CAREER: Surface Interactions in Dissimilar Material Joining

This Faculty Early Career Development (CAREER) award supports fundamental research on two thermo-mechanical joining methods for dissimilar metals, namely magnetic pulse welding and friction stir blind riveting. Joining methods for dissimilar metals are in increasing demand as manufacturers are seeking creative new structures or components with tailored properties for lightweight vehicles, energy production, consumer devices, or next-generation medical and electrical products. However, dissimilar metals cannot be joined using traditional fusion-based welding methods. This research will provide much needed understanding to enable wide applications of these two joining processes for dissimilar metals. Additionally, this award supports activities to engage students in research; raise students' interest in science, technology, and engineering; and promote advanced manufacturing to a broader population.

The research objectives are: (1) to correlate local mechanical properties (modulus, hardness, and toughness) across the joining interface with joint performance (tensile strength and failure modes); (2) to test the hypothesis that tensile strength of both magnetic pulse welding and friction stir blind riveting joints increases as the thickness of intermetallic compound or amorphous layer increases up to a few tens of micrometers, and then decreases as the thickness increases further; and (3) to establish the relationships between process parameters, microstructure, and joint performance properties. To achieve the first objective, joining samples will be prepared using the two joining processes under various process conditions. Local mechanical properties will be quantified through micro-cantilever, micro-hardness, and in situ scanning electron microscope testing. Joint performance will be measured through macro quasi-static tensile tests. To achieve the second objective, intermetallic compound or amorphous layers of different thickness values will be produced by adjusting process parameters, and the thickness will be measured by analyzing scanning electron microscope or transmission electron microscope images of the interfaces. A relationship between the layer thickness and tensile strength will be established. To achieve the third objective, a set of governing equations from kinetic modeling of diffusion or intermetallic compound growth will be coupled with finite element simulation to predict the local phase and microconstituent volume fractions, which together with the contact conditions under different process parameters will be used to predict the joint performance.