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, in particular in a thickness between 25 and 200 micrometers.
• the invention further relates to a method for producing such a component.
• Methods for hard anodization are known in order to produce hard oxide layers on components made of aluminum or aluminum alloys by using suitable electrolytes and working conditions.
• low electrolyte temperatures and higher current densities are specified.
• the Hardas process in sulfuric acid works with direct current and superimposed alternating current, at a voltage between 20 and 60 volts and a current density of 5 to 20 amperes per square decimeter. Layer thicknesses between 25 and 75 micrometers are generated. According to other processes, for example oxal If acid is used, layer thicknesses of up to approximately 200 micrometers and, in special cases, even more can be generated. Fine cracks are present in such hard oxide layers when they are removed from the electrolyte.
• micro cracks are very disadvantageous for corrosion resistance.
• the chemical resistance of a hard anodized surface, especially in acids, is moderate.
• the comparatively low chemical resistance, especially when exposed to silicones, adhesives or acids, in many cases prevented the use of components with a hard anodized surface.
• the abrasion resistance, wear resistance and hardness do not meet the ever higher requirements.
• the decrease in wear resistance could be determined under the influence of the effects of corrosion, the wear resistance of hard anodized surfaces being considerably worse after just a few days and weeks after production than immediately after production.
• the object of the invention is to further develop the component and the known hard anodization processes with little effort in such a way that improved abrasion resistance and / or corrosion resistance are achieved.
• the oxide layer is said to have improved resistance to acting media, in particular silicones, adhesives, acids and paints.
• the surface or the hard oxide layer should be reproducibly and economically protected from external influences.
• the component according to the invention is characterized in that the hard oxide layer has a pore volume of between 5 and 15%, that the hard oxide layer is essentially free of microcracks and that metal salts are absorbed in the hard oxide layer and that they are hydrolyzed to form hydroxides and / or that the hard oxide layer is a Surface roughness between 0.8 to 1 micron, preferably substantially 0.9 microns.
• the component according to the invention is characterized by a high abrasion resistance and also by a surprisingly good chemical resistance. In particular, silicones, adhesives, acid or paints are not absorbed by the hard oxide layer.
• the hard oxide layer has an essentially constant high hardness over its entire thickness.
• the Vickers hardness depending on the respective aluminum or aluminum alloy, is in the range between 300 and 600 kilopont per square mm and in particular between 400 and 500 kilopont per square mm.
• the surface roughness of the component according to the invention is between 0.8 and 1 micrometer, so that post-processing of the component of this type can be omitted after production.
• the corrosion resistance is surprisingly good, with virtually in a salt spray test for 192 hours no Korrosionseinw 'im pact were observed.
• the salt spray test was carried out according to Method 811 of Federal Test Procedure Standard No.
• the durability of the component according to the invention can be demonstrated by tests with nitric acid.
• the abrasion resistance of the hard oxide layer of the component according to the invention is improved by up to 25% compared to previously known hard oxide layers. Abrasion resistance is demonstrated in accordance with Method 6192 of Federal Test Procedure Standard No. 141, using washers CS-17 at a load of 1000 g, the disks being at a load cycle of 10,000 at a speed of 70 rpm of the hard oxide layer.
• An abrasion of about 30 mg was determined in the component according to the invention, while values of the order of 44 mg and above are achieved with known hard oxide layers.
• the metal salts absorbed according to the invention in particular nickel and / or cobalt fluoride, surprisingly significantly reduce the moisture absorption of the hard oxide layer, so that there is a high resistance to abrasion even for long periods of use.
• a method such that, following the hard anodization carried out in a manner known per se or a method for producing a comparable oxide layer, the component in an electrolyte containing metal salts, in particular nickel or cobalt fluorides, in a second method step, is dipped; Comparable metal salts, in particular sulfates or chlorides, can also be used in the context of this invention.
• a treatment, in particular immersion or spraying, of a preservative which is in particular water-repellent is preferably carried out in a third method step.
• Nickel fluoride or cobalt fluoride have proven particularly outstanding for the second process step.
• the pH of the electrolyte in the second process step is between 6 and 7.
• the metal salts are contained in the electrolyte in a concentration of 7 to 12 percent by volume according to the invention.
• the construction produced according to the method according to the invention is distinguished by a considerably improved corrosion resistance and abrasion resistance, the resistance to abrasion Test results are up to 25% above the values of previously known anodization processes. If the abrasion test according to MIL-A-86 25 C (military norm) is carried out with 10,000 load cycles, an abrasion of the order of magnitude of only 30 mg is determined; with conventional hard anodizing, the values are 44 mg. In addition, it was found that surprisingly there is 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.
• 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 components produced by the method according to the invention also have an improved hardness and surface roughness of between 0.8 and 1 micrometer, advantageously 0.9 micrometer.
• 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 or a comparable oxide layer is sealed and impregnated by the subsequent treatment, a pore closure being 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. According to the invention, it was recognized that the discoloration or color layer can surprisingly be removed again by the third process step. For a person skilled in the art, it was not foreseeable that the total of the above listed advantages in terms of abrasion resistance, corrosion resistance and resistance can be achieved.
• the anodically produced oxide layers are cleaned, for example, in building and facade cladding, be it immediately after the building has been built or also in suitable cleaning intervals.
• the cleaning agents provided for this purpose are not used in the third process step.
• the second method 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 of between 10 and 20 minutes having proven to be expedient according to the invention.
• nickel or cobalt sulfate and / or fluorides are used 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 acting agents, in particular silicones, adhesives, acids and dyes is nevertheless achieved.
• the preservative can consist of or contain mineral oil and wax dissolved in it. So can be particularly useful wax dissolved in heating oil may also be provided.
• the water-repellant preservative is expediently applied to the component by dipping or spraying, with any deposits which are subsequently wiped off from the oxide layer in the context of the invention.
• a greenish discoloration due to nickel is removed from the hard oxide layer.
• the preservative is expediently applied by dipping or spraying. According to the invention, the preservative prevents or reduces the absorption of moisture, so that the wear and tear resistance is guaranteed even 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 useful. 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)

Family

ID=6277831

Family Applications (1)

Country Status (3)

Cited By (4)

Family Cites Families (2)

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

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