Combined effects of reinforcement fraction and porosity on ultrasonic velocity in SiC particulate aluminum alloy matrix composites

This work aims at applying the broadband laser-ultrasonic spectroscopy for quantitative evaluation of combined influence of the reinforcement fraction and the porosity content on the phase velocity of longitudinal acoustic waves in stir cast SiC particulate aluminum alloy matrix composites. The investigated composites contain 3.8-15.5 wt % of SiC particles with an average size of 14 μm. The growth of SiC fraction is accompanied by the growth of the total porosity content that reaches 4.7% for the maximum fraction of SiC. These combined factors cause the occurrence of dispersion of the phase velocity - it decreases in the frequency band 3-10 MHz and increases in the frequency band 20-40 MHz in comparison with that in the matrix without any reinforcement. It was found that the relative velocity dispersion increases with the growth of the porosity content within the investigated composite area regardless of the SiC fraction. The derived empirical relation between the relative velocity dispersion and the porosity content can be used for rapid quantitative porosity characterization in stir cast SiC particulate aluminum alloy matrix composites to reveal any potential areas with a reduced strength before the fabrication of composite products.