Automated serial sectioning is presented as an attractive experimental technique for producing an accurate, large-scale three-dimensional (3-D) digital microstructural model of an extruded discontinuously reinforced aluminum composite material. The model is used as input for an elastic-plastic 3-D finite-element analysis that simulates tensile loading of the microstructure. The 3-D visualization and characterization of the resultant deformation structures within the composite microstructure has allowed some of the critical microstructural features that control the tensile response to be identified.