Role of loading direction on compressive deformation behavior of extruded ZK60 alloy plate in a wide range of temperature

Abstract

The plastic flow behavior of extruded Mg-6Zn-0.6Zr (ZK60) alloy plate in T5 treated condition was characterized in the extrusion direction (ED) and along plate normal (ND) in the temperature range of 25 °C–500 °C, with a view to study the effect of loading direction. Cylindrical specimens were compressed parallel to ED and along ND, and flow curves and specimen shapes were recorded. The flow behavior at temperatures >200 °C in the strain rate range 0.0003–10 s−1 was analyzed using the approach of processing map. The plate texture could be described as basal planes parallel to the plate surface with <101¯0> as ED. The ED specimens deformed at temperatures <175 °C showed limited plastic strain leading to shear cracks, which were attributed to the restriction of basal slip and activation of limited non-basal slip. The ND specimens showed more plastic flow due to the occurrence of {101l} slip in <112¯3> direction in the absence of both basal and prismatic slip. The processing map for the ED specimens exhibited three domains in the ranges: (1) 230 °C–375 °C and 0.0003 s−1–0.002 s−1, (2) 410 °C–500 °C and 0.0003 s−1–0.008 s−1, and (3) 370 °C–430 °C and 2 s−1–10 s−1. In Domains 1 and 3, dynamic recrystallization (DRX) occurred due to prismatic slip and recovery by lattice-diffusion controlled climb, and first-order pyramidal slip and recovery by grain-boundary self-diffusion controlled climb, respectively. In the second domain, DRX occurred by second-order pyramidal slip and cross slip, which was followed by grain boundary sliding leading to superplasticity. The processing map for ND specimens exhibited an additional domain at lower temperatures and strain rates (225 °C–350 °C and 0.0003 s−1–0.1 s−1) which was due to easy occurrence of {101l} <112¯3> slip with lattice self-diffusion controlled climb. The map for ND orientation was free from flow instability regime unlike that for ED and this was the result of extensive occurrence of slip on {101l} planes in <112¯3> direction.