The Prediction Criteria For The Linear Segregation Of ZL205A Barrel-shape Casting

This paper employs the numerical simulation software package ProCAST tosimulate the forming process of a large ZL205A thin-wall barrel-shape castingcasted under low-pressure. The linear segregation is analyzed and the intrinsic lawthat concerns the region where the segregation occurs is investigated. Furthermore,a criteria that indicates the occurrence of linear segregation is deduced.In order to ensure the credibility of the simulation result, the thermal propertiesof the ZL205A alloy during the solidification process have been experimentallymeasured.Based on the simulation result of the temperature gradient during thesolidification process, the occurrence of the linear segreatin can be summarized asfollows: the primary solidified region will be torn apart due to the presence ofhotspot where the wall-thickness changes dramatically. Considering the slit typerunner and low-pressure casting have a good feeding effect, the solute-rich metalliquid having a low melting point will fill into the hot crack and incurs linearsegegation.The criteria that predicts the linear microsegregation has been deduced asfollows:MSC G2PU1.5,and introduce into the defection criterion module inProCAST. The calculated segregation region is in good agreement with actualcasting. The solidification parameters of the segration and safe region in the as-castsample have been obtained, and the linear segregation region has a largertemperature gradient G than the safe region, while the cooling rate is smaller andverifies the accuracy of using the linear segregation in predicting the structure. Thecalculated critical value in the segregation criteria with temperature G, cooling rateU and yields673.To further validate the applicability of the criteria, simulation calculation hasbeen conducted by changing the structure of the casting and pouring process. Byintroducing the criteria into the defection prediction module in ProCAST canpredict the dangerous region where the segregation is very likely. By using X-raytransmission to locate the region where the linear segregation occurs, the actualcasting of this sample validates the applicability of this criteria.SEM investigation of the linear segregation region indicates the linearsegregation presents bone-like structure, the weight ratio of Al/Cu in the segreationphase is approximately1:1, the atomic ratio is approximately2:1, therefore its main component is mainly eutectic Al2Cu.