Abstract The flow stress and work hardening behaviour during uniaxial compression of dilute binary Mg-Sc alloys have been studied at 4.2 K, 78 K and 298 K. The influences of atomic misfit, chemical misfit, solute electronic properties and stacking fault energy (SFE) on strength and ductility have been examined. The results suggest that the small atomic misfit and the reduction of SFE due to Sc additions are decisive factors in determining the mechanical behaviour of the alloys. Mg-Sc alloys deform by basal, prismatic 〈 a 〉 , pyramidal 〈 c + a 〉 slip and extension twinning. Sc exerts limited strengthening on these modes due to the small atomic size and weak solute-dislocation and solute-twin boundary interactions. Constitutive modelling of the flow stress permits for the evaluation of the critical resolved shear stress (CRSS) of slip and twinning systems and determination of their activity during deformation. Analysis of activation volume and activation distance suggests that dislocation-dislocation interactions determine the flow stress. The strain rate sensitivity parameter is unaffected by alloy composition, but it decreases sharply with decreasing temperature. Mg-Sc alloys show some improvement in strength and ductility in comparison to Mg, however not as much as demonstrated by common Mg-RE binary systems. The enhancement in ductility is attributed in part to the activity of twinning and non-basal slip.
Abstract Flow stress and work hardening behaviour of Mg-Y binary alloys have been studied under uniaxial tension and compression at 4 K, 78 K and 298 K. Electron microscopy observations show that Yttrium forms multi-atomic clusters distributed randomly in Mg matrix. During thermomechanical processing, Y accumulates at the grain boundaries and controls recrystallization texture, which acquires lower intensity of the basal component and higher degree of randomness in comparison to polycrystalline ...
Abstract The effect of scandium on the microstructure and texture of hot rolled and annealed binary Mg-Sc alloys has been studied. Hot rolled alloys develop weaker and more random basal texture than the corresponding texture of pure Mg after undergoing the same thermomechanical processing. The increase of Sc concentration leads to a systematic weakening of the texture, however texture randomization is not as prominent as in other Mg-RE alloys. The annealed texture of Mg-Sc alloys inherits featur...
The mechanical properties of Mg-Gd and Mg-Y solid solutions have been studied under uniaxial tension and compression between 4 K and 298 K (−269 °C and 25 °C). The results reveal that Mg-Gd alloys exhibit higher strength and ductility under tension and compression attributed to the more effective solid solution strengthening and grain-boundary strengthening effects. Profuse twinning has been observed under compression, resulting in a material texture with strong dominance of basal component para...
A yield plateau occurs in some Mg alloys during compressive deformation that has been ascribed to the localization of twinning. In fine-grained AZ31, this plateau was explained by a region of large twin volume fraction nucleating in a small band and propagating, similar to a “Luders band” like phenomena. Once the band traverses the entire gauge length, the sample begins to strain harden. Similarly, ZK60 samples exhibit the same Luders like phenomena during extrusion direction compression as conf...
Mechanisms of strength and ductility in textured Mg–Gd binary alloys are investigated under conditions of uniaxial tension and compression at 4.2, 78 and 298 K. The alloys obey solution strengthening relationships between the critical stress and the concentration of the solute c, which scales as , with n assuming values 0.30–0.53 for tension and 0.73–0.87 for compression. The results suggest that Gd solute hardens the compressive yield modes more than the tensile yield modes, with basal slip and...
Abstract Thermally activated flow of dislocations has been studied in Al–Mg solid solutions under conditions of positive strain-rate sensitivity at 78 K. Thermodynamic deformation parameters determined from up-rate and down-rate changes show differences attributed to the density and types of effective obstacles intersected by the mobile dislocations. The alloys exhibit the stress equivalence of the apparent activation volume over the yield stress range as V ∗ ∼ σ 0 - 0.75 under up-rate and down-...
Abstract The deformation behaviour of two single phase binary alloys, Mg–5Y and Mg–10Y, have been examined. In compression, two twin types were observed, the common { 1 0 1 ¯ 2 } twin as well as the less common { 1 1 2 ¯ 1 } extension twin. It is shown that the { 1 1 2 ¯ 1 } twin is much less sensitive to solute concentration than the { 1 0 1 ¯ 2 } twin, and it is suggested that the simple atomic shuffle of the { 1 1 2 ¯ 1 } twin reduces the solute strengthening imparted by Y additions. The comm...
Last. William A. Curtin(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 79
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Abstract Solute strengthening of twin dislocation motion along an existing twin boundary in Mg–X (X = Al, Zn) is investigated using a new Labusch-type weak pinning model. First, the ( 10 1 ¯ 2 ) twinning dislocation structure is computed using first-principles methods. Second, the interaction energies of Al and Zn solutes with the twin boundary and twin dislocation are computed. It is shown that the interaction energies of Zn solutes scale with the Al solute energies in proportion to the misfit ...
Last. Javier Segurado(UPM: Technical University of Madrid)H-Index: 33
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Abstract An inverse optimization strategy based on crystal plasticity finite element simulations of polycrystals was used to obtain the critical resolved shear stresses of two Mg–1%Mn alloys containing neodymium from macroscopic experimental data. It was found that, with respect to pure Mg, the presence of Nd increases the CRSS basal , CRSS twinning , and the CRSS basal /CRSS twinning ratio and decreases the CRSS non-basal /CRSS twinning ratio. Additions of neodymium as high as 1 wt% result in s...
Magnesium alloys that contain certain rare-earth (RE) additions are known to have improved formability and this can be partly attributed to the different texture they display after recrystallization. Previous experimental work has identified segregation of RE to grain boundaries and dislocations as being potentially important in producing this change in behavior. In the present paper, two classical models (Langmuir–McClean and Cahn–Lucke–Stuwe) are used to explore the likely effect of RE additio...
#1Chetan Singh(IITD: Indian Institute of Technology Delhi)
#2R. Lakshmi Narayan(IITD: Indian Institute of Technology Delhi)H-Index: 6
Last. Jayant Jain(IITD: Indian Institute of Technology Delhi)H-Index: 16
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Abstract null null The effect of simultaneous addition of non-rare-earth (Ca) and rare-earth (Sc) elements on the hot rolled deformation behavior, recrystallization and texture evolution of Mg alloys is evaluated. For this purpose, the microstructures of as rolled and recrystallized ternary alloys, Mg-0.6Ca-0.5Sc and Mg-0.6Ca-1.0Sc were compared with those of binary Mg-0.6Ca and Mg-1.0Sc alloys. Results show that for all the alloys studied, null null null null null 10 null null 1 null ¯ null nul...
#1Tianshui Zhou(Lanzhou University of Technology)H-Index: 1
#2Zehua Liu(Lanzhou University of Technology)H-Index: 1
Last. Liu Dexue(Lanzhou University of Technology)H-Index: 1
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Abstract Due to their unique crystal structure, preparation of high-ductility Mg alloys is still a great challenge, especially high-ductility as-cast or heat-treated Mg alloys. Here, the effect of Sc on the microstructure, second phases, and mechanical properties of as-cast and heat-treated Mg-xSc-3Yb-1Mn-0.5Zr (x = 2, 3, 4, 6 wt%) alloys was investigated systematically. The results indicated that as-cast samples mainly consisted of α-Mg, MgSc, Mg2Yb, Mn2Zr and Mn2Sc phases. Moreover, the averag...
Abstract Diffusion behaviors in Mg–Sc hcp and bcc solid solutions between 773 and 873 K were investigated using both single-phase and multi-phase diffusion couple techniques. The EPMA detected composition-distance profiles were smoothed and fitted using the error function expansion (ERFEX). The interdiffusion coefficients were extracted using Sauer–Freise integral. The interdiffusion coefficients in hcp phase showed a slightly parabolic composition dependence at the Mg-rich part and the maximum ...
Last. Fusheng Pan(Chongqing University)H-Index: 61
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Abstract This paper studied the microstructure and corrosion behavior of Mg-xSc binary alloy (x = 0.1–1.5 wt.%) sheets. Sc has a significant effect of refining grains of Mg. The Mg-Sc binary alloys had a single-phase microstructure for Sc concentrations between 0.1−0.3 wt.%, while there were Mg-Sc precipitates for higher Sc concentrations. The Sc additions obviously improved the corrosion resistance of pure Mg due to the refinement of microstructure and the formation of a more protective corrosi...
Strain localization occurring at advanced deformation under compression of Mg-0.28 at. pctGd alloy has been studied. The strain localization develops in previously twinned microstructure in the form of shear bands (SBs) represented by narrow, heterogeneous zones of localized deformation. The onset of shear banding appears when the work hardening capacity of the material is exhausted. SBs are promoted by activation of high-stress contraction and double twins and are 18 pct harder than the surroun...
#1Z.H. Wang(TUT: Taiyuan University of Technology)H-Index: 9
#2Ji Qiu(TUT: Taiyuan University of Technology)H-Index: 3
Last. Tao Jin(TUT: Taiyuan University of Technology)H-Index: 2
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Abstract In this study, quasi-static compression, tensile, shear, and combined compression-shear tests are conducted on cast AZ91D magnesium (Mg) alloy to study its fracture behavior. Shear-compression specimens are applied instead of complex loading device to obtained the fracture response of Mg alloy under mixed compression/shear tests. Results show that the stress states of specimens can be controlled by changing the loading angle. The strength differential effect is observed, and the criteri...
Abstract To better understand the role of alloying elements on the deformation behavior of Mg, the orientation dependence of elastic properties of Mg was investigated under the influence of solute atoms using first-principles methods. Rare earth (RE) elements (Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, and Lu) and non-RE elements (Ag, Al, Cd, In, Pb, Sn, Tl, and Zn) were studied at the concentration of 2.78 at.%. The three-dimensional representation shape of Young’s modulus (E) shows that the elasticity of ...
#1Zongrui Pei(ORNL: Oak Ridge National Laboratory)H-Index: 12
#2Junqi Yin(ORNL: Oak Ridge National Laboratory)H-Index: 11
Abstract Understanding the deformation mechanisms of Mg has been a long-standing and significant problem for materials scientists. Currently, there are two widely acknowledged ductility-improving mechanisms, i.e., the dislocation nucleation mechanism and dislocation mobility mechanism. Since the two mechanisms were previously investigated using very different solute sets, hitherto there is no clear understanding of the relation between them. Based on the newly proposed descriptors for the mechan...
Last. Baolin Wu(SAU: Shenyang Aerospace University)H-Index: 5
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Room-temperature tensile behavior and associated deformation mechanisms of multiple-axial forged (MAFed) pure Mg has been investigated. The as-MAFed Mg, with a coarsely recrystallized structure, exhibited a balanced strain-hardening behavior with strain, resulting in extraordinary mechanical properties with high ultimate stress (~200 MPa) and extensive true strain (~0.30). The observation on the microstructural evolution suggests that the balanced strain-hardening behavior is correlated with de-...
