Enhanced mechanical properties of AZ31B magnesium alloy thin sheets processed by on-line heating rolling

A series of AZ31B magnesium alloy thin sheets were prepared by on-line heating rolling processing at temperatures ranging from 443 K to 623 K with intervals of 60 K to a total thickness reduction of ∼80% from initially 4 mm down to ∼0.8 mm in 7 passes. The experimental results suggest that the fracture elongation value increases rapidly at temperatures below 563 K, and then tends to be stable (563 K-623 K). Whereas the tendency of strength, including yield strength (YS) and ultimate tensile strength, is just an opposite one. Serrated edge in sheets manufactured with low temperatures of 443 K and 503 K. As temperature increases above 563 K, no obvious edge crack can be observed. In addition, YS is sensitive to the grain size at low temperatures while insensitive at higher temperatures, resulting in a significant deviation of the YS from the Hall-Petch (H-P) law. In order to elucidate this deviation, a model of framework is proposed which suggests that the strengthening effects of deformed grains and subgrains are weakened with the increase of the fraction of DRX grains till to losing efficacy when the latter surpasses a certain value, herein about 70%.