Effects of solution and quenching treatment on the residual stress in extruded ZK60 magnesium alloy

The quench induced residual stress in extruded ZK60 magnesium alloy is investigated. X-ray diffraction and layer removal technique are employed to determine the residual stress in extrusion and long transverse direction through the thickness of the extruded plate after solution and quenching treatment. FEM simulation is employed to clarify the origin of the stress state. The residual stress is not uniform through thickness, it is compressive on the surface and first decreases and then increases in absolute magnitude with increasing depth and becomes tensile in the center. Anisotropic residual stress can be detected, with larger stress in long transverse direction and smaller stress in extrusion direction. This is rationalized by the anisotropic flow stress caused by the tilted basal texture. Anisotropic residual stress can be replicated in simulation using an isotropic yield function at high temperature and an anisotropic yield function at low temperature during quenching, the smaller flow stress in extrusion direction facilitates plastic flow at low temperature and results in smaller compressive residual stress in extrusion direction. The fact that no twins can be found after quenching demonstrates that the asymmetric yield strength associated with twinning does not affect the residual stress.