Microstructure Evolution of Hypoeutectic Al-Si Alloy With Electromagnetic Stirring and Ultrasonic Treatment

Effects of electromagnetic stirring(EMS),ultrasonic treatment(UST)and the combination of EMS and UST(EU)on solidification structure were investigated in hypoeutectic A1-Si alloy.The results indicate that EMS,UST and EU can refine primaryα-Al and modify eutectic silicon by influencing their nucleation and growth processes.EMS can fracture the dendrite arms and lead to decrease of primaryα-Al grain size.It also changes the morphology of eutectic silicon and widens the separation of silicon plates.For UST,the cavitation and acoustic streaming are the principal reasons for the microstructure refinement,which enhance the undercooled and heterogeneous nucleation.EU has combined the features of EMS and UST,hence obtains the best effect on the microstructure evolution.Significant refinement of primaryμ-Al and evident modification of eutectic silicon are observed with EU.In addition,the mechanism of morphological evolution with EU was preliminarily discussed.