Elevated temperature compression behaviour of Mg-Al-Zn alloys

Flow stress behaviour of Mg - Al - Zn alloys was studied by compression testing using a Gleeble 1500 machine at temperatures of 200 - 450 degrees C and at strain rates ranging from 0.005 to 5 s(-1). The experimental results show that initial grain size and a distinctive basal texture lead to the great difference between as extruded AZ31 alloy and other two groups of cast alloys AZ31 and AZ80, including the variation in the flow stress equations and dynamic recrystallisation behaviour. The increment of alloying element Al will decrease stacking fault energy and enhance the process of dislocation climb, and therefore reduce the tendency for dislocation pile-up to cross-slip. The presence of the second phase particles will hinder both the formation and migration of recrystallisation fronts. As a result, for cast AZ80 alloy, dynamic recrystallisation is delayed and the activation energy for the plastic deformation process sharply increases from 166.75 to 220 kJ mol(-1) as compared with cast AZ31 alloy under the same deformation condition.