Intermediate temperature deformation behaviour of fine grained AZ61 alloy processed by hydrostatic extrusion

Abstract

In this work, the intermediate temperature deformation behaviour of alloy AZ61 processed by hydrostatic extrusion has been examined. By means of this thermomechanical process it is possible to refine the microstructure to generate an average grain size of about 5 μm directly from the as-cast microstructure in one single step when extruded at only 150 °C and an extrusion rate of 8 m/min. The evolution of microstructure and texture after tensile testing at 175, 200 and 225 °C in air at three different strain rates of 10−2, 10−3 and 10−4 s−1 were investigated. It was found that the alloy exhibited low temperature superplasticity at 175 °C (0.33Tm, where Tm is the melting point on the absolute scale). The maximum elongation recorded was 540% for AZ61 tested at 225 °C and 1.5 × 10−3 s−1. The intermediate temperature deformation behaviour and deformation mechanisms involved were discussed in terms of microstructure and texture development.