Role of Intermetallics and Copper in the Deposition of ZrO2 Conversion Coatings on AA6014

Zirconium oxide based conversion coatings are nickel-free alternatives to trication phosphate coatings. Here, the role of intermetallic inclusions in aluminum alloy AA6014 on the formation of Cu-rich particles inside ZrO2-based conversion layers with a film thickness of 25-30 nm was investigated. The role of the intermetallic inclusions on the deposition mechanism was characterized by varying the immersion time of the substrate and analyzing the coatings by electron microscopy and atomic force microscopy. Statistical analysis on the growth of the copper rich particles showed instantaneous nucleation of these particles, with a subsequent homogeneous in-plane growth at constant height. A strong preferential nucleation of the Cu-rich particles on the intermetallic particles was observed, and was attributed to the cathodic nature of the intermetallics. Raman spectroscopy indicated the presence of crystalline CuO and amorphous ZrO2 in the film. Enhanced layer formation in the vicinity of intermetallic particles was observed. (c) The Author(s) 2014. Published by ECS. All rights reserved.