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

摘要

Thermomechanical experiments were conducted to study the plastic flow behaviors of AZ91 magnesium alloy. The AZ91 alloy was heat treated at 430 deg C for 12 h before thermomechanical experiments. The matrix grain size is about 120 mu m and most Mg_(17)Al_(12) particles were dissolved. The temperature of the processes ranged from 250 to 450 deg C. The strain rate was varied between 0.001 and 1.0 s~(-1). Constitutive analysis was carried out by using the equation A[sinh(alpha sigma)]~n = epsilon 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 deg C, twinning is found to occur initially and DRX develops then at both twins and grain boundaries. At temperatures higher than 350 deg C, DRX occurs extensively at grain boundaries, whereas twinning becomes not essential for deformation compatibility and cannot be found at optical microscopy scale.