Heat treatment, in particular aging (or precipitation) hardening is an important step to achieve the desired strength of engineering materials, such as cast aluminum alloys A356/357 or the like. Strengthening by aging hardening is applicable to alloys in which the solid solubility of at least one alloying element decreases with decreasing temperature. Some wrought and cast aluminum alloys are age-hardenable, such as 6xxx, 7xxx, 3xx, or the like. The present invention extends to all such aluminum alloys made by various manufacturing processes including, but not limited to forging, casting, and powder metallurgy.