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Three years of outdoor corrosion tests, accelerated with a saline solution spray, and SAE J2334 and GM 9540P accelerated corrosion tests of industrially coated electrogalvanized (GE), hot-dip galvanized (GI), galvanneal (GA) interstitial free steels were performed. The samples were industrially phosphatized and painted with a modified epoxy resin, polyester resin as a primer and a base coat, and a high solid acrylic resin varnish as a clear coat. The effect of the deposition process and zinc mass on atmospheric corrosion of galvanized interstitial free low-alloyed carbon steels was analyzed. The SAE J2334 test was more effective than the GM 9540P test in differentiating the lowest corrosion resistance of the hot dip galvanized steel among the galvanized steels studied. The duration of the accelerated field test played an important role in the steel performance rating. The parameter of maximum corrosion penetration was more efficient to distinguish the effect of the zinc mass on corrosion resistance of the galvanized steel samples evaluated using accelerated field tests. [ABSTRACT FROM AUTHOR]

Abstract: Polymanganese phosphate coating is obtained on galvannealed (GA) steel surface by dipping process. Coating weight of 1.1 g/m2 is found to give dense with uniform crystallites of size 1–2 μm. Energy Dispersive X-ray Spectroscopy and X-ray Diffraction results show that the coating composes of manganese phosphate hydrate and rockbridgeite. The coefficient of the friction of polymanganese coated galvannealed steel sheet is reduced significantly from 0.22 to 0.11 on the die. Manganese phosphate in the coating behaves as an anti-sticking base, thereby the contact zone is found to be smooth. Further, the treated sheet removes only 5.9 mg of Fe powder in the form of flakes as compared to the untreated sheet producing 12 mg Fe powder from its surface. [Copyright &y& Elsevier]

Abstract: A comparative study on galvannealed (GA) and galvanised plain-skin passed (GP-SP) coatings was carried out to evaluate coating microstructures, the corrosion resistance and electrochemical behaviour in 3.5% NaCl solution. The corrosion resistance behaviour of GA coating was found to be superior compared to GP-SP coating. The Fe–Zn intermetallic phases formed in GA coating provided galvanic protection i.e., a cell reaction between Fe and Zn within a single phase. This gives rise to protective potential plateau and are believed to be responsible for the electrochemical polarisation resulting in sluggish corrosion reaction kinetics, thereby reducing the corrosion rate significantly after prolonged exposure in saline environment. It was also observed from the electrochemical impedance spectroscopy (EIS) study that the coating capacitance (C c) decreased and polarisation resistance (R p) increased with exposure time indicating a continuous charge transfer reaction across the coating and electrolyte interface. Although the corrosion potential of both coatings increased towards more noble direction with exposure time, it was observed that the potential for GA coatings was always nobler than GP-SP coating as E corr shifted towards more positive potential corresponding to a flat potential band of −850±20mV. [Copyright &y& Elsevier]