Numerical Simulation Of Thermal Stress And Prediction Of Hot Tearing In A356 Alloy Castings

In foundries, hot tearing is a common and very serious defect. Once a casting occurs hot tearing, it means that the casting must be repaired or even scraped directly, causing serious economic losses. Therefore it is significantly important to be able to accurately predict hot tearing in castings. According to the current researches on hot tearing, this paper studied the intrinsic causes and effective prediction methods of hot tearing in castings.This paper selected widely used A356 as an experimental alloy, the hot tearing situations in the castings under different casting processes were predicted by using the hot tearing prediction module programmed in the commercial software ProCAST. Through the comparison of the results of simulated thermal stress field and predicted hot tearing with the results observed in the actual poured castings, this paper studied the hot tearing situations in the castings under different preheated mold temperatures and different pouring temperatures. Meanwhile, the simulated results of the equivalent stress and plastic strain during the solidification were analyzed for thorough understanding the leading factors of the formation of hot tearing in castings and the key factors in consideration in order to establish a prediction criterion for hot tearing.Through the prediction and the experimental investigation of the hot tearing in castings under different casting processes, the results showed that the prediction module for hot tearing in the software ProCAST could accurately calculate the hot tearing sensitivity under different casting processes. The predicted results were consistent with the hot tearing sensitivity observed in the practically poured castings. In addition, through analyzing the results of simulated thermal stress field during the solidification of the castings and the situations in the actually poured castings, the results showed that improving mold preheated temperatures could reduce the equivalent stress and plastic strain during the solidification of the castings for a given pouring temperature, thereby reducing or preventing the casting hot tearing. Meanwhile when the mold preheated temperature was not good, improving the pouring temperature could effectively reduce the concentration of the plastic strain during the solidification, thus reduce the hot tearing sensitivity. But the influence on the equivalent stress was not regular. Therefore, the conclusions indicated that compared with the equivalent stress, the plastic strain in the solidification could reflect the trend of the actual hot tearing situations of the castings better. The plastic strain should be the primary factor to be considered in the later investigation of hot tearing or the establishment of the prediction criterions for hot tearing in future.