Study of microstructure and mechanical properties of Mg–3Y-1REmOn composites by Y-REmOn (RE=La, Ce, Sm, Gd) in-situ reaction

The expensive cost of master alloys for preparing high-performance Mg rare-earth alloys has prevented their large-scale production and application. This paper demonstrates that some inexpensive rare-earth oxides can replace the corresponding master alloys for material preparation by thermodynamic calculations, and low-cost Mg–3Y–1La2O3, Mg–3Y–1CeO2, Mg–3Y–1Sm2O3, and Mg–3Y–1Gd2O3 composites were prepared using the melting-casting-hot extrusion method. Y can reduce some rare earth oxides to rare earth element. When the content of rare earth element is high, it can form a second phase (Mg17La2, Mg12Ce) with Mg which is well bound to the matrix, revealing that the in-situ composite has a good particle-matrix interface relationship. In addition, the in-situ Mg17La2 is coarse and has a higher volume fraction, which plays a key role in the improvement of mechanical properties. The ultimate tensile strength of Mg–3Y–1La2O3 composite is 55.1 MPa higher than that of Mg–3Y alloy. The strengthening mechanism can be attributed to the load transfer and coefficient of thermal expansion (CTE) of the Mg17La2.