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Both a conventional flow distributer and an improved one with a flow buffer were applied respectively during the high pressure die casting (HPDC) process, and samples of AZ91D magnesium alloy with different microstructure mainly consisting of α-Mg grains, β-phase and porosities were obtained. According to the grain orientation analysis, the predominant deformation behavior in α-Mg grains was dislocation slip, supplemented by deformation twinning. Dislocation slip was more difficult to occur in the samples with the improved flow distributer on account of the fact that the size of α-Mg grains in the microstructure was finer and more uniform. During the in situ tensile deformation test, cracks were observed to initiate from gas-shrinkage pore and island-shrinkage, and two main crack propagation mechanisms, porosity growth and coalescence were found accordingly. When the crack was in contact with the β-phase, it would pass through and fracture the network β-phase, whereas bypass the island β-phase by detaching it from the surrounding α-Mg grains. Mechanical property tests showed that the samples with relatively more homogeneous microstructure would perform higher mechanical properties, which was the combined effect of matrix α-Mg grains, β-phase, and porosities.

Exploring nonprecious electrocatalysts for water splitting with high efficiency and durability is critically important. Herein, bimetallic phosphides are encapsulated into graphitized carbon to construct a C@NiCoP composite nanoarray using bimetallic metal–organic framework (MOF) as a self-sacrificial template. The resulting C@NiCoP exhibits superior performance for pH-universal electrocatalytic hydrogen evolution reaction (HER), particularly representing a low overpotential of 46.3 mV at 10 mA cm−2 and Tafel slope of 44.1 mV dec−1 in alkaline media. The structural characterizations combined with theoretical calculation demonstrate that tailored electronic structure from bimetal atoms and the synergistic effect with graphitized carbon layer could jointly optimize the adsorption ability of hydrogen on active sites in HER process, and enhance the electrical conductivity as well. In addition, the carbon layer served as a protecting shell also prevents highly dispersed NiCoP components from agglomeration and/or loss in harsh media, finally improving the durability. This work thus provides a new insight into optimizing activity and stability of pH-universal electrocatalysts by the nanostructural design and electronic structure modulation.

Different types of polymer films were used in the combined in-mold decoration and microcellular injection molding (IMD/MIM) process. The multiphase fluid-solid coupled heat transfer model was established to study the thermal response at the melt filling stage in the IMD/MIM process. It was found that the temperature distributed asymmetrically along the thickness direction due to the changed heat transfer coefficient of the melt on the film side. When polyethylene terephthalate (PET) films were applied, the temperature of the melt-film interface increased faster and to be higher at the end of melt filling stage in comparison with the application of polycarbonate (PC) and thermoplastic polyurethane (TPU) films. And the effects of film types on the cellular structure, forming defects and mechanical properties of IMD/MIM parts were also studied experimentally. The results showed that the film types had no obvious effect on the cells size in the transition layer and the mechanical properties of the parts. Under certain film thickness, the offset distance of core layer was the largest with PET film used, while the offset distance was the smallest with TPU film used. And similar results were found for the warpage of the parts. However, an exactly opposite change occurred for the thickness of film-side transition layer and the bubble marks on the surface of the parts.

In this work, effect of martensite pre-quenching on the subsequent bainite transformation kinetics of GCr15 bearing steel has been investigated by means of dilatometry. The results show that the pre-quenched martensite is significantly accelerate nucleation of subsequent bainite transformation in comparison with direct bainite austempering. Meanwhile, specimen of martensite pre-quenching at 200 °C has the shortest incubation period of bainite transformation at 240 °C. Moreover, the transformation rate of bainite transformation after martensite pre-quenching is faster than direct bainite austempering in the initial growth stage, and decrease with the decreasing of martensite pre-quenching temperature. Compared with the conventional quenched and tempered (QT) specimen, the tensile strength is slightly decrease from 2170 MPa to 2143 MPa, but the impact toughness is obviously increase from 43 J to 71 J in specimen heat-treated by martensite pre-quenching at 200 °C and subsequent bainite transformation at 240 °C. In addition, the mechanical stability of retained austenite in all martensite pre-quenching specimens are higher than that of QT specimen.

Water scarcity is a critical issue in desert and arid regions, and atmospheric water harvesting is a potential solution. The challenge is lacking ideal adsorbents that can efficiently capture water from low-humidity air and be regenerated readily. Herein, we report a hydrolytically stable metal-organic framework (MOF), [Cu2(AD)2(SA)] (Cu-AD-SA), with excellent performance in water harvesting. More importantly, this material can be facilely prepared from two easily accessible ligands adenine (HAD) and succinic acid (H2SA). Cu-AD-SA has a three-dimensional (3D) framework structure with the crs topology and intersecting channels of ∼5 A in diameter. The channel surface is decorated by uncoordinated aromatic N atoms, amine groups, and alkyl moieties. Interestingly, Cu-AD-SA shows a high water adsorption capacity of 0.16 g g-1 at low pressure of 0.2 P/P0 and 25 °C. Furthermore, dynamic water adsorption-desorption cycling experiments demonstrated a stable working capacity of 0.13 g g-1 for uptaking water from a low-humidity air (water partial pressure: 0.85 kPa, 20% RH at 30 °C, 5.3% RH at 55 °C) at 30 °C and desorption at 55 °C. The water adsorption mechanism was also studied by analyzing its single-crystal structure after water loading. The results indicated the existence of strong H-bonding interactions between water molecules and uncoordinated N atoms and amine groups on the framework, which should play an important role in the high adsorption at low pressure. All the above features suggest great potential of Cu-AD-SA for water harvesting in arid regions.

To accurately predict the dynamic behaviors of high speed ball bearings, an investigation on the sliding behavior of balls at high and low speeds, and light and heavy loads is necessary. However, existing nonlinear dynamic models fail to consider comprehensively key factors such as asperity and hydrodynamic tractions, time-varying friction coefficient and time-varying lubricant mode. In this work, these influencing factors are integrated into the nonlinear dynamic model to make it suitable for the working conditions of high and low speeds and light and heavy loads. The dynamic analysis provides the relation of angular speeds of balls with spin and sliding at light and heavy loads, also it reveals the number of pure rolling point under the combined effect of differential sliding and spin sliding. Research results provide a reliable mathematical model and theoretical bases for further studying the dynamic behaviors of high speed ball bearings.

Adhesively bonded carbon fiber reinforced polymer (CFRP)/Al joints have been widely used in engineering field. However, the bonding strength still needs to be improved. In this study, ultrasonic vibration was applied during the adhesive bonding to promote the micromechanical anchoring at the interface of CFRP/Al joints. Ultrasonic vibration was exerted on the CFRP laminate to transmit the vibration to the adhesive bonding area once the joint was assembled. The strength and the strength consistency of the joints were increased by 45% and 50%, respectively. Scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) results showed that the ultrasonic vibration promoted the filling of the adhesive into the microstructures of the adherends and achieved a more compact bonding. Viscosity and contact angle of the adhesive were measured, and both of them were decreased greatly under the ultrasonic vibration, indicating that the ultrasonic vibration can increase the fluidity of the adhesive and force the wetting between the materials. Ultrasonic capillary experiment was then conducted. The adhesive in the capillary tube was prompted to rise obviously, and the meniscus was inverted with ultrasonic vibration, showing that the ultrasonic vibration produced a driving effect on filling of the adhesive in the microstructures. Therefore, the joints exhibited improved bonding strength owing to the enhanced micromechanical anchoring and physical adsorption at the bonding interface. This study is of great significance for understanding and optimization of the ultrasonic vibration strengthened adhesive bonding.

For the robotic GMAW on complex surface, the welding position is various along the welding path at different region, which results in the diverse molten pool behaviors, forming appearance or even the defects. To investigate the molten pool behaviors and forming appearance on the complex surface, the welding pose on the surface was described, the computational fluid dynamics model of the weld pool considering the droplet impingement, gravity, arc force, heat and mass transfer for four typical welding position was developed. The influence of gravity on the fluid flow for different position was investigated, and the results were validated with the high-speed welding camera. The deposition experiments with different welding current and local inclined angle were conducted to analyze the influence of the welding parameters and surface geometrical structure on the forming appearance. The results indicated that the influence of the gravity on the flow field and forming appearance at various welding position was different. The effect increased with the welding current, the surface local inclined angle (α∈[0, 90°]), and the absolute value of speed angle (|β|∈[0, 90°]), which was minimized when the torch travel direction was perpendicular to the gravity (β = 0°), because of the attenuated influence on the backward fluid flow. The findings help explain the molten metal forming mechanism of the welding on complex surface and improve the forming appearance.

Combined with the recrystallization models, a 3D thermo-mechanical coupling finite element model is established to predict the microstructure evolution in the automotive front axle beam during the hot forging processing. It attempted to reveal the relationship between the forging processing and microstructure evolution. The numerical results show that after forging the average temperature of billet is higher than 850°C, indicating that the front axle beam is formed above the final forging temperature. During each step of forging process, the strain mainly takes place at the segment of billet with larger plastic deformation, indicating an evident recrystallization phenomenon. The initial average grain size of the billet is about 150μm, while after forming, it will be refined to almost 45μm due to the dynamic recrystallization. The established 3D FE model coupling the recrystallization models can provide a theoretical guidance for optimizing the forging processing parameters of automotive front axle beam.

Ultrasonic motor acts as a significant equipment which has been widely used in automobile, aerospace, and medical industry. As the core part of the ultrasonic motor, a novel separable stator fabricated by the fine-blanking process is proposed, and the validity and rationality as well as the operation performance of the novel stator are investigated. A finite element model is used to check the feasibility of the stator. The model of the stator contains teeth body, piezoelectric ceramic ring, inner and outer gaskets, and adhesive and welding layer. Based on the model, simulations are carried out to obtain mechanical characteristics. The inner, outer gasket and teeth body of the stator are welded together. This manufacturing process cost can be significantly reduced compared to the machining process for the conventional stator. The stator prototype is also fabricated and assembled. The maximum rotary speed and stalling torque are tested by torque speed sensor. The experimental results show that maximum rotary speed can reach to 150 r/min, and maximum stalling torque is 1.42 Nm, which shows the fine-working performance and the rationality of the stator structure. The research confirms that the separable stator fabricated by fine-blanking process has promising future in the ultrasonic motor application area.

A subsecond and novel approach of electroshock treatment (EST) is used in this study to repair defects in directed-energy-deposited Ti-5Al-5Mo-5V-3Cr-1Zr near-β titanium alloy. After EST, the porosity of the specimen decreased significantly from 0.81 to 0.1 pct. Large cracks observed at the bottom of the above mentioned near-β titanium alloy became intermittent small cracks and the number of voids decreased. The defects in the top and middle regions of the specimens are repaired. The potential defect repair is attributable to energy concentration, which promoted the coalescence of defect tips, and thermal stresses, which compressed the defects inward and closed them.

HighlightsThe flow behavior of water jets discharged from different orifices was investigated.High-speed photography (HSP) was used to obtain surface structures and spread characteristics of water jets.The deformation process in axis switching related to the corner vortices effect of non-circular jets was researched by numerical simulation.The axis switching of non-circular jets enhances entrainment ability of the jet.ABSTRACT. Low-intermediate pressure sprinkler irrigation systems are important research topics in the field of water-saving irrigation. Non-circular nozzles improve spray uniformity at lower pressures and are key components of sprinkler irrigation systems. In this article, the behavior of discharged water jets from nozzles with circular, square, and equilateral triangular orifices designed with the same flow rate was investigated. High-speed photography (HSP) was used to capture jet characteristics in the near field (z

Construction of zeolite-type frameworks is of broad interest and mainly achieved by using imidazolate linkers. Incorporation of multiple linkers/functionalities into these unique types of frameworks would potentially expand their application scope. Herein, a three-dimensional (3D) metal–organic framework, BUT-27, with a unique zeolite A structure (LTA topology) was synthesized by linker exchange via single-crystal-to-single-crystal transformation. Addition of isophthalic acid linker to the two-dimensional double layered BUT-25 changed the whole framework to a 3D structure, BUT-27, containing three kinds of linkers. The strong fluorescence and presence of free O and N atoms in the framework make BUT-27 a good luminescent sensor for the detection of Fe3+ and Cr2O72− ions with high selectivity and sensitivity, i.e. Ksv = 1.1 × 104 and 5.9 × 104, and LOD (limit of detection) of 0.19 and 0.26 μM, respectively. These values are lower than the minimum values specified by US-EPA (United States Environmental Protection Agency) indicating its high potential for practical applications.

Predicting and controlling the joining interface are the main difficulties in impact welding dissimilar metal. In this study, the smoothed particle hydrodynamics (SPH) method was used to simulate the Cu/Ti wave interface forming process during high-rate impact welding. This process simulation was verified by vaporizing foil actuator welding experiments. The forming mechanism and factors influencing the characteristics of joining interface were simultaneously investigated. Results showed that, joining interface wave forming depended on the density ratio of the flyer sheet to the target sheet. Wave formation distance was mainly related to materials yield stress. The wavelength and amplitude of wavy characteristic increased with the impact angle and impact speed. Temperature distribution analyses proved that the average temperature of the vortex at the welding interface was higher than that in the other areas, indicating that the inter-metallic distribution was mainly in the vortex of the wave interface. Investigation of the moving trail of metal particles verified that the interaction of interface materials was caused by embedded deformation.

Further development of metal-organic frameworks (MOFs) requires an establishment of hierarchical interaction within the framework. Herein, we report a series of mesoporous rare-earth (RE) MOFs that are constructed from an unusual 12-connected π-stacked pyrene secondary building unit (SBU) and a typical 12-connected RE6 cluster (RE=Eu, Y, Yb, Tb, Ce). The judicious design of a butterfly-shape pyrene ligand with a tert-butyl substituent enables the formation of the disordered 12-connected organic SBUs on its strong intermolecular π-π interactions. The assembly of 12-connected inorganic cuboctahedron SBUs and 12-connected organic distorted hexagonal prism SBUs generates an unprecedented network that can be further simplified into a 4,4-connected pts net linked from planar square and tetrahedra. This work provides fresh insights into the design and synthesis of frameworks constructed from coordinatively, covalently, and noncovalently linked building units.

Polygonal rings are widely applied to fabricate critical ring components, such as cabin of aerospace equipment and large nuts. The traditional ring rolling method is difficult to fabricate polygonal rings owing to their non-rotary geometry characteristics. This paper proposes a novel polygonal ring rolling method using a simple rotary plain ring as the ring workpiece. Firstly, the motivations and principles of polygonal ring rolling method are proposed. Then, four typical feeding tool paths are designed and the plastic deformation modes and geometry evolutions of polygonal ring under these four feeding tool paths are revealed. Meanwhile, four typical feeding tool paths are optimized based on the stability of the polygonal ring rolling process. Finally, the polygonal ring rolling experiments are carried out and it is demonstrated that the proposed polygonal ring rolling method is feasible.

The membrane fouling is a notorious problem in the practical application of separation membranes. In this study, a mixed matrix membrane based on the MOF BUT-8(A) and the polymer polydiallyldimethylammonium chloride (PDDA) has been prepared on a hydrolyzed polyacrylonitrile (HPAN) substrate by the spin-assisted layer-by-layer assembly (spin-LbL) method. Thanks to the high porosity, high stability, moderate hydrophilicity, and electronegative nature of BUT-8(A), and the good compatibility between BUT-8(A) particles and PDDA polyelectrolytes, the prepared (BUT-8(A)/PDDA)3-HPAN membrane showed high water permeances (over 164 L m−2 h−1 MPa−1) and high rejection rates (over 91.4%) for many dyes in water. Furthermore, the membrane exhibited superior antifouling performance in nanofiltration (NF) with a high flux recovery rate (95.5%) when humic acid (HA) was used as foulant. The high antifouling performance is resulted from tuning hydrophilicity and electronegativity of the membrane surface. These results suggest that the nanofiltration performance of a MOF-based membrane can be well adjusted by a judicious choice of the membrane components and fabrication methods.

Obtaining excellent mechanical properties of spur bevel gear has been widely emphasized, owing to its indispensable effect on momentum. However, the conventional long-time and high-temperature heat treatment can cause microstructure coarsening, which dramatically decreases the mechanical properties. Since the normalizing process can significantly modulate the mechanical properties of spur bevel gears by adjusting their microstructure and crystallography behaviors, in the present study, the normalizing before or after carburizing heat treatment processes (NBCP and NACP, respectively) were proposed. The effect of heat treatment processes on the microstructure and crystallography of gear specimens was investigated. The results show that both NBAP and NACP had a strong effect on microstructure refinement and hardness improvement compared to the conventional process. NBCP raised the tendency for AlN precipitation, which could retard the microstructure coarsening during carburizing. Furthermore, NACP directly promoted the precipitation of globular Cr-rich M3C carbides which achieved the strongest pinning effect and brought about extremely fine microstructure. For crystallographic analysis, the 24 martensite variants in all gear specimens held Kurdjumov–Sachs orientation relationship to parent austenite. The orientations of martensite variants in gear specimens applying conventional process and NBCP were distributed regularly. However, the orientations of martensite variants in NACP gear specimen did not follow the strict rule for variant selection inside prior austenite grains owing to the distortive effect of diffuse M3C carbides on the matrix, and the adjacent martensite variants possessed less sharing of {110} habit plane compared to NBCP and conventional process.

Resistance spot welding (RSW) quality substantially influences the autobody’s mechanical properties and safety performance. Nondestructive testing (NDT) method is widely used to evaluate the quality of RSW, but the traditional ultrasonic testing method has high requirements for coupling conditions and flat surface of the weld part. The electromagnetic acoustic transducer (EMAT) is a novel NDT technology, which has advantages of noncontact, no coupling media, and low requirements for surface flatness of the workpiece. Therefore, the electromagnetic ultrasonic transverse wave (EUTW) is developed to realize the evaluation of RSW quality in this paper. Under the COMSOL platform, the finite element method (FEM) modeling is proposed by multiphysics simulation. The multiphysical fields include electromagnetic field, acoustic field, and solid mechanics. The generation mechanism and propagation rules of EUTW in various spot welds are studied by simulation analysis. The correctness of FEM modeling is validated by EUTW experiments; results show that the experimental waveforms of EUTW are consistent with the simulation waveforms. Finally, an evaluation method of the nugget size of RSW is proposed based on the simulation and experiments analysis of EUTW detection of RSW with different nugget diameter and indentation depth. The approach presented in this paper can provide the theoretical foundation and new method for the noncontact, high efficient, and low-cost detection of RSW quality of the autobody.

Ultrasonic vibration has been applied to improve the penetration of adhesive into the anodized layer, thereby enhancing the strength of carbon fiber-reinforced plastic/aluminum alloy bonding joints with anodizing pretreatment. The ultrasonic vibration-assisted adhesive bonding process was designed by orthogonal experiments, then verified experimentally. The strengthening mechanism was studied by analyzing the morphology and elemental distribution of the cross-section of the joint. The results show that the ultrasonic vibration-assisted adhesive bonding process can further strengthen the interfacial bonding. For the studied joints, the strength can reach 18.66 MPa, being 55% higher than without ultrasonic strengthening. The ultrasonic vibration creates shock waves in the adhesive layer, causing a high-speed adhesive jet toward the adherend surface, which makes the interfacial bonding tight and promotes penetration of the adhesive into the anodized layer. The bonding strength is thereby remarkably improved by forming a larger interfacial contact area and more mechanically interlocked structures.

The modular nature of metal-organic frameworks (MOFs) permits their tunable structure and function for target application, such as in biomedicine. Herein, a green-emission Zr(IV)-MOF (BUT-88) was constructed from a customized luminescent carbazolyl ligand. BUT-88 represents the first bcu-type MOF with both organic linker and metal node in eight connections and shows medium-sized pores, rich accessible linking sites, and good water stability and biocompatibility. In virtue of these merits, BUT-88 was then fabricated into a MOF-based fluorescent nanoprobe, drDNA-BUT-88. Using it, the live-cell imaging of dual tumor biomarkers was achieved for the first time upon a MOF-based probe, offering enhanced detection precision in early cancer diagnosis. Particularly, the probe showed efficient ratiometric fluorescent sensing toward the cytoplasmic biomarker microRNA-21, further improving the detection accuracy at the cellular level. In this work, the elaborate combination of MOF engineering and the fluorescent detection technique has contributed a facile biosensing platform, unlocking more possibilities of MOF chemistry.

The temperature distribution of electrolyte in ECM affects the distribution of machining gap and the precision of forming. Considering the influence of hydrogen bubbles and electrolyte with low velocity near the wall on heat transfer, the Euler–Euler two-fluid model was used to calculate the gas volume fraction distribution and the turbulent shear stress transport (SST) model was used to calculate the electrolyte velocity. The multi-field coupling model of electric field, flow field, and temperature field was established to solve the temperature of electrolyte. The temperature detection device is set up to detect the inlet, outlet temperature of the electrolyte, and the temperature of the sampling points on the workpiece. The experimental results show that the results of the coupled model considering the hydrogen bubbles and the low flow velocity electrolyte are more accurate than those of the turbulent SST and k − e models ignoring the influence of the bubbles.

Due to the non-uniform dynamic recrystallization (DRX) and deformation behavior during hot forging process, the spur bevel gears tend to receive heterogeneous microstructure which greatly affects their mechanical properties and service life. Therefore, the aim of this study is to investigate the evolution of microstructure and texture of hot forged 20CrMnTiH steel spur bevel gear utilizing both simulation and experiment method. In the present study, a sound finite element model of hot forging of a 20CrMnTiH steel spur bevel gear was developed under the Deform-3D software. The experimental analysis was conducted by employing scanning electron microscope, electron backscatter diffraction and transmission electron microscope. The simulation results indicated that the grain size, effective strain and DRX volume fraction were inhomogeneous from the surface region to the core region of gear tooth. The experimental analysis revealed that the surface region of gear tooth possessed the strongest γ-fiber and lowest dislocation density. However, both subsurface and core regions had a combination of moderate α- and γ-fibers, and large amount of dislocations pinned by precipitates can be observed in these two regions. Furthermore, the microhardness exhibited parabola distribution through the gear tooth, and the subsurface region possessed the largest microhardness value.

Plant fiber-reinforced polypropylene composites are low-cost, good-performance and resource-saving, so has wide application prospect in automotive components. While the density of composites increa...

Electro-shocking treatment (EST) has been investigated as a pathway to optimise the microstructure and mechanical properties of titanium alloys. The thermal conditions introduced by EST resulted in a phase transformation from α to β. The fraction of β phase decreased from 25.27% to 19.47% after EST for 0.02 s, which was possibly caused by the recrystallization of α phase. The application of EST for 0.04 s resulted in an increase in volume fraction of the β phase to 26.95%. The energy introduced by EST resulted in changes to the direction and intensity of texture within the microstructure with the texture intensity of the α phase increasing from 4.94 to 8.52, and that of β both increased from 3.35 to 9.88 after 0.04 s EST. Keywords: Electroshocking treatment (EST), Microstructure, Phase transformation, Phase content, Texture, TC11 alloy

The shaping of metal–organic frameworks (MOFs), referring to the integration of small submillimeter MOF crystals into bulk samples with desired size, shape and mechanical stability, is an important step for the practical use of this class of porous materials in many applications. MOFs are constructed by the coordination bonding of metal ions/clusters and organic ligands. Since coordination bonds are mostly weaker than covalent bands, MOFs show a relatively low stability compared to conventional porous materials, such as zeolites or porous carbon-based materials. Thus, many shaping methods for the conventional porous materials involving treatments under harsh conditions could not be directly applied to prepare shaped MOFs. However, the inorganic–organic hybrid nature of MOFs also affords the opportunity of developing unique methods for shaping the materials. Herein, an overview of some classic methods for the shaping of MOFs is presented, including granulation, extrusion, spray drying, and pressing. In addition, the recently developed methods for the preparation of shaped MOFs used in separation and gas storage, including templated shaping, self-shaping, shaping by in situ growth on substrates, and shaping with sacrificial materials, are highlighted.

Large size aluminium alloy seamless ring with irregular section is usually obtained by hot ring rolling process. Because of residual stress, the ring generally experiences much deflection during subsequent aging and machining. To control this deflection and strengthen the aluminium alloy ring, cold bulging process has to be applied to the ring to homogenize residual stress before aging and machining, and the uniformity of cold deformation is the key problem. The cold bulging process was designed for the forging of the casing ring of aluminium alloy with 5-meter special-shaped section. On this basis, the stress analysis of the cold bulging process was made and the process was engineered. By using Deform-3D to conduct finite element analysis on the ring cold bulging process and stress analysis on different positions of the ring, the deformation characteristics of the ring under the cold bulging process were obtained. The uniformity of the deformation of the ring was achieved by means of the rotation of the disc die when the ring was bulging. The bulging process in the engineering scheme greatly improved the uniformity of the strain in each region of the ring, which provided a reliable theoretical analysis and engineering scheme for the cold bulging process of the ring forgings of aluminium alloy casing with irregular section.

The selective adsorption/separation of C2 hydrocarbons has been realized in a "flexible-robust" MOF, Zn2(Atz)2Ox. Owing to the distinctive guest-dependent multistep adsorption behaviors and suitable guest-framework interactions, this MOF shows outstanding separation performance for C2H2/C2H4 mixtures in a wide range of temperature confirmed by a column breakthrough experiment.

An improved nonlinear dynamic model of high-speed ball bearings with elastohydrodynamic lubrication is adopted to predict the movements of balls and power loss of ball bearings for defining the boundary conditions of a computational fluid dynamics (CFD) model. Then, this method of combining nonlinear dynamic and CFD models is validated through the experimental verification. Subsequently, oil–air flow and temperature distribution inside the bearing chamber are studied at low and high speeds and light and heavy loads. The effect of nozzle’s position on the formation of oil film and heat dissipation is revealed under combined loads. The research results provide a theoretical basis for engineering application of high-speed rolling bearings.

Effects of electroshock treatment (EST) on the microstructural evolution and mechanical properties of near-β titanium alloy (Ti-55531) formed by directed energy deposition (DED) was studied in this work. With the increase in EST time, the average hardness of specimen decreased from 426 HV to 316 HV, and the fracture strain increased significantly, which was attributed to the uniform dispersion of α phase along grain boundaries and inside the β grains. After EST, the texture intensity decreased in terms of the orientation distribution function (ODF), which was ascribed to the redistribution of α phase. Moreover, more atomic vacancies and lattice distortion were formed near the α/β interfaces, which were verified by transmission electron microscopy (TEM) observation and ascribed to the migration of atoms near the interface under EST. External loadings facilitated the dislocation motion and lattice distortions near the interfaces, which resulted in the reduction in hardness and the improvement in ductility. The above results indicated that EST can quickly alter the microstructure and mechanical properties of DED titanium alloys as a simple and energy-saving method.

A practical bimetallic casting consisting of aluminum matrix and cast iron inserts was manufactured via high pressure die casting (HPDC) process. Different surface treatment methods of the cast iron inserts, including salt membrane plating and electrogalvanizing, were adopted to improve the bonding quality of bimetallic castings. Microstructure characterization on the bonding interface was conducted at different locations of bimetallic castings. Results indicate that compounds with flawless and continuously metallurgical bonding interface can be successfully fabricated by the HPDC process with the zinc rack plating treatment on the surface of cast iron inserts which results in a dense zinc coating with an average thickness of 8 μm. The melt flow speed and heat transition during solidification of the HPDC process are two key factors in determining the bonding integrity of bimetallic castings. With the dissolution and diffusion of the very thin zinc coating during solidification, there is no obvious aggregation of zinc element at the metallurgical bonding interface. Instead, a reaction layer with an irregular tongue-like morphology is formed with an average thickness of approximately 1 μm while it mainly consists of intermetallic phases Al60Cu30Fe10 and Al2FeSi, etc.

Adhesively bonded CFRP/Al joints have been widely used in various engineering fields. However, the poor interface adhesion between the adhesive and the Al adherend limits its further use. In this s...

The effect of high-density electroshocking on the solid phase transformation of Ti–6.6Al–3.4Mo alloy was studied in this paper. The microstructure at the same position of the specimens before and after electroshocking treatment with different parameters was characterized by the optical microscopy and scanning electron microscopy. The experimental results reveal that the refined and spheroidized primary α phase can be obtained under the appropriate treatment condition. Meanwhile, the fine orthorhombic α″ phase at submicron was discovered by the X-ray diffraction and transmission electron microscopy in the transformation products. A physical model was established to analyze non-uniform current distribution at microscale and to explain the spheroidization mechanism. The phase transition process was interpreted from the point of view of thermodynamics.

A combined in-mold decoration and microcellular foaming injection molding process (IMD/Mucell) is proposed to improve the surface quality of foamed parts. Through theoretical inference, the mathematical models of temperature field, velocity profile and forces on bubble were established with combining traditional mathematical models and the different heat transfer coefficient of the mold inner surface. The effects of the non-isothermal mold on the bubble structure and forming process of inter bubble were investigated with experiments and numerical simulation. Results showed that the critical pressure of the cavity existed in the melt filling and bubble expanding stage, and it affected the cells structure obviously at the filling stage. The lift force took the bubbles to the film side based on the velocity profile of viscous fluid, and maximal bubble was closer to the transition layer with film due to higher temperature. In the combined process, the evolution rule of superficial bubbles was analyzed, and results showed that the surface quality was improved in the film side.

In this study the mechanical behavior and deformation mechanism of 7075 aluminum alloy sheets under dynamic strain aging induced by solution treatment were investigated. The uniaxial tensile tests were carried out at various strain rates (8.33 × 10−5 s−1, 1.67 × 10−3 s−1, 3.33 × 10−2 s−1 and 1.33 × 10−1 s−1) for samples treated by different solution processes (solution for 30 min at temperatures of 573 K, 623 K, 673 K and 748 K, and then quenching). The Portevin-Le Chatelier (PLC) effect (i.e., serration types of stress-strain curves, strain rate sensitivity (SRS) and critical strain) were analyzed, causing changes in tensile strength, work hardening rate and elongation. The morphology, sizes and quantities of precipitates under different solution-quenching conditions were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the dissolution of secondary phase occurs during heat treatment, accompanied by coarsening behavior at lower temperatures, which leads to the transition characteristics of mechanical properties of the aluminum alloy in solid solution state. There exists a critical point of solution temperature (623K), namely, when the solution temperature is lower than this critical point, the microstructure after quenching is mainly composed of the matrix and secondary phase; otherwise it is mainly composed of solid solution. Therefore, the samples heated at different solution temperatures have different types of PLC effects. It is worth noting that the strong effect of dynamic strain aging induced at high solution temperature and low strain rate could simultaneously enhance the strength and toughness.

The in-situ ultrasonic detection system is developed to evaluate the resistance spot welding (RSW) quality automatically. An embedded probe is used to obtain the ultrasonic testing signal of spot weld after the RSW process. It is built in the spot welding electrode. The signal eigenvalues such as acoustic pressure amplitude, distance of echoes, main frequency, main frequency amplitude, low-frequency component are obtained. The corresponding mathematic calculation models are established to realize the quantitative ultrasonic evaluation of RSW quality. A specialized evaluation software is developed to calculate the nugget sizes and classify the weld type automatically. Several verification tests are conducted and showed that the RSW quality can be rapidly and effectively evaluated by the in-situ ultrasonic detection system.

Vaporizing foil actuator welding (VFAW) was used for joining 2024-T3 and 7075-T6 aluminum alloy sheets, and the resulting joint microstructure was analyzed. 2024/7075 aluminum alloy pairs with suitable processing parameters can be prepared by using VFAW. Dynamic preform addresses the poor formability problem of target material and advantage of VFAW on dissimilar materials in some conditions. But with standoff sheet inserting in the flyer and target, 2024/7075 welded pairs gets the better weld strength, compared with flyer preformed method. The microstructure of the circular weld area of the welded joint showed a wave interface, in which a thin melt layer formed at the center and edge parts. The crystal grains near the bonding interface were remarkably elongated and refined. Therefore, the joining of the 2024/7075 pairs was facilitated through plastic forming and melting.

In this work, the carbide dissolution and precipitation of M50 bearing steel were investigated as a function of cold rolling reduction. It is observed that the prior cold rolling not only enhances the dissolution of primary carbides, but also contributes to the carbide precipitation. Additionally, the influence of prior cold rolling on the dry wear behaviors of M50 bearing steel was studied, finding that the friction coefficient as well as wear rate decreases with the increasing cold rolling reduction. This result could be attributed to the formation of stable self-lubricating film within the subsurface layer for the specimens with cold rolling.

The slider, which is made of polyoxymethylene, is the key component of an automotive window regulator. Its function is to guide the window's movement, but it is prone to wear and tear. To reduce noise and improve the wear life of slider, a study of its contact characteristic and the wear life is significant. In this paper, the wear and friction properties of polyoxymethylene under dry sliding condition and grease lubrication condition are investigated using a pin-on-disc apparatus. The complex force conditions of the slider at the normal working condition are studied by a mechanics analysis method. The contact pressure of slider is analyzed by the finite element analysis and the wear of slider is calculated by the proposed wear prediction model. Prediction of the wear life of slider is verified by a window regulator wear experiment. Results show that the value of wear rate of polyoxymethylene under unlubricated condition is much higher than that under lubricated condition. The estimation of wear depth of slider, based on the combination of finite element contact pressure analysis and wear properties of polyoxymethylene, is in accordance with window regulator wear test under unlubricated condition. Besides, the practical wear depth of slider under grease lubrication condition is also in the range of the predicted wear depth of slider under dry and grease lubrication condition.

The introduction of cold deformation prior to aging is an important strengthening method of aluminum alloy. However, it is unclear how many mechanisms of strengthening take effect, and how those mechanisms affect each other during aging process. In this paper, the precipitation kinetics parameters of θ′′ phase, θ′ phase in aging process after cold deformation were obtained by Differential Scanning Calorimeter（DSC）combined with JMA equation. Dislocation densities of the cold deformed specimens were successfully estimated from X-Ray Diffraction (XRD) profile analysis using the modified Williamson-Hall equation. A comprehensive quantitative model for the strengthening of 2A14 aluminum alloy due to precipitation strengthening, solid solution strengthening, grain/subgrain strengthening and dislocation strengthening was presented. The model revealed the evolution law of these four strengthening mechanisms during aging process, and predicted the combined effects and competitive relationship of four strengthening mechanisms on the yield strength of 2A14 aluminum alloys. The accuracy of the model prediction was verified through experiments when the cold deformations were smaller than or equal to 6% and can be used to design aging process of 2A14 aluminum alloy.

Tooth variations in spur bevel gears have significant effects on the transmission performance, noise, and vibration and directly affect the reliability and stationarity of equipment. The hot forging process is the principal method used for the mass production of spur bevel gears owing to its high efficiency and high quality of products. However, hot forging of spur bevel gears is a high-pressure, high-temperature, and instantaneous forming process; hence, the evolution of tooth variations is extremely difficult to predict and measure. An accurate prediction of tooth variations in the hot forging process of spur bevel gears is an important precondition for tooth variation control to improve tooth accuracy. In this study, a new finite element (FE) analysis strategy of tooth variation prediction in the hot forging of spur bevel gears is proposed according to transitive relations of stress, strain, and temperature. Following this new strategy, a series of FE models are developed, so that the positional and shape variations on the tooth surface caused by die shrink-fitting (DSF), die elastic deformation (DED), die thermal expansion (DTE), gear elastic recovery (GER), and nonuniform cooling shrinkage of gear (NCSG) are comprehensively investigated. To verify the reliability of this FE analysis strategy, a hot forging experiment of a spur bevel gear was carried out, and the tooth variations of the tooth die and hot forged gear were measured using a gear-measuring machine. The results show that the factors causing the positional variation in order of importance from highest to lowest are DSF, DED, GER, NCSG, and DTE, and those for shape variation are DSF, DED, GER, DTE, and NCSG. Moreover, the shape variation of the final hot forged gear increases in the tooth profile direction and decreases in the tooth lengthwise direction. Finally, the simulation results closely agree with the experimental results, confirming the reliability of the FE analysis strategy proposed in this study.

A High-Speed Photography (HSP) technique was used to investigate the breakup process and flow behavior of low-intermediate pressure water jets issued from square and triangular shaped nozzles. The non-circular orifices were designed based on the principle of equal flowrate with the same pressure in relation to the circular orifice. The breakup morphologies and boundary structures of the jets were studied under different nozzles and working pressures. Two forms of droplet formation and the process of droplet formation, in addition to the jet breakup lengths, initial amplitudes of surface waves and jet diffusion angles of different nozzles were evaluated. It was found that the jet presented a good continuity and fluidity in the initial section, and the fluid bands gradually appeared due to the air resistance and the jet break up as the disturbance intensifies. The degree of jet breakup was enhanced with the increase of pressure and cone nozzle angle. The random appearance of the fluid band structures and the dactylitic textures near the nozzles for non-circular jets appeared earlier than those produced by the circular jets. The small satellite droplets with different shapes and sizes were seen inside and outside the jet interface. Triangular jets exhibited the shortest breakup length, the initial amplitude of surface wave, and the diffusion angle of the jet at the same pressure were largest compared with square and circular jets. Two index equations of jet characteristic lengths and equivalent diameters of both circular and non-circular nozzles were fitted with a relative error of less than 10%, which means the fitting formulas are accurate. Keywords: Breakup length, High-speed photography, MATLAB simulation, Non-circular nozzle, Surface wave amplitude.

The casting-rolling compound forming process of ring parts is an advanced plastic forming technology that has been developed due to the merits of high efficiency and energy and material saving. However, cracks often occur during the hot ring rolling process, especially at the edges of the ring parts, which severely affects the forming quality. To predict and try to avoid the occurrence of cracks in the casting-rolling compound forming process of ring parts, the high-temperature fracture behaviors of as-cast 42CrMo steel were investigated by thermodynamic experiment method. The high-temperature tensile tests were carried out using the Gleeble-3500D thermomechanical simulator at various temperatures and strain rates. Stress-strain curves and fracture morphology were examined, through which the sensitivity of stress to temperature and strain rate and the effect of dynamic recrystallization and cavity evolution on fracture were found. The law of critical fracture strains was analyzed, and the model of critical fracture strain as a function of temperature and strain rate was established. Based on Oyane criterion, the thermal ductile fracture criterion was established in conjunction with the model of critical fracture strain. By embedding this thermal damage model into the finite element (FE) model for hot ring rolling of an as-cast 42CrMo ring, the damage prediction for this process was realized, and the thermal ductile fracture criterion was proved to be reliable. From the FE results for hot ring rolling, mechanism of damage and fracture in the hot ring rolling process was analyzed. The damage threshold C f is small, and the damage ratio D is large at the top and bottom edges of the inner surface area of the ring, which have the greatest propensity to cracking in the course of hot ring rolling. This is of great significance in terms of improving the forming quality of ring parts in the casting-rolling compound forming process.

In this paper, a cold orbital forging process is proposed to manufacture thin parts with high circular ribs. First, a FE model was established for the numerical process analysis. Then a verification experiment was performed to verify the validity of the FE model developed above. By using the FE simulation method, the influences of several forging parameters on the cold orbital forging of thin parts with high circular ribs were investigated. The results show that effective strain can be obviously improved by increasing feed velocity of cavity die, but has less change with different friction factors. Synchronism of metal flowing between the inner rib and the outer rib can be improved by decreasing feed velocity of cavity die and friction factor. Moreover, the circumferential metal flowing degree can be slightly reduced by increasing feed velocity of cavity die and friction factor.

For the curved layer deposition with wire and arc additive manufacturing on complex surface, the molten pool behavior and bead geometry are variant at different welding positions for the dragging effect of gravity, which lead to inconsistent layer appearance. A region-based path planning method for robotic curved layer wire and arc additive manufacturing (CL-WAAM) is developed, with which all horizontal welding position can be maintained at arbitrary region of the complex surface. The adverse effect of gravity is minimized and uniform bead appearance can be guaranteed. Firstly, with a two-stage clustering method, the complex surface was divided into a certain number of simple subregions. Then, the contour line across cluster centroid of each subregion was employed as initial path, and an adaptive bead overlapping model changed with local inclined angle was used to generate the offset curved path covering the subregion. Therefore, the overall welding paths were approximate to the contour line on the surface, and the horizontal welding position and consistent forming appearance can be achieved. Finally, three surface parts were designed to validate feasibility of the method, and the forming appearance was compared with traditional iso-parametric method and flat layer WAAM (FL-WAAM). The results suggested that the surface waviness and thickness were relatively consistent at arbitrary region of complex surface with the region-based method, and the stair-step effect appeared in FL-WAAM was significantly alleviated with the CL-WAAM. The proposed method helps achieve the uniform layer appearance deposited on complex surface, which could be widely used in the manufacturing or repairing of wear-resistant surface parts, such as the hot forging die and hydraulic turbine blade.

Compared to hot forming, cold forming can manufacture components with higher accuracy and better mechanical properties. However, for some light-weight and high-strength materials, such as 7xxx series aluminum alloy, their room-temperature plasticity is poor, which limits the production of complex structural components of these materials. In this study, the microstructure evolution of annealed 7075 aluminum alloy and its influence on room-temperature plasticity were investigated. Firstly, the annealing experiments with different annealing temperature and soaking time were conducted, and the annealed microstructure evolution was analyzed. Secondly, the room-temperature tensile tests were conducted to evaluate the room-temperature plasticity. The relationship between annealed microstructure and plastic deformation behavior was studied. The new effect mechanisms of annealed microstructure on room-temperature plasticity was found. The results indicated that the annealed grains with high Schmid factor (˃0.4) adjacent to coarse granular-shaped secondary particles exhibited easy multiple slip system activation and smoothly transformed strain through the slip bands, which promoted the grain fragmentation. Concurrently, the secondary particles underwent rupture and separation. Owing to the low strain localization and multiple slip systems of the grain fragments, they can coordinately deform around the prior particle-matrix interfaces or between the separate particle pieces, which led to good room-temperature plasticity.

Certain defects like pores, incomplete fusion and micro cracks are sometimes inevitable in Wire + Arc Additive Manufactured (WAAM) components. However, these defects cannot be detected easily by conventional ultrasonic testing due to the rough surface and high temperature of WAAM components. In this paper, a Laser Ultrasonic (LU) system, consist of a pulsed laser and a laser interferometer, is employed to achieve non-contact inspection of artificial defects (crack, flat bottom hole and through hole) in a WAAM sample without surface machining. First, several WAAM samples with different welding parameters are manufactured by a robotic Gas Metal Arc Manufacture (GMAW) system. The 2D profiles of these samples are measured and reconstructed by a geometric optical measuring instrument for Finite Element (FE) analysis. Then, the multi-physics (Heat Transfer, Solid Mechanics, Pressure Acoustics) coupled FE model is established to simulate LU inspection of defects in the WAAM sample. The propagation of laser ultrasonic waves in the WAAM sample, as well as the mechanism of interaction between ultrasonic waves and defects is investigated numerically. In addition, LU inspection experiments are designed and conducted to obtain the A- and B-scan plots of different defects in the WAAM sample. Finally, quantitative inspection of the artificial defects is realized by analyzing the A- and B-scan plots. This paper verifies the feasibility of LU inspection of WAAM components without surface machining.

Adhesive bonding is widely used in the joining of metals and carbon fiber-reinforced plastics (CFRPs). Ultrasonic vibration was used to improve adhesive bonding of CFRP/Al alloy joints grafted with silane coupling agent, and the effect of the ultrasound on the bonding was studied. The surface of Al alloy was treated with a silane coupling agent, and then the ultrasonic vibration was applied on the adherend during the adhesive bonding process. The shear strength was tested, and the mechanism was analyzed by scanning electron microscope (SEM) and Fourier transform infrared spectrometer (FTIR). It is found that the ultrasonic assisting can further promote the bonding of the Al alloy and the adhesive. For the test joins, the shear strength was increased by 267.50% using the silanization treatment plus the ultrasonic assisting. The ultrasonic assisting promoted the grafted epoxy group to react with the adhesive more sufficiently at the Al/adhesive interface by causing micro-mixing and intensified molecule collision, and thus more chemical bond was formed. Under the ultrasonic action, the interface and the adhesive layer became tighter owing to the impact contact at the interface and the oscillating flow in the adhesive layer. The ultrasonic vibration assisting increased the bonding strength by promoting the chemical bond and improving physical morphology.

The utilization of a rationally designed T-shaped ligand 4,4′,4′′-(1H-benzo[d]imidazole-2,4,7-triyl)tribenzoic acid (H3BTBA) as the platform for constructing metal–organic frameworks (MOFs) with structure diversity was achieved. Five new MOFs, [Zn4O(BTBA)2] (BUT-34), [Fe2CoO(BTBA)2(H2O)3] (BUT-35), [Cu9(BTBA)4(H2O)(DMA)] (BUT-36), [Eu2(HBTBA)2(OH)2(H2O)6] (BUT-37), and [In(BTBA)(DMF)] (BUT-38) (BUT = Beijing University of Technology), have been solvothermally synthesized and structurally characterized. Combining with several popularly used metal-cluster secondary building units, the five MOFs show novel structural features. BUT-34 with typical tetranuclear Zn4O clusters shows three-dimensional (3D) networks with a new (3,6)-connected topology. BUT-35 exhibits a (3,6)-connected flu-3 network with trinuclear [Fe2Co(μ3-O)] clusters. BUT-36 represents a mixed Cu(II)/Cu(I) based 3D framework, in which the T-shaped ligand adopts different coordination modes. However, BUT-37 and -38 consist of binuclear Eu2 padd...