Classifications

• • 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
  • C25D5/44—Aluminium
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
  • C25D15/02—Combined electrolytic and electrophoretic processes with charged materials

Definitions

• the coating is essentially constituted of nickel containing a dispersed phase of hard fine particles of silicon carbide.
• the method includes the operational phases: forming by chemical means a thin layer of zinc, then depositing electrolytically a composite layer of nickel (containing hard particles in a dispersed phase to a desired content) until the thickness desired for the whole of the coating is obtained; the wall being subjected initially to a shot-blasting treatment, and/or before any deposition of a metallic layer, attacked with a sodium compound in a bath of said compound.
• the electrolytic deposits of nickel are conducted by causing the electric current to be passing into the bath already at the moment when immersion of the elements in the course of treatment is effected, due to which a passivation of the elements prejudicial to good adherence of the final coating is avoided. Transfer of the treated element from one vat to another, iseffected in a time of the order of several seconds to one minute. Said sodium compound attack may be followed by a nitric-hydrofluoric attack in a concentrated bath. Before any deposition of nickel, two successive zinc treatments may be effected at ambient temperature, the layer of zinc deposited on the first zinc treatment being dissolved in concentrated nitric acid before the second zinc treatment.
• the invention relates to-methods for the formation, on a wall exposed in service to frictional forces and belonging to an element of light alloy (especially of an aluminium alloy with a high content of silicon), ofa composite metallic coating, resistant to wear, constituted by a matrix of nickel containing a dispersed phase of particles of great hardness generally formed essentially by silicon carbide.
• the invention relates more particularly, because it is in this case that its application seems to offer the most advantage, but not exclusively, among these methods, to those for forming a composite metallic coating (of the above-indicated type) on the inner wall of the light alloy casing (currently called trochoidal) of a rotary piston engine.
• the important problem, for a stratified coating of this type, is to obtain a good adherence of each layer on the sub-adjacent layer so that the coating proper has a monolithic character and so that the whole of said coating adheres firmly to the treated wall.
• this method comprising, among other operational phases and in manner known in itself, the formation, by chemical means of a thin layer of zinc, advantageously followed by an electrolytic treatment of prenickeling ensuring the formation of a thicker layer of nickel containing no or few hard particles in the dispersed phase,
• the electrolytic deposition of a composite layer of nickel (containing hard particles in the dispersed phase to the desired content) until the obtaining of the desired thickness for the whole of the coating the abovesaid method being characterized in that the wall to be lined with the. coating concerned is subjected initially, that is to say before any other treatment of the operational process, to a shot-blasting treatment advantageously effected by dry projection onto the abovesaid wall, of glass microbeads projected by a current of air under a pressure preferably comprised between 5 and 10 bars for a duration preferably comprised between 10 and 20 seconds per 0.05 dm2 of treated surface.
• the invention consists, apart from this main feature,
• the wall which has to receive the wear-resistant composite metallic coating is subjected before any deposition of metallic layer, to a sodium compound attack conducted in a sodium compound bath if necessary supplemented with a polyhydroxy acid (preferably glu conic acid) or with a salt of such an acid (preferably a sodium salt), this addition having'the effect of securing a slight increase in adherence by uniformization of the attack and through improvement in the rinsability of the elements, and of avoiding the formation of an interfering viscous compound on the surface to be coatedand on the walls ofthe tank.
• a sodium compound attack conducted in a sodium compound bath if necessary supplemented with a polyhydroxy acid (preferably glu conic acid) or with a salt of such an acid (preferably a sodium salt)
• Such a sodium compound attack can advantageously be conducted in a bath containing from 50 to 150 grams per liter (preferably of the order of grams per liter) of caustic soda and from 5 to 15 grams per liter (preferably of the order of 10 grams per liter) of polyhydroxy acid or of a salt of such an acid (for example sodium gluconate).
• the abovesaidbath is advantageously at ambient temperature (between 15 and 30C).
• the sodium attack which has just been considered will take place after the abovesaid shotblasting treatment and before any deposition of a constituent metallic layer of the coating.
• this sodium compound attack can be followed by a nitric-hydrofluoric attack in a concentrated bath, which enables further improvement of the adherence of the coating, especially when the treated element is of light alloy rich in silicon.
• the electrolytic deposits of nickel are conducted by causing the electric current to be passing already into the bath at the moment when immersion of the elements in the course of treatment is effected, the density of the abovesaid current being preferably comprised between 1 and 3 A/dm2 during this immersion phase, due to which alteration of the surfaces to be treated prejudicial to good adherence of the final coating is avoided.
• the adherence of the coating is further improved by subjecting the wall to be coated, before any deposition of nickel, to two successive zincing treatments effected at ambient temperature, the layerof zinc deposited on the first zincing being dissolved in concentrated nitric acid before the second zincing.
• the method comprises a prenickeling phase (electrolytic deposition of nickel containing no or few hard particles in the disdiate rinsing, so as .to avoid any passivation of the abovesaid element due to remaining in air for a prolonged period, the abovesaid transfer being effected under the passage of current so as to avoid passivation by absorption oforganic products in the following bath, which passivations would in any case be prejudicial to good adherence of the final coating.
• a prenickeling phase electrolytic deposition of nickel containing no or few hard particles in the disdiate rinsing, so as .to avoid any passivation of the abovesaid element due to remaining in air for a prolonged period, the abovesaid transfer being effected under the passage of current so as to avoid passivation by absorption oforganic products in the following bath, which passivations would in any case be prejudicial to good adherence of the final coating.
• the invention relates also to light alloy elements (for example trochoids for rotary piston engines), in particular of aluminium alloy with a high silicon content, comprising a wall provided with a metallic coating based on nickel containing a dispersed phase of hard particles (silicon carbide for example), said coating being formed according to all or some of the preceding features.
• light alloy elements for example trochoids for rotary piston engines
• aluminium alloy with a high silicon content comprising a wall provided with a metallic coating based on nickel containing a dispersed phase of hard particles (silicon carbide for example), said coating being formed according to all or some of the preceding features.
• the said wall After having effected a mechanical finishing by fine machining of the inner wall of a trochoid constituted for example of light alloy with 10% Si, the said wall is subjected to shot-blasting by production of glass beads of a diameter comprised between 75 and 150 microns, under an air pressure of 7 bars, for a duration of l minute per 0.7 dm2 of wall and per nozzle.
• the electrolytic deposition of the composite wear-resistant coating is effected in a bath at 55C, with nickel anodes, containing crystalline nickel sulfamate (400g/l), nickel chloride (4 g/l), boric acid (40 g/l), about 3 g/l of saccharine (for example in the form of a sodium saccharinate solution), particles of silicon carbide g/l), and a wetting agent.
• nickel anodes containing crystalline nickel sulfamate (400g/l), nickel chloride (4 g/l), boric acid (40 g/l), about 3 g/l of saccharine (for example in the form of a sodium saccharinate solution), particles of silicon carbide g/l), and a wetting agent.
• the immersion is carriedout under a current of l to 2 A/dm2 and it is followed by a gradual rise to 20 A/dm2 during 15 minutes, after which the deposition is pursued for one hour thirty minutes at 20 A/dm2.
• electrolytic treatments there may be used a material comprising the application of the features which are the subject of French patent applications filed 9 Nov. l97 l for: Device and method for the production of a coating, for example electrolytic, on the walls of members exposed in service to frictional forces and for: Improvements in installations for producing an electrolytic coating, under US. Pat. Nos. 71, 40, 151 and 71,40, 152, respectively.
• Method for the formation of a metallic wearresistant coating comprising primarily nickel containing a dispersed phase of hard fine particles, on a wall to be exposed in service to frictional forces, said wall comprising a light metallic alloy, said method includ ing: forming by chemical means a thin layer of zinc on said wall, then depositing electrolytically a composite layer of nickel containing hard particles in a dispersed phase; said method being characterized in initially subjecting the bare wall to a shot-blasting treatment.
• Method of claim 1 additionally comprising subjecting the bare wall to attack with a sodium compound conducted in a bath of said compound before deposition of any metallic layer on said wall.
• Method of claim 1 said method being characterized in that the electrolytic deposits of nickel are conducted by causing the electric current to be passing into the bath already at the moment when immersion of the elements in the course of treatment is effected, due to which a passivation of the elements prejudicial to good adherence of the final coating is avoided.
• Method according to claim 1 additionally comprising a prenickeling phase comprising an electrolytic deposition of nickel containing no or little hard particles in the dispersed phase, followed by electrolytic deposition of nickel containing hard particles in a dispersed phase, wherein transfer of the treated element from one vat to another is effected in a time of the order of several seconds to one minute.
• said light alloy is an aluminium alloy with a high content of silicon.
• Method according to claim 1 wherein the forming of the thin layer of zinc is followed by an electrolytic treatment of pre-nickeling ensuring the formation of a thicker layer of nickel containing no or very few hard particles in the disperse phase.

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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)
• Chemically Coating (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

Country Status (8)

Cited By (5)

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Citations (10)

• 0
  • BE BE791008D patent/BE791008A/xx unknown
• 1971
  • 1971-11-09 FR FR7140153A patent/FR2159179B1/fr not_active Expired
• 1972
  • 1972-11-07 GB GB5124272A patent/GB1409669A/en not_active Expired
  • 1972-11-08 IT IT9744/72A patent/IT970604B/it active
  • 1972-11-08 US US304842A patent/US3868311A/en not_active Expired - Lifetime
  • 1972-11-09 DE DE2254857A patent/DE2254857C3/de not_active Expired
  • 1972-11-09 JP JP47112525A patent/JPS4855135A/ja active Pending
  • 1972-11-09 NL NL7215187A patent/NL7215187A/xx not_active Application Discontinuation

Patent Citations (10)

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