Integrated Computational and Experimental Study on Rapid Heating and Cooling Conditions in Powder-Bed Fusion of Al-Si Hypoeutectic Alloys

Al alloy parts fabricated by powder-bed fusion (PBF) have garnered significant attention, and inoculant rare-earth elements are typically introduced to enhance their mechanical properties. However, extracting rare-earth elements raises powder costs and mining poses environmental risks. Therefore, a novel grain refinement method for the PBF process that does not rely on inoculation is needed. We previously proposed that the intrinsic heterogeneous nucleation caused by rapid heating during the PBF process is key to a novel grain refinement strategy. It is essential to understand the relationships between laser irradiation parameters, melting and solidification conditions, and the resulting microstructure to provide guidelines for microstructure control in the PBF process. In this study, we investigated melting and solidification conditions in the PBF process of Al-Si hypoeutectic alloy by computational thermal-fluid dynamics simulations. It was found that the heating rates in the PBF process are around 108 K/s and are 10 times higher than the cooling rates, and these rapid heating and cooling conditions are suggested to cause the intrinsic heterogeneous nucleation unique to the PBF of the Al-Si hypoeutectic alloy. Furthermore, the melting and solidification conditions vary significantly within the melt pool, and the experimental microstructural inhomogeneity at the melt pool boundary can be explained based on the distribution of melting and solidification conditions. In addition to the rapid solidification unique to the PBF process, the focus on rapid heating paves the way for a wider range of microstructure control.