Microstructural evolution of Mg-Al-Re alloy reinforced with alumina fibers

Few studies were reported on the phases’ relationships of AE44 (Mg-4.0Al-4.1RE-0.3Mn, wt.%) and its composites. In this work, AE44 alloy and Saffil (δ-Al2O3)/AE44 Metal matrix composite (MMC) were both prepared by slow shot high pressure die casting (SS-HPDC) technology and their phase constitutions were all studied in detail using experimental techniques combined with CALPHAD (Calculation of Phase Diagram) modeling. The results revealed that the alloy consists of the α-Mg matrix, Al11RE3 intermetallic phase, and one trace phase Al3RE, while the composite contains five major phases: α-Mg, δ-Al2O3, Al3RE, MgO and Mg2Si, and two trace phases of Al2RE and Al11RE3, respectively. Al11RE3 is partly derived from Al2RE, while Al3RE is a product of the peritectoid reaction between the two precipitates. The presence of MgO and Mg2Si is due to the interfacial reaction between the SiO2 binder in the fiber preforms and the molten magnesium during infiltration. The use of SiO2 binder in the preform manufacturing was limited/minimized to reduce the MgO formation in the MMC casting process, which can be detrimental to the fatigue performance of the MMC materials.