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Influence of Rescanning Process on Thermo-Mechanical Response of Molten Zone in Laser Cladding on Gray Cast Iron
P. Yi, Y-C. Liu, X-H. Zhan, P-Y. Xu, T. Liu and C-F. Fan

Surface modification of grey cast iron by using laser cladding can improve surface properties of low-cost materials, thereby expanding their applications and prolonging serving time. In this study, the laser rescanning process was designed to optimize the thermal stress distribution in the clad layer. Numerical simulation and experiments were conducted to study the thermodynamic response distribution under the laser rescanning process. The influence of scanning speeds was analysed to optimize the process parameters. Results indicated that rescanning reduced the transient thermal stress of clad layer and released internal residual tensile stress, thereby improving the anti-cracking toughness of the cast iron coating. Meanwhile, thermal input of rescanning was controlled at a low level. Thickening degree of dendritic structure in secondary development can be controlled within 20% and reducing degree of residual tensile stress reached as high as 40%. Scanning speed had an obvious influence on thermal stress, and release of tensile stress should be maximized while maintaining a fine-grain structure; moreover, 500 W power and 200 mm/min scanning speed constituted the optimal rescanning parameter combination.

Keywords: CO2 laser, HT250 grey cast iron, Fe313 alloy powder, laser cladding, rescanning, thermodynamic response, tensile stress release, dendritic structure

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