Cailiao Baohu (Feb 2024)
Effect of Phosphating Current Density on Microstructure and Adhesion Strength of Electrochemical Phosphating Film on A286 Alloy
Abstract
The surface of A286 alloy easily undergoes passivation， making it difficult to deposit a phosphating film on surface of A286 alloy using the traditional chemical phosphating method.However， electrochemical phosphating can avoid the inhibitory effect of the passivation film on the phosphating reaction.Therefore， studying the influence of phosphating current density on the microstructure and properties of the phosphating film is necessary.In this study， a compact phosphating film with high film-base adhesion strength was formed on the surface of A286 alloy using electrochemical phosphating for the first time.The potential-time (φ-t) curves of the phosphating process under various current densities were mapped using an electrochemical workstation to examine the characteristics of the growth process of electrochemical phosphating films.The microstructure and morphology of the phosphating film were observed using a scanning electron microscope (SEM).Using an energy dispersive spectrometer (EDS) to analyze the chemical composition of different areas of the phosphating film.X-ray diffraction (XRD) was employed to study the phase structure of the phosphating film， and the adhesion strength between the phosphating film and substrate was measured using a scratch tester.Results showed that the deposition mode of the electrochemical phosphating film on A286 alloy occurred through layer-by-layer growth stacking.At low current densities， the phosphating film was formed as a single Hopeite phase with a coarse and loose structure， and the bonding force between the film and the substrate was about 6 N.As the phosphating current density was increased， the phosphating film gradually transformed into a Zn＋Hopeite multiphase， resulting in a refined and dense microstructure， and the adhesion strength between the film and substrate was improved.At a cathode current density of 160 mA/cm2， the bonding force between the membrane and substrate exceeded 60 N.Generally，the increase in phosphating current density was found to be beneficial for the densification of the electrochemical phosphating film and enhanced both the adhesion strength between the film and substrate and wear resistance of the film.
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