This　paper　centers　on　high-strength　Al-Mg-Mn-Er-Zr　alloy,　which　was　developed　through　the　addition　of　Er,　a　cheap　rare　earth　element,　and　suitable　for　additive　manufacturing　(3D　printing).　The　microstructure　and　mechanical　properties　of　Al-Mg-Mn-Er-Zr　alloy　of　as-built　and　heat　treated　samples　have　been　characterized,　which　shows:　the　precipitation　of　Al3Zr　primary　phase　at　the　boundary　of　molten　pool　promotes　heterogeneous　nucleation　and　refines　the　grains,　which　suppresses　the　formation　of　solidification　cracking　in　Al-Mg　alloy.　To　bring　the　Er-Zr　synergistic　effect　into　play　during　the　aging　heat　treatment,　the　nano-scale　precipitation　phase　of　Al3Er　that　diffuses　nucleation　at　an　earlier　stage　promotes　the　precipitation　of　Zr,　leading　to　the　formation　of　Al3(Er,Zr)　core-shell　structure　and　enhancing　precipitation　strengthening　effect.　Under　the　combined　effects　of　multiple　strengthening　mechanisms,　the　yield　strength　could　reach　440　±　3　MPa;　tensile　strength,　520　±　2　MPa　and　elongation　15.5　±　1.0　%.　©　2022　The　Author(s)