STRAIN-HARDENING AND RECOVERY DURING THE CREEP OF PURE POLYCRYSTALLINE MAGNESIUM

We report on creep and stress relaxation test results for pure polycry stalline magnesium. The experiments consisted of constant load creep t ests conducted until steady-state was obtained followed by stress rela xation tests to study the strain-hardening and recovery behaviour of t he materials. The tests were carried out over a range of applied stres ses, 20-50 MPa, and test temperatures, 150-250-degrees-C, in order to determine 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, ep silon(s), and the dynamic recovery rate, R, data by using the well-kno wn Bailey-Orowan relationship. It is found that the strain-hardening c oefficient, H, during steady-state creep remains essentially constant with a magnitude of 0.27E (E is the elastic modulus) at 200-degrees-C and is independent of the applied stress. The creep strain rate is pri marily determined by the recovery rate which is the rate determining m echanism during recovery creep. This set of experimental results is th en examined in terms of creep equations and the dislocation network mo dels for recovery creep deformation. It is shown that the present expe rimental data measured for pure polycrystalline magnesium lend support to the theoretical models based on dislocation link length distributi on (dislocation network models) for recovery creep.