Finite Element Simulation Of Casting Residual Stresses In AZ91D Magnesium Alloy Components

As a"green metal structure material of the 21st century",magnesium alloy has a wide application prospect in aerospace,automobile,3C electronics and other fields.At present,cast magnesium alloy products account for about 70%of the total magnesium alloy components.However,the casting residual stress limits the further development of its commercialization.It is of great significance to regulate the casting residual stress for cast magnesium alloys.Due to the crystal structure(HCP)and properties of magnesium alloys,it is often difficult to accurately determine the residual stress by traditional test methods.In this paper,the finite element simulation of the casting process of magnesium alloy components was carried out by using Pro CAST casting simulation software,so as to study the generation and evolution of the residual stress in the components,reveal the influence of temperature gradient on the residual stress,and realize the three-dimensional reconstruction of the residual stress in the components.In this paper,the thermal property parameters of AZ91D magnesium alloy solidification process were calculated by Pro CAST software material database and JMATPRO material property calculation software.The thermal conductivity parameters were modified according to the experimental measurement results,and an accurate and reliable thermal property parameter library was established.Through the tensile test of AZ91D magnesium alloy at room temperature and high temperature,the true stress-true strain curves of AZ91D magnesium alloy at different temperatures were obtained,and the viscoplasticity of AZ91D magnesium alloy at high temperature was analyzed.The results show that the viscoplastic effect of AZ91D magnesium alloy is not obvious at low temperature(1/3 T_m<T).At medium temperature(1/3 T_m<T<1/2 T_m)and high temperature(T>1/2 T_m),viscoplasticity is more significant.According to Pro CAST software,the Perzyna elasto-viscoplastic constitutive model was established as the stress-strain constitutive model for the solidification process of AZ91D magnesium alloy.The validation test of the stress frame model shows that the finite element model of AZ91D magnesium alloy is accurate and reliable.The influence of temperature gradient on residual stress of casting was analyzed.The results of finite element simulation show that the temperature gradient caused by the casting configuration has little effect on the overall residual stress of the cylinder.The temperature gradient mainly affects the linear shrinkage caused by the solid shrinkage between the core and the surface of the cylinder,and then affects the residual stress of the two castings.The temperature gradient caused by the casting process has a great influence on the overall residual stress of the cylinder.With the increase of the preheating temperature of the die,the overall cooling rate of the cylinder decreases,the peak value of the temperature gradient between the core and the surface decreases,and the difference of the residual stress between the two decreases.With the increase of preheating temperature,the residual stress in the cylinder generally decreases,and the overall residual stress distribution tends to be flat,without obvious concentration of residual stress.