Plastic Deformation and Work Hardening

This research has been carried out to understand the relation between work hard-ening, deformation behaviour, dislocation substructure and crystallographic texture developed during plastic flow in pure Al and continuous cast and direct chill cast AA5754 AI-Mg alloys. Tensile and strain rate sensitivity tests are performed in the temperature range 4.2K-295K; details of the process of dislocation accumulation, the dislocation substructure development and texture evolution are followed using a range of techniques such as TEM, in-situ resistivity measurements and X-ray diffraction. The tensile deformation results show an unprecedented level of strength and unusual work hardening behaviour of AI-alloys at 4.2K. The electrical resistivity data suggest that fracture is initiated by the collapse of the dislocation network at places where dislocations develop a critical spacing for spontaneous annihilation. This spacing is estimated at approximately 8nm at 4.2K for both pure Al and Al alloys and rv12nm at 78K for pure AI. Strain rate sensitivity measurements suggest that deformation of high purity Al is governed by dislocation-dislocation interactions in a broad rang