Corrosion behaviour of die-cast AZ91D magnesium alloys in sodium sulphate solutions with different pH values

The corrosion behaviours of die-cast AZ91D magnesium alloys were investigated in 0.1 mol/L sodium sulphate （Na 2 SO 4 ） solutions with different pH values. The corrosion rates, morphologies, and compositions of the corrosion products were studied by means of scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy （FTIR）, and X-ray diffractometry （XRD）. The results indicate that the order of corrosion rates in Na 2 SO 4 solutions with various pH values is pH 2pH 4pH 7pH 9pH 12. The corrosion rates in acidic solutions are higher than those in alkaline solutions, and the corrosion products are mainly magnesium hydroxide （Mg（OH） 2 ） and hydrated sulphate pickeringite （MgAl 2 （SO 4 ） 4 ·22H 2 O）. The results also indicate that the solution pH can influence the corrosion rate and morphology of corrosion products. Chloride ions and sulphate ions have different pitting initiation time.

Manifestations in Corrosion Prophase of Ultra-high Strength Steel 30CrMnSiNi2 A in Sodium Chloride Solutions

The corrosion behaviors of ultra-high strength steel 30CrMnSiNi2A in sodium chloride solution were studied by weight loss and electrochemical methods. The morphology of corrosion products was observed using scanning electron microscopy（SEM） and the composition was analyzed using an energy dispersive spectroscopy（EDS） and X-Ray diffraction （XRD）. The experimental results showed that the corrosion came from pitting corrosion and the rust layer was composed of outer rust layer γ-FeOOH and inner rust layer Fe_2O_3 with a little β-FeOOH. The correlation between corrosion rate and test time accorded with exponential rule. The corrosion current measured by polarization methods was higher than that calculated by weight loss method after a long-time immersion, the main reason was that,β-FeOOH and γ-Fe_2O_3 transformed by γ-FeOOH led to overestimating corrosion rate. The processes of corrosion prophase were obtained from XRD and EIS results. The corrosion product, Fe（OH）_2 formed at the initial stage stayed at a non-steady state and then consequently transferred to γ-FeOOH, γ-Fe_2O_3 or β-FeOOH.

The effect of sodium silicate concentration on microstructure and corrosion properties of MAO-coated magnesium alloy AZ31 in simulated body fluid

In recent years,magnesium and its alloys are considered as biodegradable implants.However magnesium implants may rapidly corrode before the natural healing process of the tissue is completed.In this investigation,micro arc oxidation process has been studied for avoiding primary corrosion of the magnesium alloy in simulated body fluid.Anodized coating was formed on AZ31 alloy in nontoxic silicate-alkaline solution at constant current.The effects of silicate concentration and conductivity of electrolyte solution on microstructure and corrosion properties of coating were evaluated.Scanning electron microscopy showed that a thick and condensed coating is formed after enough anodizing period.Energy dispersive spectroscopy showed that Si,O and Mg are the main components of the coating.Corrosion resistance of the coated and uncoated samples was assessed using potentiodynamic polarization and electrochemical impedance spectroscopy tests in SBF at 37℃ and pH of 7.4.Maximum corrosion resistance was achieved at 30 g/L concentration of sodium silicate in anodizing solution.It was observed that further increase in silicate concentration decreased the corrosion resistance.

The Use of Sodium Silicate as a Corrosion Inhibitor in a Saline Drilling Fluid: A Nonaggressive Option to the Environment

The function of a corrosion inhibitor in drilling mud compositions is the corrosion protection of the equipment involved in drilling operations. Many compositions involve environmentally several products such as fatty amines of high molecular weight, polyoxylated amines, amides, imidazolines, nitrogen heterocyclic products, etc. The potential advantages of the use of silicates are the effective protection of carbon steel, especially in aerated saline fluids, low costs and non-aggressive behavior to environment. Gravimetric and electrochemical tests were carried out using an aerated solution of 3.5% NaCl and the addition of sodium silicate (Na2SiO3·9H2O) as a corrosion inhibitor at concentrations of 250 to 2000 mg/L. The efficiencies of the corrosion protection of carbon steel using silicate concentrations greater than 1250 mg/L were greater than 92%.

Corrosion Fatigue Behavior of Duplex Stainless Steel in 3.5% Sodium Chloride Solution

The corrosion fatigue behavior of duplex stainless steel (DSS) was studied at different cyclic stress levels in 3.5%NaCl (mass fraction, so as the follows) solution (pH=7) at 50 degreesC. The results showed that DSS was susceptible to pitting corrosion and corrosion fatigue. Both intergranluar corrosion cracking and transgranlular corrosion cracking initiated at the bottom of pitting holes. Furthermore, the corrosion fatigue properties of DSS in 3.5%NaCl solution may be relatived to complex electrochemical and mechanical coupling effects between the three phases (austenite, ferrite and martensite), where martensite and ferrite were anodic in the corrosion cell and could be prone to cracking under certain condition.

Sodium dodecyl sulfate (SDS) as an effective corrosion inhibitor for Mg-8Li-3Al alloy in aqueous NaCl: A combined experimental and theoretical investigation

The corrosion inhibition behavior of Mg-8Li-3Al alloy in NaCl solution with sodium dodecyl sulfate(SDS)was investigated by hydrogen analysis,scanning electron microscopy(SEM),electrochemical test,scanning Kelvin probe force microscopy(SKPFM)and computational methods.Results showed that the corrosion resistance of Mg-8Li-3Al alloy in NaCl solution was effectively improved with SDS.The SEM and SKPFM results confirmed a dense,200 nm-thick SDS-adsorbed layer had formed on the alloy surface.The separation energy ΔE_(gap) and adsorption energy E_(ads) of SDS on the Mg surface were calculated by density functional theory and molecular dynamics simulations,respectively.And the corrosion inhibition mechanism was hypothesized and described.

Adsorption Behavior and Inhibition Corrosion Effect of Sodium Carboxymethyl Cellulose on Mild Steel in Acidic Medium

The effect of sodium carboxymethyl cellulose (Na-CMC) on the corrosion behavior of mild steel in 1.0 mol·L-1 HCl solution has been investigated by using weight loss (WL) measurement, potentiodynamic polarization, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) methods. These results showed that the inhibition efficiency of Na-CMC increased with increasing the inhibitor concentration. Potentiodynamic polarization studies revealed that the Na-CMC was a mixed type inhibitor in 1.0 mol·L-1 HCl. The adsorption of the inhibitor on mild steel surface has been found to obey the Langmuir isotherm. The effect of temperature on the corrosion behavior of mild steel in 1.0 mol·L-1 HCl with addition of 0.04% of Na-CMC has been studied in the temperature range of 298-328 K. The associated apparent activation energy (E*a ) of corrosion reaction has been determined. Scanning electron microscopy (SEM) has been applied to investigate the surface morphology of mild steel in the absence and presence of the inhibitor molecules.

Corrosion Resistance ofAA6063-Type AI-Mg-Si Alloy by Silicon Carbide in Sodium Chloride Solution for Marine Application

The present work focused on corrosion inhibition of AA6063 type Al-Mg-Si alloy in sodium chloride （NaCI） solution with a silicon carbide inhibitor, using the potentiodynamic electrochemical method. The aluminium alloy surface morphology was examined, in the as-received and as-corroded in the un-inhibited state, with scanning electron microscopy equipped with energy dispersive spectroscopy （SEM-EDS）. The results obtained via linear polarization indicated a high corrosion potential for the unprotected as-received alloy. Equally, inhibition efficiency as high as 98.82% at 10.0 g/v silicon carbide addition was obtained with increased polarization resistance fRy）, while the current density reduced significantly for inhibited samples compared to the un-inhibited aluminium alloy. The adsorption mechanism of the inhibitor aluminium alloy follows the Langmuir adsorption isotherm. This shows that the corrosion rate of aluminium alloy with silicon carbide in NaCI environment decreased significantly with addition of the inhibitor.

Corrosion behaviour of aluminium magnesium alloys in molten sodium

The corrosion behaviour of the Al 1%Mg, Al 3%Mg, Al 5%Mg and Al 3%Mg 0.15%Zr alloys in molten sodium was investigated. The morphology of the corrosion products and the alloying element distribution of the specimens were analyzed by using OM, SEM and EDS. The results showed that the effects of the magnesium content and the immersion temperature on the corrosion of the specimens are related to β phase (Mg 5Al 8).

Corrosion Behavior of Oxide Dispersion Strengthened Ferritic Alloys in Liquid Sodium

Corrosion behavior of four oxide dispersion strengthened(ODS) ferritic alloys exposed in thermal convective liquid sodium loop for 4 000 h was examined.Surface observation results reveal that coral-like surfaces with deposit initially formed on surfaces of all exposed specimens.In tested alloy S2,χ-phase precipitated in specimen center,and a depleted χ- phase zone formed near the specimen surface.There is a transition area between the surface and center.In the other tested alloys,no notable change on microstructure was observed.Grain boundary attack was not found in any of the tested specimens.Tensile test results indicate that sodium corrosion of the four ODS ferritic alloys for 3 000 h had no notable effect on their tensile properties.

The Study on the Corrosion Behaviour of Welded and Unwelded Medium Carbon Steel in Sodium Chloride(Nacl)Solutions

The research work was based on the study of the corrosion behaviour of the welded and un-welded medium carbon steel in sodium chloride solutions.The Sodium chloride solutions used are 1ml,2ml,3ml and 4ml for both welded and un-welded medium carbon steel in NaCl.The experiments were conducted in two ways,the weight loss analyses of measurements and using the electrochemical analyzer workstation to determine the potential dynamic of the samples.The samples for the weight loss measurements were prepared from rolled products obtained at the foundry shop.Two medium carbon steel materials were sourced with different chemical compositions as sample A and B.The materials were prepared to accommodate the experiments for the determination of welded and un-welded medium carbon steel.A total of sixty-eight(68)samples were produced,prepared and used for the weight loss measurements/analyses the experiments.Thirty-four of the samples each were prepared for both the welded and un-welded experiments.All the samples were produced and prepared through the use of various machining processes with the use of a lathe machine for planning,milling.Thirty-four(34)of the sample preparation were further welded in readiness of the experiments.Sixty-eight breakers were sourced for and used.Ten(10)other samples were used for the determination with the use of the electrochemical analyzer.The chemical compositions of the medium carbon steel were determined with the use of SPECTRO Analytical Instruments.A metallurgical inverted optical microscope was used to determine the microstructures of the materials.The Scanning Electron Microscopy with EDS was used to determine the morphologies of the materials.The thirty-four of the samples were welded this process was performed to determine the effects of welding on the material surrounding the weldments.These materials were made into sizes with the use of power hacksaw(i.e.2cm by 2cm).Other materials were prepared to 1cm x 1cm thickness from the same materials.The Tafel plot experiments and that of the open Circuit Potential Time(OCPT)were carried out with the use of Electrochemical Analyzer/Workstation.The Medium carbon steel materials were exposed for fifty-four(54)days,with an interval of 3days.The corrosion rates analyses were determined and the graphs of the corrosion rates(mm/yr.)and other parameters were used plotted against No of days exposed.

Wear and corrosion resistant coatings on surface of cast A356 aluminum alloy by plasma electrolytic oxidation in moderately concentrated aluminate electrolytes

Plasma electrolytic oxidation of a cast A356 aluminum alloy was carried out in aluminate electrolytes to develop wear and corrosion resistant coatings. Different concentrations of 2, 16 and 24 g/L NaAlO2 solutions and a silicate electrolyte （for comparison） were employed for the investigation. Wear performance and corrosion resistance of the coatings were evaluated by WC （tungsten carbide） ball-on-flat dry sliding tests and electrochemical methods, respectively. The results show that the coating formed for a short duration of 480 s in 24 g/L NaAlO2 solution generated the best protection. The coating sustained 30 N load for sliding time of 1800 s, showing very low wear rate of -4.5×10^-7 mm3/（N· m）. A low corrosion current density of -8.81×10^-9 A/cm2 was also recorded. Despite low α-Al2O3 content of the coating, the compact and nearly single layer nature of the coating guaranteed the excellent performances.

Synergistic Corrosion Inhibition Effect of Molybdate and Phosphate Ions for Anodic Oxidation Film Formed on 2024 Aluminum Alloy

In order to effectively improve the corrosion resistance of aluminum alloys, anodic oxidation technique was used to generate the oxide film. We investigated the influences of two inorganic corrosion inhibitors(ammonium dihydrogen phosphate and sodium molybdate) on the corrosion resistance of anodic oxidation films on 2024 aluminum alloy, and studied the synergistic effect of two corrosion inhibitors. The corrosion resistance of anodic oxidation film in 3.5 wt% NaCl solution was evaluated by electrochemical impedance spectroscopy(EIS) and potentiodynamic polarization curves. Results show that, after adding the single ammonium dihydrogen phosphate or sodium molybdate of 0.01 M to oxalic acid electrolyte, inhibition efficiencies of the anodized samples are 10% and 47%, respectively. However, in the presence of two inhibitors with the same concentration of 0.01 M, inhibition efficiency can be as high as 92%. Therefore, we observed the significantly synergistic corrosion inhibition effect of molybdate and phosphate ions for anodic oxidation film formed on 2024 aluminum alloy.

Plasma electrolytic oxidation behavior and corrosion resistance of brass in aluminate electrolyte containing NaH2PO4 or Na2SiO3

Plasma electrolytic oxidation(PEO) of brass was carried out in aluminate electrolytes with the addition of NaH2PO4(S1) and Na2SiO3(S2), respectively, with the aim to investigate the effect of additives on the coating formation and corrosion resistance. For the PEO in S1 electrolyte, a mixed layer of AlPO4and Al2O3is formed at the initial stage, which leads to fast plasma discharges and formation of black coatings with the compositions of Al2O3,CuO, Cu2O and ZnO. However, in S2 electrolyte, plasma discharges are delayed and the coatings show a reddish color due to more Cu2O. Mott-Schottky tests show that the S1 coatings are p-type semiconductors;while the S2 coatings can be adjusted between n-type and p-type. Potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests show that the PEO treatment can significantly improve the corrosion resistance of brass, with protection efficiency up to 91.50% and the largest charge transfer resistance of 59.95 kΩ·cm^(2) for the S1 coating.

Corrosion behavior of as-cast Mg–8Li–3Al+xCe alloy in 3.5wt% NaCl solution

Mg-8Li-3Al＋xCe alloys（x = 0.5wt%, 1.0wt%, and 1.5wt%） were prepared through a casting route in an electric resistance furnace under a controlled atmosphere. The cast alloys were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The corrosion behavior of the as-cast Mg-8Li-3Al＋xCe alloys were studied under salt spray tests in 3.5wt% NaC l solution at 35°C, in accordance with standard ASTM B-117, in conjunction with potentiodynamic polarization（PDP） tests. The results show that the addition of Ce to Mg-8Li-3Al（LA83） alloy results in the formation of Al_2Ce intermetallic phase, refines both the α-Mg phase and the Mg_（17）Al_（12） intermetallic phase, and then increases the microhardness of the alloys. The results of PDP and salt spray tests reveal that an increase in Ce content to 1.5wt% decreases the corrosion rate. The best corrosion resistance is observed for the LA83 alloy sample with 1.0wt% Ce.

Atmospheric Corrosion Studies of Ductile Iron and Austenitic Stainless Steel in an Extreme Marine Environment

This paper presents the corrosion characteristics and the accompanying changes in the microstructure of unalloyed duc-tile iron (DI) and austenitic stainless steel (ASS) in table salt medium representing an upper limit in an extreme marine environment. The individual corrosion rates of DI and ASS was evaluated for the maximum time period of 1200 hr. Using the immersion test technique, the corrosion rate of DI was evaluated and found to be four-orders of magnitude greater than that of ASS. The corrosion product morphologies of the DI showed that the nodular matrix was gradually covered up as immersion time progressed while the corrosion channels and volume of pits that initially formed in ASS respectively deepened and increased with increased exposure time. This work is important as a reference point for the quantification of the corrosion effectiveness of alloying DI. The microstructures of the corroded samples showed corro-sion initiation and gradual accumulation of corrosion products.

Effect of microstructure variation on the corrosion behavior of high-strength low-alloy steel in 3.5wt% NaCl solution

The effect of microstructure variation on the corrosion behavior of high-strength low-alloy（HSLA） steel was investigated. The protective property of the corrosion product layer was also explored. Experimental results reveal that the type of microstructure has significant effect on the corrosion resistance of HSLA steel. The measurement results of weight loss, potentiodynamic polarization curves, and electrochemical impedance spectroscopy indicate that the steel with acicular ferrite microstructure exhibits the lowest corrosion rate. Martensite exhibits a reduced corrosion resistance compared with polygonal ferrite. It is found that the surface of the acicular ferrite specimen uniformly covered by corrosion products is seemingly denser and more compact than those of the other two microstructures, and can provide some amount of protection to the steel; thus, the charge transfer resistance and modulus values of the acicular ferrite specimen are the largest. However, corrosion products on martensite and polygonal ferrite are generally loose, porous, and defective, and can provide minor protectiveness; thus, the charge transfer resistance values for polygonal ferrite and martensite are lower.

Corrosion Behaviour of Heat Treated Rolled Medium Carbon Steel in Marine Environment

Investigation were carried out to study the corrosion behaviour of heat treated rolled medium carbon steel and as-rolled medium carbon steel in sodium chloride medium. The as-rolled medium carbon steel was heated to a temperature of 830℃ to completely austenize it and water quenched;it was reheated to the ferrite-austenite dual phase region at a temperature of 745℃ below the effective Ac3 point. The steel was then rapidly quenched in water and tempered at a temperature of 480℃. The corrosion behaviour of the steel in marine medium (NaCl) was studied by weight loss measurement. The weight loss is between 0.02g-0.11g for the as-rolled steel and 0.01g – 0.013g for the heat treated steel. The results obtained showed that the as-rolled medium carbon steel is more susceptible to corrosion than the heat treated rolled medium carbon steel.

<i>Amaranthus cordatus</i>as a Green Corrosion Inhibitor for Mild Steel in H₂SO₄and NaCl

This work studies the use of Amaranthus cordatus as the corrosion inhibitor for conventional mild steel in 0.5 M and 1.0 M of both H2SO4 and NaCl. The effects of different concentrations of the acid and base on the inhibition efficiency of Amaranthus cordatus were tested at room temperature and at different inhibitor volumes. The experiment was set for 30 days and weight-loss corrosion technique was employed in obtaining the corrosion penetration rate using the standard equation: . The result shows that the rates of corrosion of the mild steel increased with an increase in concentration of the acid or base and also decreased with increasing volume of Amaranthus cordatus. Expectedly, the inhibition efficiency was found to be greater in sodium chloride than in tetraoxosulphate VI acid. Also inhibition efficiency was found to increase with increase in extracts volume and decrease in concentration of the acid or base. These findings strongly suggest that Amaranthus cordatus can be used as the inhibitor for preventing the corrosion of mild steel.

Alkali Vapor Corrosion of Different Refractories at High Temperatures

Commercial high purity corundum brick,corundum-mullite brick,mullite brick,calcium hexaaluminate brick and calcium hexaaluminate-corundum brick were studied to investigate their reaction state and alkali vapor corrosion mechanism at 1370 and 1500℃.The results show that:(1)served in hot alkali vapor,the high-purity corundum brick has no obvious slag layer but expands dramatically;(2)the corundum-mullite brick shows obvious reactive expansion at 1370℃and melting corrosion happens at 1500℃;(3)at 1370℃alkali vapor and mullite brick react and form a slag layer without volume effect;when the temperature increases to 1500℃,the reaction melting corrosion intensifies;(4)the calcium hexaaluminate brick and the calcium hexaaluminate-corundum brick form a thin slag layer in alkali vapor,and the sample surface absorbs Na+to form a dense layer with small volume effect.