Surface Protection of the Steel Sheet with Zn-Fe Alloys
The Zn-Fe layers are recommended in automotive industry and in the adders for the following qualities: a better weldability than the zinc-coated plates, very good capacities for painting and lacquer wear resistance, good adherence, lower zinc consumption by layer thickness below 100g/m2. Important transformation of phases takes place during heating of galvanized parts due to mass transfer iron in the zinc layer and Zn-Fe alloy is formed. Galvanized steel samples were heated 10-30 sec. at 500-650oC. Heat treated samples were metallographic ally examined and X- ray diffraction tested with a view to establish structural and chemical composition change due to heat treatment. As a result of microscopic examination (both optical and electronic) and X-ray diffraction testing in coating layer were detected phase ratio changes, according to heat treatment parameters. Considering that the physico-chemical and mechanical properties differ for the two phases and phase ratio is to decide the properties of the product; these structural changes are of great importance in practice. The desirable coating would be a Zn-Fe coating with 8-10% Fe (according to some authors, up to 12% Fe), with a structure consisting mainly of phase and a small quantity of phase. The mathematical correlation between diffusion phenomena occurring in layer, depending on temperature and time of heat treatment, and iron content of coating are presented.
Luís Guerra ROSA and Fernanda MARGARIDO
T. Radu et al., "Surface Protection of the Steel Sheet with Zn-Fe Alloys", Materials Science Forum, Vols. 636-637, pp. 985-990, 2010