bluuebunny/crossref_metadata_2025 huggingface dataset:
Research on densification mechanism of Inconel 718 alloy miniature gear by electric field-assisted sintering
Authors: Ma L Y , Meng B , Zhang Z Y , Wan M
Published: December 2022

The densification mechanism of the electric field-assisted sintering (E-FAST) for Inconel 718 alloy miniature gears was studied using the Bernard-Granger model. Under the conditions of sintering temperature of 950 °C, 1000 °C and 1050 °C and dwelling time of 240 s, 300 s and 360 s, the Inconel 718 powders were subjected to E-FAST using the Gleeble thermal simulator, and the densification rate was up to 10−3 s−1. With the increase of the sintering temperature, the peak of the densification rate of the sintered sample was enlarged, and the time for the peak to appear became shorter. The densification of Inconel 718 alloy miniature gears was mainly concentrated in the dwelling stage. When the dwelling time reached 300 s, the densification rates of the samples under different temperature conditions were similar, indicating that the gear samples were close to full density at this time. Simulation and sintering test results show that the densification stages of the gear samples can be divided into low sintering stress stage with stress index n = 0.4 and high sintering stress stage with stress index n = 3.5. The apparent activation energy of the densification changes with the variation of the sintering stress stage.
Die design for fine micro-blanking process
Authors: Ji K S , Liu Y X , Zhang Y J , Zhang H
Published: December 2022

As the increase in demand for microparts of metal foil, the micro-blanking process with many advantages of plastic deformation has been widely applied on microparts manufacturing area. But the fracture zone of shearing surface is always present and affects the service life of the part. This paper proposes a new micro-blanking die based on fine blanking technology. In this die, the rubber as the power transmission device is selected to provide a blank holder force and counter force. In the FEM simulation, the influence of a few key die parameters is considered such as punching clearance and fillet radius of female die and punch. And the fine micro-blanking experiments for superalloy foils were conducted to evaluate the feasibility of the die designs. The results had shown the fine micro-blanking die proposed was able to be used for micro-blanking and obtain metal microparts.
Constitutive model and forming limit prediction of AA5182-O aluminium alloy sheet in electromagnetic forming
Authors: Liu W , Lin Y Z , Meng Z H , Li J Q , Huang S Y
Published: December 2022

Based on the electromagnetic hole-flanging (EMHF) experiment and numerical simulation, the inverse identifications of Johnson-Cook (J-C), Huh-Kang (H-K), Allen-Rule-Jones (A-R-J) and Cowper-Symonds (C-S) constitutive models were performed for AA5182-O aluminium alloy sheet at high strain rates. The accuracy of constitutive models was inspected by comparing the simulated height and thickness with experimental ones. The flow stress curves of AA5182-O aluminium alloy sheet at high strain rates were investigated. Based on the Marciniak-Kuczynski (M-K) model and constitutive models, the electromagnetic forming limit curves (EMFLC) of AA5182-O aluminium alloy sheet were predicted. The results show that the constitutive models at high strain rates can be determined by inverse identification on basis of EMHF. The flow stress curves at high strain rates predicted by different constitutive models are significantly distinguished. The constitutive model directly affects the numerical prediction of EMFLC. The EMFLC with J-C and A-R-J models shows little strain rate sensitivity, the EMFLC with H-K model shows positive strain rate sensitivity at a certain range of strain rate, and the EMFLC with C-S model shows significantly positive strain rate sensitivity.
Springback prediction model of Ti-6Al-4V tube warm bending based on modified JC model considering variable temperature field
Authors: Wang L , Wang Z L , Zhang S Y , Lin Y C , Fu M Y
Published: December 2022

The plastic forming of titanium alloy tubes at room temperature exhibits strong anisotropy, low elongation, and large deformation resistance. Numerical control warm bending assisted forming technology can improve the stability of the titanium alloy tube bending process, increase the bending limit and reduce the springback angle. This technology promotes the wide application of high-precision titanium alloy bent tubes in many high-end fields such as aerospace, shipbuilding, chemical industry, and military industry. However, the titanium alloy tube bending at high temperatures involves complex material rheological behavior and microstructure characteristics. The coupling relationship between the stress-strain properties of the material and the temperature field makes it difficult to predict the springback behavior of titanium alloy tubes after warm bending. In this paper, based on the mechanical behavior of titanium alloy tubes at high temperatures, a constitutive model of titanium alloy suitable for local heating is improved. The theoretical model of springback for warm rotary draw bending of titanium alloy tube is established. The influence of warm bending strategies on the springback of bending is studied. The theoretical model is verified by establishing a thermal-mechanical coupling finite element model for the whole process of warm bending under the state of heat balance. The results show that the bending springback theory based on the modified John-Cook model can accurately simulate the temperature change of titanium alloy tube section, adapt to local heating strategies and provide high prediction accuracy of bending springback.
High strain rate compressive behaviour of 6000-series aluminium alloy sheet under SHPB impact loading
Authors: Zhang F F , He K , Huang B , Chen H L
Published: December 2022

High velocity forming technologies are widely used in manufacturing industries to improve the formability of the aluminum alloy sheets. In order to better control the high velocity forming technologies through numerical simulation, the dynamic compression properties of the thin 6000-series aluminum alloy sheet were investigated by SHPB experiments. The influence of strain rate on the mechanical properties is analyzed in detail. Results show the elastic modulus is independent of the strain rate. However, under high strain rate condition, the yield stress, ultimate compression strength and ductility enhance with the increased high strain rate. So this 6000-series aluminum alloy sheet has significant strain rate sensitivity. As a reference, the quasi-static uniaxial tension test is also carried out and the uniaxial compressive stress-strain data in the literature is also listed. However, it is found the quasi-static uniaxial tensile yield stress is larger than the uniaxial compressive yield stress, and the quasi-static uniaxial compressive yield stress is lower than that under dynamic compressive condition. Results prove the aluminum alloy has obvious tension-compression anisotropy. For the high velocity forming technologies that take stretching as the main deformation mode, the dynamic tensile behaviour, instead of the dynamic compressive behaviour, should be used for accurate simulation.
Research on variation law of workpiece temperature of three roll skew rolling hollow axle
Authors: Wang J T , Shu X D , Zhang S , Xia Y X , Pater Z
Published: December 2022

To explore the variation law of workpiece temperature in the process of three roll skew rolling (TRSR) hollow axle, the process of TRSR hollow axle is tested and simulated in this paper. Firstly, the working principle of TRSR hollow axle is described; Then the blank and rolling process parameters are selected according to the actual performance of TRSR mill; Next, the finite element model is established, and the changes of workpiece temperature are studied; Finally, the simulation results are verified by experiments. The results show that the simulation results are basically consistent with the experimental results. The temperature change of workpiece in the rolling process is very small as a whole, and the temperature drop will be greater only at the place in contact with the die.
Development and perspectives of rolling of rib stiffened plate
Authors: Alfawzan Y , Shi Z , Lin J
Published: December 2022

Thin-wide aluminium rib stiffened plate structure reduces the weight and provides high stiffness, which makes it in high demand in transportation vehicles, marine, and structural applications for energy saving and CO2 emission reduction. In this study, the applicability of rolling in manufacturing an integral rib stiffened plate is reviewed through analysis of different rolling processes. The effect of rolling parameters and rib geometry on the formation and quality of ribs are analysed. The analysis provides an important basis to advance the understanding of metal flow, viscoplastic deformation and roll shape design during rolling, significantly helping the design of an innovative rolling process for rib stiffened plate. In addition, geometry and rolling parameters, plate curvature, and roll pass design (RPD), that highly affect the rolling process design are discussed. This paper presents the limitations and improvements of specific shape rolling processes and preliminarily concludes that rolling could be a potential method to produce high quality thin-wide panels with high stiffeners.
Study on grain deformation in bending zone of SUS304 stainless steel foil
Authors: Xu Y S , Xu L C , Zhang W G
Published: December 2022

In this paper, the grain deformation of SUS304 stainless steel foil under small fillet bending was studied. First, bending experiments were performed on 50 and 100μm thick foils, and the results showed that when the bending radius was close to the thickness of the foil, the surface grains in the bending zone collapsed and extruded, resulting in a rough surface. Then, Crystal Plastic Finite Element Method (CPFEM) was used to simulate the bending of different thickness foil (20, 50 and 100μm), in which the grains are hexagonal and the opposite edge distance is 20μm. Simulation results showed that when the relative fillet radius (the ratio of fillet radius to thickness) is similar, the surface layer of fillet becomes coarser with the increase of the foil thickness-grain size ratio. In addition, the uncoordinated intergranular deformation is caused by orientation difference, which leads to high density Geometric Necessary Dislocation (GND) in grain boundary region. Electron Backs-Scattered Diffraction (EBSD) experiments on recrystallized annealed foils with a thickness of 100μm showed that the GND density of the grain boundary after bending is significantly higher than that of the intragranular, which has the same distribution characteristics as the simulation results.
Effect of rolling reduction on the microstructure of the copper/aluminum composite strip produced by micro flexible rolling
Authors: Wang C , Ma L N , Ma X G , Wang T , Jiang Z Y , Dobrzański L A , Zhao J W
Published: December 2022

Copper/aluminum (Cu/Al) laminated composite has been extensively applied in the fields of batteries, electronics and electrochemistry owing to its cost reduction, light weight, good conductivity and resistance to corrosion. The Cu/Al composite strips produced by micro flexible rolling consist of three regions based on different thickness, i.e. the thicker, the transition and the thinner zones, and have a broad application prospect, especially in micro-electromechanical systems (MEMS). In this study, the effect of rolling reduction on the coordinated deformation of the Cu/Al interface and the microstructure of Cu/Al matrixes at three regions were investigated. The microstructure of the specimens was characterized using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and the thickness of thin strips with varying thickness (TSVT) were measured by laser scanning microscope to explore the mechanism of microstructural evolution. The results show that the increase of rolling reduction gives a rise to the proportion of deformation occurred in the Al matrix, and the fracture of the intermetallic compounds (IMCs) is observed at the interface, which plays a significant role of transmitting and releasing stress during plastic deformation.
Biaxial tension under bending and compression - development of a new formability test for incremental sheet forming
Authors: Ai S , Long H
Published: December 2022

A new testing method, Biaxial Tension under Bending and Compression (BTBC), is developed to investigate the effect of different deformation modes on material formability in Incremental Sheet Forming (ISF). A cruciform specimen is designed by simulating the material deformation under biaxial tension using Finite Element (FE) method. In the BTBC experimental testing, the cruciform specimen can be stretched in biaxial directions and the strain ratio of the two perpendicular directions can be varied. Furthermore, the superimposed effect of compression, bending and cyclic loading can be investigated. Material formability of aluminium alloy AA5251-H22 under plane strain path is tested. True strains of the specimen under different deformation modes are obtained by measuring distortions of circular grids inscribed onto the surface of the specimen. The experimental results show that the introduction of bending and compression contributes to localised material deformation. Material formability is improved by the introduction of bending, which is further enhanced by applying compression and cyclic loading. The BTBC test overcomes the limitation of commonly used testing methods in ISF formability studies, providing a fundamental explanation of the effect of strain path and loading conditions on the material deformation and fracture behaviour in ISF.
Study on dynamic recrystallization mechanism and model of TB15 titanium alloy
Authors: Zhang D , Dong X J , Xu Y , Tu Z L , Lu S Q , Gong S H
Published: December 2022

TB15 titanium alloy has shown a good application prospect in aviation large-scale structural parts. In this paper, the dynamic recrystallization (DRX) mechanism and model of TB15 titanium alloy were studied by thermal simulation compression experiment in temperature range of 810-930°C and strain rate range of 0.001s−1-10s−1. The microstructures under different deformation conditions were analyzed by optical microscopy (OM) and electron back scatter diffraction (EBSD). The results show that the degree of dynamic recrystallization decreased significantly with the increase of strain rate, and the nucleation position of dynamic recrystallization tended to migrate from the interior of grain to grain boundary. At low strain rate, the continuous dynamic recrystallization (CDRX) mechanism of subgrain merging and rotation was dominant. When the strain rate was 10s−1, the rare geometric dynamic recrystallization (GDRX) occurred due to strong strain concentration effect, and the dynamic recrystallization grains showed fine chain distribution. Finally, the DRX critical strain, volume fraction and grain size models of the studied alloy were established, and the DRX volume fraction model was modified by quantitative microstructure.
An analytical model for predicting the extrusion force for the torsion extrusion process of metals
Authors: Liu Z Y , Zhao S L , Cui Z S
Published: December 2022

Torsion extrusion (TE) method as a severe plastic deformation (SPD) process can effectively refine the microstructures and improve the mechanical properties of materials. Accurate and rapid prediction of the extrusion force in the process of TE is an important problem in industry. This paper proposed an analytical model using upper bound method (UBM) for predicting the extrusion force in the TE process. The kinematically admissible velocity field is established based on a continuous spherical extrusion velocity field coupled with a torsional velocity field constrained in a conical die. The torsional angular velocities along the radial and axial directions are assumed with quadratic and cubic function, respectively, due to the radial and axial nonlinearity of torsional velocity in the deformation zone. In addition, considering its complexity, the shape of the deformation zone is mapped to a rectangular zone. By establishing the torsional velocity field in the mapped zone, the torsional velocity field of the deformation zone is obtained according to the mapping relation. The UBM model is validated by comparing the predicted extrusion force with the simulation results obtained from the finite-element method (FEM). Moreover, the influences of the friction factor, reduction ratio and die angle on the extrusion force were investigated as well.
Analysis of grain size distribution evolution of steel during recrystallization and grain growth
Authors: Seppälä O , Pohjonen A , Ali M , Larkiola J , Fabritius T
Published: December 2022

Controlling the hot rolling process requires a deep understanding of the underlying metallurgical phenomena. Quantitative methods are of paramount importance for achieving the capability of controlling microstructural evolution. Since the final mechanical properties of steel result from microstructural evolution in the whole process, analysis of the microstructure provides an important input for numerical simulations that can be used for tailoring the mechanical properties of steel. The evolution of grain size distribution of a low-carbon CrNiMnB ultrahigh-steel in austenitic state is studied in hot forming and annealing using experimental data obtained with the Gleeble 3800 thermo-mechanical simulator. A general method is described that can be utilized to systematically compare the grain size distributions obtained from the experimental studies. The experimental data has been obtained from laser scanning confocal microscopy images using the mean linear intercept method. A custom-made semi-automatic software has been utilized to process the data rapidly and reliably.
Design of a novel experimental profile for the development of a numerical model for extrusion processing of a magnesium alloy
Authors: Plumeri J E , Misiolek W Z
Published: December 2022

Magnesium alloys are an important structural material to many global industries. Their high specific physical properties are useful in the design of lightweight engineering systems. In this study, the development of a numerical model for the prediction of high-temperature extrusion of an Mg-Zn-Ce alloy (ZE20) is presented. A novel design of an I-shaped profile for extrusion processing was created as part of this effort. This design was used to produce extrudates with large strain gradients across a single profile. In parallel, new numerical tools were developed to predict the extrusion behaviour of the ZE20 alloy. Finite element simulation of the indirect extrusion laboratory trials was used to calibrate the numerical model. Microstructural measurements of experimental samples through EBSD analysis were compared with simulation calculations, and insights into the relationship between extrusion temperature, strain, and resulting microstructure were gained. A fully recrystallised, bimodally distributed grain microstructure was observed throughout the samples. Proportions of grain refinement within the bimodal distribution were shown to correspond with localised strain gradients for a profile with nearly uniform temperature. Ultimately, extrusion press load calculations using the numerical model were shown to be within 5% of experimental trial values.
Investigation of flexible free incremental sheet forming (FFISF) process to form Ti6Al4V free-form surface panel at room temperature
Authors: Yang M , Chang Z D , Chen J
Published: December 2022

Titanium alloy sheet metal shows promising applicability in the aerospace industry with excellent mechanical properties, while its limited room-temperature formability is essential to be improved by thermal-assisted methods, with expensive equipment and much energy consumption. In this work, the flexible free incremental sheet forming process is adopted to manufacture Ti6Al4V free-form surface panel at room temperature. The strain evolution and thickness distribution during this new process are also analysed through finite element methods to reveal the deformation mechanism. Experimental and simulated results show that this process has potential advantages in rapidly fabricating low-ductility sheet metal with complex shapes at room temperature by improving strain and thickness distributions.
Plastic deformation behavior of Ti45Nb in ultrasonic vibration-assisted compression
Authors: Yu C X , Zhang L , Wang Z L , Zhai Y D , Shao C , Zhai J Q , Guan Y J , Lin J
Published: December 2022

Ti45nb is a commonly used titanium alloy with high strength for aviation. However, it is mainly cold formed under conventional conditions and cracks often occur when deformation is large. Ultrasonic vibration-assisted compression test of Ti45Nb titanium alloy was carried out on a universal testing machine equipped with an ultrasonic vibration system. The influence of ultrasonic vibration on the deformation behavior of Ti45Nb was investigated. The results showed that ultrasonic vibration can significantly reduce the flow stress in the deformation process, and the reduction amplitude increases with the continuation of the compression process. The decrease in flow stress is caused by the stress superposition and acoustic softening effect. Compared to the conventional compression test, the grain in the center of the ultrasonic vibration-assisted compressed sample is finer, and the thickness of the lamellar substructure in the shear band is thinner. Therefore, ultrasonic vibration has a promoting effect on the deformation of Ti45Nb alloy.
Model for characterizing static softening behaviour of GH4500 superalloy during two-pass thermal compression
Authors: Zhou Z Y , Wang Y W , Zhu S , Guo L G
Published: December 2022

In this work, the static softening behaviour of GH4500 superalloy during the two-pass thermal deformation was investigated via thermal-simulation compression experiments at the temperature range of 1293 K to 1373 K, strain rate range of 0.01 s−1 to 1 s−1 and interval time range of 0 s to 180 s. The metallographic structure acquired from optical microscope (OM) indicated that both static recovery (SRV) and post dynamic recrystallization (PDRX) would occur during the holding stage. Meanwhile, the influence of interval time, deformation temperatures and strain rates on static softening behaviour were revealed. The results showed that the softening effects principally induced by PDRX strengthened with the increase of the interval time, deformation temperatures and strain rates. To quantitatively describe the PDRX kinetic process of GH4500 superalloy, a model on grounds of Avrami kinetics was established to predict the PDRX softening fraction via eliminating the effect of static recovery. The predicted data of the PDRX softening fraction were well consistent with the experimental data, manifesting that the model could precisely evaluate the PDRX softening behaviour in the stage of inter-pass holding.
Experimental investigation of longitudinal and transverse welds during sideways extrusion
Authors: Lu X , Yu J , Yardley V A , Wu Z , Liu H , Shi Z , Lin J
Published: December 2022

Differential velocity sideways extrusion (DVSE) is a novel process for fabricating curved profiles; welding quality during extrusion is an important issue for its industrial application. In this study, solid bars of aluminium alloy AA1070 were extruded from multiple billets at 500 °C using the novel process and the microstructure and mechanical properties of the extrudate were investigated. The weld formed between the billets includes longitudinal and transverse solid-state weld regions formed as the metal was extruded. The longitudinal welds have better mechanical properties than the transverse welds. Dynamic recrystallisation (DRX) occurred in areas with high dislocation density during the extrusion process and as a result, grains across the bonding interfaces of longitudinal welds have been formed, which improves the weld quality. In the areas with the transverse welds, macro weld defects can be observed at the weld front. With further progress of sideways extrusion, the defect density reduced and new grains formed at the bonding surface.
Effects of annealing temperature on micro deep drawing of stainless steel-copper composite
Authors: Qi Y Y , Ma X G , Ma L N , Wang T , Jiang Z Y , Dobrzański L A , Zhao J W
Published: December 2022

With the advantages of high utilization of raw materials, high precision and low cost, micro metallic parts produced by micro deep drawing (MDD) have been tremendously used in a variety of fields such as micro-electromechanical systems (MEMS), vehicle engineering and chemical engineering. In order to study the deformation behavior of two-layer stainless steel-copper composite foils during MDD, a series of MDD tests were performed with specimens annealed at temperatures ranging from 600 to 1000 °C. The results show that complete circular cups cannot be formed using the as-received material due to its poor formability. For the specimens annealed at 600 and 700 °C, significant wrinkling is observed on the drawn cups. Differently, few wrinkles are characterized on the drawn cups when the composite foils are annealed at temperatures ranging from 800 to 1000 °C. An optimal annealing temperature of 800 °C is obtained for the MDD of stainless steel-copper composite cups with high surface quality.
A flow forming process model to predict workpiece properties in AISI 304L
Authors: Arian B , Oesterwinter A , Homberg W , Vasquez J R , Walther F , Kersting L , Trächtler A
Published: December 2022

The control of workpiece properties enables an application-oriented and time-efficient production of components. In reverse flow forming, e.g., the control of the microstructure profile, in contrast to the adjustment of the geometry, is not yet part of the state of the art. This is particularly challenging when forming seamless tubes made of metastable austenitic stainless AISI 304L steel. In this steel, a phase transformation from austenite to martensite can occur due to mechanically and/or thermally induced energy. The α’-martensite has different mechanical and micromagnetic properties, which can be advantageous depending on the application. For the purpose of local property control, the resulting α’-martensite content should be measured and controlled online during the forming process. In this paper, results from an empirical correlation model of process parameter combinations and resulting α’-martensite content as well as geometry will be presented. Based on this, the focus of the paper will be on process modeling by means of FEM in order to create the transition to a numerically supported process model. Furthermore, it will be specified how the numerical process model can be used in a predictive manner for an online closed-loop process control.
Layout optimization of robot forging unit based on genetic algorithm
Authors: Zhang N , Zhao Y B , Liu Q S , Zeng Q , Liu B , Ding X Y
Published: December 2022

To improve the productivity of automated forging production units, reasonable layout is very important. In this paper, the layout optimization method of the robot working unit was studied to improve the production efficiency of forged crankshaft products, the bottleneck production unit is taken as the research object to find a satisfactory solution to the layout planning. Based on a mathematical model, a hierarchical description method of robot workspace and a prediction method of transition points were proposed. The robot running time and operability were used as evaluation indexes of the layout. The NSGA-II algorithm was used to optimize the layout scheme to obtain a better solution, and the optimized solution has better operability and runtime performance. The simulation results of professional software showed that the proposed layout optimization method and layout scheme were reasonable and significantly improved.
Simulation and experiment of thermal deformation behavior of reflector panels with honeycomb sandwich structure
Authors: Li D S , Ye M X , Wang M M , Liu J Q
Published: December 2022

The honeycomb sandwich structure reflector panel is a multilayer structure formed by three-layer aluminum plate and two-layer honeycomb bonded by epoxy resin adhesive, and its thermal deformation behavior is complicated. In this study, the thermal deformation behavior of the reflector panel is studied by a combination of experiment and finite element simulation.

Firstly, the thermal deformation analysis finite element model of reflector panels with honeycomb sandwich structure is established. The three-layer aluminum plate is modeled according to actual geometric parameters and adopts shell element model. The honeycomb core is equivalent to a homogeneous orthotropic layer with a constant thickness. The elastic modulus of the equivalent model of the honeycomb core with adhesive are obtained through the tensile and compressive mechanical performance tests. Then, the temperature deformation experiment of the honeycomb sandwich structure panel is carried out. Combined with the experimental results and the thermal deformation simulation analysis model, the multi-island genetic algorithm is used to modify the thermal expansion coefficient of the honeycomb core layer.

Finally, the thermal deformation behavior of the reflector is verified by finite element simulation and experiment. The results show that the profile error distribution caused by the panel thermal deformation has continuous symmetry. From the error distribution trend and numerical deviation, the established simulation model can be used to predict the thermal deformation of sandwich panels.
Effect of in-situ transverse magnetic field on the fluid flow, microstructure evolution and corrosion resistance of GMAW 316L stainless steel
Authors: Zhong Y , Zheng Z Z , Li J J , Wang C
Published: December 2022

In order to modify heat and mass transfer, alter crystal orientation and suppress elemental segregation of the molten pool by electromagnetic stirring effect, a new in-situ transverse magnetic field generated by clamp-type electromagnet integrated with a 6-axis robot was firstly applied to real-time control the arc characteristic and fluid flow when welding 316L stainless steel by GMAW-CMT. As the magnetic field intensity at the end point of the wire increases from 0 mT to 14.6 mT and then 20.7 mT, the 316L welding bead morphology becomes flatter, and their cross sections clearly exhibit a lower welding reinforcement, a wider welding width and a smaller welding penetration. Microstructure observations show that the application of in-situ transverse magnetic field in GMAW-CMT process can contribute to the lower inner porosity, the smaller stress concentration, the more dispersed austenite grain orientation and the elimination of residual skeletal ferrite distributed in the austenite matrix. CPP and EIS tests indicate that 14.6 mT molten pool exhibits the highest pitting corrosion resistance and the most compact passive film, which is related with the finer cellular γ grain with dispersed orientation and less Cr-Mo atomic segregation on the boundary. The deflection of arc column and the fragmentation of dendritic tips induced by the Lorentz force under the appropriate transverse magnetic field are verified, which provides great potential for optimizing weldment performance.
Hot workability and microstructure evolution of wire arc additive manufactured 300M steel
Authors: Xiong Y B , Wen D X , Zheng Z Z , Li J J
Published: December 2022

Wire arc additive manufacturing (WAAM) technology offers a material-saving and efficient method of manufacturing the 300M steel components, but the obtained microstructure and properties hardly reach the level of wrought materials. By combining WAAM technology with forging process, a novel forming process is proposed. The preferred shape pre-forgings are easily prepared, and the number of forging steps significantly decreases. The WAAMed as-cast microstructure also can be transformed into the wrought state by the proposed forming process. The aim of this study is to investigate the hot deformation behavior and microstructure evolution of WAAMed 300M steel under various deformation temperatures and strain rates. The results show that the WAAMed 300M steel exhibits a higher plastic deformation resistance than the wrought 300M steel. With the increase of deformation temperature and strain rate, the difference of flow stress between the WAAMed and wrought 300M steel decreases. The hot deformation activation energy of WAAMed 300M steel is calculated as 374.1 kJ/mol, which is much higher than that of wrought 300M steel (332.3 kJ/mol). The possible processing windows obtained from the hot deformation activation energy maps are 1040-1120 °C/0.01-10 s−1 for the WAAMed 300M steel and 1010-1130 °C/ 0.1-10 s−1 for the wrought 300M steel. The constitutive model considering strain compensation is established to describe the hot deformation behaviors of WAAMed and wrought 300M steel. The high correlation coefficient and low average absolute relative error confirm the suitability of the developed constitutive models for predicting the flow stresses of WAAMed and wrought 300M steel.
Plastic deformation behavior of aluminum alloy fiber porous body and its filled tube under impact loading
Authors: Zheng S W , Peng Y H , Zhang Z R , Wu F
Published: December 2022

The size of aluminum alloy fiber wire with a short side of 5mm, a long side of 10mm and an arc radius of 1mm were prepared from the raw material of 6061 aluminum alloy fiber with diameter of 0.15mm by Spring machine cutting, namely the structure size of 5×10mm bending aluminum alloy fiber. The aluminum alloy fiber porous body with different porosity were prepared by vacuum hot pressing sintering furnace, and it was sleeved with 6063 aluminum alloy round tube to prepare aluminum alloy fiber porous body filled tube. The impact test was carried out with drop hammer impact testing machine, The plastic deformation behavior of aluminum alloy fiber porous body and its filled tube under impact loading with different porosity was studied. The results show that the impact process of aluminum alloy fiber porous body can be divided into three stages: plastic platform stage, densification stage and unloading stage, the filled tube with aluminum alloy fiber porous body can be divided into four stages: elastic deformation stage, progressive buckling stage, densification stage and unloading stage. Low porosity will make more fibers, and more benefit the generation of the sintering necks, the plastic deformation strength increases with the porosity decrease. The coupling effect of the aluminum alloy tube and the aluminum alloy fiber porous body makes the filled tube absorb the same energy with shorter impact displacement, and has stronger impact resistance and better mechanical properties.
Improved binarization based method for local formability characterization of modern steels
Authors: Upadhya S , Rosenthal S , Wernicke S , Yasir M , Unruh K , Tekkaya A E
Published: December 2022

True fracture strains obtained from the fracture surface area measurement of tensile test specimens allow for gauge-length independent characterization of the local formability. It is difficult and error prone to use the norm method (ASTM-E8) for fracture area measurement on modern advanced high strength steels (AHSS) owing to the irregular fracture surface and excessive necking, as this makes the accurate identification/measurement difficult and leads to high scattering. The presented work aims to solve this problem in local formability measurement and make the measurement process more robust. The results of the proposed approach, which involves specimen masking and image binarization show that through this method it is possible to improve the repeatability of the measurements, reduce the scattering due to operator influence and significantly reduce the time required for the measurements.
Investigation on thickness size effect on ductility of magnetron sputtered Niobium coatings on SS316L substrate for forming of precoated metallic bipolar plates
Authors: Li C Z , Xu Z T , Peng L F , Lai X M
Published: December 2022

Metallic bipolar plates (BPPs) are key components of the proton exchange membrane fuel cell (PEMFC). To lower the fabrication cost of metallic BPPs, precoated BPPs have attracted much attention due to the high efficiency of precoating-stamping process. However, precoatings on metallic substrate tend to crack during the forming process, leading to deterioration or even complete loss of corrosion resistance. Therefore, to avoid micro cracks of formed precoated BPPs, development of coatings with high ductility is necessary. In this study, Niobium coatings with different thicknesses on SS316L substrate are prepared with magnetron sputtering process, and uniaxial tensile tests are then conducted for the precoated specimens to evaluate their ductility. The microstructure and fracture behaviour of the Niobium precoatings are characterized by XRD, SEM, TEM, laser confocal microscope analysis. It is found that with the increase of coating thickness, the number of micro cracks at the same strain decreases significantly, and the strain for the first crack to appear also increases. Furthermore, a brittle-to-ductile transition of fracture mechanism is observed. The grain size of Niobium nanocrystalline coating increases with the thickness, which leads to the improvement of plasticity and failure strain. Therefore, the application of precoated metallic BPPs is further advanced.
Research on short process hot forming technology of a medium manganese steel
Authors: Hou Z R , Min J Y , Wang J F , Lu Q , Zhang X , Lin J P
Published: December 2022

Carbon neutrality and carbon peaking are one of the key tasks of our country in the future. As a major carbon producer, the steel industry played an important role in achieving energy conservation. The feasibility and benefits of rapidly heating (over 100 °C/s) has been proven to be effective for producing press hardening steel, which can also shorten the hot forming process. In this work, we studied the application of short hot forming process in a medium manganese steel. Results shown that the new process can greatly reduce the austenitizing time while ensuring the strength of the materials. In addition, the short-term heating of the material in a non-equilibrium state exacerbated the uneven distribution of alloying elements. Thus, the content of retained austenite in the final microstructure doubled (increased from 8.7% to 18.5%) through the new process, thereby further improving the toughness of the material. The microstructure evolution and mechanical properties of the material under the short process hot forming process was analysed, together with the feasibility of the new process in the future industrialization.
Investigation on the thermo-mechanical properties of hot stamped parts by using laser-implanted tool surfaces
Authors: Schirdewahn S , Carstensen N , Hilgenberg K , Merklein M
Published: December 2022

In the automotive industry, hot stamping has been established as a key technology for manufacturing safety-related car body components with high strength-to-weight ratio. During the forming operation, however, hot stamping tools are highly stressed by cyclic thermo-mechanical loads, which encourage the formation of severe wear and high friction at the blank-die interface. Against this background, an innovative surface engineering technology named laser implantation has been investigated for improving the formability of the parts and the efficiency of the hot stamping process. The laser implantation process is based on the generation of highly wear resistant microfeatures on tool surfaces by embedding hard ceramic particles via pulsed laser radiation. As a consequence, the contact area of the tool and thus the tribological and thermal interactions at the blank-die interface are locally influenced. In previous studies, the improved tribological performance of the modified tool surfaces has already been proven. However, the thermal interactions between tool and workpiece have not been analyzed, which in turn have a significant impact on the resulting part properties. In this regard, quenching tests have been carried out under hot stamping conditions by using conventional as well as laser-implanted tooling systems. Based on these results, Vickers hardness test and optical measurements have been performed on the quenched blanks, to qualify the mechanical properties and clarify the cause-effect relations.
Characterization of anisotropic hardening of AA3003-O
Authors: Lou Y , Chen Z , Zhang C , Jiang N , Yang G
Published: December 2022

This research aims to characterize the anisotropic hardening behaviour AA3003-O under uniaxial tension by experiments and analytical modelling. Experiments are conducted with dogbone specimens along different loading directions under quasi-static conditions to characterize the strain hardening behavior of the alloy under different loading conditions. Experimental results show the strong anisotropic hardening behaviour of the alloy under uniaxial tension along different directions. The anisotropic hardening behaviour is analytically characterized by the Yld2000-2d, Stoughton-Yoon2009 and a newly proposed anisotropic hardening models. The analytical predicted yield surfaces are compared with experiments and other constitutive models. It demonstrates that the proposed functions provide the best accuracy for the modelling of anisotropic hardening behaviour of uniaxial tension along different directions.
Investigation on temperature uniformity control of titanium extrusion in hot stretch bending process
Authors: Cao F C , Liu B S , Zeng Y S , Wu W , Wang Y J
Published: December 2022

Regarding to the impact of temperature on springback in hot stretch bending (HSB) process, this work proposed an investigation on temperature uniformity control of titanium extrusion in HSB process based on the mould which can be elevated by resistance heating. Prior to the HSB test, mould structure was designed to fit for resistance heating. Coupled thermal electrical structural finite element model of HSB process was created in ABAQUS. Resistance heating and HSB tests were performed using displacement control electrically assisted stretch bending machine. The results of simulation indicate that the temperature uniformity of titanium extrusion and the forming accuracy of curved part can be effectively improved by increasing the initial temperature of mould. At last, the curved part of titanium extrusion with L-section was achieved, and the forming accuracy of which was measured and evaluated.
Mechanical and geometrical characterisation of tumbling self-piercing riveting joints in multi-material-systems
Authors: Wituschek S , Lechner M
Published: December 2022

Increasing requirements on lightweight construction to preserve resources necessitate new processes and methods in the production of weight-optimised multi-material-systems. Common joining processes such as the conventional semi-tubular self-piercing riveting are reaching their limits because of the rigid process designs. To extend this process, the linear punch movement is superimposed by an orbital forming process with a tumbling kinematic and provides new possibilities to influence the joining process. The configuration of the tumbling strategy consisting of the parameters tumbling angle and tumbling kinematics enables a targeted control of the material flow for the production of tailored joints. Within the scope of the investigations, the influence of the two parameters is examined both for the joining process and for the resulting joint formation. Force-displacement diagrams, micrographs and rivet head geometries are analysed to determine the influence on the process itself. Further, shear tensile tests and cross section tests are carried out to characterise the load-bearing capacities of tumbled joints and to identify the effects of the tumbling strategy on the mechanical properties. The tested materials in form of a dual-phase steel HCT590X+Z and a precipitation-hardening aluminium alloy EN AW-6014 have widely varying mechanical properties to represent multi-material-systems.
Construction of anhydrous two-step organosolv pretreatment of lignocellulosic biomass for efficient lignin membrane-extraction and solvent recovery
Authors: Song Guojie , Sun Chihe , Hu Yun , Wang Chen , Xia Changlei , Tu Maobing , Zhang Ezhen , Show Pau-Loke , Sun Fubao
Published: December 2022

Glycerol organosolv (GO) pretreatment has been revealed to be potent in selectively deconstructing the lignocellulosic biomass and effectively enhancing its enzymatic hydrolysis, but the conventional solid washing and GO lignin extraction processes frequently consume large amounts of water, resulting additionally in difficulty recycling the glycerol. In this study, an anhydrous two-step organosolv pretreatment process was explored, followed by the membrane ultrafiltration of glycerol lignin. The results showed that the solid washing of the residual glycerol after the atmospheric glycerol organosolv (AGO) pretreatment was necessary for the subsequent operation of high-solid enzymatic hydrolysis. Washing with ethanol was desirable as an alternative to water as only a low glycerol content of 5.2% resided in the substrate. Membrane ultrafiltration was helpful in extracting the AGO lignin from the pretreatment liquor, in which a high lignin extraction of 81.5% was made with a regenerated cellulose membrane (cut-off for 1 kDa) under selected ultrafiltration conditions. With the characterization of membrane-extracted lignin, it was observed for the first time that the AGO lignin has a well-preserved structure of G/S type. Moreover, the lignin was enriched with reactive groups, i.e. β-O-4′ linkages and aliphatic hydroxyl groups, which was very likely due to the glycerol grafting onto the lignin via α-etherification reaction. The two-step organosolv pretreatment process allowed 86% of glycerol and 92% of the ethanol recovery with ∼78% of distillation energy savings, which was applicable for extraction of organosolv lignin and recycling use of organic solvents.