Hot deformation mechanisms, microstructure and texture evolution in extruded AZ31–nano-alumina composite

Abstract

Processing map for hot working of hot extruded AZ31–1.5 vol% nano-alumina magnesium composite (AZ31–NAL) prepared by disintegrated metal deposition (DMD) technique has been developed in the temperature range of 250–500°C and strain rate range of 0.0003–10s−1. The starting composite microstructure is fine grained and is much less textured compared with the base AZ31 material prepared by similar technique (AZ31–DMD). The processing map for the composite exhibits three domains in the temperature and strain rate ranges: (1) 250–350°C/0.0003–0.01s−1; (2) 375–500°C/0.0003–0.01s−1; (3) 300–400°C/1–10s−1, which are all similar to those exhibited by the base alloy. In Domains #1 and #3, dynamic recrystallization occurs and results in fine grained microstructure, while in Domain #2, grain boundary sliding leading to wedge cracking in compression and intercrystalline cracking in tension have been identified. In comparison with the base alloy AZ31–DMD, the efficiency in the first domain has decreased, the third domain moved to lower temperatures and the effect on second domain is marginal. These differences are attributed to the lower intensity of starting texture in the nano-composite compared with the base alloy. A study of texture changes in the deformed specimens revealed that nano-alumina additions are helpful in reducing the preferred orientation in AZ31 alloy.