Conductivity and Corrosion Resistance of Mo/Ti/Sn Conversion Coating on 6063 Aluminum Alloy

Abstract

The chromium-free conversion coatings were prepared by adding different contents of Na2SnO3 to solution containing Mo/Ti. The XPS, SEM, EDS, AFM, and Raman were used to characterize the composition and morphology of the coatings. The corrosion behavior of the coatings in 3.5% NaCl solution was investigated using the dynamic potential polarization method and EIS analysis. The Mott-Schottky and UV-Vis were used to determine the properties of coating semiconductor, such as carrier concentration and band gap. The results showed that the main components of the coating were Al2O3, SnO2, MoO3 and MoO2, and the coating presented the double layer structure, including a transition layer close to substrate and a compact layer on the surface. The coating exhibited the properties of a p-type semiconductor. The higher the carrier concentration, the better conductivity, the carrier concentration of added Na2SnO3 increased from 1.143 × 1019 cm-3 to 9.274 × 1020 cm-3, the band gap decreased from 2.281 eV to 2.232 eV. The electrical contact resistance (ECR) value of adding Na2SnO3 is decreased from 0.6187 Ω/in2 to 0.1343 Ω/in2 (in 200 psi).

Keywords: Conversion coating, Electrical contact resistance (ECR), Mott-Schottky, Semiconductor characteristics