Key Engineering Materials Vol. 491

Abstract: Extrusion is a deformation process used in metal sections fabrication. Metal flow pattern during extrusion process is of great importance. How circular initial section of billet changes to final section provides more details of extrusion process, and plays an important role in optimizing the extrusion energy. Extrusion in flat-faced die, without intermediate section, needs much more energy than is required for die having intermediate section. The aim of this study was to investigate the effect of strain rate on metal flow pattern in T-section extrusion process. Four different ram speeds were applied to realize how the shape and position of intermediate section would be affected. Flat-faced die with “T” final section was designed and manufactured. Straight layout of metal was of top concern in die design. Commercial purity aluminum, Al 99.5, was extruded in flat-faced die in hot condition. Graphite was used as lubricant in deformation process. After partial extrusion of billets, the residual part of billets pounced out of container and then mounted for metallographic tests. This part of billets consisted of dead-metal zone and deformation zone. Then, step-by-step decreasing of specimen height followed by macro-etching of metal surface paved the way for determining the metal flow pattern. An egg-shaped intermediate section appeared between initial round section and final “T” section. The size and position of the intermediate section changed by varying the strain rate of extrusion process; It was also revealed that as the strain rate of extrusion process is increased, the dead-metal zones become narrower and the dead-metal zone semi angle increases.

Abstract: Extrusion is one of the widely used metal forming processes. The extrusion process is carried out conventionally using a shear faced die, but shear faced dies have many practical problems such as a dead metal zone, more redundant work. In the present investigation, the evolution of uniform microstructure in extruded product with improved mechanical properties for quality products to get dimensional accuracy. A mathematically contoured non-linear converging die has been designed for extrusion of square section from round billet. CAD models of die profile have also been developed. The experiments have been conducted to verify the proposed theoretical model. The extrusion test rigs have been fabricated to carry out extrusion through mathematically contoured dies.

Abstract: In this work a numerical method for the simulation of extrusion processes with modeling of microstructure is presented. Extensive testing was done to provide a basis for the verification of simulation results. Circular rods of AA6005A were extruded by backward and forward extrusion with different extrusion ratios, billet temperatures and product velocities. The extruded rods were cooled either by water or at air to distinguish between dynamic and static recrystallization. Temperature and strain-rate dependent yield stresses were determined from hot compression tests. Special friction tests on cylindrical specimens under high hydrostatic stresses at high temperatures have been performed and the parameters of a friction model were identified from the experiments. The recrystallized volume fraction and grain sizes in the extruded rods were analyzed by means of optical micrographs. The obtained results were used to determine the parameters of a recrystallization model which was implemented in the FE code HyperXtrude. The transferability of the numerical model was checked by simulating forward extrusion tests using the model parameters obtained from backward extrusion tests.

Abstract: In the present study, the evolution of the grain structure of a Mg-Al-Ca-based alloy during hot extrusion was simulated with the cellular automation method. The Laasraoui-Jonas microstructure model was used to describe the dislocation evolution inside crystallites during dynamic recrystallization. The parameters in the Laasraoui-Jonas model, such as the hardening parameter, recovery parameter and material constants, were determined from the flow stress-strain data obtained from hot compression tests using a Gleeble-1500 thermomechanical simulator. The extrusion process was simulated using a DEFORM 3D FEM code. The influence of ram speed on grain structure evolution was analyzed. It was found that the average grain size increases with increasing ram speed. Good agreements between the predicted and observed grain structures were achieved.