EP0112826B1 - Revetements de conversion de phosphate de resistance alcaline et procede de fabrication - Google Patents

Revetements de conversion de phosphate de resistance alcaline et procede de fabrication Download PDF

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EP0112826B1
EP0112826B1 EP19820902566 EP82902566A EP0112826B1 EP 0112826 B1 EP0112826 B1 EP 0112826B1 EP 19820902566 EP19820902566 EP 19820902566 EP 82902566 A EP82902566 A EP 82902566A EP 0112826 B1 EP0112826 B1 EP 0112826B1
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Prior art keywords
divalent metal
cations
phosphate
coating
solution
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EP19820902566
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German (de)
English (en)
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EP0112826A4 (fr
EP0112826A1 (fr
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Ronald W. Zurilla
John Huff
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Henkel Corp
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Ford Werke GmbH
Ford France SA
Ford Motor Co Ltd
Ford Motor Co
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    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
    • C23C22/08—Orthophosphates
    • C23C22/12—Orthophosphates containing zinc cations
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
    • C23C22/36—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates
    • C23C22/362—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates containing also zinc cations

Definitions

  • Zinc phosphate conversion coatings are applied to metal surfaces to provide a base for paint and to inhibit the undercutting of paint in a corrosive environment. Initially, adherency was the main consideration in selecting a conversion coating. Any improvement in the resistance to corrosion came as a result of a tighter, more adherent coating system (see U.S. patents 3,144,360 and 3,520,737).
  • Ries Unrestricted practice of the Ries disclosure will not achieve an improvement in alkaline resistance because (a) Ries indiscriminantly uses too wide a range of nickel that blindly wanders through compositions that offer no hope of alkali resistance improvement, and (b) none of Ries' examples exhibit a quantum-jump in alkaline dissolution resistance and in corrosion resistance after painting, which Ries would have noted if he had discovered such.
  • the method by which these initial coatings were applied included spraying or immersion of the product to be coated with or in a bath solution, the solution containing layer-forming metal cations, phosphate ions, and oxidizing agents.
  • the layer-forming ions comprised zinc and, in some cases, calcium, iron or manganese, used singly or in combination.
  • the phosphate ions were typically introduced by use of phosphoric acid.
  • the oxidizing agents were commonly inorganic compounds, often consisting of a salt of the above-mentioned metals or of sodium or ammonium.
  • Nickel has been introduced to the phosphating solution; it is consistently visualized as an element useful as a layer-forming metal for phosphate coatings of a particularly homogeneous, continuous structure on steel, zinc and, occasionally, aluminum. It is clear from the prior art that nickel was not added for the purpose of enhancing corrosion resistance as a primary goal. Except for the Ries patent, nickel was added to the phosphate solution in relatively small amounts, consistently under 6% by weight of the coating. In cases where nickel was present along with zinc ions, it was added in an amount providing a nickel to zinc ratio of 1:1 or less (see U.S. Patents 4,053,328; 3,723,334; 4,110,128; 4,153,479; and 4,231,812).
  • Iron oxide is formed from the base metal by an anodic reaction in an electrolyte of water and ions of sodium chloride.
  • the dissolution of the iron to form ferrous ions (Fe 2+ ) is attended by the generation of electrons.
  • Accumulation of hydroxyl ions results in the generation of liquid of very high basicity having a pH as high as 12.5 or more.
  • Conventional zinc phosphate is soluble in this high basic liquid.
  • the main attempts by the prior art to reduce the corrosion sensitivity of phosphated metals have included (a) the introduction of inhibitors into the paint applied over the phosphate coatings to protect against corrosion; and (b) the use of an inhibitor rinse, such as chromic acid, which has been only partially successful in reducing the corrosion sensitivity; and (c) a tighter coating to prevent the lifting of the phosphate coatings during use. These approaches have not significantly reduced the alkaline sensitivity of phosphate films.
  • the invention relates to a method for coating corrodible metal substrates with a phosphate conversion coating, and a corrosion-resistant coated metal object obtained thereby.
  • the method employs an unusually critical narrow range of select layer-forming metal cations that form a unique mixed-metal phase phosphate that imparts great resistance to alkaline dissolution.
  • the coating is deposited by chemical reaction between the substrate and an acidic aqueous solution containing first and second layer-forming divalent metal cations and phosphate ions.
  • the subject matter of the invention therefore is a method for coating corrodible metal substrates with a phosphate conversion coating, said coating being deposited by exposing said substrate to an acidic, aqueous solution containing divalent metal cations and phosphate ions, all the divalent metal cations of the solution belonging to the group of first and second divalent metal cations, said method comprising:
  • the invention furtheron comprises a corrosion-resistant, coated metal object having a metal substrate and a phosphate conversion coating deposited thereon obtainable by exposing said substrate to an acidic, aqueous solution containing divalent metal cations, all the divalent metal cations of the solution belonging to the group of first and second divalent metal cations, wherein
  • the subject matter of the present invention furtheron is a corrosion-resistant, coated metal object having a metal substrate and a phosphate conversion coating deposited thereon comprising a mixed-metal phosphate in which the phosphate ions are combined with divalent metal cations, all of which belong to the group of first and second divalent metal cations, and wherein:
  • the first divalent metal cation is selected from the group consisting of nickel and cobalt (advantageously the cation is exclusively nickel) and is controlled to be 84-94 mole percent of the total divalent cations present in the solution.
  • Zinc is preferably present in the solution in an amount of at least 0.2 g/I as Zn +2 of said solution (advantageously 0.2-.6 g/I as Zn +2 or 0.79-2.38 g/I as Zn(H Z P0 4 ) 2 ).
  • the deposited coating will preferably be constituted substantially of a continuous nodular mixed-metal phosphate advantageously in the form of Zn 2 Ni(P0 4 ) 2 . 4H 2 0, but having some slight nickel variation within a narrow range.
  • the coating is deposited in a substantially uniform weight of less than 1.3 g /m 2 .
  • the substrate is preferably exposed to the phosphating solution for a sufficient time and at a sufficient temperature and pH (i.e., 30-120 seconds, 38-60°C, 2.5-3.5 pH) to chemically react and deposit a coating of phosphate on the substrate, after which excess solution is removed from the coated substrate that has not been deposited as a coating.
  • a sufficient temperature and pH i.e., 30-120 seconds, 38-60°C, 2.5-3.5 pH
  • the molar ratio range of the first and second metal cations is in the range of 5.2:1 to 16:1, and the first metal cation is present in said solution in an amount of at least 1.0 g/I of the solution.
  • the invention also comprehends a method for coating a phosphate film onto the surface of an alkali cleansed metal article by applying thereto the phosphate coating solution.
  • the improvement is the deposition of a phosphate film in an average coating weight of less than 1.3 g/m 2 i.e., 6.5-1.3 g/m 2 , having at least 15 mole percent (13.7% by weight) nickel, the film providing at least a doubling of the resistance to salt spray corrosion for any metal article coated with known phosphate films and painted.
  • the phosphate film results from the use of an acidic aqueous coating solution having an oxidizing agent content and a pH effective to chemically react with the article and a solute content consisting essentially of: (a) divalent layer-forming metal cations consisting of 84-94 mole percent nickel of the divalent metal cations and zinc in an amount of 0.2-0.6 g/I of the solution as Zn +2 ; and (b) phosphate ions in an amount at least sufficient to form dihydrogen phosphate with said metal cations.
  • the article is comprised of a metal selected from the group comprising iron, carbon and low alloy steel, aluminum and zinc. This process is particularly advantageously when employed on metal articles which carry a total surface carbon content greater than 0.4 mg/ft 2 .
  • the phosphating solution preferably possesses a total acid content of 10-40 points, a free acid content of 0.5-2.0 points, and a total acid/free acid ratio of 10-50.
  • the solution preferably contains a fluoride selected from the group consisting of a simple fluoride, fluoroborate, fluorosilicate, or other complex fluoride.
  • the phosphate solution be maintained at a pH of 2.5 ⁇ 3.5 and contains nitrite or other oxidizing agent in sufficient amount.
  • the temperature is maintained at 100-150°F (38 ⁇ 65°C) during the phosphating contact.
  • the exposure of the metal article to such solution should be preferably for a time of 30-120 seconds. It is desirable that the nitrite, used as an accelerator, be used in an amount of 0.5-2.5 points or 0.03-0.14 g/i of solution as NaN0 2 .
  • a concentrated phosphate solution is employed to replenish the phosphate bath as it is used throughout a series of article coatings.
  • the bath will become enriched with nickel relative to zinc, since more zinc than nickel is contained in the phosphate coating.
  • the replenishment solution or concentrate is preferably formulated to consist essentially of about 18 mole percent nickel cations and 82 mole percent zinc cations (16.5 nickel-83.5 zinc weight percent).
  • a portion of the nickel in the principal coating solution may be displaced by cobalt.
  • the product resulting from the practice of the above process is particularly characterized by a phosphate film in which the predominant structure is a mixed-metal phase phosphate where one of the metals is zinc and the other metal is nickel or cobalt.
  • the film preferably has a nickel content of at least 15 mole percent and the mixed-metal phosphate is nickel/zinc phosphate in a continuous nodular crystalline structure preferably of the approximate form of Zn 2 Ni(P0 4 ) 2 , wherein the nickel is about 15% of the molecular structure of such crystalline phase.
  • the phosphate coating provides more resistance to corrosion and will double the salt spray life of any painted and phosphated metal article at any specific phosphate solution chemistry by use of the prescribed high nickel content in the bath solution and ultimate nickel/zinc phosphate film.
  • Table I is a tabulation setting forth for each panel used in Figures 4, 9 and 14: (a) the bath composition used, including the amount of zinc and nickel by mole percent of the combined Ni and Zn, weight percent of nickel or zinc as percent of the combined nickel and zinc, weight in grams of each solute element per liter, and weight percent of each solute element of the total bath solution; (b) the coating composition, including mole percent nickel and zinc of the total Ni and Zn, weight percent of nickel and zinc of the total nickel and zinc, and weight percent in the coating of principal ingredients.
  • Table II is a tabulation setting forth the physical characteristics of the coatings for the panels listed in Table I.
  • Corrosion in an aqueous electrolyte is an electrochemical process involving oxidation and reduction reactions.
  • the oxidation reaction is the anodic dissolution of steel or other metal substrate where ions leave the metal to form corrosion products.
  • the excess electrons left in the metal by the oxidation reaction are consumed in the cathodic reduction reaction.
  • a principal cathodic reaction is the reduction of dissolved oxygen to form hydroxide ions.
  • Another cathodic reaction which may occur in some cases, is the reduction of hydrogen ions. Both reduction reactions produce an increase in the electrolyte pH at the cathodic sites.
  • the anodic and cathodic reactions can occur at essentially similar atom sites. However, the reaction sites may become widely separated when differential oxygen or electrolyte concentration gradients are established. After a certain amount of rust is formed at the anodic sites, the cathodic reduction of oxygen for the most part is shifted to the periphery of the rust deposit or scratch, that is, to the zinc-phosphate- coating/steel interface. The anodic oxidation of iron is confined to the rust covered areas. A differential oxygen concentration cell is established due to the restricted transport of oxygen through the rust scale and the relatively easy accessibility of the adjacent rust-free steel surfaces to the atmospheric oxygen.
  • the important consequence of the differential oxygen concentration cell is the generation of a highly alkaline electrolyte at the phosphate/steel interface.
  • the electrolyte pH can rise to above 12 in a sodium chloride environment, a condition prone to produce undercutting of the primer coating.
  • the undercutting by the alkali sodium hydroxide is due principally to the dissolution of some of the zinc phosphate coating (and to a lesser extent the saponification of the reactive ester groups present in some primer resins).
  • the degree of undercutting a primer coating undergoes in a corrosive environment is dependent on: the nature of imperfections in the paint coating (such as a scratch) the chemistry of the primer and the inhibitor used therein, the amount of contaminants present on the surface of the substrate prior to coating, and the effectiveness of the phosphate coating as a barrier to the lateral spread of the corrosion.
  • This invention has made the phosphate coating considerably more effective in spite of the first three factors.
  • the research supporting this invention shows that a significant improvement in alkaline dissolution can be obtained with zinc phosphate coatings containing at least 15 mole percent nickel of the Ni and Zn content, and a threshold level of zinc of at least 25% by weight of the phosphate film or coating.
  • the improvement is at least a doubling of the salt spray life after painting when compared to coatings without such unique nickel/zinc content.
  • a phosphate film is deposited onto the surface of an alkali-cleansed metal article or substrate by exposing the article or substrate to an acidic aqueous phosphate solution for a sufficient time and at a sufficient temperature and pH to chemically react and deposit such film.
  • the solution contains first and second layer-forming divalent metal cations and phosphate ions, the first divalent metal cations being selected from the group consisting of nickel and cobalt, while the second divalent metal cation is zinc.
  • the amount of first and second divalent metal cations is controlled in critically narrow ranges to provide a first divalent metal cation content in the resulting film of at least 15 mole percent of the total divalent metal cations.
  • the process herein is further preferably characterized by the deposition of a phosphate film in an average coating weight of less than 1.3 g/m 2 having at least 6% by weight nickel of the total coating that provides at least a doubling of the resistance to salt spray corrosion after painting.
  • the phosphate film results from the use of an acidic aqueous coating solution having an oxidizing agent and a solution pH effective to chemically react with the article or substrate.
  • the solute content of the solution preferably consists essentially of (a) divalent layer-forming metal cations consisting of 84-94 mole percent nickel of the total metal cations and zinc in an amount of 0.2-0.6 g/1 of said solution as Zn +2; and (b) phosphate ions in an amount at least sufficient to form dihydrogen phosphate with said metal cations.
  • a portion of the nickel content may be substituted by cobalt.
  • the metal article is cleansed by use of an alkaline cleaner maintained at a temperature of 38-60°C with a concentration of 2-10 points.
  • the article is subjected to the alkaline cleaner for a period of about 30-120 seconds and then rinsed with water at a temperature of 38-60°C for a period of 30-120 seconds.
  • the alkaline-cleansed metal substrate is then sprayed or immersed in a phosphate bath solution maintained at a temperature of about 38 ⁇ 60°C with a composition modified as specified above.
  • the solution has a total acid content of 10-40 points, a free acid content of 0.5-2.0 points, and a total acid/free acid ratio of 10-50.
  • the pH is controlled to 2.5-3.5 and nitrite is present in the bath in an amount preferably of 0.5-2.5 points.
  • the exposure to the phosphate bath is maintained for about 30-120 seconds, which controls the coating weight to a weight of less than 1.3 g/m 2 .
  • excess solution is removed from the article or substrate by a rinsing sequence consisting of a water rinse at ambient to 38°C for 30-120 seconds, an inhibitor rinse which contains a chromate or other dissolved corrosion inhibitor at ambient to 49°C for 30 ⁇ 60 seconds, and a deionized water rinse at ambient temperature for 15-30 seconds.
  • the phosphating solution must contain nickel and/or cobalt cations which constitute at least 84 mole percent of combined metal cations (82.5% by weight) in the solution. However, it is important that the zinc cation of the phosphating solution be at least 0.2 g/I as Zn +2 or 0.79 g/I as Zn(H 2 PO 4 ) 2 .
  • the molar ratio of Ni/Zn is in the range of 5.2:1 to 16:1.
  • the nickel/zinc cation content there must also be at least 0.2 g/I as Zn +2 in solution (preferably 0.2-0.6 g/l or 0.79-2.38 g/I as Zn(H,P0 4 ) 2 ).
  • the first divalent metal cation content therefore must be at least 1.0 g/I of the bath solution (84 mole percent of the first divalent metal/zinc total).
  • the coatings produced from such phosphate solution become very thin and nonuniform (see Figure 15), and the benefit of improved corrosion performance is decreased proportionately. It also is very difficult to achieve the desired ratio of Ni/Zn in the bath without restricting zinc content to a level which is too low, resulting in a failure to form a proper amount of the Zn 2 Ni(PO 4 ) 2 ⁇ 4H 2 0 nodular phase.
  • the nickel content of the phosphate solution is below 84 mole percent, the phosphate coating fails to produce a sufficient amount of the preferred mixed-phase nodular phosphate structure so necessary to obtain the dramatic increase in salt spray corrosion resistance. These coatings do not have the desired alkaline resistance.
  • the zinc concentration falls below 0.2 g/I as Zn +2 , the resultant coating will be deficient because a high proportion of iron oxide and iron phosphates will form, lacking the desired resistance to alkaline dissolution.
  • the initial phosphate solution may be conveniently prepared by making up a nickel and zinc phosphate solution concentrate from preferably the oxide or carbonate and concentrated phosphoric acid.
  • the metal ion concentration in each of these separate solutions can be approximately 120-140 g/I, or, more specifically, 475-550 g/I Zn(H 2 P0 4 ) 2 , 520-600 g/l Ni(H 2 PO 4 ) 2 .
  • These metal phosphate concentrate solutions can be used to make up a fresh phosphate bath by using sufficient quantities of each of such concentrated solutions with water to render the desired bath concentrations as described previously.
  • the bath will become enriched with nickel during phosphating use, since more zinc than nickel is deposited in formation of the phosphate film. It is desirable to have a separate concentrate which is formulated for replenishment; the replenishment concentrate can contain approximately 18 mole percent nickel and 82 mole percent zinc of the dissolved nickel and zinc cations.
  • the substrate is preferably selected from the group consisting of iron, carbon or low alloy steel, aluminum and zinc.
  • the phosphate solution additionally contains 0.1-1.0 g/I sodium fluoride to enhance the formation of zinc phosphate coating and to prevent precipitation of the dissolved aluminum.
  • the resulting coated product is characterized by unusually good resistance to alkali dissolution (see Figure 1 comparing several test panels of the prior art and this invention exposed to a 12.5 pH NaOH solution) and by its excellent chemical bonding to the substrate.
  • the zinc/nickel phosphate conversion coating is the result of a chemical reaction with the substrate.
  • the structure of the coating of this invention has the morphology of nodules (see Figures 10-13).
  • the product of this invention is particularly characterized by a significantly improved salt spray performance showing little or no paint undercutting after 500 test hours abruptly occurring when the nickel content exceeds 15 mole percent (at about 13.7% by weight) in the coating (see Figure 3).
  • the amount of nickel in the coating at or above 13.7% by weight can easily be controlled by regulating the amount of nickel in the bath to exceed 84 mole percent (82.5 weight %) of the Ni/Zn in the bath (see Figure 2).
  • the coating has high corrosion resistance even with high surface carbon contamination.
  • a series of test panels for Comparative Examples 1-8 and Examples 1-5 were prepared by cutting sheet metal into panels having a size of 10.2x30.5 cm. The test panels were exposed to a phosphating solution of known chemistry (see Table I), rinsed and dried. A portion of selected panels was used for determination of coating weight, composition, morphology and structure of the phosphate coating. The remaining portion from these panels was painted with taupe primer paint (epoxy ester-melamine resin primer). These samples, after baking, were then scribed in an "X" pattern to bare metal and then subjected to an accelerated salt spray test, after which the degree of paint undercutting was observed and/or measured.
  • the salt spray test essentially involves exposing panels to a mist of a 5% sodium chloride solution in an enclosed chamber maintained at 35°C in accordance with the ASTM B117 standard test method.
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 11.3 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.8 points, resulting in a total acid to free acid ratio of 14.
  • the dissolved nickel constitutes 33.3 mole percent of the dissolved divalent cations, which is typical of compositions currently used commercially in spray applied phosphating systems.
  • the first type designated as Q steel
  • the second type of panel was cut from commercial auto body sheet, identified as F4. This steel was known to have surface carbon values in the range of 1.8 to 6.2 mg/m 2 , and to be subject to early salt spray failure in tests with spray paint primers applied over conventional zinc phosphate.
  • Panels of Q steel and F4 steel were spray cleaned for two minutes with a conventional alkaline cleaner having a strength of 4.7 points and a temperature of 60°C, spray rinsed for 30 seconds with 60°C tap water, and spray phosphated for two minutes with the above phosphate bath heated to 60°C.
  • the panels were spray rinsed for one minute with 20°C deionized water and dried in an oven at82°Cforfive minutes. None of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, gray appearance and a coating weight of 1.62 g/m 2.
  • Chemical analysis showed that the nickel content of the phosphate coatings was equal to 3.2% by weight of the total nickel and zinc content of the coating on both the Q and F4 steels. This is equivalent to 3.5 mole percent Ni.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer. After baking, the paint thickness was approximately 23 pm. Salt spray testing of the painted and scribed panels was carried out in accordance with the ASTM B117 standard. The specification for the epoxy ester-melamine resin based primer employed in these tests stipulates that 3 mm undercutting of the paint from the scribe line on the tested panels, as determined by taping the entire surface of the panel, constitutes failure.
  • Salt spray testing of the test panels designated Q was discontinued after 480 hours with essentially zero undercutting from the scribe line (see Figure 4a).
  • the test panels designated F4 on the other hand, failed within 96 hours of salt spray testing (see Figure 4b).
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 14.7 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.9 points, resulting in a total acid to free acid ratio of 16.
  • the dissolved nickel constitutes 57.9 mole percent of the dissolved divalent cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned and rinsed as detailed in Comparative Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphate bath heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, gray appearance and a coating weight of 1.71 g/m 2 .
  • Chemical analysis showed that the nickel content of the phosphate coatings was equal to 5.6% by weight of the total nickel and zinc content of the coating, on both the Q and F4 steels. This is equivalent to 6.2 mole percent Ni.
  • a scanning electron microscope photograph of the phosphate coating, taken at 1500x, is shown in Figure 6. This structure remains similar to the morphology of spray applied commercial zinc phosphate coatings.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer. As in Comparative Example 1, the paint film thickness, after baking, was approximately 23 pm. Salt spray testing was again carried out exactly as detailed in Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • Salt spray testing of the test panels designated Q was discontinued after 480 hours, with essentially zero undercutting from the scribe line (see Figure 4C).
  • the test panel designated F4 on the other hand, failed within 96 hours of salt spray testing (see Figure 4d).
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 14.1 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.9 points, resulting in a total acid to free acid ratio of 16.
  • the dissolved nickel constitutes 67.7 mole percent of the dissolved divalent metal cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned and rinsed as detailed in Comparative Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphate bath, heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, gray appearance and a coating weight of 1.35 g/m 2.
  • Chemical analysis showed that the nickel content of the phosphate coatings was equal to 7.3% by weight of the total nickel and zinc content of the coating, on both the Q and F4 steels. This is equivalent to 8.1 mole percent Ni.
  • a scanning electron microscope photograph of the phosphate coating, taken at 1500x, is shown in Figure 7. This structure again remains similar to the morphology of spray applied commercial zinc phosphate coatings.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer. As in Comparative Example 1, the paint film thickness, after baking, was approximately 23 um. Salt spray testing was again carried out exactly as detailed in Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • Salt spray testing of the test panels designated Q was discontinued after 480 hours, with essentially zero undercutting from the scribe line (see Figure 4e).
  • the test panel designated F4 on the other hand, failed within 72 hours of salt spray testing (see Figure 4f).
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 14.2 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.9 points, resulting in a total acid to free acid ratio of 16.
  • the dissolved nickel constitutes 77.4 mole percent of the dissolved divalent cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned and rinsed as detailed in Comparative Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphated bath heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, gray appearance and a coating weight of 1.14 g/m 2.
  • Chemical analysis showed that the nickel content of the phosphate coatings was equal to 11.0% by weight of the total nickel and zinc content of the coating, on both the Q and F4 steels. This is equivalent to 12.1 mole percent Ni.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer. As in Comparative Example 1, the paint film thickness, after baking, was approximately 23 um. Salt spray testing was again carried out exactly as detailed in Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • Salt spray testing of the test panels designated Q was discontinued after 480 hours, with essentially zero undercutting from the scribe line (see Figure 4g).
  • the test panels designated F4 on the other hand, failed within 72 hours of salt spray testing (see Figure 4h).
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 14.2 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.8 points, resulting in a total acid to free acid ratio of 18.
  • the dissolved nickel constitutes 81.5 mole percent of the dissolved divalent cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned as detailed in Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphate bath, heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, gray appearance and a coating weight of 1.17 g/m 2 .
  • Chemical analysis showed that the nickel content of the phosphate coatings was equal to 11.8% by weight of the total nickel and zinc content of the coating, on both the Q and F4 steels. This is equivalent to 13.0 mole percent Ni.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer.
  • the paint thickness, after baking, was approximately 23 p m.
  • Salt spray testing was again carried out exactly as detailed in Comparative Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • Salt spray testing of the test panels designated Q was discontinued after 480 hours, with essentially zero undercutting from the scribe line (see Figure 9a).
  • the test panels designated F4 on the other hand, failed within 120 hours of salt spray testing (see Figure 9b).
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 14.3 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.7 points, resulting in a total acid to free acid ratio of 20.
  • the dissolved nickel constitutes 82.6 mole percent of the dissolved divalent cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned and rinsed as detailed in Comparative Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphate bath, heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, gray appearance and a coating weight of 1.09 g/m 2 .
  • Chemical analysis showed that the nickel content of the phosphate coatings was equal to 12.3% by weight of the total nickel and zinc content of the coating, on both the Q and F4 steels. This is equivalent to 13.6 mole percent Ni.
  • a scanning electron microscope photograph of the phosphate coating, taken at 1500x, is shown in Figure 8. The morphology is similar to that of commercial zinc phosphate, except for a finer-sized crystal structure.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer. As in Comparative Example 1, the paint film thickness, after baking, was approximately 23 pm. Salt spray testing was again carried out exactly as detailed in Comparative Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • Salt spray testing of the test panels designated Q was discontinued after 480 hours, with essentially zero undercutting from the scribe line (see Figure 9c).
  • the test panels designated F4 on the other hand, failed within 144 hours of salt spray testing (see Figure 9d).
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 15.6 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.6 points, resulting in a total acid to free acid ratio of 26.
  • the dissolved nickel constitutes 82.6 mole percent of the dissolved divalent cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned and rinsed as detailed in Comparative Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphate bath, heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, gray appearance and a coating weight of 1.45 g/m 2 (135 mg/ft 2 ). Chemical analysis showed that the nickel content of the phosphate coatings was equal to 13.1 % by weight of the total nickel and zinc content of the coating on both the Q and F4 steels, this is equivalent to 14.4 mole percent Ni.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer.
  • the paint film thickness, after baking, was approximately 23 urn.
  • Salt spray testing was again carried out exactly as detailed in Comparative Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • Salt spray testing of the test panels designated Q was discontinued after 480 hours, with essentially zero undercutting from the scribe line (see Figure 9e).
  • the test panel designated F4 on the other hand, failed within 456 hours of salt spray testing (see Figure 9f).
  • Comparative Example 7 The improvement in salt spray performance noted for Comparative Example 7, compared with Comparative Example 6, is an illustration of the importance of the nickel content in the phosphate coating. Note that the dissolved nickel content of the baths described in Comparative Examples 6 and 7 are both 82.6 mole percent. However, the higher total-acid to free-acid ratio in Comparative Example 7 versus Comparative Example 6 resulted in a somewhat higher nickel content in the phosphating coating which, in turn, resulted in improved corrosion performance.
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 14.1 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.8 points, resulting in a total acid to free acid ratio of 18.
  • the dissolved nickel constitutes 85.0 mole percent of the dissolved divalent cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned and rinsed as detailed in Comparative Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphate bath, heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, bluish-gray appearance and a coating weight of 0.90 g/ M 2.
  • Chemical analysis showed that the nickel content of the phosphate coatings was equal to 14.6% by weight of the total nickel and zinc content of the coating, on both the Q and F4 steels. This is equivalent to 16.0 mole percent Ni.
  • a scanning electron microscope photograph of the phosphate coating, taken at 1500x, is shown in Figure 10. This represents an abrupt change in morphology from that shown for the previous examples and suggests an overall change in structure.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer.
  • the paint film thickness, after baking, was approximately 23 urn.
  • Salt spray testing was again carried out exactly as detailed in Comparative Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • Salt spray testing of the test panels designated Q was discontinued after 480 hours, with essentially zero undercutting from the scribe line (see Figure 9g).
  • Salt spray testing of the test panels designated F4 was also discontinued after 480 hours, with essentially zero undercutting from the scribe line (see Figure 9h).
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 13.5 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.9 points, resulting in a total acid to free acid ratio of 15.
  • the dissolved nickel constitutes 90.5 mole percent of the dissolved divalent cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned and rinsed as detailed in Comparative Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphate bath, heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, bluish-gray appearance and a coating weight of 0.86 g/m 2 .
  • Chemical analysis showed that the nickel content of the phosphate coatings was equal to 15.5% by weight of the total nickel and zinc content of the coating, on both the Q and F4 steels. This is equivalent to 17.0 mole percent Ni.
  • a scanning electron microscope photograph of the phosphate coating, taken at 1500x, is shown in Figure 11. This structure confirms the abrupt change in morphology shown in Figure 10, which suggested an overall change in structure.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer.
  • the paint film thickness, after baking, was approximately 23 p m.
  • Salt spray testing was again carried out exactly as detailed in Comparative Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 24.0 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.8 points, resulting in a total acid to free acid ratio of 30.
  • the dissolved nickel constitutes 91.4 mole percent of the dissolved divalent cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned and rinsed as detailed in Comparative Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphate bath, heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, bluish-gray appearance and a coating weight of 0.62 g/m 2.
  • Chemical analysis showed that the nickel content of the phosphate coatings was equal to 21.0% by weight of the total nickel and zinc content of the coating, on both the Q and F4 steels. This is equivalent to 22.8 mole percent Ni.
  • a scanning electron microscope photograph of the phosphate coating, taken at 1500x, is shown in Figure 12. This structure is similar to that shown in Figures 10 and 11.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer.
  • the paint film thickness, after baking, was approximately 23 urn.
  • Salt spray testing was again carried out exactly as detailed in Comparative Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 24.4 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.5 points, resulting in a total acid to free acid ratio of 49.
  • the dissolved. nickel constitutes 92.3 mole percent of the dissolved divalent cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned and rinsed as detailed in Comparative Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphate bath, heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a uniform, bluish-gray appearance and a coating weight of 0.52 g/m 2 .
  • Chemical analysis showed that the nickel content of the phosphate coatings was equal to 24.8% by weight of the total nickel and zinc content of the coating, on both the Q and F4 steels. This is equivalent to 26.9 mole percent Ni.
  • a scanning electron microscope photograph of the phosphate coating, taken at 1500x, is shown in Figure 13. This structure is similar to that shown in Figures 10, 11 and 12.
  • the phosphate coated Q and F4 steel panels were spray painted with an epoxy ester-melamine resin based primer.
  • the paint film thickness, after baking, was approximately 23 urn.
  • Salt spray testing was again carried out exactly as detailed in Comparative Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 14.8 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.8 points, resulting in a total acid to free acid ratio of 18.
  • the dissolved nickel constitutes 95.2 mole percent of the dissolved divalent cations.
  • Panels of the two steels designated Q and F4, described in Comparative Example 1 were spray cleaned and rinsed as detailed in Comparative Example 1. After the rinsing step, they were spray phosphated for two minutes with the above phosphate bath, heated to 60°C. The panels were then spray rinsed with 20°C deionized water and dried in an oven at 82°C for five minutes. As in Comparative Example 1, none of the phosphated panels were post-treated with an inhibitor rinse.
  • the steel panels that were phosphate coated by this procedure had a very nonuniform, streaked and spotted appearance, and varied in color from light gray to black. Coating weight varied from 0.28 to 0.70 g/m 2 . Chemical analysis showed that the nickel content of the phosphate coatings was equal to 41.3% by weight of the total nickel and zinc content of the coating, on the Q steel panels. This is equivalent to 43.9 mole percent Ni. The coating also contained a high iron content, which is undesirable.
  • a scanning electron microscope photograph of the phosphate coating, taken at 1500x, is shown in Figure 15.
  • this structure resembles the structures observed for coatings with nickel contents in the range of 13-25% by weight, the nonuniform visual appearance, nonuniformity of coating weight, and high porosity, were judged unsatisfactory for commercial application; therefore no painted test panels were prepared for corrosion testing.
  • Comparative Examples 1 through 8 and Examples 1 through 4 show, collectively, that there is a very narrow, sharply demarcated range of nickel contents in nickel/zinc phosphate conversion coatings which will consistently confer outstanding salt spray corrosion resistance upon subsequently painted commercial steel sheet, such as auto body steel sheet, which may be contaminated with carbon.
  • This range of nickel contents which Comparative Examples 1 to 8 and Examples 1 to 4, collectively, have shown to be characterized by a phosphate coating having a microstructure distinctly different from the microstructure of ordinary commercial zinc phosphate coatings, is from 14 mole percent to 26 mole percent nickel, corresponding to about 83.5 to 93.0 mole percent dissolved nickel in the phosphating bath.
  • phosphated test panels of these substrates were corrosion tested in salt spray after the application of a commercial cathodic electrocoat primer as well as the spray primer referred to in said Examples and Comparative Examples. Again, consistently outstanding salt spray performance was observed only when the nickel content in the phosphating bath was in the range of about 84-94 mole percent of the dissolved divalent cations.
  • a phosphating bath solution was prepared having the following composition:
  • this bath had a total acid concentration of 18.1 points.
  • the bath acidity was then adjusted by the addition of NaOH to a free acid concentration of 0.7 points, resulting in a total acid to free acid ratio of 26.
  • the dissolved nickel constitutes 90.7 mole percent of the dissolved divalent cations.
  • the steel panels that were phosphate coated by this procedure had a uniform, bluish-gray appearance and a coating weight of 0.92 g/m 2. Grayish-black phosphate coatings with a weight of 1.67 g/m 2 were produced on the hot-dipped galvanized steel panels. Chemical analysis of the phosphate coating on the steels showed that the nickel content was equal to 16.2% by weight of the total nickel and zinc content of the coating. This is equivalent to 17.7 mole percent Ni.
  • the phosphate coated Q and F4 steel panels and the phosphate coated galvanized steel panels were spray painted with an epoxy ester-melamine resin based primer.
  • the paint film thickness, after baking, was approximately 23 pm. Salt spray testing was again carried out-exactly as detailed in Comparative Example 1, with 3 mm undercutting of the paint from the scribe line, again considered as failure.
  • FIG. 16 illustrates the improvement in 360 hour and 480 hour salt spray performance for galvanized steel with 17.7 mole percent nickel in the phosphate coating ( Figures 16a and 16b) vis-a-vis commercial zinc phosphate containing 3.5 mole percent nickel ( Figures 16c and 16d).
  • the high nickel phosphate shows a marked advantage in degree of salt spray undercutting of the paint as well as in the progression of undercutting with time.
  • Figure 17a-17f is the spectrum typical of commercial zinc phosphate, corresponding to Comparative Example 1. There are only gradual changes in this spectrum with increasing nickel content of the phosphating bath over the range of 33.3 mole percent, corresponding to Comparative Example 1, through 82.6 mole percent, corresponding to Comparative Example 6.

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Abstract

Procédé permettant d'augmenter la résistance à la dissolution alcaline d'un revêtement de conversion de phosphate sur un substrat métallique corrodable. Le substrat est exposé à une solution de phosphatation par giclage ou immersion pour effectuer une réaction chimique avec le substrat. La solution contient un pourcentage molaire compris entre 84 et 94 de cations métalliques d'un premier cation métallique bivalent formant une couche, lequel cation métallique possède un hydroxyde ayant une solubilité inférieure dans une solution alcaline à celle de l'hydroxyde de fer ou de zinc et est sélectionné de préférence dans le groupe comprenant le nickel, le cobalt, le magnésium et les lanthanides, et d'un second cation métallique formant une couche, sous la forme de zinc présent en une quantité de 0,2 à 0,6 g/l, tel Zn+2. La plage du rapport molaire entre le premier et le second cations métalliques est comprise entre 5,2:1 et 16:1, et le premier cation métallique est présent dans la solution en une quantité de 1,0 g/l au moins. Le revêtement appliqué possède un premier cation métallique bivalent présent en une quantité d'au moins 15 % en mol de la totalité des cations bivalents, et un second cation bivalent présent en une quantité d'au moins 25 % en poids du revêtement. Le revêtement possède de préférence un poids uniforme inférieur à 1,3 g/m2 (120 mg/ft 2).

Claims (22)

1. Procédé pour le revêtement de supports métalliques, susceptibles de corrosion, avec une couche de conversion de phosphate, ladite couche étant déposée par exposition dudit support à une solution aqueuse acide contenant des cations métalliques bivalents et des ions phosphate, tous les cations métalliques bivalents de la solution appartenant au groupe des premiers et seconds cations métalliques bivalents, ledit procédé comprenant:
(a) le choix desdits premiers cations métalliques bivalents parmi les cations cobalt et nickel;
(b) le choix de cations zinc en tant que lesdits seconds cations métalliques bivalents; et
(c) l'ajustement de la concentration desdits premiers et seconds cations métalliques bivalents dans ladite solution aqueuse, de manière que la concentration desdits premiers cations métalliques bivalents dans ladite solution, lors de l'application du revêtement, soit maintenue dans la plage de 84 à 94% en mole, par rapport à l'ensemble des cations métalliques bivalents dans ladite solution, et que la concentration desdits seconds cations métalliques bivalents dans ladite solution soit d'au moins 0,2 g/litre.
2. Procédé selon la revendication 1, caractérisé en ce que la concentration desdits premiers cations métalliques bivalents dans ladite solution est au moins 1,0 g/litre.
3. Procédé selon la revendication 1, caractérisé en ce que la concentration desdits seconds cations métalliques bivalents dans ladite solution est dans la plage de 0,2 à 0,6 g/litre.
4. Procédé selon la revendication 1, caractérisé en ce que la concentration desdits ions phosphate dans ladite solution est au moins suffisante pour former in dihydrogénophosphate avec lesdits cations métalliques.
5. Procédé selon la revendication 1, caractérisé en ce que lesdits cations métalliques bivalents sont des cations nickel.
6. Procédé selon la revendication 1, caractérisé en ce que lesdits cations métalliques bivalents sont des cations cobalt.
7. Procédé selon les revendications 1 à 6, caractérisé par le complément de la solution aqueuse acide avec un concentré de complément contenant les premiers cations métalliques bivalents et les seconds cations métalliques bivalents en fonction de et en un rapport inversement proportionnel à l'élimination desdits premiers cations métalliques bivalents et desdits seconds cations métalliques bivalents hors de ladite solution.
8. Procédé selon la revendication 7, caractérisé en ce que le rapport molaire des premiers cations métalliques bivalents aux seconds cations métalliques bivalents dans ledit concentré de complément est 18:82.
9. Procédé selon les revendications 1 à 8, caractérisé par le maintien de l'indice d'acidité totale de ladite solution aqueuse acide dans la plage de 10 à 40 points, de la teneur en acide libre de ladite solution aqueuse acide dans la plage de 0,5 à 2,0 points, et du rapport acidité totale/acide libre de ladite solution aqueuse acide dans la plage de 10 à 50.
10. Procédé selon les revendications 1 à 9, caractérisé par le maintien de la solution aqueuse acide à une température dans la gamme de 38 à 65°C, et le maintien du contact dudit support avec ladite solution pendant une durée allant de 30 à 120 secondes.
11. Procédé selon les revendications 1 à 10, caractérisé en ce que ledit support est choisi parmi le fer, l'acier au carbone ou faiblement allié, l'aluminium et le zinc.
12. Procédé selon les revendications 1 à 10, caractérisé en ce que ladite solution comprend en outre des ions fluorure.
13. Procédé selon les revendications 1 à 12, caractérisé en ce que lesdits ions fluorure sont introduits sous forme d'un fluorure simple, d'un fluoborate, d'un fluorosilicate ou d'un autre fluorure complexe, et sont présents dans ladite solution en une quantité dans la plage de 0,1 à 1,0 g/litre.
14. Procédé selon les revendications 1 à 10, caractérisé en ce que lesdits premiers cations métalliques bivalents sont des cations nickel et ledit revêtement contient essentiellement une structure nodulaire continue de type phosphate métallique mixte, sous la forme de
Figure imgb0021
15. Objet métallique revêtu, résistant à la corrosion, comportant un support métallique et une couche de conversion de phosphate déposée sur celui-ci, pouvant être obtenue par exposition dudit support à une solution aqueuse acide contenant des cations métalliques bivalents, tous les cations métalliques bivalents de la solution appartenant au groupe des premiers et seconds cations métalliques bivalents, dans lequel:
(a) on choisit les premiers cations métalliques bivalents parmi les cations cobalt et nickel;
(b) on choisit les cations zinc en tant que seconds cations métalliques bivalents;
(c) les ions phosphate sont présents en une quantité au moins suffisante pour former un dihydrogénophosphate avec lesdits cations métalliques bivalents; et
(d) on ajuste la concentration desdits premiers et seconds cations métalliques bivalents dans ladite solution aqueuse de manière à maintenir dans ladite solution, lors de l'application du revêtement, la concentration desdits premiers cations métalliques bivalents dans la plage de 84 à 94% en mole, par rapport à la somme des cations métalliques bivalents dans ladite solution, et la concentration desdits seconds cations métalliques bivalents est au moins 0,2 g/litre dans ladite solution.
16. Objet métallique revêtu selon la revendication 15, caractérisé en ce que le premier métal bivalent est le nickel.
17. Objet métallique revêtu selon la revendication 15, caractérisé en ce que ledit premier métal bivalent est le nickel et la teneur en nickel est d'au moins 15% en mole, par rapport à la teneur totale en premier métal bivalent et second métal bivalent dudit revêtement.
18. Objet métallique revêtu selon la revendication 15, caractérisé en ce que ledit revêtement contient essentiellement une structure nodulaire continue de type phosphate métallique mixte, sous la forme de
Figure imgb0022
19. Objet métallique revêtu selon la revendication 15, caractérisé en ce que ledit revêtement a un poids de couche essentiellement uniforme, inférieur à 1,3 g/m2.
20. Objet métallique revêtu selon la revendication 15, caractérisé en ce que ledit premier métal bivalent est le cobalt.
21. Objet métallique revêtu, résistant à la corrosion, comportant un support métallique et une couche de conversion de phosphate déposée sur celui-ci, comprenant un phosphate métallique mixte dans lequel les ions phosphate sont combinés avec des cations métalliques bivalents, qui appartiennent tous au groupe des premiers et seconds cations métalliques bivalents, et dans lequel:
(a) environ 15,0 à environ 43,0% en mole des premiers et seconds cations métalliques bivalents dans la couche déposée sont choisis parmi les cations nickel bivalents et les cations cobalt bivalents;
(b) ledit second cation métallique bivalent est le zinc; et
(c) environ 85,0 à environ 57,0% en mole de la somme des premiers et seconds cations métalliques bivalents dans la couche déposée sont des cations zinc.
EP19820902566 1982-07-12 1982-07-12 Revetements de conversion de phosphate de resistance alcaline et procede de fabrication Expired EP0112826B1 (fr)

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US5328526A (en) * 1992-04-03 1994-07-12 Nippon Paint Co., Ltd. Method for zinc-phosphating metal surface

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DK104684D0 (da) 1984-02-27
WO1984000386A1 (fr) 1984-02-02
EP0112826A4 (fr) 1984-11-07
BR8208086A (pt) 1984-07-17
JPS59501269A (ja) 1984-07-19
JPH0419307B2 (fr) 1992-03-30
EP0112826A1 (fr) 1984-07-11
DE3279307D1 (en) 1989-02-02
NO840917L (no) 1984-03-09
DK104684A (da) 1984-03-12
AU8826782A (en) 1984-02-08
AU569697B2 (en) 1988-02-18

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