Evolution of zinc coatings during drawing process of steel wires

Abstract

The paper shows a significant influence of the multi-stage wire drawing technology on deformability and phase transformations in the zinc coating. SEM tests proved that the coating after hot-dip galvanizing consists of a number of thin layers, ranging from 1 to 5 µm, and differing in thickness, chemical composition and properties. When pulled through the drawing die the zinc coating heats up (as a result of friction between the material and the tool) and its dynamic plastic deformation. It resulted in the fracture and partial crushing of the hard-intermetallic phases. It has been proven that as the wire passes through successive drawing dies, the coating is thinned and diffusion as well as phase remodelling of individual structural components occurs; in the place of phase ζ, the intermetallic phase δ1 develops, increasing its share in the diffusion layer. The crystals of intermetallic phases located on the border of the diffusion and outer layers break up and remain dispersed in the zinc. An analysis of the microhardness of the coating has proven that the level of the increase in the microhardness of the zinc coating is contingent on percentage of iron in particular layers of coating.

Corrosion Rate of Steel in Liquid Zn, Zn-Bi and Zn-Sn Baths

“…The coatings obtained in this process constitute an effective and economical anti-corrosion protection, providing both a barrier and sacrificial protection to steel [2]. Therefore, the use of hot dip galvanizing is constantly growing, covering a new range of products made of iron alloys with a complex chemical composition, including iron castings [3], heat-treated high-strength steels [4] or wires intended for high-speed drawing [5].…”