Effect of the heating rate on the microstructure of in situ Al2O3 particle-reinforced Al matrix composites prepared via displacement reactions in an Al/CuO system

• The heating rate has a significant effect on the microstructures of composites.
• The microstructure is determined by the diffusion rate of O and Cu in the heating stage.
• The diffusion of Cu and O atoms is influenced by the heating rate.
• With increasing heating rate, the Al2O3 particle distribution becomes more uniformly.
• With increasing heating rate, the form of Al2Cu changes from network to block-like.

In this study, an in situ Al2O3 particle-reinforced Al(Cu) matrix composite was successfully synthesized using a displacement reaction between Al and CuO powders. The powders were mixed at a weight ratio of 4:1 Al to CuO, cold-pressed and holding time at 900 °C for 1 h using varying heating rates. The effects of the heating rate on the microstructures of the composites were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), optical microscopy (MO), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results indicate that all of the composites contain Al, Al2O3 particles and Al2Cu phases. Although the heating rate does not significantly affect the phase compositions of the composites, it has a significant effect on their microstructures, most likely because it strongly influences the diffusion rates of the Cu and O atoms. As the heating rate is increased, the Al2O3 particles become more dispersed, and they have a more uniform particle size distribution. Meanwhile, the Al2Cu structure transforms from the network (Al + Al2Cu) eutectic to the block-like Al2Cu phase. The ∼2 μm Al2O3 particles and the block-like Al2Cu phase are distributed uniformly in the Al matrix when the sample is placed directly into a 900 °C furnace. This sample has a relative higher Rockwell hardness B (HRB) value of 87.