Semi-solid billet of ZA94 magnesium alloy was prepared by self-inoculation method（ SIM）. Influences of self-inoculants addition on semi-solid billet microstructure were investigated

and the mechanism of grain refinement was analyzed. The results show that the average grain size exhibits coarse with heterogeneous distribution when the inoculants addition is excessively more or less. The average grain size reaches 40. 2

45. 0 μm with 3%

5% self-inoculants addition. Nucleation particle in the melt is increased by adding inoculants

which plays a promoting role in heterogeneous nucleation. The addition of inoculants can directly affect own melting condition

and affect temperature fluctuations and energy fluctuations in the melt.