Using EIS to evaluate anti-corrosion properties of the SiCp/5A06 aluminium MMC treated by cerium conversion coatings

Abstract This paper evaluated the protection effect of the cerium conversion coatings on the SiC p /5A06 Al composite and the 5A06 Al alloy. Electrochemical impedance spectroscopy (EIS) was employed to examine the variation of the electrochemical variables of the samples treated and immersed in 3.5% NaCl solution at 35 °C for 1 h, which showed the enhancement of charge transfer resistance ( R t ) and coating film resistance ( R c ), i.e., the corrosion resistance of the conversion coated samples was improved. The best protection effect was found for the samples treated for 60 min with 1000 μg/g CeCl 3 ·7H 2 O/3.5% NaCl solution at 45 °C, followed with dried at 100 °C for 30 min. SEM/EDS examinations confirmed that the enhancement in corrosion resistance properties of these materials was due to the precipitation of cerium oxides/hydroxides over the cathodic intermetallics and SiC particulates. The XPS results revealed that the conversion coatings were composed of CeO 2 , Ce 2 O 3 , Ce(OH) 3 , Ce(OH) 4 , and Al 2 O 3 .