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

Kappes, Mariano A.; Kovařík, Libor; Mills, Michael J.; Frankel, G. S.; Miller, M.K.

doi:10.1149/1.2939212

Cited by 15 publications

(23 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has been suggested previously that the samples exhibiting surface layer dissolution were very susceptible to crevice corrosion under the edge of the mask, because the active surface layer extended on the surface beneath the lacquer mask. 11,13 There were some evidences of metastable pitting in this potential range, as indicated by small hydrogen bubbles at specific spots on the surface. However, most of the hydrogen bubbles accumulated at the edge of the mask from crevice activity.…”

Section: Resultsmentioning

confidence: 96%

Mechanism of Localized Breakdown of 7000 Series Aluminum Alloys

Wang

Frankel

Jiang

et al. 2013

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

The localized breakdown behavior of AA7055 alloy, and an Al-Zn-Mg alloy having no Cu, with different tempers was studied in 3.5 wt% NaCl solution by an in situ observation system during polarization. Three potentials at which the current increased rapidly were found for AA7055-T6 (peak-aged) samples. The first breakdown potential corresponded to the transient dissolution of an active surface layer formed during surface preparation by abrading with grinding paper. The second potential at which the current increased rapidly was associated with crevice corrosion and was not a true breakdown potential. The second breakdown potential was associated with pitting of the underlying bulk alloy. However, no surface layer attack and a single breakdown potential were observed for AA7055-T73 (over-aged) samples and for the Cu-free Al-Zn-Mg samples in the peak-aged condition. All three samples contained surface layers consisting of nano-grains with the solute-rich bands formed by surface preparation. Both the Zn-rich bands in the surface layer and the Cu content in matrix solid solution of the underlying bulk alloy are responsible for surface layer attack. The change in pitting potential with over-aged tempers could be rationalized based on the Cu content in the matrix. Precipitation-hardenable aluminum alloys are main structural materials for aircrafts due to their high strength-to-density ratio. The AlZn-Mg(-Cu) alloys form precipitates following the general precipitation sequence of supersaturated solid solution, GP zones, metastable η , and stable η.1,2 Metastable η phase is believed to be the main hardening phase and responsible for the peak hardening in Al-ZnMg(-Cu) alloys.2 The equilibrium phase η has the hexagonal structure of MgZn 2 , but Al and Cu can substitute for Zn, and the stoichiometry of this phase can be described as Mg(Zn,Al,Cu) 2 in Cu containing 7××× series Al alloys.3,4 Aging treatments produce changes in the morphology, chemistry, size and density of precipitates and the composition of the solid solution. In the past decade, much research effort has been put into evaluating the composition of nanoscale precipitates in Al alloys due to the development of advanced characterization tools such as atom probe tomography (APT).2,5-7 Sha and Cerezo studied the chemistry evolution of the early-stage precipitates in 7050 Al alloy using transmission electron microscopy (TEM) and APT.2 Marlaud and Deschamps investigated the composition of precipitates and the solid solution in Al-Zn-Mg-Cu alloys in peak-aged and over-aged conditions by combining APT and systematic anomalous small-angle X-ray scattering (ASAXS) techniques.7 This microstructural information has also facilitated a better understanding of corrosion behavior in 7××× series Al alloys with different heat treatments.The localized breakdown behavior of 7××× series Al alloys has been studied extensively. 4,[8][9][10][11][12] The anodic polarization curve for 7×××-T6 Al alloys in NaCl solution exhibits two breakdown potentials. However, only one breakdown pot...

show abstract

Section: Resultsmentioning

confidence: 96%

Mechanism of Localized Breakdown of 7000 Series Aluminum Alloys

Wang

Frankel

Jiang

et al. 2013

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

show abstract

“…Breakdown behavior similar to that of AA7055 in the present study was reported previously for AA7075 30 and AA 7050. 33 The E P increased from the under-aged to peak-aged tempers because of the decrease in the Zn content in the matrix. 32,33 The E P decreased from the peak-aged to over-aged tempers due to the depletion of Cu in the matrix solid solution.…”

Section: Resultsmentioning

confidence: 99%

“…33 The E P increased from the under-aged to peak-aged tempers because of the decrease in the Zn content in the matrix. 32,33 The E P decreased from the peak-aged to over-aged tempers due to the depletion of Cu in the matrix solid solution. 27,34 The effect of changes in the matrix Zn content dominated the effect of changes in the matrix Cu content during under-aging, while the opposite trend behaved during over-aging.…”

Section: Resultsmentioning

confidence: 99%

“…Similar results about the effect of aging condition on the pitting potential have been reported in AA7075 32 and AA7050. 33 However, a few studies reported that the E P did not change with aging conditions in Al-Zn-Mg-Cu alloys, and thus, it did not provide any indication for pitting corrosion susceptibility. 13 This contradiction may be due to the determination of the E P , which was often obscured by the first breakdown potentials associated with the transient dissolution of surface layer formed by surface preparation for Al-Zn-Mg-Cu alloys in certain tempers.…”

Section: Discussionmentioning

confidence: 98%

“…19 The relationship between the matrix concentration and pitting potentials of Al-Zn-Mg-Cu alloys has been established previously. 22,33 The effect of changes in the matrix Zn content dominates the effect of changes in the matrix Cu content from the under-aged to peak-aged tempers. The opposite trend behaves from the peak-aged to over-aged tempers.…”

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Effect of Cu Content and Aging Conditions on Pitting Corrosion Damage of 7xxx Series Aluminum Alloys

Wang

Huang

et al. 2015

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

The corrosion behavior and microstructure of AA7055 alloy with a high Cu content, and a Cu-free Al-Zn-Mg alloy in various aging conditions were studied. Polarization measurements and ASTM B117 salt-spray exposure were used to assess the corrosion characteristics. Transmission electron microscope and atom probe tomography were used to evaluate the microstructure and the composition of precipitates. The matrix composition of AA7055 changed with aging because of precipitation. Thus, the galvanic relationship between Al 7 Cu 2 Fe particles and the surrounding matrix correspondingly changed, which affected the susceptibility to pitting corrosion attack. The susceptibility to pitting corrosion damage of AA7055 was found to decrease according to: over-aged samples > under-aged samples > peak-aged sample. However, aging had only a small influence on pitting corrosion damage for the Cu-free Al-Zn-Mg alloy. Furthermore, despite the more active breakdown potential of the Cu-free Al-Zn-Mg alloy, this alloy exhibited less severe pitting corrosion damage than AA7055, in particular for the over-aged samples. This was attributed to the weaker galvanic coupling between Al 3 Fe particles and the surrounding matrix. Although Cu in the intermetallic particles is detrimental to pitting resistance, the galvanic effect can be reduced by increasing the matrix Cu content. High-strength precipitation-hardenable aluminum alloys are commonly used for structural components of aircraft due to their high strength-to-density ratio.1 However, they are also very susceptible to pitting corrosion, in particular for Navy aircraft subjected to extended periods of salt water spray and/or salt fog.2 These corrosion pits can act as initiation sites for corrosion fatigue cracks and reduce the fatigue life, which is a significant damage mechanism in aging aircraft structures. 2,3From a microstructural viewpoint, initiation of localized pitting corrosion is often associated with coarse cathodic intermetallic particles (IMPs), such as Al 7 Cu 2 Fe, Al 3 Fe, Al 2 Cu, and Al 2 CuMg, which are common in 2xxx and 7xxx series Al alloys.4-9 A number of studies have been performed on electrochemical characteristics of these particles. 4,8,9 In general, they act as local cathodes and sustain oxygen reduction at a high rate to drive the pitting corrosion attack at the particle-matrix interface. In addition, a few studies have related the precipitate size to metastable and stable pitting corrosion in Al-Cu-Mg and Al-Zn-Mg-Cu alloys.10-13 Ralston et al. 11,12 suggested that there was a critical S-phase precipitate size range from ∼3 -8 nm to trigger pitting events. Aged samples with smaller precipitate size had pitting resistance similar to as-quenched samples. The susceptibility to pitting corrosion was greatly enhanced after prolonged aging to create precipitates larger than this critical size range. Gupta et al. 13 reported that a critical precipitate size existed for a transition in electrochemical behavior of 7xxx series Al alloys. For Cu-rich AA7150, increased ...

show abstract

Cerium citrate as ecologically friendly corrosion inhibitor for AA7075 alloy

Marunkić

Pejić

Jegdić

et al. 2022

Materials & Corrosion

View full text Add to dashboard Cite

The corrosion behaviour of high-strength AA7075 aluminium alloy in NaCl solution, without and in the presence of environmentally friendly corrosion inhibitors (Ce-chloride and Ce-citrate) in low concentrations (<0.5 mM), was analysed. The degree of precipitation of the solid solution of AA7075 alloy was determined by measuring the electrical conductivity, while the surface morphology and appearance of intermetallic compounds before and after corrosion testing were analysed by SEM/EDS method. The general corrosion resistance of the tested alloy in NaCl solution and the degree of the inhibitory effect of the corrosion inhibitors were determined on the basis of electrochemical impedance spectroscopy and polarization measurements, while resistance to pit formation on the bases of E pit . AA7075 alloy showed high resistance to general corrosion in the presence of both tested inhibitors, while resistance to pit formation was significantly higher in the presence of Ce-citrate (concentration 0.5 mM). Also, Ce-citrate present in NaCl solution at lower concentrations provides satisfactory resistance of AA7075 alloy to general and pitting corrosion. A mechanism of protective action of Ce-citrate inhibitor has been proposed.

show abstract

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

Cited by 15 publications

References 31 publications

Mechanism of Localized Breakdown of 7000 Series Aluminum Alloys

Mechanism of Localized Breakdown of 7000 Series Aluminum Alloys

Effect of Cu Content and Aging Conditions on Pitting Corrosion Damage of 7xxx Series Aluminum Alloys

Cerium citrate as ecologically friendly corrosion inhibitor for AA7075 alloy

Contact Info

Product

Resources

About