In this study, the Cu/Mg ratios of the alloys were modified by adding various Mg elements, and the alloys were subjected to 77 and T8 heat treatments. The mechanical properties relative to the microstructure variations were analyzed by optical microscopy (OM), differential scanning calorimetry (DSC), electrical conductivity meter (MACS), and transmission electron microscopy (TEM). The findings indicate that reducing the Cu/Mg ratio of the alloy by increasing the amount of Mg caused Omega to become the primary strengthening phase and increased the effect of solution and strain hardening. The cold working procedure in the T8 heat treatment induces more lattice defects, which depress the formation of Al-Cu and Mg-Ag clusters, resulting in compression of the Omega phase but a boost of the theta' phase. The hardness and strength of Al-4.6Cu-Mg-0.5Ag alloys tempered to T8 condition are increased by work hardening, but the ductility is decreased. (C) 2015 Elsevier B.V. All rights reserved.