Effect of thermomechanical processing on the microstructure and mechanical properties of AlMg (5083)/SiCp and AlMg (5083)/Al2O3p composites. Part 3: Fracture mechanisms of the composites

In this paper, the last of three articles, the fracture mechanisms of as-cast composites, extruded composites and extruded monolithic 5083 aluminum alloy deformed in uniaxial tension are discussed. Dimple fracture is observed in both the monolithic 5083 aluminum alloy and the extruded composites, whereas the fracture of the as-cast composites is mainly caused by decohesion at matrix/particle interfaces and crack propagation along dendrite boundaries. For extruded composites the fracture is mainly nucleated by particle cracking and final failure occurs by shear coalescence of the small void sheets of matrix between the large reinforcing particles (or between clusters of particles). The large voids caused by fracture/decohesion of reinforcing particles induce localization of deformation in the matrix which accelerates the nucleation, growth and coalescence of the small voids in the matrix. Localization of deformation is one of the important factors which decrease the ductility of the composites. Three types of composites reinforced by SiC particles, artificially oxidized SiC particles prior to their incorporation and Al2O3 particles are examined. The effects of the interfacial reactions on the fracture of the composites are also presented.