The investigation of continuous nucleation and refinement of primary Si in Al–30Si mushy zone

In this paper, the refinement performance of Al–P master alloy on mushy Al–30Si alloys was investigated and a new refining method was proposed. The results show that primary Si can be refined partially when the Al–P master alloy is added into mushy Al–30Si alloys, proving that the heterogeneous nucleation of primary Si is a continuous process even in liquid–solid state, which is also confirmed by EPMA results. On basis of these results, a new refining method named as continuous refining method has been proposed, i.e. continuously adding refiners at different temperatures during the cooling and solidifying stage of Al–30Si. Compared with the conventional refinement method by which the alloys are refined at high temperature, better refinement effect can be obtained in the new refinement method: the average size of primary Si is decreased to 30 μm, and the tensile strength increases by 19.6%. Moreover, the mechanism of the continuous refining method was also discussed.