Search

• The Mg-1Gd/Mg-13Gd (wt.%) laminate with dual-heterostructure grain size and texture between alternating layers was designed and fabricated via accumulated extrusion bonding, exhibiting an excellent strength-ductility synergy. • Strain delocalization in the fine-grained (FG) layers was realized by generating dispersed stable strain bands, which promoted the activation of ductile mechanisms. • The lower level of geometric compatibility factor at the interface, with its heterogeneous texture, aggravated deformation incompatibility and boosted the back stress. The higher shear stress field at the interface generated by back stress led to the activation of pyramidal slip and enhanced the strength of the coarse-grained layers. • The elevated forward stress induced by the high back stress triggered the activation of non-basal slips at the interface in the FG layers, which acted together with the abundant basal slips caused by the random texture to improve the ductility of the FG layers. Heterostructures can effectively break the traditional strength-ductility trade-off dilemma. However, how the texture of materials with heterostructure under hetero-deformation induced stress (including back stress and forward stress) influences the activation of the deformation mechanism is still not clear. In this paper, a Mg-1Gd/Mg-13Gd (wt.%) laminate with an alternating distribution of dual-heterostructure grain size and texture, where the coarse-grained (CG) layers presented a bimodal texture along the extrusion direction and the fine-grained (FG) layers showed random texture, exhibited an excellent strength-ductility synergy. Strain delocalization in the Mg-13Gd layer was realized by generating dispersed stable strain bands, which promoted the activation of ductile mechanisms. In the CG layers, the bimodal texture facilitated the activation of pyramidal slip to maintain the continuity of strain at the interface. The lower level of geometric compatibility factor at the interface, with its heterogeneous texture, aggravated deformation incompatibility and boosted the back stress. The higher shear stress field at the interface generated by back stress led to the activation of pyramidal slip and enhanced the strength of the CG layers. In the FG layers, the forward stress promoted the activation of prismatic and pyramidal slips at the interface; they acted together with the abundant basal slips caused by the random texture to improve the ductility of the FG layers. The results of this work will promote the development of heterogeneous theory in textured Mg alloys. [ABSTRACT FROM AUTHOR]

Ultrafine-grained (UFG) materials produced by severe plastic deformation methods generally exhibit a higher strength, but a lower uniform ductility. In this paper, an UFG Al–Zn–Mg–Cu alloy was fabricated via cross accumulative extrusion bonding (CAEB) and subsequent aging to achieve high strength and moderate uniform elongation. The influences of CAEB and subsequent aging on microstructure and tensile properties of the alloy were investigated. After CAEB, TEM characterization revealed that the microstructure exhibited typically ED-elongated ultrafine grains (740 ± 20 nm). Post-CAEB aging led to the formation of many nano-sized particles with different morphologies. These particles precipitated in the grain interiors and at grain boundaries, among which the main strengthening phase was η′ phase. EBSD characterization showed that the fraction of high angle grain boundaries increased to 61.0% for the post-CAEB aged alloy. At the same time, microtexture was significantly weakened as the CAEB process was applied to the alloy. The main texture components were mainly composed of Cu and S as well as a small amount of Brass and Cube. In addition, the tensile test at room temperature demonstrated that the post-CAEB aged sample possessed a high ultimate tensile strength of 562 MPa while simultaneously maintaining a moderate uniform elongation of 21.5%. • UFG Al–Zn–Mg–Cu alloy (740 ± 20 nm) was produced by cross accumulative extrusion bonding (CAEB). • Post-CAEB aging made the GP zone, η′ and η phase appear on the Al matrix. • The SST+CAEB+aging alloy possessed a high strength of 562 MPa and moderate uniform elongation of 21.5%. [ABSTRACT FROM AUTHOR]

In this work, pre-compression along the extrusion direction was used to induce initial {10–12} twins in the extruded AZ31 rod. The effects of initial twins on twinning behavior during free-end torsion were investigated in detail. As-extruded AZ31 rod has a typical extrusion fiber texture. Torsional shear is equal to a bi-axial tension-compression stress state. Under the stress state, only limited grains with special orientations can be favorably twinned. The c-axis of the twin-texture via torsion is close to the compressive loading direction. Besides, basal slip also greatly contributes to torsion deformation. Basal slip will induce the axes of most grains to rotate towards compressive loading direction during torsion. The c-axes of initial twins via pre-compression have an angle range of 30° deviated from the ED. Torsion deformation causes the twin-texture to rotate towards the compressive loading direction. The transformation mechanisms contain basal slip within twins, growth of initial twins, formation of new twin variants and detwinning. The selection of mechanism depends on the orientation of the parent grains and the initial twins. Moreover, the misorientation of {10–12} twin-boundary can be reduced by 10–20° during torsion owing to the orientation change caused by basal slip. Combining pre-compression and torsion can largely increase the relative proportions of 76° ± 5°/〈11−20〉 twin boundaries and 66° ± 5°/<11–20 > twin boundaries. Finally, the influence of pre-compression on torsion properties was also discussed. • Torsion deformation remarkably modifies the texture of grains and initial twins. • Basal slip, twinning and detwinning during torsion contribute to the change of texture. • Torsion deformation largely reduces the misorientation of {10–12} twin-boundary. • Pre-twinning slightly increases the yield strength and shear fracture strain. [ABSTRACT FROM AUTHOR]

Accumulative extrusion bonding (AEB), as a recently developed severe plastic deformation method, is a promising process for large-scale preparation of ultrafine-grained (UFG) materials. In this work, cross accumulative extrusion bonding (CAEB) was developed based on AEB to produce 1060/7050 laminated composite. TEM observation showed that the ED-elongated grain structures with the average grain width of 0.68 ± 0.05 μm and 1.80 ± 0.2 μm for 7050 and 1060 were formed, respectively. Tensile test demonstrated that the CAEB-processed laminated composite exhibited an outstanding combination of strength and ductility. And the CAEB-processed composite presented an extra strengthening that was higher than the predicted result by the rule-of-mixture. This extra strengthening mechanism is referred to as hetero-deformation induced (HDI) strengthening. Subsequent aging was applied to combine the CAEB process to further improve the mechanical properties of the CAEB-processed composite. After aging, the plate-like η′ phase and rod-like η phase precipitates appeared in the 7050 layers. These nano-precipitations play a significant role in precipitation strengthening. Further EBSD characterization revealed a bimodal grain-size distribution between the constituent layers. The 7050 layer with ultrafine grains provides the high strength, while the 1060 layer with coarse grains attains strain hardening. • 1060/7050 laminated composite was produced by cross accumulative extrusion bonding (CAEB) and subsequent aging. • The complicated bonding interfaces appeared after the CAEB process. • A bimodal grain-size distribution formed in the laminated composite after aging. • The CAEB-processed composite exhibited an outstanding combination of strength and ductility. [ABSTRACT FROM AUTHOR]

Inhomogeneous deformation, which was usually found during the deformation of friction stir welding (FSW) Mg alloys joints, could deteriorate the joint performance. This work aims to understand the effect of microstructure and texture distribution in joint on mechanical properties and deformation behavior of the FSW dissimilar Mg alloys joints. Two kinds of AZ31/AM60 dissimilar Mg alloys joints were obtained via FSW at two sets of welding parameters (higher rotation rate and welding speed (HRW), lower rotation rate and welding speed (LRW)). Electron backscatter diffraction measurements were conducted to examine the microstructure and texture distribution of these two joints. The results showed that the joint with finer grains, weaker texture and higher nugget zone (NZ) interface angle was obtained with HRW. The weaker texture and finer microstructure were beneficial to the homogeneous deformation of the joint. The larger angle between the NZ interface and the transverse direction (about 75°) made it away from the maximum shear force direction (45°) to avoid premature fracture. With these advantages, the mechanical properties of the joint with HRW were better than that with LRW. The yield strength, ultimate strength and elongation were improved 14.4%, 19.7% and 63.7%, respectively. In addition, the grain size of AZ31 of NZ in two joints was smaller than that of AM60. All the joints fractured at the AM60 side near the NZ boundary during the tension tests. This was mainly attributed to the larger grain size and higher Schmid factor of basal slip at the AM60 side near the NZ interface. This study provided some insights in understanding the improvement of the dissimilar FSW Mg joint performance by controlling texture distribution and microstructure. [ABSTRACT FROM AUTHOR]

In the present study, the comprehensive effects of Ce addition and pre-twining deformation on the microstructure evolution and mechanical properties of Mg-1.0Sn-0.5Zn alloys were systematically investigated. After Ce addition, two phases (CeMgSn and CeMgZn 2) were newly emerged, which eventually hampered grain growth and postponed {10−12} tensile twin extinction during annealing subsequent to pre-compression. Besides, due to prominent grain refinement, the addition of Ce into as-extruded Mg-Sn-Zn alloy gave rise to a noticeable improvement in strength. As for the application of pre-twining deformation, it could induce a significant increase in the tensile ductility via texture tailoring, and the relative Visco-Plastic Self-Consistent (VPSC) simulation confirmed that the main reason was attributed to the vigorous activation of {10−12} tensile twins. As a result, both the strength and ductility of the as-extruded Mg-Sn-Zn alloy were substantially improved via the combination of Ce addition (obvious grain refinement) and pre-twining deformation (effective texture regulation). [Display omitted] • CeMgSn and CeMgZn 2 were newly emerged after Ce addition, which eventually hampered grain growth and postponed {10−12} tensile twin annihilation during annealing of pre-twining deformation. • The relative VPSC simulation confirmed that, after pre-twining deformation, {10−12} tensile twins are vigorously activated in the early stage of tensile deformation, while basal slip is dominant in the compressive deformation. • The strength and ductility of as-extruded TZE100 alloy were improved simultaneously through the combination of Ce addition (grain refinement) and pre-twining deformation (texture tailoring). [ABSTRACT FROM AUTHOR]

In this paper, ultrafine-grained pure aluminum was first fabricated by heavy extrusion. Subsequently, the prepared samples were annealed at 350 oC for different times to tailor heterostructures with the aim of achieving strength-ductility balance. The microstructure characterization revealed that the annealed samples formed heterostructures composed of recrystallized coarse grains, retained ultrafine grains, and coarsening banded structure. Typical rolling texture components prevailed as annealing time was below 8 min. When annealing time exceeded 8 min, these texture components were gradually replaced by the Cube-oriented and random-oriented grains, and at the same time, abnormal grain growth occurred with a faster kinetic (growth exponent ñ3.4). Tensile tests indicated that 5–8 min annealed samples obtained a reasonable strength-ductility balance, which was higher than their counterparts predicted by the rule-of-mixture based on the recrystallization model. In addition, the macro-deformation characteristics of the heterostructured sample were comparatively studied using digital image correlation, while the micro-deformation behaviors were revealed by in-situ tension. The results showed that the heterostructured sample caused inhomogeneous deformation and significant geometrically necessary dislocations gradient at the hetero-boundaries. The loading-unloading-reloading tests found that the interaction of heterostructures induced a noteworthy hetero-deformation-induced (HDI) stress, thereby contributing to HDI strengthening. [ABSTRACT FROM AUTHOR]

In this study, accumulative extrusion bonding (AEB) was used to process Mg–1Gd/Mg–13Gd laminated composites, in which the Mg–13Gd layers had much finer grains than the Mg–1Gd layers. This grain size difference was maintained after 2-pass, but diminished after the 3-pass. The 2-pass composite samples exhibited an excellent combination of ultimate tensile strength (291 MPa), elongation (20.6%) and yield strength (144 MPa), which are much superior than the individual component materials. Moreover, the 2-pass samples also exhibited maximum extra strength and ductility that is higher than what is predicted by the rule-of-mixture. The observed high strength and ductility are mainly attributed to back-stress strengthening and work hardening, respectively. The 2-pass samples exhibited the highest back stress, indicating an optimum laminate thickness for producing the highest back stress hardening. This work provide a new understanding on the design of heterogeneous laminated Mg alloys for improving mechanical properties. [ABSTRACT FROM AUTHOR]

The special microstructure distribution of the friction stir welded (FSW) Mg alloys joints is usually responsible for the non-uniform deformation and poor mechanical properties. Hence, it was possible to improve the joint mechanical properties by modifying the microstructure. In the present study, two kinds of AM60/AZ31 Mg alloys dissimilar FSW joints with different microstructure were obtained using different rotation rates (800 rpm and 1600 rpm). The results of mechanical tests showed that the tensile strength and elongation of the joint at 1600 rpm were 13.5% and 115% higher than those at 800 rpm, respectively. The microstructure observation indicated that the grain size of various zones in the joint at 1600 rpm was obviously larger than that at 800 rpm, especially at the AM60 side. However, there was no obvious difference in the texture distribution of the two welds. In addition, microstructure observation after fracture showed that there were more twins in AM60 side of the joint with coarse grains. These coarse grains promoted the activation of basal slip and twinning in the regions far away from the nugget zone (NZ) interface. This weakened the strain localization of the joint to some extent. Meanwhile, the coarse grain joint had lower concentration degree of the strain and dislocation near the NZ boundary compared with the fine grain joint. These factors led to better mechanical properties of the joint with coarse grains. This work could provide some guidelines for improving the inhomogeneous deformation behavior of dissimilar Mg alloys FSW joints. [ABSTRACT FROM AUTHOR]