Multi-material Joining of an Aluminum Alloy to Copper, Steel, and Titanium by Hybrid Metal Extrusion & Bonding

Hybrid metal extrusion & bonding (HYB) is a solid-state welding method where an aluminum (Al) filler wire is continuously extruded into the weld groove between the metal parts to be joined by the use of a rotating steel tool that provides friction and plastic deformation. Although the HYB method was originally invented for Al joining, the process has shown great potential also for multi-material joining. This potential is explored through characterization of a unique Al–copper–steel–titanium (Al–Cu–steel–Ti) butt joint made in one pass. Each of the three dissimilar metal interface regions are characterized in terms of microstructure and tensile properties. Scanning and transmission electron microscopy reveals that bonding is achieved through a combination of nanoscale intermetallic phase formation and microscale mechanical interlocking. Electron diffraction is used to identify the main intermetallic phases present in the interfacial layers. Machining of miniature specimens enables tensile testing of each interface region. Overall, the presented characterization demonstrates the great potential for multi-material joining by HYB and provides fundamental insight into solid-state welding involving bonding of Al to Ti, steel, and Cu.