Improvement of directional anisotropy and its impact on surface and mechanical properties of a rib-on-plate structure fabricated through friction stir processing of additively manufactured friction stir surfaced structure

Abstract

Maintaining isotropic properties is an essential need for large-scale metal Additive Manufacturing (AM). This paper presents a novel hybrid technique for fabricating rib-on-plate structures using Friction Stir Surfacing (FSS) and sidewall-assisted Friction Stir Processing (FSP). A reasonably high joint efficiency (${\eta }_{\mathrm{joint}}$) of 96.60 % indicates a higher utilization of FSS-based deposition volume in manufacturing metal panels. Material consolidation via FSP exerted a dominant influence on reducing the heterogeneous mechanical properties of the multi-layer FSSed structure, making it suitable for cyclic loading applications. Additionally, the structure achieved an improved tensile strength (15.97 %) than the FSSed structure. The absence of interlayer separation in the tensile fracture surface morphology confirmed the structural integrity of the end product. Microhardness and Electron Backscatter Diffraction (EBSD) analysis revealed an enhancement in interlayer quality, as evidenced by the lack of non-jointed surfaces and a narrow zone of microstructural variations in post-processed structure. The detailed investigation demonstrated that the FSP operation following four FSS-based depositions could be a wise decision for preserving the balance between the overall defect volume and process cycle time.