Zirconium conversion coating (ZrCC) was prepared on aluminum-manganese alloy AA3005 by immersion in 200 ppm of H₂ZrF₆bath for 10 min at room temperature. Potentiodynamic polarization curves and electrochemical impedance spectra were measured up to 10 and 40 days, respectively, in 0.5 M NaCl solution. Microstructural characterization of samples was carried out using scanning electron microscopy equipped with energy dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, focus ion beam microscopy and transmission electron microscopy. The coating had a tri-layer structure with a thickness of 200 nm in the proximity of intermetallic particles and 30 nm far from intermetallic particles at the coating matrix. Electrochemical measurements showed that the corrosion resistance of ZrCC on AA3005 was improving during immersion in NaCl solution, i.e., impedance value at low frequency increased with immersion time reaching the average value 8.5 ∙ 10⁶Ω∙cm²at 3 mHz after 10 days immersion. Microstructural and compositional characterization showed that this behavior is related to the change in composition and structure of conversion coating including a transformation of ZrF₄/ZrO_xF_yto ZrO₂· 2H₂O_(s)and formation of Al(OH)₃in the top layer of ZrCC, respectively, accompanied by the change in thickness of individual layers within the coating.

Zirconium conversion coatings prepared in a 200 ppm H₂ZrF₆ bath for optimal conversion times, were applied on aluminium alloys starting from AA1xxx up to AA7xxx series. The electrochemical behaviour and self-sealing abilities of the coatings were studied by electrochemical impedance spectroscopy during their immersion in 0.5 M NaCl for five days. Microstructural and surface characterization were carried out using scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry techniques. All zirconium conversion coatings had a bi-layer structure, with average thickness in the range of 30–60 nm, except for the coating applied on alloy AA2024 which exhibited a single-layer structure with a thickness of 12 nm. The coatings provided excellent corrosion protection and self-sealing behaviour when applied on AA3005, AAA356.0, and very good corrosion protection for AA380.0, AA5754 and AA1050A. On the other hand, these coatings did not provide adequate corrosion protection for AA2024 and AA7075. The results were discussed in terms of the role of intermetallic particles on the properties of the conversion coating.

The morphology, composition and corrosion properties of commercial hexafluoro-zirconate trivalent chromium coatings (SurTec^® 650) deposited on chemically cleaned aluminum alloy 3003 were studied. The coatings were deposited at room temperature using different concentrations of SurTec^® 650 (10, 25 and 50 vol.%) and different conversion times (90 s, 11 min and 18 min). Scanning electron microscopy with energy dispersive X-ray spectrometry, X-ray photoelectron spectroscopy and time-of-flight secondary ion spectrometry were employed to investigate the surface morphology, composition and thickness of uncoated and coated AA3003 samples. The morphology of the coating varied from uniform nodular to non-uniform and cracked; coatings were deposited at intermetallic particles and at the alloy matrix. The main constituents of conversion coatings were Zr(IV) and Cr(III) oxides; in addition to oxides, fluorides were also formed. The corrosion properties were investigated in two solutions: more aggressive sodium NaCl and less aggressive simulated acid rain. These commercial conversion coatings exhibited a good corrosion resistance but only after longer immersion in solution, i.e., 24 h. The results reveal an interesting behavior of zirconate-based coatings on aluminum-manganese alloy.