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.