2000 Volume 72 Issue 11 Pages 720-724
The present work is concerned with the establishment of the ultrasonic evaluation method of the thickness of remelted zone on Al alloy castings. Remelted zones with different thicknesses were formed on the surface of an Al-Cu-Si alloy casting plate, and backscattering waves were measured at various positions of the plate by the immersion method. When the ultrasonic wave was focused on a boundary between a remelted zone and a matrix, an intensity ratio of the backscattering wave of the remelted zone to that of the matrix took a maximum. The longitudinal wave velocity and density were measured with pieces containing the remelted zone to obtain the acoustic impedances of the remelted zone and matrix. The reflectivity at the boundary calculated from acoustic impedances was less than 1.5 % (-37 dB). The dendrite arm spacing and amount of porosity increased with increasing remelted zone thickness, which caused changes in the ultrasonic velocity and density of the remelted zone.
