The migration and formation curves for the A365.0 (Al-7% Si-0.4Mg) casting alloys are investigated by positron lifetime (PL) and S-parameter measurements from room Temperature (RT) to 873 K. The observed dependence of PL tau and S-parameter on quenching temperature (QT) is attributed to vacancy formation. PL results were analyzed applying the two state trapping model and the formation enthalpy H(Iv)(f) was estimated by using different methods.