Corrosion and mechanical properties of friction stir formed aluminum and steel joints

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Jaberina, Jonathan Earl Camitan
thesis / dissertation description
In the automotive industry, there is a big push to improve performance, fuel efficiency and other tailor-made engineering properties of vehicles. Manufacturers are now looking at other better, lightweight materials like magnesium and aluminum to use alongside steel. Traditional joining methods like welding are not suitable for these dissimilar materials. The friction stir forming process was developed and was able to create a single-pin fusion joint between aluminum and steel. This research now focuses on the issues that stemmed from the newly developed friction stir forming process. The first part studies the corrosion that occurred due to the usage of dissimilar metals. Friction stir formed samples were deployed to three different test sites, each with different atmospheric conditions for an 8-month period. The corrosion products were characterized and the effects of these were related to the mechanical properties of the joints. Zinc was discovered to be the first metal to be attacked, followed by aluminum, and formed corrosion products in the joint. Higher chloride concentrations proved to be a more corrosive environment. Corrosion caused significant decrease in the strength of the joints. The second part of the research aimed to change the structure and makeup of the previous single-pin fusion joint. By developing a new anvil and the usage of a different tool, a new joint called the clinch joint was produced. The optimal parameters for the friction stir clinching process were determined. The clinch joint is a mechanical interlock and its mechanical properties were compared to the previous single-pin fusion joint. The clinch joint had slightly lower shear strength but had more toughness compared to the single-pin fusion joint.