The nucleation sites of primary Si in Al-Si alloys after addition of boron and phosphorus

The influence of boron (B) and phosphorus (P) on the solidification structures of near eutectic Al-Si piston alloys (ZL109) was investigated. It has been found that the addition of B can promote the precipitation of primary Si crystals, not only enhance the modification efficiency of phosphorus (P) but also reduce the addition level of P. It has also been shown that there are several kinds of heterogeneous nucleation sites of primary Si particles in the alloys modified by boron and phosphorus, respectively, AlP, Al-B-P-Mg and Al-B-Mg compounds. The tensile strength of the piston alloy with 0.2% B addition exceeds that with 0.05% P addition; moreover, owing to form more kinds of the heterogeneous nuclei of primary Si, the solidification structures and tensile strength of the alloys modified with B and P are improved. Compared with the traditional modifying method, the addition of B and P together may be a new and better way to improve the structures and mechanical properties of the ZL109 alloys