The　precipitation　and　intergranular　corrosion　(IGC)　behavior　of　Al–1.0Mg–0.6Si–Cu　(wt.%)　alloys　with　the　addition　of　Cu　ranged　from　0.3　to　0.6　wt.%　were　investigated　by　optical　microscope　and　transmission　electron　microscopy.　The　results　indicated　that　the　Cu　addition　significantly　improves　the　hardness　of　the　alloys　during　under-aging　progress　by　accelerating　the　precipitation　of　GP　zones.　The　addition　of　Cu　has　changed　the　composition　of　precipitation　and　facilitated　the　formation　of　β′′-Mg5Si6　precipitates　with　high　density　and　fine　distribution.　When　the　Cu　content　is　added　to　0.6　wt.%,　the　type　of　precipitation　has　changed.　In　addition　to　the　needle-shaped　β′′　phase,　a　new-plate　Q′　phase　precipitated　during　peak-aging　conditions.　The　0.6　wt.%　Cu　alloy　shows　superior　strength　with　tensile　yield　strength　of　328 MPa,　ultimate　tensile　strength　of　368 MPa,　and　elongation　of　16.0%.　However,　the　IGC　resistance　decreased　with　the　Cu　content　increasing　from　0.3　to　0.6　wt.%,　which　mainly　resulted　from　the　segregation　of　Cu　elements　and　the　formation　of　continuous　Q′　precipitates　at　the　grain　boundaries.　©　2023,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH,　DE　part　of　Springer　Nature.