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In aerospace and automotive industries, SiC particulate reinforced aluminium matrix composites have found many application areas because of their excellent mechanical properties, combined with the ease of formability and low cost. Aim of this study is to investigate the interrelationships between wave velocities and reinforcement content, microstructure and hardness of SiC reinforced Al composites. Specimens were fabricated by hot pressing for various volume fractions of SiC particulate, up to 20 vol. %, and for different combinations of particulate size. SiC content can be determined by measuring the ultrasonic velocity. For a given particle size combination, the velocity of the longitudinal waves increases as SiC vol. % of the composite increases. The particle size ratio of the constituents becomes an important factor for ultrasonic velocity, especially above 10 vol. % SiC. A higher Al/SiC particle size ratio results in segregation of SiC particles along the Al powder boundaries. This yields lower ultrasound velocities with respect to the homogeneously distributed reinforcement. Therefore, an ultrasonic velocity value that is less than the expected one might be attributed to the micro-porosity in the segregated structure. Similar tendencies were also observed for the results of hardness tests.