Classifications

• • 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
  • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
• • 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
  • C23C24/00—Coating starting from inorganic powder
  • C23C24/02—Coating starting from inorganic powder by application of pressure only
  • C23C24/04—Impact or kinetic deposition of particles
  • C23C24/045—Impact or kinetic deposition of particles by trembling using impacting inert media

Definitions

• U.S. patent No. 3,531,315 to Golben (“ , 315 patent”) discloses performing a mechanical plating process in the presence of a strong acid.
• agitation of the plating metal, the impaction media, and the substrate generally was conducted in the presence of weak organic acids such as citric acid. This required that the contents of the plating barrel be rinsed free of any strong acids used to clean or copper the parts before starting the citric acid-based plating process.
• weak organic acids such as citric acid
• One form of mechanical plating produces a lighter weight, relatively thin coating of .1 to 1.0 mils thick.
• Another form of mechanical plating known as mechanical galvanizing, results in the application of a thicker (i.e. from about 1.0 to 5.3 mils) and heavier (i.e. from about .7 to 2.5 ounces per square foot) mechanically-applied metallic coating.
• a thicker i.e. from about 1.0 to 5.3 mils
• heavier i.e. from about .7 to 2.5 ounces per square foot
• the first is a flash promoter which coats the substrate with a thin adherent flash coating of a metal more noble than the plating metal prior to adding the plating metal to the system.
• the second continuing promoter is then incrementally added with some or all of the incremental additions of a finely divided mechanical plating metal, the layers of which are built up to effect mechanical galvanizing.
• mechanical plating processes are disclosed as having applicability to any number of malleable metals, metal mixtures, or alloys, certain metals such as aluminum are more difficult to plate in this manner than others.
• Aluminum has an oxide surface layer which not only is difficult to remove prior to use of aluminum powder in a mechanical plating process but which also reforms readily during the process.
• This oxide coating inhibits the plating efficiency of aluminum.
• mechanically plating metal mixtures containing aluminum powder it has been found that the aluminum deposits only in very small quantities compared to the other metal powders in the mixture. Similar problems have been encountered in mechanically plating titanium, magnesium, and mixtures containing these metal powders.
• U.S. Patent No. 3,415,672 to Levinstein et al. coats iron-nickel-cobalt superalloys in a pack-cementation process in which titanium and aluminum are codeposited onto the substrate surfaces from a vapor state (1750°F to 2150°F) in the presence of either sodium fluoride, potassium fluoride, or ammonium chloride.
• U.S. Patent No. 3,503,775 to Austin aluminum coatings are applied to ferrous metal substrates by electrostatic deposition, rolling, and heating.
• U.S. Patent No. 3,577,268 to Whitfield et al. coats iron-nickel-cobalt superalloys with an aluminum-magnesium alloy by cementation, dipping, or binder-slurrying procedures.
• German Offenlegungschrift 3,011,662 to Tolkmit describes a mechanical plating process in which the oxide problems with aluminum are said to be obviated by mechanically plating in a liquid containing aluminum, a hydrazine derivative, a polymerization product of propylene oxide and ethylene oxide, and a corrosiong inhibitor.
• the hydrazine apparently releases hydrogen which combines with oxygen residues in the liquid.
• the activity of aluminum powder is to be maintained by the polymerization product, and, if necessary, further additions of alkali fluorides or fluorosilicates.
• the present invention relates to a process for mechanically plating a metal substrate " predominately with an oxidation-prone metal (i.e. a metal which either normally has an oxide surface coating or is prone to development of an oxide coating) such as aluminum.
• an oxidation-prone metal i.e. a metal which either normally has an oxide surface coating or is prone to development of an oxide coating
• This process achieves not only a high plating efficiency but also yields strongly adherent coatings with improved resistance to corrosive environments.
• These improvements are achieved by mechanically plating with different metals in particulate form applied in a variety of sequences to coat the metal substrate with layers of individual metals and/or layers of a plurality of dispersed metals.
• These metals to be 5 plated on the metal substrate include an oxidation-prone metal, a protective metal, and an immersion metal.
• the oxidation-prone metal is normally (i.e. in its typical state) a finely-divided powder for use in a mechanical plating process which has an oxide layer on 10 its surface and is prone to reformation of an oxide surface layer even if any pre-existing oxide layer is removed.
• the immersion metal coats the oxidation-prone metal and the substrate during formation of a mechanically 15. plated coating on the metal substrate and minimizes formation of an oxide layer on the oxidation-prone metal during the plating process.
• the protective metal prevents oxidation of ' the plated metal substrate when the substrate is exposed to 20" the environment. Although the protective metal need not be utilized, such utilization is preferred due to its corrosion inhibiting effect.
• the etching agent in the aqueous admixture is effective to remove from the finely-divided 2 5 oxidation-prone metal any surface oxide layer.
• the finely-divided, oxidation-prone metal can be pretreated with the etching agent and the immersion metal apart from the mechanical plating process, and this 3 . 0 pretreated, oxidation-prone metal can then be employed in the mechanical plating process without utilizing an etching agent.
• the coating resulting from such mechanical plating comprises the oxidation-prone metal in a predominate amount, for example, as high as 90% by weight of the coating, with the remainder comprised of the immersion metal(s), any minor impurities, and, optionally, the protective metal.
• the process of the present invention is generally similar to prior art mechanical plating processes with respect to operating mode and parameters, the impaction media, the surfactants, the dispersant additives, and the corrosion inhibiting agents.
• the apparatus in which the plating process is carried out can be any of the known mechanical plating barrels or mills.
• a substrate to be plated is placed in a rotatable plating barrel containing a glass bead impaction media.
• Water and a strong acid surface conditioner such as sulfuri ⁇ acid are also added to the barrel and then dispersed by rotation of the plating barrel.
• the process according to the '315 patent can optionally include pre ⁇ leaning and rinsing prior to the addition of water and strong acid conditioner.
• precleaning can be effected in the plating barrel or in some other tank by either degreasing with an alkaline cleaner, descaling with an acid cleaner, or both degreasing and descaling.
• the substrate After precleaning, the substrate is rinsed.
• some oxide scale forms on the substrate between rinsing and the addition of water and strong acid surface conditioner, the sulfuric acid surface conditioner will remove such scale during its dispersion in the rotating barrel.
• a coppering agent e.g. copper sulfate pentahydrate
• a coppering agent e.g. copper sulfate pentahydrate
• a promoter chemical is then added to the plating barrel to provide a proper environment for mechanical plating.
• the promoter chemical may also help clean the subsequently-added plating metal powder and control the size of plating metal agglomerates.
• Suitable promoter chemicals contain a strong acid or acid engendering salt and a salt of a metal which is more noble than the subsequently-added plating and/or a corrosion inhibitor.
• the soluble salts of a metal more noble than the plating metal include cadmium, lead, and preferrably tin (e.g. stannous chloride, stannous sulfate) .
• the strong acid or acid engendering salt can be, for example, sulfuric acid, potassium or ammonium bisulfate, sulfamic acid, or sodium bisulfate.
• the dispersant and the corrosion inhibitor can be any of those disclosed in columns 3-4 of the '315 patent.
• the promoter contains per 100 square feet of plating surface up to 400 grams of the strong acid or acid engendering salt and from about 10 to about 80 grams of the soluble salts of a metal which is more noble than the plating metal.
• effective amounts of dispersant and/or corrosion inhibitor can be added as needed for their intended purposes.
• plating metal powder is added.
• the addition of the plating metal powder displaces part or all of the metal of the promoter from the liquid in the plating barrel onto the plating metal and substrate as a flash coating.
• the rotation of the barrel then causes the glass bead impaction media to strike the substrate such that the plating metal powder is pounded into adherence with the substrate.
• the promoter system disclosed by the '431 patent may be used. As noted supra. this system utilizes two promoters — i.e. a flash promoter and a continuing promoter.
• the flash promoter contains the same ingredients in the same amounts as are used with the promoters described above.
• the continuing promoter includes per pound of plating metal about 20 to about 150 grams of a strong acid or an acid engendering salt, from about 1 to about 20 grams of soluble salt of a metal more noble than the plating metal, and optionally, an effective amount of a dispersant capable of dispersing the plating metal and/or an effective amount of an inhibitor capable of inibiting corrosion of the substrate and the plating metal.
• the flash promoter is added to the rotating barrel after coppering is completed and before the addition of plating metal powder.
• the continuing promoter is added with each incremental addition of plating metal powder added to the rotating barrel.
• the dual promoter system disclosed in the '431 patent is particularly useful when there is an insufficient amount of inhibitor or dispersant in the barrel prior to completion of mechanical plating. When such deficiencies occur, as can be determined by one of ordinary skill in the art, the continuing promoter can be added. Such additions of continuing promoter may or may not be needed for each addition of particulate plating metal depending on the degree of corrosion and dispersibility in the plating barrel.
• the oxidation-prone metal, the immersion metal, and, optionally, the protective metal are all applied to the surface of the metal substrate during mechanical plating and, therefore, function generally as plating metals.
• the oxidation-prone metal normally has an oxide layer on its surface which is likely to reform even after descaling. Such metals are more likely to have oxide layers on their surface than the protective metal.
• these oxidation-prone metals include aluminum, titanium, magnesium, and mixtures thereof with the preferred oxidation-prone metal being aluminum.
• the etching agent is any compound or mixture of compounds effective to remove an oxide surface coating from the finely-divided oxidation-prone metal used in the process.
• Particularly effective in this regard are fluoride compounds such as alkali metal fluorides, ammoniated fluorides, intermetallic fluoride compounds such as K 2 ZrF g , and mixtures thereof.
• the etching agent preferably will have an instability constant smaller than the fluorides of the immersion metal but larger than the fluorides of the oxidation-prone metal to be etched.
• the fluoride is included as an ingredient in the plating liquid (e.g.
• the concentration of fluoride is generally in the range of from about 1% to about 30% based upon the weight of the oxidation-prone metal present.
• any suitable concentration of etching agent may be employed.
• the immersion metals of the present invention are those metals which coat on or otherwise associate with the finely-divided oxidation-prone metal to Minimize formation of an oxide coating during the mechanical plating process.
• the coating of the immersion metal(s) onto the oxidation-prone metal may be effected as part of the mechanical plating process or may be conducted separate from and prior to the actual plating process.
• the immersion metal include tin, copper, nickel, cadmium, zinc, lead, and mixtures thereof. These metals are provided in any non-metallic, soluble form such as oxides, salts, sulfates, or the like (e.g. SnO, CuS0 4 , and NiS0 ) .
• the immersion metal is reduced at the surface of the oxidation-prone metal to its metallic state (i.e. where its oxidation number is zero) and then mechanically applied to the substrate surface.
• concentration of the immersion metal utilized in the plating liquid or in a pretreatment step will be such that the mechanically-plated ⁇ coating contains at least about 50% by weight of the oxidation-prone metal, with the remainder comprised of the immersion metal (s) and minor impurities (e.g. iron) which are sometimes present. More preferably, the mechanically plated coating will contain at least 65% and preferably at least about 80% of the oxidation-prone metal with the concentration of the immersion metal(s) being adjusted to achieve such results.
• the metal substrate is cleaned in accordance with known processes and, if desired, provided with a copper flash in the apparatus in which mechanical plating is to be effected.
• Finely-divided oxidation-prone metal pretreated in a separate operation with an etching agent to remove oxide surface layers can be further separately pretreated in the presence of one or more immersion metals to protect the oxidation-prone metal against further oxidation and to provide enetually a merchanically plated deposit having the percentage of the oxidation-prone metal and the im mersion metal(s).
• the so-treated oxidation-prone metal powder is then added to the mechanical plating apparatus containing the metal substrate, impaction media, and any other additives (e.g.
• the oxidation-prone metal powder optionally pretreated with etching agent is added to the apparatus without prior treatment with immersion metal(s).
• the immersion metal and more of the etching agent either may be predissolved in the plating liquid prior to addition of the oxidation-porone metal or may be added at the same time as the oxidation-prone metal or may be both predissolved and added simultaneously with the oxidation-prone metal.
• a protective metal in its metallic form is also utilized, as discussed previously, to prevent oxidation of the plated metal substrate during exposure to the environment.
• Suitable protective metals are more anodic on the galvanic series than iron. Examples of 1 such protective metals include zinc, cadmium, and mixtures thereof.
• the weight ratio of protective metal to oxidation-prone metal, particularly when using zinc and aluminum, respectively, is 1:99 to 99:1, preferably 1:4 to 4:1.
• the oxidation-prone metal, the protective metal, the immersion metal, and the etching agent can be used in any of a variety of sequences, wherein the sequence of adding the oxidation-prone metal and the protective metal determines the order in which these metals coat the substrate — i.e. the metal first added to the plating liquid forms the first coating layer on the substrate, while the metal added next forms the second coating layer on the substrate, and so on. It is preferred that the etching agent and the immersion metal be added to the plating liquid in the plating barrel rather than being used to pretreat the oxidation-prone metal at some other location.
• the etching agent can be added at anytime during the mechanical plating process (i.e. before, during, or after addition of the oxidation-prone metal), regardless of the plating sequence. However, the etching agent is preferrably added to the plating liquid and dispersed therein prior to addition of the oxidation-prone metal.
• the oxidation-prone metal can be added to the plating liquid either together with or after addition of the protective metal. If the oxidation-prone metal and the protective metal are added to the plating liquid simultaneously, a coating layer containing dispersed oxidation-prone metal and protective metal is formed on the metal substrate after the plating liquid is agitated. If the oxidation-prone metal is added to the plating liquid after the protective metal with plating liquid agitation steps being carried out after each addition, the coating on the metal substrate is a layer of oxidation-prone metal around a layer of protective metal. Coating the substrate with a layer of oxidation-prone metal over a layer of protective metal is especially preferred.
• this metal coats particles of the oxidation-prone metal dispersed in the plating liquid so that plating can occur.
• immersion metal particles can also be plated over any already-plated layer containing aluminum to protect the aluminum. Although some of the particles used as immersion metal could plate by themselves on the substrate if added prior to the oxidation-prone metal along with a reducing agent for said immersion metal, this plated metal would not function as an immersion metal, because the purpose of the immersion metal is to minimize oxide formation by forming a barrier coating on the oxidation-prone metal.
• the substrate can be coated with a mixture of the oxidation-prone metal, the protective metal, and the immersion metal by simultaneously adding these metals to the plating liquid and agitating this liquid.
• another layer of the immersion metal surrounding each particle or aggregate of dispersed immersion metal, protective metal, and oxidation-prone metal can be applied to the substrate.
• the following sequence is one way of producing such a coating: (1) adding together the protective metal, the oxidation-prone metal, the etching agent, and the immersion metal to the plating liquid containing the substrate and the impaction media; (2) agitating the plating liquid; (3) adding together more of the oxidation-prone metal, the protective metal, and the immersion metal to the plating liquid; (4) agitating the plating liquid; (5) adding more immersion metal to the plating liquid; and (6) agitating the plating liquid.
• a layer of dispersed oxidation-prone metal, protective metal, and immersion metal can also be formed by adding immersion metal to the plating liquid, agitating the plating liquid, simultaneously adding oxidation-prone metal and protective metal to the plating liquid, and agitating the plating liquid.
• the immersion metal in the plating liquid will coat the subsequently-added oxidation-prone metal, and the oxidation-prone metal, the protective metal, and the immersion metal will together plate on the metal substrate.
• the substrate can be coated with a layer of dispersed oxidation-prone metal and immersion metal which surrounds a layer of the protective metal by the following sequence of steps: (1) adding the protective metal to the plating liquid containing the metal substrate and the impaction media; (2) agitating the plating liquid; (3) adding together the oxidation-prone metal, the etching agents, and the immersion metal to the plating liquid; and (4) agitating the plating liquid; (5) adding more immersion metal to the plating liquid; and (6) agitating the plating liquid.
• a layer of dispersed oxidation-prone metal, protective metal, and immersion metal can also be formed by adding immersion metal to the plating liquid. agitating the plating liquid, simultaneously adding oxidation-prone metal and protective ⁇ etal to the plating liquid, and agitating the plating liquid. In this sequence, the immersion metal in the plating liquid
• the substrate can be coated with a
• this coating can be applied by adding simultaneously the protective metal
• the oxidation-prone metal is mechanically plated on the substrate previously coated with protective metal.
• 35 dispersed oxidation-prone metal and immersion metal surrounding the layer of protective metal by adding immersion metal to the plating liquid and agitating the plating liquid.
• immersion metal alone can surround each particle or aggregate of dispersed immersion metal and oxidation-prone metal. More additions and agitation effects a build-up of the immersion metal.
• a layer of dispersed oxidation-prone metal and immersion metal can be built up by adding more immersion metal and oxidation-prone metal to the plating liquid.
• adjacent layers of the oxidation-prone metal, the protective metal, and/or the immersion metal will tend to diffuse into one another. While not wishing to be bound by theory, it is believed that this diffuse boundary is caused by the continued plating of residual metal powder for one layer in the plating barrel when metal powder for the next layer is added and begins to be plated.
• a one-third cubic foot capacity plating barrel was charged with five square feet of carbon steel nails, 4,000 grams of glass impaction spheres (0.01 to 0.2 inch diameter range) , and sufficient water to cover the nails and impaction media.
• the nails were cleaned, degreased, and copper flashed in accordance with the method set forth in the '315 patent.
• a solution of 0.64 grams of sodium sulfate, 6.4 grams of tin oxide, 5.0 grams of NH 4 F*HF, a corrosion inhibitor, and a dispersant were added to the barrel. The barrel was rotated for about two minutes to dissolve all ingredients.
• the coated nails were subjected to a salt spray corrosion test (ASTM B117) and were found to withstand 72-86 hours of salt spray before significant corrosion was observed. Nails which were chromated withstood
• Example 1 was repeated using 10 grams of K 2 ZrF 6 as the etching agent in place of the ammoniated fluoride. Similar results were obtained.
• Example 1 was repeated using 0.5 grams of sodium fluoride as the etching agent. Corrosion resistance of about 300 hours in salt spray was observed.
• Example 1 Using the process of Example 1 with the fluoride etching agent of Example 3, varying quantities of aluminum, tin, and copper were employed in the mechanical plating liquid, and the resulting coated nails were analyzed for content of the coating. The results are set forth below in Table 1.
• Example 8 was repeated using a mixture of zinc and cadmium powders (1:1 by weight, 9.7 grams for each addition) .
• the screws were found to withstand 96 hours of being sprayed with a 5% neutral salt spray (ASTM B117) before significant corrosion was observed. Screws which were chromated withstood 4,536 hours of salt spray until the first red rust was observed.
• a mixture of l-l/2pounds of hex head screws, 1/2 pound of hex head bolts, and 2 pounds of 6d common nails (3 ft 2 total surface area) were cleaned, coppered, and tinned according to example 8.
• Zinc (3 portions of 8 grams each) was then added at 3 minute intervals.
• a mixture of aluminum powder (10 grams), ammonium bifluoride (2.5 grams) and stannous oxide (3.5 grams) were added to the barrel which was ⁇ rotated for 5 minutes.
• Aluminum (10 grams) and stannous oxide (3.5 grams) were then added, and the barrel was tumbled for 5 minutes.
• cupric sulfate 2.0 grams was added, and the barrel was rotated an additional 10 minutes. After rinsing and drying, the coated screws were subjected to a neutral salt spray (ASTM B117) .
• the unchromated samples first showed red rust after 168 hours of spraying, while the chromated samples first showed red rust after 3,816 hours.
• Steel phillips head screws were either coated with zinc, aluminum on zinc, aluminum on cadmium, or aluminum codeposited with zinc to the thicknesses set forth in Table 1 below.
• the coated screws were subjected to a 5% neutral salt spray to determine how long it took before there was significant rust (i.e. over 10% rust).
• coatings of zinc were inferior to coatings of aluminum on zinc, aluminum on cadmium, and aluminum codeposited with zinc, applied in accordance with the present invention.
• Two inch bolt-nut assemblies were coated with zinc, aluminum on zinc, or aluminum codeposited with zinc to the thicknesses set forth below in Table 3. These assemblies were then fastened to a panel of aluminum and subjected to a 5% neutral salt spray to determine how many hours it took until the assemblies had significant rust (i.e. over 10% rust) and until pitting of the aluminum panel was first noticed. As shown below in Table 3, the assemblies coated with zinc were severely corroded, and the aluminum panels to which the zinc coated assemblies were attached were severely pitted as a result of galvanic corrosion. By contrast, the assemblies plated with codeposited aluminum and zinc or aluminum on zinc had virtually no corrosion, while the aluminum panels to which these assemblies are attached had little pitting.

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• Chemical & Material Sciences (AREA)
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• Organic Chemistry (AREA)
• Chemically Coating (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Electroplating Methods And Accessories (AREA)

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• 1987
  • 1987-07-06 WO PCT/US1987/001632 patent/WO1988003060A1/en not_active Application Discontinuation
  • 1987-07-06 JP JP62504313A patent/JPH01501071A/ja active Pending
  • 1987-07-06 EP EP19870904782 patent/EP0288484A4/de not_active Withdrawn
  • 1987-07-06 AU AU77040/87A patent/AU7704087A/en not_active Abandoned
  • 1987-07-21 ZA ZA875358A patent/ZA875358B/xx unknown
  • 1987-09-07 DE DE19873729921 patent/DE3729921A1/de active Granted

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