Improvement of Microstructure and Mechanical Properties of Near‐Eutectic Al–Mg₂Si Alloys by Eu Addition

To modify the microstructure and improve the tensile properties of Al–Mg₂Si alloys, different contents of Eu are added into near‐eutectic Al–Mg₂Si alloys by melting. Results show that the near‐eutectic Al–Mg₂Si alloys consist of primary α‐Al, the first eutectic and second eutectic (Al + Mg₂Si) phases, and a few Fe‐containing phase. When the addition of Eu reaches 0.05%, the first eutectic structure is refined, and the first eutectic Mg₂Si phase transforms from platelet into fiber. Meanwhile, the second eutectic phase increases, even that the alloy is almost the second eutectic phase when the Eu content is 0.3%. These changes are induced by the modification of Eu. Tensile testing shows that the ductility and the strength are improved to 8.6% and 178 MPa from 1% and 145 MPa when the Eu content is 0.05%, and fracture mode is also changed. This improvement is caused by the modification of the eutectic structure. The tensile properties are decreased or even deteriorated with further increasing the Eu content, which is induced by over‐modification of Eu addition. It is concluded that the modification of eutectic Mg₂Si phase by Eu addition contributes to the enhancement of mechanical properties of the near‐eutectic Al–Mg₂Si alloys.