Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/565—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of zinc

Definitions

• the present invention relates to zinc-nickel electroplated articles exhibiting corrosion resistance, including articles that, after being plated with a corrosion-resistant, zinc-nickel alloy, exhibit low hydrogen embrittlement characteristics.
• High-strength steels are subject to delayed, brittle failures at relatively low stresses. Such failures have been attributed to the presence of hydrogen in the steel microstructure.
• the hydrogen can be introduced into the microstructure by reaction with water or with an acid, or most importantly, by cathodically discharging hydrogen at the surface of the steel. Since most high- strength steels have corrosion-resistant coatings that are applied by less than 100 percent efficient electroplating techniques, hydrogen is discharged onto the steel surface along with the corrosion-resistant coating. Therefore, the quantity of hydrogen deposited at the coating steel interface must be carefully monitored and controlled.
• a cadmium-titanium alloy is electroplated onto high- strength steels under carefully controlled conditions.
• the resulting plated product is then heat treated at elevated temperatures to achieve an acceptable low hydrogen embrittlement level.
• the porosity of the electroplated cadmium-titantium alloy is the key to the removal of the hydrogen during a subsequent heat treatment operation; however, the cadmium-titanium plating bath is very sensitive to contamination, which can cause embrittlement characteristics in coated high-strength steel substrates. More importantly, however, the cadmium-titanium alloy plating bath contains both cadmium and cyanide, which create disposal problems unless expensive waste treatment equipment is employed.
• Zinc-nickel alloys have been suggested for electroplating onto steels to render them corrosion-resistant.
• the plating parameters of a zinc- nickel alloy plating bath are much easier to control and maintain than a cadmium-titanium bath.
• the zinc-nickel bath is cadmium and cyanide free and contains components that are relatively nontoxic compared to those in a cadmium-titanium plating bath.
• Most prior zinc-nickel baths have, however, been suggested only for high-speed plating. High-speed plating techniques are unsatisfactory for rack plating of larger metal parts.
• the present invention provides a method for producing a corrosion- resistant article, such as a high-strength steel, by applying a corrosion-resistant coating of a zinc-nickel alloy with electroplating techniques.
• a high-strength steel article coated in accordance with the present invention exhibits low hydrogen embrittlement characteristics.
• the hydrogen embrittlement of the article is maintained at a relatively low level by electroplating the zinc-nickel coating on the article in an aqueous acidic plating solution containing zinc and nickel ions, an electrolyte in the form of a soluble ammonium salt, and a polyoxyalkylated nonionic surfactant.
• These zinc-nickel alloys are preferably electroplated from a bath containing: from about 3.0 to about 75.0 grams of zinc ions selected from the group consisting of zinc chloride, zinc sulfate, zinc fluoborate, zinc acetate and mixtures thereof; from about 3.0 to about 75.0 grams of nickel ion selected from the group consisting of nickel chloride, nickel sulfate, nickel sulfamate, nickel fluoborate, nickel acetate, and mixtures thereof; from about 3.0 to about 100 grams of ammonium ion in the form of a soluble ammonium salt of hydrochloric acid, sulfurie acid, fluoboric acid, acetic acid, or mixtures thereof; and from about 0.5 to about 20 grams per liter of a nonionic polyoxyalkylated surfactant.
• the bath must also contain at least about 15 grams of an anion selected from the group consisting of chloride, fluoborate, and mixtures thereof.
• acid an ⁇ ons selected from chloride, sulfate, fluoborate, acetate, sulfamate, and mixtures thereof must be present in a molar amount at least equal to the combined molar amount of zinc, " nickel, and ammonium ions present in the bath.
• the bath can also contain a boric acid buffer, an anionic surfactant, and a brightener if desired.
• the bath can be effectively operated at a pH of from about 3.0 to about 7.0 and at a temperature ranging from about 15 C to 45 C.
• the potential applied across the anode and the cathode workpiece is sufficient to provide current densities of about 0.05 to about 200 amperes per square decimeter at the cathode workpiece surface, although current densities below about 12.0 amperes per square decimeter are preferred to produce low hydrogen embrittlement characteristics.
• the electroplating bath described above is free of cadmium ions, cyanides, and chelating agents. Yet the bath has a high cathode efficiency, and produces smooth adherent, ductile leveling and fine-grained, zinc-nickel alloy deposits over a wide range of plating conditions and cathode current density.
• an article plated with the zinc-nickel alloy exhibits lower hydrogen embrittlement and substantially greater corrosion resistance than an article coated with zinc or zinc-nickel alloys of the prior art.
• the process can also be utilized to provide zinc-nickel alloy deposits on other substrates, both metallic and nonmetallie, as long as the substrate is conductive.
• the process can be employed to provide a zinc-nickel alloy deposit on a graphite- epoxy composite structure.
• the bath is very stable, is easy to control, has a high conductivity, while requiring only simple waste treatment procedures.
• a zinc-nickel alloy can be electrodeposited onto a variety of electrically conductive substrates in accordance with the present invention.
• a zinc-nickel alloy can be electrodeposited onto a graphite-epoxy article for the purpose of making that article corrosion resistant.
• the zinc- nickel alloy deposited in accordance with the present invention is especially efficacious, however, when applied to high-strength steel articles. Not only is the steel article rendered corrosion resistant, it also exhibits little or no hydrogen embrittlement after the electroplating process. Accordingly, the present invention provides a viable and effective substitute for prior titanium- cadmium corrosion-resistant coatings.
• the article to be plated Prior to deposition of the zinc-nickel alloy, the article to be plated is preferably cleaned and activated for electrodeposition in accordance with the following procedure.
• the article to be plated is first manually solvent cleaned and vapor degreased in accordance with conventional procedures normally employed in the plating arts. After cleaning and degreasing, the article is completely dried and then cleaned with an abrasive blast. Within a relatively short period of time after the abrasive cleaning, the article is rinsed in cold water for one-half to five minutes. The part is then activated by immersing it in
• OMPI an acid solution for from five to 30 seconds. Within two minutes from the time the part is retrieved from the acid solution, it is rinsed with cold water for a minimum of 30 seconds up to approximately six minutes maximum. Within two minutes after the completion of the cold water rinse, the part can be immersed in the zinc-nickel plating bath as described below.
• the plating bath formed in accordance with the present invention is an aqueous solution containing zinc, nickel and an electrolyte in the form of a soluble ammonium salt, along with a nonionic polyoxyalkylated surfactant.
• the cations are placed in an aqueous solution of a solubilized oxide or salt of the cation. It is preferred, as will be discussed in more detail below, that the solution contain acid an ⁇ ons, and that at least a portion of the acid anions comprise chloride or fluoborate.
• a buffer such as boric acid, an anionic surfactant, and br ⁇ ghteners are optional, but preferred for the commercial plating embodiment of the present invention.
• the zinc cations can be provided by a variety of water-soluble zinc compounds. These compounds can include zinc oxide, which is capable of forming a zinc salt in the presence of acid anions, such as chloride ions that are normally present in an aqueous bath prepared in accordance with the present invention.
• the water-soluble compounds also include zinc salts such as zinc chloride, zinc sulfate, zinc fluoborate, zinc acetate and, of course, the various combinations and mixtures thereof.
• Concentration of the zinc salt should be sufficient to provide from about 3.0 to about 75.0 grams of zinc ion per liter of solution.
• the zinc ions should be present in an amount ranging from 6.0 to 30.0 grams per liter of solution.
• the nickel salts can be provided from a variety of water-soluble nickel salts, including nickel chloride, nickel sulfate, nickel sulfamate, nickel fluoborate, nickel acetate, and the various mixtures and combinations thereof.
• the nickel salt should be present in an amount sufficient to provide from about 3.0 to about 75.0 grams of nickel ion per liter of solution. It is preferred that about 3.0 to about 30.0 grams of nickel ion per liter of solution be employed.
• the nickel to zinc ratio can be varied, for example from about 0.4:1 to about 4:1, while still obtaining a satisfactory coating. At low nickel/zinc ratios hydrogen embrittlement is minimized. At low ratios, hydrogen reembrittlement tends to be aggravated. For a plated coating exhibiting optimum corrosion resistance, it is preferred that the weight ratio of nickel ion to zinc ion be on the order of about 1 to 1 to about 2 to 1.
• the conductivity of the electroplating bath is increased by the presence of the electrolyte.
• the preferred electrolytes include soluble ammonium salts of hydrochloric acid, sulfurie acid, fluoboric acid, acetic acid, and the various mixtures and combinations thereof.
• the ammonium salt should be present in the bath in an amount sufficient to provide from about 3.0 to about 100 grams of ammonium ion per liter of solution. Most preferably, the ammonium ion is present in the weight range of from about 50.0 to about 90.0 grams per liter of solution.
• ammonium chloride or ammonium fluoborate be employed as the salt from which the ammonium ion is derived. These salts provide relatively uniform plating results over a wider range of current densities. It is most preferred that the bath contain at least about 15.0 grams of chloride or fluoborate anions or mixtures thereof per liter of solution. It is also preferred that the acid anions, including chloride, sulfate, fluoborate, acetate, sulfamate and mixtures thereof be present in a molar amount at least equal to the combined molar amount of zinc, nickel and ammonium present in the solution.
• the acid anions be present in the range of from about 15.0 to 200 grams per liter of solution while 120 to 200 grams of acid anions per liter of solution are preferred.
• the chloride anion is most preferred. Consequently, the most preferred bath is one composed primarily of zinc chloride, nickel chloride, and ammonium chloride.
• a nonionic polyoxyalkylated surfactant in the zinc- nickel plating bath is critical to producing a corrosion-resistant, coated high- strength steel that has low hydrogen embrittlement.
• the presence of the nonionic polyoxyalkylated surfactant produces a zinc-nickel coating that is smooth, adherent, ductile, leveling, and fine-grained, over a wide range of plating conditions and cathode current densities.
• a wide variety of surface- active polyoxyalkylated compounds can be employed in accordance with the present invention as long as they are soluble in the aqueous bath.
• alkoxylated alkyl phenols alkoxylated alkyl naphthols, alkoxylated aliphatic monohydric alcohols, alkoxylated polyoxy- propylene glycols, alkoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol, alkoxy ⁇ lated ethylene diamine, alkoxylated fatty acids, alkoxylated amides and alkoxylated esters.
• polyethoxylated alkyl phenols have been found to be particularly effective in producing corrosion-resistant coated substrates having a low hydrogen embrittlement in accordance with the present invention.
• Particular polyethoxylated alkyl phenol surfactants that are commercially available include ethoxylated nonyl phenol sold under the trade name "Tergitol NP-15" by Union Carbide Corporation and under the trade name “Igepal CO-730" by GAF Corporation. The latter surfactant contains approximately 15 repeating ethyleneoxy units in the hydrophilie portion of the molecule.
• suitable nonionic surfactants include "Igepal CO-887" from GAF Corporation and "Nentronyx 656" from Millmaster Onyx Corporation.
• the nonionic surfactant must be present in the bath in accordance with the present invention in an amount ranging from about 0.5 to about 20.0 grams per liter of solution. It is most preferred, however, that from about 1.0 to about 5.0 grams per liter of solution be employed.
• the presence of the nonionic polyoxyalkylated surfactant in combination with the zinc, nickel and ammonium cations, and chloride and/or fluoborate anions are required to produce a corrosion-resistant coated high- strength steel substrate in accordance with the present invention, other materials can be added to enhance desirable characteristics in the plating process as well as in the final product.
• boric acid may be advantageously included in the bath to function as a buffer. Boric acid can be present in the range of from about 1.0 gram per liter of solution up to saturation of boric acid in the bath.
• anionic surfactant is preferably added to the bath to increase the high end of the cathode current density range and to further improve the low hydrogen embrittlement characteristics of the final product.
• anionic surfactants in general tend to be insoluble in plating baths, the nonionic polyoxyalkylated surfactants function as a solubilizer for the anionic surfactants.
• Numerous anionic surfactants can be employed in accordance with the present invention.
• the alcohol sulfates and the alkyl aryl sulfonates are found to be particularly successful.
• a suitable alcohol sulfate includes the sodium lauryl sulfate commercially available from E.I. du Pont de Nemours and Company, Inc. under the trade name "Duponol ME Dry".
• a suitable alkyl aryl sulfonate is the sodium dodecylbenzene sulfonate available from Stepan Chemical Company under the trade name "Naceonol 90F".
• the anionic surfac ⁇ tant can be present in the bath in amounts ranging from about 0.2 to about 7.5 grams per liter of solution, although from 0.4 to 2.0 grams per liter of the anionic surfactant are preferred. It is also to be noted that the foregoing list of anionic surfactants is not intended to be exclusive. Other anionic surfactants that are soluble in the system otherwise formulated in accordance with the present invention and that do not detract from the superior results obtained by the present invention can be employed.
• Organic brighteners can also be employed to provide bright, specular deposits over the useful cathode current density ranges, that is, from about 0.3 to about 4.5 amperes per square decimeter.
• Suitable organic brighteners include the ring-halogenated aryl aldehydes and aryl olefinic ketones.
• the ring-halogenated aryl aldehydes include ortho- chlorobenzaldehyde, para-chlorobenzaldehyde, 2,4-dichlorobenzaldehyde, and 2,6-dichlorobenzaldehyde.
• An example of a suitable aryl olefinic ketone is benzylidene acetone.
• organic brighteners such as aryl ketones, aryl aldehydes, ring-halogenated aryl ketones, heterocyclic ketones and aldehydes, as well as aryl olefinic aldehydes can be employed.
• the most preferred brighteners are ortho-chlorobenzaldehyde and benzylidene acetone. These brighteners can be employed in the bath in amounts ranging from about 0.02 to about 2.0 grams per liter of solution. The most preferred range includes the brighteners in amounts ranging from about 0.05 to about 1.0 gram per liter of solution.
• the zinc-nickel plating process can be carried out in the generally conventional pH, temperature, and current density ranges.
• an alloy containing, for example, from 80 to 95 percent by weight zinc with the balance being nickel is produced.
• This coating will provide excellent corrosion resistance as well as sufficient porosity to allow hydrogen embrittlement to be relieved.
• the bath can effectively be operated in a pH range of from about 3.0 to about 7.0 while a pH range from about 5.5 to about 6.5 is preferred. It is preferred that the pH of the bath be adjusted by the addition of ammonium hydroxide or hydrochloric acid as the need may be, so as to avoid the introduction of undesirable ions into the solution.
• the zinc-nickel alloy can be plated in accordance with the present invention over a wide variety of temperatures and current densities.
• the electrodeposition can occur over a broad temperature range of from about 15 C to about 45 C while the narrower range of from about 20°C to about 32°C is preferred.
• the cathode current densities can range from about 0.05 to about 12.0 amperes per square decimeter and still yield a satisfactory corrosion-resistant coating and article having a relatively low hydrogen embrittlement. However, current densities in the range of from 2.0 to 4.0 amperes per square decimeter are preferred.
• a chromate or phosphate treatment of the part can follow the zinc-nickel plating step. In any event, within eight hours of completion of the plating step, the part is baked to relieve hydrogen embrittlement. Most steels except carburized steel and 440 steels can be baked at temperatures on the order of 350°F to 400 °F for a minimum of 12 hours.
• Carburized steels and 440 steels should be baked at a lower temper ⁇ ature of from 250 °F to 300° F for only five to eight hours. If desired, the part can be chromate or phosphate treated subsequent to the hydrogen embrit ⁇ tlement bake.
• Example I An aqueous electroplating bath containing no surfactant was prepared containing per liter of solution, 15 grams of zinc oxide, 47.5 grams of nickel chloride ( iCl2""6 H 2 0 ⁇ ' ⁇ ® grams of ammonium chloride and 20 grams of boric acid. The pH of the bath was 5.7 and was maintained at a temperature of 40 °C. Only zinc was employed as an anode.
• a Hull cell panel was prepared with current densities up to 8.0 amperes per square decimeter. At a current density up to 1.5 amperes per square decimeter, the zinc-nickel alloy deposit was semi-bright with a blue tint, indicating a satisfactory deposit.
• Example II The procedure of Example I was repeated, with the exception that 0.375 gram per liter of solution of anionic surfactant, "Duponol ME Dry", was added. The temperature of the bath was about 31° C. The bath was cloudy. A Hull cell panel was prepared. The panel generally appeared blotchy. At a current density up to 0.7 amperes per square decimeter, the zinc-nickel alloy deposit was cloudy. At a current density of from 0.7 to 2.0 amperes per square decimeter, the deposit was bright; however, the deposit was pitted at current density up to 1.5 amperes per square deci ⁇ meter. At current densities ranging from 2.0 to 9.0 amperes per square decimeter, the deposit was cloudy. Above 9.0 amperes per square decimeter, the deposit was a blue-black.
• Example III The procedure of Example II was again repeated, but this time adding 3.0 grams per liter of "Tergitol NP-15", a nonionic surfactant, to the plating bath.
• a Hull cell panel was prepared. There was no blotchy deposit on the panel. At a current density up to 6.0 amperes per square decimeter, the zinc-nickel alloy deposit was bluish bright. At current densities ranging from 6.0 to 12.0 amperes per square decimeter, the deposit was grey. Above 12.0 amperes per square decimeter, a blue-black deposit was obtained. No spongey deposit was noted. Both the coverage of the plating bath and the throwing power of the plating were better in the presence of the nonionic surfactant when compared with the baths of both Example I and Example II.
• Example IV An aqueous electroplating bath was prepared containing per liter of solution: 47 grams of zinc chloride; 61 grams of nickel chloride; 250 grams of ammonium chloride; 20 grams of boric acid. The pH of the bath was adjus ⁇ ted to 5.9 by the addition of ammonium hydroxide. The temperature of the bath was 24 °C. Notched tensile specimens manufactured and tested in accor ⁇ dance with ASTM F-519, Type la, were plated in the bath. Two nickel and two zinc rods having similar area were used as anodes and arranged symmetrically about the specimens. The specimens were plated at preselected current densities for preselected times. After plating, the specimens were baked for 12 hours at 190 °C.
• the specimens were then tested by static tensile loading at 75 percent of established notch ultimate tensile strength.
• the specimens were loaded continuously for at least 150 hours or until failure.
• the specimens that withstand the loading for more than 150 hours exhibit satisfactory low hydrogen embrittlement characteristics.
• Example V An aqueous electroplating bath was prepared containing per liter of solution: 17.8 grams of zinc oxide; 35.6 ml of hydrochloric acid (38 percent by weight HC1); 24 grams of nickel chloride; 220 grams of ammonium chloride; 20 grams of boric acid; approximately 8 ml of ammonium hydroxide (29 percent by weight NH note).
• the pH of the bath was 6.2.
• the temperature of the bath was 2 C.
• Notched tensile specimens were prepared in accordance with the standards set forth in the previous Example. Three specimens were plated at 1.5 amperes per square decimeter for 20 minutes and three specimens were plated at 3.0 amperes per square decimeter for ten minutes.
• the zinc-nickel deposited on the specimens was dull with heavy pitting and therefore unsatisfactory from the corrosion-resistance standpoint. All of the specimens were tested by loading them in accordance with the procedure set forth in Example IV, with the exception that the specimens were loaded for 200 hours. All specimens passed the 200-hour loading test.
• Example VI The procedure of Example V was repeated with the exception that the pH of the bath was adjusted to 5.8 and 2.25 grams per liter of solution of a nonionic polyoxyalkylated surfactant ("Tergitol NP-15") were added. Five notched tensile specimens were plated at 3.0 amperes per square decimeter for 7.5 minutes. The deposit was satisfactory. The fractured cross-section had a grainy look when viewed under magnification. All specimens passed the 200-hour loading test.
• a nonionic polyoxyalkylated surfactant (“Tergitol NP-15”) were added. Five notched tensile specimens were plated at 3.0 amperes per square decimeter for 7.5 minutes. The deposit was satisfactory. The fractured cross-section had a grainy look when viewed under magnification. All specimens passed the 200-hour loading test.
• Example VII The procedure of Example VI was repeated with the exception that 0.75 gram per liter of an anionic surfactant ("Duponol ME Dry") was also added to the bath. Three notched tensile specimens were plated at 3.0 amperes per square decimeter for 7.5 minutes. When viewed under magnification, an improvement in the ductile nature of the deposits was observed. All specimens passed a 200-hour loading test.
• an anionic surfactant (“Duponol ME Dry”
• Example VIII The procedure of Example VII was repeated with the exception that the pH of the bath was adjusted to 6.2 by the addition of ammonium hydroxide. Two notched tensile specimens were plated at 3.0 amperes per square decimeter
• Example IX An aqueous electroplating bath was prepared containing per liter of solution: 50 grams of zinc oxide; 100 ml of hydrochloric acid; 167 grams of nickel chloride; 90 grams of ammonium chloride; 20 grams of boric acid; approximately 75 ml of ammonium hydroxide.
• the pH of the bath was 5.9.
• the temperature of the bath was about 28 C.
• a copper wire was plated at a current density of approximately 100 amperes per square decimeter for approximately 20 seconds at a linear speed of 98 feet per minute. The deposit was dark grey and grainy.
• the zinc-nickel coating plated in accordance with the present invention not only provides excellent corrosion resistance to steel articles but also yields an end product that, when baked, has very low hydrogen embrittlement characteristics.
• the key to producing such a product in accord ⁇ ance with the present invention is the presence of the nonionic polyoxyalkylated surfactant.
• the primary use of the present invention is currently producing a corrosion-resistant coating on steel parts that results in low hydrogen embrittlement of the steel
• the invention can also be employed to plate metal strips and wires, as well as other articles. Electroplating of steel parts to produce a product exhibiting low hydrogen embrittlement is generally performed at relatively low current densities. It is, however, generally desirable to plate metal strips and wires at high current densities while still producing a good corrosion-resistant coating.
• a plating solution containing an ammonium chloride electrolyte and a nonionic surfactant can be employed to plate at current densities up to about 200 amperes per square decimeter. At such high current densities, it is preferable to agitate the solution during plating and also to increase the zinc and nickel content in the solution over that normally used at low current densities.

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• 1981
  • 1981-12-28 EP EP82900522A patent/EP0097643B1/de not_active Expired
  • 1981-12-28 JP JP82500542A patent/JPS58502221A/ja active Pending
  • 1981-12-28 WO PCT/US1981/001750 patent/WO1983002290A1/en not_active Ceased
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• 1982
  • 1982-12-22 IL IL67542A patent/IL67542A/xx not_active IP Right Cessation
  • 1982-12-23 ES ES518534A patent/ES518534A0/es active Granted
• 1983
  • 1983-02-10 AU AU11319/83A patent/AU565093B2/en not_active Ceased

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