Enhancing delamination resistance and corrosion protection of an acrylic topcoat on low-carbon steel via silicate/tungstate post-treatment of Zr-based conversion film
Journal
Surface and Coatings Technology
Journal Volume
518
Start Page
132886
ISSN
02578972
Date Issued
2025-12-15
Author(s)
Abstract
Organic coatings are widely utilized for the corrosion protection of metals; however, their performance is strongly correlated with the stability of the interfacial film between the metal and the coating. For the applications that require high corrosion resistance, a conversion coating and an organic topcoat are essential to improve the overall protective system. Traditional conversion treatments, such as phosphate and chromate, pose significant environmental and health risks. Phosphate discharge can lead to eutrophication, while chromate treatments involve carcinogenic hexavalent chromium, which has been restricted or banned by international regulations. In this study, the use of a zirconate conversion coating, followed by a post-treatment with tungstate or silicate solutions and a subsequent organic topcoat, was investigated as an environmentally benign alternative. The results demonstrated that the steel specimens subjected to silicate or tungstate post-treatment exhibited a significant reduction in corrosion-induced defects during salt immersion tests and a marked increase in polarization resistance, with the low-frequency impedance modulus enhanced by approximately two orders of magnitude, in electrochemical impedance spectroscopy (EIS) analysis. To investigate the enhancement in delamination resistance, artificial scribes were introduced on the coated specimens and subjected to salt spray test at various temperatures. It was observed that coating delamination around the scribe was significantly inhibited by both tungstate and silicate post-treatments, with the delamination distance being reduced to approximately one-third of that observed on untreated specimens. A comparison between the two post-treatments on intact coatings revealed that a visibly smaller macroscopic corrosion area was present on the tungstate-treated specimens in the salt spray test, indicating superior corrosion protection performance over the silicate post-treatment.
Subjects
Conversion coating
Corrosion resistance
Delamination
Post-treatment
Publisher
Elsevier B.V.
Type
journal article