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铝合金电阻点焊中电极点蚀的形成机制 总被引:1,自引:0,他引:1
建立了铝合金电阻点焊过程数值模拟的有限元分析模型,考察了焊接过程中电极与试件界面上接触半径的变化,以及电极尖端表面上电极压力、电流密度和温度的分布.结果表明:所考察的焊接条件下,接触半径在焊接过程中逐渐增大,电极端面的中部温度最高,而电极压力和电流密度均在接触区边缘集中.实验研究发现电极表面上最初的点蚀部位呈环形,其半径与接触区半径基本一致,由此推断,环状电极点蚀主要是接触区边缘明显的应力集中所致.为减少电极点蚀提高电极寿命,电极的形状设计应使电极与工件接触界面上的应力集中尽可能减小. 相似文献
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采用动电位极化、交流阻抗(EIS)和电化学噪声(ECN)等电化学方法研究了304不锈钢微电极的腐蚀行为。实验结果表明:极限扩散电流密度与电极尺寸之间具有非线性关系,随着电极面积的减小,极限扩散电流密度增大,溶液阻抗减小,双电层电容增大,自腐蚀电位负移,腐蚀电流密度增大。电化学噪声谱表明,随着电极面积减小,亚稳态点蚀噪声峰的频度降低,亚稳态点蚀的发生存在一个临界尺寸。 相似文献
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对1Cr13不锈钢点蚀电位的离散分布进行统计分析,利用点蚀发生概率、门槛电流密度和电极电位的关系,结合直线外延法推测出在极限门槛电流密度下,零概率点蚀电位,即极限零概率点蚀电位,可以作为评价材料耐点蚀性能的参数。 相似文献
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热镀锌高强钢由于高强度特性以及良好的抗腐蚀性,可满足汽车轻量化与安全性需要,在车身制造中逐渐得到广泛应用.但热镀锌高强钢点焊的电极磨损严重,点蚀磨损特征变化明显,对熔核形成产生较大影响.建立点焊过程的点蚀有限元模型,采用数值分析与试验方法研究点蚀对熔核形成影响.结果表明,点蚀的产生与发展增加了工件之间的实际接触面积,使电流密度降低,熔核直径减小;同边缘位置点蚀相比,电极中心位置点蚀由于对熔核区域的电流分流作用,更加不利于熔核的形成.随着点蚀面积的增大,形成环状熔核几率增加. 相似文献
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热镀锌钢板点焊的点蚀对电极使用寿命的影响 总被引:1,自引:0,他引:1
热镀锌钢板点焊时电极磨损严重,点蚀特征变化明显.建立点焊过程中的电极端面接触电阻模型与接触热阻模型,分析点蚀变化对电极使用寿命的影响,并进行相应试验验证.结果表明.点蚀的产生与发展使电极端面接触电阻与接触热阻增大,导致电极端面温度升高、电极使用寿命降低.试验研究表明,热镀锌钢板点焊的点蚀区域在高温高压下容易产生微裂纹,镀锌层金属元素沿微裂纹渗八电极的内部,加速了电极失效. 相似文献
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This work investigated the effects of chloride ions and hydrogen-charging on the passivity and pitting corrosion behavior
of X80 pipeline steel in a bicarbonate-carbonate solution by electrochemical and photo-electrochemical techniques. It was
found that a stable passivity can be established on the steel in the absence and presence of chloride ions. The hydrogen-charging
does not alter the transpassive potential, but increases the passive current density. When chloride ions are contained in
the solution, pitting corrosion will be initiated. The pitting potential is independent of the hydrogen-charging. Hydrogen-charging
would enhance the anodic dissolution and electrochemical activity of the steel, but does not affect the pitting potential,
which indicates that the charged hydrogen is not involved in the pitting initiation. However, hydrogen may accelerate the
pit growth. Photo illumination could enhance the activity of the steel electrode, resulting in an increase of photo-induced
anodic current density. 相似文献
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Pit initiation at the passive alloy Fe5 Cr was studied and compared to the results obtained with pure iron. At constant electrode potential the addition of chloride to the solution increases the dissolution rate of Fe(III). Above the critical pitting potential the first pits develop during a time of incubation after addition of chloride. The total current density and the dissolution rate of Fe(II) rise simultaneously and suddenly. The logarithm of the times of incubation increase linearly with the reciprocal of the difference between the actual electrode potential and the pitting potential. Galvanostatic experiments show that, with Fe 5 Cr as with iron, chloride catalyzes the transfer reaction of oxygen ions at the interface between oxide and electrolyte more strongly than the dissolution of Fe(III). Addition of chloride. The total current density and the dissolution rate of Fe(II) rise simultaneously and suddenly. The logarithm of the times of incubation increase linearly with the actual electrode potential and the pitting potential. Galvanostatic experiments show that, with Fe5Cr as with iron, chloride catalyzers the transfer reaction of oxygen ions at the interface between oxide and electrolyte more strongly than the dissolution of Fe(III). Addition of Chromium lowers the current efficiency of Fe(III) dissolution and favors oxide growth. The ionic conductivity of the passivating oxide is not significantly changed by chloride but is lowered by chromium. Fluctuations connected to the onset of pitting are slower with Fe 5 Cr than with iron. 相似文献
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Finite element analysis of effect of electrode pitting in resistance spot welding of aluminium alloy
《Science & Technology of Welding & Joining》2013,18(1):61-66
AbstractThe effect of electrode pitting on the formation of the weld nugget in resistance spot welding of an aluminium alloy was investigated using the finite element method. Pitted electrodes were simulated by assuming a pre-drilled hole of varying diameter at the centre of the electrode tip surface. The results showed that a small pitting hole would not have a detrimental influence on the nugget size. The actual contact area at the electrode/sheet interface did not change significantly when the diameter of the pitting hole was increased. However, a large pitted area at the electrode tip surface resulted in a greatly increased contact area and hence reduced current density at the sheet/sheet interface, which in turn led to the formation of an undersized weld nugget. The numerical calculation of the nugget shape and dimensions agreed well with experimental observations. 相似文献
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Effects of alternating current on corrosion of a coated pipeline steel in a chloride-containing carbonate/bicarbonate solution 总被引:1,自引:0,他引:1
A.Q. Fu 《Corrosion Science》2010,52(2):612-619
In this work, the alternating current (AC)-induced corrosion of a coated pipeline steel was studied in a chloride-containing, concentrated carbonate/bicarbonate solution, which simulated the trapped high pH electrolyte under coating, by potentiodynamic polarization measurements, immersion tests and surface characterization technique. It was found that an application of AC resulted in a negative shift of corrosion potential of the steel, caused an oscillation of anodic current density, and degraded the steel passivity developed in the solution. With the increase of AC current density, the corrosion rate of the steel increased. At a low AC current density, a uniform corrosion occurred, while at a high AC current density, pitting corrosion occurred extensively on the steel electrode surface. At individual applied AC, there was a higher electrochemical dissolution activity of the coated steel electrode containing a 1 mm defect than that of the electrode containing a 10 mm defect. 相似文献
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通过动电位极化和恒电位极化研究了Cl-浓度对304不锈钢在模拟混凝土孔隙液(pH 12.6)中亚稳态点蚀的影响,并利用极值统计分布研究了亚稳态点蚀的峰值电流密度(Ipeak),亚稳态点蚀半径(rpit),亚稳态点蚀稳定性乘积(Ipeak·rpit)以及单个亚稳态点蚀的生长时间(tgrow),再钝化时间(trep),生长率(Kgrow)和再钝化率(Krep)。结果表明,在碱性介质中,Cl-浓度增加会促使亚稳态点蚀更易转变为稳定点蚀。 相似文献
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Flow dependence of the pitting corrosion of CrNi steel in NaCl solution Test (with CrNi steel 19 9 in 1 N NaCl) with supersonic agitation have confirmed the results obtained with the rotating disc electrode. Supersonic treatment increases the pitting potential for stable pitting and reduces maximum corrosion current density. The treatment has but little effect, however, on the pitting potential for repassivating pitting corrosion. Cycling tests under galvanostatic conditions show that the effect supersonic action comes to bear almost immediately. Switching on or off the supersonic source results in immediate repassivation or loss thereof. Similar to experiments on rotating discs the pits are very small and, consequently, constitute practically no corrosion risk. 相似文献