Pulsed magnetic field modulation of solidification microstructure and self-lubricating property for ternary Al–7Bi–1Sn immiscible alloy

Effective controlling the solidification microstructure of immiscible alloy to obtain a homogeneous distribution of the minor second phase remains to be a huge challenge. In this study, pulsed magnetic field (PMF) was intentionally applied during solidification process of ternary Al–7Bi–1Sn immiscible alloy, aiming to tailor its solidification microstructure. The underlying mechanisms for microstructure and self-lubricating property evolution were elucidated. The application of optimal PMF during solidification process of Al–7Bi–1Sn alloy can significantly refine the matrix and second Bi(Sn)-rich phase, and effectively suppress the severe macro-scale gravity segregation resulting from liquid-liquid phase separation. The refinement mechanism of the second Bi(Sn)-rich phase should be attributed to the cavitation effect caused by alternating squeezing and pulling forces, as well as the strong shear force generated by the existence of swirl flow. The force convection induced by the application of PMF improves the dispensability of the second Bi(Sn)-rich phase. In addition, the application of PMF can obviously enhance the self-lubricating property of the alloy. More specifically, the self-lubricating property of Al–7Bi–1Sn alloy first increases with the increasing applied PMF excitation voltage in the range of 0 V–500 V, and slightly decreases for 700 V. This should be related to the dispensability of the second Bi(Sn)-rich phase resulted from the application of PMF with different applied excitation voltage. It is anticipated that the present study would provide significant guidance for the processing of immiscible alloy with homogeneous solidification microstructure.