Effects of B on refining primary Si phase in hypereutectic Al-Si alloy were observed by OM（optical microscope）

SEM（scanning electron microscope）.The results reveal that B exhibits excellent refinement on primary Si phase in Al-20Si alloy.Size of primary Si phase is firstly decreased and then increased with increasing in B content

in which the smallest primary Si size can be observed with 0.065% B content.Trace Ca and Mg addition can promote the refining effects of B on primary Si phase

while C2Cl6 treatment can weaken the refining effects of B.The compounds formed from the reaction of B with Al

Si and Ca or Mg

which can be served as the nucleation substrates for primary Si phase

may be responsible for the refining effects of B on the primary Si phase.