Mechanical properties of Mg-Sc binary alloys under compression

The flow stress and work hardening behaviour during uniaxial compression of dilute binary Mg-Sc alloys have been studied at 4.2 K, 78 K and 298 K. The influences of atomic misfit, chemical misfit, solute electronic properties and stacking fault energy (SFE) on strength and ductility have been examined. The results suggest that the small atomic misfit and the reduction of SFE due to Sc additions are decisive factors in determining the mechanical behaviour of the alloys. Mg-Sc alloys deform by basal, prismatic 〈a〉, pyramidal 〈c+a〉 slip and extension twinning. Sc exerts limited strengthening on these modes due to the small atomic size and weak solute-dislocation and solute-twin boundary interactions. Constitutive modelling of the flow stress permits for the evaluation of the critical resolved shear stress (CRSS) of slip and twinning systems and determination of their activity during deformation. Analysis of activation volume and activation distance suggests that dislocation-dislocation interactions determine the flow stress. The strain rate sensitivity parameter is unaffected by alloy composition, but it decreases sharply with decreasing temperature. Mg-Sc alloys show some improvement in strength and ductility in comparison to Mg, however not as much as demonstrated by common Mg-RE binary systems. The enhancement in ductility is attributed in part to the activity of twinning and non-basal slip.