Abstract: This paper brings out the developments on heat-treatment and alloying to improve the stress corrosion cracking (SCC) behavior of 7010 Al-alloy. The role of microstructures including the grain boundary precipitates and recystallized grains and the relation of intergranular corrosion (IGC) on the SCC behavior of 7010 Al-alloy have been discussed.
Abstract: The anodic and cathodic reactions involved in the corrosion process on several nickel-aluminum alloys including two intermetallic compounds NiAl and Ni3Al in the NaCl solutions are studied. A procedure of pretreatment of test specimens and measuring the anodic and cathodic voltammograms is developed. It enabled us to obtain reproducible results including Tafel portions of voltammograms. The corrosion potentials Ecorr and corrosion currents icorr are determined by the coordinates of the intersection of anodic and cathodic Tafel plots. The dependences of Ecorr and icorr on the alloy composition (the content of nickel in the binary nickel-aluminum alloys), on the concentration of NaCl, and рН of unbuffered NaCl solutions with the additions of HCl or NaOH are determined.
The anodic behavior of the alloys in a wide potential range is studied using the potentiodynamic method and the method of stepwise raising anodic potential with an exposure of electrode at each potential for a certain time. The dependences of pitting potential on the concentration of solution are determined for two intermetallic compounds.
Abstract: In the main frame of the research aimed to model the corrosion growth on bronze surface, the objective of the work here reported has been to characterize the corrosion products formed on laboratory samples of bronze alloy (Cu Sn12), during the early stage of exposure to moist air with sulfur dioxide. A cycling corrosion cabinet was used to control 200 ppm gas concentration, relative humidity (RH) and temperature, according to the DIN 50018 (Kesternich test).The method is designed to evaluate how well the surface resists to sulfur dioxide corrosion; the test cycle consists of 8 hours exposure to sulfur dioxide at 40°C temperature and 100% relative humidity, followed by 12 hours drying at room condition.
Weight variation, Spectrophotometer, Scanning Electron Microscopy with X-ray microanalysis (SEM-EDS), X-ray Diffraction (XRD) analysis were carried out for the tarnish products characterization. Some of the compound identified were brochantite (Cu4(OH)6SO4), chalcanthite (CuSO4•5H2O) cuprite (Cu2O), cassiterite (SnO2) and ottemannite (Sn2O3).
Abstract: In this work, the use of a differential aeration technique (split-cell) to assist understanding of contributions to the corrosion of an aerospace aluminium alloy is demonstrated. The setup comprised two similar specimens immersed in differentially aerated test solutions and coupled by a zero resistance ammeter. The individual electrochemical responses of the coupled specimens during linear polarization were interpreted in relation to the aeration condition, alloy composition and surface preparation. Further, the same setup was employed to investigate corrosion inhibition by observing the current and potential transients after inhibitor addition to the aerated or deareated compartment. It was found that the split-cell technique provides detailed understanding of the corrosion process in multiphase alloys and provides important information on inhibitor performance.
Abstract: The aerospace industry urgently needs environmentally friendly materials and processes for corrosion protection of aluminium alloys in aircraft structures. Until now this has been achieved by hexavalent chromium based compounds in either surface pre-treatments or primers. Due to its carcinogenic properties the use of chromates is restricted and a ban is expected soon. Up to now an all over recognized replacement of chromates is not available for aircraft maintenance, although a lot of research has been done and promising results also exist for some chromium-free conversion coatings and for magnesium rich primers.
WIWeB found out in laboratory scale and by flight trials that thin layers of zinc rich primers, if applied with dry film thickness of 10 – 20 µm, can be used successfully to prevent corrosion on aluminium for aircraft. Solvent based as well as water based zinc rich primers have been tested. The major part of the work presented is from further investigations which show, that another great improvement can be achieved, when thin layers of organic adhesion inhibitors like 2-aminopropyltriethoxysilane and 4-t-butylbenzoic acid are applied on the unclad Al 2024 panels, which had been scrubbed with abrasive pads before. This process is followed by the application of the thin film of zinc rich epoxy primer before the usual 2-pack epoxy primer is applied.
Abstract: We developed multilayered, purely inorganic coatings for the corrosion protection of AZ magnesium alloys. Polymeric acid-catalyzed sols form relatively dense coatings, but any direct contact to the reactive magnesium substrate has to be avoided. However polymeric sols based on SiO2, B2O3, Al2O3, ZrO2 and up to 5% of lanthanide salts can be used to seal samples with prime coat based on aqueous nanoparticle dispersions. Without organic network modification, these sealings have to be kept thin to avoid cracks. However if the coating process with aqueous dispersions and polymeric sols is alternated, a kind of lamellar sandwich structure can be formed which stays crack-free up to several layers. The performance and the protective properties of these coatings were studied with different methods (EIS, salt spray tests and electron microscopy).
Abstract: The complex technology of the surface treatment of Al, Mg, Ti alloys for size reconstruction and strengthening is presented herein. This consists of electric arc spraying of aluminum alloys or powder wire in an aluminum shell and then treatment with plasma electrolytic oxidation (PEO). Once treated, oxide-ceramic coatings maintain extreme hardness, durability and resistance to wear. At the same time their corrosion-resistant properties are also significant. Dynamic potential dependences were studied for electric arc Al coatings and PEO treatments on Al, Mg, Ti alloys and corrosion currents were analyzed for exposure to a corrosive environment for a period of from 1 hour to 30 days. It was established that PEO treated coatings on Al alloys have a higher corrosion resistance than untreated sprayed coatings.
In Mg alloys, an intermediate layer of aluminum electric arc coating between the substrate and PEO-treated coating is necessary in order to ensure high corrosion resistance. This is due to the specifics of the formation of the MgO and Al2O3 oxide phases in the plasma discharge channels. At the same time Al coatings on Ti alloys, including those of post-PEO treatment, were characterized as having lower corrosion resistance within the range of electrode potential from corrosion potential up to repassivation potential, than were untreated Ti-alloys. Yet it was found that the corrosion resistance of PEO treated coatings increases at higher anode potentials. Under cathode polarization the hydrogen discharge is less likely to occur on PEO-coatings than on untreated Ti alloys which more effectively prevents hydrogenation.
Abstract: It was previously demonstrated that the use of a pyrrole-based silane (PySi) for surface treatment of Al alloys provides both active and barrier protection due to the deposition of a hybrid coating, containing polypyrrole and polysiloxane chains. To further explore these features, a wider range of Al substrates and different silane-based formulations in terms of silane molecule, solvent nature, water amount and pH, were investigated. Also, some tests were carried out by using aniline-based silane (AniSi). Structural/morphological characterization of the coatings, as well as the investigation of PySi solutions by diverse spectroscopic techniques, in addition to corrosion tests in NaCl, strongly support the very promising protection performance of the hybrid film. This is indicated as well from the preliminary results obtained with the AniSi-based approach. Thus, typical silane-based treatments with principally barrier action can gain in active properties if the silane compound contains monomers of conducting polymers as a funtional group.