Effect of Pulsed Current TIG Welding Parameters on Pitting Corrosion Behaviour of AA6061 Aluminium Alloy

中等力量铝合金( Al-Mg-Si 合金)收集了轻重量的制造组织要求高力量重量比率的宽 acceptancein ，如此的 astransportable 桥 girders ，军事车辆，为铝合金焊接过程的道路油轮和铁路运输 systems.Thepreferred 经常是 TIG (钨惰性的气体)焊接到期的 toits 比较地更容易的适用性和更好的 economy.In 焊接这合金的 ofthinner 节的单个通行证 TIG 的盒子。

Pitting corrosion resistance of a novel duplex alloy steel in alkali-activated slag extract in the presence of chloride ions

In this study, two types of reinforcing steels(conventional low-carbon steel and a novel duplex alloy steel with Cr and Mo) were exposed to chloride-contaminated extract solutions(ordinary Portland cement(OPC) extract and alkali-activated slag(AAS) extract) to investigate their pitting corrosion resistance. The results confirm that the pitting corrosion resistance of the alloy steel is much higher than that of the low-carbon steel in both extract solutions with various Na Cl concentrations. Moreover, for each type of steel, the AAS extract contributes to a higher pitting corrosion resistance compared with the OPC extract in the presence of chloride ions, likely because of the formation of flocculent precipitates on the steel surface.

Role of Chloride Ion and Dissolved Oxygen in Electrochemical Corrosion of AA5083-H321 Aluminum-Magnesium Alloy in NaCl Solutions under Flow Conditions

Flow-induced corrosion consists electrochemical and mechanical components. The present paper has to assessed the role of chloride ion and dissolved oxygen in the electrochemical component of flow induced corrosion for AA5083-H321 aluminum-magnesium alloy which is extensively used in the construction of high-speed boats, submarines, hovercrafts, and desalination systems, in NaCI solutions. Electrochemical tests were carried out at flow velocities of 0, ：2, 5, 7 and 10 m/s, in aerated and deaerated NaCI solutions with different sodium chloride concentrations. The results showed that the high rate of oxygen reduction under hydrodynamic conditions causes an increase in the density of pits on the surface. The increase of chloride ions concentration under flow conditions accelerates the rate of anodic reactions, but have no influence on the cathodic reactions. Thus, in the current work, it was found that under flow conditions, due to the elimination of corrosion products inside the pits, corrosion resistance of the alloy is increased.

Influence of chloride ion concentration on immersion corrosion behaviour of plasma sprayed alumina coatings on AZ31B magnesium alloy

Corrosion attack of aluminium and magnesium based alloys is a major issue worldwide.The corrosion degradation of an uncoated and atmospheric plasma sprayed alumina(APS)coatings on AZ31B magnesium alloy was investigated using immersion corrosion test in NaCl solutions of different chloride ion concentrations viz.,0.01 M,0.2 M,0.6 M and 1 M.The corroded surface was characterized by an optical microscope and X-ray diffraction.The results showed that the corrosion deterioration of uncoated and coated samples were significantly influenced by chloride ion concentration.The uncoated magnesium and alumina coatings were found to offer a superior corrosion resistance in lower chloride ion concentration NaCl solutions(0.01 M and 0.2 M NaCl).On the other hand the coatings and Mg alloy substrate were found to be highly susceptible to localized damage,and could not provide an effective corrosion protection in solutions containing higher chloride concentrations(0.6 M and 1 M).It was found that the corrosion resistance of the ceramic coatings and base metal gets deteriorated with the increase in the chloride concentrations.

Morphology Characterization and Kinetics Evaluation of Pitting Corrosion of Commercially Pure Aluminium by Digital Image Analysis

The pit morphology and growth kinetics of commercially pure aluminium in naturally aerated NaCl solutions were studied using an image processing method based on reflected light microscopy. In order to distinguish between pits and pre-existing cavities, metallographic examination and statistical analysis were carried out before and after corrosion testing. The results show that the pit shapes and sizes are more dependent on the immersion time than the chloride concentration. Pits are predominantly hemispherical, but they undergo reasonable geometric transitions associated with increased immersion time and occur without significant depth variation. The role of chloride ions is more closely associated with the pit nucleation phenomenon.

Tetrahydro-dibenzo[a,d]Annulene-5,11-Dihydrazone and Magnesium Oxide Used to Control the Corrosion of Aluminium in Chloride Ions Environment

Chloride ions interact with aluminium in marine atmosphere to form corrosion cell.Due to this corrosion reaction occurs on their surface,aluminium is oxidized into Al3+.The corrosion reaction accelerates deterioration in metal and it produces galvanic,pitting,stress,crevice,intergranular corrosion.Chloride ions decrease internal and external strength of aluminium metal.It is a very important metal so used in different appliances for e.g.road,water,air transports,housing,railways and other fields.Nanocoating and electrospray techniques used to check the corrosion of aluminium metal.For nanocoating and electrospray materials applied tetrahydro-dibenzo[a,d][7]annulene-5,11-dihydrazone and MgO.Both materials formed composite barrier and developed a passive surface for Cl-ions.This barrier reduced the corrosion rate of aluminium.Nozzle spray and chemical vapour deposition technique used for coating process.The corrosion rate of metal was determined by gravimetric method.Corrosion potential and current density were calculated by potentiostat.The composite barrier formation was confirmed by activation energy,heat of adsorption,free energy,enthalpy and entropy.These thermal parameters were obtained by Arrhenius equation,Langmuir isotherm and Transition state equation.The adsorption of tetrahydro-dibenzo[a,d][7]annulene-5,11-dihydrazone and MgO electrospray on aluminium surface was depicted by Langmuir,Frundlich and Temkin isotherm.The results of surface coverage area and coating efficiency were noticed that both materials were mitigated the corrosion rate of aluminium in chloride ions environment.

Effects of chloride ion concentration and pH values on the corrosion behavio of Cr12Ni3Co12Mo4W ultra-high-strength martensitic stainless steel

The effects of Cl ion concentration and pH values on the corrosion behavior of Cr12Ni3Co12Mo4W ultra-high-strength martensitic stainless steel（UHSMSS） were investigated by a series of electrochemical tests combined with observations by stereology microscopy and scanning electron microscopy. A critical Cl- ion concentration was found to exist（approximately 0.1wt%）, above which pitting occurred. The pitting potential decreased with increasing Cl- ion concentration. A UHSMSS specimen tempered at 600°C exhibited a better pitting corrosion resistance than the one tempered at 400°C. The corrosion current density and passive current density of the UHSMSS tempered at 600°C decreased with increasing pH values of the corrosion solution. The pits developed a shallower dish geometry with increasing polarization potential. A lacy cover on the pits of the UHSMSS tempered at 400°C accelerated pitting, whereas corrosion products deposited in the pits of the UHSMSS tempered at 600°C hindered pitting.

Dry passivation of austenitic SUS 301L stainless steel against pitting corrosion in marine atmospheric environment

Being an exclusive construction material for lightweight rail vehicles,protection from pitting corrosion in harsh marine atmospheric environment in high humidity and Cl-ion concentration is critical for austenitic SUS 301L stainless steel(SS),especially when it inevitably suff ers from mechanical damages during post disposals.Herein,an innovative dry passivation method for austenitic SUS 301L SS was established in a closed air atmosphere at low temperature and constant pressure.The process parameters were optimized,and the passivation mechanism was explained using polarization curve,electrochemical impedance spectroscopy(EIS),X-ray photoelectron spectroscopy(XPS),and contact angle measurement.The pitting corrosion susceptibility of the passive fi lm prepared in a closed air chamber under 1.0×10^(5) Pa at 80℃ for 80 min was evaluated in 3.5%NaCl solution and exhibited higher pitting potential and corrosion resistance,lower passivity-maintaining current density,and wettability when compared with conventional nitric acid treatment.Besides,dry passivation facilitated the repairing of the surface structural defect itself and the post-processing damage,similar to the accelerated aging of fi lm.The decrease in oxygen concentration and convection-diff usion strengthened the preferential chromium oxidation to form a compact chromium-rich passive fi lm to resist the aggression of Cl-ion.

Pitting Corrosion Behaviour of Monel-400 Alloy in Chloride Solutions

Pitting corrosion behaviour of Monel-400 alloy in 3.5 wt pct NaCl sodium chloride solution has been investigated using the cyclic potentiodynamic anodic polarization technique. The effect of chloride ion concentration, pH values and difFerent temperatures on the pitting parameters were determined. The morphology of the pits produced after anodic polarization treatments was inspected by scanning electron microscope (SEM). The results indicated that, the increase in chloride ion concentration shifts Epit and Eprot of the alloy toward negative values and the pitting potential is much more dependent on pH value in the basic region. The breakdown of passivity with increasing temperature may be due to kinetic changes of passivating films and dissolution rate of the alloy in its passive state

Synergistic effect of chloride ion and Shewanella algae accelerates the corrosion of Ti-6Al-4V alloy

The increasing utilization of titanium alloys in marine environments makes their microbiologically influenced corrosion study a timely matter.This work demonstrated that the corrosion ofTi-6 Al-4 V alloy was accelerated by a marine bacterium Shewanella algae in 2216 E medium with different Cl-level.Various electrochemical,pitting morphology and passive film analyses demonstrated that S.algae weakened the passive film,which made Cl-more aggressive.The synergy of those two factors caused considerable corrosion acceleration of the titanium alloy,leading to a maximum pit depth of 3.2μm and corrosion current density of 26.5 nA cm_(-2) in 2216 E medium with 3.50%(w/w)Cl^(-).

Corrosion and electrochemical behavior of AZ31D magnesium alloys in sodium chloride

The corrosion and electrochemical behavior of extruded AZ31D magnesium alloys in NaCl solution were investigated using SEM, XRD and electrochemical method. It is found that AZ31D is susceptive to Cl- ion, and the open circuit potential shifts to more negative values with increasing chloride concentration. Pitting occurs at corrosion potential and corrosion area enlarges with enhanced polarization. Tafel slopes of the cathode branches in different testing solution are almost the same. Cl-concentration affects cathode course slightly. High frequency capacitive loops shrink with the increase of Cl- concentration. Corrosion initiates from the grain boundary and spreads to entire surface with time.

Corrosion Resistance ofAA6063-Type AI-Mg-Si Alloy by Silicon Carbide in Sodium Chloride Solution for Marine Application

The present work focused on corrosion inhibition of AA6063 type Al-Mg-Si alloy in sodium chloride(Na Cl) solution with a silicon carbide inhibitor, using the potentiodynamic electrochemical method. The aluminium alloy surface morphology was examined, in the as-received and as-corroded in the un-inhibited state, with scanning electron microscopy equipped with energy dispersive spectroscopy(SEM-EDS). The results obtained via linear polarization indicated a high corrosion potential for the unprotected as-received alloy. Equally, inhibition efficiency as high as 98.82% at 10.0 g/v silicon carbide addition was obtained with increased polarization resistance(Rp), while the current density reduced significantly for inhibited samples compared to the un-inhibited aluminium alloy. The adsorption mechanism of the inhibitor aluminium alloy follows the Langmuir adsorption isotherm. This shows that the corrosion rate of aluminium alloy with silicon carbide in Na Cl environment decreased significantly with addition of the inhibitor.

Effects of cupric ions on the corrosion behavior of aluminum alloy 5A02 in ethylene glycol–water solution

The effects of cupric ions on the corrosion behavior of aluminum alloy 5A02 in ethylene glycol–water solutions were studied by potentiodynamic polarization,electrochemical noise(EN),and complementary techniques including scanning electron microscopy(SEM),atomic force microscopy(AFM),and X-ray photoelectron spectroscopy(XPS). A positive corrosion potential and increased corrosion current were observed due to the deposition of copper. The results demonstrate that the main corrosion type was pitting and the increasing cupric ion concentration augmented the pitting density. The pits became larger and deeper as a result of the embedment of copper into the surface of the alloy. Cupric ions were preferentially deposited at the defects around the secondary phase,leading to the formation of Al–Cu microgalvanic couples,which increased the corrosion rate. The corrosion rate gradually reached a stable value as the concentration of cupric ions was increased beyond 10 mmol/L.

Effects of Anodizing Parameters in Tartaric-Sulphuric Acid on Coating Thickness and Corrosion Resistance of Al 2024 T3 Alloy

2024 T3 is one of aluminium alloys which are widely used in the aircraft structures. Anodizing of alluminium alloy in tartaric-sulphuric acid (TSA) electrolyte is developed to obtain more environmentally-friendly process and to produce anodize layer with better corrosion resistance. In this research work, the influences of anodizing parameters of Al 2024 T3 in TSA on the thickness, weight and corrosion resistance of the anodize layer are studied. Corrosion resistance test was carried out by conducting salt spray test for 336 hours and anodic polarization measurements using potentiostat. Results of three-factor analysis of variance (ANOVA) demonstrated that the most influencing factor that determines the thickness and weight of the anodize layer is temperature, followed by applied voltage, duration of anodizing, voltage-temperature interaction, interaction of temperature-duration of anodizing, interaction of voltage-temperature-duration of anodizing, and interaction of voltage and duration of anodizing. The pit density and corrosion current density (icorr) were found to be dependent on the coating thickness. The anodize layer with a thickness of higher than 3 μm was not experienced to pitting corrosion during 336 hours of salt spray test.

Effects of Cl- and SO_4^(2-) Ions on Corrosion Behavior of X70 Steel

[ Manuscript received October 8, 2003, in revised form March 2, 2004]Corrosion behaviors of X70 steel were studied by means of electrochemical experiments and morphology observation. First, through potentiodynamic polarization in solution of various Cl- ions concentration, it was found that Epit began to appear in solution of Cl- concentration above 0.1 mol/L, and there was a critical point of Cl- concentration between 0.05 mol/L and 0.1 mol/L, below which the extent of pitting and general corrosion were trivial, while in solution of Cl- concentration above 0.1 mol/L, general and pitting corrosion became greater as the increasing of Cl- concentration. All of them were confirmed by the SEM observations after anodic polarization. Second, via the potentiodynamic polarization curves of X70 steel in 0.5 mol/L Cl- solution with 0, 0.05, 0.5 and 1 mol/L SO42-ions, it was found SO42- ions were able to inhibit corrosion aroused from Cl- ions, accordingly a model was set up to describe the process. In addition, to further explore the inhibited effect of SO42- ions, EIS was used in solutions of different Cl- and SO42- concentrations, the results revealed that the electrochemical resistance has a relation with the [SO42-]/[Cl-], that was, the bigger the value of [SO42-]/[CI-], the greater the electrochemical resistance.

Corrosion Behavior of Reinforcement Steel Embedded in Cement Mortars Using Different Protection Systems

Although reinforced concrete structures are able to withstand towards a variety of adverse environmental conditions, reinforcement corrosion could lead to concrete structure deterioration. The present study examines four different ways of using corrosion inhibitors against pitting corrosion. In particular, it was investigated the chloride penetration resistance of reinforced cement mortars using corrosion inhibitor applied in three different ways. The corrosion behavior of the specimens was evaluated by electrochemical methods such as Linear Polarization Resistance and Halfcell Potential Resistance. In addition, the mass loss of steel rebars against time of partially immersion in sodium chloride (NaCl) solution was carried out in the lab. The experimental results showed that the corrosion systems examined in the study provide anticorrosion protection on steel rebars against chlorides comparing with the reference group.

某油冷却器换热管泄漏原因

某公司生产的油冷却器换热管在投入使用9~12个月后发生腐蚀泄漏现象。采用宏观观察、化学成分分析、金相检验、扫描电镜和能谱分析、原子吸收光谱分析等方法分析了管道腐蚀泄漏的原因。结果表明:油冷却器换热管介质中的氯离子和硫离子在管内壁积垢中沉积并富集在管壁基体前沿,导致内壁产生大量点腐蚀,点腐蚀位置与未腐蚀位置形成大阴极小阳极腐蚀电池,增大了腐蚀速率,在管内介质的冲刷作用下,点腐蚀坑进一步扩大,最终导致管道泄漏。

904L不锈钢在含Cl^(-)和F^(-)溶液中的耐蚀性能研究

904L不锈钢因其良好的耐蚀性被广泛应用于石油、化工、排污、管道和造纸等领域中,但是其存在的Cl^(-)和F^(-)会引起904L不锈钢发生点蚀。通过对比实验,采用扫描电子显微镜和X-射线衍射研究了904L不锈钢在不同浓度Cl^(-)与F^(-)溶液中的微观形貌和腐蚀产物。采用电化学方法研究了不同浓度Cl^(-)与F^(-)和温度对904L不锈钢点蚀行为的影响,探究了904L不锈钢的耐腐蚀机理。结果表明:当F^(-)浓度从0增加到0.05 mol/L时,极化电阻Rp从2233 kΩ·cm^(2)下降到1246 kΩ·cm^(2),表明F^(-)浓度的上升会增加904L不锈钢在Cl^(-)溶液中的点蚀倾向,这是因为F^(-)会与合金中的Ni原子形成不致密的半溶性沉淀Ni F2并参与钝化膜的形成;随着F^(-)浓度的增大(从0.05 mol/L到0.30 mol/L),极化电阻Rp从1246 kΩ·cm^(2)下降到559 kΩ·cm^(2),表明当F^(-)浓度继续升高时904L不锈钢点蚀倾向继续增加,但是增加趋势逐渐减缓。温度对904L不锈钢的点蚀行为影响较大,Cl^(-)浓度对904L不锈钢的点蚀行为影响较小。

CO_(2)体系下X70天然气管线钢的电化学腐蚀行为研究

基于新疆某油田天然气输送管线采出水模拟环境,采用电化学测试方法和扫描电子显微镜等分析方法,研究了X70管线钢在4种不同CO_(2)压力下的电化学腐蚀行为。结果表明:在高含氯离子的模拟采出水溶液中,电化学阻抗谱(EIS)和极化曲线均表明X70钢试样的腐蚀程度随着CO_(2)压力的增加(0.5,1.0,2.0,3.0 MPa)变得越来越严重。失重实验结果表明X70钢试样的腐蚀速率随着CO_(2)压力的增加而增加,压力为3.0 MPa时腐蚀速率最大,为2.5739 mm/a。XRD结果表明腐蚀产物主要是FeCO_(3)。扫描电镜结果显示,试样表面的点蚀现象随CO_(2)压力的增加变得越来越严重,试样表面变得越来越粗糙。这些结果的出现归因于高压CO_(2)的作用和高浓度Cl^(-)加剧点蚀的作用。由此可以发现,高CO_(2)和Cl^(-)对X70管线钢具有严重的破坏作用。这项工作为预防这种类型的腐蚀提供了借鉴与指导。