Sharif Digital Repository

A thermo-mechanical model has been developed for modeling of hot extrusion processes. Accordingly, an admissible velocity field was first proposed by means of stream function method and then, extrusion pressure as well as temperature variations within the metal and the die were predicted employing a combined upper bound and Petrov-Galerkin finite element analysis. In order to evaluate the model predictions, hot extrusion of AA6061-10%SiCp was considered under both isothermal and non-isothermal conditions and the predicted force-displacement diagrams under various extrusion conditions were compared with the experimental ones and reasonable consistency was found between the two sets of results... 

Purpose - The purpose of this paper is to propose a mathematical model to estimate required energy and temperature distribution during cold extrusion process. Design/methodology/approach - An admissible velocity field is generated based on stream function technique. Then, the required energy and the temperature distributions in the metal and the extrusion die are determined by a coupled upper bound-finite element analysis. Findings - To examine the proposed model, cold extrusion of AA6061-10%SiCp is considered and the predicted extrusion force-displacement diagrams in different reductions are compared with the experimental ones and reasonable agreement is observed. Furthermore, it... 

To determine the curvature of the exit profile in the extrusion process of non-symmetrical flat dies, the dead metal zone profile was predicted using the energy minimization method. The dead zone is a natural non-linear die for the process and it is pragmatic to use this non-linear die to estimate the value of the exit profile curvature and the required bearing length for reducing this deviation. The velocity field is calculated based on Hermite cubic spline and some additional assumptions. In non-symmetrical dies the entrance section of the deformation region is not flat. Considering this fact, axial velocity decreases with increasing the distance to die center line which is in agreement... 

This article investigates the effect of T6 heat treatment on microstructure and mechanical properties of hot extruded in-situ Al-15wt%Mg 2Si composite. This composite has already been introduced as a new class of light materials but the brittle structure of the primary Mg 2Si which is formed during solidification limits its application. As-cast composite was directly extruded as rod by using three different dies. Microstructure after this type of extrusion was studied by optical and scanning electron microscopy. Results demonstrated that extruded and heat treated composite possesses considerably higher strength and enhanced ductility in comparison with the as-cast samples. It was also found... 

In this study, a general methodology has been developed to design the proper bearing in order to eliminate the curvature of the final product in extrusion process. Three smooth curved (advanced-surface) dies with non-symmetric T-shaped sections and different off-centricities have been studied. For each die, the proper bearing has been designed and physical and numerical modeling have been performed to validate the design. The design procedure is as follows: A formulation, based on Bezier curves, has been used to determine the exit velocity profile. Since the result of Bezier method is different from the actual velocity profile, the Chitkara corrective function has been modified and applied... 

In this study, hot extrusion of AA6061-5% SiCp composite was studied to determine the composite thermo-mechanical behaviour during deformation and the mechanical properties of extruded composite. Hot compression tests were first carried out to obtain the flow stress behaviour of the composite at different temperatures and strain rates. Then a mathematical model was used to estimate the required energy as well as to predict temperature and strain distributions during the process. Finally, hot extrusion experiments were performed in order to verify the predictions and, also, tensile and hardness testing were conducted to evaluate mechanical properties of extruded material. Comparison between... 

In current study, microstructure and high-temperature mechanical properties of ZK60 magnesium alloy reinforced by SiC whiskers were investigated after casting, the KOBO extrusion and aging processes. For this purpose, ZK60/SiCw composite specimens were prepared by stir casting technique. In order to achieve a laminar structure and improve the strength, the samples were subjected to KOBO extrusion technique and precipitation hardening, resulting in improved strength and increased ductility. The former is due to grain refining and formation of precipitates in the microstructure, while the latter is attributed to grain refining and formation of laminar structure. To evaluate the strength of the...