The effect of sintering time on synthesis of in situ submicron α-Al2O3 particles by the exothermic reactions of CuO particles in molten pure Al

In this study, in situ alpha-Al2O3 reinforcing particles have been successfully synthesised in an Al-Cu matrix alloy by means of the conventional Hot Pressing (HP) method. The effect of sintering time on the forming of the alpha-Al2O3 phase at 1000 degrees C was investigated using Differential Thermal Analysis (DTA), X-ray Diffraction (XRD) and a Scanning Electron Microscope (SEM). The sintered composites contained thermodynamically stable alpha-Al2O3 particles and theta-Al2Cu eutectic phases, which were embedded in the Al-Cu matrix. The in situ alpha-Al2O3 particles were generally spherical and their mean size was observed to be less than 0.5 mu m. The results showed that sintering time influences not only the reaction rate of copper and the formation of Al2O3. Also, an increase in the sintering time accelerates the formation of submicron in situ alpha-Al2O3 particles and decreases the quantity of theta-Al2Cu intermetallic phase in the liquid aluminium. Additionally, sintering of composite for 30 min at 1000 degrees C increased the hardness from 60 to 174 HV. (C) 2012 Elsevier B. V. All rights reserved.