General corrosion of alloy 22: Experimental determination of model parameters from electrochemical impedance spectroscopy data

Models used to predict general corrosion damage of Alloy 22 high level nuclear waste (HLNW) containers must be deterministic, relying upon the time-invariant natural laws, because of long time scales involved in the predictions compared with the time over which the corrosion of this alloy has been studied. The point defect model (PDM) is one such model and requires high-accuracy experimental data to determine model parameters that will accurately predict corrosion over the long times required for HLNW disposal. Electrochemical impedance spectroscopy (EIS) and steady-state polarization data were collected in deaerated 4 M NaCl, pH 6 solutions at 30 °C and 60 °C. This work, which was carried out under a quality assurance program, emphasized data reproducibility and adherence to the steady-state condition in order to ensure confluence between theory and experiment. Thus, fresh electrolyte was continuously flowed through test cells allowing test specimens to remain undisturbed for up to 6 weeks during data collection. Parameters for the PDM have been estimated by optimizing the PDM on the impedance data, and the ability of the parameter values to account for the steady-state passive current density and barrier oxide layer thickness has been evaluated using phase space analysis. The calculated impedance gives generally good agreement with experimental data showing that the PDM is a valid approach. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

The effect of potential and aging on the Pb-assisted stress corrosion cracking susceptibility of alloy 22 gas tungsten arc-welded weldments

The susceptibility of as-received, solutionized, and short-term thermally aged mill-annealed (MA) and gas tungsten arc-welded (GTAW) alloy 22 to Pb-assisted stress corrosion cracking (PbSCC) was evaluated in supersaturated, deaerated, acidic PbCl₂ solutions at 95 °C. Anodic polarization tests in acidic PbCl₂ solutions showed that 16,000 ppm of Pb produced a strong anodic peak and an order of magnitude greater passive current density for both MA and GTAW alloy 22 as compared to pure NaCl solutions. Current spikes were also observed in the anodic polarization plots for the PbCl₂ solutions, suggesting periodic events of passivity breakdown and repassivation. Constant deformation SCC tests were conducted using double U-bend samples of as-received, solutionized, and thermally aged MA and double U-groove welded alloy 22 plates. The results indicate that as-received, solutionized, and thermally aged MA and GTAW alloy 22 were resistant to PbSCC in supersaturated PbCl₂ solutions at 95 °C, pH 0.5, and applied potentials near the anodic peak ranging from −100 to 50 mV_SCE. Enhanced dissolution of alloy 22 was also observed in the crevice region of the double U-bend samples tested in the 16,000 ppm PbCl₂ solutions. This Pb concentration is seven orders of magnitude greater than that found in the anticipated repository environments, and chemical speciation modeling showed that Pb²⁺ is strongly immobilized in J-13 Yucca Mountain waters through the precipitation of PbCO₃ solids. Therefore, although enhanced dissolution of the inner U-bend did occur in our tests, the overall results from this PbSCC investigation suggest that as-fabricated, solutionized, and aged MA and GTAW alloy 22 are resistant to SCC in extremely aggressive, acidic, and supersaturated PbCl₂ solutions at 95 °C. Provided that these high Pb concentrations are not attainable in the anticipated repository environments, alloy 22 is unlikely to be susceptible to SCC, localized corrosion, and enhanced dissolution by the presence of Pb. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

Stress-corrosion-crack initiation and growth-rate studies on titanium grade 7 and alloy 22 in concentrated groundwater

The stress-corrosion-crack initiation and growth-rate response was evaluated on as-received, cold-worked, and aged Alloy 22 (UNS N06022) and titanium Grade 7 in 105 °C to 110 °C, aerated, concentrated, high-pH groundwater environments. Time-to-failure experiments on actively loaded tensile specimens evaluated the effects of applied stress, welding, surface finish, shot peening, cold work, crevicing, and aging treatments in Alloy 22. Titanium Grade 7 and stainless steels were also included in the matrix. Long-term crack-growth-rate data showed stable crack growth in titanium Grade 7. Alloy 22 exhibited stable growth rates under “gentle” cyclic loading, but was prone to crack arrest at fully static loading. No effect of Pb additions was observed. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

Topologically close-packed phase precipitation and thermal stability in alloy 22

The thermal stability of Alloy 22 affected by the precipitation of topologically close-packed (TCP) phases was investigated by means of experimental measurements and thermodynamic calculations. Both mill-annealed and welded specimens were exposed to various thermal aging and solution-annealing treatments. Microstructural analyses showed progressive precipitation of TCP phases in both the mill-annealed and welded specimens upon aging at 870 °C. Solution annealing of the welded material results in homogenization of the fusion zone; however, a high annealing temperature of 1300 °C leads to undesirable grain growth. All aging and solutionizing treatments of the welded material enhance precipitation of the secondary phases. Thermodynamic calculations predicted a solvus temperature of 1271 °C for the TCP phase in the interdendritic region as a result of Mo segregation during the solidification of the welded metal. This model prediction is consistent with experimental results showing that precipitates are observed in the welded material after various solution-annealing treatments. Results obtained from the present study suggest that solution-annealing treatments for Alloy 22 disposal containers should be carefully evaluated to assure that a homogeneous single-phase structure will be obtained. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

Case reviews on the effect of microstructure on the corrosion behavior of austenitic alloys for processing and storage of nuclear waste

This article describes the corrosion behavior of special austenitic alloys for waste management applications. The special stainless steels have controlled levels of alloying and impurity elements and inclusion levels. It is shown that “active” inclusions and segregation of chromium along flow lines accelerated IGC of nonsensitized stainless steels. Concentration of Cr⁺⁶ ions in the grooves of dissolved inclusions increased the potential to the transpassive region of the material, leading to accelerated attack. It is shown that a combination of cold working and controlled solution annealing resulted in a microstructure that resisted corrosion even after a sensitization heat treatment. This imparted extra resistance to corrosion by increasing the fraction of “random” grain boundaries above a threshold value. Randomization of grain boundaries made the stainless steels resistant to sensitization, IGC, and intergranular stress corrosion cracking (IGSCC) in even hot chloride environments. The increased corrosion resistance has been attributed to connectivity of random grain boundaries. The reaction mechanism between the molten glass and the material for process pot, alloy 690, during the vitrification process has been shown to result in depletion of chromium from the reacting surfaces. A comparison is drawn between the electrochemical behavior of alloys 33 and 22 in 1 M HCl at 65 °C. It is shown that a secondary phase formed during welding of alloy 33 impaired corrosion properties in the HCl environment. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

Electrochemical methods to detect susceptibility of Ni-Cr-Mo-W alloy 22 to intergranular corrosion

Alloy 22 (UNS N06022), a Ni-Cr-Mo-W based alloy, is a candidate material for the outer wall of nuclear waste package (NWP) containers. Even though the alloy is highly stable at low temperatures, it could undergo microstructural changes during processing such as welding and stress relieving. Formation of topologically close-packed (TCP) phases such as μ, P, σ, etc. and Cr-rich carbides could make the material susceptible to localized corrosion. Hence, it is important to correlate the microstructural changes with the corrosion resistance of the alloy by nondestructive and rapid electrochemical tests. In this investigation, different electrochemical test solutions were used to quantify the microstructural changes associated with aging and welding of the wrought alloy 22. The results of double-loop (DL) electrochemical potentiodynamic reactivation (EPR) tests in 1 M H₂SO₄+0.5 M NaCl+0.01 M KSCN solution indicated Cr depletion during initial stages of aging of wrought alloy 22. Results of EPR tests in 2 M HCl+0.01 M KSCN solution at 60 °C correlated well with the Mo depletion that occurred near TCP phases formed during aging of both weld and wrought alloy 22 materials. The EPR test results were compared with standard chemical weight loss measurements specified by ASTM standard G-28 methods A and B.     

Corrosion-creep interaction of stainless alloys in acid chloride solutions

Rupture of passive film is considered as an essential step in the stress corrosion cracking (SCC) process. At constant load, accumulation of creep strain is often associated with the strain to passive film rupture. Therefore, low-temperature creep behavior of a material is important from an SCC point of view. Constant load creep studies carried out on alloy 22 (a Ni-22Cr-13Mo-4W alloy) in acidified chloride environments at 80 °C showed a logarithmic creep behavior. The creep strain decayed logarithmically and reached values less than 4×10⁻⁹/s, which is lower than the detectable limit of laboratory scale SCC tests. 304 SS showed SCC failure in acidified chloride solutions in simulated open circuit conditions. A steady-state creep strain rate could be observed during SCC failures, of the order of 10⁻⁵ to 10⁻⁶/s. The high creep strain rate of 304 SS can be correlated to the observed higher corrosion currents, which were more than 40 times that observed in alloy 22. When the dissolution rate of alloy 22 was increased by impressing about 1 mA/cm² anodic current, a steady-state creep strain rate of 6.5×10⁻⁸/s was observed. The results indicated that anodic dissolution increased the localized plasticity of the material, resulting in creep strain. However, alloy 22 did not show SCC. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

Risk assessment of uniform and localized corrosion of alloy 22

The risk associated with the performance of alloy 22 waste package (WP) in the potential repository for high-level nuclear waste at Yucca Mountain (YM) was assessed using the Nuclear Regulatory Commission’s Total-System Performance Assessment (TPA) Code. The high-temperature (above 100 °C) deliquescence relative humidity (RH) from mixed salt deposits on the WP surface was evaluated by lowering the critical RH (RH_critical) for aqueous corrosion to 35 to 60 pct. For the base case values of the critical potential for initiation of localized corrosion, the estimated dose increased from 0.05 to 1 mrem/year in 10,000 years by altering RH_critical. For the modified case, by adding more data and refining the fitting, the estimated dose increased to 3.8 mrem/year at 10,000 years without lowering RH_critical. Using the new repassivation potential with nitrate as an inhibitor without changes in RH_critical, the estimated dose decreased to 0.03 mrem/year at 10,000 years. Taking credit for the remaining surface area of the WP after failure by localized corrosion reduces the estimated dose from 4 to 0.4 mrem/year. Anodic sulfur segregation at the interface of metal and passive film and subsequent spalling of passive film may enhance uniform corrosion. The cyclic process of fast active corrosion upon sulfur segregation followed by slow passive corrosion upon repassivation is unlikely to significantly reduce the WP lifetime. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

Environmental Testing of Iron-Based Amorphous Alloys

Iron (Fe)-based amorphous alloys possess enhanced hardness and are highly resistant to corrosion, which make them desirable for wear applications in corrosive environments. It was of interest to examine the behavior of amorphous alloys during anodic polarization in concentrated salt solutions and in the salt-fog testing. Results from the testing of one amorphous material (SAM2X5) both in ribbon form and as an applied coating are reported here. Cyclic polarization tests were performed on SAM2X5 ribbon as well as on other nuclear engineering materials. SAM2X5 showed the highest resistance to localized corrosion in 5 M CaCl₂ solution at 105 °C. Salt fog tests of 316L SS and alloy 22 coupons coated with amorphous SAM2X5 powder showed resistance to rusting. Partial devitrification may be responsible for isolated pinpoint rust spots in some coatings. This article is based on a presentation given in the symposium entitled “Materials Issues for Advanced Nuclear Systems,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the Corrosion and Environmental Effects Committee of ASM-TMS.     

Examination of Galvanic Action between Fe-Based Bulk Metallic Glass and Crystalline Alloys

Fe-based bulk metallic glasses (amorphous metals) have been developed, and several compositions are shown to have excellent corrosion resistance in chloride solutions. Further, thermal-spray amorphous metals are being developed for use as a barrier coating layer, to protect substrate materials from corrosion. Galvanic action between dissimilar metals and the coating/substrate for the amorphous-alloy coatings is of practical interest for a number of applications. The mixed-potential theory provides a useful approach for examining the corrosion behavior of the component materials in the galvanic couple and is applied in this study. Galvanic action was studied for an Fe-based structurally amorphous metal (SAM) 1651 and several crystalline alloys that included 1018 C-steel, stainless steel (SS) 316L, and alloy 22. Anodic and cathodic polarization curves of each of the metals were measured by potentiodynamic polarization. Based on the mixed-potential theory, the behavior of the component materials in a galvanic cell was predicted. The predictions are compared to the measured behavior of galvanic couples with the crystalline alloys. This article is based on a presentation given in the symposium entitled “Iron-Based Amorphous Metals: An Important Family of High-Performance Corrosion-Resistant Materials,” which occurred during the MSandT meeting, September 16–20, 2007, in Detroit, Michigan, under the auspices of The American Ceramics Society (ACerS), The Association for Iron and Steel Technology (AIST), ASM International, and TMS.     

采用SECM分析7075铝合金的局部腐蚀行为

使用0.6 mol/LNaCl溶液腐蚀7075铝合金, 采用扫描电化学显微镜进行逼近曲线、面扫描测试, 用X射线衍射仪对合金的形貌进行分析, 用能谱仪分析腐蚀产物成分, 研究7075铝合金局部腐蚀电化学机理.结果显示:逼近曲线呈现正反馈, 探针的电流随着与合金基底距离的减小变大; 合金表面的活性点因为氯离子活化作用不断增加, 形成大范围的点蚀; 氯离子通过吸附在合金表面钝化层并与之反应, 破坏钝化层使得内部裸露, 内部的第2相电极电位更负, 和铝基体构成腐蚀微电池, 第2相的阳极腐蚀溶解降低合金的强度和抗腐蚀能力.      

Corrosion behavior of carbon steel rock bolt in simulated Yucca Mountain ground waters

Medium carbon steel (AISI 1040) was one of the candidate materials for rock bolts to reinforce the borehole liners and emplacement drifts of the high-level nuclear waste repository in Yucca Mountain. The corrosion performance of this structural steel was investigated by techniques such as linear polarization, electrochemical impedance spectroscopy (EIS), and laboratory immersion tests in simulated ground waters. The corrosion rates of the steel were measured for the temperatures in the range from 25 °C to 85 °C, for the ionic concentrations of 1 time (1×), 10 times (10×), and a hundred times (100×) ground water concentration. The steel corroded uniformly at penetration rates of 35 to 200 μm/year in the deaerated waters, and at 200 to 1000 μm/year in the aerated waters. Increasing temperatures in the deaerated waters increased the corrosion rate of the steel. However, increasing ionic concentrations influenced the corrosion rate only slightly. In the aerated 1×and 10×waters, increasing temperatures increased the rates of the steel significantly. In the aerated 100×waters, the corrosion rate increased from 25 °C to 45 °C and decreased at higher temperatures (65 °C and up) due to the formation of oxide/hydroxide films and salt scales on the surface of the steel specimen. The steel suffered pitting corrosion in the both deaerated and aerated hot ground water environments after anodic polarization. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the. TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

Corrosion Behavior of Top and Bottom Surfaces for Single-Side and Double-Side Friction Stir Welded 7085-T7651 Aluminum Alloy Thick Plate Joints

Thick plate joints of 7085-T7451 aluminum alloy were obtained through both single-side and double-side friction stir welding (SS or DS-FSW). The chloride ions effects on the corrosion behavior of the top and bottom surfaces of the joints were examined by cyclic potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Results show that the corrosion susceptibility was suppressed significantly in the weld nugget zone, while the base material and heat-affected zone were prone to be corrosion attacked. For the SS-FSWed joint, the top surface showed a higher corrosion resistance than that of the bottom surface, but the larger corrosive heterogeneity was observed between the top and bottom surfaces compared with the two welds of DS-FSWed joint, which was confirmed by the morphology of corrosion attack. A deep insight on the microstructure of the joints indicates that the intermetallic particles played a key role in the corrosion behavior of the FSWed AA7085 aluminum alloy joints in chloride solution.     

Comparison of Crevice Corrosion of Fe-Based Amorphous Metal and Crystalline Ni-Cr-Mo Alloy

The crevice corrosion behaviors of an Fe-based bulk metallic glass alloy (SAM1651) and a Ni-Cr-Mo crystalline alloy (C-22) were studied in 4M NaCl solution at 100 °C with cyclic potentiodynamic polarization and constant-potential tests. The corrosion damage morphologies, corrosion products, and the compositions of corroded surfaces of these two alloys were studied with optical three-dimensional reconstruction, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Auger electron spectroscopy (AES). It was found that the Fe-based bulk metallic glass (amorphous alloy) SAM1651 had a more positive breakdown potential and repassivation potential than crystalline alloy C-22 in cyclic potentiodynamic polarization tests and required a more positive oxidizing potential to initiate crevice corrosion in constant-potential tests. Once crevice corrosion initiated, the corrosion propagation of C-22 was more localized near the crevice border compared to SAM1651, and SAM1651 repassivated more readily than C-22. The EDS results indicated that the corrosion products of both alloys contained a high amount of O and were enriched in Mo and Cr. The AES results indicated that a Cr-rich oxide passive film was formed on the surfaces of both alloys, and both alloys corroded congruently in the crevice corrosion damage areas. This article is based on a presentation given in the symposium entitled “Iron-Based Amorphous Metals: An Important Family of High-Performance Corrosion-Resistant Materials,” which occurred during the MSandT meeting, September 16–20, 2007, in Detroit, Michigan, under the auspices of The American Ceramics Society (ACerS), The Association for Iron and Steel Technology (AIST), ASM International, and TMS.

---

AZ31镁合金微区电偶腐蚀的数值研究

结合水平集函数方法及移动网格技术,利用有限元法模拟分析了离散型β相分布和连续型β相分布的AZ31镁合金在NaCl溶液中的腐蚀行为,通过解Nernst-Planck方程得到腐蚀过程中AZ31镁合金/NaCl界面的电势、氯离子及镁离子浓度分布,并通过扫描离子选择性电极实验验证了此模拟方法的可行性.模拟分析表明,当β相离散分布在α相周边时,在与β相相邻的α相区域腐蚀速率最快,形成腐蚀缩颈坑,坑内氯离子富集,进一步加速了α相的腐蚀,最终β相逐渐脱离合金进入溶液;当β相连续分布在α相周边时,α相不断被腐蚀,最终α相全部溶解而只剩β相,求解随即停止.扫描离子选择性电极实验结果表明此模拟模型可以对镁合金的电化学腐蚀进行较好预测和判断.      

Combined effect of chloride and pH on corrosion resistance of Cu-10Ni alloy

Cu-10Ni alloy is a standard heat exchanger material for saltwater (including seawater) applications owing to its excellent thermal conductivity and corrosion resistance. The excellent corrosion resistance is due to formation of Cu₂O film, which accords protection. However, when varying amount of H⁺, OH^? and Cl^? ions are present, CuCl₂ ^? may also form. The CuCl₂ ^? is not protective as Cu₂O and hence corrosion resistance may be affected. Present paper investigates combined effect of chloride ion and pH on corrosion resistance of Cu-10Ni alloy. Cathodic and anodic polarization test results are presented for saltwater containing various amounts of NaCl at pH 6 and 8. It is found that, i_corr increases with increasing chloride concentration. The results are discussed using dissolution mechanisms, semi-conducting behaviour of Cu₂O film and deterioration of the film in presence of chloride ions.     

NC30Fe合金在氯化钠溶液中的微动腐蚀特性

在PLINT微动磨损试验机上附加电化学测试系统,采用十字交叉接触方式,位移幅值为100μm,法向载荷20、50和80 N条件下,研究NC30Fe合金传热管在氯化钠溶液中的微动腐蚀行为.使用电化学工作站记录微动腐蚀过程中开路电位变化,运用电位扫描法测量微动过程的极化曲线;采用扫描电子显微镜观察磨痕的表面形貌,光学轮廓仪测定磨痕的三维形貌及磨损量.微动磨损使损伤区域金属原子活性增大,腐蚀倾向增大,加速了NC30Fe合金的腐蚀.在氯化钠溶液中,NC30Fe合金由于微动磨损过程产生腐蚀产物膜起到润滑减摩作用,摩擦系数较纯水中降低;但因腐蚀与磨损的交互作用,在氯化钠溶液中的磨损量比纯水中高.氯化钠溶液中的磨损机制主要表现为磨粒磨损和剥层的共同作用.      

CP-Ti在含氟离子硝酸中电化学腐蚀行为

采用开路电位(OCP)、动电位极化曲线(PPC)、电化学阻抗谱(EIS) 3种电化学测试手段对工业纯钛(CP-Ti)在含氟离子硝酸溶液中的电化学腐蚀行为进行研究。结果表明:随着硝酸溶液中氟离子浓度的增加,CP-Ti耐蚀性变差;影响CP-Ti耐蚀性转变的临界氟离子浓度为1. 25 mmol/L;氟离子与CP-Ti表面的氧化膜发生反应,致使均匀、致密的氧化膜溶解转变为多孔膜,降低了CP-Ti的耐蚀性。     

Characterization of retrogression and reaging behavior of 8090 Al-Li-Cu-Mg-Zr alloy

An 8090 Al-Li-Cu-Mg-Zr alloy in the peak-aged (T8) temper was subjected to retrogression treatment at temperatures above and below the δ′ (Al₃Li) solvus line and immediately reaged to various tempers. Retrogression and reaging (RRA) behavior is characterized by hardness testing, tensile testing, transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and electrochemical polarization studies. Retrogression of the T8 temper alloy causes dissolution primarily of δ′ (Al₃Li) precipitates into solid solution that results in a decrease of hardness and tensile strength and an increase of ductility of the alloy. Reaging of the retrogressed state causes reprecipitation of the δ′ precipitates in the matrix resulting in the restoration of strength and ductility properties. Retrogression and reaging to the peak-aged temper, designated at T77 temper, has been found to retain the strength of the conventional T8 temper, but with the gross aging time in the RRA temper almost twice that of the conventional T8 temper, the microstructure of the RRA temper approaches that of the overaged (T7) temper. Thus, RRA treatment contributes to an improvement of stress corrosion cracking (SCC) resistance over the conventional T8 temper while retaining the mechanical properties of T8 temper.     

Corrosion fatigue of a precipitation-hardened Al-Li-Zr alloy in a 0.5 M sodium chloride solution

Corrosion fatigue (CF) experiments have been performed on a high-purity Al-2.5Li-0.12Zr alloy in a deaerated 0.5 M sodium chloride solution as a function of aging time. The results of these tests were compared to the results of fatigue tests performed in dry air to investigate the effect of aging on the CF susceptibility of the alloy. It was found that the high cycle fatigue strength of the alloy was dramatically reduced by the aqueous environment. Examinations of the relative fatigue strength (Δσ_NaCl/Δσ_air) indicated that the underaged (UA) alloys were more susceptible to CF than the overaged (OA) alloys over the stress ranges studied, but the difference of the susceptibility between the UA and the OA alloys was reduced by decreasing the applied cyclic stress. The evidence suggests that, for the UA Al-Li-Zr alloys, the CF resistance is determined by both slip-enhanced dissolution and hydrogen embrittlement at high stress ranges, while at low stress ranges, the CF life is predominantly controlled by pitting-induced crack initiation regardless of the aging condition of the alloy.