The effect of different high pressure die casting parameters on 3D microstructure and mechanical properties of AE44 magnesium alloy

To understand the relationship between the process-microstructure-mechanical properties of the high-pressure die-casting(HPDC) AE44 magnesium alloy, 3D reconstruction and 2D characterization were carried out on the HPDC castings produced with different process parameters(low slow-shot speed, fast slow-shot speed, solidification pressure). Microstructural characterization revealed that the formation of shrinkage pores are closely related to ESCs, which were mainly controlled by the low slow-shot speed in shot sleeve(ESCs growth time) and fast slow-shot speed into the die cavity(distribution of ESCs). In addition, solidification pressure can significantly reduce the shrinkage porosity in the center by improving the feeding capacity of liquid metal. Tensile fracture revealed that the tearing ridge is mainly evolved from the slip band of ESCs. The quantity and distribution of ESCs determine the fracture mode of castings. The relationship between mechanical properties of castings and the morphology of ESCs and porosity is also statistically discussed.

Method for near-net forming of a sand mold with digital flexible extrusion technology

In order to further improve the precision forming efficiency of a sand mold digital patternless casting and reduce the amount of sand mold cutting, a method for near-net forming of the sand mold with digital flexible extrusion technology was put forward. The theory, optimization algorithm and technology for sand mold nearnet forming were studied. Experimental results show that the sand mold forming efficiency can be increased by 34%, and the molding sand can be reduced by 44%. The method for near-net forming of a sand mold with digital flexible extrusion technology can effectively promote the application of digital patternless casting technology in the mass production of castings and thus greatly improves the efficiency and automation of sand mold manufacturing.

6-DOF MOTION AND CENTER OF ROTATION ESTIMATION BASED ON STEREO VISION

A new motion model and estimation algorithm is proposed to compute the general rigid motion object＇s 6-DOF motion parameters and center of rotation based on stereo vision. The object＇s 6-DOF motion model is designed from the rigid object＇s motion character under the two defined reference frames. According to the rigid object＇s motion model and motion dynamics knowledge, the corresponding motion algorithm to compute the 6-DOF motion parameters is worked out. By the rigid object pure rotation motion model and space sphere geometry knowledge, the center of rotation may be calculated after eliminating the translation motion out of the 6-DOF motion. The motion equations are educed based on the motion model and the closed-form solutions are figured out. To heighten the motion estimation algorithm＇s robust, RANSAC algorithm is applied to delete the outliers. Simulation and real experiments are conducted and the experiment results are analyzed. The results prove the motion model＇s correction and algorithm＇s validity.

Analysis of the Microstructure and Mechanical Properties during Inertia Friction Welding of the Near-α TA19 Titanium Alloy

The current research of titanium alloy on friction welding process in the field of aero-engines mainly focuses on the linear friction welding.Compared to the linear friction welding,inertial friction welding of titanium alloy still has important application position in the welding of aero-engine rotating assembly.However,up to now,few reports on inertial friction welding of titanium alloy are found.In this paper,the near-alpha TA19 titanium alloy welded joint was successfully obtained by inertial friction welding(IFW)process.The microstructures and mechanical properties were investigated systematically.Results showed that the refined grains within 15‒20μm and weak texture were found in the weld zone due to dynamic recrystallization caused by high temperature and plastic deformation.The weld zone consisted of acicularα′martensite phase,αp phase and metastableβphase.Most lath-shapedαs andβphase in base metal were transformed into acicular martensiteα′phase and metastableβphase in thermo-mechanically affected zone and heat affected zone.As a result,the microhardness of welded joint gradually decreased from the weld zone to the base metal.Tensile specimens in room temperature and high temperature of 480℃ were all fractured in base metal illustrating that the inertia friction welded TA19 titanium alloy joint owned higher tensile strength compared to the base metal.

Effect of rich R-TiO2 on the rate and cycle properties of Li4Ti5O12 as anode for lithium ion batteries

Li4Ti5012 (LTO) with rich R-TiO2 (17.06, 23.69, and 34.42 wt%), namely, R-TiO2@Li4Ti5O12 composites, were synthesized using the hydrothermal method and tetrabutyl titanate (TBT) as the precursor. Rietveld refinement of X-ray diffraction (XRD) results show that the proportion of Li occupying 16d sites is extraordinary low and the lattice constants of LTO and R-TiO2 change with the ritanium dioxide content. EIS measurements showed that with in creasing R-TiO2 content, both its charge transfer impedance (Rct) and lithium ion diffusion coefficient (DLi) decreased. The changes of Rct and DLi caused by the increase of titanium dioxide content have synergic-antagonistic effects on the rate and cycle properties of Li4Ti5012. The rate performance is positively related to DLi, while the cycle property is negatively correlated with Rct, indicati ng that the rate performs nee is mainly related to DLi, while Rct more significantly affects the cycle performance. LTO-RT-17.06% exhibited excellent rate properties, especially under a high current density (5.0 C, 132.5 mAh/g) and LTO-RT-34.42% showed superior long-term cycle performance (0.012% capacity loss per cycle) compared to that of LTO-RT-17.06% and LTO-RT-23.69%.

Performance of digital patternless freeze-casting sand mould

Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology. The change law of tensile strength and air permeability of frozen sand moulds (100-mesh and 200-mesh silica sand, and zircon sand moulds) under different freezing temperatures and water contents was studied. Results show that with the decrease of freezing temperature and the increase of water contents, the tensile strength and air permeability of the sand moulds are gradually improved. Meanwhile, computed tomography technology was used to characterize the shape and size of the water film between the sand particles mixed with 4wt.% water. The results show that in silica sand moulds, the form of water film is lumpy, and 200-mesh silica sand moulds have more water films and higher proportion of small-sized water films than 100-mesh silica sand moulds, while in zircon sand moulds, the form of water film is membranous. At the same freezing temperature and water content, the tensile strength of zircon sand mould is the highest, and 100-mesh silica sand mould is the lowest. A comparative solidification experiment of A356 aluminum alloy was carried out in frozen sand mould and resin sand mould. The results show that the primary α-Al phase appears in the form of equiaxed and eutectic silicon phase is needle-like in freezing sand mould casting, but the primary α-Al phase grows in the form of dendrites, and the eutectic silicon phase is coarse needle-like in the resin sand mould casting. The difference of microstructure is caused by the different cooling rate. The cooling rate of A356 aluminum alloy in frozen sand mould is higher than that in resin sand mould.

Experimental and Numerical Investigation on Erosion Corrosion of the Air Cooler Tube Bundle in a Residue Hydrotreating Unit

Corrosion leakage occurred in the 14th tube bundle in the first row of a residual oil hydrotreating air cooler after operating for two years.The failure location was 0.5 m from the outlet header box.In this paper,the erosion corrosion of the air cooler tube bundle was investigated by experimental and numerical methods.Visual inspection,scanning electron microscopy(SEM),and X-ray diffraction(XRD)experiments were performed,and the failure morphology and material composition confirmed that the damage was caused by erosion corrosion.The shear stress transport k–ωturbulence model(SST-k–ω)was then used to investigate the flow and erosion corrosion characteristics,combined with mass transfer,corrosion rate,and ionization equilibrium models.The numerical simulation results revealed that the water phase volume fraction increased with flow and heat transfer in the fluid,which increased the mass flow rate and concentration of hydrogen sulfide.The mass transfer coefficient and corrosion rate were proposed as important parameters to characterize erosion corrosion.Moreover,the local concentration of wall shear stress was found to increase the risk of erosion corrosion.The predicted high-risk area was consistent with the actual failure area,which verified that this failure incident was attributable to erosion corrosion by the water phase.

Fabrication and performance of 3D co-continuous magnesium composites reinforced with Ti_(2)AlN_(x) MAX phase

Magnesium composites reinforced by N-deficient Ti_(2)AlN MAX phase were first fabricated by non-pressure infiltration of Mg into three-dimensional(3D)co-continuous porous Ti_(2)AlN_(x)(x=0.9,1.0)preforms.The relationship between their mechanical properties and micro-structure is discussed with the assessment of 2D and 3D characterization.X-ray diffraction(XRD)and scanning electron microscopy detected no impurities.The 3D reconstruction shows that the uniformly distributed pores in Ti_(2)AlN_(x) preforms are interconnected,which act as infiltra-tion tunnels for the melt Mg.The compressive yield strength and microhardness of Ti_(2)AlN_(0.9)/Mg are 353 MPa and 1.12 GPa,respectively,which are 8.55%and 6.67%lower than those of Ti_(2)AlN/Mg,respectively.The typical delamination and kink band occurred in Ti_(2)AlN_(x) under compressive and Vickers hardness(V_(H))tests.Owing to the continuous skeleton structure and strong interfacial bonding strength,the crack ini-tiated in Ti_(2)AlN_(x) was blocked by the plastic Mg matrix.This suggests the possibility of regulating the mechanical performance of Ti_(2)AlN/Mg composites by controlling the N vacancy and the hierarchical structure of Ti_(2)AlN skeleton.

Study on the Distribution of Frictional Forces on Z-yarn Continuous Implanted Preforms and Their Applications

To improve the quality and efciency of Z-directional 3D preform forming,the Z-yarn frictional force distribution model of the preform and its wear mechanism were investigated.In this study,a tensile force measuring device was designed to measure the force required to replace the guide sleeve,which is equivalent to the Z-yarn frictional forces.The frictional force is proportional to the number of preform layers and is applied to the preform decreased from the corner,edge,sub-edge,and middle in order.A back propagation neural network model was established to predict the friction at diferent positions of the preform with diferent layers,and the error was within 1.9%.The wear of Z-yarn was studied at diferent frictional positions and after diferent times of successive implantation into the preform.The results showed that with an increase in the number of Z-yarn implantations and frictional forces,the amount of carbon fber bundle hairiness gradually increased,and the tensile fracture strength damage of the fber was increasingly afected by the frictional forces.In the corner position of the preform,when the number of implantations was 25,the fber fracture strength decreased non-linearly and substantially;in order to avoid fber fracturing in the implantation process,the Z-yarn needs to be replaced in time after 20–25 cycles of continuous implantation.This study solves the problem of difculty in measuring the force required for individual replacements owing to the excessive number of guide sleeves,puts forward the relationship between fber wear,preform position,and implantation times,solves the phenomenon of fracture in the preform during Z-direction fber implantation,and realizes the continuous implantation of fbers.

Deep learning for predictive mechanical properties of hot-rolled strip in complex manufacturing systems

Higher requirements for the accuracy of relevant models are put throughout the transformation and upgrade of the iron and steel sector to intelligent production.It has been difficult to meet the needs of the field with the usual prediction model of mechanical properties of hotrolled strip.Insufficient data and difficult parameter adjustment limit deep learning models based on multi-layer networks in practical applications;besides,the limited discrete process parameters used make it impossible to effectively depict the actual strip processing process.In order to solve these problems,this research proposed a new sampling approach for mechanical characteristics input data of hot-rolled strip based on the multi-grained cascade forest(gcForest)framework.According to the characteristics of complex process flow and abnormal sensitivity of process path and parameters to product quality in the hot-rolled strip production,a three-dimensional continuous time series process data sampling method based on time-temperature-deformation was designed.The basic information of strip steel(chemical composition and typical process parameters)is fused with the local process information collected by multi-grained scanning,so that the next link’s input has both local and global features.Furthermore,in the multi-grained scanning structure,a sub sampling scheme with a variable window was designed,so that input data with different dimensions can get output characteristics of the same dimension after passing through the multi-grained scanning structure,allowing the cascade forest structure to be trained normally.Finally,actual production data of three steel grades was used to conduct the experimental evaluation.The results revealed that the gcForest-based mechanical property prediction model outperforms the competition in terms of comprehensive performance,ease of parameter adjustment,and ability to sustain high prediction accuracy with fewer samples.

Hot deformation behavior of a spray-deposited AZ31 magnesium alloy

The flow stress behavior of an as-spray-deposited AZ31 magnesium alloy with fine grains was investigated by means of compression tests with a Gleeble 1500 thermal mechanical simulator at isothermal constant strain rates of 0.01, 0.1, 1.0, and 10 s^-1; the testing temperatures ranged from 623 to 723 K. It is demonstrated that a linear equation can be fitted between the Zemer-Hollomon parameter Z and stress in a double-log scale. The effect of deformation parameters on the behavior of recrystallization was analyzed. Dynamic recrystallization （DRX） generally occurs at a higher temperature and at a lower strain rate. The constitutive equation of the spray-deposited AZ31 magnesium alloy is presented by calculating the deformation activation energy （199.8 kJ·mol^-1）. The as-spray-formed AZ31 alloy is easier for DRX nucleation at elevated temperatures due to the fine grain, which provides a large amount of nucleation sites and a high-diffusivity path for the atom.

High-quality manufacturing method ofcomplicated castings based on multi-materialhybrid moulding process

A multi-material hybrid patternless moulding process for complicated castings has been proposed. Moulding sands used in the hybrid moulding process include silica sand, ceramic sand, chromite sand, zircon sand, and steel shot sand. Experimental method was used to study the effects of moulding sands on the temperature field, mechanical properties, and dimensional precision of the iron castings. Under the condition that the wall thickness on different sides of the casting is the same, when the wall thickness is greater than 10 mm, the heat storage capacity of the moulding sands from strong to weak is steel shot sand, zircon sand, chromite sand, ceramic foundry sand, and silica sand. Tensile strength of the obtained castings from high to low is zircon sand, chromite sand, steel shot sand, ceramic sand, and silica sand. Contraction rate of the obtained castings from high to low is steel shot sand, zircon sand, chromite sand, silica sand, and ceramic sand. Therefore, steel shot sand and zircon sand can be used as chilled sand, and even can be used instead of cold iron when the casting wall thickness is greater than 10 mm. Zircon sand and chromite sand can be used to obtain high mechanical properties, and silica sand and ceramic sand can be selected to obtain high dimensional precision of the castings. Finally, a typical iron casting piece was tested by experiment using the hybrid moulding process. Excellent performances of iron castings confirm the feasibility of the hybrid moulding process.

Adaptive and Dynamic Mobile Phone Data Encryption Method

To enhance the security of user data in the clouds,we present an adaptive and dynamic data encryption method to encrypt user data in the mobile phone before it is uploaded.Firstly,the adopted data encryption algorithm is not static and uniform.For each encryption,this algorithm is adaptively and dynamically selected from the algorithm set in the mobile phone encryption system.From the mobile phone's character,the detail encryption algorithm selection strategy is confirmed based on the user's mobile phone hardware information,personalization information and a pseudo-random number.Secondly,the data is rearranged with a randomly selected start position in the data before being encrypted.The start position's randomness makes the mobile phone data encryption safer.Thirdly,the rearranged data is encrypted by the selected algorithm and generated key.Finally,the analysis shows this method possesses the higher security because the more dynamics and randomness are adaptively added into the encryption process.

Advances in the research of nitrogen containing stainless steels

The current status of nitrogen containing stainless steels at home and aboard has been introduced. The function and existing forms of nitrogen in the stainless steels, influence of nitrogen on mechanical properties and anti-corrosion properties as well as the application of nitrogen containing cast stainless steels were discussed in this paper. It is clear that nitrogen will be a potential and important alloying element in stainless steels. And Argon Oxygen Decarbonization (AOD) refining can provide an advanced manufacture process for nitrogen containing stainless steels with ultra-low- carbon and high cleanliness.

Evalution of Thermal Oxidative Degradation of Trimethylol-propane Trioleate by TG/DTA/DSC

In order to evaluate the thermal oxidation degradation behavior of lubricant with different antioxidants,the thermal kinetics equation based on the anlyses of thermogravimetry(TG),differential thermal analysis(DTA),and differential scanning calorimetry(DSC)was established,respectively,to calculate the activation energy of lubricant thermal-oxidative reaction.The thermal analyses of TG and DTA were employed to determine the thermal decomposition properties of ester oils trimethylolpropane trioleate(TMPTO)with butyl-octyl-diphenylamine/octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate/amine-phenol combination antioxidant.The activation energy of the lubricating oil adding antioxidant is increased relative to the TMPTO base oil,and the order of activation energy are Ec(93.732 kJ·mol^(-1))>Ed(88.71 kJ·mol^(-1))>Eb(58.41 kJ·mol^(-1))>Ea(46.32 kJ·mol^(-1)).The experimental results show that octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate in TMPTO has favorable resistance to thermal oxidation and decomposition.The thermal analysis method of DSC accurately reflects the heat exchange of lubricant thermal-oxidative reaction.The order of activation energy is calculated to ED(144.385 kJ·mol^(-1))>EC(110.05 kJ·mol^(-1))>EB(97.187 kJ·mol^(-1))>EA(66.02 kJ·mol^(-1)).It is illustrated that the amine-phenol combination antioxidant has the best thermal oxidation resistance,which is the same as what the oxidation onset temperature effected.

Simulation and experimental research on extra-squeeze forming method during gradient sand molding

The flexible extrusion forming process (FEFP) is a sand mold patternless manufacturing technology that enables digital near-net shaping of complex sand molds. But, it is difficult to achieve the gradient sand molds with high surface strength and strong interior permeability by FEFP. To solve this problem, an extra-squeeze forming method based on FEFP for gradient sand mold was developed. To further reveal the extra-squeeze forming mechanism, based on the Johnson-Kendall-Roberts (JKR) theory and “gluing” notions, the single and double-sided squeeze models of gradient sand molds were established using the EDEM software. The squeezing processes of sand molds with different cavity depths of 60, 100, 140, 180, and 220 mm were systemically studied under single and double-sided squeeze conditions. The variation in the void fraction of sand mold as also investigated at a variety of extra-squeeze distances of 2, 3, 4, 5, and 6 mm, respectively. Simulation and test results show that a deeper cavity depth weakens the extrusion force transmission, which leads to a decrease in strength. The sand mold permeability and void fraction are identified to be positively correlated, while the tensile strength and void fraction appear to be negatively correlated. The void fraction of sand molds decreases with a longer extra-squeeze distance. A 6 mm extra-squeeze distance for the sand mold with 220 mm cavity depth results in a 26.8% increase in tensile strength with only a 5.7% reduction in the permeability. Hence, the extra- squeeze forming method can improve the quality of the sand mold by producing a gradient sand mold with high surface strength and strong interior permeability.

Heat shock behavior of permanent die during non-solid near-net forming process

Heat shocks caused by alloy melt and coat spraying are the main reason of die plastic deformation and early fracture. Based on theoretical analysis of heat shock phenomenon, two characteristic parameters of die damage caused by heat shock were proposed, which are heat shock plastic deformation index (HSPI) and heat shock crack index (HSCI). The effect of heat shock on die plastic deformation and fracture behaviors was described quantitatively by these two parameters. HSPI represents approaching of heat shock stress to die yield stress. Plastic deformation will happen on a die if this index reaches 1. HSCI represents approaching of heat shock stress to die tensile strength. Die fracture will happen if this index reaches 1. According to theoretical analysis of heat transfer, theoretical models of HSPI and HSCI were established. It is found that, the smaller the interfacial thermal resistance (ITR) is, the higher the pouring temperature and die temperature are before heat shock, and the greater the HSPI and HSCI are, which can be fitted as exponential curves, linear and cubic curves.

Development of electric construction machinery in China:a review of key technologies and future directions

The issues of energy shortage and environmental pollution have accelerated the electrification of construction ma-chinery(CM)industry globally.In China,the amount of electric construction machinery(ECM)has been growing across the industry.The sales of ECM are estimated to reach 600000 vehicles by the end of 2025,while the total demand for battery power will reach 60 GWh.However,the development of ECM still faces critical challenges including reliable power supply and energy distribution among various components.In this review,we primarily focus on important technological breakthroughs and the difficulties faced by the CM industry in China.An overview of ECM including classification and characteristics is given at the beginning.Next,the selection of key components such as the electric motor and the energy storage units,and the control strategy in the pure electric drive system are discussed.The characteristics of the hybrid electric drive system such as structure design and power matching are analyzed in detail.The battery management system(BMS)is critical to ensure appropriate battery health for reliable power supply.Here,we extensively review technical developments in various BMSs.In addition,we roughly estimate the national total of CM emissions and the potential environmental benefits of employing ECMs in China.Finally,we set out future research directions and industrial development of ECM.

Triboelectric behaviors of materials under high speeds and large currents

Using special testers,the triboelectric behaviors of several materials were investigated in this paper under the conditions of high speeds and large currents.The obtained results revealed that the tribological behaviors and current-conducting characteristics have complicated interrelationships.Worsening in the servicing conditions can obviously deteriorate the tribological as well as electrical behaviors;high sliding speeds and large electrical currents can worsen the tribological and electrical conductivity properties,while an appropriate contact pressure can benefit the electrical contact properties.Further analyses reveal that the worsening effects of the above factors,such as frictional heat,arc discharge,arc heat,and surface morphology,result in poor triboelectric contact performance.Among these,the electric arc is one of the most serious factors,because the occurrence of an electric arc may cause severe oxidation,melting,and roughening of the contact surface,thereby causing deterioration in the current-conducting quality as well as material loss.

Effect of post-bond heat treatment on the microstructure and high temperature mechanical property of a TLP bonded γ'-strengthened co-based single crystal superalloy

Post-bond heat treatment(PBHT) applied to a transient liquid phase(TLP) bonding joint is an effective approach to remove the brittle borides and improve its properties.Herein,we proposed two types of PBHT strategies to obtain a TLP bonded γ'-strengthened Co-based single crystal superalloy,and the microstructural characteristics and tensile properties of the two heat treated joints were compared to identify the optimal PBHT strategy.The evolution of the brittle boride in the joint after the PBHT was studied by using in-situ microscopy.The experimental results allowed to provide a theoretic model to quantitatively evaluate the distribution of the brittle phase after the optimal PBHT and analyze the joint fractures to understand the failure mechanisms.The obtained results revealed that a post-bond solid solution treatment performed to the joint at a high temperature(over 1275℃) could decrease the area fraction of the boride from 7.2 % to 1.4 % and increase the elongation from 1.9 % to 7.8 %.This work emphasizes the relevance of solid solution temperature when a PBHT strategy is applied.