Concentration mixing and melt pool solidification behavior during the magnetic field assisted laser cladding of Fe-Cr-based alloy on 45 steel surface

Magnetic field-assisted laser cladding is an effective method in suppressing defects and improving the physical properties of the cladding layer, widely used in mold repair, aerospace, and additive manufacturing fields alike. However, magnetic field-assisted laser cladding cannot predict the effect of magnetic fields on composition mixing and melt pool solidification behavior. To solve this problem, a 3D magnetic field-assisted laser cladding numerical model including the chemical substance transfer, magnetic field, fluid flow, fluid heat transfer and dynamic grid was established in this paper. Based on the proposed model, the cladding layer geometry and concentration distributions of both the iron (Fe) and chromium (Cr) were predicted. The influences of magnetic field on the melt pool solidification behavior and the concentration mixing process were further developed. The results have shown that the maximum chromium concentration on the cladding layer marking line decreases from 10.9 wt% to 9.8 wt% within 0–0.5 T, and gradually increases to 13 wt% within 0.5–1.2 T. During the melt pool solidification, the maximum cooling rate (Gs*Rs) increases with the magnetic field strength – from 5.58 × 103 K/s to 7.1 × 103 K/s, while the morphological parameter (Gs/Rs) simultaneously decreases from 2.88 × 109 s∙K/m2 to 7.97 × 108 s∙K/m2. Such behavior implies that the crystal size decreases as the magnetic field strength increases. Additionally, the composition distribution at the beginning and bottom of the cladding layer is uneven. The crystal size decreases gradually when moving from the bottom to the top of the melt layer. Simultaneously, the crystal structure changed from slatted crystals at the bottom to columnar, cellular, and equiaxed crystals at the top. As such, the study provides an effective way to predict elemental concentrations and solidification behavior during magnetic field-assisted laser cladding.