Effect of boron on microstructure and mechanical properties of eutectic aluminum-silicon alloy modified with phosphorus

In order to understand the effect of boron on the microstructure and mechanical properties of eutectic aluminum-silicon alloy modified with phosphorus, complex modification of eutectic aluminum-silicon alloy by aluminum-3phosphorus and aluminum-3boron was conducted. The results show that the area fraction of primary α-aluminum in eutectic aluminum-silicon alloy modified with aluminum-3phosphorus increased first and then decreased with increasing amounts of aluminum-3boron. The area fraction and the size of primary silicon decreased rapidly first and then stabilized. The morphology of eutectic silicon transformed from needle-like into fine short rods or granules after complex modification with aluminum-3phosphorus and aluminum-3boron. The ultimate tensile strength of the alloy modified with 0.4 wt.% aluminum-3phosphorus and 0.2 wt.% aluminum-3boron increased by 18 %, compared with that of the eutectic aluminum-silicon alloy modified with aluminum-3phosphorus, while the elongation decreased by 5 %. It was concluded that the comprehensive mechanical properties of eutectic aluminum-silicon alloy were improved.