Novel Corrosion Control of Mg Alloys in Structural Lightweight Multi-Materials Assemblies

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Reducing the overall mass of transportation vehicles by the use of strong lightweight materials is arguably the best enabling means to improve fuel efficiency and, thus reduce harmful emissions. Wrought ZE (Zn-Zr-rare earth) Mg alloys with high specific strength, stiffness and warm formability provide enabling opportunities as an integral part of lightweight multi-material structural assemblies to achieve this goal. One key technical issue preventing widespread implementation of Mg alloy components is the high rate of dissolution (corrosion) in aqueous environments. This is driven in large part by the inherent reactivity of Mg (lowest standard reduction potential among industrial engineering metals), the high rate of the hydrogen evolution reaction that dominates the cathodic process and the tendency of the native oxide surface film to breakdown and be replaced with a significantly thicker and much less protective corrosion product film. The long-term goal of my research program is to develop a fundamental knowledge base that enables fabrication of structural lightweight multi-materials assemblies comprised of emerging advanced materials and processes (joining and surface treatment) with improved durability (corrosion and fatigue) that spurs a made-in-Canadian ingenuity to support the global transportation industry. An integrated goal is to provide an inclusive multi-disciplinary (electrochemistry, surface science and physical metallurgy) research habitat that will educate and train Canada's next generation HQP whom will drive development and implementation of innovative corrosion control solutions for strong lightweight materials. Building upon my recent research progress, the next research program milestone is to develop an enabling knowledge base that will underpin successful deployment of ZE Mg alloy in lightweight multi-material assemblies using novel approaches for improved corrosion control. Specific short-term goals include: (i) develop a novel electro-coat coating scheme comprised of a Li2CO3 conversion coating (pre-treatment) that is capable of seal-healing defects sites, (ii) develop a novel refill friction stir spot welding joining technology that mechanically incorporates a non-toxic cathode kinetics inhibitor to control corrosion of the weld and (iii) demonstrate the improved corrosion control achieved through combination of the two proposed innovations: strong lightweight coated ZE Mg alloy joints with a similar extent of corrosion control exhibited by coated Al alloys. Three HQP will be educated and trained in this research proposal: two PhD level students and one MASc level student.