This paper has studied the influence of Cu content and microelements on solution treatment of Al-Si-Cu-Mg cast alloys by a series of differential scanning calorimetry (DSC) analyses. With the increase of Cu content, the melting point of α (Al)+Si decreases and polynary eutectic phases with melting point of 507 o C form. Sodium modification has little influence on the melting point of polynary eutectic phases, but it is increased by about 5 o C in Sr modified or Be-containing alloys. Incipient melting and the determination of two-step solution treatment (conventional solution treatment followed by a high-temperature solution treatment) parameters have been analyzed in unmodified and Sr modified Al11Si4Cu0.3Mg alloy. Factors influencing segregation should be considered in determining solution treatment parameters and this has been discussed.