Properties of galvanized and galvannealed high strength hot rolled steel

Using newly developed hot strip mill technology, it appears that flat rolled sheet with a thickness greater than 1.5 mm can be produced more economically by hot rolling instead of cold rolling. Moreover, due to their desirable combination of ductility and strength as well as their potential for yield improvement, high strength hot rolled steels are outstanding candidates for automotive structures. The objectives of this work are to develop process windows for the production of high quality galvanized and galvannealed coating on high strength hot rolled steel coupons designed for automotive applications. Consequently, precipitation-strengthened hot rolled steels were both galvanized and galvannealed and the coating quality as well as the mechanical properties were determined. It was found that the galvanized coupons exhibited a good coatability in terms of reactive wetting and coating quality while achieving the target mechanical properties. Analysis of the coating cross-section exhibited an inhibition layer rich in Mn, due to the reaction between the Mn oxide layer and the Al dissolved in the zinc bath. In addition, the investigation of the galvannealing processing window allowed the formation of a well-developed galvannealed coating.