The corrosion protection of AA2024-T3 aluminium alloy by leaching of lithium-containing salts from organic coatings

2015 ◽  
Vol 180 ◽  
pp. 511-526 ◽  
Author(s):  
Peter Visser ◽  
Yanwen Liu ◽  
Xiaorong Zhou ◽  
Teruo Hashimoto ◽  
George E. Thompson ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Salt Spray ◽  
Protective Layer ◽  
Middle Layer ◽  
Organic Coating ◽  
Organic Coatings ◽  
Inhibition Mechanism ◽  
Dense Layer ◽  
Neutral Salt ◽  
Protective Layers

Lithium carbonate and lithium oxalate were incorporated as leachable corrosion inhibitors in model organic coatings for the protection of AA2024-T3. The coated samples were artificially damaged with a scribe. It was found that the lithium-salts are able to leach from the organic coating and form a protective layer in the scribe on AA2024-T3 under neutral salt spray conditions. The present paper shows the first observation and analysis of these corrosion protective layers, generated from lithium-salt loaded organic coatings. The scribed areas were examined by scanning and transmission electron microscopy before and after neutral salt spray exposure (ASTM-B117). The protective layers typically consist of three different layered regions, including a relatively dense layer near the alloy substrate, a porous middle layer and a flake-shaped outer layer, with lithium uniformly distributed throughout all three layers. Scanning electron microscopy and white light interferometry surface roughness measurements demonstrate that the formation of the layer occurs rapidly and, therefore provides an effective inhibition mechanism. Based on the observation of this work, a mechanism is proposed for the formation of these protective layers.

Characterization of a Chromium-Free Passivation Coating on Hot Dip Al-Zn Allay Coated Steel Sheets

2013 ◽  
Vol 634-638 ◽  
pp. 2931-2934
Author(s):  
Ping Yuan
Keyword(s):  
Salt Spray ◽  
Optical Emission ◽  
Acrylic Resin ◽  
Organic Coating ◽  
Neutral Salt ◽  
Coated Steel ◽  
Corrosion Performance ◽  
Steel Sheets ◽  
Coated Steel Sheet ◽  
Passivation Coating

The hot dip Al-Zn alloy coated steel sheet was passivated with chromium-free passivation solution which adopted the molybdate and acrylic resin as the main film-forming substances. The surface morphology and corrosion performance of the coating were studied experimentally by using glow discharge optical emission spectroscopy(GD-OES), scanning electron microscopy(SEM) and energy-dispersive X-ray spectroscopy(EDS), polarization curves and the neutral salt spray test. The GD-OES and SEM results show that the molybdate-containing thin organic coating is deposited on the substrate compactly and homogeneously without obvious tiny cracks. The test results of corrosion performance show that the corrosion potential and current density of the passive films decrease obviously in comparison with those of the substrate, and the corrosion resistance of the coating is comparable with that of the chromate passivation coating.

scholarly journals A Novel Accelerated Corrosion Test for Supporting Devices in a Floating Photovoltaic System

2021 ◽  
Vol 11 (8) ◽  
pp. 3308
Author(s):  
Chun-Kuo Liu ◽  
Zhong-Ri Kong ◽  
Ming-Je Kao ◽  
Teng-Chun Wu
Keyword(s):  
Corrosion Test ◽  
Salt Spray ◽  
Protective Layer ◽  
Photovoltaic System ◽  
Galvanized Steel ◽  
Neutral Salt ◽  
Accelerated Corrosion ◽  
Accelerated Corrosion Test ◽  
Type 304

Recently, countries from around the globe have been actively developing a new solar power system, namely, the floating photovoltaic (FPV) system. FPV is advantageous in terms of efficiency and cost effectiveness; however, environmental conditions on the surface of water are harsher than on the ground, and the regulations and standards for the long-term durability of supporting devices are insufficient. As a result, this study aims to investigate the durability of supporting devices through a novel type of accelerated corrosion test, copper-accelerated acetic acid salt spray (CASS). After an eight-day CASS test, the results demonstrated that only a small area of white protective layer on the SUPERDYMA shape steel was fully corroded and rusted. Moreover, five types of screw, fastened solidly on the SUPERDYMA shape steel, namely a galvanized steel screw capped with a type 316 stainless steel (SS) nut, a type 304 SS screw, a type 410 SS screw, a chromate-passivated galvanized steel screw, and a XP zinc–tin alloy coated steel screw, achieved varying degrees of rust. In general, the corrosion degree of the eight-day CASS test was more serious than that of the 136-day neutral salt spray (NSS) test. Therefore, the CASS test is faster and more efficient for the evaluation of the durability of supporting devices.

scholarly journals Influencing the anticorrosion efficiency of pigments based on zinc ferrite by conductive polymers

2018 ◽  
Vol 62 (3) ◽  
pp. 83-86
Author(s):  
K. Nechvílová ◽  
A. Kalendová
Keyword(s):  
Zinc Ferrite ◽  
Conductive Polymers ◽  
Paint Film ◽  
Conductive Polymer ◽  
Low Carbon Steel ◽  
Organic Coating ◽  
Metal Substrate ◽  
Organic Coatings ◽  
Inhibition Mechanism ◽  
Low Carbon

Abstract Generally, organic coatings which contain zinc ferrites are able to protect metal substrate, most often low-carbon steel, by inhibition mechanism. Conductive polymers are using a system of conjugated double-bonds to transfer a charge over the chain thereby providing their own electrical conductivity in the organic coatings. The charge from the chain in combination with the iron substrate generates electrons to the formation of passivation products on the surface of paint film. This paper is focused on combination of zinc ferrite with conductive polymer and using of synergic effect of these two components. The organic coatings were formulated from hematite and specularite on pigments concentration line 5, 10, 20 and 25 wt.% for better recognizing of the effectiveness of zinc ferrite component. The content of the conductive polymer was consistently set at 3 wt.% in each organic coating. A solvent-based epoxy-ester resin was used as a binder. The physico-mechanical and corrosion tests were performed for all samples. The corrosion signs were evaluated on the surface of coating and also on the surface of metal substrate. In the end, the efficiency was compared alone zinc ferrite and alone polymers and also their combinations.

Structures of Zinc-Manganese Phosphate Film and Organic Coating on Magnesium Alloys

2009 ◽  
Vol 610-613 ◽  
pp. 880-883 ◽  
Author(s):  
Wei Lan ◽  
Jian Chun Sun ◽  
An Ruo Zhou ◽  
Ding Fei Zhang
Keyword(s):  
Magnesium Alloys ◽  
Treatment Time ◽  
Ph Value ◽  
Surface Characteristics ◽  
Organic Coating ◽  
Organic Coatings ◽  
Neutral Salt ◽  
Manganese Phosphate ◽  
Salt Fog ◽  
Phosphate Film

The solution mainly containing Zn2+, Mn2+, Ni2+ and H2PO4- was used to prepare phosphate film on AZ31 magnesium alloys. The process was adjusted to the following parameters, PH value 3～4, temperature 25～40°C, treatment time 3～10 min. Surface characteristics and microstructure of the phosphate film were also investigated by SEM and XRD. The film can fit for organic coatings prepared with electrophoresis and painting.It is found that the coatings adhered well to the phosphate film, and the anti-corrosion abilities were improved. The coating has no change in 3% NaCl solution for 360h and in neutral salt fog for 168h, respectively.

scholarly journals Research on Microstructure and Corrosion Behavior of Zinc-Magnesium Coating by Powder Impregnation

2021 ◽  
Vol 2101 (1) ◽  
pp. 012057
Author(s):  
Qiuyuan Liu ◽  
Wendong Zhang ◽  
Juntao Jiang ◽  
Linjiang Yue ◽  
Wei Shen ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Phase Composition ◽  
Service Life ◽  
Current Density ◽  
Environmental Conditions ◽  
Salt Spray ◽  
Protective Layer ◽  
Neutral Salt ◽  
Large Area ◽  
Before And After

Abstract In order to improve the service life of railway fasteners under various environmental conditions, the Zn and Zn-Mg coating were prepared on the railway fastener gaskets by powder impregnation. XRD and SEM were used to characterize the phase composition, microstructure and morphology before and after the salt spray. The neutral salt spray test (NSST) and the electrochemical workstation were used to characterize the corrosion resistance of the two coatings. Results show that there was a large area of red rust on Zn coating after 480 hours of NSST, while there was no red rust on Zn-Mg coating after 1920 hours of NSST. The impedance of the Zn-Mg coating reached 1015.6 Ω·cm2, about 3.65 times of the Zn coating. Zn-Mg coating’ current density was 3.27 μA·cm−2, which was only 21% of the Zn coating. MgZn2 and Mg2Zn11 phases were easier to formed in Zn-Mg coating due to the infiltration of magnesium, forming a dense and protective layer, thereby greatly improved its corrosion resistance.

scholarly journals Aggressiveness of Different Ageing Conditions for Three Thick Marine Epoxy Systems

2021 ◽  
Vol 2 (4) ◽  
pp. 721-742
Author(s):  
Alexis Renaud ◽  
Victor Pommier ◽  
Jérémy Garnier ◽  
Simon Frappart ◽  
Laure Florimond ◽  
...  
Keyword(s):  
Salt Spray ◽  
Immersion Test ◽  
Organic Coating ◽  
Artificial Seawater ◽  
Galvanized Steel ◽  
Natural Seawater ◽  
Neutral Salt ◽  
Coating System ◽  
Coated Steel ◽  
Artificial Defect

Three different coated steel systems were aged in natural or artificial seawater, in neutral salt spray (NSS), and using alternate immersion tests in order to evaluate the aggressiveness of the different ageing conditions. Commercial epoxy coatings were applied onto steel (S355NL), hot-galvanized steel (HDG), and Zn-Al15 thermal spraying coated steel. The defect-free systems were immersed in artificial seawater at 35 °C for 1085 days and in natural seawater for 1200 days and were characterized by electrochemical impedance spectroscopy (EIS). Panels with artificial defects were immersed for 180 days in artificial seawater and, regarding adhesion, were evaluated according to ISO 16276-2. In parallel, the three coated systems were submitted to cyclic neutral salt spray (NSS) for 1440 h: defect-free panels were regularly evaluated by EIS, while the degree or corrosion was measured onto panels with artificial defect. After NSS, defect-free panels were immersed in artificial seawater at 35 °C for further EIS investigations. Finally, alternate immersion tests were performed for 860 days for the three defect-free coated systems and for 84 days for panels with a defect. The results showed that, for defect-free panels, immersions in natural or artificial seawater and NSS did not allowed us to distinguish the three different systems that show excellent anticorrosion properties. However, during the alternate immersion test, the organic coating system applied onto HDG presented blisters, showing a greater sensitivity to this test than the two other systems. For panels with a defect, NSS allowed to age the coatings more rapidly than monotone conditions, and the coating system applied onto steel presented the highest degree of corrosion. Meanwhile, the coating systems applied onto HDG and the thermal spray metallic coating showed similar behavior. During the alternate immersion test, the three coated systems with a defect showed clearly different behaviors, therefore it was possible to rank the three systems. Finally, it appeared that the alternate immersion test was the most aggressive condition. It was then proposed that a realistic thermal cycling and an artificial defect are needed when performing ageing tests of thick marine organic coating systems in order to properly rank/evaluate the different systems.

Plating Hard Chrome Plating Alternative Technologies - HVOF Tungsten Carbide Coating

2013 ◽  
Vol 712-715 ◽  
pp. 395-398 ◽  
Author(s):  
Yi Zheng
Keyword(s):  
Tungsten Carbide ◽  
Salt Spray ◽  
Protective Layer ◽  
Neutral Salt ◽  
Carbide Coating ◽  
Chrome Plating ◽  
Technology Preparation ◽  
The Matrix ◽  
Tungsten Carbide Coating ◽  
Hard Chrome

HOVF technology preparation of tungsten carbide coating, can be obtained the microhardness and neutral salt spray corrosion resistance superior to the protective layer of hard chrome plating, its own good toughness and high bonding strength of the matrix, itideal replacement for hard chrome plating technology

scholarly journals Design and Multidimensional Screening of Flash-PEO Coatings for Mg in Comparison to Commercial Chromium(VI) Conversion Coating

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 337
Author(s):  
Ewa Wierzbicka ◽  
Marta Mohedano ◽  
Endzhe Matykina ◽  
Raul Arrabal
Keyword(s):  
Corrosion Resistance ◽  
Corrosion Protection ◽  
Electrochemical Impedance ◽  
Salt Spray ◽  
Conversion Coating ◽  
Neutral Salt ◽  
Chromium Vi ◽  
Alkaline Electrolytes ◽  
Az31b Alloy ◽  
Plasma Electrolytic

REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) regulations demand for an expedient discovery of a Cr(VI)-free alternative corrosion protection for light alloys even though the green alternatives might never be as cheap as current harmful technologies. In the present work, flash- plasma electrolytic oxidation coatings (FPEO) with the process duration < 90 s are developed on AZ31B alloy in varied mixtures of silicate-, phosphate-, aluminate-, and fluoride-based alkaline electrolytes implementing current density and voltage limits. The overall evaluation of the coatings’ anticorrosion performance (electrochemical impedance spectroscopy (EIS), neutral salt spray test (NSST), paintability) shows that from nine optimized FPEO recipes, two (based on phosphate, fluoride, and aluminate or silicate mixtures) are found to be an adequate substitute for commercially used Cr(VI)-based conversion coating (CCC). The FPEO coatings with the best corrosion resistance consume a very low amount of energy (~1 kW h m−2 µm−1). It is also found that the lower the energy consumption of the FPEO process, the better the corrosion resistance of the resultant coating. The superb corrosion protection and a solid environmentally friendly outlook of PEO-based corrosion protection technology may facilitate the economic justification for industrial end-users of the current-consuming process as a replacement of the electroless CCC process.

scholarly journals Application of Commercial Surface Pretreatments on the Formation of Cerium Conversion Coating (CeCC) over High-Strength Aluminum Alloys 2024-T3 and 7075-T6

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 930
Author(s):  
Juan Jesús Alba-Galvín ◽  
Leandro González-Rovira ◽  
Francisco Javier Botana ◽  
Maria Lekka ◽  
Francesco Andreatta ◽  
...  
Keyword(s):  
Electrochemical Impedance ◽  
Salt Spray ◽  
Aluminum Matrix ◽  
Optical Emission ◽  
High Strength ◽  
Chemical Conversion ◽  
Conversion Coating ◽  
Neutral Salt ◽  
Corrosion Properties ◽  
Surface Pretreatment

The selection of appropriate surface pretreatments is one of the pending issues for the industrial application of cerium-based chemical conversion coatings (CeCC) as an alternative for toxic chromate conversion coating (CrCC). A two-step surface pretreatment based on commercial products has been successfully used here to obtain CeCC on AA2024-T3 and AA7075-T6. Specimens processed for 1 to 15 min in solutions containing CeCl3 and H2O2 have been studied by scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX), glow discharge optical emission spectroscopy (GDOES), potentiodynamic linear polarization (LP), electrochemical impedance spectroscopy (EIS), and neutral salt spray (NSS) tests. SEM-EDX showed that CeCC was firstly observed as deposits, followed by a general coverage of the surface with the formation of cracks where the coating was getting thicker. GDOES confirmed an increase of the CeCC thickness as the deposition proceed, the formation of CeCC over 7075 being faster than over 2024. There was a Ce-rich layer in both alloys and an aluminum oxide/hydroxide layer on 7075 between the upper Ce-rich layer and the aluminum matrix. According to LP and EIS, CeCC in all samples offered cathodic protection and comparable degradation in chloride-containing media. Finally, the NSS test corroborated the anti-corrosion properties of the CeCC obtained after the commercial pretreatments employed.

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