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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/565—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of zinc
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C13/00—Alloys based on tin
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C18/00—Alloys based on zinc
• • 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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/60—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of tin

Definitions

• the invention concerns new ternary tin-zinc alloys of specific compositions which contain a metal from the group iron, cobalt, or nickel as a third alloy component.
• the invention further concerns electrolytic baths and a galvanic process for producing such ternary tin-zinc alloys, as well as their use as corrosion-protection layers or decorative layers.
• ferrous materials can be protected against corrosion by coating with zinc and subsequent passivation, such as by chromating (based on Cr +6 ) or chromiting (based on Cr +3 ), evident by a yellow, blue, black, or olive-green coloration of the surface.
• passivation such as by chromating (based on Cr +6 ) or chromiting (based on Cr +3 ), evident by a yellow, blue, black, or olive-green coloration of the surface.
• More stringent requirements such as resistance of up to 1000 hours until the first appearance of red rust in the salt mist test, can be met by coating with zinc alloys which contain nickel, cobalt or iron as components of the alloy and subsequent chromating.
• the proportions of the alloying elements can, for instance, be from less than 1% by weight, such as 0.4-0.6% by weight Fe in the ZnFe system up to 15% by weight, such as 12-15% by weight Ni in the ZnNi system (Zinc alloying processes: Properties and applications in technology, Dr. A. Jimenez, B. Kerle and H. Schmidt, Galvanotechnik 89 (1998)4).
• Tin-zinc alloys can also be used as anticorrosion coatings for iron. Values of up to 1000 hours until the first appearance of red rust in salt mist testing are attained with chromated SnZn coatings. The most favorable alloy composition is 70% by weight Sn and 30% by weight Zn. The low hardness, only about 50 HV, of SnZn coatings is considered a disadvantage (Tin-Zinc Plating, E. Budmann and D. Stevens, Trans. IMF 76 (1998)3).
• the invention was, therefore, based on the objective of finding new alloy systems with particularly high corrosion resistance, and providing galvanic electrolytes for deposition of these alloys, to meet future requirements for anticorrosion effect.
• the subject of the invention is, then, ternary tin-zinc alloys characterized in that they consist of 30 to 65% by weight tin, 30 to 65% by weight zinc, and 0.1 to 15% by weight of a metal from the group iron, cobalt, or nickel as the third alloy component.
• the ternary tin-zinc alloys according to the invention preferably contain cobalt as the third alloying component.
• Tin-zinc-cobalt alloys according to the invention preferably contain 40 to 55% by weight tin, 45 to 55% by weight zinc and 0.1 to 5% by weight cobalt.
• Tin-zinc-nickel alloys according to the invention preferably contain 35 to 50% by weight tin, 50 to 65% by weight zinc and 0.1 to 5% by weight nickel.
• Tin-zinc-iron alloys according to the invention preferably contain 40 to 55% by weight tin, 40 to 60% by weight zinc and 1 to 8% by weight iron.
• the ternary tin-zinc alloys according to the invention can be produced from the individual components by fusion or powder metallurgy.
• Electrolytic preparation is preferable, particularly with respect to typical applications. That is done by electrolytic deposition from aqueous galvanic electrolyte baths which contain the alloy components in dissolved form.
• the ternary tin-zinc alloys can be deposited onto substrates from alkaline, neutral, or weakly acidic electrolytic baths.
• an alkaline electrolyte is understood to be an electrolyte with a pH greater than 10.
• a neutral electrolyte is considered to be one with a pH from 6 to 10.
• a weakly acidic electrolyte is considered to be one with a pH of 3-6.
• the alloy components are added to the aqueous electrolyte bath in the form of their compounds which are soluble and ionogenic in the particular medium.
• Tin is preferably added as the sulfate, chloride, sulfonate, or oxalate, or as sodium or potassium stannate.
• Zinc is preferably added as the sulfate, chloride, hydroxide, sulfonate or oxide.
• the element, iron, cobalt, or nickel, which acts as the third alloy component, is preferably added as the sulfate, chloride, hydroxide or carbonate.
• the galvanic electrolyte according to the invention for producing ternary tin-zinc alloy coatings can also contain other additives common and well-known in plating technology. Those can be bases for pH adjustment, such as sodium, potassium, or ammonium hydroxide, or inorganic acids, such as hydrochloric acid, sulfuric acid, phosphoric acid, or boric acid; alkali salts of these acids as buffers and/or conductive salts; organic acids such as hydroxycarboxylic acids and/or their salts, such as citric acid; complexing agents such as EDTA, wetting agents, brighteners, etc.
• pH adjustment such as sodium, potassium, or ammonium hydroxide
• inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, or boric acid
• alkali salts of these acids as buffers and/or conductive salts
• organic acids such as hydroxycarboxylic acids and/or their salts, such as citric acid
• complexing agents such as EDTA
• the proportions of the metals in the electrodeposited alloy coating can be influenced, in the known manner, by the proportion of metals in the bath composition, by the nature and proportion of the other bath components, and by the deposition parameters.
• the substrate to be coated such as a part made from a ferrous metal to be protected from corrosion
• the counterelectrodes can be anodes of insoluble or, preferably in the case of neutral or weakly acidic electrolytes, soluble materials.
• Insoluble anodes are usually of graphite or platinized titanium. It is convenient for soluble anodes to consist of the metals of the alloy to be deposited, preferably at the desired composition.
• a temperature of about 20-70° C. and a current density of about 0.1-5 A/dm 2 are considered boundary conditions for deposition of the ternary tin-zinc alloys from the electrolytes according to the invention. Deposition rates of about 0.05-1 ⁇ m/minute are attained.
• An alkaline electrolyte according to the invention can have the following typical ranges of compositions:
• the galvanic deposition of the alloy is accomplished at temperatures in the range of 40-70° C. and at current densities of 1-5 A/dm 2 at deposition rates of 0.15-0.3 ⁇ m/minute.
• Graphite or platinized titanium can be used as anodes.
• Organic acids and their salts, phosphonic acids, phosphonates, gluconates, glucoheptonic acids, glucoheptonates and ethylenediaminetetraacetic acid can be used as complexing agents.
• Surfactants, multifunctional alcohols, and betaines can be used as wetting agents and brighteners in the corresponding media.
• composition of the alloy layer can be varied by altering the proportions of the individual components in the bath. For instance, increasing the hydroxide content reduces the tin content, with corresponding increase of the other two metals in the coating.
• a neutral electrolyte according to the invention can have the following typical ranges of compositions:
• the electrolytic deposition of the alloy is accomplished at temperatures from 40 to 70 ° C., and at current densities of 0.5-3 A/dm 2 , with deposition rates of 0.05-0.3 ⁇ m/minute.
• Graphite or platinized titanium are used as the anode. It is also possible to use soluble anodes.
• the proportions in the alloy composition can be varied by varying the coating parameters.
• a weakly acidic electrolyte according to the invention can have the following typical ranges of compositions:
• the electrolytic deposition of the alloy is accomplished at temperatures of 20 to 70° C. at current densities of 0.5-5 A/dm 2 , with deposition rates of 0.1-1 ⁇ m/minute.
• Graphite or platinized titanium can be used as the anode. It is also possible to use soluble anodes. Boric acid, for example, can be used as the buffer.
• the proportions in the alloy composition can be adjusted by changing the coating parameters (concentrations of the components in the solution, working parameters). For example, increasing the current density increases the proportion of zinc and nickel, cobalt or iron in the alloy and reduces the proportion of tin. Variation of the temperature in the specified range causes only insignificant changes of the composition of the alloy layer.
• the ternary tin-zinc alloys according to the invention have very favorable material properties. On the basis of those properties, they can be used as an independent material, but also, especially, as coatings on substrates in various manners.
• the ternary tin-zinc alloys have particularly high resistance to corrosion, which is most strongly expressed in the SnZnNi and SnZnCo systems. Therefore those alloys are particularly suitable for anticorrosion layers on ferrous materials. Accordingly, the corresponding electrolyte solutions can be used preferentially to produce corrosionresistant layers on ferrous materials. Iron sheets, coated in this manner, combined with the usual passivation by chromating or chromiting, without other treatment, attain resistance to appearance of red rust of more than 3,000 hours.
• the SnZnFe and SnZnCo alloys attain the highest hardnesses.
• SnZnNi coatings have the highest resistances to wear.
• Such alloy coatings can, therefore, be used advantageously as wear-prevention layers in cases of mechanical stress.
• SnZnFe and SnZnCo coatings can be welded particularly well, and so are desirable as weldable coatings and contact surfaces in electronics.
• Table 2 shows the corresponding data for alloy systems selected as examples.
• the ternary tin-zinc alloys according to the invention can also be used as final decorative coatings.
• the three alloy systems have interesting and appealing colors in the blue range, depending on the selection of the third alloying element.
• An alkaline electrolyte for depositing an alloy consisting of 45% by weight Sn, 52% by weight Zn and 3% by weight cobalt has the following composition:
• the coating composition indicated above can be produced with this electrolyte at a temperature of 60° C. and current densities of 1-2 A/dm 2 . In this case, about 0.2 ⁇ m of coating layer is built up per minute. The density of the alloy layer is 7.27 g/cm 3 .
• a neutral electrolyte for depositing an alloy consisting of 48% by weight tin, 49% by weight zinc and 3% by weight cobalt has the following composition:
• This solution has a pH of 8.5.
• the coating composition indicated above can be produced with this electrolyte at a temperature of 60° C. and current densities of 0.5-1 A/dm 2 . 0.15 ⁇ m of coating is built up per minute.
• the density of the alloy layer is 7.27 g/cm 3 .
• This solution has a pH of 4.5.
• the coating composition indicated above can be produced with this electrolyte at a temperature of 40° C. and a current density of 1.5 A/dm 2 . In this case, about 0.4 ⁇ m of the alloy layer is produced per minute. The density of the alloy layer is 7.2 g/cm 3 .
• a weakly acidic electrolyte for depositing an alloy consisting of 52% by weight Sn, 44% by weight Zn, and 4% by weight iron has the following composition:
• the pH of this solution is 4.4.
• This electrolyte can produce the layer composition stated above at a temperature of 40° C. and a current density of 1.5 A/dm 2 . In this case, about 0.4 ⁇ m of the alloy layer is deposited per minute. The density of the alloy layer is 7.25 g/cm 3 .

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• Metallurgy (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Mechanical Engineering (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electroplating Methods And Accessories (AREA)

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• 2000
  • 2000-09-16 DE DE10045991A patent/DE10045991A1/de not_active Ceased
• 2001
  • 2001-08-16 JP JP2002527347A patent/JP4817352B2/ja not_active Expired - Fee Related
  • 2001-08-16 US US10/380,212 patent/US20040091385A1/en not_active Abandoned
  • 2001-08-16 WO PCT/EP2001/009452 patent/WO2002022913A2/de active Application Filing
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