The Annealing Strengthening Effects in a High-Ductile ZG205 Alloy Sheet

A high-ductile Mg-1.70Zn-0.47Gd (wt.%) alloy sheet was pre-tensile strained to 0.2% and 4% (0.2S & 4S) in the transverse direction with an initial strain rate of 0.001s-1, followed by annealing at temperatures ranging from 100 to 250 degrees C. The effect of annealing temperature on yield strength (& sigma;ys) was investigated. Generally, the & sigma;ys increased up to 200 degrees C annealing temperature, and beyond this temperature annealing softening was observed. In pre-tensile strained specimens, the more the amount of strain, the higher was the & sigma;ys. Thus, in 0.2S and 4S specimens, the maximum increase in & sigma;ys by annealing strengthening alone was 5 and 18 MPa, respectively. After straining at room temperature, different variants of {1012} extension twins were observed, and dominant deformation mode was established in un-twinned and severely twinned grains separately by Schmid factor analysis considering the relative activity of slip and twinning. It was concluded that the annealing strengthening mechanism was precipitation strengthening, as revealed by the similar microstructural features in TEM micrographs of 0.2S and 4S specimens.