Role of Pore Size Distribution in Ultrasonic Characterization of Microporosity in Aluminum Castings

Microshrinkage porosity in cast aluminum plates was characterized utilizing the frequency dependence of ultrasonic attenuation caused by pore scattering. The back‐surface echo spectral shape was fitted assuming various size distributions of spherical pores. Best fits were obtained for a lognormal distribution. Pore volume fraction inferred from these fits overestimates the actual volume fraction by a factor related to the complicated, nonspherical pore shapes. These results permit accurate, nondestructive laboratory measurements of porosity with 2‐mm spatial resolution.