WO2009127707A1 - Procédé anticorrosion pour pièces en aluminium brasées au fluoroaluminate - Google Patents

Procédé anticorrosion pour pièces en aluminium brasées au fluoroaluminate Download PDF

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Publication number
WO2009127707A1
WO2009127707A1 PCT/EP2009/054564 EP2009054564W WO2009127707A1 WO 2009127707 A1 WO2009127707 A1 WO 2009127707A1 EP 2009054564 W EP2009054564 W EP 2009054564W WO 2009127707 A1 WO2009127707 A1 WO 2009127707A1
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parts
flux
brazed
water
alf
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PCT/EP2009/054564
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English (en)
Inventor
Placido Garcia-Juan
Andreas Becker
Alfred Ottmann
Thomas Born
Hans-Walter Swidersky
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Solvay Fluor Gmbh
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Publication of WO2009127707A1 publication Critical patent/WO2009127707A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/226—Non-corrosive coatings; Primers applied before welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
    • C09K5/08—Materials not undergoing a change of physical state when used
    • C09K5/10—Liquid materials
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
    • C09K5/20—Antifreeze additives therefor, e.g. for radiator liquids
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
    • C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids
    • C23F11/18—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids using inorganic inhibitors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2101/00—Articles made by soldering, welding or cutting
    • B23K2101/04—Tubular or hollow articles
    • B23K2101/14—Heat exchangers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/08—Non-ferrous metals or alloys
    • B23K2103/10—Aluminium or alloys thereof

Definitions

  • the invention concerns brazed aluminium parts with improved anticorrosivity and a process for reducing the corrosive influence of fluoride ions on aluminium parts brazed using potassium fluoroaluminate.
  • brazing of aluminium parts can be performed utilizing fluxes based on alkali metal fluoroaluminates, especially potassium fluoroaluminate and cesium fluoroaluminate. Fluxes of this type are generally considered to be noncorrosive. See for example, US patent 3,971,501 which applies a flux based on KAlF 4 and K 3 AlF 6 , or US patent 4,689,092 which applies a flux based on potassium fluoroaluminate and cesium fluoroaluminate.
  • chloride fluxes which had been applied for brazing is that the latter must be removed after the brazing process to prevent corrosion induced by chloride residues to take place.
  • US patent 6,949,300 discloses kinetic spraying onto metal substrates of a brazing composition that comprises corrosion protector, brazing filler and/or non-corrosive flux. Contrary to belief in the brazing industry concerning the non-corrosive properties of potassium fluoroaluminate fluxes, it was observed that under certain circumstances, flux residues may cause a certain level of corrosion. Corrosion was especially observed if water or an aqueous composition (i.e. a composition which contains water) remained in contact long enough with brazed aluminium so that a part of the flux, though the flux is generally only very sparely soluble in water, was dissolved to a certain concentration. This was observed even if water or an aqueous composition circulated in brazed aluminium parts.
  • a aqueous composition i.e. a composition which contains water
  • the invention provides a process for reducing corrosion of potassium fluoroaluminate flux-brazed aluminium parts caused by fluoride ions leached from flux residues during the extended period of time in contact of the parts with water or aqueous compositions by applying, for brazing of the parts, a potassium fluoroaluminate flux which forms a flux residue with reduced leachable fluoride ion content, or by subjecting the brazed parts to an oxidative heat treatment after brazing, or by applying to the brazed parts at least one anticorrosive agent selected from fluoride ion scavengers and one or more compounds reducing the solubility of the flux residue.
  • a potassium fluoroaluminate flux can be applied which forms a flux residue on the brazed parts with reduced leachable fluoride ion content, and then subjecting the brazed parts to a heat treatment after brazing.
  • the invention provides a process for reducing corrosion of potassium fluoroaluminate flux-brazed aluminium parts caused by fluoride ions leached from flux residues during an extended period of time of the parts with water or aqueous compositions comprising a step of applying, for brazing of the parts, a potassium fluoroaluminate flux which forms a flux residue with reduced leachable fluoride ion content, or of subjecting the brazed parts to an oxidative heat treatment after brazing, or of applying to the brazed parts at least one anticorrosive agent selected from fluoride ion scavengers and one or more compounds reducing the solubility of the flux residue, and a step of contacting the brazed parts with water for an extended period of time.
  • a flux high in dipotassium pentafluoroaluminate or an oxidative heat treatment are applied for reducing corrosivity, then the step of contact of the brazed part with water occurs after brazing and/or heat treatment, respectively. If at least one anticorrosive agent selected from fluoride ion scavengers and one or more compounds reducing the solubility of the flux residue are applied to the brazed parts, then the step of applying these compounds and the step of contact of the parts with water can be performed simultaneously, or the contact with water occurs afterwards.
  • the present invention provides a process for brazing of aluminium parts to aluminium parts wherein a potassium fluoroaluminate flux is applied to the parts, the parts are joined, brazed and, after brazing, are contacted with water or aqueous compositions for an extended period of time with the proviso that, for brazing of the parts, a potassium fluoroaluminate flux is used which forms a flux residue with reduced leachable fluoride ion content, and/or by subjecting the brazed parts to a heat treatment after brazing, and/or by applying to the brazed parts at least one anticorrosive agent selected from fluoride ion scavengers and one or more compounds reducing the solubility of the flux residue.
  • aluminium parts denotes in the present invention parts made from pure aluminium and parts made from aluminium alloys. Aluminium often contains manganese (up to 1.5 % by weight), silicon, magnesium (often up to 0.3 % by weight), iron (up to 0.7 % by weight), copper, zinc, titanium, and sometimes low amounts of chromium or nickel. The content of alloy metals usually lowers the melting point. The melting point of aluminium alloys in the frame of the present invention should not be too low because a too low melting point may have negative effects in brazing processes. A melting point of equal to or greater than 630 0 C gives good results. If magnesium is present, it may be advantageous to apply a flux which contains cesium fluoroaluminate.
  • the invention can be applied with good results to Al AA3003 alloy.
  • Preferred brazed aluminium parts are heat exchangers.
  • the term "corrosion” preferably denotes the formation of white turbidity or a white precipitate, which is explainable by the formation of aluminium hydroxide, aluminium oxide or aluminium oxide hydroxide or hydrates thereof.
  • the term "caused by fluoride ions” is used. The reason is that the greatest corrosive influence is allocated to the fluoride ion. It is considered possible that other species originating from the dissolution of the flux residue may also have corrosive properties. Thus, the term "caused by fluoride - A -
  • ions does not exclude the possibility that corrosion is caused by other species present in the water or aqueous solution.
  • water as used in the present invention includes water from natural sources, e.g. rain water, water formed as dew, and water formed after snow melt. It includes artificial water sources, e.g. tap water.
  • natural sources e.g. rain water, water formed as dew, and water formed after snow melt. It includes artificial water sources, e.g. tap water.
  • aqueous compositions in its broadest sense includes any composition which contains water and at least one additional component, e.g. an inorganic or organic salt or an organic liquid, e.g. a monobasic or dibasic alcohol, and comes into contact with brazed aluminium parts. It includes, for example, cooling liquid which, besides water, usually additionally contains antifreeze compounds, especially glycol, and additives, for example, anticorrosives or colorants, such as those used in water coolers for stationary refrigeration equipment or stationary heat exchangers or in cooling water for vehicles.
  • the aqueous composition is a cooling liquid or a cleaning composition.
  • the terms “water” and “aqueous composition” in the frame of the present invention do not include artificially manufactured salt water or salt water from natural sources (e.g. sea water) when used for test purposes to identify properties of the brazed parts, especially salt water from a natural source or manufactured artificially to be used according to the AST-M G43 or G85 SWAT test.
  • the terms “water” and “aqueous composition” in the frame of the present invention do not include artificially manufactured salt water or salt water from natural sources (e.g. sea water) when used for test purposes to identify properties of the brazed parts, especially salt water from a natural source or manufactured artificially to be used according to the AST-M G43 or G85 SWAT test.
  • natural sources e.g. sea water
  • water and “aqueous composition” do not include water with a sodium chloride salt concentration equal to or greater than 4 % by weight; such a composition is used in the SWAT test.
  • the term “water” and “aqueous compositions” does not include sodium chloride solutions containing added acetic acid, or when contact between brazed parts and a sodium chloride solution is performed in a chamber which contains added sulfur dioxide, or water shich contains dissolved sodium chloride and added ammonium sulfate. Such solutions are used in the ASTM G 85-94 tests. Consequently, the deliberate treatment of brazed parts with sodium chloride containing solutions, especially when applied for testing, is disclaimed.
  • brazing is performed in an inert gas atmosphere.
  • This is also called Controlled Atmosphere Brazing ("CAB" process).
  • the inert gas consists of nitrogen, argon or their mixtures.
  • the oxygen content in the inert gas generally is lower than 2 % by volume, preferably lower than 1 % by volume, and especially equal to or lower than 100 ppm by volume.
  • the oxidative heat treatment, the application of a scavenger for fluoride ions and the application of one or more compounds reducing the solubility of the flux residue can be applied to brazed parts wherein any flux based on potassium fluoroaluminate had been used.
  • the oxidative treatment can be performed after brazing using fluxes based on potassium fluoroaluminate, for example as described in US 3,951,328 (fluxes containing mainly KAlF 4 and K 3 AlF 6 ), US 4,428,920 (describes how to prepare a potassium fluoroaluminate composition from tetrafluoro aluminium acid and potassium salts), US 4,579,605 (describes how to prepare fluxes with a variable content OfKAlF 4 and K 2 AlF 5 or its hydrate), US 5,318,764 (describes several methods for the preparation of KAlF 4 or K 3 AlF 6 ), or US 5,980,650 (mentions, i.a., how reversibly dehydrated flux is prepared - by drying at comparatively low temperatures; describes the preparation and uses of a flux comprising irreversibly dehydrated K 2 AlF 5 ).
  • fluxes based on potassium fluoroaluminate for example as described in US 3,951,328 (flux
  • the process can also be applied for aluminium parts brazed with fluxes which additionally comprise cesium ions; such fluxes are especially suitable to braze aluminium alloys with relatively high magnesium content.
  • fluxes which additionally comprise cesium ions; such fluxes are especially suitable to braze aluminium alloys with relatively high magnesium content.
  • parts brazed using fluxes described in EP-B-O 239642 (describes the use of cesium fluoroaluminate for brazing of Al-Mg alloys, optionally in admixture with conventional fluxes), or US4,670,067 (describes mixtures of cesium fluoroaluminates and potassium fluoroaluminates and their use for brazing of Al-Mg alloys).
  • the process can also be applied to aluminium parts brazed with fluxes based on fluoroaluminates modified by certain other metal compounds.
  • it can be applied to parts brazed by a flux modified by zirconium fluoride or titanium fluoride, optionally in the additional presence of certain metal oxides, for example, oxides of zirconium, titanium, manganese, hafnium or rhenium as described by US 2004/0163734.
  • the process can also be applied to aluminium parts brazed with fluxes based on alkali metal fluoroaluminate comprising additives.
  • flux comprising filler metal, e.g. Al-Si filler metal, e.g. in powder form.
  • filler metal e.g. Al-Si filler metal
  • alkali metal fluoroaluminate flux which comprises a filler alloy precursor. This is, for example, described in US 5,100,048.
  • filler alloy precursor for example, silicon, germanium or copper can be contained.
  • silicon dioxide or alkali metal fluoro silicates can be contained as filler metal alloy precursor.
  • the process can be applied to parts having been brazed using fluxes per se; e.g. fluxes applied as dry flux using electrostatic forces.
  • the process can also be applied to parts having been brazed using flux compositions which comprise a flux, optionally together with the modifying agents mentioned above, and additives which improve the applicability.
  • it can be applied to parts brazed with flux compositions comprising a solvent and/or a binder and/or thickeners.
  • flux compositions comprising a solvent and/or a binder and/or thickeners.
  • water or organic liquids e.g. alcohols, compounds with two or more hydroxyl groups, e.g.
  • diols for example, ethylene glycol
  • polyols for example, glycerine, ketones, pyrrolidones, nitriles, or ethers including hydroxysubstituted ethers, e.g. glycol ethers, for example, ethylene glycol
  • Isopropanol is, for example, a very suitable solvent.
  • a binder many organic compounds are useful.
  • flux compositions can be used which contain polyurethanes, organic resins, phthalates, acrylates, vinyl resins, epoxy resins, nitrocellulose, polyolefines or hydro xyethyl cellulose as a binder.
  • the binder may also be partially or completely be present in the form of a thixotropic agent, for example, in the form of gelatine, pectines, acrylates or polyurethanes.
  • compositions are described, for example, in US 3,951,328, EP-A 1287941, WO 2005/092563, and WO 2007/131993.
  • the process can be applied to parts brazed with fluxes of a very variable particle size.
  • the particles may have the particle size distribution as disclosed in US-A 6,733,598.
  • a flux comprising particles with such a particle size distribution can be applied for example in a dry flux method. In dry fluxing, the flux is applied without solvent to the surface of the metal parts to be joined by brazing. This can be supported by electrostatic power.
  • the particles of the flux may be of a coarser nature than the finer particles disclosed in said US 6,733,598.
  • Such coarser fluxes are very suitable for the application in the form of a flux composition including the flux dispersed a solvent; they can, for example, be applied by painting, printing or spraying onto the parts.
  • the process is applied to potassium fluoroaluminate brazed parts which have a contact with water or aqueous compositions for an extended period of time with a respective higher level of fluoride leaching.
  • extended period of time denotes a period of contact which lasts at least one day, preferably at least 2 days.
  • extended period of time has no specific upper limit. It may last for one week or longer. In the case of water containing cooling liquid, for example, the contact between the liquid and aluminium can last for years. Often, the upper limit is equal to or shorter than 1 year, preferably, equal to or shorter than 6 months, more preferably, equal to or shorter than 2 months.
  • Reduction of corrosive influence of fluoride ions leached from the brazed parts during extended contact with water or aqueous compositions can be achieved according to the invention by two alternatives : by using a specific flux for brazing which provides low content of leachable fluoride ion, or by treating the brazed parts.
  • the latter alternative includes a heat treatment, the application of a scavenger for fluoride ions or by applying a compound which reduces the solubility of the flux residue.
  • the brazed parts are post-treated by an oxidative heat treatment after brazing. It was observed that fluoride leached out of the flux residues after extended periods of time of contact of the aluminium parts with water or aqueous solutions has less corrosive impact on the brazed parts compared to brazed parts without heat treatment after brazing.
  • Brazing is preferably performed in an inert gas atmosphere, preferably, in an atmosphere which contains at least one inert gas selected from the group consisting of nitrogen or argon, or in an atmosphere which consists of nitrogen, argon or their mixtures.
  • the inert gas is essentially oxygen free.
  • the term "essentially” denotes preferably an atmosphere during brazing which contains less than 2 % by volume of oxygen, more preferably less than 1 % by volume, and most preferably, equal to or less than 100 ppm per volume.
  • the brazed parts are subjected to a heat treatment in an oxygen containing atmosphere. If desired, the brazed aluminium part can be treated as a whole. In a technical view, this can be performed in a very simple manner.
  • the temperature of the brazed parts at heat treatment is equal to or higher than 400 0 C. Preferably, it is equal to or lower than 530 0 C. If desired, the temperature may be higher, e.g. up to 550 0 C or even more.
  • the preferred range for the oxidative heat treatment is equal to or higher than 400 0 C and equal to or lower than 530 0 C.
  • a preferred oxygen containing atmosphere is air.
  • the duration of the heat treatment is preferably equal to or longer than 10 seconds, especially preferably equal to or longer than 30 seconds. It is preferably equal to or shorter than 1 hour, especially equal to or shorter than 15 minutes.
  • a preferred range for the oxidative heat treatment is equal to or longer than 30 seconds, and equal to or shorter than 15 minutes.
  • EP-A-O 347106 An oxidizing heat treatment to improve corrosion resistance is already known from EP-A-O 347106.
  • EP-A-O 347106 An oxidizing heat treatment to improve corrosion resistance is already known from EP-A-O 347106.
  • a reference to the examples indicates that the protection is intended against corrosion caused by salt water.
  • Said EP application is not addressing problems caused by fluoride ions leached from the flux after contact with water for an extended period of time, for example, for one day or longer.
  • a simple heat treatment can reduce corrosivity caused by contact with water containing fluoride ions leached from flux residues after an extended period of time.
  • a specific flux is used for brazing which provides low content of leachable fluoride ion after brazing is performed.
  • a potassium fluoroaluminate-based flux is applied which comprises equal to or less than 80 % by weight of KAlF 4 . It was found by the inventors that dipotassium pentafluoroaluminate has an anticorrosive effect because, compared to other potassium fluoroaluminate fluxes, less fluoride ions are leached during extended water contact of the brazed parts.
  • dipotassium pentafluoroaluminate and its hydrates are converted during brazing to form a flux residue containing mainly monopotassium tetrafluoroaluminate and tripotassium hexafluoroaluminate.
  • the formed tripotassium hexafluoroaluminate if contacted with water, forms dissolved potassium fluoride and almost insoluble dipotassium pentafluoroaluminate.
  • the surprising effect is that - though corrosive potassium fluoride is formed - the anticorrosive effect of the resulting dipotassium pentafluoroaluminate overcompensates the corrosive effect of the fluoride ions and renders an anticorrosive effect to the brazed aluminium.
  • a potassium fluoroaluminate flux the residues of which, after brazing, contain as much OfK 3 AlF 6 as possible. While it might be possible to apply a brazing flux high in K 3 AlF 6 , this is not preferred because this compound has disadvantages in brazing (for example, its melting point is rather high).
  • a flux comprising monopotassium fluoroaluminate and dipotassium pentafluoroaluminate or its hydrates containing equal to or less than 70 % by weight of KAlF 4 , preferably equal to or less than 65 % by weight, especially preferably equal to or less than 60 % by weight OfKAlF 4 .
  • the remainder to 100 % by weight is K 2 AlF 5 and/or its hydrate.
  • the content OfK 2 AlF 5 and/or its hydrate is preferably equal to or greater than 20 % by weight.
  • the flux contains or consists of 20 to 45 % by weight OfK 2 AlF 5 and/or its hydrate, more preferably, contains or consists of 25 to 45 % by weight OfK 2 AlF 5 and/or its hydrate; the remainder KAIF 4 .
  • the content of dipotassium pentafluoroaluminate and/or its hydrate in the flux is as high as possible, and is equal to or greater than 95 % by weight, especially 98 % by weight ⁇ 2 %.
  • the remainder is KAlF 4 and/or K 3 AlF 6 .
  • the weight per area of the flux coating on the parts before brazing can vary. For example, it can be in a range of 1 to 40 g/m 2 . Preferably, it is in a range between 1 and 20 g/m 2 . More preferably, it is in a range between 2 and 12 g/m 2 . It was found that the anticorrosive effect is especially remarkable in a range between 7 and 12 g/m 2 . For practical purposes, a range between 3 and 10 g/m 2 is preferred because the flux residues on parts with such a flux loading are technically preferred.
  • the dipotassium pentafluoroaluminate can be produced as described in US-A 4,579,605. According to that patent, aluminium hydroxide is dissolved in hydrofluoric acid, and the resulting product is then neutralized with a potassium compound.
  • the concentration of hydrofluoric acid is in the range of 5 to 40 % by weight
  • the ratio of A1:F:K of the starting material is in the range of 1 :4-4.5:1-1.5
  • the pH at the time of completion of the reaction is below 4
  • the reaction temperature is in the range of 30 0 C to 100 0 C.
  • the ratio needed is 1 :5-5,l :2-2,l.
  • the potassium compound may be potassium carbonate or a KOH solution with a concentration of 5 to 50 % by weight.
  • Reaction conditions which favor the production of a flux with high content of dipotassium fluoroaluminate can be taken from the many examples of that US patent.
  • the reaction temperature advantageously is lower than 60 0 C (see examples 7 to 10), and/or the content of Al and F is advantageously in the upper range, see example 17, and/or the concentration of HF and/or KOH solution is advantageously in the lower range, see examples 18, 10 and 19 and 20, 10 and 21, respectively.
  • the hydrate may be converted to irreversibly dehydrated dipotassium pentafluoroaluminate as described by US-A 5,980,650 by heating to sufficiently high temperature, e.g. shortly to 375°C or higher.
  • at least one anticorrosive agent selected from fluoride ion scavengers and one or more compounds reducing the solubility of the flux residue is applied.
  • the anticorrosive agent is applied as a coating on the brazed aluminium.
  • the anticorrosive agent is added to the water or aqueous composition.
  • “Scavenger compounds for fluoride” are compounds which react with the fluoride ion preferably under the formation of salts with lower solubility than the leached fluoride salt originally present in the water or aqueous composition.
  • calcium salts or salts, especially alkali metal salts, very preferably the potassium salt, containing the tetrafluoroaluminate anion are very suitable.
  • KAlF 4 can be applied as scavenger for fluoride ions because the tetrafluoroaluminate anion reacts with the fluoride anion under formation of pentafluoro aluminate .
  • the present invention provides a process for reducing the corrosivity of fluoride ions on potassium fluoroaluminate-brazed aluminium in water or in aqueous compositions wherein at least one anticorrosive agent selected from the group of water-soluble Ca containing salts and salts shifting the solubility equation of flux residues, preferably alkali metal salts, especially the potassium salts, containing the AlF 4 , AlF 5 or AlF 6 ion and hydrates thereof with the exception Of CaF 2 , is contacted with the fluoride containing aqueous solution. This contacting is performed after brazing is terminated.
  • the water-soluble calcium salt is the salt of an organic acid.
  • water-soluble denotes those salts which have a solubility in at 20 0 C of equal to or greater than 1 g/liter.
  • Ca containing salts includes inorganic and organic salts.
  • CaCl 2 is not applied.
  • the anion is selected from the group of organic acids.
  • the anion can be a monobasic, dibasic or polybasic acid.
  • the organic residue attached to the carboxyl group can be composed of carbon and hydrogen, and it can be linear or branched. It can be substituted by one or more oxo groups, hydroxy groups, nitro groups or halogen atoms.
  • the calcium salts containing calcium cationsions and anions of alkyl carboxylic acids with, in total, 2 to 12 carbon atoms are very suitable.
  • Calcium salts containing calcium cations and anions of alkyl carboxylic acids with, in total, 2 to 12 carbon atoms which are substituted by one or more hydroxy groups are likewise very suitable. Highly suitable are the calcium salts of acetic acid, propionic acid, lactic acid and gluconic acid.
  • Suitable inorganic calcium salts are, for example, the nitrates, iodides and thio sulfates.
  • the flux residue essentially consists of KAlF 4 and K 3 AlF 6 .
  • adding compounds which influence the solubility product or solubility of these constituents to the water or aqueous composition in contact with the brazed parts is advantageous.
  • addition of potassium compounds (but preferably not potassium chloride) is feasible.
  • KAlF 4 , K 2 AlF 5 or K 3 AlF 6 , their hydrates or mixtures thereof are preferred to the water or aqueous composition because addition of these compounds (which have a relatively low solubility in water) yield water or aqueous compositions saturated with these compounds, and thus reduce the dissolution of the flux residue.
  • addition of K 2 AlF 5 or K 3 AlF 6 is preferred.
  • the fluoride ion scavenger or the compound(s) reducing the dissolution of flux residues, especially K 2 AlF 5 or K 3 AlF 6 , but also KAlF 4 can be applied dry, as an aqueous solution or suspension.
  • brazed parts can be sprayed onto the brazed parts, or the brazed parts can be immersed into a solution or suspension, and dried thereafter so that a coating results.
  • a water-soluble binder e.g. a water-soluble polyurethane or polyvinyl alcohol
  • the scavenger or the preferred complex aluminium salts K 2 AlF 5 or K 3 AlF 6 can be added to the liquid fluid, e.g., to cooling water, if desired. They also can be added dry, as solution or as a suspension to the water or aqueous composition which is in contact with the brazed parts.
  • monopotassium tetrafluoroaluminate can be contained in the penta- or hexafluoroaluminate applied after brazing to shift the solubility equation of the flux residues.
  • potassium fluoroaluminate brazing flux usually contains or consists of monopotassium tetrafluoroaluminate and dipotassium pentafluoroaluminate.
  • the content of tripotassium hexafluoroaluminate in the flux itself before brazing is often very small, and often, the flux is produced free of that compound.
  • dipotassium pentafluoroaluminate transforms to monopotassium tetrafluoroaluminate and tripotassium hexafluoroaluminate in the flux melt.
  • tripotassium hexafluoroaluminate in contact with water, forms dipotassium pentafluoroaluminate which is sparely soluble, and dissolved potassium fluoride.
  • tripotassium hexafluoroaluminate can potentially be a source of corrosive fluoride ions.
  • dipotassium pentafluoroaluminate and tripotassium hexafluoroaluminate, as well as KAIF4 act anticorrosive if added to the aqueous solution or composition.
  • the calcium salts or the fluoroaluminate salts can be applied in many ways.
  • they can be applied to the surface of the brazed aluminium parts as dry coating, for example, by applying it in the form of a water-soluble lacquer using water-soluble binder, or by applying a suspension or solution to the surface of the aluminium parts, for example, by spraying, and then drying the aluminium parts.
  • the calcium salt or fluoro aluminium salt is added to the water or aqueous composition, as a preventive measure or when the first signs of corrosion are observed.
  • the concentration is variable.
  • the amount applied should be sufficient to guarantee the desired anticorrosive effect.
  • a concentration of equal to or greater than 1 g/1 water or aqueous composition is sufficient.
  • a concentration of equal to or less than 5 g/1 is sufficient, but could be higher if desired, usually up to the saturation concentration.
  • a solid deposit especially of the fluoroaluminate salts which have a relatively low solubility in water can be present. Such solid deposit serves as a reserve.
  • the brazed parts can be subjected to an oxidative heat treatment, and after the heat treatment, scavengers for the fluoride ion or compounds shifting the solubility equation of constituents of the flux residue are applied.
  • a specific flux high in dipotassium pentafluoroaluminate is used for brazing, and subsequently, a heat treatment as described above is performed.
  • a flux high in dipotassium pentafluoroaluminate is applied for brazing, and subsequently, a scavenger for fluoride ions as described above is applied.
  • a flux high in dipotassium pentafluoroaluminate is used for brazing, and subsequently, the brazed parts are subjected to a heat treatment, and at the same time or afterwards, scavengers for the fluoride ion or compounds shifting the solubility equation of constituents of the flux residue are applied.
  • a heat treatment at a temperature of equal to or higher than 400 0 C and preferably equal to or lower than 530 0 C in an oxygen containing atmosphere, e.g. air can be performed after brazing of the parts but before applying the anticorrosive agents of the present invention or when the specific advantageous flux high in dipotassium pentafluoroaluminate described above was used having the effect that less leachable fluoride ion is present in the flux residue.
  • the way of heat treatment is described above.
  • the respective disclosure of line 23 of page 7 to line 29 of page 8 of this description is incorporated here by reference to avoid repeating those paragraphs.
  • a scavenger for fluoride ions or of compounds especially those with a tetrafluoro- or pentafluoroaluminate anion, shifting the solubility equation of flux residues, can be applied to any aluminium parts brazed with fluxes based on potassium fluoroaluminate.
  • aluminium parts can be treated as described in lines 17 to 28 of page 3 of this description which are incorporated here by reference.
  • a technical field where the process of the invention (to reduce the corrosive influence of fluoride ions by applying a specific flux, heat treatment, adding scavengers for fluoride ions or applying compounds shifting the solubility equation of flux residues) can especially be applied are large heat exchangers which are stored outside of weather-protected rooms and are in contact with rain water.
  • the corrosivity of such heat exchangers can be reduced if a heat treatment is performed as described above, a specific flux is used for brazing as described above, and/or water-soluble calcium salts or KAlF 4 , dipotassium pentafluoroaluminate or tripotassium hexafluoroaluminate are applied to the surface of these parts before and/or during contact of these parts with rain water.
  • Another technical field concerns brazed parts in contact with an aqueous composition in the form of the cooling water of fuel-driven motors, e.g. motors operated with gas, gasoline or diesel.
  • Soluble calcium salts for example, calcium gluconate or calcium acetate, and/or monopotassium tetrafluoroaluminate, dipotassium pentafluoroaluminate and/or tripotassium hexafluoroaluminate are added to the cooling water to reduce and even prevent fluoride-induced corrosion, and/or a heat treatment of the brazed parts is performed and/or a specific flux as described above is applied for brazing.
  • compositions suitable as cooling liquid especially for motors fuelled by gas, gasoline or diesel.
  • These compositions contain water and an antifreeze compound, especially glycol and optionally additives like colorants, lubricants, and one or more compounds with anticorrosive properties.
  • the water-soluble calcium salt or the KA1F4, dipotassium pentafluoroaluminate or tripotassium hexafluoroaluminate are contained in an amount equal to or greater than 1 g/liter. Preferably, the are contained in an amount of equal to or lower than 5 g/liter.
  • the cooling liquid preferably contains an anticorrosive agent selected from the group consisting of calcium acetate, calcium propionate, calcium gluconate or calcium lactate, K 2 AlF 5 , K 2 AlF 5 H 2 O or K 3 AlF 6 .
  • the invention also provides potassium fluoroaluminate-brazed aluminium parts with enhanced protection against corrosion.
  • the parts (which comprise brazing residues) comprise a coating applied after brazing containing at least one anticorrosive agent selected from the group of water-soluble calcium containing salts and salts containing the AlF 4 , AlF 5 or AlF 6 ion and hydrates thereof with the exception of CaF 2 .
  • the coating can, for example, be applied by spraying or painting an aqueous or organic solution or suspension onto the parts and drying them.
  • a water soluble binder can be used, for example, gelatine, a water-soluble polyurethane, a polyvinylalcohol or a strippable varnish.
  • Another aspect of the present invention concerns a method of handling or using potassium fluoroaluminate flux-brazed aluminium parts wherein during handling or use, these parts come into contact with water or aqueous compositions the improvement which comprises the selection of potassium fluoroaluminate flux-brazed aluminium parts which have been obtained by selecting and applying a potassium fluoroaluminate flux forming a flux residue with reduced leachable fluoride ion and/or by subjecting the brazed parts to a heat treatment after brazing, and/or by applying to the brazed parts at least one anticorrosive agent selected from fluoride ion scavengers and one or more compounds reducing the solubility of the flux residue.
  • the term "handling” includes the steps of cleaning the parts using water or aqueous compositions, for example, cleaning compositions, for example, after the production of the parts, after transport or before or during their use, or storing the parts in a place which offers no complete protection against weather conditions like dew, snow or rain water.
  • the term "use” especially includes the use of the parts for providing heat exchange, e.g. by removing heat from or transferring heat to water-containing cooling liquids in motors.
  • Angle-on-coupon samples were prepared by brazing aluminium (AA3003) angles on coupons clad with aluminium- silicium alloy 4343. Nocolok ® flux was applied in a load of 10 g/m 2 . Then, the assembled angle/coupons parts were brazed. They were brought into a polypropylene bottle, and the pH value was measured. It was found that after 5 minutes contact between brazed part and water, the pH was between 5.4 and 5.8 for different sets of parts. After 18 days contact, the pH was between 8.4 and 8.8 for the samples. A dummy part (not brazed aluminium AA3003) had an initial pH of 6.3 and a final pH after 18 days of 7.3. The test shows that the pH of brazed samples becomes higher, i.e. the water becomes basic.
  • a flux essentially consisting of reversibly dehydrated K 2 AlF 5
  • Sample 4 6.9 (- 2.4 mg) Sample 5 7.0 (- 2.1 mg) Sample 6 7.1 (- 2.6 mg) Sample 7 6.8 (- 2.4 mg) Sample 8 7.6 (- 1.9 mg) Sample 9 6.7 (+ 10.2 mg)
  • Example 3 Tests with samples brazed with fluxes with varying K 2 AlF 5 content As described above, angle-on-coupons were prepared by brazing, using fluxes with 20mol- % 30 mol- %, 40 mol- %, 50 mol- % and 100 % K 2 AlF 5 (in % by weight : 34 % ; 37 %; 48 % ;58 % and 100 %); the remainder to 100 % being KAlF 4 . The pH of the samples with 100 % K 2 AlF 5 and with 30 % K 2 AlF 5 was determined to be 6.8. The pH of the other samples was higher.
  • Example 4 Soaking test
  • Angle-on-coupon samples were prepared by brazing aluminium (AA3003) angles on coupons clad with aluminium-silicon alloy 4343. Nocolok ® flux was applied in a load of 10 g/m 2 . Then, the assembled angle/coupons parts were brazed. They were brought into a polypropylene bottle, and the pH value was measured. It was found that after 5 minutes contact between brazed part and water, the pH was between 5.4 and 5.8 for different sets of parts. After 18 days contact, the pH was between 8.4 and 8.8 for the samples. A dummy part (not brazed aluminium AA3003) had an initial pH of 6.3 and a final pH after 18 days of 7.3. The test shows that the pH of brazed samples becomes higher, i.e. the water becomes basic.
  • a dummy sample, a sample brazed with pure KAlF 4 and two samples brazed with a flux comprising about 30 mol- % K2AIF5 were tested by contacting them with water.
  • some milligrams of KF were added after one hour contact with water, to the other, one drop of HF was added after one hour of contact.
  • the pH of the water being in contact with the dummy was 6.4
  • the pH of the water in contact with the sample brazed with pure KAlF 4 was 8.0
  • the pH of the sample with added KF was 8.1
  • the pH of the water of the sample with added HF was 7.6.
  • Example 6.2.1 was repeated, but this time, 6 mg KF were added to the soaking water.
  • the pH of the solution was measured to be 9.3. 6.2.3.
  • An angle-on-coupon was brazed using standard KAlF 4 flux.
  • the formed assembly was contacted with water under the addition of 6 mg of K 3 AlF 6 . Once again, no turbidity or corrosion was observed, the pH was measured to be 7.2.
  • Example 7 Anticorrosive activity of calcium acetate AlO* 10 cm brazed section composed of tubes and fins brazed with
  • Nocolok ® (flux load 8 g/m 2 ) resembling that of a heat exchanger was immersed in a 2 M Ca-gluconate solution for 30 seconds. Excess adhering liquid was blown off with compressed air and the sample was dried at 90 0 C. It was then kept in 90 ml water for one week. Almost no turbidity developed during that time.

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Abstract

Selon l'invention, des pièces en aluminium, par exemple des échangeurs de chaleur, ayant une résistante améliorée à la corrosion provoquée par le contact avec l'eau pendant une période de temps prolongée, peuvent être obtenues par application d'un traitement thermique ou d'un flux qui procure, après brasage, une teneur élevée en K3AlF6. L'effet corrosif peut également être supprimé si au moins un agent anticorrosion sélectionné dans le groupe des sels contenant du calcium hydrosoluble, à l'exception du CaF2, et des sels contenant l'ion AlF4, AlF5 ou AlF6 et les hydrates de ceux-ci, est mis en contact avec l'eau de contact qui contient un ion fluorure lessivé.
PCT/EP2009/054564 2008-04-18 2009-04-16 Procédé anticorrosion pour pièces en aluminium brasées au fluoroaluminate WO2009127707A1 (fr)

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WO2011076667A1 (fr) 2009-12-21 2011-06-30 Solvay Fluor Gmbh Préparation de flux dotée d'une viscosité dynamique accrue contenant k2alf5 déshydraté, son procédé de fabrication et son procédé d'utilisation
DE102010002349A1 (de) 2010-02-25 2011-08-25 Behr GmbH & Co. KG, 70469 Zusätze für Heiz- und Kühlmittel
DE102011004765A1 (de) 2010-02-25 2011-08-25 Behr GmbH & Co. KG, 70469 Zusätze für silikathaltige Heiz- und Kühlmittel
WO2011110532A1 (fr) 2010-03-11 2011-09-15 Solvay Fluor Gmbh Flux de particules fines
CN104507317A (zh) * 2012-05-30 2015-04-08 拜尔农作物科学股份公司 包含生物防治剂和选自氨基酸或蛋白质生物合成抑制剂、atp产生抑制剂和细胞壁合成抑制剂的杀真菌剂的组合物
CN104507316A (zh) * 2012-05-30 2015-04-08 拜尔农作物科学股份公司 包含生物防治剂和杀真菌剂的组合物
US9056363B2 (en) 2008-11-25 2015-06-16 Solvay Fluor Gmbh Anticorrosive flux
CN104735987A (zh) * 2012-05-30 2015-06-24 拜尔农作物科学股份公司 包含生物防治剂和杀真菌剂的组合物
WO2015091610A1 (fr) * 2013-12-19 2015-06-25 Solvay Sa Flux de brasage d'alliages d'aluminium
WO2019081690A1 (fr) * 2017-10-27 2019-05-02 Solvay Sa Procédé de brasage amélioré et pièces revêtues de flux

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Cited By (16)

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Publication number Priority date Publication date Assignee Title
US9056363B2 (en) 2008-11-25 2015-06-16 Solvay Fluor Gmbh Anticorrosive flux
WO2011076667A1 (fr) 2009-12-21 2011-06-30 Solvay Fluor Gmbh Préparation de flux dotée d'une viscosité dynamique accrue contenant k2alf5 déshydraté, son procédé de fabrication et son procédé d'utilisation
DE102010002349A1 (de) 2010-02-25 2011-08-25 Behr GmbH & Co. KG, 70469 Zusätze für Heiz- und Kühlmittel
DE102011004765A1 (de) 2010-02-25 2011-08-25 Behr GmbH & Co. KG, 70469 Zusätze für silikathaltige Heiz- und Kühlmittel
WO2011104355A2 (fr) 2010-02-25 2011-09-01 Behr Gmbh & Co. Kg Adjuvants pour fluides caloporteurs de chauffe et de refroidissement
WO2011110532A1 (fr) 2010-03-11 2011-09-15 Solvay Fluor Gmbh Flux de particules fines
US8978962B2 (en) 2010-03-11 2015-03-17 Solvay Fluor Gmbh Fine particulate flux
CN104507317A (zh) * 2012-05-30 2015-04-08 拜尔农作物科学股份公司 包含生物防治剂和选自氨基酸或蛋白质生物合成抑制剂、atp产生抑制剂和细胞壁合成抑制剂的杀真菌剂的组合物
CN104507316A (zh) * 2012-05-30 2015-04-08 拜尔农作物科学股份公司 包含生物防治剂和杀真菌剂的组合物
CN104735987A (zh) * 2012-05-30 2015-06-24 拜尔农作物科学股份公司 包含生物防治剂和杀真菌剂的组合物
CN104507316B (zh) * 2012-05-30 2018-03-06 拜尔农作物科学股份公司 包含生物防治剂和杀真菌剂的组合物
CN104735987B (zh) * 2012-05-30 2018-12-07 拜尔农作物科学股份公司 包含生物防治剂和杀真菌剂的组合物
CN104507317B (zh) * 2012-05-30 2019-11-15 拜尔农作物科学股份公司 包含生物防治剂和杀真菌剂的组合物、及其用途、试剂盒
WO2015091610A1 (fr) * 2013-12-19 2015-06-25 Solvay Sa Flux de brasage d'alliages d'aluminium
JP2017507782A (ja) * 2013-12-19 2017-03-23 ソルヴェイ（ソシエテ アノニム） アルミニウム合金のロウ付け用のフラックス
WO2019081690A1 (fr) * 2017-10-27 2019-05-02 Solvay Sa Procédé de brasage amélioré et pièces revêtues de flux

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