Development of TSA anodized/MnVO sealed coating using a statistical approach for Al 7075 alloy and a study of its corrosion behaviour

• Published in: Surface & coatings technology 2020-11, Vol.402, p.126316, Article 126316
• Main Authors: Dhanish, S., Yoganandan, G., Balaraju, J.N.
• Format: Article
• Language: English
• Subjects: Aluminum base alloys; Anodization; Anodizing; Central composite design; Corrosion; Corrosion currents; Corrosion resistance; Corrosion resistant alloys; Corrosion tests; Electrochemical impedance spectroscopy; Optimization; Parameters; Photoelectrons; Protective coatings; Raman spectroscopy; Response surface method; Response surface methodology; Spectrum analysis; Sulfuric acid; Sulfuric acid anodizing; Taguchi; Taguchi methods; Tartaric acid; X ray photoelectron spectroscopy
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126316

In this work we propose a statistical approach which optimizes the operating parameters of tartaric sulfuric acid anodizing (TSA) and MnVO oxyanion sealing on Aluminium 7075 alloy. Here we used Response Surface Methodology and Taguchi Design to find an optimum condition for the surfaces with maximum corrosion resistance. This manuscript aims to provide a mathematical model which correlates coating thickness to anodizing parameters like voltage, temperature, sulfuric acid concentration, agitation, duration and tartaric acid concentration. Such combinatory approach has not been introduced or reported till now in optimizing the sealed anodic oxide layer to exhibit improved corrosion resistance. The surface of optimized TSA-MnVO sealed anodized coatings qualified 1000 h of salt spray exposure. The optical microscopic images clearly show the coating has excellent barrier and self-healing corrosion resistance behaviour in NaCl environment. The X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy of sealed anodized surface confirmed the presence of polymerized decavanadate species. The electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization test results revealed the resistance value of the coating is >15 MΩcm2 and corrosion current density (icorr) value of 4.5 nA/cm2 respectively, indicating excellent protective behaviour of the optimized coating in aggressive chloride environment. [Display omitted] •Anodization parameters in TSA electrolyte are optimized using CCD.•A model correlating coating thickness to anodizing parameters has been developed.•MnVO sealing parameters are optimized using Taguchi.•Significant anodizing and sealing parameters have been identified.•Statistically optimized conditions were validated through characterization studies.