Effect of annealing procedure on phase formation in zinc magnesium alloy coatings on steel sheets

Abstract

Zinc magnesium alloy coatings on steel sheets have excellent properties regarding the corrosion protection both in case of painted and unpainted state. The preparation of the zinc magnesium coatings was done by physical vapor deposition using an inline vacuum coater for sheets and metal strips. About 650 nm thick magnesium layers were deposited onto hot-dip galvanized steel sheets followed by a short-time heat treatment. The effect of annealing procedure on the diffusion behavior of the magnesium into the zinc layer was systematically investigated in the temperature range between 300 and 400 deg C. The composition depth profiles after the annealing procedure were determined by glow discharge optical emission spectrometry (GD-OES). In dependence on the annealing temperature the formation of intermetallic phases MgZn2 and Mg2Zn11 could be identified by X-ray diffraction (XRD). The development of microstructure with increasing annealing temperature was characterized by SEM investigations on metallographic cross-sections