| Summary: | Submitted to the School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, December 2017 === The benefits of Al alloys to industry are significant. For the truck loading application in this study, the use of Al can deliver a greater payload than most other metals, due to its low relative density. However, it has poor tribological properties. This study investigated ways to improve the wear resistance of AA6082, an Al alloy widely used in transport. This was done by studying WC-based coatings to improve the wear resistance of the AA6082 surface. To ensure a sufficient WC-substrate bond, Al powder was used as a binder for the coatings. Although these coatings improved the wear resistance of the AA6082, it was imperative to test and establish that their corrosion resistance was not inferior to that of the AA6082 itself.
Differences in hardness and tensile properties of the substrate were evaluated for varying ageing durations. The plasma spray technique was used to coat the AA6082 substrate. The heat input from this coating process on an Al alloys with high thermal conductivity could have lowered the hardness and mechanical properties of the AA6082 substrate. Therefore, hardness tests were carried out on the cross-section of each coated substrate. The hardnesses of all coated AA6082 samples were not lowered by the heat input from the plasma spray process.
The coatings were varied to contain 20%, 40%, 60%, 80% and 100% volume of WC admixed with Al-102 powder. The wear resistance of AA6082 was significantly improved as WC content increased. From the wear resistance results, both 60% and 80% WC showed the highest wear resistance. The 60% WC coating, which contained a lower quantity of WC than the 80% WC coating, was the preferred option for truck loading applications because of cost. The 60% WC coating had a lower hardness value than the 80% WC coating, giving the 60% WC coating a higher allowance for work-hardening in service as ductile Al-102 is present in higher quantity.
Al and its alloys, with no coating, are known to have good corrosion resistance. It was therefore imperative to evaluate and compare the corrosion resistance of the coated samples with AA6082. The lowest corrosion rate of all coated samples exposed to the neutral and acidic media was the 20% WC coating. Generally, all the coated samples had very low corrosion rates in the neutral solution, which is more applicable to typical truck loading conditions. Therefore, the 60% WC coating was most preferred for wear and hardness tests and also had acceptable corrosion behaviour for the proposed truck loading application. === XL2018
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