The Characterization of Fe-rich Phases in a High-Pressure Die Cast Hypoeutectic Aluminum-Silicon Alloy

Both microstructural characteristics and fracture behavior of Fe-rich phases in a high-pressure die-cast hypoeutectic Al-Si alloy were investigated. Attention was focused on the morphology and formation mechanism of Fe-rich phases, together with their influence on fracture. Results show that primary Fe-rich phases exhibited in blocky shape precipitated from liquid while secondary Fe-rich phase in a large net shape was distributed along eutectic boundary participating in a ternary eutectic reaction. Through synchrotron X-ray tomography characterization, three Fe-rich phases with different morphologies, i.e., polyhedral shape, fine compact shape and Chinese script-type shape were extracted along the radial direction. Lower slow-shot speed promoted the polyhedral Fe-rich phase to precipitate in slow-shot sleeve while decreased the formation of fine compact and Chinese script-type Fe-rich phases in die cavity. Because of a worse deformation compatibility, polyhedral Fe-rich phases fractured and became stress concentration sources before the failure of the casting.