The influence of thermomechanical treatment on the complex modulus of Mg alloy AZ31

Abstract

Dynamic modulus analyses were performed on Mg alloy AZ31 following thermomechanical treatments to enable investigation of the influence of microstructural features created by plastic deformation on the elastic and the anelastic behavior of this alloy as quantified by variations in the complex elastic modulus (E* = E′ + iE″) with temperature. The real component or storage modulus (E′) determined for this alloy was 42.0 ± 2.5 GPa at 25 °C and it was independent of rolling direction and cold work up to 20 pct reduction in thickness. A broad peak was observed in the imaginary component or loss modulus (E″) around 175 °C (for a 1.0 Hz loading frequency), and it was determined that this peak is a superposition of at least four different relaxation mechanisms: a thermally activated mechanism related to precipitate phases near 153 °C and three peaks related to mechanical deformation at 165 °C, 188 °C, and 235 °C. The latter three peaks were also thermally activated with the activation energy determined to be 1.68 ± 0.04 eV. These mechanical relaxation peaks are attributed to microstructural features produced by cold work, and it is demonstrated that the stresses generated by cooling from heat-treatment temperatures influences these peaks. It is concluded that the grain boundary relaxation peak is above 350 °C.