Effect of milling time and addition of alumina powder on the structural properties and fracture surface of nanocrystalline Al

The effects of milling time and the addition of alumina reinforcement on the structural evolution of Al matrix were investigated. By analysing the cross section of powder, cold welding mechanism for both monolithic and composite powders was studied. Results show that presence of the alumina powder has a marked effect on variation of apparent density, preferred orientation, impurity content and thus lattice parameter of Al by milling time. The reduction of the grain size to the nanometeric scale changes the fracture mechanism of Al particles completely, from dimpled into intergranular, though alumina addition does not seem to have notable influence on the fracture mechanism.