Effect of HEA/Al composite interlayer on microstructure and mechanical property of Ti/Mg bimetal composite by solid-liquid compound casting

In this study,HEA/AI composite interlayer was used to fabricate Ti/Mg bimetal composites by solidliquid compound casting process.The Al layer was prepared on the surface of TC4 alloy by hot dipping,and the FeCoNiCr HEA layer was prepared by magnetron sputtering onto the Al layer.The influence of the HEA layer thickness and pouring temperature on interface evolution was investigated based on SEM observation and thermodynamic analysis.Results indicate that the sluggish diffusion effect of HEA can effectively inhibit the interfacial diffusion between Al and Mg,which is conducive to the formation of solid solution,especially when the thickness of HEA is 800 nm.With the increase of casting temperature from 720 ℃ to 730 ℃,740℃,and 750 ℃,α-Al(Mg),α-Al(Mg)+Al3Mg2,Al3Mg2+Al12Mg17,and Al12Mg17+δ-Mg are formed at the interface of Ti/Mg bimetal,respectively.When the thickness of the HEA layer is 800 nm and the pouring temperature is 720 ℃,the bonding strength of the Ti/Mg bimetal can reach the maximum of 93.6 MPa.

Solid liquid Mixed Casting of Al-Si Alloy

The paper presents a novel material preparation technology—Solid liquid mixed casting technology. In the technology, large amounts of homogeneous alloy powder or heterogenous powder with perfect wettability are added into the superheated melt. After strong agitation, the mixed melt can be cast or hot processed. Applying solid liquid mixed casting, three kinds of Al Si alloys were investigated. The results show that, when the mass of powder accession to alloy melt is about 1, the mean size of primary Si in hyper eutectic alloy can be controlled at less than 5 μm; and the mean grain size of α phase in hypo eutectic alloy is less than 10 μm. This technology has the advantage of preparing material with very fine microstructure by fairly simple casting process, and may be a new practicable and valuable metal preparation technology.

Mathematical Modelling of Particle Movement Ahead of the Solid-liquid Interface in Continuous Casting

Whether the particle will be trapped by the solid-liquid interface or not is dependent on its moving behavior ahead of the interface, so a mathematical model has been developed to investigate the movement of the particle ahead of the solid-liquid interface. Based on the theory for the boundary layer, the fluid velocity field near the solid-liquid interface was obtained, and the trajectories of particles were calculated by the equations of motion for particles. In this model, the drag force, the added mass force, the buoyance force, the gravitational force, the Saffman force and the Basset history force are considered. The results show that the behavior of the particle ahead of the solid-liquid interface is affected by the physical property of the particle and fluid flow. And in the continuous casting process, if it moves in the stream directed upward or downward near vertical solid-liquid interface or in the horizontal flow under the solid-liquid interface, the particle with the diameter from 5 um to 60um can reach the solid-liquid interface. But if it moves in horizontal flow above the solid-liquid interface, only the particle with the diameter from 5 um to 10 um can reach the solid-liquid interface.

Effect of droplet characteristics on liquid-phase distribution in spray zone of internal mixing air-mist nozzle

In continuous casting production,droplet characteristics are important parameters for evaluating the nozzle atomization quality,and have a significant impact on the secondary cooling effect and the slab quality.In order to study the behavior of atomized droplets after reaching the slab surface and to optimize the spray cooling effect,the influence of droplet diameter and droplet velocity on the migration behavior of droplets in the secondary cooling zone was analyzed by FLUENT software.Results show that the droplets in the spray zone and on the slab surface are mainly concentrated in the center,thus,the liquid volume fraction in the center is higher than that of either side.As the droplet diameter increases,the region of high liquid volume fraction on the slab surface becomes wider,and the liquid phase distribution in the slab width direction becomes uneven.Although increasing the droplet velocity at the nozzle exit has little effect on droplet diffusion in the spray zone,the distribution becomes more uneven due to more liquid reaches the slab surface per unit time.A prediction formula of the maximum water flow rate on the slab surface for specific droplet characteristics was proposed based on dimensionless analysis and validated by simulated data.A nozzle spacing of 210 mm was recommended under the working conditions in this study,which ensures effective coverage of the spray water over the slab surface and enhances the distribution uniformity of water flow rate in the transverse direction.

A new low-cost method of reclaiming mixed foundry waste sand based on wet-thermal composite reclamation

A lot of mixed clay-resin waste sand from large-scale iron foundries is discharged every day; so mixed waste sand reclamation in low cost and high quality has a great realistic significance. In the study to investigate the possibility of reusing two types of waste foundry sands, resin bonded sand and clay bonded sand which came from a Chinese casting factory, a new low-cost reclamation method of the mixed foundry waste sand based on the wet-thermal composite reclamation was proposed. The waste resin bonded sand was first reclaimed by a thermal method and the waste clay bonded sand was reclaimed by a wet method. Then, hot thermal reclaimed sand and the dehydrated wet reclaimed sand were mixed in certain proportions so that the hot thermal reclaimed sand dried the wet reclaimed sand leaving some water. The thermal reclamation efficiency of the waste resin bonded sand was researched at different heat levels. The optimized wet reclamation process of the waste clay bonded sand was achieved by investigating the effects of wet reclamation times, sand-water ratio and pH value on the reclaimed sand characteristics. The composite reclamation cost also was calculated. The research results showed that the properties of the mixed reclaimed sand can satisfy the application requirements of foundries; in which the temperature of the thermal reclamation waste resin bonded sand needs to be about 800 oC, the number of cycles of wet reclamation waste clay bonded sand should reach four to five, the optimal sand-water ratio of wet reclamation is around 1:1.5, and the pH value should be adjusted by adding acid. The mass ratio of hot thermal reclaimed sand to dehydrated wet reclaimed sand is about 1:2.5, and the composite reclaimed sand cost is around 100 yuan RMB per ton.

Nano-SiC_P particles distribution and mechanical properties of Al-matrix composites prepared by stir casting and ultrasonic treatment

Nano-ceramic particles are generally difficult to add into molten metal because of poor wettability. Nano-SiC_Particles reinforced A356 aluminum alloy composites were prepared by a new complex process, i.e., a molten-metal process combined with high energy ball milling and ultrasonic vibration methods. The nano particles were β-SiC_P with an average diameter of 40 nm, and pre-oxidized at about 850 °C to form an oxide layer with a thickness of approximately 3 nm. The mm-sized composite granules containing nano-SiC_P were fi rstly produced by milling the mixture of oxidized nano-SiC_P and pure Al powders, and then were remelted in the matrix-metal melt with mechanical stirring and treated by ultrasonic vibration to prepare the composite. SEM analysis results show that the nano-SiC_P articles are distributed uniformly in the matrix and no serious agglomeration is observed. The tensile strength and elongation of the composite with 2 wt.% nano-SiC_P in as-cast state are 226 MPa and 5.5%, improved by 20% and 44%, respectively, compared with the A356 alloy.

Simulation of thermomechanical behavior during continuous casting process based on MiLE method

A new method called mixed Lagrangian and Eulerian method(MiLE method) was used to simulate the thermomechanical behavior during continuous casting process of steel YF45MnV.The simulation results are basically in agreement with the measured data.The delaying period at the beginning of solidification is about 0.1 in square root of solidification time which is agreement with the data in literatures,and shell thickness increases in linear relation to square root of solidification time.The bloom surface temperature decreases gradually as the casting proceeds.The effective stress in the corner is much larger than that in the mid-face.The corner area is the dangerous zone of cracking.The effects of mold flux break temperature on the air gap and hot tearing indicator were also modeled.The model predicts that the bloom surface temperature increases with the increase of the mold flux break temperature,but the heat flux decreases with the increase of the mold flux break temperature.The hot tearing indicator is much smaller when the mold flux break temperature is higher.

复合水解酸化+催化铁+CAST处理混合化工废水的试验研究

采用复合水解酸化+催化铁+CAST工艺处理混合化工废水,探讨了该工艺对COD、NH3-N、TP、TN的去除效果以及CAST不同的运行模式对去除效果的影响。试验结果表明,该工艺对COD、NH3-N、TP、TN的平均去除率为75.0%、96.9%、47.0%、31.6%;而CAST工艺段设置为进水-搅拌-曝气-沉淀-滗水运行模式更有利于TN和TP的去除。

水泥土加固桩水平循环承载性能足尺试验研究

选取宿迁典型饱和粉土场地,采用水泥土搅拌桩加固钻孔灌注桩桩周土,开展灌注桩水平循环加载足尺试验。探究水泥土加固试验桩(TPI)和未加固试验桩(TPU)在循环水平荷载作用下的滞回特性、弯矩、刚度退化、位移延性、水平承载力与残余变形能力。试验结果表明:TPI比TPU桩的弯矩减小47%,屈服位移减小41%,水平承载力提升150%,有效刚度提升240%,等效黏滞阻尼比提升233%,桩的开裂荷载提升150%,屈服荷载阶段桩体的残余变形能力减小17%。水泥土搅拌法不仅可以限制桩侧粉土液化,增加桩基础的耗能及位移延性,而且可以显著的降低桩头水平位移和弯矩的发展。从抗震性能的角度分析,水泥土搅拌桩加固既有桩基,有效抑制了加固范围内地基土刚度衰减,增强了桩-土结构的总耗能、等效黏滞阻尼系数与变形恢复能力,提高桩基础在大变形阶段的抗震性能。

生产因素对浇注式沥青混合料性能的影响

GMA沥青混合料性能受到生产因素的影响显著,室内小型拌合设备难以模拟实际的生产情况。通过Cooker车真实模拟GMA混合料生产过程,研究不同生产因素对浇注式沥青混合料性能的影响。研究表明,当Cooker车控制好混合料的拌合温度、拌合时间时,GMA混合料的性能是可控的。Cooker车的拌合时间宜控制在2.5~3 h,生产过程中应尽量将沥青用量的精度控制在±0.2%,以稳定混合料的性能。采用浇注成型的冲击韧性试验数据较切割的试验数据稳定性好,应尽量采用浇注成型的试件制备方法。

稀盐酸对铸造镁合金回炉料混料判定的影响

在铸造镁合金熔炼过程中添加回炉料时,用稀盐酸滴在回炉料锯切的光洁面上,可根据合金表面与稀盐酸反应时不同的反应现象区分铸造镁合金材料牌号。有效识别回炉料成分,防止发生混料、造成成本浪费。

某市市域铁路基坑支护设计案例分析

开展基坑支护既要考虑支挡岩土体,又要形成有效的止水帷幕。某地下基坑支护工程采用钻孔灌注排桩+两道钢筋砼内支撑,在被动区采用三轴水泥搅拌桩加固土体的支护体系,对该基坑计算参数和施工要点进行分析,为类似基坑工程提供参考,进一步提高基坑发展水平。

ZG230-450铸钢基尔试块断后伸长率不合格原因

某熔炼炉浇注的ZG230-450铸钢基尔试块在正火后的拉伸试验过程中,其断后伸长率不合格。采用宏观观察、化学成分分析、扫描电镜与能谱分析、金相检验等方法对其断后伸长率不合格原因进行分析。结果表明:拉伸试样中存在沿初生奥氏体晶界析出的点状MnS夹杂物,弱化了晶界结合力,在拉伸载荷的作用下,裂纹沿初生奥氏体晶界扩展,形成穿晶韧窝+沿晶韧窝混合型石状断口,造成材料的断后伸长率不合格。

水泥土搅拌墙+钻孔灌注桩在基坑支护中的应用

某深大基坑周边环境及地下管线复杂,地质条件相对较差,为保证基坑施工任务的顺利进行,首先对基坑围护结构方案进行比选,然后在施工中对重点工序进行控制,同时加强基坑变形监测,最终完成了基坑施工任务。

Study on concentration and turbulence of solid-liquid FAE in dispersal process

This paper describes numerical simulation on dispersion of the solid-liquid mixed fuel driven by explosion load. A model used in numerical calculation for dispersion of solid-liquid mixed fuel was established in this study. The concentration and turbulent intensity in the multiphase cloud of the solidliquid mixed fuel were obtained by numerical simulation. It was found that the fuel concentration tended to be 0.15 kg/m^3, the turbulence intensity tended to be 7 in 90 ms. The numerical results agree with those measured in the experiment.

Numerical optimization for blades of Intermig impeller in solid-liquid stirred tank

The multiphase flow in the solid-liquid tank stirred with a new structure of Intermig impeller was analyzed by computational fluid dynamics(CFD).The Eulerian multiphase model and standard k-ε turbulence model were adopted to simulate the fluid flow,turbulent kinetic energy distribution,mixing performance and power consumption in a stirred tank.The simulation results were also verified by the water model experiments,and good agreement was achieved.The solid-liquid mixing performances of Intermig impeller with different blade structures were compared in detail.The results show that the improved Intermig impeller not only enhances the solid mixing and suspension,but also saves more than 20% power compared with the standard one.The inner blades have relatively little influence on power and the best angle of inner blades is 45°,while the outer blades affect greatly the power consumption and the optimized value is 45°.

PAC强化“水解酸化+CAST”工艺处理混合化工废水的研究

采用粉末活性炭（PAC）强化＂水解酸化＋CAST＂工艺对混合化工废水进行研究。试验结果表明：PAC强化＂水解酸化＋CAST＂工艺对进水中COD、难降解COD、BOD5、NH3-N和TP等参数的去除率分别达到了82.8%、52.8%、95.8%、88.8%和94.2%,实际出水水质有了很明显提高。PAC与活性污泥法耦合处理废水,PAC在产生吸附作用的同时,具有与生物协同的降解作用。通过改变PAC的投加方式和投加量试验,出于经济方面考虑,在保证出水水质指标达标的前提下,确定2~3天为一个比较合理的PAC投加周期。

Isolated mixing regions and mixing enhancement in a high-viscosity laminar stirred tank

Laminar mixing in the stirred tank is widely encountered in chemical and biological industries.Isolated mixing regions(IMRs)usually exist when the fluid medium has high viscosity,which are not conducive to mixing.In this work,the researches on IMRs,enhancement of laminar mixing and the phenomenon of particle clustering within IMRs are reviewed.For most studies,the aim is to destroy IMRs and improve the chaotic mixing.To this end,the mechanism of chaotic mixing and the structure of IMRs were well investigated.The methods developed to destroy IMRs include off-centered agitation,dynamic mixing protocol,special designs of impellers,baffles,etc.In addition,the methods to characterize the shape and size of IMRs as well as mixing effect by experiments and simulations are summarized.However,IMRs are not always nuisance,and it may be necessary in some situations.Finally,the present engineering applications are summarized,and the prospect of the future application is predicted.For example,particle clustering will form in the co-existing system of chaotic mixing and IMRs,which can be used for solid–liquid separation and recovery of particles from high viscosity fluid.

水解酸化强化CAST工艺处理混合化工废水的调控因素研究

通过试验研究,初步确定水解酸化池的水力停留时间THR、混合液悬浮固体浓度CMLSS、进水COD负荷等参数。通过对THR、CMLSS和进水COD负荷这3个影响因素的观察,利用正交试验确定最优工况。结果表明,当水解酸化THR为6 h,CMLSS为5 000 mg/L,进水COD负荷为1.2 kg/(m3·d)时,处理效果最好。在最优工况下,水解酸化强化CAST工艺对进水中COD、BOD、NH3-N和TP等参数的去除率分别为75.4%、91.3%、89.1%和90.1%。

搅拌叶片表面原位合成TiC颗粒增强高锰钢复合层的制备及性能

采用燃烧合成反应铸渗结合真空消失模铸造工艺,在ZG120Mn13Cr2高锰钢搅拌叶片表面制备原位合成TiC颗粒增强高锰钢复合层,研究了该复合层的显微组织、硬度以及在湿砂磨损条件下的耐磨性能,并与BTMCr20高铬铸铁和ZG120Mn13Cr2高锰钢的硬度和耐磨性能进行对比,测试了复合层叶片在稳定土条件下的现场使用寿命。结果表明:复合层与高锰钢基体呈冶金结合,其组织由原位合成的细小TiC颗粒、外加的粗大TiC颗粒和高锰钢基体相构成,原位合成的TiC颗粒呈圆球或近圆球状均匀分布在基体相中;复合层的平均硬度为58 HRC,高于高锰钢低于高铬铸铁,磨损质量损失略高于高铬铸铁但远低于高锰钢。复合层叶片的现场使用寿命为1700 h,为高锰钢叶片的2倍以上,略高于高铬铸铁叶片。