Improvement of corrosion resistance of PEO coated dissimilar Ti/Mg0.6Ca couple

Abstract

With the growing demand for weight reduction, the application of joint lightweight structural materials is increasing. Magnesium alloys feature low density, high specific strength and good formability, offering significant advantages for fuel efficiency and load capacity. Combined with Ti, a dissimilar Ti/Mg composite material provides great flexibility combining the properties of each material. However, because of the great differences in chemical and electrochemical properties between Mg and Ti, it is imperative to address the galvanic corrosion problem of such dissimilar Ti/Mg components. This work presents an investigation of the PEO processing of sintered Ti/Mg0.6Ca couples, aiming to improve the corrosion resistance of such dissimilar alloy combinations using a phosphate-aluminate electrolyte. The results show that uniform and continuous coatings can be formed on the dissimilar Ti/Mg0.6Ca couple. The coating mainly contains MgO and MgAl₂O₄ on the Mg0.6Ca side, and Al₂TiO₅ is the dominant phase on the Ti side. The work also took advantage of synchrotron X-ray computed tomography (CT) scanning to achieve 3D reconstruction of the coating morphology, which can be a fast method to assess the porosity and compactness of the coating and further predict the coating corrosion resistance. The coating effectively improved the corrosion resistance of the dissimilar Ti/Mg0.6Ca couple.