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
  • C25D11/38—Chromatising

Definitions

• the object of the present invention is a process for the protection of magnesium and magnesium-base alloys by means of a superficial coating.
• the anodic or electrolytic treatment-of magnesium and its alloys has heretofore generally been effected in alkaline solutions with a view to depositing coatings of oxide, silicates or aluminates, the said solutions sometimes containing in addition other alkaline salts such as borates, chromates, phosphates and molybdates. But coatings so obtained have never given entire satisfaction.
• the pH of the bath should be maintained at less than 2. This may be done by the appropriate addition from time to time of chromic acid and if necessary of sulfuricacid.
• This film consists' of an oxyde of chromium, intermediate be- I have further made the surprising discovery that the above mentioned protective film is porous and far from being of an insulating nature, easily permits the passage of alternating electric current. The voltage across the bath only falls slightly during the electrolytic .treatment and remains almost constant for its duration.
• Example 1 Composition of bath:
• the objects are withdrawn from the bath, copiously rinsed and dried, preferably hot. Subsequently the objects can be subjected to a finishing treatment, for example by means of paraffin, paint, etc., which increases the resistance of the protective coating to corrosion.
• the protective film is porous, one obtains excellent results by means of immersion of the pieces in hot paraflin, for example at about C.
• the previously described bath containing chromic and sulphuric acids has moreover the advantage of being one well suited to the preliminary pickling of the metal objects to be electrolytically treated, with the result that no prior pickling is necessary.
• magnesium or magnesium-base alloys assembled with an other metal such as iron or aluminium
• My invention covers, as new industrial products, not only baths as specified for the electrolytic treatment of magnesium and magneslum-base alloys with a view to producing protective coatings resistant to corrosion, but also all objects in magnesium or its alloys which are covered with the afore described protective coating consisting substantially of an oxyde of chromium, and this protective coating itself.

Landscapes

• 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)
• Chemical Treatment Of Metals (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=8685437

Family Applications (1)

Country Status (6)

Cited By (1)

• 0
  • BE BE432902D patent/BE432902A/xx unknown
  • NL NL52921D patent/NL52921C/xx active
• 1938
  • 1938-02-25 FR FR843027D patent/FR843027A/fr not_active Expired
• 1939
  • 1939-02-02 FR FR50432D patent/FR50432E/fr not_active Expired
  • 1939-02-13 GB GB4636/39A patent/GB525033A/en not_active Expired
  • 1939-02-14 CH CH221320D patent/CH221320A/fr unknown
  • 1939-02-21 US US257762A patent/US2338924A/en not_active Expired - Lifetime

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