At the beginning of the 20th Century it was discovered that it was possible to increase the mechanical properties of aluminum alloy after a heat treatment just leaving the material at room temperature for some time. It was later concluded that this effect was caused by precipitation hardening followed by aging, which formed a finely dispersed precipitate that was not possible to resolve with an optical microscope. It was not until the development of X ray diffraction and electron microscopy techniques when a real understanding of the precipitate nature was achieved. This process of heat treating is performed following three stages: i) Solid solution treatment, ii) quenching, and iii) aging. The first aluminum alloys developed using this heat treatment where those which used copper (Cu) and Magnesium (Mg). These alloys showed a limited solubility reduction with a temperature decrease. Some researchers have argued that Silver addition to these alloys increases the mechanical properties of the alloys.