Abstract: Compression waves propagating through molten metals are contributed to degassing, accelerating reaction rate, removing exclusions from molten metals and refining solidification structures during metallurgical processing of materials. In the present study, two electromagnetic methods are proposed t o generate intense compression waves directly in liquid metals. One is the simultaneous imposition of a high frequency electrical current field and a static magnetic field; the other is that of a high frequency magnetic field and a static magnetic field. A mathematical model based on compressible fluid dynamics and electromagnetic fields theory has been developed to derive pressure distributions of the generated waves in a metal. It shows that the intensity of compression waves is proportional to that of the high frequency electromagnetic force. And the frequency is the same as that of the imposed electromagnetic force. On the basis of theoretical analyses, pressure change in liquid gallium was examined by a pressure transducer under various conditions. The observed results approximately agreed with the predictions derived from the theoretical analyses and calculations. Moreover, the effect of the generated waves on improvement of solidification structures was also examined. It shows that the generated compression waves can refine solidification structures when they were applied to solidification process of Sn-Pb alloy. This study indicates a new method to generate compression waves by imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves can probably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments.

Key words: High static magnetic field, Compression wave, Electromagnetic processing of materials