Re-strengthening in AA6063 Alloy During Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) is carried out using two different configurations for the exit channel of the ECAP die, i.e., relieved and choked, with angles of 0.2 °. It is found that using a die with relieved exit channel, the sample was extruded for 6 passes with no surface cracks and an average cell size of 727 nm and a fraction of high angle grain boundaries of 54 % were achieved. Measured values of yield strength (YS) and ultimate tensile strength (UTS) were reported to be 201.1 and 259.5, respectively. By using the die with choked exit channel, it was possible to deform the sample for up to 14 passes with no sign of surface cracking. A relatively finer cell structure around 530 nm was achieved and the fraction of HAGBs increased to 64 %. Relative increases in YS and UTS were as well observed indicating that re-strengthening has been activated in the material after saturation at the 4th pass. In addition, the mechanism of grain refinement seemed to change to progressive lattice rotation evidenced by formation of trapped single grains within the size range of less than 100 nm.