Papers by Author: Yong Ning Yu

Abstract: A reaction stress model is introduced in this paper and its applications for the crystallographic texture simulation are also discussed with the comparison to the classic Taylor type model and the self consistent model. This model took the external deformation stress tensor as an initial point, and the activation process of slip systems as well as the orientation evolutions was simulated step by step. Certain relaxation of reaction stress were introduced during tensile or drawing deformation, which predicts the tensile direction distribution along the orientation line between <111> and <100> in the inverse pole figure besides the <111> and <100> fiber texture. The simulation agrees with the common experimental observations. The model supplies a simple way to follow the deformation process in the main part of polycrystals, in which the effect of grain orientation and its interaction with the surrounding matrix are considered.

Abstract: A new model describing the reaction stresses during plastic deformation of metals is proposed in which the reaction stresses among the grains and their accumulation are calculated. The model could overcome the shortages of the Sachs and Taylor deformation model. According to the model, the plastic strain tensor induced by activation of slip systems will produce certain elastic reaction stress in the surrounding matrix, which influences the choice of further activation of slip systems as well as the orientation evolution. The model gives more attention to both of the stress and strain compatibility among the grains. The simulation on the tensile deformation of pure copper indicates that the model could exhibit the main characteristics of the real deformation process.

Abstract: It is well known that the ductility of magnesium and magnesium alloy is too poor to be processed. After normal hot extrusion, the ductility of magnesium alloy will be improved, but not noticeably. In this paper, further extrusion (Extrusion Ratio is 6.25) is adopted to commercial AZ31 magnesium alloy rods (Extrusion Ratio is 2) at different temperatures in order to refine the size of grain, then the rods with the crystallite size between 4-10μm is obtained, and the influence of crystallite with different grain size on the ductility of this alloy is investigated further. A lot of experiments and research indicate that: the elongation of the initial billet with the grain size of 30μ m can reach about 12%; after extrusion at different temperatures, the grain size can be refined to below 10μm, and the ductility goes up to 24%-30%. It also shows that, when the grain size of AZ31 magnesium alloy is below 10μm, the ductility is effected obviously. Only when the grain size is about a few microns, the ductility of AZ31 magnesium alloy will be improved noticeably.