Study of reheated microstructure of AZ91D magnesium alloy

By means of equal channel angular extrusion (ECAE) test, knock down test, reheating in semi-solid state and metalloscope, reheating microstructures of raw casting ingots, material prepared by SIMA and material extruded by ECAE were investigated. The results show that compared to that of raw casting ingots and materials prepared by SIMA, reheating microstructure of materials extruded by ECAE is the best and the final grain size is finest. With the increasing holding time, a growing phenomenon takes place in reheating microstructure of materials extruded by ECAE, which can be described by so called Ostwald Repening law. The average of grain size increases firstly, subsequently decreases and the shape factor of grains approaches to 1 as reheating temperature increases. With the increasing equivalent strain, the average of grain size decreases. It illustrates that reheating material after extrusion by ECAE technology is a good method of preparing AZ91D magnesium alloy semi-solid billets.