Influences of incident angle of ultrasonic waves on measurement of remelted zone thickness

摘要

The influences of the incident angle of the ultrasonic wave on the measurement of remelted zone thickness in aluminum alloy castings were examined. When ultrasonic waves generated from a focussed probe were incident on a specimen surface with an oblique angle, the focussing of the waves in the specimen became worse with increasing angle of incidence. When an incident angle was less than 10 × (π /180) rad, the remelted zone thickness was evaluated from distributions of back scattering wave intensity, but the evaluated value of the remelted zone thickness became larger with the increase of the incident angle. When the incident angle was larger than 10 × (π/180) rad, the intensity of back scattering waves from a boundary between the remelted zone and the matrix became so small that the position of the boundary could not be detected distinctly. Thus the remelted zone thickness was not evaluated. The remelted zone thickness was also calculated numerically assuming that the intensity of the ultrasonic wave decreased with increasing travelling distance. The calculated values were in good agreement with the measured results, when the attenuation coefficient was assumed to be 1 to 2 dB/mm.