The corrosion behaviors of magnesium alloy AZ91C and its Al2O3(short fibre)-reinforced metal matrix composite (MMC) in alkaline solutions (pH 10.5) containing chloride were compared using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS) and immersion tests. Dependence of polarization characteristics (corrosion potential and corrosion current density) on chloride concentration was similar for both materials. The corrosion potential Ecorr decreased linearly with the logarithm of chloride concentration, while the corrosion current density icorr increased rapidly at chloride concentrations larger than 0.1%, with the icorr for the MMC consistently higher than that for AZ91C, reaching a factor of about 3 in 3.5% sodium chloride solution. EIS data indicated that the protective film on the MMC was inferior to that on the matrix alloy. With stirring and at frequencies higher than 5 Hz, the electrode/electrolyte interface might be described by the simplified Randles model for both materials. Immersion tests showed that the corrosion rate of the MMC, in terms of weight loss, was about 7 times that of the matrix alloy. Thus the present investigation indicated that in alkaline solutions containing chloride ions, the presence of Al2O3 short fibres in the alloy did not drastically alter the corrosion behavior, but significantly reduced its corrosion resistance.

Subject
Materials, Corrosion resistant alloys, Corrosion currents, Corrosion rate, Magnesium alloys, Alkaline solutions, Density, Acidity, Impedance measurements, Sodium chloride solution, Polarization, Chlorides, Corrosion potential
Keywords:
magnesium alloy, Al2O3-reinforced metal matrix composite, effect of chloride concentration, polarization, corroison potential, corroison rate, electrochemical impedance spectroscopy
© 1997 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).
1997
Association for Materials Protection and Performance (AMPP)
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