Multi-material structures are possibly the best alternative to achieve
structural weight reduction in the transportation sector. Such multimaterial
structures are currently joined by either adhesive bonding or
in form of mechanical connections, such as riveting. The former
brings an environmental burden and the latter a weight penalty. Solidstate
joining processes are environmental friendly technologies,
capable of producing defect free joints in dissimilar material
combinations with superior mechanical properties. These processes
are characterized by transient temperature cycles (i.e. high heating
rates and cooling rates where the maximum temperatures stays
below the melting point of the materials being joined) and high strain
rates, causing intensive material flow in the joint region. As a result,
non-equilibrium structures are formed in the interface of the joints.
Such microstructures have been shown to be directly responsible for
the mechanical performance of lightweight structures. A few isolated
studies in the literature have investigated the microstructure evolution
resulting from thermo-mechanical processes typical of solid-state
joining processes for specific materials or material combinations.
However, no systematic effort is reported on isolating the effects of
thermal cycle and material flow on joint formation in dissimilar
materials joints. Furthermore, the effect on specific alloying elements
on diffusion phenomena and IMC phase formation in interfacial
regions is sparsely reported for joints produced by solid-state
processes. The present project addresses the above mentioned
knowledge gaps in the understanding of microstructural evolution in
bi-metallic interfaces generated under non-equilibrium conditions. To
achieve this goal, friction stir welding and refill friction stir spot welding
will be employed to produce dissimilar overlap joints between
experimental Al-Si-Mg alloys (based on the AA6013 composition) and
a Ti-6Al-4V alloy, supported by corresponding numerical process
simulations. The experimental Al alloys will contain systematically
varied alloying contents to allow for the investigation of the effect of
these key elements on microstructural evolution.