Morphology and corrosion behavior of ZnO passive films for galvanized steel applications: effects of anodizing parameters

Abstract

In this study, anodic ZnO films have been potentiostatically fabricated on galvanized steel surfaces in mixed electrolytes of NaOH, KOH and Ca(OH)2. The anodization parameters were varied in the ranges: applied voltage 5–30 V, controlled temperature 5 °C–35 °C, and anodizing time 15–60 min. Effects of the anodizing parameters on the properties of anodic ZnO films deposited on galvanized steel were evaluated using x-ray diffractometer (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), measurements of water contact angle (WCA) and anodic film thickness. In addition, the synergistic effect of parameter-dependent surface characteristics of anodic films on short-term and long-term corrosion resistant was also investigated. The results showed that all anodic films formed were composed of crystalline ZnO. Transparent colorless anodic films were deposited at 5 V whereas transparent yellowish films at 20 V. Black anodic ZnO films were developed at 10 V, and these serve as effective corrosion barriers that greatly improved (2–5 fold) the corrosion resistance of galvanized steel. Among them, the optimal protection was found in the black anodic ZnO film fabricated at 10 V under 25 °C for 30 min. It was found that surface chemistry, morphology, wettability, and film thickness were important for the longevity of an anodic film. The main aim of this study is to understand the anodization of galvanized steel, which can provide controllable surface properties and wettability to ZnO anodic films by manipulation of the anodizing parameters.