Cr-free 용액 코팅에 의한 아연도금 강판의 내식특성

Abstract

Chromate surface treatment for galvanized steel sheets is in wide use since it is a low-cost white rust prevention measure. In surface treatment of steel sheets for domestic appliances, chemically surface treated steel sheets and coated steel sheets of high performance are also in wide use in line with the increasing demand for improvement of rust-prevention. Chromate surface treatment requires Cr+6, various measures have been set up in product and manufacturing process for the environment protection. However, strict regulations on the environmental load materials are being followed due to active environmental movements all across the globe. EU research regulates that toxicity of all chemical products, manufactured or imported at least 1 ton a year within EU, be examined and registered before use. China RoHS imposes restrictions on use of 6 materials(Pb, Hg, Cd, Cr+6, PBB, PBDE) within electric and electronic products. In EU RoHS, a regulation related to electronic waste, there are restrictions in effect against certain materials. To meet these regulations, for a replacement of chromating, numerous researches on environmental-friendly rust-prevention techniques are being performed, including Cr+3 chromate, Cr-free, inorganic or organic film coating. To meet the environmental regulations, this study implements Cr-free solution such as acrylic, epoxy, urethane and Si contained organic/inorganic hybrid coating solution for the development and application of environmental-friendly high corrosion-resisting Cr-free coating solution. The most corrosion resisting solution was chosen among the Cr-free solutions. Corrosion resistibility characteristics vs. dry temperature and time was investigated for galvanized steel sheet coated with organic/inorganic hybrid solution formulated by substitution of Si. Corrosion resistibility was performed according to KS D 9502, coating adhesion strength on galvanized steel sheet was performed by cross-cut according to ASTM D3359-09. Coating layer stability was evaluated by precipitation test in acid and alkaline solution. As a result, urethane solution is suitable to improve corrosion resistibility of galvanized steel sheet. It is also revealed that Si added organic/inorganic hybrid solution even improves corrosion resistibility. It is expected that the suggested method in this paper can be applied to electric and electronic parts and general purpose sheet metal as an environmental-friendly surface treatment technique which possibly replaces the conventional chromate surface treatment emitting Cr+6.