Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/42—Electroplating: Baths therefor from solutions of light metals
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
  • C25D5/42—Pretreatment of metallic surfaces to be electroplated of light metals

Definitions

• the present invention relates to a method for the electrolytic coating of materials with aluminum, magnesium or alloys of aluminum and magnesium, the material being dipped into an electrolyte for pretreatment and being anodically switched there, and the electrolytic coating being carried out in the same electrolyte immediately thereafter.
• the quality of the deposited aluminum, magnesium or aluminum / magnesium coating is improved by the method according to the invention.
• the deposition of aluminum, magnesium or aluminum / magnesium alloys on materials consisting of base metals is a tried and tested means of protecting these materials from corrosion. At the same time, they are provided with a decorative coating.
• the protective metal layer is mainly galvanically deposited on the material. It is advantageous here if the aluminum, magnesium or aluminum / magnesium layer is carried out on the material without the application of metallic intermediate layers between said metal layer and the material. If intermediate layers between the material and the surface layer made of aluminum, magnesium or aluminum / magnesium alloy are applied, there is a risk of contact corrosion due to the applied intermediate layer. In addition, thermal problems can arise due to the different expansion coefficients of the surface layer and the intermediate layer.
• the electrolytes that have proven themselves in the prior art include melt flow electrolytes, such as electrolytes, which contain aluminum halides or aluminum alkyl complexes. All these electrolyte systems have in common that the material on its surface must be cleaned before coating. This is particularly the case for materials made from base metal exist which form an oxide layer, the problem that this oxide layer must be completely removed before coating. If the surface of the materials is not completely cleaned, impurities or residues of the oxide layer of the metal from which the material is made adhere to the surface and impair the adhesion of the subsequently electrolytically applied metal layer. Furthermore, it is possible that no metal layer is applied at the points where contaminants are present on the surface, since the contaminants are generally not electrically conductive and thus electrolytic deposition is prevented at this point. This then inevitably leads to corrosion problems of the finished coated material at the point where the metal layer was not completely applied.
• DE-C3-22 60 191 describes a method for the preparation of materials made of electrically conductive materials.
• the last step in the process of shaping the materials, in which a new bare surface is created on the material, is carried out in a suitable inert gas or inert liquid medium with the exclusion of atmospheric oxygen and moisture.
• This method has the disadvantage that, in particular when using an inert liquid medium which covers the surface of the material and can thus be placed in the coating electrolyte, the latter subsequently contaminates or hydrolyzes the electrolyte.
• inert gas media When using inert gas media, the problem arises in large-scale industrial use that an absolutely oxygen-free inert gas atmosphere is practically impossible to achieve.
• DE-AS-12 12 213 describes the pretreatment of a material in a protective gas atmosphere.
• the oxide layer on the surface of the material can be removed by anodically switching the material before depositing the aluminum layer in the electrolyte, which is made from sodium fluoride and aluminum triethyl. Then the polarity of the current is reversed and aluminum is deposited on the material.
• the electrolyte can only be used for the deposition of aluminum on materials.
• the deposition of magnesium or aluminum / magnesium layers is not possible, since the presence of halide ions in the electrolyte during the anodic polarization would result in immediately insoluble magnesium halide compounds which prevent the deposition of magnesium or aluminum / magnesium on the material.
• the resulting magnesium halides would immediately prevent the current flow in the electrolyte by blocking the electrodes.
• DE-AS-21 22 610 describes a process for the anodic pretreatment of light metals for the galvanic deposition of aluminum.
• the components are cleaned by treating the light metal materials in a melt electrolyte, the materials being anodically loaded.
• the light metal materials cleaned in this way are immersed in an electrolytic cell, moist with electrolyte, i.e. still loaded with the molten electrolyte. It cannot be ruled out that atmospheric oxygen will still reach the pretreated material and oxidize it again on the surface.
• the aluminum electrolyte is contaminated by the surface treatment electrolyte, which is a melt electrolyte.
• the material consists of beryllium or aluminum is it possible that the material in the melt electrolyte, which is used for surface treatment by anodic oxidation of the material, also for the galvanic deposition of aluminum on the Beryllium or aluminum material is used.
• the melting electrolyte described in DE-AS-21 22 610 is only suitable for pretreating beryllium or aluminum materials in order to subsequently coat them with aluminum in the same melting electrolyte.
• the melting electrolyte is not suitable for the galvanic application of aluminum, magnesium or aluminum / magnesium layers on other materials.
• DE-A1-198 55 666 describes an electrolyte which is suitable for the deposition of aluminum / magnesium alloy layers.
• the disclosed aluminum-organic electrolyte contains K [AIEt 4 ] or Na [Et 3 Al-H-AlEt 3 ], as well as Na [AlEt 4 ], and trialkyl aluminum.
• the electrolyte can be in the form of a toluene solution.
• the electrolytic deposition of aluminum / magnesium alloy layers from the described electrolyte is carried out using a soluble aluminum and a likewise soluble magnesium anode or using an anode made of aluminum / magnesium alloy.
• the electrolyte composition is adjusted by pre-electrolysis so that the deposited layer has the desired aluminum / magnesium ratio.
• Mg [AlEt 4 ] 2 can also be added to the electrolyte.
• DE-A1-198 55 666 thus teaches that the ratio of aluminum and magnesium in the deposited aluminum / magnesium layer depends very much on the concentration ratio of magnesium and aluminum in the electrolyte.
• great care is required in the pretreatment of the materials to be coated, since contamination of the material surface by oxidation or other influences leads to a reduced quality of the galvanically deposited metal layer.
• the technical object of the present invention is to provide a method in which aluminum, magnesium or aluminum / magnesium layers can be applied to materials, the quality of the metal coating being increased by an improved pretreatment of the material.
• a method is to be made available be, in which the materials to be coated are reliably and inexpensively freed from adhering oxide layers or other impurities, wherein after the pretreatment of the materials a renewed contamination or oxidation of the materials should be prevented.
• the technical object of the present invention is achieved by a method for the electrolytic coating of materials with aluminum, magnesium or alloys of aluminum and magnesium, the material being immersed in the electrolyte for pretreatment, being anodically switched there and immediately thereafter the electrolytic coating in the same Electrolytes take place, the electrolyte bath organoaluminum compounds of the general formula M [(R 1 ) 3 Al- (H-Al (R 2 ) 2 ) n -R 3 ] (I) and Al (R 4 ) 3 (II) as the electrolyte contains and n is 0 or 1, M is sodium or potassium and R 1 , R 2 , R 3 , R 4 may be the same or different, where R 1 , R 2 , R 3 , R 4 is a C 1 - bis C 4 alkyl group and a halogen-free, aprotic solvent is used as the solvent for the electrolyte.
• the method according to the invention makes it possible to pretreat the material in the bath in which the electrolytic coating takes place later. Surprisingly, impurities that adhere to the non-pretreated material and any oxide layers on the material are removed.
• the impurities which are thus introduced into the electrolyte bath surprisingly do not hinder the deposition of magnesium, aluminum or alloys of aluminum and magnesium on the material. Insoluble impurities can be continuously removed from the electrolyte bath using suitable filtration systems.
• an electrolyte is used as a mixture of the complexes K [AlEt 4 ], Na [AlEt 4 ] and AlEt 3 used.
• the molar ratio of the complexes to AIEt 3 is 1: 0.5 to 1: 3, the ratio of 1: 2 being preferred.
• 0 to 25 mol%, preferably 5 to 20 mol% Na [AlEt 4 ], based on the mixture of the complexes K [AlEt 4 ] and Na [AlEt 4 ], are used.
• a mixture of 0.8 mol of K [AlEt 4 ] , 0.2 mol of Na [AlEt 4 ], 2.0 mol of AlEt 3 in 3.3 mol of toluene can preferably be used as the electrolyte.
• a mixture of Na [Et 3 Al-H-AlEt 3 ] and Na [AlEt4] and AIEt 3 can be used as the electrolyte in the process according to the invention.
• the molar ratio of Na [Et 3 Al-H-AlEt 3 ] to Na [AlEt 4 ] is 4: 1 to 1: 1, with a ratio of 2: 1 being preferred. It is further preferred that the molar ratio of Na [AlEt 4 ] to AlEt 3 is 1: 2.
• a mixture of 1 mol of Na [Et 3 Al-H-AlEt 3 ], 0.5 mol of Na [AlEt 4 ] and 1 mol of AlEt 3 in 3 mol of toluene is used as the electrolyte.
• the electrolytic coating of materials with magnesium, aluminum or aluminum / magnesium alloys is preferably carried out at a temperature of 80 to 105 ° C. A temperature of the electroplating bath of 91 to 100 ° C. is preferred.
• the electrolytic deposition of aluminum, magnesium, or aluminum / magnesium layers on the materials is carried out using a soluble aluminum and a likewise soluble magnesium anode or using an anode made of an aluminum / magnesium alloy.
• a soluble aluminum and a likewise soluble magnesium anode or using an anode made of an aluminum / magnesium alloy are soluble aluminum and a likewise soluble magnesium anode or using an anode made of an aluminum / magnesium alloy.
• the anodic switching of the material for pretreatment can be carried out for a period of 1 to 20 minutes, with 5 to 15 minutes being preferred.
• the anodic loading of the materials required for the pretreatment is carried out with a current density of 0.2 to 2 A / dm 2 , preferably 0.5 to 1.5 A / dm 2 .
• the material consists of a metal and / or a metal alloy and / or is a metallized, electrolyte-resistant material that can be dissolved in the electrolyte by anodic switching.
• the materials to be coated are preferably rack goods, bulk goods or continuous products such as wire, square sheets, screws or nuts.
• the method according to the invention is characterized in that impurities or oxide layers which adhere to the materials are reliably removed.
• impurities or oxide layers which adhere to the materials are reliably removed.
• there is no disadvantageous change in the electrolyte composition that would prevent high-quality deposition of aluminum, magnesium or aluminum / magnesium layers on the materials.
• the galvanically applied metal layers are firmly adhering and homogeneously applied to the material, since after the cleaning a renewed contamination of the material is prevented.
• the process steps mentioned also achieve a cost optimization of coating molded parts with metal layers.
• Phase b) The dry part was introduced into a coating cell flooded with argon or nitrogen and, after a pre-rinsing in toluene, was introduced immediately into the coating electrolyte. A mixture of the complexes K [AlEt 4 ], K [AlEt 4 ] and AlEt 3 was used as the electrolyte, dissolved in toluene. An AIMg25 alloy plate served as the counter electrode. The product to be coated was first anodically poled and treated at a current density of 1 A / dm 2 for 5 minutes at an electrolyte temperature of 95 C. Then the polarity was reversed without removing the part from the electrolyte and immediately for 45 minutes at a current density of 1 , 5 A / dm 2 coated. An AIMg alloy layer approximately 14 ⁇ m thick was deposited.
• the adhesive strength of the layer was checked by means of a cross cut test and a heat shock test (1 h at 220 ° C. and quenching in cold water). It was found that the deposited layer had excellent adhesion to the base material. No detachments or bubbles were found.
• a part treated as a comparative sample was pretreated and coated as in Example 1, but without anodic polarity beforehand.
• the layer could be peeled off as a film during the cross cut test. In the heat shock test, the layer showed bubbles.
• a magnesium die-cast part made of an AZ-91 alloy was blasted with corundum (grain size 0-50 ⁇ m) at 2 bar pressure. The part was then immediately placed in the inert gas atmosphere of the coating cell, rinsed in toluene and immersed in the electrolyte bath as described in Example 1.
• the product to be coated was anodized for 10 minutes at a current density of 1 A / dm 2 .
• a layer of approx. 2 ⁇ m was removed from the product surface.
• the polarity was then reversed and the part was connected cathodically for 1 hour at 1.5 A / dm 2 .
• An AIMg layer with 23-25% Mg content and a layer thickness of approx. 18 ⁇ m was deposited.

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• Chemical Kinetics & Catalysis (AREA)
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• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating Methods And Accessories (AREA)

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• 2002
  • 2002-09-25 EP EP02021402A patent/EP1403402A1/fr not_active Withdrawn
• 2003
  • 2003-07-15 AU AU2003250061A patent/AU2003250061A1/en not_active Abandoned
  • 2003-07-15 EP EP03807748A patent/EP1543180B1/fr not_active Expired - Fee Related
  • 2003-07-15 JP JP2004542263A patent/JP2006500476A/ja active Pending
  • 2003-07-15 CN CN038230569A patent/CN1685087B/zh not_active Expired - Fee Related
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  • 2003-07-15 WO PCT/EP2003/007632 patent/WO2004033762A1/fr active IP Right Grant
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