Change of Deformation Mechanisms Leading to High Strength and Large Ductility in Mg-Zn-Zr-Ca Alloy with Fully Recrystallized Ultrafine Grained Microstructures

Abstract

Recently, we have found that fully recrystallized ultrafine-grained (UFG) microstructures could be realized in a commercial precipitation-hardened Magnesium (Mg) alloy. The UFG specimens exhibited high strength and large ductility under tensile test, but underlying mechanisms for good mechanical properties remained unclear. In this study, we have carried out systematic observations of deformation microstructures for revealing the influence of grain size on the change of dominant deformation modes. We found that plastic deformation of conventionally coarse-grained specimen was predominated by {0001} <11–20> slip and {10–12} <10–11> twinning, and the quick decrease of work-hardening rate was mainly due to the early saturation of deformation twins. For the UFG specimens, {10–12} <10–11> twinning was dramatically suppressed, while non-basal slip systems containing < c > component of Burgers vector were activated, which contributed significantly to the enhanced work-hardening rate leading to high strength and large ductility. It was clarified by this study that limited ductility of hexagonal Mg alloys could be overcome by activating unusual slip systems (< c + a > dislocations) in fully recrystallized UFG microstructures.

Achieving large super-elasticity through changing relative easiness of deformation modes in Ti-Nb-Mo alloy by ultra-grain refinement

“…Tensile specimens with 11 mm gauge length, 2 mm width and 0.5 mm thickness were cut from the annealed sheets. It has been confirmed in previous studies [17][18][19] that this small-sized specimen can give reliable data of strength and tensile ductility equivalent to those obtained from standard sized specimens of the same materials. Monotonic tensile tests were performed on Shimadzu AG-X plus system at an initial strain rate of 8.3 × 10 −4 s −1 at room temperature with tensile direction parallel to the rolling direction(RD) of the sheets.…”

Proposing the Concept of Plaston and Strategy to Manage Both High Strength and Large Ductility in Advanced Structural Materials, on the Basis of Unique Mechanical Properties of Bulk Nanostructured Metals

“…1.4a). Fully annealed or recrystallized UFG metals and alloys universally show such a yield-drop phenomenon, regardless of their chemical compositions and crystal structures (Tsuji et al 2002;Tian et al 2018aTian et al , 2020aSaha et al 2013;Yoshida et al 2017Yoshida et al , 2019Terada et al 2008;Zheng et al 2017Zheng et al , 2019Zheng et al , 2020aGao et al 2014a;Bai et al 2021). As will be argued later, the yield-drop phenomenon found in bulk nanostructured metals is the sign of the activation of the plaston (or the activation of new deformation mode).…”

“…The first author of this manuscript has continuously studied bulk nanostructured metals (or ultrafine-grained (UFG) metallic materials, in other words) in the last decades, and has found their unique mechanical properties, such as the unexpected yield-drop phenomena universally found in UFG metals and alloys regardless of their chemical compositions and crystal structures (Tsuji et al 2002;Tian et al 2018aTian et al , 2020aSaha et al 2013;Yoshida et al 2017Yoshida et al , 2019Terada et al 2008;Zheng et al 2017Zheng et al , 2019Zheng et al , 2020aGao et al 2014a;Bai et al 2021), extra Hall-Petch strengthening (Gao et al 2014a;Kamikawa et al 2009;Tian et al 2020), "hardening by annealing and softening by deformation" phenomena (Huang et al 2006), and so on. Bulk nanostructured metals show very high strength compared to conventionally coarse-grained counterparts, but most of them still have a dilemma of the strengthductility trade-off (Tsuji et al 2002(Tsuji et al , 2008.…”

Toward the development of Mg alloys with simultaneously improved strength and ductility by refining grain size via the deformation process

“…For instance, many Mg alloys with high strength but low ductility (or with high ductility but low strength) have been reported [7][8][10][11]. At present, many researchers have investigated the strength-ductility trade-off [16][17][18][19][20] and reported some Mg alloys with relatively high strength and high ductility [21][22][23][24]. Refining the grain size of Mg alloys (particularly via deformation processes) is one of the feasible strategies to prepare Mg alloys with high strength and high ductility.…”