High Strain Rate Superplasticity Research Articles

The role of processing temperature for achieving superplastic properties in an Al-3Mg-0.2Sc alloy processed by high-pressure torsion

Experiments were conducted to systematically assess the superplastic properties and the microstructural changes of an Al-3Mg-0.2Sc alloy processed by 10 HPT revolutions at room temperature (RT ≈ 300 K) or at 450 K after subsequent tensile testing at temperatures from 473 to 723 K over a wide range of strain rates. The HPT processing at RT led to the development of elongated grains with an average size of ∼140 nm whereas the grain structures were equiaxed and slightly larger (∼150 nm) after HPT at 450 K. After HPT processing at RT, the Al-Mg-Sc alloy exhibited true superplastic flow at low homologous temperatures and attained a maximum elongation of ∼850 % at 523 K. Nevertheless, the elongations decreased at temperatures T ≥ 623 K and an elongation higher than 400 % was only achieved at 673 K for a strain rate of ε˙ = 4.5 × 10−3 s−1. The material processed by HPT at 450 K displayed superior microstructural stability and substantially higher superplastic ductilities. Elongations of >1100 % were attained at 673 K for strain rates from 3.3 × 10−4 to 1.0 × 10−1 s−1 and a record elongation of ∼1880 % for an HPT-processed metal was achieved at 1.5 × 10−2 s−1 at 673 K. High strain rate superplasticity was also reached for an extended range of temperatures and strain rates. Analysis of the data confirms a stress exponent of ∼2 which is consistent with superplastic flow by grain boundary sliding accommodated by dislocation glide and climb.

Effect of strain rate on the microstructure evolution and superplastic deformation behavior of cold-rolled medium Mn lightweight steel

This work investigates the high-temperature tensile behavior of a Medium Mn lightweight steel (MMLS) with a chemical composition of Fe-0.3C-7.0Mn-3.5Al. The MMLS was prepared by hot-rolling followed by cold-rolling to produce a complete martensite microstructure with a high density of dislocations. The tensile tests were conducted at 800 °C within the strain rate range of 5 × 10−4 s−1-2.5 × 10−2 s−1 to explore the effect of microstructural evolution and deformation mechanism by strain rates during the tensile deformation. The results showed that the deformation behavior and mechanism of the MMLS depend not only on the initial grain size and morphology but also on the microstructure evolution during deformation. The MMLS exhibits high strain rate superplasticity (HSRS) behavior, and the deformation mechanisms are dependent on the strain rate. At lower strain rate (5 × 10−4 s−1), dislocation slip/creep is more pronounced in the γ-phase, and grain boundary sliding (GBS) is inhibited during the early deformation period, contributing to the significant texture enhancement. At moderate rate (5 × 10−3 s−1), GBS dominates deformation, while at high strain rate (2.5 × 10−2 s−1), dislocation activity and dynamic recrystallization (DRX) play a significant role. The HSRS behavior of MMLS is related to the dynamic reverse phase transition from cold-rolled ferrite to austenitic/ferrite fine-grained dual-phase structure. This work provides a theoretical basis for the development of superplastic MMLS with improved HSRS behavior and controlled the microstructure/mechanical property of component parts.

Achieving high strain rate superplasticity in an Al-Cu-Li alloy processed by thermo-mechanical processing

In order to obtain high strain rate superplasticity, it is usually necessary to prepare fine-grained aluminum alloy by severe plastic deformation such as equal channel angular pressing. A traditional thermo-mechanical processing was exploited to prepare fine-grained Al-Cu-Li alloy with 3.1 μm grains. A maximum elongation of 1220% was obtained at a high strain rate of 1 × 10−2 s−1 and 490 °C. The high-stain rate superplasticity is attributed to the existence of stabilized fine grains and nano-scaled Al3Zr particles which inhibit the dynamic growth of grain. Furthermore, the calculated deformation activation energy and m values suggest that the grain boundary sliding mechanism is active.

High strain rate superplasticity and secondary strain hardening of Al-Mg-Sc-Zr alloy produced by friction stir processing

There have been many studies on superplasticity of Al-Mg-Sc-Zr alloy with middle magnesium content in friction stir processing (FSP), while few studies on superplasticity of FSPed Al-Mg-Sc-Zr alloy with low-magnesium were researched. In this work, the microstructure of Al-3Mg-0.1Sc-0.1Zr alloy with the grain size of ~1.6 µm and high-angle grain boundaries dominated was obtained by FSP. The high-temperature tensile test was carried out, which showed that Al-3Mg-0.1Sc-0.1Zr alloy had good superplasticity in the range of 400 ℃ ~ 500 ℃ and 3 × 10−3 s−1 ~ 3 × 10−1 s−1, and the optimal elongation reached 1850% at 475 ℃ and 10−2 s−1, showing a high strain rate superplasticity. The FSPed alloy had a significant secondary strain hardening ability with increasing flow stress in the failure fracture stage at higher temperature or relatively low strain rate, showing “H” type (continuous hardening) and “C” type + secondary hardening type (initial hardening then softening + secondary hardening) curves, which was mainly attributed to the concurrent grain growth at higher strain during high-temperature tension. By studying the microstructure evolution and constitutive equation, it was found that the main mechanism of superplastic deformation was grain boundary sliding accommodated by grain boundary diffusion, the coordination mechanism was lattice diffusion. Al3(Sc, Zr) particles hindered the coarsening of grains obviously with good thermal stability, which were conducive to the realization of excellent superplastic properties.

Relation of phase fraction to superplastic behavior of multi-principal element alloy with a multi-phase structure

An Al0.3CoCrNi medium-entropy alloy was annealed in two conditions to differentiate the phase fraction of nano-scaled B2 and sigma precipitates in FCC microstructure, processed by high-pressure torsion, and subjected to a superplasticity test. The Al0.3CoCrNi with different microstructure exhibited distinct superplastic performance, with maximum elongation of 1900% and 1735% from tensile deformation at 1073 K at the strain rate at 5 × 10−3 s−1 and 10−2 s−1, respectively. The microstructural analysis revealed that the superplasticity is dominantly governed by the grain boundary sliding mechanism with the accommodation of intragranular dislocations. The Al0.3CoCrNi alloy, after superplastic deformation, consists of the mixture of FCC, B2, and sigma phases with different phase fractions. The comparison of this multi-phase structured alloy at two conditions and the sister alloy, Al0.5CoCrFeMnNi high-entropy alloy, suggests that increment of B2 and sigma phase fraction is beneficial to promote high-strain rate superplasticity by limiting the grain growth.

Creep behavior of zirconia ceramics under a strong DC field

The tensile creep of 3 mol% Y2O3 stabilized tetragonal ZrO2 ceramics under a DC field was systematically investigated. The results show that the deformation mechanism of the material strongly depends on the current density and the applied stress. Exceptionally large uniform elongation can be obtained only when the creep is dominated by dislocation accommodated grain-boundary sliding. A maximum uniform elongation of ∼300% is achieved at a strain rate close to 10−3 s−1. At an even higher strain rate of about 10−2 s−1, uniform elongation is still near 100%. The current results suggest that high strain rate superplasticity can be induced by applying a strong electric field at proper stress and current density.

Superplastic behavior and microstructure evolution of a fine-grained Mg-Nd-Zn-Zr alloy processed by hot extrusion

In this study, the starting materials of the fine-grained Mg-Nd-Zn-Zr alloy with a grain size of ∼2.78 μm were prepared by hot extrusion with an extrusion ratio of 19.63 at 400 °C. The superplastic behavior and microstructure evolution of the fine-grained extruded Mg-Nd-Zn-Zr alloy was studied in the temperature ranges of 350 °C–500 °C and the strain rate ranged from 1 × 10−2 s−1 to 5 × 10−4 s−1. Results showed that the maximum elongation of 1015.50% was obtained at 450 °C with 5 × 10−4 s−1, and high strain rate superplasticity (HSRS) was achieved at 400 °C and 450 °C with 1 × 10−2 s−1. Moreover, theoretical calculations revealed that deformation mechanisms were grain boundary slip (DBS), m = 0.42–0.52 at 350 °C–450 °C, and solute drag creep (SDC), m = 0.37 at 500 °C. Meanwhile, there were regulated by grain boundary diffusion or lattice diffusion. In the last stage of deformation, due to grain growth and significant strain, plenty of geometrically necessary dislocations (GNDs) and {10–12} twins were generated in the grain, resulting in stress concentration. Because the stress concentration could not be eliminated in time, cavities were formed at the second phase particles and trigeminal grain boundaries. Various types of fracture, such as ductile fracture, microvoid accumulation fracture, and so on, resulted from the growth and connection of cavities.

Excellent High‐Strain‐Rate Superplasticity of Fine‐Grained ZK60 Magnesium Alloy Produced by Submerged Friction Stir Processing

ZK60 magnesium alloy is produced via submerged friction stir processing (SFSP), and its microstructural characteristics and deformation behaviors at elevated temperature are investigated. Due to the severe plastic deformation with enhanced cooling rate, dynamic recrystallization occurs but grain growth is significantly retarded. Therefore, the as‐cast microstructure is greatly refined after SFSP, and an average grain size of 1.84 μm is attained. High‐strain‐rate superplasticity (HSRS) is observed at temperature of 573–723 K. A maximum elongation of 1205% is obtained at 1 × 10−2 s−1 and 673 K. The excellent HSRS is attributed to the uniform fine‐grained structure and the relatively high fraction of high‐angle grain boundaries (71.5%), which facilitate grain boundary sliding. The comparatively high portion of dispersed fine particles/precipitates also enhances the microstructural stability of the SFSP specimens. Grain boundary sliding is the dominated deformation mechanism for superplasticity and the failure of the deformed samples is due to the coalescence of cavities.

Superplastic deformation behavior of Mg alloys: A-review

The magnesium alloys are the next-generation lightweight metal materials; however, the production of the complex shape components of thermo-mechanical processed magnesium alloys is very limited in comparison to their die-casted counterparts. Both high strain rate and low-temperature processing are required to save time and cost for the project. Uniaxial tensile testing has been vastly used for determining the plasticity of magnesium alloys at elevated temperatures. Therefore, this review article sheds light on superplastic behaviors under the uniaxial tensile loading of different magnesium alloys. This review also emphasizes low and high-temperature superplasticity, high strain rate superplasticity, deformation mechanism, thermal stability, texture evaluation, and fracture mechanism of extruded/rolled and severe plastic deformed magnesium alloys. At the end of the review, some technical issues have been addressed which can be beneficial for further enhancement in the superplasticity of magnesium alloys.

Microstructure Features and Superplasticity of Extruded, Rolled and SPD-Processed Magnesium Alloys: A Short Review

In this study, an overview of microstructure features such as grain size, grain structure, texture and its impact on strain rate sensitivity, strain hardening index, activation energy and thermal stability for achieving superplasticity of Mg alloys are presented. The deformation behavior under different strain rates and temperatures was also elaborated. For high elongation to fracture grain boundary sliding, grain boundary diffusion is the dominant deformation mechanism. In contrast, for low-temperature and high strain rate superplasticity, grain boundary sliding and solute drag creep mechanism or viscous glide dislocation followed by GBS are the dominant deformations. In addition, the results of different studies were compared, and optimal strain rate and temperature were diagnosed for achieving excellent high strain rate superplasticity.

Deformation-induced grain boundary segregation mediated high-strain rate superplasticity in medium entropy alloy

Superplasticity refers to extremely high plastic deformation of crystalline materials at homologous temperature. In particular, high-strain rate superplasticity (HSRS) at a strain rate equal to or higher than 10−2 s−1 draws great technological interest in the shape-forming of engineering materials. Besides primary mechanism as grain boundary sliding, the formation of liquid phase at grain boundaries/interfaces can assist HSRS. With the advent of multi-principle element alloys (MPEAs), designing grain boundary segregation of a low melting temperature element with the appropriate choice of composition can bring the possibility to produce the HSRS accommodated by the partial melting in MPEAs. Here, we show the trace of the liquid phase in Al0.3CoCrNi MPEA at the homologous temperature of 0.65. Careful microstructural examination reveals for the first time that deformation-induced Al-segregation occurs at grain boundaries/interfaces. The present work expedites a new path to tailoring microstructure for promoting the HSRS in high-strength materials by grain boundary segregation engineering.

Superplastic behavior of an in-situ TiB2 particle reinforced aluminum matrix composite processed by elliptical cross-section torsion extrusion

In this work, a severe plastic deformation method, namely elliptical cross-section torsion extrusion ( E -TE), was applied to achieve superplasticity of an in-situ TiB 2 /Al-Zn-Mg-Cu composite by obtaining the optimized microstructure of uniformly distributed particles and equiaxed-fine grains. The superplastic behavior and mechanisms of the E -TE processed composite were comprehensively investigated via tensile tests (at T = 350 °C–500 °C and ε ̇ = 10 −1 s −1 -10 −3 s −1 ) and microstructure characterizations. The tests demonstrated that the composite after a single pass of the E -TE gained a maximum elongation of 420% at 450 °C × 10 −3 s −1 . Even with the strain rate increasing to 10 −2 s −1 , the elongation still reached 360%, which implies a high strain rate superplasticity. Analysis based on the strain rate sensitivity ( m ≈ 0.20–0.35) and microstructure characterizations showed that the deformation and failure mechanisms of the composite vary with the temperature. When the temperature is within 350 °C–400 °C, the composite realizes deformation mainly through intragranular dislocation slip and fails by intragranular fracture. With the temperature of 425 °C–450 °C, the deformation is attributed to cooperative grain boundary sliding (CGBS) accommodated by dislocation activity and liquid phase, where a small fraction of liquid phases observed at the triple junctions of GBs facilitates the composite's superplasticity by reducing the stress concentration and deformation incompatibility. The failure is ascribed to the intergranular fracture by cavity formation/coalescence. For temperature within 475 °C–500 °C, numerous liquid phases formed at GBs and significantly weakened the GBs' strength, deteriorating the composite's superplasticity. The composite's failure is resulted from the intergranular fracture by strength weakening of GBs. • Particle reinforced aluminum matrix composites after elliptical cross-section torsion extrusion (E-TE) show superplasticity. • The E-TE processed composite exhibits an elongation of 360% at 450℃×10 -2 s -1 , implying a high strain rate superplasticity. • The superplastic deformation/failure mechanisms of the E-TE processed composite vary with temperatures. • The composite's superplasticity is facilitated by the appropriate liquid phase at the optimized temperature of 450℃.

High Strain Rate Superplasticity of WE54 Mg Alloy after Severe Friction Stir Processing

Friction stir processing (FSP) was used on coarse-grained WE54 magnesium alloy plates of as-received material. These were subjected to FSP under two different cooling conditions, refrigerated and non-refrigerated, and different severe processing conditions characterized by low rotation rate and high traverse speed. After FSP, ultrafine equiaxed grains and refinement of the coarse precipitates were observed. The processed materials exhibited high resistance at room temperature and excellent superplasticity at the high strain rate of 10−2 s−1 and temperatures between 300 and 400 °C. Maximum tensile superplastic elongation of 726% was achieved at 400 °C. Beyond 400 °C, a noticeable loss of superplastic response occurred due to a loss of thermal stability of the grain size. Grain boundary sliding is the operative deformation mechanism that can explain the high-temperature flow behavior of the ultrafine grained FSP-WE54 alloy, showing increasing superplasticity with increasing processing severity.

EFFECT OF THE BIMODAL STRUCTURE PROCESSED BY ECAP AND SUBSEQUENT ROLLING ON STATIC STRENGTH AND SUPERPLASTICITY OF Al-Mg-Sc-Zr ALLOY

Microstructure and mechanical properties of the 1570C aluminum alloy were studied after equal channel angular pressing (ECAP) to the strain of 3 at 325°C and subsequent warm and cold rolling with near 80% reductions at 325°C and 20°C, respectively. Even containing a partially recrystallized bimodal structure with a volume fraction of ultrafine grains of 0.3 and their size not exceeding 2 mm, the alloy after ECAP demonstrated an excellent balance of room temperature static strength parameters (yield strength (YS) » 300 MPa, tensile strength (UTS) » 400 MPa and elongation (El) » 26%), and high strain rate superplasticity (with maximum elongation exceeding 2500% at 520°C and a strain rate of 1.4 × 10-2 s- 1). Subsequent warm and cold rolling resulted in an increase in YS to 340 and 430 MPa and UTS to 415 and 485 MPa amid El decreased to 24 and 11%, respectively. Despite the difference in the deformation structures formed in both rolling states, similar superplastic behavior was observed with maximum elongations of up to 3000% at temperatures of 500-520°C and strain rates of about 10-2 s-1. It was concluded that the initial processing of the alloy to relatively low ECAP strains before warm/cold rolling, leading to bimodal structure with a low fraction of ultrafine grains, is sufficient to ensure a favorable combination of both service and technological properties of the sheets obtained.

Ultrahigh high-strain-rate superplasticity in a nanostructured high-entropy alloy

Superplasticity describes a material’s ability to sustain large plastic deformation in the form of a tensile elongation to over 400% of its original length, but is generally observed only at a low strain rate (~10−4 s−1), which results in long processing times that are economically undesirable for mass production. Superplasticity at high strain rates in excess of 10−2 s−1, required for viable industry-scale application, has usually only been achieved in low-strength aluminium and magnesium alloys. Here, we present a superplastic elongation to 2000% of the original length at a high strain rate of 5 × 10−2 s−1 in an Al9(CoCrFeMnNi)91 (at%) high-entropy alloy nanostructured using high-pressure torsion. The high-pressure torsion induced grain refinement in the multi-phase alloy combined with limited grain growth during hot plastic deformation enables high strain rate superplasticity through grain boundary sliding accommodated by dislocation activity.

Experimental study of the superplastic deformation mechanisms of high-strength aluminum-based alloy

The role of different deformation mechanisms and the contributing factors behind them needs to be clearly defined to develop materials exhibiting high strain rate superplasticity. It is still not fully understood to what extent the deformation conditions and microstructural parameters affect the mechanisms of superplastic deformation. A novel Al–3.9Zn–4.1Mg–0.8Cu–2.8Ni–0.25Zr alloy is employed to determine what effects the testing conditions, elemental and phase composition and evolution of grain and sub-grain structure make towards deformation mechanisms. To analyze the deformation behavior and microstructure evolution, uniaxial tensile tests are performed following two deformation regimes with the different constant strain rates and temperatures: (1) 2 × 10-3 s-1, 480°С and (2) 2 × 10-2 s-1, 440°С. The elongation to failure exceeds 650% and the strain rate sensitivity coefficient m is near 0.5 at both deformation regimes. Electron microscopy and focused ion beam techniques are employed to analyze mechanisms associated with grain boundary sliding and intragranular strain by using the samples in a stable flow. Surface grids indicated that superplastic flow is accompanied by the formation of striated regions on the surface, whereas grain boundary sliding involves grain neighbor switching and grain rotation. Intragranular deformation with increased dislocation density and dynamic recrystallization are also observed. Weaker intergranular and intense intragranular deformation are revealed at high strain rate deformation regime. Solute effect and the presence of two types of secondary phases, nanoprecipitates of L12-Al3Zr and micron-sized eutectic Al3Ni, are discussed in comparison to conventional AA7475 alloy in different aspects of grain growth, dynamic recrystallization and strain-rate sensitivity.

High Strain Rate Superplasticity in Al-Zn-Mg-Based Alloy: Microstructural Design, Deformation Behavior, and Modeling.

Increasing the strain rate at superplastic forming is a challenging technical and economic task of aluminum forming manufacturing. New aluminum sheets exhibiting high strain rate superplasticity at strain rates above 0.01 s−1 are required. This study describes the microstructure and the superplasticity properties of a new high-strength Al-Zn-Mg-based alloy processed by a simple thermomechanical treatment including hot and cold rolling. The new alloy contains Ni to form Al3Ni coarse particles and minor additions of Zr (0.19 wt.%) and Sc (0.06 wt.%) to form nanoprecipitates of the L12-Al3 (Sc,Zr) phase. The design of chemical and phase compositions of the alloy provides superplasticity with an elongation of 600–800% in a strain rate range of 0.01 to 0.6/s and residual cavitation less than 2%. A mean elongation-to-failure of 400% is observed at an extremely high constant strain rate of 1 s−1. The strain-induced evolution of the grain and dislocation structures as well as the L12 precipitates at superplastic deformation is studied. The dynamic recrystallization at superplastic deformation is confirmed. The superplastic flow behavior of the proposed alloy is modeled via a mathematical Arrhenius-type constitutive model and an artificial neural network model. Both models exhibit good predictability at low and high strain rates of superplastic deformation.

Excellent superplastic properties achieved in Mg–4Y–3RE alloy in high strain rate regime

This study is focused on high strain rate superplasticity of commercial magnesium alloy Mg–4Y–3RE (WE43) in ultrafine-grained condition prepared by equal channel angular pressing (ECAP). Attaining microstructure with the average grain size of ~340 nm and high density of secondary phase particles provided a possibility to significantly decrease temperature during the deformation at strain rates of 10−2 s−1 and 10−1 s−1 in comparison with previous studies. Consequently, extent of negative effect of grain growth was partially suppressed and the investigated alloy did exhibit exceptionally high deformability with a maximum elongation of ~1230% at strain rate of 10−2 s−1 and at two temperatures: 350 °C and 400 °C. Increase in the strain rate to 10−1 s−1 resulted in maximum elongation of ~1000% at the temperature of 400 °C. The microstructural analysis after the deformation showed that the microstructure was fine-grained even after large deformation and plasticity-controlled growth of cavities did occur only at the temperature of 450 °C. The optimization of ECAP processing resulted in very weak texture and, therefore, the deformability should be more isotropic in comparison with strongly textured materials usually investigated in this regard.

Creep and Superplasticity: Evolution and Rationalization

Detailed studies on the creep behavior of materials are of scientific and practical significance. From a scientific point of view, data obtained from such studies are critical to the characterization of creep behavior in terms of deformation mechanisms. From a practical point of view, information inferred from such studies is useful because of its relevance to many design considerations. Over the past several decades, much progress has been made in rationalizing the creep behavior of metals and solid‐solution alloys. Such progress is extended to understanding the creep behavior of new classes of materials such as powder metallurgy (PM) Al alloys, discontinuous SiC composites, superplastic alloys, and high‐entropy alloys (HEAs). Progress in micrograin superplasticity (1 μm < d < 10 μm, where d is the grain size) has been applied to the emergence of high strain rate (HSR) superplasticity using ultrafine‐grained alloys (0.3 μm < d < 1 μm). The concept of creep is utilized to develop a deformation mechanism for nanocrystalline (nc) materials (d < 100 nm). Using the details of this mechanism, it is possible (1) to explain why the behavior of nc material is not superplastic and 2) to predict a transition from superplastic behavior to nc behavior.

Successful transition from low-temperature superplasticity to high-strain-rate superplasticity with increasing temperature in an ultrafine-grained Mg–Y–Zn–Zr alloy

Simultaneous achievement of low-temperature superplasticity (LTSP) below 0.5Tm (Tm: melting temperature) and high-strain-rate superplasticity (HSRS) above 0.5Tm from the identically processed material is advantageous for industrial applications. Severe plastic deformation by high-ratio differential speed rolling (HRDSR) with different roll speed ratios (2 and 3) was applied to cast Mg–Y–Zn–Zr alloys with the eutectic icosahedral phase (I-phase) structure. Two types of microstructures were obtained, depending on the roll speed ratio. The alloy processed at a speed ratio of 3 (HRDSR3) had an ultrafine-grained microstructure (∼1 μm) and finely broken eutectic I-phase particles. The alloy processed at a speed ratio of 2 (HRDSR2) also had an ultrafine grained microstructure, but with a higher fraction of non-fully fragmented original grains and a lower density of fine I-phase particles (< 1 μm in size). In both alloys, many I-phase particles were agglomerated. Below 523 K, both materials had good LTSP but HRDSR3 showed a better LTSP than HRDSR2. This was because HRDSR3 had a higher fraction of ultrafine grained area participating in grain boundary sliding and a higher density of fine I-phase particles contributing to the pinning effect on grain growth. Above 573 K, however, HRDSR2 showed HSRS but HRDSR3 failed to show HSRS. This resulted because thermal stability of ultrafine grained structure of HRDSR3 became poorer than that of HRDSR2 as the temperature increased above 0.5Tm. When solute solubility increased with temperature, the density of the small I-phase particles (<1 μm) exerting the effective pinning effect on grain boundary migration decreased at a more rapid rate in HRDSR3 than in HRDSR2 during the sample heating and holding duration. This was because a more significant reduction in particle size by higher shear resulted in a higher rate of dissolution of particles into matrix upon temperature increase. Retension of fine grains during the sample heating and holding duration was important in achieving HSRS because it allowed for active occurrence of grain boundardy sliding during deformation. Grain boundary sliding promoted progressive dispersion of agglomerated I-phase particles into the matrix, which was equally important in achieving HSRS because as the I-phase particles were more uniformly dispersed during deformation, the pinning effect of the particles increased, leading to a more effective suppression of dynamic grain growth of the fine grains. The obtained results suggest the importance of control on the size of I-phase particles and grains in achieving LTSP and HSRS from the identically processed Mg alloys in the low and high temperature ranges, respectively. The deformation behaviors of HRDSR2 and HRDSR3 as well as the condition for the successful transition from LSPT to HSRS with increasing temperature could be explained by using the model that assumes that the two deformation mechanisms of grain-size sensitive grain boundary sliding and grain-size insensitive dislocation climb creep compete each other during plastic deformation.