Immersion Corrosion Tests Research Articles

Tribological and corrosion characteristics of aluminium–copper alloys reinforced with alumina nickel aluminide cermet powder

Aluminium–Copper (Al-10Cu) alloys are widely used for structural components in the aviation sector. This study focuses on the synthesis and characterisation of Al-10Cu alloy reinforced with Al2O3-30(Ni-20Al) cermet particles to evaluate their microstructural, mechanical, tribological and corrosion properties. The Al-10Cu alloy was cast with varying percentages of cermet (2% and 4%) using a controlled casting process. Comprehensive microstructural analyses, including optical microscopy, SEM and EBSD, were performed to assess the grain structure and cermet distribution. The mechanical properties were evaluated through Vickers microhardness and tensile testing, while tribological performance was assessed using a Pin-on-Disc tribometer. Corrosion resistance was investigated through exfoliation and immersion corrosion tests. The results indicated significant improvements in microhardness and wear resistance with the addition of cermet particles, while the tensile strength showed a complex interplay between ductility and brittleness. Corrosion tests revealed enhanced resistance in cermet-reinforced specimens. This study demonstrates the potential of Al2O3-30(Ni-20Al) cermet as an effective reinforcement for aluminium alloys to achieve superior performance in structural applications.

Synergistic effect of B and Y on the corrosion of S31254 super austenitic stainless steel under stress

The corrosion behavior of S31254 microalloying with B and Y was investigated after experiencing the tensile and compressive deformation. After three-point bending deformation test, the local misorientation and plastic deformation caused by tensile deformation were larger than compressive deformation. The synergistic effect of B and Y reduced local residual stress of samples after both tensile deformation and compressive deformation. Electrochemical test showed that the synergistic effect of B and Y enhanced corrosion resistance more effectively than microalloying with B alone. In the immersion corrosion test, the tensile region showed higher stress corrosion sensitivity due to the higher plastic deformation than that in compressive region. The 50B+50Y sample exhibited better corrosion resistance than 50B sample and 0B sample in the tensile region with low plastic deformation. With the decrease of tensile deformation, the synergistic effect of B and Y on reducing the corrosion sensitivity was more obviously than B alone.

Corrosion performance of super duplex stainless steel and pipeline steel dissimilar welded joints: a comprehensive investigation for marine structures

This study investigates the corrosion behavior of dissimilar gas tungsten arc (GTA) welded joints between super duplex stainless steel (sDSS 2507) and pipeline steel (X-70) using electrochemical and immersion corrosion tests. The GTA welds were fabricated using ER2594 and ER309L filler metals. The study examined the electrochemical characteristics and continuous corrosion behavior of samples extracted from various zones of the weldments in a 3.5 wt.% NaCl solution, employing electrochemical impedance spectroscopy, potentiodynamic polarization methods, and an immersion corrosion test. EIS and immersion investigations revealed pitting corrosion in the X-70 base metal/X-70 heat-affected zone, indicating inferior overall corrosion resistance due to galvanic coupling. The corrosion byproducts identified in complete immersion comprised α-FeOOH, γ-FeOOH, Fe3O4, and Fe2O3, whereas γ-FeOOH and Fe3O4 were predominant in dry/wet cyclic conditions. Corrosion escalated with dry/wet cycle conditions while maintaining a lower level in complete immersion. The corrosion mechanism involves three wet surface stages in dry/wet cycles and typical oxygen absorption during complete immersion. Proposed corrosion models highlight the influence of Cl−, O2, and rust layers.

Effect of laser-induced grain growth on the electrochemical and immersion corrosion behavior of electrochemical deposited Ni coatings

In this study, the introduction of laser irradiation during the electrochemical deposition of Ni coatings was employed to investigate the evolution of surface morphology, microstructure, and residual stress. Furthermore, the impact of laser on corrosion performance was examined through electrochemical and immersion corrosion tests. The results showed that introducing a laser resulted in a uniform electrochemically deposited particle size distribution, and the shape evolved from granular to pyramidal. However, the average grain size increased from 0.4 ± 0.1 μm to 0.6 ± 0.3 μm after adding laser, and the grain morphology also transformed from equiaxed to columnar grains. In addition, the surface roughness increased from 34 ± 3 nm to 122 ± 16 nm compared to not adding a laser. The internal stress changed from 54 ± 17 MPa to −113 ± 19 MPa, indicating that the original tensile stress evolved into compressive stress. Electrochemical and immersion corrosion indicate that after adding laser, the passive current density decreased from 3.8 × 10−6 A·cm−2 to 6.9 × 10−7 A·cm−2 (reduced by approximately 81.8 %), indicating a significant improvement in corrosion resistance. This is attributed to the stability and density of the passive film. Although the average grain size and surface roughness increase, the uniformity of surface deposited particles improves the uniformity of electrochemical distribution, accelerates the formation of uniformly dense passive film, and limits the expansion of corrosion pits under the combined action of compressive stress.

Investigation on corrosion behaviour of metal oxide nanoparticles reinforced magnesium composites by salt spray and immersion corrosion test methods

ABSTRACT This study explores the increasing utilisation of lightweight materials, particularly magnesium (Mg) alloy, in sectors such as automobile, aerospace, and marine due to its notable advantages such as high strength-to-weight ratio, good castability, and excellent damping capacity. Despite these merits, Mg alloy faces challenges, notably in wear and corrosion resistance. The research focuses on enhancing the corrosion resistance of Mg alloy by incorporating Zinc Oxide (ZnO), Manganese Oxide (MnO), and Titanium Oxide (TiO2) nanoparticles. The alloy AZ91D and three nanocomposites, namely AZ91D + 1% ZnO, AZ91D + 1% MnO, and AZ91D + 1% TiO2, were manufactured using a stir squeeze casting technique combined with an ultrasonication process. To confirm the even distribution of reinforcement particles, Optical Microscope (OM), Scanning Electron Microscope (SEM) and High-Resolution Scanning Electron Microscope (HR-SEM) were employed. X-ray Diffraction (XRD) analysis revealed the presence of matrix and reinforcement material with intermetallic precipitates around the grain boundaries. Corrosion properties were assessed following ASTM standards and utilising a 3.5% NaCl concentration. The study found that AZ91D + 1% TiO2 nanocomposites exhibited superior corrosion resistance compared to the AZ91D alloy, showing a remarkable 77.78% and 69.89% improvement in corrosion behaviour under salt spray and immersion environments, respectively, after 48 hours.

Effect of wire deposition rate on macro and microscopic characteristics of laser weld-brazed AA5083 aluminum alloy to galvanized steel joints and their corrosion response

ABSTRACT In this study, dissimilar metals, such as aluminium (AA5083) and galvanised interstitial free steel, were laser-brazed in a flange configuration using eutectic filler aluminium wire (4047, Al-12%Si). To investigate the effects of wire deposition rate on the characteristics of laser-brazed joints and to understand the factors contributing to corrosion in these joints. The wire deposition rates were varied while keeping other laser parameters constant. Changes in wire deposition rate were observed to affect the flow behaviour of molten metal leading to variations in the geometrical characteristics of the brazed joints and interfacial reactions as revealed by macroscopic examination. A series of corrosion tests, including electrochemical, immersion, and salt spray tests, were conducted on the laser-brazed joints. It was demonstrated by Immersion corrosion tests that the wire rate influenced the corrosion results for the laser-brazed joints. However, the salt spray test showed no substantial effect on corrosion with respect to different wire deposition rates. Furthermore, the electrochemical results indicated significant changes in the corrosion response of the brazed zone due to the presence of chemically dissimilar phases. A correlative discussion between laser parameters, observed microstructure, and their effects on the corrosion performance of the brazed samples is presented.

Influence of heat treatment on the microstructure evolution and corrosion performance of biodegradable Zn-Mg alloys

Zinc and zinc-based alloys have garnered increasing attention as biodegradable materials due to their excellent mechanical properties, lower degradation rates compared to magnesium, and favorable biocompatibility. This study investigates the impact of homogenization treatment on the microstructure and corrosion behavior of Zn-Mg alloys using scanning electron microscopy, X-ray diffraction, hardness testing, and accelerated corrosion immersion tests. The results reveal that homogenization treatment induces the fusion of eutectic cells within the alloys, causing significant morphological alternations in the eutectic structure and varying proportions of the Mg2Zn11 phase, These changes notably affect material properties. The raised content of Mg2Zn11 phase in the eutectic structure correlates with higher hardness but reduced corrosion resistance, whereas the reduced Mg2Zn11 phase content leads to enhanced corrosion resistance. Furthermore, in-situ corrosion observations demonstrate that corrosion initiates at the eutectic phase, with corrosion pits forming due to the ion release as corrosion progresses, leading to gradual enlargement of the corrosion pits. In summary, this study provides comprehensive insights into the microstructural changes in Zn-Mg alloys and their impact on corrosion resistance, offering valuable references for their engineering applications.

Effect of electrolyte pH value on microstructure and corrosion resistance of black MAO coating on 6063 aluminum alloy

Black micro-arc oxidation (MAO) coatings were obtained on the surface of 6063 aluminum alloy by using the MAO technique in silicate electrolyte with colorant NH4VO3. The work aimed to study the effect of adjusting the electrolyte pH (pH10, pH11, pH12, and pH13) on the microstructure, mechanical properties, and corrosion resistance of black MAO coatings on 6063 aluminum alloy. The experimental results showed that the electrolyte pH had an important effect on the macroscopic morphology of the MAO coatings. As the electrolyte pH value increased, the process voltage of the sample decreased, the duration of the anodic oxidation stage and the spark discharge stage were shortened, while the duration of the micro arc oxidation stage was prolonged. Reasonable adjustment of the electrolyte pH could reduce the poriness and defects of the coatings, decrease the surface roughness of the coatings, and improve the quality and wear resistance of the coatings. The corrosion resistance of the black MAO coating obtained in the electrolyte with pH12 was superior and the corrosion current density was only 3.207×10−7 A/cm2. The immersion corrosion test further demonstrated the same results of corrosion resistance.

Effect of corrosion on the fatigue damage behavior of M50 steel treated by ultrasonic surface rolling process

Ultrasonic surface rolling process (USRP) can improve the fatigue performance of M50 steel, but corrosion during service may affect the anti-fatigue performance. Microstructure and corrosion resistance of M50 steel treated by USRP is analyzed by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS). Besides, the fatigue behavior of USRP sample under corrosion is analyzed by conducting fatigue tests after immersion corrosion tests. Results show that USRP treatment refines the surface grains to nanoscale (29.8 nm), introduces a certain residual compressive stress and decrease the precipitations of M50 steel, which improve the density of passive film and the resistance to local corrosion for M50 steel. Compared to M50 steel matrix, USRP sample has fewer and smaller corrosion pits at the same corrosion time, thereby reducing the risk of crack initiation. Meanwhile, the residual compressive stress value of USRP sample remains at a higher level. So the fatigue life of USRP sample is always higher than that of untreated sample under the same corrosion time. However, the corrosion process still leads to the destruction of surface integrity and the release of residual compressive stress, and the fatigue performance of USRP sample will gradually decrease with increasing the corrosion time.

Effect of Gentamicin Sulfate and Polymeric Polyethylene Glycol Coating on the Degradation and Cytotoxicity of Iron-Based Biomaterials.

The work is focused on the degradation, cytotoxicity, and antibacterial properties, of iron-based biomaterials with a bioactive coating layer. The foam and the compact iron samples were coated with a polyethylene glycol (PEG) polymer layer without and with gentamicin sulfate (PEG + Ge). The corrosion properties of coated and uncoated samples were studied using the degradation testing in Hanks' solution at 37 °C. The electrochemical and static immersion corrosion tests revealed that the PEG-coated samples corroded faster than samples with the bioactive PEG + Ge coating and uncoated samples. The foam samples corroded faster compared with the compact samples. To determine the cytotoxicity, cell viability was monitored in the presence of porous foam and compact iron samples. The antibacterial activity of the samples with PEG and PEG + Ge against Escherichia coli CCM 3954 and Staphylococcus aureus CCM 4223 strains was also tested. Tested PEG + Ge samples showed significant antibacterial activity against both bacterial strains. Therefore, the biodegradable iron-based materials with a bioactive coating could be a suitable successor to the metal materials studied thus far as well as the materials used in the field of medicine.

Corrosion characteristics of concrete by landfill leachates of different ages

Landfill leachate is a highly corrosive pollutant, and the composition of landfill leachate varies greatly between landfill ages. Landfill leachates of different ages pose a corrosive danger to concrete structures. In this study, four landfill leachates of different ages were selected for concrete immersion corrosion tests to elucidate the corrosion characteristics of concrete. Measurements of concrete mechanical property indices were combined with microscopic analysis methods, such as X-ray diffraction and scanning electron microscopy. The effects of the compositional differences of the landfill leachate of different ages and contact times on the concrete were analyzed and evaluated. The test results showed that the young landfill leachate slowed down the hydration process of concrete and promoted the generation of expansive corrosive crystals such as gypsum and calcium sulfate, which changed the internal microstructure of the concrete and caused irreversible damage. Exposure to leachates caused a decrease of the concrete quality, compressive strength, and dynamic elastic modulus to below their initial values. The participation of intermediate and mature landfill leachate in the hydration process of concrete promoted the hydration reaction in the short term. However, with the prolongation of the test period, this enhancement gradually weakened, and at the same time, the sulfate in the landfill leachate and the hydration products generated ettringite, which produced expansion stress on the internal structure of the concrete, destroying the structure and decreasing its strength. The experimental results of this study provide theoretical support for the treatment of different ages of landfill leachates and the design and protection of landfill concrete structures.

Tensile strength and immersion corrosion behavior of nano-ZnO, rare earth Gd reinforced Mg nanocomposites developed by novel stir ultrasonication process

This paper presents the tensile and immersion corrosion properties of Mg-Zn-0.2Gd-xZnO (x = 1, 1.5, 2 and 2.5 wt.%) alloy and nanocomposites developed by stir ultrasonication coupled with squeeze casting. The immersion corrosion tests were performed under the simulated body fluid (SBF) conditions. The microscopic measurements indicate that the examined alloys/nanocomposites exhibit a significant decrease in grain size when both alloying elements Gadolinium (Gd) and Zinc Oxide (ZnO) nanoparticles are added. The examination of the phase by XRD indicates the presence of α-Mg and Mg2Zn, Mg7Zn3 secondary phases, which act as barriers against corrosion. The study confirmed that the incorporation of nanoparticles ZnO content ranging from 1 to 2.5 wt. % leads to a notable enhancement in yield strength (140 to 230 MPa). From the immersion corrosion test, the nanocomposites with the inclusion of 2 wt. % ZnO ceramic nanoparticles resulted in the highest level of corrosion resistance with a corrosion rate of 0.049 mm per year. This nanocomposite also shows better wettability with improved hydrophilicity. The developed Mg based advanced nanocomposites have the potential to be used in load bearing implant applications as it exhibited high corrosion resistance characteristics.

Investigations on corrosion behavior of 316LN and 316L austenitic stainless steel under corrosion-deformation interactions

PurposeThis paper aims to explore the influence of corrosion-deformation interactions (CDI) on the corrosion behavior and mechanisms of 316LN under applied tensile stresses.Design/methodology/approachCorrosion of metals would be aggravated by CDI under applied stress. Notably, the presence of nitrogen in 316LN austenitic stainless steel (SS) would enhance the corrosion resistance compared to the nitrogen-absent 316L SS. To clarify the CDI behaviors, electrochemical corrosion experiments were performed on 316LN specimens under different applied stress levels. Complementary analyses, including three-dimensional morphological examinations by KH-7700 digital microscope and scanning electron microscopy coupled with energy dispersive spectroscopy, were conducted to investigate the macroscopic and microscopic corrosion morphology and to characterize the composition of corrosion products within pits. Furthermore, ion chromatography was used to analyze the solution composition variations after immersion corrosion tests of 316LN in a 6 wt.% FeCl3 solution compared to original FeCl3 solution. Electrochemical experiment results revealed the linear decrease in free corrosion potential with increasing applied stress. Electrochemical impedance spectroscopy results indicated that high tensile stress level damaged the integrity of passivation film, as evidenced by the remarkable reduction in electrochemical impedance. Ion chromatography analyses proved the concentrations increase of NO3− and NH4+ ion concentrations in the corrosion media after corrosion tests.FindingsThe enhanced corrosion resistance of 316LN SS is attributable to the presence of nitrogen.Research limitations/implicationsThe scope of this study is confined to the influence of tensile stress on the electrochemical corrosion of 316LN at ambient temperatures; it does not encompass the potential effects of elevated temperatures or compressive stress.Practical implicationsThe resistance to stress electrochemical corrosion in SS may be enhanced through nitrogen alloying.Originality/valueThis paper presents a systematic investigation into the stress electrochemical corrosion of 316LN, marking the inaugural study of its impact on corrosion behaviors and underlying mechanisms.

Study on seawater corrosion resistance of calcium sulfoaluminate cement-based novel grouting materials

Grouting materials play a critical role in anchoring structures of cross-sea tunnels by safeguarding the anchors against seawater corrosion and enhancing durability. In this paper, a novel grouting material comprising ferrite-rich sulfoaluminate cement (FCSA), ordinary Portland cement (OPC), anhydrite and limestone were prepared. Accelerated corrosion immersion tests were conducted to assess the corrosion resistance of the grouting material using artificial seawater solutions with varying salt concentrations. Pull-out tests were performed to verify the material's performance, while potentiometric titration and X-ray diffraction (XRD) analysis were employed to analyze free chloride ion concentration (Cf) and corrosion products at the anchorage interface. Results indicate that after 1.5 years of corrosion in seawater with different salt concentrations, the bond strength stabilized at 1.05 MPa. No rust was observed on the anchor surfaces and the Cf exhibited a linear increase with salt concentration. The content of Friedel's salt increases with salt concentration, demonstrating adequate chloride ion binding capacity. The test results validate the exceptional seawater corrosion resistance and long-term stability of the novel grouting material.

Corrosion behaviors of W-doped laser-cladded high-entropy alloy of AlCoCrFeNi in a simulated sulfur-containing seawater environment

The localized corrosion in a simulated seawater environment is related to sulfide, and few studies have investigated the corrosion behaviors of laser-cladded AlCoCrFeNi high-entropy alloy (HEA) systems in a simulated sulfur-containing seawater environment. Corrosion behaviors of HEA/Wx (x = 0, 5, and 15 wt%) coatings have been worked out by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis, X-ray photoelectron spectroscopy (XPS) analysis, and immersion corrosion tests. W-doped HEA coatings can change the ratio of A2 to B2 phases and affect the corrosion resistance. The potentiodynamic polarization and EIS results reveal that a small quantity of W-doped (5 wt%) HEA coatings form a denser passivation film that is particularly resistant to localized corrosion. By analyzing the corrosion behaviors of the HEA/Wx coatings, it was determined that a small amount of W-doped (5 wt%) HEA coatings had better localized and improved corrosion resistance. However, excessively W-doped (15 wt%) HEA coatings have reduced corrosion resistance. The Mott-Schottky analysis revealed that the HEA/Wx coatings (x = 0, 5, and 15 wt%) have the property of P–N-type semiconductors. XPS analysis was used to analyze the film composition. The results demonstrated that the passivation film combined Cr2O3, Al2O3, Fe2O3, and WO3. Based on the immersion corrosion test, localized corrosion types were mainly intergranular and crevice.

A comparative study on resistance spot and laser beam spot welding of ultra-high strength steel for automotive applications

In this study, the effect of resistance spot welding (RSW) and laser beam spot welding (LBSW) processes on evolution of microstructure, load endurance capabilities, heat affected zone (HAZ) softening, and corrosion resistance of ultra-high-strength (UHSS) steel joints welded in lap joint design is investigated. The UHSS sheets of dual phase 1000 grade (UHSDP1000) having 1.20 mm thickness were joined using the RSW and LBSW parameters optimized by response surface methodology (RSM). The microstructural features of welding regions of RSW and LBSW joints were studied using optical microscopy (OM). The load endurance capabilities of RSW and LBSW joints were assessed using the tensile shear failure load (TSFL) and cross-tensile failure load (CTFL) tests. The ruptured surfaces of TSFL and CTFL tested samples were examined utilizing scanning electron microscopy (SEM). The microhardness distribution of divergent regions of RSW and LBSW joints was evaluated and imputed to the TSFL and CTFL failure of joints. The corrosion resistance of RSW and LBSW joints was analyzed using potentiodynamic corrosion and immersion corrosion tests. The RSW joints showed 183% and 62.79% greater TSFL and CTFL endurance capabilities than LBSW joints. The TSFL and CTFL endurance capabilities of LBSW joints are inferior to RSW joints due to the smaller load bearing area. It causes the stress concentration in FZ and HAZ of LBSW joints. The RSW joints and LBSW joints disclosed TSFL and CTFL failure in button pull out rupture mode with tearing of HAZ. The failure of RSW and LBSW joints in HAZ is due to the softening caused by martensitic tempering and coarsening of grains. The LBSW joints disclosed inferior resistance to corrosion than RSW joints due to the higher martensite content which contributes to greater fraction of favorable pitting sites and decreased corrosion resistance.

2-mercaptobenzimidazole inhibits corrosion and prolongs the lifetime of an epoxy resin coating on a copper-62 alloy surface in a simulated marine environment at 40 °C

Epoxy coatings are widely used on metal surfaces in marine environments, but are subject to corrosion. How to improve the corrosion resistance of such materials has therefore become an important research topic. In this study, the corrosion inhibitor 2-mercaptobenzimidazole (MBI) was added to the organic coating of the epoxy resin on the surface of the copper-62 alloy to extend the service life of the coating in marine environments. The corrosion inhibition efficiency of MBI for the copper-62 alloy in simulated marine environments was investigated by means of immersion corrosion tests, Tafel polarization tests, and electrochemical impedance spectroscopy (EIS). The effects of MBI on the damage process and water transport of epoxy coatings were also studied by EIS. It has been shown that MBI acts as an adsorption corrosion inhibitor by electro-attractively adsorbing on the surface of a copper substrate. For a total mass fraction of 0.5 wt. %, the corrosion inhibition efficiency was more than 90%, and the corrosion current density of the copper-62 alloy in simulated seawater with MBI was 6.01 × 10−7 A cm−2. The corrosion current density of the copper-62 alloy in simulated seawater is 1.382 × 10−5 A cm−2. When MBI was added to the epoxy organic coating at a ratio of 0.5 wt. %, the diffusion coefficient of the coating was as low as 9.72 × 10−11 cm2 s−1, and the time to failure of the coating was extended to 1656h, compared to the epoxy coating without the corrosion inhibitor. It has been demonstrated that the addition of MBI can increase the service life of copper-62 alloy/epoxy coatings in marine environments effectively.

Mechanical properties and corrosion behavior of electron beam cold hearth melting high strength and high corrosion resistant Ti-0.3Mo-0.8Ni alloy with different states

In this study, a large size Ti-0.3Mo-0.8Ni (TA10) alloy ingot melted by electron beam cold hearth melting (EBCHM) technology was investigated. The microstructure, mechanical properties, and corrosion behavior of as-cast, hot-rolled, and annealed TA10 alloys were investigated. The results show that different states of TA10 alloys have different microstructure and properties. The microstructure of the as-cast TA10 alloy exhibits the Widmanstätten α phase, and the hot-rolled TA10 sheet shows a fibrous structure with an obvious rolling streamline. After 650 °C annealing, the intergranular β phase decreases, and most of the strip α phase changes to the equiaxed α phase. With the annealing temperature increasing to 840 °C, the microstructure gradually changed from an equiaxed structure to a duplex structure. The mechanical properties of the TA10 alloy were enhanced after hot-rolling with an increase in ultimate tensile strength from 386.5 MPa to 610 MPa. Additionally, the elongation increased from 15.6 % to 23.3 %. Upon annealing at varying temperatures, it was observed that the strength decreased, reaching to 423.5 MPa at 650 °C and 478.2 MPa at 840 °C, while the plasticity increased significantly, reaching to 26.5 % at 650 °C and 28.6 % at 840 °C. The improved strength was attributed to the better grain boundary slip of the equiaxed structure. The corrosion resistance of titanium alloys is closely connected with their microstructure. The results of the immersion corrosion test indicate that the samples in various states exhibit similar corrosion behavior. Additionally, the hot-rolled TA10 alloy shows the highest corrosion resistance, with a lower corrosion rate of 0.34459 mm/year. The as-cast TA10 alloy shows the lowest corrosion resistance, with a lower corrosion rate of 1.37559 mm/year.

Enhancing corrosion resistance of the nugget in a 2519-T87 aluminum alloy friction stir welded joint via tungsten inert gas arc

The corrosion resistance of the nugget zone (NZ) in two 2519-T87 aluminum alloy joints obtained by conventional friction stir welding (FSW) and tungsten inert gas arc-assisted FSW (TIG-FSW) was evaluated by immersion corrosion tests and electrochemical measurements. The results show that TIG arc significantly enhances the corrosion resistance of the nugget, the maximum corrosion depth is reduced by about 59.6%, and the polarization resistance is increased by about 14.5%. The mechanism was discussed based on microstructural examination. TIG-FSW decreases the area fraction of coarse intermetallic compounds (IMCs) with an equivalent diameter larger than 2.0 μm and increases the number of submicron IMCs, avoids the accumulation of IMCs, leads to low local electrochemical activity, and consequently enhances the corrosion resistance of the NZ.

Tribological, oxidation and corrosion properties of ceramic coating on AISI H13 steel by rare earth-Cr composite boronizing

In this paper, a rare earth-Cr composite boronizing method to prepare boride ceramic coatings for AISI H13 steel was proposed. The effect of rare earth elements and Cr on the microstructure, hardness, wear resistance, high temperature oxidation resistance, and corrosion of boride ceramic layers was researched. The characteristics of the boride layers were investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), electron probe microanalysis (EPMA), wear tests, high-temperature oxidation tests, and corrosion immersion tests, etc. The results showed that the boride layer comprised of Fe2B, FeB, CrB and Cr2B phases. The addition of rare earth CeO2 and Cr nanopowder promoted the growth of the boride layer, and its surface hardness increased by 3.5 times compared with that of tempered AISI H13 steel. In addition, the addition of CeO2 and Cr significantly reduced the wear rate of the boride layer, with the surface wear mechanism being abrasive oxidative wear. Furthermore, the oxidation rate of the boride layer was 71 % lower than that of AISI H13 steel, demonstrating excellent high-temperature oxidation resistance; and the boride layer showed good acid corrosion resistance in corrosion immersion tests.