Characterization of an aluminium structure developed using overlapped friction stir additive manufacturing

Purpose This study aims to develop a triple-layered build structure by overlapped friction stir additive manufacturing (FSAM) technique using 7075-O 2-mm-thick aluminium sheets. This novel study primarily focused on material consolidation within the build and its corresponding microstructural changes and mechanical properties. Design/methodology/approach The cross-section of the structure and material flow across the interface was analysed using optical macroscopy, while microstructural characterisation was carried out using electron-backscattered diffraction and transmission electron microscopy methods. Mechanical properties such as hardness and tensile strength were evaluated using a Vickers hardness tester and a universal testing machine. Findings Results revealed the occurrence of complex material flow across the interface with a cavity-like defect on the advancing side of the build. Grain size varied remarkably inside the build, ranging from 1.54–3.43 µm due to the effect of dynamic recrystallisation and multiple thermal cycles. Microstructural differences significantly affected mechanical properties inside the build. A maximum hardness of 151.9 HV and a tensile strength of 404 MPa were noticed on the top zone of the build, which were 120% and 66% better compared to the base alloy. The attained improvement was due to grain refinement, re-precipitation of strengthening phases, and dense dislocations. Originality/value This article addresses the need to identify a novel approach for fabricating strong aluminium structures using the solid-state FSAM method. The findings from this study will assist researchers in gaining a comprehensive understanding of the microstructural arrangements necessary to create a defect-free structure with customised properties. Moreover, the findings will encourage scientists to consider this technique for developing various critical components in the aerospace and defence industries.