1989 年 38 巻 426 号 p. 255-260
Al-4wt% Cu alloys were solidified unidirectionally to obtain the columnar structure, and the ultrasonic velocity and the attenuation were measured by using longitudinal waves with a frequency of 5MHz, to investigate the relation between the cast structure and the ultrasonic parameters. The attenuation increased with the diameter of columnar grain, but largely scattered among different ingots. The attenuation also increased with the dendrite primary arm spacing, and a linear relation was obtained between them. Since the attenuation varied with the arm spacing after homogenization, the attenuation was found to be controlled by small pores in the ingot; the attenuation linearly increased with the fraction of porosity area and the average porosity size. The attenuation of ultrasonic waves propagated parallel to the columnar grains was three times larger than that of ultrasonic waves propagated perpendicular to the columnar grains. The ultrasonic velocity slightly decreased with distance from the ingot bottom. However, the velocity had no dependence on the diameter of columnar grain, the solute segregation or the porosity parameters.