Sealants and coatings capable of retarding the rate of crack propagation in 7075-T6 and 7075-T73 aluminum were produced by incorporating selected crack growth inhibitors in epoxy-polyamide primers and polysulfide sealants.

The mechanism of crack growth inhibition was studied by conducting corrosion and crack growth tests with three isomers of diaminopyridine The results confirm the theory that there is a correlation between the zones of high electron density of inhibitors and their ability to minimize corrosion and crack growth in aluminum alloys.

Hi-Lok fasteners were wet-installed with sealant in a 7075-T73 aluminum fatigue specimen using MIL-S-8802 sealant, with and without crack growth inhibitors. After 327,000 cycles between loads of 1818. 1 and 454.5 kg (4,000 and 1,000 1bs) at 0.2 Hz and at ambient conditions of temperature and humidity, the crack from the control fastener had grown 3.81 cm (1.5 in.) while the cracks from the fasteners installed with the inhibited sealant were 0.24 cm (0.095 in.) in length

The use of crack growth inhibitors enable the maximum degree of protection to be obtained from coating systems and sealants and help eliminate the environmental factor from environmentally enhanced cracking of aluminum.

Subject
Primers, Crack growth, Corrosion rate, Aluminum, Crack propagation, Fatigue crack growth rate, Stress cracking, Sealants, Corrosion inhibitors, Fasteners, Fatigue, Aluminum alloys, Cracks
© 1984 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).
1984
Association for Materials Protection and Performance (AMPP)
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