The evolution of microstructure during hot deformation is key to achieving good mechanical properties in aluminum alloys.We have developed a cellular automaton(CA) based model to simulate the microstructural evolution...The evolution of microstructure during hot deformation is key to achieving good mechanical properties in aluminum alloys.We have developed a cellular automaton(CA) based model to simulate the microstructural evolution in 7075 aluminum alloy during hot deformation.Isothermal compression tests were conducted to obtain material parameters for 7075 aluminum alloy,leading to the establishment of models for dislocation density,nucleation of recrystallized grains,and grain growth.Integrating these aspects with grain topological deformation,our CA model effectively predicts flow stress,dynamic recrystallization(DRX) volume fraction,and average grain size under diverse deformation conditions.A systematic comparison was made between electron back scattered diffraction(EBSD) maps and CA model simulated under different deformation temperatures(573 to 723 K),strain rates(0.001 to 1 s^(-1)),and strain amounts(30% to 70%).These analyses indicate that large strain,high temperature,and low strain rate facilitate dynamic recrystallization and grain refinement.The results from the CA model show good accuracy and predictive capability,with experimental error within 10%.展开更多
This study investigates the effects of extrusion temperature on the dynamic recrystallization(DRX)behavior of a Mg-3Al-1Zn-0.3Mn(AZ31,wt%)alloy during hot extrusion and on the microstructural characteristics and mecha...This study investigates the effects of extrusion temperature on the dynamic recrystallization(DRX)behavior of a Mg-3Al-1Zn-0.3Mn(AZ31,wt%)alloy during hot extrusion and on the microstructural characteristics and mechanical properties of materials extruded at 350 and 450℃.An increase in the extrusion temperature causes a decrease in the amount of strain energy accumulated in the material during extrusion,because of promoted activation of pyramidal<c+a>slip and dynamic recovery.This reduced strain energy weakens the DRX behavior during extrusion,which eventually results in a decrease in the area fraction of recrystallized grains of the extruded material.The material extruded at 450℃has coarser grains and a stronger basal fiber texture than that extruded at 350℃.As the extrusion temperature increases from 350 to 450℃,the tensile yield strength(TYS)of the extruded material increases from 191.8 to 201.5 MPa,whereas its compressive yield strength(CYS)decreases from 122.5 to 111.0 MPa;consequently,its tension-compression yield stress ratio(CYS/TYS)decreases from 0.64 to 0.55.The increase in the TYS is attributed mainly to the stronger texture hardening and strain hardening effects of the extruded material,and the decrease in the CYS is attributed to the reduced twinning stress resulting from grain coarsening and texture intensification.The microstructural and textural evolutions of the materials during extrusion and the deformation and hardening mechanisms of the extruded materials are discussed in detail.展开更多
Featured initial microstructures of Mg-11Gd-4Y-2Zn-0.5Zr alloy(wt%) were obtained by adjusting temperatures of solid solution and cooling methods, including island intergranular 18R and 14H LPSO phases with low-densit...Featured initial microstructures of Mg-11Gd-4Y-2Zn-0.5Zr alloy(wt%) were obtained by adjusting temperatures of solid solution and cooling methods, including island intergranular 18R and 14H LPSO phases with low-density stacking faults, differentially spaced lamellar intragranular 14H-LPSO phases, and network intergranular 18R-LPSO phases with high-density intragranular stacking faults. Effects of these featured LPSO phases and stacking faults on dynamic recrystallization(DRX) behavior were investigated via hot compression. Promoted DRX behavior via particle stimulated nucleation(PSN) is introduced by coexisting intergranular island 18R and 14H LPSO phases and intragranular wide spacing lamellar 14H-LPSO phases, contributing the highest DRX fraction of 42.6%. Conversely, it is found that DRX behavior with network intergranular 18R-LPSO phases and dense intragranular stacking fault is considerably inhibited with the lowest fraction of 22.8%. That is, the restricted DRX due to dislocations pinning by stacking faults overwhelms the enhanced DRX behavior via PSN of island intergranular 18R and 14H LPSO phases. Specially, compared with dense intragranular lamellar 14H-LPSO phases, high-density stacking faults exert a larger inhibition effect on DRX behavior.展开更多
Bridge steel has been widely used in recent years for its excellent performance. Understanding the high-temperature Dynamic Recrystallization (DRX) behavior of high-performance bridge steel plays an important role in ...Bridge steel has been widely used in recent years for its excellent performance. Understanding the high-temperature Dynamic Recrystallization (DRX) behavior of high-performance bridge steel plays an important role in guiding the thermomechanical processing process. In the present study, the hot deformation behavior of Q370qE bridge steel was investigated by hot compression tests conducted on a Gleeble 3800-GTC thermal-mechanical physical simulation system at temperatures ranging from 900 ℃ to 1100 ℃ and strain rates ranging from 0.01 s^(−1) to 10 s^(−1). The obtained results were used to plot the true stress-strain and work-hardening rate curves of the experimental steel, with the latter curves used to determine the critical strains for the initiation of DRX. The Zener-Hollomon equation was subsequently applied to establish the correspondence between temperature and strain rate during the high-temperature plastic deformation of bridge steel. In terms of the DRX volume fraction solution, a new method for establishing DRX volume fraction was proposed based on two theoretical models. The good weathering and corrosion resistance of bridge steel lead to difculties in microstructure etching. To solve this, the MTEX technology was used to further develop EBSD data to characterize the original microstructure of Q370qE bridge steel. This paper lays the theoretical foundation for studying the DRX behavior of Q370qE bridge steel.展开更多
The hot deformation behaviours of 316LN-Mn austenitic stainless steel were investigated by uniaxial isothermal compression tests at different temperatures and strain rates.The microstructural evolutions were also stud...The hot deformation behaviours of 316LN-Mn austenitic stainless steel were investigated by uniaxial isothermal compression tests at different temperatures and strain rates.The microstructural evolutions were also studied using electron backscatter diffraction.The flow stress decreases with the increasing temperature and decreasing strain rate.A constitutive equation was established to characterize the relationship among the deformation parameters,and the deformation activation energy was calculated to be 497.92 k J/mol.Processing maps were constructed to describe the appropriate processing window,and the optimum processing parameters were determined at a temperature of 1107-1160℃ and a strain rate of 0.005-0.026 s^(-1).Experimental results showed that the main nucleation mechanism is discontinuous dynamic recrystallization(DDRX),followed by continuous dynamic recrystallization(CDRX).In addition,the formation of twin boundaries facilitated the nucleation of dynamic recrystallization.展开更多
Flow softening behavior of a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy under compression to a final strain of∼1.8 at elevated temperatures of 450∼550℃ and a constant strain rate of 2s^(−1) has been investigated by opti...Flow softening behavior of a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy under compression to a final strain of∼1.8 at elevated temperatures of 450∼550℃ and a constant strain rate of 2s^(−1) has been investigated by optical microscopy,scanning electron microscopy,electron back-scattered diffraction and transmission electron microscopy.The results show that true stress first rises to the peak point and then drops to the bottom value and increases again with further increasing strain at each temperature.Twinning dynamic recrystallization(DRX)and continuous DRX contribute to the formation of new fine grains at temperatures 450∼475℃ when the restoration is caused by both DRX and texture change due to extension twinning,resulting in the larger softening degrees compared with the softening effects owing to continuous DRX and discontinuous DRX at 500∼550℃ when twinning activation is suppressed.500℃ is the transition temperature denoting a significant decline in the contribution of twinning and TDRX to the strain with increasing temperature.The cuboid-shape phase exists in both homogenized and compressed samples,while the compositions are varied.展开更多
We utilized electron backscatter diffraction to investigate the microstructure evolutions of a newly developed magnesium-rare earth alloy(Mg–9.80 Gd–3.78 Y–1.12 Sm–0.48 Zr)during instantaneous hot indirect extrusi...We utilized electron backscatter diffraction to investigate the microstructure evolutions of a newly developed magnesium-rare earth alloy(Mg–9.80 Gd–3.78 Y–1.12 Sm–0.48 Zr)during instantaneous hot indirect extrusion.An equiaxed fine-grained(average grain size of 3.4±0.2μm)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.展开更多
The effects of strain rates on the hot working characteristics and nucleation mechanisms of dynamic recrystallization (DRX) were studied by optical microscopy and electron backscatter diffraction (EBSD) technique. Hot...The effects of strain rates on the hot working characteristics and nucleation mechanisms of dynamic recrystallization (DRX) were studied by optical microscopy and electron backscatter diffraction (EBSD) technique. Hot compression tests were conducted using a Gleeble-1500 simulator at a true strain of 0.7 in the temperature range of 1000 to 1150 °C and strain rate range of 0.01 to 10.00 s-1. It is found that the size and volume fraction of the DRX grains in hot-deformed Inconel 625 superalloy firstly decrease and then increase with increasing strain rate. Meanwhile, the nucleation mechanism of DRX is closely related to the deformation strain rate due to the deformation thermal effect. The discontinuous DRX (DDRX) with bulging of original grain boundaries is the primary nucleation mechanism of DRX, while the continuous DRX (CDRX) with progressive subgrain rotation acts as a secondary nucleation mechanism. The twinning formation can activate the nucleation of DRX. The effects of bulging of original grain boundaries and twinning formation are firstly gradually weakened and then strengthened with the increasing strain rate due to the deformation thermal effect. On the contrary, the effect of subgrain rotation is firstly gradually strengthened and then weakened with the increasing strain rate.展开更多
In this study,the effect of strontium addition on hot deformation of AZ61 alloy was investigated by hot compression tests.A reference alloy(AZ61)and an Sr-containing alloy(AZ61+Sr)was cast while their average initial ...In this study,the effect of strontium addition on hot deformation of AZ61 alloy was investigated by hot compression tests.A reference alloy(AZ61)and an Sr-containing alloy(AZ61+Sr)was cast while their average initial grain size were supposed to be about 140 and 40μm,respectively.In AZ61+Sr alloy,the Sr-containing precipitations were stable at homogenization temperature.Analysing the hot compression curves,it was revealed that dynamic recrystallization phenomenon had occurred and controlled the thermomechanical behaviour of the alloys.The derived constitutive equations showed that the hot deformation parameters(n and Q)in AZ61+Sr alloy is smaller than those of AZ61 alloy;this can be related to the small initial grain size and the lower amounts of solute aluminium atoms.The analysis of DRX kinetics along with the micrographs of the deformed microstructures showed that at the same condition the development of DRXed microstructure in AZ61+Sr alloy was faster than AZ61 alloy.The increased recrystallized microstructure was interpretated to be attributed to(1)the more grain boundaries present and(2)the existance of the Al-Mg-Sr precipitations assisted the PSN mechanism.Also,the attenuated intensity of the basal texture of AZ61+Sr was related to the DRX fraction of microstructure.展开更多
Gleeble-3500 thermal simulator was applied to realize the rotary backward extrusion forming of Mg-13Gd-4Y-2Zn-0.5Zr(wt%)alloy at different circumferential strain rate from 0.009 s^(-1)to 0.027 s^(-1)at 400℃and the dy...Gleeble-3500 thermal simulator was applied to realize the rotary backward extrusion forming of Mg-13Gd-4Y-2Zn-0.5Zr(wt%)alloy at different circumferential strain rate from 0.009 s^(-1)to 0.027 s^(-1)at 400℃and the dynamic recrystallization mechanism and texture evolution were studied.The results show that the grain size of the alloy was obviously refined after rotary backward extrusion.As the circumferenlial strain rate increased,the dynamic recrystallization fraction gradually increased causing the grain size decreased and the distribution of microstructure became more uniform.At the same time,the texture of{0001},{10-10},{11-20}was weakened and the grain orientation distribution became more random.With the increase of circumferential strain rate,the discontinuous dynamic recrystallization mechanism became dominant,which promoted the weakening of texture and grain refinement of the alloy.展开更多
Texture evolution of an extruded dilute Mg-1Sn-1Zn-1Al alloy was thoroughly investigated based on the twinning and dynamic recrystallization(DRX)behavior via hot compression at a strain rate of 10 s^(-1)and temperatur...Texture evolution of an extruded dilute Mg-1Sn-1Zn-1Al alloy was thoroughly investigated based on the twinning and dynamic recrystallization(DRX)behavior via hot compression at a strain rate of 10 s^(-1)and temperature of 225℃.It was found that the types and intensities of the texture are strongly dependent on the fraction of twins and DRX modes as well as regions where sub-grain boundaries(sub-GBs)are intensively accumulated.At the initial stage of deformation,the formation of compression direction(CD)-tilted basal texture was mainly determined by the occurrence of{101^(-)2}extension twins.As the strain increases,the variation in the texture intensity was greatly dominated by the DRX modes but the type of main texture remained unchanged.These findings are of great importance for texture modification of wrought Mg-Sn-based alloys during post-deformation.展开更多
A new wrought magnesium(Mg)alloy based on Mg-6.0Zn-0.5Mn(ZM60)is developed,which performs excellent combination of high tensile yield strength and good ductility.We investigate the effects of micro-alloying on dynamic...A new wrought magnesium(Mg)alloy based on Mg-6.0Zn-0.5Mn(ZM60)is developed,which performs excellent combination of high tensile yield strength and good ductility.We investigate the effects of micro-alloying on dynamic precipitation,dynamic recrystallization(DRX)and mechanical properties of ZM60 alloy.The co-addition of minor(0.6 wt%)neodymium(Nd)and(0.3 wt%)erbium(Er)can accelerate the twinning and DRX process of ZM60 alloy at the initial compression deformation stage.The dynamic precipitation process is also accelerated due to Nd and Er co-alloying.Dislocation accumulation disappears and a higher density of rodβ_(1) precipitates and some thick β_(2) precipitates in matrix and fine twins,which inhibits the growth of DRX grains in compressed ZM60-0.6Nd-0.3Er alloy.The as-extruded ZM60-0.6Nd-0.3Er alloy has a yield strength(YS)of 245.8 MPa,ultimate tensile strength(UTS)of 347.2 MPa and elongation(EL)of 16.3%.The yield strength and tensile strength are improved via minor Nd and Er additions due to fine complete DRX grains,second phase particles and high density of precipitates.The grain refinement,weakened reserved working hardening and weakened basal fiber texture improve the elongation of ZM60-0.6Nd-0.3Er alloy.展开更多
In this paper,(500 nm 1%+5μm 3%)bimodal scale Al2O3p/AZ31 composites was fabricated by solid state synthesis and the effect of bimodal scale Al2O3 particulates on its dynamic recrystallization behavior and mechanical...In this paper,(500 nm 1%+5μm 3%)bimodal scale Al2O3p/AZ31 composites was fabricated by solid state synthesis and the effect of bimodal scale Al2O3 particulates on its dynamic recrystallization behavior and mechanical properties was investigated.The optical microscopy,scanning electron microscopy,transmission electron microscopy and electron universal strength tester composites were used to characterize the composites.The results indicate that the grains size of the composites are significantly refined and the mechanical properties are obviously improved.Due to the presence of the bimodal scale Al2o3 particulates,the high-density dislocation zone is formed around nano-Al2o3p and the particle deformation zone is formed near micron-ABOap.These zones are ideal sites for the formation of recrystallization nucleus.Meanwhile,the addition of the bimodal scale Al2o3 particulates may delay or hinder the growth of matrix grain through the pining effect on the grain boundaries,resulting in significantly improving the yield strength and tensile strength of Al2O3p/AZ31 composites.展开更多
To investigate the dynamic recrystallization behavior of 7xxx aluminum alloys,the isothermal compression tests were carried on the 7056 aluminum alloy in the temperatures range of 320-440℃and in the strain rates rang...To investigate the dynamic recrystallization behavior of 7xxx aluminum alloys,the isothermal compression tests were carried on the 7056 aluminum alloy in the temperatures range of 320-440℃and in the strain rates range of 0.001-1 s^(-1).In addition,the microstructure of samples were observed via electron back scanning diffraction microscope.According to the results,true stress and true strain curves were established and an Arrhenius-type equation was established,showing the flow stress increases with the temperature decreasing and the strain rate increasing.The critical strain(ε_(c))and the critical stress(σ_(c))of the onset of dynamic recrystallization were identified via the strain hardening rate and constructed relationship between deformation parameters as follows:ε_(c)=6.71×10^(-4)Z^(0.1373) and σ_(p)=1.202σ_(c)+12.691.The DRX is incomplete in this alloy,whose volume fraction is only 20%even if the strain reaches 0.9.Through this study,the flow stress behavior and DRX behavior of 7056 aluminum alloys are deeply understood,which gives benefit to control the hot working process.展开更多
Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high...Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional展开更多
The corrosion susceptibility of recrystallized and un-recrystallized grains in equal channel angular pressed(ECAPed)Mg-9Al-lZn(AZ91)alloys immersed in chloride containing media was investigated through immersion testi...The corrosion susceptibility of recrystallized and un-recrystallized grains in equal channel angular pressed(ECAPed)Mg-9Al-lZn(AZ91)alloys immersed in chloride containing media was investigated through immersion testing and an electrochemical microcell technique coupledwith high resolution techniques such as scanning Kelvin probe force microscopy(SKPFM),transmission electron microscopy(TEM),andelectron backscatter diffraction(EBSD).During ECAP,dynamic recrystallization(DRX)and strain-induced dynamic precipitation(SIDP)simultaneously occurred,resulting in a bimodal grain structure of original elongated coarse grains and newly formed equiaxed fine grainswith a large volume fraction ofβ-Mg17Al12 precipitates.Corrosion preferentially initiates and propagates in the DRXed grains,owing tothe greater microchemistry difference between theβ-Mg17Al12 precipitates formed at the DRXed grain boundaries and the adjacentα-Mgmatrix,which induces a strong microgalvanic coupling between these phases.Additionally,the weaker basal texture of the DRXed grainsalso makes these grains more susceptible to electrochemical reactions than the highly textured un-DRXed grains.The influence of dynamicrecrystallization and dynamic precipitation was also studied in ECAPed alloys with differenl levels of deformation strain through corrosion andelectrochemical techniques.Increasing the strain level led to a more uniform corrosion with a shallow penetration depth,lower corrosion ratevalues,and higher protective ability of the oxide film.Furthermore,higher levels of strain resulted in greater hardness values of the ECAPedalloys.The superior corrosion resistance and strength of the ECAPed alloys with increasing strain level was attributed to the combination ofsmaller DRXed grain size,higher DRX ratio,and higher volume fraction of uniformly distributed fineβ-Mg17Al12 precipitates.c 2020 Published by Elsevier B.V.on behalf of Chongqing University.展开更多
The hot deformation behavior of a Nb microalloyed anti-seismic rebar was investigated at deformation temperatures of 950-1 100 ℃ and strain rates of 0. 01-0. 1 s- 1 on a Gleeble-3800 thermo-mechnical simulator. The f...The hot deformation behavior of a Nb microalloyed anti-seismic rebar was investigated at deformation temperatures of 950-1 100 ℃ and strain rates of 0. 01-0. 1 s- 1 on a Gleeble-3800 thermo-mechnical simulator. The flow stress-strain curves show the typical dynamic recrystallization with a peak,before reaching the steady state flow at higher deformation temperatures and lower strain rates. The constitutive equation governing the dynamic recrystallization( DRX) was obtained and the average activation energy of deformation was calculated as Q = 389. 5 kJ / mol by the regression analysis. The DRX grain size was also found to decrease with the increasing strain rate and the decreasing deformation temperature. The austenite grain size was refined from 118. 0 μm to 15. 07-40. 01 μm by DRX. The DRX grain size under diverse deformation conditions predicted by mathematical model agrees well with experimental results.展开更多
Compared to cold drawing,dieless drawing has shown great potential for manufacturing biodegradable Mg alloy microtubes due to the large reduction in area acquired in a single pass.However,owing to the local heating an...Compared to cold drawing,dieless drawing has shown great potential for manufacturing biodegradable Mg alloy microtubes due to the large reduction in area acquired in a single pass.However,owing to the local heating and local deformation,the deformation mechanism during dieless drawing is not clear,and thus causing difficulties in controlling the microstructure of dieless drawn tubes.For the purpose of acquiring a desired microstructure.in this study the deformation mechanism of ZM21 Mg alloy tube was clarified by conducting continuous observation of the microstructural evolution during dieless drawing.The results show that both SRX and DRX occurred during dieless drawing.SRX occurred before the plastic deformation to soften dieless drawn tubes.With increase of feeding speed,the deformation mechanism changed accordingly:(1) At the low-speed of 0.02 mm/s,the deformation mechanism was dominated by twin-slip sliding,during which {10-12} tension twins were generated inside grains to accommodate the plastic deformation by changing the crystal orientation.(2) At the intermediate-speed of 2 mm/s,a twin-DRX process related to {10-12} tension twin was observed,which was characterized by the generation of abundant {10-12} tension twins and the evolution of misorientation angle of {10-12} tension twins.Moreover,the transformation from twin-DRX to CDRX can be observed at the late stage of plastic deformation,which was attributed to the inhomogeneous conditions of dieless drawing.(3) At the high-speed of 5 mm/s,a CDRX process was observed,during which grain boundary sliding and grain tilting were observed,in addition to the gradual rotation of subgrains.These results show that during dieless drawing,DRX is not only a temperature-dependent phenomenon,but also influenced by the variation of feeding speed.展开更多
The hot deformation behavior of an ultralow-carbon microalloyed steel was investigated using an MMS-200 thermal simulation test machine in a temperature range of 1073-1373 K and strain rate range of 0.01-10 s-1.The re...The hot deformation behavior of an ultralow-carbon microalloyed steel was investigated using an MMS-200 thermal simulation test machine in a temperature range of 1073-1373 K and strain rate range of 0.01-10 s-1.The results show that the flow stress decreases with increasing deformation temperature or decreasing strain rate.The strain-compensated constitutive model based on the Arrhenius equation for this steel was established using the true stress-strain data obtained from a hot compression test.Furthermore,a new constitutive model based on the Z-parameter was proposed for this steel.The predictive ability of two constitutive models was compared with statistical measures.The results indicate the new constitutive model based on the Z-parameter can more accurately predict the flow stress of an ultralow-carbon microalloyed steel during hot deformation.The dynamic recrystallization(DRX)nucleation mechanism at different deformation temperatures was observed and analyzed by transmission electron microscopy(TEM),and strain-induced grain boundary migration was observed at 1373 K/0.01 s^-1.展开更多
In the present research,the dynamic recrystallization(DRX) behavior of a newly-developed Mg-Al-Zn-RE alloy with abundant secondphase particles during hot extrusion is investigated by coupling finite element(FE) and ce...In the present research,the dynamic recrystallization(DRX) behavior of a newly-developed Mg-Al-Zn-RE alloy with abundant secondphase particles during hot extrusion is investigated by coupling finite element(FE) and cellular automaton(CA) models.A two-dimensional CA model is developed to quantitatively and topologically evaluate the DRX process during deformation with constant forming conditions.Considering the fact that second-phase particles with various sizes extensively exist in the studied Mg-Al-Zn-RE magnesium alloy,models of DRX nucleation and grain growth velocity are modified.The coefficients of the modified CA model are calibrated by isothermal compression experiments of the magnesium alloy.Subsequently,the CA model is coupled with FE analysis to investigate the DRX behavior during the hot extrusions of the Mg-Al-Zn-RE alloy.The DRX behavior of the magnesium alloy at different stages and positions of extruded plates is simulated by the established model.Finer grains near the edge than in the inner of the plates result from higher strain and strain rate.The influence of extrusion conditions on microstructural evolution is explored.Under the employed forming conditions,average grain size decreases 28-62 times from as-cast and solution-treated to as-extruded state due to grain refinement by DRX.With increasing initial billet temperature or extrusion speed,average grain size increases.The finest grains are obtained at the initial billet temperature of 623 K and the extrusion speed of 7.83 mm/s.Low initial billet temperature or high extrusion speed benefits homogeneous grain distribution.The simulated results are in good agreement with experimental ones.展开更多
基金Funded by the Central Government Guides Local Funds for Science and Technology Development(No.YDZJSX20231A045)the Fundamental Research Program of Shanxi Province(Nos.202103021223288 and 202103021224282)。
文摘The evolution of microstructure during hot deformation is key to achieving good mechanical properties in aluminum alloys.We have developed a cellular automaton(CA) based model to simulate the microstructural evolution in 7075 aluminum alloy during hot deformation.Isothermal compression tests were conducted to obtain material parameters for 7075 aluminum alloy,leading to the establishment of models for dislocation density,nucleation of recrystallized grains,and grain growth.Integrating these aspects with grain topological deformation,our CA model effectively predicts flow stress,dynamic recrystallization(DRX) volume fraction,and average grain size under diverse deformation conditions.A systematic comparison was made between electron back scattered diffraction(EBSD) maps and CA model simulated under different deformation temperatures(573 to 723 K),strain rates(0.001 to 1 s^(-1)),and strain amounts(30% to 70%).These analyses indicate that large strain,high temperature,and low strain rate facilitate dynamic recrystallization and grain refinement.The results from the CA model show good accuracy and predictive capability,with experimental error within 10%.
基金supported by the National Research Foundation of Korea(NRF)grant(No.2019R1A2C1085272)funded by the Ministry of Science,ICT and Future Planning(MSIP,South Korea).
文摘This study investigates the effects of extrusion temperature on the dynamic recrystallization(DRX)behavior of a Mg-3Al-1Zn-0.3Mn(AZ31,wt%)alloy during hot extrusion and on the microstructural characteristics and mechanical properties of materials extruded at 350 and 450℃.An increase in the extrusion temperature causes a decrease in the amount of strain energy accumulated in the material during extrusion,because of promoted activation of pyramidal<c+a>slip and dynamic recovery.This reduced strain energy weakens the DRX behavior during extrusion,which eventually results in a decrease in the area fraction of recrystallized grains of the extruded material.The material extruded at 450℃has coarser grains and a stronger basal fiber texture than that extruded at 350℃.As the extrusion temperature increases from 350 to 450℃,the tensile yield strength(TYS)of the extruded material increases from 191.8 to 201.5 MPa,whereas its compressive yield strength(CYS)decreases from 122.5 to 111.0 MPa;consequently,its tension-compression yield stress ratio(CYS/TYS)decreases from 0.64 to 0.55.The increase in the TYS is attributed mainly to the stronger texture hardening and strain hardening effects of the extruded material,and the decrease in the CYS is attributed to the reduced twinning stress resulting from grain coarsening and texture intensification.The microstructural and textural evolutions of the materials during extrusion and the deformation and hardening mechanisms of the extruded materials are discussed in detail.
基金supported by the National Key Research and Development Program of China (No.2021YFB3701100)the National Key Research and Development Program of China (Grant No.2018YFE0115800)the National Natural Science Foundation of China (Grant No.52105412)。
文摘Featured initial microstructures of Mg-11Gd-4Y-2Zn-0.5Zr alloy(wt%) were obtained by adjusting temperatures of solid solution and cooling methods, including island intergranular 18R and 14H LPSO phases with low-density stacking faults, differentially spaced lamellar intragranular 14H-LPSO phases, and network intergranular 18R-LPSO phases with high-density intragranular stacking faults. Effects of these featured LPSO phases and stacking faults on dynamic recrystallization(DRX) behavior were investigated via hot compression. Promoted DRX behavior via particle stimulated nucleation(PSN) is introduced by coexisting intergranular island 18R and 14H LPSO phases and intragranular wide spacing lamellar 14H-LPSO phases, contributing the highest DRX fraction of 42.6%. Conversely, it is found that DRX behavior with network intergranular 18R-LPSO phases and dense intragranular stacking fault is considerably inhibited with the lowest fraction of 22.8%. That is, the restricted DRX due to dislocations pinning by stacking faults overwhelms the enhanced DRX behavior via PSN of island intergranular 18R and 14H LPSO phases. Specially, compared with dense intragranular lamellar 14H-LPSO phases, high-density stacking faults exert a larger inhibition effect on DRX behavior.
基金Supported by Regional Joint Funds of National Natural Science Foundation of China(Grant No.U20A20289)Hebei Provincial Innovative Research Groups Project of Natural Science Foundation of China(Grant No.E2021203011)+2 种基金General Program of National Natural Science Foundation of China(Grant Nos.52075471,52075473)Hebei Provincial Excellent Youth Science Foundation of China(Grant No.E2021203190)Hebei Provincial Innovative Capacity Cultivation Funding Project for Postgraduates of China(Grant No.CXZZSS2023040).
文摘Bridge steel has been widely used in recent years for its excellent performance. Understanding the high-temperature Dynamic Recrystallization (DRX) behavior of high-performance bridge steel plays an important role in guiding the thermomechanical processing process. In the present study, the hot deformation behavior of Q370qE bridge steel was investigated by hot compression tests conducted on a Gleeble 3800-GTC thermal-mechanical physical simulation system at temperatures ranging from 900 ℃ to 1100 ℃ and strain rates ranging from 0.01 s^(−1) to 10 s^(−1). The obtained results were used to plot the true stress-strain and work-hardening rate curves of the experimental steel, with the latter curves used to determine the critical strains for the initiation of DRX. The Zener-Hollomon equation was subsequently applied to establish the correspondence between temperature and strain rate during the high-temperature plastic deformation of bridge steel. In terms of the DRX volume fraction solution, a new method for establishing DRX volume fraction was proposed based on two theoretical models. The good weathering and corrosion resistance of bridge steel lead to difculties in microstructure etching. To solve this, the MTEX technology was used to further develop EBSD data to characterize the original microstructure of Q370qE bridge steel. This paper lays the theoretical foundation for studying the DRX behavior of Q370qE bridge steel.
基金financial support of the National Natural Science Foundation of China(Nos.52101105 and 51975263)。
文摘The hot deformation behaviours of 316LN-Mn austenitic stainless steel were investigated by uniaxial isothermal compression tests at different temperatures and strain rates.The microstructural evolutions were also studied using electron backscatter diffraction.The flow stress decreases with the increasing temperature and decreasing strain rate.A constitutive equation was established to characterize the relationship among the deformation parameters,and the deformation activation energy was calculated to be 497.92 k J/mol.Processing maps were constructed to describe the appropriate processing window,and the optimum processing parameters were determined at a temperature of 1107-1160℃ and a strain rate of 0.005-0.026 s^(-1).Experimental results showed that the main nucleation mechanism is discontinuous dynamic recrystallization(DDRX),followed by continuous dynamic recrystallization(CDRX).In addition,the formation of twin boundaries facilitated the nucleation of dynamic recrystallization.
基金This work was supported by the Changsha University Talent Introduction Project(50800-92808)the Excellent youth project of Hunan Provincial Department of Education(19B055,18B418,19C0156)the Natural Science Foundation of Hunan Province of China(2020JJ4645).
文摘Flow softening behavior of a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy under compression to a final strain of∼1.8 at elevated temperatures of 450∼550℃ and a constant strain rate of 2s^(−1) has been investigated by optical microscopy,scanning electron microscopy,electron back-scattered diffraction and transmission electron microscopy.The results show that true stress first rises to the peak point and then drops to the bottom value and increases again with further increasing strain at each temperature.Twinning dynamic recrystallization(DRX)and continuous DRX contribute to the formation of new fine grains at temperatures 450∼475℃ when the restoration is caused by both DRX and texture change due to extension twinning,resulting in the larger softening degrees compared with the softening effects owing to continuous DRX and discontinuous DRX at 500∼550℃ when twinning activation is suppressed.500℃ is the transition temperature denoting a significant decline in the contribution of twinning and TDRX to the strain with increasing temperature.The cuboid-shape phase exists in both homogenized and compressed samples,while the compositions are varied.
基金financial support from the National Natural Science Foundation of China(Grant no.51571084)financial support from the Grant-in-Aid for Early-Career Scientists(Grant no.18K14024)financial support from the China Scholarship Council(Grant No.201908410208)
文摘We utilized electron backscatter diffraction to investigate the microstructure evolutions of a newly developed magnesium-rare earth alloy(Mg–9.80 Gd–3.78 Y–1.12 Sm–0.48 Zr)during instantaneous hot indirect extrusion.An equiaxed fine-grained(average grain size of 3.4±0.2μm)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.
基金co-funded by the National Natural Science Foundation of China and Baoshan Iron & Steel Co., Ltd. (No. 50834008)
文摘The effects of strain rates on the hot working characteristics and nucleation mechanisms of dynamic recrystallization (DRX) were studied by optical microscopy and electron backscatter diffraction (EBSD) technique. Hot compression tests were conducted using a Gleeble-1500 simulator at a true strain of 0.7 in the temperature range of 1000 to 1150 °C and strain rate range of 0.01 to 10.00 s-1. It is found that the size and volume fraction of the DRX grains in hot-deformed Inconel 625 superalloy firstly decrease and then increase with increasing strain rate. Meanwhile, the nucleation mechanism of DRX is closely related to the deformation strain rate due to the deformation thermal effect. The discontinuous DRX (DDRX) with bulging of original grain boundaries is the primary nucleation mechanism of DRX, while the continuous DRX (CDRX) with progressive subgrain rotation acts as a secondary nucleation mechanism. The twinning formation can activate the nucleation of DRX. The effects of bulging of original grain boundaries and twinning formation are firstly gradually weakened and then strengthened with the increasing strain rate due to the deformation thermal effect. On the contrary, the effect of subgrain rotation is firstly gradually strengthened and then weakened with the increasing strain rate.
文摘In this study,the effect of strontium addition on hot deformation of AZ61 alloy was investigated by hot compression tests.A reference alloy(AZ61)and an Sr-containing alloy(AZ61+Sr)was cast while their average initial grain size were supposed to be about 140 and 40μm,respectively.In AZ61+Sr alloy,the Sr-containing precipitations were stable at homogenization temperature.Analysing the hot compression curves,it was revealed that dynamic recrystallization phenomenon had occurred and controlled the thermomechanical behaviour of the alloys.The derived constitutive equations showed that the hot deformation parameters(n and Q)in AZ61+Sr alloy is smaller than those of AZ61 alloy;this can be related to the small initial grain size and the lower amounts of solute aluminium atoms.The analysis of DRX kinetics along with the micrographs of the deformed microstructures showed that at the same condition the development of DRXed microstructure in AZ61+Sr alloy was faster than AZ61 alloy.The increased recrystallized microstructure was interpretated to be attributed to(1)the more grain boundaries present and(2)the existance of the Al-Mg-Sr precipitations assisted the PSN mechanism.Also,the attenuated intensity of the basal texture of AZ61+Sr was related to the DRX fraction of microstructure.
基金the National Natural Science Foundation of China(Grant No.51775520)the National Key Research and Development Plan(Grant No.2016YFB0301103-3).
文摘Gleeble-3500 thermal simulator was applied to realize the rotary backward extrusion forming of Mg-13Gd-4Y-2Zn-0.5Zr(wt%)alloy at different circumferential strain rate from 0.009 s^(-1)to 0.027 s^(-1)at 400℃and the dynamic recrystallization mechanism and texture evolution were studied.The results show that the grain size of the alloy was obviously refined after rotary backward extrusion.As the circumferenlial strain rate increased,the dynamic recrystallization fraction gradually increased causing the grain size decreased and the distribution of microstructure became more uniform.At the same time,the texture of{0001},{10-10},{11-20}was weakened and the grain orientation distribution became more random.With the increase of circumferential strain rate,the discontinuous dynamic recrystallization mechanism became dominant,which promoted the weakening of texture and grain refinement of the alloy.
基金the Natural Science Foundation of China(51404166 and 51704209)Natural Science Foundation of Shanxi(201801D121088)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(2014017 and 201802034).
文摘Texture evolution of an extruded dilute Mg-1Sn-1Zn-1Al alloy was thoroughly investigated based on the twinning and dynamic recrystallization(DRX)behavior via hot compression at a strain rate of 10 s^(-1)and temperature of 225℃.It was found that the types and intensities of the texture are strongly dependent on the fraction of twins and DRX modes as well as regions where sub-grain boundaries(sub-GBs)are intensively accumulated.At the initial stage of deformation,the formation of compression direction(CD)-tilted basal texture was mainly determined by the occurrence of{101^(-)2}extension twins.As the strain increases,the variation in the texture intensity was greatly dominated by the DRX modes but the type of main texture remained unchanged.These findings are of great importance for texture modification of wrought Mg-Sn-based alloys during post-deformation.
基金the support of the Major Research Development Program of Shandong Province of China(Project No.2019GGX102060)the Chinese Postdoctoral Science Foundation(Project No.2017M612224)the Natural Science Foundation of Shandong Province of China(Project No.ZR2016EMQ08)。
文摘A new wrought magnesium(Mg)alloy based on Mg-6.0Zn-0.5Mn(ZM60)is developed,which performs excellent combination of high tensile yield strength and good ductility.We investigate the effects of micro-alloying on dynamic precipitation,dynamic recrystallization(DRX)and mechanical properties of ZM60 alloy.The co-addition of minor(0.6 wt%)neodymium(Nd)and(0.3 wt%)erbium(Er)can accelerate the twinning and DRX process of ZM60 alloy at the initial compression deformation stage.The dynamic precipitation process is also accelerated due to Nd and Er co-alloying.Dislocation accumulation disappears and a higher density of rodβ_(1) precipitates and some thick β_(2) precipitates in matrix and fine twins,which inhibits the growth of DRX grains in compressed ZM60-0.6Nd-0.3Er alloy.The as-extruded ZM60-0.6Nd-0.3Er alloy has a yield strength(YS)of 245.8 MPa,ultimate tensile strength(UTS)of 347.2 MPa and elongation(EL)of 16.3%.The yield strength and tensile strength are improved via minor Nd and Er additions due to fine complete DRX grains,second phase particles and high density of precipitates.The grain refinement,weakened reserved working hardening and weakened basal fiber texture improve the elongation of ZM60-0.6Nd-0.3Er alloy.
基金the National Key Research and Development Program(2019YFB2006500)National Natural Science Foundation of China(51404082).
文摘In this paper,(500 nm 1%+5μm 3%)bimodal scale Al2O3p/AZ31 composites was fabricated by solid state synthesis and the effect of bimodal scale Al2O3 particulates on its dynamic recrystallization behavior and mechanical properties was investigated.The optical microscopy,scanning electron microscopy,transmission electron microscopy and electron universal strength tester composites were used to characterize the composites.The results indicate that the grains size of the composites are significantly refined and the mechanical properties are obviously improved.Due to the presence of the bimodal scale Al2o3 particulates,the high-density dislocation zone is formed around nano-Al2o3p and the particle deformation zone is formed near micron-ABOap.These zones are ideal sites for the formation of recrystallization nucleus.Meanwhile,the addition of the bimodal scale Al2o3 particulates may delay or hinder the growth of matrix grain through the pining effect on the grain boundaries,resulting in significantly improving the yield strength and tensile strength of Al2O3p/AZ31 composites.
基金Funded by the National Key R&D Program of China(Nos.2016YFB0300803,2016YFB0300903)the National Program of China(No.2012CB619504)
文摘To investigate the dynamic recrystallization behavior of 7xxx aluminum alloys,the isothermal compression tests were carried on the 7056 aluminum alloy in the temperatures range of 320-440℃and in the strain rates range of 0.001-1 s^(-1).In addition,the microstructure of samples were observed via electron back scanning diffraction microscope.According to the results,true stress and true strain curves were established and an Arrhenius-type equation was established,showing the flow stress increases with the temperature decreasing and the strain rate increasing.The critical strain(ε_(c))and the critical stress(σ_(c))of the onset of dynamic recrystallization were identified via the strain hardening rate and constructed relationship between deformation parameters as follows:ε_(c)=6.71×10^(-4)Z^(0.1373) and σ_(p)=1.202σ_(c)+12.691.The DRX is incomplete in this alloy,whose volume fraction is only 20%even if the strain reaches 0.9.Through this study,the flow stress behavior and DRX behavior of 7056 aluminum alloys are deeply understood,which gives benefit to control the hot working process.
文摘Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional
基金This research did not receive any specific grant from funding agencies in the public,commercial,or not-for-profit sectors.
文摘The corrosion susceptibility of recrystallized and un-recrystallized grains in equal channel angular pressed(ECAPed)Mg-9Al-lZn(AZ91)alloys immersed in chloride containing media was investigated through immersion testing and an electrochemical microcell technique coupledwith high resolution techniques such as scanning Kelvin probe force microscopy(SKPFM),transmission electron microscopy(TEM),andelectron backscatter diffraction(EBSD).During ECAP,dynamic recrystallization(DRX)and strain-induced dynamic precipitation(SIDP)simultaneously occurred,resulting in a bimodal grain structure of original elongated coarse grains and newly formed equiaxed fine grainswith a large volume fraction ofβ-Mg17Al12 precipitates.Corrosion preferentially initiates and propagates in the DRXed grains,owing tothe greater microchemistry difference between theβ-Mg17Al12 precipitates formed at the DRXed grain boundaries and the adjacentα-Mgmatrix,which induces a strong microgalvanic coupling between these phases.Additionally,the weaker basal texture of the DRXed grainsalso makes these grains more susceptible to electrochemical reactions than the highly textured un-DRXed grains.The influence of dynamicrecrystallization and dynamic precipitation was also studied in ECAPed alloys with differenl levels of deformation strain through corrosion andelectrochemical techniques.Increasing the strain level led to a more uniform corrosion with a shallow penetration depth,lower corrosion ratevalues,and higher protective ability of the oxide film.Furthermore,higher levels of strain resulted in greater hardness values of the ECAPedalloys.The superior corrosion resistance and strength of the ECAPed alloys with increasing strain level was attributed to the combination ofsmaller DRXed grain size,higher DRX ratio,and higher volume fraction of uniformly distributed fineβ-Mg17Al12 precipitates.c 2020 Published by Elsevier B.V.on behalf of Chongqing University.
基金National Natural Science Foundation of China(No.51261009)
文摘The hot deformation behavior of a Nb microalloyed anti-seismic rebar was investigated at deformation temperatures of 950-1 100 ℃ and strain rates of 0. 01-0. 1 s- 1 on a Gleeble-3800 thermo-mechnical simulator. The flow stress-strain curves show the typical dynamic recrystallization with a peak,before reaching the steady state flow at higher deformation temperatures and lower strain rates. The constitutive equation governing the dynamic recrystallization( DRX) was obtained and the average activation energy of deformation was calculated as Q = 389. 5 kJ / mol by the regression analysis. The DRX grain size was also found to decrease with the increasing strain rate and the decreasing deformation temperature. The austenite grain size was refined from 118. 0 μm to 15. 07-40. 01 μm by DRX. The DRX grain size under diverse deformation conditions predicted by mathematical model agrees well with experimental results.
基金supported by JSTP KAKENHI Grant No. 19H02476The Light Meal Education Foundation, Inc.China Scholarship Council for the award of fellowship and funding (No. 201707040058)
文摘Compared to cold drawing,dieless drawing has shown great potential for manufacturing biodegradable Mg alloy microtubes due to the large reduction in area acquired in a single pass.However,owing to the local heating and local deformation,the deformation mechanism during dieless drawing is not clear,and thus causing difficulties in controlling the microstructure of dieless drawn tubes.For the purpose of acquiring a desired microstructure.in this study the deformation mechanism of ZM21 Mg alloy tube was clarified by conducting continuous observation of the microstructural evolution during dieless drawing.The results show that both SRX and DRX occurred during dieless drawing.SRX occurred before the plastic deformation to soften dieless drawn tubes.With increase of feeding speed,the deformation mechanism changed accordingly:(1) At the low-speed of 0.02 mm/s,the deformation mechanism was dominated by twin-slip sliding,during which {10-12} tension twins were generated inside grains to accommodate the plastic deformation by changing the crystal orientation.(2) At the intermediate-speed of 2 mm/s,a twin-DRX process related to {10-12} tension twin was observed,which was characterized by the generation of abundant {10-12} tension twins and the evolution of misorientation angle of {10-12} tension twins.Moreover,the transformation from twin-DRX to CDRX can be observed at the late stage of plastic deformation,which was attributed to the inhomogeneous conditions of dieless drawing.(3) At the high-speed of 5 mm/s,a CDRX process was observed,during which grain boundary sliding and grain tilting were observed,in addition to the gradual rotation of subgrains.These results show that during dieless drawing,DRX is not only a temperature-dependent phenomenon,but also influenced by the variation of feeding speed.
基金Funded by the Fundamental Research Funds for the Central Universities(Nos.HEUCFP201731 and HEUCFP201719)the"One Three Five"Equipment Pre-research National Defense Science and Technology Key Laboratory Fund(No.KZ42180125)。
文摘The hot deformation behavior of an ultralow-carbon microalloyed steel was investigated using an MMS-200 thermal simulation test machine in a temperature range of 1073-1373 K and strain rate range of 0.01-10 s-1.The results show that the flow stress decreases with increasing deformation temperature or decreasing strain rate.The strain-compensated constitutive model based on the Arrhenius equation for this steel was established using the true stress-strain data obtained from a hot compression test.Furthermore,a new constitutive model based on the Z-parameter was proposed for this steel.The predictive ability of two constitutive models was compared with statistical measures.The results indicate the new constitutive model based on the Z-parameter can more accurately predict the flow stress of an ultralow-carbon microalloyed steel during hot deformation.The dynamic recrystallization(DRX)nucleation mechanism at different deformation temperatures was observed and analyzed by transmission electron microscopy(TEM),and strain-induced grain boundary migration was observed at 1373 K/0.01 s^-1.
基金the financial support of the National Key Research and Development Program of China(No.2017YFB0701801)the National Natural Science Foundation of China(No.51675300).
文摘In the present research,the dynamic recrystallization(DRX) behavior of a newly-developed Mg-Al-Zn-RE alloy with abundant secondphase particles during hot extrusion is investigated by coupling finite element(FE) and cellular automaton(CA) models.A two-dimensional CA model is developed to quantitatively and topologically evaluate the DRX process during deformation with constant forming conditions.Considering the fact that second-phase particles with various sizes extensively exist in the studied Mg-Al-Zn-RE magnesium alloy,models of DRX nucleation and grain growth velocity are modified.The coefficients of the modified CA model are calibrated by isothermal compression experiments of the magnesium alloy.Subsequently,the CA model is coupled with FE analysis to investigate the DRX behavior during the hot extrusions of the Mg-Al-Zn-RE alloy.The DRX behavior of the magnesium alloy at different stages and positions of extruded plates is simulated by the established model.Finer grains near the edge than in the inner of the plates result from higher strain and strain rate.The influence of extrusion conditions on microstructural evolution is explored.Under the employed forming conditions,average grain size decreases 28-62 times from as-cast and solution-treated to as-extruded state due to grain refinement by DRX.With increasing initial billet temperature or extrusion speed,average grain size increases.The finest grains are obtained at the initial billet temperature of 623 K and the extrusion speed of 7.83 mm/s.Low initial billet temperature or high extrusion speed benefits homogeneous grain distribution.The simulated results are in good agreement with experimental ones.