Microstructure Formation Mechanism of AZ31 Magnesium Alloy Processed by Rheo-Forming

AZ31 magnesium alloy sheets with a cross section of 5mm×50mm were prepared by semisolid metallic rheo-rolling device self-designed, and microstructure formation mechanism of AZ31 magnesium alloy during rheo-rolling was investigated. The results reveal that during the preparation of semisolid slurry, melt firstly nucleates heterogeneously on the surface of sloping plate. Under the vibration and shear of sloping plate, a relatively homogenous temperature field and composition filed are formed around some grains and are favorable for the direct growths of globular grains; meantime, dendrites formed under the vibration and shear are broken up and rounded gradually and better semisolid slurry is formed. During rheo-rolling, under the action of roll interfacial friction and rolling force, laminar flow shear inside the alloy is enhanced, and grains are further broken up and elongated. When the pouring temperature is 670°C, excellent AZ31 magnesium alloy sheet with good microstructure can be obtained.