Effect of Cryogenic Treatment Prior to Rolling on Microstructure and Mechanical Properties of AZ31 Magnesium Alloy

The effects of cryogenic treatment prior to hot rolling on the strength, toughness and ductility of as-cast AZ31 magnesium alloy plates were investigated. The cryogenic treatment conditions were −60 °C/12 h, −120 °C/12 h, −180 °C/12 h, −60 °C/2 h, and −180 °C/2 h. Experimental results show that appropriate cryogenic treatment conditions can significantly refine the grain size and the improve strength, toughness and ductility. A large number of twins appear in both kinds of samples cryogenically treated for 2 h. The sample experienced cryogenic treatment for 12 h at −60 °C followed by rolling process shows the finest and most uniform and increase in yield strength by 25.8%. Meanwhile, a four-time increase in extension rate (3.06% to 12.31%) is attains. The tensile fracture present a mixed-mode fracture, which is characteristic of brittle and ductile fracture mechanisms.