Abstract: To improve the microstructure and mechanical properties of arc additively manufactured aluminum alloys, an arc-friction stir processing hybrid additive manufacturing method was employed for aluminum alloy fabrication, and the microstructure and mechanical properties of the additively manufactured aluminum alloys were tested and analyzed. Results show that the pore size and number in the middle samples of the additively manufactured aluminum alloy straight-arm wall are larger than those in the upper and bottom samples; the average grain size is largest in the middle position, followed by the bottom position, and smallest in the upper position. The second phase morphology in the stirred zone of the additively manufactured Al-Mg alloy is mainly discrete granular, and the second phase in the upper, middle, and bottom regions mainly exhibits granular and linear morphologies. During the interlayer friction stir processing, the coupled force-heat effect generated by the stir tool fragments the second phase and causes partial redissolution. The average microhardness is highest at the upper position and lowest at the bottom position. Regarding the variation trend of mechanical properties in the horizontal direction of the additively manufactured straight-arm wall, the upper layer samples have the highest strength, while the bottom layer samples have the lowest strength. The middle position exhibits the lowest elongation after fracture. The tensile strength and elongation after fracture of the vertical samples are significantly lower than those in the horizontal direction. The optimal mechanical properties of the additively manufactured samples are a tensile strength of 291.60 MPa and an elongation after fracture of 31.17%.