plastic flow at a strainhardening exponent 0.5 < n < 0.2 and is accompanied by an oscillatory change in the local strain rate in the hardening-softening mode in the deformation zone. This is also accompanied by a periodical progressive decrease in the cross section of a sample and necking. In (3), we revealed the relation between an oscillatory change in the local strain rate and the cyclicity of microstructural evolution in the deformation zone, which is accompanied by a change in the size, elongation, and coarsening of structural elements; as a result, it can be related to texture forma� tion in a material. Indeed, the change in the specimen geometry induced by a change in the state of stress and flow localization in plastic anisotropy materials is inevitably accompanied by the appearance of texture heterogeneity (4). Although the deformation behavior of α�Zr and its alloys has been extensively studied, the mechanisms of their texture formation are still incom� pletely clear, which is caused by insufficient experi� mental data on the laws of crystallographic reorienta� tion of individual grains determined by shear stresses and the slip and twinning systems activated in them. The possibility of the operation of certain secondary slip systems during lowtemperature deformation and the role of basal slip and twinning in the formation and development of deformation textures are still being discussed (5, 6). Information on the relation between the activities of various slip systems in α�Zr and the development of a microstructure (structural dispersity, grain and subgrain morphology, grain misorientation spectrum) is absent. However, it is obvious that the microtexture and microstructure evolution in the materials with a pronounced anisotropy of elastic and plastic properties can determine the physical causes of the nonmonotonic deformation behavior. Therefore, the purpose of this work is to reveal the relation between the appearance of an unstable plastic flow during tension of hcp zirconium alloys and the mech� anisms of their texture formation and the relation between the evolution of a defect structure and the crystallographic orientation of a local deformed microvolume in a material. Abstract—The evolution of a microstructure and Schmid factors during tension under necking conditions are analyzed by electron backscatter diffraction. The oscillatory instability of the plastic flow in the deforma� tion zone in the hardening-softening mode is found to be related to geometrical hardening (softening) during the reorientation of easy slip planes in grains with respect to the loading axis. A relation between the activities of various slip systems and the evolution of quantitative microstructure parameters is revealed.