为了实现再生Al-Si-Mg合金的高强韧化，本工作采用SEM、TEM、DSC、热力学计算和同步辐射X射线断层扫描等手段，研究了Mg含量对Al-7Si-0.4Fe-xMg合金组织和性能的影响。结果表明，随着Mg含量的增加，初生α-Al的二次枝晶间距减小，富Fe相的二维形貌由细小针状逐渐转变为粗针状、汉字状和块状，而三维形貌由复杂的珊瑚状逐渐转变为独立的片状和多分支结构。随着Mg含量增加，富Fe相的类型则由单一的β-Fe相转变成β-Fe与π-Fe的混合类型，π-Fe相的数量、体积分数和球形度显著增加，而β-Fe相的数量和体积分数逐渐降低。当Mg含量为0.7%时，β-Fe的数量和体积分数较0.1%Mg合金降低了95.3%和73.6%，但等效直径增加73%。DSC结果显示Mg含量的增加降低了共晶硅的形成温度，促进了β-Fe相的粗化，同时促进了β-Fe相与熔体的包晶反应，形成了大量小尺寸和高球形度的π-Fe相。随着Mg含量的增加，合金的抗拉和屈服强度逐渐提高，而塑性逐渐降低。Al–7Si–0.4Fe–0.7Mg合金的抗拉强度、屈服强度和塑性分别达到197 MPa、135 MPa和10.9%，其抗拉强度和屈服强度较不含Mg合金分别提高了36.8%和137.0%，但伸长率降低了51.1%。β-Fe相的粗化加速了裂纹的扩展，对合金塑性造成了不利的影响。

The influence of Mg content on the microstructure and properties of recycled Al-7Si alloys using scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermodynamic software Jmat Pro, and synchrotron radiation X-ray computed tomography (SRXCT). The results show that as Mg content increases, the secondary dendrite arm spacing of the primary α-Al phase decreases. The morphology of the Fe-rich phase evolves from fine needle-like to coarse needle-like, Chinese-script, and granular forms, accompanied by a transition from a single β-Fe phase to a mixed structure of β-Fe and π-Fe phases. The three-dimensional (3D) morphology of the Fe-rich phase transforms from complex coral-like to independent flake-like and multi-branched structures. Simultaneously, the number, volume fraction, and sphericity of the π-Fe phase significantly increase. In contrast, the number and volume fraction of the β-Fe phase decrease by 95.3% and 73.6%, respectively, despite a 73% increase in its equivalent diameter. The increase of Mg content lowers the eutectic silicon formation temperature, promoting the coarsening of the β-Fe phase. When the Mg content is 0.4% and above, the β-Fe phase undergoes a peritectic reaction with the melt, resulting in the formation of a large number of small-sized, highly spherical π-Fe phases, which significantly reduces the volume fraction of the β-Fe phase. The 0.7Mg alloy demonstrates substantial improvements in tensile and yield strengths, increasing by 36.8% and 137%, respectively, compared to the Mg-free alloy. However, its elongation decreases by 51.1%. The formation of large-sized β-Fe phases intensifies crack propagation, leading to a marked reduction in the plasticity of high-Mg Al-7Si alloys. This study revealed the influence mechanisms of Mg content on the type and morphology of Fe-rich phases in Al-Si alloys with high Fe content.