Effect of Convection on Initial Deposition during Electrocoating of Galvanized Steel

Abstract

The objective of this work is to advance the mechanistic understanding of cathodic electrocoating. These efforts focus on the initial processes responsible for deposition, which are examined through direct experimentation and simulation. Electrocoating is a global industrial process providing a corrosion-resistant, base-paint layer to automobile bodies. Presently, empirical models are used to model coating thickness; these models tend to overpredict deposition in occluded areas. Convection is implemented to study electrochemical mechanisms at the surface of the coated part. The impact of surface H 2 bubbles and early e-coat deposition on the local current density is studied using current distribution simulations. Results show an increase in current density locally around surface H 2 bubbles and early e-coat deposition influences film growth. When surface H 2 bubbles are displaced by convection before sufficient e-coat is deposited, deposition is slowed under lower local current density. However, when the e-coat covers sufficient surface area, and convection is then applied, the induction period is unaffected, implying the early deposition is sufficient to keep the local current density high enough to drive deposition. These results provide an increased understanding of fundamental processes responsible for e-coat deposition, which is the foundation needed for advanced physics-based models of the electrocoating process.