Thermal Stress Prediction in AA5182 Rectangular Ingots

In DC casting of aluminum alloys, thermal strains can cause cracks during and after solidification and rejection of the ingot. Previous numerical models have simulated strain and stress in rounds, but less attention has been paid to slabs. To study residual stresses as a function of rectangular ingot aspect ratio and absolute ingot size, a 3D finite element model is used with simplified dynamic thermal boundary conditions. In industrial practice, a wiper is sometimes placed below the mold to isolate the lower part of ingot from cooling water, and that effect is also simulated. Stresses throughout the process start-up are predicted; the surface is first under tension, and later in compression, while the center has the opposite history. Results indicate decreasing stress magnitudes with the addition of a wiper. Also, placing the wiper closer to the mold will further reduce the residual tension in ingot center, but, if the wiper is too close, the ingot surface temperature will rebound and the surface may begin to remelt. A height limit of wiper position is determined to prevent the surface remelting. Larger ingots and slabs with larger aspect ratios are found out to have a higher overall tension level.