Microstructure Formation Mechanism During a Novel Semisolid Rheo-rolling Process of AZ91 Magnesium Alloy

A novel semisolid rheo-rolling process of AZ91 alloy was proposed. The microstructure formation mechanism of AZ91 magnesium alloy during the process was studied. The results reveal that the eruptive nucleation and the heterogeneous nucleation exist. During the grain growth process, the grain breakage took place and transformed into fine spherical or rosette grains on the sloping plate gradually, the other grain growth style is direct globular growth. Due to the secondary crystallization of the remnant liquids in the roll gap, the microstructure of the strip becomes finer with the increment of the casting temperature from 650 degrees C to 690 degrees C. But when the casting temperature reached 710 degrees C, a part of the liquid alloy transformed into the eutectic phases, and the primary grains ripened to form coarse dendrites. In the casting temperature range from 650 degrees C to 690 degrees C, AZ91 alloy strip with fine spherical or rosette grains was prepared by the proposed process.