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An examination of the corrosion resistance of zinc-magnesium and zinc-aluminium-magnesium coated steels. / Chris, Weirman
Swansea University Author: Chris, Weirman
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This project has investigated the development of the optimum combination levels andprocessing conditions for zinc and magnesium coatings deposited by a Physical VapourDeposition (PVD) process under investigation by Tata Steel Europe Ltd.Temperatures in the range of 100°C to 350°C and times ranges of...
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This project has investigated the development of the optimum combination levels andprocessing conditions for zinc and magnesium coatings deposited by a Physical VapourDeposition (PVD) process under investigation by Tata Steel Europe Ltd.Temperatures in the range of 100°C to 350°C and times ranges of 2-10 hours and 30 -300 seconds were investigated and the coatings characterised by optical microscopy,scanning electron microscopy (SEM) with energy dispersive x-ray analysis, (EDX), alsoknown as electron probe microanalysis (EPMA), glow discharge optical emissionspectrophotometry (GDOES) and x-ray diffraction (XRD), and examined for corrosionresistance using the scanning vibrating electrode technique (SVET) and acceleratedweathering cabinet tests; prohesion and salt spray.The work has shown that the initial zinc magnesium coatings prepared via the developingTata Steel Europe PVD process did not perform as well as the current and developing hotdipped zinc-aluminium or zinc-aluminium-magnesium alloys in continuously submergedsodium chloride solutions.In support of this work, and to contrast the coatings prepared via the PVD process theproject investigated changes to the coating composition and substrate gauge of a range ofconventionally prepared hot dip galvanised samples. This part of the project has lookedat variations in the alloying additions to zinc using magnesium in the range of 0-2wt%and aluminium in the range of 0-5wt%.Changing coating composition and/or changing processing conditions produced coatingswith dendrites per mm2 (dendrite number) ranging from 350 to 7600. Primary zinc% hasalso been found to vary in the range of 29% to 95% and the relative corrosion rates havebeen found to vary between 49% and 477% that of benchmark samples of conventionalhot-dip galvanised steel of 275g/m2.Conventional and more recently developed coatings have been studied in mildly alkalineenvironments by immersion mass loss and SVET testing, as part of a study to investigateif Tata Steel Europe can substitute a lower coating weight, newly developed MagiZincmetallic coating into construction industry in the UK. It was found that both conventionaland the new alloy chemistries were seen to have sufficient coating weight after the 28days, the total cement curing time, to allow the substitution.
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