The failure mechanisms of organic coatings on Zinc Aluminium Magnesium substrates under exposure to natural conditions & accelerated corrosion environ

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Full Title: The failure mechanisms of organic coatings on Zinc Aluminium Magnesium substrates under exposure to natural conditions and accelerated corrosion environmentsCoil coatings are used to protect aluminium and steel from natural environments, whereby adhesion and anticorrosive protection are the essential properties to maintain good corrosion resistance. Many steel products are based of hot dip galvanised steel coated with a pre-treatment, a primer, and a topcoat. In the last few years, steel producers have developed lower thicknesses of the galvanising layer-using an alloy of 10 microns of zinc aluminium magnesium (ZAM) in order to decrease the total cost of the substrate by reducing the thickness of the sacrificial layer, offering the same corrosion protection as thicker zinc layer of 20 microns.In the last decade, the industry partner, Becker Industrial Coatings Ltd. (Beckers) has developed and commercialised chromate free primers for ZAM substrates with varying success. The same primer was found to have varying corrosion resistance when coated on different grades of ZAM substrates. In addition, polyester cross-linked with isocyanate generally has better corrosion resistance than polyester cross-linked with melamine.The aims of the project are to investigate and monitor the corrosion failure mechanisms of coil coatings on different grades of ZAM substrates. To study the coatings behaviour when exposed in salt spray, Prohesion, and the natural site at Bohus Malmon and to correlate with electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode (SVET). Raman or IR spectroscopy could be used to identify the corrosion products produced during the testing.