Influence of cavitation treatment of melts on the processes of nucleation and growth of crystals during solidification of ingots and castings from light alloys

Abstract

Actual melts of light alloys contain a large amount of insoluble impurities; for aluminium and its alloys these are mainly oxides of the Al 2O 3 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 particles ⩽ 1.0 μm in size. These impurities being nonwettable by the melt do not take part in the solidification process. Generation of cavitation bubbles, their nonlinear pulsation and compression, surface distortion, and formation of new bubbles from fragments of the former ones result in the appearance of impact pulses of pressure and cumulative jets. Under such conditions of the active cavitation 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 especially on the features of the attainment of the extremely refined cast grain structure and the transition to nondendritic solidification of aluminium alloys ingots in acoustic cavitation field.