The refining effect of Al5Ti1B0.5RE master alloy on A356 Al alloy was studied

and microstructures of A356 Al alloy and the master alloy were analysed by OM、SEM、EDAX etc. The results showed that the master alloy had not only obvious effect of grain refinement

also a significant role in refining dendrite grain of A356 Al alloy. RE elements played an important role in the master alloy

that is

RE could easily form （AlTiRE） phase in the master alloy

but （AlTiRE） phase was unstable in Al melt and could dissolve quickly by releasing RE elements

which deceased the surface energy of Al melt and the tendency of TiB2 particles getting together in Al melt

thus increasing. the number of nuclear particles. Moreover

RE elements could easily get adsorption together between the grain boundary and the phase boundary of Al alloy

thus filling the defects of grain surface

and hindering TiAl3 growing and the formation of needle or strip TiAl3 phase

which increased the nucleation rate on refinement nuclei. Furthermore

RE could effectively guarantee metallurgical quality.of the grain refiner and Al melt

thus also enhancing the effect of the grain refiner.