Abnormal Dynamic Recrystallization Behavior of Coarse‐Grained AM60B Magnesium Alloy during Plane Strain Compression

While the deformation mechanisms of fine‐grained magnesium alloys have been extensively documented, the hot deformation behavior and underlying microstructural evolution of ultra‐coarse‐grained cast magnesium alloys, commonly found in industrial‐scale castings, remain largely unexplored and poorly understood. To address this gap, plane strain compression tests are conducted to simulate the rolling process of a coarse‐grained AM60B magnesium alloy (≈378.3 μm) at 250–310 °C with strain rates ranging from 0.5 to 12.75 s −1 . The stress–strain curves reveal a pronounced decrease in stress at 250 °C/0.5 s −1 , indicating an unusual softening phenomenon. The microstructural evolution of coarse‐grained alloy is systematically investigated. Results reveal that extensive lamellar twinning occurs in strain‐localized regions, leading to twin‐induced dynamic recrystallization (TDRX) at lower temperatures (250 °C). Subsequently, continuous dynamic recrystallization (CDRX) mediates the bridging of TDRX lamellae, while discontinuous dynamic recrystallization (DDRX) contributes to their broadening, with twin extension being DDRX‐driven. This elucidated TDRX‐dominated synergistic mechanism is established as the fundamental cause of both the abnormal flow softening and the enhanced microstructural refinement observed during deformation at 250 °C and 0.5 s −1 in coarse‐grained AM60B magnesium alloy. At higher temperatures of 280 °C and 310 °C, DDRX and CDRX become the dominant mechanisms, superseding TDRX.