Effect of external ultrasonic treatment on hypereutectic cast aluminium-silicon alloy

The effect of ultrasonic treatment during casting of a hypereutectic Al-Si alloy (Etial 195) containing 18%Si on the microstructure and some mechanical properties has been investigated. For this purpose, a steel mould was placed inside an ultrasonic bath, and molten aluminium alloy at 740 degrees C was poured into the mould. Ultrasound was applied to the casts from the external side of the mould during solidification. Cooling curves were obtained by measuring and recording the temperature of the cast. The samples were subjected to X-ray diffraction analysis and hardness, wear and impact tests. The microstructure of the samples was examined by optical and scanning electron microscopies and investigated statistically with image analysis software. Hardness values increased from 49.8-52.3 to 57.7-61.6 HRB upon ultrasonic treatment during solidification. The application of ultrasonic vibration to the cast from the external side of the mould resulted in modification of the microstructure and improvement in mechanical properties.