, the true stress-true strain curves along the rolling and transverse directions are higher than that along the diagonal direction. The Hocket-Sherby hardening model is more accurate to represent the true stress-true strain curve of LZ91 Mg-Li alloy sheet. Then, the anisotropic coefficients increase with the plastic strain increasing up to about 10%. After that, the anisotropic coefficients become stable, and the ones along the rolling and transverse directions are below 1 while the ones along the diagonal direction is above 1. At last, the yielding stresses in the plane strain tests along the rolling and transverse directions were adopted instead of equi-biaxial yield stress and anisotropic coefficient to simplify the experimental procedures for parameter identification of Yld2000-2d yield function. By comparison of the predicted and experimental results, the Yld2000-2d yield function was validated to describe the anisotropic yielding behavior of LZ91 Mg-Li alloy sheet.