Microstructure of A356 aluminum alloy refined by Al5Ti1B0.5RE master alloy was observed by OM （optical microscope）

SEM （scanning electronic microscope） and EDAX to understand the refining effects of the master alloy. The results indicate that the master alloy can greatly refine the grain size and dendrite in A356 aluminum alloy

in which the RE exhibits significantly positive role. AlTiRE phase formed in the master alloy with RE is unstable in Al melt it and could dissolved quickly into Al melt to release RE elements

which can decrease surface energy and tendency of segregation of TiB2 phase

increasing nuclei amounts. Meanwhile

RE can restrain the growth of TiAl3 phase and the formation of acicular TiAl3 phase as a result of RE easily segregating in grain boundary and phase interface of Al melt

raising the nucleation rate. In addition

RE can improve the refining effects of the master alloy due to effectively purifying the metallurgical quality of the master alloy and Al melt.