Electrochemical Corrosion Rate Research Articles

Effects of Li addition on the properties of biodegradable Zn–Fe–Li alloy: Microstructure, mechanical properties, corrosion behavior, and cytocompatibility

Biodegradable Zn-based alloys have excellent mechanical properties, a good corrosion rate, and favorable biocompatibility, which have broad application prospects. In this study, new biodegradable Zn-0.5Fe-xLi (x = 0, 0.2, 0.5, 0.8 wt%) alloys were successively prepared by melting and hot extrusion, and the effects of Li content on the microstructure, mechanical properties, corrosion behavior, and biocompatibility of the alloys were investigated. The formation of FeZn13 and eutectic LiZn4 phases in the Zn-0.5Fe-xLi alloys and the grain size of the Zn-0.5Fe-0.5Li alloys significantly reduced with an increase in Li content. The synergistic effect of solid solution and grain refinement of Li significantly improved the strength of the Zn-0.5Fe-0.5Li alloy and ensured the ductility of the alloy, which resulted in its optimum overall performance. The yield strength was 353.6 ± 6.8 MPa, the ultimate tensile strength was 441.9 ± 2.6 MPa, and the elongation was 26.8 ± 0.8%. In addition, the Zn-0.5Fe-0.5Li alloy showed excellent corrosion properties. The electrochemical corrosion rate was 0.735 mm/year, and the surface corrosion degradation morphology was uniform after immersion. The Zn-0.5Fe-0.5Li alloy also demonstrated the most favorable in vitro cytocompatibility in cellular experiments. Overall, the extruded Zn-0.5Fe-0.5Li alloy is a promising biodegradable implant material with excellent mechanical properties, a suitable corrosion rate, and good cytocompatibility.

A biodegradable Zn-5Gd alloy with biomechanical compatibility, cytocompatibility, antibacterial ability, and in vitro and in vivo osteogenesis for orthopedic applications

Zinc (Zn) and some of its alloys are recognized as promising biodegradable implant materials due to their acceptable biocompatibility, facile processability, and moderate degradation rate. Nevertheless, the limited mechanical properties and stability of as-cast Zn alloys hinder their clinical application. In this work, hot-rolled (HR) and hot-extruded (HE) Zn-5 wt.% gadolinium (Zn-5Gd) samples were prepared by casting and respectively combining with hot rolling and hot extrusion for bone-implant applications. Their microstructure evolution, mechanical properties, corrosion behavior, cytotoxicity, antibacterial ability, and in vitro and in vivo osteogenesis were systematically evaluated. The HR and HE Zn-5Gd exhibited significantly improved mechanical properties compared with those of their pure Zn counterparts and the HR Zn-5Gd showed a unique combination of tensile properties with an ultimate tensile strength of ∼311.6 MPa, yield strength of ∼236.5 MPa, and elongation of ∼40.6%, all of which are greater than the mechanical properties required for bone-implant materials. The HR and HE Zn-5Gd showed higher corrosion resistance than their pure Zn counterpart in Hanks’ solution and the HE Zn-5Gd had the lowest corrosion rate of 155 µm/y measured by electrochemical corrosion and degradation rate of 26.9 µm/y measured by immersion testing. The HR and HE Zn-5Gd showed high cytocompatibility toward MC3T3-E1 and MG-63 cells, high antibacterial effects against S. aureus, and better in vitro osteogenic activity than their pure Zn counterparts. Furthermore, the HE Zn-5Gd exhibited better in vivo biocompatibility, osteogenesis, and osteointegration ability than pure Zn and pure Ti. Statement of significanceThis work reports the mechanical properties, corrosion behaviors, cytocompatibility, antibacterial ability, in vitro and in vivo osteogenesis of biodegradable Zn–Gd alloy for bone-implant applications. Our findings demonstrate that the hot-rolled (HR) Zn–5Gd showed a unique combination of tensile properties with an ultimate tensile strength of ∼311.6 MPa, yield strength of ∼236.5 MPa, and elongation of ∼40.6%. The HR and HE Zn-5Gd showed higher corrosion resistance than their pure Zn counterpart in Hanks’ solution. The HR and HE Zn-5Gd showed high cytocompatibility toward MC3T3-E1 and MG-63 cells, good antibacterial effects against S. aureus, and better in vitro osteogenic activity. Furthermore, the HE Zn-5Gd exhibited better in vivo biocompatibility, osteogenesis, and osteointegration ability than pure Zn and pure Ti.

Degradable Zn–5Ce alloys with high strength, suitable degradability, good cytocompatibility, and osteogenic differentiation fabricated via hot-rolling, hot-extrusion, and high-pressure torsion for potential load-bearing bone-implant application

Zinc (Zn)-based alloys are considered the next-generation biodegradable material for promising bone-implant devices due to their good degradability, formability, and functionality. Nevertheless, the as-cast Zn alloys showed a low strength-toughness, making it challenging to meet the mechanical properties requirements for high-load-bearing bone implants due to their hexagonal close-packed structure, coarse grain size, and less sliding system. Herein, we have developed biodegradable Zn–5Ce alloys by cerium (Ce) alloying followed by hot-rolling, hot-extrusion, and high-pressure torsion (HPT), respectively, for potential bone-implant application. Mechanical testing revealed that the HPT sample exhibited the best mechanical performance matching among the Zn–5Ce samples with a high ultimate tensile strength of ∼345 MPa, yield strength of ∼230 MPa, a moderate elongation of ∼11.4%, and macro-hardness of ∼96.6 HB. Electrochemical corrosion and static immersion testing revealed that the HPT sample showed the highest electrochemical corrosion rate of ∼416 μm/y and degradation rate of ∼43.8 μm/y in Hanks' solution among the Zn–5Ce samples, which is suitable for degradation rate requirements for bone-implant application. Bio-tribological testing revealed that the HPT sample showed high bio-tribological properties matching in Hanks’ solution with the lowest friction coefficients of ∼0.530 and moderate wear loss of ∼2.2 mg. Cytocompatibility and osteogenic differentiation assessment revealed that the diluted extract of the HPT sample showed the highest cytocompatibility towards 3T3 and MG-63 cells and osteogenic differentiation performance towards 3T3 cells among the most diluted extracts. Accordingly, the HPT Zn–5Ce sample is expected to be used for high-load-bearing degradable bone-implant devices, including bone fixation and guided bone regeneration systems.

Copper, Iron and Aluminium Electrochemical Corrosion Investigation during Electrolysis and Temperature Increasing

An experimental method to calculate average charge of metal ions by electrolysis at different temperatures is proposed. Aluminium undergoes dissolution to the Al3+ ions at all temperatures. Iron undergoes dissolution to the Fe2+ or the Fe3+ ions and copper undergoes dissolution to the Cu+ or the Cu2+. It depends on temperature and electric current density. Direct electric current value and anode mass decreasing were measured during electrolysis into concentrated NaCl solution in water (5 mol/kg or 23.1%, freezing point equals -22°C, pH 6.5–7.5) at room temperature and 100°C. The average charges of copper, iron, and aluminium ions were calculated using Faraday’s law of electrolysis at electric current density 3,000 A/m2 (or 30 A/dm2): +3 for aluminium; +2 for iron; and +1 for copper at room temperature, and +3 for aluminium; +2 for iron; and +1.5 for copper at temperature 100°C. The main condition was zAl=3. We concluded that calculations of the average metal ions charges, zFe and zCu, were correct since zAl=3. The result is as follows: the Al3+, the Fe2+, and the Cu+ ions dissolve into concentrated NaCl solution in water at room temperature; the Al3+, the Fe2+, the Cu+ and the Cu2+ ions (50%/50%) dissolve into the solution at temperature 100°C. We have obtained experimentally and by mathematical modelling that aluminium anodes (cylindrical or spherical) dissolve into the solution more rapidly with temperature increasing during electrolysis accordingly to the Arrhenius law, while copper anodes (cylindrical or spherical) dissolve more slowly with temperature increasing from room temperature to temperature 180°C like “inverse Arrhenius law”. Iron electrochemical corrosion rate practically does not depend on temperature below 100°C (and, obviously, up to 180°C) like “zeroth Arrhenius law”. The spherical anode effect is greater than the cylindrical anode effect in 1.5 times.

Computational Prediction of Electrochemical Corrosion Rates of Copper in the Presence of Corrosion Inhibitors

Computational prediction of corrosion rates is still a challenging issue in the field of metal corrosion. In this study, we proposed a computational model to predict the corrosion rates of copper in the presence of adsorption-type corrosion inhibitors using density functional theory calculations, microkinetic simulation, and machine learning. The model-calculated corrosion current and potential of clean copper are close to values obtained in available experiments. The copper corrosion rates in the presence of inhibitors were further predicted using the adsorption free energy of adsorbed inhibitors and the inhibitor concentration in solution to describe the effects of inhibitors. The proposed model was applied to predict corrosion inhibition efficiency by combining it with a machine learning model. The combining model exhibited that it was more interpretative and accurate than a machine-learning-only model in predicting corrosion inhibition efficiencies of organic compounds on copper.

Iron, copper, and aluminium electrochemical corrosion in motionless and moving electrolytes investigation during electrolysis

An experimental method to calculate average charge of metal ions by electrolysis at different temperatures is proposed. Aluminium undergoes dissolution to the Al3+ ions at all temperatures. Iron undergoes dissolution to the Fe2+ or the Fe3+ ions and copper undergoes dissolution to the Cu+ or the Cu2+. It depends on temperature and electric current density. Direct electric current value and anode mass decreasing were measured during electrolysis into concentrated NaCl solution in water (5 mol/kg or 23.1 %, freezing point equals −22 °C, pH 6.5–7.5) at room temperature and 100 °C. The average charges of copper, iron, and aluminium ions were calculated using Faraday's law of electrolysis at electric current density 3000 A/m2 (or 30 A/dm2 = 3 mA/mm2): +3 for aluminium; +2 for iron; and +1 for copper at room temperature, and +3 for aluminium; +2 for iron; and +1.5 for copper at temperature 100 °C. The main condition was zAl = 3. We concluded that calculations of the average metal ions charges, zFe and zCu, were correct since zAl = 3. The result is as follows: the Al3+, the Fe2+, and the Cu+ ions dissolve into concentrated NaCl solution in water at room temperature; the Al3+, the Fe2+, the Cu+ and the Cu2+ ions (50 %/50 %) dissolve into the solution at temperature 100 °C. We have obtained experimentally and by mathematical modelling that aluminium anodes (cylindrical or spherical) dissolve into the solution more rapidly with temperature increasing during electrolysis accordingly to the Arrhenius law, while copper anodes (cylindrical or spherical) dissolve more slowly with temperature increasing from room temperature to temperature 180 °C like “inverse Arrhenius law”. Iron electrochemical corrosion rate practically does not depend on temperature below 100 °C (and, obviously, up to 180 °C) like “zeroth Arrhenius law”. The spherical anode effect is practically the same as the cylindrical anode effect. The galvanic current dependence on ratio of cathodic surface area to anodic surface area in the system Fe-chromium (Cr) stainless steel and the time of the iron anodes dissolution in motionless electrolyte and in moving electrolyte are also analysed using literature experimental data.

Biodegradable iron-based foams prepared by the space holder technique using urea

Iron-based degradable biomaterials have attracted much attention as next-generation bone implants due to their excellent mechanical properties and good biocompatibility. Many studies are now focusing on the preparation and detailed study of porous versus non-porous degradable materials. Porous degradable biomaterials have many advantages over the non-porous ones owing to their structure, which allows easier bone tissue ingrowth. The aim of this work was to prepare Fe-based biodegradable porous materials in a cost-effective way via powder metallurgy technique using urea space holders. Five different samples with increasing space holder weight ratio (up to 20 wt%) were prepared. Surface morphology and sample structure were studied using the optical microscopy, Raman spectroscopy, and scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDX). Electrochemical corrosion rate analysis confirmed that the samples corroded faster with increasing number of pores. With an increasing amount of urea, the number of pores increased proportionally, which can potentially be used to tune the corrosion rate. However, mechanical integrity of the samples was not maintained when more than 10 wt% of space holder was used.Graphical abstract

Mechanical properties, corrosion and degradation behaviors, and in vitro cytocompatibility of a biodegradable Zn-5La alloy for bone-implant applications.

Zinc (Zn) and its alloys are used in bone-fixation devices as biodegradable bone-implant materials due to their good biosafety, biological function, biodegradability, and formability. Unfortunately, the clinical application of pure Zn is hindered by its insufficient mechanical properties and slow degradation rate. In this study, a Zn-5 wt.% lanthanum (Zn-5La) alloy with enhanced mechanical properties, suitable degradation rate, and cytocompatibility was developed through La alloying and hot extrusion. The hot-extruded (HE) Zn-5La alloy showed ultimate tensile strength of 286.3MPa, tensile yield strength of 139.7MPa, elongation of 35.7%, compressive yield strength of 262.7MPa, and microhardness of 109.7 HV. The corrosion resistance of the HE Zn-5La in Hanks' and Dulbecco's modified Eagle medium (DMEM) solutions gradually increased with prolonged immersion time. Further, the HE Zn-5La exhibited an electrochemical corrosion rate of 36.7μm/y in Hanks' solution and 11.4μm/y in DMEM solution, and a degradation rate of 49.5μm/y in Hanks' solution and 30.3μm/y in DMEM solution, after 30 d of immersion. The corrosion resistance of both HE Zn and Zn-5La in DMEM solution was higher than in Hanks' solution. The 25% concentration extract of the HE Zn-5La showed a cell viability of 106.5%, indicating no cytotoxicity toward MG-63 cells. We recommend the HE Zn-5La alloy as a promising candidate material for biodegradable bone-implant applications. STATEMENT OF SIGNIFICANCE: This work reports the mechanical properties, corrosion and degradation behaviors, in vitro cytocompatibility and antibacterial ability of biodegradable Zn-5La alloy for bone-implant applications. Our findings demonstrate that the hot-extruded (HE) Zn-5La alloy showed an ultimate tensile strength of 286.3MPa, a yield strength of 139.7MPa, an elongation of 35.7%, compressive yield strength of 262.7MPa, and microhardness of 109.7 HV. HE Zn-5La exhibited appropriate degradation rates in Hanks' and DMEM solutions. Furthermore, the HE Zn-5La alloy showed good cytocompatibility toward MG-63 and MC3T3-E1 cells and greater antibacterial ability against S. aureus.

Microstructural evolution and corrosion mechanism of micro-alloyed 2024 (Zr, Sc, Ag) aluminum alloys

The 2024 aluminum alloy has excellent mechanical and low corrosion due to the existence of the high Cu levels, which shortens its service life. In this paper, we have systematically investigated the mechanism of the influence of three elements (Sc, Zr, and Ag) on the microstructure and corrosion behavior of 2024 aluminum alloy after microalloying. The results showed that microalloying treatment of 2024 aluminum alloy reduced the dendritic spacing of cast aluminum alloy; decreased the sizes of Cu-rich intermetallic particles (Cu-IMPs) within the peak aging of the T6 alloy to make their distribution more uniform; and changed the grain boundary phases (GBPs) and precipitate-free zones (PFZs) width of the T6 alloy. Microalloying treatment significantly changed the corrosion resistance of the alloy. Both Zr and Ag elements significantly improved the corrosion resistance of the alloy and reduced IGC depth and electrochemical corrosion rate, however, the Sc elements deteriorated the corrosion resistance of the alloy. Moreover, the corrosion mechanism of the alloy was also discussed in detail.

The crystallographic orientation dependent anisotropic corrosion behavior of aluminum in 3.5 wt% NaCl solution

In this paper, a quantitative method to evaluate the degree of differences in corrosive behavior of different crystallographic-oriented planes of Al and Al alloys in 3.5 wt% NaCl solution is provided. The corrosion potential Ucorr, corrosion current density Icorr and electrochemical corrosion rate of (100), (110) and (111) ideal surfaces and corresponding surfaces with vacancy and chloride ion adsorption considerations in single-crystal aluminum were derived by first principles calculation. The results show that the corrosion potential and corrosive current density increases in the order of U(110)corr<U(100)corr<U(111)corr and I(111)corr<I(100)corr<I(110)corr, respectively, and the electrochemical corrosion rate of (111) surface is 0.01×10-3 mm/a, showing the superior corrosion resistance. Moreover, the effect of the addition of alloying elements on the corrosion behavior of M−alloying Al alloy matrix in comparison with pure Al was further investigated by first principles calculation, and elements of Li, Mg, Zn, Ag and Cd are selected to improve the corrosion resistance of Al alloy.

The efficient solid electrochemical corrosion prelithiation of graphite and SiOx/C anodes for longer-lasting lithium ion batteries

In order to avoid side reactions with liquid electrolyte for the prelithiation method using metal lithium for the improvement of initial coulombic efficiency and prelithiation efficiency, we propose the solid electrochemical corrosion (SEC) of lithium replacing liquid electrolyte with solid electrolyte of lithium phosphorus oxynitride (LiPON) in previous works. However, the low prelithiation rate of solid electrochemical corrosion with LiPON interlayer between anode and lithium hinders its possible large-scale application. Here, an ultrathin film of Bi2O3 is introduced as the interface layer to improve the prelithiation rate of SEC, the prelithiation effects are investigated on both graphite and SiOx/C anodes by morphological, spectroscopic and electrochemical characterizations. The initial coulombic efficiencies of graphite and SiOx/C anodes can be respectively increased by about 5.1% and 9.7% after the prelithiation. The prelithiation efficiency values are as high as 79.3% for graphite and 86.7% for SiOx/C with SEC prelithiation. Our results demonstrate that SEC prelithiation with Bi2O3 interface layer could be applied to improve the capacity and cycling performance of lithium-ion batteries.

Contribution of the oxygen reduction reaction to the electrochemical cathodic partial reaction for Mg-Al-Ca solid solutions

The electrochemical corrosion rate of magnesium depends on the stability of the surface layer formed. Based on the Mg substrate, the oxide structure comprises a dense MgO/Mg(OH)2 mixture underneath a porous plate-like Mg(OH)2 layer. While the kinetics of the anodic partial reaction have been mainly attributed to MgO, recent studies have showed an effect of the Mg(OH)2 layer thickness on the cathodic partial reaction. A thinner Mg(OH)2 layer has been associated with higher kinetics of the oxygen reduction reaction. In the present study, the mechanism has been further investigated via in situ respirometric measurements using Mg-Al-Ca solid solution in electrolytes with different pH values (pH = 8.0–13.0). The results indicate an additional effect based on the structure of the surface layer for Mg-Al-Ca alloys in the passive state. Furthermore, two different Al-enriched interfaces were observed and discussed in terms of their thermodynamic stability under alkaline immersion conditions.

Construction of Mo doped CoMoCH–Cu2SeS/NF composite electrocatalyst with high catalytic activity and corrosion resistance in seawater electrolysis: A case study on cleaner energy

The electrolysis of seawater into clean hydrogen energy requires the development of effective electrocatalysts. Yet, most current research focuses on the activity of electrocatalysts while disregarding their corrosion resistance. We developed a unique porous stake-like composite catalyst on a nickel foam substrate (designated by CoMoCH–Cu2SeS/NF) using a new monometallic cation release method, demonstrating an outstanding catalytic activity and a high resistance to seawater corrosion. CoMoCH–Cu2SeS/NF porous stake-like structure provides a large reaction zone and lots of catalytic active centers. Moreover, the synergistic effect of Cu2SeS and CoMoCH facilitates the electron transfer. Doping high-valence Mo element into CoCH generates a strong electronic structural interactions between metals. Hence, the CoMoCH–Cu2SeS/NF composite catalyst demonstrates an outstanding OER/HER performance in different alkaline solutions, with a low overpotential and good continuous electrolysis durability. The electrode pair assembled by such a composite catalyst delivers a current density of 100 mA cm−2 at 1.72 V in alkaline simulated seawater. In natural seawater, CoMoCH/NF has a lower electrochemical corrosion rate of 0.85 mm/a than Cu2SeS/NF (9.97 mm/a) and CoCH/NF (5.72 mm/a). The carbonate anions in the CoCH intercalation structure and the doping of Mo element with strong corrosion resistance enhanced the chlorine corrosion resistance of CoMoCH–Cu2SeS/NF in natural seawater and protected the Cu2SeS active components. This research may guide the design and development of high-activity and corrosion-resistant composite electrocatalysts with novel architectures for hydrogen production by seawater electrolysis.

Densification, microstructure, tribological and electrochemical properties of pure Zn fabricated by laser powder bed fusion

The fabrication of Zn-based materials by laser powder bed fusion (LPBF) has been proved to be feasible. In this work, high relative density (98.10 %) of LPBF pure Zn samples were successfully obtained by optimizing the process parameters at low power (30–60 W). The microstructural formation mechanism and evolution of LPBF pure Zn under different power were investigated. With the increase of power, the recrystallization during the printing process became more completely, resulting in the increase of equiaxed grains integral number of the sample. The microhardness of the samples increases with the increase of the power, but the tribological properties change unobvious and the coefficient of friction of LPBF pure Zn in SBF solution is about 0.56–0.57. The electrochemical test manifests that, with the increase of power, the electrochemical corrosion rate of LPBF pure Zn increased, and the corresponding corrosion resistance decreased.

Laser cladding remanufacturing of aircraft landing gear based on 30CrMnSiNi2A steel

Remanufacturing landing gear is of great importance due to its vital function for the aircraft. The 30CrMnSiNi2A steel surface is remanufactured through laser cladding based on the actual service environment of landing gear. Six Ni-based wolfram carbide (WC) composite coatings with different proportions are prepared during the experiment. The microstructure, phase composition, microhardness, wear and corrosive resistance of the coatings are analyzed considering actual working conditions. Results show that the remanufactured coating well bonds with the substrate metallurgically without cracks and pores on the surface, except for the coating with 25 wt% WC content. The wear and corrosive resistance of the repaired coating greatly improve compared with those of substrate. It suggests that corrosive resistance for coating and substrate is different especially in a salt spray environment. The coating that is well-bonded with the substrate and has a compact structure can be obtained when the WC content is 20 wt%. In this case, the coating is characterized by an optimal hardness, wear and corrosive resistance. The coating microhardness is 542HV0.2. The weight loss of coating only accounts for 25.92 % of that of the substrate under dry friction. The electrochemical corrosion rate is 0.0025 mm/a, accounting for 1.37 % of that of the substrate. The surface of coating exhibits a good performance under a salt spray environment for 1000 h. This experiment aims to realize the remanufacturing of landing gear and hence provide a reference in its practical application.

The impact of non-uniformity and resistivity on the homogenised corrosion parameters of rebars in concrete – a circuit model analysis

ABSTRACT When rebar corrosion parameters are characterised from an electrochemical polarisation curve, the non-uniform rebar surface conditions need to be considered. In this research, a circuit model was developed to simulate the polarisation behaviour of rebar in concrete. It is found that the resistivity of concrete leads to non-uniform potential on the rebar, which causes the polarisation curve of the entire rebar to deviate from the Butler–Volmer kinetics. This, in turn, leads to an overestimation of the Tafel constants and the corrosion current density. Such deviations are more pronounced with higher concrete resistivity, especially when the active and passive rebar surfaces have a similar area ratio. The study recommends using potentiodynamic scans of representative reinforced concrete samples of the field conditions or the calculated parameters using an averaging technique, such as the proposed circuit model, to obtain accurate E-I curves or parameters for electrochemical modelling and corrosion rate prediction.

Study on corrosion behavior of Ni–P/Ni–Cu–P superhydrophobic composite coatings preparation on L360 steel by two-step method

The two-step process of electroless plating and electrodeposition was used to successfully prepare a bilayer composite film by electroplating a Ni–Cu–P film with hydrophobic properties on the Ni–P film. The histological features of the two membrane layers were compared. The L360 pipeline steel, Ni–P coating and Ni–Cu–P composite film were evaluated by electrochemical test and erosion corrosion method. Under simulated seawater conditions, the material properties changed before and after different periods of service. The experimental results show that the introduction of Cu can inhibit the growth of cellular structures on the surface of the coating, increase the number of nucleation points, and improve the microstructure of the coating during the deposition of Ni–Cu–P films. The Ni–P/Ni–Cu–P bilayer composite film has a pinecone-like convex structure, which can greatly reduce the surface energy of the film layer and endow the film layer with hydrophobicity. At the same time, it effectively resists the adsorption of water and other external impurities on its surface, and has good anti-fouling performance, thereby slowing down the surface corrosion and improving corrosion resistance. In addition, copper enables the composite coating to have passivation and a uniform and dense coating structure, which is the main reason for the improvement of the corrosion protection performance of the composite coating. The protective effect of the coating can effectively improve the electrochemical resistance and erosion resistance of L360. The Ni–P/Ni–Cu–P bilayer composite film reduces the electrochemical corrosion rate of the substrate from 0.417mmpY to 0.025mmpY, and the scouring weight loss rate of the film decreases to 0.05% of the substrate.

Microstructure and Corrosion Resistance of AZ91 Magnesium Alloy after Surface Remelting Treatment.

The effect of surface remelting treatment on the microstructure and corrosion resistance of the AZ91 magnesium alloy was studied. The surface layer was remelted by GTAW (gas tungsten arc welding). An original two-burner system with welding torches operating in a tandem configuration was used, allowing the combination of cleaning the surface from oxides with the remelting process. The studies of the corrosion resistance of the alloy included electrochemical tests and measurements of the rate of hydrogen evolution. The results showed that surface remelting treatment leads to favorable microstructural changes, manifested in strong grain refinement and a more uniform arrangement of the β-Mg17Al12 phase. The changes in the microstructure caused by remelting and the accompanying fast crystallization contributed to an increase in the corrosion resistance of the remelted samples in comparison to their non-remelted equivalents. The results obtained on the basis of the polarization curves showed three-fold lower values of the corrosion current density in the case of the remelted material than the value of the corrosion current density determined for the starting material. In turn, in the case of measurements of the electrochemical noise and corrosion rate determined by the method of measuring the rate of hydrogen evolution, this value for the remelted alloy was two times lower. The research also showed that GTAW technology is highly effective and can be a valuable alternative to laser techniques. The complete experimental details, obtained results and their analyses are presented in this paper.

Current state of electrochemical techniques and corrosion rate analysis for next-generation materials

Current theoretical models and electrochemical techniques used to investigate corrosion mechanisms, including corrosion rates, have been tailored for conventional alloy systems. However, the application of conventional theories and techniques toward next-generation alloys such as multi-principal element alloys and additively manufactured alloys needs to be revisited due to the increased chemical complexity and refined microstructures of these alloys, which may yield different electrochemical properties from the conventional alloys. This review aims to discuss to which extent the current models and techniques used in corrosion science can be applied to these new alloy systems, and outline some of the challenges that need to be overcome to accurately describe their electrochemical reactivity.

Electrochemical behavior and corrosion rate prediction study of alloy 690

Alloy 690 is a material commonly used in heat transfer tubes of steam generators (SGTs). The electrochemical corrosion behavior in different volumes (V) of NaCl–Na2S2O3 solution for different surface roughness (Ra) of alloy 690 was studied, and a BPNN model for predicting electrochemical corrosion parameters of alloy 690 was established (CP and CCD). The results show that Ra on the surface of alloy 690 destroys the passivation film and changes the oxygen vacancies in the passivation film, so that Cl− is more easily attached to the passivation film. Finally, accelerated electrochemical reactions on the surface of SGTs. When the solution is Na2S2O3, with the increase of Ra on the metal surface (0.0977≤ Ra ≤ 1.1661), the corrosion potential gradually decreases. BPNN can accurately predict the electrochemical corrosion rate of alloy 690 under different conditions, and the relative error is less than 10%. In this paper, an artificial intelligence model is established for the first time to predict the relationship between Ra and electrochemical corrosion, and the conclusion can be used to schedule the maintenance process of the SG, thereby reducing the risk of structural failure and maintenance costs.