Showing papers by "A. Karimi Taheri published in 2010"

Strengthening study on 6082 Al alloy after combination of aging treatment and ECAP process

Abstract: Equal channel angular pressing (ECAP) was used before and after various aging treatments in order to strengthen a commercial 6082 Al alloy. Experiments were carried out to study the strengthening of the alloy due to pre and post-ECAP aging treatment. It was found that aging before and after ECAP processing is an effective method for strengthening of the alloy. An increase in both strength and ductility of the ECAPed specimen was achieved via appropriate post-aging treatment. This was in such a manner that for maximal strengthening, post-ECAP aging is best conducted at temperatures lower than those usually used for aging if prior work hardening is not undertaken. Pre-ECAP aging was also discussed in the light of dislocation density and work hardening.

Study on static strain aging of 6082 aluminium alloy

Abstract: In this study both the quench aging and static strain aging kinetics of a 6082 Al alloy were investigated at a temperature range of 130–200°C using the Vickers hardness and tensile test. The activation energy and dislocation density were determined at different stages of the aging phenomenon. The former was used to analyse the kinetics of aging and the latter to interpret the competition of strengthening and recovery mechanisms during aging. It is shown that different activation energies are achieved depending on the aging time and temperature relating to formation of appropriate precipitates at different stages of aging. Moreover, it is revealed that prestrain reduces the activation energy. A linear equation is proposed between the dislocation density and the plastic strain after static strain aging. The competition of recovery with strengthening mechanisms during strain aging is discussed with regard to dislocation density after aging.

The effect of aging treatment on mechanical properties of aa6082 alloy: modeling and experiment

Abstract: A novel constitutive equation has been proposed to predict the effect of aging treatment on mechanical properties of AA6082 aluminum alloy. Considering that aging phenomenon affects the distribution of alloying element in matrix, and the fact that different distribution of alloying elements has different impediments to dislocation movement, a material model based on microstructure, has been developed in this research. A relative volume fraction or mean radius of precipitations is introduced into the flow stress by using the appropriate relationships. The GA-based optimization technique is used to evaluate the material constants within the equations from the uni-axial tensile test data of AA6082 alloy. Finally, using the proposed model with optimized constants, the flow behavior of the alloy at different conditions of heat treatment is predicted. The results predicted by the model showed a good agreement with experimental data, indicating the capability of the model in prediction of the material flow behavior after different heat treatment cycles. Also, the calculated flow stress was used for determination of the material property in Abaqus Software to analyze the uniaxial compression test. The force- displacement curves of the analysis were compared to the experimental data obtained in the same condition, and a good agreement was found between the two sets of results.

The effect of aging treatment on mechanical properties ofaa6082 alloy: modelingand experiment

Abstract: A novel constitutive equation has been proposed to predict the effect of aging treatment on mechanical properties of AA6082 aluminum alloy. Considering that aging phenomenon affects the distribution of alloying element in matrix, and the fact that different distribution of alloying elements has different impediments to dislocation movement, a material model based on microstructure, has been developed in this research. A relative volume fraction or mean radius of precipitations is introduced into the flow stress by using the appropriate relationships. The GA-based optimization technique is used to evaluate the material constants within the equations from the uni-axial tensile test data of AA6082 alloy. Finally, using the proposed model with optimized constants, the flow behavior of the alloy at different conditions of heat treatment is predicted. The results predicted by the model showed a good agreement with experimental data, indicating the capability of the model in prediction of the material flow behavior after different heat treatment cycles. Also, the calculated flow stress was used for determination of the material property in Abaqus Software to analyze the uniaxial compression test. The forcedisplacement curves of the analysis were compared to the experimental data obtained in the same condition, and a good agreement was found between the two sets of results.

A kinematical dislocation based model and admissible velocity field for prediction of nanostructural changes and mechanical properties of al-cu-al laminated composite during ecae process

Abstract: In this research, a mathematical model based on Bezier equations was developed in order to predict the admissible velocity field during the deformation of the aluminum-copper-aluminum laminated composite in a plane strain equal channel angular extrusion (ECAE) process. The strain and strain rate fields were evaluated using the fixed Taylor factor based on the proposed streamline and the modified ETMB microstructural model for the nanostructural changes in aluminum-copper layers. The results showed that the size of the dislocation cells formed in copper layer was smaller than that of the Al layer, especially when the aluminum layer was located adjacent to the outer corner angle and when a lower die angle was used. Furthermore, the results predicted by the model regarding the different passes of ECAE process were in good agreement with the results obtained from the microstructural and textural examinations performed using TEM and EBSD techniques.