EP3307925A1 - Electrolyte for plasma electrolytic oxidation - Google Patents

Electrolyte for plasma electrolytic oxidation

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Publication number
EP3307925A1
EP3307925A1 EP16732922.6A EP16732922A EP3307925A1 EP 3307925 A1 EP3307925 A1 EP 3307925A1 EP 16732922 A EP16732922 A EP 16732922A EP 3307925 A1 EP3307925 A1 EP 3307925A1
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EP
European Patent Office
Prior art keywords
electrolyte
electrolytic oxidation
plasma
light metal
pulses
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EP16732922.6A
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German (de)
French (fr)
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EP3307925B1 (en
Inventor
Wolfgang Hansal
Selma Hansal
Rudolf Mann
Veronika GRMAN
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Hirtenberger Engineered Surfaces GmbH
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Hirtenberger Engineered Surfaces GmbH
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/024—Anodisation under pulsed or modulated current or potential
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/18—Electroplating using modulated, pulsed or reversing current
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/026—Anodisation with spark discharge
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/04—Anodisation of aluminium or alloys based thereon
    • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/26—Anodisation of refractory metals or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/30—Anodisation of magnesium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/34—Anodisation of metals or alloys not provided for in groups C25D11/04 - C25D11/32
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires

Definitions

  • the invention relates to an electrolyte for the plasma-electrolytic oxidation of workpieces produced from light metal and / or light alloys, comprising a salt solution, wherein at least one salt or a combination of two or more salts is selected from a group comprising metal salts, in particular borates, phosphates, nitrates, sulfates, Aluminates, silicates, manganites, molybdate, tungstates, and / or salts of organic acids, in particular methanesulfonates and / or amidosulfonates, and / or metal complexes and combinations thereof, and a method for this purpose.
  • metal salts in particular borates, phosphates, nitrates, sulfates, Aluminates, silicates, manganites, molybdate, tungstates, and / or salts of organic acids, in particular methanesulfonates and / or amidosulfonates, and / or
  • An additional possibility for controlling the layer properties is the incorporation of particles which are dispersed in the electrolyte.
  • the incorporation of unmodified oxides, carbides and nitrides using alternating current is described in the article by VN Malyshev, KM Zorin, "Features of microarc oxidation coatings formation technologies in slurry electrolytes", Appl. Surf. Be. 254 (2007), 1511-1516.
  • a control of the superficial charge of In this process particles are only possible via the pH of the electrolyte.
  • the plasma electrolytic oxidation process is possible only in certain pH ranges, which represents a significant limitation in the selection of the candidate particles.
  • inorganic non-metallic particles are suspended in this salt solution.
  • the inorganic non-metallic particles are preferably selected from a group which contains insoluble oxides, hydroxides or silicates in the salt solution of the electrolyte.
  • the inorganic non-metallic particles have an average diameter of at least 10 nm, and are preferably surface-modified, so that their surface energy and / or zeta potential is increased or reduced in terms of their initial state.
  • Such a surface modification causes the inorganic non-metallic particles to be uniformly suspended in the electrolyte, allowing uniform incorporation into the oxidation layer during the deposition process.
  • hydroxyl groups are chemically reactive and can be reacted, for example, with siloxanes according to the reaction scheme
  • This modification can be carried out both in an organic medium, such as toluene, and in aqueous solution.
  • a positive charge is achieved, for example, by the use of siloxanes having amino groups, e.g. 3-aminopropyltrimethoxysilane achieved.
  • the amino groups are protonated in an acidic medium, whereby the thus modified particle receives a positive surface charge.
  • 3-mercaptopropyltrimethoxysiloxane and the subsequent oxidation to sulfonic acid according to the reaction equation
  • R-SH + 3 H 2 0 2 - "a negative surface charge can be achieved in neutral and basic media ⁇ R-SO3H + 3H 2 0 (2).
  • the modification of the surface on the one hand causes a high surface charge of the particles in the electrolyte in question to prevent precipitation, on the other hand, the particles can be transported electrophoretically to the electrode surface in the course of the deposition process. In this way, the incorporation rate of the particles in the resulting oxide layer can be controlled via the electrical parameters.
  • the inorganic non-metallic particles are selected from a group comprising clay minerals, in particular bentonite, kaolinite and / or montmorillonite. These clay minerals naturally have a favorable surface energy or zeta potential, which leads to a stable electrolyte suspension.
  • the invention furthermore relates to a process for the plasma-electrolytic oxidation of workpieces produced from light metal and / or light metal alloys with an electrolyte according to the invention described above.
  • the plasma-electrolytic oxidation takes place by means of direct current, in particular at a voltage of 250 V to 700 V. It is particularly preferred here that the current density is between 1 A / dm 2 and 30 A / dm 2 .
  • Oxidation layers produced in this way have a particularly compact, dense layer which has only a very low porosity. Such a low porosity is particularly desirable when a particularly high corrosion resistance of the workpiece is required.
  • the plasma electrolytic oxidation is carried out by means of pulse methods, with anodic pulses preferably being applied at a voltage of 250 V to 700 V.
  • the current density be between 1 A / dm 2 and 30 A / dm 2 during the on fashionable pulses.
  • the use of the pulse method has the advantage that the plasma-chemical reaction at the surface of the workpiece can be controlled by targeted control of the pulses. This makes it possible, in particular, to achieve a low surface roughness and a lower porosity of the oxidation layer on the workpiece. Investigations by the applicant have also shown that a higher pulse frequency has a positive effect on the corrosion resistance of the coated workpieces.
  • additional cathodic pulses are applied whose voltage is preferably between 30 V and 200 V.
  • the current pulses have a duration of at least 5 ⁇ and are separated by pauses of at least 3 ⁇ .
  • the thickness and / or duration of the anodic and / or cathodic current pulses can also be varied during the production of the oxidation layer on the workpiece.
  • FIG. 1 shows a scanning electron micrograph of the surface of a surface-modified SiO 2 particles produced PEO layer.
  • FIG. 2 shows the EDX spectrum of the surface of FIG. 1;
  • FIG. 3 shows a scanning electron micrograph of a cross section through the PEO layer from FIG. 1;
  • FIG. 5 shows a scanning electron micrograph of the surface of a PEO layer produced with bentonite additive
  • FIG. 6 shows the EDX spectrum of the surface of FIG. 5;
  • FIG. 7 is a scanning electron micrograph of a cross section through the PEO layer of FIG. 5; FIG.
  • Fig. 8 shows the EDX spectrum of a cross section of the PEO layer
  • Aerosil 200 (a non-porous, amorphous silica having a specific surface area of 200 m 2 / g, Evonik Industries) were suspended in 1 l of n-butanol. Subsequently, a solution of 20 ml of 35% hydrochloric acid, 200 ml of 3-mercaptopropyltrimethoxysiloxane and 20 ml of water and a solution of 120 ml of 3-mercaptopropyltrimethoxysiloxane in 100 ml of n-butanol were added and the mixture was stirred at 40 ° C for 8 to 10 hours. Thereafter, a solution of 40 ml of 25% ammonia, 200 ml of 3-mercaptopropyltrimethoxysiloxane and 100 ml of n-butanol was added and the mixture was stirred overnight.
  • Aerosil 200 a non-porous, amorphous silica having a specific surface area of 200
  • modified Aerosil was taken up in 2 l of 35% H 2 O 2 and stirred at 60 ° C. for 24 hours in order to oxidise the surface-bonded thiol groups to sulfonic acid.
  • the thus-obtained surface-modified Aerosil was added to an electrolyte consisting of a solution of 3 g / L KOH and 3 g / L K 2 S 13 O 3 in a concentration of 30 g / L.
  • the substrate used was a 1 mm thick sheet of the industrially used 6082 aluminum alloy measuring 25 mm ⁇ 100 mm.
  • a bipolar rectangular pulse was used to produce the layer, the anodic and cathodic current density being 10 A / dm 2 and the respective pulse duration 500 MS, which corresponds to a frequency of 1 kHz.
  • the coating time was 30 minutes.
  • the scanning electron images according to FIGS. 1 and 3 and the associated EDX spectra according to FIGS. 2 and 4 show the formation of a compact, dense layer due to the presence of the surface-modified particles in the electrolyte, which in contrast to the particle-free produced layers only one has low porosity.
  • Example 2 Layer with bentonite a. ) Preparation of the electrolyte
  • the substrate used was a 1 mm thick sheet of the copper-containing aluminum alloy 2017 with the dimensions 25 mm x 100 mm.
  • a bipolar rectangular pulse was used to produce the layer, the anodic and cathodic current density being 10 A / dm 2 and the respective pulse duration 500 ⁇ , which corresponds to a frequency of 1 kHz.
  • the coating time was 30 minutes.

Abstract

The invention relates to an electrolyte for plasma electrolytic oxidation of workpieces produced from light metal and/or light metal alloys, containing a saline solution, wherein at least one salt or a combination of two or more salts is selected from a group comprising metal salts, in particular borates, phosphates, nitrates, sulphates, aluminates, silicates, manganates, molybdates, tungstates, and/or salts of organic acids, especially methane sulfonates and/or amidosulfonates, and/or metal complexes as well as combinations thereof, wherein inorganic non-metallic particles are suspended in this saline solution. The invention also relates to a method for plasma electrolytic oxidation of workpieces produced from light metal and/or light metal alloys.

Description

Elektrolyt zur plasmaelektrolytischen Oxidation  Electrolyte for plasma electrolytic oxidation
Die Erfindung betrifft einen Elektrolyten zur plasmaelektrolytischen Oxidation von aus Leichtmetall und/oder Leichtmetalllegierungen hergestellten Werkstücken entaltend eine Salzlösung, wobei zumindest ein Salz oder eine Kombination zweier oder mehrerer Salze aus einer Gruppe ausgewählt ist, die Metallsalze, insbesondere Borate, Phosphate, Nitrate, Sulfate, Aluminate, Silikate, Mangana- te, Molybdate, Wolframate, und/oder Salze von organischen Säuren, insbesondere Methansulfonate und/oder Amidosulfonate, und/oder Metallkomplexe sowie Kombinationen hieraus enthält, sowie ein Verfahren hierzu. The invention relates to an electrolyte for the plasma-electrolytic oxidation of workpieces produced from light metal and / or light alloys, comprising a salt solution, wherein at least one salt or a combination of two or more salts is selected from a group comprising metal salts, in particular borates, phosphates, nitrates, sulfates, Aluminates, silicates, manganites, molybdate, tungstates, and / or salts of organic acids, in particular methanesulfonates and / or amidosulfonates, and / or metal complexes and combinations thereof, and a method for this purpose.
Werkstücke aus Leichtmetallen, insbesondere Aluminium, Magnesium und Titan, werden in der Technik aufgrund ihres geringen Gewichts, aber auch aufgrund ihrer Eigenschaft, an ihrer Oberfläche eine dichte, festhaftende Oxidschicht auszubilden, vielseitig eingesetzt. Elektrochemische Verfahren zur Ausbildung dieser Oxidationsschichten sind seit langem bekannt, für dekorative Schichten werden üblicherweise Spannungen bis 25 V, für härtere und/oder dickere Schichten bis etwa 100 V verwendet. Workpieces of light metals, in particular aluminum, magnesium and titanium, are used in the art because of their low weight, but also because of their property to form a dense, adherent oxide layer on their surface, versatile. Electrochemical processes for forming these oxidation layers have long been known, for decorative layers usually voltages up to 25 V, for harder and / or thicker layers up to about 100 V are used.
Des Weiteren sind hochenergetische Abscheideverfahren bekannt geworden, bei denen unter der Bezeichnung plasmaelektrolytische Oxidation ("PEO") eine Be- schichtung von Werkstücken bei hohen Spannungen durchgeführt wird, wobei es zu starken lokalen Bogenentladungen ("microarcs") unter Ausbildung eines leitfähigen Plasmakanals zwischen Elektrolyt und Werkstück, der in seinem Inneren innerhalb weniger Mikrosekunden Temperaturen zwischen 5.000 K und 20.000 K aufweist, kommt. Dies führte zur Entstehung einer keramischen Schicht mittels plasmachemischer Reaktion, die eine hohe Härte und Abriebsfestigkeit sowie eine hervorragende Haftfestigkeit aufweist. Furthermore, high-energy deposition methods have become known in which under the name plasma electrolytic oxidation ("PEO"), a coating of workpieces is carried out at high voltages, resulting in strong local arc discharges ("microarcs") to form a conductive plasma channel between the electrolyte and workpiece having inside it within a few microseconds temperatures between 5,000 K and 20,000 K comes. This led to the formation of a ceramic layer by means of plasma-chemical reaction, which has a high hardness and abrasion resistance and excellent adhesion.
In der WO 2012/107754 A2 wird ein derartiges plasmaelektrolytisches Verfahren beschrieben, bei welchem mittels trapezförmiger Pulse die Oxidation von metallischen Substraten erfolgt. Ein ähnliches Verfahren ist auch in der WO 2008/120046 AI beschrieben. In WO 2012/107754 A2, such a plasma electrolytic method is described, in which by means of trapezoidal pulses, the oxidation of metallic substrates. A similar method is also described in WO 2008/120046 Al.
Eine zusätzliche Möglichkeit zur Steuerung der Schichteigenschaften ist der Einbau von Partikeln, die im Elektrolyten dispergiert sind. Der Einbau von unmodifi- zierten Oxiden, Carbiden und Nitriden unter Verwendung von Wechselstrom ist im Artikel von V.N. Malyshev, K.M. Zorin, "Features of microarc oxidation coatings formation technologies in slurry electrolytes", Appl. Surf. Sei. 254 (2007), 1511-1516 beschrieben. Eine Kontrolle der oberflächlichen Ladung der Partikel ist bei diesem Verfahren nur über den pH-Wert des Elektrolyten möglich. Damit ist der plasmaelektrolytische Oxidationsprozess nur in bestimmten pH- Bereichen möglich, was eine erhebliche Einschränkung in der Auswahl der in Frage kommenden Partikel darstellt. An additional possibility for controlling the layer properties is the incorporation of particles which are dispersed in the electrolyte. The incorporation of unmodified oxides, carbides and nitrides using alternating current is described in the article by VN Malyshev, KM Zorin, "Features of microarc oxidation coatings formation technologies in slurry electrolytes", Appl. Surf. Be. 254 (2007), 1511-1516. A control of the superficial charge of In this process, particles are only possible via the pH of the electrolyte. Thus, the plasma electrolytic oxidation process is possible only in certain pH ranges, which represents a significant limitation in the selection of the candidate particles.
Es ist die Aufgabe der Erfindung, einen Elektrolyten sowie ein Verfahren bereitzustellen, um eine verbesserte Schicht durch plasmaelektrolytische Oxidation herzustellen, deren Eigenschaften sowohl durch die im Elektrolyten dispergierten Partikel als auch durch die elektrischen Parameter der Abscheidung bestimmt werden kann. It is the object of the invention to provide an electrolyte as well as a method to produce an improved layer by plasma electrolytic oxidation, the properties of which can be determined both by the particles dispersed in the electrolyte and by the electrical parameters of the deposition.
Diese Aufgabe wird erfindungsgemäß dadurch gelöst, dass anorganische nichtmetallische Partikel in dieser Salzlösung suspendiert sind. Hierbei sind bevorzugterweise die anorganischen nichtmetallischen Partikel aus einer Gruppe ausgewählt, die in der Salzlösung des Elektrolyten unlösliche Oxide, Hydroxide oder Silikate enthält. This object is achieved in that inorganic non-metallic particles are suspended in this salt solution. In this case, the inorganic non-metallic particles are preferably selected from a group which contains insoluble oxides, hydroxides or silicates in the salt solution of the electrolyte.
Hierbei weisen die anorganischen nichtmetallischen Partikel einen durchschnittlichen Durchmesser von mindestens 10 nm auf und sind bevorzugterweise oberflächenmodifiziert, sodass ihre Oberflächenenergie und/oder Zetapotential in Hinblick auf ihren Ausgangszustand erhöht oder reduziert ist. Eine derartige Oberflächenmodifikation bewirkt, dass die anorganischen nichtmetallischen Partikel gleichmäßig im Elektrolyten suspendiert sind, was einen gleichmäßigen Einbau in die Oxidationsschicht während des Abscheideverfahrens ermöglicht. Here, the inorganic non-metallic particles have an average diameter of at least 10 nm, and are preferably surface-modified, so that their surface energy and / or zeta potential is increased or reduced in terms of their initial state. Such a surface modification causes the inorganic non-metallic particles to be uniformly suspended in the electrolyte, allowing uniform incorporation into the oxidation layer during the deposition process.
Die Oberflächen von Oxiden, Silikaten, Gläsern, vielen Mineralien, aber auch von oxidierbaren Metallen sind mit Hydroxylgruppen belegt. Diese Hydroxylgruppen sind chemisch reaktiv und können zum Beispiel mit Siloxanen gemäß dem Reaktionsschema The surfaces of oxides, silicates, glasses, many minerals, but also of oxidizable metals are coated with hydroxyl groups. These hydroxyl groups are chemically reactive and can be reacted, for example, with siloxanes according to the reaction scheme
X-OH + (EtO)3Si-R X-0-Si(OEt)2-R (1) reagieren. Dadurch werden die chemischen Eigenschaften der Oberfläche der Partikel dahingehend geändert, dass die funktionelle Gruppe des Siloxans die chemischen Oberflächeneigenschaften bestimmt. X-OH + (EtO) 3 Si-R X-O-Si (OEt) 2 -R (1). As a result, the chemical properties of the surface of the particles are changed such that the functional group of the siloxane determines the chemical surface properties.
Diese Modifikation kann sowohl in einem organischen Medium, wie beispielsweise Toluol, als auch in wässriger Lösung durchgeführt werden. This modification can be carried out both in an organic medium, such as toluene, and in aqueous solution.
Um Partikel im Größenbereich von Mikrometern bis Nanometern in einer stabilen Suspension zu halten, ist es erforderlich, dass diese Partikel eine elektrische Oberflächenladung aufweisen, wodurch sie sich in Suspension elektrostatisch abstoßen, was ein Ausflocken verhindert. Diese elektrische Oberflächenladung (Zetapotenzial) kann auch dazu verwendet werden, die Partikel elektrophoretisch an eine entgegengesetzt geladene Elektrodenoberfläche anzulagern. Zusammen mit der plasmaelektrolytischen Oxidation ist es so möglich, siloxanmodifizierte Partikel in eine plasmaelektrolytisch hergestellte Schicht einzulagern. Dies kann zum Beispiel dazu verwendet werden, um höhere Schichtdicken zu erzeugen oder bestimmte Eigenschaften der Partikel (z.B. chemische Zusammensetzung oder Strukturmerkmale) auf die Schicht zu übertragen. In order to keep particles in the size range of micrometers to nanometers in a stable suspension, it is necessary that these particles have an electrical surface charge, whereby they repel electrostatically in suspension, which prevents flocculation. This electrical surface charge (zeta potential) can also be used to electrophoretically attach the particles to an oppositely charged electrode surface. Together with the plasma electrolytic oxidation, it is thus possible to store siloxane-modified particles in a plasma-electrolytically produced layer. This can be used, for example, to produce higher layer thicknesses or to transfer certain properties of the particles (eg chemical composition or structural features) to the layer.
Je nach pH-Wert des Elektrolyten ist eine positive oder negative Oberflächenladung anzustreben. Eine positive Ladung wird zum Beispiel durch die Verwendung von Siloxanen mit Aminogruppen, z.B. 3-Aminopropyltrimethoxysilan, erreicht. Die Aminogruppen werden im sauren Milieu protoniert, wodurch das derart modifizierte Teilchen eine positive Oberflächenladung erhält. Alternativ dazu kann durch die Verwendung von 3-Mercaptopropyltrimethoxysiloxan und die anschließende Oxidation zu Sulfonsäure nach der Reaktionsgleichung Depending on the pH of the electrolyte, a positive or negative surface charge should be sought. A positive charge is achieved, for example, by the use of siloxanes having amino groups, e.g. 3-aminopropyltrimethoxysilane achieved. The amino groups are protonated in an acidic medium, whereby the thus modified particle receives a positive surface charge. Alternatively, by the use of 3-mercaptopropyltrimethoxysiloxane and the subsequent oxidation to sulfonic acid according to the reaction equation
R-SH + 3 H202 -»■ R-SO3H +3H20 (2) eine negative Oberflächenladung im neutralen und basischen Medium erreicht werden. Die Modifikation der Oberfläche bewirkt einerseits eine hohe Oberflächenladung der Partikel im betreffenden Elektrolyten zur Verhinderung der Ausfällung, andererseits können die Partikel im Zuge des Abscheideverfahrens elektrophoretisch zur Elektrodenoberfläche transportiert werden. Auf diese Art kann die Einbaurate der Partikel in die entstehende Oxidschicht über die elektrischen Parameter gesteuert werden. R-SH + 3 H 2 0 2 - "a negative surface charge can be achieved in neutral and basic media ■ R-SO3H + 3H 2 0 (2). The modification of the surface on the one hand causes a high surface charge of the particles in the electrolyte in question to prevent precipitation, on the other hand, the particles can be transported electrophoretically to the electrode surface in the course of the deposition process. In this way, the incorporation rate of the particles in the resulting oxide layer can be controlled via the electrical parameters.
Hierbei sind bevor besonders bevorzugt Oberflächenmodifikationen mittels reaktiver Verbindungen vorgesehen, die aus einer Gruppe gewählt sind, die Silizium- und/oder Germaniumverbindungen, insbesondere Germaniumhalogenide und/ oder Siloxane und/oder halogenierte Silane enthält. Surface modifications by means of reactive compounds which are selected from a group which contains silicon and / or germanium compounds, in particular germanium halides and / or siloxanes and / or halogenated silanes, are particularly preferred.
In einer alternativen Ausführung des erfindungsgemäßen Elektrolyten sind die anorganischen nichtmetallischen Partikel aus einer Gruppe ausgewählt, die Tonminerale, insbesondere Bentonit, Kaolinit und/oder Montmorrillonit enthält. Diese Tonminerale haben von Natur aus eine günstige Oberflächenenergie beziehungsweise Zetapotential, die zu einer stabilen Elektrolytsuspension führt. In an alternative embodiment of the electrolyte according to the invention, the inorganic non-metallic particles are selected from a group comprising clay minerals, in particular bentonite, kaolinite and / or montmorillonite. These clay minerals naturally have a favorable surface energy or zeta potential, which leads to a stable electrolyte suspension.
Die Erfindung betrifft des Weiteren ein Verfahren zur plasmaelektrolytischen Oxidation von aus Leichtmetall und/oder Leichtmetalllegierungen hergestellten Werkstücken mit einem oben beschriebenen erfindungsgemäßen Elektrolyten. In einer ersten Variante des erfindungsgemäßen Verfahrens ist vorgesehen, dass die plasmaelektrolytische Oxidation mittels Gleichstrom, insbesondere bei einer Spannung von 250 V bis 700 V erfolgt. Besonders bevorzugt ist hierbei, dass die Stromdichte zwischen 1 A/dm2 und 30 A/dm2 beträgt. Derart hergestellte Oxida- tionsschichten weisen eine besonders kompakte, dichte Schicht auf, die nur eine sehr geringe Porosität aufweist. Eine derartig geringe Porosität ist insbesondere dann gewünscht, wenn eine besonders hohe Korrosionsfestigkeit des Werkstücks erforderlich ist. The invention furthermore relates to a process for the plasma-electrolytic oxidation of workpieces produced from light metal and / or light metal alloys with an electrolyte according to the invention described above. In a first variant of the method according to the invention, it is provided that the plasma-electrolytic oxidation takes place by means of direct current, in particular at a voltage of 250 V to 700 V. It is particularly preferred here that the current density is between 1 A / dm 2 and 30 A / dm 2 . Oxidation layers produced in this way have a particularly compact, dense layer which has only a very low porosity. Such a low porosity is particularly desirable when a particularly high corrosion resistance of the workpiece is required.
Alternativ hierzu erfolgt die plasmaelektrolytische Oxidation mittels Pulsverfahren, wobei anodische Pulse bevorzugterweise mit einer Spannung von 250 V bis 700 V angelegt werden. Hierbei ist besonders bevorzugter Weise vorgesehen, dass während der an modischen Pulse die Stromdichte zwischen 1 A/dm2 und 30 A/dm2 beträgt. Der Einsatz des Pulsverfahrens hat den Vorteil, dass durch gezielte Steuerung der Pulse die plasmachemische Reaktion an der Oberfläche des Werkstücks kontrolliert werden kann. Damit lassen sich insbesondere eine geringe Oberflächenrauhigkeit sowie eine geringere Porosität der Oxidations- schicht auf dem Werkstück erzielen. Untersuchungen der Anmelderin haben zudem gezeigt, dass sich eine höhere Pulsfrequenz positiv auf die Korrosionsfestigkeit der beschichteten Werkstücke auswirkt. Alternatively, the plasma electrolytic oxidation is carried out by means of pulse methods, with anodic pulses preferably being applied at a voltage of 250 V to 700 V. In this case, it is particularly preferred that the current density be between 1 A / dm 2 and 30 A / dm 2 during the on fashionable pulses. The use of the pulse method has the advantage that the plasma-chemical reaction at the surface of the workpiece can be controlled by targeted control of the pulses. This makes it possible, in particular, to achieve a low surface roughness and a lower porosity of the oxidation layer on the workpiece. Investigations by the applicant have also shown that a higher pulse frequency has a positive effect on the corrosion resistance of the coated workpieces.
Um die die Eigenschaften der Oxidationsschicht in Hinblick auf ihre Porosität, ihrer Haftfestigkeit und/oder Abriebsfestigkeit variieren zu können, werden in einer weiteren Ausführung der Erfindung zusätzlich kathodische Pulse angelegt, deren Spannung vorzugsweise zwischen 30 V und 200 V beträgt. In order to be able to vary the properties of the oxidation layer with regard to its porosity, its adhesive strength and / or abrasion resistance, in a further embodiment of the invention additional cathodic pulses are applied whose voltage is preferably between 30 V and 200 V.
Hierbei ist besonders bevorzugt vorgesehen, dass die Strompulse eine Dauer von zumindest 5 με aufweisen und durch Pausen von zumindest 3 με getrennt sind. In this case, it is particularly preferably provided that the current pulses have a duration of at least 5 με and are separated by pauses of at least 3 με.
Weitere Variationsmöglichkeiten ergeben sich durch die Überlagerung der anodischen und/oder kathodischen Strompulse mit einem konstanten Basisstrom. Further possible variations result from the superposition of the anodic and / or cathodic current pulses with a constant base current.
Schließlich können auch während der Herstellung der Oxidationsschicht auf dem Werkstück die Stärke und/oder Dauer der anodischen und/oder kathodischen Strompulse variiert werden. Finally, the thickness and / or duration of the anodic and / or cathodic current pulses can also be varied during the production of the oxidation layer on the workpiece.
Im Folgenden wird anhand von nichteinschränkenden Ausführungsbeispielen mit zugehörigen Figuren die Erfindung näher erläutert. Hierin zeigen : The invention is explained in more detail below with reference to non-limiting exemplary embodiments with associated figures. Herein show:
Fig. 1 eine rasterelektronenmikroskopische Aufnahme der Oberfläche einer mit oberflächenmodifizierten Si02-Partikeln hergestellten PEO- Schicht; Fig. 2 das EDX-Spektrum der Oberfläche aus Fig. 1; 1 shows a scanning electron micrograph of the surface of a surface-modified SiO 2 particles produced PEO layer. FIG. 2 shows the EDX spectrum of the surface of FIG. 1; FIG.
Fig. 3 eine rasterelektronenmikroskopische Aufnahme eines Querschliffs durch die PEO-Schicht aus Fig. 1; FIG. 3 shows a scanning electron micrograph of a cross section through the PEO layer from FIG. 1; FIG.
Fig. 4 das EDX-Spektrum eines Querschliffs aus der PEO-Schicht aus 4 shows the EDX spectrum of a cross section from the PEO layer
Fig. 3;  Fig. 3;
Fig. 5 eine rasterelektronenmikroskopische Aufnahme der Oberfläche einer mit Bentonit-Zusatz hergestellten PEO-Schicht; FIG. 5 shows a scanning electron micrograph of the surface of a PEO layer produced with bentonite additive; FIG.
Fig. 6 das EDX-Spektrum der Oberfläche aus Fig. 5; FIG. 6 shows the EDX spectrum of the surface of FIG. 5; FIG.
Fig. 7 eine rasterelektronenmikroskopische Aufnahme eines Querschliffs durch die PEO-Schicht aus Fig. 5; FIG. 7 is a scanning electron micrograph of a cross section through the PEO layer of FIG. 5; FIG.
Fig. 8 das EDX-Spektrum eines Querschliffs aus der PEO-Schicht aus Fig. 8 shows the EDX spectrum of a cross section of the PEO layer
Fig. 7; und  Fig. 7; and
Fig. 9 ein Röntgendiffrakrogramm der PEO-Schicht aus Fig. 7. Beispiel 1 : Beschichtung mit oberflächenmodifiziertem Aerosil 200 a. ) Modifikation der Aerosil-Partikel und Herstellung des Elektrolyten 9 shows an X-ray diffraction program of the PEO layer from FIG. 7. EXAMPLE 1 Coating with surface-modified Aerosil 200 a. ) Modification of the Aerosil Particles and Preparation of the Electrolyte
25 g Aerosil 200 (eine nichtporöse, amorphe Kieselsäure mit einer spezifischen Oberfläche von 200 m2/g, Evonik Industries) wurden in 1 I n-Butanol suspendiert. Anschließend wurden eine Lösung aus 20 ml 35%ige Salzsäure, 200 ml 3- Mercaptopropyltrimethoxysiloxan und 20 ml Wasser sowie eine Lösung von 120 ml 3-Mercaptopropyltrimethoxysiloxan in 100 ml n-Butanol hinzugefügt und die Mischung bei 40°C 8 bis 10 Stunden gerührt. Danach wurde eine Lösung von 40 ml 25%igem Ammoniak, 200 ml 3-Mercaptopropyltrimethoxysiloxan und 100 ml n-Butanol zugegeben und die Mischung über Nacht gerührt. 25 g of Aerosil 200 (a non-porous, amorphous silica having a specific surface area of 200 m 2 / g, Evonik Industries) were suspended in 1 l of n-butanol. Subsequently, a solution of 20 ml of 35% hydrochloric acid, 200 ml of 3-mercaptopropyltrimethoxysiloxane and 20 ml of water and a solution of 120 ml of 3-mercaptopropyltrimethoxysiloxane in 100 ml of n-butanol were added and the mixture was stirred at 40 ° C for 8 to 10 hours. Thereafter, a solution of 40 ml of 25% ammonia, 200 ml of 3-mercaptopropyltrimethoxysiloxane and 100 ml of n-butanol was added and the mixture was stirred overnight.
Nach dem Abfiltrieren, Waschen und Trocknen wurde das modifizierte Aerosil in 2 I 35%igem H2O2 aufgenommen und 24 Stunden bei 60°C gerührt, um die oberflächlich gebundenen Thiolgruppen zu Sulfonsäure zu oxidieren. After filtering off, washing and drying, the modified Aerosil was taken up in 2 l of 35% H 2 O 2 and stirred at 60 ° C. for 24 hours in order to oxidise the surface-bonded thiol groups to sulfonic acid.
Das so erhaltene oberflächenmodifizierte Aerosil wurde einem Elektrolyten, bestehend aus einer Lösung von 3 g/l KOH und 3 g/l K2S1O3 in einer Konzentration von 30 g/l zugesetzt. The thus-obtained surface-modified Aerosil was added to an electrolyte consisting of a solution of 3 g / L KOH and 3 g / L K 2 S 13 O 3 in a concentration of 30 g / L.
b. ) Durchführung des PEO-Prozesses Als Substrat wurde ein 1 mm starkes Blech aus der industriell verbreiteten Aluminiumlegierung 6082 mit den Maßen 25 mm x 100 mm verwendet. b. ) Implementation of the PEO process The substrate used was a 1 mm thick sheet of the industrially used 6082 aluminum alloy measuring 25 mm × 100 mm.
Zur Herstellung der Schicht wurde ein bipolarer Rechteckpuls verwendet, wobei die anodische und kathodische Stromdichte 10 A/dm2 und die jeweilige Pulsdauer 500 MS betrug, was einer Frequenz von 1 kHz entspricht. Die Beschichtungsdauer betrug 30 Minuten. A bipolar rectangular pulse was used to produce the layer, the anodic and cathodic current density being 10 A / dm 2 and the respective pulse duration 500 MS, which corresponds to a frequency of 1 kHz. The coating time was 30 minutes.
Die rasterelektronischen Aufnahmen gemäß den Figs.1 und 3 sowie den zugehörigen EDX-Spektren gemäß den Figs.2 und 4 zeigen die Entstehung einer kompakten, dichten Schicht durch das Vorhandensein der oberflächenmodifizierten Partikel im Elektrolyten, die im Gegensatz zu den partikelfrei hergestellten Schichten nur eine geringe Porosität aufweist. The scanning electron images according to FIGS. 1 and 3 and the associated EDX spectra according to FIGS. 2 and 4 show the formation of a compact, dense layer due to the presence of the surface-modified particles in the electrolyte, which in contrast to the particle-free produced layers only one has low porosity.
Beispiel 2: Schicht mit Bentonit a. ) Herstellung des Elektrolyten Example 2: Layer with bentonite a. ) Preparation of the electrolyte
Zu einem Elektrolyten bestehend aus 3 g/l NaOH und 3 g/l Na2Si03 wurden 30 g/l Bentonit zugegeben und gerührt, bis eine gleichmäßige Suspension entstanden ist. b. ) Durchführung des PEO-Prozesses To an electrolyte consisting of 3 g / l NaOH and 3 g / l Na 2 SiO 3, 30 g / l bentonite were added and stirred until a uniform suspension had formed. b. ) Implementation of the PEO process
Als Substrat diente ein 1 mm starkes Blech aus der kupferhältigen Aluminiumlegierung 2017 mit den Abmessungen 25 mm x 100 mm. Zur Herstellung der Schicht wurde ein bipolarer Rechteckpuls verwendet, wobei die anodische und kathodische Stromdichte 10 A/dm2 und die jeweilige Pulsdauer 500 με betrug, was einer Frequenz von 1 kHz entspricht. Die Beschichtungsdauer betrug 30 Minuten. The substrate used was a 1 mm thick sheet of the copper-containing aluminum alloy 2017 with the dimensions 25 mm x 100 mm. A bipolar rectangular pulse was used to produce the layer, the anodic and cathodic current density being 10 A / dm 2 and the respective pulse duration 500 με, which corresponds to a frequency of 1 kHz. The coating time was 30 minutes.
Die Zugabe dieser Partikel bewirkte ebenfalls die Ausbildung einer verhältnismäßig dicken, kompakten und porenarmen Schicht, wobei in diesem Fall die Schichtstruktur des Montmorillonits (Hauptbestandteil von Bentonit) zumindest teilweise erhalten bleibt, wie anhand der röntgendiffraktometrischen Messung gemäß der Fig. 9 nachgewiesen wurde. The addition of these particles also caused the formation of a relatively thick, compact and low-pore layer, in which case the layer structure of montmorillonite (main constituent of bentonite) is at least partially preserved, as evidenced by the X-ray diffractometric measurement of FIG.

Claims

P A T E N T A N S P R Ü C H E PATENT APPLICATIONS
1. Elektrolyt zur plasmaelektrolytischen Oxidation von aus Leichtmetall und/oder Leichtmetalllegierungen hergestellten Werkstücken enthaltend eine Salzlösung, wobei zumindest ein Salz oder eine Kombination zweier oder mehrerer Salze aus einer Gruppe ausgewählt ist, die Metallsalze, insbesondere Borate, Phosphate, Nitrate, Sulfate, Aluminate, Silikate, Manganate, Molybdate, Wolframate, und/oder Salze von organischen Säuren, insbesondere Methansulfonate und/oder Amidosulfonate, und/oder Metallkomplexe sowie Kombinationen hieraus enthält, dadurch gekennzeichnet, dass anorganische nichtmetallische Partikel in dieser Salzlösung suspendiert sind. 1. Electrolyte for the plasma-electrolytic oxidation of workpieces produced from light metal and / or light metal alloys containing a salt solution, wherein at least one salt or a combination of two or more salts is selected from a group comprising metal salts, in particular borates, phosphates, nitrates, sulfates, aluminates, Silicates, manganates, molybdate, tungstates, and / or salts of organic acids, in particular methanesulfonates and / or amidosulfonates, and / or metal complexes and combinations thereof, characterized in that inorganic non-metallic particles are suspended in this salt solution.
2. Elektrolyt nach Anspruch 1, dadurch gekennzeichnet, dass die anorganischen nichtmetallischen Partikel aus einer Gruppe ausgewählt sind, die in der Salzlösung unlösliche Oxide, Hydroxide oder Silikate enthält. 2. An electrolyte according to claim 1, characterized in that the inorganic non-metallic particles are selected from a group containing in the salt solution insoluble oxides, hydroxides or silicates.
3. Elektrolyt nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die anorganischen nichtmetallischen Partikel einen durchschnittlichen Durchmesser von mindestens 10 nm ausweisen, und bevorzugterweise oberflächenmodifiziert sind, sodass ihre Oberflächenenergie und/oder Zetapotential in Hinblick auf ihren Ausgangszustand erhöht oder reduziert ist. 3. Electrolyte according to claim 1 or 2, characterized in that the inorganic non-metallic particles have an average diameter of at least 10 nm, and are preferably surface-modified, so that their surface energy and / or zeta potential is increased or reduced in terms of their initial state.
4. Elektrolyt nach Anspruch 3, dadurch gekennzeichnet, dass die anorganischen nichtmetallischen Partikel mittels reaktiver Verbindungen modifiziert sind, die aus einer Gruppe gewählt sind, die Silizium- und/oder Germaniumverbindungen, insbesondere Germaniumhalogenide und/oder Siloxane und/oder halogenierte Silane enthält. 4. An electrolyte according to claim 3, characterized in that the inorganic non-metallic particles are modified by means of reactive compounds which are selected from a group which contains silicon and / or germanium compounds, in particular germanium halides and / or siloxanes and / or halogenated silanes.
5. Elektrolyt nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass die anorganischen nichtmetallischen Partikel aus einer Gruppe ausgewählt sind, die Tonminerale, insbesondere Bentonit, Kaolinit und/oder Mont- morrillonit enthält. 5. An electrolyte according to any one of claims 1 to 4, characterized in that the inorganic non-metallic particles are selected from a group containing clay minerals, in particular bentonite, kaolinite and / or montmorrillonite.
6. Verfahren zur plasmaelektrolytischen Oxidation von aus Leichtmetall und/ oder Leichtmetalllegierungen hergestellten Werkstücken, gekennzeichnet durch durch einen Elektrolyten nach einem der Ansprüche 1 bis 5. 6. A process for the plasma electrolytic oxidation of workpieces produced from light metal and / or light metal alloys, characterized by an electrolyte according to one of claims 1 to 5.
7. Verfahren nach Anspruch 6, dadurch gekennzeichnet, dass die plasma- elektrolytische Oxidation mittels Gleichstrom, insbesondere bei einer Spannung von 250 V bis 700 V erfolgt. 7. The method according to claim 6, characterized in that the plasma-electrolytic oxidation by means of direct current, in particular at a voltage of 250 V to 700 V takes place.
8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, dass die Stromdichte zwischen 1 A/dm2 und 30 A/dm2 beträgt. 8. The method according to claim 7, characterized in that the current density between 1 A / dm 2 and 30 A / dm 2 .
9. Verfahren nach Anspruch 6, dadurch gekennzeichnet, dass die plasma- elektrolytische Oxidation mittels Pulsverfahren erfolgt, wobei anodische Pulse bevorzugterweise mit einer Spannung von 250 V bis 700 V angelegt werden. 9. The method according to claim 6, characterized in that the plasma-electrolytic oxidation takes place by means of pulse method, wherein anodic pulses are preferably applied with a voltage of 250 V to 700 V.
10. Verfahren nach Anspruch 9, dadurch gekennzeichnet, dass die Stromdichte während der anodischen Pulse zwischen 1 A/dm2 und 30 A/dm2 beträgt. 10. The method according to claim 9, characterized in that the current density during the anodic pulses between 1 A / dm 2 and 30 A / dm 2 .
11. Verfahren nach Anspruch 9 oder 10, dadurch gekennzeichnet, dass zusätzlich kathodische Pulse angelegt werden, deren Spannung vorzugsweise zwischen 30 V und 200 V beträgt. 11. The method according to claim 9 or 10, characterized in that additional cathodic pulses are applied, whose voltage is preferably between 30 V and 200 V.
12. Verfahren nach einem der Ansprüche 9 bis 11, dadurch gekennzeichnet, dass die Strompulse eine Dauer von zumindest 5 με aufweisen und durch Pausen von zumindest 3 με getrennt sind. 12. The method according to any one of claims 9 to 11, characterized in that the current pulses have a duration of at least 5 με and are separated by pauses of at least 3 με.
13. Verfahren nach einem der Ansprüche 9 bis 12, dadurch gekennzeichnet, dass die anodischen und/oder kathodischen Strompulse mit einem konstanten Basisstrom überlagert werden. 13. The method according to any one of claims 9 to 12, characterized in that the anodic and / or cathodic current pulses are superimposed with a constant base current.
14. Verfahren nach einem der Ansprüche 9 bis 13, dadurch gekennzeichnet, dass während der Herstellung der Oxidationsschicht auf dem Werkstück aus Leichtmetall oder Leichtmetalllegierung die Stärke und/oder Dauer der anodischen und/oder kathodischen Strompulse variiert werden. 14. The method according to any one of claims 9 to 13, characterized in that during the production of the oxidation layer on the workpiece made of light metal or light alloy, the strength and / or duration of the anodic and / or cathodic current pulses are varied.
15. Verwendung des Verfahrens nach einem der Ansprüche 6 bis 14 zur plas- malektrolytischen Oxidation von Werkstoffen aus Leichtmetallen und deren Legierungen, insbesondere aus Aluminium, Magnesium, Titan, Beryllium, Tantal oder Zirkon sowie deren Legierungen. 15. Use of the method according to any one of claims 6 to 14 for the plasma electrolytic oxidation of materials of light metals and their alloys, in particular of aluminum, magnesium, titanium, beryllium, tantalum or zirconium and their alloys.
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