Heat treatment response and influence of overaging on mechanical properties of C355 cast aluminum alloy

The research activity was focused on the optimization of heat treatment parameters for C355 (Al-Si-Cu-Mg) cast aluminum alloy and on its microstructural and mechanical characterization in T6 condition, also evaluating the effect of subsequent high temperature exposure. Differential thermal analyses were carried out to identify the solution heat treatment optimal temperature. After solution heat treatment and quenching, samples were subjected to artificial aging, at different times and temperatures, as to obtain the corresponding hardness curves. Samples for successive hardness and tensile tests were subjected to hot isostatic pressing (HIP) and T6 heat treatment, according to the parameters optimized in the foregoing research phase. Some of the T6 heat treated samples were also characterized after overaging, induced by holding at 210 °C for 41 h. Aiming to carry out a comparative study, tensile properties of C355 alloy, both in T6 and overaged conditions, were compared to those of A356 alloy (results from a previous study), which is currently more widely employed than C355. Experimental results showed how C355-T6 alloy is characterized by superior mechanical properties as compared to A356-T6, especially in the overaged condition, due to the higher thermal stability induced by Cu-based strengthening precipitates.