Hybrid friction diffusion bonding of aluminium tube-to-tube-sheet connections in coil-wound heat exchangers

•Application of a new joining process for the energy industry developed.•Underlying joining mechanism investigated.•Main parameters for process stability and joint quality identified.•Requirements of the joints for industrial application met.

The present study presents and evaluates an application of a new solid-state bonding process, hybrid friction diffusion bonding (HFDB). HFDB is used to fabricate tube-to-tube-sheet connections for aluminium coil-wound heat exchangers. An industry-applicable process variant is developed, and its feasibility is demonstrated by gas leak tightness tests and tensile pull-out tests. The joints meet the requirements of industrial applications. Furthermore, the process is characterised by the thermal field development in the weld area and the applied process forces. The microstructure of the joint is investigated, and dynamic recrystallization is assumed to be the primary grain refinement mechanism in the thermo-mechanically affected zone.