Particle-reinforced aluminium matrix composites are of high interest for applications requiring exceptional wear resistance. By powder metallurgical processes such as the field-assisted sintering technique (FAST) high volume percentages of mostly hard ceramic reinforcement can be realized, which enable good wear resistance and thermal stability as well as high specific strength and stiffness. Due to the ductile aluminium matrix these properties are combined with a high toughness, which is required for applications under dynamic loading. As the toughness is primarily influenced by the matrix alloy, the focus of our work was on the influence of the used powder size fractions and the resulting mechanical and microstructural properties. We investigated the age-hardenable aluminium cast alloy 357, manufactured by FAST using three different powder size fractions. The microstructure was analysed by optical microscopy and the mechanical properties were characterised using tensile and compression tests. For the same sintering parameters, a finer matrix powder mixture as well as a wider powder size distribution resulted in better mechanical properties, when compared to the as-received aluminium powder. Further, our systematic investigations show, that a heat-treatment after sintering is also a major influencing factor for the resulting properties. An underaging heat-treatment T61 was chosen to achieve a high strength combined with a good ductility of the sintered powder alloy. However, the ductility was significantly decreased by the heat-treatment due to the formation of pores, presumably located at former powder particle corners, and the resulting decreased density of the sintered alloy. As the combination of FAST sintering followed by heat-treatment has hardly been studied in literature so far, our results demonstrate the importance of an exact parameter setting regarding the sintering process and the heat-treatment to achieve good mechanical properties. We investigate a strategy for adapting the FAST sintering process parameters and optimising the heat treatment routine to minimize the pores and their negative effect on the microstructure and the toughness.