Influence of laser power, scanning speed, and power-to-scanning speed ratio on elemental mixing during laser cladding of sulphur-containing matrix

Process parameters and active sulphur jointly govern the thermal history and elemental composition of laser cladding coatings, yet their interplay with element mixing in sulphur-containing substrates remains unclear. To solve this problem, a 3D laser cladding model incorporating sulphur was developed using COMSOL Multiphysics. This model simulates the dynamic evolution of elements during laser cladding on the surface of sulphur-containing 45# steel matrix. It predicts the concentration distributions of S, Ni and B, as well as the geometry of the molten pool, under varying laser power, scanning speed and specific energy input conditions.Validation was performed by comparing predicted and measured geometric dimensions, Fe and Ni concentrations. The influence of scanning speed and laser power on element mixing was analyzed through convective mixing time, Peclet number, and flow patterns. Results indicate that when the scanning speed was fixed at 10 mm/s, increasing the laser power from 800 W to 1100 W caused the sulphur concentration to rise from 137 μmol/m³ to 192 μmol/m³ , whilst the concentrations of nickel, boron and chromium decreased from 72 mmol/m³ , 24 mmol/m³ and 133 mmol/m³ to 62 mmol/m³ , 21 mmol/m³ and 114 mmol/m³ , respectively. At constant laser power, sulphur concentration exhibited a non-monotonic variation with scanning speed. Conversely, at a constant laser power, the sulphur concentration first increases and then decreases as the scanning speed increases. At a constant power-speed ratio of 90 J/mm², minimum sulphur concentration and cladding width increased by 45 % and 27 %, respectively, with higher scanning speed also promoting more uniform sulphur distribution. These findings offer quantitative insights for tailoring composition and homogeneity in sulphur-containing laser-cladding layers.