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
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/12—Electroplating: Baths therefor from solutions of nickel or cobalt
• • 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
  • C25D3/20—Electroplating: Baths therefor from solutions of iron
• • 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
  • C25D5/60—Electroplating characterised by the structure or texture of the layers

Definitions

• the present invention relates to a method of applying a metal layer onto at least one surface of an aluminium or aluminium alloy workpiece or article, comprising the steps of a simple pre-treating step of cleaning and activating the surface and yet producing good adhesion of the subsequently applied metal layer.
• the invention also relates to an aluminium alloy product plated on at least one surface with a metal layer. More specifically, the invention relates to a method of applying a metal layer of a braze-promoting metal onto the clad layer of an aluminium alloy brazing sheet product to be used in a fluxless brazing operation.
• alloy designations and temper designations refer to the Aluminium Association designations in Aluminium Standards and Data and the Registration Records, as published by the Aluminium Association.
• Nickel plating of aluminium products is widely used because nickel provides a bright, shiny appearance, is long lasting and can conduct electricity. Another, more particular use of nickel plating is made in the manufacture of brazing sheet products. Aluminium alloy brazing sheets comprise an aluminium alloy core and a clad layer of filler alloy on one or both sides. Aluminium brazing sheets are widely used, e.g., in the production of heat exchangers.
• aluminium-silicon alloys as filler material is problematic because the aluminium oxide layer has to be disrupted during brazing. This may be effected by applying a chemical flux onto the workpiece before brazing.
• Fluxes for use in brazing aluminium alloys usually consist of mixtures of alkali and alkaline earth chlorides and fluorides or cryolite. The flux operates at the brazing temperature to disrupt, spread and dissolve the oxide film.
• applying the chemical flux onto the workpiece is a rather laborious and therefore expensive process.
• a braze-promoting metal of cobalt, iron, or more preferably nickel is coated on a part to be brazed.
• the nickel reacts exothermically with the underlying aluminium alloy, thereby disrupting the aluminium oxide layer and permitting the underlying molten aluminium clad metal to flow together and join.
• this method does not require a fluoride flux, it is also suitable for utilization with magnesium-enriched aluminium alloys, such as are beneficially used in heat- exchanger constructions.
• a wetting agent may also be added in order to improve the wettability of the clad alloy during the brazing process.
• nickel plating requires extensive pre-treatment of the metal surface such as cleaning, etching, desmutting, etc. This is again due to the presence of the tenacious oxide layer. If the aluminium alloy surface has not been properly pre-treated, the nickel coating will either have poor adhesion, or will be contaminated and thereby impede the brazeability of the product. Therefore, nickel plating with all necessary pre-treatment steps is an expensive and environmentally unfriendly process.
• the present invention solves one or more of these objects through the method of applying a metal coating according to claim 1 and the aluminium alloy product according to claim 14.
• the method of applying a metal layer onto at least one surface of an aluminium or aluminium alloy workpiece comprises the steps of pre-treating the surface by cathodic activation in a pre-treatment bath containing sulphuric acid and metal-ions selected from the group consisting of nickel, iron and cobalt, and applying a metal layer by electroplating the pre-treated workpiece, and wherein the metal layer is selected from the group consisting of nickel, iron, cobalt, and alloys thereof.
• Fig. 1 shows an angle-on-coupon for brazing tests.
• the invention is based on the finding that direct metal, for example nickel, plating of aluminium alloy products is possible after cathodic activation in a simple sulphuric acid solution to which only nickel ions, e.g. in the form of nickel sulphate, has been added. No fluoride components are needed in this activation process. Because the activation bath contains the same ingredients as a Watts bath which is preferably used as nickel plating bath, cross- contamination is excluded. Also, no problems in effluent treatment are expected.
• the cathodic activation step has the same effect as the creation of a thin bonding layer between the aluminium surface and the nickel coating. The same applies mutatis mutandis for the situation where iron or cobalt is being used.
• the pre-treatment bath preferably contains about 15 to 200 g/l, and preferably 80 to 150 g/l, of NiSO 4 -H 2 O, and about 50 to 350 g/l, preferably about 150 to 250 g/l of H 2 SO 4 .
• the pre-treatment bath also contains boric acid as a buffer, e.g. in a range of 1 to 50 g/l, and preferably 20 to 40 g/l.
• the preferred bath for pure nickel plating is a Watts bath containing nickel sulphate, nickel chloride and boric acid.
• a preferred bath for nickel-bismuth plating is a citrate-gluconate bath containing nickel sulphate, nickel chloride, (NH 4 J 2 SO 4 , bismuth concentrate, sodium citrate and sodium gluconate.
• Preferred concentration ranges of these substances are 100 to 180 g/l of NiSO 4 -6H 2 O, 10 to 50 g/l of NiCI 2 -6H 2 O, 1 to 10 ml/I of a bismuth concentrate containing 100 g/l of Bi, 10 to 50 g/l of (NH 4 ) 2 SO 4 , 100 to 180 g/l of sodium citrate-2H2 ⁇ , and 10 to 50 g/l of sodium gluconate.
• This bath may be used for pure nickel plating as well, in which case the bismuth concentrate is omitted. It has been found that the pre-treatment is already effective at elevated temperatures of less than 95 0 C, and preferably in the range of 55°C and 80 0 C. This is a great advantage, since working at lower temperatures makes the introduction into a strip plating line much easier, because evaporation losses will be limited. Furthermore, aluminium dissolution is much lower at temperatures below 70 0 C, thereby increasing the lifetime of the activation bath. Hence, the pre-treatment bath is preferably maintained at temperatures between 55°C and 80 0 C, and most preferred between about 60°C and 70°C.
• the activation current is cathodic. As demonstrated by the examples, the current density is not critical to the quality of the final product. The same applies to activation time of the product in the pre-treatment bath.
• the activation current of the cathodic activation is preferably in a range of -200 to -2000 PJm 2 , and more preferably in a range of -500 to -1400 A/m 2 .
• the time spent by the product in the pre-treatment bath is typically in the range of 1 to 50 sec, and preferably in the range of 5 to 15 sec.
• the average thickness of the applied metal layer of Ni, Co, Fe or alloys of each of these metals is preferably less than 2 ⁇ m, more preferably less than 1.0 ⁇ m, and even more preferably in a range of 0.2 to 1.0 ⁇ m.
• the method is preferably carried out as a continuous plating operation, which allows the continuous treatment of an infinite strip of metal.
• a further metal layer may be applied on top of the layer of Ni, Fe, Co, or alloys thereof, in order to improve for example the corrosion resistance of the final product.
• a thin layer of tin can be applied onto the nickel-layer on a brazing sheet product, which results in a significant improvement of the post-braze corrosion resistance.
• the method according to this invention may include the additional step of degreasing of the surface prior to the cathodic activation and/or the electroplating step in order the clean the surface.
• full hard material is easier to slit than soft annealed material.
• the coils may be soft annealed afterwards.
• the aluminium workpiece is a brazing sheet product, the brazing sheet product including a core layer and a clad layer formed of a brazing alloy including aluminium and 2- 18 wt.% silicon, preferably in the range of 7 to 14%, (such as AA4343 and 4045 alloys), and whereby the metal layer is applied on the clad layer.
• the metal layer of nickel, iron, cobalt or alloys of each of these metals act as a braze- promoting element during brazing.
• the clad layer further comprises a wetting agent as alloying element in a range of up to 1 wt.% in order to improve the wettability of the clad alloy during the brazing process.
• the wetting agent is selected from the group consisting of lead, bismuth, lithium, antimony, tin, silver, thallium and any mixture thereof.
• the aluminium workpiece is an aluminium conductor, and preferably made of an alloy selected from the group consisting of AA1370, AA1110 and AA6101.
• the aluminium conductor can be in the form of an aluminium strip or aluminium wire or aluminium tube.
• the applied metal layer is preferably consisting of nickel in order to improve the electrical contact properties.
• the aluminium conductors can be used for the transmission of electrical and/or thermal energy. These conductors are usually in the form of bars, wire or cables when used as electrical conductors, and in the form of strips, bars or tubes when used as thermal conductors.
• an aluminium alloy product preferably a brazing sheet product, electroplated with a metal layer selected from the group consisting of nickel, iron, cobalt and alloys thereof manufactured with the method of the invention as set out in the present specification and claims.
• a brazing sheet product can be applied successfully in a Controlled Atmosphere Brazing ("CAB") process in the absence of a brazing flux.
• CAB Controlled Atmosphere Brazing
• the aluminium alloy product according to the invention has an excellently adhering nickel or nickel-bismuth coating.
• the product is an aluminium alloy brazing sheet comprising a core, a clad layer and a nickel-containing layer plated on top of the clad layer. This brazing sheet will have good brazeability and low manufacturing costs. It may either contain a wetting agent like Bi in the clad alloy, or in the nickel-containing layer.
• aluminium brazing sheets products of 0.4 mm thickness have been used for plating with a nickel or nickel-alloy layer having an average thickness of 0.5 ⁇ m.
• the aluminium brazing sheets used consisted of an AA3003-series aluminium core alloy conventionally clad on both sides with an AISi brazing alloy, whereby clad layer A contained, in wt.%, 10% Si, 1.5% Mg and 0.08% Bi, whereas clad layer B contained, in wt.%, 12%Si and no Mg or Bi.
• a fluoride based activation bath was used (see Table 2) and consisting of anodic activation at a current density of +1000A/m 2 , and which is disclosed in US-6,780,303-B2, incorporated herein by reference.
• the cathodic activation was carried at various temperatures.
• Two Samples 10 and 11 have been carried out using the same activation bath but whereby the current was reversed such that anodic activation occurred.
• a nickel layer was plated from a Watts bath (see Table 3) or a nickel-bismuth alloy layer from a citrate-gluconate bath (see Table
• the quality of the resulting plated substrates were evaluated using an adhesion test and a brazeability test.
• the adhesion tests consisted on the Erichsen dome test (cup height of 5 mm), whereafter adhesive tape (Scotch Tape 3M No. 610) is applied to the deformed area and pulled off in one move. Adhesion is quantified by classifying the amount of nickel on the tape. An overall adhesion assessment was rated from 1 (poor) to 10 (excellent), wherein a level of 6 was considered acceptable as it was comparable to existing commercially available brazing sheet with a Ni-Pb layer.
• a wetting agent such as Bi is favourable for the brazeability performance of the resultant brazing sheet product. From the Samples 1 and 8 it can be seen that the wetting agent might be added either to the Ni layer or to the brazing clad layer without affecting the adhesion or the brazeability. Adding the wetting agent to both the clad layer and the nickel layer has no adverse effect on the brazeability.

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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)
• Electroplating And Plating Baths Therefor (AREA)

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• 2006
  • 2006-01-09 BR BRPI0606419-1A patent/BRPI0606419A2/pt not_active Application Discontinuation
  • 2006-01-09 JP JP2007551588A patent/JP2008527178A/ja not_active Withdrawn
  • 2006-01-09 EP EP06706199A patent/EP1838490A1/en not_active Withdrawn
  • 2006-01-09 CN CNA2006800018028A patent/CN101098771A/zh active Pending
  • 2006-01-09 CA CA002591116A patent/CA2591116A1/en not_active Abandoned
  • 2006-01-09 WO PCT/EP2006/000185 patent/WO2006077041A1/en active Application Filing
  • 2006-01-09 MX MX2007007955A patent/MX2007007955A/es unknown
  • 2006-01-09 AU AU2006207665A patent/AU2006207665A1/en not_active Abandoned
  • 2006-01-09 KR KR1020077016083A patent/KR20070095331A/ko not_active Application Discontinuation
  • 2006-01-16 FR FR0600371A patent/FR2880899A1/fr active Pending

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