The evolution of the 3D Fe-rich phases of Al-7.0Si-1.2Fe alloys with different Mn contents was visualized and character-ized using synchrotron X-ray computed tomography,and the effect of Fe-rich phases with typical morphologies on the fracture behavior during tensile testing was analyzed.The results showed that the Fe-rich phase changed from platelet-like β-Al5FeSi into α-Al15(FeMn)3Si2 with various morphologies after the addition of Mn.The Mn addition not only significantly reduced the volume fraction,equivalent diameter and interconnectivity of the Fe-rich phase but also greatly increased the sphericity,surface thickness,and distribution of the mean curvature and surface thickness.Furthermore,the equivalent diameter of α-Al15(FeMn)3Si2 had an inverse exponential function relationship with its sphericity.The 3D morphology of α-Al15(FeMn)3Si2 can be summarized as massive and regular polyhedrons,hollow and regular polyhedrons,and multi-branched polyhedrons.The fraction of the different 3D morphologies in each alloy is related to the Mn content,where excess Mn increased the number and volume fraction of the large Fe-rich particles with a low sphericity.The ductility of each alloy was significantly improved by the addition of Mn but gradually decreased when the Mn/Fe ratio exceeded 1.2.The increase in large α-Al15(MnFe)3Si2 with a low sphericity was the main reason for the decreased ductility of alloys with a high Mn content.