An important possibility to improve the corrosion behaviour of magnesium alloys is the application of protective coatings. The quality of such coatings depends mainly on the pretreatment and the exposure conditions after pretreatment. Since magnesium surfaces change much faster under atmospheric conditions than those of almost any other technical material, it is necessary to pay special attention to this particular feature. The activity of acidpickled surfaces of the magnesium alloys AZ31 and AZ91 in dependence on the exposure time and the humidity conditions was investigated with electrochemical noise (EN) measurements. In addition to pickling, plasma chemical vapour deposition processes open new possibilities for an economical, as well as ecologically quite safe, pretreatment. The results of EN investigations after acid pickling as well as specific plasma oxidation treatments of the two magnesium alloys after exposure to air with different humidities are presented.
The ageing of organic protective coatings depends on environmental impacts and is associated with a variety of ichemical and physical processes. The results of former thermal ageing studies indicate that evaporation and polymer degradation are the decisive processes for changes in coating properties. For the verification of these assumptions the impact of ‐ the thermal exposure temperature TL and ‐ the length of the exposure time tL on properties of clear lacquer coatings was determined by further studies. The gradation of TL was aimed at creating conditions where on the one hand only evaporation processes occur, while on the other hand evaporation and polymer degradation reactions occur in parallel. The objective was to find the time tL and the temperature TL at which degradation starts to prevail.
Der Zusammenhang zwischen der Abgabe niedermolekularer Stoffe aus Beschichtungen unter dem Einfluss erhöhter Temperatur und ihren Eigenschaften wurde ermittelt. Dazu wurden Beschichtungen unterschiedlicher Lösemittelbasis und Trocknungsmechanismen wärmegelagert und die Änderungen der Beschichtungseigenschaften sowie die Abgabe flüchtiger organischer Verbindungen in Zeitabhängigkeit durch Prüfungen und Analysen erfasst.
Die plasmabasierte Oberflächentechnik ermöglicht wissenschaftlich‐technisch, wirtschaftlich und ökologisch interessante Alternativen zu herkömmlichen Vorbehandlungsverfahren.Daher stand am iLF in den vergangenen Jahren die Entwicklung eines neuen Verfahrens zur Verbesserung der Korrosionsbeständigkeit von niedriglegierten Stahloberflächen durch ultradünne Plasmapolymerschichten im Vordergrund.Im Anschluss an eine Plasmafeinstreinigung unter oxidativen Bedingungen sollten Plasmapolymerschichten mit einer korrosionsinhibierenden/passivierenden Wirkung abgeschieden werden.Dazu werden während des Prozesses der Plasmapolymerisation siliziumorganischer Monomere Korrosionsinhibitormoleküle in die sonst elektrochemisch inaktive Schicht implantiert. Dadurch verbessert sich nachweislich der langfristige Korrosionsschutz. Ferner kann durch plasmatechnische Verfahren die Oberfläche der abgeschiedenen Plasmapolymerschicht so modifiziert werden, dass sie auch eine optimale Haftvermittlung aufweist.
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