The effects of potassium on the solid-liquid interface stability and on the shape

size and growth dynamics of eutectic Si in Al-Si eutectic alloy have been investigated under unidirectional solidification. The ways to enhance the mechanical properties of the alloy and the mechanism of modification of patassiurn have also been discussed. It can be summarized that（l）The shape of eutectic Si tends to be transformed from lamellar to fibrous and to nodular under given

solidifying conditions with strong modifying elements. （2） The potassium atoms tend to accumulate on the L-S interface of Si （111） plane and to blockade the growth steps of that plane and to reduce the growth rate of Si and

in turn. to made the phase become the leading phase of growth and in same time to remote the branching of Si twins.