Effect of Heat Treatment Temperature on Corrosion Resistance of Electrodeposited Ni-Co Coating on Steel-Strip

The steel-strip with nickel-cobalt coating was heat treated for 3 h at the temperatures of 550 ℃, 650 ℃ and 750 ℃. Electrochemical was used to test the corrosion resistance of nickel-cobalt coating on steel-strip in 1.0% NaCl and 0.1% H2SO4 mixed solutions and 10% NaOH solution before and after heat treatment. The morphology, composition and texture orientation of nickel-cobalt coating on steel-strip at different temperatures were studied by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The results showed that with the increase of heat treatment temperatures, the grain size of nickel-cobalt coating increased correspondingly, a nickel-cobalt/iron diffusion layer between coating and substrate was formed. When the heat treatment temperature was 650 ℃, the corrosion resistance of nickel-cobalt coating on steel-strip was the best both in 1.0% NaCl-0.1% H2SO4 mixed solution and 10% NaOH solution, and then decreased when the temperature exceeded 650 ℃, indicating that a suitable heat treatment temperature can improve the corrosion resistance of the coating.