Deformation Behavior Of Mg Research Articles

Study on microstructure evolution and deformation behavior of Mg– Zn base alloy pipes during hot bending

The strong basal fiber texture of magnesium (Mg) alloy pipes usually leads to poor secondary forming performance. In this study, Mg–2Zn-0.4Ce-0.4Mn (ZME) and Mg–2Zn-0.4Ce-0.4Mn-0.2Ca (ZMEX) pipes were prepared. Compared with the ZME pipe, the ZMEX pipe with a weaker initial texture exhibits excellent bending performance, with a peak load displacement (PLD) of 14.5 ± 0.5 mm and a total energy absorption (TEA) of 142.9 ± 1.7 J. The difference in bending performance between the two pipes is related to the deformation mechanism during hot bending. In the hardening stage, the deformation of the compression zone (CZ) of the two pipes is mainly ETW nucleation, and the overall proportion of twin grains is similar. However, in the tensile zone (TZ), the deformation of the ZME pipe is mainly prismatic slip, while the weak initial texture of the ZMEX pipe leads to the deformation dominated by both prismatic and multiple pyramidal slips, resulting in a higher hardening rate. In the softening stage, the deformation behavior in the CZ and TZ of both pipes tends to be similar. In addition, it is revealed that the softening phenomenon of both pipes after the bending displacement reaches PLD is caused by discontinuous dynamic recrystallization (DDRX) driven by high-density dislocations accumulated in the later CZ and TZ. The research on the microstructure evolution and deformation mechanism of Mg alloy pipe during bending deformation carried out in this study is of great significance for optimizing its secondary forming controllability and further expanding its application.

Plastic deformation behavior of Mg–8Li dual phase alloy during multi-directional compression

The Mg–8Li dual phase alloy was deformed by multi-directional compression with different passes. Microstructure evolution of deformed Mg–8Li alloy was analyzed by electron backscatter diffraction. X-ray diffraction profile was used to calculate the dislocation density in α-Mg and β-Li phase to reveal the quantitively change trend under different compression passes. The mechanical properties were assessed through tensile and compressive tests. The Mg–8Li alloy exhibited optimal mechanical properties when compressed with 12 passes (sample 12MDC), with a compression yield strength of 183.1 MPa and a tensile yield strength of 124.2 MPa. The improved mechanical properties in sample 12MDC were attributed to an increase in {10 1‾ 2} twin and {101‾ 3}-{101‾ 2} double twin boundaries, along with the presence of sub-grain boundaries and a reduced grain size in the α-Mg phase. Additionally, the inconsistent results between microhardness and dislocation density calculation manifests the uneven distribution of dislocations in β-Li phase. Broken α-Mg phase brings more phase interface to relieve the strain in β-Li phase, which results to a decreased dislocation density in sample 12MDC (1.19 × 1011/m2). Results show that weaken tension-compression yield asymmetry and more even distribution of dislocation in both phases could be achieved when the compression passes increases to 12.

Effects of Trace Zn on the Deformation Mechanisms of Mg–Gd–Y–Zr Alloy Investigated by In Situ Synchrotron Diffraction

Addition of trace Zn can impose notable effect on the deformation behavior of Mg–Gd–Y–Zr alloy, while the underlying mechanisms have not been revealed. In the present work, Mg–8.5Gd–2.5Y–0.3Zr (wt%) (0Zn) and Mg–8.5Gd–2.5Y–0.5Zn–0.3Zr (wt%) (0.5Zn) alloys are fabricated by casting and extrusion, to obtain a bimodal microstructure containing fine dynamic recrystallized (DRXed) grains and coarse unDRXed grains. The as‐extruded 0Zn and 0.5Zn alloys are studied by in situ synchrotron diffraction under uniaxial tension and compression to clarify the effect of trace Zn on the deformation mechanisms. It is found that both alloys exhibit stress softening in the basal slip‐favored grains under both tension and compression, and adding trace Zn highly enhances the stress softening. Furthermore, the addition of Zn stimulates the occurrence of discontinuous yielding which is in connection with the stress softening, resulting from the interaction between basal dislocations and solute atmospheres. The tension–compression‐yielding symmetry of the alloy is improved by adding Zn, which is mainly attributed to the suppression effect of γ′ phases and Gd/Y–Zn dimers on tensile twinning. Finally, the addition of Zn can promote the tensile and compressive strength, owing to the strength enhancement of the relevant deformation modes and the increase of the fraction of unDRXed regions.

The effect of hydrostatic pressure on grain refinement and deformation behaviors of Mg–Gd–Y–Zn–Zr alloy under complex shear stress

The effects of hydrostatic pressure on grain refinement and deformation behaviors of Mg–13Gd–4Y–2Zn–0.5Zr alloy were investigated. With the increase of hydrostatic pressure, the equivalent stress and forming load increase, and stress triaxiality also increases. The hydrostatic pressure has little effect on dynamic recrystallization (DRX) fraction and grain size, and the DRX fraction difference is not greater than 10%. This is because DRX critical strain and grain nucleation are almost unaffected by hydrostatic pressure. The slight increase in DRX fraction under higher hydrostatic pressure is attributed to the enhanced <a> dislocation activity near the lamellar long-period stacking ordered (LPSO) phase and significant local temperature elevation in the deformation zone. The high hydrostatic pressure is mainly borne by the LPSO phase. The bending deformation energy of the lamellar LPSO phase increases with the increase of hydrostatic pressure. The area fraction of samples is decreased from 18.5% of one direction compression & simple shear (1-CS) sample to 13.6% of three directions compression & simple shear (3-CS) sample. The solute diffusion and deconstruction of the bulk LPSO phase occur at higher hydrostatic pressure. The hydrostatic pressure has little effect on the basal texture strength of α-Mg phase under strong shear stress. The activation of <c+a> dislocation, as the primary source of non-basal slip, shows the same distribution characteristics.

Effect of pre-aging on microstructure, activation energy, texture evolution of Mg–9Gd–4Y–2Zn–0.5Zr alloy during compression deformation

This paper illustrated the effects of pre-aging on the microstructure, texture evolution, and deformation behavior of Mg–9Gd–4Y–2Zn–0.5Zr alloy during hot compression. Dynamic recrystallization (DRX) behavior, texture evolution, stress-strain curve, and activation energy of the solid solution and pre-aged alloy were evaluated. The results showed that the second-phase particles of the pre-aged samples exhibit combination of two types particles structure, which is composed of coarse dynamic precipitation particles and fine nanoparticles. The combination of these two types particles showed the best grain refinement effect by accelerating the DRX process, as the coarse dynamic precipitation particles promoted DRX through the PSN mechanism and the fine granular phase pinned dislocations and inhibited grain growth. As a result, the pre-aged samples had a higher DRX grain volume fractions and smaller average grain sizes than the solid solution alloys. In addition, the pre-aged sample had higher deformation activation energy (Q = 294.8 kJ/mol) than solid solution sample (Q = 223 kJ/mol) because β-phase pin dislocations formed during deformation restrained the movement of grain boundaries. The pre-aged alloys also showed a more concentrated texture than the solid solution alloys, with the c-axis of the coarse grains distributed from the compression direction (CD) at 30° inclination to the normal direction (ND). The c-axis distribution of the coarse grains was more scattered in the solid solution alloys. A hot processing map was constructed for the pre-aged alloy and used for evaluation. The optimal deformation parameters for the pre-aged Mg–9Gd–4Y–2Zn–0.5Zr alloy were between 0.001 and 0.1 s−1 at 400 °C–480 °C. These significant observations not only provide theoretical guidance but also practical application for setting plastic forming deformation parameters in industrial production.

Effect of AlLi phase on deformation behavior and dynamic recrystallization of Mg-Li alloy during hot compression

Hot deformation behavior of Mg−5Li−3Al−2Zn (LAZ532) alloy with AlLi phase was studied by using isothermal hot compression experiments at the deformation temperature of 473−623 K and the strain rate of 0.001−1 s−1. AlLi phase could significantly increase the peak stress of LAZ532 alloy during hot deformation because of its obstructing effect on the movement of dislocation. A relevant strain-compensated Arrhenius constitutive model was constructed to predict the hot deformation behavior of LAZ532 alloy, and the predicted results were in good agreement with experimental ones. The corresponding hot processing maps were established based on the Murty criterion, and the optimal processing domain was located in the range of 538−623 K and 0.001−0.01 s−1. At the high strain rate, AlLi phase was not beneficial for the flow stability and dynamic recrystallization of LAZ532 alloy during hot compression. In addition, deformation temperature would change the nucleation mechanism of the dynamic recrystallization of LAZ532 alloy.

Thermal deformation behavior of Mg–3Sn–1Mn alloy based on constitutive relation model and artificial neural network

The flow stress behavior of Mg–3Sn–1Mn alloy during thermal compression deformation was systematically studied. The thermal compression simulation experiment was carried out at different deformation temperatures and different strain rates in the range of 523–673 K and 0.001-1s−1, respectively. It is found that at low temperatures and high strain rates, a large number of twins were generated at the initial stage of thermal deformation, causing an increase in the corresponding flow stress, which makes the traditional constitutive relation model insensitive to predicting the thermal deformation behavior of Magnesium (Mg) alloys with twinning effect. To better evaluate the rheological behavior of Mg alloys, an artificial neural network (ANN) model based on a feedforward and back-propagation algorithm was developed to predict the thermal deformation behavior of Mg–3Sn–1Mn alloy affected by twinning phenomena. The inputs of the model were deformation temperature, strain rate and strain, the output was the flow stress. The comparative evaluation of the obtained results using statistical standard R2 and relative error R¯. The correlation coefficients predicted by the constitutive model were 0.964 and 0.869 at low and high stress levels, respectively. And the correlation coefficient of the neural network predictive model was 0.992. The result shows that the trained ANN is more accurate than the traditional constitutive relation model in predicting the thermal deformation behavior with the twinning effect.

Revealing the dynamic recrystallization mechanism, extrusion deformation mechanism, and tensile deformation behavior of Mg–6Al–1Zn–1.1Sc alloy

In this study, extruded deformed billet and extruded rod of Mg–6Al–1Zn–1.1Sc (wt. %) alloy were characterized by optical microscopy (OM) and electron backscatter diffraction (EBSD). The room temperature tensile properties and deformation behavior of extruded alloy were investigated using a universal testing machine and the visco-plastic self-consistent (VPSC) model. The results indicated that the coarse deformed grains (DGs) progressively disappeared and the degree of dynamic recrystallization (DRX) of the alloy increased as the sampling position approached the outlet of the extrusion die. In addition, the grain boundary strengthening induced by DRX increased the corresponding Vickers hardness. DRX mechanisms during extrusion included discontinuous DRX, continuous DRX, twin-induced DRX, and particle-stimulated nucleation (PSN). The EBSD-based in-grain misorientation axes (IGMA) analysis revealed that the slip modes within DGs were dominated by prismatic slip in the early stages of extrusion and by multiple slip modes in the later stages. The yield strength, ultimate tensile strength, and elongation of the extruded alloy were 172.4 MPa, 290.1 MPa, and 26.9%, respectively. The combination of grain boundary strengthening, texture strengthening, and secondary phase strengthening resulted in the high yield strength. The VPSC model well simulated the tensile deformation of the extruded alloy with (0001)//ED (extrusion direction) fiber texture. The superior plasticity of the extruded alloy was ascribed to the high Schmid factor (SF) of the non-basal slip and the activation of the non-basal slip facilitated by the reduction in the ratio of the critical resolved shear stress (CRSS) between the non-basal slip and the basal slip.

Role of disclinations around kink bands on deformation behavior in Mg–Zn–Y alloys with a long-period stacking ordered phase

Mg–Zn–Y alloys that contain an Mg-based long-period stacking ordered (LPSO) phase exhibit excellent mechanical properties because of the kink bands formed by plastic deformation. Such “kink-band strengthening” has attracted significant attention. Herein, we conducted deformation tests on directionally solidified single-phase LPSO Mg85Zn6Y9 alloys to investigate the kink-band strengthening mechanism. High-angular resolution electron backscatter diffraction was performed to detect misorientation between the matrices on either side of the kink bands. The misorientations corresponded to the magnitudes of the Frank vectors of the disclinations around the kink, and closely matched the estimations from geometric analysis, which supported the existence of disclinations. Moreover, the Frank vector of the kink bands increased after shear deformation, which indicates that shear deformation introduced new disclinations around the kinks. Scanning electron microscopy demonstrated that the kinks clearly obstructed basal ⟨a⟩ slip. Furthermore, scanning transmission electron microscopy of a sheared kink band revealed dislocation pile-ups on both sides of the kink/matrix interface, as well as the formation of secondary kinks that stabilized the structure against shear deformation (i.e., self-accommodation) and bend contours caused by elastic stress fields. The results suggest that disclinations behave as long-range obstacles to dislocation motion (e.g., by reducing the increase in kink-band self-energy or by the elastic stress field of disclinations). We believe that this study will play a key role in identifying the factors responsible for kink-band strengthening in LPSO-phase Mg alloys and in understanding the phenomena underlying the strengthening mechanism.

Plastic deformation behavior of a Mg-1.5Zn-0.1Ca (mass%) alloy sheet under different strain paths

Mg–Zn–Ca alloy sheets with weak basal texture are expected to improve the room-temperature press formability of Mg-alloy sheets. The plastic deformation behavior of Mg–Zn–Ca alloy sheets should differ significantly from that of typical Mg-alloy sheets with strong basal texture. However, this has not yet been substantially studied. In this study, the plastic deformation behavior of a rolled Mg-1.5Zn-0.1Ca (mass%) alloy sheet with a thickness of 1 mm is studied experimentally. Tests of uniaxial tension, compression, reverse loadings from tension to compression, and from compression to tension are conducted in the rolling and transverse directions, and the work-hardening behavior and evolution of the Lankford value are investigated. Electron backscattered diffraction measurements are also conducted to examine the texture evolution. Under tension, the stress was less in the transverse direction than that in the rolling direction, and an apparent plateau region appeared only in the transverse direction. Under compression, the stress-strain curves exhibited plateau regions at the initial stage and were similar in the rolling and transverse directions. The Lankford values were less under compression than under tension in both directions. Under reverse loading from compression to tension, sigmoidal curves appeared, irrespective of the loading direction; however, they were more pronounced in the rolling direction than in the transverse direction. Under reverse loading from tension to compression, sigmoidal trends did not occur, irrespective of the loading direction, and the in-plane anisotropy in the work-hardening behavior was small. The mechanisms yielding these macroscopic deformation behaviors are discussed in terms of twinning and slip activities.

Investigations on the tensile deformation of pure Mg and Mg–15Gd alloy by in-situ X-ray synchrotron radiation and visco-plastic self-consistent modeling

In this study, the texture evolutions of two Mg materials during tension are explored. In-situ X-ray synchrotron and Visco-Plastic Self-Consistent (VPSC) modeling are employed to investigate the different deformation modes between pure Mg and Mg–15Gd (wt.%) alloy. These two materials with a strong extrusion texture show large different slip/twinning activity behaviors during tensile deformation. The basal 〈a〉 slip has the highest contribution to the initial stage of plastic deformation for pure Mg. During the subsequent plastic deformation, the prismatic slip is dominant due to the strong ED // 〈100〉 fiber texture. In contrast, the deformation behavior of Mg–15Gd alloy is more complex. Twinning and basal slip are dominant at the early stage of plastic deformation, but further deformation results in the increased activation of prismatic and pyramidal slips. In comparison to pure Mg, the ratios of the critical resolved shear stress (CRSS) between non-basal slip and basal slip of the Mg–15Gd alloy are much lower.

Deformation behavior of the Mg–Zn–Zr–Nd–Gd alloy

Gd and Nd added Mg–Rare Earth (Mg–RE) alloys have attracted high-temperature applications due to their excellent combinations of high specific strength, high specific stiffness, good damping capacity, and better creep life. Despite these advantages, such Mg–RE alloys have attracted applications only in the cast form, owing to the difficulty in hot workability. Therefore, to understand the hot deformation behavior of Mg–Zn–Zr–Nd–Gd alloy, the present study correlates the results of hot compression studies with microstructure and texture. Serrated flow behavior is observed due to the dynamic strain aging. Maximum strain rate sensitivity is achieved between 580 K–650 K at lower strain rates 0.001 s−1–0.01 s−1. Dynamic recovery is predominantly active within this range of temperature and strain rate. Dynamic precipitation produces ultra-fine precipitates and leads to the suppression of dynamic recrystallization behavior. All deformed samples develop a relatively weak basal texture with the [0 0 0 1] axis parallel to the compression direction.

Adjustable room temperature deformation behavior of Mg–Sc alloy: From superelasticity to slip deformation via TRIP effect

This study investigated the transformation-induced plasticity (TRIP) effect in Mg–Sc alloys with β single-phase (body-centered cubic) structure. A Mg-19.8 at% Sc alloy showed fracture strain of ∼53 % accompanied by necking propagation with increasing the tensile strain at room temperature. An X-ray diffraction analysis and transmission electron microscopy observations confirmed the existence of a hexagonal close-packed phase beside the β matrix phase during and after the tensile test; this indicates a strain-induced martensitic transformation, i.e., the TRIP effect induced superior ductility. Moreover, the study revealed a threshold Sc content of ∼19.5 at% Sc at which the deformation behavior at room temperature changes from superelasticity to TRIP. The TRIP Mg–Sc alloys exhibited fracture strain from 45 % to 66 % and ultimate tensile strength (UTS) above 220 MPa to overcome the tradeoff between the fracture strain and UTS of conventional Mg alloys.

Effect of Sn on Hot Deformation Behavior of Mg–Ca–Mn Mg Alloys

Effect of Sn on Hot Deformation Behavior of Mg–Ca–Mn Mg Alloys

Local deformation of Mg–7Gd–5Y–1.2Nd–0.5Zr magnesium alloy under high speed impact along extrusion direction

The high strain rate deformation behavior of Mg–7Gd–5Y–1.2Nd–0.5Zr alloy was carried out at several temperatures. Through the truncated test of cap specimen, it was found that the local deformation occurred in the design shear zone, but no adiabatic shear band was observed. The deformation mechanism was mainly pyramidal slip, supplemented by prismatic slip, basal slip, and dynamic recrystallization. Among them, pyramidal 〈c + a〉 slip could coordinate deformation through the slip component along the 〈c〉 direction. The Johnson–Cook constitutive model and failure model were modified, and then the local deformation of the cap specimen along the extrusion direction was simulated by LS-DANY software. The results showed that the local severe deformation occurred in the area of the cap specimen with sharp change in shape, which was at an angle of 45 ° with the impact compression loading along extrusion direction. The temperature increased continuously with the amount of deformation until fracture occurred. The results showed that the alloy had high resistance to local high strain deformation and fracture.

Thermal Deformation Behavior of Mg–3sn–1mn Mg Alloy Based on Constitutive Relation Model and Artificial Neural Network

Thermal Deformation Behavior of Mg–3sn–1mn Mg Alloy Based on Constitutive Relation Model and Artificial Neural Network

Thermal Deformation Behavior of Mg–3sn–1mn Mg Alloy Based on Constitutive Relation Model and Artificial Neural Network

Thermal Deformation Behavior of Mg–3sn–1mn Mg Alloy Based on Constitutive Relation Model and Artificial Neural Network

Cyclic deformation behavior of Mg–SiC nanocomposites on the macroscale and nanoscale

AbstractMetal‐ceramic nanocomposites are promising candidates for applications necessitating light weight and excellent fatigue resistance. We produced Mg–SiC nanocomposites from mechanically milled powders, yielding a homogeneous nanocrystalline structure and excellent quasistatic strength values. Little is known, however, about the fatigue behavior of such composites. Here, we used load increase tests on the macroscale to yield estimation values of the fatigue endurance limit. Fatigue strength increased significantly for the materials processed by the powder metallurgical route. We further investigated the cyclic deformation behavior under stress‐controlled conditions on the macroscale and nanoscale. Cyclic nanoindentation showed that indentation depth and cyclic plastic deformation decreased with increasing reinforcement content, hinting to a higher cyclic strength and corroborating the results from the macroscopic load increase tests. Our results therefore show that cyclic nanoindentation reliably determines the plastic deformation behavior of Mg nanocomposites offering the possibility of fast material analysis.

Hot deformation behavior and finite element simulation of Mg–8.3Gd–4.4Y–1.5Zn–0.8Mn alloy

To study the hot deformation behavior of Mg–8.3Gd–4.4Y–1.5Zn–0.8Mn (wt%) alloy, hot compression tests were conducted using a Gleeble–3500 thermal simulator at temperatures ranging from 653 to 773 K, true strain rates of 0.001–1 s−1, and a deformation degree of 60%. Results of hot compression experiments show that the flow stress of the alloy increases with the strain rate. The true stress–true strain curves are corrected by correcting the effect of temperature rise in the deformation process. Activation energy, Q, equal to 287380 J/mol and material constant, n, equal to 4.59 were calculated by fitting the true stress–true strain curves. Then, the constitutive equation was established and verified via finite element simulation. Results of the hot processing map show that the probability of material instability increases with the degree of deformation, which indicates that the material is not suitable for large deformation in a single pass. On the whole, the alloy is appropriate for multipass processing with small deformation and a suitable processing temperature and strain rate are 733 K and 0.01 s−1, respectively.

The strengthening mechanism and deformation behavior of Mg–Li matrix composite reinforced by Al3La phase formed in-situ through La2O3 particle

Here, the low-cost submicron La2O3 particle modified by lithium salts as a precursor was added to Mg–5Li–3Al–2Zn (LAZ532) alloy melt to form in-situ plenty of submicron Al3La phase, finally, the composite with high strength and plasticity reinforced by Al3La phase formed in-situ was obtained. Compared with the LAZ532 matrix alloy, the properties of the composite exhibited significant improvement of UTS~340.1 MPa, TFS~22.4%, UCS~415.5 MPa and CFS~20.3%. The results showed that the Al3La phase formed in-situ not only had a coherent boundary with Mg matrix, but also refined the grains and weakened the {0001} basal texture, which greatly improved the strength and plasticity of the composite. Based on theoretical analysis, the high strength of the composite was mainly attributed to grain refinement, texture strengthening and Orowan strengthening. In addition, according to the slip trace analysis of in-situ EBSD tensile deformation and the results of ex-situ EBSD compression deformation, during the tensile deformation along the extrusion direction (ED), the texture type had no obvious change, and the deformation was dominated by prismatic slip, next pyramidal I <a> slip; during the compressive deformation along the ED, the initial deformation was dominated by basal slip; with the increase of strain, the formation of {1210}<1010> texture was caused by the nucleation of a large number of {1012} extension twins and the rotation of some grains.