Galvannealed

Galvanneal steel is an important material widely used in the production of automobiles. The accurate determination of temperature of galvanneal sheet during manufacture is a critical problem, which has recently been addressed with fluorescence thermometry. In the galvanneal process, steel strip is dipped into a zinc... 

Manges, W.W. Allison, S.W. Vehec, J.R. Galvanneal thermometry with a thermographic phosphor system. Iron Steel Engineer 1997, 74 (12), 33-36. 

While the adsorption theory is the most accepted one, mechanical interlocking comes into play in case of substrates with a special kind of roughness such as galvannealed steel where the liquid can spread into cavities and thereby interlock with the substrate. The diffusion theory does not play an important role for polymer-metal interfaces. The contribution of the electrostatic theory is not easy to estimate. However, the electrical component of the adhesive force between the planar surfaces of solids becomes important if the charge exchange density corresponds to 10 electronic charges, meaning about 1% of the surface atoms [71]. 

Surface or interface friction is an important characteristic that affects the formabil-ity of sheet metal products. Sheets and tooling surface characteristics, deformation behavior, and the lubricant are reported to play important roles affecting the surface friction conditions [49]. Recently, increased attention has been given on reducing the surface friction for enhancement in formability of sheet steel products through the application of solid-film lubricants or special po.sttreatments such as phosphates, Cr/CrOx, and so forth on top of electrodeposited zinc or galvannealed Zn-Fe-alloy-coated surfaces [56]. 

Iron can be beneficial in coatings. The iron-zinc alloys formed in hot dipping or sherardizing can be up to 30% more resistant in mildly acidic conditions, but some workers report lower corrosion resistance with some galvannealed coatings. The iron-zinc alloy layers, while continuing to protect... 

Akerdida and Lyon (1988) incidentally used continuous immersion potentiodynamic polarization tests, and weight loss and ac impedence tests, in intermittent immersion to compare heat-treated (45 min at 450°C) and nonheat-treated coatings in 0.6 M NaCI. They found that the galvannealed coatings (in 8-day tests) corroded twice as fast in intermittent immersion in the NaCl solution. Analysis by ac impedence indicated that a passive film probably consisting of zinc hydroxy compounds was more effective on zinc than on the iron-zinc alloy. 

Jagannathan, V. (1992). The influence of coating characteristics on the powdering and corrosion resistance of galvannealed coated steel sheet. Galvatech 92, Verlag Stahleisen, Diisseldorf, Germany, pp. 127-131. 

Nomi, R., and Fukii, S. (1991). Galvanneal and organic composite coatings. Steel Times, 219(9), 490 91. 

This method requires a preliminary step followed by thermal treatment and diffusion of the coating metal into the substrate. A commercial material known as galvannealed steel is made by coating steel with zinc followed by heat treatment and the formation of an iron-zinc intennetalUc coating by diffusion. 

One additional attribute of metallic coatings, although not typically the only reason for their use, is their suitability to the application of paints. Metallic coatings, such as the iron-zinc coating galvanneal, have a high degree of surface texture, which enhances paint adhesion compared to a relatively smooth steel surface. 

Electroplated zinc (30 g/nf), phosphate B Electroplated zinc (70 g/m ), phosphate B Hot dip galvannealed (5-9 g/m, phosphate B Hot dip galvannealed (67 g/m ), phosphate B Electroplated zinc/nickel (18 g/m, phosphate B Electroplated zinc/nickel (44 g/m ), phosphate B Cold-rolled steel, phosphate B Cold-rolled steel, no phosphate Cold-rolled steel, phosphate A Hot dip galvanized (108 g/m ), phosphate A... 

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