The influence of cathodic θ-Al2Cu intermetallic geometry on the localized-corrosion-triggered conversion coating deposition

Abstract

Micro-galvanic activity between the cathodic intermetallics and the anodic matrix in an aluminium alloy drives the localized deposition of cerium conversion coatings. It is at the cathodic sites that conversion coating deposition is initiated due to the local pH gradient created because of cathodic reduction reaction over them. The intermetallics’ chemical, electrochemical and geometrical properties critically influence the deposition, but very little is empirically known about the latter. With the objective of understanding the effect of intermetallic geometry, this work looks closely into the deposition on nearly 550 eutectic θ-Al2Cu type intermetallics with different size regimes to decipher the controlling geometrical variables. While this work investigates influence of intermetallic geometry on localized deposition, parallel conclusions may also be drawn about the corrosion activity around intermetallics as a function of their geometry due to these coatings being triggered by localized corrosion.