Age hardening has been recognized as a method for strengthening Al-Si-Mg-Cu alloys. The age hardening process involves strengthening the alloys by coherent precipitates which capable of withstanding dislocation. The effect of age hardening depending on the kind, amount, size, and uniform of the precipitate, which involves alloy elements dissolve in aluminium. This paper review the growth of precipitates (?"-Mg2Si, Q'-Al3.8Mg8.6Si7Cu1 dan ?'-Al2Cu) influenced by containing alloy in Al-Si-Mg-Cu alloys during age hardening. Al-Si-Mg-Cu responds to age hardening depending on rapid hardening influenced by high nucleation rate precipitate ?"and formation Q', which would accelerate growth precipitate ?' and result in fine precipitate ?'. In composition, precipitate ?' is influenced only by composition Cu, when alloy with Cu 4-4.5wt% observed fine precipitate ?' at the most. However, nucleation and growth ?' depending on formation Q' influenced by the composition Mg and Si. Furthermore, a high nucleation rate of ?"resulted in rapid hardening alloy on the initial stage of artificial aging. In conclusion, all three of the precipitate played a crucial role in the improved mechanical properties of aluminium alloy by age hardening. Al-Si-Cu-Mg alloy has the highest mechanical properties due to the precipitation-hardening process. Al-Si-Cu-Mg alloy with ?'-Al2Cu and minor Q'-Al4Cu2Mg8Si7 provide better precipitation hardening effect compare to ?"and Q' followed by Al-Si-Mg alloy with ?"-Mg2Si precipitate and Al-Si-Cu alloy with ?'-Al2Cu precipitate.