Aluminium Alloy Corrosion of Aircraft Structures

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1 Aluminium Alloy Corrosion of Aircraft Structures WITpress WIT Press publishes leading books in Science and Technology. Visit our website for the current list of titles. WITeLibrary Home of the Transactions of the Wessex Institute, the WIT electronic-library provides the international scientific community with immediate and permanent access to individual papers presented at WIT conferences Visit the WIT elibrary at

3 Aluminium Alloy Corrosion of Aircraft Structures Modelling and Simulation Editors J. DeRose Laboratory for Joining Technologies and Corrosion, EMPA, Switzerland T. Suter Laboratory for Joining Technologies and Corrosion, EMPA, Switzerland T. Hack Innovation Works, EADS Deutschland GmbH, Germany R.A. Adey C M BEASY Ltd, UK

4 J. DeRose Laboratory for Joining Technologies and Corrosion, EMPA, Switzerland T. Suter Laboratory for Joining Technologies and Corrosion, EMPA, Switzerland T. Hack Innovation Works, EADS Deutschland GmbH, Germany R.A. Adey C M BEASY Ltd, UK Published by WIT Press Ashurst Lodge, Ashurst, Southampton, SO40 7AA, UK Tel: 44 (0) ; Fax: 44 (0) witpress@witpress.com For USA, Canada and Mexico WIT Press 25 Bridge Street, Billerica, MA 01821, USA Tel: ; Fax: infousa@witpress.com British Library Cataloguing-in-Publication Data A Catalogue record for this book is available from the British Library ISBN: eisbn: Library of Congress Catalog Card Number: No responsibility is assumed by the Publisher, the Editors and Authors for any injury and/ or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. The Publisher does not necessarily endorse the ideas held, or views expressed by the Editors or Authors of the material contained in its publications. WIT Press 2013 Printed in Great Britain by Print on Demand Worldwide 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 the Publisher.

5 Contents Section 1 Introduction and Overview Introduction and Overview 3 1 Motivation Objectives Participants in model development Summary and conclusions Impact and intentions for use...7 Section 2 Definition of Parameters Needed for Modelling and Simulation of Aluminium Alloy Corrosion in Aircraft Environments Subsection 2a Basic Needs and Parameters for Aluminium Alloy Corrosion Modelling as Applied in the Aviation Industry 13 1 Introduction Relevant aircraft needs to be considered for modelling and simulation Main geometrical and material input parameters for corrosion simulation In-service behaviour Reasonable assumptions for boundary conditions Other aspects to consider in modelling and simulation Conclusions...20 Subsection 2b Microscopic and Macroscopic Characterisation of an Aerospace Aluminium Alloy (AA2024) 23 1 Introduction Experimental methods Al 2024 alloy composition Sample preparation Electrochemical measurements Microstructural analysis...26

6 3 Results and discussion Al 2024 microstructure: intermetallic particles and matrix S and θ phase precipitates AlCuFeMnSi (second phase) particles Matrix Statistical analysis of the particles Al 2024 corrosion properties Microscale electrochemical measurements (micropolarisation curves) Difference in localised corrosion between the Al 2024 alloys (low Mg versus the more common composition) Variation in potential values measured with micropolarisation curves Conclusions...36 Section 3 Modelling and Simulation of Aluminium Alloy Corrosion in Aircraft Environments at the Microscopic, Mesoscopic, and Macroscopic Scales Subsection 3a Modelling of the Aluminium Alloy AA2024 at the Microscale: Pitting and Intergranular Corrosion 41 1 Introduction MITReM for localised corrosion of Al Boundary conditions Onset of localised corrosion Model specifications Results and discussion MTM for a deep, narrow crevice in Al Experimental input Model geometry Boundary conditions Homogeneous solution chemistry Results Stationary analysis Time-dependent analysis Achievements: model benefits Conclusions...56 Subsection 3b Modelling of the Aluminium Alloy Al 2024 from the Microscale to the Macroscale: Intergranular Corrosion 59 1 Introduction Materials and experiment Material Experimental details and results...60

7 2.2.1 Grain boundary (GB) angle and electron backscattered diffraction (EBSD) measurements Coupon testing Modelling Cellular automaton (CA) modelling approach Model Role of model parameters Optimisation by differential evolution (DE) Validation of model Conclusions...73 Subsection 3c Modelling of an Aluminium Alloy at the Mesoscale: Crevice Corrosion 77 1 Introduction Context State of the art of aluminium corrosion in confined media Simulation approach Mathematical background Chemical and electrochemical reactions Choice of the representative geometries for simulation Results Simulation for a one-sided aluminium crevice : 2-D side view Simulation for a one-sided aluminium crevice : 2-D top view Instrumented cavities of medium size Experimental set-up Results and discussion Experimental results for Al Comparison between simulation and experiment Possible application of the developed models Conclusions...91 Subsection 3d Macroscale Galvanic Corrosion Modelling of an Aluminium Alloy 95 1 Introduction Corrosion risk in aircraft structures Galvanic corrosion model Modelling approach Validation Deep electrolyte environment Case Scenario Case Scenario Deep electrolyte summary Thin electrolyte environment Electrochemical input...110

8 2.2.2 Experimental theoretical background Experimental procedures Results Simulation results Validation Thin film discussion Thin film summary Localised coating damage Experimental and modelling procedures Methodology Modelling approach Results Summary Galvanic corrosion applications Case Study Case Study Conclusions Section 4 Investigation of Corrosion Prevention Methods for Aluminium Alloy Aircraft Structures Subsection 4a The Effect of Local Cladding on Aluminium Alloy Corrosion Introduction Experimental investigation and results Corrosion evaluation of the unprotected material Corrosion damage with simple local cladding patterns Effect of scale on the protection performance of a clad spot and statistical analysis of the corrosion damage Validation of a clad pattern Conclusions Subsection 4b Effect of Surface Treatment, Anodisation, and Inhibitors on Corrosion of the Aluminium Alloy AA Introduction Experimental methods Al 2024 sample preparation Microstructure analysis Pretreatment and anodisation of Al 2024-T Pretreatment Anodisation Combined pretreatment and anodisation Electrochemical measurements...150

9 2.4 Corrosion inhibitors Sample preparation Electrochemical measurements Results and discussion Pretreated Al Pretreated and anodised Al Effect of pretreatment and anodisation on corrosion behaviour of Al Inhibitors Conclusions Section 5 Decision Support Tool for Aluminium Alloy Corrosion in Aircraft Environments Decision Support Tool for Aluminium Alloy Corrosion in Aircraft Environments Introduction Decision support tool objectives Simulation models incorporated in the DST Integration approach Input data for aircraft structures Galvanic simulation Parametric models Documentation and reports Case study optimisation of surface protection Case study defect in protection system Conclusions Section 6 Impact on Industry Impact on Industry Use of corrosion modelling and simulation methods in industry Use in the aeronautics industry Contributions to standards, education, and training Application of the results in other industries Conclusions...186

DYNAMICS IN THE PRACTICE OF STRUCTURAL DESIGN

DYNAMICS IN THE PRACTICE OF STRUCTURAL DESIGN WIT Press publishes leading books in Science and Technology. Visit our website for the current list of titles. www.witpress.com WITeLibrary Home of the Transactions