3D finite element simulation of microstructure evolution in blade forging of Ti-6Al-4V alloy based on the internal state variable models

The physically-based internal state variable （ISV） models were used to describe the changes of dislocation density, grain size, and flow stress in the high temperature deformation of titanium alloys in this study. The constants of the present models could be identified based on experimental results, which were conducted at deformation temperatures ranging from 1093 K to 1303 K, height reductions ranging from 20% to 60%, and the strain rates of 0.001, 0.01, 0.1, 1.0, and 10.0 s-1. The physically-based internal state variable models were implemented into the commercial finite element （FE） code. Then, a three-dimensional （3D） FE simulation system coupling of deformation, heat transfer, and microstructure evolution was developed for the blade forging of Ti-6Al-4V alloy. FE analysis was carried out to simulate the microstructure evolution in the blade forging of Ti-6Al-4V alloy. Finally, the blade forging tests of Ti-6Al-4V alloy were performed to validate the results of FE simulation. According to the tensile tests, it is seen that the mechanical properties, such as tensile strength and elongation, satisfy the application requirements well. The maximum and minimum differences between the calculated and experimental grain size of primary α phase are 11.71% and 4.23%, respectively. Thus, the industrial trials show a good agreement with FE simulation of blade forging.

Modeling of microstructure evolution of AZ80 magnesium alloy during hot working process using a unified internal state variable method

In this paper, a unified internal state variable(ISV) model for predicting microstructure evolution during hot working process of AZ80 magnesium alloy was developed. A novel aspect of the proposed model is that the interactive effects of material hardening, recovery and dynamic recrystallization(DRX) on the characteristic deformation behavior were considered by incorporating the evolution laws of viscoplastic flow, dislocation activities, DRX nucleation and boundary migration in a coupled manner. The model parameters were calibrated based on the experimental data analysis and genetic algorithm(GA) based objective optimization. The predicted flow stress, DRX fraction and average grain size match well with experimental results. The proposed model was embedded in the finite element(FE) software DEFORM-3 D via user defined subroutine to simulate the hot compression and equal channel angular extrusion(ECAE) processes. The heterogeneous microstructure distributions at different deformation zones and the dislocation density evolution with competitive deformation mechanisms were captured.This study can provide a theoretical solution for the hot working problems of magnesium alloy.

Effect of variable thickness cross rolling on edge crack and microstructure gradient of AZ31 magnesium alloy

The hot rolling experiment of AZ31 magnesium alloy was carried out by laying anoverlay mold at the initial temperature of 400℃.According to the Mizushima automatic plan view pattern control system(MAS)rolling theory and the cross rolling process,different reductions in the middle and edges of the magnesium alloy were realized,and the influence of the regional controlled reduction rolling on the edge cracks and microstructure gradient of the magnesium alloy were analyzed.It is shown that this rolling approach has reduced the maximum edge crack depth of the rolled piece by 56.85%,and there is a weakening tendency in the base surface texture of the strip edge,the base surface texture density drops from 23.97 to 17.48 after ordinary flat rolling.It exhibits basal texture gradients from the edge to the middle of the sheet along the RD direction,which reflected the uneven deformation of the sheets.It is suitable for the processing of metal molds that require large edge reductions such as mobile phone shells,and provided a theoretical basis for the variable thickness rolling of the magnesium alloy strip.

Diffusion tensor imaging of spinal microstructure in healthy adults： improved resolution with the readout segmentation of long variable echo-trains

Diffusion tensor imaging plays an important role in the accurate diagnosis and prognosis of spinal cord diseases. However, because of technical limitations, the imaging sequences used in this technique cannot reveal the fine structure of the spinal cord with precision. We used the readout segmentation of long variable echo-trains（RESOLVE） sequence in this cross-sectional study of 45 healthy volunteers aged 20 to 63 years. We found that the RESOLVE sequence significantly increased the resolution of the diffusion images and improved the median signal-to-noise ratio of the middle（C4–6） and lower（C7–T1） cervical segments to the level of the upper cervical segment. In addition, the values of fractional anisotropy and radial diffusivity were significantly higher in white matter than in gray matter. Our study verified that the RESOLVE sequence could improve resolution of diffusion tensor imaging in clinical applications and provide accurate baseline data for the diagnosis and treatment of cervical spinal cord diseases.

Effect of post weld heat treatment on properties of variable polarity TIG welded AA2219 aluminium alloy joints

AA2219 aluminium alloy joints were fabricated by variable polarity tungsten inert gas （VPTIG） welding process and the effects of post weld heat treatment （PWHT） on the tensile properties, microstructure and fatigue behaviour of the welded joints were investigated. The VPTIG welding process was adopted because it could meet the need of cathode cleaning and meanwhile it could reduce the deterioration of tungsten electrode furthest. The welded samples were divided into as-welded （AW） sample and PWHT sample. The PWHT method used on the samples was solution treatment （535 ℃, 30 rain）, water quenching and artificial aging （175 ℃, 12 h）. The experimental results show that, compared with the AW samples, the microstructure characteristics and mechanical properties of the AA2219 joints after PWHT were significantly improved. The improvement of yield strength, ultimate tensile strength, and fatigue strength are 42.6%, 43.1% and 18.4%, respectively.

Effects of process parameters on the microstructure during the hot compression of a TC6 titanium alloy

The effects of process parameters on the microstructural evolution, includinggrain size and volume traction of the a phase during hot forming of a TC6 alloy were investigatedusing compression tests. Experiments were conducted on the material with (α + β) phases atdeformation temperatures of 800, 860, 920, and 950℃, strain rates of 0.001, 0.01, 1, and 50 s^(-1),and height direction reductions of 30%, 40%, and 50%. After reaching a peak value near 920℃, thegrain size and volume fraction decrease with further increase of deformation temperature. The strainrate affects the morphologies and grain size of α phase of the TC6 titanium alloy. At a lowerstrain rate, the effect of the strain rate on the volume fraction is greater than that at a higherstrain rate under the experimental conditions. The effects of the strain rate on the microstructurealso result from deformation heating. The grain size of the α phase increases with an increase inheight direction reduction after an early drop. The effect of height direction reduction on thevolume fraction is similar to that of the grain size. All of the optical micrographs andquantitative metallography show that deformation process parameters affect the microstructure duringhot forming of the TC6 alloy, and a correlation between the temperature, strain, and strain rateappears to be a significant fuzzy characteristic.

Relationships between daily growth of different groups of swordtip squid(Uroteuthis edulis)and environmental variables in the East China Sea

Swordtip squid(Uroteuthis edulis)is one of the important economical fishing target species in the East China Sea.Uroteuthis edulis is characterized by rapid growth,extensive migration,and long spawning period and sensitive to surrounding environment.In order to assess its stock status,it is necessary to explore its spawning season,growth patterns of different populations and their relationship with the environment in advance.In this paper,based on the samples of U.edulis collected in the East China Sea from September 2017 to March 2018,we explored the relationships between daily growth of statolith microstructure and environmental variables by gradient forest method and generalized additive model.The spawning season of U.edulis was found to be nearly one year,and two dominant season groups were found:the spring group with the peak period of April and the summer group with the peak period of August.Water temperature in the depth of 25 m(Temp_25),sea surface temperature(SST)and zonal velocity were the key environmental variables for the daily growth of April-spawning group.The most suitable environmental conditions for the growth of April-spawning group were water temperature(24-27℃)and velocity(0.1-0.3 m/s).SST,Temp_25 and mixed layer depth were the key environment variables for the daily growth of August-spawning group.The most suitable environmental conditions for the growth of Augustspawning group were water temperature(21-28℃)and water depth(0-50 m).Key environmental variables of different groups suggested that early growth was significantly affected by seasonal changes of water temperature,current velocity and prey abundance.This study explored the relationships between early growth and environmental variables and provided the scientific guidance for the management and conservation of U.edulis.

Mechanical properties of welded joints in vertical-up variable polarity plasma arc welding of 2219 aluminum alloy

The mechanical properties of the 2219 aluminum alloy welded joints by vertical-up variant polarity plasma arc welding (VPPAW) with keyhole were analyzed. The tensile strength of welded joints can reach 55% of that of base metal. The microstructure of weld joints was studied to explain the mechanical properties of the weld. The results show that the intensity of weld center is less than that of HAZ, and the intensity of weld center is the worst. So an advanced welding procedures is presented to reduce the heat input and increase the welding speed. The results in this procedures show that the tensile strength of welded joints reaches more than 60% of that of the parent metal, and the specific elongation does not descend.

电解双喷中心复合响应曲面试验方法

采用电解双喷方法制备DC56D+Z钢透射电镜试样,试验设计包括试样预制、因子和水平选择,试验设计方法选择以及试验模型分析,其中试验设计选择中心复合响应曲面方法,建立响应变量和因子变量的关系模型,利用系统散点图分析模型的准确性,并对试验条件下响应变量的范围进行预测分析。对DC56D+Z钢的透射电镜薄区形态和显微组织形貌进行观察,研究结果可为金属材料的透射电镜试样制备提供参考依据。

铝合金VPPAW穿孔焊接匙孔闭合处的微观组织与力学性能

铝合金因其密度低,比强度高等特性,被广泛应用到航空航天、军事工业等领域.与其他焊接工艺相比,变极性等离子弧焊接在大型铝合金结构件加工方面具有突出优势.针对轻金属合金等离子弧焊接过程中匙孔难以自由闭合的问题,提出了气电分离时序脉冲等离子弧环焊缝收弧方法,对比研究了环焊缝收弧方法与手工钨极惰性气体保护焊(tungsten inert gas welding, TIG焊)填补法焊缝匙孔闭合处的微观组织与力学性能.结果表明,通过调节焊接起弧、收弧策略,实现了等离子弧匙孔自由闭合,焊缝收弧区成形良好,组织为均匀的等轴晶;抗拉强度为329.9 MPa,断后伸长率为16.3%,比TIG填补法的抗拉强度提高了22.91%,断后伸长率提高了55.24%.平均硬度值为78.9 HV0.2,热影响区硬度呈下降趋势,熔合线处硬度呈升高趋势,焊缝区硬度波动范围为75~81 HV0.2.

变化蜂巢织物基压力传感器的制备及性能研究

为改善织物基柔性压力传感器的灵敏度、响应性和稳定性,通过机织结构设计将微结构引入棉织物中,织造了具有圆顶形微表面结构的变化蜂巢组织织物。以变化蜂巢织物、炭黑(CB)和聚乙烯醇(PVA)为原料,采用浸烘法制备了不同的传感织物。测试了炭黑质量分数与传感器电阻的关系,并对制备的传感器结构形貌和力学传感性能进行表征,探讨其在人体运动监测中的应用。结果表明:在炭黑质量分数为5%时,传感器电阻降至20 kΩ/cm,制备的传感器具有较高的灵敏度,较小的迟滞性,在不同压力和压缩速率条件下均能保持良好的稳定性、重复性及耐用性。认为:制备的传感器可以应用于人体运动监测,包括手指按压、指关节、手腕和肘关节弯曲运动等。

大型阀门环形焊缝变姿态焊接路径规划

针对大型阀门环形焊缝,采用等高圆弧填充路径规划策略,建立了基于坡口尺寸和焊接道次、焊枪碰撞验证、焊枪角度修正的多层多道路径规划方法。通过将焊缝拟合成扇形焊缝、等腰圆弧梯形焊缝与扇环焊缝,计算出每一道焊缝的焊枪位置、焊枪角度、摆动幅度,对焊缝干涉判断,确定焊枪偏转角,实现机器人阀门变姿态焊接的离线编程,避免了焊接过程中的机器人干涉碰撞。最终实现了大型蝶阀的焊接,焊接接头表面平面,无裂纹、未熔合的缺陷,经过超声探伤,无内部缺陷,焊缝合格率为100%。焊接接头组织由珠光体和铁素体组成,晶粒细小均匀,其抗拉强度为536 MPa,屈服强度为468 MPa,断后伸长率为14%,0℃冲击吸收能量为54 J。

热控凝固工艺对薄壁变截面铸件凝固组织和力学性能的影响

先进航空发动机用机匣等高温合金构件不断向结构复杂化和薄壁轻量化发展,易导致充型困难、组织不均匀和凝固缺陷等问题,对该类铸件的精密铸造技术和工艺控制提出了新的挑战。针对上述问题,文中比较了常规铸造工艺与热控凝固工艺下K4169合金薄壁变截面特征件的充型情况、缩松、组织以及力学性能,并对热控凝固工艺参数进行了探索。结果表明,在常规铸造工艺下,特征件薄壁部位的充型率仅为26%,变截面部位出现了缩松。采用浇注温度为1360℃的热控凝固工艺可以使铸件薄壁部位的充型面积提高226%,显著减少铸件中的缩松,获得了细小的晶粒组织,平均晶粒尺寸为624μm,二次枝晶间距为116μm,Laves相的数量相对较少。同时,由于低浇注温度的热控凝固工艺有效实现了凝固组织细化和缺陷控制,合金在700℃条件下的抗拉强度提高了7%,伸长率由6%提高至8%。

匀变速抽拉对镍基单晶高温合金显微组织及晶体取向演化行为的影响

定向凝固熔模铸造单晶叶片过程中凝固过程难以达到稳态。本文采用定向凝固实验结合数值模拟的方法,研究了匀变速抽拉条件(0~200μm/s和200~0μm/s)下镍基单晶高温合金非稳态凝固过程中的显微组织与晶体取向演化过程。结果表明:同一瞬时抽拉速率下匀加速抽拉样品的一次枝晶间距大于匀减速的情况。定向凝固过程中晶体取向偏差具有随机波动性,匀加速抽拉下的晶体取向波动幅度大于匀减速的情形。最后,结合数值模拟的温度场结果分析了凝固组织和晶体取向演化机制。

亚共晶合金晶粒尺寸与相图变量相关双参数模型的检验

提出用于描述晶粒尺寸与工艺条件和相图变量相关联的简单双参数数学模型,然而,这些模型还没有通过良好的实验数据进行充分检验。采用精选的亚共晶合金实验数据检验这些模型,并提出实验数据的选择标准。采用这些双参数模型拟合被选择的实验数据,检查曲线的拟合质量和适用性,从而确定与实验数据吻合更好的数学模型。基于数据分析,探讨溶质元素细化晶粒尺寸的机理。结果表明,晶粒尺寸与合金凝固间隔之间存在明确的依赖关系,这种关系可采用P变量加以描述。晶粒尺寸对凝固间隔的这种明显依赖表明,在充型和凝固过程存在对流的铸锭和铸件中,与枝晶破碎有关的机理是控制溶质元素细化晶粒的主要运行机制。

Nb含量和热变形参数对纵向变截面耐候桥梁钢变形抗力及组织的影响

通过Gleeble 3800热模拟试验机,对一种新型不同Nb含量纵向变截面耐候桥梁钢进行变形抗力试验,测定了试验钢在变形速率为1、5、10 s-1,变形温度为750~1000℃,变形量为50%等不同变形参数下的变形-应力曲线。并通过金相显微镜、扫描电镜和透射电镜等手段,研究了试验钢在不同热变形参数下的显微组织变化。根据试验结果,分析了变形参数和Nb含量对纵向变截面耐候桥梁钢的变形抗力和显微组织的影响。结果表明:当Nb含量≥0.03%时,钢板的变形抗力显著增大,组织明显细化,添加一定量的Nb元素可提高钢板再结晶温度50℃以上,使LP耐候桥梁钢能够在变形温度为850~950℃的高温区轧制,以更好的保证LP钢板的板型和综合性能,为LP钢板产品的试制提供了理论依据。

基于耳石微结构的渤海带鱼早期生长与环境的关系分析

在长期气候变化和捕捞压力下渤海带鱼(Trichiurus japonicus)仍保持较高产量,为探究这一现象是否与渤海带鱼早期生长有关,本研究通过对渤海带鱼耳石微结构分析,追溯其产卵时间,使用梯度森林模型以及广义加性模型分析渤海带鱼早期生长与环境因子之间的关系。研究表明,渤海带鱼产卵高峰期为5月。海底温度(SBT)、混合层深度(MLD)和海表盐度(SSS)是影响带鱼早期生长的重要环境因子。其中,带鱼早期生长速度随SBT的升高而持续增加,且在10~12℃范围内生长速度最快。同时,随着MLD的增加,带鱼早期生长速度呈减缓趋势。以上结果表明,温度的升高以及充足的饵料供给可以促进带鱼的早期生长和种群的补充。

面向超材料微结构的离散变量拓扑优化设计

由周期性微结构组成的材料结构因其独特性质在飞行器结构设计中展现出良好的应用潜力。为了避免超材料微结构拓扑优化过程引入的中间密度所导致的灰度模糊设计结果,基于一种离散变量的拓扑优化方法,利用序列近似整数规划和正则松弛算法实现材料体积约束下的微结构拓扑优化设计。利用离散变量的特点首先给出了两种微结构的几何形状初始猜测,并根据这两种初始设计的构型分别进行了体积模量最大化和剪切模量最大化问题的求解。结果表明,微结构拓扑优化设计构型受初始设计和材料体积约束的影响较大,考虑不同的性能目标所获得的优化设计构型差异明显。数值算例展现了文中基于离散变量实现超材料微结构拓扑优化设计的可行性和有效性,避免了中间密度引起的灰度模糊问题,清晰的微结构拓扑构型提高了结构的可制造性。

微构造识别技术在×油田的应用

×油田微构造广泛发育,对微构造的认识精度在一定程度上影响着该油田的开发水平。该油田为复杂断块油藏,断层多期发育,精细刻画微构造的难度较大。为解决上述问题,通过研究形成了以精细地震构造解释为基础、以井控变速构造成图为关键的微构造精细表征技术。研究成果提高了对该油田微构造的认识和刻画精度,促进该油田取得良好的生产效果,提高了该油田的产量。

Microstructural characteristics and deformation of magnesium alloy AZ31 produced by continuous variable cross-section direct extrusion

Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and scanning electron microscopy（SEM） were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional extrusion（CE） and CVCDE with 1 interim die, and the grains were finer and more uniform.Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.