The atmospheric corrosion was evaluated on aluminum ingots and sheets from 99.6% Al after 60 month of exposure in clean atmosphere (with high condensation) and in an unheated concrete warehouse at the same location. The ingots were stored in the rectangular storage stacks on top of each other.

A chemical method of corrosion products removal was developed, using phosphoric acid and chromium oxide at 100°C (212°F) and allowing the corrosion loss determination without initial weight data. The laboratory apparatus was built for this purpose. The composition of the products was calculated from aluminum content, determined in known volume of corrosion products applying chemical stoichiometry.

"Degree of Hydration (°H)" was derived to express the nature of corrosion products. There was found no difference between composition of corrosion products in free atmosphere and in unheated warehouse. The corrosion products were formed by hydrated aluminum hydroxide Al(°H)3. 3H2O.

The atmospheric corrosion rate was dependent on the mass and the method of ingots exposure. The larger mass of aluminum exhibited higher corrosion rates (eight times higher in the storage and four times higher in the open atmosphere). The corrosion rate of ingots was ten to twenty-four times higher in the open atmosphere than in the unheated storage area.

It was also demonstrated in parallel laboratory studies that the simultaneous interactions between the moisture and temperature of air and metal surface, including the metal mass and its heat capacity, are important factors of the atmospheric corrosion kinetics.

Subject
Atmospheric corrosion, Water, Corrosion rate, Aluminum, Chromium, Atmosphere, Condensation, Storage, Metal loss, Corrosion products, Ingots, Metals, Heat
Keywords:
Atmospheric corrosion, corrosion kinetics, aluminum, intensity of condensation (ik), intensity of evaporation (iv), Degree of Hydration (°H), specific heat (cal, °Cg), mass of metal
© 1987 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).
1987
Association for Materials Protection and Performance (AMPP)
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