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 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 ann 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 (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 measurements could be used as a duality control tool to determine percentage porosity in castings. It also appeals that high-frequency probes may be more useful to determine the grain size of the castings.