EFFECTS OF FORCED ELECTROMAGNETIC VIBRATIONS DURING THE SOLIDIFICATION OF ALUMINUM-ALLOYS .1. SOLIDIFICATION IN THE PRESENCE OF CROSSED ALTERNATING ELECTRIC-FIELDS AND STATIONARY MAGNETIC-FIELDS

A new magnetohydrodynamic method of transmitting forced vibrations to solidifying aluminum alloy melts has been developed. Contrary to the c ase of the conventional mechanoacoustic systems, this device lends its elf very well to a fundamental investigation. The relatively accurate knowledge of both the electromagnetic pressure and the local velocity peaks has enabled us to reveal the specific effects of the oscillatory flow and of the cavitation phenomena on grain refinement. It has been shown that the cavitation threshold depends both on the surface state of the crucible internal walls and on the electromagnetic pressure pe ak. In the presence of well-developed cavitation situations, a very fi ne and homogeneous microstructure has been observed throughout the ing ot. A laboratory prototype of a new magnetohydrodynamic cavity resonat or, allowing for significant energy saving and likely to be used for i ndustrial applications, including the elaboration of metal matrix comp osites by means of a preform infiltration process, was also the subjec t of experimentation.