Strain-hardening and recovery during the creep of pure polycrystalline magnesium

Abstract

We report on creep and stress relaxation test results for pure polycrystalline magnesium. The experiments consisted of constant load creep tests conducted until steady-state was obtained followed by stress relaxation tests to study the strain-hardening and recovery behaviour of the materials. The tests were carried out over a range of applied stresses, 20–50 MPa, and test temperatures, 150–250°C, in order to determined stress and temperature dependencies of the high temperature plastic deformation behaviour. The strain-hardening coefficient, H, is derived from the experimentally generated steady-state creep rate, ε ̇ s , and the dynamic recovery rate, R, data by using the well-known Bailey-Orowan relationship. It is found that the strain-hardening coefficient, H, during steady-state creep remains essentially constant with a magnitude of 0.27 E ( E is the elastic modulus) at 200°C and is independent of the applied stress. The creep strain rate is primarily determined by the recovery rate which is the rate determining mechanism during recovery creep. This set of experimental results is then examined in terms of creep equations and the dislocation network models for recovery creep deformation. It is shown that the present experimental data measured for pure polycrystalline magnesium lend support to the theoretical models based on dislocation link length distribution (dislocation network models) for recovery creep.