EDS + EBSD Phase Analysis of the Zinc Coating Formed on Steel in a Melt with Nickel Microadditives

We study the structure of a zinc coating on steels with a silicon concentration of 0.02, 0.06, 0.20, and 0.67 wt %. The coating is applied by dipping into a pure zinc melt and in a zinc melt with 0.05 wt % of nickel for 5 min at a temperature of 450°С. The features of the morphology of the ζ phase of the coating are found depending on the silicon concentration in the steel. With a silicon concentration of 0.06 wt %, the ζ phase is presented by branched dendrites growing to the surface. This leads to the so-called "Sandelin effect", when the coating thickness is not the same over the entire surface of the substrate. On high-silicon steels (with a silicon concentration of 0.67 wt %), the ζ phase consists of large crystallites and makes up 90% of the entire coating thickness. Growth of the coating phases is effectively suppressed by alloying the zinc melt with nickel in an amount of 0.05 wt %. We find a change in the structure of the individual phases of the coating upon alloying the zinc melt. Energy-dispersive microanalysis revealed coating areas with a jump in the nickel concentration up to 0.33 wt %. Interpreting the Kikuchi patterns shows that the initial structural type of the ζ phase of the coating is kept for all steels and corresponds to the FeZn13 intermetallic compound with a monoclinic crystal lattice, in which 0.30–0.33 wt % of iron is replaced by nickel. A finely dispersed mixture of phases is found in the coating on high-silicon steel, located between the crystallites of the δ phase and ζ phase with an increased concentration of silicon (0.61 wt %) and nickel (0.2 wt %). The coincident Kikuchi patterns and the small values of the average angular deviation confirm the detection of Fe3Zn10, FeZn13, and Ni2Zn3Si intermetallic compounds.