Study of strip-shaped chromatic aberration defects on the surface of an electro-galvanized fingerprint-resistant sheet

Strip-shaped chromatic aberration defects on the surface of an electro-galvanized fingerprint-resistant sheet were systematically studied using Thermo-Calc thermodynamic calculations,scanning electron microscope and X-ray diffractometer analyses,and rapid heat treatment simulation technology.The formation mechanism of these defects was also analyzed.The results show a strong correlation between the defects and the uneven distribution of the Fe(001)component on the surface of the steel substrate.The relatively high proportion of Fe(001)components on the surface of the steel substrate affects the distribution density of the Zn crystal cells in different orientations during the electrodeposition process,which causes the reflection intensity of the light of the galvanized layer to differ from various visual perspectives,and macroscopic strip-shaped chromatic aberration defects are finally formed.The high proportion of the Fe(001)component on the surface of the steel substrate is mainly related to the following two factors.First,when the strip steel is hot-rolled,the finishing hot-rolling temperature is close to theγ→αphase transition temperature.When the local temperature on the upper surface of the strip steel is low,γ+αtwo-phase rolling easily occurs,and this results in an uneven stress distribution between theγandαphases after the hot-rolling process.This uneven distribution of hot-rolling stress results in the formation of a coarse grain structure in the local area on the surface of the hot-rolled sheet,which strongly affects the subsequent cold rolling and annealing process,and the annealed steel sheet substrate ultimately contains a greater proportion of the Fe(001)component.And second,a fast cooling rate(>10 K/s)during the slow cooling stage in the continuous annealing process inhibits the transformation of the Fe(001)to the Fe(111)component on the surface of the cold-rolled steel sheet,and it is then not possible to effectively eliminate the influence of the unevenly distributed Fe(001)component on the surface of the annealed steel sheet(originating from the uneven hot-rolled microstructure).This uneven distribution of the Fe(001)component on the surface of the annealed steel sheet following the continuous annealing heat treatment has a strong effect on the electrodeposition behavior of the Zn crystal cell in the subsequent electroplating process and the formation of macroscopic strip-shaped chromatic aberration defects on the surface of electro-galvanized fingerprint-resistant sheet.

Corrosion Protection of Electro-Galvanized Steel by Green Conversion Coatings

A A cerium-based chemical conversion process was studied. First, zinc coating obtained from a free-cyanide alkaline bath, with derivative of imidazol with new brightener, was investigated, zinc-plated steel specimens were treated with a solution of 50 mmol· L^-1 Ce（NO3 ）3 The corrosion behavior of bare and treated mild galvanized steel was evaluated during exposure to 0.5 mol · L^-1 NaCl for different immersion time, using Tafel polarization curves and electrochemical impedance spectroscopy （EIS） measurements. The surface morphology of the coating was studied using scanning electron microscopy （SEM）. The composition and chemical percent of the coating were examined by X-ray dispersion energy （EDAX）. The results of these measurements showed that the newly developed cerium-based conversion coating process was a promising candidate for replacing the conventional chromate treatments used at present for galvanized steel.