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Investigations were made into the fatigue in the magnesium alloy AZ 91C cast in corrosive fluids and air at varied NaCl solution concentrations. Fatigue specimens will be subjected to surface stress testing in corrosive conditions with a stress amplitude of 75 MPa both after and before coating. To comprehend the behavior of the magnesium material, its fatigue life, corrosion product (X-ray spectra), and fracture properties will be examined. The corroding medium (NaCl) has been found to significantly shorten the fatigue life of the magnesium alloy AZ91C. Chemical conversion treatment was applied to the AZ91C alloy to improve corrosion resistance and corrosion fatigue resistance. MgSnO3 was found in the XRD patterns of the stannite-treated AZ91C alloy, and this treatment slightly improved the alloy's corrosion resistance in an alkaline stannite solution with a pH of 7. H2O and SEM images demonstrate that chloride ions can penetrate the substrate through porous structures.

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Ti6Al4V alloy is an exceptional biomaterial compared to other metals used for implants that replace bone tissue. Despite being corrosion-resistant, Ti6Al4V can release ions that may cause adverse effects to tissues after long implantation times. Several researchers have studied the thermal oxidation of this alloy, which generated layers of mainly TiO 2 rutile phase to increase its wear and corrosion resistance. However, one of the shortcomings of these layers is their susceptibility to pitting corrosion. To extend the useful life of Ti6Al4V, a coating system consisting of thermally grown TiO 2 and CeO 2 obtained using chemical conversion treatment was proposed, which would be advantageous owing to its non-toxic, antiseptic, and anticorrosive properties. In this study TiO 2 rutile phase was obtained on the surface of Ti6Al4V after quenching at 650 °C for 90 min followed by tempering at 450 °C. Cerium conversion treatments produced a surface film consisting of Ce3+ and Ce4+, which was characterised using X-ray diffraction, scanning electron microscopy, atomic force microscopy, X-ray photoelectronic spectroscopy, cyclic polarisation curves, electrochemical impedance spectroscopy, and scanning Kelvin probe. The obtained coating system reduced the corrosion rate of the substrate: TiO 2 worked as main passive film and the cerium coating reduced the susceptibility to pitting corrosion. Unlabelled Image • Thermally grown films are mainly compoused of TiO 2 in rutile phase after applied a treatment at 650 °C. • Systems confirms that conversion film is composed of Ce3+ and Ce4+ oxide/hydroxides, follow the mechanism proposed by Hinton. • TiO 2 forms by thermal treatment functions as a passivation, however, it presents localized corrosion. • Cerium coating reduce the suceptibility of Ti6Al4V to pitting corrosion. [ABSTRACT FROM AUTHOR]

Abstract: Alternative pretreatments are proposed in order to avoid the environmental aggressive impact produced by using surface finishing processes based on Cr(VI) compounds. In this work, blueing method is proposed as chemical conversion treatments (CCTs) in AISI 1010 commercial steel. CCTs were carried out by the so-called “Swiss blueing” method using a solution with 20 g HNO3 +5 g CH3CH2OH+5 g CuSO4·5H2O+160 g FeCl3 dissolved in water (1:1). This solution was added onto steel sheets using spray impregnation technique. Anticorrosion protection and adhesion properties were evaluated using polarization resistance (Rp), ac impedance and pull-off test, respectively. The thickness, morphology and microstructure of the protective films have been examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Although, no-treated specimens showed the highest polarization resistance (Rp) and impedance values, the oxide compounds are porous and unstable, while samples with the CCTs increased anticorrosive protection and favoured a strong adhesion between substrate and top coating. Continuous immersion values obtained by ac impedance showed remarkable variations in the coating resistance. SEM micrographs indicate that chemical treatment increased the surface porosity–roughness. XRD patterns showed some iron oxide compounds: mainly magnetite, and a small quantity of hematite, which have influenced the electrochemical behavior and adhesion. Pull-off tests showed good adhesion in the previously treated samples. These results indicate that obtained roughness with one CCTs using “Swiss blueing” method increased anticorrosion protection and adhesion properties. [Copyright &y& Elsevier]

Chemical conversion treatment of Mg−Al alloy (AZ91) using colloidal silica as an alternative to chromate conversion was investigated as a function of solution pH, temperature, solution conditions, and treatment time. The solution used for the colloidal silica coating consisted of colloidal silica, titanium sulfate, and cobalt ions to maintain good anti-corrosion and adhesion properties. Adding CoSO4 to the colloidal silica solution enhanced the adhesion force between the silica film and magnesium substrate. The optimum conditions for the chemical conversion treatment solution were pH 2, 90-sec treatment, and 25°C. [ABSTRACT FROM AUTHOR]

• Zr- and Ti-based conversion treatments increase the polar component of the surface free energy by a factor ten. • Organic additives initially improve interfacial stability of Zr-and Ti-treated galvanized steel, but have an adverse effect on long term interfacial stability. • The impact of organic additives is higher when added to Ti-based than to Zr-based conversion solutions. • Tetravalent Zr and Ti cations behave considerably differently when precipitating from aqueous solutions, resulting in a different conversion layer build-up. The bonding properties of zirconium- and titanium-based conversion coatings were evaluated using model conversion solutions of H 2 ZrF 6 and H 2 TiF 6 with addition of various organic additives (PAA, PVA, PVP). Macroscopic testing techniques such as contact angle and pull-off adhesion measurements were performed on galvanized steel sheets. Complementary to this, molecular studies were performed on model zinc substrates using ATR-FTIR in the Kretschmann configuration. The macroscopic and molecular approaches showed a good correlation demonstrating ATR-FTIR in the Kretschmann configuration to be a valuable tool to gain fundamental insights in metal oxide-polymer interfacial phenomena. Zirconium-treated galvanized steel substrates were shown to have a higher bonding affinity for the polyester coil coat primer than titanium-treated galvanized steel substrates. The presence of organic additives did not further improve the bonding properties. Yet, organic additives initially improved the interfacial stability of titanium-treated substrates. However, on the long term, organic additives are shown to be detrimental for polyester coil coat adhesion. This adverse effect of organic additives on the long term was assigned to its selective dissolution during immersion and was most pronounced for titanium-treatments. The limited effect of organic additives in case of zirconium-treatments was attributed to the higher portion of chemical interfacial bonds, as well as its tendency for crosslinking reactions causing entanglement of polymeric compounds in the zirconium oxide structure. [ABSTRACT FROM AUTHOR]