Effects of Cu-Flash Treatments on Phosphatability of Zn-Fe Alloy Electroplated Steel Sheets
조용균 Yong Kyun Cho , 김영근 Young Geun Kim
Abstract
Bus makers have applied Zn-Fe coated steel sheet to bus outer bodies because of its high corrosion resistance. But it was difficult for the makers to phosphate the bus bodies by themselves because the size of bus body was too big to immerse it in phosphating bath. Therefore. the bus makers have required steel makers to provide Zn-Fe coated steel sheet that was phosphated directly in EGL(Electro-Galvanizing Line). But it was also found to be difficult that Zn-Fe electroplated steel sheet was phosphated in the high speed continuous EGL. because the phosphating time in the process was too short to complete the phosphating reaction. It was observed on this process that the Zn-Fe coated steel sheet could be phosphated perfectly even in as short reaction time-about 3~7 seconds-as EGL by precipitating copper on it before phosphating. Precipitating copper on Zn-Fe coated steel sheet was carried out by dipping the steel sheet for 3~7 seconds in copper solution of about 0.5~1.0g/l concentration. This method. reducing phosphating time by precipitating copper on Zn-Fe coated steel sheet before phosphating was named as Cu-Dash treatment.