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
  • C25D11/04—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.

Landscapes

• 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)

Applications Claiming Priority (2)

Publications (3)

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Family Applications (1)

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• 1985
  • 1985-08-06 DE DE19853528180 patent/DE3528180A1/de active Granted
• 1986
  • 1986-07-10 EP EP86109418A patent/EP0213331B1/de not_active Expired - Lifetime
  • 1986-07-10 DE DE8686109418T patent/DE3672221D1/de not_active Expired - Lifetime
  • 1986-08-06 ES ES8600912A patent/ES2000131A6/es not_active Expired

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