A wide study of the effect of heat treatments on mechanical properties of a thixocast A356 aluminium alloys was carried out and described in the present paper. The material was analyzed by using hardness and tensile tests as well as optical and electron microscopy (SEM). The main conclusions can be summarized as follows:
(i) A good ductile behaviour is revealed by the specimens after solution treatment thanks to the sferoidization of silicon particles due to the heat treatment. The spheroids favours the plastic deformation until fracture.
(ii) During treatment at higher temperatures different microstructural phenomenon take place: in particular, on lower times the hardening of the material is predominant due to dissolution of intermetallic particles in the matrix, whereas on higher times softening is more relevant thanks to the spheroidization of particles.
(iii) The ageing treatment both in the T5 and T6 conditions produces an increase in mechanical properties of the material. With respect to this, it was observed that YS and UTS do not differ for the temperatures of 160 and 200◦C, while ductility differs very much from one temperatures and the other.
(iv) The analysis of fracture surface showed a ductile behaviour in the specimens after T6 treatment, while it revealed a brittle behaviour in the as-thixo and T5 ones with fracture which propagate preferentially in the eutectic region around the primary globules in all the tested condition