Multimodal defect analysis and application of virtual machining for solid-state manufactured aluminium structure

Additive friction stir deposition (AFSD) is an emerging solid-state non-fusion additive manufacturing (AM) technology, which produces parts with wrought-like material properties, high deposition rates, and low residual stresses. However, impact of process interruption on defect formation and mechanical properties has not yet been well addressed in the literature. In this study, Al6061 aluminium structure with two final heights and deposition interruption is successfully manufactured via AFSD and characterised. Defect analysis conducted via optical microscopy, electron microscopy, and X-ray computed tomography reveals > 99% relative density with minimal defects in centre of the parts. However, tunnel defects at interface between substrate and deposit as well as kissing bonds are present. Edge of deposit contains tunnel defects due to preference for greater material deposition on advancing side of rotating tool. Virtual machining highlights the ability to remove defects via post-processing, avoiding mechanical performance impact of stress concentrating pores. Electron backscatter diffraction revealed regions with localised shear bands that contain 1–5 µm equivalent circular diameter grains. Kissing bonds are exhibited in areas separated by large grain size difference. Meanwhile, Vickers hardness testing reveals hardness variation with deposit height. This work advances the understanding of complex microstructure development, material flow, and mechanical behaviour of AFSD Al6061 alloy.