Ultrasonic attenuation of polycrystalline aluminum wetted with liquid gallium

Ultrasonic attenuation measurements were carried out on polycrystalline aluminum specimens that contain gallium in the grain boundaries as a function of temperature by using longitudinal waves of 10 MHz. When the specimen is cooled from 308 K to below 200 K, the attenuation exhibits a sharp drop below the melting temperature of gallium (302.9 K). In the heating process from 200 to 308 K, the attenuation shows an abrupt increase near the melting point of gallium. The change in attenuation is due to gallium in the grain boundaries and may be related to the brittle to ductile fracture transition observed for aluminum containing gallium in the grain boundaries.