Hot Tearing Behavior in Double Ternary Eutectic Alloy System: Al-Mg-Si Alloys

The hot tearing behavior of the double ternary eutectic alloy system, Al-6Mg-xSi (0 to 6.0 wt pct Si) alloys, was evaluated by a constrained rod casting mold equipped with a thermocouple and a load cell connected to a data acquisition system. Experimental results were compared with the results calculated by Scheil's model using Pandat software to predict the occurrence of hot tearing in Al-6Mg-xSi alloys. The curve of hot tearing susceptibility contained two peaks, which were mainly affected by the double ternary eutectic reactions and the solidification phases evolution. And it agreed with the Kou's hot tearing index precisely. The types and fractions of solidification phases (Al3Mg2, Mg2Si, and eutectic Si) determined by the addition of Si content changed the freezing range and eutectic liquid fraction greatly. In addition, the types, fractions, sizes, and distributions of solidification phases affected the nucleation, propagation, and healing of hot tear cracks. The maximum contraction force value decreased as the reduction of volume shrinkage coefficient due to the addition of Si content. The drop-in force value on the contraction force curve could indicate the occurrence of hot tearing, and predict the hot tearing susceptibility when considering the shrinkage coefficient.