The evolution of the microstructure and mechanical properties of quasibinary Al–6.5Cu–2.3Y and Al–6Cu–4.05Er alloys during homogenization and subsequent thermomechanical treatment has been studied in this work. The Cu concentration in the aluminum solid solution increases during homogenization before quenching owing to the dissolution of a nonequilibrium excess of phases of crystallization origin and is 1.8 and 2.3% for the alloys containing Y and Er, respectively. The size of intermetallic phases in the Al–6.5Cu–2.3Y and Al–6Cu–4.05Er alloys homogenized at 605°С for 3 hours is 1.2 and 0.75 μm, respectively, and does not increase significantly with an increased annealing time. The Al–6Cu–4.05Er alloy is less prone to softening during annealing after rolling than the Y-containing alloy. This is explained by a greater degree of alloying of the aluminum solid solution (Al) and by a greater degree of dispersity of phases of crystallization origin. However, because of the same factor, the Er-containing alloy has a higher inclination to recrystallization and thereby a coarser recrystallized grain. As a result, the Al–6Cu–4.05Er alloy demonstrates higher mechanical tensile characteristics, especially after annealing at temperatures above 150°С.