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Modelling the Geometric Dynamic Recrystallization of AlMg6 alloy using the Combination of Finite Element Method and Dislocation Based Model

Rafiei, Morteza | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39342 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali
  7. Abstract:
  8. Taking advantage of aluminum and its alloys in industry is increasing. A common method in metal forming is hot forming. In this condition a precise prediction of flow behaviour of the alloy is necessary to achieve a product of desirable mechanical and physical properties. In this situation, influence of parameters such as chemical composition, temperature, strain, strain rate as well as recovery and recrystallization phenomena should be considered and by using a suitable model, the metal behavior prediction is possible. Distribution of coherent Al3Sc dispersoids in high volume fraction accompany with Al6Mn result in strengthening to this alloy. Because of the high stacking fault energy, recovery reactions definitely take place and hence dislocation density decrease and then cell structures form. Since dispersoids lock subgrain boundaries, recrystallization nucleation retards. In this thesis, based on elastic predictor-plastic corrector algorithm and utilizing finite element method, an elasto-plasic analysis of hot compression test is performed and a model is proposed for estimating geometric dynamic recrystallization fraction. In the plastic corrector, in order to predict the flow stress in each step, a mathematical model based on dislocation density is used. In each step, equivalent stress determined by the FEM analysis is compared with the flow stress predicted by the mathematical model. Whenever the plastic flow is occurred, modification of stress tensor is performed by the Return-Mapping Algorithm. To verify the flow stress results predicted by the mathematical model, they are compared with the results of isothermal hot compression test and a good agreement is observed between the two sets of results, Moreover, the modified stress tensor as well as strain contours determined from the FEM analysis are plotted and the formation of shear bands during deformation is discussed. Furthermore, by taking into consideration the proposed model for estimating the geometric dynamic recrystallization fraction, by combination of large deformation finite element method with dislocation density based model, subgrain size is predicted. It is seen that with increasing temperature, the critical strain for occurrence of geometric dynamic recrystallization decreases
  9. Keywords:
  10. Dynamic Recrystallization ; Finite Element Method ; Dislocation Density ; Hot Compression ; Subgrain Size

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