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
  • C25D11/14—Producing integrally coloured layers

Definitions

• the present invention relates to an anodizing process and, more particularly, to a method of producing a colored oxide layer on an aluminum-containing metal body.
• aluminum or aluminum alloy bodies which should not reflect a substantial amount of light and preferably should be of a color which may range from the color of dull old silver to the color of smoke or to deep dark brown and even black.
• the color of the aluminum or the aluminum alloy element must be capable of withstanding atmospheric influences and, furthermore, the surface of the metal elements must possess a sufficiently high corrosion resistance so as to be able to withstand the chemical and physical attacks to which, for instance, outer building walls and the like are exposed. For this reason, it is desirable to form a protective surface layer on the aluminum or aluminum alloy body or structural element, preferably by anodic oxidation.
• such metal elements formed of aluminum or aluminum alloys are subjected to anodic oxidation, for instance, in accordance with the direct current-sulfuric acid method, and the thus formed oxide layer is then dyed with inorganic or organic dyestuffs or by application of chromogeni-c compounds.
• the last mentioned method causes a rather strong development of hydrogen gas which also affects the electrolyte since after proceeding with the anodic oxidation for only a short period of time, a change in the color tone is observed and, furthermore, the color layer becomes "ice less and less uniform. Only by introducing additional amounts of sulfosalicyclic acid has it been possible to obtain again the same color tone as was obtained at the start of the anodic oxidation, and a short while after introduction of the additional amount of sulfosalicyclic acid there will be again a change in color tone and lesser uniformity of the color layer. Thus, this method does not possess the desired reliability.
• a further disadvantage of the last mentioned method is the fact that at the generally required current densities of at least between about 3 and 4 amperes per one hundred cm. the final voltage will be very high, in fact, up to about volts.
• the present invention contemplates a method of producing a colored oxide layer on an aluminum-containing metal body, comprising the step of subjecting the metal body to anodic oxidation in an electrolyte consisting essentially of an aqueous solution of at least one substance selected from the group consisting of sulfuric acid and metal sulfates, sulfosalicyclic acid, and at least one substance selected from the group consisting of maleic acid and maleic acid anhydride.
• the anodic treatment or anodic oxidation of the aluminum or aluminum alloy body is carried out in an electrolyte which consists of an aqueous solution of sulfosalicyclic acid, maleic acid and/or maleic acid anhydride and which also contains either sulfuric acid or a water soluble metal sulfate.
• the concentration of sulfosalicyclic acid in the aqueous electrolyte solution will be between 1 and 5% and most preferably between 3 and 5%, the concentration of the maleic acid and or maleic acid anhydride between 0.5 and 1.5% and most preferably about 1%, and sulfuric acid and/ or the metal sulfate will be present in an amount equivalent to a concentration of between 0.1 and 1% most preferably about 0.5% of sulfuric acid.
• the metal sulfate which fully or in part may replace the sulfuric acid of the electrolyte Will be chosen from those metal sulfates which are water soluble. Furthermore, metal sulfates which contain a metal which in the presence of aluminum may be precipitated from the solution should not be introduced since such metal sulfates would give cause to local corrosion and an uneven color tone. Of the easily available water soluble metal sulfates, preferably manganese sulfate, iron sulfate and zinc sulfate may be advantageously used. It is also possible to operate in accordance with the present invention with an electrolyte containing aluminum sulfate, provided that the concentration of the total aluminum dissolved in the electrolyte will not exceed between about 2.5 and 3 grams per liter. The concentration of up to 2.5 and 3 grams per liter is to include the aluminum which is introduced in the form of aluminum sulfate as Well as the aluminum which during anodic oxidation of the aluminum or the aluminum alloy body may be dissolved by the electrolyte.
• the concentration of aluminum in the electrolyte solution should be maintained so as to correspond to the above-mentioned limits of sulfuric acid concentration.
• Anodic oxidation according to the present invention is preferably carried out at ambient temperature, i.e., a temperature of between about 15 and 25 C.
• ambient temperature i.e., a temperature of between about 15 and 25 C.
• the temperature of the electrolyte may increase to, for instance, 30 or 35 C. or even up to about 40 C.
• temperatures considerably below 15 C the time required for obtaining the desired anodic oxide layer would be prolonged and thereby the process would become more and more uneconomical.
• anodic oxidation according to the present invention can be carried out advantageously at a current density of between 1 and 5, preferably between 1.5 and 3 amperes per 100 cm. Thereby, a potential of between 30 and up to a maximum of about 70 volts will be reached.
• the electrolyte according to the present invention differs qualitatively from the electrolytes of the prior art discussed hereinabove by containing maleic acid or maleic acid anhydride.
• the present invention is preferably carried out at relatively low concentrations of sulfosalicylic acid and sulfuric acid or metal sulfate.
• the desired dull old silver, smoky or deep-dark brown to black colors can be obtained on aluminum or aluminum alloy bodies in accordance with the present invention, whereby the specific color tone at a given bath temperature and otherwise equal operating conditions will depend on the composition of the aluminum or aluminum alloy body.
• the current density is primarily dependent on the quality of the aluminum or aluminum alloy.
• Certain aluminum alloys are of higher conductivity than others. Those of lesser conductivity are preferably treated at lower current densities, since otherwise the final voltage would be too high and this would lead to localized excessive load conditions. Furthermore, on weakened portions of the aluminum or alloy body it could then happen that local corrosions and uneven color tones would occur.
• the length of time for which the aluminum body is subjected to anodic oxidation must be correspondingly increased, as described in some of the examples following further below.
• aluminum alloys which are of higher electric conductivity may be anodized at greater current densities, such as for instance, between 3 and 4 amperes per 100 cm.
• Aluminum alloys of relatively low conductivity are preferably electrolytically oxidized at a current density of between 1 and up to at most 2 amperes per 100 cm.
• the foregoing presumes that the oxide layer formed by anodic oxidation is to be of a thickness of at least about 20 millimicrons and at most 30 millimicrons. Only in the case of metal bodies of very high conductivity it may also be desired to form an oxide layer having a thickness of about 40 millimicrons.
• Examples 120 are summarized in Table I.
• the description of the aluminum or aluminum alloy composition in Table I corresponds to that in the German ofiicial standards DIN 1712, Sheet 1, edition of 1961 and DIN 1725, Sheet 1, edition of 1961. These standards are de scribed in Tables III and IV further below.
• maleic acid 0.5% maleic acid anhydrite. 18 A1999 d0 5% sulfosalicylic acid, 0.5% sulfuric acid, 1% 3 30 30 Do.
• Example 14 shows the results obtained at substantially the lower limit of concentration of all components of the TABLE II.-APPEARANCE OF ALUMINUM ALLOY BODY ANODIZED AT DIFFERENT TEMPERATURES Current Treating Thick- Tempera- Ex. Material Shape Electrolyte, percent by weight, balance density, period, ness of turc, 0. Appearance water amp. /100 minutes Oxide 0111. Layer,
• all aluminum alloys which may be anodically oxidized are also capable of being treated in accordance with the present invention.
• aluminum alloys which contain more than 1% copper should be exelectrolytic bath. In this manner a rather light colored surface is obtained. It is not advisable to reduce the concentration of the constituents of the electrolytic bath below those given in Example 14, since at lower concentrations the body surface does not become dark and at the same time an attack at the grain boundaries of the material is to be seen.
• the upper limit of concentration of the individual components of the electrolytic bath may be somewhat higher than given in the examples in Table I. Thus, for instance it is possible to operate with higher concentrations than 5% of sulfosalicylic acid. However, for economic reasons, it is undesirable to increase the consumption of this relatively expensive acid. It also would be possible to increase the concentration of maleic acid, for instance to about 2%, without affecting the color tone. However, depending on the overall conditions of concentration in the bath, there will be a certain danger that at concentrations higher than 1.5% maleic acid may crystallize and this would result in an uneven coloration of the metal body.
• the method of the present invention is primarily used for the treatment of aluminum and aluminum alloy bodies for architectural purposes, such aluminum and aluminum alloy bodies are of primary interest which may be anodized so as to achieve a decorative effect thereby.
• These alloys include in addition to AlMg3, AlMgSi0.5 and AlMgSil which were used in the examples, also alloys such as AlMgl and AlMgZ.
• AlMn as well as pure aluminum of a purity of 99.0, 99.3, 99.5 and 99.9 may be advantageously treated according to the present invention.
• To use aluminum of a higher purity than 99.9% would not be practical for economic reasons.
• the composition of the aluminum of varying purity and of the aluminum alloys described hereinabove by their '5 DIN designations will be found in the following Tab es III and IV.
• a method of producing a colored oxide layer on a surface of a body formed of a metal selected from the group consisting of aluminum and aluminum alloys comprising the step of subjecting said body to anodic oxidation in an electrolyte consisting essentially of an aqueous solution of at least one substance selected from the group consisting of sulfuric acid and water-soluble meta-l sulfates, said substance being present in an amount equivalent to between 0.1% and 1% by Weight of sulfuric acid, between 1% and 5% by weight of sulfosalicylic acid, and between 0.5% and 1.5% by weight of a substance selected from the group consisting of maleic acid and maleic acid lanhydride.
• a method of producing a colored oxide layer on a surface of a body formed of a metal selected from the group consisting of aluminum and aluminum alloys comprising the step of subjecting said body at substantially ambient temperature to anodic oxidation in an electrolyte consisting essentially of an aqueous solution of at least one substance selected from the group consisting of sulfuric acid and water-soluble metal sulfates, said sub- 8 stance being present in an amount equivalent to between 0.1% and 1% by Weight of sulfuric acid, between 1% and 5% by weight of sulfosalicylic acid, and between 0.5 and 1.5% by weight of a substance selected from the group consisting of maleic acid and maleic acid anhydride.
• a method of producing a colored oxide layer on a surface of a body formed of a metal selected from the group consisting of aluminum and aluminum alloys comprising the step of subjecting said body at a temperature of up to 40 C. to ⁇ anodic oxidation in an electrolyte consisting essentially of an aqueous solution of at least one substance selected from the group consisting of sulfuric acid and water-soluble metal sulfates, said substance being present in an amount equivalent to between 0.1 and 1% by weight of sulfuric acid, between 1% and 5% by weight of sulfosalicylic acid, and between 0.5% and 1.5% by weight of a substance selected from the group consisting of maleic acid and maleic acid .anhydride.
• a method of producing a colored oxide layer on a surface of a body formed of a metal selected from the group consisting of aluminum and aluminum alloys comprising the step of subjecting said body to anodic oxidation at a current density of between about 1 and 5 amperes per cm. in an electrolyte consisting essentially of an aqueous solution of at least one substance selected from the group consisting of sulfuric acid and water-soluble metal sulfates, said substance being present in an amount equivalent to between 0.1% and 1% by weight of sulfuric acid, between 1% and 5% by weight of sulfosalicylic acid, and between 0.5% and 1.5% by Weight of a substance selected from the group consisting of maleic acid and maleic acid 'anhydride.
• a method of producing a colored oxide layer on a surface of a body formed of a metal selected from the group consisting of aluminum and aluminum alloys comprising the steps of subjecting said body to anodic oxidation in an electrolyte consisting essentially of an aqueous solutionof at least one substance selected from the group consisting of sulfuric acid and water-soluble metal sulfates, said substance being present in an amount equivalent to about 0.5 by weight of sulfuric acid, between 3% and 5% by weight of sulfosalicylic acid, and about 1% by weight of a substance selected from the group consisting of maleic acid and maleic acid anhydride.
• a method of producing a colored oxide layer on a surface of a body formed of a metal selected from the group consisting of aluminum and aluminum alloys comprising the step of subjecting said body to anodic oxidation at a current density of between about 1.5 and 3 amperes per 100 cm. in an electrolyte consisting essentially of an aqueous solution of at least one substance selected from the group consisting of sulfuric acid and water-soluble metal sulfates, :said substance being present in an amount equivalent to between 0.1% and 1% by weight of sulfuric acid, between 1% and 5% by weight of sulfosalicylic acid, and between 0.5% and 1.5% by weight of a substance selected from the group consisting of maleic acid and maleic acid anhydride.
• a method of producing a colored oxide layer on a surface of a body formed of a metal selected from the group consisting of aluminum and aluminum alloys comprising the step of subjecting said body at a temperature of up to 40 C. to anodic oxidation at a current density of between about 1.5 and 3 amperes per 100 cm? in an electrolyte consisting essentially of an aqueous solution of at least one substance selected from the group consisting of sulfuric acid and water-soluble metal sulfates, said substance being present in an amount equivalent to about 0.5% by weight of sulfuric acid, between 3% and 5% by weight of sulfosalicylic acid, and about 1% by weight of a substance selected from the group consisting of maleic acid and maleic acid anhydride.
• a method of producing a colored oxide layer on a surface of a body formed of a metal selected from the group consisting of aluminum and aluminum alloys comprising the step of subjecting said body at a temperature of between about 15 C. and 25 C. to anodic oxidation in an electrolyte consisting essentially of an aqueous solution of at least one substance selected from the group consisting of sulfuric acid and water-soluble metal sulfates, said substance being present in an amount equivalent to between 0.1% and 1% by weight of sulfuric acid, between 1% and 5% by weight of sulfosalicylic acid, and between 0.5% and 1.5% by weight of a substance selected from the group consisting of maleic acid and maleic acid anhydride.
• a method of producing a colored oxide layer on a suri ace of a body formed of a metal selected from the group consisting of aluminum and aluminum alloys comprising the step of subjecting said body to anodic oxidation in an electrolyte consisting essentially of an aqueous solution containing sulfate ions in an amount equivalent to between 0.1% and 1% by weight of sulfuric acid, between 1% and 5% by weight of su-lfosalicylic acid, and between 0.5% and 1.5% by weight of a substance selected from the group consisting of maleic acid and maleic acid anhydride.

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)
• Cookers (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=7580009

Family Applications (1)

Country Status (7)

Cited By (6)

Families Citing this family (1)

Citations (3)

• 0
  • NL NL121366D patent/NL121366C/xx active
  • BE BE632655D patent/BE632655A/xx unknown
  • NL NL293256D patent/NL293256A/xx unknown
• 1962
  • 1962-06-16 DE DEV22651A patent/DE1178272B/de active Pending
• 1963
  • 1963-05-07 LU LU43691D patent/LU43691A1/xx unknown
  • 1963-06-04 US US293920A patent/US3265597A/en not_active Expired - Lifetime
  • 1963-06-10 DK DK273063AA patent/DK102887C/da active
  • 1963-06-12 GB GB23467/63A patent/GB973391A/en not_active Expired

Patent Citations (4)

Also Published As

Similar Documents