Investigations on the internal flow behavior and microstructural evolution of the Al-7 wt%Si alloy under external multifields

In this paper, the effects of a direct current (DC), a complex magnetic field (a combination of a static magnetic field (SMF) and a rotating magnetic field (RMF)), and a combined field (DC + SMF + RMF) on the flow behavior, microstructure, and mechanical properties of the Al-7 wt%Si alloy were studied by experimental and numerical simulation method. The results showed that the combined field significantly extended the effective range and intensity of the flow field, which increased the internal melt flow from 4.5 mm/s to 18.31 mm/s, and improved the surface shrinkage. On the cross-section of 55 mm height, the velocity difference of the melt between the vicinity of the side wall and the center decreased from 20 mm/s to 3.5 mm/s, which indicated a significant improvement in the stability and uniformity of the flow field and mitigating silicon segregation. Consequently, Quantitative analysis revealed that the maximum grain size decreased from 1393 μm (natural solidification) to 515 μm under composite field treatment, and the tensile strength was improved from 95.81 MPa to 121.44 MPa. It indicated a new approach for homogenizing the solidification structure, refining the grain size in Al-7 wt%Si alloys, and improving the mechanical properties of castings.