The effects of neodymium addition on the intermetallic microstructure and mechanical properties of Al-7Si-0.3Mg-0.3Fe alloys

The effects of neodymium (Nd) addition (0, 0.03, 0.06 and 0.09 wt.%) on the intermetallic microstructure and mechanical properties of Al-7Si-0.3Mg-0.3Fe (wt.%) alloys were investigated in this study. The microstructures of the intermetallic compounds in the alloys were observed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The Nd-rich particles gradually coarsened with increase of Nd addition and attached to the β-AlFeSi phase surface. Besides, the larger Nd-rich particles in the alloys decreased in size and became spherical after T6 heat treatment. In addition, the Nd addition could influence the amount of the π-AlSiMgFe phase by affecting the undercooling of the quaternary eutectic reaction (Liq. → Al + Si + Mg2Si + Al8FeMg3Si6). The amount of the π-AlSiMgFe phase increased when a little (0.03 wt.%) Nd was added, however with the further increasing Nd content, the larger Nd-rich particles often tightly attached on the β-AlFeSi phase surface and reduced the amount of the π-AlSiMgFe phase. Furthermore, the 0.03Nd as-cast alloy had the optimal conditions for the formation of the π-AlSiMgFe and the spherical Nd-rich particles with the ultimate tensile strength about 302 MPa and elongation about 3.1% after T6 heat treatment.