Fundamentals of grain coalescence and applications to aluminum alloy industrial solidification processes

近终形铸造为制造复杂形状的轻金属合金零件提供了最具成本效益的方法。然而，热裂等铸造缺陷会降低产品质量和工艺效率。热撕裂是半固态金属合金由于晶间液膜破裂而发生的自发断裂，发生在凝固末期，变形集中在晶界。热撕裂的发生与半固态从被液体包围的孤立颗粒逐渐演变为连贯的、渗入的固体网络密切相关，这一过程被称为颗粒合并。如果颗粒聚结被延缓，从而在较低温度下完成，则热裂敏感性显著增加。

Near-net-shape casting provides the most cost-effective way to manufacture light metal alloy components of complex shape. However, casting defects such as hot tearing reduce product quality and process efficiency. Hot tearing is characterized as a spontaneous failure of semi-solid metallic alloys due to the rupture of liquid films between grains, and occurs near the end of solidification where deformation becomes localized to the grain boundaries. The occurrence of hot tearing is intimately linked with the semi-solid’s gradual evolution from isolated grains surrounded by liquid to a coherent and percolated solid network, a process known as grain coalescence. If grain coalescence is retarded and therefore finishes at lower temperatures, hot tearing susceptibility is significantly increased.