Thixotropic aluminium alloy used at a liquid fraction of around 50% presents, with respect to its 100% liquid homologue use dinconventional highpressure die casting, three major difference [4]: (i) a much higher viscosity, that permits to inject the material at relatively high speeds; (ii) a lower heat content allowing a considerable increase in production rate; and
less contraction during solidification reducing risering problems. The very good mechanical properties are due to the globular microstructure which results very fine and homogeneous an disaccompanied with very low levels of voids produced during the solidification process [5, 6]. By using heat treatments the mechanical properties of such material can be strongly improved[2,7].The aim of this work was to study the effect of T5 and T6 heat treatments on the mechanical properties of A356 thixocast alloy and to correlate the mechanical behaviour to the microstructural evolution