Influence of drying temperature on the corrosion performance of chromate coatings on galvanized steel

Abstract

The influence of drying temperature on the corrosion performance of chromate coatings on electro-galvanized (EG) steel has been investigated using electrochemical impedance spectroscopy (EIS) and potentiodynamic measurements in 3.5% NaCl solutions. The chromate coatings were applied to the EG steel in a solution (pH 1.2) containing sodium dichromate and sulfuric acid at room temperature. The coatings were dried in an oven at three different temperatures: 60, 110 and 210 8C. The surface of the chromate coatings was analyzed using atomic force microscopy (AFM) and scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS). The results show that the drying temperature significantly affects the morphology of the chromate coatings and consequently affects their corrosion behavior. The chromate coatings dried at 110 8C had few cracks and the lowest corrosion current. The chromate coatings dried at 60 8C showed passivity. The EIS results show that the chromate coatings dried at 60 8C has the largest impedance in a neutral 3.5% NaCl solution. Drying at higher temperature (210 8C) degrades the chromate coatings by widening the cracks and reducing soluble Cr(VI) in the chromate layer. The favorable drying temperature for the chromate coatings on the EG steel is between 60 and 110 8C.

Effect of nano‐silica on the corrosion behavior of silicate conversion coatings on hot‐dip galvanized steel

“…The corrosion rate of Zn is high due to the large potential difference between iron substrate and zinc layer . It is well known that chromate coatings are very effective anticorrosives and inhibitors with self‐healing property . However, due to toxicity and carcinogenic effects of chromate coatings, there have been extensive efforts in order to find an appropriate alternative for it .…”

Characterization and Corrosion Resistance of Galvanized Steel/Passivation Composite/ Polyurethane Paint Systems

“…1c depicts that despite having a micro-rough surface and homogenous structure, the ZTRI samples also exhibited the characteristics cracks of chromate layers. According to previous reports [82][83][84] during the drying step of the conversion treatment, the chromium-based layer could shrink due to internal tensile stresses causing micro-cracks or fissures to develop, i.e., make it permeable to the zinc dissolution. This consideration is important because the bare ZHEX and ZTRI samples showed localized corrosion during the exposure to 0.05 M NaCl or 0.1 M SO 4 Na 2 solutions.…”

Surface Modification with Phosphate and Hydroxyapatite of Porous Magnesium Scaffolds Fabricated by Binder Jet Additive Manufacturing

“…As there is still excess liquid upon applying the stock solution on the sample's surface, removing an excess solvent is necessary. Variations in drying temperature have been known to influence the corrosion protection properties of coatings due to the potential to form microcracks at high drying temperatures [50]. To investigate the influence of drying temperature on the corrosion properties of the applied HA coating, the dense Mg-Zn-Zr samples were coated with the same stock solution of HA and dried at temperatures of 25 • C, 40 • C, 55 • C, and 100 • C. Similarly, differences in the composition of the initial stock phosphate solution prior to the application of the conversion coating are known to induce variations in the properties of the final coated samples [27,28].…”