Investigations on the Stress and Strain Evolution in AZ91D Magnesium Alloy Castings During Hot Tearing

Hot tearing in magnesium and aluminum alloys has been rigorously investigated in the past decades. To date, the interactions between the solidification parameters, microstructural development, and stress and strain at the onset of hot tearing in magnesium alloys remain unclear. In particular, the stress and strain conditions required to nucleate hot tears are unknown. In this research, ex situ neutron diffraction residual strain mapping was carried out on AZ91D magnesium alloy castings at the onset of hot tearing. The results indicate that tensile strain alone was not sufficient to nucleate a hot tear. A minimum threshold tensile stress of ~12 MPa was necessary to open interdendritic shrinkage pores into hot tears and enable their propagation. Further, deformation along \( (10\overline{1} 1) \)and \( (10\overline{1} 2) \) crystallographic planes played a dominant role on the high-temperature deformation and hot tearing in the AZ91D alloy.