Microstructure characterization of Al-Al2O3p composites produced by high energy ball milling

Ultra fine grained composites of an aluminum alloy reinforced with particulate Al2O3 of 5 and 15 vol% were produced using the high energy ball milling (HEM) method. The changes in size and distribution of particles, i.e. Al2O3 and CuAl2 hard phase, in the aluminum matrix were scrutinized during the milling process, ranging from 10 min to 8 h. Evaluation of the microstructures has shown that after short milling times reinforcing particles are observed rarely inside the matrix-powder showing almost no change in particle size but smearing and sticking to the deformed particles. With further milling of composite powders, 2 h and more, the reinforcement particles were broken into small particles becoming finer (less than 1 mu m) and more uniformly distributed in the aluminum matrix. SEM investigations also revealed that longer periods of milling lead to ultrafine intermetallic compound phase of Cu Al-2 within the aluminum matrix, which could be also confirmed by XRD