Characterization and corrosion protection properties of cerium conversion coating on Gr_(f)/Al composite surface

The aim of this work is to investigate corrosion protection properties of Ce conversion coating on the graphite fiber-reinforced aluminum matrix (Gr_(f)/Al) composite surface by electrochemical measurements, and microstructure of the Ce conversion coating was studied by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). It is found that the coating covers the whole surface of Gr_(f)/Al composites as oxidized islands, since there are some micro-cracks on the coating. The Ce conversion coating consists of Ce-rich nano-particles, and the contact sites between particles have some porosity. The porosity is not obvious during initial deposition, however, as deposition time prolonged development apparently. Moreover, some severe cracks may appear during the drying process, since evaporation of water molecules would cause shrinkage and large stress is induced. In addition, pretreatment of surface has an effect on the formation of cracks. Ce conversion coating has the composition of Ce³⁺ and Ce⁴⁺. Deposition of Ce-rich coating on Gr_(f)/Al composite surfaces shifts the polarization curves toward lower current density values. Electrochemical impedance spectroscopy (EIS) data show that Ce conversion coating improved corrosion resistance as compared with samples that have no coating.