A conversion coating method has been developed based on precipitation of Li2[Al2(OH)6]2·CO3·3H2O from alkaline lithium salt solutions. The process is procedurally similar to chromate conversion coating but does not use or produce hazardous chemicals. The coating that forms is polycrystalline, continuous and conformal. The coating meets the MIL-C-5541E corrosion resistance, electrical contact resistance and paint adhesion requirements for certain aluminum alloys, but does not match the levels of performance exhibited by chromate conversion coatings.

In this paper, methods for producing the coating are described. Corrosion resistance has been characterized using electrochemical impedance spectroscopy and salt spray exposure. The structural, compositional and property changes attending post-coating thermal exposure are discussed. Performance in standardized corrosion, electrical and paint adhesion tests is also presented.

Subject
Paint removal, Test methods, Electrochemical impedance spectroscopy, Coating performance, Zinc rich coatings, Coatings, Probes, Salt spray corrosion testing, Chromate conversion coatings, Corrosion resistance, Aluminum alloys, Chemical conversion coatings, Paints
Keywords:
hydrotalcite, talc conversion coatings, chromate conversion coatings, electrochemical impedance spectroscopy, aluminum alloys
© 1995 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).
1995
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.