Abstract: This study was conducted to clarify the influence of different addition levels of an Al-Mg-Sc-Zr alloy on the microstructure and corrosion behavior of Al-Si-based alloys fabricated via powder bed fusion-laser beam (PBF-LB). Al-Si-Fe-Mn-Ni-Sc-Zr cross-over alloy powders were prepared by incorporating 10 wt.%, 20 wt.% and 30 wt.% of Al-Mg-Sc-Zr powder into the Al-Si-Fe-Mn-Ni master powder. After PBF-LB processing, the microstructures, electrochemical properties and immersion corrosion morphologies of the as-built alloys were systematically characterized and compared. The results demonstrated that a moderate addition of Al-Mg-Sc-Zr effectively suppressed grain coarsening in both the equiaxed-grain and columnar-grain regions. Specifically, the α-Al grains in the equiaxed zone were refined, accompanied by the formation of a finer Si network, while the Si particles in the columnar zone were refined to a size range of 10-100 nm. Electrochemical measurements revealed that the cross-over alloy with ASF-M10 addition exhibited higher impedance and a lower corrosion current density and excellent pitting corrosion resistance than the master alloy. In contrast, the cross-over alloys with ASF-M20 and ASF-M30 additions showed reduced corrosion resistance compared with the master alloy. Further Analysis of immersion corrosion morphology indicated that with the addition of Al-Mg-Sc-Zr alloy, the intergranular corrosion of ASF-M alloy is suppressed, and only a few pitting corrosion pits appear. This transition was mainly attributed to two factors: first, the refined Si network structure weakened the micro-galvanic coupling effect; second, the presence of Mg promoted the formation of a more stable surface oxide film.