The effect of cerium pretreatment on the corrosion behaviour of aluminium composites

Abstract:

The effect of cerium pretreatment on the corrosion behaviour of the metal matrix composite AA6061 T6-10% Al2O3 was studied in aerated 3.5% NaCl solution after different immersion times, ranging between one and 30 days at room temperature. Series of specimens were prepared under the following conditions: (1) as-polished specimens without CeCl3 treatment; (2) treated in NaCl solution containing cerium at different concentrations; and (3) treated in solution of pure CeCl3 with different concentrations, times, and pH. Electrochemical-impedance spectroscopy technique (EIS) was used to investigate the corrosion behaviour of the treated and untreated specimens. Optical microscopy and SEM were used to investigate the occurrence of localized corrosion after immersion in NaCl. Both the untreated and the treated specimens in NaCl+CeCl3 solution suffered from pitting as well as crevice corrosion. The size of pits increased in the presence of cerium at low concentration (500ppm) in NaCl solution. By increasing the concentration of cerium in NaCl, the number and the size of the pits decreased. SEM showed a significant improvement after treatment in the solutions of pure CeCl3. XPS analysis revealed the presence of cerium as a very thin film. The mechanism of corrosion inhibition by cerium mainly depends on blocking the cathodic active surface sites. Moreover, cerium plays an important part to reject the chloride ions from the surface. The degree of protection is a function of time. To achieve significant surface improvement, long-time immersion is required. Because the passive film due to cerium treatment was very thin and adsorbed in a non-uniform way, localized corrosion was always present even after long time of treatment.

Año de publicación:

2001

Keywords:

Fuente:

scopus