Steven Michael Ford, do hereby declare that this thesis is my own unaided work. This
thesis has not been submitted in part or in full at this or any other university. This report is
submitted in fulfilment of the degree of Master of Science in Engineering at the University
of the Witwatersrand. / Aluminium, although often possessing adequate strength and toughness for a specific
application, may be deemed unsuitable due to a less than satisfactory corrosion resistance.
This unacceptable behaviour is especially prominent in the local mining industry where
aluminium alloys corrode severely in the high chloride and sulphate containing waters. Of
notable importance and the major motivating force for this research was the historically poor
perfomance of aluminium alloy mine cages, which are suited to the task excepting for their
unsatisfactory corrosion resistance. Of general importance however, is that the mining sector
in South Africa represents a sizeable portion of the economy and could thus become a much
greater consumer of aluminium if the metal's corrosion resistance could be improving
Apart from varying the composition of the alloy, the other basic technique of increasing a
metal's resistance to an environment is by applying a coating of some sort. This research
looks into the use of aluminium-based metal sprayed coatings as a form of protection for
various aluminium and steel substrate alloys.
The purpose of a metal sprayed layer is not merely to isolate the substrate from the
environment, hut also to act as a sacrificial anode at regions where the substrate is exposed.
Previous work suggested that alloys of aluminium/zinc/indium produced excellent sacrificial
anodes and were thus selected for this research. The zinc and indium were always alloyed
with pure aluminium, with the percentage zinc varying between 0 and 12%. All the coating
alloys were sprayed on a AA6261 and AA5083 aluminium alloys, a metal matrix composite
and a mild steel alloy, Various electrochemical and immersion trials were then carried out in
several synthetic mine waters and other corrosive media.
The basic conclusion to be drawn from the results achieved is that the optimum coating for
a particular substrate alloy is the one that provides the greatest potential difference between
it and the substrate, while still lasting the required lifetime of the component. The reason for
this is that the greater the potential difference, the better the sacrificial protection and hence
the better the protection offered to any exposed areas on the surface. The fact that the coating
corrodes away with time means that a balance must be found between sacrificial behaviour
and required lifetime. / Andrew Chakane 2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/24678 |
| Date | January 1992 |
| Creators | Ford, Steven Michael. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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