Effect of Coupling Low-Flow Pouring with Inoculation on the As-Cast Microstructure of 7055 Alloys

Achieving uniform grain size in ingots is challenging in traditional direct chill (DC) casting. The thermal conditions during solidification often result in smaller grain size at the edge of the ingot compared to the center, leading to grain size inhomogeneity even in centimeter-scale samples. In this study, a low-flow pouring technique with the addition of grain refiner is employed to create similar thermal conditions from the edge to the center of the ingot during solidification, resulting in a homogeneous ingot. The grain size at the center of the prepared ingot consistently matches it at the edge. Finite element analysis confirms that low-flow pouring provides suitable thermal conditions for ensuring homogenous grains. Additionally, based on experimental results, a novel analytical model is proposed to precisely identify all active nucleation substrates. The grain size predicted by the proposed model aligns well with the experimental results, outperforming previous models. Our experimental and analytical results provide valuable guidance for the production of homogeneous ingots on an industrial scale.