Cr-free 코팅액을 사용한 아연도금 강판의 내식성 향상에 대한 연구

Abstract

The life time of much steel structure can be remarkably improved by protecting the steel with zinc layers. However, also the zinc coating can be involved by corrosion phenomena with the consequence that some steel surface is unprotected. The reduction of the corrosion rate of zinc is therefore an important topic. These results can be obtained by introducing zinc alloys with lower corrosion rate (ZnNi, ZnFe, etc.) or by protecting the zinc surface with organic or inorganic layers able to reduce the corrosion rate. In the past a very popular way to reduce the corrosion rate of zinc was the use of chemical conversion layers based on Cr6+, able to increase the passivation tendency of the zinc (chromating). This procedure is quite effective also for improving the adhesion of organic coatings deposited on the zinc surface, but there is the important problem that the use of chromium salts is now restricted because of environmental protection legislation. It is therefore very important to develop new zinc surface treatments environmentally friendly to improve the corrosion resistance of zinc and the adhesion with the final organic protective layer. In this study, acrylic, epoxy and urethane (S-700) solutions were carefully scrutinized for base material of coating solution to replace chromate. According to result of salt spray test of 72 h, performance of Urethane coating solution was the most excellent. And the result shows that the corrosion resistance of the S-700 (only Urethane 20%) coated specimen at 190 ℃ for 5 minute is superior more than the other heat treatment conditions. Added Si coating solution (LRO-317 : Si polysilicate 10% + Urethane 10%) has an effect more than S-700 coating solution. Also, the corrosion resistance of the LRO-317 coated specimen at 190 ℃ or 5 minute is superior more than the other heat treatment conditions. In addition, the S-700 and LRO-317 coating solution showed excellent adhesion with galvanized iron. The hot dipped galvanized iron (HDGI) showed good acid/alkali resistance than electronic galvanized iron (EGI).