Study on hardness and corrosion resistance of Co-Mo-P/ZrO2 composite coating electrodeposited on Q345 steel

Co-Mo-P/ZrO2 composite coating was prepared on the surface of Q345 steel by electrodeposition technology, and the effect of different ZrO2 particle concentrations on the surface morphology, chemical composition, thickness, microstructure and mechanical properties of the composite coating was investigated. The results show that different composite coatings prepared by changing the concentration of ZrO2 particles in the bath show aggregated cellular surface morphology, which is composed of Co, Mo, P, Zr, and O elements. With the concentration of ZrO2 particles increasing from 4 g/L to 20 g/L, the average grain size and the amount of ZrO2 particles incorporated both decrease first and then increase. Moreover, along with the increase in concentration of ZrO2 particles, the hardness and scratch resistance of the composite coating both show a trend of increasing first and then decreasing. However, changing the concentration of ZrO2 particles has no obvious effect on the grain structure and growth orientation of the composite coating. When the concentration of ZrO2 particles is 12 g/L, the surface of the composite coating is relatively dense with an average grain size of 40.78 nm and (200) crystal face preferred orientation. More ZrO2 particles are incorporated on the surface and boundary of the grain aggregation, which plays an obvious dispersion strengthening effect. The hardness of the composite coating reaches 580.2 HV, showing good scratch and corrosion resistance.