钛合金焊缝金属在酸性硫酸铜溶液中的阳极极化行为

针对钛焊区优先腐蚀问题,研究了电子束扫描焊接对钛合金焊缝金属在酸性硫酸铜溶液中阳极极化行为的影响,结果表明,通过改变电子束扫描频率控制焊缝金属凝固组织形态及尺寸,从而控制的焊缝金属的阳极极化行为,找出了焊缝金属与母材相同的阳极极化曲线的最佳匹配,提出了通过控制焊接凝固结晶,使钛合金焊缝金属与母材均等耐腐蚀的新技术。     

低合金钢焊缝金属的腐蚀行为

研究了多种焊接工艺参数下,母材分别为16Mn和X70钢的焊接接头各部位在25℃空气中、25℃通N2除氧NACE溶液和3．5％NaCl溶液中的腐蚀行为。结果表明,针状铁素体腐蚀倾向较大,但其腐蚀速度很慢;焊接接头中针状铁素体数量对其腐蚀性能有着明显的作用,较多数量的针状铁素体对应着较强的焊缝金属抗腐蚀能力,但过量针状铁素体的出现可能会加快低合金钢焊接接头的腐蚀。     

Influences of Cr/Ni equivalent ratios of filler wires on pitting corrosion and ductility-dip cracking of AISI 316L weld metals

To study the pitting corrosion of AISI 316L weld metals according to the chromium/nickel equivalent ratio (Cr_eq/Ni_eq ratio), three filler wires were newly designed for the flux-cored arc welding process. The weld metal with delta-ferrite at less than 3 vol.%, was observed for ductility-dip cracking (DDC) in the reheated region after multi-pass welding. The tensile strength and yield strength increased with increasing Cr_eq/Ni_eq ratio. The result of anodic polarization tests in a 0.1 M NaCl solution at the room temperature (25) for 45 min, revealed that the base metal and weld metals have a similar corrosion potential of −0.34 V_SCE. The weld metal with the highest content of Cr had the highest pitting potential (0.39 V_SCE) and the passivation range (0.64 V_SCE) was higher than the base metal (0.21 V_SCE and 0.46 V_SCE, respectively). Adding 0.001 M Na₂S to the 0.1M NaCl solution, the corrosion occurred more severely by H2S. The corrosion potentials of the base metal and three weld metals decreased to −1.0 V_SCE. DDC caused the decrease of the pitting potential by inducing a locally intense corrosion attack around the crack openings.     

Al3Zr/Al基原位复合材料等离子体焊接区的组织及表面腐蚀行为

摘要： 本文以5wt%Al3Zr/铝基复合材料为研究对象,以Ar气体为离子气体,Al-Ti-B为丝材进行等离子焊接。用电化学综合测试仪测定了焊接区在3.5%NaCl溶液中的腐蚀极化曲线。采用扫描电子显微镜（SEM）、X射线衍射仪（XRD）对复合材料及其焊缝的组织和相组成进行了分析和表征,研究了Al3Zr/Al基复合材料等离子焊接后在3.5%NaCl溶液中的腐蚀行为和腐蚀机理。SEM分析结果表明,等离子弧焊接可获得较好的焊缝组织,焊缝组织主要由Al3Ti相和Al基体组成,Al3Ti相呈条状和球形。电化学极化曲线表明,材料在熔核处的耐蚀性略低于母材,焊缝处浸泡腐蚀机理为Al3Ti相和基体相的电极电位不同形成原电池反应造成。     

异质污染对316L不锈钢焊缝组织及耐蚀性影响的显色研究

目的 针对核电站管道焊缝中不明原因显色现象,设计了一种模拟工程现场引入异质污染的情形,研究异质污染对管道焊缝的影响.方法运用邻菲罗啉显色检测法,分别评价了以ER316L焊丝、掺杂了铁丝与铁粉的焊丝以及纯铁丝作为焊丝的316L不锈钢焊缝异质铁污染,结合能谱和动电位极化测试,分析了异质铁污染对焊缝组织和耐蚀性的影响.结果焊缝表面大面积持续显色主要为铁氧化物和焊缝中的富铁相,焊缝内部的点状持续显色为铁氧化物夹渣.在打磨条件下,无污染和富铁相作用下的焊缝,随空气放置时间的延长,显色程度a*逐渐降低,而点状显色没有明显改变,根据临界红色像素下临界色度(ac=5.3)时的积分面积百分比表明,点状显色的百分比低于1％,带状显色的积分面积百分比为20％～30％,ac=5.3时,显色开始显现.在3.5％NaCl溶液中,316L不锈钢焊缝的耐电化学腐蚀能力由大到小的顺序为ER316L+铁粉焊缝>ER316L焊缝>ER316L+铁丝焊缝>纯铁丝焊缝.结论铁污染的加入会导致显色现象更易产生,同时也会降低316L不锈钢焊缝的耐腐蚀性能.     

Evaluation of nanometer-sized zirconium oxide incorporated Al—Mg—Ga—Sn alloy as anode for alkaline aluminum batteries

Zirconium oxide nanoparticles with 0.4 wt.% and 0.8 wt.% are incorporated into the Al—0.65Mg—0.05Ga— 0.15Sn (wt.%) alloy anode (base alloy) in order to improve the performance of the resulting anodes. Electrochemical characterization of the reinforced alloys was done by potentiodynamic polarization, electrochemical impedance spectroscopy and galvanostatic discharge and corrosion behavior was evaluated using self-corrosion rate and hydrogen evolution in 4 mol/L KOH solution. The surface morphology of the alloys was also studied using field emission scanning electron microscope (FESEM). The obtained results indicate that the base alloy shows high corrosion rate in 4 mol/L KOH solution by releasing 0.47 mL/(min·cm²) hydrogen gas, whereas the alloy containing 0.8 wt.% ZrO₂ provides the lowest hydrogen evolution rate by releasing 0.32 mL/(min·cm²) hydrogen gas. Furthermore, by increasing zirconium oxide nanoparticles, the corrosion current density of the aluminum anodes is decreased and their corrosion resistance increases significantly compared to the base alloy in alkaline solution. In addition, nanometer-sized zirconium oxide incorporated anodes exhibit the improved galvanic discharge efficiencies, so that 0.8 wt.% nano-zirconium oxide incorporated base alloy displays the highest power density and anodic utilization compared with the others in 4 mol/L KOH solution.     

Post-weld heat treatment influence on galvanic corrosion of GTAW of 17-4PH stainless steel in 3·5%NaCl

Abstract

The influence of post-weld heat treatment (PWHT), solution annealing followed by aging at 480, 550 and 620°C on the galvanic corrosion in 17-4PH stainless steel weldment in 3·5%NaCl was studied. Potentiodynamic polarisation revealed that all PWHTs improve the passivity of weld region by increasing the pitting potential. Heat affected zone disappears, and base and weld regions act as the anode and the cathode respectively. Zero resistance ammetry measurement for 42 h showed that PWHTs improve the galvanic corrosion resistance by decreasing the galvanic current density to a few to tenths of nanoampere per square centimetre. Aging at 620°C has the highest risk of galvanic corrosion among the three PWHTs. Difference in corrosion characteristic of base and weld were addressed to microstructure variations including ferrite, copper rich precipitates and reverted austenite.     

Effects of PWHT on Microstructure and Mechanical Properties of Weld Metals of Ni-Based Superalloy 617 and 263 for Hyper-Supercritical Power Plants

It is well known that solid solution-strengthened alloy 617 and γ' precipitation-strengthened alloy 263 have excellent mechanical properties and corrosion resistance at high temperatures.Hyper-supercritical power plants work at temperatures above 700 ℃,and these superalloys are considered candidate materials for steam turbines components of these power plants.In this study,gas tungsten arc weldability of these superalloys was evaluated,and the effects of postweld heat treatment(PWHT) on the microstructural characteristics and the mechanical properties of their weld metals were investigated.Scanning transmission electron microscopy,energy-dispersive spectroscopy and electron probe microanalysis were utilized for the investigation.The experimental results confirmed that these weld metals had different characteristics in microstructure and mechanical properties.PWHT resulted in the precipitation of intergranular carbides,γ' particles and an increase in tensile strength of these superalloy weld metals.Furthermore,fine γ' particles,which were not detected in the as-welded metal of alloy 263,were precipitated after PWHT and those particles were the reason for the drastic increase in tensile strength.     

Influence of nitrogen addition on microstructure and pitting corrosion resistance of austenitic weld metals

A study to investigate the role of nitrogen in improving the pitting corrosion resistance of types 316 and 304 stainless steel weld metals has been attempted. Weld metals were prepared by autogenous TIG welding process with argon-nitrogen mixture as the shielding gas. Delta-ferrite measurements, made with Magne-Gage, showed the absence of delta-ferrite in all the samples of type 316 ss weld metal whereas for type 304 ss it decreased from 3.8 to 0 FN with increase in the levels of nitrogen. Potentiodynamic anodic polarization studies carried out on weld metal samples in deaerated neutral chloride medium showed improved resistance to pitting attack with increase in the amount of nitrogen. This improvement in pitting resistance could be due to the dissolution of nitrogen and formation of inhibiting compounds at the pit sites. The ESCA results of the anodically polarized weld metal samples showed the presence of nitrogen in a compound form. SEM and optical microscopic studies of the pitted samples showed that the initiation sites for pitting attack were triple points, austenite centres and delta-ferrite/austenite interfaces.     

Effect of delta ferrite content on the corrosion resistance of type 316 clad metals

Austenitic claddings of type 316 were obtained by SMAW (Shielded Metal Arc Welding) and SAW (Submerged Arc Welding) processes, using type 316 L electrodes on low carbon boiler steel (SA 515 Gr 60) with type 309 L as a barrier layer deposited by the SAW process. Welding heat input was changed in order to obtain different ferrite contents in the cladding. The clad samples were post-weld heat treated at 650°C for 50 and 200 h. The top layer of the cladding was removed and the specimens were then subjected to intergranular corrosion tests (ASTM A-262-75, practices A, B, C and E, viz. 10% oxalic acid electrolytic etch; ferric sulfate ?50% sulfuric acid; 65% nitric acid and copper-copper sulfate ?16% sulfuric acid tests) and controlled potential etching test. The study indicated that the ferrite content of the cladding decreases with increasing current. Ferrite transformed after PWHT (post weld heat treatment) was relatively more in claddings obtained with low heat input and containing high ferrite content in the as-clad condition. PWHT led to brittle fracture of high ferrite claddings (above 10 FN). The corrosion attack of ferrite was found to depend on environment. 65% nitric acid attacked ferrite preferentially, whereas in acid-ferric sulfate, ferrite was intact and austenite was attacked. No sample exhibited susceptibility to intergranular corrosion in the as-clad or PWHT conditions in the copper-copper sulfate ?16% acid test. However, PWHT specimens with low ferrite contents (3.55 FN) exhibited grain boundary precipitation at the interface of two adjacent layers. In general, ferrite was found to be beneficial in controlling corrosion rates of clad metals after PWHT. Heat input, within the range studied, did not affect the corrosion rates significantly.     

SPV50Q钢焊接接头腐蚀和氢渗透性能分析

具有不同组织结构的焊接接头是腐蚀环境中服役焊接设备或管道的薄弱环节,这与焊接接头处发生的非均匀腐蚀密切相关.利用动电位极化、交流阻抗技术和氢渗透技术,研究了液化石油气（LPG,liquefied petroleum gas）球罐用SPV50Q钢焊接接头在含H2S溶液中的腐蚀和氢渗透特性.结果表明,具有不同组织结构的SPV50Q钢焊接接头各区金属（母材、热影响区和焊缝）,在含H2S溶液中的耐腐蚀性和氢渗透性能都具有一定的差异性,母材的耐蚀性最好,热影响区次之,焊缝金属的最差;对氢渗透性能而言,焊缝金属的氢扩散速度和扩散系数最大,热影响区的次之,母材的最小.     

CO2环境下油酸咪唑啉对X65钢异种金属焊缝电偶腐蚀的抑制作用研究

研究了X65管线钢与316L不锈钢、Inconel 625双金属复合管的异种金属焊缝在CO2环境下的电偶腐蚀行为,以及油酸咪唑啉的缓蚀作用。结果表明,随着电偶电位差的增大,异种金属焊缝的腐蚀速率明显升高,并且都显著高于母材。添加油酸基咪唑啉缓蚀剂能降低异种金属焊缝在CO2环境下的均匀腐蚀速率。但是,当缓蚀剂浓度添加较低时,异种金属焊接试样的碳钢一侧出现了严重的沟槽腐蚀或密集的点蚀坑;进一步增加缓蚀剂浓度才能消除沟槽腐蚀现象。讨论了缓蚀剂对异种金属焊缝电偶腐蚀的抑制机理,该项研究可为异金属焊接接头处的腐蚀防护提供借鉴。     

时效处理对铝锂合金电子束焊接头耐蚀性能的影响

对铝锂合金电子束焊接头进行焊后热处理,研究了时效处理前后接头各区域的晶间腐蚀、剥蚀和电化学腐蚀行为。结果表明,接头经过时效处理后,焊缝晶界析出的T1(Al_2CuLi)相数量增加,并且形成了明显的晶界无沉淀带(Precipitate Free Zone,PFZ)。焊态下接头未出现晶间腐蚀,热影响区和母材区均出现了孔蚀;焊后时效处理增大了接头的晶间腐蚀倾向,热影响区同时发生了孔蚀和晶间腐蚀,母材区出现了严重的晶间腐蚀。焊态下焊缝和热影响区均具有优异的抗剥蚀能力,母材区对剥蚀的敏感性较高;焊后时效处理可提高接头母材区的抗剥蚀能力,但会增大热影响区的剥蚀敏感性。电化学腐蚀测试表明,与时效后的接头焊缝相比,焊态下焊缝的自腐蚀电位较高,腐蚀电流密度小,具有相对较好的耐蚀性。     

Evaluation of microstructure and electrochemical corrosion behavior of austenitic 316 stainless steel weld metals with varying chemical compositions

Austenitic stainless steel weld metals have, in general, inferior corrosion resistance compared with the base metals. This is due to the fact that the weld metal has an inhomogeneous and dendritic microstructure with microsegregation of major elements (i.e., Cr, Mo, and Ni) as well as minor elements (i.e., S and P) at the δ-γ interface boundaries. The nonuniform alloying element concentration around ferrite particles plays a major role in determining the electrochemical corrosion behavior of such weld metals. Although the presence of ferrite is considered to be detrimental as far as the localized corrosion is considered, its exact role in uniform corrosion is still not clear. The uniform corrosion behavior of an alloy is determined by the fundamental electrochemical parameters of the major alloying elements. In this study, an attempt has been made to correlate the microstructure and uniform corrosion behavior of type 316 stainless steel weld metals with varying concentrations of Cr and Mo, and different ferrite contents. From the empirical equations obtained during the analysis of the electrochemical corrosion data, an attempt has been made to understand the role of Cr, Mo, and ferrite in altering the electrochemical corrosion parameters of the weld metal. Based on the extensive microstructural characterization, a dissolution model for the weld metal in the moderately oxidizing medium has been proposed.     

AZ31镁合金搅拌摩擦焊焊缝电化学性能的分析

试验的样品为3 mm厚挤压态AZ31镁合金,采用搅拌摩擦焊接工艺对焊而成.通过静态失重法、动电位极化曲线以及交流阻抗谱(electrochemical impedance spectroscopy,EIS)测试,研究了室温下浓度5%(质量分数)NaCl溶液中AZ31镁合金搅拌摩擦焊焊缝和母材的电化学行为.结果表明,在室温腐蚀介质中通过静态失重法测得AZ31镁合金母材和焊缝在168 h后的平均腐蚀速率分别为0.154和0.135 g/(m2·h),通过动电位极化曲线及交流阻抗谱(EIS)测得AZ31镁合金母材和焊缝的腐蚀电流分别为0.001 63和0.000 45 A/cm2,极化电阻分别为9.553和12.61Ω/cm2.AZ31镁合金搅拌摩擦焊焊缝的抗腐蚀性能优于其母材的表现.     

In-situ evaluation for corrosion process at fusion boundary of stainless steel strip overlay joints in H2S containing solution

The present work studied the corrosion properties around the fusion boundaries of 2.25Cr-1Mo steel with stainless steel strip overlay joints under as welded condition and after post-weld heat treatment (PWHT) in H2 S containing solution (NACE TM-01-77 standard) with different time. An in-situ observation method was introduced for evaluating corrosive progress in the fusion boundary in H2 S containing solution, that is, the samples were marked firstly at the boundary and then treated in the solution for variant time. Each time after the corrosion treatment, the observations were kept to focus at the same marked area by using scanning electron microscopy (SEM) to observe the corrosion progress. The results reveal that the fusion boundary is the worst region for corrosion resistance when comparing with other boundaries, and a broad fusion boundary has a stronger resistance for "hydrogen induced disbonding" than a narrow one.     

2219铝合金母材及焊接接头的腐蚀行为

采用剥蚀试验和动电位极化曲线测试对2219铝合金母材、搅拌摩擦焊(FSW)和钨极氩弧焊(TIG)焊接头的腐蚀行为进行了研究。通过腐蚀失重测试、电化学试验与剥蚀后表面及深度方向腐蚀微观形貌观察,对三者的腐蚀形式和机理进行了分析。结果表明:母材腐蚀速率最大,自腐蚀电位最低,而腐蚀电流密度最大;两种接头焊缝/焊核的耐蚀性总体接近,都优于母材的,FSW焊核的耐蚀性最优。合金母材的腐蚀形式为层状剥蚀,TIG焊缝为晶间腐蚀,深度较小,FSW焊核为点蚀。三者的腐蚀均与析出相有关,母材的析出相粗大,与基体之间的电偶效应最明显;TIG焊缝析出相沿枝晶晶界排列,但析出相尺寸小,电偶作用弱于母材;FSW焊核析出相尺寸由于机械搅拌而变小且分布弥散,腐蚀性能有所改善。     

On the microstructure-polarization behavior correlation of a 9Cr-1Mo steel weld joint

The use of 9Cr-1Mo ferritic steel necessitates its fabrication by the process of welding. The heat-affected zone (HAZ) of 9Cr-1Mo ferritic steel is a combination of many microstructures. In the present study, the corrosion properties of the base metal, weld metal, and the various regions of the HAZ are assessed with respect to their microstructures. The various microstructures in the HAZ were simulated by heat treatment of the normalized and tempered base metal at 1463, 1200, and 1138 K for 5 min followed by oil quenching. The microstructure of the base metal in the normalized and tempered condition revealed martensite laths with M₂₃C₆ carbides at lath boundaries, and uniform dispersion of fine, acicular M₂C. The weld metal showed predominantly martensitic structure with dispersion of carbides. Simulation of the microstructures of the HAZ by heat treatment resulted in the following microstructures: coarse-grained martensite of 75 μm size at 1463 K, fine-grained martensite at 1200 K, and martensite + proeutectoid α-ferrite at 1138 K. In all cases, carbide precipitation was observed in the martensitic matrix. Microhardness measurements of HAZ-simulated base metal showed increasing hardness with increasing heat treatment temperature. The hardness values obtained corresponded very well with the regions of the actual HAZ in the weld joint. Electrochemical polarization studies were carried out on the base metal, weld metal, weldment (base metal + weld metal + HAZ), and the simulated HAZ structures in 0.5 M sulfuric acid solution. Critical current densities (i _crit1 and i _crit2), passive current densities (i _pass and i _sec-pass), and transpassive potential (E _tp) were the parameters considered for evaluating the corrosion resistance. The HAZ structures simulated at 1463 and 1200 K, corresponding to coarse- and fine-grained martensitic regions of an actual HAZ, had corrosion properties as good as the normalized and tempered base metal. Of the various simulated HAZ structures, the intercritical region, which was simulated at 1138 K, possessed the worst corrosion resistance. The weld metal possessed the worst corrosion resistance of the various microstructural regions in the weld joint. The weldment adopted the degraded corrosion properties of the weld metal.     

“原位观察”下的水龙头激光焊接头腐蚀性能分析

采用低耗能激光焊新工艺制造水龙头薄壳,替代传统高污染、高耗能的整体铸造工艺,对304、310 s不锈钢激光焊接头进行沸腾硫酸-硫酸铁及室温浸蚀对比腐蚀研究.在设定的腐蚀时间内,采用“原位观察”腐蚀过程焊缝及熔合区微观组织变化.结果表明,310 s比304耐腐蚀性更好,随腐蚀时间加长,接头熔合区晶粒晶界未明显加宽,焊缝断口微观特征主要为韧窝,证明其未发生晶间腐蚀.焊缝金属成分分析表明焊缝中心晶粒与母材相近,腐蚀沟Cr元素降至20.81%高于12%,保证其耐腐蚀性能.     

Effect of cooling conditions on corrosion resistance of friction stir welded 2219-T62 aluminum alloy thick plate joint

Friction stir welding (FSW) with water cooling and air cooling was used to weld 2219-T62 aluminum alloy joints with a thickness of 20 mm. The effect of cooling conditions on the corrosion resistance of joints in 3.5% NaCl solution was investigated using the open circuit potential (OCP), the potentiodynamic polarization, and the corrosion morphology after immersing for different time. And the precipitates distribution was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that the weld nugget zone (WNZ) owning positive potential, lower corrosion current density and fine and uniform precipitates, is much more difficult to corrode than the heat affected zone (HAZ) and the base metal (BM). Compared with air-cooled joint, the water-cooled joint has better corrosion resistance. In addition, the results of microstructure observation show that the potential, distribution and size of second phase particles determine the corrosion resistance of FSW AA2219 alloy joints in chlorine-contained solution.