The European collaborative research project ADALFIC (Advanced Aluminium Fittings in CFRP tubes) focuses on the design, analysis, manufacturing and testing of ultra-lightweight carbon fiber reinforced plastic (CFRP) tubes with integrated aluminium end fittings. Reliable joining technologies for combining aluminium and CFRP are of great interest since the combination of superior mechanical properties and low density offer a wide range of applications. One such approach is the use of form locking micro-pins on the surface of the metallic part enabling the joint between metal and CFRP by mechanical interlocking. In this work Fronius’ Cold-Metal-Transfer (CMT) Print welding technology was used to generate very small, minimum-mass, spike-head pins, which are optimized for form-locked joints between aluminium and CFRP components. The aluminium pins are characterized on a macroscopic and microscopic level using light optical microscopy and hardness testing. To evaluate the behavior of the pins under mode II load conditions a new shear testing method for pins was developed and implemented. With this test equipment the maximum shear force and ultimate shear strength of individual pins were measured at different temperatures and heat treatment conditions. The failure modes and fracture surfaces were analyzed via scanning electron microscopy. The results demonstrate that the novel spike-head CMT aluminium pins can withstand considerable shear forces, especially in the peak aged condition. This makes them a viable, flexible and lightweight option for form-locked aluminium-CFRP joints.

Advanced and reliable joining technologies for ultra-light weight structures combining aluminium with carbon fibre reinforced plastics (CFRP) are of great interest for aerospace industries. The combination of superior mechanical properties and low density offer a wide range of possible application. The European collaborative research project ADALFIC (Advanced Aluminium Fittings in CFRP tubes) focuses on the design, analysis, manufacturing and testing of ultra-lightweight CFRP tubes with integrated aluminium end fittings. These aluminium end fittings are equipped with very small, minimum-mass, spike-head pins realized by Fronius' cold-metal-transfer (CMT) Print welding technology. These pins are optimized for form-locked joints between aluminium and CFRP components. In this work the aluminium pins are characterized on a macroscopic and microscopic level using light optical microscopy and hardness testing. To evaluate the behavior of the pins under mode II load conditions a new shear testing method for pins was developed and implemented. With this test equipment the maximum shear force and ultimate shear strength of individual pins was measured at different temperatures and heat treatment conditions. The failure modes and fracture surfaces were analyzed via scanning electron microscopy. The results demonstrate that CMT aluminium pins are a viable, flexible and lightweight option for form-locked aluminium-CFRP joints.

Wire arc additive manufacturing, employing conventional fusion welding processes, shows excellent versatility and can therefore be used for structural modifications of existing parts to create hybrid components. This study evaluates the modification of cold-formed AA2024 metal sheets with 2xxx filler metals to produce 2xxx hybrid structures. The alloys are investigated by thermodynamic simulations and the solidification crack susceptibility is assessed by calculating the index for hot cracking susceptibility. Using cold metal transfer, single-layer depositions are generated on profile sheets after which the specimens are characterised by three analysis procedures: metallographic analysis, chemical analysis, and hardness testing. Results indicate that AA2024 wire material, although generally considered difficult to weld, is more suitable for the additive modification of AA2024 sheets and profiles, as crack-free specimens can be deposited on cold-formed substrates.