高速列车用厚板铝合金CMT焊接工艺

针对低热输入、高质量焊接技术的需求,研究厚板铝合金多层多道冷金属过渡技术(cold matal transter,CMT)焊接工艺和脉冲MIG焊接工艺的区别,对CMT焊接和脉冲MIG焊接进行热循环曲线测量,焊接接头拉伸、弯曲、硬度等常规力学性能试验和接头微观组织分析.结果表明,铝合金厚板焊接时相对脉冲MIG焊接方法,CMT方法焊接温度场低,焊接接头软化明显减弱,冲击韧性得到提高,厚板多层多道焊接接头组织明显改善,晶粒明显细化.试验表明CMT焊接方法可获得相对脉冲焊接更加优良的铝合金焊接接头.     

7A52铝合金-钢异种结构CMT熔钎焊接头组织及镀镍层的行为与影响

以ER4043铝硅焊丝为填充金属,研究了Q235钢螺柱与7A52铝合金板CMT焊接工艺,在焊接电流115~135 A,电弧电压14.5~16.5 V,焊接速度0.3 m/min条件下,焊接过程稳定,焊缝成形连续美观.结果表明,7A52铝合金侧熔合区界面为熔焊特征,铝母材发生熔合,熔合良好;钢螺柱侧熔合区为钎焊特征,界面存在反应层,由靠近钢螺柱的Fe₂Al₅层和靠近焊缝侧的FeAl₃层组成,整体反应层厚度由根趾向焊趾方向逐渐减小.焊趾部位出现富镍区,主要由Al₃Ni的共晶组织及少量Al₃Ni₂组成.与无镀镍层焊缝比较表明,镀镍层在焊接过程的行为降低了界面反应层厚度,且通过形成富镍区,降低了接头的脆性,使接头抗剪切强度提高了15%~19%,最高达到146.9 MPa,满足了高强铝合金螺柱焊接的质量要求.     

Abrasive wear/corrosion properties and TEM analysis of Al2O3 coatings fabricated using plasma electrolysis

Alumina coatings were deposited on Al alloy substrates using an electrolytic plasma technique, based on a dielectric barrier discharge created during anodic oxidation in an aqueous electrolyte. The substrate material (BS Al 6082) was biased anodically with an unbalanced AC high voltage. During processing, a plasma current density of 100 mA/cm² was used, at which a coating deposition rate of 1.67 μm/min was achieved. Coating abrasive wear and corrosion properties were assessed by conducting dry and wet rubber wheel abrasive tests and potentiodynamic polarization experiments, respectively. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate the coating microstructure, and the coating/substrate interface. The property test results show that the coatings possess excellent abrasive wear and corrosion resistance. XRD analyses indicate that the coatings consist of α- and γ-Al₂O₃. An amorphous+nanocrystalline inner layer (1.5-μm thick) and a nanocrystalline (50–60 nm) intermediate layer in the coating were observed by TEM. The higher resistance to wear and corrosion can in part be attributed to the presence of these interlayers.     

Erosion-corrosion of thermally sprayed coatings in simulated splash zone

The damage of marine steel structures in the splash zone is very severe. Applying thermally sprayed metal coatings is among the most important protective technologies, but the service life of current coatings is limited. In this paper, arc spray was used to prepare four types of metal coatings, that is, aluminum (Al), zinc bottom coating combined with aluminum topcoat (Zn + Al), aluminum-zinc pseudo alloy (Al/Zn) and aluminum-titanium pseudo alloy (Al/Ti) coatings. These metal coatings were sealed with epoxy priming and aliphatic polyurethane topcoat. Erosion-corrosion experiments were carried out on self-made device by simulating the splash zone working environment of steel structures and protective coatings. The results show that all the sealed coatings could improve the steel resistance to erosion-corrosion, and the aluminum-zinc pseudo alloy is the most excellent coating. In the coating failure process, mechanical erosion rather than corrosion is the key factor causing coating erosion-corrosion in splash zone. Improving the anti-cutting properties could help to prolong the coating life.     

镁合金表面冷喷涂层防护研究进展

镁合金作为最轻质的金属结构材料,由于其密度低和比强度高等优良的物理和力学性能,在航空、航天、汽车以及电子等领域引起广泛关注。然而,镁合金化学性质活泼、耐腐蚀和耐磨损性差等缺点严重制约其进一步应用。近些年发展起来的冷喷涂技术,在固态下制备涂层,涂层致密且与基体结合良好,因此可为镁合金表面防护提供一种新的有效方法。主要综述了镁合金表面冷喷涂耐腐蚀涂层(纯铝、铝合金和复合材料涂层)和耐磨损涂层(合金和复合材料涂层),论述了影响冷喷涂层耐腐蚀、耐磨损以及其他力学性能(硬度和涂层/基体结合强度)的主要因素,包括杂质元素含量、合金种类以及复合材料涂层中陶瓷颗粒含量、尺寸和形貌等。对比了几种常用表面处理技术制备的纯铝涂层的耐腐蚀性能,并阐述了冷喷涂技术在镁合金表面防护方面的优势。此外,还分析了热处理对冷喷涂纯铝和复合材料涂层耐蚀性的影响。最后提出了目前冷喷涂技术在镁合金防护方面的局限性以及发展难题,对未来研究趋势进行了展望。     

Characterisation of the cold metal transfer (CMT) process and its application for low dilution cladding

The process characteristics of the synergic cold metal transfer (CMT) process have been examined for welding aluminium alloy. Utilising a simple backlighting system and through the arc monitoring the droplet transfer modes were identified. Whilst the modified short circuit mode was evident for the lower parameter range, a two part transfer mode based upon a combination of spray and short circuit transfer was observed for the mid to upper parameter range. The technology was also explored as a cladding process for applying to ternary alloyed (Al-Cu-Mg) aluminium plate. This alloy system is known to be susceptible to solidification cracking when MIG welded using the binary Al-2319 (Al-Cu) filler wire, this being due to the wide element freezing range of the weld resulting from mixing with the base material. Utilising this filler, weld dilution ratios for both CMT and pulsed welding were identified across the examined parameter range. The CMT process exhibited greater control of dilution that enabled deposition of a quasi-binary (Al-Cu) layer exhibiting a less crack susceptible composition. Onto this layer conventional MIG welding could be applied which could potentially eradicate cracking using a binary filler wire.     

电弧喷涂Zn-Al伪合金涂层耐腐蚀性能研究进展

通过在钢基体表面制备涂层可以很好地延长钢铁材料的服役时间,减少因腐蚀造成的重大事故和人员伤亡。相较于传统的纯Zn涂层、纯Al涂层以及Zn-Al合金涂层,Zn-Al伪合金涂层能够为基体材料提供长久有效的腐蚀防护,在钢铁材料的腐蚀防护中具有巨大的应用潜力。简述了Zn-Al伪合金涂层电弧喷涂制备工艺的特点;介绍了Zn、Al、Zn-Al合金及Zn-Al伪合金涂层在模拟海洋环境下的腐蚀防护原理;在此基础上从组分、喷涂工艺参数(喷涂距离、喷涂电流和喷涂电压)、元素掺杂(Mg、Si及Re)及后处理工艺(封孔、激光重熔)等角度,论述了其对Zn-Al伪合金涂层耐蚀性的影响;讨论了Zn-Al伪合金涂层防腐体系在桥梁、海洋钢结构件、地下运输管道中的应用现状;最后总结了目前研究工作中存在的挑战,提出了电弧喷涂Zn-Al伪合金涂层尚需深入研究的重点问题,为提高钢铁材料使用寿命提供了参考。     

Dilution and Ferrite Number Prediction in Pulsed Current Cladding of Super-Duplex Stainless Steel Using RSM

Super-duplex stainless steels have an excellent combination of mechanical properties and corrosion resistance at relatively low temperatures and can be used as a coating to improve the corrosion and wear resistance of low carbon and low alloy steels. Such coatings can be produced using weld cladding. In this study, pulsed current gas tungsten arc cladding process was utilized to deposit super-duplex stainless steel on high strength low alloy steel substrates. In such claddings, it is essential to understand how the dilution affects the composition and ferrite number of super-duplex stainless steel layer in order to be able to estimate its corrosion resistance and mechanical properties. In the current study, the effect of pulsed current gas tungsten arc cladding process parameters on the dilution and ferrite number of super-duplex stainless steel clad layer was investigated by applying response surface methodology. The validity of the proposed models was investigated by using quadratic regression models and analysis of variance. The results showed an inverse relationship between dilution and ferrite number. They also showed that increasing the heat input decreases the ferrite number. The proposed mathematical models are useful for predicting and controlling the ferrite number within an acceptable range for super-duplex stainless steel cladding.     

Corrosion behaviour of boiler steels,coatings and welds in flue gas environments

In recent years there has been a steadily increasing focus on energy efficiency as a means to reduce the negative impact of human activity on climate, and in particular the effect that industrial emissions have on changes in the climate, specifically global warming. As far as power generation is concerned, emissions can be limited by maximizing energy efficiency while ensuring high levels of plant reliability. This paper reports on materials development work involving coated heat exchange alloys and the effect of welding of the coated alloys, simulating fabrication, on subsequent corrosion performance under laboratory conditions. Samples of the common boiler steels P91 (9% Cr) and HCM12A (12% Cr) were treated by chemical vapour deposition (CVD) in a pack cementation process to produce Al‐rich coatings up to 100 µm thick. The samples were machined to give bevelled edges for welding. Welding was carried out using commonly available alloy 625 filler metal. It was found that sound weldments could readily be produced provided that care was taken to limit the heat input during the welding process. Excessive heat input could lead to cracking, but more importantly to dilution of Al in the coating adjacent to the weldment and in segregation of elements (Mo and Nb) in the weldment itself. Both dilution and segregation effects led to decreased corrosion resistance.     

原位微锻造冷喷涂制备高致密铝基涂层及耐腐蚀性能

目的提出一种基于原位微锻造冷喷涂制备高致密度金属沉积体的新方法,旨在为镁合金腐蚀防护提供一种低成本的涂层制备方法。方法通过在Al喷涂粉末中混入20%～60%(体积分数)的大粒径喷丸颗粒,借助其在喷涂过程中对已沉积Al涂层的原位微锻造效应,实现Al涂层制备中的实时致密化,研究了原位微锻造强度对涂层显微组织及耐腐蚀性能的影响规律。采用SEM分析了涂层的显微结构,采用电化学测试及长期浸泡试验测试了涂层的耐腐蚀性能。结果随着微锻造强度的提高,金属沉积体的致密度逐渐增加,当混合粉末中的喷丸颗粒含量高于40%时,可获得孔隙率低于0.3%的高致密度Al涂层。电化学测试及长达1000 h的Na Cl溶液浸泡腐蚀结果显示,高致密度Al涂层包覆后的镁合金表现出与冶金块材铝相当的耐腐蚀性能,比无保护镁合金腐蚀速率降低两个数量级以上;在1000h的盐雾腐蚀后,涂层与基材界面无腐蚀产物生成,表明涂层可完全对腐蚀介质进行物理隔绝。同时,致密铝涂层表面形成了微米级的钝化膜,可进一步提高耐腐蚀性能。结论通过原位微锻造辅助冷喷涂技术,可在较低的气体温度和气体压力条件下在镁合金表面获得完全致密的Al腐蚀防护涂层。该技术还有望用于诸如高导热、高导电涂层的制备,金属构件修复及增材制造等其他对金属沉积体有致密度要求的领域。     

Compound Ceramic Coatings on Ti-6Al-4V by Micro-Plasma Oxidation in NaAlO2 Solution

MICRO PLASMA OXIDATION(MPO)technique,bywhich compound ceramic coating can be grown in situon Al,Ti,Mg and many other valve-metals,has apromising application prospect in the fields likemilitary,aerospace,textile,automobile,hospital,decoration aspects,and so on tl"3).Although there aretwo much work on the composition and the structure ofthe coatings l4"61,the application of ElectrochemicalImpedance Spectroscopy(EIS)technique on suchcoatings is seldom reported.And EIS is a powerfulan…     

铝合金焊接区喷射式微弧氧化陶瓷层耐腐蚀性研究

目的研究喷射式微弧氧化对改善铝合金焊接区耐腐蚀性能的可行性。方法使用自行研制的喷射式微弧氧化设备,在铝合金焊接区表面制备一层陶瓷膜,并在同等参数下制备一层浸入式微弧氧化陶瓷层进行对比。通过扫描电镜观察陶瓷膜表面和截面的微观形貌,并对陶瓷膜截面进行元素分析;分别利用铜加速盐雾腐蚀实验和动电位极化实验检测陶瓷膜的耐腐蚀性能,分析陶瓷膜的耐腐蚀性能。结果两种方法制备的陶瓷膜微观形貌相似,表面都有许多"火山口"状产物并伴有裂纹,截面疏松多孔,主要元素为Al和O;经240 h盐雾腐蚀后,3种试样均有不同程度的腐蚀,其中铝合金焊接基体腐蚀最严重,浸入式、喷射式次之,其腐蚀失重率分别是0.0072,0.0039,0.0023 g/cm2;极化曲线显示,铝合金基体、焊接基体、浸入式陶瓷膜、喷射式陶瓷膜腐蚀电位分别为-0.794,-0.742,-0.615,-0.578 V,耐腐蚀性依次增强。结论喷射式微弧氧化陶瓷层耐腐蚀性能表现较好,基本达到制备要求,在不适于浸入式微弧氧化的条件下可采用喷射式方法处理。     

单一成分活性剂对铝合金作用效果的研究

活性化TIG(A-TIG)焊已成为近年来的研究热点,但主要集中在不锈钢和钛合金两种材料,在铝合金中的应用较少.针对铝合金A-TIG焊进行了初步的研究和探索,选择四种单一成分的活性剂,采用表面两侧涂敷方式,通过2A14铝合金的平板堆焊实验,研究了在相同规范下不同活性剂对焊缝熔深、焊缝成形、气孔和微观组织的影响.实验结果表...     

大跨度桥梁缆索用钢丝热浸镀层研究综述

综述了热浸镀Zn、Zn-Al和Zn-Al-Mg系合金镀层的性能特点和研究现状。在Zn-Al合金中添加Al元素可以减缓Zn的腐蚀氧化,同时可以在镀层表面形成致密的Al_2O_3薄膜起到屏蔽保护作用。在此基础上,采用Mg合金化,不仅可细化镀层组织,还可抑制疏松腐蚀产物的生成,进一步延长合金镀层的寿命。阐明了桥梁缆索用钢丝热浸镀工艺的特点和不足。采用中性盐雾试验评估了应力加载对桥梁缆索用热浸镀层组织和耐腐蚀性能的影响。应力加载会使镀层表面的腐蚀产物保护层破裂,加快腐蚀进程。同时指出了现有桥梁缆索用钢丝镀层评价标准尚存在一些争议,应结合现行的评价体系,重视讨论和探索新的更合适的评价标准。需要研究新一代(Zn-Al-Mg)合金镀层的制备技术和评价标准,推动具有高耐蚀性的多元合金镀层在桥梁缆索用钢丝上的推广应用。同时,桥梁缆索用钢丝热浸镀层的腐蚀性能应考虑应力加载下的腐蚀破坏和相关机理研究。     

Electrochemical Impedance Spectroscopy of protective coatings

Electrochemical impedance spectroscopy (EIS) carried out over a wide frequency range (10⁵ to 10^?2 Hz) allows us to obtain mechanistic information concerning corrosion protection by coatings. Examples are given for polymer coatings on an Al alloy as a function of surface petreatment and for anodized Al alloys. For polymer coatings on metals, information concerning the coating's properties and its changes with exposure time can be obtained from the high and medium frequency regions of the impedance spectrum, while the corrosion reaction at the metal/coating interface can be evaluated from the low frequency part. The pore resistance of the coating and its changes with exposure time have been used to rank different pretreatment procedures for a given metal/coating combination. For Al alloys, pronounced differences in corrosion resistance between a conversion coating and an anodized layer under a polyurethane coating have been observed. The use of a segmented electrode allows measurements of the impedance across as well as under a coating. From these data, information concerning delamination can be obtained. An example is given for an epoxy coating on steel. The use of EIS as a quality control and corrosion test for anodized Al alloys is discussed. The effects of the anodization procedure (sulfuric acid and chromic acid), sealing procedure (hot water and dichromate) and alloy chemistry (Al 2024, 6061 and 7075) have been studied during exposure to aerated 0.5 N NaCl. All these parameters play an important role in the corrosion resistance of the alloys. The sealing process can be evaluated from the high frequency part of the spectrum. Pronounced differences in the spectra for the two sealing procedures are observed. The corrosion behavior is reflected in the low frequency part, which is essentially dominated by barrier layer properties.     

Some Features of High-Temperature Oxidation of Aluminide Coatings on Alloy TsNK-7P

Special features of high-temperature oxidation of aluminide coatings (slip-deposited Al – Si and ion-plasma-deposited VSDP-11) on alloy TsNK-7P are considered. The kinetics of the oxidation process, the element composition, and the microhardness of coatings with different thicknesses are described. Results of thermal fatigue tests of alloy TsNK-7P with aluminide diffusion coatings are presented. It is shown that the VSDP-11 coating ensures a higher heat resistance and thermal fatigue strength on alloy TsNK-7P than the Al – Si coating and can replace the latter on turbine vanes of gas compressor units.     

Formation of MoSi2 and Al doped MoSi2 coatings on molybdenum base TZM (Mo–0.5Ti–0.1Zr–0.02C) alloy

Formation of aluminium (Al) doped molybdenum di-silicide (MoSi₂) coatings was studied to improve the high temperature oxidation behavior of TZM (Mo–0.5Ti–0.1Zr–0.02C) alloy. The pack composition of the halide activated pack cementation process was successfully optimized to form silicide and Al doped silicide coatings on the TZM alloy substrates. Mo(Si, Al)₂ phase was found to form at the outer layer of the coating prepared by doping Al in MoSi₂. A change in composition of the phases with increase in coating temperature was detected with Al doping, whereas un-doped silicide coating process was dominated by the formation and growth of MoSi₂ phase. Oxidation test and the characterization studies using SEM, EDS, XRD, and micro-hardness measurements indicated the improved performance of Al doped silicide coating during high temperature oxidation in dry air due to the formation of the protective alumina scale.     

Zn-Al系列高速电弧喷涂层电化学防腐性能研究

采用粉芯丝材和高速电弧喷涂技术制备高Al含量的Zn-26％Al涂层。通过电化学的方法测试涂层在5％NaCl溶液下的腐蚀行为，并与由实芯丝材纯Zn、纯Al及Zn-15％A1所制备的涂层作比较。结果表明：Zn-26％A1涂层在电解质溶液中表现出更优越的防腐性能。动电位极化测试结果说明zn-Al涂层随着Al含量的增加，其耐蚀性也提高。纯Al涂层的电化学腐蚀行为与其它涂层有明显差异，其腐蚀机理类似于点蚀。     

7N01铝合金脉冲MIG焊与直流CMT焊多次补焊试验

高速列车用7N01铝合金有较大热裂纹倾向,而补焊时该问题更突出.分别采用脉冲MIG焊和低热输入直流CMT焊对4 mm厚7N01铝合金对接接头进行1次、2次、3次补焊,分析了补焊焊接接头的宏观成形、微观组织和硬度.结果表明,脉冲MIG补焊时下塌量和熔宽均大于直流CMT补焊,脉冲MIG补焊焊道与先焊焊缝微观组织界面明显,先焊焊缝晶粒粗大且晶界发生重熔,熔合区变宽,而直流CMT补焊焊道界面不明显,焊缝微观组织晶粒细小,熔合区无明显变化;脉冲MIG焊3次补焊后软化现象较直流CMT补焊严重.采用直流CMT焊进行7N01铝合金补焊,可有效降低热裂纹倾向并缓解接头性能下降.     

Influence of Concentrations of KOH and Na_2SiO_3 Electrolytes on the Electrochemical Behavior of Ceramic Coatings on 6061 Al Alloy Processed by Plasma Electrolytic Oxidation

In this study,ceramic coatings were deposited on 6061 Al alloy using a plasma electrolytic oxidation(PEO)technique,and the effect of concentrations of KOH and Na_2SiO_3 as electrolytes for PEO process was studied on microstructure,chemical composition,and electrochemical behavior of PEO coatings formed on the 6061 Al alloy.The results indicated that the increase in concentration of KOH led to rise in electrical conductivity of electrolyte.Consequently,the breakdown voltage reduced,which in turn improved the surface quality and the corrosion behavior.Moreover,the increase in concentration of Na_2SiO_3 resulted in the increase in incorporation of Si in the coating,which led to a higher corrosion potential in the concentration of 4 g L~(-1).According to this investigation,the best protection behavior of coatings can be obtained when the KOH and Na_2SiO_3 concentrations in PEO electrolyte are equal to 4 g L~(-1).