Zum Spannungsrißkorrosionsverhalten rekristallisierter Bleche der AlLi-Legierung 8090-T81

On the stress corrosion cracking behaviour of recrystallized 8090-T81 Sheets The stress corrosion cracking behaviour of a recrystallized sheet of the Al-Li-Cu-Mg-Zr alloy 8090-T81 was studied performing accelerated tests under constant deformation, constant load, and slow strain rate conditions. The used electrolytes were an aqueous 3.5% NaCl solution, an aqueous solution of 2% NaCl + 0.5% Na₂CrO₄ at pH = 3, and synthetic seawater according to ASTM D1141. Alternately immersed in 3.5% NaCl solution according to ASTM G44 the investigated alloy was found to be susceptible to stress corrosion cracking was not promoted by continuous immersion in aerated 3.5% NaCl solution, 3.5% NaCl solution saturated with carbon dioxide, and in acid chromate inhibited 2% NaCl solution. Using the slow strain rate technique with continuously immersed flat tensile specimens stress corrosion cracking was only observed in synthetic seawater. Under specific environmental conditions hydrogen embrittlement can occur in the investigated material.     

Investigation of the SCC behaviour of alloy 2024 using the slow strain rate technique

The stress corrosion cracking (SCC) behaviour of 2024 plate in T351 and T851 tempers was investigated in short transverse direction performing accelerated tests under constant deformation, constant load and slow strain rate conditions. Corrosive media used were: aqueous 3.5% NaCl solution, an aqueous solution of 2% NaCl + 0.5% Na₂CrO₄ at pH 3 (according to LN 65666), an aqueous solution of 3% NaCl + 0.3% H₂O₂, and substitute ocean water according to ASTM D1141. Alternate immersion tests in 3.5% NaCl solution indicated the low SCC resistance of the alloy 2024-T351 as well as the improved SCC behaviour due to aging to T851 condition. Similar results were obtained from constant load tests under permanent immersion conditions in the acidified chloride-chromate solution, in 3% NaCl solution with peroxide, and in substitute ocean water, whereas no SCC failure was observed with specimens which were permanently immersed in 3.5% NaCl solution. Using the slow strain rate method, 3% NaCl + 0.3% H₂O₂ and substitute ocean water were found to be effective synthetic environments. The other two electrolytes did not promote severe stress corrosion cracking with alloy 2024-T351. The SCC behaviour of 2024-T851 was difficult to determine employing the slow strain rate technique. Large scatter in data, observed even in inert environment, and the low elongation of the aged material, exacerbated by a further degradation of ductility due to pitting and intergranular corrosion, precluded an evaluation.     

Spannungsrißkorrosionsuntersuchungen an Strangpreßbarren der Legierungen 8090-T851 und 2091-T851

On the stress corrosion cracking behaviour of flat extrusions of the alloys 8090-T851 and 2091-T851 The stress corrosion cracking (SCC) behaviour of flat extrusions of the Al-Li-Cu-Mg-Zr alloys 8090-T851 and 2091-T851 was investigated performing accelerated tests under constant deformation, constant load, and slow strain rate conditions. The used corrosive environments were an aqueous 3.5% NaCl solution and an aqueous solution of 2% NaCl + 0.5% Na₂CrO₄ at pH = 3. Round tensile specimens and tuning fork type specimens were alternately immersed in 3.5% NaCl solution according to ASTM G44 under constant deformation, whereas they were continuously immersed in the other tests. The investigated flat extrusions of the alloy 8090-T851 were stress corrosion resistant in the extrusion and the long transverse directions. With the alloy 2091-T851 failure was observed at 75% of the 0.2 proof stress which may be caused by stress corrosion cracking or stress assisted intergranular corrosion. In the short transverse direction the SCC behaviour of the extrusions of both Al-Li alloys is comparable with that of a 2024-T351 alloy plate revealing a high SCC susceptibility.     

Comparison of accelerated SCC tests performed on the aluminium alloy 2014-T651

The stress corrosion cracking (SCC) behaviour of plates of the Al-Cu-Si-Mn-Mg alloy 2014-T651 was investigated in short transverse direction performing various accelerated tests. Corrosive media used were: aqueous 3.5% NaCl solution, an aqueous solution of 2% NaCl + 0.5% Na₂CrO₄ at pH = 3 (according to LN 65666), and substitute ocean water according to ASTM D1141. C-ring and tensile specimens were loaded under constant deformation, constant load and slow strain rate conditions. Alternate immersion tests in 3.5% NaCl solution clearly indicate the low SCC resistance of the alloy 2014-T651 in short transverse direction. Under continuous immersion conditions the acidified 2% NaCl solution containing chromate is an appropriate synthetic environment, while neutral 3.5% NaCl solution does not promote severe stress corrosion cracking. The SCC susceptibility of 2014-T651 is also observed in slow strain rate tests using substitute ocean water as well as acidified 2% NaCl solution inhibited by chromate. In 3.5% NaCl solution the evaluation of slow strain rate data is complicated by pre-exposure effects.     

LC4高强铝合金的腐蚀性能研究

利用慢应变速率拉伸试验方法研究了LC4铝合金在空气和3．5％NaCl溶液中的应力腐蚀断裂行为；利用HB5455－90标准研究了LC4铝合金的剥蚀行为；利用HB5255－83标准研究了LC4铝合金的晶间腐蚀行为。结果表明：LC4铝合金具有应力腐蚀敏感性，应力腐蚀的断口形貌受应变速率ε的影响较大；LC4铝合金对剥蚀很敏感，对晶间腐蚀不是很敏感。     

2219铝合金母材及搅拌摩擦焊接头应力腐蚀敏感性

利用慢应变速率拉伸试验,研究2219铝合金母材及搅拌摩擦焊接头在不同腐蚀介质环境中的应力腐蚀行为.运用性能损失率指标和应力腐蚀指数评价材料的应力腐蚀敏感性.结果表明,应变速率为10-6 s-1时,2219铝合金母材和FSW接头在3.5%Na Cl介质环境中SCC敏感性小,断口由韧窝塑性区和腐蚀区组成;在剥蚀介质环境中,母材和FSW接头SCC敏感性大,断口呈冰糖状,有较深的腐蚀坑和二次裂纹,为沿晶脆性断裂.FSW接头SCC敏感性较母材大.     

On the resistance of duplex steel to stress corrosion cracking

The paper gives the results of tests carried out into the stress corrosion cracking in duplex stainless steel (Type 02Cr22Ni5Mo3N, W.Nr. 1.4462); this grade is characterized by high resistance to intergranular corrosion, while resistance to stress corrosion cracking may be impaired by temperature and mode of loading. This behaviour requires special attention. The tests included testing in 35% MgCl₂ solution under constant load at 120°C, the drop evaporation test using a 0.1 mol · 1^? NaCl solution and the slow strain rate test in 35% MgCl₂ solution at 120°C.     

Stress corrosion cracking of a recent rare-earth containing magnesium alloy,EV31A,and a common Al-containing alloy,AZ91E

Stress corrosion cracking of the magnesium alloy Elektron 21 (ASTM–EV31A) and AZ91E was studied using constant load test in 0.1 M NaCl solution (saturated with Mg(OH)₂), and slow strain rate test using glycerol, distilled water and Mg(OH)₂ saturated, 0.01 M and 0.1 M NaCl solutions. Slow strain rate test indicated that EV31A was less susceptible to stress corrosion cracking than AZ91E. Under less intense loading of constant load, EV31A was found to be resistant to stress corrosion cracking. Fractography of EV31A specimens showed little evidence of hydrogen embrittlement. The superior resistance of EV31A is attributed to a more robust oxide/hydroxide layer.     

On the Stress corrosion cracking behaviour of aluminium alloy sheet in an aqueous solution of 3% NaCl + 0.3% H2O2

The stress corrosion cracking (SCC) behaviour of aluminium alloy sheet was investigated in the long transverse direction using the slow strain rate testing technique. The synthetic environment used was an aqueous solution of 3% NaCl + 0.3% H₂O₂. No indications of SCC sensitivity are observed for the alloys 2024-T351, 8090-T81, and 2091 CPHK-T8X. The alloys 2091 T8X and 6061-T4 are found to be susceptible to intergranular stress corrosion cracking. At strain rates below 4 · 10^?7 s^?1, the slow strain rate testing technique indicates a slight SCC sensitivity with alloy 6013-T6. Fractography reveals transgranular stress corrosion cracking. Transgranular stress corrosion cracking is also observed with 6061-T4 specimens which are dynamically strained at strain rates below 5 · 10^?7 s^?1. Aqueous 3% NaCl solution with hydrogen peroxide addition promotes pitting and intergranular corrosion. The loss of ductility caused by these corrosion processes interferes with the evaluation of the results of the slow strain rate testing technique.     

国产825合金的耐腐蚀性能研究

采用腐蚀失重法、电化学测试和慢应变速率拉伸应力腐蚀研究了国产825合金在HCl、NaOH和NaCl溶液中的腐蚀行为,并采用金相显微镜和扫描电镜（SEM）对腐蚀后的样品进行观察。结果表明,国产825合金在HCl溶液中浸泡7 d后发生了明显的腐蚀,腐蚀速率随HCl浓度的增加而增大,而在NaOH和NaCl溶液中浸泡5个月后未发生明显腐蚀,并且在HCl、NaOH和NaCl溶液中合金的腐蚀电流随溶液浓度增加而增大。慢应变速率拉伸应力腐蚀结果表明在HCl、NaOH和NaCl溶液中合金的应力腐蚀敏感性很小,因此,一般情况下不会发生应力腐蚀开裂。     

Effect of pre-deformation on the stress corrosion cracking susceptibility of aluminum alloy 2519

The effects of pre-deformation and strain rate on the stress corrosion cracking （SCC） behavior of aluminum alloy 2519 in air and in 3.5% NaCI water solution were investigated by means of slow strain rate tension （SSRT）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results indicate that the alloy is susceptible to SCC in 3.5% NaCI water solution and not in air. At the same pre-deformation, the alloy is more susceptible to SCC at 1.33 × 10^-5 s^-1 than at 6.66 × 10^-5 s^-1. Moreover, it is more susceptible to SCC at free pre-deformation than at 10% pre-deformation at the same strain rate. The number of 0 precipitated along the grain boundaries is reduced and distributed discontinuously, at the same time, the precipitate-free zones （PFZ） become narrow and the susceptibility to stress corrosion cracking is reduced after 10% pre-deformation.     

Corrosion susceptibility of peened friction stir welded 7075 aluminum alloy joints

Effects of surface treatment techniques like laser and shot peening on stress corrosion cracking (SCC) susceptibility of friction stir welded (FSW) 7075 aluminum alloy joints were investigated. This study had two parts; the first part investigated the peening effects on stress corrosion cracking susceptibility in FSW samples by slow strain rate testing in a 3.5% NaCl solution. The second part of the study investigated the effects of peening on corrosion while submerged in a 3.5% NaCl solution with no external loads applied. No signs of corrosion pitting or SCC were evident on any of the tensile samples during the slow strain rate testing. The FSW plates exposed in 3.5% NaCl solution for 60 days were inspected periodically for signs of corrosion and stress corrosion cracking in the areas expected to have residual stresses due to welding. Pitting corrosion was seen on the samples, but even after 60 day exposure no stress corrosion cracking was detected on any of the peened or unpeened samples.     

Slow strain rate testing of high-strength aluminium alloy plate in an aqueous solution of 3% NaCl + 0.3% H2O2

The stress corrosion cracking (SCC) behaviour of aluminium alloy plate materials was investigated in the short transverse direction using the slow strain rate (SSR) testing technique. The synthetic environment used was an aqueous solution of 3% NaCl + 0.3% H₂O₂. Reference tests under constant deformation and alternate immersion conditions according to ASTM G44 were performed, too. Both static and dynamic loading tests indicate high SCC susceptibility with the alloys 2024-T351, 2091-T8X51, 7050 T651 and 7475-T651. For the alloy 8090-T8171, a low SCC resistance is found in the alternate immersion tests, whereas a rather moderate sensitivity is observed performing SSR tests. The SSR testing technique fails to indicate the SCC sensitivity of the more resistant alloys 2024-T851 and 7050-T7651. As demonstrated by pre-exposure tests, the reduction of fracture energy observed with the latter alloys as well as with the immune alloys 7050-T7351 and 7475-T7351 is caused by pitting and intergranular corrosion. Using an aqueous solution of 3% NaCl + 0.3% H₂O₂, the SSR testing technique is a useful rapid method to screen wrought aluminium alloys which are quite sensitive to environmentally assisted cracking. Because chloride-peroxide solutions are also conducive to corrosion processes independent of stress, pre exposure tests are required to be incorporated into such sorting tests.     

Environmentally assisted cracking behaviour of plasma electrolytic oxidation coated AZ31 magnesium alloy

Abstract

A wrought AZ31 magnesium alloy was plasma electrolytic oxidation (PEO) coated in phosphate and silicate based alkaline electrolytes. The effect of these PEO coatings on the stress corrosion cracking (SCC) behaviour of the alloy was investigated by slow strain rate tensile (SSRT) tests in ASTM D1384 solution. The untreated and PEO coated AZ31 magnesium alloy specimens were found to be susceptible to SCC, despite the fact that the PEO coatings offered an excellent general corrosion resistance. The results of the polarisation tests on the untreated AZ31 alloy specimen after prolonged immersion in ASTM D1384 electrolyte suggested the formation of a film on the surface constituted by the corrosion products. The cracking of this film and the evolution/ingress of hydrogen at these defective sites during the SSRT tests in the corrosive environment was believed to be responsible for the SCC of the untreated alloy. Similarly, the cracking of the PEO coatings during the SSRT test, the consequent exposure of the underneath magnesium alloy substrate and the associated electrochemical reactions were attributed as reasons for the SCC of the PEO coated specimens. The transgranular mode of fracture in all the cases avowed that the hydrogen induced cracking was the mechanism of SCC.     

Stress corrosion cracking behaviour of 2091 Al—Li alloy in sulphate and chloride containing solutions

Abstract

The stress corrosion cracking resistance of 2091 Al—Li alloy in underaged, and in peak aged condition was investigated in chloride solutions with or without sulphate addition using both the static load technique and the slow strain rate technique. It is shown that the underaged material is more resistant than peak aged material. Sulphate additions to chloride solutions increase the stress corrosion cracking susceptibility. Metallographic cross-section observations show the simultaneous occurrence of other kinds of corrosion: generalised. corrosion, pitting corrosion, intergranular corrosion, and exfoliation corrosion. It appears that stress corrosion cracking susceptibility increases as the extent of intergranular corrosion decreases.     

Pitting and stress corrosion cracking resistance of friction stir welded AA 5083

The corrosion behaviour of friction stir welded (FSW) joints of AA 5083 has been compared to that of MIG welded joints. Pitting and stress corrosion cracking (SCC) resistance in 3.5% NaCl + 0.3 g/l H₂O₂ and in EXCO (4 M KCl + 0.5 M KNO₃ + 0.1 M HNO₃) solutions has been determined at 25°C. SCC susceptibility was evaluated by slow strain rate tests (SSRT), at a strain rate of 1 × 10⁻⁶ s⁻¹.Welds obtained by FSW technique showed a higher corrosion resistance in EXCO solution and a lower pitting tendency than the base alloy. Electrochemical measurements (corrosion potential measurements, polarization curves recording) evidenced that FSW weld was cathodic to base alloy. FSW joints were not susceptible to SCC in both test solutions, whereas MIG joints cracked in both solutions.     

Effects of nonhalide anions on the stress corrosion cracking behaviour of alloy 7475 in the tempers T651 and T7351

The stress corrosion cracking behaviour of 7475 plate material in the tempers T651 and T7351 was investigated performing constant load tests. Short transverse specimens were permanently immersed in aerated aqueous 0.6 M sodium chloride solutions with additions of 0.03 M sodium sulphate, 0.03 M sodium nitrate and 0.1 M sodium bicarbonate. Chloride solutions containing sulphate, nitrate or/and bicarbonate promoted environment‐induced cracking. A short transverse threshold stress below 50 MPa was found for 7475‐T651 plate material. Neutral 0.6 M NaCl solution was less conducive to stress corrosion cracking. Specimens of alloy 7475 in the overaged temper T7351 failed at applied stresses above 300 MPa. This failure resulted from overload fracture caused by a reduction of cross‐sectional area due to pitting corrosion, as confirmed by fractography showing severe pitting attack. Fractographic examinations of 7475‐T7351 specimens failed during immersion in chloride‐nitrate‐bicarbonate containing solutions with or without addition of sulphate after long exposure time periods revealed slight transgranular stress corrosion cracking, too. Pronounced transgranular environment‐induced cracking was observed on the fracture surfaces of specimens which were exposed to an aqueous solution containing chloride, sulphate, nitrate, and bicarbonate for 30 days at applied stress and were subsequently tensile tested in an inert environment.     

The effects of low frequency load cycles on crack initiation in low alloy steels

The stress corrosion behaviour of low alloy steels was investigated with low frequency cyclic loading in 2 M (NH₄)₂CO₃ at 70°C. The tests were carried out using triangular and sawtooth load cycles with a constant critical strain-rate prevailing within periods of increasing stress irrespective of frequency. Since frequency changes with stress amplitude when using equal ?-values, the effects of frequency were also determined. The experiments were concentrated on crack initiation and initial crack propagation. The results show that the threshold stress which causes stress corrosion cracking (SCC) in ammonium carbonate solution is considerably reduced for all steels tested during low-frequency load cycles. In contrast to tests with constant load, propagating stress corrosion cracks can be initiated below the lower yield strength. The effects of stress/strain amplitude and of the magnitude of deformation on crack propagation were determined.     

Effect of Cooling Rate on SCC Susceptibility of β-Processed Ti–6Al–4V Alloy in 0.6M NaCl Solution

The effects of cooling rate on the stress corrosion cracking (SCC) susceptibility of β-processed Ti–6Al–4V (Ti64) alloy, including BA/S specimen with furnace cooling and BQ/S specimen with water quenching, were investigated in 0.6M NaCl solution under various applied potentials using a slow strain rate test technique. It was found that the SCC susceptibility of β-processed Ti64 alloy in aqueous NaCl solution decreased with fast cooling rate, which was particularly substantial under an anodic applied potential. The micrographic and fractographic analyses suggested that the enhancement with fast cooling rate was related to the random orientation of acicular α platelets in BQ/S specimen. Based on the experimental results, the effect of cooling rate on the SCC behavior of β-processed Ti64 alloy in aqueous NaCl solution was discussed.     

Environmentally assisted cracking resistance of Al–Cu–Li alloy AA2195 using slow strain rate test in 3.5% NaCl solution

The general corrosion and environmental cracking resistances of Al–Cu–Li alloy AA2195 were investigated in 3.5% NaCl environment and compared with those of another high strength alloy AA2219. The general corrosion resistance of these alloys was examined using immersion corrosion and potentiodynamic polarization tests, while the stress corrosion cracking (SCC) resistance was evaluated by slow strain rate test (SSRT) method. The tested samples were further characterized by SEM–EDS and optical profilometry to study the change in corrosion morphology, elemental content and depth of corrosion attack. The reduction in ductility was used as a parameter to evaluate the SCC susceptibility of the alloys. The results indicated that the corrosion resistance of AA2195 alloy was better than that of AA2219 alloy as it exhibited lower corrosion rate, along with lower pit depth and density. However, the SCC index (?_NaCl/?_air) measured was greater than 0.90, indicating good environmental cracking resistance of both the alloys. Detailed fractography of the failed samples under SEM–EDS, in general, revealed a typical ductile cracking morphology for both the alloys.