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

• This invention refers to a process for anodising aluminium or aluminium alloy parts, including pure or almost pure aluminium and all its combinations with other elements in any proportion.
• the acidic solutions used in anodising procedures are composed of sulphuric acid in high concentrations, or of chromic acid.
• the latter is the main component used in the aerospace industry.
• Sulphuric acid is not used in the aerospace industry due to the low adherence in the treated parts, while chromic acid has a high toxicity in live beings and is hazardous for the environment.
• the aqueous tartaric-sulphuric acid solution is an alternative method to anodise parts through an electrolytic process with low environmental impact. This method is described in patent number US 2002/0157961 A1.
• Another alternative method is an aqueous solution of sulphuric acid and boric acid described in U.S. Pat. No. 4,894,127. These methods do not provide the aluminium or aluminium alloy parts with the same properties pertaining to corrosion as the chromic acid treatment.
• the procedure in this invention uses the aluminium or aluminium alloy parts, described as anodes in an electrolytic cell with an aqueous acidic electrolyte, in order to create a superficial layer of aluminium oxide on said parts.
• This superficial aluminium oxide improves the properties pertaining to resistance against corrosion and surface layer adherence of an aluminium or aluminium alloy part.
• This invention refers to an anodising procedure for aluminium or aluminium alloys in which the aluminium or aluminium alloy parts are submerged in an aqueous solution at a temperature between 0C and 130° C., and where said solution includes:
• the inorganic salt of the transition metal may be present in a concentration between 5 ⁇ 10 ⁇ 7 and 1.5 M, preferably in a concentration between 1 ⁇ 10 ⁇ 6 and 1 M.
• said inorganic salt of the transition metal may be a salt of at least one metal selected between metals from the IIIB, IVB, VB, VIB, VIIB, VIIIB, IB, and IIB groups, a salt from a lanthanide or actinide element, combinations of the previous ones, and preferably a molybdenum salt.
• inorganic salt or salts behave as corrosion inhibitors by preventing the development of the different corrosion reactions (depending on the type of inorganic salt), therefore improving the behaviour of the parts pertaining to corrosion.
• the same aluminium or aluminium alloy parts to be anodised can be used as an anode.
• the electrolyte is an aqueous acidic electrolyte; preferably it is an aqueous solution of tartaric-sulphuric acid.
• the aqueous solution that acts as an electrolyte has a concentration of sulphuric acid between 0.1 and 1.5 M, preferably between 0.2 M and 0.9 M, and a concentration of L(+)tartaric acid between 0.1 and 1.5 M, preferably between 0.2 and 0.8M.
• said solution has a concentration of sulphuric acid between 0.2 M and 0.9 M, L(+)-tartaric acid with a concentration between 0.2 and 0.8M, and one or several inorganic salts composed of at least one or several transition metals in a concentration between 1 ⁇ 10 ⁇ 6 and 1 M.
• the temperature of the aqueous solution is kept between 0° C. and 140° C., preferably between 0° C. and 130° C., even more preferably between 5° C. and 80° C., and most preferably between 30 and 40° C.
• the electrolytic cell is subject to a potential difference 0.5V and 130V, preferably between 1 V and 120 V, even more preferably between 2 V and 100 V, and most preferably between 10 and 30 V according to the procedure.
• the duration of the anodising procedure is between 1 and 130 minutes, preferably between 5 and 120 minutes, and more preferably between 5 and 40 minutes.
• This procedure has a duration cycle of about 40% less time as regards traditional chromic acid anodising.
• a 2000 series aluminium alloy part, 150 ⁇ 100 ⁇ 2 mm, is subjected to a conventional cleaning and surface layer removal treatment: degreasing by immersion for approximately 10 minutes, rinse in distilled water for approximately 5 minutes, surface layer removal for approximately 10 minutes, and rinse in distilled water for 5 minutes.
• the part is completely submerged in an electrolytic cell, where the part functions as an anode;
• the cathode is composed of AISI 321 stainless steel, and it has a geometric area equal to or larger than the anode's geometric area.
• the electrolyte is an aqueous acidic solution made of 0.40 M sulphuric acid, 0.53 M L (+)-tartaric acid, and 0.25M sodium molybdenum.
• the cell's temperature is at 37° C. ⁇ 1° C.
• the potential difference increases from 0 to 14 V at a rate of 2.8 V ⁇ min ⁇ 1, and it stays at 14 V for 20 minutes, creating an oxide layer of approximately 2 ⁇ m.
• the part is rinsed in anodised water for approximately 5 minutes, and it is sealed in anodised water at boiling point for approximately 40 minutes. Then it is dried with hot air.
• a 2000 series plaqued aluminium part, 150 ⁇ 100 ⁇ 2 mm, is subjected to a conventional cleaning and surface layer removal treatment, as described in Example 1.
• the part is completely submerged in an electrolytic cell, where the part functions as an anode; the cathode is made of AISI 321 stainless steel, and it has a geometric area equal to or larger than the anode's geometric area.
• the electrolyte and the anodising conditions are the same as those described in Example 1, obtaining an oxide layer of approximately 2 82 m.
• the anodised part is rinsed and sealed in the same manner as that described in example 1.
• a 2000 series aluminium alloy part, 150 ⁇ 100 ⁇ 2 mm, is subjected to a conventional cleaning and surface layer removal treatment, as described in Example 1.
• the part is completely submerged in an electrolytic cell, where the part functions as an anode; the cathode is made of AISI 321 stainless steel, and it has a geometric area equal to or larger than the anode's geometric area.
• the electrolyte and the anodising conditions are the same as those described in Example 1, obtaining an oxide layer of approximately 3 ⁇ m.
• the anodised part is rinsed and sealed in the same manner as that described in example 1.
• a 2000 series plaqued aluminium part, 150 ⁇ 100 ⁇ 2 mm, is subjected to a conventional cleaning and surface layer removal treatment, as described in Example 1.
• the part is completely submerged in an electrolytic cell, where the part functions as an anode;
• the cathode is made of AISI 321 stainless steel, and it has a geometric area equal to or larger than the anode's geometric area.
• the electrolyte is an aqueous acidic solution made of 0.40 M sulphuric acid and 0.53 M L (+)-tartaric acid.
• the cell's temperature is maintained at 37° C. ⁇ 1° C.
• the potential difference increases from 0 to 14 V at a rate of 2.8 V ⁇ min ⁇ 1, and it is maintained at 14 V for 20 minutes, creating an oxide layer of approximately 3 ⁇ m.
• the anodised part is rinsed and sealed as in Example 1.
• a 2000 series plaqued aluminium part, 150 ⁇ 100 ⁇ 2 mm, is subjected to a conventional cleaning and surface layer removal treatment, as described in Example 1.
• the part is completely submerged in an electrolytic cell, where the part functions as an anode;
• the cathode is made of AISI 321 stainless steel, and it has a geometric area equal to or larger than the anode's geometric area.
• the electrolyte is an aqueous acidic solution with chromic acid.
• the cell's temperature is maintained between 35° C. and 40° C.
• the potential difference increases from 0 to 40 V at a rate of 5 V ⁇ min ⁇ 1, and it stays at 14 V for 45 minutes, creating an oxide layer of approximately 3 ⁇ m.
• the anodised part is rinsed and sealed as in Example 1.
• the parts treated according to the invention exceed 336 hours in saline fog according to the requirement established in section 3.7.1.2 of the military standard MIL-A-8625-F for IC type anodic layers.
• the comparison of the obtained results for the tests done on the example parts according to the invention and the comparative example conclude that the oxides created by the invention have better properties pertaining to corrosion than the oxides created in aqueous acidic mediums without inorganic salts. These properties are equal to or better than the ones obtained through anodising in chromic 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)
• Chemical Treatment Of Metals (AREA)
• Water Treatment By Electricity Or Magnetism (AREA)
• Printing Plates And Materials Therefor (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

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• 2007
  • 2007-10-29 ES ES200702842A patent/ES2324850B1/es not_active Expired - Fee Related
• 2008
  • 2008-03-07 US US12/073,632 patent/US20090107848A1/en not_active Abandoned
  • 2008-03-07 EP EP08380076A patent/EP2055810A3/en not_active Withdrawn
  • 2008-03-07 CA CA002624579A patent/CA2624579A1/en not_active Abandoned
  • 2008-03-13 EA EA200800582A patent/EA015400B1/ru not_active IP Right Cessation
  • 2008-03-14 BR BRPI0800622-9A patent/BRPI0800622A2/pt not_active IP Right Cessation
  • 2008-03-17 CN CNA2008100963066A patent/CN101423965A/zh active Pending

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