Evaluation of cracking resistance of DC casting high strength aluminum ingots

In direct chill (DC) casting of aluminum ingots uneven cooling rates at different regions of the ingot generate thermal stresses, which cause solidification cracks that might propagate to failure. As the microstructure changes in different parts of the ingot due to the different cooling rates, it is important to evaluate the cracking resistance at different locations of the ingot during DC ingot casting. Quench cracking tests, which simulate the cold crack propagation of the cast ingots under thermal stresses, were conducted for Al 2024 and Al 3004 alloys to determine the cracking resistance. Coupon specimens which represent the different locations of the cast ingot having different solidification rates were tested under specific thermomechanical loading conditions. The cracking resistance was observed to increase in the region with higher solidification rate and the cracking resistance of Al 3004 was observed to be higher than Al 2024 for a given solidification rate. The variations were investigated and found to correlate well with the microstructural and fractography analyses. The results provide further understanding of the often-observed center crack failure of casting ingot at the production runs.