预时效温度及回归加热速率对7150铝合金显微组织及性能的影响

采用硬度、电导率、室温拉伸测试、差示扫描量热分析(DSC)、极化曲线及透射电镜(TEM)观察研究预时效温度及回归加热速率对7150铝合金显微组织及性能的影响。结果表明:合金的抗拉强度对预时效温度敏感,耐腐蚀性能对回归加热速率敏感。再时效后合金的抗拉强度随预时效温度的升高而增加,耐腐蚀性能随回归加热速率的提高而降低。经(65℃,24 h)+(4.25℃/min)(190℃,50 min)+(120℃,24 h)的三级时效处理后,7150铝合金的电导率(IACS)大于36%,抗拉强度损失小于峰时效态(T6)合金强度的3%。     

机加工AA7150铝合金的抗丝状腐蚀性能（英文）

采用扫描及透射电子显微技术表征机加工AA7150铝合金近表面变形层的显微组织,并结合动电位极化曲线及丝状腐蚀测试研究机加工后AA7150铝合金的丝状腐蚀行为。研究发现,机加工后AA7150铝合金近表面区域出现晶粒细化、合金元素重新分布以及晶界偏析等特征。机加工过程中强烈的塑性变形导致近表面区域显微组织的改变,从而极大地提高合金近表面变形层的腐蚀倾向。机加工使合金表面粗糙度增大,并导致形成电化学活性明显提高的近表面变形层。在二者共同影响下,机加工后AA7150铝合金的抗丝状腐蚀性能明显下降。     

Effect of solution treatment on the corrosion behaviour of aluminium alloy AA7150: Optimisation for corrosion resistance

Studies for Al-alloys normally employ specimens subject to a fixed solution heat treatment (SHT), and hence the specific role of solutionising is overlooked. It is revealed that SHT has a major role in corrosion of AA7150 as judged by electrochemical, microscopic and profilometry studies. SHT dictates the constituent particle type and population remaining in the alloy for subsequent processing, and is thus not only a principal factor in corrosion, but a factor that can be engineered in developing more damage tolerant AA7150. Effect of an optimised SHT minimising the residual MgZn₂ and Al₂MgCu content on corrosion resistance is demonstrated.     

Investigation of the relationship between intergranular corrosion and retrogression and reaging in the AA6063

AA6063 was heat treated with different retrogression temperatures and durations, and the effect of heat treatment conditions on the microstructure, hardness, electrical conductivity, intergranular corrosion (IGC) and electrochemical corrosion behaviours of the AA6063 was determined compared with the T6 condition. The IGC test was applied according to the BS EN ISO 11846: 2008 standard. Moreover, potentiodynamic polarization tests were applied to determine the electrochemical corrosion behaviour of the heat‐treated samples. Electrochemical corrosion tests were carried out by using a Ivium Compactstat potentiostat in 3.5 wt.%. NaCl solution at 24°C with a scanning rate of 0.5 mV/s. The corrosion test cell consisted of the reference electrode (Ag/AgCl), working electrode (test sample) and a reference electrode (platinum). The effect of IGC on the microstructure of AA6063 and corrosion depth values was investigated by using a stereo optical microscope and a light metal microscope, respectively. Corrosion depth examinations were performed on microstructures taken from the cross‐sections of the samples. The chemistry of the precipitates formed at grain boundaries and distribution of the precipitates in the microstructure were investigated by scanning electron microscope, energy dispersive X‐ray and transmission electron microscope analyses. The results showed that retrogression and reaging heat treatment improves both the corrosion resistance and the mechanical properties of AA6063. After 50°C/15 min RRA heat treatment, the highest corrosion resistance and a higher hardness value than the T6 level were obtained.     

The effect of inhibitor structure on the corrosion of AA2024 and AA7075

A range of structurally-related compounds were tested for their capacity to inhibit corrosion on aluminium alloys AA2024-T3 and AA7075-T6 in 0.1 M NaCl solution. It was found that the thiol group, positions para- and ortho- to a carboxylate, and substitution of N for C in certain positions strongly inhibited corrosion. The hydroxyl group was slightly inhibitive, while the carboxylate group provided little or no corrosion inhibition on its own. In several cases, different activities were found on the different alloys, with some compounds (particularly thiol-containing compounds) being more effective on AA2024 than on AA7075.     

The effect of recrystallization on corrosion and electrochemical behavior of 7150 Al alloy

By weight loss, potentiodynamic polarization, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) techniques complemented by optical and scanning electron microscopy observations, the effect of recrystallization on the corrosion, and electrochemical behavior of 7150 Al alloy was studied. The results indicated that the high recrystallization fraction 7150‐1# was worse than the low recrystallization fraction 7150‐2# on corrosion resistance. The analysis of EIS indicated that 7150‐1# exhibited obvious pitting corrosion at 5 h immersion time, whereas 7150‐2# showed no obvious pitting corrosion even at 33 h. The corrosion route developed along the grain boundary of recrystallization grains, not along the grain boundary of unrecrystallization grains.     

The effect of temperature on corrosion behavior of AA5083 in brackish water and seawater

Al‐alloy, AA5083, as a lightweight structural material with favorable mechanical properties and, compared with other lightweight materials, good corrosion resistance has an increased usage in the marine environment. It is well known that all Al‐alloys, including AA5083, in the presence of chloride ions are more prone to corrosion. Determination of corrosion behavior of AA5083 in seawater and brackish water has been investigated and compared at 18, 25, and at 30°C. To obtain more accurate and realistic results, fresh seawater and brackish water were sampled as an electrolyte in Sibenik region. The investigation was carried out using the following electrochemical methods: open circuit potential measurement, electrochemical impedance spectroscopy, linear polarization resistance, potentiodynamic polarization, and cyclic polarization. After potentiodynamic polarization measurement, each alloy was examined using a metallographic microscope to clarify corrosion morphology. Obtained results have shown that an increase in temperature leads to an increase in corrosion activity of AA5083 in both electrolytes, while microscopic examination reveals that the dominant type of corrosion is pitting.     

回归再时效7150铝合金的蠕变时效行为（英文）

通过蠕变时效实验、拉伸性能测试、电导率测试和透射电镜观察,系统研究回归再时效状态的7150铝合金的蠕变时效行为。蠕变时效实验结果表明,回归再时效状态7150铝合金的稳态蠕变主要是位错攀移机制(应力指数≈5.8),其稳态蠕变行为对晶内和晶界的析出相变化不敏感,但总的蠕变变形随着再时效时间的延长而增大。另外,在140°C蠕变时效16 h后,4种回归再时效样品的屈服强度和抗拉强度基本相同,但伸长率随着再时效时间的延长略有下降。而且回归再时效处理有利于提高7150铝合金的硬度和电导率。研究结果表明,蠕变时效前的回归再时效处理可以改善7150铝合金的晶内和晶界组织,提高合金的成形效率,改善合金的综合性能,包括力学性能和电导率。     

The effect of welding parameters on the corrosion behaviour of friction stir welded AA2024-T351

The effect of welding parameters (rotation speed and travel speed) on the corrosion behaviour of friction stir welds in the high strength aluminium alloy AA2024-T351 was investigated. It was found that rotation speed plays a major role in controlling the location of corrosion attack. Localised intergranular attack was observed in the nugget region for low rotation speed welds, whereas for higher rotation speed welds, attack occurred predominantly in the heat-affected zone. The increase in anodic reactivity in the weld zone was due to the sensitisation of the grain boundaries leading to intergranular attack. Enhancement of cathodic reactivity was also found in the nugget as a result of the precipitation of S-phase. The results were compared with samples of AA2024-T351 that had been heat treated to simulate the thermal cycle associated with welding, and with samples that had been exposed to high temperatures for extended periods to cause significant over-ageing.     

Effects of retrogression heating rate on microstructures and mechanical properties of aluminum alloy 7050

The effects of the retrogression heating rate(340℃/min,57℃/min,4.3℃/min)on the microstructures and mechanical properties of aluminum alloy 7050 were investigated by means of hardness measurement,tensile properties testing,differential scanning calorimetry(DSC)and transmission electron microscopy(TEM).The results show that the retrogression heating rate significantly affects the microstructures and mechanical properties of the alloys treated by retrogression and re-aging(RRA)process, and it is found that the medium rate(57℃/min)leads to the highest mechanical properties.The strengthening phases in the matrix are mainly the fine dispersed η′precipitates and GP zones,and the grain boundary precipitates are coarse and discontinuous η phases.     

The effect of cryogenic CO2 cooling on corrosion behaviour of friction stir welded AA2024-T351

Abstract

Cryogenic cooling with CO₂ was applied during friction stir welding of AA2024-T351 in order to reduce the temperature increase during welding, and thus improve the corrosion resistance of the weld. The effect of cryogenic cooling on corrosion susceptibility was investigated with gel visualisation, immersion tests and local electrochemical measurements. The most susceptible area for both uncooled and cooled welds was in the heat-affected zone (HAZ) region, which showed intergranular attack. Cryogenic cooling had no detectable influence on the degree of anodic reactivity in the weld region. However, it did decrease the width of the reactive HAZ.     

Effect of aging temperature and of retrogression treatment time on the microstructure and mechanical properties of alloy AA 7075

Alloy AA 7075-T6 is studied after retrogression and re-aging. The retrogression heat treatment is performed at various temperatures and hold times, and subsequent aging is performed at 130°C for 12 h. The microstructure and mechanical properties of the alloy are studied depending on the temperature and the hold time of the retrogression heat treatment. Electron microscopic studies are preformed and mechanical characteristics are determined in tensile and impact tests. The HRB microhardness is measured.     

The effect of adatoms on the corrosion rate of copper

On the premises that corrosion is a surface process and adatoms modify the electronic states of the surface, the influence of Zn, Sn, S, I, F, Ta, Sb, Ti, Bi and Cr adatoms on the corrosion rate of copper was investigated. Adatoms were adsorbed at open-circuit from a solution containing 1.0×10⁻² mol l⁻¹ of the ions of the adatom element. The coverage of the adatoms at the surface was calculated by integration of the area under one of the peaks on the voltammogram of the copper electrode before and after dosing the electrode with the adatom. A significant difference in adsorbability of the adatoms at copper surface was observed. This difference was inter alia attributed to atomic size, crystallographic and kinetic effects. The surface properties were characterized by cyclic voltammetry, and for selected systems by SEM and electron microprobe. Corrosion of the surface in presence and in absence of the adatoms was followed by weight-loss method while surface oxidation, ‘surface corrosion’ was investigated by cyclic voltammetry and by electrochemical polarization techniques. The results showed that the nonmetals (F, S and I) markedly enhanced the rate of corrosion; Cr, Ta, Sb, Bi, Ti, Sn slightly enhanced the rate of corrosion of copper. Zinc, however, was the only element which decreased the rate of corrosion.     

二次回归再时效对Al-Zn-Mg-Cu组织、强度及剥蚀性能的影响(英文)

采用硬度、拉伸和剥落腐蚀测试手段,结合透射电镜和扫描电镜观察以及能谱分析,研究二次回归再时效对组织、力学和剥蚀性能的影响。二次回归再时效处理保持了类似一次回归再时效处理的晶内析出相,得到比T76过时效更粗大且离散的晶界析出相。与T76相比,二次回归再时效处理的晶界析出相具有更高的铜含量和更低的锌含量。因此,二次回归再时效处理保持了一次回归再时效处理的强度,同时得到了比T76过时效处理更高的剥蚀抗力。     

回归冷却速率对7050铝合金力学性能及晶间腐蚀抗力的影响

采用室温拉伸、抗晶间腐蚀性能测试(IGC)、光学显微镜(OM)及透射电镜(TEM)观察等手段,研究3种回归冷却速率(17℃/s,3℃/s,0.02℃/s)对回归再时效(RRA)态7050铝合金力学性能及抗晶间腐蚀性能的影响。结果表明,在快冷(17℃/s)条件下,回归态组织的过饱和固溶体含有较高的空位浓度,有利于再时效析出,再时效态组织的晶界析出相为较粗大的非连续颗粒,并有较宽的无沉淀析出带(PFZ);慢冷(3℃/s或0.02℃/s)条件下,在冷却过程中晶界和晶内均析出了微小的第二相,导致固溶体内空位浓度降低,影响再时效析出,使得再时效态组织的晶界析出相颗粒粗细不均匀,无沉淀析出带变窄。相应地,随冷却速率降低,合金的拉伸强度单调下降,抗晶间腐蚀性能先下降,后略有升高。     

Effects of retrogression and reaging heat treatment on the microstructure,exfoliation corrosion,electrical conductivity,and mechanical properties of AA7050

The effects of different retrogression times and temperatures on the microstructure, electrical conductivity, exfoliation corrosion (EXCO), and hardness of the 7050 aluminium alloy were compared with the T6 and T7451 condition. The EXCO solution was prepared in accordance with ASTM G34‐01 standard and the samples were kept in the solution for 48 hr. Corrosion depths were examined by using scanning electron microscope (SEM) in the cross‐sections microstructure of the samples. The effect of EXCO on the material was investigated using stereo optical microscope images. In microstructure investigations, SEM and energy dispersive X‐ray (EDX) analyses were used to determine the distribution and chemistry of the precipitates at the grain boundaries. The results show that retrogression and reaging (RRA) times and temperatures have significant effects on AA7050 EXCO. Especially after 200°C/30 min RRA process, it has been found that 7050 aluminium alloy has higher mechanical strength than T6 level and high corrosion resistance from T7451 level. According to the results of this study, it has been shown that there is a direct connection between electrical conductivity and EXCO.     

Effect of temperature on the Electrochemical corrosion behaviour of titanium

The influence of variations in temperature on the electrochemical corrosion properties of VT 1-0 commercial titanium was studied in deaerated 1 mol/dm³ sulphuric acid between 293 and 353 K. Galvanostatic and quasi-potentiostatic polarization measurements were carried out. Corrosion rates were determined by mass loss measurements, too. The slopes of the cathodic Tafel-like lines obtained with galvanostatic polarization change anomalously with temperature. The corrosion rates calculated from the mass loss data increase with increasing temperature at a higher rate than those determined with the polarization method, pointing to a self-dissolution process. The results are attributed to a hydride layer with a H/Ti ratio increasing with temperature. Titanium hydride may play a dominant role both in the hydrogen evolution reaction and in the self-dissolution process.     

The effect of creep aging on localized corrosion resistance of AA2060 alloy

The influence of creep aging at varied stresses on the localized corrosion behavior of AA2060 has been studied in this paper. Samples were subjected to stress free aging (SFA) and creep aging (CA) under two stress levels, after which tensile tests and intergranular corrosion (IGC) tests were carried out. The corrosion morphology and depth were examined using optical microscope. Compared with SFA, CA can enhance the mechanical properties and increase the IGC resistance of Al–Cu–Li alloy but high-stress CA would intensify the intragranular corrosion penetration in the first 25 hr of aging time. The microstructure observation results show that dislocations introduced by CA provide favorable nucleation sites for T1 precipitates in the grain and impede the growth of T1 precipitates at grain boundary. Therefore, the potential difference between the grain interior and grain boundary can be reduced compared to that for the SFA. The mechanism by which CA affects the corrosion resistance of Al–Cu–Li alloys, as is essential to understand and optimize the creep aging process, has been proposed by considering the effect of creep-deformation-induced dislocations.     

The effect of molybdenum ion implantation on the general and pitting corrosion behaviour of pure aluminium and a high strength aluminium alloy

The effect of Ar and Mo ion implantation on the corrosion behaviour of pure Al and a high strength aluminium alloy (7075-T6) has been investigated in Cl^?-free and Cl^?-containing sulphate solutions. In Cl^?-free environments, Mo implantation markedly affects the general corrosion behaviour of both the pure metal and the alloy. Ar implantation, on the other hand, has no permanent effect on the potentiodynamic polarization behaviour of pure Al but does alter somewhat the polarization characteristics of 7075-T6. In Cl^?-containing environments, Mo implantation significantly improves the resistance of pure Al to pitting corrosion, and increases the breakdown potential by about 200 mV. A similar, though less marked effect is observed with the alloy. Ar implantation has no major effect on the behaviour of either the pure metal or 7075-T6 in Cl^?-containing environments. On the basis of Rutherford backscattering and potential-time measurements it is suggested that the beneficial effect of Mo may be due to either the incorporation of Mo in the passive film or to dissolution and reprecipitation of some Mo-containing species on the passive film.     

The effect of impurity inclusions on the pitting corrosion behaviour of beryllium

An electrochemical polarisation study has been conducted to determine the effect of impurity inclusions on the pitting corrosion behaviour of beryllium. Three grades of commercial beryllium differing in impurity levels were used. This work showed a strong relationship between the pitting potential of the beryllium and the level of impurity inclusions, the grade with the least number of overall inclusions being the most resistant to pitting corrosion. The work also revealed the preferred sites for pit initiation, with most corrosion pits initiating at intermetallic Fe/Al/Be inclusions, and to a smaller extent at inclusion sites containing either elemental silicon or carbides.