An investigation of direct-chill cast 2024 aluminum alloy under the influence of high shearing with regards to different shear positions

Abstract

Abstract The 2024 aluminum alloy ingot with a diameter of 300 mm was prepared by a direct-chill (DC) cast with the application of a high-shear unit in the sump to study the influence of the intensive melt shearing on the 2024 aluminum alloy. During the DC casting process, the head of the high-shear unit was set to different positions in the sump and the corresponding temperature curves were recorded to further study the role of the position of the high shear unit in the DC casting process with the influence of the intensive melt shearing. The experimental results showed that the intensive melt shearing during the DC casting process results in uniform temperature distribution in the sump, significant grain refinement and reduction of negative centerline macrosegregation. The average grain size in the center of the ingot was reduced from 739.7 μm to 193.8 μm, and the negative centerline macrosegregation of Cu element was reduced from -0.094 to -0.041. It was also found that the shear position plays a significant role in uniforming temperature field, eliminating melt superheating and refining grains. When the high shear position lowered to slurry region, the morphology of grain in the center of the ingot transformed from equiaxed dendritic into finer globular equiaxed grain. The reduction of negative centerline macrosegregation is believed to be due to the forced convection caused by the intensive melt shearing and consequently refined microstructure and uniform distribution of floating grains through the whole section of the ingot.