Multiple phases growth dynamics of a recycled Al alloy under pulse magnetic fields – an operando study by the ESRF-EBS and multiphysics modelling

Abstract

Many previous studies have demonstrated that pulse magnetic field (PMF) is an effective technique for controlling the morphology and evolution of different phases of metallic alloys during the solidification processes. However, systematic knowledge and guidance on how to use PMF to alter or control the 3D microstructural evolution of complex intermetallic phases have not been established. Here, we used the ESRF Extremely Brilliant Source (EBS) to study in real time and in operando conditions the multiphase growth dynamics during solidification of a recycled Al alloy (Al5Cu1.5Fe1Si alloy, wt.%) under PMF. By analyzing systematically the ∼10 TB image and tomography data collected in-situ, complemented by multiphysics modelling of the PMF induced melt flow and stress fields, we have revealed and elucidated how an α-Fe phase nucleated heterogeneously on an α-Al dendrite, and how it grew into skeletal tetragonal prism with complex, interconnected 3D network. PMF was able to produce sufficient differential stresses into the platelet-shaped β-Fe phases and fracturing them via a cyclic fatigue mechanism in a few to hundreds of pulse cycles. The stresses produced were dependent on the peak magnetic flux and geometrical/morphological characteristics of the phases. PMF was able to change the solute boundary layers in the interdendritic regions, changing the local solute fluctuation and constitutional undercooling, and therefore changing the nucleation condition for Fe phases. These effects can be further explored for controlling and refining of the Fe phases in recycled Al alloys.