Effect of Li Content on Hot-Tearing Susceptibility of Ternary Al-Cu-Li Alloys: Experimental Investigation, Criterion Prediction, and Simulation Assessment

Al-Cu-Li alloys are promising structural materials due to their combined properties of low density and high specific strength. However, the severe hot-tearing susceptibility (HTS) during solidification inevitably deteriorates their casting quality. In this work, the influence of Li addition on the HTS of Al-2Cu-xLi (x = 0, 1, 2, 2.5, 3, and 4 wt pct) alloys was investigated by using a constrained rod-casting (CRC) apparatus equipped with a temperature-force acquisition system. Results revealed that the HTS does not follow the Lambda-shaped curve with the addition of Li but exhibits an abnormal increase when Li exceeds 2.5 wt pct. Among the tested alloys, the Al-2Cu-2.5Li alloy shows the best hot-tearing resistance, while the Al-2Cu-4Li alloy presents the highest HTS. The experimental results were then compared with the predictions of Kou ' s criterion and numerical simulation by using ProCAST software. These predictions are in good agreement with the experimental HTS for Li below 2.5 wt pct. However, they demonstrate a continuous decreasing trend with further increase of Li, which significantly deviates from the experimental curve. Further analysis indicated that the vulnerable temperature range is the most influential variable dominating HTS at low Li content. On the other hand, the abnormally severe HTS observed in high Li-containing alloys is attributed to the formation of Li-rich oxide inclusions, which induce strain localization between adjacent dendrites and obstruct liquid feeding in the mushy zone. In addition, the ratio curve of drop-in (DI) force to ultimate force exhibits a similar trend to the HTS curve, indicating that the severity of hot tearing can be predicted by evaluating the DI force/ultimate force ratio. These findings contribute to a profound understanding of the HTS in Al-Cu-Li alloys and are expected to provide reliable theoretical references for widespread applications.