To research physical fields evolution and microstructures for compound extrusion of AZ31 Alloy, A kind of compound extrusion technology including extrusion and following shears for AZ31 magnesium bil lets have been explored. Three dimensional finite element simulations of extruding AZ31 magnesium alloy billets into small rods at certain ram speed have been performed by compound extrusion with extrusion ratio 28 and channel angle 150°. Parameters including workpiece material characteristics and process conditions have been taken into consideration. High cumulative strains and low temperatures rise was the main reason for grain refinement during compound process. The observation results of microstructures and rod surface quality showed that the compound process effectively refine the grains of AZ31 magnesium and product mag nesium alloy rods.
In order to predict defects of extrusion especially the surface cracks caused by hyperbolic curve die and parabolic curve die in direct extrusion process, three dimensional (3D) thermo mechanically coupled finite element simulations of extruding AZ31 alloy into small rod at certain ram speeds have been performed using DEFORM TM 3D. A half of the geometries including billet and dies with hyperbolic curve die and par abolic curve die have been designed and meshed due to symmetry. Simulation parameters including work piece characteristics and process conditions (e.g., billet temperature, extrusion ratio, and ram speed) have been taken into consideration. The simulation results have been verified in extrusion experiments under iden tical conditions as simulation conditions. It can be found that hyperbolic curve die could improve homoge neity of the metal flow, avoid the formation of the dead zone, decrease additional tensile stresses and increase uniformity comparing with parabolic curve die. The parabolic curve die may cause continuous cracks on the surface of the extruded rod. Theoretical results obtained by the simulations agree well with the experiments data. The obtained results provide the fundamentals and practical guidelines for the choice and design of die structures to produce magnesium rods with finish surface.
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