Localized Corrosion Of Aluminum Alloys Research Articles

Pitting corrosion of 2A12 aluminum alloy long-scale specimen in simulated seawater splash zone, dynamic waterline zone and full immersion zone

PurposeThe aim of this paper is to construct a device that simulated the seawater splash zone, dynamic waterline zone (splash zone) and full immersion zone. Localized corrosion of 2A12 aluminum alloy long-scale specimen was studied.Design/methodology/approachCorrosion morphologies before and after the corrosion product removal were used to identify corrosion intensity at full seawater immersion zone, dynamic waterline zone (splash zone) and atmospheric zone. The average depth and diameter of corrosion pits in the three zones were evaluated by three-dimensional optical microscopy. The impact of wetting time of the atmospheric zone on the localized corrosion was investigated.FindingsCorrosion pits were observed on the surface on day 4 for the wetted atmospheric zone (Case 1), and on the surface on day 8 for the alternant wet/dry atmospheric zone (Case 2). The corrosion product layer on the surface for Case 1 was partially broken down while the layer on the surface for Case 2 was intact. Average pitting depth and pitting diameters for Case 1 were more serious than that for Case 2.Originality/valueThe above findings revealed that the humidity of the atmospheric zone had great impact on the localized corrosion of aluminum alloy at the seawater splash zone.

Clarifying the Role of Mg2Si and Si in Localized Corrosion of Aluminum Alloys by Quasi In Situ Transmission Electron Microscopy

The role of magnesium silicide (Mg2Si) and silicon (Si) particles in the localized corrosion of aluminum (Al) alloys was investigated herein. Sub-micrometer-sized Mg2Si and Si particles were grown in the Al matrix of Al-Mg-Si and Al-Si alloys, respectively, and characterized by transmission electron microscopy (TEM). A quasi in situ TEM technique was used to study an identical location containing Mg2Si or Si particle in the Al matrix, prior to and following a period of immersion in 0.1 M NaCl at pH 6, 2, and 12. At pH 6 and 2, Mg2Si was initially “anodic,” preferentially dealloying via selective dissolution of Mg, resulting in the development of SiO-rich remnants that are electrochemically inert. The SiO-rich remnants at pH 2 physically detached from the Al matrix. Silicon particles were electrochemically inert at pH 6, while “cathodic” at pH 2, dissolving the Al matrix at their periphery. It was observed that copper (Cu) was redeposited on Si particles at pH 2. At pH 12, Mg2Si and Si were “cathodic” to the Al matrix. This study clarifies, and provides new insights into, the characteristics of Al alloy physical manifestation of corrosion associated with Mg2Si and Si at the nanoscale.

Numerical simulation of micro-galvanic corrosion of Al alloys: Effect of density of Al(OH)3 precipitate

This work is a further step to develop a finite element model to simulate localized corrosion of aluminum alloys driven by micro-galvanic effects. The focus herein is to explore the effect of density (porosity and tortuosity) of Al(OH)3 precipitates generated both on the electrode surface and in the liquid phase. Two coupled processes are identified and discussed, both influencing the local pH: the Al3+ dissolution from the electrode surface, and the steric hindrance effects on mass transport of species between the bulk solution and the anolyte next to the corroding surface. With the densest precipitate investigated, Al3+ dissolution is more effectively blocked and the mass transport largely hindered of Al3+ ions leaving the electrode surface. With increasing porosity of the precipitate, Al3+ dissolution is enhanced, also the mass transport of species in the electrolyte. The most severe localized acidification inside the occluded volume occurs when the density, namely ascribed by porosity, of precipitate is at an intermediate level with εc = 0.01. In qualitative agreement with experimental observations, this work highlights the importance of corrosion product density on the progress of localized corrosion.

Localized corrosion of aluminum alloy 6061 in the presence of Aspergillus niger

The corrosion behavior of anodized and non-anodized aluminum alloy 6061 in the presence of Aspergillus niger fungus was studied using electrochemical noise, recurrence plots and electrochemical impedance spectroscopy techniques. Corrosion potential measurements were also obtained. The fungus generated organic acids causing microbially induced corrosion of the specimens, which was more evident on non-anodized than on anodized aluminum alloy 6061, showing uniform and localized corrosion and a change in the attack as a function of the fungus growth time. A biomass growth curve was obtained to compare the behavior of anodized and non-anodized aluminum alloy 6061. A long-term electron transfer mechanism was proposed for localized corrosion of aluminum alloy 6061.

Volta Potential Evolution\xa0of Intermetallics in Aluminum Alloy Microstructure\xa0Under Thin Aqueous Adlayers: A combined DFT and Experimental Study

In this work, first-principle density functional theory (DFT) was used to calculate the work function and Volta potential differences between aluminum alloy matrix and two intermetallic phases (Mg2Si and Al2Cu) with varying surface terminations as a function of adhering monolayers (ML) of water. The calculated data were compared with experimental local Volta potential data obtained by the scanning Kelvin probe force microscopy (SKPFM) on a commercial aluminum alloy AA6063-T5 in atmospheric environments with varying relative humidity (RH). The calculations suggest that the surface termination has a major effect on the magnitude and polarity of the Volta potential of both intermetallic phases (IMP’s). The Volta potential difference between the IMP’s and the aluminum matrix decreases when the surface is gradually covered by water molecules, and may further change as a function of adhering ML’s of water. This can lead to nobility inversions of the IMP’s relative to the aluminum matrix. The measured Volta potential difference between both IMP’s and their neighboring matrix is dependent on RH. Natural oxidation in ambient indoor air for 2 months led to a nobility inversion of the IMP’s with respect to the aluminum matrix, with the intermetallics showing anodic nature already in dry condition. The anodic nature of Al2Cu remained with the introduction of RH, whereas Mg2Si became cathodic at high RH, presumably due to de-alloying of Mg and oxide dissolution. The DFT calculations predicted an anodic character of both IMP’s in reference to the oxidized aluminum matrix, being in good agreement with the SKPFM data. The DFT and SKPFM data were discussed in light of understanding localized corrosion of aluminum alloys under conditions akin to atmospheric exposure.

Alloying effect of copper concentration on the localized corrosion of aluminum alloy for heat exchanger tube

This study examined the alloying effect of Cu content on the localized corrosion properties of Al alloy in synthetic acid rain containing 200 ppm of Cl- ion. In aluminum alloy tubes, a small amount of Cu is contained as the additive to improve the mechanical strength or as the impurity. The Cu-containing intermetallic compound, Al2Cu can cause galvanic corrosion because it has more noble potential than Al matrix. Therefore aluminum tube could be penetrated by localized corrosion attack. The results were obtained from electrochemical test, scanning electron microscopy, and time of flight secondary ion mass spectrometry (ToF-SIMS) mapping. Severe localized corrosion was occurred on the Al-0.03 wt% Cu alloy. The negative effect of Cu on the pitting corrosion was attributed to the presence of the Al2Cu precipitates.

Comparison of corrosion behavior of Al‐Mn and Al‐Mg alloys in chloride aqueous solution

The microstructure and corrosion behavior of Al‐Mn alloy 3A21 and Al‐Mg alloy 5A05 in 3.5% NaCl solution were examined and compared. The results of the microstructure survey performed by optical microscope confirm the inhomogeneous nature of the intermetallic particles of the two alloys. The X‐ray diffraction (XRD) analysis reveals the presence of intermetallic Al6Mn and Al6(FeMn) particles in the 3A21 alloy and Al3Mg2, Mg2Si and FeAl3 particles in the 5A05 alloy, respectively. Electrochemical results, in parallel with corrosion morphology characterization, show that these two alloys both suffer pitting corrosion type attack under the conditions employed in the present study, with better corrosion resistance and stronger repassivating capability for the 5A05 alloy. Furthermore, the validity of the difference ΔE (Epit–Ecorr, Ecorr–Eprot) and Eptp as criteria for susceptibility to localized corrosion of aluminum alloys are also discussed.

Usefulness of Ultrahigh Resolution Microstructural Studies for Understanding Localized Corrosion Behavior of Al Alloys

The corrosion behavior of different tempers of two aluminum alloys, AA7050 and an experimental Al–Mg–Cu–Si alloy, was studied in NaCl solution by anodic polarization and scanning electron microscopy and was correlated with differences in the microstructure. Potentiodynamic polarization experiments were performed on samples from the exact sheets used by others to study the microstructure evolution during the early stages of the precipitation sequence by high-resolution characterization tools [i.e., high-resolution transmission electron microscopy and atom probe tomography (APT)]. The usefulness of information from these state-of-the-art tools to lead to a better understanding about the effects of nanoscale segregation on localized corrosion of aluminum alloys is discussed. APT was able to provide information about the composition of the solid solution matrix region between the fine-scale hardening particles, which is not possible by any other technique. Some of the changes in corrosion behavior, e.g., the breakdown potentials, with temper could be rationalized based on changes in the matrix composition. The formation of corrosion-susceptible surface layers on as-polished AA7050 depended on the predominant type of hardening particle. The lack of detailed knowledge of the grain boundary region limited the applicability of the microstructural information generated by previous studies for understanding intergranular corrosion.

Inhibition of Aluminum Alloy 2024 Corrosion by Vanadates: An In Situ Atomic Force Microscopy Scratching Investigation

Abstract The morphology and kinetics of the localized corrosion of aluminum alloy (AA)2024-T3 (UNS A92024) at the open-circuit potential were investigated by in situ atomic force microscopy (AFM) scratching. The addition of metavanadate to chloride solutions resulted in outstanding corrosion inhibition. Samples exposed to 0.1 M sodium chloride (NaCl) with no inhibitor developed a trench-like attack at the periphery of large Al-Cu-Fe-Mn-(Si) intermetallic phases. The addition of dilute metavanadate markedly reduced the kinetics of the attack. In addition, most S-phase particles remained free of attack. Higher concentrations of metavanadate increased protection even further so that only high AFM tip forces could induce pitting corrosion. Corrosion attack was immediately observed when AA2024-T3 samples were exposed to chloride solutions containing orange decavanadates. The attack nucleated on the exposed surface but not under the AFM tip. The attack grew continuously, accompanied by gas evolution and formation of corrosion products. Optical inspection after the test indicated severe corrosion damage, confirming an overall poor performance of orange decavanadate solutions as corrosion inhibitors.

Detection of Localized Corrosion of Aluminum Alloys Using Fluorescence Microscopy

Confocal laser scanning microscopy was used in an in situ fluorescence mode to investigate localized corrosion of aluminum alloys in the presence of 0.1 M KCl. Fluorescein dye was used to indicate pH changes and surface chemistry over and around the active sites. Al 6061 was found to have at least two kinds of inclusions according to their elemental constituents. Active inclusions that are rich in Mg, Si, and Al show fluorescence activity in early stages of exposure. The inclusions that are rich in Fe, Si, and Cr show no fluorescence activity at the early stages. Al 2024 was also studied and had different fluorescent activities that were associated with different inclusions.

Electrochemical Impedance Spectroscopy as a Monitoring Tool for Passivation and Localized Corrosion of Aluminum Alloys

Pitting and crevice corrosion of Al alloys and Al-based metal matrix composites can be detected by characteristic changes of the impedance spectra in the low frequency region. A pitting model has been developed which is in agreement with the experimental data. A fitting procedure has been used to analyze a large number of data which have been obtained for as-received samples and samples which had been passivated in CeCl3 solutions. This chemical passivation process produces surfaces which are very resistant to localized corrosion. Al 6061, Al/SiC and Al/graphite which had been passivated in CeCl3 for one week did not pit in 0.5 N NaCl for at least one month. Electrochemical impedance spectroscopy (EIS) is a convenient tool for monitoring of the passivation and the corrosion processes. Elektrochemische Impedanzspektroskopie als Hilfsmittel fur die kontinuierliche Untersuchung der Passivierung und ortlichen Korrosion von Aluminiumlegierungen Loch- und Spaltkorrosion von Aluminiumlegierungen sowie Verbundwerkstoffen mit Aluminiumlegierungen kann aufgrund der charakteristischen Veranderungen der Impedanzspektren im Bereich niedriger Frequenzen nachgewiesen werden. Ein Modell der Lochkorrosion, das in diesem Zusammenhang entwickelt wurde, stimmt mit experimentellen Daten uberein. Mit Hilfe eines Anpassungsverfahrens wurde eine grose Zahl von Daten ausgewertet, die mit Metallproben im Lieferzustand und mit Metallproben nach Passivierung in Certrichloridlosungen erhalten worden waren. Dieses chemische Passivierverfahren liefert Oberflachen mit hoher Bestandigkeit gegen ortliche Korrosion. Al 6061, Al/SiC und Al/Graphit zeigten nach Passivierung in Certrichlorid (Behandlungsdauer 1 Woche) nach mindestens einem Monat in 0,5 n NaCl keine Lochkorrosion. Die elektrochemische Impedanzspektroskopie ist demnach ein bequemes Hilfsmittel zur Uberwachung von Passivierungs- und Korrosionsprozessen.

Electrochemical Behavior of Aluminum‐Base Intermetallics Containing Iron

The effect of components Fe, Mn, and Si on the electrochemical behavior of phases , αAl (Fe, Mn)Si, and were investigated in solutions. Anodic polarization of the phases leads, under certain conditions, to an enrichment of the surface with the more noble components. Enrichment with Fe is detrimental to cathodic behavior. The added presence of Mn or Si in the phase reduced the effect of Fe on both the anodic and cathodic reaction rates. The mechanisms are discussed briefly along with the significance of these phenomena on the localized corrosion of aluminum alloys.

Electrochemical impedance spectroscopy as a monitoring tool for passivation and localized Corrosion of aluminum alloys

AbstractPitting and crevice corrosion of Al alloys and Al‐based metal matrix composites can be detected by characteristic changes of the impedance spectra in the low frequency region. A pitting model has been developed which is in agreement with the experimental data. A fitting procedure has been used to analyze a large number of data which have been obtained for as‐received samples and samples which had been passivated in CeCl3 solutions. This chemical passivation process produces surfaces which are very resistant to localized corrosion. Al 6061, Al/SiC and Al/graphite which had been passivated in CeCl3 for one week did not pit in 0.5 N NaCl for at least one month. Electrochemical impedance spectroscopy (EIS) is a convenient tool for monitoring of the passivation and the corrosion processes.