Development of Corrosion Resistant

Development of Corrosion Resistant Galvanizing Alloys
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   DEVELOPMENT OF CORROSION RESISTANT GALVANISING ALLOYS   By BO ZHANG   A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY Metallurgy and Materials School of Engineering The University of Birmingham July 2005      University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation.  Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.   I  ABSTRACT In this work an investigation into the effect of alloying additions (Mn, Cu, Sb and Zr) on microstructure and corrosion of Zn alloys and hot dip galvanised coatings was undertaken. The first part of this thesis focuses on the effect of alloying additions on the corrosion of Zn alloys. The result shows that Mn is the most beneficial addition, which can significantly improve the resistance of Zn. The effect of Cu depends on its concentration. A high level of Cu addition has a deleterious effect on the corrosion resistance as the Cu-rich  particles are catalytic cathodic sites for oxygen reduction. Additions of Zr and Sb were found to have minor effect on the corrosion behaviour of Zn alloys. The effect of these additions on the microstructure of hot dip galvanised coatings was investigated in the second part. Both Zr and Mn can inhibit the layer growth of active steels with high Si content. Thus, Mn and Zr might be an alternative addition to Ni which can control the excessive reaction of the active steels. Addition of 0.8 wt % Cu significantly increases the coating thickness of the galvanised steel containing 0.02 wt % Si. The growth kinetics of the alloy layers follows a linear law. The final part of this thesis focuses on the effect of these additions on the atmospheric corrosion resistance and electrochemistry of hot dip galvanised coatings. Among the alloying additions investigated in this study, Mn is the most beneficial addition to the Zn bath and can significantly improve the resistance of the hot dip galvanised coating to atmospheric corrosion. The effect of other additions on corrosion resistance is minor. The beneficial effect of Mn addition is mainly due to the formation of a Mn-rich oxide layer on the top surface during the galvanising process, which can greatly inhibit the cathodic reactivity of the hot dip galvanised coating. Coupled with the relatively low cost and ease of alloying of this element, these various factors suggest that Mn might have  broader applications in general galvanising.   II  ACKNOWLEDGEMENTS I would like to express my great thanks to my supervisor Dr Alison J. Davenport for her continuous help, support, and encouragement in this project. I would also like to thank Joseph Ash Galvanising and UUK for the financial support for the project. A special thank to Adam Kent and Terry Felton in Joseph Ash Galvanising for providing materials, equipments, and discussion. I would like to thank Dr Allan Walton in the Applied Alloy Chemistry Group for his help with preparing the master alloys. I would like to thank Chris Hardy for her help with XPS and Paul Stanley for his help with FEG ESEM. The help from Derek in the workshop was also very much appreciated. I would also like to say thanks to Dr Stuart Lyon at UMIST, the University of Manchester and Dr Neil Short at Aston University for providing useful papers and suggestions. I would like to thank all the people of the electrochemical group for their experimental help. The atmosphere in the group has always been friendly, and I have received help whenever I have asked for it. Finally I would like to thank my wife, Lina Zhou, for her understanding and moral support and encouragement over the last four years.


Jul 23, 2017
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