Influence of surface hydroxyls on the formation of Zr-based conversion coatings on AA6014 aluminum alloy

This study investigates the influence of surface conditioning on the deposition of Zr-based conversion films on AA6014. For that purpose, different treatments were used to control the formation of well-defined oxides layers with different hydroxyl fractions and similar thicknesses prior to the conversion layer formation process. The elemental distribution and surface chemistry of the treated samples before and after the formation of the Zr-based conversion layer were evaluated by Auger Electron Spectroscopy (AES) depth profiling and X-ray Photoelectron Spectroscopy (XPS). Moreover, the Open Circuit Potential (OCP) evolution as a function of time was recorded during the formation of the Zr-based conversion layers in order to evaluate the electrochemical surface activity and formation mechanism in-situ. The results have shown that a higher initial hydroxyl fraction encourages the formation of a thicker Zr-based layer.