1998 年 70 巻 4 号 p. 266-272
Effects of silicon content are investigated on tensile properties and crack propagation behavior of Al-Si-Cu alloy die castings. The specimens are made by the low velocity shot die casting method. Silicon content of alloy is varied from 8.6 mass % to 15.4 mass %. The tensile strength and the elongation of hypo-eutectic Al-Si alloys are higher than those of hyper-eutectic Al-Si alloys. In the case of hypo-eutectic Al-Si-Cu alloys, a crack propagates through the eutectic phase in inter-dendrite region or α-Al dendrite. In the case of hyper-eutectic silicon alloy, the primary silicon acts as the origin of fracture because primary silicon crystallizes with facet planes. The crack mainly propagates through primary silicon grains or along eutectic silicon. Primary silicon particles tend to segregate in case of low velocity injection casting. This macro-segregation of primary silicon particles deteriorates the mechanical properties. Especially tensile strength decreases with increase of segregation.