Corrosion behavior of Cu/Al casting-rolled clad plates in different alkaline solution

The effect of pH value and different kinds of anions on the corrosion behavior of Cu/Al casting-rolled clad plates in the alkaline solution was evaluated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), weight loss analysis, 3D confocal laser scanning microscopy (CLSM) and electrochemical test. Results show the corrosion mainly occurs on the aluminum side. The corrosion resistance of the Cu/Al decreases as the pH value increases. When pH≥12, the dissolution of the film layer is faster than the passivation process. The addition of Cl⁻ ions reduces the corrosion resistance of the Cu/Al clad plates, which leads to pitting corrosion. The higher the concentration of Cl⁻ ions, the more prone the pitting to occur. The addition of SO₄²⁻ ions causes the denudation of the samples. The corrosion resistance of the Cu/Al is better in the alkaline solution containing NO₃⁻ ions than that in the solution containing Cl⁻ ions or SO₄²⁻ ions. When adding SO₄²⁻, NO₃⁻ and Cl⁻ to the pure alkaline solution, the corrosion resistance of the Cu/Al clad plates decreases.

     

The effect of molybdenum ion implantation on the general and pitting corrosion behaviour of pure aluminium and a high strength aluminium alloy

The effect of Ar and Mo ion implantation on the corrosion behaviour of pure Al and a high strength aluminium alloy (7075-T6) has been investigated in Cl^?-free and Cl^?-containing sulphate solutions. In Cl^?-free environments, Mo implantation markedly affects the general corrosion behaviour of both the pure metal and the alloy. Ar implantation, on the other hand, has no permanent effect on the potentiodynamic polarization behaviour of pure Al but does alter somewhat the polarization characteristics of 7075-T6. In Cl^?-containing environments, Mo implantation significantly improves the resistance of pure Al to pitting corrosion, and increases the breakdown potential by about 200 mV. A similar, though less marked effect is observed with the alloy. Ar implantation has no major effect on the behaviour of either the pure metal or 7075-T6 in Cl^?-containing environments. On the basis of Rutherford backscattering and potential-time measurements it is suggested that the beneficial effect of Mo may be due to either the incorporation of Mo in the passive film or to dissolution and reprecipitation of some Mo-containing species on the passive film.     

Initiation and Inhibition of Pitting Corrosion in Alkali Solutions under potentiostatic polarization conditions

The variation of the critical pitting potential of a zincalloy was studied in aerated NaOH solutions as a function of the concentration of the aggressive ions, Cl^?, Br^? and I^?. Curves with segmented nature were obtained when E_pitting was plotted versus logarithm of the halogen ion concentrations. Initiation of pitting corrosion was discussed on the basis of formation of complex halo-compounds with the oxides/hydroxides that constitute the passive surface film. Addition of chromate, phosphate and carbonate ions to the halogen-containing solutions causes the shift of the critical pitting potential in the noble direction, accounting for increased resistance to pitting attack. Nitrite-ion additions contribute with the halogen ions in the destruction of the passive film. Sufficient concentrations of the carbonate ions cause complete inhibition of pitting corrosion.     

Improvement on the pitting corrosion resistance of 304 stainless steel via duplex passivation treatment

A remarkable improvement in the pitting corrosion resistance of 304 stainless steel was attempted using a novel duplex passivation treatment method. First, chemical passivation in nitric acid followed electrochemical passivation via potential polarization of step cycling in sodium nitrate electrolyte. Compared with traditional chemical passivation, breakdown potential was increased from 0.31 V_SCE to positive than 0.9 V_SCE at 70°C in a solution bearing 0.6 M [Cl^?] concentration. The critical pitting temperature was enhanced from 21.5°C to above 70°C in a solution with 6 M [Cl^?] concentration. Impedance analysis and X‐ray photoelectron spectroscopy results show that a more compact passive film with a higher ratio of chromium oxide on iron oxide was achieved by electrochemical passivation compared with chemical passivation. Morphology observation suggested that the potential polarization of step cycling slightly increased the dissolution of inclusions after being subjected to chemical passivation. The probable reason for the improvement on pitting resistance is discussed in detail based on inclusion dissolution and the protectiveness in passive film.     

Corrosion behaviour of the aluminium alloy AA 6351 in glycol/water solutions degraded at elevated temperature

A research programme has been developed to characterize the corrosion behaviour of the metals most widely used in solar collector systems. Common heat transfer fluids such as glycol/water solutions show a low aggressivity, unless pollution or high temperature exposure (degradation) occur. This paper deals with the study of the corrosion behaviour of the aluminium alloy 6351 (nominal composition: 1% Si, 0.6%Mg, 0.3% Mn, the balance Al) in ethylene or propylene glycol (EG or PG)/water solutions (1:1 in volume) degraded at 108°C in contact with AA 6351 as glycol oxidative degradation catalyzer. The tests in degraded solutions, performed at 80°C over a period of 60 days, showed that degradation causes an increase in the uniform corrosion rates and a remarkable pitting attack. Pitting corrosion has been mainly attributed to the action of copper ions dissolved from the aluminium alloy and detected in the solutions by atomic adsorption analysis. In conjunction with the degradation studies, tests were also performed at 80°C in buffered PG/water solutions (pH 4) containing the acids reported to be produced during the process of glycol oxidative degradation (oxalic, glycolic, acetic and formic acids), at the concentrations 10^?3 or 10^?2 M. In these solutions the corrosion behaviour of AA 6351 was investigated over a period of 30 days by measuring the gravimetric corrosion rates and the polarization resistance values and by recording the polarization curves after 2 h or 30 days of immersion. Only oxalic acid and 10^?2 M glycolic acid significantly increased the AA 6351 corrosion rates, but only in the first period of immersion. On the contrary, when the surface films were formed in the solutions of these acids, they afforded the highest protectivity. The analogous behaviour of AA 6351 in oxalic and glycolic solutions has not been attributed to the formation of an insoluble aluminium salt film with the organic anions, but rather to the growth of an oxide film with peculiar characteristics of thickness and protectivity.     

Effect of ascorbic acid on the pitting resistance of 316L stainless steel in synthetic tap water

This study examined the effect of L-ascorbic acid (A.A) concentration on the pitting corrosion properties of 316L stainless steel (316L STS) of heat exchanger in synthetic tap water containing 400 ppm of Cl- ion. The pitting corrosion of 316L STS can be effectively inhibited by the 10^-4 M of A.A concentration. In this condition, the adsorption of A.A reinforced the passive film of steel by blocking the Cl^- ions at the active site. However, the passive film was deteriorated and severe pitting corrosion occurred above the 10^-4 M of A.A concentration. Above the 10^-4 M of A.A concentration, A.A generates soluble chelate rather than absorbs on the steel surface and it causes passive film deterioration and severe pitting corrosion. The critical ratio, which is a critical ratio of surface coverage of aggressive to inhibitive ion necessary to initiate localized corrosion, calculated 2.93 up to the 10^-4 M. It has approximately 2.93:1 ratio of the coverage of local Cl^- ions to A.A. Above the critical ratio, the pitting corrosion will occur with degradation of the passive film. On the other hands, above the 10^-4 M A.A concentration caused a negative effect because the heat energy for adsorption is increased.     

Role of second phase particles in pitting corrosion of 3003 Al alloy in NaCl solution

The second phase particles in 3003 aluminum (Al) alloy were characterized by scanning electron microscope, energy‐dispersive X‐ray analysis and X‐ray diffraction techniques. The role of second phase particles in Al alloy pitting corrosion was investigated by cyclic polarization measurement, and scanning vibrating electrode technique. Results demonstrated that the second phase particles in 3003 Al alloy are mainly Al_x(Fe,Mn) intermetallics, with an average diameter of about 5 µm. The enrichment of Mn in second phase particles forms a galvanic cell effect relative to the adjacent Al alloy substrate. The initiation of pitting corrosion of 3003 Al alloy is the local dissolution of Al substrate around the second phase particles. When a sufficient amount of Al is dissolved away, the second phase particles drop off from the Al substrate, forming large pitting cavities that are usually linked each other.     

Role of alloyed copper on corrosion resistance of austenitic stainless steel in H2S–Cl− environment

Corrosion test, surface analysis and thermodynamic calculation were carried out in the H₂S–Cl⁻ environments to clarify the role of alloyed Cu on the corrosion resistance of austenitic alloys. The alloyed Cu improved pitting corrosion resistance in the H₂S–Cl⁻ environment. The surface film of Cu-containing alloy indicated double layer consists of copper sulfide and chromium oxide, and the copper sulfide was able to exist stably compared to iron sulfide and nickel sulfide. It is concluded that the copper sulfide would enhance the formation of chromium oxide film which improve the pitting corrosion resistance in the H₂S–Cl⁻ environment.     

Corrosion behavior of 2205 stainless steel in simulated flue gas condensate with different chloride concentrations in a waste incineration power plant

The effect of Cl⁻ on the initial corrosion behavior of 2205 duplex stainless steel (2205 DSS) in simulated flue gas condensate from a waste incineration power plant was investigated using Mott–Schottky plot, micro-area electrochemical methods, and microscopic surface morphology observation. The results show that at 150°C, the carrier concentration of the 2205 DSS passive film was maintained at a small value and changed little when the Cl⁻ concentration is less than 25 g/L, indicating that it has good pitting resistance. When the Cl⁻ concentration reaches 30 g/L and above, the carrier concentration of the passive film increases remarkably, and pitting corrosion appears on the 2205 DSS surface. At 180°C, there is no obvious pitting on the surface when the Cl⁻ concentration is not more than 15 g/L. When the Cl⁻ concentration is 20 g/L or above, the carrier concentration of the passive film significantly increases, and pitting corrosion appears on the surface. When the Cl⁻ concentration reaches 30 g/L, the carrier concentration of the passive film increases sharply. The passive film on a 2205 DSS surface is seriously damaged and accompanied by the occurrence of uniform corrosion.     

Corrosion behaviour of zirconium electrode in sodium azide electrolyte as compared to the alkali halide solutions

The kinetics of open circuit growth of an oxide film on zirconium electrode in NaN₃ solution of various concentrations was investigated using potential and capacitance measurements. The protective oxide film formed in azide solutions was found to thicken with time in two steps, the rate of oxide growth was found to decrease as the azide concentration increased. The corrosion behaviour of the electrode was characterized by ac impedance measurements to obtain detailed information about the effect of azide ion concentration on the electrical properties of the Zr electrode surface. The impedance response for the metal‐metal oxide‐electrolyte system was modeled with a transfer function. The potentiodynamic oxidation of Zr was also studied as a function of the azide ion concentration. The polarization curves showed the peak‐shaped active‐to‐passive transition and the corrosion rate was found to increase with increase of azide ion concentration. The activation energy of corrosion was calculated according to Arrhenius plot and found to be 14.5 kJ mol^?1. The polarization results in azide solutions were compared to those obtained in solutions of different halide ions, namely, F^?, Cl^?, Br^? and I^? ions. The rate of corrosion was found to decrease in the order Br^? > Cl^? > F^?, I^? > azide. Opposite to the behaviour in azide solutions, the halide ions do not show the active‐passive transition.     

On the pitting corrosion of tin in aqueous solutions

Four independent techniques were employed to prove that Sn undergoes pitting corrosion. The first was based on the measurement of the variation of the open circuit potential of the Sn electrode in aerated Cl^? solutions of various concentrations. Steady-state potentials were attained slowly and erratically from negative values, and were more positive the higher the dilution. Sn electrodes prepassivated in CrO₄^2? solutions responded readily to additions of Cl^? ion. The potentials developed were more noble than those measured in presence of the passivator alone, and changed to positive values with the increase of the concentration of the pitting corrosion agent. Attack was under cathodic control.Galvanostatic polarization of the Sri electrode was carried out in 0.005 to 0.1M NaOH, in the presence of various additions of Cl^?. Above a certain Cl^? content, contingent upon the alkali concentration, the aggressive anion prevented the evolution of Oa on the electrode, and oscillations in the E?t curves were recorded. Competitive adsorption of Cl^? and OH^? is assumed to occur, which affected both the quantity of electricity, Q_p, consumed along the oxide formation steps, and the rate of potential increase, dE/dt, following oxidation. Plots of the two variables as a function of the Cl^? ion concentration exhibited a definite break at the value characteristic for the initiation of pitting attack. Potentiodynamic polarization showed that the pitting corrosion potential progressively shifts towards negative values as the concentration of the aggressive agent in solution was increased. The pitting corrosion currents resulting from the addition of Cl^? to Sn electrodes prepassivated in CrO₄^2? solutions were measured. The dependence of the maximum currents on solution composition is explained on the basis of competitive adsorption.     

Effects of environmental factors on corrosion behavior of aluminum

Aluminum, used as a material for heat exchangers in air conditioners, often has problems of leakage of refrigerant on the Al surface due to corrosion. The problems originate from pitting corrosion of the Al in an external environment. To understand corrosion problems, it is necessary to study the corrosion behavior of Al in various environments. In this study, the effects of environmental factors on the corrosion behavior of Al were studied by the surface analysis and electrochemical testing in 3.5 wt% NaCl solutions, with changes of dissolved oxygen, temperature, and concentration of Cl⁻ and S ions. Among the external environmental factors, the presence of oxygen and the increase of Cl⁻ ion concentration do not significantly affect the corrosion potential of Al, leading to an increase of only 1.1 and 6 times, respectively. There was a significant decrease in the corrosion resistance of Al, approximately 40 and 800 times, respectively, with the increase of concentration of S and temperature.     

Mg-15Li合金在碱性NaCl溶液中的腐蚀行为

    用电化学方法研究了Mg-15Li合金在碱性NaCl溶液中的腐蚀行为.结果表明：在强碱性pH=13及扫描电镜环境下,当Cl^-浓度低于0.4 mol/L时,合金表面形成稳定的钝化膜;随Cl^-浓度增加,点蚀电位逐渐降低.     

Characterization of Atmospheric Corrosion of 2A12 Aluminum Alloy in Tropical Marine Environment

In this work, corrosion product formed on 2A12 aluminum (Al) alloy after 3 months of natural exposure in South China Sea atmosphere was characterized by various surface analysis techniques, including scanning electron microscopy, energy-dispersive x-ray analysis, x-ray photoelectron spectroscopy, and x-ray diffraction. The atmospheric corrosion mechanism of Al alloy in marine environment was derived. Results demonstrated that Al alloy specimen experiences serious general corrosion and pitting corrosion. Al and O are enriched in the product film, and Ca and Cl are also found in the film and corrosion pits in Al alloy substrate. The main component compounds existing in the film include Al₂O₃, Al(OH)₃, and AlOOH while AlCl₃ and CaCO₃ are also identified. Al alloy encounters corrosion under tropical marine atmosphere. Although somewhat protective, the formed surface film on Al alloy specimen is attacked by chloride ions, resulting in significant pitting corrosion of Al alloy.     

The effect of fluoride on the electrochemical behavior of Ti and some of its alloys for dental applications

Titanium is the best metal for making dental implants and restorations. In the last decade, new titanium alloys have been developed in different areas of dentistry. Concurrently, treatments using fluoride supplementation, such as odontology fluoride containing gels, have also been widely used in odontology. The aim of this study is to investigate the electrochemical behaviour of a new titanium alloy containing Cu and Ag, in fluoride‐containing media, and compare it with the behavior of Ti and Ti6Al4V, which are used frequently as biomaterials. Open circuit potential, polarization resistance and electrochemical impedance spectroscopy measurements revealed that the corrosion resistance of titanium and its alloys is controlled by the fluoride ion concentration and the pH of the solution. The presence of F^? ions in neutral solution does not hinder the formation of a protective layer of Ti and its alloys. Thus, the corrosion resistance of Ti is maintained in this medium. However, the corrosion of Ti and its alloys are enhanced in an acidic environment, because F^? ions in the solution combines with H⁺ ion to form HF, even in low fluoride concentration.     

Influence of fluoride concentration and pH on corrosion behavior of Ti‐6Al‐4V and Ti‐23Ta alloys in artificial saliva

Titanium alloys exhibit an excellent corrosion resistance in most aqueous media due to the formation of a stable oxide film and some of these alloys (particularly Ti‐6Al‐4V) were chosen for surgical and odontological implants for this resistance and their biocompatibility. Treatments with fluorides (F^?) are known as the main method to prevent plaque formation and dental caries. Toothpastes, mouthwashes and prophylactic gels can contain from 200 to 20 000 ppm F^? and can present neutral to acidic character, which can affect the corrosion behavior of titanium alloys devices present in the oral cavity. In this work, the behavior of Ti‐6Al‐4V and the new experimental Ti‐23Ta has been evaluated in artificial saliva of pH 2, 5 and 7 and different F^? concentrations (0, 1000, 5000 and 10 000 ppm), through open‐circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. A defined correlation between pH and F^? concentration settled the active or passive character of the materials. For both alloys, an active behavior was observed for pH 2 and 1000 to 10 000 ppm F^? and for pH 5 and 5000 and 10 000 ppm F^?. The passive behavior was observed for the other investigated conditions. The F^? concentration increase and pH decrease reduced the corrosion resistance of the alloys and decreased the stability of their passive film. The corrosion behavior of both alloys was very similar, but the Ti‐23Ta alloy generally presented slightly higher corrosion resistance.     

Corrosion and self‐healing behaviour of AZ91D magnesium alloy in ethylene glycol/water solutions

Corrosion behaviour of magnesium alloy‐based engine parts in cooling system is an urgent fundamental issue in automotive field where magnesium alloys are increasingly used. In the present work, the corrosion behaviour of AZ91D magnesium alloys in various ethylene glycol/water solutions was studied by electrochemical measurements and immersion tests at room temperature. The surfaces of the samples after immersion tests were examined using scanning electron microscope (SEM) and X‐ray diffraction (XRD). The results showed that the corrosion rates of AZ91D magnesium alloys decreased with the increase of ethylene glycol concentration in ethylene glycol/water solutions and the corrosion process was dominated by pitting corrosion. A continuous protective film transferred from corrosion products was formed on the corroded surface after sufficient immersion duration in ethylene glycol/water solutions, which is able to heal the corrosion pits. The self‐healing behaviour inhibited the further corrosion of AZ91D magnesium alloy.     

Corrosion mechanism of aluminum alloy by ethylene glycol‐based solution

Corrosion and failure mechanisms on an aluminum (Al) alloy by ethylene glycol base solution have been studied. Extensive crevice corrosion damage and localized scale deposition are clearly observed between the failed Al alloy surface and the rubber hose, in which the leakage of ethylene glycol‐based solution occurred under an actual operating. In addition, many micro‐cracks are found at the rubber hose which is clamped with the Al alloy. The scales on the Al surface appear to be due to the occurrence of Al corrosion, followed by the precipitation of additives of ethylene glycol‐based solution in the crevice between Al alloy and rubber hose. The mechanisms that can account for the crevice corrosion and solution leakage on the Al alloy surface are discussed.     

Kinetic and thermodynamic studies of AISI 4130 steel alloy corrosion in ethylene glycol-water mixture in presence of inhibitors

The electrochemical behavior of steel alloy in ethylene glycol-water mixture was investigated by electrochemical methods. The results obtained showed that corrosion rate was decreased with increasing ethylene glycol concentration. The effect of inorganic inhibitors including NO₃ ^?, NO₂ ^?, Cr₂O₇ ^2? and CrO₄ ^2? were studied using electrochemical techniques where the highest inhibition efficiency was obtained for CrO₄ ^2?. In the presence of chromate the inhibitor efficiency increased with its concentration. The inhibiting effect of the chromate was explained on the basis of the competitive adsorption between the inorganic anions and the aggressive Cl^? ions, and the adsorption isotherm basically obeys the Langmuir adsorption isotherm. Thermodynamic parameters for steel corrosion and inhibitor adsorption were determined and reveal that the adsorption process is spontaneous. Also, a phenomenon of both physical and chemical adsorption is proposed.     

Inhibition of Corrosion of 3003 Aluminum Alloy in Ethylene Glycol-Water Solutions

In this study, the inhibiting effects of four types of inhibitors, including gluconate, cinnamate, molybdate, and nitrate, on corrosion of a 3003 aluminum (Al) alloy were investigated in ethylene glycol-water solutions that simulate the automotive coolant by various electrochemical measurements. It was found that the tested inhibitors were effective to inhibit corrosion of 3003 Al alloy under both static and turbulent flow conditions. They all behave as anodic inhibitors, which inhibit the Al alloy corrosion by passivating Al alloy and decreasing its anodic current density. A turbulent flow of the solution decreases the corrosion resistance of Al alloy and the inhibiting effect of the inhibitors. The inhibiting effect of the inhibitors is ranked as: nitrate > cinnamate > gluconate > molybdate.