The kinematics of deformation and the development of substructure in the particle deformation zone

Abstract

The details of the deformation near undeformable particles influence the recrystallization behaviour of commercial aluminium alloys. It has been shown that the size of the particle deformation zone (PDZ) and the local lattice rotation decrease with particle size and that a uniform distribution of very small closely spaced particles makes the deformation more homogeneous. Although a number of models have been proposed to describe the development of the PDZ, an explanation for this particle size effect remains elusive. In this paper, high resolution digital image correlation was used to map the deformation around particles of different sizes in a model Al-Si alloy. Deformation maps were compared to maps of local lattice rotation obtained using electron back scattered diffraction (EBSD) to elucidate the link between the kinematics and the resultant substructure. These results were also compared to crystal plasticity finite element predictions. The deformation maps revealed that deformation is concentrated in intense slip bands that have a characteristic spacing and which are strongly correlated to the deformation substructure. Whereas particles larger than this characteristic spacing interact strongly with the slip bands, causing large local rotations, smaller particles either interact more weakly or not at all. Since the strain between the bands is only a fraction of that in the bands, the rotations associated with the smaller particles are invariably smaller. Very small, closely spaced particles change the slip band pattern, decreasing the band spacing and decreasing the amount of shear within the bands. CFEM modelling was able to reproduce general features of the particle deformation zone but because it does not predict the development of slip bands and their characteristic spacing it fails to predict an effect of size on the local rotation.