Study and characterization of high strength aluminium alloys (2009)

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.

This work presents the development of aluminum alloys with 4% wt Cu, 0.65% wt Mg and Silver with different proportions which ranges up to 0.9% wt Ag, in order to obtain high strength alloys. The fusion and heat treatment processes used to obtain the alloys with varying contents of silver will be described along with the characterization techniques employed. Results of hardness for aluminum alloys reinforced and not reinforced with silver will be presented in order to analyze the effect of this element on the heat treatment response of the alloys. It was found that an increase on silver content improves the hardness of the alloys. However, it was found that alloys with 0.6% wt Ag showed a better response to heat treatment in comparison with higher and lower silver content alloys.