Investigation of microstructure-ultrasonic velocity relationship in SiCp-reinforced aluminium metal matrix composites

Twenty-one sets of specimens were fabricated by hot pressing powder mixtures containing various volume and size combinations of pure Al and SiC particles. Neither heat treatment nor secondary deformation processes were applied. The microstructures of the specimens were characterised by optical and scanning electron microscopy. Using a 10 MHz probe, the velocity of ultrasonic longitudinal waves was measured. The results show that in general the ultrasonic velocity increases with an increase in SiC content. However, for larger Al/SiC particle size ratio and higher volume fraction of SiC, ultrasonic velocity decreases owing to microporosity caused by the segregation of SiC particles along the grain boundaries of aluminium. It is concluded that ultrasonic techniques providing fast and non-destructive information are promising for quality assurance of the composites, and may also help to optimise process parameters.