%0 Journal Article
%T Corrosion Study of Powder-Coated Galvanised Steel
%A Manish Kumar Bhadu
%A Akshya Kumar Guin
%A Veena Singh
%A Shyam K. Choudhary
%J ISRN Corrosion
%D 2013
%R 10.1155/2013/464710
%X In general, steel is protected from corrosive environments by conversion coatings, that is, phosphating, chromating, and so forth, and then followed by different layers of paints. Nowadays, strict pollution laws and regulations are creating significant challenges for coating experts to develop an environmentally friendly product. Powder coatings have demonstrated their ability as alternative to traditional solvent-borne coatings. In the present work, polyester-based two coating systems have been investigated and their performances have been evaluated for surface topographical properties by Scanning electron microscope (SEM), and energy dispersive spectrometry (EDX), accelerated corrosion resistance by salt spray test, and impedance property by electrochemical impedance spectroscopy. Coating adhesion with the steel and hardness were evaluated by bond strength, cross cut adhesion, and pencil hardness. This paper explains the results and performance of the coatings by the above two systems. 1. Introduction Galvanised steel is widely used in construction, automobile, and white goods sector. Zinc coating is the most effective and economic means to protect the steel substrate exposed to atmospheric corroding environments. It protects the steel substrate by acting as a barrier against the corrosive environment and by sacrificially corroding themselves to provide cathodic protection. Protective ability of galvanised (GI) steel may be enhanced by employing thicker zinc coatings or by painting the metallic substrate [1]. Paints improve the surface life of underlying zinc coating acting as a barrier against zinc reaction with environmental agents. Cracks, crater, and pin holes occurring in the paint are sealed by corroded zinc products. Moreover, corroded zinc products occupy a 20¨C25% more volume than zinc, while iron oxides (corrosion product of steel) occupy a volume several times larger than the steel; thus, expansive forces are reduced at the zinc-paint interface compared to those at the steel-paint one [2]. The main practical problem concerning painting of zinc-coated surface lies in achieving good bond strength, that is, good adhesion of polymer with GI sheet. Often adhesion looks satisfactory immediately after painting, but it prematurely degrades after water, oxygen, and other corrosive ingredients diffuse through the polymeric coating. Several pretreatment processes were reported to improve coating adhesion. The main function of pretreatment for GI steel surface is to form a very stable passive film which will enhance the adhesion with subsequent
%U http://www.hindawi.com/journals/isrn.corrosion/2013/464710/