Casting stress refers to the internal stress generated in an ingot during solidification and subsequent cooling. By nature, casting stress can be classified into tensile stress and compressive stress. Based on the duration of action, it is divided into transient stress (which disappears once the cause of stress formation is eliminated) and residual stress (which persists even after the root cause is removed). According to the formation mechanism, it consists of thermal stress, transformation stress, and mechanical stress. All mechanical stresses are tensile stresses and belong to transient stress. Thermal stress and transformation stress can manifest as either tensile or compressive stress; thermal stress is usually residual stress, while transformation stress can be either transient or residual stress, depending on the timing and degree of phase transformation.

Thermal stress is the fundamental cause of cracking in wrought aluminum alloy ingots. During continuous casting, inconsistent cooling rates across different sections of the ingot result in non-uniform shrinkage amounts and rates at the same moment. The mutual restraint of shrinkage between different parts leads to the formation of internal stress in the ingot. As this stress is induced by temperature variations, it is defined as thermal stress. Thermal stress can only form when the metallic material enters an elastic state, or exists in a mixed elastic-plastic state. Generally, the greater the elastic modulus and linear shrinkage coefficient of the metallic material, and the larger the temperature gradient across the ingot section, the higher the thermal stress generated in the ingot. Measurements of residual thermal stress in ingots indicate that residual thermal stress increases with higher strength, lower ductility of the aluminum alloy, greater cooling intensity, lower crystallizer height, larger width-to-thickness ratio of flat ingots, and larger diameter of round ingots. Increasing the casting speed usually causes a slight reduction in residual thermal stress, while concentrated flow guidance leads to a moderate increase. Under identical conditions, the shallower the sump, the lower the residual thermal stress.

Transformation stress arises when the volume change induced by phase transformation is restricted during the cooling process of the ingot. For wrought aluminum alloys, solid-state phase transformation is generally absent except for variations in solid solubility, so transformation stress in ingots is insignificant during the casting process.

Mechanical stress is generated when the ingot shrinks horizontally or vertically and is mechanically restrained by external components such as the crystallizer, base plate, and core. Ingot pulling resistance is a unique type of mechanical stress in casting with sliding crystallizers, caused by friction and adhesion between the ingot and the crystallizer during relative sliding. Cracking occurs when the ingot pulling resistance exceeds the ultimate strength of the ingot surface at that temperature.