Investigation into the role of rare earth oxides in controlling the microstructure and enhancing the mechanical and corrosion properties of as-cast Al-Si-Mg alloys
Wei Chen, Xinru Xu, Peipei Jiang, Wei Qiu, Lang Gan, Kang Chen, Cong Li, Jian Chen, Dao‐Guang He, Yongcheng Lin
Abstract
This study examines the impact of the rare earth oxide La 2 O 3 on the microstructure, mechanical and corrosion resistance properties of as-cast Al-Si-Mg (A356) alloys, with a specific focus on the A356 alloy. By incorporating varying amounts of La 2 O 3 (0 wt%, 0.2 wt%, 0.3 wt%, and 0.4 wt%) into the A356 alloy, four samples (AL0, AL2, AL3, and AL4) were produced. The findings demonstrate that an optimal addition of La 2 O 3 (0.3 wt%) can effectively reduce the secondary dendrite arm spacing (SDAS), refine the eutectic Si phase, and modify the morphology of Fe-rich phases, thereby significantly enhancing the overall performance of the alloy. The transformation in the morphology of the Fe-rich phases is accompanied by changes in their elemental composition , including the transition from elongated rod-like AlFeSi phases to shorter rod-like Al 7 Fe 6 La phases. Specifically, the AL3 sample displays the best mechanical properties, with increases in hardness, yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of 11.11 %, 71.43 %, 36.45 % and 233.46 %, respectively. Moreover, AL3 exhibits superior corrosion resistance , characterized by the highest corrosion potential (-0.88 V) and the lowest corrosion current density (3.6 ×10 −7 A/cm 2 ). The addition of La 2 O 3 promotes grain refinement, reduces the size of secondary phase particles, and the formation of Al 7 Fe 6 La phase collectively contributing to the enhanced performance of the A356 alloy. The present study provides theoretical support for utilizing rare earth oxides as a viable alternative to pure rare earth metals in Al alloys , presenting a cost-efficient strategy tailored for industrial implementations.