Based on Power-Cutoff model,using ProCAST casting simulation software,the die-casting process for magnesium alloy gearbox case at liquidus and semi-solid temperature region was analyzed.By orthogonal experiments,effects of plunger injection speed,casting temperature,mold temperature and the heat transfer coefficient between die mold and die castings on the defect rate were visualized,and the processing parameters were optimized.The results reveal that injection velocity on the maximum defect rate in die casting can be neglected,while lower injection speed can greatly reduce the total casting defect rate with ingate velocity between 40～90 m/s.Moreover,both the maximum and total casting defect rate can be significantly reduced with semi-solid casting temperature,higher mold temperature and lower heat transfer coefficient between die mold and castings.The optimized processing parameters were presented as follows:the plunger injection speed of 5 m/s,pouring temperature of 570 ℃,mold temperature more than 200 ℃ and heat transfer coefficient between die mold and castings of 500 W/(m2 · K).
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