Relationship between solid fraction and distribution of Pb in Al-Pb ingot

The influence of solid fraction of Al 28Pb alloy mushy on distribution of Pb in Al Pb ingot was studied. The special electromagnetic stirring apparatus was used to prepare Al 28Pb alloy mushy and the relationship between solid fraction and stirring temperature was gotten. The results show that when solid fraction of Al 28Pb alloy mushy is less than 45%, Pb precipitation usually happens in the ingot. However, Pb precipitation in casting reduces gradually with increasing solid fraction of mushy, and when solid fraction is larger than 45%, Pb precipitation in casting can be removed. [

Conception of tooling adapted to thixoforging of high solid fraction hot-crack-sensitive aluminium alloys

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<φs<1), which involves the processing of alloys in the semi-solid state.Tooling has to be adapted to this particular process to benefit shear thinning and thixotropic behaviour of such semi-solid material.Tooling parameters, such as the forming speed and tool temperature, have to be accurately controlled because of their influence on thermal exchanges between material flow and tool.These thermal exchanges influence the high-cracking tendency and the rheology of the semi-solid material during forming, which affects parts properties and therefore their quality.Extrusion tests show how thermal exchanges influence quality of thixoforged parts made of 7075 aluminium alloys at high solid fraction by modifying process parameters like forming speed, tool temperature and tool thermal protector.Thus an optimum in terms of thermal exchanges has to be found between surface quality and mechanical properties of the part.A direct application is the evaluation of surface quality of thixoforged thin wall parts made of 7075 aluminium alloy.

Solid fraction evolution characteristics of semi-solid A356 alloy and in-situ A356–TiB_2 composites investigated by differential thermal analysis

The key factor in semi-solid metal processing is the solid fraction at the forming temperature because it affects the microstructure and mechanical properties of the thixoformed components. Though an enormous amount of data exists on the solid fraction-temperature re- lationship in A356 alloy, information regarding the solid fraction evolution characteristics of A356-TiB2 composites is scarce. The present article establishes the temperature-solid fraction correlation in A356 alloy and A356-xTiB2 （x = 2.5wt% and 5wt%） composites using dif- ferential thermal analysis （DTA）. The DTA results indicate that the solidification characteristics of the composites exhibited a variation of 2℃ and 3℃ in liquidus temperatures and a variation of 3℃ and 5℃ in solidus temperatures with respect to the base alloy. Moreover, the eutectic growth temperature and the solid fraction（fs） vs. temperature characteristics of the composites were found to be higher than those of the base alloy. The investigation revealed that in-situ formed TiB2 particles in the molten metal introduced more nucleation sites and reduced undercooling.

Simulation of jet-flow solid fraction during spray forming

A numerical model was developed to simulate the jet-flow solid fraction of W18Cr4 V high-speed steel during spray forming. The whole model comprises two submodels: one is an individual droplet model, which describes the motion and thermal behaviors of individual droplets on the basis of Newton's laws of motion and the convection heat transfer mechanism; the other is a droplet distribution model, which is used to calculate the droplet size distribution. After being verified, the model was used to analyze the effects of parameters, including the initial gas velocity, deposition distance, superheat degree, and the ratio of gas-to-metal mass flow rates, on the jet-flow solid fraction. Finally, an equation to predict the jet-flow solid fraction directly and conveniently according to the parameters was presented. The values predicted by the equation show good agreement with those calculated by the numerical model.

Relationship between solid fraction of slurry and property of steel/mushy Al-20Sn semi-solid bonding

The slurry of Al-20Sn alloy was prepared using electromagnetic-mechanical stirring method. The bonding of steel/mushy Al-20Sn was conducted using casting rolling technique. The bonding parameters were 505 ℃ for preheat temperature of steel plate and 10 mm/s for rolling speed. The interfacial mechanical property and structure of steel/mushy Al-20Sn bonding plate were studied. The results show that the relationship between solid fraction of Al-20Sn slurry and interfacial shear strength of bonding plate is S=52.9+0.998φ s-0.014 4φ 2 s (where S is interfacial shear strength, φ s is solid fraction). The largest interfacial shear strength is 70.2 MPa when solid fraction is 34.6%. The interface of bonding plate is made up of Fe-Al compound and Fe-Al solid solution alternatively.

Influence of aluminum solid fraction on property of steel-mushy aluminum bonding plate

The interfacial shear property of steel-mushy aluminum bonding plate was studied, and the relationship between aluminum solid fraction and the interfacial shear strength of bonding plate was determined. The results showed that when aluminum solid fraction is 34.3 %, the maximum interfacial shear strength of bonding plate is 71 .0 MPa.

Fractional four-step finite element method for analysis of thermally coupled fluid-solid interaction problems

An integrated fluid-thermal-structural analysis approach is presented. In this approach, the heat conduction in a solid is coupled with the heat convection in the viscous flow of the fluid resulting in the thermal stress in the solid. The fractional four-step finite element method and the streamline upwind Petrov-Galerkin （SUPG） method are used to analyze the viscous thermal flow in the fluid. Analyses of the heat transfer and the thermal stress in the solid axe performed by the Galerkin method. The second-order semi- implicit Crank-Nicolson scheme is used for the time integration. The resulting nonlinear equations are lineaxized to improve the computational efficiency. The integrated analysis method uses a three-node triangular element with equal-order interpolation functions for the fluid velocity components, the pressure, the temperature, and the solid displacements to simplify the overall finite element formulation. The main advantage of the present method is to consistently couple the heat transfer along the fluid-solid interface. Results of several tested problems show effectiveness of the present finite element method, which provides insight into the integrated fluid-thermal-structural interaction phenomena.

Effect of solid fraction on steel-mushy Cu-graphite pressing bonding

The pressing bonding of steel plate to QTi3.5-3.5graphite slurry was studied. The bonding conditions were 620 ℃ for preheating temperature of steel plate, 530 ℃ for preheating temperature of dies, 50 MPa for pressure and 2 min for pressing time. The relationship between the solid fraction of QTi3.5-3.5graphite slurry and the interfacial mechanical property of bonding plate was obtained. The results show that when the solid fraction of QTi3.5-3.5graphite slurry is smaller than 45.8%, the interfacial shear strength of bonding plate increases with the increasing of solid fraction. When the solid fraction is larger than 45.8%, the interfacial shear strength decreases with the increasing of solid fraction. When the solid fraction is 45.8%, the largest interfacial shear strength of bonding plate 127 MPa can be got, and the interface is made up of Fe-Cu solid solution.

基于粘附功计算的不同微形貌表面抗冰差异

超疏水表面的防水性与表面的微观结构直接相关,不同微观形貌将呈现不同的疏水性能,从而亦产生不同的防覆冰性。代表性的选择动植物叶片、翼片、金属与非金属等工程材料固体表面做结冰和覆冰粘附强度测试,结果表明表面材料、微观结构不同,疏水、覆冰粘附性能不一样。设计了几种不同表面微形貌模型仿真自然和人工疏水表面微结构,用高粗糙度维持复合润湿状态,以具有矩形微形貌的表面为例建立覆冰粘附功与表面固体份数的解析关系,并推及其它模型。据粘附功、固体份数和粗糙度计算,发现不同微形貌表面覆冰粘附功的差异,固体份数对粘附功的决定作用以及粗糙度对复合润湿态的维持。理论上提出了选择适合的微观形貌用于防冰的定性标准:高粗糙度,低固体份数,低粘附功。按粘附功从小到大顺序确定适合于防冰、除冰微形貌;从固体份数和粗糙度的大小关系予以证实。

放射形相变蓄热器的释热特性实验与数值研究

针对太阳能热利用的时空不匹配问题,设计并制备一种放射形相变蓄热器,通过实验与数值模拟研究了蓄热器释热功率及相变材料固相率在释热过程中的响应特性,探讨了冷却工质流量、进水方式、翅片型式对释热性能的影响规律。研究结果表明:蓄热器的释热过程可划分为液态显热区间、潜热区间、固态显热区间3个阶段,潜热区间相变材料的潜热作用使得释热功率下降相对缓慢;冷却工质流量越大,释热功率下降速率越快,完全凝固时间越短;不同进水方式对换热效果影响不明显,但可改善蓄热器的换热均匀性;与平板翅片相比,放射形翅片各翅片单元间相变材料的导热更均匀,凝固时间缩短31%,提高了换热速率。

含油、固污水对泡沫液发泡性能的影响研究

为指导消防污水的处理回用,选取柴油、汽油2种典型成品油以及硅胶、二氧化硅2种微米级固体粉末配置不同含量的污水发泡,测试油、固含量对发泡性能的影响。结果表明:在0~3%质量分数范围内,柴油主要影响发泡倍数,降幅可达40.15%;汽油主要影响25%析液时间,降幅可达33.05%;直径大于10μm的固体颗粒对发泡倍数和析液时间均有影响,前者降幅可达25.22%,后者降幅可达18.49%。

多釜连续溶解加料计算模型用于调控醋酸纤维素浆液固形分浓度

建立了多釜连续溶解加料计算模型,用于测算不同生产条件对醋酸纤维素浆液固形分浓度的影响程度,并进一步通过在实际生产过程中的运行监测,表明在进入溶解釜之前掌握醋酸纤维素和回收浆液等主要原料的关键指标后,通过模型可预测目标浆液固形分浓度的变化,从而通过调整相应参数后有效稳定浆液固形分浓度,确保丝束总旦的稳定。

Analysis of semi-solid response under rapid compression tests using multi-scale modelling and experiments

Simulating semi-solid metal forming requires modelling semi-solid behaviour.However, such modelling is difficult because semi-solid behavior is thixotropic and depends on the liquid-solid spatial distribution within the material.In order to better understand and model relationships between microstructure and behavior, a model based on micromechanical approaches and homogenisation techniques is presented.This model is an extension of a previous model established in a pure viscoplastic framework to account for elasticity.Indeed, experimental load-displacement signals reveal the presence of an elastic-type response in the earlier stages of deformation when semi-solids are loaded under rapid compression.This elastic feature of the behaviour is attributed to the response of the porous solid skeleton saturated by incompressible liquid.A good quantitative agreement is found between the elastic-viscoplastic predicted response and the experimental data.More precisely, the strong initial rising part of the load-displacement curve, the peak load and the subsequent fall in load are well captured.The effect of solid fraction on mechanical response is in qualitative agreement with experiments.

SEMI-SOLID MICROSTRUCTURE AND ITS EVOLUTION OF WROUGHT ALUMINUM ALLOY BY DIRECTLYHEATING-ISOTHERMAL TREATMENT

Microstructure evolution of wrought aluminum alloy extruded rods and the mechanism of liquid phase formation during reheating were investigated. And the relation between the volume fraction of liquid phase and the recrystallization microstructure was proposed. The results show that increase in reheating temperature and time can augment the volume fraction of liquid phase and accelerate the grain spheroidization, as a result of which the requirement of semi-solid forming can be satisfied. Due to the higher aberration energy of grain boundary, the melting point is lowered as a result of the easy diffusion of atoms. At higher reheating temperature the grain boundary melts, the growth of the recrystallized grain is inhibited and the grain is refined. The composition of the low melt-point phase along the recrystallized grains was determined using EDS. It can be seen from the experimental results that when the extrusion rod of the wrought aluminum alloy is reheated at 610℃ for 20min, perfect fine equiaxial grains can be obtained, the average grain size is about 66.34μm and the volume fraction of solid phase is about 68%.

Semi-solid Processing of Al-7Graghite Composite

Al-7graphite composite was processed using Al-7graphite mushy prepared by electromagnetic-mechanical stirring method, and the influence of solid fraction on the distributing of graphite particles in ingot was studied. The results shows that the relationship between solid fraction and stirring temperature of mushy is: f(s) = 591.5-0.897 t (where f(s) is the solid fraction, t is the stirring temperature). For Al-7graphite composite, with the increasing of solid fraction, the aggregation extent of graphite particles reduced gradually, and when solid fraction was larger than 30%, graphite particles could distribute evenly in ingot.

Numerical Simulation of Gas-Solid Flow in Square Cyclone Separators with Downward Exit

Cyclone separators are widely used in industrial applications. The separation efficiency and pressure drop are the most important parameters to evaluate the performance of processing system. In the simulations,the flow behavior of gas and particles within a square cyclone separator is simulated by means of computational fluid dynamics. The RNG k- ε model and the Reynolds stress model( RSM) are used to model gas turbulence. The flow behavior is examined in the term of tangential velocity components,static pressure and pressure drop contour plots for flow field and solid volume fraction. The effects of the turbulence model and solid volume fraction on the square cyclone are discussed. The results indicate that the pressure drop increases with the increase of solid volume fraction,and increase with the increase of inlet velocities for two turbulence models, moreover,the simulations results are compared with pressure field. For all runs,the RSM model gives a higher pressure drop compared to the RNG k- ε model. The RSM model provides well the forced vortex and free vortex,and captures better the phenomena occurring during intense vortex flow in the presence of walls within cyclone separators.

Rheological Behavior of Semi-Solid AZ91D Magnesium Alloy at Steady State

The rheological behavior of semi-solid AZ91D magnesium alloy was investigated in isothermal steady state condition. The effects of stirring temperature and shearing rate on apparent viscosity of semi-solid alloy slurry at steady state were discussed. The results show that the apparent viscosity of semisolid AZ91D alloy increases with increasing solid fraction. It increases slightly before the solid fraction reaches a certain value, about 0.4, and then goes up rapidly aider the solid fraction reaches the critical value. However, the apparent viscosity decreases with increasing shearing rate, and the reduction amplitude is higher when the solid fraction is higher. According to the experimental data, an empirical equation that shows the effect of solid fraction and sheafing rate on the apparent viscosity of semi-solid AZ91D alloy can be built as ηa=9.7×10^-2 exp（13.87fs）γ^-0.58.

Commercial AM60 alloy for semisolid processing:Alloy optimization and thermodynamic analysis

Semisolid processing is now a commercially successful manufacturing route to produce net-shape parts in automotive industry. The conspicuous results of alloy optimization with thermodynamic simulations for semisolid processing of commercial AM60 alloy were present. The results indicate that the available processing temperature range of AM60 alloy is 170 ℃. The temperature sensitivity of solid fraction decreases with increasing solid fraction or with decreasing temperature above eutectic reaction temperature of AM60 alloy. When the solid fraction φs is 0.4, corresponding processing temperature is 603.8 ℃ and the sensitivity -dφs/dT is 0.0184. The effects of various alloying elements on the solidification behavior and SSM processability of AM60 alloy were calculated with Pandat software.

Changes in soil organic carbon contents and fractionations of forests along a climatic gradient in China

Background: Soil organic carbon(SOC) is a large reservoir of terrestrial carbon(C); it consists of different fractions of varying complexity and stability. Partitioning SOC into different pools of decomposability help better predict the trend of changes in SOC dynamics under climate change. Information on how physical fractions and chemical structures of SOC are related to climate and vegetation types is essential for spatial model ing of SOC processes and responses to global change factors.Method: Soil samples were col ected from multiple representative forest sites of three contrasting climatic zones(i.e. cool temperate, warm temperate, and subtropical) in eastern China. Measurements were made on SOC contents and physical fractions of the 0–20 cm soil layer, and the chemical composition of SOC of the 0–5 cm soil layer, along with measurements and compilation of the basic site and forest stand variables. The long-term effects of temperature, litter inputs, soil characteristics and vegetation type on the SOC contents and factions were examined by means of "space for time substitution" approach and statistical analysis.Result: Mean annual temperature(MAT) varied from 2.1 °C at the cool temperate sites to 20.8 °C at the subtropical sites. Total SOC of the 0–20 cm soil layer decreased with increasing MAT, ranging from 89.2 g·kg^(-1) in cool temperate forests to 57.7 g·kg^(-1) in subtropical forests, at an average rate of 1.87% reduction in SOC with a 1 °C increase in MAT.With increasing MAT, the proportions of aromatic C and phenolic C displayed a tendency of decreases, whereas the proportion of alkyl C and A/O-A value(the ratio of alkyl C to the sum of O-alkyl C and acetal C) displayed a tendency of increases. Overall, there were no significant changes with MAT and forest type in either the physical fractions or the chemical composition. Based on the relationship between the SOC content and MAT, we estimate that SOC in the top 20 soil layer of forests potentially contribute 6.58–26.3 Pg C globally to the atmosphere if global MAT increases by 1 °C–4 °C by the end of the twenty-first century, with nearly half of which(cf. 2.87–11.5 Pg C) occurring in the 0–5 cm mineral soils.Conclusion: Forest topsoil SOC content decreased and became chemical y more recalcitrant with increasing MAT,without apparent changes in the physical fractions of SOC.

On Solutions of Generalized Bacterial Chemotaxis Model in a Semi-Solid Medium

In this paper, the Adomian’s decomposition method has been developed to yield approximate solution of bacterial chemotaxis model of fractional order in a semi-solid medium. The fractional derivatives are described in the Caputo sense. The method introduces a promising tool for solving many linear and nonlinear fractional differential equations.