Particle redistribution and matrix microstructure evolution during hot extrusion of cast SiC p reinforced aluminium alloy matrix composites

The aim of the present investigation is to understand particle redistribution and matrix microstructure development during hot extrusion of aluminium matrix composites and the influence of process parameters on these two key microstructural features. Cast composite billets have been partially extruded to study the sequence of microstructure development. Strain and strain rate distribution in the partial extrudates have been measured using a ‘visioplasticity’ technique. Results indicate that strain and strain rate distribution are more homogeneous in the composites than in the unreinforced alloy. Extrudate microstructures reveal the presence of particle bands and deformation bands aligned in the extrusion direction. It is noted that shearing of SiC particle clusters leads to particle banding, and an increase in extrusion ratio and/or a decrease in particle size enhances particle band formation. This phenomenon is attributed to increasing strain partitioning between the cluster and the matrix with increasing strain and/or decreasing particle size. The formation of deformation bands is attributed to a grain splitting phenomenon which is found to be more extensive in composites compared with the unreinforced alloys.