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The relationship between the mechanical properties and precipitation behavior of Al-Zn-Mg-Cu-Zr aluminum alloys with low Sc content (0.02wt%, 0.07wt%, 0.12wt%) was investigated by OM, SEM, TEM, and universal material testing machine. With the increase in Sc content, microstructure of as-cast alloy is gradually refined, and the coarse secondary phase at the grain boundary increases, thus weakening the effect of fine grain strengthening. In the alloy at rolling+T6 state, the Al₃(Sc,Zr) phase inhibits the precipitation of the main strengthening phase η', and the inhibition effect becomes more obvious with the increase in Sc content, thus weakening the precipitation strengthening effect. The grain refinement is conducive to the formation of more and finer dimples during the tensile deformation, thus improving the ductility of the alloy. The low Sc content alloy (0.02wt%) shows the excellent mechanical properties after rolling and T6 heat treatment, whose tensile strength and elongation are 683 MPa and 21%, respectively.