Softening of Al during multi-axial forging in a channel die

Microstructural and mechanical properties of AA1100 aluminum processed by multi-axial incremental forging and shearing

“…Besides the effect of usual dynamic recovery, by the way, some investigations made suggestions about the effect of heat generation resulted from a high strain rate on the coarsening of the ultrafine grains during and after deformation which induces softening [11,41] thereby switching from dislocation strengthening to Hall-Petch strengthening [50]. The present results are also consistent with these theoretical predictions and thus, the softening observed in going from 4 to 6 passes may be related to this effect.…”

“…On the other hand, since the flattening of grains seems inevitable after some passes of MAIFS process such as second and eighth pass, a kind of geometric dynamic recrystallization can be regarded as another possible mechanism for the generation of a fine-grained structure during process, as implied in the literature [42,43,50,51].…”

“…Dynamic recovery (DRV) as a thermal process then will turn GNBs and IDBs to more equilibrium grain boundaries through increasing their misorientation. In fact, both continuous dynamic recrystallization and probable geometric dynamic recrystallization mechanisms proposed for grain refinement occurred during MAIFS process are forms of a recovery process where the continuous evolution of dislocations is coupled with their interaction with boundaries [43,50]. Thus, it seems that the continuation of the dynamic recovery process at large strains can cause the more absorption of dislocations into grain boundaries and subsequent coarsening of microstructure.…”

The influence of deformation path on strain characteristics of AA1050 aluminium processed by equal-channel angular pressing followed by rolling

“…Only dislocation density is correlated to the saturation of yield stress and hardness observed during SPD obeying the Taylor relationship [6] (1) -where  0 is the yield strength of the annealed material, M is the Taylor factor (usually 3 )  a constant (0.33 for pure Al), G the shear modulus, b the Burgers vector and  the dislocation density. This relationship is independent of the applied deformation process; for example for ARB [7,8], ECAP [9], multi directional forging [10], or HPT [11], the literature indicates a saturation value of 160-165 MPa for AA1050, achieved after a von Mises strain between 2 and 3 and a dislocation density at the saturation point of about 1.5 -3 x10 14 m -2 , this last figure having been confirmed by x-ray diffraction [12,13]. This indicates that strength is basically determined by the interaction between dislocations, and in the case of high Stacking Fault Energy (SFE) metals, (which is the case of Al), operates mainly by the overall deformation of the cell blocks within the grain [14].…”

Microstructure and mechanical properties of an Al–Mg–Si tube processed by severe plastic deformation and subsequent annealing

“…The step sizes of EBSD measurement were selected between 0.5 to 0.1 ȝm. The cut off angle for definition of HABs in EBSD maps was considered as 5° since it has been shown that the appearance of grain boundaries with angle higher than 5° in aluminum results in Hall-Pitch strengthening [24][25].…”