Influence of electrolyte components on the microstructure and growth mechanism of plasma electrolytic oxidation coatings on 1060 aluminum alloy

Electrolyte systems have a significant impact on plasma electrolytic oxidation (PEO). In this work, the surface, aluminum/coating (A/C) interface and fracture cross-section microstructure and element distribution of PEO coatings prepared in silicate, phosphate and mixed electrolyte were characterized in detail by FESEM, EDS, XRD and XPS. The growth mechanisms of PEO coatings in different electrolytes were also discussed. Results demonstrated that the deposition of silicate dominated the growth of coating in silicate system, many loose nodules were present on the coating surface. Si element occupied almost the entire coating and was enriched at the nodules and cavity edges. In phosphate system, the growth of coating was primarily dependent on the oxidation of aluminum. There are a large number of hill-like protrusions at A/C interface. The main component of this coating was a-Al2O3, and a small amount of P was distributed at A/C interface. In the mixed electrolyte, the film-formation process was mainly the matrix oxidation, and supplemented by deposition of electrolytes. Meanwhile, the growth models of PEO coating in different electrolyte were established.