Additive manufacturing of aluminum (Al) alloys has attracted significant attention in the aerospace industry. However, achieving ultrahigh-strength (>500 MPa) Al alloys remains challenging due to their intrinsic poor printability. Here, we report a novel hybrid additive manufacturing (HAM) approach to process ultrahigh-strength AlMgSc alloy, which combines laser powder bed fusion (LPBF) with interlayer ultrasonic shot peening (USP). The results show that the interlayer ultrasonic shot peening depth reached ~700 µm, leading to almost full density and residual stress convection from tension to compression. The HAM method promotes equiaxed grain formation and refines grain due to grain recrystallizations. Interestingly, the HAM followed by aging treatment tailors the hierarchically multi-gradient structures, inhibits Mg element intragranular segregation, and promotes the multi-nanoprecipitates (e.g. Al₃(Sc, Zr) and Al₆Mn) precipitation. Remarkably, the HAM followed by aging treatment achieves yield strength of 609 MPa and breaks elongation of 7.5%, demonstrating ultrahigh strength and good ductility compared with other Al alloys manufactured by AM and forging as reported in the literature. The strength enhancement mechanisms in this AlMgSc alloy are discussed. The high-density Al₃(Sc, Zr) precipitates are the main strengthening contributor, and unique hetero-deformation induced (HDI) strengthening (originates from the heterogeneous microstructures) further enhances the strength of the material. This work highlights a novel approach for processing complex-structured ultrahigh strength Al alloy components by hybrid additive manufacturing.

Welding quality of electron beam welded joint is usually susceptible to the stability of keyhole during welding process. The more stable the keyhole, the better the welding quality. To reveal the evolution mechanism of keyhole and welding quality of the electron beam welded joint of magnesium-gadolinium alloy under different scanning path, numerical simulation was conducted for the changes in morphology of keyhole and liquid flow in molten pool. The magnesium-gadolinium alloy was welded by electron beam in vacuum with two different scanning paths, sinusoid path and cochleoid path, indicating the identical heat input, welding speed, and focusing state. The stability of keyhole was mainly related to the frequency of keyhole collapse. When the sinusoid scanning path was adopted, the fluids both inside the molten pool and at keyhole wall were disorder, corresponding to the numerous independent vortices and dramatically chaotic flows at their junctions. The maximum velocity of fluids ranged from 0.79 m/s to 1.02 m/s. The average and maximum depth of keyhole were 3.48 mm and 4.51 mm, respectively, meaning that the keyhole collapsed frequently. As the scanning path was changed into cochleoid mode, the electron beam scanned in a homogeneous manner without abrupt change in direction and speed like sinusoid path at its peaks and troughs. The maximum velocity of fluids was more uniform without drastic variation, ranging from 0.90 m/s to 1.01 m/s. The average and maximum depth of keyhole were decreased to 3.30 mm and 4.05 mm, respectively, indicating the more stable keyhole and alleviated collapse. Both the actual in-situ capture of molten pool signature and porosity inside the weld corresponded to the analysis of the change in keyhole stability.