Comparison of edge crack behavior of Mg sheets prepared by online heating rolling

Abstract

Low-alloying and low-cost magnesium alloy sheets have the potential for large-scale application. Therefore, the edge cracking developed during the rolling is of great importance. In this work, Mg-1.0Mn-0.5Al (MA10), Mg–2Zn-1.5Mn (ZM21), and Mg-3.0Al-1.0Zn (AZ31) alloy sheets were rolled at 150 °C in different single-pass reductions using online heating rolling. Their edge cracking behaviors at the edge of rolled sheets after large strain rolling were investigated and compared through the scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and digital image correlation (DIC) technique. The results show that compared with ZM21 and AZ31 rolled sheets, MA10 rolled sheets exhibit the most severe edge cracking behavior after large strain rolling. This is mainly attributed to the lower recrystallization degree and ultimate compressive strength, as well as higher strain localization during the plastic deformation. Meanwhile, both coarser second phase particles at the edge and larger grain size difference also promote the initiation and propagation of edge crack in MA10 alloy rolled sheets. In addition, the small crack is developed in front of the crack tip in all of Mg alloys rolled sheets after a single-pass reduction of 75% due to the stress concentration at triple junctions caused by large rolling reduction and maximum shear stress along the plane collinear with the major crack.