Zr and Zr-Cr Commercial Conversion Coatings Deposited on 3003 Aluminium Alloy Foil

The study aimed to study the formation and characteristics of commercial zirconium conversion coatings referred to as MAVOMcoat MC1300 (Zr-Cr-based coating) and MC1700 (Zr-based coating) on chemically pre-treated aluminium alloy 3003. Conversion times varied from 80 s to 45 min. After deposition, the samples were subjected to three post-treatments: air drying for 15 min, air drying for 24 h, and immersion in 3.5 wt% NaCl solution for 24 h. Corrosion resistance was evaluated using electrochemical measurements, whereas scanning electron microscopy with energy dispersive spectroscopy and X-ray photoelectron spectroscopy were employed for surface analysis. Based on the evaluation of corrosion parameters, the optimal conversion times for MC1700 and MC1300 were determined to be 10 min and 7 min, respectively. The conversion coatings MC1700 and MC1300 were characterised by distinct elemental compositions, with the former predominantly comprising Zr, O, Al and F, and the latter Zr, O, Al, Cr and F. Notably, the thickness of coatings was between 10 and 170 nm, depending on the type of coating and location (matrix or intermetallic particles). The 24-hour immersion of MC1700 ZrCC in 3.5 wt% NaCl led to progressive build-up of Zr oxide and release of fluoride from the coating.