Surface Of AZ91D Magnesium Alloy Research Articles

Hydrothermal preparation of magnesium alloy surface composite coatings and its performance research

Magnesium alloys have great potential for industrial and aerospace applications due to their low density and high strength. Aiming at its defects of poor corrosion resistance and susceptibility to galvanic coupling corrosion in metal coatings, a composite coating was prepared on the surface of AZ91D magnesium alloy by the hydrothermal method. Scanning electron microscope, x-ray diffraction, and x-ray photoelectron spectroscopy were used to characterize the surface micromorphology, phase composition, and elemental valence and evaluate the adhesion of the coating to the substrate by the ASTM D3359-09 test standard. Electrochemical experiments were done in a 3.5% NaCl solution. The results show that there are nanoscale dense granular structures on the surface of the samples, and the main components of the coatings are Mg(OH)2, Al2O3, and MgSiO3. ASTM grade 4B is between coating and substrate. The corrosion rate of the best sample was reduced by a factor of 238.96 compared to the substrate, and the corrosion current density was reduced by two orders of magnitude. The corrosion rate and corrosion current of the samples after repeated friction did not change much compared with those before friction, which proved that the composite coating had better corrosion resistance and friction stability.

THE PREPARATION AND CHARACTERIZATION OF A LANTHANUM-BASED RARE EARTH CONVERSION COATING ON MAGNESIUM ALLOY AZ91D AND ITS DEGRADATION IN 3.5% NaCl SOLUTION

Magnesium alloys have a huge market and broad prospects due to their high specific strength, good ductility, and strong thermal conductivity. However, the active chemical properties of elemental magnesium and the negative standard electrode potential result in magnesium alloys being highly susceptible to corrosion and failure. Chemical conversion treatment of magnesium alloy can improve its corrosion resistance by preparing a chemical conversion film on its surface. Rare earth conversion treatment has the advantages of effortless process, moderate price, no pollution, good corrosion resistance, and synergistic effect with inorganic or organic additives, which is in line with the pursuit of “green chemical” in industrial production. At present, there is little research and application on lanthanum-based rare earth conversion coatings (La-RECC). This paper selects rare earth element lanthanum (La) to prepare La-RECC on the surface of AZ91D magnesium alloy through chemical conversion treatment. The microstructure, chemical composition, and protective properties of La-RECC were discovered, as well as their interrelationships, revealing the degradation process of La-RECC in 3.5% NaCl solution. La-RECC is composed of La(OH)3 and Mg(OH)2, exhibiting a crystal cluster structure with cracks, and there are a large number of needle-like crystals on the crystal cluster of La-RECC, with a thickness of 2.14 [Formula: see text]m. The degradation process of La-RECC can be divided into three stages: Rapid degradation, slow degradation, and complete degradation. The complete degradation time of La-RECC in 3.5% NaCl solution is 82.5[Formula: see text]h.

Effect of CNTs concentration on the microstructure and properties of B, Ni, CNTs co-doped diamond like carbon films

B, Ni, and CNTs co-doped diamond-like carbon (B, Ni, CNTs co-doped DLC) films were synthesized on the surface of AZ91D magnesium alloy by electrodeposition with low cost. The effect of CNTs concentration on the microstructure, microhardness, tribological properties and corrosion behavior of B, Ni, CNTs co-doped DLC films were evaluated. Results revealed that the B, Ni, CNTs co-doped DLC films were hydrogenated amorphous carbon films. Raman spectra showed that the D and G peaks of DLC films appear near 1330 cm−1 near 1580 cm−1, respectively. When the concentration of CNTs was 0.25 g/L, the CNTs were evenly distributed, making the structure of co-doped DLC films uniform, dense and flat. At this time, since the combined synergistic effect of reticulation of CNTs and the network-like structure of DLC films, the microhardness of the co-doped DLC films reached the maximum of 248.3 HV. The tubular structure of CNT supports and lubricates the substrate, which weakens the frictional resistance between the friction partners and reduces the friction coefficient to the lowest value of 0.128. The wear loss was the minimum with 0.1 × 10−5 kg/m, which is the result of CNTs exerting their self-lubricating properties to improve the wear resistance of the DLC film so that less wear occurs during the repeated friction process. Meanwhile, the positive corrosion potentials of B, Ni, CNTs co-doped DLC films indicate that the three elements co-doped DLC films can improve the corrosion resistance of magnesium alloy substrates.

One-step hydrothermal preparation of corrosion-resistant coatings with microsphere structure

Rapid corrosion rate is limiting the engineering application of magnesium alloys. In this paper, an attempt was made to produce a corrosion resistant coating on the surface of AZ91D magnesium alloy using hydrothermal method. The coating surface is covered with microspheres and has a dense structure, which effectively isolates the contact between the outside world and the substrate. The corrosion potential(E) raised from −1.57 V to −0.45 V compared to the bare sample. The corrosion current density and corrosion rate of the coating can be reduced by 6 orders of magnitude, and the polarization resistance raised by 6 orders of magnitude. The thickness of the coating is 45.4 μm at the moment, with a minimum of defects on the surface, resulting in excellent corrosion resistance in the immersion test. The coating also has good adhesion strength at 4B, which can expand the application range of magnesium alloy in corrosive environments.

One-step Preparation of Silicate Coatings on AZ91D Magnesium Alloy Surface for Boosting its Corrosion Resistance

One-step Preparation of Silicate Coatings on AZ91D Magnesium Alloy Surface for Boosting its Corrosion Resistance

Preparation of corrosion‐resistant composite coating on AZ91D magnesium alloy through hydrothermal method

AbstractThe high corrosion susceptibility of magnesium alloy has become a practical problem which restricts its wide application in many fields. To improve its surface properties, a composite coating has been successfully prepared on the surface of AZ91D magnesium alloy using a one‐step hydrothermal method. The coating surface possesses a dense structure in the form of scales and has an adhesion strength of 3B. The effect of different preparation conditions on the coating thickness and corrosion resistance is discussed. The coating heated at 180°C for 2 h showed the best corrosion resistance in a 3.5 wt% sodium chloride solution, with a reduction in corrosion current density of 5 orders of magnitude compared to the bare sample. This solution significantly improved the corrosion resistance of the magnesium alloy and helped to further realize the application of magnesium alloys in corrosive environments.

Effect of Y2O3 Addition on Microstructure and Properties of Laser Cladded Al-Si Coatings on AZ91D Magnesium Alloy

The effect of Y2O3 addition on the microstructure and properties of the laser cladded Al-Si alloy coating on the surface of AZ91D magnesium alloy was investigated in this study. The experimental results showed that the Al-Si + Y2O3 cladding layers contained α-Mg, Mg2Si, Al4MgY and a small amount of Al12Mg17 phases. The coarse dendrites, reticulated eutectic structures and massive phases in the coatings tended to be refined and gradually uniformly distributed with the increased amount of Y2O3. The introduction of Y2O3 into the cladding layer favored the improvement of microhardness and wear resistance due to the grain refinement strengthening and dispersion strengthening. The addition of Y2O3 also promoted the reduction of localized corrosion sites and made the corrosion surface smoother, implying that the corrosion resistance of the Y2O3-modified coatings was better than that of the unmodified cladding layer.

Analysis of microstructure, treatment pattern, and corrosion behaviour of AZ91D magnesium alloy processed by selective laser surface remelting

In this work, we show that selective laser surface remelting, apart from modifying the microstructure, can also act as a design method to treat the surface of AZ91D magnesium alloy with varying treatment patterns, thus providing a feasible approach to tailor the electrochemical behaviour and to improve its corrosion resistance. Two treatment patterns, spots and stripes, are designed, in which cases, the boundary ratio and geometrical complexity are analyzed and compared. Besides microstructure, Hydrogen evolution, and potentiodynamic polarization curves are studied. It is found that in the central treated area, corrosion is hindered by formation of the greatly refined β-Mg17Al12 continuous network, together with the uniform distribution of surface potential. As a comparison, in the boundary region, extensive micro/galvanic couples are detrimental to the corrosion resistance, due to the oriented dendritic microstructure. As a result, good corrosion resistance, 3–5 times higher than the as-received material, is obtained despite of the variation of treatment patterns and presence of extensive micro/galvanic couples in the boundary region, indicating that selective laser surface remelting could act as a feasible way to tailor the corrosion behaviour of AZ91D. It is suggested that this technique provides not only a metallurgical approach, and also a design one to improve the corrosion resistance of AZ91D, which may lead to numerous applications of both AZ91D and laser surface treatment.

Synthesis of a green inhibitor and its inhibition behavior on AZ91D magnesium alloy in distilled water

In this paper, a green inhibitor (pheophorbide) was synthesized, and its inhibition mechanism on AZ91D magnesium alloy in distilled water was studied by electrochemical methods, surface analysis technologies, quantum chemical calculation and molecular dynamics simulation. The effect of chloride ions on the inhibition behavior of pheophorbide was also discussed. The results showed that pheophorbide alleviated the corrosion of AZ91D magnesium alloy, and it still had good inhibition effect with the prolongation of immersion time.The addition of 0.5 mg/L chloride ion improved its inhibition efficiency, but reduced its long-term effectiveness. The adsorption of pheophorbide on the surface of AZ91D magnesium alloy conformed to Langmuir adsorption model. The pheophorbide molecules were adsorbed on the surface of AZ91D magnesium alloy in parallel.

Preparation and characterization of Nd-doped double-layer silane anticorrosion coating on AZ91D magnesium alloy surface

Abstract Magnesium alloys have found widespread application as engineering and functional materials in automobile, aerospace, electronics, and biomedical industries. However, these alloys are susceptible to corrosion, and the development of new anticorrosion coatings on Mg alloys surface is urgently needed. In this work, pristine and doped double-layer silane coatings were applied to the AZ91D Mg alloy surface in order to improve its corrosion resistance properties in a 3.5% NaCl solution. The doped silane coatings consisted of KH-550 as the bottom layer and Nd(NO3)3-doped bis-(γ-triethoxysilylpropyl)-tetrasulfide (BTESPT) as the top layer. The effect of Nd(NO3)3 concentration on the corrosion inhibition properties of silane coatings was studied, and the highest corrosion resistance was achieved when the Nd(NO3)3 concentration was 5 × 10−3 mol/L. Compared to the pristine coating, the doped coating had enhanced hydrophobicity with a water contact angle of 108° and, to the best of our knowledge, one of the lowest corrosion current densities (1.51 × 10−2 μA/cm2) reported to date for treated AZ91D. These significant improvements were attributed to the presence of the Si-O-Nd network in the doped coating, leading to the uniform and homogeneous nature and excellent anticorrosion properties of Nd-doped silane coating.

Electrodeposition and microstructure of Ni and B co-doped diamond-like carbon (Ni/B-DLC) films

Ni and B co-doped diamond-like carbon (Ni/B-DLC) films were synthesized on the surface of AZ91D magnesium alloy by electrodeposition under mild environment. The formation mechanism of Ni/B-DLC films was discussed. The microstructure of the films was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Results conveyed that the Ni-DLC and Ni/B-DLC films were hydrogenated amorphous carbon films. With the co-doping of Ni and B, the protruding mulberry-like structure of carbon-based films gave way to the compact and uniform granular structure. The intensity ratio (ID/IG) of D and G lines was decreased from 0.75 to 0.71. XRD patterns revealed that the doping of boron favored the sp3 hybridization of carbon atoms. Simultaneously, the infrared spectra demonstrated that hydrogen for Ni/B-DLC films was preferentially bonded with sp2 carbon atom. In addition, Ni/B-DLC films had excellent wear resistance, which was mainly attributed to the homogeneous and dense structure and considerable micro-indentation hardness.

A Facile Method to Prepare a Superhydrophobic Magnesium Alloy Surface.

The application of superhydrophobic materials has been handicapped by complex processes and poor environmental friendliness. Magnesium alloys are widely used in daily production due to their low density and good casting properties. A facile and environmentally friendly method was proposed to prepare a superhydrophobic layer with coral-like microstructure on the surface of AZ91D magnesium alloy by high temperature heating. The prepared superhydrophobic surface has a contact angle of 159.1° and a rolling angle of 4.8°. The corrosion current of superhydrophobic surface has been reduced by about two orders of magnitude relative to the magnesium alloy substrate and its inhibition efficiency is 96.94%, which demonstrates its great corrosion resistance. In addition, the superhydrophobic surface has great thermal stability. When the temperature rises to 190 °C, the contact is still above 150°. Excellent self-cleaning and advantages in preparation efficiency, environmental protection and cost-effectiveness will boost its good application prospects.

Characterisation and tribological properties of Stellite-coated magnesium alloy by high-velocity oxy-fuel

In the present study, the surface of AZ91D magnesium (Mg) alloy was coated with Stellite-1 powder by using the high-velocity oxy-fuel method and surface coatings were carried out at different heat inputs and spray distances. The cross-sections of the coating layers were examined by optical microscopy and scanning electron microscopy. The phase compositions and phases formed on the coating layers were determined by energy-dispersive X-ray spectroscopy and X-ray diffraction, respectively. Surface roughness, porosity percentages and microhardness were measured. The dry sliding wear and friction behaviour of the AZ91D and coated samples at 5.0, 7.5 and 10.0 N normal loads were determined by using a disc-on-disc wear test device. In the coating layers, hard oxide and carbide phases were detected. The surface roughness and porosity increased with decreasing heat input and increasing spray distance. The surface roughness of the coated samples was higher than the substrate. The microhardness values of coating layers were varied between 982 and 1449 HV0.1, and the sample with the highest hardness was the sample coated at high heat input and low spray distance. The wear resistance of coating layers reduced with decreasing microhardness, and it was much higher than that of AZ91D.

Process of environmentally-friendly direct electroless nickel plating on AZ91D magnesium alloy surface

Process of environmentally-friendly direct electroless nickel plating on AZ91D magnesium alloy surface

Production, Characterization and Surface Properties of Sr Doped Hydroxyapatite Coating on Magnesium Alloy by Hydrothermal Method

In this study, the surface of AZ91D magnesium alloy was coated with undoped and at different ratios strontium doped hydroxyapatite. Coatings were carried out at 180 °C in 3 hours. The surface roughness of the coated samples was determined and the microstructure of the phases forming on the coated surfaces were examined by scanning electron microscopy (SEM). The chemical composition of the phases formed on the coated surfaces was determined by energy dispersed X-ray spectroscopy (EDS). The phases formed on the surfaces were characterized by X-Ray diffraction (XRD) and Fourier transform infrared spectrometry (FT-IR). The AZ91D magnesium alloy was coated successfully with undoped and strontium doped hydroxyapatite by hydrothermal method. The highest surface roughness value was measured as Ra = 8.255 µm in 15% strontium doped sample. It was determined that the (Ca + Sr) / P ratios of the coatings were higher than the stoichiometric ratio of hydroxyapatite, 1.67. It was determined that the closest coating to the stoichiometric ratio was 10% Sr doped coating.

Corrosion resistance enhancement of magnesium alloy by N-doped graphene quantum dots and polymethyltrimethoxysilane composite coating

A composite coating of N-doped graphene quantum dots (N-GQDs)/polymethyltrimethoxysilane (PMTMS) is prepared on the surface of AZ91D magnesium alloy via electrodeposition and subsequent silane treatment. The microstructure of the N-GQDs/PMTMS composite coating is characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The corrosion resistance performance is investigated by electrochemical impedance spectroscopy (EIS) and immersion test in NaCl solution (3.5 wt%). The N-GQDs/PMTMS composite coating exhibits a significant enhancement of corrosion resistance due to the chemical bonding of N-GQDs coating with Mg substrate and PMTMS coating. The formation mechanisms and nature of the corrosion resistance of the N-GQDs/PMTMS coating are discussed.

Microstructure, mechanical properties and ELM based wear loss prediction of plasma sprayed ZrO2-MgO coatings on a magnesium alloy

Abstract In this study, the surface of AZ91D magnesium alloy was coated with ZrO2–wt.-% 22 MgO by the plasma spray method. The coatings were made at two different current levels (600 and 500 A) and three different spraying distances (120, 130 and 140 mm). The surface roughness was measured by a profilometer and hardness was measured via a microhardness test. Coated cross-sections were examined under an optical microscope (OM) and scanning electron microscope (SEM). The phases formed on the coating surfaces were detected by x-ray diffractometer (XRD). A dry sliding wear test was performed at 5, 7.5 and 10 N normal loads. Mg2Zr5O12, ZrO2, MgO, and Zr formed on the coating layers. Surface roughness and porosity percentages were enhanced by increasing the spray distance and decreasing current. The maximum microhardness value was reached at 1152 (HV0.1), and significant improvements were observed in the wear resistance of the coatings compared with that of the AZ91D. An extreme learning machine (ELM) algorithm, which is one of the machine learning algorithms, was applied to the wear loss data obtained. The success rate for the model designed using the ELM algorithm, was calculated as 0.9287 (R-squared).

A gradient Al/Ni-Cr-Al layer formed by direct current pulse metal inert gas welding combined laser cladding on AZ91D magnesium alloy

A gradient modified layer, containing an Al-Si interlayer and a Ni-Cr-Al top layer, was formed by direct current pulse metal inert gas welding combined laser cladding on AZ91D magnesium alloy. Firstly, the direct current pulse metal inert gas welding was used to prepare an interlayer with enough thickness on the surface of AZ91D magnesium alloy. After that, a pulsed YAG laser was applied to clad Ni-Cr-Al powders on the interlayer to form a top modified layer with higher micro-hardness and better corrosion resistance. The SEM, EDS and XRD results show that the interlayer is mainly composed of α-Al, Al + Al3Mg2 and Mg2Si while the top layer is mainly composed of α-Al, Al3Ni, Al45Cr7, Mg2Si and Al + Al3Mg2. Furthermore, Y2O3 was added to ameliorate the microstructure and properties of the gradient layer. The addition of Y2O3 could refine the grain size, forming uniform microstructure in the top layer. The micro-hardness of the top layer is about five times higher than that of the AZ91D substrate and two times higher than that of the interlayer. The micro-hardness and corrosion resistance of the top layer were enhanced with the addition of Y2O3.

Wear and Corrosion Resistance of Al0.5CoCrCuFeNi High-Entropy Alloy Coating Deposited on AZ91D Magnesium Alloy by Laser Cladding.

In order to improve the wear and corrosion resistance of an AZ91D magnesium alloy substrate, an Al0.5CoCrCuFeNi high-entropy alloy coating was successfully prepared on an AZ91D magnesium alloy surface by laser cladding using mixed elemental powders. Optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction were used to characterize the microstructure of the coating. The wear resistance and corrosion resistance of the coating were evaluated by dry sliding wear and potentiodynamic polarization curve test methods, respectively. The results show that the coating was composed of a simple FCC solid solution phase with a microhardness about 3.7 times higher than that of the AZ91D matrix and even higher than that of the same high-entropy alloy prepared by an arc melting method. The coating had better wear resistance than the AZ91D matrix, and the wear rate was about 2.5 times lower than that of the AZ91D matrix. Moreover, the main wear mechanisms of the coating and the AZ91D matrix were different. The former was abrasive wear and the latter was adhesive wear. The corrosion resistance of the coating was also better than that of the AZ91D matrix because the corrosion potential of the former was more positive and the corrosion current was smaller.

Effect of Electrolyte Constituent on Morphology and Composition of the Microarc Oxidation Coating on Magnesium Alloy

Microarc oxidation (MAO) coating was prepared on the surface of AZ91D magnesium alloy in Na2SiO4-NaOH-C3H8O3 based electrolyte. The morphology and composition of the coating with different electrolyte constituent were analyzed by SEM and XRD. The result showed that the MAO coating was composed of loose layer and dense layer. The coating mainly comprised MgO, Mg2SiO4 and MgAl2O4. When the Na2SiO3 concentration was 20g/L, the pores of the coating were very uniform and the coating surface was smooth with homogeneous pore. The coating with addition of NaF to the electrolyte had the maximum thickness of 17~25μm.