Mechanical and microstructural characterization of aluminium micro-pins realized by cold metal transfer

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.