Variation in Crystallographic Orientation and Twinning Activation with Size of Individual Grains in Rolled Magnesium Alloy

This study demonstrates that the size of an individual grain in a rolled AZ31 alloy is significantly related to the crystallographic orientation of the grain and the area fraction of the {10-12} twinned region formed in the grain after compression along the rolling direction. With an increase in the size of an individual grain from 11 mu m to 80 mu m, the angle between the c-axis of the grain and the normal direction of rolling plane decreases from 38 degrees to 5.5 degrees and the Schmid factor for {10-12} twinning of the grain increases from 0.29 to 0.5. As a result, the area fraction of the twinned region formed in the grain increases from 30% to 100% owing to the combined effect of an increase in the Schmid factor value and a decrease in the stress required for activation of twinning by the increased grain size. The grain size (GS), Schmid factor for {10-12} twinning (SFtwin), and twin fraction (TF) have the relation TF/SFtwin = 109.8 + 1.45GS.