Microstructure Evolution in the Thermal- Mechanical Behaviours of Magnesium alloysPart of:
The thermal-mechanical tensile behaviours of AZ31B (Mg-Al-Zn alloys class) and E717 (Mg-Zr-rare earth alloys class) magnesium alloys at various temperatures and strain rates were experimentally studied. The microstructure evolution of AZ31B and E717 magnesium alloys at different temperatures and strain rates were observed by Electron Backscatter Diffraction (EBSD). It has been found that the strength of AZ31B and E717 Mg alloys at high temperature decreases with temperature and increases with strain rate. However, the ductility of these Mg alloys increased with temperature increasing, and had a non-monotonic relationship with strain rate. In some cases, Mg alloys behaved better ductility at higher strain rate. The mechanisms for these phenomena have been discussed using EBSD, and it indicated that it was mainly resulted from various fractions of dynamic recrystallization at different conditions. E717 alloys show much lower ductility than that of AZ31B alloys at high temperatures, but the hardening rate of E717 behaves less sensitive to strain rates and temperatures than that of AZ31B. It is mainly attributed to the lower fraction of dynamic recrystallization in E717 alloys, because additions of rare earth elements suppressed its dynamic recrystallization. Compared the microstructure evolution of AZ31B with E717, it is concluded that additions of rare earth elements facilitated texture weakening and grains refinement. Much higher geometrically necessary dislocations was observed in lower temperature or higher strain rate, which contributes to the higher strength.