STP1134

    Passivation in Rare Earth Metal Chlorides—A New Conversion Coating Process for Aluminum Alloys

    Published: Jan 1992


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    Abstract

    Investigations in this laboratory have shown that immersion of Al 6061-T6 and Al 7075-T6 in 1000 ppm CeCl3 produces very corrosion-resistant surfaces. For Al 6061-T6 that had been treated in 1000 ppm CeCl3 for one week, pitting did not occur in 0.5N NaCl for two months. Similar results have been obtained for immersion in NdCl3 and PrCl3, but not in LaCl3 and YCl3. The effects of the concentration of the passivation solutions, the length of exposure time and type of surface preparation have been investigated in more detail using electrochemical impedance spectroscopy (EIS) and d-c techniques. EIS data and d-c polarization curves have been determined during the passivation process and during subsequent exposure to NaCl. In addition, surface analysis has been performed using scanning electron microscopy with energy-dispersive X-ray analysis (SEM/EDAX) and scanning Auger electron spectroscopy (AES). More recent efforts have concentrated on shortening the passivation time. Comparisons with the corrosion behavior of chromate conversion coated aluminum alloys suggest that passivation in rare earth metal chlorides can produce surface films with a corrosion resistance similar to that provided by chromate conversion coatings.

    Keywords:

    aluminum alloys, corrosion, conversion coatings, passivation, electrochemical impedance spectroscopy (EIS), surface analysis


    Author Information:

    Shih, H
    Research assistant professor and professor, University of Southern California, Los Angeles, CA

    Mansfeld, F
    Research assistant professor and professor, University of Southern California, Los Angeles, CA


    Paper ID: STP19589S

    Committee/Subcommittee: G01.11

    DOI: 10.1520/STP19589S


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