Study Of Process And Corrosion Mechanism Of Hot-dip Galfan Coating

Galfan coating can significantly improve the corrosion resistance, adhesion and appearanceof the steel material. Hot-dip process by flux method is simple, low cost and versatile. The singlehot dipping process, coating microstructure and corrosion resistance of hot-dip Galfan on thestructure steel were studied.Firstly, the orthogonal test and control variables were used to research the main processparameters affecting the coating quality. The coating gradually became thick with the hot-diptime increase, the thickness was almost stable at20to30μm after25s. The coating had goodquality at85s. The thickness of coating decreased with the drying time. The coating surface hadgood quality at5min under220℃, also the thickness increased at the same time. As the hot-diptemperature elevated, the coating thickness was decreased which is32μm under450℃. Thecoating surface could also have good quality under450℃.In addition, the effects of adding Mg and wet blasting process were discussed for coatingquality. Adding0.2%wt. Mg, although the surface quality was inferior, the corrosion resistancewas improved because the transition and Galfan coating became thick. Mg was uniformity in thecoating as the form of MgZn2. Although wet blasting process had a certain influence on surfacefinish and corrosion resistance of the coating, it suppressed the growt.h of the transition layer,the coating was toughened.The transition layer between the Galfan alloy layer and matrix prepared with the fluxmethod was much thinner than that with the double hot dipping. Al mainly concentrated in thetransition layer. Galfan alloy plating was a typical lamellar zinc aluminum eutectic structure. Nocompounds were found obviously between the overlay and matrix. As the extension ofimmersion plating time, hot dip Galfan alloy transition layer was gradually transformed fromFeAl3into Fe2Al5. The transition layer was loose granular structure. The corrosion of coatingbegan with intergranular corrosion which gradually evolved to uniform corrosion. The beginningproducts of the corrosion were Al2O3and ZnO, later products were complex products asZn6AlO9, Zn5(OH)8Cl2H2O.