Effect of Cr, Yb and Zr additions on localized corrosion of Al–Zn–Mg–Cu alloy

The effect of Cr, Yb and Zr additions on localized corrosion of Al–Zn–Mg–Cu alloy has been investigated. Additions of Cr, Yb and Zr to Al–Zn–Mg–Cu alloy stabilized the deformation-recovery microstructure with low angle grain boundaries on which grain boundary precipitates distributed discretely. The exfoliation and stress corrosion cracking of Al–Zn–Mg–Cu alloys propagated along the high angle recrystallized grain boundaries. The unrecrystallized Al–Zn–Mg–Cu–Zr–Cr–Yb alloy exhibited higher resistance to stress corrosion cracking and exfoliation corrosion, compared to the partial recrystallized Al–Zn–Mg–Cu–Zr alloy with high angle grain boundaries.     

Effects of bovine serum albumin on the corrosion behaviour of AISI 316L, Co–28Cr–6Mo, and Ti–6Al–4V alloys in phosphate buffered saline solutions

The corrosion behaviour of AISI 316L, wrought Co–28Cr–6Mo and Ti–6Al–4V was studied in aerated solutions of phosphate buffered saline (PBS) at various concentrations of bovine serum albumin (BSA) at 37 °C. Open circuit potential, potentiodynamic polarization, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) experiments along with X-ray photoelectron spectroscopy (XPS) on Co–28Cr–6Mo oxide layer were conducted to study the interaction of BSA and passive layers and to measure the corrosion rates. Ti–6Al–4V alloy had the lowest corrosion rate and the highest breakdown potential. It was shown that BSA has enhanced the alloy passive film stability at higher concentrations.     

Selective corrosion of 550 °C aged Cu10Ni–3Al–1.3Fe alloy in NaCl aqueous solution

This work studied the electrochemical behavior of a solution treated or 550 °C aged Cu10Ni–3Al–1.3Fe alloy, in 0.01 M NaCl aqueous solution, through potentiodynamic polarization in both stagnant condition or under erosion process. Results showed the occurrence of a passivity break potential (E_pb), related to the beginning of the denickelification process, which occurred as a localized attack under stagnant electrolyte. Under erosion conditions localized denickelification was not observed, despite of the presence of E_pb. This could indicate that selective corrosion of Ni, which caused the observed E_pb, occurred as a dissolution–redeposition process, with removal of the Cu deposits during erosion process.     

The corrosion behavior of Cu–Al and Cu–Al–Be shape-memory alloys in 0.5 M H2SO4 solution

The corrosion behavior of Cu–Al and Cu–Al–Be (0.55–1.0 wt%) shape-memory alloys in 0.5 M H₂SO₄ solution at 25 °C was studied by means of anodic polarization, cyclic voltammetry, and alternative current impedance measurements. The results of anodic polarization test show that anodic dissolution rates of alloys decreased slightly with increasing the concentrations of aluminum or beryllium. Severe intergranular corrosion of Cu–Al alloy was observed after alternative current impedance measurement performed at the anodic potential of 0.6 V. However, the addition of a small amount of beryllium was effective to prevent the intergranular corrosion. The effect of beryllium addition on the prevention of intergranular corrosion is possibly attributed to the diffusion of beryllium atoms into grain boundaries, which in turn deactivates the grain boundaries.     

Corrosion behaviour of Al/Al3Ti and Al/Al3Zr functionally graded materials produced by centrifugal solid-particle method: Influence of the intermetallics volume fraction

Intermetallic particles, Al₃Ti and Al₃Zr were formed in Al–5mass%Ti and Al–5mass%Zr alloys, respectively, by centrifugal casting, in order to create functionally graded materials (FGMs). At present, no information is available on the influence of the amount of intermetallics on the electrochemical properties of these alloys.In this paper, the corrosion resistance of Al/Al₃Ti and Al/Al₃Zr FGMs was investigated by open-circuit measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. Results suggests that the corrosion resistance of the FGMs is affected by galvanic effects between the intermetallic particles and the metallic matrix. Lower centrifugal forces resulted in an improvement of the electrochemical properties.     

Internal oxidation and phase transformations of multi-phase Fe–Ni–Al and Fe–Ni–Al–Cr alloys induced by KCl corrosion

The corrosion of two multiphase Fe–Ni–Al and Fe–Ni–Al–Cr alloys is studied at 650 °C in KCl-contaminated air. The oxidation rate of the alloys in air alone is low. When KCl is introduced, the corrosion is accelerated, producing a thick external scale of iron oxides, an intermediate layer of spinel, and a region of internal oxidation of Al. Potassium chromate is detected on Fe–Ni–Al–Cr surface that accounts for the degradation of protective chromia. An Al-depleted single phase region is observed in the front of the internal oxidation, due to the selective consumption of Al via an “active oxidation” process.     

Modelling the anodizing behaviour of aluminium alloys in sulphuric acid through alloy analogues

Anodic film morphologies on aluminium aerospace alloys are strongly influenced by alloying elements. The present study uses model alloys to interpret the early stages of anodizing of AA2024-T3 and AA7075-T6 aluminium alloys in 0.4 M sulphuric acid electrolyte. Further, coupled model alloys, representative of matrix and second phase regions, are employed as alloy analogues. The findings enable assignment of transient anodic currents during potentiodynamic polarization of the commercial alloys to oxidation of Al₂CuMg phase at 0 V SCE and of Al₂Cu, Al₇Cu₂Fe and Al–Cu–Fe phases at 5–6 V SCE. The phases that oxidize at the latter potential also cause voltage arrests during galvanostatic anodizing.     

Interfacial morphology and corrosion resistance of Fe–B cast steel containing chromium and nickel in liquid zinc

The interfacial morphology and corrosion resistance of low carbon Fe–B cast steels in zinc bath at 520 °C were investigated. The results show Fe–B cast steel containing high Cr and Ni exhibits the best corrosion resistance to liquid zinc. The corrosion layers are composed of Γ-Fe₃Zn₁₀, δ-FeZn₁₀, ξ-FeZn₁₃ and η-Zn. The corrosion behaviour of Fe–B cast steels includes the following processes: the preferential leach and dissolution of Cr and Ni, the formation of Fe–Zn compounds controlled by zinc atom diffusion, and the spalling of borides without the supporting role of α-(Fe, Cr) matrix corroded by liquid zinc.     

Corrosion behaviour of a 2219 aluminium alloy treated with a chromate conversion coating exposed to a 3.5% NaCl solution

This study investigates the formation of a chromate conversion coating at Al–Cu–Fe–Mn intermetallic sites of an Al2219 alloy and the corrosion initiation at these sites in a 3.5% NaCl solution, using SEM, AES and EDX. Changes in the surface chemistry were monitored after progressive exposures to the solution up to 42 h. The coating was found to be thinner and more defective on the intermetallic. Initially, Al is dissolved and Al(OH)₃ deposited on and around the intermetallic. After 42 h of exposure, Al(OH)₃, Fe and Mn oxides and small particles of elemental Cu are deposited as corrosion products.     

Corrosion mechanism of Mo/Nd16Fe71B13/Mo film in a simulated marine atmosphere

This study describes the corrosion mechanism of Mo/Nd₁₆Fe₇₁B₁₃/Mo film induced by sodium chloride particles in 80% relative humidity (RH) environment. The deliquescence of sodium chloride particles on the Mo/Nd₁₆Fe₇₁B₁₃/Mo film caused the step by step attacks. Initial loosening of the Mo layer allows permeation of electrolyte into Nd–Fe–B layer, resulting in cavitations of electrolyte and subsequent film failure. The second failure step involves corrosion of Nd element in the Nd–Fe–B layer, with Fe element remaining beneath the corrosion product. Corrosion of Fe constitutes the third-step failure, forming a mixture of Nd and Fe corrosion product.     

Influence of silicon on the corrosion behaviour of Al–Zn–In–Mg–Ti sacrificial anode

The influence of Si on the corrosion behaviour of Al–5Zn–0.03In–1Mg–0.05Ti (wt.%) alloy was investigated by the microstructure observation and electrochemical measurements in order to improve its corrosion non-uniform and electrochemical properties. The main precipitates in Al–5Zn–0.03In–1Mg–0.05Ti–0.1Si (wt.%) alloy is Mg₂Si phase, which decrease the galvanic corrosion because the potential difference between Mg₂Si and a-Al is smaller than that between MgZn₂ and a-Al. The addition of Si improves the corrosion uniformity of the anode due to the fine equiaxed grains and grain boundaries where Mg₂Si particles uniformly distributed. The results indicate that the microstructure, electrochemical characteristics and corrosion uniformity can be improved significantly after adding 0.1 wt.% Si into Al–5Zn–0.03In–1Mg–0.05Ti (wt.%) alloy.     

Electrochemical behaviour of Ti–6Al–4V alloy and Ti in azide and halide solutions

Electrochemical techniques including open circuit potential measurement, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion and passivation behaviour of Ti–6Al–4V alloy in sodium azide (NaN₃) solutions compared to the behaviour of its pure base metal Ti. The results showed that increasing azide concentration increases the rate of corrosion (i_corr) and shifts negatively the rest potential (E_f), as well as decreases the spontaneous thickening rates of the inner and outer layers constituting the passive oxide film on each sample. These effects are more accentuated for the alloy than for the metal. Moreover, the electrical resistance (R_ox) and the relative thickness (1/C_ox) of the oxide films on the two samples exhibit an almost linear decrease vs. NaN₃ concentration. The results suggested that addition of Al and V to Ti, although improves its machinability, yet it decreases the performance of its surface oxide film to protect the degradation of the metal. The alloy was found to be more susceptible to corrosion than its base metal, since Ti expresses higher apparent activation energy (E_a) for the corrosion process than Ti–6Al–4V. Electrochemical behaviour of Ti in azide medium was also compared with that in various halide solutions. It was found that Ti has a stronger propensity to form spontaneous passivating oxide layers in bromide more than in azide and other halide media, where the positive shift in the value of E_f and the simultaneous increase in the oxide film resistance (R_ox) follow the sequence: Br⁻ > > Cl⁻ > I⁻ > F⁻.     

On the constitution of Al4(Cr,Fe)

Using metallographic, diffraction and thermal analysis examinations the base centered orthorhombic Al₄(Cr,Fe) phase reported by Sui et al. (Philos Mag Lett 1995;71:139) was found to be a ternary extension of the Al–Cr η-phase. The constitution of the Al–Cr–Fe alloy system was specified in a compositional region close to this phase.     

Corrosion of an Al–Mg–Si alloy under MgCl2 solution droplets

The corrosion behavior of an Al–0.63Mg–0.28Si alloy under droplets of MgCl₂ solution in environments of 75% and 33% RH was studied using a Kelvin Probe. The equilibrium chloride concentrations in these two environments are 5.8 and 9.8 M chloride, respectively. In the 33% RH environment, metastable pitting was the main form of corrosion. In some cases at 75% RH, the potential baseline decreased slowly by hundreds of millivolts and remained at the lower value. These samples exhibited filiform-like corrosion inside micro-droplets that formed outside of the main MgCl₂ drop. A model for the filiform-like attack in a micro-droplet is presented.     

Discontinuities in the porous anodic film formed on AA2099-T8 aluminium alloy

The anodizing behaviour of constituent particles (Al–Fe–Mn–Cu) and dispersoids (Al–Cu–Mn–Li and β′(Al₃Zr)) in AA2099-T8 has been investigated. Low-copper-containing Al–Fe–Mn–Cu particles anodized more slowly than the alloy matrix, forming a highly porous anodic oxide film. Medium- and high-copper-containing Al–Fe–Mn–Cu particles were rapidly dissolved, resulting in defects in the anodic film. The anodizing of Al–Cu–Mn–Li dispersoids is slightly slower than the alloy matrix, forming a less regular anodic oxide film. β′(Al₃Zr) dispersoids anodized at a similar rate to the alloy matrix. Further, the potential impact of the discontinuities in the resultant anodic films on the performance of the filmed alloy is discussed.     

Chromium–palladium films on 316L stainless steel by pulse electrodeposition and their corrosion resistance in hot sulfuric acid solutions

Chromium–palladium alloy films with good adhesive strength and higher micro-hardness have been deposited on 316L stainless steel by pulse electroplating. The films are composed mainly of chromium and palladium crystallites in the metallic state, with grain sizes less than 100 nm. On the film surface Cr(OH)₃ and Cr₂O₃ are present. The co-deposited Cr and Pd in the films show a synergetic effect on passivation. In boiling 20 wt.% H₂SO₄ solution, boiling acetic–formic acid mixture, and simulated PEM fuel cells environment, the Cr–Pd-plated 316L steel shows excellent corrosion resistance.     

Oxidation behaviour of Ti–Al–C films composed mainly of a Ti2AlC phase

This paper addresses the oxidation behaviour of Ti–Al–C films composed mainly of a Ti₂AlC phase. The films exhibited rather low oxidation rates at 600 and 700 °C, with an oxygen-rich zone or a thin oxide layer appearing on the film surfaces. Much faster oxidation rates were observed at 800 and 900 °C. The Ti₂AlC phase was quickly consumed by oxidation. From the film surface to the inner zone, TiO₂-rich layer, Al₂O₃-rich layer, and TiO₂ + Al₂O₃ mixed layer was observed, respectively. The oxidation mechanism of the Ti–Al–C film is discussed based on the experimental results.     

N-Aminorhodanine as an effective corrosion inhibitor for mild steel in 0.5 M H2SO4

The corrosion inhibition effect of N-aminorhodanine (N-AR) on mild steel (MS) in 0.5 M H₂SO₄ was studied in both short and long immersion duration using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), chronoamperometry and hydrogen gas evolution. The surface morphology of MS was examined with scanning electron microscopy (SEM) in absence and presence inhibitor. The inhibitor adsorption process on MS surfaces obeys the Langmuir adsorption isotherm. The results show that NAR is a good inhibitor for MS in the acidic medium. The inhibition efficiency obtained from potentiodynamic polarization, EIS and LPR up to 98% is determined.     

Wear and corrosion behaviour of Ti–13Nb–13Zr and Ti–6Al–4V alloys in simulated physiological solution

Wear and corrosion behaviour of cold-rolled Ti–13Nb–13Zr alloy, with martensitic microstructure, and Ti–6Al–4V ELI alloy, in martensitic and two-phase (α + β) microstructural conditions, was studied in a Ringer’s solution. The wear experiments were performed at room temperature with a normal load of 40 N and sliding speeds 0.26, 0.5 and 1.0 m/s. The corrosion behaviour was studied at 37 °C using open circuit potential-time measurements and potentiodynamic polarization. It was found that Ti–13Nb–13Zr alloy has a substantially lower wear resistance than Ti–6Al–4V ELI alloy in both microstructural conditions. Surface damage extent increases with sliding speed increase and is always smallest for martensitic Ti–6Al–4V ELI alloy with highest hardness. Both alloys exhibit spontaneous passivity in Ringer’s solution. Corrosion potential values are similar for all three materials. However, Ti–13Nb–13Zr and martensitic Ti–6Al–4V ELI alloys show improved corrosion resistance comparatively to Ti–6Al–4V ELI alloy with (α + β) microstructure. Martensitic Ti–6Al–4V ELI alloy possesses the best combination of both corrosion and wear resistance, although its corrosion resistance is found to be slightly higher than that of the Ti–13Nb–13Zr alloy.     

Growth of anodic oxide films on AC2A alloy in sulphuric acid solution

Growth behaviour of anodic oxide films on AC2A Al cast alloy was investigated in sulphuric acid solution using SEM, optical microscope (OM) and confocal scanning laser microscope (CSLM) and energy dispersive spectroscopy (EDS). The AC2A alloy contains three different types of second-phase particles: Al–Cu, Al–Cu–Fe–Si and Al–Si particles. The growth of anodic oxide films was critically retarded by the presence of non-reactive particles of Al–Si, while little effect was observed by the presence of active particles of Al–Cu and Al–Cu–Fe–Si. The most severe retardation effect on the growth of anodic films on AC2A alloy resulted from agglomerated Al–Si particles.