FEM and metallurgical analysis of modified 6082 aluminium alloys processed by multipass ECAP: Influence of material properties and different process settings on induced plastic strain

Abstract

Equal channel angular pressing (ECAP) is a very interesting method for modifying microstructure in producing ultra fine grained (UFG) materials. It consists of pressing test samples through a die containing two channels, equal in cross section and intersecting at an angle Φ. As a result of pressing, the sample theoretically deforms by simple shear and retains the same cross sectional area to repeat the pressing for several cycles. Two-dimensional and three-dimensional finite element method (FEM) simulations of both one and four ECAP passes of two modified aluminium alloys were performed in order to investigate the deformation state of processed workpiece and, moreover, the effect of different strain hardening rate, die geometry (in terms of variation of channel outer angle) and friction on deformation distribution and magnitude. FEM results showed a lower equivalent plastic strain on the outer side of both cross and longitudinal sections of the billets after one and four passes. Microhardness tests performed on the same sections of ECAP processed billets supported these findings. Moreover, FEM analysis indicated that a higher strain hardening rate means a greater strain inhomogeneity on cross section of the processed billet when the channel outer angle is small. As the channel outer angle increases and when friction is computed, the effect of strain hardening on strain inhomogeneity tends to decrease, while the die geometry and friction affect plastic strain distribution more than the hardening behaviour of the studied alloys.