In-situ monitoring of additive friction stir deposition of AA6061: Effect of rotation speed on the microstructure and mechanical properties

The AA6061 alloy depositions fabricated under three rotation speeds (Si, 450, 500 and 550 rpm) are obtained by the additive friction stir deposition (AFSD) technique in this study. The real-time temperature, force and torque during the AFSD process were monitored by a self-developed process-aware kit, helping to thoroughly investigate the influence of Si on the microstructure and mechanical properties of the depositions. Combined with the results of the electron back scattered diffraction (EBSD) analysis on a large area (4 x 4 mm2), it is found that the grain size increases with the increase of Si due to high heat generation. The proportion of deformation texture components reduces because of the lower strain distribution as well as the slight deformation behavior. A higher average micro-hardness is found on the 550 rpm-deposition because of the dislocation strengthening effect. Furthermore, the values of yield strength (87.8 MPa) and ultimate tensile strength (147.2 MPa) of the depositions are the highest when the Si is the lowest (450 rpm), owing to the lowest thermal cycle. All the results are intended to provide useful guidance and a theoretical basis for producing high-performance Al-based alloys through AFSD.