Abstract
The high strength of Al-Si hypoeutectic alloys additively manufactured by powder-bed fusion is of great scientifc interest. To date, the mechanism of grain refnement near the fusion line, which contradicts conventional Hunt's columnar-equiaxed transition criteria, remains to be elucidated. Here we present the frst report on the mechanism of grain refnement. When a laser was irradiated on cast Al-Si alloy consisting of coarse α-Al grain and α-Al/Si eutectic regions, grain refnement occurred only near the eutectic regions. This strongly suggests that the Si phase is crucial for grain refnement. Multi-phase-feld simulation revealed that rapid heating due to the laser irradiation results in unmelted Si particles even above the liquidus temperature and that the particles act as heterogeneous nucleation sites during the subsequent re-solidi-fcation. These results suggest the feasibility of a novel inoculant-free grain refnement that is applicable to eutectic alloys comprising phases with a signifcant melting point difference.
NSTL
Elsevier