Papers by Keyword: Conversion Coating

Abstract: This work is focused on the damage and wear mechanisms of phosphate conversion coatings which were deposited onto steel substrates by a wet-chemical process. For studying the damage mechanism, sets of multiple scratches were performed. Scratch tests along with SEM micrographs revealed the early damage mechanisms as well as the running-in friction and wear behaviour of phosphate conversion coatings. The deeper understanding allows to increase tribological performance in terms of controlled friction and wear resistance of technical components. This way, promising measures in reduction of seizing and increase of lifetime for such components could be developed.

Abstract: Ti-containing coatings as chromate replacement were prepared on electrogalvanized steel. Zinc coatings were deposited from a weak acid chloride bath. Cr-free conversion coatings were deposited from bath composed of: TiCl₃, H₂SiF₆, H₂O₂ and oxalic acid. XPS was used to evaluate chemical composition of the coatings as a function of deposition time. Deposited coating were of conversion type. Regardless of the achieved conversion coating thickness, Zn from the substrate was always present. In the coatings were identified: Zn₂SiO₄ / Zn₄Si₂O₇(OH)₂, ZnTiO₃, ZnO, Zn (OH)₂, Zn⁰, SiOx and Ti-O-Si in varying proportions. The chemical composition of the outer surface of the coating depended on deposition time, e.g. in a time interval 0-300 s 30 fold increase of the Si:Ti ratio and 20 fold of the Si:Zn ratio were observed. Estimated thickness of conversion coating was 3, 14, 35, and 100 nm for the time deposition of 1, 40, 80 and 300 s respectively. It is the proposed model for distinguishing Zn (0) phase from Zn (2+) quantitatively, based on the Zn L₃M₄₅M₄₅ spectrum. The composition of the ZnTiSi conversion coating determined its mechanical properties and corrosion resistance. Standard tests carried out showed that the coatings obtained at the time of 20-40 s had the best corrosion performance and mechanical resistance

Abstract: Mg and its alloys draw more and more attentions to be used as biodegradable medical materials. But the rapid degradation of those materials limits their clinical applications. In this article, a phosphate coating was prepared on AZ31B magnesium alloy to improve its anti-corrosion property. Morphology, composition and corrosion resistance of the coating were studied. The SEM research showed that the coating that composed of rod-like phosphates with small amount of random distributed micro-voids was approximately10-20μm in thickness. The XRD analysis indicated that the coating was mainly composed of MgO, Mg₃(PO₄)₂and Zn₃(PO₄)₂·xH₂O. Electrochemical test showed the phosphate treatment could significant improve the corrosion resistance of AZ31B.

Abstract: Alkaline phosphate-permanganate conversion coating, chrome-free conversion coating was studied for corrosion resistance of AZ91D magnesium alloy. Also, conventional acid phosphate -permanganate conversion coating was studied for comparison. Analysis and morphology observation for conversion coating layers was investigated in details by using SEM-EDS, XRD. SEM observation showed that a lot of cracks in surface and interface between conversion coating layer and AZ91D magnesium alloy substrate was observed in acid conversion coating, whereas cracks was not almost observed in alkaline conversion coating layer. SEM-EDS and XRD analysis showed that the main elements of both alkaline and acid conversion coating were Mg, O, K, P and Mn. It was found that both conversion coating layers was consisted of MgO, Mg (OH)₂ and MnO₂. Salt spray test showed that the alkaline conversion coating have a good corrosion resistance compared with acid conversion coating.

Abstract: Self-assembled monolayer (SAM) was adsorbed on the surface of vanadate conversion coated AZ31 magnesium alloy. The SAM thin film was deposited using (Tridecafluoro-1, 1, 2, 2-tetrahydrooctyl) trimethoxysilane (FAS13) and Tetrakis (trimethylsiloxy) titanium as a catalyst. Contact angles measurement, SEM, XRD, EDS and XPS were employed to analyze the surface morphologies, molecular composition, phase structure and wettability of the coatings formed on Mg alloy substrate. Corrosion resistance property of the coatings was also examined using the anodic polarization method and salt spray test. The anticorrosion property was improved with SAM post treatment. Furthermore, the contact angle increases from 12 deg. to 165 deg. indicating to production of super hydrophobic surface with SAM post treatment.

Abstract: Conversion coatings on cast AZ91D magnesium alloy were prepared in the manganese dihydro phosphate baths. The corrosion behavior of the coated and uncoated alloys has been investigated by polarization curve methods. The morphology and composition of coated surfaces were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX ) as well as X-ray photoelectron spectroscopy (XPS) techniques. It is found that the conversion coating surface characterized by crystal particle and was composed of Mn3(PO4)2. Electrochemical investigation results indicated that the phosphate conversion coating could enhance the corrosion potential in great extent of about 1300mV compared with Mg alloy substrate.

Abstract: Phosphate conversion coatings was investigated on the surface of AZ91D magnesium alloy in a manganese dihydro phosphate baths. The influence of Ca²⁺ on coating microstructure was evaluate by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques, and the corrosion resistance of the coating was tested by polarization curve methods in 3.5%NaCl. Surface observation results show that the conversion coating presents in crystal feature, and the coating containning Ca was uneven with large grains and small grains. The adding of Ca²⁺ compound in the bath was found to be important for the attainment of good combination between the coating and Mg alloy substrate. Polarization curve results indicate that the phosphate conversion coating containing Ca could enhance the corrosion potential and improve corrosion resistance.

Abstract: Environmentally friendly anti-corrosion surface treatment reinforced by nano-ceramic metal oxide particles were developed as a protective layer for galvanized steel. The treatment bath is based on a nano-ceramic conversion coating composed of dilute hexafluorozirconic acid with small quantities of additive components containing H₂O₂. The corrosion resistance of treated substrate was compared to samples treated in phosphate conversion coating bath and in a hexafluorozirconic acid without the addition. The effect of other parameters such as pH solution and H₂O₂ concentration as oxidant on coating morphology were evaluated. Scanning electron microscopy/energy dispersive spectroscopy(SEM/EDS) was used to characterize the coating surface morphology. Utilizing DC polarization and salt spray test were performed on the treated substrate for studying the corrosion performance of the coatings. During surface examination, uniform distribution of Zr along the surface of all treated samples was observed. Results of corrosion tests showed that phosphate-free coating have a higher corrosion resistance than simple galvanized steel samples and provided long term corrosion performance comparable to that of phosphate.

Abstract: A permanganate conversion coating was prepared on biodegradable AZ31B magnesium alloy to improve its anti-corrosion property. Morphology, composition and corrosion resistance of the coating were studied in this paper. The SEM research showed that the coating was approximately 10-12μm in thickness with net-like microcracks. The XRD analysis indicated that the coating was mainly composed of MgO, MnO and Mn₂O₃. Electrochemical test showed manganese conversion treatment could significant improve the corrosion resistance of AZ31B.

Abstract: Today, in the area of material design conversion coatings play an important role in applications where temperature, corrosion, oxidation and wear come in to play. Manganese Phosphate is used to reduce friction and improve lubrication in sliding components. In this study, Prediction of wear coefficient of uncoated, Manganese Phosphate coated, Manganese Phosphate with oil lubricant AISI D2 steels was investigated using Archards equation. The Surface morphology of Manganese Phosphate coatings was examined by scanning electron microscope (SEM) and Energy dispersive X-ray Spectroscopy (EDX) .The wear tests were performed in a pin on disk apparatus as per ASTM G-99 Standard. The wear loss and wear coefficient were evaluated through pin on disc test using a sliding velocity of 0.35 m/s under normal load of 10 to60 N and controlled condition of temperature and humidity. Based on the results of the wear test, the Manganese Phosphate with lubricant exhibited the lowest average wear coefficient of1.24 X10^-10 and the lowest wear loss 0.37 mm³ under 60 N load.