Microstructural Response in Friction Stir Additive Manufacturing of 5A06 Aluminum Alloy

Friction stir additive manufacturing (FSAM) technology is the ideal technique for aluminum alloy additive manufacturing from the perspective of defect control, microstructure regulation, and performance optimization. However, there is limited systematic fundamental research on the aluminum alloy FSAM. This study implemented a consumable-tool-based 5A06 FSAM process. By incorporating carbon nanotubes during the FSAM process, our research investigated its impact on grain refinement and the performance of the additive structure. The results show that the well-formed additive structure is composed of multiple layers of stirred metal. The microstructure of the additive structure of AA5A06 consists of refined recrystallized grains and deformed grains within each layer, while the interface between layers is composed of a finer-grain band, with an average grain size of 6 µm, whose tensile strength ranges from 225 MPa to 260 MPa, with an elongation of 26% to 32%. After the addition of carbon nanotubes, although the grain size was refined to 2 µm, there was no improvement in tensile strength, and the elongation was reduced. The tensile strength now ranges from 225 MPa to 270 MPa, with elongation between 12% and 16%.