Corrosion Resistance and Adhesion of Paint Coating Film on Zn-Mg-Al Hot-Dip Galvanized Steel Sheets

Zn-Al-Mg alloy galvanized steel sheets have excellent corrosion resistance and improved cut-edge corrosion resistance. Most of the galvanized steel sheets used for outdoor applications are coated again on the galvanizing layer, or after a plastic film is laminated. As the corrosion products formed by the corrosion of Zn accumulate over time, the painting film blisters and peels, which causes a significant reduction in the value of the product. In this study, the coating adhesion and corrosion resistance of a Zn-Al alloy galvanized steel sheet with Mg added were evaluated by the salt spray test. The deterioraion of the coating film was also evaluated by Electrochemical Impedance spectroscopy(EIS) measurement. A quantitative evaluation of the coating film adhesion following water penetration between the plated layer and coating film under constant temperature and humidity condition was carried out using a Scanning Kelvin Probe(SKP). Key words: Zn-Al-Mg hot-dip galvanized steel sheets, paint coating film, corrosion, salt spray test, adhesion