IMPROVEMENT METHOD OF CORROSION RESISTANCE OF PLATING FILM

摘要

PURPOSE: To improve corrosion resistance of plating film of hot dip alloy coated steels without phosphate treatment or primer coating. CONSTITUTION: The method is characterized in that after a steel sheet is hot dip galvanized at 440 to 500 deg.C for more than 3 minutes, the hot dip galvanized steel sheet is dipped in an alloy coating bath containing 5 to 15 wt.% of Al, 0 to 1 wt.% of Si and 0 to 1 wt.% of Mg for 1 minute so that the thickness of Zn coat is greater than 20 micrometers.