EFFECT OF POROSITY, PORE DIAMETER AND GRAIN-SIZE ON ULTRASONIC-ATTENUATION IN ALUMINUM-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 ca stings exhibit section sensitivity there is a need for metallurgists t o non-destructively examine the castings to assess their grain size an d porosity content in order to establish the quality ann hence the per formance of the casting. In this paper experimental results and regres sion analysis correlating ultrasonic attenuation measurements with por osity, pore diameter grain size and ultrasonic frequency for cast spec imens made in Al-4.5% Cu alloy are presented. The results indicate tha t the attenuation coefficient (a) increases with the probe frequency ( f) used and the exponent n in the relationship (alpha proportional to f(n)) was found to be equal to one. The pore diameter appears to play a very significant role in determining whether attenuation measurement s could be used as a duality control tool to determine percentage poro sity in castings. It also appeals that high-frequency probes may be mo re useful to determine the grain size of the castings.