The present work was performed on seven alloys containing in common Al-6.5 wt%Si-3.5 wt% Cu, with magnesium in the range 0.04-0.45wt%, and strontium in the range 0-300 p.p.m. The alloys were cast in the form of tensile test bars, solution heat treated in the temperature range 480-540 degrees C for times up to 24 h. Two types of solution heat treatment were applied: (i) single-stage, where the test bars were solution treated at a certain temperature for 12 h prior to quenching in hot water (60 degrees C); (ii) two-stage, where the test bars were solution treated for 12 h/510 degrees C + 12 h/T degrees C (T = 510, 520, 530, 540 degrees C), followed by quenching in hot water. In the low-magnesium alloys (i.e. with Mg similar to 0.04 wt%), melting of the Al2Cu phase commenced at 540 degrees C. Increasing the magnesium content to similar to 0.5 wt% reduced the incipient melting temperature of the Al5Mg8Si6Cu2 phase to 505 degrees C. The mechanism of incipient melting and its effect on the tensile properties have been discussed in detail.