In the welding process of SiCp/Al composites,Al reacts with SiC particles in the molten pool to form Al_(4)C_(3),a brittle phase,damaging the reinforcement and causing a sharp decline in the mechanical properties of w...In the welding process of SiCp/Al composites,Al reacts with SiC particles in the molten pool to form Al_(4)C_(3),a brittle phase,damaging the reinforcement and causing a sharp decline in the mechanical properties of weld joints.To mitigate this,a method of welding SiCp/Al composites by pulsed laser welding with powder-filling is proposed,inhibiting the interface reaction between Al and SiC particles in the molten pool.This study investigates the effect of pulse frequency on the temperature field of the molten pool,and combines thermal-fluid numerical simulation to analyze the peak temperature at different pulse frequencies,optimizing the Si content to ultimately inhibit the interface reaction in the molten pool.Results indicate that an appropriate pulse frequency achieves good welding formation and effectively regulates the peak temperature of the molten pool.Only a small amount of brittle phase is present in the weld joint,creating favorable conditions for the addition of alloying elements.The interface reaction is slowed down by adjusting the pulse frequency,though it is not completely inhibited.When the addition of Si content reaches 8%,the occurrence of the interface reaction is effectively inhibited.In weld joints with the addition of 8wt%Si powder,no Al_(4)C_(3)brittle phase is present,and the tensile strength of the weld joint is 266 MPa,up to 70%of the base material.展开更多
35% SiCp/2024 Al（volume fraction） composite was prepared by powder metallurgy method. The microstructures of Si Cp/Al interfaces and precipitate phase/Al interfaces were characterized by HRTEM, and the interface con...35% SiCp/2024 Al（volume fraction） composite was prepared by powder metallurgy method. The microstructures of Si Cp/Al interfaces and precipitate phase/Al interfaces were characterized by HRTEM, and the interface conditions were evaluated by tensile modules of elasticity and Brinell hardness measurement. The results show that the overall Si Cp/Al interface condition in this experiment is good and three kinds of Si Cp/Al interfaces are present in the composites, which include vast majority of clean planer interfaces, few slight reaction interfaces and tiny amorphous interfaces. The combination mechanism of Si C and Al in the clean planer interface is the formation of a semi-coherent interface by closely matching of atoms and there are no fixed or preferential crystallographic orientation relationships between Si C and Al. MgAl2O4 spinel particles act as an intermediate to form semi-coherent interface with SiC and Al respectively at the slight reaction interfaces. When the composite is aged at 190 °C for 9 h after being solution-treated at 510 °C for 2 h, numerous discoid-shaped and needle-shaped nanosized precipitates dispersively exist in the composite and are semi-coherent of low mismatch with Al matrix. The Brinell hardness of composites arrives peak value at this time.展开更多
The research on high-performance electromagnetic wave absorption materials with high-temperature and oxidative stability in extreme environments is gaining popularity.Herein,the lightweight silicon carbide nanowires(S...The research on high-performance electromagnetic wave absorption materials with high-temperature and oxidative stability in extreme environments is gaining popularity.Herein,the lightweight silicon carbide nanowires(SiC_(nws))/SiC composites are fabricated with in-situ SiC interface on one-dimensional oriented SiC_(nws)skeleton,which collaborative configuration by 3D printing and freeze casting assembly.The con-structed porous structure optimizes the impedance matching degree and scattering intensity,the maximum effective absorption bandwidth(EAB_(max))of 5.9 GHz and the minimum reflection loss(RL_(min))of−41.4 dB can be realized.Considering the inherent oxidation resistance of SiC,the composites present well-maintained absorption performance at 600℃.Even at 1100℃,the EAB_(max)of 4.9 GHz and RLmin of−30.4 dB also demonstrate the high-temperature absorption stability of the composites,indicating exceptional wave absorption properties and thermal stability.The slight attenuation can be attributed to the decrease in impedance matching capability accompanying the elevated dielectric constant.This work clarifies the impact of structure and component synergy on wave absorption behavior,and offers a novel approach to producing high-performance and high-temperature resistance ceramic-based electromagnetic wave absorption materials suitable for extreme environments.展开更多
为研究SiC_(f)/Ti_(3)Al复合材料在单轴拉伸中产生的热残余应力对拉伸性能的影响,采用ABAQUS有限元模拟结合内聚力模型(cohesive zone model,CZM),构建了包含纤维、基体及界面的三维细观结构模型,分析了复合材料的应力分布、裂纹扩展、...为研究SiC_(f)/Ti_(3)Al复合材料在单轴拉伸中产生的热残余应力对拉伸性能的影响,采用ABAQUS有限元模拟结合内聚力模型(cohesive zone model,CZM),构建了包含纤维、基体及界面的三维细观结构模型,分析了复合材料的应力分布、裂纹扩展、界面失效等。结果表明:在横向拉伸中,界面脱黏为主要失效机制,基体内等效应力的重新分配对整体性能起关键作用;在纵向拉伸中,热残余应力导致应力场非均匀分布并影响基体屈服,同时界面径向压应力有效减缓界面脱黏,延缓材料失效。研究结果揭示了热残余应力与界面特性对SiC_(f)/Ti_(3)Al复合材料横纵向拉伸性能的影响机制,为优化纤维增强金属基复合材料的设计与性能提升提供了理论支持。展开更多
In this study,the cold-spraying process was utilized to deposit Al particles onto an Al slab,an Mg slab,and both Al and Mg slabs to form an ultra-thin interlayer,and then the clad slabs were rolled at 400℃,developing...In this study,the cold-spraying process was utilized to deposit Al particles onto an Al slab,an Mg slab,and both Al and Mg slabs to form an ultra-thin interlayer,and then the clad slabs were rolled at 400℃,developing three roll-bonding processes:the roll-bonding process with cold-sprayed Al powder on the Al slab(CS-Al),the roll-bonding process with cold-sprayed Al powder on the Mg slab(CS-Mg),and the rollbonding process with cold-sprayed Al powder on both the Al slab and the Mg slab(CS-Both).The effects of three different cold-sprayed Al particle interlayer processes on the mechanical properties of rolled Mg/Al clad plates were investigated to improve the mechanical properties.The microstructure,texture evolution,intermetallic compound formation,mechanical properties,and mechanisms involved in the Mg/Al clad plate rolling were systematically investigated.The results showed that the pre-bonding between the particles and the substrates through coldspraying had a significant impact on the bonding strength of the Mg/Al clad plates,and the CS-Both process can increase the average shear strength of the Mg/Al clad plates to 49.24 MPa at a medium reduction rate of 37.5%,2.5 times that of the conventional rolling process.The CS-Both process constructed more evident dual microscopic three-dimensional interfaces and promoted more thorough atomic diffusion at the interface through the double-sided cold-spraying process.Meanwhile,the dual cold-sprayed Al coatings on both the Mg slab and Al slab underwent dynamic recrystallization during rolling to form a homogeneous unit with no additional coating interfaces.Fine grain strengthening and dislocation strengthening were judged to be important mechanisms for improving the mechanical performance of the interfacial layer.展开更多
Fabricating Mg/Al laminate is an effective strategy to circumvent the inherently low formability and poor corrosion resistance of Mg alloys.Here,Mg/Al laminate with good bonding quality and mechanical properties was s...Fabricating Mg/Al laminate is an effective strategy to circumvent the inherently low formability and poor corrosion resistance of Mg alloys.Here,Mg/Al laminate with good bonding quality and mechanical properties was successfully fabricated via porthole die co-extrusion process using ZK60 Mg and TiB_(2)/6061Al composite as constituted layers.Integrating the results from microstructural characterization and mechanical testing,the effects of extrusion temperature on microstructure,interfacial structure,element diffusion,and mechanical properties were investigated.The results show that Mg/Al laminate achieves a sound welding quality by mechanical bonding and diffusion bonding.The obvious intermetallic compounds(βandγ)layer forms at Mg/Al interface,and its thickness increases to 8.3μm as the extrusion temperature reaches 400℃.High extrusion temperature promotes the dynamic recrystallization and grain growth of Mg and Al layers,while the dislocation density decreases.β/γinterface shows a coherent feature,whileγ/Mg interface is semi-coherent with a locally ordered transition zone of 4.5 nm.The rich Mg and Cr layers are found at TiB_(2)/6061 interface,which is conducive to improving the bonding quality.When the extrusion temperature is 370℃,the thickness of diffusion layer is around 5.0μm,and the bonding strength reaches 18.68 MPa,resulting in the best comprehensive mechanical properties.This work provides a new direction for the development of Mg/Al laminate with excellent strength and ductility.展开更多
The paper study the interfacial mechanical properties and structural evolution mechanisms in 6061/AZ31B/6061 composite plates with and without Ni foil interlayers.For Ni-free interfaces,a continuous diffusion layer(3....The paper study the interfacial mechanical properties and structural evolution mechanisms in 6061/AZ31B/6061 composite plates with and without Ni foil interlayers.For Ni-free interfaces,a continuous diffusion layer(3.5-4.0μm)forms,dominated by brittle columnar Al_(12)Mg_(17) intermetallic compounds(IMCs,0.27-0.35μm thick),which act as preferential crack initiation sites.In contrast,Ni foil implantation induces interfacial restructuring during hot rolling:Constrained deformation fragments the Ni foil into grid-like segments with"olive"-shaped crosssections,embedded into Mg/Al matrices.These fragments(56% areal coverage)coexist with dispersed multiphase IMCs(Mg_(2)Ni,Al_(3)Ni,Mg_(3)AlNi,Al_(12)Mg_(17);10-20 nm grains)at fragment edges,forming a hybrid interface of"willow-leaf"Al_(12)Mg_(17) islands and nanoscale Mg_(2)Ni/Al_(3)Ni layers(15-25 nm).Hall-Petch analysis reveals the multiphase IMC interface exhibits 3.6×higher"kd^(-1/2)"strengthening contribution than single-phase Al_(12)Mg_(17) systems,attributed to grain refinement(20 nm vs.260 nm average grain size).Synergistic effects of mechanical interlocking,adhesion hierarchy(Ni-Al>Ni-Mg>Al-Mg),and nanoscale reinforcement collectively enhance peel strength by 78%without compromising bulk tensile properties.展开更多
Al/Cu laminate composite was fabricated based on hot press sintering using Cu sheet and Al powders as raw materials.The effects of sintering parameters on interfacial structure and mechanical properties were investiga...Al/Cu laminate composite was fabricated based on hot press sintering using Cu sheet and Al powders as raw materials.The effects of sintering parameters on interfacial structure and mechanical properties were investigated.The results revealed that a uniform Al/Cu interface with excellent bonding quality was achieved.The thickness of intermetallic compounds(IMCs)reached 33.88μm after sintering at 620℃for 2 h,whereas it was only 14.88μm when sintered at 600℃for 1 h.AlCu phase was developed through the reaction between Al4Cu9 and Al2Cu with prolonging sintering time,and an amorphous oxide strip formed at AlCu/Al4Cu9 interface.Both the grain morphology and interfacial structure affected the tensile strength of Al/Cu laminate,whereas the mode of tensile fracture strongly relied on the interfacial bonding strength.The highest tensile strength of 151.1 MPa and bonding strength of 93.7 MPa were achieved after sintering at 600℃for 1 h.展开更多
Thickness of the intermetallic compounds(IMC)layer at the interface has a significant effect on the mechanical properties of Mg/Al dissimilar joints.However,the thickness of IMC layer can be only obtained by metallurg...Thickness of the intermetallic compounds(IMC)layer at the interface has a significant effect on the mechanical properties of Mg/Al dissimilar joints.However,the thickness of IMC layer can be only obtained by metallurgical microscopy,which is destructive and has to break down the weld.Therefore,it is crucial to find a reliable approach that can non-destructively predict the thickness of IMC layer in practical application.In the current study,Mg alloy and Al alloy were friction stir butt welded(FSW)under different tool rotation speeds(TRS)to obtain different thicknesses of IMC layers.As the TRS increased from 400 rpm to 1000 rpm,thickness of the IMC layer increased from 0.4μm to 1.3μm,the peak welding temperatures increased from 259℃to 402℃,and the Z-axis downforces decreased from10.5 kN to 3.2 k N during welding process.Higher TRS would generally induce higher welding heat input,which promotes the growth of the IMC layer and the softening of base materials.The IMC layer formed through solid-state diffusion and transformation instead of eutectic reaction according to the welding temperature history and interfacial microstructure,and its evolution process was clearly observed by plan view.In order to incorporate the effect of dramatic change of welding temperature which is the characteristic feature of FSW,Psd Voigt function was used to fit the welding temperature histories.A new prediction formula was then established to predict thicknesses of IMC layers with considering sharp welding temperature change.Predicted thicknesses gave good agreement with measured thicknesses obtained experimentally under different welding parameters,which confirmed the accuracy and reliability of the new prediction formula.Based on this prediction formula,the time period of temperature higher than 200℃during welding was found critical for the thickening of interfacial IMC layers.展开更多
Non-isothermal aging(NIA)treatments have presented significant advantages in improving the comprehensive performance and aging hardening efficiency of the 7000 series aluminum alloys,but there is no attention paid to ...Non-isothermal aging(NIA)treatments have presented significant advantages in improving the comprehensive performance and aging hardening efficiency of the 7000 series aluminum alloys,but there is no attention paid to their composites.This study takes a linear heating aging process as an example to reveal the precipitation behaviors of a 15 vol.%SiC/7085Al composite as well as its impact on mechanical properties using differential scanning calorimetry,transmission electron microscopy,small-angle neutron scattering,hardness measurements,and tensile testing.The results indicated the formation of GP(Ⅰ,Ⅱ)zones,η’andηprecipitates in sequence,leading to the hardness and strength initially increasing and then decreasing with rising NIA temperatures.The maximums were reached at 183℃,corresponding to the appearance ofη’precipitates in large quantities.Owing to the rapid temperature rise during the NIA process,the precipitates entered the coarsening and redissolution stage before they were entirely formed,resulting in reduced peak strength compared to the T6 treatment.The composite exhibited a more significant reduction in strength than the 7085Al alloy because:(i)the annihilation of vacancies suppressed the formation of GPII zones,thereby weakening their transition toη’precipitates;(ii)quenching dislocations promoted the coarsening of precipitates.An improved NIA process,incorporating both heating and cooling aging treatments,was effectively designed with the assistance of in-situ SANS technology to address this issue,which allows for achieving strength comparable to that after the T6 treatment with only 15%of the aging time consumption.This research fills the gap in investigating the NIA precipitation behaviors of aluminum matrix composites,providing guidance for the formulation of NIA schedules.展开更多
SiCp/Al composites are used in aerospace and deep-space exploration equipment because of their extremely high strength and thrust-to-weight ratios;however,the differences in the properties of the reinforcement and mat...SiCp/Al composites are used in aerospace and deep-space exploration equipment because of their extremely high strength and thrust-to-weight ratios;however,the differences in the properties of the reinforcement and matrix materials in this type of composites have restricted their applications.The ultrahigh-frequency vibration characteristics of ultrasonic vibration processing technology can effectively solve the above bottlenecks,but the effect of high-frequency vibration on the interfacial properties of SiCp/Al composites is still unclear.The effects of ultrasonic vibration on the interface strength of composites were analyzed from a microscale perspective by means of single particle push-out Molecular Dynamics(MD)simulations and tests under different conditions.The results show that the interface strength is negatively correlated with particle size but positively correlated with ultrasonic amplitude,with a maximum increase of about 51%relative to no ultrasound.Brittle-plastic transition was observed on the surface of particles with high interface strength,and lateral microcracks due to stress concentration were present on the surface of particles with low interface strength.Higher strains and grain refinement were obtained for larger amplitudes,and stacking faults and tangle dislocations appeared on the side of the interface layer close to the Al matrix.The results provide potential insights to improve the micromechanical and mechanical properties of SiCp/Al composites,enhance the longevity of the materials,and realize the sustainable use of resources by expanding the efficient,precise,and clean machining of such materials.展开更多
The effects of interface shape on stress wave distribution and attenuation were investiga- ted using finite element method （ FEM ）. The simulation results indicate that when the stress wave propagates from SiC ceram...The effects of interface shape on stress wave distribution and attenuation were investiga- ted using finite element method （ FEM ）. The simulation results indicate that when the stress wave propagates from SiC ceramic to A1 alloy, the tensile stress decreases and the attenuation coefficient of the stress wave increases with increasing central angle of the concave interface between SiC and A1. But for the convex interface, the tensile stress increases and attenuation coefficient decreases with increasing central angle. As the stress wave propagates from A1 alloy to SiC ceramic, the atten- uation coefficient of stress wave decreases with increasing the central angle of the concave interface. For the convex interface, the attenuation coefficient increases with increasing central angle.展开更多
This paper studies two-dimensional analysis of the surface state effect on current gain for a 4H-SiC bipolar junction transistor （BJT）. Simulation results indicate the mechanism of current gain degradation, which is...This paper studies two-dimensional analysis of the surface state effect on current gain for a 4H-SiC bipolar junction transistor （BJT）. Simulation results indicate the mechanism of current gain degradation, which is surface Fermi level pinning leading to a strong downward bending of the energy bands to form the channel of surface electron recombination current. The experimental results are well-matched with the simulation, which is modeled by exponential distributions of the interface state density replacing the single interface state trap. Furthermore, the simulation reveals that the oxide quality of the base emitter junction interface is very important for 4H-SiC BJT performance.展开更多
基金Supported by Equipment Pre-Research Foundation of China(Grant No.50923030512)。
文摘In the welding process of SiCp/Al composites,Al reacts with SiC particles in the molten pool to form Al_(4)C_(3),a brittle phase,damaging the reinforcement and causing a sharp decline in the mechanical properties of weld joints.To mitigate this,a method of welding SiCp/Al composites by pulsed laser welding with powder-filling is proposed,inhibiting the interface reaction between Al and SiC particles in the molten pool.This study investigates the effect of pulse frequency on the temperature field of the molten pool,and combines thermal-fluid numerical simulation to analyze the peak temperature at different pulse frequencies,optimizing the Si content to ultimately inhibit the interface reaction in the molten pool.Results indicate that an appropriate pulse frequency achieves good welding formation and effectively regulates the peak temperature of the molten pool.Only a small amount of brittle phase is present in the weld joint,creating favorable conditions for the addition of alloying elements.The interface reaction is slowed down by adjusting the pulse frequency,though it is not completely inhibited.When the addition of Si content reaches 8%,the occurrence of the interface reaction is effectively inhibited.In weld joints with the addition of 8wt%Si powder,no Al_(4)C_(3)brittle phase is present,and the tensile strength of the weld joint is 266 MPa,up to 70%of the base material.
基金Project(51371077)supported by the National Natural Science Foundation of China
文摘35% SiCp/2024 Al（volume fraction） composite was prepared by powder metallurgy method. The microstructures of Si Cp/Al interfaces and precipitate phase/Al interfaces were characterized by HRTEM, and the interface conditions were evaluated by tensile modules of elasticity and Brinell hardness measurement. The results show that the overall Si Cp/Al interface condition in this experiment is good and three kinds of Si Cp/Al interfaces are present in the composites, which include vast majority of clean planer interfaces, few slight reaction interfaces and tiny amorphous interfaces. The combination mechanism of Si C and Al in the clean planer interface is the formation of a semi-coherent interface by closely matching of atoms and there are no fixed or preferential crystallographic orientation relationships between Si C and Al. MgAl2O4 spinel particles act as an intermediate to form semi-coherent interface with SiC and Al respectively at the slight reaction interfaces. When the composite is aged at 190 °C for 9 h after being solution-treated at 510 °C for 2 h, numerous discoid-shaped and needle-shaped nanosized precipitates dispersively exist in the composite and are semi-coherent of low mismatch with Al matrix. The Brinell hardness of composites arrives peak value at this time.
基金supported by the National Key R&D Program of China(No.2022YFB3707700)National Natural Science Foundation of China(No.52302121)+3 种基金Shanghai Sailing Program(No.23YF1454700)Shanghai Natural Science Foundation(No.23ZR1472700)Shanghai Post-doctoral Excellent Program(No.2022664)Shanghai Science and Technology Innovation Action Plan(No.21511104800).
文摘The research on high-performance electromagnetic wave absorption materials with high-temperature and oxidative stability in extreme environments is gaining popularity.Herein,the lightweight silicon carbide nanowires(SiC_(nws))/SiC composites are fabricated with in-situ SiC interface on one-dimensional oriented SiC_(nws)skeleton,which collaborative configuration by 3D printing and freeze casting assembly.The con-structed porous structure optimizes the impedance matching degree and scattering intensity,the maximum effective absorption bandwidth(EAB_(max))of 5.9 GHz and the minimum reflection loss(RL_(min))of−41.4 dB can be realized.Considering the inherent oxidation resistance of SiC,the composites present well-maintained absorption performance at 600℃.Even at 1100℃,the EAB_(max)of 4.9 GHz and RLmin of−30.4 dB also demonstrate the high-temperature absorption stability of the composites,indicating exceptional wave absorption properties and thermal stability.The slight attenuation can be attributed to the decrease in impedance matching capability accompanying the elevated dielectric constant.This work clarifies the impact of structure and component synergy on wave absorption behavior,and offers a novel approach to producing high-performance and high-temperature resistance ceramic-based electromagnetic wave absorption materials suitable for extreme environments.
文摘为研究SiC_(f)/Ti_(3)Al复合材料在单轴拉伸中产生的热残余应力对拉伸性能的影响,采用ABAQUS有限元模拟结合内聚力模型(cohesive zone model,CZM),构建了包含纤维、基体及界面的三维细观结构模型,分析了复合材料的应力分布、裂纹扩展、界面失效等。结果表明:在横向拉伸中,界面脱黏为主要失效机制,基体内等效应力的重新分配对整体性能起关键作用;在纵向拉伸中,热残余应力导致应力场非均匀分布并影响基体屈服,同时界面径向压应力有效减缓界面脱黏,延缓材料失效。研究结果揭示了热残余应力与界面特性对SiC_(f)/Ti_(3)Al复合材料横纵向拉伸性能的影响机制,为优化纤维增强金属基复合材料的设计与性能提升提供了理论支持。
基金funded by the National Natural Science Foundation of China(Grant No.52305405,52075359)the Natural Science Foundation Research Program of Shanxi Province(Grant No.202203021222121)+1 种基金the Fund for Shanxi“1331Project”Key Innovative Research Teamthe Chinese Postdoctoral Science Foundation(Grant No.2021M702544)。
文摘In this study,the cold-spraying process was utilized to deposit Al particles onto an Al slab,an Mg slab,and both Al and Mg slabs to form an ultra-thin interlayer,and then the clad slabs were rolled at 400℃,developing three roll-bonding processes:the roll-bonding process with cold-sprayed Al powder on the Al slab(CS-Al),the roll-bonding process with cold-sprayed Al powder on the Mg slab(CS-Mg),and the rollbonding process with cold-sprayed Al powder on both the Al slab and the Mg slab(CS-Both).The effects of three different cold-sprayed Al particle interlayer processes on the mechanical properties of rolled Mg/Al clad plates were investigated to improve the mechanical properties.The microstructure,texture evolution,intermetallic compound formation,mechanical properties,and mechanisms involved in the Mg/Al clad plate rolling were systematically investigated.The results showed that the pre-bonding between the particles and the substrates through coldspraying had a significant impact on the bonding strength of the Mg/Al clad plates,and the CS-Both process can increase the average shear strength of the Mg/Al clad plates to 49.24 MPa at a medium reduction rate of 37.5%,2.5 times that of the conventional rolling process.The CS-Both process constructed more evident dual microscopic three-dimensional interfaces and promoted more thorough atomic diffusion at the interface through the double-sided cold-spraying process.Meanwhile,the dual cold-sprayed Al coatings on both the Mg slab and Al slab underwent dynamic recrystallization during rolling to form a homogeneous unit with no additional coating interfaces.Fine grain strengthening and dislocation strengthening were judged to be important mechanisms for improving the mechanical performance of the interfacial layer.
基金supports from the National Natural Science Foundation of China(52175338 and 52222510)Science Fund for Distinguished Young Scholars of Shandong Province(ZR2021JQ21)Key Research and Development Program of Shandong Province(2021ZLGX01).
文摘Fabricating Mg/Al laminate is an effective strategy to circumvent the inherently low formability and poor corrosion resistance of Mg alloys.Here,Mg/Al laminate with good bonding quality and mechanical properties was successfully fabricated via porthole die co-extrusion process using ZK60 Mg and TiB_(2)/6061Al composite as constituted layers.Integrating the results from microstructural characterization and mechanical testing,the effects of extrusion temperature on microstructure,interfacial structure,element diffusion,and mechanical properties were investigated.The results show that Mg/Al laminate achieves a sound welding quality by mechanical bonding and diffusion bonding.The obvious intermetallic compounds(βandγ)layer forms at Mg/Al interface,and its thickness increases to 8.3μm as the extrusion temperature reaches 400℃.High extrusion temperature promotes the dynamic recrystallization and grain growth of Mg and Al layers,while the dislocation density decreases.β/γinterface shows a coherent feature,whileγ/Mg interface is semi-coherent with a locally ordered transition zone of 4.5 nm.The rich Mg and Cr layers are found at TiB_(2)/6061 interface,which is conducive to improving the bonding quality.When the extrusion temperature is 370℃,the thickness of diffusion layer is around 5.0μm,and the bonding strength reaches 18.68 MPa,resulting in the best comprehensive mechanical properties.This work provides a new direction for the development of Mg/Al laminate with excellent strength and ductility.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research(2020B0301030006)Key Project of Chongqing Technology Innovation and Application Development Special Project(CSTB2023TIADKPX0016,CSTB2022TIAD-KPX0027)+1 种基金National Natural Science Foundation of China(51971183)the Science and Technology Program of Xinjiang Production and Construction Corps(2024AB056).
文摘The paper study the interfacial mechanical properties and structural evolution mechanisms in 6061/AZ31B/6061 composite plates with and without Ni foil interlayers.For Ni-free interfaces,a continuous diffusion layer(3.5-4.0μm)forms,dominated by brittle columnar Al_(12)Mg_(17) intermetallic compounds(IMCs,0.27-0.35μm thick),which act as preferential crack initiation sites.In contrast,Ni foil implantation induces interfacial restructuring during hot rolling:Constrained deformation fragments the Ni foil into grid-like segments with"olive"-shaped crosssections,embedded into Mg/Al matrices.These fragments(56% areal coverage)coexist with dispersed multiphase IMCs(Mg_(2)Ni,Al_(3)Ni,Mg_(3)AlNi,Al_(12)Mg_(17);10-20 nm grains)at fragment edges,forming a hybrid interface of"willow-leaf"Al_(12)Mg_(17) islands and nanoscale Mg_(2)Ni/Al_(3)Ni layers(15-25 nm).Hall-Petch analysis reveals the multiphase IMC interface exhibits 3.6×higher"kd^(-1/2)"strengthening contribution than single-phase Al_(12)Mg_(17) systems,attributed to grain refinement(20 nm vs.260 nm average grain size).Synergistic effects of mechanical interlocking,adhesion hierarchy(Ni-Al>Ni-Mg>Al-Mg),and nanoscale reinforcement collectively enhance peel strength by 78%without compromising bulk tensile properties.
基金the financial support from the National Natural Science Foundation of China(Nos.51875317,52222510)Key Research and Development Program of Shandong Province,China(No.2021ZLGX01)。
文摘Al/Cu laminate composite was fabricated based on hot press sintering using Cu sheet and Al powders as raw materials.The effects of sintering parameters on interfacial structure and mechanical properties were investigated.The results revealed that a uniform Al/Cu interface with excellent bonding quality was achieved.The thickness of intermetallic compounds(IMCs)reached 33.88μm after sintering at 620℃for 2 h,whereas it was only 14.88μm when sintered at 600℃for 1 h.AlCu phase was developed through the reaction between Al4Cu9 and Al2Cu with prolonging sintering time,and an amorphous oxide strip formed at AlCu/Al4Cu9 interface.Both the grain morphology and interfacial structure affected the tensile strength of Al/Cu laminate,whereas the mode of tensile fracture strongly relied on the interfacial bonding strength.The highest tensile strength of 151.1 MPa and bonding strength of 93.7 MPa were achieved after sintering at 600℃for 1 h.
基金supported by the National Natural Science Foundation of China(No.52075330)the Interdisciplinary Program of Shanghai Jiao Tong University(No.YG2019QNA15)the Foundation of National Facility for Translational Medicine(Shanghai)(No.TMSK-2020-107)。
文摘Thickness of the intermetallic compounds(IMC)layer at the interface has a significant effect on the mechanical properties of Mg/Al dissimilar joints.However,the thickness of IMC layer can be only obtained by metallurgical microscopy,which is destructive and has to break down the weld.Therefore,it is crucial to find a reliable approach that can non-destructively predict the thickness of IMC layer in practical application.In the current study,Mg alloy and Al alloy were friction stir butt welded(FSW)under different tool rotation speeds(TRS)to obtain different thicknesses of IMC layers.As the TRS increased from 400 rpm to 1000 rpm,thickness of the IMC layer increased from 0.4μm to 1.3μm,the peak welding temperatures increased from 259℃to 402℃,and the Z-axis downforces decreased from10.5 kN to 3.2 k N during welding process.Higher TRS would generally induce higher welding heat input,which promotes the growth of the IMC layer and the softening of base materials.The IMC layer formed through solid-state diffusion and transformation instead of eutectic reaction according to the welding temperature history and interfacial microstructure,and its evolution process was clearly observed by plan view.In order to incorporate the effect of dramatic change of welding temperature which is the characteristic feature of FSW,Psd Voigt function was used to fit the welding temperature histories.A new prediction formula was then established to predict thicknesses of IMC layers with considering sharp welding temperature change.Predicted thicknesses gave good agreement with measured thicknesses obtained experimentally under different welding parameters,which confirmed the accuracy and reliability of the new prediction formula.Based on this prediction formula,the time period of temperature higher than 200℃during welding was found critical for the thickening of interfacial IMC layers.
基金support of the Na-tional Key R&D Program of China(No.2021YFA1600700)the Na-tional Natural Science Foundation of China(grant Nos.U22A20114,52322106,52192595,and 52301200)+2 种基金the Project funded by China Postdoctoral Science Foundation(No.2023M733573)CSNS Con-sortium on High-performance Materials of Chinese Academy of Sciences(No.JZHKYPT-2021-01)the Natural Science Foun-dation of Liaoning Province(No.2023-BS-020)。
文摘Non-isothermal aging(NIA)treatments have presented significant advantages in improving the comprehensive performance and aging hardening efficiency of the 7000 series aluminum alloys,but there is no attention paid to their composites.This study takes a linear heating aging process as an example to reveal the precipitation behaviors of a 15 vol.%SiC/7085Al composite as well as its impact on mechanical properties using differential scanning calorimetry,transmission electron microscopy,small-angle neutron scattering,hardness measurements,and tensile testing.The results indicated the formation of GP(Ⅰ,Ⅱ)zones,η’andηprecipitates in sequence,leading to the hardness and strength initially increasing and then decreasing with rising NIA temperatures.The maximums were reached at 183℃,corresponding to the appearance ofη’precipitates in large quantities.Owing to the rapid temperature rise during the NIA process,the precipitates entered the coarsening and redissolution stage before they were entirely formed,resulting in reduced peak strength compared to the T6 treatment.The composite exhibited a more significant reduction in strength than the 7085Al alloy because:(i)the annihilation of vacancies suppressed the formation of GPII zones,thereby weakening their transition toη’precipitates;(ii)quenching dislocations promoted the coarsening of precipitates.An improved NIA process,incorporating both heating and cooling aging treatments,was effectively designed with the assistance of in-situ SANS technology to address this issue,which allows for achieving strength comparable to that after the T6 treatment with only 15%of the aging time consumption.This research fills the gap in investigating the NIA precipitation behaviors of aluminum matrix composites,providing guidance for the formulation of NIA schedules.
基金supported by the National Natural Science Foundation of China(Nos.52475448,51975188)the Henan Provincial Science and Technology Research Project,China(No.222102220005).
文摘SiCp/Al composites are used in aerospace and deep-space exploration equipment because of their extremely high strength and thrust-to-weight ratios;however,the differences in the properties of the reinforcement and matrix materials in this type of composites have restricted their applications.The ultrahigh-frequency vibration characteristics of ultrasonic vibration processing technology can effectively solve the above bottlenecks,but the effect of high-frequency vibration on the interfacial properties of SiCp/Al composites is still unclear.The effects of ultrasonic vibration on the interface strength of composites were analyzed from a microscale perspective by means of single particle push-out Molecular Dynamics(MD)simulations and tests under different conditions.The results show that the interface strength is negatively correlated with particle size but positively correlated with ultrasonic amplitude,with a maximum increase of about 51%relative to no ultrasound.Brittle-plastic transition was observed on the surface of particles with high interface strength,and lateral microcracks due to stress concentration were present on the surface of particles with low interface strength.Higher strains and grain refinement were obtained for larger amplitudes,and stacking faults and tangle dislocations appeared on the side of the interface layer close to the Al matrix.The results provide potential insights to improve the micromechanical and mechanical properties of SiCp/Al composites,enhance the longevity of the materials,and realize the sustainable use of resources by expanding the efficient,precise,and clean machining of such materials.
基金Supported by the National Basic Research Program of China("973" Program)(613135)
文摘The effects of interface shape on stress wave distribution and attenuation were investiga- ted using finite element method （ FEM ）. The simulation results indicate that when the stress wave propagates from SiC ceramic to A1 alloy, the tensile stress decreases and the attenuation coefficient of the stress wave increases with increasing central angle of the concave interface between SiC and A1. But for the convex interface, the tensile stress increases and attenuation coefficient decreases with increasing central angle. As the stress wave propagates from A1 alloy to SiC ceramic, the atten- uation coefficient of stress wave decreases with increasing the central angle of the concave interface. For the convex interface, the attenuation coefficient increases with increasing central angle.
文摘This paper studies two-dimensional analysis of the surface state effect on current gain for a 4H-SiC bipolar junction transistor （BJT）. Simulation results indicate the mechanism of current gain degradation, which is surface Fermi level pinning leading to a strong downward bending of the energy bands to form the channel of surface electron recombination current. The experimental results are well-matched with the simulation, which is modeled by exponential distributions of the interface state density replacing the single interface state trap. Furthermore, the simulation reveals that the oxide quality of the base emitter junction interface is very important for 4H-SiC BJT performance.
