Deformation behaviour of magnesium alloys at elevated temperatures

Polycrystals of magnesium alloy AZ91 and AS21 were deformed in compression and tensile tests. The tests were performed in the temperature range from room temperature to 300 degreesC at various but constant strain rates. It is observed that the flow stress decreases with increasing temperature and that at elevated temperatures, the work-hardening rate beyond a certain strain is zero or decreases with strain. This work hardening behaviour indicates dynamic recovery and dynamic recrystallisation. This is confirmed by microstructural changes. In order to explain the work hardening behaviour the stress dependence of the work hardening rate was analysed. The analysis shows that cross slip should be assumed as the process responsible for dynamic recovery.