Study of the plastic flow behaviors of AZ91 magnesium alloy during thermomechanical processes

Thermomechanical experiments were conducted to study the plastic flow behaviors of AZ91 magnesium alloy. The AZ91 alloy was heat treated at 430 degrees C for 12 h before thermomechanical experiments. The matrix grain size is about 120 mu m and Most Mg17Al12 particles were dissolved. The temperature of the processes ranged from 250 to 450 degrees C. The strain rate was varied between 0.001 and 1.0s(-1). Constitutive analysis was carried out by using the equation A[sinh(alpha sigma)](n) = (epsilon) over dot exp(Q/RT) = Z. The value of alpha is deduced to be 0.013 MPa-1. The stress exponent n and activation energy Q is 5.578 and 176 kJ/mol, respectively. During the deformation processes at temperatures lower than 300 degrees C, twinning is found to occur initially and DRX develops then at both twins and grain boundaries. At temperatures higher than 350 degrees C, DRX occurs extensively at grain boundaries, whereas twinning becomes not essential for deformation compatibility and cannot be found at optical microscopy scale. (C) 2009 Elsevier B.V. All rights reserved.