NUMERICAL DESIGN OF DIE LAND FOR SHAPE EXTRUSION

In the extrusion of shapes with flat faced die,the proper design of die land is of critical importance in avoiding the generations of geometry defects.A methodology for the design of die land,which consists of a simulation adjustment iteration,is proposed.The metal flow in extrusion is simulated by the three dimensional finite element method and the die land is adjusted according to the simulation result.Both the formulae for adjustment of the die land and the criterion for the judgment of proper die land are suggested.The extrusion of an L section shape is chosen as the computational example and the result is compared with the industrial design.

Extrusion deformation process of ground surface during the Lushan earthquake in China

Based on finite element method, the extrusion deformation process of ground surface during the Lushan earthquake （April 20, 2013） is investigated in this work. In order to construct the finite element model of Lushan earthquake structure, the geophysical layer model of Lushan area, the frictional characteristic of slip-weaken along the fault surface, and the Coulomb failure criterion are considered. Through the computation and the comparison with achievement on the Lushan focal dynamics, our researches indicate that： （1） The most extrusion deformation of ground surface occurred in the initial phase of earthquake procession, i.e., between the fourth and sixth seconds after the earthquake occurred. （2） Between the first and sixth seconds after the earthquake, the extrusion deformation concentrates on the surface projection of earthquake fault. （3） Between the first and third seconds after the earthquake, the extrusion deformation of ground surface is very tiny. Meanwhile, the extrusion deformation reaches maximum at the sixth second after earthquake. （4） After 6 s of Lushan earthquake, the extrusion deformation spread out of earthquake structure projection. （5） During the earthquake, the maximum of extrusion deformation on ground surface is larger than the final deformation of the post-earthquake, in other words, the ground extrusion deformation will lastly reach a relatively small value after the Lushan earthquake occurred.

Dynamic Recrystallization Mechanism and Texture Evolution during Interactive Alternating Extruded Magnesium Alloy

Alternating extrusion(AFE)is a new way to effectively alter the texture and enhance the mechanical properties of the extruded bars.However,the mechanisms of microstructure evolution and enhancement of hardness are still unknown by different extrusion ratios(ERs)during extrusion.This work systematically investigated the microstructure and hardness of AZ31 alloy with various extrusion ratios of 8.1,15.6,and 24.8 by electron backscattered diffraction.The most striking result to emerge from the data is that when the ERs were increased from 8.1 to 15.6,the grain size was refined to 7.13μm.However,when the ER reached 24.8,the average grain size was 11.43μm.The proportion of recrystallization was only 2.92%,there was a continuous rotation of sub-grains at coarse grain boundaries,and non-basal slip<a>dislocations were activated and enriched near low-angle grain boundaries.At present,the recrystallization has not been completed.The grains of the product are coarsened,and the hardness is reduced.Whenλ=15.6,the AFE has a significant grain refinement effect and the highest hardness value.