High efficiency corrosion inhibitor 8-hydroxyquinoline and its synergistic effect with sodium dodecylbenzenesulphonate on AZ91D magnesium alloy

The inhibition effects of sodium dodecylbenzenesulphonate (SDBS) and 8-hydroxyquinoline (8HQ) on the corrosion of AZ91D magnesium alloy in ASTM D1384-87 corrosive solution were investigated by the electrochemical impedance spectroscopy and potentiodynamic polarization tests. For SDBS, the inhibition effect was not significant. For 8HQ, a monotonic increase in inhibition efficiency was observed as a function of the immersion time, and the component of the film was Mg(8HQ)₂, which was characterized by three spectra methods. Upon mixing 8HQ and SDBS inhibitors, a synergistic inhibition behavior was observed, and a proper synergistic inhibition mechanism was proposed.     

Influence of inorganic acid pickling on the corrosion resistance of magnesium alloy AZ31 sheet

Surface contaminants as a result of thermo-mechanical processing of magnesium alloys, e.g. sheet rolling, can have a negative effect on the corrosion resistance of magnesium alloys. Especially contaminants such as Fe, Ni and Cu, left on the surface of magnesium alloys result in the formation of micro-galvanic couples and can therefore increase corrosion attack on these alloys. Due to this influence they should be removed to obtain good corrosion resistance.In this study, the effect of inorganic acid pickling on the corrosion behaviour of a commercial AZ31 magnesium alloy sheet was investigated. Sulphuric, nitric and phosphoric acids of different concentrations were used to clean the alloy for various pickling times. The surface morphology, composition and phases were elucidated using scanning electron microscopy, X-ray fluorescence analysis, spark discharge-optical emission spectroscopy, energy dispersive X-ray spectroscopy and infrared spectroscopy. The effect of surface cleaning on the corrosion properties was studied using salt spray test and electrochemical impedance spectroscopy. The experimental results show that acid pickling reduces the surface impurities and therefore enhances the corrosion resistance of the alloy. The cleaning efficiency of the three acids used and the corrosion protection mechanisms were found to be remarkably different. Best corrosion results were obtained with nitric acid, followed closely by phosphoric acid. Only the sulphuric acid failed more or less when cleaning the AZ31 sheet. However, to obtain reasonable corrosion resistance at least 5 μm of the surface of AZ31 magnesium alloy sheet have to be removed.     

Tracking the corrosion of magnesium sand cast AM50 alloy in chloride environments

An experimental procedure for tracking corrosion on lightweight alloys has been developed using a combination of microscopy and corrosion studies using commercial sand cast magnesium AM50 alloys. Corrosion penetration depths were measured and characterized with CLSM and SEM/XEDS, respectively. Corrosion depths on α-grains in the alloys were expressed as a function of their Al content. Al-rich β-phases and eutectic α-phase microstructures were observed to be most corrosion resistant due to an enrichment of Al, identified with TEM, near the oxide/alloy interface. Sand cast alloys were found to be susceptible to major corrosion events in regions with depleted Al content.     

Microbially influenced corrosion of zinc and aluminium - Two-year subjection to influence of Aspergillus niger

Aspergillus niger. Tiegh., a filamentous ascomycete fungus, was isolated from the metal samples exposed to marine, rural and urban sites in Lithuania. Al and Zn samples were subjected to two-year influence of A. niger under laboratory conditions in humid atmosphere. Electrochemical impedance spectroscopy (EIS) ascertained microbially influenced corrosion acceleration (MICA) of Zn and inhibition (MICI) of Al. EIS data indicated a two-layer structure of corrosion products on Zn. The microorganisms reduced the thickness of the inner layer, whose passivating capacity was much higher when compared to that of the outer layer. An increase in aluminium oxide layer resistance but decrease in the layer thickness implied that MICI affected primarily the sites of localized corrosion of Al (pores, micro-cracks, etc.). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies indicated that bioproducts (i.e. organic acids) did not form crystalline phases with corrosion products of zinc. The study suggested a hypothesis that microorganisms could be used as corrosion protectors instead of toxic chemicals, application of which tends to be increasingly restricted.     

About some corrosion mechanisms of AZ91D magnesium alloy

The present work is dedicated to a study of the corrosion resistance of AZ91D (91% Mg) alloy in wet environments. Three industrial alloys obtained by die-casting or sand casting were subjected to salt spray corrosion tests (ASTM-B117 standard) and immersion tests. Weight loss kinetic curves were measured. Surface analysis was performed by X-ray photoelectron diffraction (XPS). After corrosion the sand cast alloy presents a surface mainly enriched in hydroxides and carbonates while the die-cast alloy presents a surface enriched also in mixed Mg-Al oxides. The quantitative analysis of the rate Mg/Al shows an enrichment in aluminium for the die-cast alloys in comparison to the sand cast alloy.     

Substitution of Cu and/or Al in η phase (MgZn2) and the implications for precipitation in Al–Zn–Mg–(Cu) alloys

The effects of Cu and Al substituting for Zn within bulk samples of η phase (nominally MgZn₂) have been studied by laboratory X-ray powder diffraction and nuclear magnetic resonance. Increasing Al concentration causes both of the η phase lattice parameters to increase linearly, while increasing Cu concentration causes both parameters to decrease linearly. These effects also appear to combine in a linear fashion if both Al and Cu are substituted into the MgZn₂ structure, particularly in the case of the a lattice parameter. Al was found to substitute evenly onto both Zn sites, while Cu substitutes preferentially onto the 6(h) site at low Cu concentrations, before causing significant disruptions to the structure at concentrations above 1.1 at.%, leading to the transition to long period stacking phases at the expense of η. High-resolution synchrotron powder diffraction from a commercial Al–Zn–Mg–(Cu) alloy revealed that the η phase precipitates with lattice parameters that are substantially smaller than for pure MgZn₂, indicating Cu concentrations of at least 8.9 at.% and probably higher. It is likely that the Al matrix provides a mechanical constraint on the formation of any long period stacking phases and allows the η phase to exist in these alloys with such high Cu concentrations.     

Corrosion behaviour of magnesium/aluminium alloys in 3.5 wt.% NaCl

Corrosion behaviour of commercial magnesium/aluminium alloys (AZ31, AZ80 and AZ91D) was investigated by electrochemical and gravimetric tests in 3.5 wt.% NaCl at 25 °C. Corrosion products were analysed by scanning electron microscopy, energy dispersive X-ray analysis and low-angle X-ray diffraction. Corrosion damage was mainly caused by formation of a Mg(OH)₂ corrosion layer. AZ80 and AZ91D alloys revealed the highest corrosion resistance. The relatively fine β-phase (Mg₁₇Al₁₂) network and the aluminium enrichment produced on the corroded surface were the key factors limiting progression of the corrosion attack. Preferential attack was located at the matrix/β-phase and matrix/MnAl intermetallic compounds interfaces.     

Corrosion behavior of Cu–Al–Be shape memory alloys with different compositions and microstructures

The corrosion behavior of Cu–Al–Be shape memory alloys with different microstructures and Be content in a 3.5% NaCl solution was studied by weight loss, cyclic anodic polarization and chronoamperometric measurements. The beryllium has a beneficial effect in β alloys. A pitting potential of −100 mV/SCE was found by anodic polarization tests for all the studied alloys, corresponding to the formation of pits produced by severe dealuminization. Samples with precipitates were more susceptible to pit formation. The corrosion behavior is strongly affected by the alloy microstructural conditions, and the β samples present higher pitting resistance and repassivation ability.     

Corrosion behaviour of thermally sprayed Al and Al/SiCp composite coatings on ZE41 magnesium alloy in chloride medium

Thermally sprayed Al and Al/SiCp composite coatings have been deposited on ZE41 magnesium alloy and mechanical compaction at room temperature was applied to the Al and Al/SiCp coatings to reduce their porosity. Corrosion behaviour of coated samples was evaluated and compared to that of uncoated substrate in 3.5 wt.% NaCl solution using electrochemical measurements. Al and Al/SiCp composite coatings reduced the corrosion current density of Mg-Zn alloys by three and two orders of magnitude, respectively, and reductions up to four orders of magnitude were obtained after mechanical compaction.     

Corrosion behaviour of Al–29at%Co alloy in aqueous NaCl

Microstructure and corrosion behaviour of a binary Al–29 at%Co alloy have been studied. The alloy was prepared by arc-melting of Al and Co in high purity Ar and rapidly solidified on a water-cooled Cu mould. The alloy chemical composition and microstructure were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Furthermore, the corrosion behaviour was studied by potentiodynamic polarization in aqueous NaCl (0.6 mol dm⁻³) at room temperature. The alloy was found to consist of three phases: hexagonal Al₅Co₂, Z-phase and AlCo (β). The corrosion resistance of different intermetallic phases is characterized. The results are compared to previously published results of Al–TM (TM = transition metal) alloys.     

Copper(II) 8-hydroxyquinolinate 3D network film with corrosion inhibitor embedded for self-healing corrosion protection

This work presents a self-healing protective coating for copper. The complex coating is composed of copper(II) 8-hydroxyquinolinate (Cu(8HQ)₂) 3D network film storing corrosion inhibitor as base layer and epoxy as top layer covering on the base layer. The results of EIS and polarization curves reveal the self-healing effect of Cu(8HQ)₂ 3D network film with corrosion inhibitor embedded. After being scratched with a knife-edge, the complex coating rapidly releases inhibitor embedded in 3D network structure to suppress the corrosion process. The scratch on the coating is covered with inhibitor adsorption film and the anodic activity is restrained.     

Electrochemical investigation of the influence of laser surface melting on the microstructure and corrosion behaviour of ZE41 magnesium alloy – An EIS based study

Surface melting of a magnesium alloy, ZE41 (4%-Zn, 1%-RE) was performed to achieve electrochemical homogeneity at the surface by microstructure refinement. Large secondary precipitates are particularly known to cause severe pitting in magnesium alloys. The corrosion resistance of the laser treated and untreated alloy was investigated by potentiodynamic polarisation and electrochemical impedance spectroscopy. Contrary to the reported behaviour of other magnesium alloys (such as AZ series alloys), laser surface melting did not significantly improve the corrosion resistance of ZE41. This observation is attributed to the absence of beneficial alloying elements such as Al in ZE41 alloy.     

Rust formation and corrosion performance of Si- and Al-bearing ultrafine grained weathering steel

A high Si, Al type ultrafine-grained (UFG) weathering steel was produced by the multi-pass warm rolling method, and its corrosion resistance was estimated by a cyclic wet/dry corrosion test using chloride ions. The Si- and Al-bearing UFG steel exhibited excellent corrosion resistance in comparison with Si–Mn carbon steel (SM).

EPMA and TEM analyses showed that Si and Al mainly exist in nano-scale iron complex oxides in the inner rust layer formed on the developed steel. The Al K X-ray spectrum of Al₂O₃ and metallic Al had different peak positions due to chemical shifts, and that of the test sample was the same as that of Al₂O₃ in the EPMA analysis. This result suggested that Al was present in the complex oxides as Al³⁺. In the same way, Si was identified as an intermediate state such as Si²⁺ in the complex oxides of the inner rust.

EIS (electrochemical impedance spectroscopy) measurement of the corrosion test samples revealed that the rust resistance (R_rust) and corrosion reaction resistance (R_t) of the developed steel were much larger than those of SM. It was found that nano-scale complex iron oxides formed in the lower layer of iron rust in the developed steel, resulting in increased R_rust and R_t, and finally suppressing corrosion.     

Comparison of the corrosion behaviour of bulk and thin film magnesium alloys

The corrosion behaviour of bulk and thin film specimens consisting of commercial magnesium alloys AZ31 and AZ80 was investigated by electrochemical tests in 3.5 wt.% NaCl solution and in phosphate buffered saline solution (PBS) at room temperature. Corrosion tests indicated that the corrosion rates are nearly equal, but localized attack was more pronounced for the bulk specimens than for the thin film samples. XRD analyses showed that this behaviour can be attributed to the fact that the as-deposited thin film specimens do not contain any precipitates, which are present in the bulk samples and are considered to enhance localized corrosion.     

Development of novel brasses to resist dezincification

The effect of alloying Sn, Pb, As, Sb and P on the dezincification of commercial brass 60Cu-39Zn-1Pb has been investigated in 1% CuCl₂ solution by immersion studies and electrochemical measurements. Specimens with a smooth surface finish exhibited more resistance to dezincification. Appreciable inhibitive effect on dezincification was observed for the 55Cu-40Zn-3Pb-2Sn brass composition. The galvanic coupling of lead phase with the matrix accelerated corrosion. To improve the dezincification resistance of the Sn containing brass, As, Sb and P were added at two different levels (0.05% and 0.1%). Brass of composition 48.95Cu-45Zn-5Pb-1Sn-0.05As was more resistant indicating the synergistic effect of Sn and As. The effect of 0.05 and 0.1% of arsenic addition with various concentrations of zinc was also studied. The alloy of composition 57.90Cu-40Zn-2Pb-0.1As showed better corrosion resistance than the alloy containing 1% Sn and 0.05% As (48.95Cu-45Zn-5Pb-1Sn-0.05As). To understand the influence of Sn and As on the dezincification of commercial brass, linear polarization and cyclic voltammetry experiments were conducted for the alloys 60Cu-39Zn-1Pb, 55Cu-40Zn-3Pb-2Sn and 57.90Cu-40Zn-2Pb-0.1As. Linear polarization measurements indicated that the alloys 55Cu-40Zn-3Pb-2Sn and 57.90Cu-40Zn-2Pb-0.1As possessed higher resistance to corrosion than commercial brass. Inspection of cyclic voltammograms revealed that the peak current densities as well as the passive current density were lower for the alloys 55Cu-40Zn-3Pb-2Sn and 57.90Cu-40Zn-2Pb-0.1As than the alloy 60Cu-39Zn-1Pb. The surface layer on the alloys 60Cu-39Zn-1Pb, 55Cu-40Zn-3Pb-2Sn and 57.90Cu-40Zn-2Pb-0.1As after immersion of 72 h in 1% CuCl₂ solution were analyzed by X-ray diffraction and scanning electron microscopy. Higher enrichment of Sn and As at the interface of surface layer and metal was indicated for the alloys 55Cu-40Zn-3Pb-2Sn and 57.90Cu-40Zn-2Pb-0.1As, respectively.     

The investigation of synergistic inhibition effect of rhodanine and iodide ion on the corrosion of copper in sulphuric acid solution

The synergistic inhibition effect of rhodanine (Rdn) and iodide ion on the corrosion of copper in 0.5 M H₂SO₄ solution was studied using electrochemical techniques. The surface morphologies of the substrates were examined by scanning electron microscopy (SEM). Elemental analysis of electrode surface exposed to test solution was determined by energy dispersive X-ray spectroscopy (EDX). It was found that Rdn provided satisfactory inhibition on the corrosion of copper. Moreover, its inhibition efficiency further increased in the presence of iodide ions due to synergistic effect. Finally, a mechanism of inhibition is proposed and discussed.     

Corrosion behavior of aluminum alloy 2024-T3 by 8-hydroxy-quinoline and its derivative in 3.5% chloride solution

The corrosion behavior of aluminum alloy 2024-T3 was studied in 3.5% NaCl solutinn with two fluorescence quinoline compounds named 8-hydroxy-quinoline（8HQ） and 8-hydroxy-quinoline-5-sulfonic acid（HQS）. The open circuit potential（OCP） test result indicates that both compounds change the alloy corrosion potential by adsorbing on the electrode surface. Polarization measurements show that 8HQ is a mixed type inhibitor by blocking the active sites of the metal surface, while HQS is a corrosion accelerator by activating the cathodic reaction. Changes of the impedance parameters in the electrochemical impedance spectroscopy（EIS） are related to the adsorption of 8HQ on the metal surface, which leads to the formation of a protective layer. The impedance diagram in the solution with HQS is similar to the one without additional organic compounds. The morphology and composition of the protective layer were studied by using SEM/EDS. The result confirms the function of the additions that the effect of 8HQ is due to the insoluble aluminum chelate, AI（HQ）3, to prevent adsorption of chloride ion, while the effect of HQS is to break down the oxide film.     

Comparison of the corrosion of Cu50Pd50 and Cu50Pd44M6 (M = Y,Mg, or Al) hydrogen separation membrane alloys in simulated syngas containing H2S

The resistance to sulfidation was examined by exposing coupons including a Cu–Pd binary alloy and three ternary alloys with 6 at% Y, Mg, or Al to simulated syngas containing varying amounts of H₂S. The mass change of the samples was determined and the exposed surfaces were characterized by SEM/EDS and XRD. The best corrosion resistance of the ternary alloys was observed in the Cu₅₀Pd₄₄Al₆ alloy. A slight decrease was observed when Mg was added, but both the Al and Mg alloys were roughly on par with the binary composition. The Y addition resulted in a degradation in the corrosion resistance by forming extensive internal Y₂O₃ and Cu_1−xY_xS and external Pd_4−xCu_xS and Pd ₁₃Cu₃S₇.     

Composition and processing effects on the electrochemical characteristics of biomedical titanium alloys

The electrochemical behaviour of the Ti–13Nb–13Zr and Ti–6Al–4V ELI alloys with martensitic microstructures was investigated by polarization and electrochemical impedance spectroscopy (EIS) in Ringer’s solution. The impedance spectra were interpreted by a two time-constants equivalent circuit. Both investigated alloys showed high corrosion resistance, but the thin and uniform passive film on the Ti–6Al–4V ELI alloy surface was more protective. The inner barrier and outer porous layer were highly resistant and capacitive. However, thicker and more porous passive film on the Ti–13Nb–13Zr alloy surface may be beneficial for osteointegration. The suitable thermomechanical processing improved the corrosion resistance of Ti–13Nb–13Zr alloy.     

The influence of zirconium additions on the corrosion of magnesium

Sixteen custom binary Mg–Zr alloys and four commercial Zr-containing Mg-alloys were used to investigate the role of Zr on the corrosion of Mg. Mg–Zr alloys were manufactured with a range of different Zr concentrations. It was observed that the Mg–Zr alloys with a smaller mean Zr particle size had more Zr dissolved in solid solution. Both the Zr in solid solution and in metallic particle form were observed to have a deleterious effect on the corrosion rate of Mg. However, this deleterious effect is less pronounced to effect in alloys with multiple alloying additions.