Effect of production parameters on the structure and corrosion resistance of hot-dip galvanized coating

In this research, effects of some production parameters such as lead content of the zinc bath, jet wipers distance from sheet surface and galvanizing line speed on corrosion behaviour and structure of hot-dip galvanized coating produced in Mobarakeh Steel Company was investigated. Lead content of the zinc bath was changed in the range of 0.01 to 0.11Wt.% and its effects on the texture and corrosion behaviour and spangle size was studied. Coating texture was determined using X-ray diffraction and Corrosion behaviour of the coating was analyzed employing salt spray and Tafel polarization test. Then, influences of increasing the lead content of the zinc bath, variations of jet wipers distance from the sheet surface and galvanizing line speed on the coating structure were assessed. Results showed that increasing the lead content of the zinc bath, has decreased the relative texture coefficient of basal component and conversely, has increased the relative texture coefficient of high angle pyramids, low angle pyramids and prism plane components. Also, it was discerned that increasing the lead content of the zinc bath would result in the increase of spangle size and number of dull spangles in the surface. After investigation of the effects of increasing the lead content of the zinc bath, increasing the jet wipers distance and decreasing the galvanizing line speed, it was found that gamma layer thickness, the detrimental layer for corrosion resistance and formability, has been increased.