Experimental observations of the mechanisms associated with the high hardening and low strain to failure of magnesium

Magnesium holds considerable promise as a lightweight structural material, but structural applications of Mg alloys are generally limited to cast components because of its limited formability. Mg exhibits high hardening and low strain to failure, the attendant mechanisms of which remain elusive. In this work, we performed detailed TEM investigations on the dislocation structures in the c-axis compressed Mg single crystals. Systematic filling experiments in TEM revealed the majority of < c + +a > dislocations to be dissociated and basal bound, suggesting that glissile pyramidal < c + +a > dislocations may transition and dissociate into a sessile configuration. Other < c + +a > dislocations were observed to decompose into individual < a > and < c > dislocations. Since < a > and < c > dislocations cannot accommodate c-axis compression, this process also manifests a glissile-to-sessile transition. Moreover, numerous sessile nanoscale dislocation loops were observed to form during plastic deformation, which can obstruct the movement of the mobile < c + +a > dislocations. These three mechanisms all impede the motion of glissile < c + +a > dislocations. Comparing these experimental with simulations that have been published in the literature is used to glean insight on the characteristics of < c + +a > dislocations and to explain the high hardening and low strain to failure that are widely observed in Mg.