Effect of ageing and Mg content on the quality index of two model AlCuSiMg alloys

The evolution of the quality index of two Al-1%Cu-4.5%SiMg alloys as the materials are aged is examined. When underaged and up to the peak ageing condition the yield strength of the alloys increases while the ductility decreases. The quality index is high and remains approximately constant. At moderate overageing the strength of the alloys decreases rapidly without increase in the ductility and the quality index falls. As the degree of overageing increases the ductility increases again and the quality index tends to increase marginally. The quality index has been related to the material properties using an analytical model. Using this model it is possible to generate a quality index chart that takes into account the change in strain hardening characteristics of the materials with ageing.