Influence of temperature on the transition of deformation characteristics of Al1Mg alloy in the power law creep regime

Abstract

The influences of stress and temperature on the steady state creep rate ϵdots of Al-1.09mol.Mg alloy have been examined at 570, 600 and 640 K under stresses from 1.7 to 35 MPa. The stress exponent n varies with stress, but temperature has little effect on the value of n, which is about 4.4 in the high stress region (region H), about 3.4 in the intermediate stress region (region M) and about 4.4 in the low stress region (region L). The activation energies for creep are close to the activation energies for diffusion in regions H and M, i.e. QH = 140 kJmol−1 and QM = 138 kJmol−1, but in region L it is obviously larger than the activation energy for diffusion, i.e. QL ≈' 170 kJmol−1. The upper transition stress is independent of temperature, whereas the lower transition stress decreases significantly with increasing temperature. For creep in region H, where ϵdotS ∝ σ4.4C−2.4D (C is the solute concentration and D the diffusion coefficient), it is suggested that recovery is the rate-determining step as for pure metals but the stress level is determined by the solid solution hardening with immobile solute atoms distributed randomly in the matrix.