Hot Dip Galvanizing
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University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties.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.
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
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University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties.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.
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