Effect and Mechanism of Refinement on Macro-segregation in Squeeze Casting Low-Tin Bearing Alloys

During the investigation of the direct squeeze casting process for the production of Al-5Sn-Cu low-tin bearing alloy parts, particularly floating bushings, this study has explored the effect and mechanism of grain refiner on reducing macro-segregation within low-tin bearing alloys. This has provided an effective solution for Sn segregation in the alloy and broadened its application prospects in the bearing field. The findings revealed significant microstructural differences both in the longitudinal and transverse sections, and abnormal macro-segregation of Sn at hot spots without grain refiner. Conversely, grain refinement improved the microstructure, resulting in a uniform distribution of Sn, effectively mitigating the macro-segregation phenomena, especially at hot spot positions. The grain refiner promoted the growth of equiaxed crystals by generating numerous heterogeneous nucleation sites. These played a crucial role during the later stages of solidification by uniformly isolating the Sn-rich liquid phase and preventing the formation of feeding channels for this phase as solidification completed. These actions ultimately prevented the macro-segregation of Sn. The approach not only enhances the quality and reliability of these castings but also provides critical guidance for optimizing the manufacturing of aluminum-based bearing alloys.