铝合金等离子弧立焊穿孔熔池的计算机模拟

根据流体力学理论和传热学机理,建立了运动等离子弧作用下立焊穿孔焊接熔池流场和温度场的三维瞬态数值分析模型,并采用有限元法对模型进行离散化处理。模型中,考虑了熔池内部液态金属的对流传热和熔池外部的固体导热、材料热物理性能参数随温度的变化、焊件表面通过对流和辐射向周围环境的散热以及熔化／凝固相变潜热对熔池流场与温度场的影响,焊接热源采用高斯分布函数,计算中对边界条件进行了处理,根据穿孔熔池温度场与流场模型的特点,采用非均匀网格对单元进行划分,并采用分区异步长算法确定时间步长,利用ANSYS(一种有限元计算软件)有限元软件对所建立的模型进行了求解。通过试验测量焊缝几何尺寸与计算结果相比较,验证了本模型的计算结果和实际相差不大,是基本正确和可靠的。     

铝合金穿孔型等离子弧立焊的BP神经网络预测模型

基于MATLAB6.1的神经网络工具箱 ,利用BP神经网络建立铝合金穿孔型等离子弧立焊的输入 -输出的网络模型 ,通过训练该网络 ,能够根据输入节点数值预测输出结果。当给定网络输入节点的各个焊接工艺参数值 ,能够预测网络的输出 ,即焊缝形状的各个参数。用这个工艺的匹配值进行焊接试验。结果表明 ,焊缝的形状参数与网络模型的预测结果之间的误差在 8%以内。仿真试验的结果表明 ,这个方案是可行的。     

等离子弧产生臭氧机理及防治措施

介绍了等离子弧产生臭氧机理及对人体的危害，实测表明，在等离子弧区，影响臭氧浓度的主要工艺参数是电流，电流愈大，紫外幅射愈强，产生臭氧愈多，提高５０Ａ电流，等离子弧区臭氧浓度可增加１６．９％，因此对臭氧危害应采取“防”和“治”两方面措施。所谓“防”是指正确调节等离子弧工艺参数，在满足工艺要求条件下，尽量降低电流，减少气体流量；所谓“治”是指合理安装排风除尘装置，把等离子弧产臭氧及粉尘对人体危害控制在     

等离子弧喷焊分布式微机控制系统的研究

以等离子弧喷焊为例，介绍了分布式控制系统对焊接过程进行控制的原理和方法，提出当控制对象较多时，采用计算机分级结构，即以一个主计算机和多个从计算机为基础的结构体系，可达到理想的综合控制效果。试验结果表明，采用分散控制，集中管理的方法，使系统的可靠性大大提高，控制更加灵活，精度更高，功能更强。     

焊粉受潮对等离子弧堆焊层气孔的影响

某先进堆型高温液态金属泵的静压轴承内壁需大面积堆焊司太立合金,由于司太立合金硬度高、韧性差,堆焊过程中预热温度高,熔池冷却速度慢,且连续堆焊时间长,堆焊层易出现裂纹、未熔合、气孔等问题.针对堆焊层内部出现的气孔,逐一排查可能原因,确定主要原因是焊粉受潮.对焊粉进行烘干试验和烘干前后的堆焊试验,再现了焊接缺陷,由此规定焊...     

5052铝合金交流脉冲等离子弧焊接工艺

采用交流等离子焊接方法,使用焊材ER5356对8 mm 5052铝合金进行了等离子弧立向上焊接试验。通过合理的设计焊接工艺和严格控制焊接关键因素,解决了5052铝合金焊接性的问题。结果表明,交流等离子弧焊接方法适用于5052铝合金的焊接,根据标准对焊接接头进行力学性能检测、X射线检测与焊接接头金相分析。结果表明,焊接接头弯曲和拉伸性能符合检测标准要求,冲击吸收能量在15 ℃条件下均大于19 J;焊缝无气孔、夹渣等缺陷,焊缝中组织基体为α(Al)固溶体。     

焊接电弧及性质和等离子弧及特点

电弧是一种空气导电的现象,在两电极之间产生强烈而持久的放电现象,称为电弧。     

铸钢件内孔等离子弧喷焊修复技术

材料为ZG310-570的铸钢件因承受冲击载荷的频繁作用导致其内孔磨损失效,是该类铸钢件最主要的失效形式。利用粉末等离子弧喷焊技术对铸钢件受损内孔进行修复,并利用火花直读光谱仪、金相显微镜、布氏硬度计、冲击试验机和扫描电子显微镜分别对喷焊层外观质量、显微组织和力学性能进行分析。分析结果表明,采用粉末等离子弧喷焊修复方法使铸钢件内孔尺寸得到恢复;喷焊层与基体为冶金结合,结合线清晰;喷焊层的硬度值为267.5 HBW,优于基体材料的180.2 HBW,修复后的内孔冲击吸收功为15.40 J,满足技术要求;喷焊层的断口存在大量撕裂,说明喷焊层具有一定的冲击韧性。     

玻璃模具型腔等离子弧喷焊工艺试验

采用等离子弧喷焊工艺方法,选用镍基合金粉末在玻璃模具型腔的关键部位进行了等离子弧喷焊工艺试验,对喷焊层金属的显微组织进行了分析,测试了喷焊层的显微硬度.试验结果表明,喷焊层与基体为冶金结合,喷焊层呈枝状晶组织,硬度达到HV296.通过对玻璃模具型腔进行等离子弧喷焊镍基合金,玻璃模具的耐磨性、抗高温氧化性能得到显著提高,其使用寿命也得到延长.     

穿孔法变极性等离子立焊的收弧过程

研究了穿孔法等离子弧焊的收弧规律。发现焊接电流、离子气流量和焊接速度对收弧过程影响较大。在收弧阶段采用适当焊接电流,增大送丝速度,减小离子气流量和焊接速度,以增加焊接热输入,可以实现收弧弧坑的填充。对于不同厚度的铝合金,收弧阶段的规范参数有一最佳区间。研究了收弧坑的接头性能,其抗拉强度和伸长率均不低于中间焊缝。     

A new type of pilot arc power source used for A．C． plasma arc welding of aluminum alloys

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Impact of transient chemistry on the corrosion potential of a steam turbine disc steel

The adoption of two-shifting in coal-fired power generation (switching from on-load to off-load conditions on a daily basis and off-load for the weekend) results in regular cycling of the solution chemistry of the condensed steam on the turbine discs. A first stage investigation has been made of the effect of such chemistry cycling on the corrosion potential of the disc steel. The corrosion potential is typically about +0.05 V (SCE) in off-load chemistry (aerated pure water) and below −0.6 V (SCE) in on-load chemistry (deaerated solution containing chloride or chloride and sulphate anions). The critical observation was the sluggish response of the corrosion potential upon restoration of deaerated on-load conditions with the implication of a likely increase in pit and stress corrosion crack development.     

同步方波交流电源负半波时间随总电流增加而增加的原因

对同步方波交流电源（ＳＹＮＣＲＯＷＡＶＥ－３００（Ｓ）方波交流电源）的负半波时间随总电流增加而增加的原因进行了详细的试验研究和理论分析。结果表明：这种陡降特性的可控硅－电抗器式的交流电源的总电流的增加必须通过增加负半波的时间才能实现。这将会造成铝合金交流ＴＩＧ焊和等离子弧焊在大电流焊接时钨极严重烧损,降低电弧和焊缝成型的稳定性。该结论不但对更好地理解可控制硅－电抗器式方波交流电源的工作原理有重要的     

交流MAG焊接电弧稳定性及其控制

介绍了一种新型交流ＭＡＧ焊接电弧稳定性及其控制的研究成果,提出了一种崭新的双凹电流波形,解决了ＭＡＧ焊交流电弧稳定这个一直很难解决的问题,对交流脉冲ＭＡＧ焊接电弧稳定性进行了较为系统的研究表明,脉冲参数是影响电弧稳定和实现合理的最主要因素,保护气体成分和流量、稳弧剂也是重要的影响因素。经过精收配置焊接参数的交流脉冲ＭＡＦＧ焊接法能实现电弧稳定并具有较合理的熔滴过渡形式,是一种具有重要应用前景的焊接     

Effect of Fe-Zn alloy layer on the corrosion resistance of galvanized steel in chloride containing environments

In this study, the effect of Fe-Zn alloy layer that is formed during galvanizing process on the corrosion behavior of galvanized steel has been investigated. The galvanostatic dissolution of galvanized steel was carried out in 0.5 M NaCl solution to obtain the Fe-Zn alloy layer on the base steel. The alloy layer was characterized to be composed of FeZn₁₃, FeZn₇ and Fe₃Zn₁₀ intermetallic phases, which constitute the zeta, delta1 and gamma layers of galvanized steel, respectively. It was observed that the alloy layer has similar cathodic polarization behavior but different anodic polarization behavior compared to galvanized steel. The anodic current plateau of alloy layer was up to 100 times lower than that of galvanized coating. Corrosion test performed in wet-dry cyclic condition has shown that the alloy layer has lower corrosion rate as compared to galvanized steel. From the results of corrosion test of alloy layer and base steel, it was concluded that Zn²⁺ has positive effect on the protectiveness of the zinc corrosion products. The measurement of surface potential over the alloy/steel galvanic couple has confirmed the galvanic ability of alloy layer to protect both the alloy layer itself and the base iron during initial stage of atmospheric corrosion.     

Limits determination of toleration of aggressive anions by a certain passivator on zinc surface

The open circuit potentials of Zn electrode were followed as a function of time in different concentrations Na₂B₄O₇ solutions until steady-state, E_st., values were attained. The potential shifts immediately towards positive values, indicating film thickening and repair. The effect of addition of NaCl, NaBr and NaI as aggressive agent on the steady-state potential of a Zn electrode previously equilibrated in a passivating borate solution was also established. For each Na₂B₄O₇ concentration, the variation in the potential with the quantity of aggressive anions follows an S-shaped relationship. The new potentials are established after an induction period which decreases with the increase in the concentration of the aggressive anion, C_agg., and/or decreases in that of the passivator anion, C_pass.. The concentration, C_agg., that can be tolerated by a certain concentration of the passivator anion, C_pass., is given by the relation: log C_pass. = k + n log C_agg., where k and n are constants. This is derived on the basis of competitive adsorption of both types of anion and the structure of the double layer at the metal/solution interface. The implications of the equations are briefly discussed.     

Oxide film formation on zinc in borate solutions under open circuit

The open circuit potentials of Zn electrode were followed as a function of time in different concentration of Na₂B₄O₇ solution until steady-state, E_st., values were attained. The potential shifts immediately towards positive values, indicating film thickening and repair. The rate of oxide film thickening was determined from the linear relationship between the open circuit potential, E, of the Zn electrode and the logarithm of immersion time t as E = a₁ + b₁ log t. The liner plots consist of two segments indicating the duplex nature of the formed oxide film on the Zn surface. The final steady- state potential, E_st., varied with the logarithm of molar concentration of Na₂B₄O₇ solution according to: E_st. = a₂ − b₂ log C_Na2B4O7. The effect of rising pH and temperature was also studied. It was found that the rising of pH and temperature of the solution affect on the rate of oxide film thickening and the final steady- state potential.     

Film conversion and breakdown processes on carbon steel in the presence of halides

The kinetics of oxide film formation/conversion on carbon steel in the presence of halide anions at pH 10.6 were studied by electrochemical and surface analytical techniques. While variations in breakdown potential are observed in the presence of the different halides, the breakdown potential does not show any systematic dependence on halide type and concentration, and never occurs below 0.0 V vs. SCE. It is proposed that the conversion of Fe₃O₄/γ-Fe₂O₃ to γ-FeOOH leads to a volume change, causing the film to fracture. The halide anion then takes advantage of the opportunity to accelerate breakdown and inhibit repassivation.     

Molten glass corrosion resistance of MoxRuySiz compounds at 1350 °C in an alkali borosilicate glass

Corrosion of Mo-silicides and Mo_xRu_ySi_z compounds in molten glass is studied by electrochemical techniques at 1350 °C, metallographic observations (SEM) and chemical analysis (EPMA). The open circuit potential measurements (free-potential) enabled the determination of the reactions responsible for the degradation of the materials.The degradation of Mo-silicide occurs through selective oxidation of Si. Mo_xRu_ySi_z compounds were subjected to reactions leading to the successive oxidation of silicon and molybdenum. The progressive depletion of Si and Mo resulted in the more or less quick formation of a thick, porous and low adherent Ru-layer. Therefore, Ru-additions had no positive effect on the molten glass corrosion resistance of MoSi₂-based materials and should even accelerate the degradation kinetics of the later through galvanic coupling.