Correlation of mechanical and ultrasonic properties of Al-SiC metal-matrix composite

Test specimens fabricated from a silicon-carbide (SiC) reinforced aluminum metal-matrix composite forging were examined ultrasonically and subjected to fracture testing. A-scans of ultrasonic backscatter were recorded, and the velocities of longitudinal and shear waves and the mean density were measured from which elastic moduli were computed. Tensile and fracture toughness specimens were made, and respectively subjected to mechanical testing followed by careful metallographic and fractographic examinations. Correlation of mechanical test results, fractographic and metallographic evaluations, and observed ultrasonic back-scatter and reflection phenomena indicates that an inhomogeneous distribution of SiC significantly degrades mechanical properties. Furthermore, nonuniformity of SiC concentrations is shown to be detectable by ultrasonic examination. The ultrasonic method shows promise for differentiating between regions in a composite sample that has varying mechanical properties.