Wire and arc additive manufacturing of 4043 Al alloy using a cold metal transfer method

Cold metal transfer plus pulse(C+P)arc was applied in the additive manufacturing of 4043 Al alloy parts.Parameters in the manufacturing of the parts were investigated.The properties and microstructure of the parts were also characterized.Experimental results showed that welding at a speed of 8 mm/s and a wire feeding speed of 4.0 m/min was suitable to manufacture thin-walled parts,and the reciprocating scanning method could be adopted to manufacture thick-walled parts.The thin-walled parts of the C+P mode had fewer pores than those of the cold metal transfer(CMT)mode.The thin-and thick-walled parts of the C+P mode showed maximum tensile strengths of 172 and 178 MPa,respectively.Hardness decreased at the interface and in the coarse dendrite and increased in the refined grain area.

Cold metal transfer(CMT) technology-An overview

Cold Metal Transfer technology has revolutionized the welding of dissimilar metals and thicker materials by producing improved weld bead aesthetics with controlled metal deposition and low heat-input. In this study, the process, weld combinations, laser-CMT hybrid welding and applications of CMT welding are critically reviewed. Microstructure and other weld characteristics have been discussed at length for various base metal combinations. Particularly, the welding of aluminium and steel with better results has been possible with CMT Welding. The results reviewed in this article indicate that the CMT-Laser hybrid welding is more preferable to Laser or Laser hybrid welding. CMT welding has found applications in automobile industries, defence sectors and power plants as a method of additive manufacturing.

Microstructure and mechanical properties of dissimilar joint between aluminum and aluminum-coated steel by cold metal transfer process

Two dissimilar materials, aluminum alloy and aluminum-coated steel, were joined by cold metal transfer process using AlSi5 filler wire. To this end, the steel was coated with Al-Si. The steel did not melt and aluminum was melt to form the joint during the process, it was actually cold metal transfer welding-brazing. The macrostructure, microstructure, alloy element distribution, and inter-metallic compounds were analyzed by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. It was found that the Al-Si coating dissolved into the weld metal. The pre-existing thin Fe-Al- Si ternary inter-metallic compounds in the interface between the Ak-Si coating layer and base metal steel also partially dissolved into the weld zone, tending to reduce the thickness of inter-metallic compounds. Approximate 3 μm thick undissolved intermetallic compound was found at the interface after welding which could guarantee sound bonding strength in dissimilar materials joining. The sample was fractured at the fusion zone near the aluminum side in the tensile test. The ultimate tensile strength was about 156 MPa, and the fracture mode is ductile failure in nature according to its morphology.

Study on Relationship Between Arc Behavior and Joint Forming in Cold Metal Transfer Welding Technology with Polarity⁃Exchanging

Cold metal transfer with polarity⁃exchanging is a new integrated welding technology based on MIG.Due to the alternation of the positive and negative polarities of the wire,favorable control upon the deposition rate and the welding shape coefficient was obtained in order to meet the desired joint design,and the related controlling principles and joint characteristics were reported.Droplet transfer physical behavior exhibited strong dependability on the studied welding parameters,such as welding voltage,welding current,wire feeding speed,and polarity⁃exchanging.This welding technology provides a new way for the welding of body⁃in⁃white(BIW)thin sheet with special demands.Moreover,the typical quality defects of MIG were greatly improved.Our study provides important technical information from the perspective of industrial application of MIG and sheds light on the higher application level of MIG in BIW welding.

Continuously transferring cold atoms in caesium double magneto-optical trap

We have established a caesium double magneto-optical trap （MOT） system for cavity-QED experiment, and demonstrated the continuous transfer of cold caesium atoms from the vapour-cell MOT with a pressure of - 1 × 10^-6 Pa to the ultra-high-vacuum （UHV） MOT with a pressure of - 8 × 10^-8 Pa via a focused continuous-wave transfer laser beam. The effect of frequency detuning as well as the intensity of the transfer beam is systematically investigated, which makes the transverse cooling adequate before the atoms leak out of the vapour-cell MOT to reduce divergence of the cold atomic beam. The typical cold atomic flux got from vapour-cell MOT is - 2 × 10^7 atoms/s. About 5 × 10^6 caesium atoms are recaptured in the UHV MOT.

Cu对铝/钢CMT熔钎焊接头界面区组织的影响研究

采用冷金属过渡方法,以AlSi5焊丝为填充金属,在5052铝合金和镀锌钢板之间添加铜箔片进行搭接熔钎焊,使用扫描电子显微镜结合能谱分析和拉伸试验机对接头的界面区组织与性能进行研究。结果表明,未加入铜箔时,界面区组织主要由FeAl_(3)金属间化合物组成;铜箔的加入使得界面区组织中新生成了CuAl_(2)金属间化合物,同时改善了Zn在界面区的分布。Zn固溶于Al中,一定程度上抑制了Fe-Al金属间化合物产生。加入铜箔后的试样断裂位置发生改变,接头的承载能力与未加入铜箔的相近。

基于BAS算法优化的电弧增材制造焊道尺寸预测

目的为提高实际应用中电弧增材制造对工艺参数的选取效率及成形形貌的控制效果,建立高效且精准的成形尺寸预测模型,实现对焊道尺寸的合理预测。方法在单层单道CMT电弧增材制造实验的基础上,建立基于天牛须搜索算法(Beetle Antennae Search,BAS)优化BP神经网络的焊道尺寸预测模型,利用BAS算法实现对BP神经网络初始权值和阈值的优化,可以实现预测不同工艺参数(焊接速度、送丝速度、干伸长)下焊道的成形尺寸(熔宽、余高)。利用试验验证BAS-BP预测模型的性能,与现有模型进行对比,结果结果表明该模型具有较高精度的预测效果,能够有效映射工艺参数与焊道尺寸之间的非线性关系,印证了该模型具有良好的拟合和泛化能力,同时其对焊道熔宽和余高的预测误差分别不超过0.2、0.12 mm,预测平均误差率均不超过6%,相对于其他预测模型表现出较好的准确性和稳定性。结论BAS-BP神经网络预测模型的输出误差较小,网络训练收敛速度加快,避免了过拟合及欠拟合的风险,有效提高了预测模型的泛化能力和预测精度,可以实现一定工艺参数范围内的焊道尺寸预测,为后续电弧增材的实时预测及控制参数应用提供了技术支持。

Resonant Energy Transfer, with Creation of Hyper-Excited Atoms, and Molecular Auto-Ionization in a Cold Rydberg Gas

A cold Rydberg gas, with its atoms prepared initially all in the excited state |n0> , with n0 »1, contains an excessive amount of energy, and presumably is to relax by the Penning-type molecular auto-ionization (MAI), in which a portion of excess energy of one atom is given to another near-by atom and ionizing it. Its complementary process, the resonant energy transfer (RET), is discussed, in which the excess energy of one atom is used on another to form a hyper-excited atomic state |na> with na»n0. This process is always present, provided certain resonance energy conditions are satisfied. In this report, the n0 and density dependences of the RET rates are studied in detail, employing a simple model: 1) at low densities, the RET is mediated by the dipole-dipole coupling Vdd and its rates are generally much smaller than that of MAI, especially for small n0. But 2) as the density increases, our model shows that the rates become of comparable magnitude or even larger than the MAI rates. The Vdd is no longer adequate. We, then construct a semi-empirical potential to describe the RET process. 3) At high densities, we show that the atomic orbital of |na> overlaps with that of neighboring atoms, and the electron-electron potential becomes prominent, resulting in much higher rates.

基于工程应用的CW-GMAW熔滴过渡形态表征

综述了涉及工程应用的冷丝熔化极气体保护焊(Cold wire gas metal arc welding,CW-GMAW)熔滴过渡形态特征。结果表明,在大电流、强规范、富氩混合气体保护下,CW-GMAW工艺的熔滴过渡形态呈喷射过渡;当电流较小、电弧电压较低时,可能为滴状过渡,甚至在弧压很低时,呈现短路过渡形态。该工艺电弧发生偏向冷丝的位移,弧长变短甚至发生短路,与冷丝送进速率比增高及冷丝在电弧中产生大量金属蒸气时弧柱电阻下降有关。在具有富氩混合保护气体的相同工艺参数下,CWGMAW转变电流比GMAW降低了4%~7%。焊接工艺参数对CW-GMAW和GMAW工艺熔滴过渡形态的影响规律大致相近,但前者因涉及冷丝送进速率比和电极焊丝送进速度,以及它们的匹配等,使焊接电流的影响更为复杂。

泵驱动的制冷剂相变冷板冷却系统实验研究

元器件的小型化和性能的提升使电子器件功率不断提高,优越的散热性能对于保证电子器件的可靠性具有重要意义。本文搭建了泵驱动的制冷剂相变冷板冷却实验系统,设计加工了4块不同材质(铜、铝)和流道高度(10、15 mm)的相变冷板,对散热功率为200~1000 W、热流密度为4.4~22.2 W/cm^(2)的集中热源在制冷能力为3~11 kW和不同热源位置时的冷板换热性能、阻力特性及泵功耗进行了研究。结果表明:相变冷板换热性能优越,在应对散热量为1 kW、热流密度为22.2 W/cm^(2)的集中热源时,传热系数最高可达26 kW/(m^(2)·℃),在系统总阻力小于20 kPa、制冷剂泵功耗小于20 W时可以实现模拟热源表面与制冷剂温差小于15℃,可以利用天然冷源进行散热,实现节能;相变冷板的换热特性可由翅片效率计算式和Kandlikar传热关联式进行描述,使用理论公式计算出的冷板温差与实际值偏差小于1℃,可以指导冷板流道设计。

4043铝合金电弧增材制造的组织及力学性能

为了研究4043铝合金电弧增材制造中工艺参数、组织与力学性能之间的相关规律,采用CMT电弧增材制造技术制备了4043铝合金薄壁件。通过金相显微镜、扫描电子显微镜、电子万能试验机等检测设备,对不同工艺参数(焊接速度和送丝速度)制备的制件内部组织与力学性能进行了研究。结果表明,WAAM4043铝合金薄壁件内部组织为α(Al)相和β(Al_(3.21)Si_(0.47))相。随着焊接线能量的增加,Al-Si共晶相会增多,晶界处的β相变得粗大、松散,晶粒也变得粗大。4043铝合金薄壁件的抗拉强度最高为153.7 MPa,伸长率最高为22.5%。拉伸性能在横向与竖向上呈各向异性。过大或过小的焊接线能量都不利于获得好的力学性能。

焊接模式对电弧增材制造316不锈钢组织及力学性能的影响

基于冷金属过渡、冷金属过渡-脉冲以及直流脉冲三种焊接模式,开展了316不锈钢单道多层薄壁试样的电弧增材制造,并对试样进行了组织与性能的对比分析.结果表明,三种模式下成形构件均无塌陷和宏观气孔现象,凝固组织以柱状树枝晶为主,并伴随有大量的二次枝晶、胞状晶,通过金相观察和背散射电子衍射技术发现,组织表现出强<001>//z织构,构件中段稳态区的平均枝晶间距随不同焊接模式下的热输入变化而变化:由小到大依次为CMT—CMT-P—DC-P.通过X射线衍射和扫描电镜-能谱分析确定基体组织为γ-Fe(Cr0.19Fe0.7Ni0.11),基体间网状组织为残余δ-Fe.CMT-P模式下的构件强度最高,屈服强度达237 MPa,抗拉强度达555 MPa,平均硬度值达209 HV0.3,DC-P模式构件的断后伸长率最高达52%.

寒区相变蓄热墙体多因素热特性研究

在墙体中应用相变材料可以显著改善墙体的保温蓄热能力,但相变材料厚度和墙体构造的选择尚需科学论证。基于寒区气象特点,选择适用于寒区建筑外墙的相变储能材料,从墙体的传热特性角度出发,通过建立不同相变材料层厚度和多种构造的相变墙体模型,研究多种情况相变墙体的热特性。结果表明,相变墙体在冬季的保温蓄热能力受相变材料层位置和厚度影响,夏季效果主要受相变材料厚度影响;相变材料厚度为40 mm的中间型相变墙体和相变材料厚度为60 mm的内侧型相变墙体比较适合寒区建筑应用。研究所得结论可为寒区相变墙体的结构设计优化提供参考。

MH油田常温转输系统含水原油黏壁温度研究

MH油田原油含蜡易凝,冬季极寒(-40℃)环境下常温集输过程中原油黏壁概率增大,威胁管道安全运行。因此,亟需判断MH油田在实际运行工况以及未来工况下的常温转输可能性。通过改进后的冷指实验测得MH油田各转油站油品在不同含水率和不同流速下的黏壁温度,并采用极端梯度上升(XGBOOST)算法开展黏壁温度预测。其结果表明,M131、M18、BL、M2转油站原油在55%~80%含水率和0.90~2.72 m/s流速下的黏壁温度均低于凝点0.25~11.01℃,随含水率和流速增大,原油黏壁倾向减弱,黏壁温度降低。不同工况下XGBOOST算法黏壁温度预测结果与实验结果平均误差仅为8.36%。原油黏壁温度与各因素的重要度排序为含水率、原油凝点、流速,XGBOOST算法可用于预测MH油田转输系统变工况下常温转输的可行性。

乙烯装置冷箱工艺技术提升措施

冷箱是乙烯装置的重要过程设备之一,对质量可靠性的要求很高,其运行的好坏直接影响着乙烯装置的长周期安全稳定运行。冷箱的工艺设计和传热设计非常关键,需要给予足够的重视。通过调研国内乙烯装置冷箱在操作和运行中所遇到的问题,归纳冷箱在工程设计中面临的难点和要点,总结冷箱工艺设计技术,并提出了工艺优化的各项建议措施,对乙烯装置中深冷分离单元的工艺设计和操作具有一定指导意义。

目标域特征感知与互补用户迁移的跨域推荐模型

冷启动问题一直是推荐系统中十分有挑战性的问题.目前,基于映射的跨域推荐技术在解决冷启动问题上已取得了十分不错的效果,其方法主要分为两类,一类关注共性,即所有用户共享一个映射函数;另一类则关注个性,即为每个用户分别分配个性化的映射函数;然而,这两类方法均没有考虑到用户共性与个性的互补性;此外,这两类方法也忽视了目标域知识本身的挖掘.为了解决以上问题,本文提出了目标域特征感知与互补用户迁移的跨域推荐模型.一方面,提出个性-共性互补映射模块以显式建模用户个性和共性的互补信息,另一方面,提出了关系网络以挖掘目标域知识.最后,在Amazon数据集上的实验取得了目前最优的效果,验证了本文所提出模型的有效性.

寒冷地区复合自保温砌块墙体热湿耦合迁移特性研究

为研究自保温砌块墙体的热湿耦合传递规律,将当前主流构造型式的复合自保温砌块墙体与同等厚度的外保温墙体进行对比。以寒冷地区保定市为例,通过数值软件进行模拟计算,分析自然环境下墙体内部的热湿耦合传递过程。模拟结果表明:自保温砌块墙体的保温隔热效果优于外保温墙体。在夏季工况下,墙体湿风险较低,不存在霉菌滋生与冷凝风险。在冬季工况下,自保温砌块墙体内部湿风险均高于外保温墙体。填芯自保温砌块墙体、夹芯自保温砌块墙体、外保温墙体内部相对湿度最大值分别为73.9%、92.1%、68.6%。其中,夹芯自保温砌块由于空腔的存在降低了墙体的传湿阻力,相对湿度超过80%,湿积累明显且霉变风险较大,使得墙体长期使用稳定性与保温性能受到影响。因此,填芯自保温砌块具有更好的适用性,有利于减小建筑热湿负荷,降低建筑能耗水平。

夏热冬冷地区动态传热保温设计室外典型气象参数确定方法

GB50176-2016《民用建筑热工设计规范》中围护结构外墙保温设计采用稳态方法,但夏热冬冷地区由于特有的建筑运行模式,使外墙传热方向发生逆转,故稳态方法难以满足冬季室内热环境水平提升的实际需求。提出一种基于动态传热的冬季外墙保温设计室外计算温度确定方法,探究室外干球温度和太阳辐射逐时波动的最不利组合,将保温设计的目标由“日”提升到“时”。基于典型城市2007-2017年逐时气象数据,以外墙内表面温度的累计不保证天数作为热工设计指标,将累计不保证天数恰好不为0(指各朝向外墙内表面温度低于室内基本热舒适条件下所能允许温差的天数)时作为典型日挑选的依据,并将典型日出现频率最高的日期作为室外计算温度选取的依据,获得冬季保温设计典型日,并获得了典型日计算时长的影响。可为夏热冬冷地区围护结构外墙保温设计室外计算参数的挑选提供理论支撑。

寒冷地区绿色建筑结构散热过程仿真

由于寒冷地区气候条件复杂,温度变化剧烈,需要合理控制建筑散热以降低建筑能耗,防止能源过度消耗。因此,提出了寒冷地区绿色节能建筑散热过程的仿真研究。运用Z传递函数计算建筑墙壁传热,获得屋顶或墙壁等热传导的热量,根据建筑的热学性能和特殊边界条件,算出周期实际扰量。建立多层结构建筑散热的非定态热湿耦合传输模型,分析室内外空气的水蒸气交换量,并结合生命周期成本分析法获得节约能耗成本,实现绿色节能建筑散热过程的模拟。实验结果表明,所提方法的建筑散热控制好,建筑节能率高,且有效减少能源消耗的同时保持室内温度稳定。

LYZH型急冷箱数值模拟与结构优化

为适应加氢反应器大型化趋势,开发了集旋流、撞击及挡板分流等功能于一体的LYZH型急冷箱,其结构由上至下依次为旋流冷氢管、冷氢盘、喷射管和接液盘。采用CFD软件对LYZH型急冷箱进行数值模拟研究,结果表明LYZH型急冷箱具有优秀的传热性能及气液混合性能。为使LYZH型急冷箱的性能得到进一步提升,对其结构进行了优化,最优结构的旋流冷氢管中径为2218.9 mm、喷射管直径为526.9 mm以及接液盘到冷氢盘高度为175.4 mm。与原始结构相比,最优结构的传热性能提高7.61%,压力降降低14.4%,LYZH型急冷箱的综合性能得到较大改善。