Neutral Salt Spray Test Research Articles

Improvement of anti-corrosive and anti-oxidative properties of electroless Ni-P coating

ABSTRACTIn order to improve the anti-corrosive and anti-oxidative properties of electroless Ni-P coating (ENPC), a vanadium conversion coating (VCC) was fabricated on the surface of the ENPC. SEM images and EDX line scanning spectra indicate that as-prepared VCC is supposed to be a thin film with a thickness of a few nanometres. XPS analyses demonstrate that the VCC is mainly consisted of V2O5 or V2O5·nH2O. The acid exposure test data indicate that the VCC-treated ENPC, compared with the pristine one, demonstrates a highly enhanced anti-oxidative property. Furthermore, the result of neutral salt spray test manifests that the VCC-treated ENPC has also a highly enhanced anti-corrosive property, which is further confirmed by the result of electrochemical corrosion test.

Corrosion behavior of spangle on a batch hot-dip galvanized Zn-0.05Al-0.2Sb coating in 3.5 wt.% NaCl solution

The corrosion behavior of shiny and dull spangle on a batch hot-dip galvanized Zn-0.05Al-0.2Sb coating in an aerated 3.5 wt.% NaCl solution was evaluated by potentiodynamic polarization curves, electrochemical impedance spectroscopy and neutral salt spray test. Experimental results demonstrated that shiny spangle shows a better corrosion resistance than dull spangle. β-Sb3Zn4 particles precipitated on the spangle surface motivate the cathodic activity and thereby increase the corrosion rate of spangle in NaCl solution. Finally, the degradation mechanism and the role of galvanic protection of spangle have been discussed by a proposed corrosion model.

A novel CeO2/MgAl2O4 composite coating for the protection of AZ31 magnesium alloys

A novel CeO2/MgAl2O4 composite coating, fabricated via a cathode plasma electrolytic deposition (CPED) technique followed by hydrothermal synthesis, was developed in this study to explore its potential application as corrosion protection for AZ31 magnesium alloys. The microstructure observed through scanning electron microscopy indicated that reducing the duty cycle of the power source within a reasonable range during the CPED process was beneficial to form a uniform and dense MgAl2O4 coating, which served as an ideal adhesive matrix for a uniform CeO2 coating as the outermost layer. The results of electrochemical impedance spectra and neutral salt spray tests showed that the decoration of the CeO2 layer significantly improved the corrosion resistance of the CeO2/MgAl2O4 composite coating compared to the single MgAl2O4 coating and bare substrate. Cross-cut tests revealed that the adhesion of the MgAl2O4 coating and the CeO2/MgAl2O4 composite coating were both excellent due to the strong binding between the MgAl2O4 coating and the substrate.

Effect of Si addition on corrosion behaviors of Cu/Al dissimilar joint brazed with novel Zn-Al-xSi filler metals

Novel Zn-Al-Si filler metals were used to enhance the corrosion resistance of Cu/Al brazed joint. The corrosion behaviors of the joint were investigated by neutral salt spray test. The effect of Si addition on the corrosion behaviors of the joint was discussed, and the corrosion resistance was evaluated for the first time. The results showed that the thickness of the diffusion layer on Al side was remarkably reduced with the addition of Si. Meanwhile, the Zn element aggregation degree was alleviated because the Zn-Al eutectic was divided into narrow strips by scattered fine CuAl2 phases, especially the Zn-rich Zn-Al eutectic. Thinner diffusion layer suppressed the initiation and propagation of the stress corrosion crack, while the alleviated degree of Zn aggregation significantly slowed down the deepening and expansion rate of the corrosion pit. After 36h salt spray test, Zn-22Al-1.5Si joints turned out to possess the best corrosion resistance.

The Role of Lithium Salt Concentration in the Active Corrosion Protection of Aluminium Alloys

It has been demonstrated previously that lithium salts containing organic coatings offer effective active corrosion protection on AA2024-T3 alloys when exposed to neutral salt spray test for 168 hours [1, 2]. In the presence of a coating defect the lithium salts leach from the organic coating to the exposed metal substrate increasing the local pH to moderate alkaline conditions followed by the formation of a protective layer within the defect site [2, 3]. The lithium accumulation at the defect site and hence the formation of the protective layer is influenced by the inhibitor loading and solubility in the coating as well as the coating defect size. Three different surface compositions of the lithium protective layer have been recently identified as lithium-based layered double hydroxide (Li-LDH), lithium mixed pseudo-boehmite (Li-PB) and pseudo-boehmite (PB) each depending on the lithium leaching rate and the coating defect size [4]. For small defect sizes a high lithium concentration is hypothesized to result in the generation of Li-LDH. Furthermore, Li-PB is identified within moderate defect sizes and moderate inhibitor concentration and PB is generated within large defect sizes where low lithium concentrations are expected. On this basis, this paper describes the lithium active corrosion protection on aerospace aluminium alloys as a function of the inhibitor concentration. In doing so, commercial AA2198-T8 and AA2024-T3 aluminium alloys are immersed for 24 hours in lithium salt containing aqueous solutions at systematically varied lithium salts concentration from 10-6 M to 10-1 M. The alloys are then transferred to 10-1 M aqueous NaCl solution at near neutral pH conditions and either LPR measurements are performed as a function of time over 100 hours or anodic polarization is performed. The surface composition of the alloys after 24 hours immersion in lithium containing aqueous solution is also characterized. The surface composition and the electrochemical characteristics of each lithium passive layer generated is determined as a function of the lithium concentration. The surface composition of the passive layer ranges from PB to Li-PB and Li-LDH with increasing inhibitor concentration. The polarization resistance obtained as a function of time is correlated to the corrosion rate of each generated passive layer thus demonstrating the corrosion protection performance of Li-LDH, Li-PB and PB. The generation and corrosion protection performance of each passive layer is also demonstrated under relatively thin electrolyte layers mimicking the exposure of a coating defect and the leaching of lithium salt from the coating matrix under atmospheric conditions. Visser, P., et al., Study of the formation of a protective layer in a defect from lithium-leaching organic coatings. Progress in Organic Coatings, 2016. 99: p. 80-90.Visser, P., et al., Electrochemical Evaluation of Corrosion Inhibiting Layers Formed in a Defect from Lithium-Leaching Organic Coatings. Journal of The Electrochemical Society, 2017. 164(7): p. C396-C406.Visser, P., et al., Mechanism of Passive Layer Formation on AA2024-T3 from Alkaline Lithium Carbonate Solutions in the Presence of Sodium Chloride. Journal of The Electrochemical Society, 2018. 165(2): p. C60-C70.Visser, P., et al., The chemical throwing power of lithium-based inhibitors from organic coatings on AA2024-T3. Corrosion Science, 2019. 150: p. 194-206.

Study on Corrosion Resistance and Wear Resistance of Zn–Al–Mg/ZnO Composite Coating Prepared by Cold Spraying

Two composite coatings, Zn65Al15Mg5ZnO15 and Zn45Al35Mg5ZnO15, were prepared by the cold spray technique and were found to be compact, with no pits or cracks, based on scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) investigations. The results of the neutral salt spray (NSS) and electrochemical tests showed that the two composite coatings possess a suitable corrosion performance. However, the Zn45Al35Mg5ZnO15 composite coatings were more corrosion resistant and allowed a better long-term stability. In addition, they were found to exhibit the best wear resistance and photocatalytic degradation efficiency.

Production of ship steel—titanium bimetallic composites through explosive cladding

Titanium was combined with ship steel sheet through the explosive cladding technique using different explosive ratios. The effects of the explosive ratio on the microstructure, mechanical and corrosion properties of the ship steel-titanium bimetallic composites were investigated. The microstructural characterization of the bimetallic composites was studied by optical microscopy (OM), scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). The mechanical properties were determined through tensile-shear, impact toughness, bending, twisting and microhardness testing, while the corrosion behaviour was examined using neutral salt spray (NSS) tests. The microstructure studies revealed that a wavy joining interface was attained at higher explosive ratios, while a completely smooth interface was achieved at the lowest explosive ratio. In the microhardness tests, the highest hardness values were attained from both sides of the joining interface. Conclusions of the mechanical tests separation did not occur in the interfaces of the bimetallic composite specimens. In the corrosion test, the titanium was found to have higher corrosion resistance than the ship steel sheet. It was concluded that the mechanical and corrosion properties of the ship steel sheet can be enhanced by explosive cladding with titanium.

The Durability of an Organic-Inorganic Sol-Gel Interlayer in Al-GFRP-CFRP Laminates in a Saline Environment.

The aim of the study was to assess the selected properties of a hybrid organic–inorganic silane sol–gel coating (HSG) used in hybrid fiber metal laminates (FML) in a corrosion environment. The HSG coating on the aluminum alloy was produced using 3M™ AC130-2 formulation consisting of 3-glycidoxypropyl-trimethoxysilane (GPTMS) and tetra-n-propoxyzirconium (zirconium(IV) propoxide) (TPOZ). Laminates consisted of aluminum alloy AA2024-T3 sheets, with carbon fiber reinforced polymers (CFRPs) and a glass fiber reinforced metal–composite structure (GFRP). Potentiodynamic and polarization curve and impedance (EIS) tests were carried out on HSG at ambient temperatures after 1 h and 150 h of soaking. Neutral 0.5 M NaCl and 0.8 M NaCl solutions were used for open circuit potential (OCP) and potentiodynamic tests, and 0.5 NaCl was used for the EIS test. A neutral salt spray (NSS) test was applied to laminates with a 12 week exposure period. The results obtained revealed that the HSG coating did not provide sufficient protection against corrosion of the aluminum alloy in direct contact with an aggressive environment but was effective as an interlayer. Local aluminum sheet perforation did not lead to delamination at the metal–composite interface regardless of the type or configuration of the composite. This confirms the durability of HSG used in FMLs.

Corrosion protection of steel substrates by magnetron sputtered TiMgN hard coatings: Influence of surface morphology and Mg content on Mg release in NaCl solutions

TiMgN coatings with three different Mg contents (10, 20 and 35 at.%) were prepared by reactive magnetron co-sputtering. Three different coating microstructures have been studied by using i) polished and ii) sand-blasted sample surfaces and iii) by employing the Glancing angle deposition (GLAD) technique on polished substrates. The chemical composition was analyzed by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometry or by glow discharge optical emission spectrometry and coating morphology was characterized by SEM on focused ion beam sliced samples. To determine the Mg release from the TiMgN samples two techniques measuring the open circuit potential were employed: a) an in-situ technique by using a scanning flow cell coupled to an inductively coupled plasma mass spectrometer and b) an ex-situ technique, namely inductively coupled plasma optical emission spectroscopy. The results (measured Mg release) from these two analysis techniques are compared and discussed with respect to results obtained from corrosion studies performed in neutral salt spray tests. It was found that the lowest Mg release has been determined for polished and the highest for GLAD samples. A correlation between the amount and duration of Mg release with the corrosion behavior of the samples could be established and formerly proposed corrosion protection mechanisms could be confirmed.

Polyacrylic acid/Ca nanoparticles hybrid hydrosol: Synthesis, characterization and application in pretreatment layer

Pretreatment layers have attracted much attention due to their irreplaceable role in paint system. However, the commonly used pretreatment layers face with one common problem, which the environmental friendliness and excellent properties can not be simultaneous realization. This work reported one facile method to synthesize one stable polyacrylic acid/Ca nanoparticles hybrid hydrosol through the electrostatic interaction between polyacrylic acid and Ca2+. Ulteriorly, the fabricated stable hydrosol was utilized as one environmentally friendly pretreatment layer material to fabricate new generation pretreatment layer on cold-roll steel surface through immersion method. The electrochemical and microstructure results indicated that the polyacrylic acid/Ca hybrid hydrosol based pretreatment layer exhibited better anti-corrosion performance and higher root mean square roughness value than polyacrylic acid layer. Meanwhile, neutral salt spray test results reflected that the polyacrylic acid/Ca hybrid pretreatment layer based coating system exhibited better service performance than the no pretreatment or polyacrylic acid layer based coating system. Because of the environmental friendliness, good anti-corrosion performance and higher root mean square roughness value, the polyacrylic acid/Ca nanoparticles hybrid hydrosol based pretreatment layer are expected to act as substitutes for chromate and phosphate conversion layers and will find widespread application in metal surface pretreatment field.

Improved anti-corrosion performance of epoxy zinc rich coating on rusted steel surface with aluminum triphosphate as rust converter

Epoxy resin based zinc rich coating was thoroughly investigated with aluminum triphosphate as rust converter. About 10.39 MPa of adhesion strength was achieved on rusted steel surface without any complex surface pre-treatment even with 86 wt% of zinc content in dry film, which has resolved previous contradiction between adhesion strength and high zinc content. Only slight amounts of white rust was observed on coating surface after being exposed to neutral salt spray test for 500 h. Protective mechanism suggested that aluminum triphosphate could improve the barrier resistance of coating by converting surface rust into passive film, while high zinc content ensured its excellent cathodic protection.

Enhancement in the corrosive and tribological properties of the inner wall of 6063Al and CI pipes by thick multilayer Si-DLC coatings

Corrosion and wear on the inner wall of metal pipes is considered as a challenging issue for their service lifetime in application of delivery systems. Diamond-like Carbon (DLC) coating is a widely investigated material and one of the best choices to be used as protective coating. In this report, Thick multilayer Si-doped DLC (Si-DLC) coatings with high quality was deposited on the inner wall of 6063 aluminum alloy (6063Al/Si-DLC) and cast iron (CI/Si-DLC) pipes by hollow cathode plasma enhanced chemical vapor deposition (HC-PECVD). The structure of the as-deposited coatings on 6063Al and CI pipe are similar, which consists of 10 deposition periods. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests were employed to assess the corrosive resistance of 6063Al/Si-DLC and CI/Si-DLC in 3.5 wt% NaCl solution. The long-term corrosive resistance of the coatings system was measured by neutral salt spray test. Compared with bare 6063Al and CI pipes, 6063Al/Si-DLC and CI/Si-DLC possess excellent corrosion resistance and long-term stability when exposed to corrosive medium, which attributes to the deposition of the coatings on bare substrates. In addition, 6063Al/Si-DLC and CI/Si-DLC show lower and stable friction coefficients and lower wear rate. Consequently, the coatings system what afforded in this study is an extremely potential design to enhance the service life of 6063Al and CI pipes for industrial delivery.

Effect of Heat Treatment on Microstructure and Properties of Clad Plates 316L/Q370qE.

Mechanical properties of Q370qE carbon steel can be improved by cladding it with 316L stainless steel. After rolling these materials together, microstructure, hardness, shear strength, and corrosion properties of the cladded metals were evaluated. Hardness and shear tests were performed according to appropriate standards to evaluate the bonds. The results show that the remarkable diffusion of Ni and Cr formed a hard transition zone. The width of this diffusion zone increases with increasing temperature. The shear strength of the clad interface reached a minimum of 385 MPa. In addition, the surfaces of samples were examined by neutral salt spray (NSS) tests and potentiodynamic polarization tests to examine corrosion behavior. The 316L side primarily exhibited pitting corrosion, while the Q370qE side was dominated by uniform corrosion.

Characterisation and corrosion behaviour of WAP coating on 300M steel

ABSTRACTIn this work, a special water-based aluminium phosphate (WAP) coating containing primer and finishing layers was applied on 300M steel. The curing temperature of the primer layer was about 250°C and that of the finishing layer was 200°C. The aluminium phosphate binder in both primer and finishing layers was barely crystallised, and the most effective binding phases were Al and aluminium phosphate. WAP coating showed the formation of corrosion product after 1000 h of neutral salt spray test. The results of electrochemical tests showed that the corrosion potential of the WAP coating was significantly higher than that of the high-strength substrate, and the capacitance arc amplitude of the coating was larger than that the substrate. The protection efficiency of WAP coating for 300M steel was 69.1%.

ПЛАЗМОХИМИЧЕСКОЕ МОДИФИЦИРОВАНИЕ БЛОЧНЫХ ТЕПЛОИЗОЛЯЦИОННЫХ МАТЕРИАЛОВ С ДЕКОРАТИВНЫМ ПОКРЫТИЕМ

The impact of plasma of an arc plasmatron on plasmochemical modification of a two-layer heat-resistant decorative covering on the protecting foam glass blocks is investigated. The optimum technological parameters of plasma processing of such blocks with a preliminary basis of finely divided glass containers and high-quality glass breakage are determined. It is shown that the texture and quality of a two-layer heat-resistant decorative covering are affected by speed characteristics of the plasma torch. It is established experimentally that when the arc-plasma reflow rate is 5 mm /s, a continuous wavy coating is formed on the surface of the foam glass block, and at 10 mm /s – a continuous coating with even spill. Intermediate heat-resistant and basic compositions of decorative two-layer coating for plasma-chemical modification of enclosing blocks of heat-insulating materials have been developed. The intermediate heat-resistant structure includes the following ingredients: heat-resistant aluminous cement, crushed and fractioned high-aluminous refractory material, liquid glass. The basic structure includes mixture of fine ground glass powder of tare and high-quality glasses with the crushed high-aluminous refractory material. The following performance indicators are investigated: adhesion strength of the coating with the matrix, frost resistance, microhardness, acid resistance, water resistance, abrasion resistance, moisture resistance and resistance to neutral salt spray test.

Corrosion resistance and mechanism of one-component organic Zn15Al-rich coating

The anti-corrosion performance of Zn and Zn15Al organic coating was investigated mainly by neutral salt spray test and electrochemical impedance spectroscopy. X-ray diffraction, scanning electron microscope and energy disperse spectroscopy were applied to analyze the corrosion behavior of the coating during the test. The facilitated formation of protective corrosion product simonkolleite on the Zn15Al coating surface was observed. Also, layered double hydroxides (LDH) consisting of Zn2+ and Al3+ were detected at the interface of coating/steel substrate of Zn15Al. This LDH was believed to function as ion exchanger that prevents Cl− from contacting the steel substrate.

Environmentally-friendly superhydrophobic surface based on Al2O3@KH560@SiO2 electrokinetic nanoparticle for long-term anti-corrosion in sea water

Superhydrophobic surface has aroused wide concern over the years due to its extensive application prospect. However, a simple, cost-effective and environmental friendly preparation method is still lacking. Here, we present an effective approach to prepare a superhydrophobic surface for long-term metal corrosion protection. Positively charged SiO2 composite nanoparticles were successfully prepared by a simple and multiple ultrafiltration method firstly, after that the particles were sol-gel electrodeposited on steel to build micro-nano roughness surface, and then the surface was modified by cost-effective and fluorine-free chemical stearic acid with low energy surface. The results of wettability experiment show a strong repulsive force between the modified surfaces and water droplets, with static contact angles over 158°. The corrosion resistance and corrosion current density of the Al2O3@KH560@SiO2 composite film assessed by the electrochemical impedance spectroscopy (EIS) and the polarization and neutral salt spray test indicate that the corrosion rate of the metal is reduced and the corrosion performance of the matrix is improved at the same time.

Anticorrosion Properties of Zn–Al Composite Coating Prepared by Cold Spraying

In order to slow down the corrosion and wear of offshore equipment, the Zn–Al composite coating was prepared on Q345 substrate by cold spray technique. The mass fraction of Zn and Al in the raw material was 2:3. The microstructure of the original coating was observed by scanning electron microscopy (SEM) and was characterized by energy dispersive spectrometer (EDS). From the composite alloy coating obtained by cold spraying, it was observed that the Zn and Al particles were uniformly distributed without oxidation product, and the powder particles were significantly plastically deformed. The microstructure of the composite coating is very dense and has strong adhesion to the substrate. Neutral salt spray test (NSS) and electrochemical accelerated corrosion test results showed that Zn–Al composite coating can effectively provide corrosion protection.

Electrochemical impedance spectroscopy and corrosion point counting on metal sheet edges with different cathodic dip coat materials

Edge coverage with organic coatings is a very important but insufficiently investigated topic in the automotive industry. Several examinations in other scopes show an influence of different coating materials as well as the metal edge radii. For an improved understanding, the edge coating coverage of defined steel sheet edges is investigated regarding its corrosion protection potential in automotive use. Therefore, four different cathodic dip coat (CDC) materials are applied in different Mercedes‐Benz plants on well‐defined and topological analyzed edges. The coating thickness and edge coverage are determined in a non‐exposed state before a 7‐days exposure in a neutral salt spray (NSS) test. To quantify the behavior of the different materials edge coverage under corrosive load, electrochemical impedance spectroscopy and corrosion point counting are performed. The results demonstrate that the type of applied CDC‐material has a great influence on edge coating coverage as well as corrosion protection. A higher edge coverage causes a higher and more stable impedance and subsequently less counted corrosion points over the whole exposure time frame.

Corrosion Behavior of FeCrMoCBY Amorphous Coating Fabricated by High-Velocity Air Fuel Spraying

For the purpose of enhancing the corrosion resistance of AISI 1045 mild steel, (Fe48Cr15Mo14C15B6Y2, at.%) Fe-based amorphous alloy coating (Fe-AAC) has been fabricated via a high-velocity air fuel (HVAF) spraying process. The corrosive performances of Fe-AAC under electrochemical corrosive conditions and a neutral salt spray environment were investigated. Experimental results show that the Fe-AAC has a hardness of ~ 900 HV0.1, a crystallization temperature of ~ 950 K, and a thickness of 300 μm. The Fe-AAC shows better corrosion-preventing performances under electrochemical corrosive conditions compared with steel, such as a low corrosion current density of ~ 1.13 × 10−5 A and a corrosion potential of ~ − 0.458 V in NaCl solution. Under a neutral salt spray environment, Fe-AAC also exhibits outstanding long-term corrosion resistance. After 15 days of neutral salt spray tests, no obvious red rust or peeling can be found on the surface of Fe-AAC.