Microstructure Evolution and Mechanical Properties of Multilayer AA6061 Alloy Fabricated by Additive Friction Stir Deposition

Multilayer AA6061 aluminum alloy components are successfully fabricated by the additive friction stir deposition (AFSD) process. The surface morphology, microstructure, and mechanical property are investigated to evaluate the quality of AFSD-deposited AA6061 alloy. The surface of the final AFSD-deposited samples is relatively smooth, and the average surface roughness (Sa) is 2.490 μm. The recrystallized grains recovered dynamically under the action of high thermal cycling. Grain nucleation and directional growth in the layer–layer interface increase the proportion of HAGBs. Many blocky and rod-like AlFeSi phases can be seen in the AFSD-deposited layer. The cross-sectional microhardness of AFSD-deposited AA6061 alloy shows gradient characteristics. The minimum value of microhardness appeared in the interface between the substrate and the 1st layer. The maximum value of ultimate tensile strength of the 3rd layer samples without interface can reach 308 MPa with elongation at break of approximately 32.6 pct. The present work provides a pathway for solid-state additive manufacturing of light alloy parts.