Investigation on the Creep Behavior of AZ91 Magnesium Alloy Processed by Severe Plastic Deformation

Abstract

This paper describes the grain refinement due to equal-channel angular pressing (ECAP) and the creep properties of the ECAP-processed AZ91 magnesium alloy. The resulting microstructure and creep properties were examined by scanning electron microscope and impression creep test method. Microstructural evolution reveals that the grains were refined to 14 µm after four ECAP passes at 628 K, following route Bc. The creep tests were carried out under stresses in the range of 35 to 95 MPa at temperatures in the range of 538 to 583 K. Based on a power law between the impression rate and stress, the stress exponents were about 2 and the activation energies were about 129 kJ/mol, which are close to that for lattice diffusion of magnesium. Considering the obtained results, it can be stated that the grain boundary sliding is the dominant creep mechanism at low stresses and high temperatures. Deformation mechanism is grain boundary sliding (GBS) during creep of the AZ91 alloy at low stresses and high temperature and deformation behavior can be determined from:$$\upvarepsilon^{\cdot } = 7.25\left({\frac{{\text{b}}}{{\text{d}}}} \right)^{2} \left({\frac{{\text{Gb}}}{{\text{kT}}}} \right)\left( {\frac{\upsigma}{{\text{G}}}} \right)^{{2.02}} {\text{D}}_{L}$$