Corrosion of LY12 aluminum alloy in sodium chloride solution

1　INTRODUCTIONBecauseofitshighmechanicalperformanceandlowdensity ,LY12alloy(USAA2 0 2 4 )iswidelyusedintheaircraftindustryfornumerousapplicationssuchasfuselage ,doorskin ,dorsalfinandtrailingedgepanels .Nevertheless ,thisalloycaneasilybeaffectedbylocalizedcorrosion ,suchaspittingandexfoliation ,especiallyinchloridecontainingenvironment .Thislocalizedattackcanresultinprematurebreakdownofstructuralparts[1] .Inordertominimizethelocalizedattackonthealuminumalloy ,thecorrosionmecha nismshou…     

Investigation of the weldability of an aluminium–lithium alloy

Investigations were carried out to study the effect of the chemical composition of filler material in welding an alloy of the Al–Mg–Li system on the hot crack formation resistance and the mechanical properties of welded joints. The effect of metallurgical factors on the formation of defects in the fusion zone was investigated using the spot weldability testpiece. The chemical composition of 1420 alloy was optimized and this greatly reduced the number of defects. The investigations were carried out in the framework of the research project 10.8. Technology of fusion welding of new constructional materials (‘Strategic directions of development of materials and technologies of processing these materials for the period up to 2030’) [1 Kablov EN. The strategic directions of development of materials and technologies of processing these materials for the period to 2030. Aviatsionnye materialy i tekhnologii. 2012;5:7–17. [Google Scholar]].     

Analysis of corrosion behavior of LY12 in sodium chloride solution with wavelet transform technique

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｓｔｕｄｙｏｆｓｐｏｎｔａｎｅｏｕｓｃｕｒｒｅｎｔｏｒｐｏｔｅｎｔｉａｌｆｌｕｃ ｔｕａｔｉｏｎｓ,ｗｈｉｃｈｈａｓｂｅｅｎｄｅｓｉｇｎａｔｅｄａｓｅｌｅｃｔｒｏｃｈｅｍｉｃａｌｎｏｉｓｅ(ＥＮ) ,ｆｏｒｔｈｅｃｈａｒａｃｔｅ     

Effect of pH on corrosion and monotonic loading behaviour of 90Cu–10Ni in 3·5% sodium chloride solution

Abstract

Polarisation studies were performed on 90Cu–10Ni (alloy UNS C70600, hot rolled and annealed) in 3·5% NaCl solutions over a range of initial pH levels. It was found that film formation was dependent on the applied current and the relative concentrations of the ionic species H⁺, (OH)^?, and Cl^? in solution which ultimately influenced the formation of the corrosion products. Constant extension rate tests at different applied currents and pH levels suggested that a higher pH level increased the time to failure although no evidence of stress corrosion cracking was found. These observations are rationalised through surface film formation mechanisms.     

Influence of microstructural characteristics on corrosion behavior of Mg–5Sn–3In alloy in Hank's solution

The microstructural observation, the mass loss test, potentiodynamic polarization measurements and corrosion morphology examinations were conducted to study the influence of microstructural characteristics on corrosion behavior of Mg–5Sn–3In alloys in Hank's solution after extrusion. The results show that the corrosion rate of the as-cast alloy is similar to that of as-extruded alloy; however, the local corrosion susceptibility is greatly weakened in the as-extruded alloy, especially in the extrusion direction. The relatively uniform corrosion morphology of the as-extruded alloy is attributed to refined Mg₂Sn particles, uniform distribution of Mg₂Sn particles and favorable crystal orientation. Meanwhile, the cytotoxicity tests confirm that the Mg–5Sn–3In alloy exhibits cytotoxicity of Grade 0–1 for NIH3T3 cells, suggesting an acceptable cytotoxicity of this alloy in the vitro assay.     

Increasing the reliability of welded joints in high-strength V-1461 aluminium–lithium alloy

Filler materials for welding V-1461 alloy, ensuring high cracking resistance, corrosion resistance and mechanical properties, are selected. The results of tests of the welded joints in static tensile loading and bending and the impact toughness of the weld metal and low-cycle fatigue strength are presented. The experimental results show that the application of impact ultrasound treatment increases by an order of magnitude the values of low-cycle fatigue resistance of the welded joints as a result of the formation of the nanostructured surface layers. The level of residual stresses in welded joints is determined.     

An electrochemical investigation of fretting corrosion of a number of pure metals in 0·5M sodium chloride

An electrochemical study based on free potential measurements and supplemented by the method of transient linear polarization has been used to study the effect of fretting on the metals Zn, Al, Ag, Ta, Cu, Cr and Ni in 0·5M NaCl. The base metals Al, Cr and Ta indicate substantial negative falls in free potential on fretting whilst the remaining metals show little or no measurable change. The observations strongly suggest that it is the disruption of oxide films and their rapid reformation which is the important factor in the electrochemical fretting situation rather than any solution vibration effect or increased activation caused by metal deformation.     

An investigation of the corrosion behaviour of a FeNiCoAlTa shape memory alloy in 3.5 wt-% NaCl solution

In this study, the corrosion behaviour of an FeNiCoAlTa (NCAT) shape memory alloy in 3.5% (w?w^?1) NaCl solution was evaluated. Linear polarisation resistance and potentiodynamic polarisation tests were conducted at 25°C. An open circuit potential (OCP) of ?381?mV (vs. saturated calomel reference electrode) and a corrosion rate (CR) of 0.0174?mm?y^?1 were obtained. The NCAT alloy did not show any passivation in the 3.5% (w?w^?1) NaCl solution. Its corrosion behaviour was very similar to that of G10180 (AISI 1018) carbon steel with the NCAT showing a lower CR and a less active OCP. Its corrosion in the solution was a combination of general dissolution and localised attack (pitting). Aging heat treatment caused β-Ni₃Al phase, and tantalum to precipitate on the grain boundaries, resulting in chemical species segregation between the grain boundaries and the grains. The chemical segregation caused intergranular corrosion of the alloy.     

Effect of ultrasonic vibration on the dechromisation corrosion of a CuCr alloy in HCl solution

The effect of ultrasonic vibration on the dechromisation corrosion of a CuCr alloy in HC1 solution was studied and the corrosion mechanisms were analyzed. It is found that ultlasonic vibration reduces the dechromisation incubation time, accelerates the dechromisafion corrosion rate, decreases the temperature and concentration of HC1 solution, and when the dechromisation occurs it seriously weakens the microstmcture of dechromisation layer. It is concluded that ultrasonic vibration can accelerate destruction of the passivation film on the Cr surface and increase the activities of Cl^- and Cr.     

Influences of Si on corrosion of Fe–B alloy in liquid zinc

Abstract

Influences of silicon content on the microstructure and corrosion resistance of a Fe–2·5 wt-%B alloy have been investigated by using scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. Si can change the microstructure from hypereutectic to eutectic and furthermore, enhance the corrosion resistance of the alloy in molten zinc. The high corrosion resistance of the alloy was mainly attributed to the eutectic phase increase and solubility of Si in α phase enhancement. The corrosion of these alloys in liquid zinc was controlled by the diffusion mechanism. The reaction products are FeZn_6·67, Fe₅SiB₂ and FeSi. The reaction layer further prevents the diffusion of zinc atoms into the base material and delays the reaction between the substrate and the molten zinc efficiently.     

Localized dissolution initiated at single and clustered intermetallic particles during immersion of Al–Cu–Mg alloy in sodium chloride solution

Aiming at understanding how intermetallic phases response when AA2024-T3 aluminium alloy is exposed to chloride-containing aqueous medium, scanning electron microscopy was employed to provide morphological information on alloy surface before and after corrosion testing. Energy dispersive X-ray spectroscopy was carried out to determine compositional change in intermetallic particles. Atomic force microscopy was used to examine topographical variation introduced by the reactions of intermetallic phases. Transmission electron microscopy combined with ultramicrotomy was carried out on dealloyed Al₂CuMg particles and their periphery region. It is found that dealloyed Al₂CuMg particles exhibited porous, polycrystalline structure comprised of body-centred cubic copper particles with sizes of 5 to 20 nm. Aluminium matrix started to trench in the periphery of Al₂CuMg particles at the early stage of dealloying. Development of trenching in Al–Cu–Fe–Mn–(Si) particle's periphery was not uniform and took longer time to initiate than Al₂CuMg dealloying. Localized corrosion at a cluster of Al₂CuMg and Al₂Cu particles was mainly associated with Al₂CuMg particles.     

Evaluation of pitting corrosion of Al-Mg-Mn-Sc-Zr alloy in EXCO solution by EIS

In order to evaluate the degree and severity of Al-Mg-Mn-Sc-Zr alloy in exfoliation corrosion（EXCO） solution quickly and nondestructively, electrochemical impedance spectroscopy（EIS） technique was employed. The Al- Mg-Mn-Sc-Zr alloy suffers pitting corrosion in the EXCO solution. During pit incubation, the Nyquist diagram is composed of a depressed capacitive arc at high-mediate frequency and an inductive arc at low frequency. The inductive arc fades with immersion time, and the beginning of pitting corrosion and the appearance of two capacitive arcs have simultaneity. During pit propagation, the Nyquist diagram is composed of two overlapped capacitive arcs. As time goes on, two time constants are more clearly distinguished. The high frequency and low frequency capacitive arc are aroused hy passive surface and new interface, respectively. An equivalent circuit is designed to fit EIS, and the experimental results and the fitted results have good correspondence. The degree and severity of pitting corrosion can be obtained by the features of EIS and comparing the fitted values of parameters at different times.     

Effect of heat treatment of the mechanical properties and corrosion resistance of welded joints in high-strength aluminium–lithium alloys

Experimental results show that the maximum level of strength characteristics is obtained in complete heat treatment (quenching + artificial ageing) after welding. The heat treatment of friction stir welded joints results in the equalization of the structural heterogeneity and removal of softening in the heat-affected zone. Post-weld heat treatment conditions have almost no effect on the protective properties of non-metallic inorganic coatings. The susceptibility to intercrystalline corrosion (ICC) of welded joints with anodic oxide and chemical oxide coatings is also eliminated.     

Effect of inhibitors on corrosion behavior of copper—nickel in concentrated lithium bromide solution at high temperature

1　ＩＮＴＲＯＤＵＣＴＩＯＮＷｉｔｈｔｈｅｉｎｃｒｅａｓｉｎｇｏｆｃｏｎｓｃｉｏｕｓｎｅｓｓｏｆｅｎｖｉｒｏｎ ｍｅｎｔａｌｐｒｏｔｅｃｔｉｏｎ ,ｍｏｒｅａｎｄｍｏｒｅｐｒｏｄｕｃｔｓａｒｅｒｅ ｑｕｉｒｅｄｎｏｔｔｏｐｏｌｌｕｔｅｅｎｖｉｒｏｎｍｅｎｔ .Ｌ     

Electrodeposition of high corrosion resistant Ni–Sn–P alloy coatings from an ionic liquid based on choline chloride

With the objective of obtaining corrosion resistant coatings, ternary Ni–Sn–P alloy coatings were electrodeposited from a deep eutectic solvent and their composition, morphology and corrosion resistance were investigated as a function of electrodeposition potential. A comparison was made with a Ni–P binary alloy coating electrodeposited under similar conditions. Cyclic voltammetry, energy dispersive analysis of X-rays, potentiodynamic polarisation, open circuit potential-time and electrochemical impedance spectroscopy techniques were used for studying the electrodeposition behaviour, chemical composition and coatings corrosion performances, respectively. The chemical compositions of the ternary Ni–Sn–P alloy films contained about 4.4–10.3?wt-% Sn, 7.2–8.1?wt-% P and Ni (balance). X-ray diffraction patterns of the ternary Ni–Sn–P deposits revealed a single and broad peak, becoming wide with an increase in Sn content, showing that the structures of all the deposits were nanocrystalline or amorphous. Corrosion tests showed that ternary Ni–Sn–P alloy coatings exhibited considerably better barrier corrosion resistance than binary Ni–P coatings, and their corrosion resistance improved with an increase in Sn content.     

Interfacial reactions of chalcopyrite in ammonia–ammonium chloride solution

The interfacial reactions of chalcopyrite in ammonia–ammonium chloride solution were investigated. The chalcopyrite surface was examined by scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) techniques. It was found that interfacial passivation layers of chalcopyrite were formed from an iron oxide layer on top of a copper sulfide layer overlaying the bulk chalcopyrite, whereas CuFe_1–xS₂ or copper sulfides were formed via the preferential dissolution of Fe. The copper sulfide layer formed a new passivation layer, whereas the iron oxide layer peeled off spontaneously and partially from the chalcopyrite surface. The state of the copper sulfide layer was discussed after being deduced from the appearance of S^2–, S^2?₂, S^2?_n, S⁰ and SO^2?₄. A mechanism for the oxidation and passivation of chalcopyrite under different pH values and redox potentials was proposed. Accordingly, a model of the interfacial reaction on the chalcopyrite surface was constructed using a three-step reaction pathway, which demonstrated the formation and transformation of passivation layers under the present experimental conditions.     

Effect of flame rectification on corrosion property of Al–Zn–Mg alloy

The corrosion resistance of Al–Zn–Mg alloy subjected to different times in flame rectification was investigated based on the exfoliation corrosion test. The results indicate that the flame rectification deteriorates the exfoliation corrosion resistance of Al–Zn–Mg alloy. The corrosion resistance of Al–Zn–Mg alloy is ranked in the following order: base metal>two times>three times>one time of flame rectification. The exfoliation corrosion behavior was discussed based on the transformation of precipitates at grain boundaries and matrix. With increasing the number of times in flame rectification, the precipitate-free zones disappeared and the precipitates experienced dissolution and re-precipitation. The sample was seriously corroded after one time of flame rectification, because the precipitates at grain boundaries are more continuous than those in other samples.     

Effect of mischmetal on the corrosion properties of Mg–5Al alloy

The effect of mischmetal (Mm) on the corrosion properties of Mg–5Al alloy was investigated by electrochemical techniques in 0.01 M NaCl solution as the alkaline condition (pH 12) and surface analyses. The electrochemical tests indicated that the pitting potential, time to pitting initiation, and charge transfer resistance of the Mg–5Al specimens increased with increasing Mm content. Surface analyses indicated that Mm promoted the formation of passive film in the absence of Mm products. In addition, the benefits of Mm addition are the refinement of the precipitates and reduction in grain size.     

Effect of sizing on the corrosion behaviour of Alumix 123 P/M alloy in 3.5 wt-% NaCl solution

The corrosion behaviour of the commercial aluminium powder metallurgy alloy ‘Alumix 123’ after undergone ‘sizing’, a standard cold forming operation, has been studied in naturally aerated 3.5?wt-% NaCl solution through open circuit potential (OCP), cathodic potentiodynamic polarisation, cyclic potentiodynamic polarisation and potentiostatic polarisation experiments, and the subsequent corrosion morphology was characterised by scanning electron microscopy and energy dispersive X-ray spectroscopy. The results were compared to those obtained for Alumix 123 in the ‘as-sintered’ condition and to a compositionally similar wrought alloy, AA2014-T6. The sizing operation significantly affected the OCP, corrosion control, cathodic process, corrosion rate and corrosion morphology of Alumix 123. These changes are attributed to the reduction in open surface porosity brought about by the sizing operation. It appears that with a single secondary operation, sizing, the corrosion resistance of Alumix 123 is significantly improved and approaches that of AA2014-T6.     

Enhanced corrosion resistance of Zn–Cu–Ti alloy with addition of Cu–Ti amorphous ribbons in 3.5% NaCl solution

In the present study, Zn–0.3Cu–0.3Ti alloy (sample I) was fabricated by a simple low-temperature melting method using Cu–50Ti amorphous alloy ribbons for corrosion in 3.5% NaCl solution. As a comparison, crystalline Cu–50Ti master alloy was used to prepare Zn–0.3Cu–0.3Ti alloy (sample II). Sample I comprising Zn, TiZn₃, and TiZn₁₅ phases exhibits an equiaxed microstructure with subgrain structure. Large TiZn₃ particles show cluster feature, whereas intermittent small TiZn₁₅ particles exist at grain boundaries and subgrain boundaries. In sample II, the Zn matrix with typical dendritic microstructure is observed and no large particles are found. Compared with sample II, sample I shows lower weight gain and corrosion current density and a higher slope of cathode polarization curve. The weight gain for sample I is only 0.59 mg·cm⁻², but for sample II, this value reaches 0.70 mg·cm⁻². After 8 days of corrosion, corrosion products are mainly Zn₅(OH)₈Cl·H₂O and ZnO, showing loose particle shape. As corrosion time increases from 2 days to 8 days, corrosion layer thickness increases from about 15 to 24 μm for sample 1.