The influence of Cr(lll)-based conversion layers on the corrosion resistance of Zn and nano-composite Zn in chloride containing solutions

摘要

In view ot the increasing demand tor novel galvanic coatings with superior performance, compared to the traditionally applied ones, this paper reports on the corrosion behaviour of innovative nano-composite Zn coatings, studied in parallel to conventional galvanic Zn in chloride-containing environment. Further, with relevance to the necessity of substituting Cr(VI) conversion layers with eco-friendly such, the properties of Zn and nano-composite Zn coatings, treated and not-treated with a Cr(lll) conversion layer (so called "green passivation") were investigated. The electrochemical behavior of all investigated coatings was determined via Electrochemical Impedance Spectroscopy (EIS), Potentio-dynamic polarization (PDP) and Scanning vibrating electrode technique (SVET). Morphological observations (after treatment) and surface analysis (EDX and XRD) were performed as well. For the hereby investigated time intervals of 2h to 240h, the best corrosion performance was recorded for the nano-composite coating. The chromated coatings (both pure Zn and composite Zn) exhibited increased corrosion resistance within the initial time intervals, whereas perform similarly to Zn later on. For the final stage of 240 h, the composite and chromated Zn coating is with higher corrosion resistance than the pure galvanic and chromated galvanic Zn.