Periodically, I receive useful information on materials. This short note was sent from ASM. Two most common methods to increase the strength of aluminum alloys are to: Disperse second-phase constituents or elements in solid solution and cold work the alloy (non heat treatable alloys) Dissolve alloying elements into solid solution and precipitate them as coherent submicroscopic particles (heat treatable or precipitation-hardening alloys) Elements most commonly present in commercial aluminum alloys to provide increased strength, particularly when coupled with strain hardening by cold working or with heat treatment (or both) are copper, magnesium, manganese, silicon, and zinc. These elements all have significant solid solubility in aluminum, and in all cases, the solubility increases with increasing temperature. Of all the elements, zinc has the highest solid solubility in aluminum (a maximum of 66.4 at.%). The maximum solid solubility in aluminum alloys occurs at the eutectic, peritectic, or monotectic temperature.