Investigation on microstructural and microhardness evolution in as-cast and T6/heat-treated samples of a horizontally solidified AlSiCu alloy

In this investigation, in order to evaluate the influence of microstructures on the microhardness of an aluminum-based multicomponent alloy, samples of the horizontally solidified Al-7 wt.%Si-3 wt.%Cu alloy were subjected to the T6 heat treatment. Microhardness (HV) measurements were carried out in specific zones, like in the center of the dendrites (α/Al-rich) and interdendritic regions. As expected, in as-cast samples, it has been observed high HV values in the interdendritic regions, due to the presence of the harder phases in the eutectic mixture (Si particles + Al2Cu (θ) + Fe intermetallic phases). As a highlight, hardening has been observed in both analyzed regions (α/Al-rich and interdendritic), and a similar behavior in the HV evolution, between the two investigated regions, has also been evidenced. In addition, mathematical equations have characterized the HV dependence as a function of the aging time (taging).