Cerium-based thermal conversion treatments on silicon carbide reinforced 2009 aluminum alloy composites

The conversion coatings on SiC_p/2009 aluminum (Al) composites and 2009 Al alloy were obtained by immersing the samples into the cerium (Ce)-based solutions with varying the chemical concentration (CeCl ₃·7H₂O, NaCl), solution pH/temperature, immersing time, and drying temperature. The corrosion inhibition mechanism and kinetics were studied by using the electrochemical techniques and surface analyses. Potentiodynamic polarization tests showed that coatings improved corrosion resistance as compared to untreated samples and environmental factors played important role in the formation of conversion layer. Scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) analysis revealed that relatively high inhibition efficiency for composite with 25avol% SiC_p was due to the existence of rather high surface area of cathodic intermetallics/SiC_p, which support to deposit Ce oxides/hydroxides on the entire surface.