This paper describes the procedure used to determine a suitable frequency range for the testing of UNS A23800 aluminum alloy castings while accommodating material variations within the part. The results obtained from immersed pulse/echo ultrasonic testing indicate that focused probes operating at frequencies between 5 and 10 MHz are more suited to the testing of aluminum alloy die castings with surface roughness Ra values varying from 50 to 100 μm (2 × 10-3 to 4 × 10-3 in.). Nevertheless the final selection of a suitable frequency will depend largely on the size of discontinuities to be detected.

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