Springback is considered to be one of the most important problems in aluminum sheet stamp forming,leading to deviation from the designed target shape and assembly defects.In this study,a springback simulation model ba...Springback is considered to be one of the most important problems in aluminum sheet stamp forming,leading to deviation from the designed target shape and assembly defects.In this study,a springback simulation model based on the benchmark of a Jaguar Land Rover aluminum panel is established.We embed several elastoplastic constitutive models(Barlat's 89,Barlat's YLD2000,Yoshida-Uemori(YU) + Barlat's 89,and YU +Barlat's YLD2000) in the finite element model,in order to discuss the influence of the constitutive model selection on springback prediction in aluminum sheet forming.展开更多
The flow stress feature of aluminum sheet used for pressure can during plastic deformation at elevated temperature was studied by isothermal compression test using Gleeble 1 500 dynamic materials testing machine. The ...The flow stress feature of aluminum sheet used for pressure can during plastic deformation at elevated temperature was studied by isothermal compression test using Gleeble 1 500 dynamic materials testing machine. The experimental results show that the steady state deformation is remarkable when the material is deformed in the temperature range of 350～500 ℃ at strain rates within the range of 10 -2 ～10.0 s -1 . The material is sensitive to positive strain rate. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate, and an Arrhenius relationship with the temperature. Semi empirical constitutive equations of the flow stress are derived from all experimental data for tested material during plastic deformation at elevated temperature by polyelement linear regression analysis. [展开更多
The isothermal compression test at elevated temperature was carried out for aluminum sheets prepared by different melt-treatment methods with aid of dynamic hot/mechanical simulation experimental technology. The mater...The isothermal compression test at elevated temperature was carried out for aluminum sheets prepared by different melt-treatment methods with aid of dynamic hot/mechanical simulation experimental technology. The material constants of hot deformation have been solved by multivariate regression directly. Influence of metallurgy factors on the constants was analyzed. The results show that at some strain, the relationship of sheets’ flow stress with deformation temperature and strain rate can be expressed more suitably with Arrhenius equation modified by hyperbolic sine function. Structure factor A1, stress-level coefficient α, strain rate sensibility exponent m and deformation activation energy Q all increase with increment of strain, while stress exponent n decreases gradually. The bigger α value or the smaller n value is, the more obvious the dynamic softening is, but the α value will increase for the metallurgy defects existing in the sheets. Influence of melt-treatment on Q depends upon the synthesis effect of all kinds of metallurgy defects. The Q and n values of the sheet prepared by high-efficient melt-treatment are the least, while the m value is the biggest, and the sheet can deform easily and evenly.展开更多
The effects of an external DC(direct current)electric field on recrystallization texture evolution in the cold-rolled aluminum sheets with 99.99%purity were investigated by means of X-ray diffraction techniques.The co...The effects of an external DC(direct current)electric field on recrystallization texture evolution in the cold-rolled aluminum sheets with 99.99%purity were investigated by means of X-ray diffraction techniques.The cold-rolled high-purity aluminum sheets were annealed for 60 min at 200,300 and 400℃,respectively with and without an external DC electric field of 800 V/mm.The results show that with DC electric field,the recrystallization cube texture is strengthened at the stage of grain growth. Possible reason for the strengthening of the recrystallization cube texture with the applied electric field may be attributed to both selected nucleation and selected growth of cube oriented crystal nuclei.展开更多
The texture of a rolled AA3104 aluminum sheet was measured by the X-ray transmission method. The Lankford values or r values (ratio of plastic strain) and yield strengths in directions of 0, 15, 30, 45, 60, 75, and 90...The texture of a rolled AA3104 aluminum sheet was measured by the X-ray transmission method. The Lankford values or r values (ratio of plastic strain) and yield strengths in directions of 0, 15, 30, 45, 60, 75, and 90° to RD (rolling direction) of the sheet were tested during tensile loading at a strain of 2%. r values were predicted by the Sachs model and the reaction stress model in con- sideration of the measured texture. The simulated results indicate that r values calculated by the Sachs model are more exactly ap- proaching with the experimental values on the whole than those predicted by the reaction stress model. The deformation behavior of the AA3104 aluminum sheet reveals characteristic predicted by the Sachs model, which should be resulted from the sheet geometry different from bulk material as well as the low tensile deformation degree.展开更多
Aluminum alloy sheets are used more and more to manufacture auto panels. Because the friction behavior is very complicated, it is necessary to study the friction during the aluminum sheet warm forming process. The aut...Aluminum alloy sheets are used more and more to manufacture auto panels. Because the friction behavior is very complicated, it is necessary to study the friction during the aluminum sheet warm forming process. The author has designed a new probe sensor based on an online tribotest method which directly measures friction coefficient in the forming process. Experiments of cup drawing have been conducted and the friction coefficients under different forming conditions have been measured. The results indicate that the forming parameters, such as forming temperature, blankholding force and lubrication status have great effect upon the friction coefficient.展开更多
An approximate macroscopic yield criterion for anisotropic porous sheet metals is adopted in a failure prediction methodology that can be used to investigate the failure of sheet metals under forming operations. This ...An approximate macroscopic yield criterion for anisotropic porous sheet metals is adopted in a failure prediction methodology that can be used to investigate the failure of sheet metals under forming operations. This failure prediction methodology is developed based on the Marciniak-Kuczynski approach by assuming a slightly higher void volume fraction inside randomly oriented imperfecte analysis. Here, a nonproportional deformation history including relative rotation of principal stretch directions is identified in a selected critical element of an aluminum sheet from a FEM fender forming simulation. Based on the failure prediction methodology, the failure of the critical sheet element is investigated under the non-proportional deformation history. The results show that thiven non-proportional deformation history.展开更多
The application of four widely used anisotropic yield criteria,namely,Hill'48,Hill'90,Barlat'89,and Yld2000,on the formability analysis of an automobile aluminum sheet is investigated. The applicability an...The application of four widely used anisotropic yield criteria,namely,Hill'48,Hill'90,Barlat'89,and Yld2000,on the formability analysis of an automobile aluminum sheet is investigated. The applicability and reliability of these four yield criteria are identified on the basis of uniaxial tensile and stamping tests of an aluminum covering panel by embedding the specimen in the corresponding finite element models. Results show that the strain distribution and safety margin of the aluminum sheet after stamping can be predicted with a high accuracy by applying Yld2000 compared to those subjected to the three other yield criteria. The significant effects of the anisotropic plastic characteristics of the aluminum sheet on stamping are discussed by applying the advanced simulation technology.展开更多
The micro crack of aluminum sheet during cold rolling lubricated with emulsions is investigated. Experi-ments show that micro cracks occur after cold rolling process and this is attributed to various parameters, for i...The micro crack of aluminum sheet during cold rolling lubricated with emulsions is investigated. Experi-ments show that micro cracks occur after cold rolling process and this is attributed to various parameters, for instance, the thin oxide film formed at the sheet surface. The micro crack spacing thus becomes an important parameter which deserves more concerns. The aspect ratio of these micro cracks is then analyzed theoreti-cally, which takes into consideration of the oxide fracture process. The good agreement between the obser-vations and the theoretical predictions validates the analysis. The approach can shed some new lights on the mechanical process of aluminium sheet during cold rolling.展开更多
The behavior of flow stress of Al sheets used for pressure can prepared by different melt-treat- ment during plastic deformation at elevated temperature was studied by isothermal compression test using Gleeble1500 dyn...The behavior of flow stress of Al sheets used for pressure can prepared by different melt-treat- ment during plastic deformation at elevated temperature was studied by isothermal compression test using Gleeble1500 dynamic hot-simulation testing machine. The results show that the Al sheets possess the remarkable characteristic of steady state flow stress when they are deformed in the temperature range of 350-500°C at strain rates within the range of 0.01-10.0s-1. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate, and an Arrhenius relationship with the temperature, which implies that the process of plastic deformation at ele- vated temperature for this material is thermally activated. Compared with the Al pieces prepared by no or conventional melt-treatment, hot deformation activation energy of Al sheets prepared by high-efficient melt-treatment is the smallest (Q = 168.0kJ/mol), which reveals that the hot work- ing formability of this material is very better, and has directly to do with the effective improve- ment of its metallurgical quality.展开更多
Aluminum sheets were polished to reduce ruggedness and then textured in varying acid-ethanol concentration etchant to form pores. The textured surface was characterized structurally by using X-ray diffraction (XRD) wh...Aluminum sheets were polished to reduce ruggedness and then textured in varying acid-ethanol concentration etchant to form pores. The textured surface was characterized structurally by using X-ray diffraction (XRD) which revealed aluminum crystallographic planes (1 1 1), (2 0 0), (2 2 0) and (3 1 1). Its morphology was studied by using energy dispersive X-ray (EDX) and scanning electron microscope (SEM) that confirmed purity of aluminum sheet to be 99.66% at. Reflectance of textured and plain aluminum sheet was analyzed by spectrophotometric measurements which showed that texturing reduced the reflectance of the polished surface by 26% in the UV-VIS-NIR spectrum of solar radiation. With reduced reflectance of the textured aluminum sheet, it was applicable for solar radiation absorption.展开更多
The formation process of copper type rolling texture in f.c.c. Metals was simulated based on a deformation modelconsidering internal reaction stresses induced by the neighboring matrix as well as external shear stress...The formation process of copper type rolling texture in f.c.c. Metals was simulated based on a deformation modelconsidering internal reaction stresses induced by the neighboring matrix as well as external shear stress induced byrollers. It is indicated that the external shear stress will reduce the brass type texture and increase the copper typetexture obviously.展开更多
We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surf...We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surface layers. After cross-section observation of the Al/CFs composite sheet, we found that the CFs discretely distributed within the sandwich layer. Besides, the tensile test showed that the contribution of the sandwich CFs layer to tensile strength was less than 11% compared with annealed pure Al sheet. With ex-situ observation of the CFs breakage evolution with-16%,-32%, and-45% rolling reduction during the ARB process, the plastic instability of the Al layer was found to bring shear damages to the CFs. At last, the bridging strengthening mechanism introduced by CFs was sacrificed. We provide new insight into and instruction on Al/CFs composite sheet preparation method and processing parameters.展开更多
A Ni–P alloy gradient coating consisting of multiple electroless Ni–P layers with various phosphorus contents was prepared on the aviation aluminum alloy. Several characterization and electrochemical techniques were...A Ni–P alloy gradient coating consisting of multiple electroless Ni–P layers with various phosphorus contents was prepared on the aviation aluminum alloy. Several characterization and electrochemical techniques were used to characterize the different Ni–P coatings’ morphologies, phase structures, elemental compositions, and corrosion protection. The gradient coating showed good adhesion and high corrosion and wear resistance, enabling the application of aluminum alloy in harsh environments. The results showed that the double zinc immersion was vital in obtaining excellent adhesion (81.2 N). The optimal coating was not peeled and shredded even after bending tests with angles higher than 90°and was not corroded visually after 500 h of neutral salt spray test at 35℃. The high corrosion resistance was attributed to the misaligning of these micro defects in the three different nickel alloy layers and the amorphous structure of the high P content in the outer layer. These findings guide the exploration of functional gradient coatings that meet the high application requirement of aluminum alloy parts in complicated and harsh aviation environments.展开更多
Two-mm thick A1050 pure aluminum plates were successfully joined by conventional and rapid cooling friction stir welding(FSW), respectively. The microstructure and mechanical properties of the welded joints were inves...Two-mm thick A1050 pure aluminum plates were successfully joined by conventional and rapid cooling friction stir welding(FSW), respectively. The microstructure and mechanical properties of the welded joints were investigated by electron backscatter diffraction characterization, Vickers hardness measurements, and tensile testing. The results showed that liquid CO_(2) coolant significantly reduced the peak temperature and increased the cooling rate, so the rapidly cooled FSW joint exhibited fine grains with a large number of dislocations. The grain refinement mechanism of the FSW A1050 pure aluminum joint was primarily attributed to the combined effects of continuous dynamic recrystallization, grain subdivision, and geometric dynamic recrystallization. Compared with conventional FSW, the yield strength, ultimate tensile strength, and fracture elongation of rapidly cooled FSW joint were significantly enhanced, and the welding efficiency was increased from 80% to 93%. The enhanced mechanical properties and improved synergy of strength and ductility were obtained due to the increased dislocation density and remarkable grain refinement. The wear of the tool can produce several WC particles retained in the joint, and the contribution of second phase strengthening to the enhanced strength should not be ignored.展开更多
Aluminum hypophosphite microspheres(AHP) were synthesized by hydrothermal method using NaH2PO2·H2O and AlCl3·6H2O as raw materials, and then the AHP microspheres were polymerized by surface polymerization of...Aluminum hypophosphite microspheres(AHP) were synthesized by hydrothermal method using NaH2PO2·H2O and AlCl3·6H2O as raw materials, and then the AHP microspheres were polymerized by surface polymerization of micro-nanospheres with cyclic cross-linked poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol)(PZS). A new organic-inorganic poly(phosphonitrile)-modified aluminum hypophosphite microspheres(PZS-AHP) were synthesized by encapsulation and applied to flame retardant thermoplastic polyurethane(TPU). The microstructure and chemical composition of the PZS-AHP microsphere were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray spectroscopy. The thermal stability of PZS-AHP microsphere was explored with thermogravimetric analysis. Thermogravimetric data indicate that the PZS-AHP microspheres have excellent thermal stability. The thermal and flame-retarding properties of the TPU composites were evaluated by thermogravimetric(TG), limited oxygen index tests(LOI), and cone calorimeter test(CCT). The TPU composite achieved vertical burning(UL-94) V-0 grade and LOI value reached 29.2% when 10 wt% PZS-AHP was incorporated. Compared with those of pure TPU, the peak heat release rate(pHRR) and total heat release(THR) of TPU/10%PZS-AHP decreased by 82.2% and 42.5%, respectively. The results of CCT indicated that PZS-AHP microsphere could improve the flame retardancy of TPU composites.展开更多
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
We report on the magnetohydrodynamic impact on the axisymmetric flow of Al_(2)O_(3)/Cu nanoparticles suspended in H_(2)O past a stretched/shrinked sheet.With the use of partial differential equations and the correspon...We report on the magnetohydrodynamic impact on the axisymmetric flow of Al_(2)O_(3)/Cu nanoparticles suspended in H_(2)O past a stretched/shrinked sheet.With the use of partial differential equations and the corresponding thermophysical characteristics of nanoparticles,the physical flow process is illustrated.The resultant nonlinear system of partial differential equations is converted into a system of ordinary differential equations using the suitable similarity transformations.The transformed differential equations are solved analytically.Impacts of the magnetic parameter,solid volume fraction and stretching/shrinking parameter on momentum and temperature distribution have been analyzed and interpreted graphically.The skin friction and Nusselt number were also evaluated.In addition,existence of dual solution was deduced for the shrinking sheet and unique solution for the stretching one.Further,Al_(2)O_(3)/H_(2)O nanofluid flow has better thermal conductivity on comparing with Cu/H_(2)O nanofluid.Furthermore,it was found that the first solutions of the stream are stable and physically realizable,whereas those of the second ones are unstable.展开更多
With the large-scale service of lithium-ion batteries(LIBs),their failures have attracted significant attentions.While the decay of active materials is the primary cause for LIB failures,the degradation of auxiliary m...With the large-scale service of lithium-ion batteries(LIBs),their failures have attracted significant attentions.While the decay of active materials is the primary cause for LIB failures,the degradation of auxiliary materials,such as current collector corrosion,should not be disregarded.Therefore,it is necessary to conduct a comprehensive review in this field.In this review,from the perspectives of electrochemistry and materials,we systematically summarize the corrosion behavior of aluminum cathode current collector and propose corresponding countermeasures.Firstly,the corrosion type is clarified based on the properties of passivation layers in different organic electrolyte components.Furthermore,a thoroughgoing analysis is presented to examine the impact of various factors on aluminum corrosion,including lithium salts,organic solvents,water impurities,and operating conditions.Subsequently,strategies for electrolyte and protection layer employed to suppress corrosion are discussed in detail.Lastly and most importantly,we provide insights and recommendations to prevent corrosion of current collectors,facilitate the development of advanced current collectors and the implementation of next-generation high-voltage stable LIBs.展开更多
For the safety of railroad operations,sand barriers are utilized to mitigate wind-sand disaster effects.These disasters,characterized by multi-directional wind patterns,result in diverse angles among the barriers.In t...For the safety of railroad operations,sand barriers are utilized to mitigate wind-sand disaster effects.These disasters,characterized by multi-directional wind patterns,result in diverse angles among the barriers.In this study,using numerical simulations,we examined the behavior of High Density Polyethylene(HDPE)sheet sand barriers under different wind angles,focusing on flow field distribution,windproof efficiency,and sedimentation erosion dynamics.This study discovered that at a steady wind speed,airflow velocity varies as the angle between the airflow and the HDPE barrier changes.Specifically,a 90°angle results in the widest low-speed airflow area on the barrier’s downwind side.If the airflow is not perpendicular to the barrier,it prompts a lateral airflow movement which decreases as the angle expands.The windproof efficiency correlates directly with this angle but inversely with the wind’s speed.Notably,with a wind angle of 90°,wind speed drops by 81%.The minimum wind speed is found at 5.1H(the sand barrier height)on the barrier’s downwind side.As the angle grows,the barrier’s windproof efficiency improves,extending its protective reach.Sedimentation is most prominent on the barrier’s downwind side,as the wind angle shifts from 30°to 90°,the sand sedimentation area on the barrier’s downwind side enlarges by 14.8H.As the angle grows,sedimentation intensifies,eventually overtakes the forward erosion and enlarges the sedimentation area.展开更多
文摘Springback is considered to be one of the most important problems in aluminum sheet stamp forming,leading to deviation from the designed target shape and assembly defects.In this study,a springback simulation model based on the benchmark of a Jaguar Land Rover aluminum panel is established.We embed several elastoplastic constitutive models(Barlat's 89,Barlat's YLD2000,Yoshida-Uemori(YU) + Barlat's 89,and YU +Barlat's YLD2000) in the finite element model,in order to discuss the influence of the constitutive model selection on springback prediction in aluminum sheet forming.
基金Project (E981 0 0 0 3)supportedbytheNaturalScienceFoundationofFujianProvince P .R .China
文摘The flow stress feature of aluminum sheet used for pressure can during plastic deformation at elevated temperature was studied by isothermal compression test using Gleeble 1 500 dynamic materials testing machine. The experimental results show that the steady state deformation is remarkable when the material is deformed in the temperature range of 350～500 ℃ at strain rates within the range of 10 -2 ～10.0 s -1 . The material is sensitive to positive strain rate. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate, and an Arrhenius relationship with the temperature. Semi empirical constitutive equations of the flow stress are derived from all experimental data for tested material during plastic deformation at elevated temperature by polyelement linear regression analysis. [
基金Project(JA04251) supported by the Education Department of Fujian Province, China Project(E0210011) supported by the Natural Science Foundation of Fujian Province, China
文摘The isothermal compression test at elevated temperature was carried out for aluminum sheets prepared by different melt-treatment methods with aid of dynamic hot/mechanical simulation experimental technology. The material constants of hot deformation have been solved by multivariate regression directly. Influence of metallurgy factors on the constants was analyzed. The results show that at some strain, the relationship of sheets’ flow stress with deformation temperature and strain rate can be expressed more suitably with Arrhenius equation modified by hyperbolic sine function. Structure factor A1, stress-level coefficient α, strain rate sensibility exponent m and deformation activation energy Q all increase with increment of strain, while stress exponent n decreases gradually. The bigger α value or the smaller n value is, the more obvious the dynamic softening is, but the α value will increase for the metallurgy defects existing in the sheets. Influence of melt-treatment on Q depends upon the synthesis effect of all kinds of metallurgy defects. The Q and n values of the sheet prepared by high-efficient melt-treatment are the least, while the m value is the biggest, and the sheet can deform easily and evenly.
基金Project(50374028)supported by the National Natural Science Foundation of China and Shanghai Bao Steel Group of ChinaProject(PRAMX04-02)supported by Sino-French Cooperation Program
文摘The effects of an external DC(direct current)electric field on recrystallization texture evolution in the cold-rolled aluminum sheets with 99.99%purity were investigated by means of X-ray diffraction techniques.The cold-rolled high-purity aluminum sheets were annealed for 60 min at 200,300 and 400℃,respectively with and without an external DC electric field of 800 V/mm.The results show that with DC electric field,the recrystallization cube texture is strengthened at the stage of grain growth. Possible reason for the strengthening of the recrystallization cube texture with the applied electric field may be attributed to both selected nucleation and selected growth of cube oriented crystal nuclei.
基金This work was financially supported by the National Nature Science Foundation of China (No.50171014) and the National High-Tech Research and Development Program of China (No.2003AA331080)
文摘The texture of a rolled AA3104 aluminum sheet was measured by the X-ray transmission method. The Lankford values or r values (ratio of plastic strain) and yield strengths in directions of 0, 15, 30, 45, 60, 75, and 90° to RD (rolling direction) of the sheet were tested during tensile loading at a strain of 2%. r values were predicted by the Sachs model and the reaction stress model in con- sideration of the measured texture. The simulated results indicate that r values calculated by the Sachs model are more exactly ap- proaching with the experimental values on the whole than those predicted by the reaction stress model. The deformation behavior of the AA3104 aluminum sheet reveals characteristic predicted by the Sachs model, which should be resulted from the sheet geometry different from bulk material as well as the low tensile deformation degree.
基金Sponsored by General Motor Corporation of U.S.A.
文摘Aluminum alloy sheets are used more and more to manufacture auto panels. Because the friction behavior is very complicated, it is necessary to study the friction during the aluminum sheet warm forming process. The author has designed a new probe sensor based on an online tribotest method which directly measures friction coefficient in the forming process. Experiments of cup drawing have been conducted and the friction coefficients under different forming conditions have been measured. The results indicate that the forming parameters, such as forming temperature, blankholding force and lubrication status have great effect upon the friction coefficient.
文摘An approximate macroscopic yield criterion for anisotropic porous sheet metals is adopted in a failure prediction methodology that can be used to investigate the failure of sheet metals under forming operations. This failure prediction methodology is developed based on the Marciniak-Kuczynski approach by assuming a slightly higher void volume fraction inside randomly oriented imperfecte analysis. Here, a nonproportional deformation history including relative rotation of principal stretch directions is identified in a selected critical element of an aluminum sheet from a FEM fender forming simulation. Based on the failure prediction methodology, the failure of the critical sheet element is investigated under the non-proportional deformation history. The results show that thiven non-proportional deformation history.
文摘The application of four widely used anisotropic yield criteria,namely,Hill'48,Hill'90,Barlat'89,and Yld2000,on the formability analysis of an automobile aluminum sheet is investigated. The applicability and reliability of these four yield criteria are identified on the basis of uniaxial tensile and stamping tests of an aluminum covering panel by embedding the specimen in the corresponding finite element models. Results show that the strain distribution and safety margin of the aluminum sheet after stamping can be predicted with a high accuracy by applying Yld2000 compared to those subjected to the three other yield criteria. The significant effects of the anisotropic plastic characteristics of the aluminum sheet on stamping are discussed by applying the advanced simulation technology.
文摘The micro crack of aluminum sheet during cold rolling lubricated with emulsions is investigated. Experi-ments show that micro cracks occur after cold rolling process and this is attributed to various parameters, for instance, the thin oxide film formed at the sheet surface. The micro crack spacing thus becomes an important parameter which deserves more concerns. The aspect ratio of these micro cracks is then analyzed theoreti-cally, which takes into consideration of the oxide fracture process. The good agreement between the obser-vations and the theoretical predictions validates the analysis. The approach can shed some new lights on the mechanical process of aluminium sheet during cold rolling.
基金supported by the Fujian Provincial Natural Science Foundation(No.E0210011)the Educational Commission of Fujian province(No.K20014).
文摘The behavior of flow stress of Al sheets used for pressure can prepared by different melt-treat- ment during plastic deformation at elevated temperature was studied by isothermal compression test using Gleeble1500 dynamic hot-simulation testing machine. The results show that the Al sheets possess the remarkable characteristic of steady state flow stress when they are deformed in the temperature range of 350-500°C at strain rates within the range of 0.01-10.0s-1. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate, and an Arrhenius relationship with the temperature, which implies that the process of plastic deformation at ele- vated temperature for this material is thermally activated. Compared with the Al pieces prepared by no or conventional melt-treatment, hot deformation activation energy of Al sheets prepared by high-efficient melt-treatment is the smallest (Q = 168.0kJ/mol), which reveals that the hot work- ing formability of this material is very better, and has directly to do with the effective improve- ment of its metallurgical quality.
文摘Aluminum sheets were polished to reduce ruggedness and then textured in varying acid-ethanol concentration etchant to form pores. The textured surface was characterized structurally by using X-ray diffraction (XRD) which revealed aluminum crystallographic planes (1 1 1), (2 0 0), (2 2 0) and (3 1 1). Its morphology was studied by using energy dispersive X-ray (EDX) and scanning electron microscope (SEM) that confirmed purity of aluminum sheet to be 99.66% at. Reflectance of textured and plain aluminum sheet was analyzed by spectrophotometric measurements which showed that texturing reduced the reflectance of the polished surface by 26% in the UV-VIS-NIR spectrum of solar radiation. With reduced reflectance of the textured aluminum sheet, it was applicable for solar radiation absorption.
基金The author would like to acknowledge the financial support of the Natural Science Foundation of Beijing(Grant No. 2002014)the Science and Technology Committee of Beijing (Grant No. 9550310400)He is also grateful to Dr. T.Leffers from Riso National La
文摘The formation process of copper type rolling texture in f.c.c. Metals was simulated based on a deformation modelconsidering internal reaction stresses induced by the neighboring matrix as well as external shear stress induced byrollers. It is indicated that the external shear stress will reduce the brass type texture and increase the copper typetexture obviously.
基金Supported by Innovation and Technology Fund (No.ITP/045/19AP)Commercial Research&Development (CRD) Funding Supported by Hong Kong Productivity Council (No.10008787)。
文摘We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surface layers. After cross-section observation of the Al/CFs composite sheet, we found that the CFs discretely distributed within the sandwich layer. Besides, the tensile test showed that the contribution of the sandwich CFs layer to tensile strength was less than 11% compared with annealed pure Al sheet. With ex-situ observation of the CFs breakage evolution with-16%,-32%, and-45% rolling reduction during the ARB process, the plastic instability of the Al layer was found to bring shear damages to the CFs. At last, the bridging strengthening mechanism introduced by CFs was sacrificed. We provide new insight into and instruction on Al/CFs composite sheet preparation method and processing parameters.
基金financially supported by the National Natural Science Foundation of China (No.52271073)。
文摘A Ni–P alloy gradient coating consisting of multiple electroless Ni–P layers with various phosphorus contents was prepared on the aviation aluminum alloy. Several characterization and electrochemical techniques were used to characterize the different Ni–P coatings’ morphologies, phase structures, elemental compositions, and corrosion protection. The gradient coating showed good adhesion and high corrosion and wear resistance, enabling the application of aluminum alloy in harsh environments. The results showed that the double zinc immersion was vital in obtaining excellent adhesion (81.2 N). The optimal coating was not peeled and shredded even after bending tests with angles higher than 90°and was not corroded visually after 500 h of neutral salt spray test at 35℃. The high corrosion resistance was attributed to the misaligning of these micro defects in the three different nickel alloy layers and the amorphous structure of the high P content in the outer layer. These findings guide the exploration of functional gradient coatings that meet the high application requirement of aluminum alloy parts in complicated and harsh aviation environments.
基金Funded by the Natural Science Foundation of Jiangsu Province(No.BK20211067)“Qing Lan” Project of Jiangsu Province。
文摘Two-mm thick A1050 pure aluminum plates were successfully joined by conventional and rapid cooling friction stir welding(FSW), respectively. The microstructure and mechanical properties of the welded joints were investigated by electron backscatter diffraction characterization, Vickers hardness measurements, and tensile testing. The results showed that liquid CO_(2) coolant significantly reduced the peak temperature and increased the cooling rate, so the rapidly cooled FSW joint exhibited fine grains with a large number of dislocations. The grain refinement mechanism of the FSW A1050 pure aluminum joint was primarily attributed to the combined effects of continuous dynamic recrystallization, grain subdivision, and geometric dynamic recrystallization. Compared with conventional FSW, the yield strength, ultimate tensile strength, and fracture elongation of rapidly cooled FSW joint were significantly enhanced, and the welding efficiency was increased from 80% to 93%. The enhanced mechanical properties and improved synergy of strength and ductility were obtained due to the increased dislocation density and remarkable grain refinement. The wear of the tool can produce several WC particles retained in the joint, and the contribution of second phase strengthening to the enhanced strength should not be ignored.
基金Supported by the Opening Project of Hubei Three Gorges Laboratory (No.SK213008)the Innovation Fund of Key Laboratory of Green Chemical Process of Ministry of Education (No.GCXP202109)。
文摘Aluminum hypophosphite microspheres(AHP) were synthesized by hydrothermal method using NaH2PO2·H2O and AlCl3·6H2O as raw materials, and then the AHP microspheres were polymerized by surface polymerization of micro-nanospheres with cyclic cross-linked poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol)(PZS). A new organic-inorganic poly(phosphonitrile)-modified aluminum hypophosphite microspheres(PZS-AHP) were synthesized by encapsulation and applied to flame retardant thermoplastic polyurethane(TPU). The microstructure and chemical composition of the PZS-AHP microsphere were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray spectroscopy. The thermal stability of PZS-AHP microsphere was explored with thermogravimetric analysis. Thermogravimetric data indicate that the PZS-AHP microspheres have excellent thermal stability. The thermal and flame-retarding properties of the TPU composites were evaluated by thermogravimetric(TG), limited oxygen index tests(LOI), and cone calorimeter test(CCT). The TPU composite achieved vertical burning(UL-94) V-0 grade and LOI value reached 29.2% when 10 wt% PZS-AHP was incorporated. Compared with those of pure TPU, the peak heat release rate(pHRR) and total heat release(THR) of TPU/10%PZS-AHP decreased by 82.2% and 42.5%, respectively. The results of CCT indicated that PZS-AHP microsphere could improve the flame retardancy of TPU composites.
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LMP acknowledges financial support from ANID through Convocatoria Nacional Subvención a Instalación en la Academia Convocatoria Año 2021,Grant SA77210040。
文摘We report on the magnetohydrodynamic impact on the axisymmetric flow of Al_(2)O_(3)/Cu nanoparticles suspended in H_(2)O past a stretched/shrinked sheet.With the use of partial differential equations and the corresponding thermophysical characteristics of nanoparticles,the physical flow process is illustrated.The resultant nonlinear system of partial differential equations is converted into a system of ordinary differential equations using the suitable similarity transformations.The transformed differential equations are solved analytically.Impacts of the magnetic parameter,solid volume fraction and stretching/shrinking parameter on momentum and temperature distribution have been analyzed and interpreted graphically.The skin friction and Nusselt number were also evaluated.In addition,existence of dual solution was deduced for the shrinking sheet and unique solution for the stretching one.Further,Al_(2)O_(3)/H_(2)O nanofluid flow has better thermal conductivity on comparing with Cu/H_(2)O nanofluid.Furthermore,it was found that the first solutions of the stream are stable and physically realizable,whereas those of the second ones are unstable.
文摘With the large-scale service of lithium-ion batteries(LIBs),their failures have attracted significant attentions.While the decay of active materials is the primary cause for LIB failures,the degradation of auxiliary materials,such as current collector corrosion,should not be disregarded.Therefore,it is necessary to conduct a comprehensive review in this field.In this review,from the perspectives of electrochemistry and materials,we systematically summarize the corrosion behavior of aluminum cathode current collector and propose corresponding countermeasures.Firstly,the corrosion type is clarified based on the properties of passivation layers in different organic electrolyte components.Furthermore,a thoroughgoing analysis is presented to examine the impact of various factors on aluminum corrosion,including lithium salts,organic solvents,water impurities,and operating conditions.Subsequently,strategies for electrolyte and protection layer employed to suppress corrosion are discussed in detail.Lastly and most importantly,we provide insights and recommendations to prevent corrosion of current collectors,facilitate the development of advanced current collectors and the implementation of next-generation high-voltage stable LIBs.
基金financially supported by the Natural Science Foundation of Gansu Province,China(22JR5RA050,20JR10RA231)the fellowship of the China Postdoctoral Science Foundation(2021M703466)the Basic Research Innovation Group Project of Gansu Province,China(21JR7RA347).
文摘For the safety of railroad operations,sand barriers are utilized to mitigate wind-sand disaster effects.These disasters,characterized by multi-directional wind patterns,result in diverse angles among the barriers.In this study,using numerical simulations,we examined the behavior of High Density Polyethylene(HDPE)sheet sand barriers under different wind angles,focusing on flow field distribution,windproof efficiency,and sedimentation erosion dynamics.This study discovered that at a steady wind speed,airflow velocity varies as the angle between the airflow and the HDPE barrier changes.Specifically,a 90°angle results in the widest low-speed airflow area on the barrier’s downwind side.If the airflow is not perpendicular to the barrier,it prompts a lateral airflow movement which decreases as the angle expands.The windproof efficiency correlates directly with this angle but inversely with the wind’s speed.Notably,with a wind angle of 90°,wind speed drops by 81%.The minimum wind speed is found at 5.1H(the sand barrier height)on the barrier’s downwind side.As the angle grows,the barrier’s windproof efficiency improves,extending its protective reach.Sedimentation is most prominent on the barrier’s downwind side,as the wind angle shifts from 30°to 90°,the sand sedimentation area on the barrier’s downwind side enlarges by 14.8H.As the angle grows,sedimentation intensifies,eventually overtakes the forward erosion and enlarges the sedimentation area.
