Nanotechnology-Based Self-Healing Coating System to Enable Extensive Use of Magnesium Alloys in Automotives

The use of lightweight metals such as magnesium can increase the fuel efficiency of automobiles. However, large scale use of magnesium is prevented due to its high propensity to corrode. In particular, galvanic corrosion is a severe problem when magnesium is used in the exterior sub-assemblies of automobiles. Hence, there is an unmet need for advanced protective coatings to protect magnesium from general and galvanic corrosion. Current non-chromate pretreatments and powder coats are not effective because defects form in the coating and expose the bare metal. This project will develop a self-healing waterborne pretreatment and a self-healing powder coat that will provide damage-responsive corrosion protection to magnesium. In Phase I, the pretreatment and powder coats, which contained a dispersion of corrosion inhibitor particles, were synthesized and deposited on AZ91D substrates. Accelerated corrosion and electrochemical tests demonstrated (1) the beneficial attributes of the nanoscale additive in the pretreatment, and (2) the ability of inhibitor particles in the powder coat to form a passivating film. Phase II will optimize the pretreatment and powder coat chemistries, determine the mechanism of corrosion inhibition by the particles dispersed in the coatings, and perform galvanic and general corrosion tests on magnesium test coupons in laboratory and field environments. Commercial Applications and other Benefits as described by the awardee: The self-healing coatings should significantly increase the use of magnesium-based components in automobiles. Magnesium-based components in the chassis and powertrain could reduce the weight of a car by up to 10 %, thereby increasing its fuel efficiency. In addition, the aerospace industry uses magnesium in gear box and engine casings; corrosion protection of these components could be further enhanced by the self-healing coating system