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
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used

Definitions

• the present invention relates to the oxidation of aluminum and its alloys, with the object of obtaining hard coatings on precision mechanical components, which require good resistance to friction, wear and corrosion.
• a .10 to 20% sulphuric acid solution with various additives is used as an electrolyte.
• electrolysis a well-known phenomenon occurs, which is the oxidation of the surface of the elements forming the anode, by the oxygen being formed by the decomposition of the water by the current: a more complex chemical phenomenon also occurs which is the attack of the aluminum oxide coating by the sulphuric acid.
• the alloys used for the mechanical parts contain addition elements which increase their mechanical characteristics.
• the constituents of alloys which give solid solutions are uniformly oxidized and have no harmful effect on the quality of the coatings, but the elements not in solution precipitate at the grain joints, and they are attacked by the sulphuric acid in the electrolyte and an inter-granular attack is produced.
• the process according to the invention permits hard anodic coatings to be obtained, whose thickness can reach and exceed 170 microns, while operating at ambient temperature, for example, in the region of 15 C.
• the structure of the resulting coating is finer and more homogeneous than previously and the hardness is at least equal and the resistance to corrosion is improved.
• the electrolyte according to the invention for anodic treatment of aluminum and its alloys is constituted as follows G./ liter Al (SO .l8H O 200 to 400 (COO'H) .2H O 20 to 50 CH OHCHOH-CH OH 7 to 20
• the invention is also directed to an anodic oxidation treatment with the above electrolyte, at a temperature which is between and 20, with a current of density between 2.5 and 3.5 amperes/dm. for a period which is between one hour and 2 /2 hours.
• the present invention is also directed to an anodic oxidation process for aluminum and its alloys, comprising the following additional operations:
• the invention is also concerned with the products obtained by treatment with the above electrolyte.
• the following table indicates the results obtained by application of the method of the invention to conventional aluminum alloys Resistance to salt spray, ac- Breakdown cording to AFN OR voltage in standard PNX Thickness in Vrckers n for an anodhardness ization time of It is possible to obtain coatings of greater thickness by extending the anodizing time.
• a treatment lasting 2 to 2 /2 hours gives anodic layers of to microns, depending on the alloys.
• the coatings thus obtained have a very fine structure, without any crackling or powdering on the edges of the parts, and they can be obtained in the dimensions as required or corrected by grinding, permitting mechanical parts to be obtained which are of very high precision.
• the application of the invention should permit a rapid industrial development of mechanical parts consisting of aluminum alloy, when it is desired simultaneously to obtain lightness, good surface hardness and high resistance to corrosion.
• the hardness properties of the anodic coatings obtained 7 by the method of the invention conform to the standards of US AMS 2 468 and in particular to the standard MPD 3 707 p 3-6, Knoop hardness corresponding to 427 HV.
• a very stable electrolyte is formed from nontoxic and inexpensive commercial products, which can be more easily handled than the sulphuric acid usually employed,
• Coatings of high quality which are very hard and not cracked, can be obtained in desired size or corrected by grinding.
• a process for forming a hard, thick anodic coating on a surface of a pure or alloyed aluminum article comprising anodizing the aluminum article in an aqueous bath consisting essentially of aluminum sulfate in the propor- 4 tion of 200 to 400 g./ liter, 20 to 50 g./ liter of oxalic acid, and 7 to 20 g./liter of glycerol.
• An electrolyte for forming hard anodizing coatings consisting essentially of an aqueous solution of 200 to 400 g./ liter of aluminum sulfate, 20 to 50 g./liter of oxalic acid and 7 to 20 g./liter of glycerol.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)
• Detergent Compositions (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=9058490

Family Applications (1)

Country Status (4)

Cited By (1)

• 1970
  • 1970-07-09 FR FR707025414A patent/FR2096872B1/fr not_active Expired
• 1971
  • 1971-06-14 GB GB2783271A patent/GB1305842A/en not_active Expired
  • 1971-07-06 DE DE19712133472 patent/DE2133472A1/de active Pending
  • 1971-07-08 US US00160921A patent/US3738921A/en not_active Expired - Lifetime

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