Effect of Feeding Strategy on the Microstructure and Microhardness in Friction Stir-Based Additive Manufacturing of Aluminum Alloy Powder

Abstract Powder-based friction stir additive manufacturing employs various methods to deliver powder to the deposition zone, which can influence the deposits' microstructure by altering how the powder interacts with the tool. However, this area has not been extensively explored in existing research. To investigate this, AA6061 powder was deposited using two powder-based techniques: additive friction stir deposition (P-AFSD) and additive friction stir processing (AFSP). The resulting microstructural evolution was subsequently analyzed to establish correlations with each method's respective deposit formation mechanisms. The AFSP microstructure exhibited ∼20% more recrystallized grains than P-AFSD but contained ∼1% fewer high-angle grain boundaries. This may be due to the powder material undergoing deposition and recrystallization under relatively higher temperature and deformation conditions during AFSP, followed by additional strain as most of the tool's front and entire rear section passed over the deposited material. Texture evolution was examined using pole figures and orientation distribution functions. The initial extrusion of partially plasticized material through the central hole of the P-AFSD tool led to a strong presence of A-type textures and the absence of any plane strain component. Moreover, the average Vicker's microhardness was 78 HV for P-AFSD and 65 HV for AFSP.