Misrun is one of the common casting defects in low-pressure casting of copper alloy.Numerical simulation can not only predict the final morphology of misrun

but also further analyze the formation and evolution of misrun.The key to predict misrun is to deal with the effect of alloy mushy zone on flow behavior.The model of variable viscosity-porous medium-critical solid fraction of copper alloys in the mushy region was modified

and based on the parameters of variable physical properties

the simulated results between it and the model of variable viscosity-critical solid fraction were calculated and analyzed comparatively.The actual production shows that the modified model of variable viscosity-porous medium-critical solid fraction can predict accurately the misrun defects

and the numerical calculation model is more reliable.