Wedge castings were produced using six Al-Zn-Mg-Cu aluminum alloys with zinc concentrations ranging from 8 to 15 wt%, Zn/Mg ratios ranging from 1.7 to 6.5, and copper ranging from 0.6 to 1 wt%. Thermal analysis and microstructural characterization of the samples in the ascast, solution-treated, and aged conditions were performed and compared to Calculation of Phase Diagram simulations. The calculated phase stability in the alloys was overall remarkably accurate for both the solidification and equilibrium phase formation. Additional equilibrium calculations were made to determine the range of alloying concentrations that would not contain eutectic T or η phase. The phase stability in a total of 195 chemistries was calculated.