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
• • 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
  • C25D11/16—Pretreatment, e.g. desmutting

Definitions

• Anodizing layers on die-cast aluminum parts are not homogeneous and pure. she contain silicon and / or, depending on the aluminum base alloy used Metal precipitates, e.g. is the anodizing layer on a die-cast aluminum alloy like GD-AlSi12, GD-AlSi9Cu3 inhomogeneous and unclean due to the unequal aluminum base alloy. As a result, too Properties regarding corrosion and wear protection, electrical insulation and colorability in quality worse than that of a homogeneous Anodizing layers made of aluminum material. They are also die-cast aluminum often only with high technical effort at all anodizable.
• the aim of the invention is to provide a homogeneous anodizing layer with a uniform one Pore structure on die-cast aluminum with high corrosion protection and Wear protection properties and improved electrical insulation and colorability to accomplish.
• the object is achieved in that the aluminum die-cast workpiece with a dense, pure aluminum layer at least 5 ⁇ m thick adherent coated and then anodized so that the pure aluminum layer completely and the underlying die casting partially in an aluminum oxide conversion layer being transformed.
• the degree of purity of the aluminum is at least 99.5% by weight.
• the dense, pure aluminum layer adheres firmly to the die-cast aluminum parts applied electrochemically, physically or mechanically. Serve in itself known processes, such as electrolytic deposition from aprotic electrolytes or melting by fire aluminizing or thermal spraying or vapor deposition in PVD processes or plating.
• the thickness of the layer is at least 5 ⁇ m.
• the maximum layer thickness of pure aluminum is up not limited and depends essentially on the type of application. Layer thicknesses up to 50 ⁇ m have proven to be sufficient. If the density pure aluminum layer is applied electrochemically, layer thicknesses are recommended from 5 to 30 ⁇ m.
• All technically relevant metal alloys such as GD-AlSi9Cu3, GD-AlSi12, GD-AlMg3Si, GD-AlSi10Mg, GD-AlMg9.
• the die-cast aluminum coated with a dense, pure aluminum layer is anodized in inorganic and / or organic acids or in bases in such a way that the dense, pure aluminum layer is completely converted and part of the aluminum die-casting underneath is converted into an aluminum oxide conversion layer.
• the known conditions of hard anodization are preferably chosen for the anodization.
• This aluminum oxide conversion layer consists of two phases. From the evaluation of the metallographic sections, it can be seen that the phase of the aluminum oxide layer which extends into the die-cast aluminum is of a coarse-grained, irregular structure, while the outer phase facing the eye has a fine-grained, homogeneous, uniform structure.
• This phase of the conversion layer gives the anodizing layer the properties which are improved in quality, such as higher corrosion stability, greater wear protection, higher electrical insulation and improved colorability in comparison to a conventional anodizing layer on the die-cast aluminum.
• the invention accordingly also relates to an aluminum die-cast part with an aluminum oxide conversion layer, in which the latter consists of two phases, of which the outer has a homogeneous fine-grained structure and the phase extending into the aluminum die-casting has a coarse-grained irregular structure.
• the outer homogeneous fine-grained phase of the Al 2 O 3 conversion layer preferably has a thickness of 10 to 100 ⁇ m and the total thickness of the two phases of the Al 2 O 3 conversion layer is, in particular 20 to 200 ⁇ m.
• Two die-cast aluminum housings made of GD-AlSi12 with a surface area of 2 dm 2 are electrochemically coated on all sides and uniformly in an aprotic electrolyte with a 5 ⁇ m or 20 ⁇ m thick, dense, pure aluminum layer (degree of purity 99.99%) and then in a sulfuric acid electrolyte 3.5 A / dm 2 hard anodized (according to ISO 10 074).
• the layer thickness of the hard anodizing layer (HC layer) is 40 ⁇ m.
• An aluminum die-cast housing of the same dimensions and quality serves as a reference and has been hard anodized under the above conditions.
• the HC layer on the pure Al die casting was stained, as was the following one Coloring.
• the HC layers on the previously aluminized die-cast aluminum housings were homogeneous, with a uniform gray color and were excellent coloring, e.g. with SANODAL - Jet Black HBL liquid.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

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Citations (3)

• 1997
  • 1997-11-19 DE DE1997151256 patent/DE19751256C2/de not_active Expired - Lifetime
• 1998
  • 1998-11-16 EP EP98121771A patent/EP0919645A3/fr not_active Withdrawn

Patent Citations (3)

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