Galvanic corrosion of AZ31B joined to dual-phase steel with and without Zn layer by ultrasonic and friction stir welding

Galvanic corrosion of AZ31B joined with bare or Zn-coated DP590 steel by ultrasonic spot welding or linear friction stir welding was quantitatively studied by pre-defining anode and cathode in the lap joint samples. Corrosion volume and depth from Mg anode surfaces exposed to 0.1 M sodium chloride solution was analyzed as functions of cathode surface type and welding method. Characterization of as-welded joints was performed to identify any microstructural feature of the bonding zone that could impact galvanic corrosion behavior.COMSOL modeling with modified user subroutine was conducted to simulate the progression of Mg corrosion in the same joint and electrode configurations used for the corrosion experiments. The experimental results indicated that Zn-coated cathode surface can reduce Mg galvanic corrosion significantly as galvanic polarization and cathodic current on Zn-coated surface remained relatively low for Mg in the weld joints.COMSOL modeling described the growth of Mg galvanic corrosion in a reasonable manner but showed limitation by underestimating the corrosion volume as it did not capture self-corrosion.

Microstructure and Wear Performance of High Volume Fraction Carbide M_7C_3 Reinforced Fe-based Composite Coating Fabricated by Plasma Transferred Arc Welding

The fabrication of high volume fraction （HVF） M7C3 （M=Cr, Fe） reinforced Fe-based composite coating on ASTM A36 steel plate using plasma transferred arc （PTA） welding was studied. The results showed that the volume fraction of carbide M7C3 was more than sixty percent, and the relative wear resistance of the coating tested on a block-on-ring dry sliding tester at constant load （100 N） and variable loads （from 100 to 300 N） respectively was about 9 and 14 times higher than that of non-reinforced a-Fe coating. In addition, under constant load condition the friction coefficients （FCs） of two coatings increased first and then decreased with increasing sliding distance. However, under variable loads condition the FCs of non-reinforced a-Fe based coating increased gradually, while that of HVF MTC3 reinforced coating decreased as the load exceeded 220 N. The worn surface of non-reinforced a-Fe based coating was easily deformed and grooved, while that of the HVF M7C3 reinforced coating was difficult to be deformed and grooved.

Dynamic simulation of resistance spot welding of zinc-coated steels

A model was developed to simulate the temperature distribution and nugget formation during resistance spot welding （ RS1V） of zinc-coated steels. It employs a coupled thermal-electrical-mechanical analysis simulating the dynamic RSW process. Temperature-dependent thermal-electrical-mechanical material properties were considered including contact-resistance. The contact area was determined from a coupled thermal-mechanical analysis. A layer of transition elements was used to represent the change of contact area by killing or activating elements. The heat generation and temperature field were computed in a coupled thermal-electrical model. All these analyses were solved using the commercial finite element method （FEM） based on ANSYS code, and some advanced functions were used by writing a paragraph of codes by the authors. Compared with the results from only coupled thermal-electrical model in which contact area was uniform during the whole process, the result matches better to the experimental results.

Electrode degradation mechanism during resistance spot welding of zinc coated steel using Cu-TiB_2 electrodes

The TiB2 dispersion-reinforced copper-matrix composite used as electrode material in resistance spot welding of zinc coated steels was studied. The service life of the composite electrode reaches （7700） welds, which is 4 times that of the conventional Cu-Cr-Zr electrode. Little gross deformation is observed on the composite （electrodes） because of the higher thermal strength; therefore, it is believed that wear is the only mechanism for the composite （electrode） deterioration. However, both wear and plastic deformation are responsible for the large increase in the tip diameter of the Cu-Cr-Zr electrodes. Moreover, the large deformation of the Cu-Cr-Zr electrodes may contribute to the increased wear rate of the tips.

Monitoring and phenomena observation during YAG laser lap welding of Zn-coated steel sheets

A study was performed with the objectives of understanding lap welding phenomena of Zn-coated steels with a Nd:YAG laser as well as obtaining a fundamental knowledge of monitoring signals for the formation judgment of sound or bad weld beads. The behavior of a molten pool and a reflected beam was simultaneously observed through a high-speed video together with the monitoring of reflected beam intensity.The effect of a gap between sheets on porosity formation and bead appearances was confirmed,and characteristic monitoring signals were obtained according to the gaps.In the case of no gap,spatters were frequently generated,and a reflected beam was fluctuated intensively at low frequencies.On the other hand,in welding sheets with a wide gap,lap welds were not produced and the high frequency signals of a reflected beam were detected.Moreover,sound welds were produced in the sheets with a proper gap,and a moderate reflected beam was monitored.From these results,it was found that monitoring of a reflected beam was beneficial to the judgment of sound,under-filled or incomplete lap welds.

Microstructures and Properties of NiCrBSi/WC Biomimetic Coatings Prepared by Plasma Spray Welding

The NiCrBSi/WC biomimetic coatings were prepared on the low carbon steel substrate by plasma spray welding with mixed powders （WC-Col2＋NiCrBSi） based on the bionic principles, and the coating characteristics were investigated. The results indicate that the coatings have a full metallurgical bond in coating/substrate interface, and consist mainly ofy-Ni, WC, Cr23C6, Cr7C3, Ni3Si, CrsB3, and FeNi3 phases. The powder composition influences the microstructures and properties of the coatings. The WC content and the hardness of coatings increase with the mass fraction of WC-Co 12 powder. The biomimetic coatings have much higher wear resistance compared with the low carbon steel, which is attributed to the combination of hard WC and chromium carbide particles （bionic units） and soft y-Ni matrix in the coatings. It is favorable to prepare the biomimetic coating by plasma spray welding with the mixed powders （20wt%WC-Col2＋80wt%NiCrBSi） for improving the wear resis- tance of the coating.

Synthesis and Surface Modification of Spindle-Type Magnetic Nanoparticles: Gold Coating and PEG Functionalization

In this paper, we describe the synthesis of gold coated spindle-type iron nanoparticles and its surface modification by a thiolated fluorescently-labelled polyethylene glycol (PEG) polymer. A forced hydrolysis of ferric salts in the presence of phosphate ions was used to produce α-Fe2O3 spindle-type particles. The oxide powders were first reduced to α-iron under high temperature and controlled dihydrogen atmosphere. Then, the resulting magnetic spindle-type particles were covered by a shell of gold. The formation of the core@shell structure was driven by a redox-transmetalation reaction between iron(0) at the surface of particles and a gold(III) salt. Protected against oxidation, the Fe@Au core@shell nanoparticles were then grafted with a water soluble fluorescent-PEG-thiol. TEM, XRD, EDX and measurements of magnetic properties of particles confirm 1) the conversion of hematite into iron and 2) their subsequent surface protection with a gold shell. Furthermore, the functionalization of the gold nanoparticle surface with a PEG carrying a fluorescent dye was unambiguously attested by confocal laser scanning microscopy.

不同镀层板的电阻点焊腐蚀行为

[目的]研究点焊对不同镀层板腐蚀行为的影响。[方法]对镀锌板和镀锌铝镁板进行电阻点焊,采用扫描电镜和能谱仪分析了点焊部位的微观形貌和元素分布。通过中性盐雾试验和电化学阻抗谱测试研究了两种板材点焊前后在相同环境下的腐蚀行为。[结果]点焊镀锌板的焊点边缘存在大量凸起和凹坑,而点焊镀锌铝镁板的焊点边缘无明显的凸起和凹坑。二者的焊点位置Zn元素挥发明显,均有部分基体裸露。无论点焊与否,镀锌板在中性盐雾试验中的耐腐蚀能力都不如镀锌铝镁板。[结论]电阻点焊容易导致镀层局部破损,影响镀层的耐蚀性。

无取向硅钢无铬环保涂层激光焊接性能研究

通过金相显微镜、电子背散射衍射(EBSD),研究了无取向硅钢涂层厚度、涂层种类、焊接工艺对焊接性能的影响。研究结果表明,在本实验条件下,涂层厚度与焊接起泡面积百分数呈正比,涂层中的有机物是影响焊接起泡的主要因素,焊接过程中,组织由等轴晶逐渐长大,形成柱状晶,最终形成较大、较均匀的大晶粒。

车顶焊缝涂胶机器人智能视觉系统设计与实现

车顶焊缝是车身密封性最重要、最常用,也是最薄弱的一环,同时也是车身密封性检测中重要组成部分。为了提高车顶焊缝的涂胶质量,必须对其进行准确的检测与涂胶控制。为了使焊接机器人能与车顶焊缝同时实现涂胶,以激光跟踪仪为主要测量仪器,针对车顶焊缝涂胶的需求,设计了一套基于激光跟踪仪的视觉系统,并在此基础上提出了一种基于圆心检测的涂胶策略。该系统能在焊枪扫描过程中实时识别目标对象,通过对目标对象的距离、旋转角度和圆心等参数进行测量,实现对涂胶路径的实时控制。

高参数垃圾电站锅炉防腐涂层体系的设计策略与评价

随着国家“双碳”战略目标的提出,垃圾发电成为城市垃圾处理的主流方式。针对高参数垃圾电站锅炉管道腐蚀减薄到一定程度时,造成泄漏甚至爆管的严重安全问题,本文在简介了高参数对锅炉腐蚀影响规律的基础上,评述了高参数条件下管道的基材特性及主流涂层防护技术,重点论述了Inconel堆焊、感应熔焊、HVOF等技术及性能。因为涂层系统设计主要是对管道基体和涂层材料与工艺进行选配,同时匹配参数也是对涂层系统的主要评价指标,所以本文对热膨胀系数、导热系数、结合强度、孔隙率、服役寿命以及经济性等参数进行了系统评价,并阐述了涂层结构设计策略,包括防腐涂层的厚度设计、涂层结构设计、涂层材料组分设计等内容。根据涂层防护技术现存的主要问题,提出粉末合成设计-涂层结构设计-服役性能评价一体化研究的重要性;针对目前主要的材料体系设计比较集中于高Cr含量的FeCr系和NiCr系合金的现状,指出应开发以NiCr基辅以W、Mo等元素涂层材料,使其兼具优异的耐腐蚀和抗磨损的综合性能。最后对涂层防护技术的发展前景进行展望。

Microstructure of Fe-Based Alloy Hardfacing Coating Reinforced by TiC-VC Particles

Mierostrueture of the Fe-based alloy hardfaeing coating reinforced by TiC-VC particles was investigated by means of SEM, TEM, XRD and EPMA. The thermodynamics and effect of elements on the carbides were discussed. The result shows that TiC-VC carbides can be formed during arc welding. Carbides with particle size of 2 ～4μm are uniformly dispersed in the matrix. Evidently the covering components and their amount affect the microstrueture and hardness of the coatings. An excellent microstructure and hardness of hardfacing coating were obtained, while the amount of graphite, FeTi and FeV was controlled within the range of 8%- 10%, 15%- 18% and 8%- 12%, respectively.

钛合金搅拌摩擦焊搅拌头磨损机理及其涂层强化

为了提高钛合金搅拌摩擦焊搅拌头的寿命,在搅拌头表面增加涂层,对比研究表面涂层的作用机理。本文选用无涂层搅拌头和带AlCrN涂层搅拌头对TC4钛合金进行搅拌摩擦焊(FSW)试验,通过3D影像仪表征搅拌头的磨损情况,采用扫描电镜(SEM)及能谱仪(EDS)对接头的组织及成分进行分析,研究了AlCrN基涂层对搅拌头的寿命影响规律。试验结果表明,对比无镀层搅拌头,带AlCrN基涂层搅拌头的有效焊接距离由600 mm增加到800 mm,且在焊接800 mm后,仍可获得成形良好,抗拉强度达到母材95.32%的焊接接头。另外,带AlCrN基涂层搅拌头的搅拌针和轴肩磨损率分别减少50.41%和22.41%,AlCrN基涂层可有效提高搅拌头的寿命。对比分析搅拌头的磨损情况发现,无涂层搅拌头的磨损包括磨粒磨损、黏结磨损和氧化磨损,其磨损过程主要包含3个阶段:初始磨损阶段、剧烈磨损阶段和稳定磨损阶段。比较而言,带涂层搅拌头的磨损过程则为“打断”和“撕裂”两个阶段。

电阻缝焊制备铁基非晶涂层温度场数值模拟

通过电阻缝焊成功在SUS304上制备出铁基非晶涂层,并测量制备过程的温度热循环.基于Comsol采用电-热耦合的有限元方法,重点分析制备过程电流密度及温度场的动态分布及换热机理,对比温度场的试验和模拟结果可知,相同位置模拟与试验的温度热循环曲线误差很小,验证了电-热耦合方法计算电阻缝焊制备制备铁基非晶涂层温度场的可靠性.结果表明,高电流密度区域主要存在于电极轮正下方粉末层底部的某些点位、以电极轮与粉末层接触面左右两端为中心的邻近区域,铁基非晶涂层制备过程的温度场不仅与电流密度分布相关,还受电极轮移动及涂层与附近区域的热交换所影响,使稳定时,在纵向温度几乎没有变化,在x-z截面呈左边高、右边次之、中间低的“凹”字形分布,相对应的热循环曲线则呈“升-降-升”的整体升温趋势.

铝合金与镀铜钢CMT熔钎焊技术研究

采用Al Si12药芯焊丝作为填充材料,对2 mm厚的6082铝合金与Q235B镀铜钢进行对接冷金属过渡(CMT)熔钎焊接试验,研究不同焊接速度和镀铜层厚度对接头焊缝成型、界面组织和力学性能的影响,探讨Cu元素对金属间化合物层(IMC)生长的影响。结果表明:当焊接速度为350 mm/min时,铝在钢板正反面均有良好的润湿铺展,焊缝成型美观;IMC层厚度过大或过小均会对接头性能产生不利影响,当镀铜层厚度为10μm时,IMC层厚度为2.38μm,接头抗拉强度达到峰值138.7 MPa,相较于未镀铜接头的提高了31.9%,接头断裂于铝侧热影响区。镀铜层可以抑制界面层中θ-Fe(Al,Si)_(3)相的生成,阻碍Al、Fe反应,降低IMC层厚度。适当的镀铜层厚度可以有效改善接头的力学性能。镀铜层厚度过大促使Al_(2)Cu相产生,成为接头的薄弱区域。

Effect of Al_2O_3on Structure and Wearability of Composite Coating

The composite coating was prepared by thermal spray welding after making composite powder,which is composed of Ni-based self-melted alloy and AlOceramic powder including nano,sub-micron and micron powders.The influences of contents and sizes of AlOon the structure and wearability were investigated.The results show that the wear resistance of the coating would be increased greatly by adding AlO,but the spray weldability decreases with increasing AlOcontent.So there is an optimal content of AlOpowder.The composite coating with AlOnano or sub-micron powder of 0.5% has the best abrasive resistance,while the optimal content of AlOmicron powder is 1 %.

Improvement in hot corrosion resistance of dissimilar alloy 825 and AISI 321 CO2-laser weldment by HVOF coating in aggressive salt environment at 900℃

This study investigated the hot corrosion performance of a dissimilar weldment of Ni-based superalloy and stainless steel joined by CO2-laser welding and improved by high-velocity oxy-fuel(HVOF)coating in a Na2SO4-60wt%V2O5 environment at 900℃.A dissimilar butt joint of AISI 321 and alloy 825 was fabricated by CO2-laser welding with low heat input after obtaining the optimum welding parameters by bead-on-plate trials.The metallurgical and mechanical properties of the laser weldment were evaluated.The tensile test results indicated the occurrence of fracture in the base metal AISI 321 side.The HVOF process was employed to coat Ni-20wt%Cr on the weldment.To evaluate the surface morphology of the corrosion products formed on the uncoated and Ni-20wt%Cr-coated weldments,scanning electron microscopy(SEM)analysis was performed.Energy-dispersive spectroscopy(EDS)was used to determine the different elements present on the surface scales.The existence of oxide phases on the weldments was determined by X-ray diffraction(XRD).The cross sections of the weldments were characterized by SEM with EDS line mapping analysis.The results indicated that the Ni-20wt%Cr-coated weldment exhibited superior hot corrosion resistance due to the development of Cr2O3 and NiCr2O4 protective oxide scales.

Evolution behavior of phase and performance in Ni-based coating layer based on high temperature thermal field

Effect of post-welding heat treatment on the microstructure and properties of BNi-2 brazing coating was analyzed. The phase transformation in the heat treatment process was analyzed by high temperature metallographic microscope, scanning electron microscope and X-ray diffraction, and the microhardness after the post heat treatment was tested by microhardness tester. The results show that the microstructure of brazing BNi-2 brazing coating is mainly CrB phase, Ni solid solution phase and eutectic phase of Ni_(3)B and Ni_(3)Si. After brazing,the overall hardness value is higher, generally higher than 510 HV, and the microhardness in some areas is higher than 700 HV. After quenching, the solid solution phase of Ni increased, and the eutectic phase of Ni and Ni_(3)Si decreased, leading to the softening of the brazing coating, the area whose microhardness in the range of 342 HV–454 HV increased. After tempering the brazed coating samples, the eutectic phases of Ni and Ni_(3)Si grew and the hardness recovered, but the overall hardness distribution was still lower than the brazing one. The results of the brazing post-heat treatment test show that the post-welding heat treatment will bring adverse effects on the hardness distribution of the coating, which may affect the wear resistance of the coating.

PEMFC金属双极板金涂层原电池腐蚀机理研究

为了追求低接触电阻和高耐腐蚀性能,金涂层虽然成本高昂但是仍然在金属双极板涂层中得到广泛应用。通过镀金涂层金属双极板在3000 h电堆实际测试分析了金涂层的电化学腐蚀情况,同时采用电化学加速测试分析了其原电池腐蚀机理。研究结果表明,金属双极板金层在寿命测试过程中首先因为点蚀而出现轻微缺陷,钛层裸露到质子交换膜燃料电池(PEMFC)的酸性环境中而与金层形成原电池腐蚀。本研究将有助于提出缓解金涂层腐蚀失效的方案,为镀金涂层金属双极板在PEMFC上的应用提供理论指导。

Sn95Sb5焊料与ENIG/ENEPIG镀层焊点界面可靠性研究

研究了Sn95Sb5焊料在化学镍金(ENIG)镀层、化学镍钯浸金(ENEPIG)镀层表面形成的焊点界面微观组织形貌与剪切强度。使用Sn95Sb5焊料在FR4印制板上焊接0805片式电容,焊点在高温时效测试和温度循环过程中均表现出较高的剪切强度,焊点界面连续且完整,剪切强度下降的最大幅度不超过19.2%。Sn95Sb5焊料在ENIG镀层表面形成的焊点(Sn95Sb5/ENIG焊点)强度更高。Sn95Sb5焊料在ENEPIG镀层表面形成的焊点(Sn95Sb5/ENEPIG焊点)界面反应更为复杂,在焊点界面附近可观察到条块状的(Pd,Ni,Au) Sn4。Sn95Sb5/ENEPIG焊点界面的金属间化合物层平均厚度约为Sn95Sb5/ENIG焊点界面的2倍。