Investigation On Optimal Extrusion Route Of Pure Aluminum And Aluminum Alloy During ECAP Process

Equal Channel Angular Pressing achieves severe plastic deformation of the material by the way of pure shear deformation without composition and shape changed.It is an effective technical method of producing super-fine grain metal materials.The effects of different process routes and extrusion passes on the microstructure and mechanical properties of 5N5 high purity aluminum,industrial pure aluminum and 2A12 aluminum alloy are investigated by scanning electron microscopy,optical microscopy,transmission electron microscopy,electrical conductivity and hardness testing.At the same time,different annealing temperatures of industrial pure aluminum are studied to determine the complete recrystallization temperature and thermal stability.The following results are obtained:(1)Compared the same pass of three routes,route X is better than route 135 and route 145.5.After six ECAP passes of route X,the average grain size of high pure aluminum can reach 59?m.As the number of extrusion passes increase,the proportion of large angle grain boundaries increase.The cubic and rotating cubic texture appeared after six passes of route X,and the dynamic recrystallization of high purity aluminum during the extrusion process is observed.As the number of extrusion passes increase,the hardness of high purity aluminum increases after extrusion of three different process routes,and the hardness of the route X is higher than the other two routes.High-purity aluminum undergoes severe plastic deformation and produces high density dislocations during extrusion.Dislocations continue to move and rearrange and form subgrain boundaries.Subgrain boundaries split the original large grains resulting in grain refinement.(2)After six ECAP passes of route X and route Bc,industrial pure aluminum shows fibrous tissue of deformation through the optical microscope.With the increasing annealing temperature,the fibrous tissue disappear and recrystallized grains appear and grow up.The microstructure of industrial pure aluminum is mainly subgrains through scanning electron microscope.As the temperature increases,the grain size increases,and the proportion of large angle grain boundaries increase gradually.The grain size distribution of route X specimen is more average than that of route BC.Compared two routes,the route X is superior to the route BC on thermal stability.When the temperature reaches 350?,industrial pure aluminum samples of route X have strong cubic texture and a little brass R texture.As the temperature increases,the hardness of industrial pure aluminum reduces and the dislocation in the tissue migrates continuously which cause that subgrains merge and grow.(3)The size of precipitated phase which is distributed more uniform decreases for 2A12 aluminum alloy after ECAP six passes of route X and route BC.As the number of extrusion passes increase,the hardness and electrical conductivity of the samples increase gradually after extrusion of two different process routes.The hardness and electrical conductivity of the route X is higher than the other route.