Effect of the heating rate on the microstructure of in situ Al_2O_3 particle-reinforced Al matrix composites prepared via displacement reactions in an Al/CuO system

摘要

In this study, an in situ Al_2O_3 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 ℃ 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, Al_2O_3 particles and Al_2Cu 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 0 atoms. As the heating rate is increased, the Al_2O_3 particles become more dispersed, and they have a more uniform particle size distribution. Meanwhile, the Al_2Cu structure transforms from the network (Al + Al_2Cu) eutectic to the block-like Al_2Cu phase. The ～2 μm Al_2O_3 particles and the block-like Al_2Cu phase are distributed uniformly in the Al matrix when the sample is placed directly into a 900 ℃ furnace. This sample has a relative higher Rockwell hardness B (HRB) value of 87.