Effect of rare earth addition on {101Ì 2} twinning induced hardening in magnesium

We investigated the effect of Gd and Ce additions in magnesium on sigmoidal hardening behavior associated with {101̅2} twinning after extrusion. Compression along extrusion direction revealed that rare earth additions enhance the flow stress, while 〈c+a〉 softening was expected. This phenomenon has been explained by the enhancement of 〈c+a〉 dislocations activity and the ensuing increase in forest hardening due to solute drag. It is expected that dislocation transmutation of basal to prismatic will be enhanced during {101̅2} twin growth in rare earth containing alloys, which would exacerbate 〈c+a〉 entanglement with the dislocation forests inside the twins. Forest hardening events overcompensated for the softening effects from lowering the critical resolved shear stresses of 〈c+a〉 dislocations, and resulted in higher flow stress for the binary rare earth containing alloys.