Abstract: As a new severe plastic deformation method(SPD), twist extrusion(TE)is a complex forming process because of the main shear plastic deformation and many factors affecting; and it is difficult to accurately establish the relationship between process parameters and the forming quality. Selecting optimized rational process parameters matching is the key to acquire quality i.e. fine plastic and dense, no rupture for materials forming especially powder materials. The finite element simulation about pure aluminum powder in tubes-twist extrusion is carried out by Deform-3D software after the establishment of orthogonal experimental design to the factors about the cross-section torsion angle, helix angle, the friction factor, extrusion speed, the initial relative density. The average equivalent plastic strain, hydrostatic pressure, the average maximum damage value and the average relative density as the optimization design goal and process parameters are optimized by means of track-point method and gray system theory before the weight of multi-object is calculated by analytic hierarchy process. Ultimately it is achieved that there have maximum of equivalent strain, maximum of hydrostatic pressure, minimum of the maximum damage value, maximum of relative density. Results of simulation and experimental validation show that twist extrusion used of multi-objective optimization of parameters makes value of the effective strain and hydrostatic pressure accumulated rapidly, the maximum damage significantly reduced, dense significant and grain refinement obtained, and comprehensive and good quality materials obtained too.

Key words: Analytic hierarchy process, Grey system theory, Multi-objective optimization, Severe plastic deformation(SPD), Tubes-equal channel twist extrusion