Abstract: To investigate the effects of adding different mass fractions of Al–Mg–Sc–Zr alloys on the microstructure and corrosion behavior of Al–Si alloy formed by powder bed fusion-laser beam (PBF-LB), 10%, 20%, and 30% mass fractions of Al–Mg–Sc–Zr powders were added to the Al–Si–Fe–Mn–Ni (ASF) alloy powder. The ASF-M cross-over alloy was fabricated through powder bed fusion-laser beam technology, and the microstructure and corrosion resistance of the ASF-M alloy were compared and analyzed. The results show that adding an appropriate amount of Al–Mg–Sc–Zr alloy can effectively inhibit the growth of grains in the equiaxed zone and columnar zone of the ASF-M alloy, refine the α-Al grains and Si network structure in the equiaxed zone, and reduce the size of Si particles in the columnar zone (10～100 nm). The electrochemical test results show that the ASF-M10 alloy exhibits higher impedance, lower corrosion current density, and superior pitting resistance compared to the ASF-M0 alloy; while the corrosion resistance of the ASF-M20 and ASF-M30 alloys is slightly lower than that of the ASF-M0 alloy. The analysis of immersion corrosion morphology indicates that with the addition of Al–Mg–Sc–Zr alloy, the interlayer corrosion of the continuous layer of ASF-M alloy is inhibited, and a few pitting corrosion pits appear; this is mainly because the refined Si reticular structure can effectively inhibit galvanic corrosion, and at the same time, the Mg element can play a role in stabilizing the oxide film.