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.     

The effects of lanthanum on microstructure and electrochemical properties of Al–Zn–In based sacrificial anode alloys

In order to improve the non-uniform corrosion of Al–0.5Zn–0.03In–1Mg–0.05Ti alloys, Al–5Zn–0.03In–1Mg–0.05Ti–xLa (x = 0.3, 0.5 and 0.7 wt.%) alloys were developed. Microstructures and electrochemical properties of the alloys were investigated. The results show that the optimal microstructures and electrochemical properties are obtained in Al–5Zn–0.03In–1Mg–0.05Ti–0.5La alloy. The main precipitate phase is Al₂LaZn₂ particles. The excellent electrochemical properties of Al–5Zn–0.03In–1Mg–0.05Ti–0.5La alloy is mainly attributed to fine grains and grain boundaries containing fine Al₂LaZn₂ precipitates. At the same time the fine grains can improve the non-uniform corrosion of Al–0.5Zn–0.03In–1Mg–0.05Ti alloy.     

Passivation of Al–Cr–Fe and Al–Cu–Fe–Cr complex metallic alloys in 1 M H2SO4 and 1 M NaOH solutions

The corrosion mechanisms of Al–Cr–Fe and Al–Cu–Fe–Cr complex metallic alloys have been investigated by potentiodynamic and potentiostatic polarization. Very good passivation of the Al–Cr–Fe surface is exhibited from 1 M H₂SO₄ to 1 M NaOH solutions, which was confirmed by ICP-OES analysis over a period of 273 days. Potentiostatically formed passive films analysed by XPS revealed chromium enrichment in the outermost layer of the aluminium oxy-hydroxide film. Although Al–Cu–Fe–Cr showed passivation during potentiodynamic polarization, heavy active corrosion at OCP was revealed by ICP-OES. For the Al–Cu–Fe–Cr alloy, the 10% content of Cr is insufficient to maintain a protective “chemically stable” Cr oxide/hydroxide.     

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.     

Effects of precipitates on the electrochemical performance of Al sacrificial anode

The influence of precipitates on the electrochemical performance of Al–Zn–In–Mg–Ti–Si sacrificial anode was investigated by the TEM observation and electrochemical measurements. The results indicate that the shape and size of precipitates in the alloys has great impact on the electrochemical performance. The anodes with rod-like precipitates are easily corroded along grain boundaries, resulting in the low current efficiency caused by serious grain loss. In comparison, the anodes with spherical or discal precipitates have high current efficiency and even corrosion morphology. The precipitates with a size of about 400 nm are conducive to improve the electrochemical performance of anodes.     

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.     

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.     

Anodic dissolution of Al sacrificial anodes in NaCl solution containing Ce

The corrosion behaviour of Al–Zn–In sacrificial anodes has been investigated in a sodium chloride solution containing CeCl₃. Scanning electron microscopy, energy-dispersive X-ray analysis, and inductively coupled plasma mass spectrometry have been employed to gain knowledge of the micro-morphology and corrosion process of the Al alloy. Cerium, both as the alloy element and as the additive in the NaCl solution, improves the electrochemical properties of the Al–Zn–In alloy. The activation of Ce in the Al–Zn–In alloy in the NaCl solution has been studied.     

Electrochemical noise analysis on the pit corrosion susceptibility of Mg–10Gd–2Y–0.5Zr, AZ91D alloy and pure magnesium using stochastic model

Pit corrosion susceptibilities of Mg–10Gd–2Y–0.5Zr alloy, AZ91D alloy and pure magnesium were investigated by means of electrochemical noise (EN). The EN data have been analyzed based upon the combined stochastic theory and shot-noise theory. Pit initiation process has been modeled as a nonhomogeneous Poisson process and analyzed using a Weibull distribution function. Pit growth process has been simulated by a nonhomogeneous Markov process and analyzed using Gumbel distribution function. The EN results implied that Mg–10Gd–2Y–0.5Zr alloy had the highest pit initiation rate and pit growth probability, which revealed that Mg–10Gd–2Y–0.5Zr alloy had the highest pit susceptibility.     

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.     

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.     

Effect of Mg Additions and Thermal Treatment on Corrosion Properties of Al–Li–Cu-Base Alloys

An investigation on the corrosion and electrochemical behavior of experimental and industrial semifinished items of Al–Li–Cu–base alloys offers possibilities of increasing the corrosion resistance of aluminum–lithium alloys by alloying and an nontraditional thermal treatment. Magnesium added in a concentration of no more than 0.4% leads to a improvement of the corrosion and mechanical characteristics of the alloy, whereas increasing its concentration up to 1.0% deteriorates all the corrosion characteristics. An investigation of the effect of the cathodic additions of Zr, Mn, and Mn + Cr shows that the corrosion properties are nonchanged by substitution of Mn or Mn + Cr for Zr. The resistance to general corrosion, exfoliation corrosion, and corrosion cracking is enhanced by a nontraditional artificial aging.     

Cr、Yb合金化对Al-Zn-Mg-Cu-Zr合金组织和断裂特征的影响

研究复合添加微量Cr、Yb、Zr对Al-Zn-Mg-Cu合金的显微组织和断裂特征的影响,分析其对合金韧化的作用机制.结果表明:在Al-Zn-Mg-Cu合金中复合添加Cr、Yb、Zr形成了含Cr、Yb、Zr的球形弥散相,这些均匀分布于基体上的弥散相能强烈钉扎位错和亚晶界,使基体保持形变回复组织,保持小角度晶界,抑制基体再结晶;T6态断裂机制主要为韧窝型穿晶断裂,与仅添加Zr相比,沿晶断裂抗力显著提高;晶界的无沉淀区(PFZs)较宽,且析出相在晶界呈明显不连续分布.     

Hydrogen entry behaviour of hot-dip Al–Mg–Si coated steel

A ternary hot-dip Al–Mg–Si coating was formed on a steel substrate and tested as an alternative to conventional zinc coatings particularly in high-strength steel application with respect to hydrogen entry behaviour. Hydrogen entry behaviour was evaluated under wet–dry conditions using a Devanathan cell. The new hot-dip Al–Mg–Si coating shows relatively low corrosion potential during the initial stage of the wet period; however, the potential shifts in a noble direction in a short time resulting in smaller amount of hydrogen entry than that in the conventional zinc coating.     

Scandium-alloyed aluminum alloys

Conclusion The basic principles of alloying of aluminum alloys with scandium are: it is desirable to add scandium to aluminum alloys in a quantity from 0.1 to 0.3% together with zirconium (0.05–0.15%), which strengthens the positive influence of scandium on the structure and properties of alloys;the greatest effect (that is, the positive influence on mechanical properties and other characteristics) from addition of scandium together with zirconium is observed for alloys not containing alloy elements combining scandium in insoluble phases, specifically the Al–Mg, Al–Zn–Mg, and Al–Mg–Li systems;with a limited copper content alloying with scandium together with zirconium of Al–Zn–Mg–Cu and Al–Cu–Li system alloys is possible.At present on the basis of or taking into consideration the principles developed of alloying of aluminum alloys with scandium commercial aluminum alloys based on the Al–Mg–Sc–Sr (01570, 01571, 01523, 01505), Al–Zn–Mg–Sc–Zr (01970, 01975), and Al–Li–Mg–Sc–Zr (10421, 01423) systems have been developed.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 24–28, January, 1992.     

Transgranular SCC mechanism of thermally treated alloy 600 in alkaline water containing lead

This work aims to understand a SCC failure mode of thermally treated steam generator tubing materials in high temperature water containing lead. The effect of lead contents on the anodic polarization curves of alloy 600 (UNS NO6600) and alloy 690 (UNS NO6900) has been studied in a solution of pH 10 at 200 °C and 315 °C. Lead increased the active peaks of alloy 600 and alloy 690 in mild alkaline water at high temperatures. A reduction of PbO to a metallic lead in alloy 690 is easier than that of alloy 600. When lead was added into the solution, a relative ratio of Cr from among the main metallic elements (Cr, Fe, and Ni) of alloy 600 and alloy 690 decreased in the outer corrosion film. Alloy 690 TT showed a transgranular stress corrosion cracking (TGSCC) in a 10 M NaOH solution with 5000 ppm of lead. Intergranular stress corrosion racking (IGSCC) was observed in the 100 ppm lead condition, and some TGSCC was detected on the fracture surface of the alloy 600 MA cracked in the 10,000 ppm lead solution. IGSCC seemed to be retarded by a crack blunting around the grain boundaries, and the TG cracking mode of the thermally treated alloy 600 and 690 seemed to be related to a crack blunting at the grain boundary carbide and a film dissolution by lead in an alkaline solution.     

Effects of cold working path on strain concentration, grain boundary microstructure and stress corrosion cracking in Alloy 600

Grain boundary microstructure, strain distribution and stress corrosion cracking (SCC) in one dimensional (1D), two dimensional (2D) and three dimensional (3D) cold worked Alloy 600 were investigated. The cold working decreased the annealing twins and increased low angle boundaries. 2D cold working caused lower strain concentration at grain boundaries than 1D and 3D cold working. The intergranular SCC (IGSCC) susceptibility was the highest in 1D cold worked alloy while lowest in 2D cold worked alloy. The IGSCC susceptibility displayed a strong correlation with the grain boundary strain concentration and the grain boundary microstructure.     

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.     

Effects of cold working degrees on grain boundary characters and strain concentration at grain boundaries in Alloy 600

Strain concentration at grain boundaries and grain boundary microstructure in cold worked Alloy 600 were characterized. Excluding the annealing twin boundaries, the base and 20% cold worked alloys exhibited higher random grain boundary fractions than the 8% and 40% cold worked alloys. An increased low angle boundaries and decreased annealing twins were observed with deformation. The 20% cold worked alloy displayed a maximum strain concentration at grain boundaries. The stress corrosion cracking growth in cold worked Alloy 600 in high temperature water showed a strong correlation with the strain concentration at grain boundaries.     

Hydrogen entry behaviour of newly developed Al–Mg–Si coating produced by physical vapour deposition

A ternary Al–Mg–Si alloy was prepared by co-evaporation technique and tested with respect to hydrogen entry behaviour as an alternative to conventional zinc coating on steel. Hydrogen entry behaviour evaluated using Devanathan cell showed a smaller hydrogen entry for this new coating than conventional zinc coating. Compared to an unscratched surface, hydrogen entry increased by more than 100 times in the scratched surface, but it was lower than that for the zinc coating with a scratched surface owing to the moderate galvanic corrosion potential of the new coating. This new coating is proposed especially for high-strength steel application.