Cyclic behavior and microstructural stability of ultrafine-grained AA6060 under strain-controlled fatigue

The Cyclic Deformation Behavior of Severe Plastic Deformation (SPD) Metals and the Influential Factors

“…Such relationship between the extent of grain coarsening and cyclic softening with regard to the cyclic lifespan can also be found for technical purity copper. In which case, massive grain coarsening could be found in the wake of the crack upon cyclic loading to 7 × 10 8 cycles [36], although this is not commonly reported in other reports on technical purity copper [45][46][47][48][49][50][51]. …”

“…Many of the reports on the cyclic deformation behavior of SPDed metals have been based on metals processed by ECAP, e.g., for high purity copper [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38], technical purity copper [33,[39][40][41][42][43][44], aluminium and aluminum alloys [45][46][47][48][49][50][51], commercial purity titanium [52], IF steel [53,54], and α-brass [55]. There are also reports, albeit fewer in quantity, based on products of different techniques, such as high purity copper processed by HPT [36], high purity copper processed by ARB [56,57], and aluminum and aluminum alloys processed by cryogenic rolling [58,59].…”

“…A transition from cyclic hardening response to cyclic softening response with increasing applied plastic strain amplitudes or increasing cyclic stress amplitudes can be observed in many of the cases with technical purity copper [40][41][42], and that of aluminum alloys [45][46][47][49][50][51]. It is worth mentioning that Kunz et al [44] have reported that cyclic softening is observed only in strain controlled tests, whereas load controlled tests generally yield cyclic hardening or cyclic saturation response.…”

“…A lack of grain coarsening has been noted in many of the above reports, especially in those that have only noted a minor or insignificant cyclic softening response [40][41][42]47,48,52,59]. However, grain coarsening has been reported in some cases of lower purity SPDed metals, especially those that have exhibited some extent of cyclic softening [44,51,58]. Although the extent of coarsening is commonly reported to be much lower than the case of high purity SPDed metals.…”

“…Consequently, the cyclic deformation response is expected to be influenced by the applied cyclic stress or strain, more importantly by the cyclic plastic strain. Such influence from the applied cyclic plastic strain is evidenced from the observed transition from cyclic hardening to cyclic softening with increasing applied cyclic plastic strain for SPDed technical purity copper samples upon cyclic deformation [40][41][42][44][45][46][47][49][50][51]. A similar dependence of the extent of cyclic softening response on the imposed cyclic plastic strain can be seen in Figure 2 for both ECAPed and ARBed high purity copper at low imposed plastic strain amplitudes (i.e., at ε pl /2 < 2 × 10…”