Production of Al/NiTi composites by friction stir welding assisted by electrical current

Abstract Composite Al structures reinforced with NiTi have been produced by solid-state joining process in order to prevent brittle intermetallics to form. For this, friction stir welding (FSW) was used in both the conventional and the hybrid variant assisted by electrical current. The hybrid process allows for a better bonding along the NiTi/Al interface since the material viscoplasticity promoted by the higher temperatures achieved during the process facilitates the material flow around the reinforcement. Mechanical characterization of the composites showed that upon bending and pull-out tests, the composites produced by FSW assisted by electrical current have increasing mechanical properties. Microstructural characterization using synchrotron X-ray diffraction, revealed that composites produced with the hybrid process exhibited a different transformation temperature of the NiTi reinforcements. The originally fully austenitic NiTi presented both martensite and austenite at room temperature after processing, which can be taken as an advantage for applications where damping capacity of the shape memory alloy is required. The ability to successfully join NiTi to Al may open new structural applications based on these composites.