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.
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