Damage Responsive Polymer Nanocomposite Coatings for Dip Coating of Mg Alloys for Corrosion Protection and Color Enhancement

Part of the recent improvement in automotive fuel economy has been a direct result of the use of lightweight alloys. However, the use of alloys of the lightest metal, magnesium (Mg), has been limited due to the monetary and environmental expense of corrosion protection. A less expensive and more environmentally friendly alternative to chromate conversion coatings is needed to allow the use of Mg alloys for automotive components that are exposed to the road environment. This project will develop a new class of easily applied, damage-responsive (i.e., self-repairing), polymer nanocomposite coatings for the corrosion protection of Mg alloys, thereby eliminating the need for cathodic electrocoats. The multifunctional, water-based polyurethane coatings will contain a dispersion of active nanomaterials that will provide the anodic protection, along with high resistance to electron flow in the galvanic corrosion cells formed when damage to the coating occurs. Phase I will demonstrate the feasibility of synthesizing functionalized nanomaterials, forming f aqueous dispersions, and incorporating the nanomaterial into polyester/urethane polyol coating formulations. The Mg alloy substrates will be coated using an in-house dip-coater. Corrosion testing under salt fog conditions will be conducted, and the results will be compared to conventional chromate conversion coatings. Commercial Applications and other Benefits as described by the awardee: The damage-responsive, tinted-polymer nanocomposite coatings should enable automotive manufacturers to safely and economically increase their use of lightweight Mg alloys for improved fuel efficiency. In addition, the number of coating steps would be reduced. The $425 million market for electrocoating is approximatly 26% of the overall automotive coating market. The combination of corrosion protection and primer application into a single dip-coating step should result in significant savings to automotive manufacturers and the public.