The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forgin...The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forging(MDF)experiments were carried out.The microstructure and mechanical properties of different regions(the center,middle and edge regions)in the MDFed alloys were systematically investigated,and the effect of LPSO phase on them was discussed.The results show that the alloys in different regions undergo significant grain refinement during the MDF process.Inhomogeneous microstructures with different degrees of dynamic recrystallization(DRX)are formed,resulting in microhardness heterogeneity.The alloy with the LPSO phase has higher microstructure homogeneity,a higher degree of recrystallization,and better comprehensive mechanical properties than the alloy without the LPSO phase.The furnace-cooled alloy after 18 passes of MDF has the best comprehensive mechanical properties,with an ultimate compressive strength of 488 MPa,yield strength of 258 MPa,and fracture strain of 21.2%.DRX behavior is closely related to the LPSO phase and deformation temperature.The kinked LPSO phase can act as a potential nucleation site for DRX grains,while the fragmented LPSO phase promotes DRX nucleation through the particle-stimulated nucleation mechanism.展开更多
The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate t...The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate that after MDF at a temperature of 350℃and strain rates of 0.1 and 0.01 s^(−1)(1-MDFed and 2-MDFed),the superplasticity of the alloy can be significantly improved.The elongations of the MDFed alloys exceed 400%under the strain rate of 6.06×10^(−4)s^(−1)and temperatures of 350,375,and 400℃,and reach the maximum values of 766%(1-MDFed)and 693%(2-MDFed)at 375℃.The grain boundary sliding of the MDFed alloy is sufficient,and the energy barrier of deformation decreases.Theβphase limits the grain growth and promotes dynamic recrystallization,maintaining the stability of the fine-grained structure during superplastic deformation.Several Y-rich phases nucleate in the high-strain region(i.e.,the final fracture region)at high temperatures,accelerating the fracture of the specimen.展开更多
The effect of forging passes on the refinement of high purity aluminum during multi-forging was investigated. The attention was focused on the structure uniformity due to deformation uniformity and the grain refinemen...The effect of forging passes on the refinement of high purity aluminum during multi-forging was investigated. The attention was focused on the structure uniformity due to deformation uniformity and the grain refinement limitation with very high strains. The results show that the fine grain zone in the center of sample expands gradually with the increase of forging passes. When the forging passes reach 6, an X-shape fine grain zone is initially formed. With a further increase of the passes, this X-shape zone tends to spread the whole sample. Limitation in the structural refinement is observed with increasing strains during multi-forging process at the room temperature. The grains size in the center is refined to a certain size （110 μm as forging passes reach 12, and there is no further grain refinement in the center with increasing the forging passes to 24. However, the size of the coarse grains near the surface is continuously decreased with increasing the forging passes to 24.展开更多
In this study,the Mg-7Gd-5Y-1Nd-0.5Zr alloy can reach a high ductility by the process of multi-directional forging,and the evolution of the microstructure,texture and the mechanical properties were discussed systemati...In this study,the Mg-7Gd-5Y-1Nd-0.5Zr alloy can reach a high ductility by the process of multi-directional forging,and the evolution of the microstructure,texture and the mechanical properties were discussed systematically.The results show that after the solutionized sample was multi-forged at 500℃,its grain size can be refined from 292 um to 58 um.As the forging temperature decreased,fine particles precipitated in the matrix.The volume fraction of the particles increased with the forging temperature decreasing,so the nucleation and growth of crystallization were strongly restricted.There was no recrystallization as the forging temperature fell to 410℃,and the severe deformed grains distributed as streamlines perpendicular to the final compression axis.The texture intensity decreased with increasing forging passes.The sample with best ductility was obtained after compressed at 470℃,with an elongation to failure of 21%at room temperature,which is increased by 200%,in comparison with that of the samples in solutionized condition.EBSD results revealed that the mean grain size was 15 um.Refined grains as well as the weakened texture were the key factors to its high ductility.展开更多
In this study,the mechanical properties and damping capacities of cast Mg-5.5 Zn-0.6 Zr(weight percent,ZK60)alloys have been simultaneously improved by a facile multi-directional forging(MDF)processing,and the mechani...In this study,the mechanical properties and damping capacities of cast Mg-5.5 Zn-0.6 Zr(weight percent,ZK60)alloys have been simultaneously improved by a facile multi-directional forging(MDF)processing,and the mechanisms of microstructure evolution and texture modification are systematically investigated.The activation of tension twinning occurs during the initial MDF stage,due to the coarse-grained structure of the as-cast alloy.With increasing MDF passes,the continuous dynamic recrystallization(CDRX)results in a fine equiaxed-grain structure.The typical non-basal texture is formed in the as-MDFed alloy for 6 passes,with the(0001)planes inclined 60°–70°to forged direction and 10°–20°to transverse direction,respectively.A good balance between the strength(~194.9 MPa)and ductility(~24.9%)has been achieved,which can be ascribed to the grain refinement,non-basal texture and fine precipitate particles.The damping capacity is remarkably improved after MDF processing,because the severe deformation increases the dislocation density,which effectively enlarges the sweep areas of mobile dislocations.展开更多
Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The result...Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The results show that the morphology of the β-Mg17Al12 phases during forging process dynamically precipitates and aging process（statically precipitation） exhibited granular and laminar shapes, respectively. During the MDF, the inhomogeneous dynamic precipitation of the β-Mg17Al12 phases results in the uniformity on grain size, which is fine in the area with many granular Mg17Al12 phases but the grain is still coarse where there is no Mg17Al12 phases. During the aging process, the morphology of newly formed β-Mg17Al12 phases depends on the structural character of the forged sample. The newly precipitated β-Mg17Al12 phases are coarse laminar and needle-like shape in area with coarse grain. While, the fine newly precipitated β-Mg17Al12 phases are fine granular and needle-like in the area with fine grain.展开更多
The void evolution of large-section plastic mold steel during multi-directional forging(MDF)was investigated using multiscale analysis.To simulate the forging process of the plastic mold steel(SDP1 steel)and realize m...The void evolution of large-section plastic mold steel during multi-directional forging(MDF)was investigated using multiscale analysis.To simulate the forging process of the plastic mold steel(SDP1 steel)and realize micro-void reconstruction in a representative volume element(RVE),MDF experiment and void-characteristic evaluation of the SDP1 steel were carried out.Traditional upsetting and stretching forging(TUSF)and MDF were simulated to comparatively analyze the evolution of temperature,effective stress,and effective strain.By embedding RVE with a micro-void and using boundary condition by point tracking into the forging process,the single-void evolution in TUSF and MDF was studied.The effect of void orientation on single-void evolution was also investigated.The multi-scale analysis revealed the following results.(1)Compared with TUSF,MDF achieved a higher efficiency in void closure.(2)The closing efficiency of the void increased with the increase in angle h(the angle between the Z and long axes of the void).(3)The closing efficiency increased with the increase in the orientation angle during the forging process.On the basis of the important role of the main stress in each forging step on the void closure,an integral formula of the main stress was proposed.When main compressive-stress integration reached-0.4,the closed state of the void could be accurately determined.展开更多
This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 ℃. For this purpose, wear test was conducted by d...This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 ℃. For this purpose, wear test was conducted by dry sliding pin-on-disk method on the initial and ultrafine grained samples using different stress magnitudes of 1, 1.5 and 2 MPa. The results showed that wear resistance of CP titanium increases after the first pass of MDF in comparison with the initial condition, irrespective of the applied normal stress. For example, the average wear rate of MDFed samples was decreased about 30% and 24%, after first pass at room temperature and 220 ℃, respectively. However, average wear rate of the samples processed by six MDF passes was reduced about 40% at lower normal loads;it was increased about 9% at higher ones as compared to the initial condition. It was also found that the dominated wear mechanisms were abrasive and delaminated at the lower stresses, while the delamination mechanism was intensified and a slight adhesion was observed during the higher applied normal loads.展开更多
Grain size and texture changes of magnesium alloy AZ31 were studied in multidirectional forging(MDF) under decreasing temperature conditions.MDF was carried out up to large cumulative strains of 4.8 with changing the ...Grain size and texture changes of magnesium alloy AZ31 were studied in multidirectional forging(MDF) under decreasing temperature conditions.MDF was carried out up to large cumulative strains of 4.8 with changing the loading direction during decrease in temperature from pass to pass.MDF can accelerate the uniform development of fine-grained structures and increase the plastic workability at low temperatures.As a result,the MDFed alloy shows excellent higher strength as well as moderate ductility at room temperature even at the grain size below 1μm.Superplastic flow takes place at 423 K and depends on the anisotropy of MDFed samples.The mechanisms of strain-induced fine-grained structure development and of the plastic deformation were discussed in detail.展开更多
This study systematically investigated the microstructure,mechanical properties,and corrosion behavior of an extruded Zn-0.2Mg alloy processed by multi-directional forging(MDF)at 100℃.The mean grain size was remarkab...This study systematically investigated the microstructure,mechanical properties,and corrosion behavior of an extruded Zn-0.2Mg alloy processed by multi-directional forging(MDF)at 100℃.The mean grain size was remarkably decreased from 17.2±0.5µm to 1.9±0.3µm,and 84.4%of the microstructure was occupied by grains of below 1µm in size after applying three MDF passes.Electron backscattered difraction examinations revealed that continuous dynamic recrystallization,progressive lattice rotation,and particle-stimulated nucleation mechanisms were recognized as contributing to microstructural evolution.Furthermore,transmission electron microscopy results showed that nanoparticles of Mg/Zn dynamically formed under high strain MDF,while the initial extrusion fber texture was altered to be<0001>parallel to the fnal forging axis.A synergistic efect of grain refnement,texture evolution,second-phase precipitates,and dislocation strengthening resulted in an increased ultimate tensile strength of 232±5 MPa after three MDF passes.However,this was accompanied by a reduction in the elongation(8±2.1%).Additionally,a high corrosion rate of 0.59 mm/year was measured for the experimental alloy fabricated by 3 MDF passes.In agreement with the latter,electrochemical impedance spectroscopy results indicated that the grain refnement improved the passivation kinetics of the oxide layer.展开更多
This review explores multi-directional functionally graded(MDFG)nanostructures,focusing on their material characteristics,modeling approaches,and mechanical behavior.It starts by classifying different types of functio...This review explores multi-directional functionally graded(MDFG)nanostructures,focusing on their material characteristics,modeling approaches,and mechanical behavior.It starts by classifying different types of functionally graded(FG)materials such as conventional,axial,bi-directional,and tri-directional,and the material distribution models like power-law,exponential,trigonometric,polynomial functions,etc.It also discusses the application of advanced size-dependent theories like Eringen’s nonlocal elasticity,nonlocal strain gradient,modified couple stress,and consistent couple stress theories,which are essential to predict the behavior of structures at small scales.The review covers the mechanical analysis of MDFG nanostructures in nanobeams,nanopipes,nanoplates,and nanoshells and their dynamic and static responses under different loading conditions.The effect of multi-directional material gradation on stiffness,stability and vibration is discussed.Moreover,the review highlights the need for more advanced analytical,semi-analytical,and numerical methods to solve the complex vibration problems ofMDFG nanostructures.It is evident that the continued development of these methods is crucial for the design,optimization,and real-world application of MDFG nanostructures in advanced engineering fields like aerospace,biomedicine,and micro/nanoelectromechanical systems(MEMS/NEMS).This study is a reference for researchers and engineers working in the domain of MDFG nanostructures.展开更多
The differences in damage values,residual stresses,microstructure and mechanical properties of Ti–6Al–4V alloy under hammer forging and press forging were explored through physical experiments and numerical simulati...The differences in damage values,residual stresses,microstructure and mechanical properties of Ti–6Al–4V alloy under hammer forging and press forging were explored through physical experiments and numerical simulations.The results showed that the temperature field and equivalent strain field of forgings under the hammer forging process were more uniformly distributed,resulting in smaller surface cracks and better residual stress distribution.The impact dynamic loading of hammer forging leads to forgings with higher dislocation densities,while the stabilized strain rate of press forging results in forgings exhibiting finer grain sizes.In this context,the yield strength enhancement of forgings by both processes was nearly identical,while the forgings demonstrated more excellent elongation under the hammer forging process.Additionally,increasing the number of blows in the hammer forging process or enhancing the loading rate in the press forging process can optimize the residual stress distribution of the forgings while simultaneously promoting dislocation multiplication and grain refinement.展开更多
Digital modeling and autonomous control of the die forging process are significant challenges in realizing high-quality intelli-gent forging of components.Using the die forging of AA2014 aluminum alloy as a case study...Digital modeling and autonomous control of the die forging process are significant challenges in realizing high-quality intelli-gent forging of components.Using the die forging of AA2014 aluminum alloy as a case study,a machine-learning-assisted method for di-gital modeling of the forging force and autonomous control in response to forging parameter disturbances was proposed.First,finite ele-ment simulations of the forging processes were conducted under varying friction factors,die temperatures,billet temperatures,and for-ging velocities,and the sample data,including process parameters and forging force under different forging strokes,were gathered.Pre-diction models for the forging force were established using the support vector regression algorithm.The prediction error of F_(f),that is,the forging force required to fill the die cavity fully,was as low as 4.1%.To further improve the prediction accuracy of the model for the ac-tual F_(f),two rounds of iterative forging experiments were conducted using the Bayesian optimization algorithm,and the prediction error of F_(f) in the forging experiments was reduced from 6.0%to 1.5%.Finally,the prediction model of F_(f) combined with a genetic algorithm was used to establish an autonomous optimization strategy for the forging velocity at each stage of the forging stroke,when the billet and die temperatures were disturbed,which realized the autonomous control in response to disturbances.In cases of−20 or−40℃ reductions in the die and billet temperatures,forging experiments conducted with the autonomous optimization strategy maintained the measured F_(f) around the target value of 180 t,with the relative error ranging from−1.3%to+3.1%.This work provides a reference for the study of di-gital modeling and autonomous optimization control of quality factors in the forging process.展开更多
Magnesium alloy thin-walled cylindrical components with the advantages of high specific stiffness and strength present broad prospect for the lightweight of aerospace components.However,poor formability resulting from...Magnesium alloy thin-walled cylindrical components with the advantages of high specific stiffness and strength present broad prospect for the lightweight of aerospace components.However,poor formability resulting from the hexagonal close-packed crystal structure in magnesium alloy puts forwards a great challenge for thin-walled cylindrical components fabrication,especially for extreme structure with the thicknesschanging web and the high thin-wall.In this research,an ZK61 magnesium alloy thin-walled cylindrical component was successfully fabricated by two-step forging,i.e.,the pre-forging and final-forging is mainly used for wed and thin-wall formation,respectively.Microstructure and mechanical properties at the core,middle and margin of the web and the thin-wall of the pre-forged and final-forged components are studied in detail.Due to the large strain-effectiveness and metal flow along the radial direction(RD),the grains of the web are all elongated along RD for the pre-forged component,where an increasingly elongated trend is found from the core to the margin of the wed.A relatively low recrystallized degree occurs during pre-forging,and the web at different positions are all with prismatic and pyramid textures.During finalforging,the microstructures of the web and the thin-wall are almost equiaxed due to the remarkable occurrence of dynamic recrystallization.Similarity,except for few basal texture of the thin-wall,only prismatic and pyramid textures are found for the final-forged component.Compared with the initial billet,an obviously improved mechanical isotropy is achieved during pre-forging,which is well-maintained during final-forging.展开更多
The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results sh...The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results showed that when tempered at 620–680°C,the main microstructure of the test steel was tempered sorbite,and the main microstructure of tempered steel changed to martensite at 700℃.At 700℃,the dislocation density increased and some retained austenite existed.With the tempering temperature increasing,the yield strength showed a decreasing trend,the formation of fresh martensite made the tensile strength first decrease and then increase slightly,the impact energy at−40℃increased first and then decreased,and the impact energy at 660℃had the maximum value.The precipitates of MC type were mainly(Mo,V,Ti)C.The test steel had excellent strength and toughness matching at 660℃tempering,the tensile strength at different cross section locations was above 750 MPa,the impact energy was above 200 J at−40℃,and the relative percentage reduction of area(ZH2/ZN2)was above 75%at hydrogen environment of 6.3 MPa.展开更多
This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace appl...This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace applications.The PCF process,utilizing cryogenic deformation,significantly refines the coarse grains at the surface of the forgings,resulting in a finer and more uniform microstructure,thereby effectively addressing the issue of surface coarse grains associated with traditional methods.The findings indicate that the PCF process can accumulate higher stored energy,facilitating static recrystallization(SRX)during subsequent heat treatment and enhancing the microstructural uniformity.Utilizing various analytical techniques,including optical microscopy(OM),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM).This study reveals the superiority of the PCF process in terms of strain accumulation,dislocation density,and grain refinement.In conclusion,this method offers advantages in enhancing the performance and microstructural uniformity of 7050 aluminum forgings,presenting new opportunities for applications in the aluminum forging industry.展开更多
To explore ambient strengthening and high temperature ductility,a combined forming approach of multidirectional forging and asymmetric rolling was proposed.A novel multicomponent ultralight Mg-3.11Li-2.31Al-1.95Sn-0.9...To explore ambient strengthening and high temperature ductility,a combined forming approach of multidirectional forging and asymmetric rolling was proposed.A novel multicomponent ultralight Mg-3.11Li-2.31Al-1.95Sn-0.94Y-0.45Er alloy was fabricated.The microstructural evolution and mechanical properties were investigated by microstructural characterization and tensile test.The combined forming results in remarkable grain refinement.The ultimate tensile strength and elongation of(255±7)MPa and 24.9%,respectively,were obtained at room temperature.The contribution of various strengthening mechanisms of the rolled alloy was obtained.Microstructural examination revealed the occurrence of dynamic recrystallization at 473-573 K and dynamic grain growth at 573-623 K.The maximum elongation of 293.9%was demonstrated at 623 K and 5×10^(-4)s^(-1).The dominate deformation mechanism at elevated temperatures is dislocation viscous glide.展开更多
Today,I want to share how international standards can forge trust and fuel innovation,laying the foundation for a future where AI benefits everyone,everywhere.First,AI standards,developed jointly by ISO and IEC-the In...Today,I want to share how international standards can forge trust and fuel innovation,laying the foundation for a future where AI benefits everyone,everywhere.First,AI standards,developed jointly by ISO and IEC-the International Electrotechnical Commission-help build global trust and enable responsible innovation by bringing clarity and coherence to an ever-changing AI landscape.As developments in AI continue to emerge at speed,regulation is struggling to keep up and the proliferation of competing standards has created confusion rather than clarity.ISO and our partner IEC are addressing this challenge through the work of our expert committee on AI,SC 42,which takes a holistic,cohesive approach to AI standardization.展开更多
In-situ TiB_(2)/Al–Cu composite was processed by multidirectional forging(MDF)for six passes.The microstructure evolution of the forged workpiece was examined across various regions.The mechanical properties of the a...In-situ TiB_(2)/Al–Cu composite was processed by multidirectional forging(MDF)for six passes.The microstructure evolution of the forged workpiece was examined across various regions.The mechanical properties of the as-cast and MDFed composites were compared,and their strengthening mechanisms were analyzed.Results indicate that the grain refinement achieved through the MDF process is mainly due to the subdivision of the original grains through mechanical geometric fragmentation and the occurrence of dynamic recrystallization(DRX).DRX grains are formed through discontinuous DRX,continuous DRX,and recrystallization induced by particle-stimulated nucleation.A rise in accumulated equivalent strain(Σ?ε)results in finerα-Al grains and a more uniform distribution of TiB_(2)particles,which enhance the Vickers hardness of the composite.In addition,the tensile properties of the MDFed composite significantly improve compared with those of the as-cast composites,with ultimate tensile strength and yield strength increasing by 51.2%and 54%,respectively.This enhancement is primarily due to grain refinement strengthening and dislocation strengthening achieved by the MDF process.展开更多
The microstructure and mechanical properties of the Ti-5Al-5Mo-5V-1Cr-1Fe(Ti-55511)alloy under different strains were investigated through the design of step-shaped die forging.The results indicate that continuous dyn...The microstructure and mechanical properties of the Ti-5Al-5Mo-5V-1Cr-1Fe(Ti-55511)alloy under different strains were investigated through the design of step-shaped die forging.The results indicate that continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX)occur in the high strain region.The orientation of the grains produced by CDRX is random and does not weaken the fiber texture.<100>-oriented grains expand gradually with increasing strain,thereby enhancing the strength of{100}texture.Significant anisotropic mechanical properties are observed in the large strain region and analyzed through in-situ tensile experiments.When the loading direction is parallel to the longitudinal(L)direction,strain concentration is observed near the dynamically recrystallized(DRXed)grains and inside grains oriented along<100>,leading to crack initiation.Furthermore,the small angle between the loading direction and the c-axis hinders the activation of prismatic and basal slip,thereby enhancing the strength.When the loading direction is parallel to the short transverse(ST)direction,cracks are initiated not only within grains oriented along<100>,but also at the grain boundaries.Regarding impact toughness,the elongatedβgrains in the L direction enhance the resistance to crack propagation.展开更多
基金the financial supports from the Key Research and Development Program of Hunan Province,China(No.2023GK2020)。
文摘The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forging(MDF)experiments were carried out.The microstructure and mechanical properties of different regions(the center,middle and edge regions)in the MDFed alloys were systematically investigated,and the effect of LPSO phase on them was discussed.The results show that the alloys in different regions undergo significant grain refinement during the MDF process.Inhomogeneous microstructures with different degrees of dynamic recrystallization(DRX)are formed,resulting in microhardness heterogeneity.The alloy with the LPSO phase has higher microstructure homogeneity,a higher degree of recrystallization,and better comprehensive mechanical properties than the alloy without the LPSO phase.The furnace-cooled alloy after 18 passes of MDF has the best comprehensive mechanical properties,with an ultimate compressive strength of 488 MPa,yield strength of 258 MPa,and fracture strain of 21.2%.DRX behavior is closely related to the LPSO phase and deformation temperature.The kinked LPSO phase can act as a potential nucleation site for DRX grains,while the fragmented LPSO phase promotes DRX nucleation through the particle-stimulated nucleation mechanism.
基金supported by the National Natural Science Foundation of China(No.52127808)。
文摘The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate that after MDF at a temperature of 350℃and strain rates of 0.1 and 0.01 s^(−1)(1-MDFed and 2-MDFed),the superplasticity of the alloy can be significantly improved.The elongations of the MDFed alloys exceed 400%under the strain rate of 6.06×10^(−4)s^(−1)and temperatures of 350,375,and 400℃,and reach the maximum values of 766%(1-MDFed)and 693%(2-MDFed)at 375℃.The grain boundary sliding of the MDFed alloy is sufficient,and the energy barrier of deformation decreases.Theβphase limits the grain growth and promotes dynamic recrystallization,maintaining the stability of the fine-grained structure during superplastic deformation.Several Y-rich phases nucleate in the high-strain region(i.e.,the final fracture region)at high temperatures,accelerating the fracture of the specimen.
基金Projects(51204053,51074048,51204048)supported by the National Natural Science Foundation of ChinaProject(20110491518)supported by China Postdoctoral Science FoundationProject(2012CB619506)supported by the National Basic Research Program of China
文摘The effect of forging passes on the refinement of high purity aluminum during multi-forging was investigated. The attention was focused on the structure uniformity due to deformation uniformity and the grain refinement limitation with very high strains. The results show that the fine grain zone in the center of sample expands gradually with the increase of forging passes. When the forging passes reach 6, an X-shape fine grain zone is initially formed. With a further increase of the passes, this X-shape zone tends to spread the whole sample. Limitation in the structural refinement is observed with increasing strains during multi-forging process at the room temperature. The grains size in the center is refined to a certain size （110 μm as forging passes reach 12, and there is no further grain refinement in the center with increasing the forging passes to 24. However, the size of the coarse grains near the surface is continuously decreased with increasing the forging passes to 24.
基金Project supported by the National Foundation of Natural Science(No.51105350 and No.51301173)project 973(No.2013CB632202)of National Ministry of Science and Technology+1 种基金This work was funded by the National Basic Research Program of China(973 Program)through project No.2013CB632202National Natural Science Foundation of China(NSFC)through projects No.51105350 and No.51301173,respectively.
文摘In this study,the Mg-7Gd-5Y-1Nd-0.5Zr alloy can reach a high ductility by the process of multi-directional forging,and the evolution of the microstructure,texture and the mechanical properties were discussed systematically.The results show that after the solutionized sample was multi-forged at 500℃,its grain size can be refined from 292 um to 58 um.As the forging temperature decreased,fine particles precipitated in the matrix.The volume fraction of the particles increased with the forging temperature decreasing,so the nucleation and growth of crystallization were strongly restricted.There was no recrystallization as the forging temperature fell to 410℃,and the severe deformed grains distributed as streamlines perpendicular to the final compression axis.The texture intensity decreased with increasing forging passes.The sample with best ductility was obtained after compressed at 470℃,with an elongation to failure of 21%at room temperature,which is increased by 200%,in comparison with that of the samples in solutionized condition.EBSD results revealed that the mean grain size was 15 um.Refined grains as well as the weakened texture were the key factors to its high ductility.
基金financially supported by the National Natural Science Foundation of China(No.51771178)the Shanxi Provincial Key Research and Development Project(Nos.2020KWZ-007,2018ZDXM-GY-149)the Natural Science Foundation of Jilin Province(No.20180414016GH)。
文摘In this study,the mechanical properties and damping capacities of cast Mg-5.5 Zn-0.6 Zr(weight percent,ZK60)alloys have been simultaneously improved by a facile multi-directional forging(MDF)processing,and the mechanisms of microstructure evolution and texture modification are systematically investigated.The activation of tension twinning occurs during the initial MDF stage,due to the coarse-grained structure of the as-cast alloy.With increasing MDF passes,the continuous dynamic recrystallization(CDRX)results in a fine equiaxed-grain structure.The typical non-basal texture is formed in the as-MDFed alloy for 6 passes,with the(0001)planes inclined 60°–70°to forged direction and 10°–20°to transverse direction,respectively.A good balance between the strength(~194.9 MPa)and ductility(~24.9%)has been achieved,which can be ascribed to the grain refinement,non-basal texture and fine precipitate particles.The damping capacity is remarkably improved after MDF processing,because the severe deformation increases the dislocation density,which effectively enlarges the sweep areas of mobile dislocations.
基金supported by the National Natural Science Foundation of China (Nos.51204053,51674078 and 51374067)the Fundamental Research Fund for Central Universities (Nos.N160913002,N130409005 and N130209001)A Project supported by Scientific Research Fund of Liaoning Province (No.2015022003)
文摘Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The results show that the morphology of the β-Mg17Al12 phases during forging process dynamically precipitates and aging process（statically precipitation） exhibited granular and laminar shapes, respectively. During the MDF, the inhomogeneous dynamic precipitation of the β-Mg17Al12 phases results in the uniformity on grain size, which is fine in the area with many granular Mg17Al12 phases but the grain is still coarse where there is no Mg17Al12 phases. During the aging process, the morphology of newly formed β-Mg17Al12 phases depends on the structural character of the forged sample. The newly precipitated β-Mg17Al12 phases are coarse laminar and needle-like shape in area with coarse grain. While, the fine newly precipitated β-Mg17Al12 phases are fine granular and needle-like in the area with fine grain.
基金This work is supported by National KeyR&D Program of China(Gran Nt oS.2016YFB0300400 and 2016YFB0300404).
文摘The void evolution of large-section plastic mold steel during multi-directional forging(MDF)was investigated using multiscale analysis.To simulate the forging process of the plastic mold steel(SDP1 steel)and realize micro-void reconstruction in a representative volume element(RVE),MDF experiment and void-characteristic evaluation of the SDP1 steel were carried out.Traditional upsetting and stretching forging(TUSF)and MDF were simulated to comparatively analyze the evolution of temperature,effective stress,and effective strain.By embedding RVE with a micro-void and using boundary condition by point tracking into the forging process,the single-void evolution in TUSF and MDF was studied.The effect of void orientation on single-void evolution was also investigated.The multi-scale analysis revealed the following results.(1)Compared with TUSF,MDF achieved a higher efficiency in void closure.(2)The closing efficiency of the void increased with the increase in angle h(the angle between the Z and long axes of the void).(3)The closing efficiency increased with the increase in the orientation angle during the forging process.On the basis of the important role of the main stress in each forging step on the void closure,an integral formula of the main stress was proposed.When main compressive-stress integration reached-0.4,the closed state of the void could be accurately determined.
基金supported financially by the Iran National Science Foundation (No.94809610)the Czech Science Foundation Project (No.GB 14-36566G)
文摘This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 ℃. For this purpose, wear test was conducted by dry sliding pin-on-disk method on the initial and ultrafine grained samples using different stress magnitudes of 1, 1.5 and 2 MPa. The results showed that wear resistance of CP titanium increases after the first pass of MDF in comparison with the initial condition, irrespective of the applied normal stress. For example, the average wear rate of MDFed samples was decreased about 30% and 24%, after first pass at room temperature and 220 ℃, respectively. However, average wear rate of the samples processed by six MDF passes was reduced about 40% at lower normal loads;it was increased about 9% at higher ones as compared to the initial condition. It was also found that the dominated wear mechanisms were abrasive and delaminated at the lower stresses, while the delamination mechanism was intensified and a slight adhesion was observed during the higher applied normal loads.
文摘Grain size and texture changes of magnesium alloy AZ31 were studied in multidirectional forging(MDF) under decreasing temperature conditions.MDF was carried out up to large cumulative strains of 4.8 with changing the loading direction during decrease in temperature from pass to pass.MDF can accelerate the uniform development of fine-grained structures and increase the plastic workability at low temperatures.As a result,the MDFed alloy shows excellent higher strength as well as moderate ductility at room temperature even at the grain size below 1μm.Superplastic flow takes place at 423 K and depends on the anisotropy of MDFed samples.The mechanisms of strain-induced fine-grained structure development and of the plastic deformation were discussed in detail.
文摘This study systematically investigated the microstructure,mechanical properties,and corrosion behavior of an extruded Zn-0.2Mg alloy processed by multi-directional forging(MDF)at 100℃.The mean grain size was remarkably decreased from 17.2±0.5µm to 1.9±0.3µm,and 84.4%of the microstructure was occupied by grains of below 1µm in size after applying three MDF passes.Electron backscattered difraction examinations revealed that continuous dynamic recrystallization,progressive lattice rotation,and particle-stimulated nucleation mechanisms were recognized as contributing to microstructural evolution.Furthermore,transmission electron microscopy results showed that nanoparticles of Mg/Zn dynamically formed under high strain MDF,while the initial extrusion fber texture was altered to be<0001>parallel to the fnal forging axis.A synergistic efect of grain refnement,texture evolution,second-phase precipitates,and dislocation strengthening resulted in an increased ultimate tensile strength of 232±5 MPa after three MDF passes.However,this was accompanied by a reduction in the elongation(8±2.1%).Additionally,a high corrosion rate of 0.59 mm/year was measured for the experimental alloy fabricated by 3 MDF passes.In agreement with the latter,electrochemical impedance spectroscopy results indicated that the grain refnement improved the passivation kinetics of the oxide layer.
文摘This review explores multi-directional functionally graded(MDFG)nanostructures,focusing on their material characteristics,modeling approaches,and mechanical behavior.It starts by classifying different types of functionally graded(FG)materials such as conventional,axial,bi-directional,and tri-directional,and the material distribution models like power-law,exponential,trigonometric,polynomial functions,etc.It also discusses the application of advanced size-dependent theories like Eringen’s nonlocal elasticity,nonlocal strain gradient,modified couple stress,and consistent couple stress theories,which are essential to predict the behavior of structures at small scales.The review covers the mechanical analysis of MDFG nanostructures in nanobeams,nanopipes,nanoplates,and nanoshells and their dynamic and static responses under different loading conditions.The effect of multi-directional material gradation on stiffness,stability and vibration is discussed.Moreover,the review highlights the need for more advanced analytical,semi-analytical,and numerical methods to solve the complex vibration problems ofMDFG nanostructures.It is evident that the continued development of these methods is crucial for the design,optimization,and real-world application of MDFG nanostructures in advanced engineering fields like aerospace,biomedicine,and micro/nanoelectromechanical systems(MEMS/NEMS).This study is a reference for researchers and engineers working in the domain of MDFG nanostructures.
基金supported by the National Natural Science Foundation of China(Nos.52175145 and 51775427)the Key Research and Development Projects of Shaanxi Province(Grant No.2023-YBGY-335).
文摘The differences in damage values,residual stresses,microstructure and mechanical properties of Ti–6Al–4V alloy under hammer forging and press forging were explored through physical experiments and numerical simulations.The results showed that the temperature field and equivalent strain field of forgings under the hammer forging process were more uniformly distributed,resulting in smaller surface cracks and better residual stress distribution.The impact dynamic loading of hammer forging leads to forgings with higher dislocation densities,while the stabilized strain rate of press forging results in forgings exhibiting finer grain sizes.In this context,the yield strength enhancement of forgings by both processes was nearly identical,while the forgings demonstrated more excellent elongation under the hammer forging process.Additionally,increasing the number of blows in the hammer forging process or enhancing the loading rate in the press forging process can optimize the residual stress distribution of the forgings while simultaneously promoting dislocation multiplication and grain refinement.
基金financially supported by the National Key Research and Development Program of China(No.2022YFB3706901)the National Natural Science Foundation of China(No.52090041)the Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC 001).
文摘Digital modeling and autonomous control of the die forging process are significant challenges in realizing high-quality intelli-gent forging of components.Using the die forging of AA2014 aluminum alloy as a case study,a machine-learning-assisted method for di-gital modeling of the forging force and autonomous control in response to forging parameter disturbances was proposed.First,finite ele-ment simulations of the forging processes were conducted under varying friction factors,die temperatures,billet temperatures,and for-ging velocities,and the sample data,including process parameters and forging force under different forging strokes,were gathered.Pre-diction models for the forging force were established using the support vector regression algorithm.The prediction error of F_(f),that is,the forging force required to fill the die cavity fully,was as low as 4.1%.To further improve the prediction accuracy of the model for the ac-tual F_(f),two rounds of iterative forging experiments were conducted using the Bayesian optimization algorithm,and the prediction error of F_(f) in the forging experiments was reduced from 6.0%to 1.5%.Finally,the prediction model of F_(f) combined with a genetic algorithm was used to establish an autonomous optimization strategy for the forging velocity at each stage of the forging stroke,when the billet and die temperatures were disturbed,which realized the autonomous control in response to disturbances.In cases of−20 or−40℃ reductions in the die and billet temperatures,forging experiments conducted with the autonomous optimization strategy maintained the measured F_(f) around the target value of 180 t,with the relative error ranging from−1.3%to+3.1%.This work provides a reference for the study of di-gital modeling and autonomous optimization control of quality factors in the forging process.
基金supported by the National Natural Science Foundation of China(No.52405408,No.U21A20131,No.U2037204,No.52422510)the Natural Science Foundation of Hubei Province(No.2023AFB116)+1 种基金the State Key Laboratory of Materials Processing and Die&Mould TechnologyHuazhong University of Science and Technology(No.P2022-005)。
文摘Magnesium alloy thin-walled cylindrical components with the advantages of high specific stiffness and strength present broad prospect for the lightweight of aerospace components.However,poor formability resulting from the hexagonal close-packed crystal structure in magnesium alloy puts forwards a great challenge for thin-walled cylindrical components fabrication,especially for extreme structure with the thicknesschanging web and the high thin-wall.In this research,an ZK61 magnesium alloy thin-walled cylindrical component was successfully fabricated by two-step forging,i.e.,the pre-forging and final-forging is mainly used for wed and thin-wall formation,respectively.Microstructure and mechanical properties at the core,middle and margin of the web and the thin-wall of the pre-forged and final-forged components are studied in detail.Due to the large strain-effectiveness and metal flow along the radial direction(RD),the grains of the web are all elongated along RD for the pre-forged component,where an increasingly elongated trend is found from the core to the margin of the wed.A relatively low recrystallized degree occurs during pre-forging,and the web at different positions are all with prismatic and pyramid textures.During finalforging,the microstructures of the web and the thin-wall are almost equiaxed due to the remarkable occurrence of dynamic recrystallization.Similarity,except for few basal texture of the thin-wall,only prismatic and pyramid textures are found for the final-forged component.Compared with the initial billet,an obviously improved mechanical isotropy is achieved during pre-forging,which is well-maintained during final-forging.
基金supported by the National Key research and Development Program of China(No.2022YFB4003001).
文摘The mechanical properties,microstructure and second phase precipitation behavior of flange forgings for high-pressure hydrogen storage vessels at different tempering temperatures(620–700℃)were studied.The results showed that when tempered at 620–680°C,the main microstructure of the test steel was tempered sorbite,and the main microstructure of tempered steel changed to martensite at 700℃.At 700℃,the dislocation density increased and some retained austenite existed.With the tempering temperature increasing,the yield strength showed a decreasing trend,the formation of fresh martensite made the tensile strength first decrease and then increase slightly,the impact energy at−40℃increased first and then decreased,and the impact energy at 660℃had the maximum value.The precipitates of MC type were mainly(Mo,V,Ti)C.The test steel had excellent strength and toughness matching at 660℃tempering,the tensile strength at different cross section locations was above 750 MPa,the impact energy was above 200 J at−40℃,and the relative percentage reduction of area(ZH2/ZN2)was above 75%at hydrogen environment of 6.3 MPa.
基金Project(2021GK1040) supported by the Major Projects of Scientific and Technology Innovation of Hunan Province,ChinaProjects(52375398,52171018) supported by the National Natural Science Foundation of China+1 种基金Project(Kfkt2023-09) supported by the Open Research Fund of State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University,ChinaProject(E2021203059) supported by the Natural Science Foundation of Hebei Province,China。
文摘This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace applications.The PCF process,utilizing cryogenic deformation,significantly refines the coarse grains at the surface of the forgings,resulting in a finer and more uniform microstructure,thereby effectively addressing the issue of surface coarse grains associated with traditional methods.The findings indicate that the PCF process can accumulate higher stored energy,facilitating static recrystallization(SRX)during subsequent heat treatment and enhancing the microstructural uniformity.Utilizing various analytical techniques,including optical microscopy(OM),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM).This study reveals the superiority of the PCF process in terms of strain accumulation,dislocation density,and grain refinement.In conclusion,this method offers advantages in enhancing the performance and microstructural uniformity of 7050 aluminum forgings,presenting new opportunities for applications in the aluminum forging industry.
基金supported by the National Natural Science Foundation of China(No.51334006)。
文摘To explore ambient strengthening and high temperature ductility,a combined forming approach of multidirectional forging and asymmetric rolling was proposed.A novel multicomponent ultralight Mg-3.11Li-2.31Al-1.95Sn-0.94Y-0.45Er alloy was fabricated.The microstructural evolution and mechanical properties were investigated by microstructural characterization and tensile test.The combined forming results in remarkable grain refinement.The ultimate tensile strength and elongation of(255±7)MPa and 24.9%,respectively,were obtained at room temperature.The contribution of various strengthening mechanisms of the rolled alloy was obtained.Microstructural examination revealed the occurrence of dynamic recrystallization at 473-573 K and dynamic grain growth at 573-623 K.The maximum elongation of 293.9%was demonstrated at 623 K and 5×10^(-4)s^(-1).The dominate deformation mechanism at elevated temperatures is dislocation viscous glide.
文摘Today,I want to share how international standards can forge trust and fuel innovation,laying the foundation for a future where AI benefits everyone,everywhere.First,AI standards,developed jointly by ISO and IEC-the International Electrotechnical Commission-help build global trust and enable responsible innovation by bringing clarity and coherence to an ever-changing AI landscape.As developments in AI continue to emerge at speed,regulation is struggling to keep up and the proliferation of competing standards has created confusion rather than clarity.ISO and our partner IEC are addressing this challenge through the work of our expert committee on AI,SC 42,which takes a holistic,cohesive approach to AI standardization.
基金supported by the Key Program for International Cooperation of the Ministry of Science and Technology,China(No.ZCGX2022001L)。
文摘In-situ TiB_(2)/Al–Cu composite was processed by multidirectional forging(MDF)for six passes.The microstructure evolution of the forged workpiece was examined across various regions.The mechanical properties of the as-cast and MDFed composites were compared,and their strengthening mechanisms were analyzed.Results indicate that the grain refinement achieved through the MDF process is mainly due to the subdivision of the original grains through mechanical geometric fragmentation and the occurrence of dynamic recrystallization(DRX).DRX grains are formed through discontinuous DRX,continuous DRX,and recrystallization induced by particle-stimulated nucleation.A rise in accumulated equivalent strain(Σ?ε)results in finerα-Al grains and a more uniform distribution of TiB_(2)particles,which enhance the Vickers hardness of the composite.In addition,the tensile properties of the MDFed composite significantly improve compared with those of the as-cast composites,with ultimate tensile strength and yield strength increasing by 51.2%and 54%,respectively.This enhancement is primarily due to grain refinement strengthening and dislocation strengthening achieved by the MDF process.
基金funded by Department of Science and Technology of Sichuan Province,China(No.2022YFG0102)the China Postdoctoral Science Foundation(No.2023M733314).
文摘The microstructure and mechanical properties of the Ti-5Al-5Mo-5V-1Cr-1Fe(Ti-55511)alloy under different strains were investigated through the design of step-shaped die forging.The results indicate that continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX)occur in the high strain region.The orientation of the grains produced by CDRX is random and does not weaken the fiber texture.<100>-oriented grains expand gradually with increasing strain,thereby enhancing the strength of{100}texture.Significant anisotropic mechanical properties are observed in the large strain region and analyzed through in-situ tensile experiments.When the loading direction is parallel to the longitudinal(L)direction,strain concentration is observed near the dynamically recrystallized(DRXed)grains and inside grains oriented along<100>,leading to crack initiation.Furthermore,the small angle between the loading direction and the c-axis hinders the activation of prismatic and basal slip,thereby enhancing the strength.When the loading direction is parallel to the short transverse(ST)direction,cracks are initiated not only within grains oriented along<100>,but also at the grain boundaries.Regarding impact toughness,the elongatedβgrains in the L direction enhance the resistance to crack propagation.
