Instrumented constrained rod casting method and the controlled diffusion solidification (CDS) process were used to study the high susceptibility of the aluminum alloy AA 7068 to hot tearing. A precise analysis of the measured hot-tearing curves is provided considering the casting design and different feeding mechanisms. Scanning electron microscopy was used to study the hot-tear surfaces. It was found that the solidification of the eutectic liquid at the film stage and the phenomenon of solid feeding strongly affects the hot-tear formation. The early formation of an absorbed eutectic layer on the primary phase due to low rate of back-diffusion is proposed to explain the loss of ductility at the film stage. The layer can serve as an efficient substrate for the eutectic nucleation and growth; hence, its formation can advance the eutectic solidification. The isolation of liquid eutectic by its partial solidification results in development of solid-feeding stresses breaking the solid eutectic and provides the required tearing initiators. By increasing the back-diffusion rate, the CDS process avoids formation of the adsorbed solid layer which postpones eutectic solidification thereby mitigating the hot-tearing susceptibility.

仪器约束棒铸造方法和受控扩散凝固 (CDS) 工艺用于研究铝合金 AA 7068 对热撕裂的高敏感性。考虑到铸件设计和不同的喂料机制，对测得的热裂曲线进行了精确分析。使用扫描电子显微镜来研究热撕裂表面。发现共晶液在成膜阶段的凝固和固体进料现象对热撕裂的形成有很大影响。提出由于低反向扩散率在主相上早期形成吸收的共晶层来解释薄膜阶段的延展性损失。该层可以作为共晶成核和生长的有效衬底；因此，它的形成可以促进共晶凝固。通过部分凝固分离液体共晶导致固体进料应力的产生，从而破坏固体共晶并提供所需的撕裂引发剂。通过增加反向扩散速率，CDS 工艺避免了吸附固体层的形成，从而推迟了共晶凝固，从而减轻了热裂敏感性。