Effect of high-intensity ultrasonic treatment on modification of primary Mg_2Si in the hypereutectic Mg-Si alloys

摘要

The effect of high intensity ultrasonic treatment (H1UST) on modification of primary Mg_2Si in the hypereutectic Mg-5 v/tXSi alloy have been studied. Various resulted microstructures were produced in this alloy by employing ultrasonic vibrations during solidification process at different pouring temperatures and for different application times. The results showed clearly that in the absence of HIUST, the dendrites of primary Mg_2Si were coarser and non-uniform in size. Upon HIUST of the alloy during solidification process, nearly uniform and polyhedral shape of primary Mg_2Si with a network of Mg phase segregated along the grain boundaries were obtained. Interestingly, the average size of primary Mg_2Si decreased significantly with increasing the pouring temperature and the vibration time of HIUST reached a minimum at 800 °C and 90 s. After that the average size of primary Mg_2Si increased slightly with further increasing the pouring temperature and the ultrasonic vibration time. Modification mechanism resulting in the development of microstructure is also investigated.