Mn Alloy Coatings Research Articles

Modulating tribological properties and degradation rate in Hank's solution of Zn–Mn alloys electrodeposited on Mg with variable Mn content

Zn–Mn alloy coatings with small amounts of Mn (Zn-0.19 wt.% Mn, Zn-0.21 wt.% Mn, Zn-0.26 wt.% Mn and Zn-0.34 wt.% Mn) were formed by electrodeposition, onto pre-treated Mg substrates (Mgt) covered with a Zn film (Zn/Mgt). The chemical composition in depth profiles, morphological and structural characteristics of the Zn–Mn coatings on Zn/Mgt (labeled as Zn–Mn/(Zn/Mgt)) were analyzed using Glow Discharge Optical Emission Spectroscopy (GD-OES), Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDS), and X-ray diffraction (XRD). When the manganese content was greater than 0.19 wt.%, the results reveal the formation of two Zn–Mn phases: η-ZnMn and ζ-MnZn13; while the formation of the ζ-MnZn13 phase was favored by increasing the Mn content in the alloy. On the other hand, microhardness, wear resistance, and coefficient of friction significantly increase when coating Zn/Mgt substrate with the Zn–Mn alloy. The corrosion performance of this alloy was evaluated by potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The degradation rate in Hank's solutions of the pristine Mg substrate (0.29 mm yr−1) decreases due to the Zn–Mn coating. Furthermore, the degradation rate of Zn–Mn was further decreased from 0.051 to 0.022 mm yr−1, by varying the amount of Mn in the Zn–Mn alloy from 0.19 to 0.26 wt.% Mn, respectively. However, the rate of degradation increases up to 0.064 mm yr−1 at higher Mn content, Zn-0.34 wt.% Mn. Therefore, the microhardness, wear volume, and degradation rate of Zn–Mn/(Zn/Mg) in Hank's solution can be modulated by varying the Mn composition in the alloy.

Production of Al–Mn/WC Composite Coatings with Electrodeposition in AlCl3–NaCl–KCl–MnCl2 Molten Salts

The hardness and wear resistance of amorphous Al–Mn alloy coatings can be improved by incorporating ceramic particles into them to extend their application. In this paper, Al–Mn/WC composite coatings have been prepared with electrodeposition in stirred AlCl3–NaCl–KCl–MnCl2 molten salts at 180 °C with the addition of WC particles. The effects of stirring speed (400–700 rpm) and cathode current density (15–75 mA/cm2) on the produced Al–Mn/WC composite coatings have been studied. At 600 rpm and 700 rpm, the Al–Mn/WC composite coatings exhibited the best uniform distribution of the embedded WC particles, with the tested microhardness value up to 650 HV0.1, compared with 530 HV0.1 of the Al–Mn alloy. Moreover, under various cathode current densities, the best quality of the Al–Mn/WC composite coating was obtained at 55 mA/cm2, with a homogeneous distribution of WC particles and the highest microhardness value (670 HV0.1). It is expected that this method could be extended to be applied for the preparation of aluminum-based and magnesium-based ceramic composite coatings.

Hardness and corrosion resistance of Zn−Mn/Al2O3 composite coatings produced by electrochemical deposition

The aim of this study is development and characterization of the novel Zn-Mn/Al2O3 composite coatings. The coatingswere electrodeposited with constant current density on steel, from chloride solution, without any commercial additives. TheZn−Mn alloy coatings that show high corrosion resistance, may be used in future as an alternative to cadmium coatings.However, the pure Zn and Zn alloy coatings are characterized with poor mechanical properties. Therefore, in this work thealumina particles were incorporated into the Zn-Mn matrix, and the hardness and corrosion resistance of the obtainedcomposite coatings were tested. The mechanical and ultrasound agitation were used to achieve good dispersion of platingsolution and homogeneous co-deposition of second phase. The goal was to examine the effect of the agitation type in bath,on the attributes of the deposited composite coatings. The incorporation of Al2O3 particles was enhanced when themechanical agitation of the solution was applied. However, in case that this agitation method was used, the agglomeration ofthe alumina particles occurred. In contrast, when an ultrasonic agitation of the plating solution was applied, the uniformdistribution of the alumina particles could be achieved. The presence of particles in the matrix, along with appliedultrasound, resulted in grain refinement and homogeneous microstructure. The Al2O3 nanoparticles incorporated in Zn-Mnalloy matrix, resulted in a significant increment in the indentation hardness and a modest increase in the coating corrosionresistance. However, the coating hardness increased with alumina addition, only in case when an ultrasonic agitation of theelectrodeposition solution was used.

Wear Resistance of Electrodeposited Ni–Mn–SiC Composite Coatings

To improve the wear resistance of type 45 steel surfaces, Ni–Mn alloy coatings are prepared through electrodeposition under different sodium citrate concentrations based on which SiC particles of varying concentrations are added to prepare Ni–Mn–SiC composite coatings. The coatings are characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, microhardness testing, surface roughness meter, composite material surface performance testing, and laser scanning confocal microscopy. The results show that adding an appropriate concentration of sodium citrate into the electrolyte can significantly improve the Mn content in the coatings; however, an excessively high concentration increases the residual stress of the coatings and induces cracks on the surface. When the sodium citrate concentration is 40 g/L, the microhardness and wear resistance of the coatings are optimum. The average microhardness of the Ni–Mn alloy coatings is 522.8 HV0.05, and the minimum scratch area of the wear mark is 9526.26 μm2. The addition of SiC particles improves the surface integrity of the composite coatings and further improves the microhardness and wear resistance of the coatings. The composite coating has a maximum average microhardness value of 648.7 HV0.05 for SiC particle concentration of 4 g/L; this value is nearly 25% higher than that of pure Ni–Mn alloy coatings; the minimum scratch area of the wear mark is reduced to 7160.46 μm2.

Electrodeposition and corrosion behavior of Zn−Ni−Mn alloy coatings deposited from alkaline solution

Abstract The potentiostatic electrodeposition of Zn−Ni−Mn was carried out in an alkaline solution with the addition of Mn salt. The effects of electrolyte Mn2+ concentration and deposition potential on the surface morphology, phase structure and corrosion behavior of coatings were studied. The results of corrosion polarization showed that the presence of higher Mn content in Zn−Ni−Mn coatings could lead to the formation of a good passive layer with a 7-fold increase in Rp of coating and a significant decrease in the corrosion current density compared to those of Zn−Ni coating. The XRD and the XPS analyses from the surface of Zn−Ni−Mn after corrosion test showed that the passive layer was composed of zinc hydroxide chloride, zinc oxide, zinc hydroxide carbonate, and manganese oxides.

Zn–Mn alloy coatings from acidic chloride bath: Effect of deposition conditions on the Zn–Mn electrodeposition-morphological and structural characterization

Zn–Mn alloy electrodeposition on steel electrode in chloride bath was investigated using cyclic voltammetric, chronopotentiometric and chronoamperometric techniques. Cyclic voltammetries (CV) reveal a deep understanding of electrochemical behaviors of each metal Zn, Mn, proton discharge and Zn–Mn co-deposition.The electrochemical results show that with increasing Mn2+ ions concentration in the electrolytic bath, Mn2+ reduction occurs at lower over-potential leading to an enhancement of Mn content into the Zn–Mn deposits. A dimensionless graph model was used to analyze the effect of Mn2+ ions concentration on Zn–Mn nucleation process. It was found that the nucleation process is not extremely affected by Mn2+ concentration. Nevertheless, it significantly depends on the applied potential.Several parameters such as Mn2+ ions concentration, current density and stirring were investigated with regard to the Mn content into the final Zn–Mn coatings. It was found that the Mn content increases with increasing the applied current density jimp and Mn2+ ions concentration in the electrolytic bath. However, stirring of the solution decreases the Mn content in the Zn–Mn coatings. The phase structure and surface morphology of Zn–Mn deposits are characterized by means of X-ray diffraction analysis and Scanning Electron Microscopy (SEM), respectively. The Zn–Mn deposited at low current density is tri-phasic and consisting of η-Zn, ζ-MnZn13 and hexagonal close packed ε-Zn–Mn. An increase in current density leads to a transition from crystalline to amorphous structure, arising from the hydroxide inclusions in the Zn–Mn coating at high current density.

Deposition Potential Influence on the Electrodeposition of Zn–Ni–Mn Alloy

The effect of deposition potential on the electrodeposition, composition, surface characteristics and corrosion resistance properties of Zn–Ni–Mn alloy coatings were investigated. During the deposition potential range from −0.500 to −1.000 V, normal codeposition of the alloy components occurred, meanwhile at deposition potentials more cathodic than −1.000 V, the anomalous codeposition took place. Shifting the deposition potentials toward the negative direction led to an increase in the thickness of the deposit, incremented the adhesion and compactness and improved the corrosion resistance properties. X-ray diffraction studies of the deposit showed the presence of hexagonal pure Zn phase, hexagonal Mn0.27Zn0.73 phase and cubic γ-Ni5Zn21 and/or tetragonal δ-Ni3Zn22 phases.

Effect of pH on nucleation mechanism of Zn–Mn coatings electrodeposited at different deposition potential

Zn–Mn alloy coatings were galvanostatically deposited from an acidic chloride bath at pH 2·0 and 4·9. Effects of pH on nucleation mode, surface morphology and corrosion resistance of Zn–Mn coatings were studied. Analysis of current-time transients indicated that the nucleation mode of Zn–Mn coatings at pH 2·0 is instantaneous. With increasing the pH to 4·9 at potentials of −1·08 and −1·59 V, the experimental data were observed to be near the theoretical instantaneous nucleation, but at higher potentials of −1·12 and −1·2 V, the progressive mode of nucleation was dominant. From AFM images, the average nuclei density N values for Zn–Mn deposition at pH 2·0 and 4·9 were 9·2×109 and 10×109 cm−2 respectively. At pH 2·0, this value was near that obtained by the model, but it was found to be far away at pH 4·9. Potentiodynamic polarisation indicated that the corrosion resistance of Zn–Mn coatings at pH 4·9 is slightly improved.

ELECTRODEPOSITION BEHAVIOR OF Mn WITH Ni IN ACIDIC SULFATE SOLUTIONS

The influence of Mn 2+/ Ni 2+ mole ratio in electrolytes on the Ni – Mn alloy deposits was studied. The electrodeposition mechanism of Mn with Ni is analyzed by the cyclic voltammogram (CV) and an "induced co-deposition" mechanism is proposed for Ni – Mn alloy electrodeposition. The results show that the Mn content in Ni – Mn alloy deposit and the hardness increased with the increase of Mn 2+/ Ni 2+ mole ratio in electrolytes. When the Mn 2+/ Ni 2+ mole ratio in bath was 2/1, the corrosion current density of the deposit coating was the lowest and the corresponding corrosion potential was higher, and under these conditions the coating with a Mn content of 1.20 wt.% showed good corrosion resistance. The scanning electron microscopy (SEM) of the alloy coatings exhibited that the morphology of Ni – Mn alloy coatings were different from Pure Ni coating, and when Mn 2+/ Ni 2+ was 2/1, the surface was compact and homogeneous.

The protective properties of epoxy coating electrodeposited on Zn–Mn alloy substrate

• Epoxy coating was cataphoretically deposited on Zn–Mn alloy and bare steel substrates. • The corrosion stability of epoxy coating increases with Mn content in Zn–Mn substrate. • Metallic substrate dissolves during cataphoretic deposition. • Mn has protective role in the prevention of Zn dissolution in an alkaline medium. The epoxy coating was cataphoretically deposited on steel and steel modified by electroplated Zn–Mn alloy of different chemical contents. The samples were immersed in 0.5 mol dm −3 NaCl solution for 60 days. The electrochemical impedance spectroscopy (EIS) analysis showed that the values of pore resistance for epoxy coating on steel and Zn–Mn alloy with 16 at.% Mn were two orders of magnitude higher, while the capacitance values were two orders of magnitude lower than those for the epoxy coating on Zn–Mn alloy substrates with 5 and 8 at.% Mn. It was assumed that the main reason for such a difference was metallic substrate dissolution during cataphoretic deposition, due to high pH (12.9). This assumption was supported by energy dispersive X-ray spectrometry (EDS) measurements showing that the amount of released Zn in epoxy coatings decreased as Mn percent in the Zn–Mn alloys increased. In addition, Zn–Mn alloy coatings on steel, as well as bare steel, were immersed in 0.1 mol dm −3 NaOH solution, pH 12.9, simulating conditions during cataphoretic deposition, and polarization resistance measurement in this solution indicated that Mn inclusions in Zn–Mn alloy substrate prevent Zn dissolution in alkaline medium.

Characterisation and corrosion resistance of Zn–Mn coatings electrodeposited from acidic chloride bath

Zn–Mn alloy coatings were galvanostatically electrodeposited from an acidic chloride bath. Effects of deposition current density, pH and temperature on surface morphology, microstructure and corrosion resistance of Zn–Mn coatings were studied. The coatings deposited at 10, 50 and 100 mA cm−2 had a single η-Zn phase structure. However, a dual phase structure of η-Zn and ϵ-Zn–Mn with higher Mn content was found for the coatings deposited at 200 mA cm−2. The dual structure degraded the corrosion resistance of the coatings. The highest corrosion resistance was achieved for the Zn–Mn coating deposited at 100 mA cm−2, pH 4·9 and 25°C. This coating contained 4·1 wt-%Mn and showed a unique surface morphology consisting of randomly arranged packs of very thin platelets, laid perpendicular to the surface and provided a high compactness deficient free structure.

Influence of Na2TeO3 additive on electrodeposition of Zn–Mn alloy coatings from sulphate–citrate bath

The influence of Na2TeO3 additive in sulphate–citrate bath on electrodeposition of Zn–Mn alloy coatings was investigated by material characterisation methods and electrochemical techniques. The effects of small amounts (0·39–3·10 mM) of Na2TeO3 additive on cathode polarisation, composition and current efficiency were estimated. The crystal structure and surface morphology of Zn–Mn alloy coatings were studied by scanning electron microscopy (SEM) and powder X-ray diffraction spectroscopy (XRD) respectively. The SEM and XRD data showed that Na2TeO3 additive effectively accelerates phase transformation and reduces crystallite size.

The influence of anion type in electrolyte on the properties of electrodeposited Zn[sbnd]Mn alloy coatings

ZnMn alloy electrodeposition on steel electrode, in electrolytes containing chloride or sulfate anions, was investigated by chronopotentiometry. Galvanostatically obtained electrodeposits were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), and atomic absorption spectrophotometry (AAS). It was found that Zn2+ and Mn2+ ion reduction occurred at higher overpotentials in sulfate bath, leading to a higher Mn content in the deposit and smaller crystallites as compared to the chloride electrolyte. AFM images of deposits revealed that with the increase in deposition current density, bigger agglomerates formed in both electrolytes, leading to higher roughness and heterogeneity of the samples. In relation to this observation, the ZnMn coatings were deposited at current densities of up to 80mAcm−2 because at higher current densities the samples from sulfate electrolyte were non adherent and dendritic. Depending on the deposition current density, the XRD patterns of the ZnMn deposits produced from chloride electrolyte indicated that the coatings were formed of either η- or ε-ZnMn phase, while the coatings obtained from sulfate bath consisted of ε-ZnMn phase. The linear polarization method showed that ZnMn alloys deposited from sulfate electrolyte exhibited higher corrosion resistance in NaCl corrosive media.

Electrodeposition of Zn and Zn–Mn alloy coatings from an electrolytic bath prepared by recovery of exhausted zinc–carbon batteries

The electrodeposition of galvanic coatings was performed using a chloride-based acidic electrolytic bath containing polyethylene glycol (PEG) as an additive. The electrolytic bath was prepared using Zn and Mn recovered from exhausted zinc–carbon batteries by means of acid leaching with HCl. The coatings were obtained potentiostatically at −1.2V and −1.6V (vs. Ag/AgCl) and galvanostatically with a current density of −10mAcm−2. The results indicated that the presence of PEG in the bath during galvanostatic deposition favored the formation of a coating containing a mixture of Zn and Zn–Mn alloy with an Mn content of around 2wt%.

Initial corrosion protection of Zn–Mn alloys electrodeposited from alkaline solution

The effects of a deposition current density (c.d .) on the corrosion behaviour of Zn–Mn alloy coatings, deposited from alkaline pyrophosphate solution, were investigated by atomic absorption spectrophotometry (AAS), X-ray diffraction (XRD), atomic force microscopy (AFM), optical microscopy, electrochemical impedance spectroscopy (EIS) and measurement of corrosion potential ( E corr). XRD analysis disclosed that zinc hydroxide chloride was the main corrosion product on Zn–Mn coatings immersed in 0.5 mol dm −3 NaCl solution. EIS investigations revealed that less porous protective layer was produced on the alloy coating deposited at c.d . of 30 mA cm −2 as compared to that deposited at 80 mA cm −2.

Fabrication of nanoporous manganese by laser cladding and selective electrochemical de-alloying

Fabrication of nanoporous Cu–Mn alloy coatings was investigated by a two-step process involving high power laser cladding of a homogeneous Cu40Mn60 alloy coatings followed by selectively electrochemical de-alloying. Auger mapping results indicate that nanoporous manganese was obtained by selective electrochemical etching of the less active Cu component owing to the passivation of the more active manganese in potassium nitrate solution. The surface morphology of the porous Mn was a ribbon-like structure, different from interconnected bicontinuous nanopores that are usually obtained by de-alloying. The influence of de-alloying time, electric potential and temperature on the formation of nanoprosity is systematically investigated. Nanopore sizes can be tailored to be less than 100nm. Under optimal etching conditions the nanopore size was below 25nm. The surface area of the nanoporous manganese layer was enhanced by up to 990 times compared with that of a polished sample.

Influence of cobalt on manganese incorporation in Ni–Co coatings

The effect of alloying <1 wt% Mn with plain Ni, Ni–Co alloys and plain Co coatings in terms of the structure and properties has been studied. The alloys were electrodeposited from an additive free sulphamate electrolyte. The Mn concentration in the electrolyte was maintained at 5 g L−1 so as to obtain <1 wt% Mn content in the alloy coatings. The Energy Dispersive X-ray analysis (EDX) showed that the Mn content reduced from 0.97 to 0.05 wt% with increase in Co content from 0 to 98 wt% in the alloy coating. An increase in microhardness was obtained on the addition of Mn to Ni/Ni–Co alloys. The X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) studies revealed a change in crystal structure and morphology. Pin-on-disc tribology test revealed better wear performance of Ni–18 wt%Co–Mn alloy coating compared to the other Ni–Mn/Ni–Co–Mn alloy coatings.

Influence of ammonium selenate and thiourea mixture on mechanical properties and morphology of Zn–Mn alloy coatings electrodeposited from sulphate–citrate bath

The influence of thiourea (TU, 0·5 g L−1) and additive mixture of ammonium selenate and thiourea (AS–TU, 0·5 g L−1) on electrodeposition of Zn–Mn alloy coatings from sulphate–citrate bath (SCB) has been studied. Investigations of alloy composition were carried out by atomic absorption spectroscopy and inductively coupled plasma. A profile of the relative concentration of sulphur was obtained using glow discharge spectroscopy. The morphology of the coatings was studied by scanning electron microscopy. The crystal structure was investigated by X-ray diffraction. Two phases (metastable ϵ and β) were detected in coatings electrodeposited from SCB with TU and mixture of AS–TU at jc≥10 A dm−2 (≥50%Mn). Zn–Mn alloy coatings, electrodeposited from an SCB with 0·5 g L−1 TU were harder than coatings electrodeposited from SCB with AS alone, and a mixture of AS–TU. Coatings electrodeposited from SCB with a mixture of AS–TU had the lowest tensile stress.

Electrochemical codeposition of copper and manganese from room-temperature N-butyl- N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid

The voltammetric behavior of N-butyl- N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid (BMP-TFSI) containing Cu(I), Mn(II), or mixtures of Cu(I) and Mn(II) as well as the electrodeposition of copper–manganese alloy coatings (Cu–Mn alloy coatings) was studied at 323 K. The Cu(I) and Mn(II) species required to prepare these coatings were introduced into the BMP-TFSI by anodic dissolution of the relevant metallic electrodes. Electrodeposits of Cu, Mn, and Cu–Mn with various contents of Mn can be obtained by controlled-potential electrolysis. It was found that the compositions and surface morphology of the electrodeposited Cu–Mn alloy coatings depend on the deposition potentials and the concentration ratio of [Cu(I)]/[Mn(II)] in BMP-TFSI. The Cu–Mn alloy coatings obtained in this study were compact and adherent. They did not show any significant X-ray diffraction signal that could be assigned to the crystalline structures of Cu, Mn, or Cu–Mn alloys. In the aqueous solution containing 0.1 M NaCl, the Cu–Mn alloy coatings demonstrated passive behavior—no continuous oxidation was observed. However, a significant oxidation current was observed at the electrodes deposited with Cu or Mn.

Electrodeposition of Al–Mn alloy on AZ31B magnesium alloy in molten salts

The Al–Mn alloy coatings were electrodeposited on AZ31B Mg alloy in AlCl 3–NaCl–KCl–MnCl 2 molten salts at 170 °C aiming to improve the corrosion resistance. However, in order to prevent AZ31B Mg alloy from corrosion during electrodeposition in molten salts and to ensure excellent adhesion of coatings to the substrate, AZ31B Mg alloy should be pre-plated with a thin zinc layer as intermediate layer. Then the microstructure, composition and phase constituents of the coatings were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD). It was indicated that, by adjusting the MnCl 2 content in the molten salts from 0.5 wt% to 2 wt%, the Mn content in the alloy coating was increased and the phase constituents were changed from f.c.c Al–Mn solid solution to amorphous phase. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization measurements in 3.5% NaCl solution. It was confirmed that the Al–Mn alloy coatings exhibited good corrosion resistance with a chear passive region and significantly reduced corrosion current density at anodic potentiodynamic polarization. The corrosion resistance of the alloy coatings was also related with the microstructure and Mn content of the coatings.