Chemical passivation by immersion of Al alloys and Al 6061/SiC and Al 6061/ graphite metal matrix composites in a CeCl3 solution produces very corrosion resistant surfaces. Al 6061 and Al 7075-T6 which had been immersed in 1000 ppm CeCl3 for one week did not suffer from pitting corrosion during immersion in aerated 0.5 N NaCl for three weeks. For Al 7075-T73 some improvement of the corrosion resistance was also achieved, but to a much lesser extent. Chemical passivation in CeCl3 was also successful for Al/SiC and Al/ graphite. A comparison with the improvements of the corrosion resistance of Al alloys by treatment 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 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 is presented.

Subject
Pits, Coatings, Materials, Sodium chloride, Impedance, Capacitance, Sodium chloride solution, Corrosion modeling, Pitting, Passivation, Immersion, Corrosion resistance, Aluminum alloys
© 1988 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1988
Association for Materials Protection and Performance (AMPP)
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