Study of the composition and structure of zinc-nickel coatings deposited from weakly acidic electrolytes at iron sublayer

Zinc-nickel alloy coatings have great advantages over many monometallic coatings. However, their use in practice is limited due to the complex mechanism of processes that is studied insufficiently. The paper is devoted to the investigation of the electrolysis parameters on zinc-nickel coating composition and structure during еlectroplating at the iron underlayer of copper substrate from weakly acidic chloride electrolyte. The chemical composition of the electrolyte was monitored by dichromatometriс and complexometric titration. Study of phase composition was performed using an X-ray diffractometer Rigaku Ultima IV. Gross composition was measured using a scanning electron microscope JEOL JSM-6460LV. It was found that аn increase of the current density increases the rate of deposition of the alloy. Increase of temperature leads to an increase of the proportion of nickel in the alloy, and an increase in the nickel deposition rate. Zinc deposition rate is not affected by temperature. Moreover, an abnormal codeposition of the alloy was observed in the entire investigated range of temperatures and current densities. As the temperature changes, The surface of the micro-relief changes with increasing temperature, the grain size becoming smaller and the surface smoother. X-ray analysis of the coatings showed that they are a homogeneous nickel-base solid solution. Сoating structure corresponds best to the face-centered cubic lattice.