Effect of porosity, pore diameter and grain size on ultrasonic attenuation in aluminium alloy castings

The quality of a casting depends on the presence or absence of defects such as porosity and on the final metallurgical microstructure. As castings exhibit section sensitivity, there is a need for metallurgists to non-destructively examine the castings to assess their grain size and porosity content in order to establish the quality and hence the performance of the casting. In this paper; experimental results and regression analysis correlating ultrasonic attenuation measurements with porosity, pore diameter, grain size and ultrasonic frequency for cast specimens made in Al-4.5% Cu alloy are presented. The results indicate that the attenuation coefficient (α) increases with the probe frequency (f) used and the exponent n in the relationship (α ∝ fn) was found to be equal to one. The pore diameter appears to play a very significant role in determining whether attenuation measurements could be used as a quality control tool to determine percentage porosity in castings. It also appears that high-frequency probes may be more useful to determine the grain size of the castings.