EP0213331B1 - Element of aluminium or an aluminium alloy with a hard oxide layer, and process for the manufacture of such an element - Google Patents

Element of aluminium or an aluminium alloy with a hard oxide layer, and process for the manufacture of such an element Download PDF

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Publication number
EP0213331B1
EP0213331B1 EP86109418A EP86109418A EP0213331B1 EP 0213331 B1 EP0213331 B1 EP 0213331B1 EP 86109418 A EP86109418 A EP 86109418A EP 86109418 A EP86109418 A EP 86109418A EP 0213331 B1 EP0213331 B1 EP 0213331B1
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Prior art keywords
hard oxide
process according
oxide layer
electrolyte
component
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EP86109418A
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German (de)
French (fr)
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EP0213331A3 (en
EP0213331A2 (en
Inventor
Heinz Georg Baus
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Altura Leiden Holding BV
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Duscholux GmbH
Altura Leiden Holding BV
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    • 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
    • C25D11/18—After-treatment, e.g. pore-sealing
    • C25D11/24—Chemical after-treatment
    • 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
    • C25D11/18—After-treatment, e.g. pore-sealing

Definitions

  • the invention relates to a component made of aluminum or an aluminum alloy, which has a hard oxide layer on its surface according to the features specified in the preamble of claim 1.
  • the invention further relates to a method for producing such a component.
  • a hard oxide layer In contrast to oxide layers, which are used for decorative purposes and have a considerably lower layer thickness, a hard oxide layer is softened in a noticeable manner by the sealing, the wear resistance or abrasion resistance being adversely affected.
  • An increase in the abrasion resistance leads to a re-evaluation of the corrosion resistance, as can be seen, for example, from the above-mentioned book, page 351.
  • an increase in corrosion resistance results in a reduction in abrasion resistance.
  • the by no means outstanding resistance of known hard anodized components to acids, silicones, adhesives or paints has hitherto prevented use in many applications.
  • the sealing of oxide layers in aqueous solutions is greatly influenced by the temperature. Effective sealing using nickel / cobalt acetate only takes place at comparatively high temperatures up to 100 ° Celsius. The high amount of energy required in this respect requires additional measures and the manufacturing outlay is not insignificant. Additional protection of already sealed oxide layers can be achieved by preservation with organic substances such as varnishes, waxes, oils or resins. It is disadvantageous here that such water-repellent agents can easily be dissolved out of the oxide layer by organic solvents.
  • a post-compression process is known from PCT patent application WO 84/00982, which is used for components which are anodized according to standard processes and whose layers have a small thickness, ie do not constitute hard oxide layers. Such components are primarily intended for use indoors or outdoors, and they have to withstand the weather conditions. Such components have no special requirements with regard to abrasion resistance.
  • DE-A 34 11 678 discloses a process for the post-compression of aluminum and aluminum alloys following the anodization. This post-compression process is used for oxide layers with a small layer thickness, for example in the order of 15 micrometers.
  • the component to be treated is immersed in a post-compression bath, which is kept at a temperature between 15 and 30 ° Celsius and contains an aqueous solution of nickel salts in a concentration of 0.1 to 50 g / l.
  • a nonionic surfactant is added to the solution, which is intended to lower the surface tension of the bath.
  • the object of the invention is to eliminate the disadvantages indicated above and to propose a component which has improved abrasion resistance and corrosion resistance. Furthermore, a method is to be proposed that enables the manufacture of such a component in a simple manner and with low energy consumption.
  • the proposed component is characterized by a high abrasion resistance and a high corrosion resistance.
  • silicones, adhesives, acids or paints are practically not absorbed by the hard oxide layer of the component.
  • the hard oxide layer With a pore volume of between 5 and 15%, the hard oxide layer is essentially free of microcracks, the surface roughness being between 0.8 and 1 micrometer, preferably essentially 0.9 micrometer. Due to the good corrosion resistance, practically no corrosion effects were found in a salt spray test after 192 hours.
  • the salt spray test was carried out according to Method 811 of Federal Test Procedure Standard No. 151 or ASTMB 117 "Method for Salt Spray Test" with a 5% salt spray solution.
  • the acid resistance of the component can also be demonstrated by testing with nitric acid.
  • the abrasion resistance of the hard oxide layer of the proposed component is improved by up to 25% compared to previously known hard oxide layers.
  • the abrasion resistance is demonstrable in accordance with Method 6192 of Federal Test Procedure Standard No. 141, using disks CS-17 at a load of 1000 grams, the disks at a load cycle of 10,000, at a speed of 70 revolutions per minute turn on the hard oxide layer. Accordingly, the abrasion resistance according to MIL-A-86 25 C (military norm) be determined.
  • MIL-A-86 25 C military norm
  • an abrasion of about 30 milligrams was determined, while values of the order of 44 milligrams and above are achieved in known hard oxide layers.
  • the metal salts absorbed in the hard oxide layer, in particular nickel and / or cobalt fluoride significantly reduce the moisture absorption of the hard oxide layer, and high abrasion resistance is also provided for long periods of use.
  • a special embodiment of the component is specified in claim 2.
  • the Vickers hardness is in the range between 2940 and 5880 N / mm 2 (300 and 600 Kp / mm 2 ), in particular between 3920 and 4900 N / mm 2 (400 and 500 Kp / mm 2 ).
  • the method specified in claim 4 for producing the component can be carried out with low energy consumption.
  • the application of the mineral oil-containing solution according to the third process step can be carried out with little expenditure on equipment and also with little expenditure of time.
  • the preservative can be applied to the component in a simple manner by dipping or spraying.
  • the electrolyte / nickel or cobalt fluoride or comparable metal salts provided for the second process step contains. Furthermore, according to claim 8, the pH of the electrolyte in the second process step is between 6 and 7. Finally, it has proven to be advantageous if, according to claim 9, the metal salts are contained in the electrolyte in a concentration of 7 to 12 percent by volume.
  • the component produced by the method according to the invention has a special resistance to silicones, adhesives, acids and colors, in particular stamping inks. So far, such agents have left unsightly and practically indelible marks on the anodized surface.
  • the method according to the invention thus creates new areas of application and possible uses for anodized workpieces. For example, reference is only made to the use in aircraft, in particular as worktops in the galley, etc. Discoloration of the surface of such plates as a result of overflowing fruit juices, coffee etc. has hitherto prevented the use of anodized aluminum plates.
  • the method according to the invention it is now possible to add components with a hard oxide layer even and precisely in such critical applications.
  • a discoloration is formed on the oxide layer, for example a green discoloration in the case of nickel. Such discoloration is undesirable in practice.
  • the hard oxide layer is sealed and impregnated by the subsequent treatment, whereby a pore closure is achieved. It should be noted that while the usual compression with other means had a pore seal, there was also a reduction in wear resistance. It was recognized according to the invention that the discoloration or colored layer can be removed again by the third method step. It was not foreseeable for a person skilled in the art that the above-mentioned advantages with regard to abrasion resistance, corrosion resistance and resistance are achieved overall.
  • the anodically produced oxide layers are cleaned, for example, in building and facade cladding, be it immediately after the building has been built or at suitable cleaning intervals.
  • the cleaning agents provided for this purpose are not used in the third process step.
  • the second process step is carried out in a temperature range between 10 ° and 50 ° C, in particular between 25 to 35 ° C.
  • the microporous anodic oxide layer is pore-sealed with little or no energy used for heating.
  • the second method step can be carried out with or alternatively without power supply, a duration between 10 and 20 minutes having proven to be expedient.
  • nickel or cobalt sulfate and / or fluorides are used in order to obtain a pore seal in the hard oxide layer or a similar oxide layer in the workpiece.
  • a high level of abrasion resistance, corrosion resistance and excellent resistance to active agents, in particular silicones, adhesives, acids and dyes is nevertheless achieved.
  • a mineral oil-containing solution is used as the water-repellent preservative in the third process step.
  • Alcohol is used as a solvent.
  • the mineral oil-containing solution has a density of 0.8, is colorless and reacts neutrally.
  • the mineral oil content is less than 10 g per liter.
  • the preservative can contain mineral oil and wax dissolved in it. In this way, wax dissolved in heating oil can also be provided particularly expediently.
  • the water-repellant preservative is expediently applied to the component by dipping or spraying, with any deposits subsequently being wiped off the oxide layer. So at for example, a greenish discoloration caused by nickel is removed from the hard oxide layer.
  • the preservative prevents or reduces moisture absorption and the wear and abrasion resistance is guaranteed for a long period of time.
  • the oxide layer that is to say the first method step known per se, is expediently produced when AC and DC current are superimposed.
  • a current density in the range between 1 to 10 amperes per square decimeter is specified at an initial voltage of 10 to 60 volts. Raising the voltage to a maximum final value of up to 100 volts has proven to be particularly expedient. 10 to 25 percent sulfuric acid is used as the electrolyte.
  • the electrolyte may also contain organic or inorganic additives.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

Description

Die Erfindung bezieht sich auf ein Bauteil aus Aluminium oder einer Aluminiumlegierung, das auf seiner Oberfläche eine Hartoxidschicht gemäß den im Oberbegriff des Patentanspruchs 1 angegebenen Merkmalen aufweist. Ferner bezieht sich der Erfindung auf ein Verfahren zur Herstellung eines derartigen Bauteils.The invention relates to a component made of aluminum or an aluminum alloy, which has a hard oxide layer on its surface according to the features specified in the preamble of claim 1. The invention further relates to a method for producing such a component.

Aus dem Buch "Die Oberflächenbehandlung von Aluminium, S. Wernick und R. Pinner, 1969, Eugen G. Leuze Verlag, D-7968 Saulgau, S. 334ff" ist es bekannt, ein Bauteil aus Aluminium oder einer Aluminiumlegierung mit einer Hartoxidschicht zu versehen. So wird beispielsweise nach dem Hardas-Verfahren das Bauteil in Schwefelsäure gebracht, wobei mit Gleichstrom und überlagertem Wechselstrom bei einer Spannung zwischen 20 und 60 Volt sowie einer Stromdichte von 10 bis 20 A/cm2, eine Oxidschicht mit einer Dicke zwischen 25 und 205 Mikrometern erzeugt wird. In dem genannten Buch ist auf Seite 347 ausgeführt, daß bei der Forderung nach einer hohen Verschleißfestigkeit in wässrigen Lösungen nicht gedichtet wird. Im Gegensatz zu Oxidschichten, die für dekorative Zwecke zum Einsatz gelangen und eine erheblich niedrigere Schichtdicke aufweisen, wird nämlich eine Hartoxidschicht durch das Dichten in merklicher Weise aufgeweicht, wobei die Verschleißfestigkeit bzw. Abriebfestigkeit nachteilig beeinflußt werden. Bei Hartoxidschichten ist ein relevanter Zusammenhang zwischen Verschleißfestigkeit einerseits und Korrosionsbeständigkeit andererseits festzustellen. Eine Erhöhung der Abriebfestigkeit führt zu einer Reudizierung der Korrosionsbeständigkeit, wie es beispielsweise dem genannten Buch, Seite 351 zu entnehmen ist. Umgekehrt ergibt eine Erhöhung der Korrosionsbeständigkeit eine Reduzierung der Abriebfestigkeit. Die keineswegs überragende Resistenz bekannter hartanodisierter Bauteile gegen Säuren, Silikone, Klebstoffe oder Farben stand bisher dem Einsatz in vielen Anwendungsfällen entgegen. Ferner wird das Dichten von Oxidschichten in wässrigen Lösungen in starkem Maße von der Temperatur beeinflußt. So erfolgt ein effektives Dichten mittels Nickel/Kobaltacetat nur bei vergleichsweise hohen Temperaturen bis zu 100° Celsius. Der insoweit erforderliche hohe Energieeinsatz erfordert zusätzliche Maßnahmen und der Fertigungsaufwand ist nicht unerheblich. Ein zusätzlicher Schutz bereits gedichteter Oxidschichten kann durch Konservierung mit organischen Stoffen, wie Lacken, Wachsen, Ölen oder Harzen erreicht werden. Es ist hierbei von Nachteil, daß derartige Wasser abstoßende Mittel von organischen Lösungsmitteln leicht aus der Oxidschicht herausgelöst werden können.From the book "The surface treatment of aluminum, S. Wernick and R. Pinner, 1969, Eugen G. Leuze Verlag, D-7968 Saulgau, p. 334ff" it is known to provide a component made of aluminum or an aluminum alloy with a hard oxide layer . For example, according to the Hardas process, the component is brought into sulfuric acid, with an oxide layer with a thickness between 25 and 205 micrometers using direct current and superimposed alternating current at a voltage between 20 and 60 volts and a current density of 10 to 20 A / cm 2 is produced. In the book mentioned on page 347 it is stated that when high wear resistance is demanded, sealing is not carried out in aqueous solutions. In contrast to oxide layers, which are used for decorative purposes and have a considerably lower layer thickness, a hard oxide layer is softened in a noticeable manner by the sealing, the wear resistance or abrasion resistance being adversely affected. In the case of hard oxide layers, there is a relevant relationship between wear resistance on the one hand and corrosion resistance on the other. An increase in the abrasion resistance leads to a re-evaluation of the corrosion resistance, as can be seen, for example, from the above-mentioned book, page 351. Conversely, an increase in corrosion resistance results in a reduction in abrasion resistance. The by no means outstanding resistance of known hard anodized components to acids, silicones, adhesives or paints has hitherto prevented use in many applications. Furthermore, the sealing of oxide layers in aqueous solutions is greatly influenced by the temperature. Effective sealing using nickel / cobalt acetate only takes place at comparatively high temperatures up to 100 ° Celsius. The high amount of energy required in this respect requires additional measures and the manufacturing outlay is not insignificant. Additional protection of already sealed oxide layers can be achieved by preservation with organic substances such as varnishes, waxes, oils or resins. It is disadvantageous here that such water-repellent agents can easily be dissolved out of the oxide layer by organic solvents.

Aus der PCT-Patentanmeldung WO 84/00982 ist ein Nachverdichtungsverfahren bekannt, das bei solchen Bauteilen zum Einsatz gelangt, die nach Standard-Verfahren eloxiert sind und deren Schichten eine geringe Dicke aufweisen, also keine Hartoxidschichten darstellen. Derartige Bauteile werden vor allem im Bauwesen im Innen- oder Außeneinsatz vorgesehen und sie müssen den Witterungsbedingungen standhalten. Besondere Anforderungen hinsichtlich der Abriebsfestigkeit werden an solche Bauteile nicht gestellt.A post-compression process is known from PCT patent application WO 84/00982, which is used for components which are anodized according to standard processes and whose layers have a small thickness, ie do not constitute hard oxide layers. Such components are primarily intended for use indoors or outdoors, and they have to withstand the weather conditions. Such components have no special requirements with regard to abrasion resistance.

Ferner ist aus der DE-A 34 11 678 ein Verfahren zur Nachverdichtung von Aluminium und Aluminiumlegierungen im Anschluß an die Eloxierung bekannt. Dieses Nachverdichtungsverfahren gelangt für Oxidschichten von geringer Schichtdicke, beispielsweise in der Größenordnung von 15 Mikrometern, zum Einsatz. Das zu behandelnde Bauteil wird in ein Nachverdichtungsbad getaucht, das auf einer Temperatur zwischen 15 bis 30° Celsius gehalten wird und eine wässrige Lösung von Nickelsalzen in einer Konzentration von 0,1 bis 50 g/I enthält. Der Lösung ist ein nichtionisches Tensid zugesetzt, das eine Erniedrigung der Oberflächenspannung des Bades bewirken soll.Furthermore, DE-A 34 11 678 discloses a process for the post-compression of aluminum and aluminum alloys following the anodization. This post-compression process is used for oxide layers with a small layer thickness, for example in the order of 15 micrometers. The component to be treated is immersed in a post-compression bath, which is kept at a temperature between 15 and 30 ° Celsius and contains an aqueous solution of nickel salts in a concentration of 0.1 to 50 g / l. A nonionic surfactant is added to the solution, which is intended to lower the surface tension of the bath.

Der Erfindung liegt die Aufgabe zugrunde, die oben aufgezeigten Nachteile zu beseitigen und ein Bauteil vorzuschlagen, das eine verbesserte Abriebfestigkeit und Korrosionsbeständigkeit aufweist. Ferner soll ein Verfahren vorgeschlagen werden, das in einfacher Weise und mit geringem Energieeinsatz die Herstellung eines derartigen Bauteils ermöglicht.The object of the invention is to eliminate the disadvantages indicated above and to propose a component which has improved abrasion resistance and corrosion resistance. Furthermore, a method is to be proposed that enables the manufacture of such a component in a simple manner and with low energy consumption.

Die Lösung der Aufgabe erfolgt für das gattungsgemäße Bauteil gemäß den im Kennzeichen des Patentanspruchs 1 angegebenen Merkmalen. Das Verfahren zur Herstellung dieses Bauteiles ist im Patentanspruch 4 angegeben.The problem is solved for the generic component according to the features specified in the characterizing part of patent claim 1. The method for producing this component is specified in claim 4.

Das vorgeschlagene Bauteil zeichnet sich durch eine hohe Abriebfestigkeit sowie eine hohe Korrosionsbeständigkeit aus. So werden vor allem Silikone, Klebstoffe, Säuren oder Farben von der Hartoxidschicht des Bauteils praktisch nicht aufgenommen. Die Hartoxidschicht ist bei einem Porenvolumen zwischen 5 bis 15% im wesentlichen frei von Mikrorissen, wobei die Oberflächenrauheit zwischen 0,8 bis 1 Mikrometer, bevorzugt im wesentlichen 0,9 Mikrometer, groß ist. Aufgrund der guten Korrosionsbeständigkeit waren in einem Salzsprühtest nach 192 Stunden praktisch noch keine Korrosionseinwirkungen festzustellen. Der Salzsprühtest wurde nach der Methode 811 der Federal-Prüfverfahrensnorm Nr. 151 bzw. ASTMB 117 "Methode zur Salzsprühprüfung" mit einer 5% igen Salzsprühlösung ausgeführt. Die Säurebeständigkeit des Bauteils ist durch Test mit Salpetersäure ebenso nachweisbar. Die Abriebfestigkeit der Hartoxidschicht des vorgeschlagenen Bauteils ist gegenüber vorbekannten Hartoxidschichten bis zu 25% verbessert. Die Abriebfestigkeit ist nachweisbar in Übereinstimmung mit der Methode 6192 der Federal-Prüfverfahrensnorm Nr. 141, unter Verwendung von Scheiben CS-17 bei einer Belastung von 1000 Gramm, wobei sich die Scheiben bei einer Lastspielzahl von 10.000, bei einer Geschwindigkeit von 70 Umdrehungen pro Minute auf der Hartoxidschicht drehen. Entsprechend kann die Abriebfestigkeit nach MIL-A-86 25 C (military norm) festgestellt werden. Bei dem erfindungsgemäß vorgeschlagenen Bauteil wurde hierbei ein Abrieb von etwa 30 Milligramm ermittelt, während bei bekannten Hartoxidschichten Werte in der Größenordnung von 44 Milligramm und darüber erreicht werden. Durch die in der Hartoxidschicht absorbierten Metallsalze, und zwar insbesondere Nickel- und/oder Kobaltfluorid, wird die Feuchtigkeitsaufnahme der Hartoxidschicht wesentlich reduziert, und auch für lange Gebrauchszeiten ist eine hohe Abriebfestigkeit gegeben.The proposed component is characterized by a high abrasion resistance and a high corrosion resistance. In particular, silicones, adhesives, acids or paints are practically not absorbed by the hard oxide layer of the component. With a pore volume of between 5 and 15%, the hard oxide layer is essentially free of microcracks, the surface roughness being between 0.8 and 1 micrometer, preferably essentially 0.9 micrometer. Due to the good corrosion resistance, practically no corrosion effects were found in a salt spray test after 192 hours. The salt spray test was carried out according to Method 811 of Federal Test Procedure Standard No. 151 or ASTMB 117 "Method for Salt Spray Test" with a 5% salt spray solution. The acid resistance of the component can also be demonstrated by testing with nitric acid. The abrasion resistance of the hard oxide layer of the proposed component is improved by up to 25% compared to previously known hard oxide layers. The abrasion resistance is demonstrable in accordance with Method 6192 of Federal Test Procedure Standard No. 141, using disks CS-17 at a load of 1000 grams, the disks at a load cycle of 10,000, at a speed of 70 revolutions per minute turn on the hard oxide layer. Accordingly, the abrasion resistance according to MIL-A-86 25 C (military norm) be determined. In the case of the component proposed according to the invention, an abrasion of about 30 milligrams was determined, while values of the order of 44 milligrams and above are achieved in known hard oxide layers. The metal salts absorbed in the hard oxide layer, in particular nickel and / or cobalt fluoride, significantly reduce the moisture absorption of the hard oxide layer, and high abrasion resistance is also provided for long periods of use.

Eine besondere Ausgestaltung des Bauteils ist im Patentanspruch 2 angegeben. Abhängig vom jeweils zum Einsatz gelangenden Aluminium oder der Aluminiumlegierung des Bauteils liegt die Härte nach Vickers im Bereich zwischen 2940 und 5880 N/mm2 (300 und 600 Kp/mm2), insbesondere zwischen 3920 und 4900 N/mm2 (400 und 500 Kp/ mm2). Der bei vorbekannten Bauteilen festzustellende Abfalle der Härte von innen nach außen um bis zu 100 Einheiten bei verdichteten Hartoxidschichten wird vermieden.A special embodiment of the component is specified in claim 2. Depending on the aluminum used or the aluminum alloy of the component, the Vickers hardness is in the range between 2940 and 5880 N / mm 2 (300 and 600 Kp / mm 2 ), in particular between 3920 and 4900 N / mm 2 (400 and 500 Kp / mm 2 ). The drop in hardness from inside to outside of up to 100 units in the case of compacted hard oxide layers, which can be determined in known components, is avoided.

Das im Patentanspruch 4 angegebene Verfahren zur Herstellung des Bauteiles kann mit geringem Energieeinsatz durchgeführt werden. Die Aufbringung der mineralölhaltigen Lösung gemäß dem dritten Verfahrensschritt kann mit geringem apparativen Aufwand und auch mit geringem Zeitaufwand durchgeführt werden. Das Konservierungsmittel kann durch Tauchen oder Aufsprühen auf das Bauteil in einfacher Weise aufgebracht werden.The method specified in claim 4 for producing the component can be carried out with low energy consumption. The application of the mineral oil-containing solution according to the third process step can be carried out with little expenditure on equipment and also with little expenditure of time. The preservative can be applied to the component in a simple manner by dipping or spraying.

Wie im Patentanspruch 5 angegeben, enthält der für den zweiten Verfahrensschritt vorgesehene Elektrolyt/Nickel- oder Kobaltfluoride oder vergleichbare Metallsalze. Desweiteren ist gemäß dem Patentanspruch 8 der PH-Wert des Elektrolyten im zweiten Verfahrensschritt zwischen 6 bis 7. Schließlich hat es sich als zweckmäßig erwiesen, wenn gemäß dem Patentanspruch 9 in dem Elektrolyten die Metallsalze in einer Konzentration von 7 bis 12 Volumenprozent enthalten sind.As stated in claim 5, the electrolyte / nickel or cobalt fluoride or comparable metal salts provided for the second process step contains. Furthermore, according to claim 8, the pH of the electrolyte in the second process step is between 6 and 7. Finally, it has proven to be advantageous if, according to claim 9, the metal salts are contained in the electrolyte in a concentration of 7 to 12 percent by volume.

Das nach dem erfindungsgemäßen Verfahren hergestellte Bauteil besitzt eine besondere Resistenz gegen Silikone, Klebstoffe, Säuren sowie Farben, insbesondere Stempelfarben. Bisher hinterließen derartige Mittel auf der eloxierten Oberfläche unansehnliche und praktisch nicht zu entfernende Spuren. Durch das erfindungsgemäße Verfahren werden somit neue Einsatzgebiete und Anwendungsmöglichkeiten für eloxierte Werkstücke geschaffen. So sei nur beispielshaft auf den Einsatz in Flugzeugen, und zwar insbesondere als Arbeitsplatten in der Bordküche usw., verwiesen. Verfärbungen der Oberfläche derartiger Platten infolge von übergelaufenen Fruchtsäften, Kaffee usw. stand bisher einem Einsatz von eloxierten Aluminiumplatten entgegen. Durch das erfindungsgemäße Verfahren ist es nunmehr möglich, auch und gerade in derart kritischen Anwendungsfällen Bauteile mit einer Hartoxidschicht ein zusetzen.The component produced by the method according to the invention has a special resistance to silicones, adhesives, acids and colors, in particular stamping inks. So far, such agents have left unsightly and practically indelible marks on the anodized surface. The method according to the invention thus creates new areas of application and possible uses for anodized workpieces. For example, reference is only made to the use in aircraft, in particular as worktops in the galley, etc. Discoloration of the surface of such plates as a result of overflowing fruit juices, coffee etc. has hitherto prevented the use of anodized aluminum plates. By means of the method according to the invention it is now possible to add components with a hard oxide layer even and precisely in such critical applications.

Beim Behandeln mit einem Elektrolyten, der Metallsalze und ggfs. auch organische und anorganische Zusatzstoffe enthält, bildet sich auf der Oxidschicht eine Verfärbung, und zwar beispielshaft bei Nickel eine grüne Verfärbung. Eine solche Verfärbung ist in der Praxis unerwünscht. Die Hartoxidschicht wird durch die nachfolgende Behandlung versiegelt und imprägniert, wobei ein Porenverschluß erreicht wird. Es sei festgehalten, daß bei dem bisher üblichen Verdichten mit anderen Mitteln zwar ein Porenverschluß darüberhinaus aber eine Verminderung der Verschleißfestigkeit gegeben war. Erfindungsgemäß wurde erkannt, daß durch den dritten Verfahrensschritt die Verfärbung bzw. Farbschicht wieder entfernt werden kann. Es war für einen Fachmann nicht vorauszusehen, daß insgesamt die oben aufgeführten Vorteile im Hinblick auf Abriebfestigkeit, Korrosionsbeständigkeit und Resistenz erzielt werden. Es sei festgehalten, daß für den dritten Verfahrensschritt kein üblicher Eloxalreiniger, also abrasives Mittel, zum Einsatz gelangt, sondern ein wasserabstoßendes Konservierungsmittel. Bekanntlich werden beispielsweise bei Gebäude- und Fassadenverkleidungen die anodisch erzeugten Oxidschichten gereinigt, sei es unmittelbar nach Erstellung des Gebäudes oder auch in geeigneten Reinigungsintervallen. Die hierzu vorgesehenen Reinigungsmittel gelangen in dem dritten Verfahrensschritt nicht zum Einsatz.When treated with an electrolyte that contains metal salts and possibly also organic and inorganic additives, a discoloration is formed on the oxide layer, for example a green discoloration in the case of nickel. Such discoloration is undesirable in practice. The hard oxide layer is sealed and impregnated by the subsequent treatment, whereby a pore closure is achieved. It should be noted that while the usual compression with other means had a pore seal, there was also a reduction in wear resistance. It was recognized according to the invention that the discoloration or colored layer can be removed again by the third method step. It was not foreseeable for a person skilled in the art that the above-mentioned advantages with regard to abrasion resistance, corrosion resistance and resistance are achieved overall. It should be noted that no conventional anodizing agent, ie abrasive agent, is used for the third process step, but a water-repellent preservative. As is known, the anodically produced oxide layers are cleaned, for example, in building and facade cladding, be it immediately after the building has been built or at suitable cleaning intervals. The cleaning agents provided for this purpose are not used in the third process step.

Der zweite Verfahrensschritt wird in einem Temperaturbereich zwischen 10° und 50°C, insbesondere zwischen 25 bis 35°C, durchgeführt. In diesem Verfahrensschritt erfolgt bei keinem oder auch nur geringen Energieeinsatz zur Heizung ein Porenverschluß der mikroporösen anodisch erzeugten Oxidschicht. Der zweite Verfahrensschritt kann mit oder alternativ auch ohne Stromzufuhr durchgeführt werden, wobei eine Dauer zwischen 10 und 20 Minuten sich als zweckmäßig erwiesen hat. Es gelangen insbesondere Nickel-oder Kobaltsulfat und/oder Fluoride zum Einsatz, um einen Porenverschluß der Hartoxidschicht oder einer ähnlichen Oxidschicht des Werkstükkes zu erhalten. In Verbindung mit dem dritten Verfahrensschritt wird in überraschender Weise gleichwohl eine hohe Abriebfestigkeit, Korrosionsbeständigkeit und hervorragende Resistenz gegen einwirkende Mittel, und zwar insbesondere Silikone, Klebestoffe, Säuren sowie Farbstoffe, erreicht.The second process step is carried out in a temperature range between 10 ° and 50 ° C, in particular between 25 to 35 ° C. In this process step, the microporous anodic oxide layer is pore-sealed with little or no energy used for heating. The second method step can be carried out with or alternatively without power supply, a duration between 10 and 20 minutes having proven to be expedient. In particular, nickel or cobalt sulfate and / or fluorides are used in order to obtain a pore seal in the hard oxide layer or a similar oxide layer in the workpiece. In connection with the third process step, a high level of abrasion resistance, corrosion resistance and excellent resistance to active agents, in particular silicones, adhesives, acids and dyes, is nevertheless achieved.

Es wird als wasserabstoßendes Konservierungsmittel im dritten Verfahrensschritt eine mineralölhaltige Lösung verwendet. Als Lösungsmittel gelangt Alkohol zum Einsatz. Die mineralölhaltige Lösung weist ein Dichte von 0,8 auf, ist farblos und reagiert neutral. Der Mineralölgehalt ist kleiner als 10 g pro Liter. Das Konservierungsmittel kann Mineralöl und in diesem gelöstes Wachs enthalten. So kann besonders zweckmäßig auch in Heizöl gelöstes Wachs vorgesehen werden. Die Auftragung des wasserabstoßenden Konservierungsmittels auf das Bauteil erfolgt zweckmäßig durch Tauchen oder Aufsprühen, wobei nachfolgend eventuelle Beläge von der Oxidschicht abgewischt werden. So wird beispielsweise eine durch Nickel bedingte grünliche Verfärbung von der Hartoxidschicht entfernt. Das Konservierungsmittel verhindert oder reduziert die Feuchtigkeitsaufnahme und für eine lange Zeitdauer werden die Verschleiß- und Abriebfestigkeit gewährleistet.A mineral oil-containing solution is used as the water-repellent preservative in the third process step. Alcohol is used as a solvent. The mineral oil-containing solution has a density of 0.8, is colorless and reacts neutrally. The mineral oil content is less than 10 g per liter. The preservative can contain mineral oil and wax dissolved in it. In this way, wax dissolved in heating oil can also be provided particularly expediently. The water-repellant preservative is expediently applied to the component by dipping or spraying, with any deposits subsequently being wiped off the oxide layer. So at for example, a greenish discoloration caused by nickel is removed from the hard oxide layer. The preservative prevents or reduces moisture absorption and the wear and abrasion resistance is guaranteed for a long period of time.

Zweckmäßig wird die Oxidschicht, also der an sich bekannte erste Verfahrensschritt, bei einer Überlagerung von Wechsel- und Gleichstrom erzeugt. Es wird eine Stromdichte im Bereich zwischen 1 bis 10 Ampere pro Quadratdezimeter bei einer anfänglichen Spannung von 10 bis 60 Volt vorgegeben. Das Hochfahren der Spannung auf einen maximalen Endwert bis 100 Volt hat sich als besonders zweckmäßig erwiesen. Als Elektrolyt gelangt 10 bis 25 prozentige Schwefelsäure zum Einsatz. Ferner kann der Elektrolyt gegebenenfalls organische oder anorganische Zusatzstoffe enthalten.The oxide layer, that is to say the first method step known per se, is expediently produced when AC and DC current are superimposed. A current density in the range between 1 to 10 amperes per square decimeter is specified at an initial voltage of 10 to 60 volts. Raising the voltage to a maximum final value of up to 100 volts has proven to be particularly expedient. 10 to 25 percent sulfuric acid is used as the electrolyte. The electrolyte may also contain organic or inorganic additives.

Claims (14)

1. A component made of aluminium or an aluminium alloy which has on its surface a hard oxide coating with a thickness of between 25 and 250 microns, the hard oxide coating being treated with an electrolyte which contains metal salts and preserved with a water-repellent agent,
characterised in that the hard oxide layer has a pore volume of between 5 and 15%,
the hard oxide layer is substantially free from microcracks,
metal salts are absorbed into the hard oxide layer and hydrolysed to form hydroxides
and the hard oxide layer has a surface roughness of between 0.8 and 1 micron.
2. A component according to claim 1, characterised in that the Vickers hardness of the hard oxide coating is substantially constant over its entire thickness and is between 2940 and 5880 N/ mm2 (300 to 600 Kp/mm2).
3. A component according to claim 1 or 2, characterised in that the hard oxide layer contains a substantially smaller amount of hydrated oxide than is achieved with a sealing treatment using hot water or saturated steam.
4. A process for preparing the component of aluminium or aluminium alloy according to one of claims 1 to 3, wherein the component is first provided with the hard oxide coating, more particularly in an electrolyte consisting of 10 to 25% of sulphuric acid and optionally organic and/or inorganic additives, and in a second step treatment with the electrolyte is carried out and in a third step the water-repellent preserving agent is applied to the hard oxide coating, characterised in that, in the second step, the treatment is carried out in a temperature range of between 10° and 50°C and in the third step a solution which contains mineral oil is used as the preserving agent.
5. A process according to claim 4, characterised in that the electrolyte provided for the second step contains nickel or cobalt fluorides or comparable metal salts (fluorides).
6. A process according to claim 5, characterised in that organic or inorganic additives are present in the electrolyte.
7. A process according to one of claims 4 to 6, characterised in that the second step is carried out at a temperature in the range from 25 to 35°C, the component being immersed in the electrolyte for a period of between 10 and 20 minutes.
8. A process according to one of claims 4 to 7, characterised in that the electrolyte has a pH of between 6 and 7.
9. A process according to one of claims 4 to 8, characterised in that the concentration of the metal salt is between 7 and 12 percent by volume.
10. A process according to one of claims 4 to 9, characterised in that, in the third step, the preserving agent is applied by immersion or spraying onto the oxide coating.
11. A process according to one of claims 4 to 10, characterised in that the preserving agent has a density of approximately 0.8 and a substantially neutral pH.
12. A process according to one of claims 4 to 11, characterised in that mineral oil in a concentration of less than 10 g/I in a solvent is used for the third step.
13. A process according to one of claims 4 to 12, characterised in that the preserving agent contains a thin mineral oil, preferably heating oil.
14. A process according to one of claims 4to 13, characterised in that the preserving agent contains wax dissolved therein.
EP86109418A 1985-08-06 1986-07-10 Element of aluminium or an aluminium alloy with a hard oxide layer, and process for the manufacture of such an element Expired - Lifetime EP0213331B1 (en)

Applications Claiming Priority (2)

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DE19853528180 DE3528180A1 (en) 1985-08-06 1985-08-06 METHOD FOR ANODIC HARDOXIDATION
DE3528180 1985-08-06

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EP0213331A2 EP0213331A2 (en) 1987-03-11
EP0213331A3 EP0213331A3 (en) 1987-03-25
EP0213331B1 true EP0213331B1 (en) 1990-06-27

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AT404245B (en) * 1996-09-20 1998-09-25 Weber Guenter BOLT STORAGE DEVICE
WO2000039368A2 (en) * 1998-12-24 2000-07-06 Bayer Aktiengesellschaft Method for producing an ultraphobic surface on an aluminium base
DE10028772B4 (en) * 2000-06-07 2005-03-17 Technische Universität Dresden Aluminum material with ultrahydrophobic surface, process for its preparation and use
WO2014185835A1 (en) * 2013-05-14 2014-11-20 Saab Ab Aircraft porous metal surface filled with wax and method in production line

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DE1137280B (en) * 1958-07-17 1962-09-27 Knapsack Ag Process for compressing surface-treated workpieces made of light metals and light metal alloys to improve corrosion resistance and wear resistance
IT1205633B (en) * 1983-03-28 1989-03-23 Boston Spa PROCESS AND BATH FOR FIXING OF ALUMINUM AND ALUMINUM ALLOYS FOLLOWING THE ANODIZATION TREATMENT

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EP0213331A2 (en) 1987-03-11
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DE3528180A1 (en) 1987-02-19
ES2000131A6 (en) 1987-12-16
DE3672221D1 (en) 1990-08-02

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