Recrystallization Of Mg Research Articles

Understanding Dislocation-Interface Interactions during Recrystallization of Mg-(Ca, Zn) Alloys

Understanding Dislocation-Interface Interactions during Recrystallization of Mg-(Ca, Zn) Alloys

Anelasticity of Mg-Mn and Mg-Gd alloys

Anelastic relaxation at sub-resonance frequency (from 0.01 to 100 Hz), temperature (from 0 to 450°C) and amplitude (ε0 from 5×10−5 to 10−3) range in binary Mg-0.8 wt%Mn (0.36 at%) and Mg-2 wt%Gd (0.31 at%) in as-extruded and annealed states was experimentally studied and analyzed, to characterize acting thermally activated and structural relaxation effects. Activation parameters for thermally activated anelastic effect and structural studies suggest that it is the grain boundary relaxation with dominating large angle boundaries, while the high-temperature background is mainly controlled by dislocations sliding. Pseudo peak at ∼290 °C (Mg-Mn) and ∼410 °C (Mg-Gd) is the result of the recrystallization process in the as-extruded samples, which indicates that the addition of Gd restricts the recrystallization of Mg compared with the addition of Mn. Analysis of amplitude dependencies of internal friction in the frames of Granato and Lücke approach suggests higher density of movable dislocations in as-extruded Mg-Mn alloy.

Impact of Cl- on the performance of magnesium oxysulfate (MOS) cement

As magnesium oxysulfate (MOS) cement finds more applications in the engineering field, the influence of Cl- on the mechanical properties of MOS cement has gained more attention. In this paper, MgCl2·6 H2O served as the source of Cl- to investigate its influence on the evolving properties of MOS cement. The results showed that MgCl2·6 H2O extended the formation time of the 5Mg(OH)2·MgSO4·7 H2O phase, reduced the dispersion of the MOS cement system, and decreased the crystalline size of the 5Mg(OH)2·MgSO4·7 H2O phase (200) crystal plane. The addition of MgCl2·6 H2O had a positive effect on improving flexural strength and increasing the content of gel. During the curing process, the presence of Cl- facilitated the dissolution and recrystallization of Mg(OH)2, altering its growth tendency and promoting the formation of hexagonal crystal Mg(OH)2. During soaking in water, the increased content of MgCl2·6 H2O led to a decrease in the softening coefficient due to the dissolution of excess MgCl2. The structure of the 5Mg(OH)2·MgSO4·7 H2O phase underwent changes as Cl- entered the crystal interior, leading to an increase in the d-spacing of the 5Mg(OH)2·MgSO4·7 H2O phase at the (222) crystal plane. The introduction of Cl- endowed the 5Mg(OH)2·MgSO4·7 H2O phase with the potential to transform into 5Mg(OH)2·MgCl2·8 H2O. Following immersion in water, the modified structure of the 5Mg(OH)2·MgSO4·7 H2O phase retained its relative integrity, resulting in a higher softening coefficient of 0.73 after a 90-day soaking period, attributed to the proper introduction of Cl-.

Dynamic precipitation and twinning-induced dynamic recrystallization in Mg–6Al–3Sn–1Zn alloy during multi-pass high-speed rolling

Ultrafine-grained microstructure was successfully obtained in Mg–6Al–3Sn–1Zn (ATZ631) alloy by multi-pass high-speed rolling (HSR) at a rolling speed of 1100 m/min and a rolling temperature of 400 °C. The grain refinement mechanism of ATZ631 alloy during HSR was investigated, which is attributed to mechanically fragmented grains and twinning-induced dynamic recrystallization (TDRX). During the initial stages of rolling, the initial coarse grains are refined by the intersection of twins. With increasing strain, the grain refinement mechanism is the typical dynamic recovery and TDRX. In general, twins are filled with a high density of dislocations and nano-sized precipitates at the dislocations, which can accelerate DRX by increasing the driving force or particle-stimulated nucleation (PSN) within the twins. Subsequently, the coarse grains are refined by forming fine DRXed grains via dislocation entanglement, dislocation rearrangement, and dislocation absorption. As the process proceeds, grain boundaries (GBs) migration is suppressed by the precipitates at the GBs of new DRXed grains. Thus, the growth of the DRXed grains can be inhibited. Finally, ultrafine-grained microstructure with an average size of ∼116 nm is obtained. Moreover, the new grains formed by TDRX exhibit random orientation during this process, indicating that the basal texture gets effectively weakened by increasing the fraction of DRXed grains. These findings bring forward the microstructural evolution during dynamic precipitation and DRX, thus providing a novel notion for improving microstructures and grain refinement in Mg alloys.

Effect of Bimodal Quasicrystal Phase on the Dynamic Recrystallization of Mg–Zn–Gd Alloy during High-Pressure Torsion

Effect of Bimodal Quasicrystal Phase on the Dynamic Recrystallization of Mg–Zn–Gd Alloy during High-Pressure Torsion

Effect of solute concentration on microstructure evolution during static recrystallization in Mg-0.2%Ce alloy using cellular automata

A new cellular automata model has been developed to evaluate the effect of solute drag on the microstructure and texture evolution during static recrystallization of Mg and its alloys in the temperature range of 200 – 400 °C. In the present model, the site saturation nucleation was assumed and all the nuclei are present at the grain boundaries. The growth of each nucleus depends on the solute concentration and dislocation density difference between neighboring grains. The microstructural analysis of the newly developed cellular automata model showed the evolution of grain size at different temperatures compared to the equilibrium microstructure containing the equilibrium concentration of solute atoms at the grain boundaries. Further, the texture evolution showed that there is an increase in the texture strength with an increase in the annealing temperature when the solute concentration was lower than the equilibrium concentration at the boundaries, whereas the texture strength decreased with increasing the annealing temperature when the solute concentration was higher than the equilibrium solute concentration at the boundaries. The present model shows that solute drag pressure increased continuously with increasing the annealing temperature when the solute concentration was lower than the equilibrium concentration at the boundaries. However, the solute drag pressure decreased with an increase in the annealing temperature when the solute concentration was higher than the equilibrium solute concentration at the boundaries.

An in-situ study of static recrystallization in Mg using high temperature EBSD

It has been a common method to improve the mechanical properties of metals by manipulating their microstructures via static recrystallization, i.e., through heat treatment. Therefore, the knowledge of recrystallization and grain growth is critical to the success of the technique. In the present work, by using in-situ high temperature EBSD, the mechanisms that control recrystallization and grain growth of an extruded pure Mg were studied. The experimental results revealed that the grains of priority for dynamic recrystallization exhibit fading competitiveness under static recrystallization. It is also found that grain boundary movement or grain growth is likely to show an inverse energy gradient effect, i.e., low energy grains tend to swallow or grow into high energy grains, and grain boundaries of close to 30° exhibit superior growth advantage to others. Another finding is that {10–12} tensile twin boundaries are sites of hardly observed for recrystallization, and are finally swallowed by adjacent recrystallized grains. The above findings may give comprehensive insights of static recrystallization and grain growth of Mg, and may guide the design of advanced materials processing in microstructural engineering.

{[formula omitted]} twin–twin intersection-induced lattice rotation and dynamic recrystallization in Mg–6Al–3Sn–2Zn alloy

This study investigated the formation mechanism of new grains due to twin–twin intersections in a coarse-grained Mg–6Al–3Sn–2Zn alloy during different strain rates of an isothermal compression. The results of electron backscattered diffraction investigations showed that the activated twins were primarily {101¯2} tension twins, and 60° <101¯0> boundaries formed due to twin–twin intersections under different strain rates. Isolated twin variants with 60° <101¯0> boundaries transformed into new grains through lattice rotations at a low strain rate (0.01 s−1). At a high strain rate (10 s−1), the regions surrounded by subgrain boundaries through high-density dislocation arrangement and the 60° <101¯0> boundaries transformed into new grains via dynamic recrystallization.

Elucidating dynamic precipitation and yield strength of rolled Mg–Al–Ca–Mn alloy

Although the precipitation and recrystallization of Mg–Al–Ca–Mn based alloys have been well investigated individually, there is still a lack of a detailed investigation on the effect of the Al-rich clusters, Mn-rich precipitates and/or Ca-rich Laves phases formed from dynamic precipitation during rolling on the grain size and texture as well as yield strength. Here, we have investigated the effect of Mn (1 wt. %) on the dynamic precipitation and yield strength of rolled Mg–3Al–1Ca alloy after rolling up to 1 and 6 passes (at 350 °C and 300 °C). It was found that an effective grain refinement can be obtained due to the fact that the dynamic precipitation enhances dynamic recrystallization by particle stimulated nucleation (PSN) mechanism. No significant texture change was obtained although the dynamic precipitation of Mn-rich particles due to the addition of 1 wt. % Mn results in a change from an RD-split texture to a strong basal texture. Three different Mn-rich phases ((i) large primary Al8Mn5 phase, (ii) the long plated-shaped Al8Mn5 phase, and (iii) nanoscale Al8Mn5 phase), C15 Laves phase (Al2Ca) and Al-rich clusters (G.P. zone), were observed, while no plate-shaped Al–Ca precipitate was observed on the basal plane of α-Mg matrix, indicating a competition among the formation of Al-rich clusters, plate-like Al–Ca precipitates, Ca-rich Laves phase, and Mn–rich phase within α-Mg matrix. Dispersion strengthening by the Ca-rich Laves phase, Mn–rich phase and Al-rich clusters is proposed to be attributed to the significant improvement of yield strength. This investigation highlights the importance of elucidating the effect of the dynamic precipitation on yield strength of rolled Mg–3Al–1Ca–1Mn alloys and provides helpful hints to further optimize the deformation and mechanical properties of Mg–Al–Ca–Mn based alloys.

Dynamic recrystallization and deformation constitutive analysis of Mg–Zn-Nd-Zr alloys during hot rolling

Due to limited basal slips, the recrystallization of Mg–Zn-Nd-Zr alloys originated at grain boundaries with large orientation gradient based on strain-induced-boundary-migration nucleation mechanism. The primary driving force of the recrystallization was the distortion energy difference around grain boundaries. However, more non-basal slips occurred near the grain boundary at larger strain deformation, so that some dislocations of adjacent subgrain boundaries with less orientation difference transferred to other subgrain boundaries by means of dissociation and disassembly, which is called the subgrain boundary merging. Meanwhile, some ductile shear zones appeared surrounding the primary grain, which held multiple slip systems moving around the grain boundary, gave rise to larger orientation gradients and facilitated recrystallization grains growing.

Effect of twinning and Al–Nd phase on dynamic recrystallization in rolled Mg–Al–Zn–Nd alloy at the moderate strain rate

The dynamic recrystallization of Mg–Al–Zn–Nd alloy during moderate strain rate rolling was studied using electron backscatter diffraction (EBSD) and an energy dispersive spectrometer (EDS). The results showed three kinds of twinnings produced in the alloy in the strain rate range of 4.2 s−1∼7.3 s−1, including extension twinning, contraction twinning, and double twinning. The extension twinnings decreased gradually with the increase of strain rate. The dynamic recrystallization mechanisms during hot rolling under moderate strain rate conditions mainly include grain boundary nucleation, twinning nucleation, and secondary particle assistant nucleation. The dynamic recrystallization mechanism induced by twinning is mainly double twinnings. In addition, the strain value near the Al–Nd phase and grain boundary is higher than in grain. The Al–Nd particles in Mg–Al–Zn–Nd alloy play an auxiliary nucleation effect on dynamic recrystallization during hot rolling deformation.

A multiscale multimodal approach to studying static recrystallization in Mg–3Zn–0.1Ca

A multiscale multimodal approach to studying static recrystallization in Mg–3Zn–0.1Ca

Twinning and dynamic recrystallization of Mg–7Sn–3Zn alloy under high strain rate hot compression

Abstract In this study, we investigate the twinning behavior and dynamic recrystallization (DRX) of Mg–7Sn–3Zn alloy under a high strain rate (10 s−1) during hot compression deformation. At a relatively low temperature (300 °C) and high strain rate (10 s−1), the preferential occurrence of multiple { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twin variant at the initial compressed stage is attributed to the Schmid factor (SF) criterion, and the following { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twin variants nucleate because of the geometric compatibility factor mʹ of the ortho-position twin pair. Because of the growth and interaction between the ortho-position { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twin pairs, the volume fraction of 60° 10 1 ‾ 0 > boundaries evidently increases. Moreover, as the logarithmic strain increases, the volume fraction of { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twins and 60° 10 1 ‾ 0 > boundaries significantly decreases, and a few { 10 1 ‾ 1 } 10 1 ‾ 2 > compression twins and { 10 1 ‾ 2 }–{ 10 1 ‾ 1 } double twins form. Then, twinning-induced dynamic recrystallization (TDRX) as a primary DRX mechanism occurs in { 10 1 ‾ 1 } 10 1 ‾ 2 > compression twins and { 10 1 ‾ 2 }–{ 10 1 ‾ 1 } double twins. These results indicate that at a high temperature (400 °C) and 10 s−1, certain { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twins form during the early stage compression in accordance with the SF criterion, and discontinuous DRX (DDRX) occurs along the original grain boundaries because of the higher deformation temperature, which increases the nucleation rate and promotes the migration of grain boundaries. With the accumulation of logarithmic strain, continuous DRX (CDRX) occurs. The recrystallization grains consume the twin boundaries, which causes the { 10 1 ‾ 2 } 10 1 ‾ 1 > tension twins to merge. Under the same logarithmic strain, when the deformation temperature increases from 300 °C to 400 °C, the DRX process is significantly improved.

Grain refinement and weak-textured structures based on the dynamic recrystallization of Mg–9.80Gd–3.78Y–1.12Sm–0.48Zr alloy

We utilized electron backscatter diffraction to investigate the microstructure evolutions of a newly developed magnesium-rare earth alloy (Mg–9.80Gd–3.78Y–1.12Sm–0.48Zr) during instantaneous hot indirect extrusion. An equiaxed fine-grained (average grain size of 3.4 ± 0.2 µm) microstructure with a weak texture was obtained. The grain refinement was mainly attributed to the discontinuous dynamic recrystallization (DDRX) and continuous DRX (CDRX) processes during the hot indirect extrusion process. The twin boundaries formed during the initial deformation stage effectively increased the number of high angle grain boundaries (HAGBs), which provided sites for new grain nuclei, and hence, resulted in an improved DDRX process. Along with DDRX, CDRX processes characterized by low angle grain boundary (LAGB) networks were also observed in the grain interior due to effective dynamic recovery (DRV) at a relatively high temperature of 773 K and high strain rates. Thereafter, LAGB networks were transformed into HAGB networks by the progressive rotation of subgrains during the CDRX process.

Modeling the Dynamic Recrystallization of Mg–11Gd–4Y–2Zn–0.4Zr Alloy Considering Non-uniform Deformation and LPSO Kinking During Hot Compression

Hot compression tests of Mg–11Gd–4Y–2Zn–0.4Zr alloy (GWZK114) were conducted at a deformation temperature range of 300–500 °C and a strain rate range of 0.01–10.0 s−1. Based on systematic microstructure observation, it is confirmed that long period stacking ordered (LPSO) phase displays essential and evolving roles on the dynamic recrystallization (DRX) behavior. The results indicate that the plastic deformation is mainly coordinated by simultaneous exist of LPSO kinking of lamella 14H-LPSO phase and DRX at 350–450 °C, and DRX at 500 °C. Further, it is found that the LPSO kinking induced during 350–450 °C can delay the DRX. A phenomenological DRX model of GWZK114 alloy is established to be $$X_{\text{DRX}} = 1 - \exp [ - 0.5(\frac{{\varepsilon - \varepsilon_{\text{c}} }}{{\varepsilon^{*} }})^{0.91} ]$$ . Non-uniform distribution of plastic strain during compression was considered via finite element method and it ensures a good prediction of DRX fraction under a large plastic strain. Meanwhile, an enhanced DRX model, taking its formulation as $$X_{\text{DRX}} = \{ 1 - \exp [ - 0.5(\frac{{\varepsilon - \varepsilon_{c} }}{{\varepsilon^{*} }})^{0.91} ]\} (\frac{T}{226.8} - 1)^{n}$$ , $$n = 3.82\dot{\varepsilon }^{0.083}$$ , is proposed for the first time to capture the hindering effect of 14H-LPSO kinking on DRX behavior. The predicted results of this enhanced DRX model agree well with the experimental cases, where 14H-LPSO kinking is dominated or partially involved (300–450 °C). Besides, a size model of DRX grains is also established and can depict the evolution of DRX grain size for all the investigated compression conditions with accounting for temperature rising at high strain rates (5 s−1 and 10 s−1).

The influence of the hydration procedure of MgO expansive agent on the expansive behavior of shrinkage-compensating mortar

The objective of this paper is to evaluate the influence of the hydration process of MgO expansive agent in binder on the expansion of shrinkage-compensating mortar. The variation of MgO and Mg(OH)2 content in binder at certain curing ages was examined quantitatively through X-ray diffraction (XRD) Rietveld analysis. Expansive behavior of shrinkage-compensating mortars containing MgO expansive agent was also investigated as a comparison with the hydration process. Results indicated that the hydration speed of MgO is determined by its reactivity, highly reactive MgO results to a fast hydration and expansion speed. The curing condition (sealed or saturated) hardly influences the hydration speed of MgO, but largely influences the expansion rate of mortars. The expansion effect due to MgO hydration lags behind its reaction in the binder paste. Sufficient pore water contributes to the recrystallization of Mg(OH)2, which thus causes high crystal growth pressure and promotes the expansion of mortars.

Microstructure evolution during high cycle fatigue in Mg–6Zn–1Mn alloy

Microstructure evolution during high cycle fatigue in extruded Mg–6Zn–1Mn alloy was investigated by servo-hydraulic fatigue testing machine with pull–push sinusoidal loading. The results show that in high stress cycles (cyclic stress≥129MPa) high cycle fatigue tests promote deformation; however, in low stress cycles (cyclic stress≤125MPa) high cycle fatigue tests make a contribution to room temperature recrystallization in Mg–6Zn–1Mn alloy. The grain refinement increased with increasing cycles. Electron Back-Scattered Diffraction (EBSD) analyses showed that dynamic recrystallization (DRX) has occurred in post-fatigued alloys, accompanied by the presence of a high number density of low-angle grain boundaries (LAGBs). LAGBs generated in the vicinity of initiation grain boundaries and subdivided coarse grains. In the specimens that subjected to higher cycles, the fraction of LAGBs decreased and high-angle grain boundaries (HAGBs) gradually increased. With the cyclic number increasing the texture intensity was significantly weakened. The DRX in post-fatigued specimens was related to Continuous DRX (CDRX) mechanism.

Material model for dynamic recrystallization of Mg–8Al–0.5Zn alloy under uni-axial compressive deformation with variation of forming temperatures

Due to insufficient formability of magnesium (Mg) alloys at the room temperature, it leads to a hot forming process for Mg alloys to enhance the formability and plastic workability. Mg alloy undergoes the dynamic recrystallization (DRX) during hot working process, which is a restoration or softening mechanism to reduce the dislocation density and release the accumulated energy to facilitate plastic deformation. Even though there are substantial progresses on the establishment in terms of the DRX principles and evolution with the view point of the materials science, an appropriate flow curve modeling for the finite element analysis has been deficient to take into consideration of softening behavior. This paper mainly concerns the material modeling of Mg alloy at the elevated forming temperature in terms of thermomechanical flow curves, which enables implementation of flow curve softening in the finite element analysis, efficiently.

Effect of strain-induced precipitation on dynamic recrystallization in Mg–Al–Sn alloys

Abstract Two different amounts of tin (Sn) were added to a Mg–3 wt% Al binary alloy to form different amounts of precipitates during hot deformation. The thermodynamic modeling software, FactSage ™ , was used to calculate the amounts of Sn to generate the desired relative levels of precipitation. The alloys were deformed at four different temperatures and three different strain rates to generate different amounts of precipitates. The objective was to study the effect of these precipitates on dynamic recrystallization. The results indicated that the formation of strain-induced precipitates is a function of deformation temperature, strain, and strain rate. The findings also revealed that higher amounts of precipitates reduced the volume fraction of dynamic recrystallization and refined the dynamically recrystallized grain size.

Effect of Ca-addition on dynamic recrystallization of Mg–Zn alloy during hot deformation

This study was conducted to compare the development of microstructures of Mg–3.6Zn and Mg–3.6Zn–0.4Ca alloys (in wt%) tested in uniaxial compression (UC) at 200–280°C with strain rates ranging from 0.001s−1 to 1s−1. The stress–strain curves with average values of the flow stress slightly higher in the ternary alloy than in the binary alloy exhibit the typical features of dynamic recrystallization (DRX). Microstructure analyses showed that the volume fraction and average size of DRX grains increase with increasing temperature, and a more homogeneous bimodal microstructure is developed. Lower temperatures and lower strain rates initialize deformation-induced precipitation, which results in heterogeneous evolution of the microstructure in the binary alloy. On the other hand, this precipitation controls, via pinning of grain boundaries, the growth of DRX grains and promotes continuous DRX mechanism. The results indicate that the addition of Ca is favorable to recrystallization occurring during the hot deformation process.