US3867266A - Method of plating aluminum-chromium alloys - Google Patents

Method of plating aluminum-chromium alloys Download PDF

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Publication number
US3867266A
US3867266A US250525A US25052572A US3867266A US 3867266 A US3867266 A US 3867266A US 250525 A US250525 A US 250525A US 25052572 A US25052572 A US 25052572A US 3867266 A US3867266 A US 3867266A
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Prior art keywords
chromium
aluminum
bath
plated
plating
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Expired - Lifetime
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US250525A
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English (en)
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Akira Miyata
Hideyo Okubo
Chikayoshi Tomita
Akio Suzuki
Hidenobu Ito
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JFE Engineering Corp
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Nippon Kokan Ltd
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    • 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
    • C25D3/66—Electroplating: Baths therefor from melts

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  • U.S. Pat. Nos. 3,l67,403 and 3,268,422 disclose a method wherein 0.25% of manganese is incorporated into a molten aluminum salt bath to plate an Al- Mn alloy containing to 70% manganese.
  • the manganese in the plated layer obtained by this method acts to decrease flexibility and workability of plated metal articles, this tendency increasing with the amount of the manganese incorporated.
  • U.S. Pat. No. 3,567,409 discloses a coated sheet steel, the coating consisting essentially of IS to 50 weight percent of one selected from the group consisting of chromium and titanium, and the balance of aluminum, and a method of manufacturing the coated sheet steels by vacuum vapour deposition technique.
  • An object of this invention is to provide a novel method of electroplating capable of decreasing the amount of chlorine contained in the plated aluminum layer which is formed by the molten chloride salt bath method.
  • Another object of this invention is to provide a method of electroplating capable of preventing the deterioration of the molten salt bath.
  • Still another object of this invention is to provide a metal article plated with an -AlCr alloy film of excellent adhesiveness and in which the aluminum alloy is prevented from depositing in dendritic form.
  • a further object of this invention is to provide a metal article provided with a homogeneous coating having excellent corrosion resistance properties.
  • a still further object of this invention is to provide a plated metal article having higher flexibility and workability than prior art plated metal articles.
  • FIG. 1 is a graph showing the relationship between cathode current density and the quantity of the deposit in the form of dendrite;
  • the metal substrate utilized in this invention is a moulded or shaped article which may be a single metal or an alloy.
  • the type and composition of the metal and the configuration of the article are immaterial to the invention.
  • the invention is especially suitable for metal substrates of titanium, titanium alloys, steel or alloy steels. Steel is the most commonly used metal for the substrate and the substrate is shaped to have a desired configuration before or after plating. In the latter case, the plated metal substrate is required to have excellent workability.
  • Titanium and titanium alloys are used in applications wherein anti-corrosion properties and fatigue resistant properties are essential under severe operating condi tions. Since the presence of chlorine in the coating adversely affects the foregoing properties and since the plated alloy coating prepared by the method of this invention contains only an extremely small quantity of chlorine, the invention is especially suitable for plating metal articles of titanium or titanium alloys. Usually, since the substrates of titanium or titanium alloys are not worked after plating, the workability of the coated article is not important. For this reason, it is not necessary to limit to any particular value the weight ratio of aluminum to chromium in the plated alloy coating. Practically, however, it is advantageous to use a chromium percentage of from 1.0 to 27.0, by weight.
  • the metal substrate may take any configurations such as strips, plates, wires, bolts, nuts or may be of very complicated ones as in the case of electric machines and apparatus.
  • Any source of chromium ions may be used for incorporating chromium into the molten salt bath, but it is advantageous to use granules of metallic chromium or an auxiliary electrode of chromium or chromium-
  • the temperature of the bath was maintained at 160 C, the cathode current density was 2.0 A/dm and the plating time was 30 minutes.
  • Chromium ion was added by dissolving granules ofmetallic chromium in the molten bath.
  • the molten salt bath may be any bath usually em- EXAMPLE 2 ployed as the alummum electro'platmg bath for exam- A steel bolt was used as a metal substrate and the surple a bath consisting of aluminum chloride, sodium chloride and potassium chloride.
  • chromium ion exists in the electrolyte and that chromium at once takes oxygen out of the electrolyte by easily being oxidized to assure excellent plating.
  • the chromium oxide formed in the electrolyte in this manner is in the form of line colloidal particles in the nascent state, the chromium oxide functions in the same manner as a brightener commonly added to the electroplating solution, thereby manifesting a remarkable effect of preventing the deposition of dendrite which otherwise is formed on the plated surface in electrolytic aluminum plating.
  • EXAMPLE 1 Examples of the novel method of alloy plating and characteristics of the resulting plated coatings are shown in the following table 1.
  • the metal substrates employed in these examples were cold rolled steel plates, each having a thickness of 0.2 mm, a width of 50 mm, a length of 100 mm, and the molten salt bath used for the plating had following composition.
  • 1,285g of aluminum chloride, 238g of sodium chloride, and 180g of potassium chloride were put in a cylindrical hard glass beaker having a capacity of 1 litre, and the mixture was heated at a temcrature of 160 C to re are an ordinar molten salt P P P y bath for electroplating aluminum.
  • 1.5g of granules of metallic chromium was incorporated into the bath and the bath was let standstill for 24 hours. Then the metallic chromium was dissolved completely.
  • An aluminum rod (21 diameter of 10 mm and a length of 50 mm) as an anode, and an aluminum plate (15 mm X mm) for supplying cathode current to steel bolts to be plated were dipped in the bath.
  • each bolt was covered with an Al-Cr coating having a thickness of9 microns and containing 6% of chromium.
  • EXAMPLE 3 In the same manner as in examples 1 and 2, 1,285g of aluminum chloride, 238g of sodium chloride and 180g of potassium chloride were put into one litre cylindrical beaker of hard glass and heated up to 160 C and melted. With this plating bath, aluminum chloride sublimes from the liquid surface so that when the beaker is closed by a lid of hard glass, sublimed aluminum chloride was deposited on the inner surface of the lid. After the bath was left alone for 16 hours the deposited aluminum chloride'amounted to 128g. A plating bath was prepared under the same conditions and 1.5g of granules of metallic chromium were added and dissolved in the plating bath.
  • EXAMPLE 4 Using both types of the molten plating baths described in example 3, the conventional aluminum plating bath, and a bath containing with 1.5g of granules of metallic chromium, cold rolled steel plates, each having a thickness of 0.2 mm, a width of 50 mm, and a length of 100 mm, were electroplated with current densities of0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 5.0 and 7.0 A/dm, respectively. The characteristics of the plated films were measured and the results were plotted as shown in FIGS. 1 and 2. As shown in FIG. 1, where the electroplating was carried out at a constant electric quantity (l Ampere hour), the tendency to deposit the dendritic structure of poor adhesiveness increased as the current density increased.
  • the quantity of the dendritic deposits is greatly decreased by the addition of the chromium into the plating bath.
  • the plating bath containing chromium enables electroplating at higher efficiencies at much higher current densities than the plating bath not containing chromium.
  • EXAMPLE 5 cage 4 having an inner diameter of 12 mm and a length of 100 mm, an aluminum rod 5 having a diameter of 5 mm and a length of 150 mm and inserted in the cage 4, and 20g. of small pieces of metallic chromium packed between the cage 4 and the aluminum rod 5.
  • chromium source electrodes 2 and 3 were connected to the positive line of a DC source and a cold rolled steel plate 8 having a thickness of 0.2 mm, a width of 50 mm and a length of 100 mm was connected to the negative line. Then, the small pieces of chromium were electrolytically dissolved into the plating bath. After 2A of DC was passed through the chromium anodes, a desired quantity of chromium has been added, and the chromium source electrodes 2 and 3 and the steel plate 8 were removed from the plating bath. Thereafter, two aluminum rod anodes (6 mmtb) and steel sheet (50 mm X 100 mm) plated were dipped in the bath to electroplate, and electroplating was carried out for 15 minutes with a current of 2A.
  • Table 2 shows the relationship between the time in which current was passed through the chromium electrodes and the quantity of chromium contained in the bath and the plated film which was formed on the metal article immediately after incorporation of chromium.
  • the chromium cource electrodes were removed from the plating bath. Then two aluminum rods of 5 mm diameter each were dipped in the plating bath as the anodes and a cold rolled steel plate having a length of 100 mm, a width of 50 mm and a thickness of 0.2 mm was placed between the anodes as the cathode. The electrolytic plating was carried out for 30 minutes with a current of 2A. The resulting plated aluminum alloy film was contained 4.9% of chromium. However, as the plating operation was repeated under the same plating condition, the content of chromium in the plating bath and plated film gradually decreased and it was found that the content of chromium in the fifth plated film was 2.3%.
  • electroplating was repeated several times by utilizing two sheets of aluminum-chromium alloy plates as the anode electrodes, each alloy plate containing 5% of chromium and having a length of 100 mm, a width of 20 mm and a thickness of 14 mm. The same plating condition mentioned above was used. At first the content of chromium in the plating bath was 1.5 g/l and firstly plated aluminum alloy film contained 4.2% of chromium.
  • the content of chromium in the fourth plated film was 4.1% and the content of chromium in the plating bath was 1.4 g/l. Even in the eighth plated film, the content of chromium was 3.6% and the content of chromium in the bath was 1.1 g/l.
  • EXAMPLE 7 In this example, an aluminum coating containing chromium was electro-plated on the surface of a substrate of a titanium alloy. Electroplating was performed by dissolving 1.5g of metallic chromium in a one liter plating bath consisting of 1 ,2 85g of aluminum chloride, 235g of sodium chloride and 180g of potassium chloride while blowing hydrogen chloride gas through the bath.
  • the Ti-6A -4V alloy bolts having a diamter of 6 mm and a length of 30 mm were plated.
  • the bolts were cleansed with water agitated by ultrasonic waves, dried thoroughly and subjected to a glass bead peening treatment. These films contained 5% of chromium.
  • EXAMPLE 8 In this example, an aluminum coating containing chromium was electroplated on the surface of a titanium plate in accordance with the method of this invention.
  • chromium content in this bath was 1.5 g/l.
  • the titanium plate had a length of 300 mm, a width of 100 mm and a thickness of 0.2 mm, degreased with acetone, and pickled with a 10:1 nitric-hydrofluoric acid for 30 seconds. After drying thoroughly in the air, the pretreated titanium plate was dipped in the plating bath to a depth of 180 mm then electroplated by a plating current of 7.2A by using the plate as the cathode and two aluminum rods, each having a diameter of 5 mm and a length of 180 mm as the anode electrodes. Plating for 30 minutes formed a plated film having a thickness of 10 microns and high adhesiveness. The film contained 5.6% of chromium.
  • EXAMPLE 9 In this example, an aluminum coating containing chromium was electroplated on the surface of an aluminum plate.
  • the aluminum plate was commercial aluminum having a purity of 99.7%, a length of 50 mm, a width of 10 mmand a thickness of 3 mm.
  • the aluminum plate was degreased with acetone and then dipped in a 3% aqueous solution of hydrofluoric acid for several seconds. After thoroughly drying in the air, the resulting aluminum plate was dipped in the plating bath and plated for one and one half hours by passing a plating current of 0.2A by using two aluminum rod anodes, each having a diameter of 5 mm and a length of 10 cm, and placed on the opposite side of the plate. A highly adhesive plated film having a thickness of 30 microns was formed. The content of chromium in the plated film was 4.8%.
  • EXAMPLE 10 In this example the surface of a stainless steel plate was electroplated with an aluminum coating containing chromium according to the method of this invention.
  • the plated stainless steel plate had a length of 60 mm, a width of 20 mm and a thickness of 3 mm.
  • the plate was degreased with acetone. dipped in 3% aqueous solution of hydrofluoric acid and then washed thoroughly with water. The plate was dried thoroughly and then dipped in the plating bath.
  • Two aluminum rods, each having a diameter of 5 mm and a length of 10 cm were used as the anode electrode.
  • the plating operation was carried out for 30 minutes with a plating current of 0.48A to obtain a highly adhesive AlCr alloy film having a thickness of 10 microns.
  • the film contained 4.0% of chromium.
  • EXAMPLE 11 the surface ofan alloy steel was electroplated with an aluminum film containing chromium in accordance with the method of this invention and then the aluminum film was anodized.
  • test piece was cleaned by blasting No. emery powder with compressed air under pressure of4 kg/cm and pickled with 10% hydrochloric acid containing 2% of an inhibitor and then washed with water. After drying, this alloy steel test piece was dipped in the plating bath and plated with a current of 1A; using two aluminum rods each having a diameter of 5 mm and a length of 120 mm as the anode electrode. After electroplating for 1.5 hours a highly adhesive aluminum alloy coating having a thickness of 30 microns was formed. The film contained 1% of chromium. After peening with 80 120 ,u. glass beads, the film was subjected to anodic oxidation under the following conditions.
  • a method of electroplating a chromiumcontaining aluminum coating on the surface ofa metal article by immersing said metal article in a molten aluminum salt bath comprising aluminum chloride and containing at least one alkali metal chloride and chromium ions in an amount of l to 5.5 g/l and electrodepositing a coating of an aluminum-chromium alloy onto the surface of said metal article.
  • said molten salt bath comprises aluminum chloride. sodium chloride and potassium chloride.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Coating With Molten Metal (AREA)
US250525A 1971-05-14 1972-05-05 Method of plating aluminum-chromium alloys Expired - Lifetime US3867266A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080093222A1 (en) * 2004-11-24 2008-04-24 Sumitomo Electric Inudstries Ltd. Molten Salt Bath, Deposit, and Method of Producing Metal Deposit
US9909019B2 (en) 2015-06-24 2018-03-06 General Electric Company Diffusion coatings for metal-based substrate and methods of preparation thereof
US10053779B2 (en) 2016-06-22 2018-08-21 General Electric Company Coating process for applying a bifurcated coating
US10077494B2 (en) 2016-09-13 2018-09-18 General Electric Company Process for forming diffusion coating on substrate
CN115579485A (zh) * 2022-10-25 2023-01-06 沈伟 一种双极板的制备方法和应用

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0613512B2 (ja) * 1987-07-30 1994-02-23 ヤマハ株式会社 ホトクロミック化合物

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3480521A (en) * 1964-11-13 1969-11-25 Nippon Kokan Kk Process for the electrolytic formation of aluminum coatings on metallic surfaces in molten salt bath
US3489537A (en) * 1966-11-10 1970-01-13 Gen Electric Aluminiding
US3689381A (en) * 1970-04-13 1972-09-05 Akira Miyata Method of electroplating aluminum in a bath of molten salts

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3480521A (en) * 1964-11-13 1969-11-25 Nippon Kokan Kk Process for the electrolytic formation of aluminum coatings on metallic surfaces in molten salt bath
US3489537A (en) * 1966-11-10 1970-01-13 Gen Electric Aluminiding
US3689381A (en) * 1970-04-13 1972-09-05 Akira Miyata Method of electroplating aluminum in a bath of molten salts

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080093222A1 (en) * 2004-11-24 2008-04-24 Sumitomo Electric Inudstries Ltd. Molten Salt Bath, Deposit, and Method of Producing Metal Deposit
US9512530B2 (en) * 2004-11-24 2016-12-06 Sumitomo Electric Industries, Ltd. Molten salt bath, deposit, and method of producing metal deposit
US9909019B2 (en) 2015-06-24 2018-03-06 General Electric Company Diffusion coatings for metal-based substrate and methods of preparation thereof
US10053779B2 (en) 2016-06-22 2018-08-21 General Electric Company Coating process for applying a bifurcated coating
US10077494B2 (en) 2016-09-13 2018-09-18 General Electric Company Process for forming diffusion coating on substrate
CN115579485A (zh) * 2022-10-25 2023-01-06 沈伟 一种双极板的制备方法和应用

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FR2137888A1 (enExample) 1972-12-29
JPS531212B2 (enExample) 1978-01-17
DE2223372B2 (de) 1976-06-24
JPS4742536A (enExample) 1972-12-16
DE2223372A1 (de) 1972-11-30
GB1363324A (en) 1974-08-14
FR2137888B1 (enExample) 1974-10-25

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