Columnar to equiaxed transition in directional solidification of inoculated melts

Abstract Experiments on transient directional solidification were carried out with Al–3% Si and Al–7% Si alloys to study the modification by melt inoculation of the as-cast ingot macrostructure with columnar and equiaxed zones into a completely refined equiaxed structure. Without inoculation the macrostructure consists of typical columnar and equiaxed zones, separated by a relatively thin region of columnar to equiaxed transition. As the inoculant Al–3% Ti–1% B was added to the melt in a series of experiments relatively small equiaxed grains were observed in the as-cast macrostructure. For larger inoculant additions the number of these equiaxed grains increased. The macrostructure became completely refined and equiaxed as the Ti concentration in the melt increased in the small range 0.002