Surface Modification of Al Alloys and Al-Based Metal Matrix Composites by Chemical Passivation.

摘要

Chemical passivation by immersion of Aluminum 6061 and Aluminum 6061/Silicon Carbide and Al 6061/graphite metal matrix composites in a Cerous Chloride solution produces very corrosion resistant surfaces. Al 6061 which had been immersed in 1000 ppm Cerous Chloride for one week did not suffer from pitting corrosion during immersion in aerated 0.5 N Sodium Chloride for 90 days. A comparison with the corrosion resistance of Aluminum alloys treated with chromate conversion coatings shows that chemical passivation provides a valuable alternative to this process. The passivation process in CeCl3 and the corrosion process in NaCl have been monitored continuously with electrochemical impedance spectroscopy (EIS) which has been shown to be a very sensitive technique for the evaluation of these reactions. Pitting can be detected by the occurrence of a new time constant at low frequencies and a decrease of the impedance in the capacitive region. A model which describes the impedance for a surface which undergoes pitting and a fitting procedure for the analysis of the experimental EIS-data are presented. Reprints. (AW)