Abstract: The aim is to study the influence of the laser rescanning process on the cladding layer structure (grain size and grain morphology) to determine the best laser rescanning power. In this work, the temperature field of laser cladding and laser rescanning was established and the thermal cycle curve of its key nodes was extracted. Combined with experimental verification, the effect of peak temperature and heat dissipation capacity on the microstructure growth of coating was analyzed. The results show that no matter in the stage of laser cladding or the laser rescanning, with the peak temperature and heat dissipation capacity gradually increasing along the molten pool center from the bonding zone to the top of the cladding layer, the coating microstructure gradually transits from planar crystal to cellular crystal, columnar cell crystal, dendrite and equiaxed crystal. With the increase of the laser rescanning power, the crystal grains of the cladding layer will grow thicker and larger, and the performance is particularly remarkable when the laser rescanning power is 1 200 W and 1 500 W. And if the rescanning power is too large, it will increase the melting of the substrate and the dilution rate of the coating. In contrast, when the laser rescanning power is 900 W, the crystal grains are relatively small and the increase of dilution ratio can be avoided. In addition, after the laser rescanning, the pores retained in the cladding layer can be released again. The unmelted powder particles on the surface of the cladding layer are fully melted, becoming more flat, smooth and full of metallic luster. The loose structure at the top of cladding layer is also significantly improved, which not only improves the quality of the coating, but also shortens the subsequent processing cycle, while also saving a certain amount of cladding materials.
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2022, Vol. 36 
