Deformation Behavior Of Mg Research Articles

Finite Element Analysis for Mechanical Response of Magnesium Foams with Regular Structure Obtained by Powder Metallurgy Method

Magnesium and Magnesium alloys have attracted immense attention as a biomedical implant material due to favourable mechanical properties and biocompatibility. Biodegradable nature of Magnesium dismisses the need of revision surgery for removal of implant. Porous Mg- foams are advantageous as presence of pores allows the higher degree of osseointegration. The mechanical properties of the porous foam material is a function of its density, thus a Finite Element Method (FEM) approach is required to predict the behaviour of Mg- foam under various stresses for real-time application. The author has attempted to quantitatively assess the mechanical properties of Mg foam with a 40-45% porosity with 100-300μm pore size. The deformation behaviour of Mg- foams with different porosity under the compressive and bending loads has been described by “Deshpande and Fleck model” with ABAQUS FEM software. The simulation results have been compared with the recent publications. An agreeable comparison has been seen in the results.

Effect of Ca and CaO on the microstructure and hot compressive deformation behavior of Mg–9.5Zn–2.0Y alloy

In this study, the effect of adding 0.3wt% Ca to a Mg–9.5Zn–2.0Y alloy with icosahedral (I) phase (Mg3Zn6Y) was examined. The Ca alloying was done by two different routes, either through a master alloy produced with Mg and CaO (which is convenient from the points of view of safety and cost) or by direct addition of powdered Ca to the molten alloy. The small addition of Ca (CaO) effectively increased the ignition temperature of the alloys (by about 90K), which is promising for fire suppression and safe handling with the molten alloys, but it led to the formation of Ca2Mg5Zn13 phase at grain boundaries or interdendritic interfaces, causing partial melting and intergranular cracking during compressive deformation near ∼615K. As a result, the upper limit of hot workability temperature decreased to 598K, which is lower than that of the Mg–9.5Zn–2.0Y alloy by 125K. The cast Mg–9.5Zn–2.0Y–0.3Ca alloys prepared using the two different routes exhibited high similarity in ignition temperature, chemical composition, microstructure, hot compressive behaviors and processing maps, indicating that the use of CaO is as effective as the use of Ca in producing the same quality of Ca containing Mg alloys. The flow stresses during hot compressive deformation and the activation energy for plastic flow remained unaffected by the Ca (CaO) alloying, but decreased the strain rate sensitivity at high strain rates over 10−3s−1 due to the initiation of either power-law breakdown or partial melting by adiabatic heating. Because of this, the Ca containing alloy lost hot workability at high strain rates by comparison to the Ca-free alloy.

Constitutive modeling for the hot deformation behavior of Mg–3.06Zn–0.58Zr–1.07Y alloy

In order to improve the understanding flow behaviors of hot compressive deformation as‐homogenized of Mg–3.06Zn–0.58Zr–1.07Y alloy, carried out a series of isothermal compressive tests with 60% height reduction of specimens were performed at constant temperature of 523 K, 573 K, 623 K, 673 K, and 723 K, and strain rates of 0.001, 0.01, 0.1, and 1 s−1 on Gleeble‐1500 thermo‐mechanical simulator. The results of the true stress–strain curves show that the flow stress increases with the increasing strain rate and decreasing deformation temperature. The flow behavior at constant strain rate was characterized by the dynamic recrystallization and dynamic recovery softening mechanisms occur simultaneously. The number of the dynamic recrystallization curve increases with increasing strain rate. A nonlinear flow model and its constitutive equation, based on the Arrhenius‐type equation, were employed for studying the deformation behavior and relationships between the deformation temperature, strain rate, and flow stress. Finally, the processing map of Mg–3.06Zn–0.58Zr–1.07Y alloy at the strain of 0.3 was obtained through the dynamic materials modeling. The optimal processing temperature and strain rate, using the microstructure and constitutive modeling, were found to be in the rage 623–723 K and 0.1–1 s−1, respectively.

Deformation mechanisms of Mg–3Al–1Zn alloy by polycrystal plasticity modeling

A polycrystal plasticity model was developed to analyze the room-temperature deformation behaviors of Mg–3Al–1Zn alloy (AZ31). The uniaxial tension and compression tests at room temperature were conducted using cast and extruded AZ31 rods with different textures and combined with the proposed model to reveal the deformation mechanisms. It is shown that, different flow curves of two specimens under tension and compression tests can be simulated by this model. The flow curves of AZ31 extrusions exhibit different shapes for tension and compression due to different activities of tensile twinning and pyramidal 〈c+a〉 slip. The metallographic and TEM observations showed the equal twinning activities at the initial stage in tension and compression tests and the occurrence of pyramidal 〈c+a〉 slip in compression of as-cast Mg–3Al–1Zn alloy with increasing the strain, which is consistent with the simulated results by the proposed model.

Constitutive modeling of Mg–9Li–3Al–2Sr–2Y at elevated temperatures

Hot deformation behavior of Mg–9Li–3Al–2Sr–2Y alloy was studied via hot compression tests in the temperature range of 423–573K with different strain rates ranging from 0.001 to 1.0s−1 using the Gleeble® 3500 thermal–mechanical simulation testing system at the University of Waterloo. A number of constitutive equation models including the Ludwik, Zener–Hollomon and modified Hensel–Spittel models were used to evaluate the correct material parameters for this alloy and assessed in terms of their ability to accurately predict the constitutive behavior. The analysis of the experimental data by the three constitutive models resulted in an excellent description of the flow curves. The results showed that the Ludwik and Zener–Hollomon models lead to a good agreement between the calculated and measured flow stresses during work softening. Whereas, the modified Hensel–Spittel equation was able to describe the entire deformation process for the deformation temperatures studied. The developed models were then applied to predict the stress strain behavior of this alloy under different thermomechanical behavior paths and showed good accuracy.

The beneficial effect of AgIn addition on deformation behavior, microstructure and texture in Mg–Al–Zn alloy during single pass warm rolling

Abstract In this study microstructure, texture and deformation behavior of Mg–3Al–1Zn (alloy-1) and Mg–3Al–1Zn–0.5AgIn (alloy-2) were investigated. The alloys were subjected to single pass thickness reductions of 30%, 50% and 60% at 300 °C (573 K) followed by annealing at 400 °C (673 K). Scanning electron microscopy (SEM), X-ray based macro-texture, transmission electron microscopy (TEM) and electron backscatter diffraction analysis (EBSD) were performed to investigate the effect of AgIn addition on deformation and annealing behavior. A silver-containing second phase in the form of fine precipitates was observed in alloy-2 during rolling which remained thermally stable during subsequent annealing. An ultrafine microstructure was observed for alloy-2 in comparison to alloy-1 after rolling. EBSD based Schmid factor (SF) analysis revealed a significant contribution of extension twinning, basal slip, pyramidal 〈 c + a 〉 slip and prismatic slip in alloy-2. In contrast, contraction twinning was the predominant deformation mode in alloy-1. The combined activity of larger number of deformation modes resulted in improved formability, refined microstructure and a weak deformation texture in alloy-2. The improved rolling response was mainly attributed to the combined contribution of multi deformation modes.

Hot compression behavior of GZ31 magnesium alloy

Hot deformation behavior of Mg–3Gd–1Zn (GZ31) magnesium alloy was studied by hot compression tests over the temperature range of 300–500°C under strain rates of 0.0001–0.1s−1. This material exhibited typical broad single-peak dynamic recrystallization behavior followed by a gradual drop towards the steady state stress. The constitutive behavior of the tested alloy was studied by the power, exponential, and hyperbolic sine laws. The stress multiplier and the hyperbolic sine exponent were calculated as 0.024MPa−1 and 3.42, respectively. The deformation activation energy was found to be about 173.2kJ/mol, which is higher than the lattice self-diffusion activation energy of magnesium (135kJ/mol). The latter can be ascribed to the presence of gadolinium, which shows the importance of rare earth elements in increasing the deformation resistance at high temperatures.

Modified embedded-atom method interatomic potentials for Mg–X (X=Y, Sn, Ca) binary systems

Interatomic potentials for pure Ca and Mg–X (X=Y, Sn, Ca) binary systems have been developed on the basis of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The potentials can describe various fundamental physical properties of pure Ca (bulk, defect and thermal properties) and the alloy behavior (structural, thermodynamic and defect properties of solid solutions and compounds) of binary systems in reasonable agreement with experimental data or first-principles and other calculations. The applicability of the developed potentials to atomistic investigations of the deformation behavior of Mg and its alloys is discussed together with some challenging points that need further attention.

Hot deformation behaviour of Mg–Al–Zn alloys

The hot working behaviour of Mg–Al–Zn alloy was studied in the temperature range of 270–370°C and strain rate range of 0·001–0·1 s−1. In order to eliminate the influence of Mg17AL12 phase, the magnesium alloy was solutionised at 420°C for 24 h and then quenched in water before hot compression. Results show that the microstructures are mainly characterised by twinning and dynamic recrystallised grains during the hot compression process. The twinning forms at lower temperature, while the dynamic recrystallised grains are usually found at higher temperature and lower strain rate. Moreover, constitutive analysis was carried out by the hyperbolic sine law function, which illustrated that the deformation mechanism of the present alloy is controlled by dislocation climb. The critical conditions associated with the onset of dynamic recrystallisation determine the changes of the strain hardening rate (θ), and the amount of dynamic recrystallised grains increases with the increasing strain in the form of sigmoid scheme.

Effect of Micro-Alloying Elements on Deformation Behavior in Mg–Y Binary Alloys

Effect of Micro-Alloying Elements on Deformation Behavior in Mg–Y Binary Alloys

Effect of microstructure on the uniaxial tensile deformation behavior of Mg–4Y–3RE alloy

This paper reports microstructure–mechanical property correlations for a Mg–4Y–3RE (WE43) alloy. Friction stir (FS) processing was employed to modify the microstructure of hot-rolled (as-received) WE43 alloy. The grain size decreased from 10 to 300µm in as-received condition to an average of 3.1±0.4µm in FS processed condition. The alloy in AR condition contained globular, acicular, and rectangular (cuboidal) shaped precipitates located at twin boundaries, grain boundaries, and intragranular regions, along with fine scale honeycomb network of intragranular β1 precipitates. A very good combination of strength and ductility was observed for the alloy tested in FS processed condition. Detailed fractography was done to differentiate mode of fracture between as-received and FS processed conditions. Based on Schmid factor analysis, it was concluded that basal slip system controlled the yielding of the material in both the conditions. An empirical relationship was developed between work hardening rate and ductility. This can be applied to microstructural design of magnesium alloys used for applications where high uniform ductility is needed.

Effect of high temperature heat treatments on the deformation behavior of Mg–2%Mn–0.7%Ce extrusions investigated by in-situ energy-dispersive synchrotron X-ray diffraction and elasto-plastic self-consistent modeling

The effect of high temperature heat treatments on the deformation behavior of ME21 extrusions was analyzed. Heat treatments at temperatures >475°C result in significant grain growth with an associated enhancement of the rare earth (RE) texture component and in the growth of Mg12Ce precipitates and manganese containing dispersoids. Additionally, the number density of the dispersoids is decreased drastically. These microstructural changes produce a dramatic increase in the elongation to failure in room-temperature uniaxial compression tests. Thereby, elongations to failure up to 0.7 true strain where observed. The combination of in-situ energy-dispersive synchrotron X-ray diffraction and Elasto-Plastic Self-Consistent (EPSC) modeling shows that the texture modification increases the activity of slip-systems reducing the twin volume fraction. The deformation at high strains is predominantly realized by 〈c+a〉-pyramidal and 〈a〉-basal slip.

Compressive deformation behavior of Mg–Zn–Ca alloy at elevated temperature

The compressive deformation behavior at elevated temperature of the as-extruded and as-ECAPed Mg–5.3Zn–0.6Ca (wt%) alloys was investigated in the current study. The flow stress in the as-ECAPed alloy was lower than that of the as-extruded alloy when the compressive temperature was above 200°C, due to the grain boundary softening effect. The strain rate sensitivity (SRS) was remarkably enhanced with the decrease of grain size or the increase of test temperature, and the corresponding m-value was calculated as 0.06–0.13, which indicated that the deformation was mainly dominated by the climb-controlled dislocation creep. Furthermore, the grain boundary sliding (GBS) mechanism might also be activated, which contributed to the higher SRS in the as-ECAPed alloy. The true deformation activation energy (Q') modified by threshold stress was calculated as 92–98 and 70–76kJ/mol in the as-extruded and as-ECAPed alloy, respectively, which was close to the activation energy for grain boundary diffusion, and the lower Q'-value in the as-ECAPed alloy might be derived from the non-equilibrium grain boundaries.

Hot deformation behavior of Mg–2Sn–2Ca alloy in as-cast condition and after homogenization

The hot deformation behavior of Mg–2Sn–2Ca (TX22) alloy has been characterized in the temperature range 300–500°C and strain rate range 0.0003–10s−1 using isothermal constant true strain rate tests. A processing map has been developed on the basis of flow stress data obtained as a function of temperature and strain rate, which revealed two windows or domains for hot working the alloy: (1) 300–370°C/0.0003–0.001s−1 and (2) 400–500°C/0.005–1s−1. Microstructural observations indicated that dynamic recrystallization occurs in both these windows with a finer resulting grain size in the first window. Apparent activation energy values of 183 and 178kJ/mole have been estimated in these windows, respectively and these are much higher than that for self-diffusion in Mg suggesting that considerable back stress is being generated due to the intermetallic particles (CaMgSn) present in the matrix. The mechanisms involving basal+prismatic slip and recovery by climb in the first domain and that of second order pyramidal slip and softening by cross-slip in the second domain are suggested to be occurring in these two domains. The processing map obtained on homogenized alloy is identical to that of the as-cast alloy suggesting that there is no benefit of homogenization treatment as regards hot workability and this is attributed to the thermal stability of the as-cast microstructure.

Deformation behaviour of Mg/Y2O3 nanocomposite at elevated temperatures

In this study, we focused on the tensile deformation behaviour of Mg and Mg/Y2O3 nanocomposite that includes temperature dependent strength, ductility, strain rate sensitivity and activation volume. Bulk nanocomposite with monolithic Mg as the matrix, reinforced by 2vol.% nano-yttria (Y2O3) particulate was prepared by powder metallurgy technique incorporating energy efficient microwave assisted rapid sintering process followed by hot extrusion. Results revealed that the presence of thermally stable nano-Y2O3 particulates as reinforcement leads to a significant improvement in 0.2% yield strength and tensile strength at all test temperatures (25–250°C) when compared to pure Mg. No apparent necking was detected in the composite samples following tensile testing at any of the test temperatures. These results suggest that an increase in test temperature up to 250°C does not affect the homogeneous deformation process exhibited by the composite samples. Strain rate sensitivity and the apparent activation volume were measured by the repeated stress relaxation test. High strain rate sensitivity and low activation volume at room temperature as compared to pure Mg suggest that different rate controlling deformation mechanisms exist in the composite samples. Low temperature sensitivity was observed in the composite.

Application of mixture rule to finite element analysis for forging of cast Mg–Zn–Y alloys with long period stacking ordered structure

Abstract To establish forging process for high strength Mg–Zn–Y alloys with a long period stacking ordered (LPSO) structure, the flow stresses of Mg–Zn–Y alloys with different volume fractions of LPSO phase were measured by the upsettability test. Since mixture rule for the flow stress was satisfied in Mg–Zn–Y two-phase (α-Mg and LPSO) alloys, the flow stresses of α-Mg and LPSO single phase alloys were estimated from the flow stresses of Mg–Zn–Y alloys with different volume fractions of LPSO phase. To examine the validity of the mixture rule, the finite element analysis for tensile test and forging of as-cast Mg–Zn–Y alloy was carried out using the estimated flow stresses of α-Mg and LPSO single phase alloys on the basis of mixture rule of the properties of Mg–Zn–Y alloy. The calculated load-stroke curves in tensile test and forging agreed well with the experimental ones, and the deformation behaviour of Mg–Zn–Y alloy was discussed.

Deformation behavior of Mg–8Al magnesium alloy compressed at medium and high temperatures

The mechanisms of plastic deformation of Mg–8Al magnesium alloy were studied by compression tests at temperatures between 250 and 450°C and strain rates ranging from 0.01 to 50s−1. It was found that the mechanisms of dynamic recrystallization depend on the deformation temperature. In the intermediate temperature range (250–300°C), continuous dynamic recrystallization was observed and associated with extensive cross slip. Coarse primary grains are replaced by the new fine grains with the progress of deformation, leading to a “necklace structure”. At temperatures ranging from 350°C to 450°C, the deformation was self-diffusion controlled. Equiaxed dynamic recrystallization grain structures are obtained during the whole deformation process. New dynamic recrystallization grains are preferred to nucleate in areas where extensive multiple slip bands have formed. Twinning plays an important role during the deformation of Mg–8Al magnesium alloy both at intermediate and high temperature ranges.

Plastic Deformation Behavior of Mg<SUB>12</SUB>ZnY LPSO-Phase with 14H-Typed Structure

We investigated the influence of a change in the stacking sequence of the close-packed plane in a Mg12ZnY long-period stacking ordered (LPSO) phase on its mechanical properties. A 14H-typed LPSO-phase crystal was fabricated by annealing a directionally solidified (DS) crystal with a 18R-typed LPSO-structure at 525°C for 3 days, and the temperature dependence and orientation dependence of the yield stress were examined via compression tests. (0001)〈11\\bar20〉 basal slip was identified as a dominant deformation mode, and deformation kink bands were formed under compression in the case of suppression of basal slip motion. The deformation mechanism of the 14H-typed LPSO-phase is almost similar to that of the 18R-typed LPSO-phase, even though a slight difference was observed at temperatures above 300°C.

Room-temperature compressive deformation behavior of Mg–Zn–Ca alloy processed by equal channel angular pressing

The ultra-fine grained (UFG) Mg–5.25 wt.% Zn–0.6 wt.% Ca alloy was processed by equal channel angular pressing (ECAP), and the coarse grained (CG) alloy was prepared by subsequent annealing treatment. The microstructure, texture evolution and mechanical properties of the UFG and CG alloys during compressive deformation at ambient temperature were investigated. The results indicated that the dislocation slip was dominant in the UFG Mg alloy, and the compressive yield stress (CYS) of the UFG alloy was higher than that of the CG alloy due to grain refinement. In the CG Mg alloy, the activation of tension twinning also occurred in addition to basal slip, the work hardening rate was increased because of twin-induced additional hardening. Dynamic recrystallization (DRX) was observed in the CG alloy compressed to large strains at ambient temperature. Most of the {0 0 0 2} planes in both UFG and CG Mg alloys were rotated gradually to be perpendicular to the compressive direction (CD).

Compressive deformation behavior of Mg and Mg/(Y 2O 3 + Ni) nanocomposites

Uniaxial compressive properties of Mg and Mg/(Y 2O 3 + Ni) hybrid nanocomposite are studied in the present paper. A remarkable improvement in both 0.2% CYS and UCS is exhibited by hybrid nanocomposites when compared to pure Mg. Subsequently, plastic deformation due to twinning activity and basal plane orientation detected by X-ray diffraction at different strain levels are investigated. Both Mg and hybrid composites yield by twinning deformation and extensive twinning supports reorientation of basal (0 0 0 2) planes after yielding. Upon twin saturation, basal planes get orientated perpendicular to the compression axis in composite sample, causing a steep increment in work hardening with limited failure strain. However, in the case of pure Mg, complete basal reorientation did not take place. As a result, continuous twin deformation provided gradual work hardening leading to appreciable failure strain in the case of Mg when compared to its reinforced counterparts.