Hydrotalcite coatings on aluminum alloys are being developed for corrosion protection of aluminum in aggressive saline environments. The coating bath composition, surface pretreatment, and alloying elements in aluminum all influence the performance of these coatings during salt spray testing. The coating bath, comprised of lithium carbonate, requires aging by dissolution of aluminum into the bath in order to grow corrosion resistant coatings. Coatings formed in non-aged baths do not perform well in salt spray testing. The alloying elements in aluminum alloys, especially copper, influence the coating growth and formation leading to thin coatings. The effect of the alloy elements is to increase the open circuit potential to a level where the hydrogen evolution and corresponding aluminum dissolution reactions are limited, so that hydrotalcite coating formation and growth are limited.

Subject
Coatings, Composition, Metal surfaces, Hydrogen evolution, Aluminum, Spray coating, Copper alloys, Open circuits, Lithium, Salt spray corrosion testing, Copper, Aluminum alloys, Electrode potential
Keywords:
conversion coatings, aluminum alloys, surface analysis, acid de-oxidation, hydrotalcite
© 1994 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).
1994
Association for Materials Protection and Performance (AMPP)
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