On the elemental segregation and melt flow behavior of pure copper laser cladding

Laser cladding of pure copper on the surface of low carbon steel remains a challenge originated in part from the differences between copper and steel in terms of melting point, thermal conductivity, solubility, etc., causing elemental segregation, formation of pores, and unfused defects. On the basis of previous studies that identified laser scanning speed as a possible cause to these defects, we report a new focused investigation using a coaxial powder-feeding laser cladding system to fabricate single-track pure copper cladding layers on a Q245R substrate by varying laser scanning speed. Under different laser scanning speeds, the morphology, elemental distribution, and phase constituents of coatings were examined by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Finite element analysis (FEA) numerical simulations were also carried out to investigate the relationship between the elemental segregation and the melt flow behavior in the molten pool. The results indicated that Fe gradually flew from the bottom to the topmost surface of the Cu cladding layer as the laser scanning speed increased. More specially, the numerical simulation revealed that the convection in the molten pool was more turbulent at a higher laser scanning speed, resulting in severe segregation of Fe covering the outer surface of the Cu cladding layer.