The Studies Of Zn-Fe Alloy Anomalous Co-deposition Behavior And Preparation Of Cerium Conversion Coating

Metal corrosion has brought the human society huge economic loss and social harm, so the protection of metal is relative to the sustainable development of national economy. The beginning of metal corrosion process occurs in the interface between metal and corrosion medium, so we can slow or even prevent the occurrence of corrosion via a treatment of the metal surface, and then further expansion of the corrosion is also been restrained. As one of the surface technologies, electroplating is one of the most effective methods for metal protection.Zinc-based coating is most commonly used in steel's protection. Its protection performance is concerned with the composition, organization, phase structure, surface morphology and so on, which is determined by electroplating solution and electroplating process.Electrochemical methods is used to study the influence of [Fe2+]/[Zn2+], deposition current, deposition voltage, other metal ions and additive agents on the composition and structure of alloy coating. Some conclusions are obtained according to the experiments. Such as iron content of alloy coating increases when [Fe2+]/[Zn2+] increases. Deposition current and deposition voltage influence the coating's composition and structure. Ce3+ in the electroplating solutions can make the alloy coating more homogeneous.Ternary alloy coating is obtained in the solutions, which contains Zn2+, Fe2+ and Ni2+. And then the surface morphology is characterized by SEM, coating structure is characterized by XRD, anticorrosion performance is characterized by electrochemical methods and immersion test. It is found that the Zn-Fe-Ni ternary alloy coating with a certain composition and structure has a better performance on anticorrosion than that of a Zn-Fe or Zn-Ni binary alloy coating. Zinc-based alloy is often passivated by chromate. But chromate is toxic, so its use has been limited with the enhancement of environmental awareness among the people. As a green and environment-friendly surface technology, cerium conversion coating treatment technology has received more and more attention. Cerium conversion coating is obtained on the surface of Zn-Fe alloy coating by immersing samples to the solution that contains Ce3+. The influence of several main factors (CeCl3 concentration, H2O2 concentration, immersion time) on the protection performance parameters is also studied by electrochemical methods. The optimal reaction condition for the preparation of cerium conversion coating is obtained by Latin orthogonal design experiment. That is CeCl3 concentration 10g/L, H2O2 concentration 13mL/L, immersion time 1h.