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
• • 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
• • 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
• • 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
  • C25D3/38—Electroplating: Baths therefor from solutions of copper
  • C25D3/40—Electroplating: Baths therefor from solutions of copper from cyanide baths, e.g. with Cu+

Definitions

• the present invention relates to a method for the galvanic deposition of metal layers on magnesium or magnesium alloy surfaces.
• magnesium has been increasingly used in the automotive industry, in commercial aircraft construction and in the electronics industry. Especially in the production of high-quality products magnesium or magnesium alloys are used in order to save weight. Compared to other light alloys, magnesium or magnesium alloys have the advantage that they offer excellent casting properties, so that both injection- molded parts and die-cast parts having very good production qualities can be produced from corresponding magnesium alloys or from magnesium. Particularly the production of construction parts by means of a magnesium injection molding process seems to be of high interest also in future times, especially in the field of the automotive industry. During injection molding of magnesium or magnesium alloys the same are not heated until their complete melting but only to approx 100° below the melting point. A thixotropic state of the magnesium will be achieved thereby, in which state it can be correspondingly injection- molded.
• the substrates which have been produced by means of corresponding casting processes must be subject as a rule to a surface finishing treatment.
• the same may serve to corrosion protection of the magnesium or the magnesium alloy surface on one side and on the other side to the production of corresponding glossy or dull decorative surfaces by means of a deposition of metal layers on the surface.
• Magnesium alloys which are frequently employed in the industry are such of the type AZ31 to AZ91, wherein AZ symbolize aluminum and zinc that have been added as alloy elements, and the subsequent numerals identify the size of the fraction of these alloy elements in the magnesium.
• the invention is directed to a process for the galvanic coating of a magnesium or magnesium alloy surface with a metal-based layer, the process comprising a) an alkaline cleaning process, b) an alkaline deposition process for depositing the metal-based layer after the alkaline cleaning process, and no intermediate processes between (a) and (b) which involve exposure of the surface to an acidic solution.
• the present invention is therefore based on the object of providing a process for the galvanic coating of magnesium or magnesium alloys, which process achieves a satisfying coating result for a great number of different magnesium alloys while avoiding the formation of pores as the same is known in prior art.
• This object is solved by a process for the galvanic coating of magnesium or magnesium alloy surfaces, characterized in that during the entire coating process and until the complete coverage with a metal layer of the metal to be deposited, the surfaces to be coated are contacted exclusively with process solutions and washing solutions which have a pH value > pH7, preferably > pH 8.
• the cleaning of the substrate to be coated can be performed with the aid of hot degreasing.
• the substrate to be cleaned is treated with a suitable degreasing agent at a temperature of about 70 - 80 0 C for a duration of 10 minutes.
• a suitable degreasing agent at a temperature of about 70 - 80 0 C for a duration of 10 minutes.
• the selection of the degreasing agents to be used being made in dependence of the contaminations present on the substrates or substrate surfaces to be treated.
• the degreasing agents that are to be employed are alkaline degreasing agents.
• Kavitec modulus or of eductor nozzles may be provided in accordance with the invention.
• Kavitec systems are high-pressure water nozzles which support the cleaning-off by cavitation effects.
• a treatment of the substrate surface with an alkaline, cyanide-free pre-bonding etchant is performed.
• a pre-bonding etchant is a zincate etchant, which in addition to sodium pyrophosphate (Na 4 P 2 O ?
• zinc sulfate sodium carbonate
• sodium fluoride includes suitable wetting agents for reducing the surface tension of the zincate etchant.
• the zincate etchant which has been described and which is to be used in accordance with the invention has a pH value adjusted with sodium carbonate to within the range of pH 9 to 11, in preferred embodiments between 9.7 and 10.3, and in certain embodiments between 9.9 and 10.1
• the substrate surface to be treated of the magnesium or magnesium alloy substrate to be coated is contacted with the zincate etchant at a temperature between 60 and 80 0 C, preferably between 65 and 75°C.
• the exposing time is between 5 and 15 minutes, preferably between 9 and 11 minutes.
• Zincate etchant 100 - 300 g/1 sodium pyrophosphate x 10 H 2 O
• the composition of the zincate etchant is
• a wetting agent known as Nonpitter 62 A or a wetting agent known as EnPREP TTM WA may be preferably used as a wetting agent.
• a wetting agent known as EnPREP TTM WA may be preferably used as a wetting agent.
• also combinations of different wetting agents may be employed.
• a pre-bonding zincate layer is formed on the magnesium or magnesium alloy surface to be coated.
• the thickness of the zincate layer is not narrowly critical and is most influenced by the nature of the substrates. In many embodiments it is a continuous layer having a thickness of on the order of less about 1 micron.
• a cyanidic glossy copper electrolyte for example an electrolyte of the type CUPRALYTE 1545 from Enthone Inc., at a temperature between 40 and 55°C.
• a current density between 0.5 and 2.0 A/dm 2 is set.
• a current density is to be provided here which is lower for the use of plate or billet anodes than for the use of copper pieces in corresponding anode baskets.
• the voltage to be applied lies within a range of 2.0 to 12.0 Volts, depending on the anodes which are used and on the substrates or substrate surfaces which are to be coated.
• the cyanidic copper electrolyte which is used in the herein described embodiment of the process according to the invention exhibits a photometrically determined pH value within a range of pH 11.0 and pH 12.0.
• the copper concentration in the copper electrolyte which is to be employed according to the invention is between 20 g/1 and 50 g/1.
• the free potassium cyanide concentration in the cyanidic copper electrolyte which is to be employed here is between 20 g/1 and 35 g/1.
• the electrolyte includes potassium carbonate of maximally 120 g/1.
• the density of an electrolyte as described above is approximately 1.15 g/cm 3 .
• copper layers can be deposited at a deposition speed in the order of approximately 0.4 ⁇ m/min at a set current density of 1 A/dm 2 on the substrate surfaces of the magnesium or magnesium alloy substrates which have been pre-treated in the above-described way.
• the deposited copper layers are strongly adhering and show a uniform gloss.
• additional metal layers can be applied to the so deposited copper layers, and this subsequent deposition of metal layers may take place both in acidic and alkaline coating electrolytes, provided that the underlying magnesium or magnesium alloy layer is completely covered with a corresponding copper layer.

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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)
• Electroplating Methods And Accessories (AREA)

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Citations (3)

• 2007
  • 2007-10-05 DE DE200710048043 patent/DE102007048043A1/de not_active Withdrawn
• 2008
  • 2008-09-16 EP EP20080016260 patent/EP2045364A2/de not_active Withdrawn
  • 2008-10-03 WO PCT/US2008/078792 patent/WO2009046328A1/en active Application Filing

Patent Citations (3)

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