Salt Spray Test Research Articles

Achieving Superior Corrosion Resistance of TiB2 Reinforced Al-Zn-Mg-Cu Composites via Optimizing Particle Distribution and Anodic Oxidation Time

In this study, the effects of particle distribution and anodizing time on the microstructure and corrosion resistance of the TiB2 particle-reinforced Al-Zn-Mg-Cu composite were investigated. Relationships between TiB2 particle distribution, anodizing time, coating growth rule, and corrosion resistance were characterized and discussed using an optical microscope, a scanning electron microscope, an electrochemical test, and a salt spray test. Dispersion of TiB2 particles by powder metallurgy improved the corrosion resistance of the anodized coating on composites. Compared with the matrix, the corrosion potential (Ecorr) of the anodized coating shifted to the positive direction, and the corrosion current density (icorr) decreased. Meanwhile, the icorr of the coating decreased initially and then increased with the extension of the anodization time. The corrosion resistance of the coating was optimal at an anodization time of 20 min. The corrosion resistance of the composite was determined by both the porosity and thickness of the coating. Additionally, all samples treated by potassium dichromate sealing had no corrosion points after a 336-h salt spray test, demonstrating an excellent corrosion resistance suitable for harsh environmental applications in industry.

Corrosion behavior and mechanical properties of plasma sprayed Al2O3-aluminum bronze and Ca2SiO4-aluminum bronze coatings

NiCr–Al2O3-aluminum bronze (NAC) and NiCr–Ca2SiO4-aluminum bronze (NDC) coatings were prepared by atmospheric plasma spraying. Corrosion experiments were performed on coatings including immersion in simulated seawater and dry-wet composite salt spray test. Phase composition and microstructure of the coatings were investigated by X-ray diffraction, energy dispersive spectrometry and scanning electron microscopy, before and after the corrosion tests. The adhesion strength and hardness of coatings were also evaluated. As observed, Ca2SiO4 had much lower hardness than Al2O3 layer. Due to the rougher surface and higher thermal expansion of Ca2SiO4 layer, NDC coatings possessed better adhesion. Further, NDC coatings exhibited relatively superior corrosion resistance. According to the microstructure and phase analysis, this finding was attributed to the hydration reaction of Ca2SiO4 during the tests.

Initial dissolution of Mg-containing phase and corrosion product formation in cut-edge corrosion of Zn-11%Al-3%Mg-0.2%Si coated steel

Simulated cut-edge specimens of Zn-11%Al-3%Mg-0.2%Si coated steel were fabricated, and their corrosion behaviors were assessed using salt spray test (SST). The Mg-containing phases in the coating near the simulated cut-edge dissolved during early corrosion, leading to the formation of protective corrosion products on the steel surface. The corrosion products suppressed the oxygen reduction reaction on the steel. Additionally, the anodic dissolution rate of the coating layer decreased after the SST. Consequently, the cut-edge corrosion rate of the Zn-Al-Mg coating after the deposition of the corrosion products decreased compared with that of a conventional Zn coating.

A comparative study between PVD-TiMgN and PVD-TiMgGdN sputtered coatings to evaluate the influence of Gd and its effect on the corrosion properties of the individual coatings

DC-PVD TiMgGdN coatings with excellent corrosion properties have been successfully developed using a powder metallurgy TiMgGd target while maintaining the well known tribological properties of TiN. In this study, TiMgGdN coatings were compared with TiMgN coatings using identical deposition parameters to investigate the influence of Gd on the corrosion behavior. For this purpose, a TiMg powder metallurgical target was used with an identical Ti/ Mg ratio as the TiMgGd target. The coatings were comprehensively analysed by different analytical methods such as X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-Ray Photonelectron Spectroscopy (XPS) and Glow Discharge Optical Emission Spectroscopy (GDOES) regarding their chemical, structural and microstructural characteristics. The corrosion properties were investigated using the neutral salt spray test (NSS test) in 5 % NaCl solution as well as with potentiodynamic tests in 0.5 % NaCl solution saturated with Mg(OH)2.Based on the findings of this study, it can be concluded that the excellent corrosion performance along with the mechanical properties are supported by the Gd addition to the coatings. The TiMgN coatings show a change in chemical composition, microstructure as well as in hardness after corrosive exposure, which cannot be observed on TiMgGdN coatings. Consequently, alloying TiMgN with Gd maintains the stability of the coating during corrosive exposure. The analytical results show that the excellent corrosion performance and stability of the TiMgGdN coatings are due to a stable and stronger passivation layer by the formation of Mg(OH)2 and Gd2O3 on the TiMgGdN surface. Furthermore, the Gd2O3 contributes to a strong hydrophobic effect. Regarding the microstructure, TiMgGdN coatings are seemingly denser compared to the TiMgN coatings, which positively influences the corrosion resistance of this coating.

Morphological and structural changes of sintered Cu-10 wt% Al materials with different alloying levels in salt spray environment

Morphological and structural changes of spark plasma sintered Cu-10 wt% Al materials in salt spray environment were studied. The tested materials possessed the same elemental composition but different phase compositions (Cu-Al composite, Cu(Al) solid solution and Cu-Cu(Al)-Cu9Al4 alloy). The oxide films formed on the surface of the corroded samples were confirmed to be enriched with Al. The subsurface regions of the Cu-Al composite and Cu(Al) solid solution did not reveal any microstructural changes after the salt spray test. When the Cu-Cu(Al)-Cu9Al4 alloy corroded, the aluminum contained in the alloy oxidized such that the oxide particles formed both on the surface of the sample and in the subsurface region. While the Cu-Al composite and Cu(Al) solid solution maintained integrity, the Cu-Cu(Al)-Cu9Al4 alloy experienced swelling and cracking during the salt spray test.

Corrosion and wear resistant polyp-xylene composite coating on AZ31 magnesium alloy prepared by micro-arc oxidation and vapor deposition

To improve the wear and corrosion resistance of magnesium alloy, a multifunctional organic/inorganic hybrid coating was prepared on AZ31 magnesium alloy by microarc oxidation and vapor deposition of Polyp-xylene (MAO-PPX). Electrochemical tests show that the MAO-PPX composite coating can effectively block the corrosive medium and improve the corrosion resistance of magnesium alloy. Long-term corrosion protection was confirmed by neutral salt spray tests at 35 °C with 5 wt% NaCl. In addition, the MAO-PPX composite coating demonstrated a much lower friction coefficient which could be attributed to the polyp-xylene filled in the micropores of the MAO layer and transferred on the counterpart sphere. This composite coating with excellent anti-corrosion and decent lubricating properties has broad application prospects in surface protection of magnesium alloys.

Effect of Carbohydrates on the Formation Process and Performance of Micro-Arc Oxidation Coatings on AZ31B Magnesium Alloy

An environmentally friendly alkaline electrolyte of silicate and borate, which contained the addition of carbohydrates (lactose, starch, and dextrin), was applied to produce micro-arc oxidation (MAO) coatings on AZ31B magnesium alloy surfaces in constant current mode. The effects of the carbohydrates on the performance of the MAO coatings were investigated using a scanning electron microscope (SEM), an X-ray diffractometer (XRD), energy-dispersive spectroscopy (EDS), the salt spray test, potentiodynamic polarization curves, and electrochemical impedance spectroscopy (EIS). The results show that the carbohydrates effectively inhibited spark discharge, so the anodized growth process, surface morphology, composition, and corrosion resistance of the MAO coatings were strongly dependent on the carbohydrate concentration. This is ascribed to the surface adsorption layer formed on the surface of the magnesium alloy. When the carbohydrate concentration was 10 g/L, smooth, compact, and thick MAO coatings with excellent corrosion resistance on the magnesium alloy were obtained.

Multi-functional and durable anti-corrosion coatings with hydrophobic, freeze time retardation and photothermal properties by means of a simple spraying method

In this study, a composite material consisting of perfluorinated quaternary silane-modified graphene oxide and modified CeO2 nanoparticles was prepared, and a hydrophobic, corrosion-resistant, self-cleaning and anti-icing composite coating was prepared by combining the composite material with polyphenylene sulfide (PPS) through high-temperature curing in a simple spraying method for the protection of iron sheets. The results show that the composite coating has excellent corrosion resistance, strong mechanical properties and certain photothermal properties. When the content of perfluorinated quaternary silane modified CeO2 nanoparticles with graphene oxide (P-GKC) was 10 wt%, the composite coating had a water contact angle of 145.6 ± 3° and a sliding angle of 5 ± 1°, with good hydrophobicity and low surface energy. Meanwhile, the hydrophobic modification of perfluoroquaternary silanes reduced the surface energy of the particles in the composite coatings and greatly improved the hydrophobicity. Surface temperature and laser irradiation tests of the composite coatings showed that the photothermal properties of the composite coatings were better than those of the single PPS and graphene oxide (GO) coatings, with good photothermal cycling stability.The Tafel curves and the EIS results showed that the PPS/10 wt% P-GKC composite coatings had the best corrosion resistance, with a corrosion current density of 5.01 × 10−9A cm−2. After 200 h of salt spray test in 3.5 % NaCl environment, the PPS/10 wt% P-GKC composite coating still has good substrate protection effect, which provides a practical basis for the research of composite coating anticorrosion.

Comparative corrosion analysis of acrylic precoated aluminum foil under natural exposure and neutral salt-spray (NSS) testing

Conducting research on the corrosion behavior of condenser fins is of great significance for evaluating the performance of the air conditioner during service. The corrosion behavior of precoated aluminum foil for air conditioner condenser fins after natural exposure test and neuter salt-spray (NSS) test were investigated through surface morphology, chemical composition, contact angle and electrochemical analysis. The results showed that there were significant differences between the microenvironment surrounding air conditioner condenser fins and the natural atmospheric environment. The operating status, the air conditioner model, and the ambient atmospheric conditions will influence the microenvironment of the fins. The precoated aluminum foils exhibit the identical same corrosion characteristics in both natural exposure test and NSS test with corrosion mainly observed in the edge region. Compared with the sample after NSS test for 60 days, the sample after natural exposure test for 2 year had lager corrosion extension distance of edge area, smaller low-frequency impedance modulus and larger contact angle, which indicated more severe corrosion. The comparative analysis of results indicates that the NSS test recommended by standards for a duration of 500–1500 h cannot accurately evaluate the service performance of precoated aluminum foil used in air conditioner in marine atmospheric environment.

In situ growth of flower-like ZnO onto graphene oxide for the synergistically enhanced anti-corrosion ability of epoxy coating

Two-dimensional graphene oxide (GO) has shown the favorable candidate as functional filler for enhancing the anticorrosive performance of epoxy coating, but its poor dispersion and low antimicrobial ability limited the further application in complex corrosive environment. To overcome these obstacles, a two-dimensional GO-based antimicrobial anticorrosion epoxy composite coating was developed via synergy of graphene oxide and zinc oxide. To achieve this goal, the flower-like ZnO with antimicrobial activity was situ grown on the surface of graphene oxide by hydrothermal route, which was further modified via the dopamine triggered chemical cross-linking with polyethyleneimine (GO-ZnO@DP). Thanks to the good dispersion and the excellent physical barrier property of the GO-ZnO@DP functional filler, the epoxy composite coating exhibited superior ability of corrosion resistance. With the addition of 1.0 wt% GO-ZnO@DP functional filler (G2/EP), the low frequency impedance modulus |Z|0.01Hz reached 1.57 × 109 Ω cm2 after immersion in 3.5 wt% NaCl medium for 30 days. Meanwhile, due to the introduction of flower-like ZnO, the composite coating exhibited the enhanced antibacterial properties toward the inhibitory experiment of E. coli. Besides, the results of salt spray test, EDS analysis, and mechanical properties strongly supported the long-term corrosion resistance of epoxy coating, which shows promising application of metal protection in the complicated corrosive environment.

Ni-based coating on 5083 aluminum alloy with Cu-Ni interlayer fabricated by ultra-high-speed laser directed energy deposition

Through the innovative design of interlayer connection materials, a high-performance wear-resistant and corrosion-resistant composite protective coating was successfully prepared on the surface of 5083 aluminum alloy using ultra-high-speed (0.5 m/s) laser energy deposition technology. By conducting orthogonal experiments and analyzing the coating morphology and non-destructive testing results, the optimal process parameters for preparing the Cu-Ni25 alloy interlayer and nickel-based alloy surface protection layer were determined. The bond strength and friction resistance of the composite coating and the substrate were tested by shearing and scratch tests. Furthermore, the wear and corrosion resistance of the nickel-based alloy protective layer and substrate were comparatively assessed using an abrasive wear tester, electrochemical workstation, and salt spray test chamber. The results show that the Cu-Ni25 alloy interlayer plays a good bridge role and realizes metallurgical bonding with the aluminum alloy matrix. Additionally, the addition of the nickel-based alloy surface protection layer yields a significant improvement in deformation resistance, wear resistance, and seawater corrosion resistance compared to the aluminum alloy substrate.

Synergistic impact of the functionalized graphene oxide (fGO) nano-sheets and Mn2+-doped zinc phosphate conversion film on the polyester coating corrosion protection properties

Corrosion protection is crucial for steel, and one effective method is applying organic coatings as a barrier between the steel and corrosive surroundings. However, defects and poor adhesion can compromise their effectiveness. Phosphating-based treatment is a widely used method to enhance corrosion resistance, but traditional processes are time-consuming. Recent advancements include low-temperature phosphating and nanoparticle-based accelerators. Graphene oxide (GO) nanoparticles have gained attention for improving corrosion resistance. The purpose of this study is to investigate the corrosion resistance of zinc phosphate conversion coatings on steel with functionalized graphene oxide (fGO) and Mn2+ cations, as well as polyester coatings. FT-IR, Raman, XRD, XPS, and FE-SEM analyses were conducted for thin film characterization. Furthermore, results show improved corrosion resistance for coated samples, especially with fGO and Mn2+. EIS, polarization tests, and salt spray tests confirm the enhanced protection. Evaluation of the intact and scratched coatings further demonstrates the barrier properties and self-healing ability. Overall, the study highlights the potential of incorporating nanomaterials and phosphating treatments to enhance the corrosion resistance of steel.

Corrosion resistance and microstructural characterization of Ti-Zr-V/waterborne resin composite conversion coating on 1060 aluminum alloy

A Ti-Zr-V/waterborne resin composite conversion coating (TZVRC) was prepared on an aluminum substrate using a simple and environmentally friendly coated-bake, non-washing one-step film-forming method. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, neutral salt spray (NSS) testing, and scanning electron microscopy (SEM) results indicated that TZVRC exhibited the best corrosion resistance and topcoat adhesion when the concentration of sodium orthovanadate in the composite conversion solution was 1 g/L. It also exhibited a relatively uniform and dense microstructure. The corrosion resistance of the coating is comparable to traditional chromate conversion coatings. The corrosion current density (icorr) is 0.1426 μA/cm², the corrosion rate is 0.0015 mm/year, the coating resistance (Rc) reaches 384 kΩ·cm², and the coating thickness is approximately 0.4 µm. Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that the upper part of the coating primarily consisted of cured waterborne resin, while the bottom part was mainly composed of insoluble inorganic substances. Additionally, there were concentration gradient variations in the distribution of inorganic components within the lower part of the coating. Near the interface between the aluminum substrate and the bottom of the coating, the main components were Al, AlPO4, Al2O3, and AlF3, while the upper layer of the inorganic substances primarily consisted of TiO2, ZrO2, complexes of V ions, AlPO4, Al2O3, and AlF3. This composite conversion coating not only possesses excellent corrosion resistance but also eliminates the post-film washing step, streamlining the process. Additionally, the composite conversion system, which combines waterborne resin with inorganic components, offers a potential solution for the integration of chemical conversion coatings and primers on aluminum surfaces.

Research on Nano-Titanium Modified Phenolic Resin Coating and Corrosion Resistance

Nano-titanium can be used in the field of anticorrosive coatings due to its excellent corrosion resistance. In this paper, phenolic resin was modified by nano-titanium using a physicochemical method. The nano-titanium-modified phenolic resin was used as a matrix to prepare the anticorrosive coating. The microstructures of the coatings were analyzed by Scanning Electron Microscope (SEM), X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). Raman and UV spectrum adhesion of the coating was tested by a scratching method. The corrosion behavior was studied by electrochemical workstation and salt spray test. The results showed that the corrosion resistance of pure phenolic resin coating was significantly improved by the nano-titanium-modified phenolic resin. The coating containing 4% titanium nanoparticles exhibited the best corrosion resistance, with the highest impedance and the smallest corrosion current. The coating remained intact after 480 h of salt spray, showing the best salt spray resistance performance.

Improving the Protection Performance of Waterborne Coatings with a Corrosion Inhibitor Encapsulated in Polyaniline-Modified Halloysite Nanotubes

Organic coatings provide an effective way to improve the corrosion resistance of metals. Traditional organic varnishes, however, either contain highly polluting or toxic components or lack self-healing ability. In this article, we report a feasible method of preparing polyaniline-modified halloysite nanotubes (PANI@HNTs). They were loaded with a corrosion inhibitor, benzotriazole (BTA), and were tested as multifunctional anticorrosion additives for environmentally friendly epoxy waterborne coatings. The PANI@HNTs were formed via the in situ polymerization of aniline in the presence of halloysites. The BTA loading was then carried out and reached up to 14.5 wt.%. The BTA retention ability of the PANI@HNTs was significantly improved in comparison to that of pure HNT. Electrochemical impedance spectroscopy (EIS) tests of the coatings immersed in a 3.5 wt.% NaCl solution showed that the barrier and corrosion inhibition effects were enhanced by two to four orders of magnitude with the incorporation of BTA-loaded PANI@HNTs. The salt spray tests on artificially scratched coatings revealed that the surfaces protected by varnishes doped with the BTA-loaded PANI@HNTs exhibited the lowest degree of corrosion compared to the control samples, illustrating the self-healing potential of the modified coatings.

Synergistic Effect of Nanoclay and Barium Sulfate Fillers on the Corrosion Resistance of Polyester Powder Coatings

Nanoclay has proven to be an active anti-corrosive additive due to the self-repairing effect from nanoclay swelling and expansion, except for its passive barrier effect due to the high aspect ratio. But it is still uncertain how these effects of nanoclay are intertwined with the other components in a complex coating system in corrosive environments. In this study, we examined the combined effects of nanoclays of two particle sizes with a commonly used cost-reducing filler, BaSO4. By employing neutral salt spray tests, electrochemical analysis, and surface characterization, we identified the optimal conditions for achieving a strong barrier effect. Surprisingly, a relatively low nanoclay dosage of 2% combined with BaSO4 filler exhibited synergistic behavior. Nanoclay not only compensated for the reduction in the barrier effect owing to the addition of BaSO4 by offering self-repairing and barrier effects, but also overcame the delamination issues observed at higher nanoclay dosages (4% and above). The coating panel with 2% larger nanoclay and BaSO4 showed two orders of magnitude higher pore resistance than the coating without nanoclay, remaining at 107 Ω∙cm2 after 25 days of immersion. As a result, this coating panel demonstrated significantly slower corrosion expansion and reached a lifetime of 2500 h when creepage exceeded 2 mm in salt spray tests. This study contributes to a full understanding and proper utilization of nanoclay for high-performance, smart anti-corrosive coatings.

INCIDENCE OF HEAT TREATMENT ON THE CORROSIVE BEHAVIOR OF AISI 316L AUSTENITIC STAINLESS STEEL

Heat treatments of AISI 316L samples were conducted at 900°C with slow cooling in air to induce varied precipitation of chromium-rich carbide particles at grain boundaries, resulting in a microstructure susceptible to intergranular corrosion. The corrosion behavior of the material in this state was investigated in a salt spray chamber containing 5% NaCl. The temperature inside the chamber was set at 35°C, while the saturated air temperature was recorded at 47°C. Samples were periodically extracted for observation and analysis using a stereoscopic magnifying glass, optical microscope, and scanning electron microscope. The results revealed the detrimental effect of chloride ions on the corrosion behavior of these stainless steels. Metallographic examination of corroded specimens after the salt spray test confirmed that the passive layer's breakdown was responsible for the intergranular corrosion occurring along preferential paths of chromium carbides.

Anticorrosive coatings made from polydopamine modified graphitic C3N4 composites with synergistic anticorrosion effects

Since uniform dispersion and robust interfacial compatibility of nanofiller with epoxy resin are the most critical parameters to improve the corrosion protection property, a new effective anticorrosion nanofiller [polydopamine (PDA)@g-C3N4-CeO2] is designed by stacking PDA modified g-C3N4 and nano-CeO2 with the help of a silane coupling agent. The structure and morphology of PDA@g-C3N4-CeO2 are characterized by FTIR, XRD, XPS, SEM, and TEM. Furthermore, the PDA@g-C3N4-CeO2 nanofiller is loaded within waterborne epoxy coating (WEC) and the corrosion resistance of the prepared nanocomposite coating is studied. It can be inferred from the dispersion test that g-C3N4 modified by PDA and nano-CeO2 exhibits excellent dispersion and compatibility in de-ionized water. The Electrochemical impedance spectroscope (EIS) results indicate that nanocomposite coating with PDA@g-C3N4-CeO2 exhibits the best corrosion resistance, and its low-frequency impedance (Zf=0.01Hz) is 1.78 × 109 Ω cm2, which is two orders of magnitude higher than that of pure WEC (4.27 × 107 Ω cm2). In the salt spray test, PDA@g-C3N4-CeO2/WEC also showed excellent long-term corrosion resistance with few corrosion products even after 600 h, which was consistent with the results of the EIS test. In addition, PDA@g-C3N4-CeO2/WEC also reflects the most fantastic adhesion strength (14.22 MPa), which is improved by 45.40% than that of pure WEC (9.78 MPa). Generally, the excellent protection properties of PDA@g-C3N4-CeO2/WEC are attributed to the presence of PDA and KH-550 modified nano-CeO2 on the surface of g-C3N4, which increase the compatibility and surface interactions between nanofillers and epoxy resin.

Molybdate-doped sulfonated-polyaniline (SPni.Mo) grafted CNT nano-particles for fabrication of a dual-functional epoxy composite coating with durable corrosion resistance function

Carbon nanotubes nano-particles modified with organic-inorganic hybrid inhibitors, i.e., sulfonated polyaniline doped with molybdate (OMC.SPni.Mo) was designed to improve the anti-corrosion capability of carbon nanotubes for application in an epoxy polymer coating. The ability to release the inhibitors from the OMC.SPni.Mo surface in the saline solution at different pHs was demonstrated by EIS and ICP techniques. Epoxy resin reinforced with this nanohybrid, (OMC.SPni.Mo.EPoxy) was applied to the steel plate. EIS test outcomes revealed that after 90 days of immersion, the OMC.SPni.Mo.EPoxy sample did not show a significant change in the Log|Z|10mHz (≥10.5 Ωcm2). The OMC.SPni.Mo.EPoxy coating active corrosion mitigation after scratching was evaluated by the EIS technique and accelerated salt spray test. In this case, the total resistance reached 106.200 Ω cm2, which is 118% more than the pure coating. The improvement of the coating resistance is due to the film development in the scratched area and the prevention of corrosive agents from reaching the metal surface. The enhancement of the barrier protection against the progress of harmful ions in the coating-substrate interface and the adhesion of the OMC.SPni.Mo.EPoxy coating to the substrate compared to the sample coated with epoxy was presented by cathodic delamination and pull-off tests.

Improved corrosion resistance properties of CSS-42 L alloy fabricated by strengthening grinding process

The present study focuses on the influence of the strengthening grinding process (SGP) on the corrosion resistance of CSS-42 L alloy. To this end, the surface and cross-sectional characteristics of samples before and after SGP treatment were examined. In this regard, the surface morphology, roughness, microstructure, and phase content were analyzed. The results demonstrate a dense surface layer and a high surface roughness in SGP-treated samples. Through electrochemical and salt spray tests, it is confirmed that SGP treatment for 3 and 6 min improves the corrosion resistance of samples. It was found that the highest corrosion resistance can be achieved after SGP treatment for 6 min. The enhanced corrosion resistance of the SGP-treated samples originates from the synergistic effects of various factors, including surface roughness, dislocation density, the presence of compressive residual stress, the precipitation of Cr-phases, and the deformation of a dense surface layer.