In order for advanced aluminum alloys to be used in structural applications it is necessary to understand and mitigate failures that can occur due to localized corrosion events. Mechanical and electrochemical stresses interacting with a microstructural heterogeneity can result in the rapid growth of a flaw in the material; this phenomenon is a form of environmentally assisted cracking (EAC). One possible mechanism of EAC in Al-Li-X alloys is the preferential dissolution of an electrochemically active microstructural feature along a grain or sub-grain boundary. To examine this mechanism it is necessary to obtain information on the occluded environment that develops in a growing crack and the electrochemical behavior of boundary phases in the occluded environment. The electrochemistry of three relevant boundary phases (matrix phase (SHT 2095), T1 precipitate (Al2CuLi) and Cu-depleted zone (99.99% Al)) in several model environments has been documented using a variety of electrochemical techniques including scratching and straining electrode experiments. The electrochemical behavior of these phases has been linked to the SCC behavior of several Al-Li-X alloys using constant load testing under applied potentials in NaCl/Li2CO3 and NaCl/Na2CrO4 environments. The occluded environment model is being evaluated and refined by analysis of occluded chemistries using pH measurements and capillary electrophoresis.

Subject
Environmental cracking, Materials, Repassivation potentials, Aqueous environments, Sodium chloride, Acidity, Sodium chloride solution, Lithium, Aluminum alloys, Alloys, Electrodes, Stress corrosion cracking, Electrode potential
Keywords:
aluminum lithium alloy, stress corrosion cracking, copper depletion, lithium carbonate, scratching electrode, anodic dissolution, active phase, capillary electrophoresis, occluded environment
© 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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