Towards extraordinary strength-ductility synergy in pure Mg via dislocation transmutation

Abstract

Navigating the strength-ductility trade-off has been a persistent challenge in Mg alloys. Here, we address this issue through a novel multiple-direction pre-deformation at room temperature that introduces a high density of <c+a> dislocations into pure Mg via dislocation transmutation. This approach achieves a remarkable enhancement in the strength-ductility synergy, increasing the yield strength from 87.6 MPa to 156.6 MPa and improving elongation to failure from 7.7% to 17.6%. In general, introducing a high-density <c+a> dislocations in Mg alloys have been difficult due to the high CRSS at room temperature. Our findings reveal that extension twinning can act as a “dislocation converter,” transforming basal <a> dislocations in the matrix into <c+a> dislocations within twins. Intensive basal <a> dislocations were induced in pure Mg through pre-tension and subsequently transformed into <c+a> dislocations via extension twinning during compression. This process led to a substantial number of <c+a> dislocations and I₁ stacking faults, contributing to the enhanced strength. The high density of <c+a> dislocations, combined with I₁ stacking faults and a reduced c/a ratio within twins, enhances the activity of pyramidal <c+a> slip, thereby significantly improving ductility. This dislocation transmutation strategy offers a promising way for producing strength-ductility synergy in Mg alloys.