Investigation of ZnCoP coating electrodeposited on Q235B steel and its corrosion resistance in simulated acid rain solution

In order to further improve the corrosion resistance of Q235B steel used for sports equipment, the Zn coating, ZnCo coating, and ZnCoP coating are electrodeposited respectively on the Q235B steel. The relationship between corrosion resistance, surface morphology, structure, and surface roughness of different coatings is studied. All the electrodeposited coatings are crystalline with typical diffraction peaks. Three diffraction peaks of Co(111),Co(200), and Co(220) can be observed on the XRD pattern of ZnCoP that indicate that the addition of sodium hypophosphite in the plating solution is conducive to the electrodeposition of cobalt. The Zn coating shows strip-like surface morphology with the roughest surface (1.431 µm) while the ZnCo coating and ZnCoP coating are both composed of granular structures with compact surfaces. Compared with all the coatings, the corrosion current density of Zn coating is about 345.78 μA/cm2 which is the largest indicating poor corrosion resistance. The corrosion current density of ZnCo coating and ZnCoP coating is 47.83 μA/cm2 and 15.63 μA/cm2 respectively which are both lower than that of Q235B. The ZnCoP coating has the best corrosion resistance due to phosphorus and cobalt doped in the coating that refine the grain size and improve the surface compactness.