To obtain the aluminum alloy with high thermal and mechanical properties, the effects of alloying elements and the second phases on the thermal conductivity of Al alloys were investigated by CALPHAD and first-principles calculation, respectively. The properties of the second phases, including Young's modulus, Poisson's ratio and minimum thermal conductivity, were systematically studied. Results show that the ranking order of the effects of the alloying elements on the thermal conductivity is Mg>Cu>Fe>Si, and for Al-12Si alloys, the mathematical model of the relationship between the alloying elements and the thermal conductivity can be expressed as λ=ax²-bx+c when the second phase precipitates in the matrix. All kinds of ternary phases of Al-Fe-Si have higher deformation resistance, rigidity, theoretical hardness, Debye temperature and thermal conductivity than the other phases which possibly exist in the Al-12Si alloys. Based on the guidance of CALPHAD and first-principles calculation, the optimized chemical composition of Al alloy with high conductivity is Al-11.5Si-0.4Fe-0.2Mg (wt.%) with a thermal conductivity of 137.50 Wm^-1·K^-1 and a hardness of 81.3 HBW.

To meet the requirements of crashworthiness design of electric vehicle power battery packs， the failure mechanism of lithium-ion batteries was studied under different mechanical abuse conditions. Based on local indentation and plane compression loading tests on three different capacity NCR18650 cylindrical lithium-ion batteries， the force-electric-thermal responses of lithium-ion batteries were analyzed and the cross-section failure modes of the compressed battery samples were given. Then the effects of loading types and battery capacity on the failure mechanism of cylindrical batteries were discussed. The results show that internal short circuit and external short circuit failure modes of batteries may be caused by local indentation and plane compression， respectively. With the increase of battery capacity， the bearing performances of the batteries may reduce， which leads to the failure displacements decrease. Loading types and rated capacity also have an effect on the surface temperature changes of the batteries. The maximum surface temperature of the batteries after the local indentation is higher， and the surface temperature changes of the medium-capacity batteries are relatively smooth.

To refine the microstructure and improve the mechanical properties of AZ91D alloy by expendable pattern shell casting (EPSC), the mechanical vibration method was applied in the solidification process of the alloy. The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91D magnesium alloy were studied. The results indicated that the mechanical vibration remarkably improved the sizes, morphologies and distributions of the primary α-Mg phase and β-Mg₁₇Al₁₂ phase, and the densification and tensile properties of the AZ91D alloy. With an increase in amplitude, the microstructures were gradually refined, resulting in a continuous increase in mechanical properties of the AZ91D alloy. While, with the increase of pouring temperature, the microstructures were continuously coarsened, leading to an obvious decrease of the mechanical properties. The tensile strength and yield strength of the AZ91D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730℃ were 60% and 38% higher than those of the alloy without vibration, respectively.

In order to improve the current loop frequency response capability and speed response performance of the surface-mounted permanent magnet synchronous motor, and aiming at the problem of excessive unknown parameters of the expected interconnection matrix due to the coupling of d-axis and q-axis current in the passive controller design process, a new design method of passive controller based on current decoupling was proposed by combining with voltage feedforward decoupling control.Firstly, according to the energy balance principle and voltage feedforward decoupling control, the port control Hamilton system with dissipation(PCHD)model of surface-mounted permanent magnet synchronous motor based on current decoupling was constructed.Then, the passive controller of surfacemounted permanent magnet synchronous motor was designed by the interconnection and damping assignment passive-based control(IDA-PBC)method, and the voltage feedforward decoupling control was introduced in the design process to eliminate the coupling between d-axis and q-axis current, so that the unknown parameters of the expected interconnection matrix were reduced from 3 to 1.Finally, the test platform of surface-mounted permanent magnet synchronous motor was built for experimental verification.The experimental results showed that when the passive controller based on current decoupling was used in the current loop of surface-mounted permanent magnet synchronous motor, the q-axis current response frequency increased from less than 250 Hz to more than 333 Hz; the speed response time at rated speed decreased from 0.16 s to 0.11 s, the overshoot decreased from 2.0% to 0.6%, and the steady-state error decreased from 5.98 r/min to 1.15 r/min.The research results can provide a new idea for the passive controller design of permanent magnet synchronous motor.

Based on STL (stereo lithography) format file and with Microsoft Visual C⁺⁺ 6.0 programming language,a 3D printing slicing software appropriate for the surface strengthening of the parts has been developed,which includes three functions:3D model import,model slicing and data export.Through the grouping of STL model triangle facets before slicing,the judgment times of the relationship between the triangle facets and the cutting planes are reduced,and the slicing efficiency is improved.Aiming at the fact that the surface should be strengthened when the part is formed by using of 3D printing process,the function of identifying and marking the surface of the geometric entity is accomplished in the slicing software,which can strengthen the surface of the part according to the user’s requirements.The developed slicing software can provide an entity slicing file for 3D printing equipment.The related functions can be adjusted and improved according to user’s needs,which makes the software convenient and flexible to use.

In the process of hot-dip Zn-Al-Mg alloy coating, the plating solution dissipates heat in the direction perpendicular to the steel plate, which is considered to be a process of directional solidification. To understand the relationship between microstructure and cooling rate of Zn-Al-Mg alloys, both the phase constitution and microstructure characteristic length scales of Zn-9.5Al-3Mg-0.01Ce (wt.%) alloy were investigated by the directional solidification experiments at different growth velocities (V=40, 80, 160, 250 μm·s^-1). The experimental results show that the microstructure of directionally solidified Zn-9.5Al-3Mg-0.01Ce alloy is composed of primary Al dendrites and (Zn-Al-Mg₂Zn₁₁) ternary eutectics at the growth velocities ranging from 40 to 250 μm·s^-1. The primary Al dendrites are aligned regularly along the growth direction, accompanied with obvious secondary dendrites. The relationship between the microstructure length scale and the thermal parameters of solidification is obtained: λ₁=374.66V^-0.383, and λ₂=167.5V^-0.563 (λ₁ is the primary dendrite arm spacing, and λ₂ is the secondary dendrit arm spacing). In addition, through the interface response function (IRF) and the nucleation and constitutional undercooling (NCU), the phase selection of Zn-9.5Al-3Mg-0.01Ce is obtained: (Zn+Al+Mg₂Zn₁₁) ternary eutectics in the Zn-9.5Al-3Mg-0.01Ce alloy will be replaced by ternary eutectics (Zn+Al+MgZn₂) when the growth rate is lower than 7.53 μm·s^-1.

Due to the immaturity of intelligent technology in universality， robustness and security， intelligent interactive products were prone to “behavior conflict” due to the mismatch with user behavior patterns in intention expression， information processing， decision logic， interaction timing and action intensity. Unified modeling and optimization of multi domain behavior processes of human-machine environmental systems were the key to realize behavior characteristic regulation and forward design of intelligent interactive products. This paper systematically reviewed the research progresses of multi domain behavior process representation model， modeling language and tool， model validation and behavior process optimization of human-machine environmental systems from four dimensions：how to represent， what to represent， how to verify and how to optimize. The existing problems and limitations in this field were analyzed， and the future research focus and development trend were prospected.

AZ91D and 8.5vol.% SiC_p/AZ91D magnesium matrix composites were fabricated by a semi-solid extruded processing method,and treated with solution and aging heat treatment.The effects of SiC_p on the microstructures of the semi-solid extruded AZ91D magnesium alloy during recrystallization were studied by observing and analyzing the microstructure evolution during extrusions and heat treatments.The results show that the addition of SiC_p inhibits the dynamic recrystallization of AZ91D during the semi-solid extrusion with only 26% of the volume fraction of recrystallization.Furthermore,the addition of SiC_p refines the sizes of grains and second phases,and upgrades the volume fraction of second phase.After solution and aging treatment,the recrystallization continues,and the addition of SiC_p promotes the recrystallization and the recrystallized microstructure is much more stable.Meanwhile,the sizes of grains and second phases continue to be refined,and the volume fraction of second phases continues to increase.

A novel Ti-5.55Al-6.70Zr-1.50V-0.70Mo-3.41Nb-0.21Si alloy was designed using the cluster formula approach (cluster-plus-glue-atom model) and prepared by laser melting deposition (LMD). Its composition formula 12[Al-Ti₁₂](AlTi₂)+5[Al_0.8Si_0.2-Ti₁₂Zr₂](V_0.8Mo_0.2Nb₁Ti) features an enhanced β-Ti via co-alloying of Zr, V, Mo, Nb and Si. The experimental results show that the cluster formula of α and β phases in the novel alloy are respectively α-[Al-Ti_11.5Zr_0.5](Al₁Ti₂) and β-[Al_0.8Si_0.2-Ti_13.2Zr_0.8](V₁Mo_0.4Nb_1.6), both containing Zr elements. The fitted composition via the α and β phase cluster formulas has little difference with the actual alloy composition, suggesting that the validity of cluster-plus-glue-atom model in the alloy composition design. After hot isostatic pressing (HIP), both the Ti-6Al-4V and the novel alloy by LMD are characterized by prior-β columnar grains, while the typical <100> texture disappears. Compared with Ti-6Al-4V, Ti-5.55Al-6.70Zr-1.50V-0.70Mo-3.41Nb-0.21Si alloy exhibits a combination of higher strength (1,056 MPa) and higher ductility (14%) at room temperature and higher strength (580 MPa) at 550 ℃ after HIP, and can potentially serves as LMD materials.

In order to meet the rehabilitation training needs of patients with lower limb motor dysfunction at different stages, a traction lower limb rehabilitation robot that could realize the training modes of lying and sitting postures was proposed in view of the single training mode of existing lower limb rehabilitation robots.Firstly, according to the motion mechanism and bionic principle of human lower limbs, a five-degree-of-freedom hybrid mechanism configuration was designed.Then, the kinematics model of the robot was established, and the forward and inverse kinematics solutions were calculated, respectively.Then, taking the workspace coincidence degree between the end of human lower limb and the end of robot as the objective function, the mechanism parameters of robot were optimized by the genetic algorithm, and the effective workspace ratio of human lower limb in the sagittal plane of the human-machine system was 0.71.Finally, three kinds of rehabilitation training trajectories including CPM(continuous passive motion), circular motion and spiral motion were planned, and a robot prototype was built according to the optimized mechanism parameters.Through motion capture experiments, the rationality of the robot structure design and optimization results and the correctness of trajectory planning were verified, which indicated that the robot could meet the rehabilitation needs of patients with lower limb motor dysfunction.

Hot tearing is one of the most serious defects during the casting solidification process. In this study, a new type of multichannel "cross" hot tearing device was designed. The hot cracks initiation and propagation were predicted by the relationship between temperature, shrinkage force and solidification time during the casting solidification process. The reliability and practicability of the multichannel "cross" hot tearing device were verified by casting experiments and numerical simulations. The theoretical calculation based on Clyne-Davies model and numerical simulation results show that the hot tearing tendency decreases in the order:2024 Al alloy>Al-Cu alloy>Al-Si alloy at a pouring temperature of 670℃ and a mold temperature of 25℃. Feeding of liquid films at the end of solidification plays an important role in the propagation process of hot tearing. The decrease of hot tearing tendency is attributed to the feeding of liquid film and intergranular bridging.

The present study designed two kinds of Fe-18Mn-1.3C-2Cr-(4, 11)Al (wt.%) low-density steels. Tensile and impact tests were carried out to evaluate the work hardening and impact toughness properties via aluminum (Al) alloying control. Meanwhile, microstructure evolution and fracture morphology were investigated by X-ray diffraction (XRD), a scanning electron microscope (SEM) equipped with electron backscatter diffraction (EBSD), a transmission electron microscope (TEM), and a stereo-optical microscope (OM). It is found that the Al addition obviously promotes the dislocation planar slipping, resulting in cleavage and brittle impact fracture in 11wt.% Al steel. Besides, the microband-induced plasticity (MBIP) mechanism is found in 4wt.% Al containing steel, introducing considerable work hardening capacity and impact toughness of 156.8±17.4 J. The present study provides a direct illustration of the relationship between work hardening and impact toughness behaviors of these two low-density steels for potential application as impact-resistant components.

Two important factors affecting the performance of sand mold/core generated by 3D printing (3DP) are strength and dimensional accuracy,which are not only closely related to the reactivity of furan resin and the phase transition of silica sand,but also the curing agent system of furan resin.This paper studies the influence of gel time on the strength and dimensional accuracy of a 3DP sand mold/core,taking the furan resin system as an example and using a sand specimen generated by a 3DP inkjet molding machine.The experiment demonstrates that the gel time of 3 to 6 min for the sand mixture suits 3DP core-making most under the experimental condition.However,it should be noted that under the same resin condition,the strength of a no-bake sand mold/core is higher than that of a 3DP sand mold/core.The dimensional accuracy of the sand mold/core does not change significantly when the gel time is less than 15 min.Improving the activity of binder and developing ultra-strong acid with low corrosion shall be an effective way to improve the quality of the mold/core by 3D printing.

The laser powder bed fusion (L-PBF) method of additive manufacturing (AM) is increasingly used in various industrial manufacturing fields due to its high material utilization and design freedom of parts. However, the parts produced by L-PBF usually contain such defects as crack and porosity because of the technological characteristics of L-PBF, which affect the quality of the product. Laser ultrasonic testing (LUT) is a potential technology for on-line testing of the L-PBF process. It is a non-contact and non-destructive approach based on signals from abundant waveforms with a wide frequency-band. In this study, a method of LUT for on-line inspection of L-PBF process was proposed, and a system of LUT was established approaching the actual environment of on-line detection to evaluate the method applicability for defects detection of L-PBF parts. The detection results of near-surface defects in L-PBF 316L stainless steel parts show that the crack-type defects with a sub-millimeter level within 0.5 mm depth can be identified, and accordingly, the positions and dimensions information can be acquired. The results were verified by X-ray computed tomography, which indicates that the present method exhibits great potential for on-line inspection of AM processes.

Aero-engine hollow turbine blades are work under prolonged high temperature, requiring high dimensional accuracy. Blade profile and wall thickness are important parameters to ensure the comprehensive performance of blades, which need to be measured accurately during manufacturing process. In this study, a high accuracy industrial computed tomography (ICT) measuring method was developed based on standard cylindrical pin and ring workpieces of different sizes. Combining ICT with cubic spline interpolation, a sub-pixel accuracy was achieved in measuring the dimension of component. Compared with the traditional and whole-pixel level image measurement method, the cubic spline interpolation algorithm has the advantages of high accuracy in image edge detection and thus high accuracy of dimensional measurement. Further, the technique was employed to measure the profile and wall thickness of a typical aerospace engine turbine blade, and an accuracy higher than 0.015 mm was obtained.

Aiming at the problems of insufficient oil suction and slow system response caused by the unreasonable parameters of the distribution check valve in single plunger pump system, a multi parameter optimization method based on linear regression was proposed.Firstly, the simulation analysis of single plunger pump system was carried out by AMESim software, and the relationship between different check valve parameters(spring pre-tightening force, spring stiffness and valve core mass)and oil inlet flow was discussed by using MATLAB fitting toolbox.Then, on the basis of using the principal component analysis method to eliminate the correlation between the parameters, taking the oil inlet flow as the dependent variable, the spring pre-tightening force, spring stiffness and valve core mass as the independent variable, and the value range of each parameter as the constraint condition, a check valve parameter optimization model based on linear regression was established, and the genetic algorithm was used to optimize the solution.Finally, according to the parameters of the check valve before and after optimization, the simulation analysis and experimental verification of the single plunger pump system were carried out.The simulation results showed that the oil inlet flow was increased by 21.3% after optimization; the experimental results showed that the actual oil inlet flow was increased by 16.8% after optimization.The research shows that the proposed multi parameter optimization method is an effective method, which can provide reference for the parameter optimization of the distribution check valve in single plunger pump system.

Effect of solution treatment on microstructure and mechanical properties of Al-12Si-4Cu-2Ni-0.8Mg-0.2Gd alloy was investigated. Results show the Si particles become stable and more intermetallic compounds dissolve in the matrix after solution treatment at 500℃ for 2 h followed by 540℃ for 3 h (T4). The skeleton-like Al₃CuNi develops into two parts in the T4 alloy:one is Al₃CuNi which has the framework shape; the other is intermetallics including the Al₃CuNi (size:5-10 μm) and AlSiCuNiGd phases (size: ≤ 5 μm) with complex structure. Adding 0.2% Gd can improve the mechanical properties of the alloys after two-step solution treatment (500℃/2 h followed by 540℃/3 h), the hardness of the alloy increases from 130.9 HV to 135.8 HV compared with the alloy with one-step solution treatment (500℃/2 h), the engineering strength increases from 335.45 MPa to 352.03 MPa and the fracture engineering strain increases from 1.44% to 1.67%.

To meet the requirements of cavity feature recognition for corner box parts， an automatic cavity feature recognition method was proposed based on improved graph matching. The cavity features of corner box parts were analyzed and the common template attributes of feature simplified model were extracted. The raster height point cloud data of the model was obtained， and the median height was taken as the threshold value to transform it into a 0-1 matrix. The projection eigenvalues of the cavity surfaces were extracted from the 0-1 matrix to separate and recognize the cavity wall and edge surfaces. Face adjacency attribute was used to search the side wall surface of the cavity， and the complete machining features of the cavities were finally identified， including the bottom surface set， the wall side surface set and the side wall surface set. The results of example verification show that the proposed method is more efficient and robust than those of the fixed template matching method to identify the machining features of the cavity of corner box parts.

With the increasing complexity and diversity of 3D printed parts, the single-material parts can no longer meet various special performance requirements.Functionally graded material parts have gradually become a research hotspot in rapid prototyping manufacturing industry.In order to meet the manufacturing requirements of functionally graded material, a spatial mapping modeling method for functionally graded material based on coordinate transformation was proposed.The key of this method was to effectively combine geometry information with material information.Firstly, the material space of functionally graded material model was constructed by using the single gradient source method and multi-gradient source method.When the cross-gradient source model was encountered, the material distribution was calculated by using a specific intersection operator with a certain weight ratio.Then, in the process of combining the geometric space and the material space, the coordinate system of material space and geometric space was cleverly cooverlapped through coordinate transformation to realize the mapping of material space to geometric space, so as to obtain a functionally gradient material model with material information.The required functionally graded material model could be obtained by modifying the gradient source, material distribution function and coordinate transformation method.The results of visual analysis of the instance model through Visual Studio 2019 and OpenGL programming languages showed that the proposed modeling method greatly shortened the modeling time compared with most valuation modeling and non-valuation modeling methods, and fundamentally solved some problems of insufficient storage space and cumbersome modeling process caused by some algorithms.The spatial mapping modeling method for functional gradient material based on coordinate transformation can provide a new modeling method for the additive manufacturing industry and has good application value.

Zr-based metallic glasses (MGs) possess a wide supercooled liquid region, which gives a wide processing window for superplastic forming to make microdevices with demanding size accuracy and surface finishing. The existence of oxygen may have an influence on the thermoplastic deformation process. Therefore, the effect of oxidation on the mechanical behavior of the MGs in the vicinity of glass transition temperature is of great significance for practical forming of MG components. In the present study, the effect of oxidation on tensile properties of Zr₅₀Cu₄₀Al₁₀ metallic glass was investigated. The tested samples were characterized by XRD and SEM analysis. For the samples tested in air, the strength decreases 187 MPa, 61 MPa and 59 MPa and the ductility increases 0.31, 0.36, and 0.77 at 420 ℃, 430 ℃, and 440 ℃, respectively, compared with those tested in flowing argon. ZrO₂ preferentially formed during the tensile testing at 420 ℃, and both ZrO₂ and Al₂O₃ oxides formed at 430 ℃. The dilution of Zr elements in the remaining amorphous matrix caused by preferential oxidation on the surface layer attributes to the decrease in strength and enhancement in ductility of the Zr₅₀Cu₄₀Al₁₀ metallic glasses.

Numerical simulation technology has been widely used in the foundry industry to analyze and improve casting processes. During the casting filling process, many filling-related defects form easily at the confluences of liquid metal streams. The main filling-related defects are cold shut defects. To calculate the positions of casting defects, the characteristics of liquid metal confluences were analyzed. The flow front of liquid metal was captured by the volume-of-fluid algorithm to obtain a time field, which was used to calculate the time derivatives of the liquid front position and the confluences of liquid metal streams. To distinguish small confluences from the main confluences, the concept of confluent scale was developed, which was used to filter the small confluences based on a threshold. The calculation process was demonstrated through the post-processing of numerical simulation. A "W" shaped casting and a steering wheel casting were calculated to validate the accuracy of the method developed in this study. The positions of cold shut defects were predicted by calculating the confluences of liquid metal streams. The method was proved to be practical by comparing the calculation results with the positions of cold shut defects in an end cover casting. The computation of confluences and cold shut defects can improve the analysis efficiency and provide assurance for the optimization of a casting process plan.

K439B nickel-based superalloy is a new type of high-temperature material. There is insufficient research on its constitutive equations and numerical modeling of thermal stress. Isothermal tensile experiments of K439B superalloy at different temperatures (20 ℃-1,000 ℃) and strain rates (1.33×10^-3 s^-1-5.33×10^-3 s^-1) were performed by using a Gleeble-3800 simulator. The elastic moduli at different temperatures (20 ℃-650 ℃) were measured by resonance method. Subsequently, stress-strain curves were measured for K439B superalloy under different conditions. The elastic-viscoplastic constitutive equations were established and the correspongding parameters were solved by employing the Perzyna model. The verification results indicate that the calculated values of the constitutive equations are in good agreement with the experimental values. On this basis, the influence of process parameters on thermal stress was investigated by numerical simulation and orthogonal experimental design. The results of orthogonal experimental design reveal that the cooling mode of casting has a significant influence on the thermal stress, while pouring temperature and preheating temperature of shell mold have minimal impact. The distribution of physical fields under optimal process parameters, determined based on the orthogonal experimental design results, was simulated. The simulation results determine separately the specific positions with maximum values for effective stress, plastic strain, and displacement within the casting. The maximum stress is about 1,000.0 MPa, the plastic strain is about 0.135, and the displacement is about 1.47 mm. Moreover, the distribution states of thermal stress, strain, and displacement are closely related to the distribution of the temperature gradient and cooling rate in the casting. The research would provide a theoretical reference for exploring the stress-strain behavior and numerical modeling of the effective stress of the alloy during the casting process.

The total content of Al and Ti in advanced Ni-based wrought superalloys is up to 7.5wt.%, which makes it easier to form harmful nonequilibrium eutectic (γ+γ') and η phase. It has been reported that the addition of certain amount of Zr can modify precipitation of the nonequilibrium phases obviously, but the mechanism is still controversial. The effect of Zr ranging from <0.0006wt.% to 0.150wt.% on solidification behavior, segregation and microstructure of a Ni-based superalloy with high Al and Ti contents was investigated, eliminating the interferences of C and B. Results show that increase in Zr content significantly promotes the formation of eutectic (γ+γ'), η and Zr-rich phase in the interdendritic region. Besides the Zr-rich phase, Zr dissolves slightly in the eutectic γ' and obviously in the η phase. An interesting phenomenon is discovered that the Zr addition significantly increases the area fraction of liquid pools and enlarges the forming range of γ dendrites, which suggests that Zr markedly retards the solidification. Zr affects the eutectic (γ+γ') and η formation mainly due to the retard of solidification and dissolution of Zr in them. The retard of solidification obviously increases the residual liquid fraction and undercooling. Zr can serve as a forming element for the eutectic (γ+γ') and η phase, and the obvious dissolution of Zr in η phase significantly decreases the critical concentration of Ti for its precipitation.

Boron and carbon contents are the main factors influencing the properties of high-boron steel. In this study, experimental samples with different boron-to-carbon ratios (%B/%C) were prepared. The microstructures of the different samples were observed, and their hardness, bending strength, and impact toughness were investigated. Results show that the main microstructures in the investigated high-boron steel samples are the eutectic Fe₂B structure with a fishbone shape and the ternary peritectic Fe₃(C, B) structure with a chrysanthemum shape. When the boron content is 2.5wt.% and the carbon content is 0.43wt.% (i.e., %B/%C=5.82), the overall mechanical properties of the alloy are the best. The alloy’s hardness, bending strength and impact toughness reach their maximums, which are 67.3 HRC, 1,267.36 MPa and 6.19 J·cm^-2, respectively. The optimized alloy is compared with conventional materials exhibiting excellent wear resistance (namely, high-manganese steel and high-chromium cast iron) through two-body and three-body abrasion tests. The wear resistance of this high-boron steelinvestigated in this work is found to be superior to those of the more common materials.

Microstructure, mechanical properties and phase transformation of a heat-resistant rare-earth (RE) Mg-16.1Gd-3.5Nd-0.38Zn-0.26Zr-0.15Y (wt.%) alloy were investigated. The as-cast alloy is composed of equiaxed α-Mg matrix, net-shaped Mg₅RE and Zr-rich phases. According to aging hardening curves and tensile properties variation, the optimized condition of solution treatment at 520 ℃ for 8 h and subsequent aging at 204 ℃ for 12 h was selected. The continuous secondary Mg₅RE phase predominantly formed at grain boundaries during solidification transforms to residual discontinuous β-Mg₅RE phase and fine cuboid REH₂ particles after heat treatment. The annealed alloy exhibits good comprehensive tensile property at 350 ℃, with ultimate tensile strength of 153 MPa and elongation to fracture of 6.9%. Segregation of RE elements and eventually RE-rich precipitation at grain boundaries are responsible for the high strength at elevated temperature.

Ti-Ni composite sub-micron powders with different compositions were prepared by vacuum melting and atomization technology. These powders, after being mixed with a solution of phenolic resin and alcohol, were applied on the mold cavity wall, by which a casting-infiltration layer was introduced on the surface of ZG45 steel via reactions between the powders and molten steel under the heat released by solidification. The effects of the powders’ composition and pouring temperature on the corrosion resistance of the casting-infiltration layer were studied. An optimal casting-infiltration layer with a thickness of ～7 mm was obtained by infiltrating the Ti-Ni composite powders containing 35wt.% Ti to ZG45 steel pouring at 1,650 ℃. The casting-infiltration layer has a good metallurgic bonding with the matrix, and is mainly composed of Fe₂Ti phase and continuous γ-(Fe, Ni) solid solution. In the corrosive H₂SO₄ solution, the corrosion potential of the casting-infiltration layer is lower than the matrix, tending to form a passivation film, which lowers the dissolution rate especially when the potential rises to 0.50 V. After dipping in the 10wt.% NaCl solution for 480 h, a lot of corrosion holes appear in the ZG45 steel matrix, while there are no obvious traces of corrosion on the casting-infiltration layer.

Aiming at the problem that the horizontal rotating equipment of space station cabin is easy to deform in the length direction after bearing load of 30 t, a six-point leveling algorithm and synchronous control method was proposed.On the basis of installing one screw lifting outrigger at each of the four corners of the original horizontal rotating equipment of space station cabin, one screw lifting outrigger was added at the center of two long sides, and the levelness of the horizontal rotating equipment upper plane was within 0.001°through the coordinated control of the height of each screwlifting outrigger, so as to ensure the centroid stability and no structure deformation of the space station cabin.At the same time, the feasibility of six-point leveling algorithm and synchronous control method was verified by theoretical simulation.The experimental test showed that the proposed method had good leveling effect, and the synchronous control error of six screw lifting outriggers was less than 8 ms; after leveling, the maximum error of upper plane levelness of the horizontal rotating equipment was 0.000 8°, and the maximum deformation was 0.074 mm, which could be ignored and met the expected goal.The results showed that the application of the six-point leveling algorithm and synchronous control method effectively avoided the deformation in the length direction of the horizontal rotating equipment of space station cabin after bearing load of 30 t, improved the levelness of the horizontal rotating equipment and extended its service life, and ensured the centroid stability of the space station cabin after it was placed on the horizontal rotating equipment, which could provide technical support for the subsequent space station assembly process.

The application of additive manufacturing technology is one of the main approaches to achieving the rapid casting. Additive manufacturing technology can directly prepare casting molds (cores) with no need of patterns, and quickly cast complex castings. The combination of additive manufacturing and traditional casting technology can break the constraint of traditional casting technology, improve casting flexibility, and ameliorate the working environment. Besides, additive manufacturing promotes the realization of "free casting", greatly simplifying the processing procedures and shortening the manufacturing cycle. This paper summarizes the basic principle of additive manufacturing technology and its development situation domestically and overseas, mainly focusing on the development status of several main additive manufacturing technologies applicable to the foundry field, including three-dimensional printing, selective laser sintering, stereolithography, layered extrusion forming, etc. Finally, the future development trend of additive manufacturing technology in the foundry field is prospected.

Fused corundum is a rather promising raw material for preparing an alumina-based ceramic core due to its excellent high temperature resistance and chemical inertness.In this study,alumina-based ceramic cores were prepared using fused corundum as the matrix material,and the effect of varying silica powder contents on the properties of the alumina-based ceramic cores,including the sintering shrinkage,the flexural strength,and the high temperature deformation was investigated.The mineralization mechanisms of the silica on the alumina-based ceramic core were also analyzed.The optimum addition amount of silica in this experiment is 8% in weight.At that moment,the aluminum-based core has both a low sintering shrinkage coefficient of 0.66% and better properties:the room temperature flexural strength is 22.19 MPa,the high temperature flexural strength is 21.54 MPa,the high temperature deformation is 0.93 mm,and the residual flexural strength is 47.41 MPa.

The infiltration casting fabrication process based on spherical CaCl₂ space-holders and the compressive behavior including the mechanical performance and energy absorption capacity of open-cell aluminum foams were investigated. Open-cell aluminum foams with different porosities in the range of 63.1% to 87.3% can be fabricated by adjusting compression ratios of CaCl₂ preforms prepared by precision hot-pressing. The compression tests show that a strain-hardening phenomenon always occurs especially for open-cell aluminum foam with low porosity, resulting in the inclining stress-strain curve in the plateau region. The energy absorption capacity of open-cell aluminum foam decreases with increasing porosity when compared at the same strain. However, when compared at a given stress, each foam can absorb the maximal energy among the five foams in a special stress range. Additionally, open-cell aluminum foam possesses the maximum energy absorption efficiency at its optimum operating stress. At this stress condition, the foam can absorb the highest energy compared with other foams at the same stress point. The optimum operating stress and the corresponding maximal energy absorption decrease with increasing the porosity. The optimum operating stress for energy absorption can also be determined similarly when taking into consideration of the lightweight extent of foams.

Al-5Ti-B and Al-5Ti-B-Gd master alloy refiners were fabricated by fluorine salt casting method. The microstructure and phase constitution of the master alloys were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that Al-Ti-B alloy refiner consists of Al₃Ti phase and TiB₂ phase. After Gd is introduced into the intermediate alloy, Ti₂Al₂₀Gd phase appears in the alloy, the size of Al₃Ti is significantly reduced, and Ti-Al-Gd phase is found in the edge of Al₃Ti phase. At the same time, some independent Ti-Al-Gd phases appear in local areas, which are Ti₂Al₂₀Gd phase determined by micro-area electron diffraction analysis. Analysis and calculation results of the high-resolution images of the Ti₂Al₂₀Gd/Al structure show that there is no other compound at the junction between the Ti₂Al₂₀Gd phase and Al, and Ti₂Al₂₀Gd phase has a great difference in atomic space with the α-Al, which cannot be directly used as heterogeneous nucleus. But, after being decomposed in the aluminum melt, the Ti₂Al₂₀Gd phase can promote the refinement effect of the refiner. In the Al-Ti-B-Gd master alloy, there are many dispersed Al₃Ti particles with a size of less than 1 μm, which can promote the Al-5Ti-B refining effect.

The initiation and propagation of thermal fatigue cracks in gray cast iron and vemicular graphite cast iron were investigated by Uddeholm method to reveal the complex thermal fatigue behaviors of cast iron. Differences of thermal fatigue behaviors of gray cast iron and vemicular graphite cast iron were observed and analyzed. It is found that the observed differences are related to the combination of graphite morphology and the oxidization of matrix. More oxidized matrix is observed in gray cast iron due to its large specific surface area. The brittle oxidized matrix facilitates the propagation of microcracks along the oxidization layer. By contrast, the radial microcracks are formed in vermicular graphite at the edge of graphite due to fewer oxidization layers. It indicates that the thermal fatigue resistance of gray cast iron is dominated by graphite content and morphology while that of vermicular graphite cast iron strongly relates to the strength of the matrix.

Progressive solidification is usually considered an effective strategy to reduce the hot tearing susceptibility of a cast component. In this study, special constrained plate castings with progressive changes in cross-section were designed, which enabled progressive solidification. The hot tearing behavior of a newly developed NZ30K Mg alloy (Mg-3.0Nd-0.2Zn-Zr, wt.%) was studied under progressive solidification using various mold temperature distributions and constraint lengths. Of these, a homogeneous mold temperature distribution is found to be the best option to avoid hot tearing, followed by a local low mold temperature distribution (with a chiller), then a gradient mold temperature distribution. Unexpectedly, compared with the homogeneous mold temperature distribution, adding a chiller does not provide any further reduction in the hot tearing susceptibility of the NZ30K Mg alloy. A high mold temperature and a short constraint length increase the hot tearing resistance of cast Mg alloys. Progressive solidification is not a sufficient and necessary condition to avoid the formation of hot tearing. The two key factors that determine the occurrence of hot tearing under progressive solidification are the maximum cooling rate and the constraint length. Decreasing these values can reduce the incidence of hot tearing.

The two-phase zone continuous casting (TZCC) technique was used to continuously cast high-strength aluminum alloy hollow billets, and a verified 3D model of TZCC was used to simulate the flow and temperature fields at casting speeds of 2-6 mm·min^-1. Hollow billets under the same conditions were prepared, and their macro/microstructures were analyzed by an optical microscope and a scanning electron microscope. During the TZCC process, a circular fluid flow appears in front of the mushy zone, and the induction heated stepped mold and convective heat transfer result in a curved solidification front with depressed region near the inner wall and a vertical temperature gradient. The deflection of the solidification front decreases and the average cooling rate in the mushy zone increases with increasing casting speed. Experimental results for a 2D12 alloy show that hot tearing periodically appears in the hollow billet accompanied by macrosegregation near the inner wall at casting speeds of 2 and 4 mm·min^-1, while macroscopic defects of hot tearing and macrosegregation weaken and the average size of columnar crystals in the hollow billets decreases with further increasing casting speed. 2D12 aluminum alloy hollow billets with no macroscopic defects, the finest columnar crystals, and excellent mechanical properties were prepared by TZCC at a casting speed of 6 mm·min^-1, which is beneficial for the further plastic forming process.

No-bake resin-bonded sand is commonly used in casting production. However, its air pollution is relatively serious, especially in the molding and pouring process. For this reason, it is necessary to study the gas evolution characteristics of no-bake resin-bonded sand from room temperature to high temperatures, and not only the amount of gaseous products, but also the composition of the gaseous products. No-bake furan resin-bonded sand (#1), phenolic urethane no-bake resin-bonded sand (#2), and alkaline phenolic no-bake resin-bonded sand (#3) are the three most common no-bake resin-bonded sands in casting. The gas evolution volume and rate of these three no-bake resin-bonded sands were studied. Thermogravimetry-mass spectrometer (TG-MS), headspace-gas chromatography/mass spectrometer (HS-GC/MS), and pyrolysis-gas chromatography/mass spectrometer (PY-GC/MS) were used to measure the composition of the gaseous products emitted from binders at room temperature and high temperatures. The differences between formaldehyde, heterocyclic aromatic compounds (HAC), monocyclic aromatic hydrocarbons (MAH), and polycyclic aromatic hydrocarbons (PAHs) gaseous products from the three types of no-bake resin-bonded sands during the molding and casting process were compared. From the perspective of environmental protection, alkaline phenolic no-bake resin-bonded sand and no-bake furan resin-bonded sand are better than phenolic urethane no-bake resin-bonded sand.

Central region coarse grains and centerline segregation are common defects in aluminum ingots fabricated by direct chill (DC) casting. A double cooling field was introduced into the DC casting process to reduce these defects, whereby the external cooling was supplied by the mold and water jets, and intercooling was achieved by inserting a rod of the same alloy into the molten pool along the central axis of the ingot. Rather than forming a good metallurgical interface during solid-liquid compound casting, in the present work, the purpose of inserting the rod is to enforce internal cooling and consequently decrease the sump depth. Moreover, the insertion provides more nucleation sites with the unmolten á-Al particles. The structure and the macrosegregation of 2024 Al alloy ingots prepared by DC casting with and without the inserts were investigated. Results show that when the inserting position is 50 mm above the upper edge of the graphite ring, significant grain refinement in the central region of the ingot and a reduced centerline segregation are achieved.

In view of the problem that the transmission accuracy of RV(rotate vector)reducer decreased due to the wear of its parts in the working process, a dynamic reliability model of the transmission accuracy of RV reducer considering the wear of cycloid wheel was established, the reliability of transmission accuracy was analyzed, and the tolerance of key parts and the modification parameters of cycloid wheel were optimized.Taking a heavy-load RV reducer as the research object, the wear depth of cycloidal gear was calculated by using Archard wear formula, the distribution of gear tooth profile wear was analyzed, and the wear amount was predicted by using Gaussian process regression model based on numerical simulation data; the reliability model of RV reducer transmission accuracy with dynamic wear was established, and its dynamic reliability was solved by Monte Carlo method; an optimization model was established with the dynamic reliability of transmission accuracy as the constraint condition, the minimum machining cost and the minimum maximum wear in the rated life cycle as the optimization objectives, and the optimal solution was obtained adopting multi-objective genetic algorithm.The results showed that after optimization, the wear of cycloidal gear was slightly increased, and the machining cost of reducer was obviously reduced; the reliability of transmission accuracy of the reducer had been significantly improved, and the reliability within the rated life of 6 000 h met expected requirements.The research results can provide reference for the design of high-precision RV reducer.

Based on wire arc additive manufacturing (WAAM) technology, AZ31 magnesium alloy in bulk was successfully fabricated, and its microstructure as well as mechanical properties in different planes were observed and analyzed. The AZ31 magnesium alloy has a similar microstructure in the building direction (Z) and travel direction (X), both of which are equiaxed grains. There are heat-affected zones (HAZs) with coarse grains below the fusion line. The second phase is primarily composed of the Mg₁₇Al₁₂ phase, which is evenly distributed in different directions. In addition, the residual stress varies in different directions. There is no significant difference in the hardness of the AZ31 alloy along the Z and X directions, with the average hardness being 68.4 HV and 67.9 HV, respectively. Even though the specimens' ultimate tensile strength along the travel direction is higher in comparison to that along the building direction, their differences in elongation and yield strength are smaller, indicating that the anisotropy of the mechanical properties of the material is small.

Laser directed energy deposition (DED) is a multi-physics process that accompanies mass flow, energy transfer, and complex phase transitions. The printing characteristics of small size parts are significantly affected by the progressive variations of the temperature fields and the fluid flow within the molten pool. In this work, the deposition characteristics during multi-layer and multi-track laser DED were explored through a well-tested phenomenological model and corresponding experimental results. The variations of the build profiles and the decoupled track and layer profiles were systematically examined. Moreover, the printing characteristics of the builds with different scanning lengths were compared. Results showed that the multi-layer and multi-track transient deposition processes generated a significantly wavy surface profile. Compared with the long scanning length part, the beginning region of the short build produced an obvious bulge followed by sharply decreased height along the scanning direction. The transverse section of the short build varied significantly at different positions. Two adjacent columns of tracks were extracted from the overall build, demonstrating that the tracks tilted outwards and the angle increases along the scanning direction. The 3D numerical model was validated with corresponding experiments for builds with various layers. The scientific findings from this work can provide useful insights for the understanding of the additive mechanisms during laser DED for the precise shape control of small size parts.