It is shown from experiment that the pure B contained salt exhibits little refining effect, while the pure Ti contained salt, especially the salt containing 5Ti/1B, shows obvious refining effect on the pure aluminum. Crystallographic study indicates that Al 3 Ti particle is a more suitable nucleation site for the aluminum matrix than (Ti, Al)B 2 type particles (TiB 2 , AlB 2 and (Ti, Al)B 2 ), because there exist more coherent planes with aluminum matrix in the former. Thermodynamics estimation, X-ray diffraction (XRD) and SEM detection show that the refining mechanism of (Ti, B)-contained refiners is mainly contributed to the heterogeneous nuclei of fine Al 3 Ti particles dispersed in the melting, which comes from the reaction between the Ti and aluminum. (Al, Ti)B 2 type particle shows little or no direct refining effect, but it will reduce the size of Al 3 Ti since the Al 3 Ti nucleates and grows along the (Al, Ti)B 2 type particle interface.