The　effects　of　Mg/Si　ratios　(0.86,　1.73　and　2.57)　on　the　mechanical　properties　of　aging　Al–Mg–Si　alloys　containing　Er　and　Zr　micro-alloying　elements　were　studied.　The　mechanical　properties　of　the　alloys　were　studied　by　Vickers　micro-hardness　(HV)　measurements　and　tensile　testing.　Optical　microscopy　(OM)　and　transmission　electron　microscope　(TEM)　were　used　to　observe　the　microstructures　of　the　alloys.　The　results　showed　that　different　alloys　with　different　Mg/Si　ratios　have　four　stages　of　age　hardening.　The　alloy　with　a　Mg/Si　ratio　of　1.73　possesses　the　highest　hardness.　In　the　peak-hardness　aged　condition　(T6　state),　the　density　of　needle-like　β″　phase　increases　first　and　then　drops　with　the　increase　of　Mg/Si　ratio.　When　the　Mg/Si　ratio　reaches　1.73,　the　highest　density　of　needle-like　β″　phase　can　be　achieved.　Er　and　Zr　can　improve　the　hardness　of　the　alloys.　©　2019,　Springer　Nature　Singapore　Pte　Ltd.