INFLUENCE OF CAVITATION TREATMENT OF MELTS ON THE PROCESSES OF NUCLEATION AND GROWTH OF CRYSTALS DURING SOLIDIFICATION OF INGOTS AND CASTINGS FROM LIGHT ALLOYS

Actual melts of light alloys contain a large amount of insoluble impur ities; for aluminium and its alloys these are mainly oxides of the Al2 O3 type, so one could not consider such melts as the ideal liquid. As a rule, the most part of the impurities is represented by insoluble pa rticles less than or equal to .01 mu m in size. These impurities being nonwettable by the melt do not take part in the solidification proces s. Generation of cavitation bubbles, their nonlinear pulsation and com pression, surface distortion, and formation of new bubbles from fragme nts of the former ones result in the appearance of impact pulses of pr essure and cumulative jets. Under such conditions of the active cavita tion treatment of the melt, defects on oxide particle surfaces filled with the matrix melt ensure the transformation of these noncontrolled impurities to active solidification nuclei. This paper focuses especia lly on the features of the attainment of the extremely refined cast gr ain structure and the transition to nondendritic solidification of alu minium alloy ingots in acoustic cavitation field.