Ultrasonic characterization of SiC-reinforced aluminium

The nondestructive characterization of the elastic and the anelastic behavior of metal-matrix composites is essential to their manufacturing processes. The effects of volume fraction of second-phase SiC-particles on the second and third-order elastic constants have been investigated in the aluminium alloys 8091, 7064, and 6061. The influence of second phase on the ultrasonic absorption and dispersion has also been studied. For relatively small amount of reinforcement (20 volume percent), the second-order elastic constants are found to increase linearly with SiC content. The measurements also show a high degree of anisotropy along the extrusion direction where the constants have the highest values. The third-order elastic constants 1, m and n are found to increase with increasing SiC content, while n decreases with SiC content. As expected, the presence of SiC increases the absorption coefficient in these composites, and indicated that the reinforcements is a dominant factor in the anel astic behavior of these materials. It is also shown that the dispersion measurements can be used to estimate the size of the second-phase scatterers which influences the physical and mechanical properties of the composites.