Search

ZrO2-5CrMnMo composites were fabricated by ceramic injection molding in this research. The hardness and wear properties of ZrO2 ceramic layer and 5CrMnMo substrate were investigated. Moreover, physical properties and microstructures of ZrO2 ceramic coatings were studied and the interfaces of composite samples were observed. The results illustrated that the interface was smooth and properly bonded, and it was concluded that the 5CrMnMo substrate ceramic layer could be provided effectively by ZrO2 ceramic coating. Thermal insulation and thermal shock cycle tests were carried out. The heat insulating property of ZrO2 ceramic coating was remarkable, and even better at a high temperature. The composite samples prepared at 1200 °C did not failed until after more than 68 thermal shocks. The main reasons of limiting the application of this composites so far were still the physical and thermodynamic mismatch between ceramics and steel. But the composite samples fabricated by ceramic injection molding showed excellent thermal shock resistance and high bonding strength in this work.

ZrO2-5CrMnMo composite samples were prepared by hot press sintering. When NiCoCrAlY powders were used as the bonding layer and the different mixtures of NiCoCrAlY alloy and 3YSZ (3mol% yttria stabilized zirconia) ceramic powders were used as the transition layers, the connection between zirconia ceramic and 5CrMnMo steel were strengthened. Three composite samples with different structures were fabricated by heat spraying and hot press sintering. Shear and thermal shock cycle tests were conducted to characterize connection strength and thermal shock resistance of these samples. The shear strength reached 95.69 MPa, and the heating shock cycles achieved to the maximum value of 27.7 times. Microstructures and connection interfaces were analyzed by scanning electron microscopy. The hardness and wearing resistance of 3YSZ coat and 5CrMnMo substrate were compared, and the heat insulation property of composite samples were also discussed. It is shown that these composite materials fabricated in this research are benefited to be used as squeeze casting dies.

Composite mold samples used in squeeze casting was fabricated by plasma spraying with 5CrMnMo and 3YSZ, which was shown high bonding strength and good thermal shock resistance. The best parameters with transition coat were explored by mechanical analyses. As results, the transition layer structure made of 75 percent NiCoCrAlY powders showed bonding strength was higher to 34.35MPa and that thermal cycles were up to 46.8 times. The effect of the transition layer was analyzed by microstructures and the failure mechanism of the coating material with a transition layer was discussed. The conclusion was that the physical mismatch and thermodynamic mismatch between the matrix and ceramic layers were the main cause of the failure.

The development of novel cermet composites based on porous ceramics with high porosity, interconnected pore structure and good mechanical property has attracted considerable attention in engineering application. In this work, water-based freeze casting process was employed to fabricate ZrB2-SiC porous ceramic with aligned lamellar-channels structure using PAA-NH4 as the dispersant. The results revealed that the well-dispersed suspension with best rheological behavior was obtained using 1.0 wt% PAA-NH4 at pH 9. The crack-free porous ceramic exhibited small volume shrinkage ranging from 2.59 % to 1.87 %. By varying the solid loading, the fabricated samples displayed a tailored porosity ranging from 76.12% to 59.37% and an excellent compressive strength of 7 MPa to 78 MPa. After oxidation, the samples displayed a decreased porosity and an increased compressive strength. The ZrB2­SiC porous ceramic fabricated in this work will be a promising candidate for the framework of cermet composite.

The research on the ceramic/metal composites with interpenetrating continuous lamellar structure has attracted much interest in structural materials field. In this work, we proposed an innovative approach to fabricate co-continuous ZrB2–SiC/Zn–5Al composites by combining freeze casting with ultrasonic-assisted spontaneous infiltration. The ZrB2–SiC porous ceramic with orderly lamellar channels (30 vol%) was fabricated by freeze casting using ammonium polyacrylate as the dispersant. The effects of ultrasonication duration on the microstructure and mechanical properties of the composites were investigated in detail. Results indicated that the ultrasonication improved the wettability and facilitated the spontaneous infiltration. The composites obtained the excellent comprehensive properties when the duration was 300 s, which can be attributed to not only the sufficient infiltration of lamellar channels but also the longer infiltration distance inside the ceramic walls induced by the ultrasonic capillary and cavitation.

In this paper, 45# steel supports prepared by liquid forging showed excellent performances and the effects of processing techniques on the development of microstructures and mechanical properties of these steel supports were researched. The liquid forging process was simulated and technological parameters were optimized via a ProCAST simulation software. The solidification time, temperature distribution, first principal stress distribution of the 45# steel supports varied with time, temperatures, and position. Two principal parameters, pouring temperature and dwell time, were assessed for their effects on microstructures, mechanical properties, and wear resistance properties of 45# steel supports. Results showed that the optimal pouring temperature of the molten metal and the pressure-holding time were between 1540 °C and 1560 °C and between 35 s and 40 s, respectively. The microstructure, mechanical properties, and fracture behavior of different positions in the support were also discussed, and the central position performed better than the edge because of plastic deformation. Finally, the dynamic solidification process was also investigated and the liquid forging process of 45# steel supports was complex and contained some special metal liquid convection and several plastic deformation stages.

Herein, warm drawing technology assisted by an electric current heating system is proposed to minimize the formation of wrinkles and cracks on the surface of Q390A high-strength steel V-shaped stiffeners during cold forming. V-shaped stiffeners with excellent properties were obtained by elevating the forming temperature and improving the material plasticity. The influence of temperature and tensile rate on the mechanical properties of the Q390A high-strength steel at 400-800°C was investigated. The effects of blankholder force and friction coefficient on the formed parts were simulated and analyzed by the finite element simulation software DYNAFORM. The law of heating and cooling for the formed parts during the forming process was studied through the electric current heating experiments. The forming temperature was controlled from 530 to 720 °C as the current density was maintained in the range from 7.3 to 8.5 A/mm2. Surface oxidation, cracks, sheet warping degree, sectional thickness distribution, mechanical properties, and microstructure of the V-shaped stiffeners formed at 400 to 700 °C were analyzed. The results show that the V-shaped stiffeners formed at 600 °C possess excellent overall properties.

In order to significantly enhance the performance of graphene in metal matrix composites, in situ SiC nanorods were successfully fabricated to enhance graphene nanoplatelets (GNPs)-reinforced Al2024 composite, which was prepared by powder semi-solid processing and friction stir processing. The SiC–GNPs dispersed in the Al matrix uniformly, SiC nanorods were randomly grown on GNPs sheets in any direction, bridging GNPs as well as GNPs and the Al matrix. Meanwhile, the interfacial bonding was effective. The hybrid reinforcement of SiC and GNPs endowed composites with superior mechanical properties and thermal conductivity. The in situ SiC nanorods transfer phonons and reduce phonon scattering effect in the through-plane direction of GNPs, which conducive to heat transmission. The composite exhibits improved mechanical properties, maximum tensile strength and hardness of 589 MPa and 193 HV are obtained, with 1.0 wt% GNPs addition, respectively. The thermal conductivity of composite increases with the content of SiC–GNPs. When the content of SiC–GNPs reaches 1.5 wt%, the composite has significantly enhanced thermal conductivity (224 W m−1 K−1), which is 115% times higher than that of Al2024. Moreover, the effects of SiC–GNPs on the properties were discussed.

When lithium-ion batteries (LIBs) are located at high altitude and low pressure,the characteristics of thermal runaway (TR) and its propagation are different,such as time to TR, the toxicity of TR gases, TR propagation time, mass loss rate, etc. In this article, the author summarized a series of relevant literatures and proposed an instrument that can be used to analyse the TR behavior at different pressure. It is found that: with the decrease of ambient pressure, the TR trigger time becomes longer and the maximum surface temperature decrease. Moreover, the gas released by TR becomes more toxic as the environmental pressure decreases. Beside, the average propagation time between adjacent LIBs is not much difference when the environmental pressure decreases, and when the 18,650 battery module is distributed in a cylindrical shape, the thermal runaway propagation path is basically unchanged as the environmental pressure decreases. This work details TR and its propagation feature under different pressure, and can provide the guidelines for the Air transportation of LIBs.

During the process of liquid forging, a host of hot cracking defects were found in the Al-Cu-Mg-Zn aluminum alloy. Therefore, mechanical tests and analyses by optical microscope, scanning electron microscope, and X-ray diffraction were performed to research the influences of zinc, magnesium, and copper (three main alloying elements) on hot cracking tendency and mechanical properties. It was concluded that all the three alloying elements exerted different effects on the performances of newly designed alloys. And the impact of microstructures on properties of alloys was stronger than that of solution strengthening. Among new alloys, Al-5Cu-4.5Mg-2.5Zn alloy shows better properties as follows: σb=327 MPa, δ=2.7%, HB=107 N/mm2, and HCS=40.

In order to meet the high mobility and lightweight requirements of tracked special vehicles, a novel dual-grouser track shoe component was designed and formed by forging. The thickness of thinnest connection area between two grousers was only 3mm. The low-alloy wear-resisting steel 42CrMo was chosen as the raw material, which enables to solve the drawbacks of non-ferrous metal under the low-intensity-impacting condition. The stress-strain fields of the part during forming were simulated and analyzed using the Finite Element (FE) simulation software, Deform-3D. In addition, the microstructure and mechanical properties of the formed parts demonstrated that the forging process could exhibit a good forming effect with precise dimension and stable quality accomplished. The yield strength, ultimate tensile strength and fracture elongation of the connection area between two grousers were 788MPa, 467MPa and 19.5%. Furthermore, the wear rate and coefficient of friction of this area were 0.015mg/(km·N) and 0.37. Such kind of novel 42CrMo dual-grouser track shoe component is able to offer a lower production costs and longer service duration.

The objective of this study is to investigate the impact of different fractions (0–0.05) of C6F12O addition on laminar flame speed of hydrocarbon syngas by varying the fuel/oxidizer equivalence ratio (0.6–1.2) using Bunsen burner method. The determination of the syngas composition comes from the venting gas of lithium-ion cell during thermal runaway. It is found that C6F12O is significantly more effective at stoichiometric and fuel-rich conditions compared to lean flames regardless of fuel species, which implies more suitable for syngas/air flame inhibition than CH4. The laminar flame speeds of syngas/air increased with lower concentration (

A novel environmental-friendly unpacking powder for fireworks which has no sulfur, no magnesium, no aluminum or their alloys has been prepared in this study: potassium perchlorate (75%), potassium hydrogen terephthalate (13%), micronano porous silicon (9%), carbon (2%), ferrocene (1%). The PM2.5 and PM10 were collected by the ambient air particulate sampler, and the gas product was tested with a smoke analyzer and gas chromatograph to investigate its environmental-friendly performance. The detonation radius was measured by similar triangulation method, and p–t curves were measured in a closed bomb to investigate its practicality. The heat of combustion, sensitivity and hygroscopicity of the formula were measured according to China fireworks industry standard to verify the safety of the novel unpacking powder. The test results suggest that new unpacking powder using micronano porous silicon can effectively reduce the PM content and the product does not contain SO2, so it can be applied to export.

The effects of a variable-cavity liquid forging process on the microstructure and mechanical properties of an Mg-5Zn-1Y-0.6Zr magnesium alloy are described based on the results and analysis. The results indicate that the microstructure of the alloy changed clearly during the deformation process. After variable-cavity liquid forging, the dendrites are elongated along the deformation direction. The alloys with different deformation temperatures consist of α-Mg, the Mg-Zn phase, the I-phase (Mg3YZn6) and the W-phase (Mg3Y2Zn3). The I- and W-phases are mainly distributed in the grain boundaries, and the Mg-Zn phase is mainly dispersed in the grains. Most of second phase is broken into fine particles during the variable-cavity forging process. There is high dislocation density in the elongated grains at a deformation temperature of 350 °C, especially near the grain boundaries. Due to the dislocations, there are some tiny subgrain structures (less than 1 μm) formed near the second phase. After the variable-cavity liquid forging process, the subgrain structures did not recrystallize. The mechanical properties are significantly affected by the second phase and size of the grains. The highest tensile strength is 351.5 MPa at a deformation temperature of 350 °C, which is due to retained eutectic pockets. The best elongation is 7.15% at a deformation temperature of 450 °C, which is due to the tiny second phase particles and fine grains.

A ZK61-Y magnesium (Mg) alloy wheel hub was prepared via liquid forging&mdash, isothermal forging process. The effects of Y-element contents on the microstructure and mechanical properties of liquid forging blanks were investigated. The formation order of the second phase was I-phase (Mg3Zn6Y) &rarr, W-phase (Mg3Zn3Y2) &rarr, Z-phase (Mg12ZnY) with the increase of the Y-element content. Meanwhile, the I-phase and Z-phase formed in the liquid forging process were beneficial to the grain refinement. The numerical simulation of the isothermal forging process was carried out to analyze the effects of forming temperature on the temperature and stress field in the forming parts using the software Deform-3D. Isothermal forging experiments and post heat treatments were conducted. The influence of isothermal forging temperature, heat treatment temperature and preservation time on the microstructure and mechanical properties of the forming parts were also studied. The dynamic recrystallization (DRX), second-phase hardening, and work hardening account for the improvement of properties after the isothermal forging process. The forming part forged at 380 &deg, C displayed the outstanding properties. The elongation, yield strength, and ultimate tensile strength were 18.5%, 150 MPa and 315 MPa, respectively. The samples displayed an increased elongation and decreased strength after heat treatments. The 520 &deg, C&mdash, 1 h sample possessed the best mechanical properties, the elongation was 25.5%, the yield stress was 125 MPa and the ultimate tensile strength was 282 MPa. This can be ascribed to the recrystallization and the elimination of working hardening. Meanwhile, the second phase transformation (I-phase &rarr, W-phase &rarr, Mg2Y + MgZn2), dissolution, and decomposition can be observed, as well.

A quantitative feeding system of molten metal was designed based on a special vehicle cover, which achieved the quantitative transport of molten metal in a fully enclosed environment. There are lots of advantages of this novel device, such as improving the accuracy of the molten metal pouring, reducing the oxide inclusions defects, improving the quality of forming parts, etc. The numerical simulation of the casting process of filling mold was carried out based on the software ProCAST, which optimized the processing parameters of the quantitative feeding device. The result shows that the optimal movement speed of the punch piston is 0.08 m/s. The forming process of the aluminum alloy cover was designed and the process was conducted on the novel quantitative feeding device of molten metal. The structure and process performance of the forming parts were summarized and the defects were analyzed. The influence of technological parameters such as pouring temperature, filling speed, initial mold temperature, and feeding distance on the quality of forming parts was studied, which resulted in the optimum process parameters for the dosing device.

Thermal runaway and its propagation are bottlenecks for the safe operation of lithium-ion battery systems. This study investigates the influence of characteristic thermophysical parameters during battery thermal runaway, such as the self-heating temperature (T1), triggering temperature (T2), mass loss, and critical heat transfer power (Pc), on the failure propagation behavior in a battery system. A parametric study is conducted based on a failure propagation model. This model not only captures the behavior of thermal failure, but also accounts for the changes in the thermophysical parameters before and after thermal runaway. The results of the modeling analysis demonstrate that increasing T1 and T2 can both delay the thermal runaway propagation. The delay achieved by increasing T2 is greater than that observed by increasing T1. The peak heat transfer power Pc plays a critical role in delaying the thermal runaway propagation. When the peak heat transfer power level is greater than Pc, thermal runaway propagation mainly results from heat transfer, whereas when the peak heat transfer power level is less than Pc, thermal runaway propagation mainly arises from self-heating. This study reveals the dynamic mechanism of thermal runaway propagation within a battery module, thus providing guidance for the safety design of battery systems.

Gas generators are the functional materials producing gas by combustion. In situations such as pneumatics, fire extinguishing bomb, air bag, deep-water salvage, the gas generators can be ignited to provide power and energy through rapid release of gas. However, the research about gas generators with low water vapor is blank in world. The most widely used gas generators (such as nitroguanidine gas generators) produce a lot of water vapor through combustion, whose liquefaction will cause the reduction of gas pressure. This work selected 4,5-diazolyl-1,2,3-triazole (BTTZ) as gas-generating material. Two kinds of gas generator formulations based on BTTZ with common oxometallate (KNO3) and metal oxide (CuO) were designed. The properties of these gas generator formulations were studied by calculation and experiments. The gas production, gas production rate, water vapor content, compatibility and mechanical sensitivity were measured. The gas specific volume of the formulation 1 was 4.08 m3 kg−1. The clean harmless gas content reaches 93.55%. The water vapor content of the product was 6.08% (volume percentage), which is much lower than the nitroguanidine gas generators (53.47%). Therefore, formulation 1 is a low-water vapor environmental-friendly gas generator as a cleaner production material with practical value.

In this work, 7075 Al alloy, a high-strength wrought aluminum alloy with high hot tearing sensibility, was used in the squeeze casting of an asymmetric part. The solidification defects, microstructures and mechanical properties of the part solidified under different forming pressures were studied. Furthermore, the uniformities of the microstructures, mechanical properties and the solidification mechanisms were investigated. Results show that increasing the forming pressure is helpful to improve the liquid/solid feeding for counteracting the particularly serious shrinkage during the wide mushy zone of 7075 Al alloy. Therefore, the solidification defect can be avoided. Moreover, increasing the forming pressure is helpful to not only obtaining fine equiaxed grains, but also diminishing the intergranular segregation of alloying elements. With the increasement of forming pressures, the strengths of the part increased, along with the decreases in the ductile due to the work hardening resulted from the serious solid feeding. The microstructures and mechanical properties are impacted by the solidification rate of the melt at different regions. When the forming pressure was 150 MPa, fine microstructures and excellent mechanical properties were obtained. The uniformity of the microstructures and mechanical properties are dominated by the solidification location sequence of the melt. Further on, it is determined by the thermal gradient of the melt at different locations. For 7xxx series alloys, more solid feeding is needed for counteracting the serious shrinkage at the first solidified regions, causing a work hardening and associated strengths increasements. A near uniform part thickness and direct feeding loads are appreciated to improve the uniformities. In this work, the optimal tensile properties tested in the part were tested to be as follows: the yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) are 345.5 MPa, 483.2 MPa, and 7.6%, respectively. The UTS uniformity is tested to be 86.4%.

The development of electric vehicle batteries has resulted in high energy density battery pack. Cell-to-Pack (CTP) omits the cell module assembly, can reduce battery pack parts by 40%, improve the battery pack volume utilization rate by 15%–20%. However, the thermal characteristics of CTP under full operating conditions has yet to be verified, the CTP temperature calibration cycle under full working condition is time-consuming, and little analysis has been conducted on CTP internal temperature differentials and heat flow. The present study aims to thermal characteristics of CTP. Results show that CTP temperature calibration based on a thermal resistance grid can realize internal temperature reconstruction, optimum temperature arrangement, and shorten the calibration period by more than 60%. In addition, higher ambient temperatures can increase the maximum temperature of the jelly rolls in CTP cells, while lower ambient temperature can lead to larger differences in jelly roll temperature within a cell; and high-speed driving and fast charging can lead to the highest temperature increase rates under different working conditions up to 0.05 °C s−1.70% of the heat generated during cell discharge is used for self-heating, and the heat dissipation of liquid cooled plate is the main heat dissipation channel.

Black powder is often used as propellant in the fireworks industry, but the sulphur in the black powder will pose great risks to the environment and human health. Although there are sulphur-free propellant with metal powder and smokeless propellant prepared from expired military gunpowder to solve the problem, the high sensitivity and huge explosive power of the mental powder and instability of the expired military gunpowder lead to low security in actual application. Therefore, sulphur-free propellant which can replace black powder is urgently needed. In this study, a discharge height test was conducted for the sulphur-free environmental protection formulation [potassium perchlorate (70%), potassium hydrogen terephthalate (10%), carbon (11%), ferrocene (1%), phenolic resin (7%), calcium stearate (2%)] optimized by an orthogonal test. The thermal explosion in critical temperature was used to determine the thermal stability of sulphur-free propellant and black powder, then compared with combustion heat. The preesure-time test was used to compare the peak pressure of this two propellant. The impact, friction and flame sensitivity were also measured. It is thought that sulphur-free propellant can replace the black powder as the new environmental-friendly propellant in the fireworks industry with low sensitivity and excellent storage performance, and have great potential in application.

This work sets focus on producing hydrophobic silica and fire-extinguishing-composition solution into dry water extinguishant powder by high-speed shearing. The solid-to-liquid ratio, different stirring periods and rotational speed were taken into account to analyze their influence on the covering effect. The dry water extinguishants containing ammonium dihydrogen phosphate (ADP) and phosphoric acid are respectively produced added with gel. The jet apparatus is improved for the experiment. According to the results, the phosphoric acid gel dry water extinguishant works best to put out Type-A fire. The ADP dry water extinguishant excels in putting out Type-B fire, equivalent to superfine ABC dry powder extinguishant in terms of effectiveness but with a low cost. For this reason, dry water extinguishant has a broad prospect of application.

Mg-Zn-Zr-Y billets with different mass fraction of Y (wt%(Y)=0.2%、0.5%、1.0%、1.5%、2.0%) was prepared by permanent mold casting. The increase in Y content has shown grain refinement effects on the microstructure morphologies of Mg–Zn–Y–Zr alloys. When the content of Y achieves 1.0 wt%, the grain refinement effect of the Y is most obvious than any more contents of the Y content. In the test result of XRD, the type of precipitated phase in Mg-Zn-Zr-Y alloys is related to atomic ratio of Y/Zn. With content of Y increases, atomic ratio of Y/Zn increases,the precipitated phase in alloy is changed from Phase I to Phase W. Tensile strength and extension rate of alloy increase with the increasing of Y content; When Y content reaches 1.0%, mechanical property reaches maximum value.When content of Y exceeds 1.0%, with the increasing of Y content, mechanical property of alloy declines gradually.

A human torso finite element model with high bio-fidelity was developed to study the behind armor blunt trauma (BABT) of pistol cartridge on human torso with bulletproof composite structure (BCS) and the effect of buffer layer (expandable polyethylene, EPE) on BABT. The bulletproof structure was made of multilayered composite of aluminum alloy (AlSi10Mg) and thermoplastic polyurethanes (TPU), and the ANSYS/LS-DYNA software was used to simulate the blunt ballistic impact process of pistol cartridge on human torso. Results indicated that the BCS could resist the shooting speed of 515 m/s without being broken. During the process of pistol cartridge shooting the BCS, the energy of pistol cartridge was transmitted to the human organs through the BCS, thereby causing human injury. Moreover, the mechanical response parameters of various organs were determined by the distance between the human organs and the impact point. The sternal fracture and liver rupture were not produced based on the threshold stress of sternum and liver injury, no matter whether the buffer layer was added or not. According to the Axelsson injury model, a slight to moderate injury was created when there was no buffer layer, but the injury level was trace to slight caused by the buffer layer with thickness of 1.0 mm, and the buffer layer with thickness of 2.5 mm and 5.0 mm caused subtle BABT. It was concluded that the buffer layer could effectively reduce the BABT, and the reduction was related to the thickness of the buffer layer. This study reveals the mechanism of the BABT, which can provide a theoretical basis for the design of the bulletproof structure and the evaluation of structural bulletproof performance and protection performance.

In order to study the thermal safety of cylindrical battery deeply, based on the theory of heat transfer, thermal explosion and nonlinear modeling, a three-dimensional non-steady state thermal explosion mathematical model of cylindrical fireworks with non-uniform heat dissipation of the lateral surface was established for the first time (three-dimensional partial differential equation group). Combining seven point difference method and Newton-homotopy algorithm, the numerical calculation method of the three-dimensional non-steady state thermal explosion partial differential equation was established and the numerical calculation program was written base on Matlab. The validity of calculation program has been demonstrated by comparison of numerical solutions and classical solutions. The accuracy of model has been validated by example computation and analysis. The critical parameters describing non-steady state model of cylindrical fireworks when stored individually and stored in combination form were calculated in this paper, including temperature distribution, temperature–time history, thermal explosion time to ignition, etc. The results show that when the ambient temperature is 450 K, the fireworks stored individually do not have thermal explosion, but the fireworks stored in combination form will explode finally and the thermal explosion time to ignition is 19013.53 s. When the ambient temperature is 460 K, thermal explosion will occur in both the fireworks stored individually and stored in combination form, and the thermal explosion time to ignition are 3187.07 s and 3066.60 s respectively. It shows a more exact analytical methods and solutions of thermal safety evaluation of fireworks was established in this paper. Thus, it is need to strengthen the safety monitoring and management of cylindrical battery (combined fireworks) because of the higher thermal hazard.

Solid–liquid segregation often occurred during thixoforming of wrought aluminum alloys, which can result in uneven structures and mechanical properties. In this work, a novel compound loading method was introduced in thixoforming 7075 aluminum alloys. The results show that the solid–liquid segregation can be alleviated evidently by compound loading, and the microstructures of periphery area were improved significantly. As the secondary loading displacement increased from 0 mm to 5 mm, the ultimate tensile strength (UTS) of the periphery area increased little (∼510 MPa), and the yield strength (YS) even decreased slightly from 486 MPa to 470 MPa. However, the elongation to fracture of the periphery area increased from 1.94% to 4.3% with increment of 122%. On the contrary, the compound loading has limited effect on the tensile mechanical properties of the center area. The tensile fracture surfaces exhibited typical brittle rupture in the periphery area, while the fracture surfaces of the center were dominated by a large number of dimples and tear ridges showing typical ductile fracture features. Compound loading is an effective method to homogenize the microstructures and mechanical properties of thixoformed wrought aluminum alloys.

To study the effect of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition, considering the heat transfer coefficient as the power function of temperature, mathematical thermal explosion steady state and unsteady-state model of finite cylindrical fireworks and crackers with complex shell structures are established based on two-dimensional steady state thermal explosion theory. The influence of variable heat transfer coefficient on thermal explosion critical ambient temperature and time to ignition are analyzed. When heat transfer coefficient is changing with temperature and in the condition of natural convection heat transfer, critical ambient temperature lessen, thermal explosion time to ignition shorten. If ambient temperature is close to critical ambient temperature, the influence of variable heat transfer coefficient on time to ignition become large. For firework with inner barrel in example analysis, the critical ambient temperature of propellant is 463.88 K and the time to ignition is 4054.9s at 466 K, 0.26 K and 450.8s less than without considering the change of heat transfer coefficient respectively. The calculation results show that the influence of variable heat transfer coefficient on thermal explosion time to ignition is greater in this example. Therefore, the effect of variable heat transfer coefficient should be considered into thermal safety evaluation of fireworks to reduce potential safety hazard.

The formation process of Al3Ti was studied based on the in-situ reaction between globular solid Ti powders with almost uniform size and 2024 Al melt under ultrasonic vibration. The microstructures of the Al3Ti/Al composite were examined at different reaction time. The reaction mechanism was analyzed based on the phase diagram and empirical reaction kinetics. Moreover, the effects of ultrasonic vibration on the formation of Al3Ti were discussed. The results show that the Al3Ti formed a layer around the unreacted Ti particle and was ruptured as the reaction continuing. An empirical reaction kinetics model of in-situ Al3Ti was established. The kinetic exponent n is determined to be 0.86, which is much higher than that of the standard diffusion-controlled growth (n = 0.5). The ultrasound assisted reaction follows an interface-controlled growth which means a higher reaction rate. The comprehensive effects of instantaneous pressure, high-intensity shock waves and local high-temperature caused by acoustic streaming and cavitation, are responsible for the high reaction rate and fine Al3Ti particles during the reaction process under ultrasonic vibration.

To study the injury of blast wave on the human torso, a human torso finite element model (HTFEM) consisted of multiple organs with high fidelity was developed. Based on LS-DYNA finite element software, the LBE-ALE method was used to simulate the mechanical response process of human torso under blast loading. The effect of blast loading on the mechanical response of human organs was analyzed, which indicated that as the blast loading increased, the greater the stress and velocity of human organs, and when the mass of TNT charge was constant, the earlier the onset time and peak time of stress and velocity response, the faster the stress and velocity changed; meanwhile the gap in stress and velocity of same human organ widened under different masses of TNT charge, the gap in stress and velocity between different human organs widened under the same mass of TNT charge, but the gap between different human organs narrowed under the same scaled distance. Besides, the location of human organs and the action direction of blast loading had a significant effect on the mechanical response. The stress threshold of human organs was proposed, which ranged between 218.42 kPa and 153.65 MPa corresponding to 50% lethality.

The synthesis mechanism of 3-nitro-4-(tetrazol-5-yl)furazan (NTZF) was calculated by Gaussian 09 for the first time, and NTZF was successfully synthesized based on the theoretical design. Its ionic salts (RbNTZF and CsNTZF) were synthesized and studied by single-crystal X-ray diffraction firstly. The thermal stability of NTZF was investigated by TG-DSC and the kinetic data of thermal decomposition were calculated. The sensitivity of NTZF was measured. The formation heat, detonation velocity (D) and detonation pressure (P) of NTZF were calculated. NTZF is insensitive to impact and friction (impact > 40 J, friction > 360 J) and has higher detonation velocity and pressure (D = 7.838 km s−1, P = 27.32 GPa) compared to TNT (D = 6881 m s−1, P = 19.5 GPa). NTZF has appropriate sensitivity and detonation performance, so it can be used as a low explosive and gas generant.

Al-Zn-Mg-Cu alloys are the strongest aluminum alloys which have been widely used for aerospace applications. They are usually machined from the wrought state usually with a high waste percentage. To reduce waste, it is important to thixoform these alloys in near net shape. In this work, the thixoformability of a commercial high performance Al-Zn-Mg-Cu alloy 7075 was studied. A novel multistep reheating regime was developed in recrystallization and partial melting (RAP) route to obtain spheroidal semi-solid microstructures. The as-extruded 7075 alloy was fully recrystallized for a short holding time using the multistep reheating regime. Semi-solid microstructures with fine and spherical solid grains with a grain size of 40-50 μm embedded in liquid matrix were obtained. The advantage of the multistep reheating regimes over those conventional routes was also discussed. Some wheel-shaped components were thixoformed from the as-received 7075 alloy. The ultimate tensile strength, yield strength and elongation to fracture of the thixoformed component based on multistep reheating regime, are 510 MPa, 446 MPa and 17.5% respectively. These values are superior to those of the products manufactured with the conventional RAP route. As the results indicated, thixoforming could be conducted based on commercial extruded Al-Zn-Mg-Cu alloys, which has important practical significance.

Taking carbon series conductive coatings as the research object, research on a modificatory filler was carried out to achieve higher electrical conductivity. Under the condition of this paper, the conductivity of the modified carbon black was improved, while the performance of the modified graphite was not obviously improved. The conductivity and dispersion of the modified carbon fibre were both improved. Analysing the impact of the additive on the performance of conductive coatings in which carbon black accounted for 10%, the conductivity was best when the weight of the tetra-butyl titanate was 1% of the filler. Adding an anti-settlement agent also improved the performance of the conductive coatings, and the best consumption was about 0.6% of the weight of the filler.

In order to study the thermal safety of cylindrical battery and solve the three-dimensional cylindrical battery thermal explosion problem, a common thermal explosion physical model of cylindrical battery and three-dimensional thermal explosion mathematical model of cylindrical fireworks with non-uniform heat dissipation of the lateral surface were established for the first time. By applying the theory of heat transfer, the boundary conditions of cylindrical battery were simplified reasonably. The seven-point difference method was introduced to disperse the model. The three-dimensional numerical program was written by homotopy continuation method and Newton iteration method based on Matlab. Comparison of two-dimensional numerical solutions obtained by taking ϕ = 0 and classical solutions proved the accuracy of model. A common kind of fireworks was calculated in this paper. When this single cylinder firework stored individually, the criterion of thermal explosion is 1.796, and critical ambient temperature is 450.484 K. When stored in combination form (that is battery), the criterion of thermal explosion is 1.363 and critical ambient temperature is 447.964 K. The results show that the cylindrical fireworks stored in combination form is more dangerous than this single cylinder firework stored individually, so the cylindrical battery is the focus of safety prevention of fireworks.

In view of the complexity of the storage environment in the process of storage and transportation, typical storage environment of cylindrical battery was analyzed in this paper. The corresponding three-dimensional thermal explosion models were established which considering non-uniform heat dissipation of the lateral surface and different heat dissipation of top and bottom surfaces. Based on the seven-point difference method and Newton–homotopy method, calculation algorithm and program of partial differential equation group have been established and verified. The influence of H and Biot on the criticality of system was analyzed. The results of a kind of cylindrical battery which stored in two typical environments (shelf and ground) were obtained by the calculation program. The critical thermal explosion ambient temperature of cylindrical battery is, respectively, 568.0 and 566.6 K. When the ambient temperature is 575 K, the thermal explosion time to ignition is, respectively, 1.504 (5194.7 s) and 1.596 (5512.1 s).

In the present study, 7050 supplied in extruded state was heated to different temperatures below solidus or the semisolid state and microstructural evolution and coarsening were investigated. The results showed that complete recrystallisation only occurs after soaking for 5 minutes at 545°C, which is characterised by formation of a lot of fine equiaxed grains. RAP is suitable for fabricating high-quality semisolid billet of 7050 aluminum alloy with an average grain size ranging from 47.4 um to 70.5 um and a roundness ranging from 1.3 to 1.7. Grain growth occurs as the samples were soaked at 610°C and 615°Cfor prolonged soaking time. When the isothermal temperatures were 610°C and 615°C, the coarsening rate constants were 359.5μm3s-1 and 470.5μm3s-1, respectively, indicating an increase of coarsening rate constant (K) with the increasing isothermal temperature. Coarsening tends to occur via Ostwald ripening and coalescence. Ostwald ripening plays an important role during the whole coarsening process, but the grain coalescence only contributes to coarsening after soaking for 12 minutes. 625°C is an optimal temperature to keep cylinder shape of the sample due to collapse of the sample above this temperature, leading to difficult clamping.

Ag/TiO 2 anodes treated with TiCl 4 were prepared by sol and powder combination technology. Scanning electron microscope (SEM) shows that Ag/TiO 2 film is denser and has fewer gaps after TiCl 4 treatment. X-ray diffraction (XRD) indicates that the TiCl 4 treatment can significantly make the TiO 2 particle size become smaller on the electrode surface. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy associated with NH 3 adsorption confirms that the amount of anode surface acidity increase after TiCl 4 treatment. Electrochemical impedance spectroscopy (EIS) measurements show that the R ct2 corresponding to the TiO 2 /dye/electrolyte interface decrease to 3.5 Ω. The TiCl 4 treatment can provide more specific binding sites to the alkaline dyes. Much more dyes can be adsorbed. Therefore, the photoelectric conversion efficiency of dye-sensitized solar cell (DSSC) was improved.

The high strength 7xxx series aluminium alloys are usually difficult to be prepared as semi-solid feedstock, because some dispersoid particles (soluble only in liquid) could pin at grain and subgrain boundary to make the alloy difficultly recrystallise. In this work, a novel multistep reheating regime is developed for recrystallisation and partial melting (RAP) route to prepare fine spheroidal microstructure of semi-solid Al–Zn–Mg–Cu alloy. After reheating to 665 °C, holding for 4 min and subsequent isothermally holding at 620 °C with total heating time of 15 min, fine spheroidal microstructures with grain size of ∼40 μm were prepared without remained unrecrystallised grains and directionality, which are much finer than the conventionally obtained microstructures (∼100 μm).

A set of novel forming die combining the advantages of dies casting and forging was designed, by which double control forming idea was firstly proposed. The motorcycle wheel made of AM60B alloy was used as the typical component to demonstrate advantages of the double control forming. The effect of pressure on the mechanical properties and microstructure of the parts formed by double control forming was investigated. The results showed that high mechanical properties and complex shape were achieved in the parts formed by double control forming. Compared to die casting, the mechanical properties of the formed part significantly increased and the microstructure changed from the coarse dendrites to fine equiaxed grains. The shrinkage voids and microcracks in the formed parts were obviously reduced or even completely eliminated with the increase of pressure. When a pressure of 4000 kN was applied, the optimal mechanical properties such as ultimate tensile strength of 265.6 MPa and elongation of 21% were achieved and the microstructure was characterized by fine and uniform equiaxed grains due to the large undercooling degree caused by the high pressure.

Thin-wall and high-rib components of AM60B Mg alloy were formed by double control forming (DCF) under the optimal conditions. Numerical simulation of high-speed filling process was carried out on Flow-3D software. The microstructure and properties of the components formed by DCF under the optimal conditions were investigated. The results showed that the design of the overflow launders and runners were feasible. The velocity magnitude in the component region was less than that in the regions of the runners and overflow launders. The temperature decreased gradually from the runners to overflow launders. Finer and more uniform microstructure without defects such as microcrack and microporosity was found in the components formed by DCF as compared to die casting. The reason was due to the dual effect of high pressure on increasing the nucleation rate and removing the defects. The mechanical properties of the components formed by DCF under the optimal conditions were significantly improved in comparison to die casting and DCF under non-optimal conditions. Fine and uniform microstructure without defects led to the improvement of mechanical properties. The fracture morphology of the components formed by die casting was characterized by brittle cleavage fracture and some microporosities, deteriorating the mechanical properties. Ductile fracture morphology with a large number of dimples was found in the fracture microstructure of the components formed by DCF under the optimal conditions, enhancing the mechanical properties.

A pyrotechnical battery is successfully prepared, including an anode and cathode having pyrotechnic charges with Zr, CuO and asbestos. The anode and cathode are separated by a separator formed from LiF, ZrO2, and a fibrous sponge. A digital phosphor oscilloscope (DPO) is used to analyze discharge characterization of the pyrotechnical battery. Then the properties of the electrode materials are characterized by EDS, SEM and a temperature recorder, respectively. The discharge mechanism and safety characteristic are also discussed. The results indicate that the combustion temperature of electrode materials is determined as 1 500.6 °C according to thermometry analysis (the case temperature of the battery is lower). The combustion product is identified as ZrO2, Cu2O and Cu by X-ray diffraction (XRD). When the diaphragm is completely melted, Li+ migration and an embedded-based conductive process are formed. Then an electromotive force will immediately reach to the maximum. The discharge performance of the pyrotechnical battery then takes on stability. The electromotive force is up to 2.29 V, and that discharge time continues for more than 18 s. The current density in the small area (less than 2.88 Acm−2) is most effective. The conversion efficiency of electric energy is 96%. The pyrotechnical battery is very safe for the production and use processes.

Commercial thixoforming is generally based on conventional aluminum-based casting alloys such as A356 and A357, which provide high fluidity and good castability. However, these alloys do not give such high mechanical properties as the alloys that are conventionally wrought such as Al–Cu–Si–Mg alloys, which generally has wide freezing ranges and tend to be prone to inhomogeneous microstructure and hot tearing. In this paper, one kind of aluminum alloy based on Al–Cu–Si–Mg system was thixoformed under different mechanical conditions. The strain induced melt activated (SIMA) route was used to obtain the semisolid slug for thixoforming. The effect of mechanical conditions on the microstructures and tensile mechanical properties in the T6 condition of the thixoformed aluminum alloy were studied. On proper mechanical condition (the base of component is 15 mm), the thixoformed sample reveals a relatively homogeneous structure among different regions and presents no evidence of macro and microporosities, moreover, the tensile mechanical properties are uniform between the wall and the base. The ultimate tensile strength (376 MPa) is close to the wrought target, and the elongation to fracture (18.7%) is even better, nevertheless, the yield strength (220 MPa) is considerably short of the wrought value. On improper mechanical condition (the base of component is 5 mm), the microstructures are inhomogeneous and inferior with respect to those of the former, and present some microporosities and microcracks. Although, a few cracks were filled by the supplied liquid metal, the mechanical properties are not satisfactory (tensile strength of 346 MPa, yield strength of 216 MPa and elongation to fracture of 11.5%).

An easy method to synthesize hollow carbon nanospheres (HCSs) with polystyrene as template and phenol as precursor is reported. The obtained HCSs have very thin shells and big hollow cores. The diffraction peaks of X-ray diffraction patterns located at about 2 θ = 22° and 43° are assigned to the (0 0 2) and (1 1 0) graphite plane of HCSs. Transmission electron microscopy shows every state in the synthesis process of HCSs.

Ultrasonic vibration have positive effect on formation of in-situ TiAl 3 /7050Al composites, the role of ultrasound in the reaction process was described systematically. The best solution-aging treatment parameters were discussed and effects of the selected treatment on the resultant microstructure and mechanical properties were investigated. The results show that ultrasonic vibration not only promote the reaction process, but also result in significant spreading particles fallen off from the reaction interface, therefore creating a finer and homogeneous distribution of TiAl 3 particles in the composite. In solution process, the skeleton second phase dissolve into matrix with increasing temperature and holding time, the transformation is more sensitive to solution temperature. Residual second phase transform into finer-size rod or discoid shape and a large amount of finer phase (MgZn 2 and CuAl 2 )precipitates after aging-treated. As a result, the strength, hardness and elongation of the composite are slightly increased after using ultrasonic vibration and significantly increased after solution-aging treatment.