Corrosion inhibition of AA6063 alloy by vanadates in alkaline media

Vanadium aqueous compounds are considered as promising environmentally friendly inhibitors for heterogeneous aluminium alloys. In this study, mechanism of corrosion inhibition of AA6063 in alkaline media by vanadate inhibitors is presented. A combination of weight loss and open circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy was used to compare corrosion behavior of AA6063 alloy in aerated pH 10 0.05 M sodium chloride solutions in the absence and presence of 0.003 mol/l sodium orthovanadate. Tetrahedrally coordinated mono‐ and polyvanadates, that are main forms in such solutions, cause a decrease in corrosion current density and significantly increase amplitude of impedance spectra and impedance modulus |Z| values due to mixed cathodic‐anodic inhibition effect mainly associated with the formation of adherent surface film on cathodic and anodic intermetallic particles of alloy.     

Das Verhalten von Aluminium-Werkstoffen in der Hausinstallation

The corrosion behaviour of aluminium alloys . The corrosion behaviour of the aluminium alloys AlMgMn, AlMgSi 0,8 and AlZn 1 was investigated at two temperatures in two natural waters with different contents with and without oxygen. These measurements were performed as well separated as in contact with copper, brass, iron and zinc; the electrode potentials and the galvanic currents were measured and registrated. The results of the metallographic investigations concerning pitting corrosion of the aluminium samples and of the measurements under potentiostatic conditions were summarized in especial corrosion diagrams. Out of these the corrosion risks of the aluminium materials can be seen. The investigated aluminium alloys – except AlZn 1 – showed unpolarized a good corrosion resistance. The best of them was AlMgMn. In contact with iron and copper containing alloys aluminium were polarized in anodic direction depending of the different metals and of oxygen content of the water. The limit of the pitting corrosion has been exceeded at times. In the cold waters zinc polarized the aluminium alloys cathodic. References were given for applications of aluminium building parts in the home installation and it was informed about experiences which corresponds with these results.     

Effect of heat treatment on the Inhibition of the acidic corrosion of aluminum alloy

The effect of heat treatment on the inhibition of acid corrosion of duralumin has been studied using gasometry, mass loss measurements and potentiodynamic technique. All the data reveal that the duralumin generally developed good corrosion resistance after heat treatment and the corrosion rate ranked as follows: Non treated > Naturally aged > quenched. This improvement in the corrosion resistance was attributed to the structural homogeneity of the heat-treated alloys. The presence of some selected aryl and alkyl triazoline derivatives at the thershold concentration of 5 × 10^?3 M indicate that these compounds retard the corrosion rate of duralumin and the extend of inhibition depends on the molecular structure of the inhibitors. Polarization curves show that the triazoline compounds act as mixed-type inhibitors affecting both the cathodic and anodic process. Moreover, there is no noticeable difference in the degree by which the triazoline derivatives inhibit the corrosion of pure aluminium and heat treated duralumin alloy.     

Effect of alloying with zinc on SFE of aluminium by study of lattice imperfections in cold worked Al-Zn alloys

A detailed X-ray Fourier line shape analysis has been performed on three compositions of Al-Zn alloys viz. Al-3.55 wt% Zn, Al-14.7 wt% Zn and Al-19.3 wt% Zn infcc phase. It has been found that deformation stacking faults, both intrinsic ά and extrinsic α are absent in the cold worked state and twin fault β is found to be slightly present in the deformed lattice of the two initial compositions of the alloys. Similar to the effect of solute germanium and copper, respectively in Al-Ge and Al-Cu systems, hexagonal zinc also fails to impart faulting infcc Al-Zn system. This corroborates the fact that aluminium has high stacking fault energy.     

Al-Zn coatings for the corrosion protection of steel

Aluminum coatings have been reported to be the most suitable for replacing toxic cadmium for the protection of steel and titanium alloys against corrosion. The relatively poor galvanic corrosion protection of aluminium coatings, however, has led to a search for a more effective coating. To this end, pure aluminium and controlled-composition Al-Zn alloy coatings were ion plated onto steel substrates. Over a range of coating conditions the aluminium and the Al-Zn alloy coatings have very similar columnar structures. They were equally successful in protecting the underlying steel. However, a simulation of the coating damage by masking the steel substrate during plating showed the galvanic corrosion protection of Al-2.5%Zn alloy coatings to be superior to that of aluminium. It is probable that this very effective sacrificial corrosion protection means that the structure of the coating is relatively unimportant and that excellent galvanic corrosion protection can be provided by low density columnar structure coatings of Al-Zn alloys.     

Stress corrosion cracking and hydrogen embrittlement cracking of welded weathering steel and carbon steel in a simulated acid rain environment

Abstract

The stress corrosion cracking (SCC) and hydrogen embrittlement cracking (HEC) characteristics of welded weathering steel and carbon steel were investigated in aerated acid chloride solution. The electrochemical properties of welded steels were investigated by polarisation and galvanic corrosion tests. Neither weathering steel nor carbon steel showed passive behaviour in this acid chloride solution. The results indicated that weathering steel had better corrosion resistance than carbon steel. Galvanic corrosion between the weldment and the base metal was not observed in the case of weathering steel because the base metal was anodic to the weldment. However, the carbon steel was susceptible to galvanic corrosion because the weldment acts as an anode. Slow strain rate tests (SSRT) were conducted at a constant strain rate of 7.87 × 10⁷ s^-1 at corrosion potential, and at potentiostatically controlled anodic and cathodic potentials, to investigate the SCC and HEC properties in acid chloride solution. The welded weathering steel and carbon steel were susceptible to both anodic dissolution SCC and hydrogen evolution HEC. However, weathering steel showed less susceptibility of SCC and HEC than carbon steel at anodic potential because of Cr and Cu compounds in the rust layer, which retarded anodic dissolution, and at cathodic potential due to the presence of Cr, Cu, and Ni in alloy elements, which inhibit the reduction of hydrogen ions. SEM fractographs of both steels revealed a quasicleavage fracture in the embrittled region at applied anodic and cathodic potentials.     

Effect of microstructure on the corrosion behaviour of dental gold alloys

The effect of microstructure on the corrosion behaviour of Au-Cu-11 at % Pd, Au-Cu-11 at % Ag and (Au-Cu-11 at % Ag)-5 at % Pd alloys was studied by anodic potentiodynamic and potentiostatic polarization tests. The single-phase Au-Cu-11 at % Pd alloys had high corrosion resistance and their potentiodynamic polarization curves were simple. The high-nobility Au-Cu-11 at % Ag alloy displayed high corrosion resistance regardless of its microstructure. The two-phase Au-Cu-11 at % Ag and (Au-Cu-11 at % Ag)-5 at % Pd alloys had lowered corrosion resistance compared with the single-phase alloys. Anodic potentiodynamic polarization curves of the two-phase alloys were complex, but they were explained by superimposing the curves of each phase using the principle of additivity. The potential at which the current density sharply increased corresponded with that of each phase, and the value of current density was calculated as the sum of the current density of each phase and taking account of their volume fractions. In the anodic potentiodynamic polarization, there was little galvanic effect between the two phases.     

Influence of nitrogen addition on the crevice corrosion resistance of nitrogen-bearing austenitic stainless steels

Crevice corrosion studies were carried out on nitrogen-bearing types 304, 316 and 317 austenitic stainless steels (SS) by a potentiodynamic anodic polarisation method in an acidic chloride medium. A special all-glass crevice assembly was used for providing reproducible crevice effects on the surface of the test specimen. The results indicated that the increase in nitrogen content improved the crevice corrosion resistance of the alloys by decreasing the active dissolution, and increasing both passive film stability and the potential at which crevice attack was stable. This was very significant for 304 and 316 SS alloys in comparison with 317 SS alloys. The combined influence of nitrogen and molybdenum was found to be very significant in providing high crevice corrosion resistance for 317 SS alloys. Optical microscopic observation revealed severe crevice attack on types 304 and 316 SS alloys compared to mild crevice attack on type 317 alloys. Based on the results of the present investigation a possible mechanism by which nitrogen addition improved the crevice corrosion resistance is discussed.     

Cu(II), Co(II) and Ni(II) complexes of –Br and –OCH<Subscript>2</Subscript>CH<Subscript>3</Subscript> substituted Schiff bases as corrosion inhibitors for aluminium in acidic media

A group of Cu(II), Ni(II) and Co(II) complexes of –Br and –OCH₂CH₃ substituted Schiff bases as a new class of corrosion inhibitors for aluminium has been studied in 0.1 M HCl by the addition of 10 ppm compound using potentiodynamic polarization, electrochemical impedance spectroscopy, linear polarization methods and gas evolution tests at 25 °C. The inhibition efficiencies obtained from all methods employed are in good agreement. Results show Ni(II) complex of –OCH₂CH₃ substituted Schiff bases was the best inhibitor with a mean efficiency of 69% at 10 ppm additive concentration. The potentiodynamic polarization curves showed both the cathodic and the anodic processes of aluminium corrosion were suppressed, and the Nyquist plots of impedance gave mainly a capacitive loop. Scanning electron microscopy (SEM) was done from the surface of the exposed sample indicating uniform film on the surface.     

Electrochemical corrosion behaviour of Sn-Zn-xBi alloys used for miniature detonating cords

Recently, Sn-Zn-Bi alloys have been reported to be the sheath material for miniature detonating cords, due to appropriate mechanical properties, ease of manufacturing, and low cost. Bi addition was found beneficial to the mechanical performance of Sn-Zn. However, limited information about the influence of Bi on the corrosion properties of Sn-Zn alloys has been provided. In this work, electrochemical corrosion behaviours of Sn-3Zn-xBi (x = 0, 1, 3, 5, 7 wt%) alloys were investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques, to explore the effects of Bi on the corrosion performance of Sn-Zn alloys. The corrosion mechanism of Sn-Zn-Bi alloys was analysed through microstructure examination on the surface of alloys after corrosion measurements. Results indicated that the addition of 1 wt% Bi increased the corrosion susceptibility of the Sn-3Zn alloy, mainly attributed to the coarsened and more uniformly distributed corrosion-vulnerable Zn-rich precipitates, while further increasing the Bi contents decreased the corrosion susceptibility of Sn-3Zn-xBi alloys due to the higher fraction of nobler Bi particles serving as anodic barriers. The Sn-3Zn-7Bi possessed the best corrosion resistance among all Sn-Zn-Bi alloys investigated. The role of Bi on corrosion was considerably discussed.     

Mikrostrukturelle,mechanische und korrosive Eigenschaften reibrührgeschweißter Stumpfnähte in Aluminiumlegierungen

Microstructural, mechanical and corrosive properties of friction stir welded aluminium joints Friction stir welding (FSW) is a novel solid state welding process. It allows joining of high strength aluminum alloys, generally considered as difficult-to-weld with conventional technologies, without loss in joint strength. Results of investigations on selfmade FSW butt joints of the aluminum alloys 2024-T3 and 6013-T4 are presented. First, the microstructure of the weld seam and heat affected zone is characterised metallographically and by hardness measurements. By tensile, fatigue endurance (SN) and fatigue crack propagation tests it is demonstrated, that especially the FSW-joints of 2024–T3 sustain high mechanical loadings. Investigations on the corrosion properties reveal a certain sensitivity of the 2024-T3 joints to intergranular and exfoliation corrosion.     

7075铝合金的力学与电化学交互作用

用慢应变速率拉伸(SSRT)技术研究了7075铝合金在应力腐蚀过程中的力学与电化学交互作用.结果表明,外加极化会提高7075铝合金的应力腐蚀敏感性,这种通过极化而改变铝合金表面电化学反应从而影响断裂应力的现象是一种电化学-力学效应.然而,对于不同热处理状态的7075铝合金,外加极化对敏感性的影响程度不同.增加拉伸应力,7075-RRA铝合金的阳极极化曲线略向正移,滞后环面积扩大,但并不显著.这种拉伸应力对极化曲线的影响是一种力学-电化学效应,有利于应力腐蚀裂纹的扩展.铝合金在应力腐蚀过程中的电化学作用和力学作用是交互的,彼此促进的.     

The corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy: Effects of HCl concentration and temperature

Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application.Herein,we systematically investigate the corrosion behavior of a newfound Ti-6Al-3Nb-2Zr-1 Mo (Ti80) alloy in hydrochloric acid (HCI) ranging from 1.37 to 7 M,and temperature ranging from 25 to 55 ℃,by means of electrochemical measurements,static immersion tests and surface analysis.Results manifest that increasing either HCI concentration or temperature can accelerate the corrosion of Ti80 alloy via promoting the breakdown of native protective oxide film and then further facilitating the active dissolution of Ti80 matrix.According to potentiodynamic polarization curves,Ti80 alloy displays a spontaneous passive behavior in 1.37 M HCI at 25 ℃,compared to a typical active-passive behavior under the other conditions.As indicated by cathodic Tafel slope,the rate determining step for cathodic hydrogen evolution reaction is likely the discharge reaction step.The apparent activation energies obtained from corrosion current density and maximum anodic current density for Ti80 alloy in 5 M HCI solution are 62.4 and 55.6 kJ mol-1,respectively,which signifies that the rate determining step in the corrosion process of Ti80 alloy is mainly determined by surface-chemical reaction rather than diffusion.Besides,the electrochemical impedance spectroscopy tests demonstrate that a stable and compact oxide film exists in 1.37 M HCl at 25 ℃,whereas a porous corrosion product film forms under the other conditions.Overall,the critical HCI concentration at which Ti80 alloy can maintain passivation at 25 ℃ can be determined as a value between 1.37 and 3 M.Furthermore,the corroded surface morphology characterization reveals that equiaxed α phase is more susceptible to corrosion compared to intergranular β3 phase due to a lower content of Nb,Mo,and Zr in the former.     

Electrodeposition of polypyrrole on aluminium in the presence of sodium bis(2-ethylhexyl) sulfosuccinate

Stable and adherent polypyrrole films have been successfully electrodeposited onto aluminium electrode over a wide solution pH interval by using sodium bis(2-ethylhexyl) sulfosuccinate as dopant. The redox behaviour of the deposited coating was studied by cyclic voltammetry in different electrolytes and the corrosion protection properties were examined in chloride solution by polarisation studies and open circuit measurements. The polymer film was characterised by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The obtained results are explained considering the surfactant remains entrapped into the polymer matrix. The coatings inhibit the oxidation of the aluminium substrate even on polarisation to high anodic potentials.     

Elektrolytische Abscheidung von Aluminium‐Magnesium‐Legierungen aus aluminiumorganischen Komplexelektrolyten

Electrolytic Deposition of Aluminium‐Magnesium‐Alloys from Electrolytes Containing Organo‐Aluminium Complexes The galvanic deposition of pure aluminium from fluoride‐containing electrolytes has been developed further and for the first time aluminium and magnesium have been deposited from a toluene‐solution of a halide‐free organo‐aluminium complex electrolyte. The rate of incorporation of magnesium can be controlled over a wide range by either adjusting the composition of the aluminium‐magnesium anode or by using separate aluminium or magnesium anodic circuits. The current efficiency for both anode and cathode approaches 100%. The resulting coating is optically attractive and, depending upon the magnesium‐content or the cathodic current density, can be formed as a dull or polished surface. Investigations using an electron microscope show that the surface, in contrast to that of pure aluminium, consists of spherical particles. The aluminium‐magnesium coating provides excellent protection against the corrosion of magnesium components. Electrochemical investigations using, for example 25% by weight magnesium incorporation, indicate a pronounced passivity interval compared to the alloy AZ91hp. In contrast to galvanic zinc‐plated and silicate‐sealed examples, cyclic corrosion tests on screws simulating 10 years of exposure, show no corrosion.     

Comparative corrosion studies of zirconia particle reinforced high‐alloyed 14‐6‐6 CrMnNi‐steel by potentiodynamic polarisation and one year outdoor exposure

The corrosion behaviour of a spark plasma sintered CrMnNi high‐alloyed steel, without and with 10 vol.% zirconia particle reinforcement was investigated by potentiodynamic polarisation in 5 wt.% sodium chloride solution and by an one year outdoor exposure test. After the polarisation test both materials revealed a similar damage behaviour as in the outdoor exposure test. The unreinforced material was attacked by pitting corrosion, whereas the particle reinforced material showed a more homogeneous corrosion attack involving an intensified particle detachment. Furthermore, investigations of the unreinforced steel by white light interferometry revealed pit depths of approximately 65 µm after potentiodynamic polarisation and 36 µm after one year outdoor exposure. In contrast, for the composite a damage evolution due to particle detachment was found in both experiments.     

Simulation of clusters formation in Al-Cu based and Al-Zn based alloys

A Monte Carlo computer simulation is adopted to investigate the role of micro-alloying elements Mg and Ag in Al-Cu and Al-Zn alloys. Small amount additions of Mg to the Al-Cu alloy markedly retard the formation of Cu clusters due to the preferential trapping of free-vacancies available for Cu diffusion. On the other hand, additions of Mg to the Al-Zn alloy promote the formation of Zn clusters due to the preferential Mg-Zn interaction. As for the effect of Ag, it is found that, in both Al-Cu-Mg and Al-Zn-Mg alloys, Ag atoms are preferentially bounded to Mg-Cu-vacancy or Mg-Zn-vacancy complexes. However, in Al-Cu-Mg alloy Ag atoms interact with Mg, while in Al-Zn-Mg alloy they interact with both Mg and Zn.     

缓蚀型添加剂对阳极氧化后铝合金耐蚀性的影响

选择海洋用铝合金进行阳极氧化处理,运用电化学极化及交流阻抗技术,结合微观分析,比较阳极氧化后铝合金的耐蚀性。结果表明,所研究的铝合金中主要存在Al-Cu-Mn-Fe-Si-Cr和Al-Mg-Si第二相,Al-Cu-Mn-Fe-Si-Cr相不溶解,在氧化膜中呈突起状态;而Al-Mg-Si相溶解形成孔洞,易受到侵蚀,成为腐蚀源。对于特定的铝合金,阳极氧化电解液中添加Na2MoO4缓蚀剂后,MoO4^2-进入阳极氧化膜,抑制侵蚀性离子的有害作用,提高了铝合金的耐蚀性。     

Characterization of the protective effect of aluminium surface treatments by d.c. and a.c. measurements

Steady-state and electrochemical impedance spectroscopy measurements have been made on anodic layers on 1050 and 2024T3 aluminium alloys prepared from solutions of phosphoric acid, boric acid and sodium tetraborate, before and after impregnation treatment with zinc. Corrosion characteristics of the anodic layers were dependent on the aluminium substrate and the electrolyte. Aluminium alloy composition was found to be the most important factor for corrosion resistance; alloying elements of 2024T3 alloy (like copper) had a harmful influence on this layer property. Steady-state measurements allowed the oxide layer behaviour to be studied in the anodic range by the determination of an anodic passivity domain. This domain was characterized by a weak aluminium oxidation through the oxide layer. The zinc impregnation treatment had a marked protective effect on each studied anodic layer. This treatment can be used as an alternative to hot sealing in water or chromic acid solution.     

Aluminium alloys exposed to borderline solutions – a methodology to evaluate the susceptibility to corrosion fatigue with respect to corrosive de‐icers

In addition to high mechanical loads certain components for the automotive industry are exposed to corrosive environments, especially during winter, when corrosion promoting de‐icers are essential to sustain road traffic. The underlying research work contributes to the evaluation of the corrosion fatigue performance of aluminium alloys relevant for automotive application generally, while the present text focuses on wrought alloys. Aluminium alloys are of special interest because of the opportunity to reduce expenses for an additional corrosion protection and to support lightweight construction of vehicles. Components exposed to simultaneous mechanical and corrosive service loads as well as corrosion tests of different scale level (immersion and cabinet testing, long term outdoor exposure of components, usage on test carriers) were analysed to evaluate typical forms of corrosion. Based upon the prevailing damaging mechanism of material conditions with known differences in susceptibility to specific forms of corrosion, like intergranular corrosion or pitting, methods were derived to evolve service relevant types of corrosion during laboratory tests.