An aluminum-based alloy composition having improved combinations of strength and fracture toughness consists essentially of 2.5-5.5 percent copper, 0.10-2.30 percent magnesium, with minor amounts of grain refining elements, dispersoid additions and impurities and the balance aluminum. The amounts of copper and magnesium are controlled such that the solid solubility limit for these elements in aluminum is not exceeded. The inventive alloy composition may also include 0.10-1.00 percent silver for improved mechanical properties. The alloys are useful as high strength, high fracture toughness components for aircraft and aerospace structural parts.