Analysis of abnormal texture formation and strengthening mechanism in an extruded Mg-Gd-Y-Zn-Zr alloy

Abstract

A Mg-Gd-Y-Zn-Zr magnesium alloy with different initial states was extruded under different extrusion parameters. The effect of solution treatment and extrusion parameters on the microstructure, texture and mechanical properties were analyzed in detail, and the abnormal texture formation and strengthening mechanism was revealed. When extruded at low temperature and small extrusion ratio, the bimodal microstructure consisting of fine dynamically recrystallized grains and coarse deformed grains occurred both in the as-cast alloy and solution-treated alloy. When the extrusion temperature and extrusion ratio were increased, the amount and size of dynamically recrystallized grains increased and the grain size of the solution-treated alloy showed higher growth rate. Furthermore, an abnormal texture with <0001> parallel with extrusion direction developed due to the occurrence of non-basal slip and continuous dynamic recrystallization. This could be enhanced by solution treatment, high temperature, and large extrusion ratio. Both the as-cast alloy and solution-treated alloy exhibited the highest tensile strength after extrusion at 300 °C with an extrusion ratio of 9. Grain refinement was the main strengthening mechanism utilized in both the as-cast alloy and the solution-treated alloy. Work hardening played an important role in the sample extruded at low temperature and small extrusion ratio, with the highest contribution of about 33 MPa after extrusion at 300 °C with an extrusion ratio of 9. Texture strengthening contributed more in the sample extruded at high temperature and large extrusion ratio, but no more than 24.1 MPa. Solution strengthening was another strengthening mechanism in the extruded as-cast alloy, especially at high temperature and large extrusion ratio (no more than 9 MPa).