Formation of Mg–Mg₂Cu nanostructured eutectic in Mg-based metal matrix composite

We report the fabrication and characterization of a Mg-based metal matrix composite reinforced by MgO ceramic and Mg–Mg₂Cu eutectic. The composite was fabricated by sintering and quenching of a Mg–20 wt.% CuO sample. We performed differential scanning calorimetry (DSC) on the sample and found that the reaction between Mg and CuO took place at about 420 °C. When the sample was sintered to 550 °C and cooled down, the two-phase Mg–Mg₂ Cu eutectic formed. The final composite product contained MgO particles and Mg–Mg₂Cu eutectic, which were embedded in the Mg matrix. Based on the results from DSC and scanning and transmission electron microscopies, a model is proposed to describe the competitive growth of Mg and the eutectic during solidification. We also found that the microstructure of the Mg–Mg₂ Cu eutectic strongly depended on the rate of cooling. The lamellar thickness of the eutectic could be reduced to 120 nm by oil-quenching the sintered sample.