Optimizing the parameters for in situ fabrication of hybrid Al-Al2O3 composites

A new powder metallurgy technique was developed in order to increase the reinforcement proportion of aluminum with two different fractions of Al2O3. Aluminum powders were mixed with 20 % vol of alumina particles as primarily reinforcement, and additional alumina was produced in situ as a result of reaction between Al and additional 7.5 % vol of Fe2O3 powder. The three grades of powders were milled and hot-pressed into small preforms, and differential scanning analysis (DSC) was performed to determine the kinetics of microstructural transformations produced on heating. DSC curves were mathematically processed to separate the superposing effects of thermal reactions. Transformation points on resulting theoretical curves evidenced two distinct exothermal reaction peaks close to the melting point of aluminum that were correlated with formation of Fe-Al compounds and oxidation of aluminum. Microstructural investigations by means of SEM-EDX and XRD suggested that these exothermal reactions produced complete decomposition of iron (III) oxide and formation of Fe-Al compounds during sintering at 700 A degrees C, and therefore, heating at higher temperatures would not be necessary. These results, along with calculation of activation energies, based on Kissinger's method, could be used to optimize the fabrication of Al-Al2O3 composites by means of reactive sintering at moderate temperatures.