(Semi-)Solid-state joining of aluminium and titanium alloys – A critical review

Joining dissimilar lightweight alloys is one key challenge for achieving cost and weight reduction in structural parts especially for transport applications. In this work, the state of the art in joining of aluminium and titanium alloys via solid-state techniques is critically analysed and discussed, particularly regarding generalisable statements in terms of process- and material-related findings. Processes are compared regarding their time-temperature-cycles and mechanical impact on the materials. Focus is laid on the interface evolution, diffusion, formation of intermetallic compounds as well as the influence of alloying elements. Findings are critically reviewed, discrepancies and knowledge gaps regarding diffusion coefficients, preconditions for and influence of intermetallics, and the influence of plastic deformation highlighted. Although there is no systematic experimental investigation of fundamental factors available in the literature, it can be stated that mechanical deformation has a strong accelerative effect on the interdiffusion and lowers the diffusion start temperature significantly. Alloying elements like Al, Cu and Si decrease while Mg accelerates the interdiffusion of Al and Ti. TiAl 3 is typically the primary intermetallic compound to form in solid-state processes but is found to be no precondition for firm bonding.