Designing for the cerium‐based conversion coating with excellent corrosion resistance on Mg–4Y–2Al magnesium alloy

Abstract The cerium salt chemical conversion baths containing KMnO4 are applied to prepare protective coatings on the WA42 alloy surface, and the effect of the concentration of KMnO4 on the microstructure and corrosion properties of the coatings is investigated by scanning electron microscopy, X‐ray photoelectron spectroscopy, and electrochemical tests. The results indicate that with the addition of KMnO4 to the conversion bath, the microstructure of the coating is more uniform and denser, and the coating with the KMnO4 concentration of 4 g/L (4M coating) has the most uniform microstructure with the least microcracks. The 4M coating exhibits a two‐layered structure, and it is mainly composed of MgO, Mg(OH)2, CeO2, Ce2O3, Ce(OH)3, MnO, and MnO2. In addition, as the KMnO4 concentration increases from 0 to 6 g/L, the Icorr of the coatings in 3.5% NaCl solution decreases first and then increases, and the 4M coating shows the best corrosion resistance, which should attribute to the uniform and dense microstructure.