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

• a hard anodic oxide film is formed uniformly on an aluminum base alloy containing 1% by weight or more of copper by subjecting the aluminum base alloy to anodic oxidation using an electrolyte comprising an aqueous solution containing to 40% by weight of an aromatic sulfonic acid such as sulfosalicylic acid, napthalenedisulfonic acid, naphthalene-trisulfonic acid, phenol sulfonic acid and sulfophthalic acid, and 15 to 40% by weight of sulfuric acid.
• an aromatic sulfonic acid such as sulfosalicylic acid, napthalenedisulfonic acid, naphthalene-trisulfonic acid, phenol sulfonic acid and sulfophthalic acid, and 15 to 40% by weight of sulfuric acid.
• This invention relates to a process for forming on an aluminum base alloy an anodic oxide film which is hard and excellent in corrosion resistance and rigidity.
• the present inventors made extensive studies or processses for forming anodic oxide films on aluminum base alloys. As the result, the inventors have found that a uniform and hard anodic oxide film is formed on a copper- 3,804,731 Patented Apr. 16, 1974 containing aluminum base alloy by subjecting the alloy to anodic oxidation treatment in an aqueous electrolyte containing an aromatic sulfonic acid and a high concentration sulfuric acid which solution has not been known hitherto. Particularly, it has been clarified that a hard anodic oxide film having an excellent quality is formed on an Al-Si-Cu alloy containing 6% by weight or more of silicon and 1% by weight or more of copper.
• the object of the present invention is to provide a process for forming a hard anodic oxide film on an aluminum base alloy, characterized by subjecting an aluminum alloy containing 1% by weight or more of copper to anodic oxidation treatment using as an electrolyte an aqueous solution containing 5 to 40% by weight of an aromatic sulfonic acid and 15 to 40% by weight of sulfuric acid.
• the aromatic sulfonic acid is an essential component for forming an anodic oxide film on an aluminum base alloy. If the concentration of the aromatic sulfonic acid is less than 5% by weight, no effect of increasing the hardness of the resulting film can be observed. Further, the aromatic sulfonic acid is difficultly dissolved to a concentration of more than 40% by weight in an aqueous sulfuric acid solution of such a concentration as adopted in the present invention. If the concentration of sulfuric acid is less than 15% by weight, not only no uniform anodic oxide film can be formed on a copper-containing aluminum alloy or a high silicon content aluminum alloy, but also the cell voltage becomes higher with formation and growth of the film to easily cause burning.
• the concentration of sulfuric acid is more than 40% by weight, the organic acid is lowered in solubility to decrease the hardness-improving effect of the aromatic sulfonic acid.
• a part of the sulfuric acid may be replaced by a water-soluble sulfate or bisulfate such as sulfate or bisulfate of an alkali metal.
• the aromatic sulfonic acid used in the present invention is sulfosalicylic acid, naphthalenedisulfonic acid, napthalene-trisulfonic acid, phenolsulfonic acid, sulfophthalic acid or the like aromatic sulfonic acid having at least one sulfone group.
• the electrolyte used in the present invention may be incorporated with a small amount of a carboxylic acid such as oxalic or maleic acid. 1
• Aluminum-copper alloys containing 1% by weight or more of copper which are to be treated according to the present process are not particularly limited in form but may be products of any forms such as castings, sheets, extrusions and the like. According to the present process, hard and uniform anodic oxide films can be formed on aluminum-silicon-copper alloys containing 6% by weight or more of silicon and 1% by weight or more of copper on which such films have been diflicultly formed hitherto.
• the hardness of the resulting film tends to lower with increasing anodic oxidation temperature. Accordingly, the electrolyte temperature is desirably below 20 C., more advantageously within the range from 0 to 15 C.
• the current density is in the range from 1 to 4 amp./dm. and the treatment period varies depending on the thickness of the resulting film.
• anodic oxide films formed according to the present process are subjected to conventional sealing treatment.
• aluminum alloy products having anodic oxide films formed according to the present process are to be used for pistons, cylinders, bearings, etc., however, it is sometimes preferable that the anodic oxide films are not subjected to sealing treatment, since the films, which have not been subjected to sealing treatment, are high in oil retainability.
• the present invention is illustrated in detail below with thickness and hardness from those formed according to reference to examples, but it is needless to say that the the known processes, and that the present process can invention is not limited to the examples. form hard and uniform anodic oxide films on copper- Aluminum alloy materials used in the examples and containing aluminum base alloys on which complete thick in comparative examples are shown in Table 1. 5 films have been difiicultly formed hitherto.
• EXAMPLE 1 EXAMPLE 8 The aluminum alloy 1 in Table 1 was degreased, etched and desmutted according to ordinary procedures, and then subjected to anodic oxidation treatment at a current den- 20 o 2 i of 2 2 for 60 minutes at a temperature of xldation treatment at a current denslty of 2.5 A./dm.
• the film formed by said anodic oxidation treatment was subment was subjected to sealing by means of boiling water. J' ed t0 Seali g treatment by use of boiling water.
• the film had a thickness of about 60,5 and a hardness of film had a thickness of about 60,71 and a hardness of about about Hvz370 in terms of Vickers hardness. HvzSOO in terms of Vickers hardness.
• Example 1 was repeated, except that the electrolyte composition was varied. The results obtained were as set Example 8 Was repeated, except that the elfictrolyte forth in Table 2.
• Example number Example number:
• Naphthalene-disuli'onic acid 15 9 igrso u nn a3 ⁇ a one sn 0 c ac 1o 4 5 2.5 5-7 40 40 450 4 ⁇ H280 2. 5 5-7 40 40 470 4 ⁇ H250 2. 5 10-12 55 420 ⁇ H2804 20 2. 5 5-7 60 60 510 C00 1% ⁇ H2804 2. 5 5-7 00 45 480 ⁇ H250 20 2. 5 10-12 50 440 15 2.
• a process for forming a hard anodic oxide film on an aluminum alloy characterized by subjecting an aluminum base alloy containing 1% by weight or more of copper to anodic oxidation treatment at a temperature below 20 C. using an aqueous electrolyte containing 5 to 40% by weight of an aromatic sulfonic acid selected from the group consisting of sulfosalicyclic acid, naphthalene-disulfonic acid, naphthalene-trisulfonic acid,
• Cited phenol-sulfonic acid and sulfophthalic acid and 15 to GERALD KAPLAN Primary Examiner by weight of sulfuric acid.

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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)
• Electroplating And Plating Baths Therefor (AREA)
• Electrochemical Coating By Surface Reaction (AREA)
• Electroplating Methods And Accessories (AREA)

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Cited By (6)

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• 1971
  • 1971-09-07 JP JP46069528A patent/JPS5140537B2/ja not_active Expired
• 1972
  • 1972-09-01 US US00285595A patent/US3804731A/en not_active Expired - Lifetime
  • 1972-09-01 DE DE2243178A patent/DE2243178C3/de not_active Expired
  • 1972-09-06 GB GB4132872A patent/GB1366738A/en not_active Expired
  • 1972-09-06 FR FR7231604A patent/FR2152678B1/fr not_active Expired
  • 1972-09-06 IT IT52581/72A patent/IT965235B/it active

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