Considering the S-L interface morphology stability, the S-L interface energy, the Joule heat produced by electric current at the S-L interface, and the change of solute concentration at the S-L interface indirectly caused by elec-tric current, the mechanism of reduction of columnar dendrite spacing in unidirectional solidification caused by electric cur-rent passing through solid-liquid interface was studied. The following conclusions can be drawn that: 1) under sub-rapid solidification condition, increasing electric current density will improve the stability of S-L interface, thus decreasing the columnar dendrite spacing; 2) there are two ways by which the increase of electric current decreases the columnar dendrite spacing, one is promoting the splitting of the protruding tips at the S-L interface, the other is promoting the forming of new convex parts at the bottom of the concave interface.

Based on theoretical analyses, the effect of electric current density on stability of solidification interface mor-phology of QAl24 alloy was studied experimentally. The results show that the experimental results agree well with the theoretical analyses, and the following conclusions can be drawn: the increase of electric current density improves the stability of the solidification interface morphology under the condition of no convection of the liquid metal. Otherwise this convection will slow down the trend of solidification interface developing to stability caused by increasing electric current density.

When current passes through the solid-liquid interface, the growth rate of crystal, solid-liquid interface energy and radius of curvature at dendritic tip will change. Based on this fact, the theoretical relation between the distribution of solute at solid-liquid interface and current density was established, and the effect of current on the distribution coefficient of solute through effecting the rate of crystal growth, the solid-liquid interface energy and the radius of curvature at the dendritic tip was discussed. The results show that as the current density increases, the distribution coefficient of solute tends to rise in a whole, and when the former is larger than about 400 A/ cm-, the latter varies significantly.

A continuous unidirectional solidification equipment with the advantages of electric-slag remelting, induction heating, continuous casting and unidirectional solidification was built to study the QAl924 Cu-Al alloy. The results show that the electro-slag induction continuous unidirectional solidification process can be used for the steady continuous unidirectional solidification of QAl924, and revitalizes the down-pulling continuous unidirectional solidification process; that the temperature distribution in the mold wall reflects that of the molten metal in the mold, thus the temperature distribution in the mold wall can be used to control the electric-slag induction continuous unidirectional solidificationprocess; and that the mutual matching of the technological parameters is the key to stabilize the solidification process.