Abstract
New zinc alloy coated steel sheets have been developed by continuous vapor deposition apparatus.
In a deposition chamber, zinc and alloying metal were evaporated individually by Electron-Beam (EB) irradiation, and were deposited on steel strip continuously.
Some properties of Zn-Al, Zn-Cr, Zn-Mg, Zn-Ni and Zn-Ti alloy coated steel sheets were investigated. Crystal orientation of these coatings was affected by alloying metals. Depth profiles of alloy composition in Zn-Al and Zn-Mg coatings are almost uniform. The other coatings had double-layered structure, composed of an intermetallic compound layer and a zinc rich layer. The intermetallic compound phases were not the same as those shown in a equilibrium phase diagram for binary alloys.
Corrosion resistance of Zn-Mg alloy coated steel without painting is excellent in salt spray test. Corrosion product layer of this coating consists of only ZnCl2·4Zn(OH)2 without ZnO and c-axis of hcp structure of ZnCl2·4Zn(OH)2 was parallel to the direction of the film growth.
Mg ion dissolved from the coating during corrosion seemed to play a role to form this corrosion product layer.
