Investigation of defect control in selective laser melted La–Fe–Co–Si alloys through energy optimization and thermal modeling

La-Fe-Co-Si alloys are among the most promising magnetocaloric materials but suffer from intrinsic brittleness and long annealing times that hinder their processing and application. In this study, selective laser melting was employed to fabricate La-Fe-Co-Si alloys, and a quantitative process-structure-property correlation was established by combining experimental analysis with finite element modeling. The optimal processing parameters were identified as a laser power of 210 W and a scanning speed of 450 mm/s, corresponding to an energy density of 164.6 J/mm 3 . By optimizing the volumetric energy density to 140-222 J/mm 3 , keyhole defects were eliminated, yielding the lowest reported porosity (1.04 ± 0.18 vol.%) and crack rate (0.22 ± 0.08 vol.%) for quaternary La-Fe-Co-Si alloys, with 92% of pores smaller than 100 μm. Thermal modeling revealed that when the energy input exceeded 222 J/mm 3 , the maximum temperature rose to nearly twice the melting point, leading to evaporation and keyhole formation. However, below this threshold the temperature remained above the melting point, suppressing evaporation while maintaining adequate fluidity. The residual tensile stress decreased from 76 MPa to 47 MPa as the scan velocity increased from 350 mm/s to 450 mm/s at laser power of 210 W. After a 12 h-annealing process at 1323 K, the alloys demonstrated outstanding mechanical performance with a compressive strength 843 MPa and excellent magnetocaloric behavior with a refrigeration capacity of 229.9 J/kg under a 2 T magnetic field.