Effect of laser remelting on copper‑nickel alloy coating prepared by extreme high-speed laser cladding

Abstract

Copper‑nickel alloy is an important corrosion resistant material for marine environment. Advanced extreme high-speed laser cladding (EHLA) technology can realize a metallurgical bonding of copper‑nickel alloy and obtain better surface and structural characteristics. However, because of the high heat conductivity and high reflectivity of copper, copper-alloy coatings prepared by EHLA have defects such as segregation, blowhole, and cracks. In this study, EHLA copper‑nickel alloy coating was improved by in-situ laser remelting process. A single pass finite-element-model of the remelting process was built to analyze the effect of remelting speed on the solidification of molten pool. The surface morphology, microstructure, element distribution, and phase composites of coatings at different remelting speeds were characterized, and the anti-corrosion of the coatings was further discussed by constant potential polarization and EIS. The results show that heat input increases the convection strength of liquid in molten pool, promotes the uniformity of the coating microstructure and reduces the defects. Although the columnar crystals to equiaxed crystals transformation of the coatings did not obviously changed at different remelting speed, the high heat input during remelting speed of 5 m/min promoted the alloying of copper‑nickel coating and eliminated the defects, obtaining the best corrosion resistance. The research will provide some technical guidance and theoretical support for the practical application of copper‑nickel alloy coating with EHLA-LR process in marine equipment.