An effort has been made to present optimum alloy designs of commercial 7175 and 7050 type alloys to be used in thick forgings with proper microstructures and properties. The effects of changing alloy constitutions, primarily [Zn+Mg+Cu] and Zn:Mg ratio, on the evolutions of the coarse equilibrium phases and age hardening response are investigated. As a result, equilibrium phases (M,T,S) are evolved depending on alloy constitutions and cooling rate following solutionizing. The formation of the T- and S-phases is effectively controlled in the novel alloys (dilute and with high Zn:Mg ratio). In the slow quench, the redesign promotes homogeneous precipitation of eta-phases, leading to higher mechanical properties than conventional alloys. The novel alloys provide microstructural. homogeneity and extended heating range, ensuring 7xxx thick forging applications.