Relationship between microstructures and contents of Ca/P in near-eutectic Al-Si piston alloys

The relationship between microstructures and contents of Ca/P in near-eutectic Al-Si piston alloy (ZL109) was investigated by optical microscopy and electron probe microanalyzer (EPMA). Ca was found to have an obvious influence on the microstructures of ZL109 alloys. It is difficult to present phosphorus refinement effect when the Ca content in the ZL109 alloy exceeds 100 ppm. In order to obtain a good phosphorus refinement effect, the content of Ca impurity in the alloy should be under 50 ppm. It has also been shown that Ca can modify eutectic Si and enhance the formation of α-Al dendrites and fibrous eutectic Si in the alloy. Controlling the content of Ca impurity by the addition of C2Cl6 to the melt resulted in the appearance of phosphorus refinement effect. With the decrease of Ca content from 100 ppm to 12 ppm, the average primary silicon particle size is reduced to 16.2 μm from 31.7 μm.