Studies on Pitting Corrosion of Al-Cu-Li Alloys Part II: Breakdown Potential and Pit Initiation

Abstract

Prediction of the accumulated pitting corrosion damage in aluminum-lithium (Al-Li) is of great importance due to the wide application of these alloys in the aerospace industry. The Point Defect Model (PDM) is arguably one of the most well-developed techniques for evaluating the electrochemical behavior of passive metals. In this paper, the passivity breakdown and pitting corrosion performance of AA 2098-T851 was investigated using the PDM with the potentiodynamic polarization (PDP) technique in NaCl solutions at different scan rates, Cl− concentrations and pH. Both the PDM predictions and experiments reveal linear relationships between the critical breakdown potential (Ec) of the alloy and various independent variables, such as a C l − and pH. Optimization of the PDM of the near-normally distributed Ec as measured in at least 20 replicate experiments under each set of conditions, allowing for the estimation of some of the critical parameters on barrier layer generation and dissolution, such as the critical areal concentration of condensed cation vacancies (ξ) at the metal/barrier layer interface and the mean diffusivity of the cation vacancy in the barrier layer (D). With these values obtained—using PDM optimization—in one set of conditions, the Ec distribution can be predicted for any other set of conditions (combinations of a Cl − , pH and T). The PDM predictions and experimental observations in this work are in close agreement.

Studies on Pitting Corrosion of Al–Cu–Li Alloys Part III: Passivation Kinetics of AA2098–T851 Based on the Point Defect Model

“…Using the point defect model (PDM), the near-normal distribution of breakdown potential of AA2098–T851 for one [Cl − ] was optimized and the optimized model parameters were used to predict the distributions for other [Cl − ] concentrations. The predicted distributions were found to be in close agreement with experimental results [14]. However, no further insight in regard to the passivation kinetics and underlying mechanisms of the phenomena was provided by the previous papers.…”

“…In previous papers of this series (paper I and II), passivity breakdown and pit initiation on AA2098–T851 along with two other Al alloys with comparable composition, except for Li content, were investigated using the potentiodynamic polarization technique and damage morphology characterizations. AA2098–T851, which had higher Li content than the other two alloys (AA2029–T8 and AA2060–T8), showed the best pitting resistance behavior [13,14]. Using the point defect model (PDM), the near-normal distribution of breakdown potential of AA2098–T851 for one [Cl − ] was optimized and the optimized model parameters were used to predict the distributions for other [Cl − ] concentrations.…”

Insights on the Al-Cu-Fe-Mn intermetallic particles induced pitting corrosion of Al-Cu-Li alloy

“…The corrosion can be inhibited by the higher concentration of OH − which produced by the reaction of metallic Li with water. This OH − which can neutralize the acidic pitting region and make the pits more superficial [28,29]. Ghanbari and Lei [28,29] applied various electron microscopy and electrochemistry techniques and point defect model method to investigate the localized corrosion of Al-Li alloys in order to prove the effect of Li.…”

Effect of different aging processes on the corrosion behavior of new Al–Cu–Li–Zr–Sc alloys

“…With advantages such as low density, high modulus, good abrasion resistance, high thermal stability, good processability, and small anisotropy, the Al–Li alloy is an essential lightweight structural material used in the aerospace, shipbuilding, and other industries . To enhance the strength and toughness of Al–Li alloys, multielement alloying is often carried out by adding various elements, most commonly, main alloying elements such as Cu and Mg and trace elements such as Ag, Ce, Y, La, Ti, Mn, Sc, and Zr . Al–Li–Cu–Zr alloys (ie, the 2xxx system) are one of the main Al–Li alloys currently used .…”