Effect of pretreatment process on the performance of Ni-Co-Al2O3(sol) nanocomposite coatings via electro-brush plating on steel substrate

The electro-brush plating process is flexible, and its deposition rate is relatively fast. However, the pretreatment process of brush plating is cumbersome, which leads to many problems in practical applications. The impact of different pretreatment techniques on the surface quality and the related properties of Ni-Co-Al2O3 nanocomposite coatings electro-brushed on 45 steel substrates were studied in this paper. The surface roughness, morphology, cross-sectional morphology, and the thickness of deposited layers were analyzed by white-light interferometry, SEM, and metallographic microscopy. The adhesion, hardness, and elastic-plastic mechanical properties of Ni-Co-Al2O3 nanocomposite coatings were discussed in-detail by scratch tester, hardness tester, and nanoindenter. The results show that the two-step method of alkali solution–hydrochloric acid not only has a simple process but also a good pretreatment effect. The Ni-Co-Al2O3 nanocomposite coating obtained by this method is flat, uniform, and has fewer defects. The prepared coating thickness reaches 11.68 µm, the average hardness value is 630 HV, and the elastic recovery ratio he/hmax value is 0.28. The adhesion between the coating and the substrate is significantly better than that of the traditional electro-brush plating process. This is expected to open a new path for the optimization and industrial application of the electro-brush plating process.