Search

The bottleneck challenge of laser‐cladded coating preparation of magnesium alloys is the low melting point of alloys. This greatly restricts the selection of coating material. In this article, the composition of Ni–Ti–Cu coating is designed by cluster line criterion, and the thermal properties of the coating are simulated by JMatPro software. Through the analysis of simulation results, the Ni51.6Ti34.4Cu14 coating is selected and successfully prepared on AZ91D magnesium alloy via laser cladding technology. Then the microstructure, wear resistance, and corrosion resistance of the coating are studied in detail. The results of X‐Ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and transmission electron microscope (TEM) demonstrated that there is a good metallurgical bond between the coating and the substrate, and the coating is mainly composed of Ni3Ti, TiNi0.8Cu0.2, and (Cu, Ni) solid solution phases. Also, there are no obvious pores and crack defects in the coating. Remarkably, AZ91D alloy showed significant improvement in corrosion resistance and wear resistance. Among them, the wear volume of the coating is decreased by 71.9% than that of AZ91D alloy. In particular, the corrosion current density of the coating is three orders of magnitude lower than that of AZ91D alloy. [ABSTRACT FROM AUTHOR]

Two kinds of layered double hydroxides inhibition materials were synthesized on graphene oxide, and applied to strengthen the Ni-based coating on Mg-Li alloy. The composition and release properties of corrosion inhibition materials were studied. The formation of passivated film and the corrosion resistance mechanism of coating were summarized. The results show that two kinds of corrosion inhibition materials had good release properties. The addition of corrosion inhibition materials was helpful to form Ni-based composite coatings with fine and dense cell clusters, which strengthened the corrosion resistance of the coating, especially for a long time. • Two kinds of graphene-based corrosion inhibition materials were synthesized. • Corrosion resistance of Ni-based coatings in different soaking time was studied. • Inhibition materials enhanced the corrosion resistance of coatings on Mg-Li alloy. • Passivation film formation and corrosion resistance mechanism were studied. [ABSTRACT FROM AUTHOR]

For the application of lightweight alloys, the corrosion and wear problems of magnesium-lithium (Mg-Li) alloys have always been important problems that cannot be ignored. The coupling protection of multiple technologies has gradually become a new trend. In this study, layered double hydroxides (LDH) nanosheet arrays were in-situ grown on Ni-P coating by the electroless plating technology combined with hydrothermal synthesis technology. The optimum deposition conditions (temperature-time-pH) were selected by orthogonal test. The surface morphology, structure, corrosion resistance and wear resistance of LDH/Ni composite coatings under different conditions were systematically studied by SEM, XRD, FT-IR, DSC, electrochemical and tribological tests. The growth mechanism of LDH suitable for Ni-P coating surface was proposed by analyzing the growth process of LDH nanosheet arrays. The results showed that the condition of 125 °C-12 h-13 was conducive to the growth of LDH nanosheet arrays. Compared with the Ni-P coating and the composite coating under other conditions, the LDH 125°C-12h-13 /Ni composite coating has the lowest self-etching current density (7.50 × 10−7 A·cm−2) and the average friction coefficient (0.35). The defect sealing effect and Cl− barrier property of LDH effectively improved the corrosion resistance of the coating. The frictional properties were improved by lubrication and heat absorption properties of LDH. In addition, it was found that the growth of LDH on the Ni-P coating surface followed the mechanism of "deposition nucleation-diffusion growth". • Nanosheet arrays in-situ coupled Ni-based coatings on Mg-Li alloy were prepared. • Optimum growth conditions of nanosheet arrays were selected by orthogonal test. • The composite coating had better corrosion and wear resistance for Mg-Li alloy. • Wear mechanism and growth mechanism of LDH nanosheet arrays were studied. [ABSTRACT FROM AUTHOR]

• A metallurgical AlCuTiVCr HEA coating was prepared on Mg-Li alloy. • Cu-Al layer can balance the thermal matching disparity among HEA layer and Mg-Li. • HEA coating consists of (V, Cr)-rich BCC 1 , Mg-rich BCC 2 , AlCu 2 Ti and β-Ti phases. • The corrosion resistance of Mg-Li alloy was significantly improved. AlCuTiVCr/Cu-Al lightweight high-entropy alloy gradient coating was successfully prepared by laser cladding to improve the corrosion resistance of Mg-Li alloy. The boundaries between AlCuTiVCr protective layer, Cu-Al transition layer and Mg-Li alloy substrate are distinct, forming an excellent metallurgical bonding. The gradient coating design has effectively balanced the thermal matching difference between HEA coating. The prepared AlCuTiVCr protective layer comprises (V, Cr)-rich BCC 1 , Mg-rich BCC 2 , AlCu 2 Ti and β-Ti phases. The Cu-Al transition layer is composed of β-Li, Cu 2 Mg and Al 2 Cu 3 phases. The corrosion potential of AlCuTiVCr protective layer (−0.46 V SEC) is 1.09 V SEC higher than that of Mg-Li alloy (−1.55 V SEC), while the corrosion current density of the protective layer (9.41 × 10−7 A cm−2) is about three orders of magnitude lower than that of the substrate (5.97 × 10−4 A cm−2). [ABSTRACT FROM AUTHOR]

As a lightweight material, the wide application of Mg-Li alloy is restricted by its corrosion resistance. Focusing on this, an innovative superhydrophobic composite coatings of nickel-based metal coupled with layered double hydroxides (LDHs) was prepared on Mg-Li alloy. The microstructure, hydrophobic property and corrosion resistance of coatings were investigated by SEM, TEM, XRD, FT-IR, AFM, contact angle tester and electrochemical test. The results indicated that the MgAl LDHs uniformly grown in situ on the NiP coating deposited on Mg-Li alloy through electroless plating and hydrothermal treatment. The MgAl LDHs with a complex honeycomb micro-nano structure improved the surface roughness of the composite coating to 126 nm. The two-step treatment achieved an excellent coupling between the metal-based coating and inorganic compounds. The low surface energy treatment of micro-nano structure on NiP coating surface with stearic acid (@SA) realized the superhydrophobic transition of the composite coating (WAC=154.27° ± 2.56°). Besides, MgAl LDHs showed better trapping properties for Cl-. Under the synergistic effect of anion capture and hydrophobic effect, the corrosion current density (1.35 ×10−7 A⋅cm−2) and impedance modulus of NiP/MgAl LDHs@SA coating were significantly better than those of NiP and NiP/MgAl LDHs coating. The superhydrophobic composite coating provided a better anticorrosion choice for Mg-Li alloy. [Display omitted] • A new superhydrophobic double-layer coatings were prepared on the Mg-Li alloy. • MgAl LDHs with uniform honeycomb structure were in situ grown on the NiP coating. • Modified by stearic acid, the double-layer coatings had good superhydrophobicity. • The superhydrophobic double-layer coatings showed excellent corrosion resistance. [ABSTRACT FROM AUTHOR]

Brush plating provides an effective method for creating a coating on substrates of various shapes. A corroded zirconium-based conversion coating was removed from the surface of a magnesium alloy and then replaced with new coatings prepared via brush plating. The structure and composition of the remanufactured coating were determined via x-ray photoelectron spectroscopy, x-ray diffraction, and Fourier transform infrared spectroscopy. The results revealed that the coatings consist of oxide, fluoride, and tannin-related organics. The composition of the coatings varied with the voltage. Furthermore, as revealed via potentiodynamic polarization spectroscopy, these coatings yielded a significant increase in the corrosion resistance of the magnesium alloy. The friction coefficient remained constant for almost 300s during wear resistance measurements performed under a 1-N load and dry sliding conditions, indicating that the remanufactured coatings provide effective inhibition to corrosion. [ABSTRACT FROM AUTHOR]

Microcapsules with self-healing coatings for corrosion protection of magnesium substrates have attracted tremendous interest due to their capability of preventing the propagation of cracks in protective coatings by releasing inhibitors from the microcapsules. Gelatin-chitosan microcapsules containing La(NO 3 ) 3 were prepared by complex coacervation. The morphology of the cerium-based conversion coating shows a globular structure with microcapsules distributing in the tiny cracks of the coating. In 3.5 wt% sodium chloride solution environment, the coating is damaged and microcapsules migrate into the damaged area, the triggering release of inhibitors supplement to the conversion coating. The cerium conversion coating with microcapsules shows a much higher corrosive resistance than the coating without microcapsules, and demonstrates the achievement of a self-healing performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • TiB/Ti 50 Zr 25 Al 15 Cu 10 medium-entropy alloy composite coating (MEACC) was successfully prepared on the surface of magnesium alloy by laser cladding. • La rare earth element was added into the self-designed Ti 50 Zr 25 Al 15 Cu 10 non-equiatomic medium-entropy alloy in the form of LaB 6. • The strengthening mechanism with LaB 6 addition was investigated. • The corrosion and wear resistance of magnesium alloy got huge improvement. The improvement of corrosion resistance and wear resistance levels is of great significance because of the far-ranging impacts of them on the further application of magnesium alloys. In this work, a novel TiB/Ti 50 Zr 25 Al 15 Cu 10 medium-entropy alloy composite coating (MEACC) was successfully prepared on the surface of magnesium alloy by laser cladding. The effect of LaB 6 content on microstructure, micro-hardness, wear resistance and corrosion resistance of Ti 50 Zr 25 Al 15 Cu 10 coatings was studied in detail. The results show that TiB/Ti 50 Zr 25 Al 15 Cu 10 MEACCs are mainly composed of α-Ti, BCC and TiB phases. With LaB 6 content increased, the microstructure of the coating is refined and homogenized. And when the addition amount is excessive, Cu 2 La clusters appear. The lattice distortion caused by La3+ with large ion radius leading to the formation of hard BCC solid solution, as well as the dispersion strengthening of TiB in-situ, the coating presents high micro-hardness and excellent wear resistance. Especially, the average micro-hardness values of Ti 50 Zr 25 Al 15 Cu 10 coating with 4 wt% LaB 6 is ∼679.4 HV 0.3 , which is about 11 times than that of the substrate (∼61.6 HV 0.3). Besides, TiB/Ti 50 Zr 25 Al 15 Cu 10 MEACC displays excellent corrosion resistance. The minimum corrosion current density is 8.52 × 10−7 A·cm−2, and the oxidation phenomenon emerged in the coating. The oxide film is mainly composed of the oxidation state of Ti, Zr, Al, Cu and the sub-oxide state of Cu. [ABSTRACT FROM AUTHOR]

[Display omitted] • CeO 2 nanoparticles modified GO composites were synthesized by hydrothermal method. • Electroless Ni-P coatings enhanced by modified GO were prepared on Mg-Li alloys. • The microstructure of coatings became uniform and dense after adding modified GO. • Adding modified GO was conducive to improving the wear resistance of coatings. • Modified GO significantly improved the corrosion resistance of coatings. A new strategy of CeO 2 nanoparticles integration with GO nanosheets (CeO 2 @GO composites) was adopted for reinforcing Ni-P coating on Mg-Li alloys. Besides, the effect of GO nanosheets and CeO 2 @GO composites as reinforced particles on the microstructure, corrosion resistance and wear resistance of Ni-P coating were investigated. CeO 2 nanoparticles with average size of 4.19 nm were uniformly synthesized on GO nanosheets by hydrothermal method. The cellular nodules of coatings were refined after adding GO nanosheets and CeO 2 @GO composites. Moreover, the compactness and flatness of CeO 2 @GO-Ni-P composite coating were better than that of GO-Ni-P composite coating. The average friction coefficient of CeO 2 @GO-Ni-P composite coating (0.331) was decreased by 17%, 35.5%, and 39.6% than that of GO-Ni-P composite coating, Ni-P coating and Mg-Li substrate, respectively. The addition of GO nanosheets and CeO 2 @GO composites both improved the corrosion resistance of coatings, while CeO 2 @GO-Ni-P composite coating has the best corrosion resistance. Compared with Mg-Li alloys, the self-corrosion potential of CeO 2 @GO-Ni-P composite coating (-0.35 ± 0.006 V) shifted to positive potential by 1.28 V, and the self-corrosion current density was reduced by two order of magnitude (1.41 ± 0.13 × 10-6 A⋅cm−2). This was mainly attributed to the synergistic effect of the CeO 2 nanoparticles on the GO nanosheets. [ABSTRACT FROM AUTHOR]

The new carboxylic acid-neodymium anhydrous conversion films were successfully prepared and applied on the AZ91D magnesium alloy surface by taking absolute ethyl alcohol as solvent and four kinds of soluble carboxylic acid as activators. The corrosion resistance of the coating was measured by potentiodynamic polarization test in 3.5 wt.% NaCl solution in pH 7.0. The morphology, structure, and constituents of the coating were observed by scanning electron microscope, energy dispersivespectrum, x-ray photoelectron spectrum, and Fourier infrared spectrometer. Results show that corrosion resistance properties of samples coated with four different anhydrous conversion films were improved obviously. The corrosion potential increased, corrosion current density decreased, and polarization resistance increased. Among these four kinds of conversion films the one added with phytic exhibits the best corrosion resistant property. The mechanism of anhydrous-neodymium conversion film formation is also analyzed in this paper. It reveals that the gadolinium conversion coating is mainly composed of stable NdO, MgO, Mg(OH), and carboxylate of Nd. And that the sample surface is rich in organic functional groups. [ABSTRACT FROM AUTHOR]

Aluminum bronze coatings were prepared on MBLS10A-200 magnesium-lithium alloy substrate by cold spraying technology to improve the surface properties of Mg–Li alloys. The microstructure, phase composition, microhardness, tribological properties and corrosion resistance of the coatings were systematically analyzed. The results show that aluminum bronze coatings are mainly composed of α phase. β phase in the original aluminum bronze powder disappeared in the coating due to the eutectoid transition of β→α + γ 2 during the cold spraying. Compared with the Mg–Li alloy substrate, the aluminum bronze coating exhibits the higher microhardness (222.88 HV 0.3) and wear resistance (friction coefficients, wear track widths and wear mass losses are 0.37, 0.79 mm and 2.47 mg, respectively). The dominant wear mechanism of the coatings was abrasive wear. In the electrochemical test, the corrosion current density of the aluminum bronze coating (3.07 × 10−5 A/cm2) was an order of magnitude lower than that of Mg–Li alloy substrate (6.15 × 10−4 A/cm2), indicating that the coating had superior corrosion resistance. The above analysis confirms that preparing a cold sprayed aluminum bronze coating has outstanding tribological and corrosion resistance properties. • Aluminum bronze coatings were prepared on Mg–Li alloy by cold spraying. • Aluminum bronze coatings are mainly composed of α phase. • The eutectoid transformation of β. →α + γ 2 occurred during the cold spraying process. • The wear and corrosion resistance of Mg–Li alloy are comprehensively improved. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, neodymium-based conversion coating is used as a substitute for toxic chromate conversion coating on AZ91D magnesium alloys. Its formation and growth were observed via SEM, EDS, XPS, electrochemical tests and weighting experiment. The influence of post-treatment on neodymium conversion coating was measured by FTIR and electrochemical experiments in terms of morphology, component, surface functional group and corrosion resistance. The dissolution of matrix and the deposition of neodymium/magnesium oxides compete with each other in initial time. Then the deposition of neodymium oxides dominates the process. Compact coating is obtained after 20min immersion and it is mainly made of neodymium oxides and a small amount of magnesium oxides/hydroxides. The coating post-treated is rich in OH− and PO4 3+. The post-treatment can improve the corrosion resistance of the neodymium conversion coating effectually examined by EIS. [Copyright &y& Elsevier]

Abstract: In this paper, a non-toxic Ce-based conversion coating was obtained on the surface of bio-medical AZ31 magnesium alloys. The micro-morphology of the coating prepared with optimal technical parameters and immersed in physiological solution (Hank''s solution) in different time was observed by scanning electron microscopy (SEM), composition of the cerium conversion coating and corrosion products in Hank''s solution were characterized by X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS), respectively. In addition, the corrosion property in Hank''s solution was studied by electrochemical experiment and immersion test. The results show that the dense Ce-based conversion coating is obtained on the surface of AZ31 magnesium alloys in optimal technical parameters and the conversion coating consists of a mass of trivalent and tetravalent cerium oxides. The cerium conversion coating can provide obvious protection of magnesium alloys and can effectively reduce the degradation speed in Hank''s solution. Also the degradation products have little influence on human body. [Copyright &y& Elsevier]

Abstract: A phytic acid conversion film with especial functional groups was proposed as the pretreatment layer between Ni–P coating and AZ91D magnesium alloy substrate, to replace the traditional pretreatment. In the process, the silane coupling agent was adopted as connector between conversion film and palladium ion with catalysis. The microstructure of the phytic acid conversion coatings was observed using scanning electronic microscopy, while the composition and functional groups were analyzed by energy dispersive spectrometer and Fourier transform infrared spectroscopy. The bonding between Si–OH of the silane coupling agent and hydroxyl of phytic acid was validated by X-ray photoelectron spectroscopy, and the existence of palladium ion was also verified. The subsequent Ni–P deposited on the layer was also characterized by its structure, morphology, and corrosion resistance. The results show that the Ni–P coatings with the phytic acid pretreatment on AZ91D magnesium alloy have good corrosion resistance. [Copyright &y& Elsevier]

Abstract: In this paper, a new innoxious and pollution-free chemical protective coating for magnesium alloys, phytic acid conversion coating, was prepared. The conversion coatings are found to have high cover ratio and no cracks are found by atomic force microscopes (AFM) and scanning electron microscopy (SEM). The main elements of the conversion coatings are Mg, Al, O, P and C by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The chemical state of the elements in the coatings was also investigated by Fourier transform infrared spectroscopy (FTIR). AES depth profile analysis suggests that the thickness of the conversion coating is about 340nm. The corrosion resistance of the coatings was evaluated by polarization curves. The results indicate that the corrosion resistance for the conversion coated AZ91D magnesium alloys in 3.5% NaCl solution increases markedly. The mechanisms of corrosion resistance and coatings formation are also discussed. [Copyright &y& Elsevier]

[Display omitted] • A multi-step ultrasonic assisted laser cladding for Mg-Li alloy was proposed. • A metallurgical Ni 2 MnCuSnAl 0.1 MPEA coating was prepared on Mg-Li alloy. • Typical gradient microstructure was obtained in Ni 2 MnCuSnAl 0.1 MPEA coating. • The corrosion-resistance and wear-resistance of Mg-Li alloy were improved. The evaporation and dilution of substrate are the key deficiencies that limit the performance of laser-cladded coatings on Mg-Li alloys (or Mg alloys). In order to overcome these drawbacks, in this work, a novel Ni 2 MnCuSnAl 0.1 multi-principal element alloy (MPEA) coating and a multi-step ultrasonic assisted laser cladding technique were proposed. Dense metallurgical Ni 2 MnCuSnAl 0.1 MPEA coatings were successfully synthesized on Mg-Li alloy. Typical gradient microstructure of low-diluted layer, diffusive layer and interfacial layer were obtained in the coating. The low-diluted layer was composed of BCC solid solution, Ni 2 MnAl and Ni 2 MnSn while the diffusive layer and interfacial layer showed an interactive microstructure of Mg-CuMg 2 eutectic, Ni 2 MnAl, Li 2 MgSn/SnMg 2 and Mg/Mg-Li substrate. The corrosion potential of Ni 2 MnCuSnAl 0.1 MPEA coating (-108 mV SHE) was 1283 mV SHE higher than that of Mg-Li alloy (-1391 mV SHE), while the corrosion current density of the coating (5.85 × 10−7 A·cm−2) was about three orders of magnitude lower than that of Mg-Li alloy (1.12 × 10−4 A·cm−2). The micro-hardness gradually increased from the substrate to the coating, and the average micro-hardness of the coating was ~ 541.2 HV 0.2 , which is about 10 times higher than that of Mg-Li alloy (~57.8 HV 0.2). The wear resistance of Mg-Li alloy was also improved approximately 10 times by cladding Ni 2 MnCuSnAl 0.1 MPEA coating. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the phytic acid conversion coating, a new environmentally friendly chemical protective coating for magnesium alloys, was prepared. The influences of phytic acid concentration on the formation process, microstructure, chemical state and corrosion resistance of the conversion coatings on AZ91D magnesium alloy were investigated by means of weight gain measurement, field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS), respectively. And the depth profile of all elements in the optimal conversion coatings was analyzed by auger electron spectroscopy (AES). The results show that the growth, microstructure, chemical state and corrosion resistance of the conversion coatings are all obviously affected by the phytic acid concentration. The concentration of 5gl−1 corresponds to the maximum weight gain. The main elements of the coating are Mg, Al, O, P, and C, which are distributed gradually in depth. The functional groups of conversion coatings formed in higher concentration phytic acid solution are closer to the constituent of phytic acid than those formed in lower concentration phytic acid solution. The coatings formed in 1–5gl−1 are integrated and uniform. However, those formed in 20–50gl−1 have some micro-cracks on the α phase. The coating formed in 5gl−1 has the best corrosion resistance, whose open circuit current density decreases about six orders than that of the untreated sample, although the coatings deposited in 1–20gl−1 can all improve the corrosion resistance of AZ91D. [Copyright &y& Elsevier]

Abstract: In this paper, Hf–Si–N films were deposited on AZ31 magnesium alloys by ion beam assisted deposition (IBAD) technology. The phase structure, chemical valence state and nano-mechanical property of the films were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and nano-indentation test, respectively. The corrosion resistance in physiological solution was studied by electrochemical system. The results show that the main phases of the films are HfN phase and Si3N4 phase. And the films have good corrosion resistance in physiological solution. [Copyright &y& Elsevier]

Abstract: The microstructure of chrome-free neodymium-based conversion coating on magnesium alloy was investigated and the corrosion resistance was evaluated as well. The micro-morphology, transverse section, crystal structure and composition of the coating were observed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), respectively. The corrosion resistance was evaluated by potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS). The results revealed that the morphology of neodymium conversion coating is of crack-mud structure. Tiny cracks distribute in the compact coating deposited by neodymium oxides. EDS results characterize that the coating is made of neodymium oxides. The potentiodynamic polarization curve, EIS and OCP indicate that the neodymium conversion coating can improve the corrosion resistance of magnesium alloys. [Copyright &y& Elsevier]