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Coatings on Light Alloys Substrate

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Metals and Alloys".

Deadline for manuscript submissions: closed (10 January 2023) | Viewed by 26271

Special Issue Editor

Prof. Dr. Hongxiang Li

E-Mail Website
Guest Editor
State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China
Interests: corrosion and protection of magnesium alloys, including corrosion- and wear-resistant coatings on the magnesium alloy substrates; degradable magnesium alloys; alloy design, microstructure and properties of casting aluminum alloys; soft-magnetic Fe-based amorphous alloys
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue of “Coatings on Light Metal Substrates” focuses on the significant developments and in-depth understanding in surface engineering technology to modify and improve the surface properties of magnesium, aluminum and titanium alloys for protection in aggressive environments or enhanced functional performance. Under the premise that the substrate is light metal, the scope of contributions is as follows:

  • Improvement and breakthrough of surface engineering technology, including cold and thermal spraying, plasma spraying, surface modification by directed energy techniques, such as ion, electron and laser beams, thermo-chemical treatment, wet chemical and electrochemical processes, such as plating, sol–gel coating, anodization, plasma electrolytic oxidation, etc.
  • Engineering application and/or function application of metallic, inorganic, organic and composite coatings.
  • Relationships among the processing, the structure and the properties/performance of coatings; the properties/performance contain friction performance, wear resistance (e.g., abrasion, erosion, fretting, etc.), corrosion and oxidation resistance, thermal protection, diffusion resistance, hydrophilicity/hydrophobicity, enhanced multifunctional performance for environmental, energy and medical applications, etc.
  • Theory and/or simulation of the preparation, the service or the failure of coatings; the theory or simulation can substantially advance our understanding on the formation process, the structure and properties of coatings on light metal substrates.

Prof. Dr. Hongxiang Li
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • light metal substrates
  • surface engineering technology
  • coatings
  • structure
  • properties and performance
  • engineering application

Published Papers (14 papers)

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Research

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23 pages, 7778 KiB  
Article
Numerical and Experimental Investigations of Cold-Sprayed Basalt Fiber-Reinforced Metal Matrix Composite Coating
by Sihan Liang, Yingying Wang, Bernard Normand, Yingchun Xie, Junlei Tang, Hailong Zhang, Bing Lin and Hongpeng Zheng
Materials 2023, 16(5), 1862; https://doi.org/10.3390/ma16051862 - 24 Feb 2023
Cited by 1 | Viewed by 1238
Abstract
The aluminum-basalt fiber composite coating was prepared for the first time with basalt fiber as the spraying material by cold-spraying technology. Hybrid deposition behavior was studied by numerical simulation based on Fluent and ABAQUS. The microstructure of the composite coating was observed on [...] Read more.
The aluminum-basalt fiber composite coating was prepared for the first time with basalt fiber as the spraying material by cold-spraying technology. Hybrid deposition behavior was studied by numerical simulation based on Fluent and ABAQUS. The microstructure of the composite coating was observed on the as-sprayed, cross-sectional, and fracture surfaces by SEM, focusing on the deposited morphology of the reinforcing phase basalt fibers in the coating, the distribution of basalt fibers, and the interaction between basalt fibers and metallic aluminum. The results show that there are four main morphologies of the basalt fiber-reinforced phase, i.e., transverse cracking, brittle fracture, deformation, and bending in the coating. At the same time, there are two modes of contact between aluminum and basalt fibers. Firstly, the thermally softened aluminum envelops the basalt fibers, forming a seamless connection. Secondly, the aluminum that has not undergone the softening effect creates a closed space, with the basalt fibers securely trapped within it. Moreover, the Rockwell hardness test and the friction-wear test were conducted on Al–basalt fiber composite coating, and the results showed that the composite coating has high wear resistance and high hardness. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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17 pages, 8909 KiB  
Article
Effects of Temperature and Pressure on Corrosion Behavior of HVOF-Sprayed Fe-Based Amorphous Coating on the Mg-RE Alloy for Dissolvable Plugging Tools
by Yijiao Sun, Hongxiang Li, Jun Yang and Jishan Zhang
Materials 2023, 16(3), 1313; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16031313 - 03 Feb 2023
Cited by 3 | Viewed by 1573
Abstract
To retard the degradation of the magnesium alloys for dissolvable ball seats, Fe-based amorphous coatings were deposited on dissolvable Mg-RE alloy substrates using high velocity oxygen-fuel spraying technology. The results show that the Fe-based amorphous coatings possess low porosity (0.82%) and high amorphous [...] Read more.
To retard the degradation of the magnesium alloys for dissolvable ball seats, Fe-based amorphous coatings were deposited on dissolvable Mg-RE alloy substrates using high velocity oxygen-fuel spraying technology. The results show that the Fe-based amorphous coatings possess low porosity (0.82%) and high amorphous contents (91.4%) and their corrosion resistance decreases with the increase of temperature or pressure. However, with the help of Fe-based amorphous coatings, the degradation time of dissolvable Mg-RE alloy has been significantly prolonged. In particular, the service life of coated Mg-RE alloy exceeds 360 h at temperatures below 50 °C and reaches 87 h at 120 °C and 80 atm. Under high temperature and high pressure, the compactness of passive films decreases and the chemical activities of ions and metal elements increase, leading to the degradation of corrosion resistance of Fe-based amorphous coatings. In long-term corrosion, the crystallized splats are prone to corrosion because of the multiphase structures. The corroded crystallized splats are connected to the inevitable pores by the corroded intersplat regions, resulting in the formation of corrosion channels and the corrosion failure of coatings. This study provides a useful guidance for the corrosion protection of dissolvable plugging tools made of magnesium alloys. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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16 pages, 3591 KiB  
Article
Anticorrosion Superhydrophobic Surfaces on AA6082 Aluminum Alloy by HF/HCl Texturing and Self-Assembling of Silane Monolayer
by Amani Khaskhoussi, Luigi Calabrese and Edoardo Proverbio
Materials 2022, 15(23), 8549; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15238549 - 30 Nov 2022
Cited by 4 | Viewed by 1154
Abstract
In this paper, the tailoring of superhydrophobic surfaces on AA6082 aluminum alloy by chemical etching in an HF/HCl solution, followed by silane self-assembling, was applied for enhanced corrosion protection in the marine field. In particular, different etching times were considered in order to [...] Read more.
In this paper, the tailoring of superhydrophobic surfaces on AA6082 aluminum alloy by chemical etching in an HF/HCl solution, followed by silane self-assembling, was applied for enhanced corrosion protection in the marine field. In particular, different etching times were considered in order to optimize the treatment effect. The results indicate that all the prepared surfaces, after silanization, were characterized by superhydrophobic behavior with a contact angle higher than 150°. The contact and sliding angles strongly depend on the surface morphology at varying etching times. The optimum was observed with an etching time of 20 s, where a microscale coral-like structure coupled with a homogeneous and ordered pixel-like nanostructure was obtained on the aluminum surface showing a Cassie–Baxter superhydrophobic behavior with a water contact angle of 180° and a sliding angle equal to 0°. All superhydrophobic surfaces achieved an enhanced corrosion protection efficiency and impedance modulus up to two orders of magnitude higher than the as-received AA6082 in simulated seawater. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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12 pages, 3095 KiB  
Article
Influence of Different Aqueous Media on the Corrosion Behavior of B4C-Modified Lightweight Al-Mg-Si Matrix Composites
by Neeraj Kumar, Ashutosh Sharma and Manoranjan Kumar Manoj
Materials 2022, 15(23), 8531; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15238531 - 30 Nov 2022
Cited by 5 | Viewed by 1247
Abstract
In this study, we have investigated the electrochemical corrosion behavior of boron carbide (B4C) ceramic-reinforced Al-Mg-Si matrix composites in various aqueous environments (NaOH, NaCl, HCl, and H2SO4). The samples were produced by the powder metallurgy (P/M) route [...] Read more.
In this study, we have investigated the electrochemical corrosion behavior of boron carbide (B4C) ceramic-reinforced Al-Mg-Si matrix composites in various aqueous environments (NaOH, NaCl, HCl, and H2SO4). The samples were produced by the powder metallurgy (P/M) route and the corrosion investigations were conducted by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) methods. The morphology of the as-prepared and corroded samples was examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies. The investigations revealed that the corrosion resistance of Al-Mg-Si composites is highest in NaCl medium due to a less negative corrosion potential, higher charge transfer (Rct) resistance, and lower double-layer capacitance (Cdl) as compared to other media. The SEM morphology suggests that B4C ceramics enhance corrosion resistance by forming a protective barrier layer of OH- and Cl- deposits in the composite and unreinforced alloy, respectively. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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15 pages, 5319 KiB  
Article
A Study of Early-Stage Corrosion Behavior of AZ91 Alloy and MAO-Coated Alloy in 3.5% NaCl Solutions
by Yuxiang Liu and Xiaoting Liu
Materials 2022, 15(22), 7909; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15227909 - 09 Nov 2022
Viewed by 818
Abstract
The early-stage (1 h) corrosion behavior of AZ91 alloy before and after microarc oxidation treatment in a 3.5% NaCl solution was revealed using open circuit potential, potentiodynamic polarization, electrochemical impedance spectroscopy, and the observations of corroded surfaces at different immersion time (5, 25 [...] Read more.
The early-stage (1 h) corrosion behavior of AZ91 alloy before and after microarc oxidation treatment in a 3.5% NaCl solution was revealed using open circuit potential, potentiodynamic polarization, electrochemical impedance spectroscopy, and the observations of corroded surfaces at different immersion time (5, 25 and 45 min). The coating offers excellent corrosion resistance for the substrate for 1 h immersion corrosion by serving as a physical barrier. For the alloy, pitting corrosion initiates easily, but propagates difficultly, due to the formation of oxides/hydroxides in the pits. By comparison, the localized corrosion of the coated alloy proceeds continuously via the through pores, and the newly formed corrosion products inside the pores are easily damaged. Based on the electrochemical results, the alloy exhibits quasi-uniform corrosion, and the coated alloy reveals localized corrosion, both of which are under cathodic control. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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17 pages, 6860 KiB  
Article
A Comparative Study on Microstructure and Properties of Ultra-High-Speed Laser Cladding and Traditional Laser Cladding of Inconel625 Coatings
by Yuhang Ding, Wenya Bi, Cheng Zhong, Tao Wu and Wanyuan Gui
Materials 2022, 15(18), 6400; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15186400 - 15 Sep 2022
Cited by 10 | Viewed by 2120
Abstract
In this study, ultra-high-speed laser cladding (UHSLC) and traditional low-speed laser cladding (LSLC) were employed to prepare high-quality Inconel625 coatings on 27SiMn substrates. UHSLC has cladding speeds of 30 m/min, which are 15 times faster than those of LSLC, and it produces a [...] Read more.
In this study, ultra-high-speed laser cladding (UHSLC) and traditional low-speed laser cladding (LSLC) were employed to prepare high-quality Inconel625 coatings on 27SiMn substrates. UHSLC has cladding speeds of 30 m/min, which are 15 times faster than those of LSLC, and it produces a much greater cladding efficiency, which is 13.9 times greater than LSLC. The microstructure of the Inconel625 coatings was investigated in detail utilizing field emission scanning electron microscopy (FESEM) and electron probe microanalyzer (EPMA). According to the FESEM results, UHSLC Inconel625 coatings have more refined crystals than LSLC Inconel625 coatings. Nevertheless, the EPMA results indicate that the UHSLC Inconel625 coatings exhibit much more severe elemental segregation. Moreover, the hardness, wear and corrosion resistance of Inconel625 coatings are significantly enhanced by increasing the laser cladding speed. Furthermore, the reasons for the differences in microstructure and properties of Inconel625 coatings prepared by UHSLC and LSLC were clarified by finite element simulation. UHSLC technique is, therefore, more suitable for preparing Inconel625 coatings on 27SiMn steel surfaces than LSLC. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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16 pages, 30006 KiB  
Communication
Single Dense Layer of PEO Coating on Aluminum Fabricated by “Chain-like” Discharges
by Liye Zhu, Wei Zhang, Haitao Liu, Lei Liu, Fuhui Wang and Ziping Qiao
Materials 2022, 15(13), 4635; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15134635 - 01 Jul 2022
Cited by 6 | Viewed by 1497
Abstract
Reducing the loose-layer-to-dense-layer ratio in PEO coatings on aluminum and its alloys is the key to improving their corrosion resistance and expanding their applications in the aerospace industry and other fields. In this paper, we describe the discharge evolution during the PEO process [...] Read more.
Reducing the loose-layer-to-dense-layer ratio in PEO coatings on aluminum and its alloys is the key to improving their corrosion resistance and expanding their applications in the aerospace industry and other fields. In this paper, we describe the discharge evolution during the PEO process in exhaustive detail and report the appearance of a novel “chain-like” discharge for the first time. We investigated the microstructure and composition of PEO coatings using a scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer (EDS) and an X-ray diffractometer (XRD). The results reflected that the coating composition changed from amorphous Al2O3 to crystalline γ-Al2O3 and α-Al2O3 phases with the evolution of the plasma spark discharge state. We evaluated the electrochemical behavior of the coatings using a potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. Under “chain-like” discharge, the icorr of the coating on Al was 8.564 × 10–9 A∙cm−2, which was five orders of magnitude lower than that of the sample without the PEO coating. Moreover, we evaluated the adhesion strength of the coatings at different stages using a pull-off test. The adhesion strength of the PEO coatings at stage V reached 70 MPa. Furthermore, the high content of α-Al2O3 increased the hardness of the coating to 2000 HV. Therefore, the “chain-like” discharge promoted the formation of a single dense layer with 2.8% porosity and that demonstrated excellent properties. We also propose a mechanism to explain the influence of the plasma spark discharge state on the microstructure and composition of the PEO coatings. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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15 pages, 7349 KiB  
Article
Reinforcing Mechanism of WC Particles in Fe-Based Amorphous Matrix Coating on Magnesium Alloy Surface
by Haoran Zhang, Hongyan Wu, Shanlin Wang, Yuhua Chen, Yongde Huang and Hongxiang Li
Materials 2021, 14(21), 6571; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14216571 - 01 Nov 2021
Cited by 2 | Viewed by 1581
Abstract
To protect magnesium alloy surfaces from wear and corrosion, an Fe-based amorphous coating was prepared on WE43 through the Ni60 interlayer by high-velocity oxygen-fuel (HVOF) spraying. The porosity was ~1%, and the amorphous content exceeded 90%. The wear and corrosion resistance of the [...] Read more.
To protect magnesium alloy surfaces from wear and corrosion, an Fe-based amorphous coating was prepared on WE43 through the Ni60 interlayer by high-velocity oxygen-fuel (HVOF) spraying. The porosity was ~1%, and the amorphous content exceeded 90%. The wear and corrosion resistance of the composite coating with WC particles wrapped in a Ni layer as the reinforcing phase were compared with that of the completely amorphous coating. The friction coefficient (COF) of the composite coating was 0.3, which is only half of that of the WE43 substrate, and the composite coating exhibited a more stable wear behavior than the completely amorphous coating. The corrosion tendency of the composite coating is lower than that of stainless steel, with a corrosion potential of −0.331 V, and the addition of WC particles did not deteriorate the corrosion resistance considerably. The bonding mechanism of the bonding interface between the amorphous structure and the particles of the reinforcing phase was investigated by transmission electron microscopy (TEM). Reinforcing particles were confirmed to form metallurgical bonding with the coating. It was found that the Ni layer showed excellent bonding performance in the form of a mixture that is amorphous and nanocrystalline. Therefore, the Fe-based amorphous composite coating on a magnesium alloy surface shows a potential protective effect. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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17 pages, 4870 KiB  
Article
High-Performance HVOF-Sprayed Fe-Based Amorphous Coating on LA141 Magnesium Alloy via Optimizing Oxygen Flow and Kerosene Flow
by Yijiao Sun, Weichao Wang, Hongxiang Li, Lu Xie, Yongbing Li, Shanlin Wang, Wenrui Wang, Jiaming Zhang and Jishan Zhang
Materials 2021, 14(17), 4786; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14174786 - 24 Aug 2021
Cited by 3 | Viewed by 1641
Abstract
To solve the problem of poor corrosion and wear resistance of Mg-Li alloys, Fe-based amorphous coatings were prepared by high velocity oxygen-fuel spraying technology (HVOF) on the LA141 magnesium alloy substrate with a Ni60 intermediate layer. The microstructure and performance of Fe-based amorphous [...] Read more.
To solve the problem of poor corrosion and wear resistance of Mg-Li alloys, Fe-based amorphous coatings were prepared by high velocity oxygen-fuel spraying technology (HVOF) on the LA141 magnesium alloy substrate with a Ni60 intermediate layer. The microstructure and performance of Fe-based amorphous coatings with different oxygen flow and kerosene flow were characterized and analyzed. The results demonstrate that there is an optimal oxygen/kerosene ratio where the porosity of Fe-based amorphous coating is the lowest. Moreover, the amorphous content increases with the decrease in the oxygen/kerosene ratio. In particular, when the oxygen flow is 53.8 m3/h and the kerosene flow is 26.5 L/h, the Fe-based amorphous coating possesses the lowest porosity (0.87%), the highest hardness (801 HV0.1), the highest bonding strength (56.9 MPa), and an excellent corrosion and wear resistance. Additionally, it can be seen that the Fe-based amorphous coating is composed of amorphous splats and amorphous oxides, but the Ni60 intermediate layer exhibits an amorphous and crystalline multi-phase structure. The high bonding strength of the coating is attributed to the low porosity of Fe-based amorphous coating and the localized metallurgical bonding between different layers. Finally, the mechanisms on corrosion and wear of Fe-based amorphous coatings are also discussed. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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13 pages, 6932 KiB  
Article
Wear and Corrosion Resistance of Plasma Electrolytic Oxidation Coatings on 6061 Al Alloy in Electrolytes with Aluminate and Phosphate
by Zhenjun Peng, Hui Xu, Siqin Liu, Yuming Qi and Jun Liang
Materials 2021, 14(14), 4037; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14144037 - 19 Jul 2021
Cited by 12 | Viewed by 2102
Abstract
Phosphate and aluminate electrolytes were used to prepare plasma electrolytic oxidation (PEO) coatings on 6061 aluminum alloy. The surface and cross-section microstructure, element distribution, and phase composition of the PEO coatings were characterized by SEM, EDS, XPS, and XRD. The friction and wear [...] Read more.
Phosphate and aluminate electrolytes were used to prepare plasma electrolytic oxidation (PEO) coatings on 6061 aluminum alloy. The surface and cross-section microstructure, element distribution, and phase composition of the PEO coatings were characterized by SEM, EDS, XPS, and XRD. The friction and wear properties were evaluated by pin-on-disk sliding tests under dry conditions. The corrosion resistance of PEO coatings was investigated by electrochemical corrosion and salt spray tests in acidic environments. It was found that the PEO coatings prepared from both phosphate and aluminate electrolytes were mainly composed of α-Al2O3 and γ-Al2O3. The results demonstrate that a bi-layer coating is formed in the phosphate electrolyte, and a single-layered dense alumina coating with a hardness of 1300 HV is realizable in the aluminate electrolyte. The aluminate PEO coating had a lower wear rate than the phosphate PEO coating. However, the phosphate PEO coating showed a better corrosion resistance in acidic environment, which is mainly attributed to the presence of an amorphous P element at the substrate/coating interface. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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13 pages, 38712 KiB  
Article
Preparation and Characterization of Hydroxyapatite Coating on AZ31 Magnesium Alloy Induced by Carboxymethyl Cellulose-Dopamine
by Yanxia Yang, Yuanzhi Wu, Yu Wei, Tian Zeng, Baocheng Cao and Jun Liang
Materials 2021, 14(8), 1849; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14081849 - 08 Apr 2021
Cited by 8 | Viewed by 2145
Abstract
Magnesium and its alloys have become potential implant materials in the future because of light weight, mechanical properties similar to natural bone, good biocompatibility, and degradability in physiological environment. However, due to the rapid corrosion and degradation of magnesium alloys in vivo, especially [...] Read more.
Magnesium and its alloys have become potential implant materials in the future because of light weight, mechanical properties similar to natural bone, good biocompatibility, and degradability in physiological environment. However, due to the rapid corrosion and degradation of magnesium alloys in vivo, especially in the environment containing chloride ions, the application of magnesium alloys as implant materials has been limited. Therefore, improving the corrosion resistance of magnesium alloy and ensuring good biocompatibility is the main focus of the current research. In this study, hydroxyapatite coating was prepared on magnesium alloy surface using carboxymethyl cellulose-dopamine hydrogel as inducer to improve corrosion resistance and biocompatibility. Surface characterization techniques (scanning electron microscopy, Fourier-transformed infrared spectroscopy, energy dispersive X-ray spectroscopy- and X-ray diffraction) confirmed the formation of hydroxyapatite on the surface of AZ31 alloy. Corrosion resistance tests have proved the protective effect of Carboxymethyl cellulose-Dopamine/hydroxyapatite (CMC-DA/HA) coating on the surface of AZ31 alloy. According to MC3T3-E1 cell viability and Live/Dead staining, the coating also showed good biocompatibility. The results will provide new ideas for the biological application of magnesium alloys. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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Review

Jump to: Research

68 pages, 7190 KiB  
Review
Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: PART I—Pre-Treatment and Conversion Coating
by Bahram Vaghefinazari, Ewa Wierzbicka, Peter Visser, Ralf Posner, Raúl Arrabal, Endzhe Matykina, Marta Mohedano, Carsten Blawert, Mikhail Zheludkevich and Sviatlana Lamaka
Materials 2022, 15(23), 8676; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15238676 - 05 Dec 2022
Cited by 13 | Viewed by 2809
Abstract
Corrosion protection systems based on hexavalent chromium are traditionally perceived to be a panacea for many engineering metals including magnesium alloys. However, bans and strict application regulations attributed to environmental concerns and the carcinogenic nature of hexavalent chromium have driven a considerable amount [...] Read more.
Corrosion protection systems based on hexavalent chromium are traditionally perceived to be a panacea for many engineering metals including magnesium alloys. However, bans and strict application regulations attributed to environmental concerns and the carcinogenic nature of hexavalent chromium have driven a considerable amount of effort into developing safer and more environmentally friendly alternative techniques that provide the desired corrosion protection performance for magnesium and its alloys. Part I of this review series considers the various pre-treatment methods as the earliest step involved in the preparation of Mg surfaces for the purpose of further anti-corrosion treatments. The decisive effect of pre-treatment on the corrosion properties of both bare and coated magnesium is discussed. The second section of this review covers the fundamentals and performance of conventional and state-of-the-art conversion coating formulations including phosphate-based, rare-earth-based, vanadate, fluoride-based, and LDH. In addition, the advantages and challenges of each conversion coating formulation are discussed to accommodate the perspectives on their application and future development. Several auspicious corrosion protection performances have been reported as the outcome of extensive ongoing research dedicated to the development of conversion coatings, which can potentially replace hazardous chromium(VI)-based technologies in industries. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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56 pages, 14024 KiB  
Review
Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: Part II—PEO and Anodizing
by Ewa Wierzbicka, Bahram Vaghefinazari, Marta Mohedano, Peter Visser, Ralf Posner, Carsten Blawert, Mikhail Zheludkevich, Sviatlana Lamaka, Endzhe Matykina and Raúl Arrabal
Materials 2022, 15(23), 8515; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15238515 - 29 Nov 2022
Cited by 14 | Viewed by 2718
Abstract
Although hexavalent chromium-based protection systems are effective and their long-term performance is well understood, they can no longer be used due to their proven Cr(VI) toxicity and carcinogenic effect. The search for alternative protection technologies for Mg alloys has been going on for [...] Read more.
Although hexavalent chromium-based protection systems are effective and their long-term performance is well understood, they can no longer be used due to their proven Cr(VI) toxicity and carcinogenic effect. The search for alternative protection technologies for Mg alloys has been going on for at least a couple of decades. However, surface treatment systems with equivalent efficacies to that of Cr(VI)-based ones have only begun to emerge much more recently. It is still proving challenging to find sufficiently protective replacements for Cr(VI) that do not give rise to safety concerns related to corrosion, especially in terms of fulfilling the requirements of the transportation industry. Additionally, in overcoming these obstacles, the advantages of newly introduced technologies have to include not only health safety but also need to be balanced against their added cost, as well as being environmentally friendly and simple to implement and maintain. Anodizing, especially when carried out above the breakdown potential (technology known as Plasma Electrolytic Oxidation (PEO)) is an electrochemical oxidation process which has been recognized as one of the most effective methods to significantly improve the corrosion resistance of Mg and its alloys by forming a protective ceramic-like layer on their surface that isolates the base material from aggressive environmental agents. Part II of this review summarizes developments in and future outlooks for Mg anodizing, including traditional chromium-based processes and newly developed chromium-free alternatives, such as PEO technology and the use of organic electrolytes. This work provides an overview of processing parameters such as electrolyte composition and additives, voltage/current regimes, and post-treatment sealing strategies that influence the corrosion performance of the coatings. This large variability of the fabrication conditions makes it possible to obtain Cr-free products that meet the industrial requirements for performance, as expected from traditional Cr-based technologies. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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51 pages, 12316 KiB  
Review
Chromate-Free Corrosion Protection Strategies for Magnesium Alloys—A Review: Part III—Corrosion Inhibitors and Combining Them with Other Protection Strategies
by Bahram Vaghefinazari, Ewa Wierzbicka, Peter Visser, Ralf Posner, Raúl Arrabal, Endzhe Matykina, Marta Mohedano, Carsten Blawert, Mikhail L. Zheludkevich and Sviatlana V. Lamaka
Materials 2022, 15(23), 8489; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15238489 - 28 Nov 2022
Cited by 14 | Viewed by 2311
Abstract
Owing to the unique active corrosion protection characteristic of hexavalent chromium-based systems, they have been projected to be highly effective solutions against the corrosion of many engineering metals. However, hexavalent chromium, rendered a highly toxic and carcinogenic substance, is being phased out of [...] Read more.
Owing to the unique active corrosion protection characteristic of hexavalent chromium-based systems, they have been projected to be highly effective solutions against the corrosion of many engineering metals. However, hexavalent chromium, rendered a highly toxic and carcinogenic substance, is being phased out of industrial applications. Thus, over the past few years, extensive and concerted efforts have been made to develop environmentally friendly alternative technologies with comparable or better corrosion protection performance to that of hexavalent chromium-based technologies. The introduction of corrosion inhibitors to a coating system on magnesium surface is a cost-effective approach not only for improving the overall corrosion protection performance, but also for imparting active inhibition during the service life of the magnesium part. Therefore, in an attempt to resemble the unique active corrosion protection characteristic of the hexavalent chromium-based systems, the incorporation of inhibitors to barrier coatings on magnesium alloys has been extensively investigated. In Part III of the Review, several types of corrosion inhibitors for magnesium and its alloys are reviewed. A discussion of the state-of-the-art inhibitor systems, such as iron-binding inhibitors and inhibitor mixtures, is presented, and perspective directions of research are outlined, including in silico or computational screening of corrosion inhibitors. Finally, the combination of corrosion inhibitors with other corrosion protection strategies is reviewed. Several reported highly protective coatings with active inhibition capabilities stemming from the on-demand activation of incorporated inhibitors can be considered a promising replacement for hexavalent chromium-based technologies, as long as their deployment is adequately addressed. Full article
(This article belongs to the Special Issue Coatings on Light Alloys Substrate)
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