Mechanical properties and Hall-Petch relationship of the extruded Mg-Zn-Y alloys with different volume fractions of icosahedral phase

The effect of the volume fraction (0.6-8.4%) of the icosahedral phase (I-phase) on the microstructure, texture and mechanical properties of extruded Mg-Zn-Y alloys was examined. During extrusion, the eutectic and divorced eutectic I-phase in the cast microstructures was broken into small particles, and the particles were dispersed along the extrusion direction, forming parallel particle bands. The broken I-phase particles promoted grain refinement via a particle-stimulated nucleation mechanism and led to basal texture weakening through dynamic recrystallization. The work hardening rate increased with an increase in the volume fraction of I-phase. However, the strength decreased with an increase in the volume fraction of I-phase due to the texture softening effect. To incorporate the texture softening effect into the Hall-Petch relation, a modified Hall-Petch equation, which simultaneously considers the effects of grain size and texture on strength, was developed using the Schmid factors for basal slip. The proposed equation predicts smaller Hall-Petch slope, friction stress and yield strength with easier activation of basal slip, agreeing with the experimental observations.