Grain refinement in hypoeutectic Al-Si alloys using ultrasonic vibrations

In this study the effect of ultrasonic vibrations on the microstructure of a commercial hypoeutectic Al-Si alloy, (Al-7Si-0.4Mg), was investigated during solidification. In this work, the common chemical agents for grain refinement and modification of hypoeutectic Al-Si alloys (Al-3Ti-B, Al-5Ti and Al-Sr) were used to assess the structural enhancement resulted from ultrasonic vibrations. Solidified alloys were studied using optical microscopy to investigate the effect of grain refiners and eutectic modifiers alongside the effect of ultrasonic treatment. It was found that when used along with compared to common grain refiners, ultrasonic treatment lead to an extra grain refinement of the primary aluminium. Studying the recorded cooling curves showed that ultrasonic treatment lowered the melt undercooling and increased the eutectic nucleation and arrest temperatures. Moreover, strontium-modified specimens showed a significant level of primary aluminium grain refinement after being treated by ultrasonic vibrations.