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
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H37/00—Thermally-actuated switches
  • H01H37/02—Details
  • H01H37/32—Thermally-sensitive members
  • H01H37/58—Thermally-sensitive members actuated due to thermally controlled change of magnetic permeability
  • H01H37/585—Thermally-sensitive members actuated due to thermally controlled change of magnetic permeability the switch being of the reed switch type

Definitions

• This invention relates to a method of electroplating readily oxidizable metals and alloys such as aluminum alloys, titanium alloys, chromium alloys, stainless steel and the like whose surfaces tend to be instantly oxidized in the air and are covered by dense oxide films. Accordingly according to conventional methods it has been difiicult to apply adhesive metal coatings on these metals by electroplating due to the unavoidable presence of such oxide films.
• the workpiece is Washed with a mixture of nitric acid and hydrofluoric acid or a mixture of boric acid and hydrofluoric acid to completely dissolve the existing oxide film on the surface of the workpiece to expose an inner new metal surface.
• the hydrogen evolved during pickling is prevented from being absorbed in the base metal to deteriorate it by applying ultrasonic wave vibrations to the acids.
• the workpiece is usually washed with water after pickling.
• readily oxidizable metals are oxidized by the oxygen dissolved in the water during washing to form oxide films on the surface or to react with water to form films of hydroxide thus interferring with plating.
• This invention is characterized in that after removing most of the acids remaining after pickling by washing with water for a short time or without washing with water after pickling, the workpiece is washed with a dehydrating organic solvent to remove acids and water from the surface of the workpiece.
• the solvent suitable for this purpose must mix well with acids and water to remove them perfectly from the metal surface, should not react with the metal of the workpiece, and can readily vapourize or should not adversely effect the plating operation even when such solvent is introduced into the plating bath without being removed from the metal surface.
• ketones and alcohols such as ethylene glycol, methyl alcohol, ethyl alcohol and glycerin are most suitable solvents and that ethers and carboxylic acids are also efliective.
• an inert gas with or without heating, is blasted against the surface to evaporate the remaining solvent, or the Washed workpiece is put in an evacuated vessel to evaporate the solvent.
• the washed workpiece can be immediately immersed in the plating bath along with the organic solvent.
• the surface of the metal workpiece is cleared enough and becomes free from any moisture or oxide film; however, in order to prevent prompt oxidation of the surface of the workpiece before electroplating the workpiece is handled in an inert gas such as nitrogen and argon and is then immersed in the plating bath without being exposed to the atmosphere.
• an inert gas such as nitrogen and argon
• this thin oxide film is dissolved off while the workpiece is immersed in the plating bath.
• the electroplating bath comprising molten salt has a property to dissolve metal oxides, it is possible to dissolve off the metal oxides by immersing the workpiece in the plating bath for a suitable time without passing current through the bath. Dissolution of the oxides can be accelerated by passing alternating current between the plating bath and the workpiece thus removing a small quantity of the oxides on the surface thereof.
• the workpiece is connected to the negative pole of the source to commence an electroplating operation to obtain a firmly bonded plating film.
• Example 1 Sample: titanium alloy (Ti-6 Al-4V) 0. 8 mm. thick x 25 mm. wide x 100 mm. long Treatment: after degreasing and pickling the sample was washed with acetone and then electroplated without drying.
• the sample was degreased by dipping it in petroleum benzene and acetone and then immersed in a mixture of 450 cc. of concentrated nitric acid and 66 cc. of hydrofluoric acid for 1 and one half minutes at room temperature.
• the sample was immediately dipped in acetone and washed while being moved slowly for 10 seconds to completely remove acids remaining on the sample.
• composition of the plated bath consisted of 60 mol percent of aluminum chloride, 25 mol percent of sodium chloride and mol percent of potassium chloride and maintained at a temperature of 160 C.
• Two pure aluminum plates having substantially the same dimensions as the sample were placed in parallel with the sample on the opposite sides thereof and an alternating current of the intensity of 2 a./dm. was passed between the aluminum plates and sample for 3 minutes to clear the surface of the sample.
• aqueduct water hereinafter, merely designated water: To assure perfect washing and rinsing ultrasonic wave vibrations were applied to the water during washing. After washing the sample was dried in hot air.
• Example 2 Sample: Titanium alloy identical to that of Example 1.
• Example 1 The sample was washed with water for 10 seconds while being moved slowly and rinsed with ethyl alcohol for 10 seconds. The sample was then plated with aluminum films under the same conditions of electroplating and with the identical plating bath as in Example 1. The plated sample was Washed with water under supersonic vizrations in the same manner as in Example 1.
• Example 3 Sample: titanium alloy identical to that of Example 1.
• Example 2 In the same maner as in Example 1 the sample was degreased with petroleum benzene and acetone, and then pickled with the mixture of nitric acid and hydrofluoric acid for 1.5 minutes.
• the sample was then washed with water for 10 seconds followed by a rinsing with ethyl alcohol for 10 seconds.
• Example 1 Thereafter the sample was plated With aluminum under the same conditions of electroplating and with the identical molten salt bath as in Example 1.
• Example 4 Sample: titanium alloy identical to that of Example 1.
• Example 1 The sample was again degreased by immersing it in petroleum benzene and acetone and then pickled with the mixture of nitric acid and hydrofluoric acid in the same manner as in Example 1.
• Example 1 Thereafter the sample was washed with water for 10 seconds, rinsed with a 1:1 mixture of glycerine and ethyl alcohol for 10 seconds and then immediately dipped in a plating bath.
• Aluminum plating was performed with the identical molten salt bath and under the same plating conditions as in Example 1.
• Example 6 Sample: titanium alloy identical to that of Example 1.
• Example 1 The sample was degreased with petroleum benzene and acetone and then pickled for 1.5 minutes with the mixture of nitric acid and hydrofluoric acid, in the same manner as in Example 1.
• the sample was washed with water for seconds, rinsed with methyl alcohol for 10 seconds, and then nitrogen gas was blasted against the sample at normal temperature for 30 seconds to evaporate off the methyl alcohol remaining on the surface of the sample.
• Example 1 The sample was plated with aluminum under the same condition of electroplating and with the identical molten salt bath as in Example 1.
• the plated aluminum layer did not peel off during Washing with water under supersonic waves thus showing strong bonding.
• Example 7 Sample: titanium alloy identical to that of Example 1. Treatment: After degreasing, pickling and washing with water, the sample was rinsed with ethyl ether and then immediately plated.
• the sample was degreased with petroleum benzene and acetone pick-led for 1.5 minutes with the mixture of nitric acid and hydrofluoric acid.
• Example 1 Thereafter the sample was washed with water for 10 seconds, rinsed with ethyl ether for minutes, and then immediately immersed in the plating bath to be plated with aluminum under the same conditions and with a molten salt bath identical to that of Example 1.
• the plated aluminum layer peeled off only at one point during washing with water under supersonic waves but other points showed good bonding.
• Example 8 Sample: titanium alloy identical to that of Example 1.
• Example 2 In the same manner as in Example 1, the sample was degreased by dipping it in petroleum benzene and acetone and then pickled for 1.5 minutes with the mixture of nitric acid and hydrofluoric acid.
• Example 1 After washing with water for 10 seconds, the sample was rinsed with acetic acid anhydride for 20 seconds and then immediately dipped in the plating bath to be plated with aluminum film under the same conditions and with an identical molten salt bath as that of Example 1.
• titanium alloy plates can be plated with aluminum layers having a high bonding force by the method of this invention.
• the following examples are shown to compare the results of this invention as aplied to a titanium alloy having a composition of Ti, 8 Al, 1 Mo and 1 V which has been considered diflicult to plate with aluminum platings diflicult to peel off.
• Example 9 Sample: titanium alloy of the composition of Ti, 6 Al and 4 V of the dimension of 0.8 mm. thick x 100 mm. wide x 150 mm. long.
• the sample was degreased by washing it with petroleum benzene, and then immersing it in acetone for one minute.
• the sample was immediately dipped in acetone and moved slowly to completely remove the acids remaining on the sample. Thereafter the sample was immediately immersed in a plating bath while still wetted with acetone.
• the plating bath used was a molten salt bath having a composition of 60 mol percent of aluminum chloride anhydride, 25 mol percent of sodium chloride and 15 mol percent of potassium chloride maintained at a temperature of 160 C.
• Aluminum was then plated with the sample connected to act as the cathode and aluminum plates as the anode at a current density of about 0.4 "a./dm. for the first five minutes and at a current density of 2 a./dm. for a subsequent 35 minutes.
• the reason for using low current density during the initial period and increasing it later to the normal current density is to improve the adhesion of the plated film to corners and peripheries where the current density becomes higher.
• Example 2 In the same manner as in Example 1 the plated sample was washed with water under supersonic waves and then dried with hot air.
• Aluminum plating formed in this manner had a thickness of about 10 microns and purely white appearance and did not peel off under ultrasonic waves.
• the aluminum plating was also subjected to a peening treatment by blasting minute beads of glass With compressed air against the plated sample.
• plated layers of poor bonding generally tend to peel oif from the substrate and swell.
• the plated aluminum layer plated by the method of this invention did not swell and maintained its silver white beautiful metallic luster appearance even when subjected to the peening operation. This means that the plated layers of this invention have an excellent adhesive property.
• Example 10 Sample titanium alloy of the composition of Ti, 8 Al, 1 Mo and 1 V and having dimensions of 1 mm. thick, 25 mm. wide and mm. long.
• Example 11 shows examples wherein aluminum layers were electroplated on aluminum substrates in a molten bath of aluminum salt.
• Example 11 Sample: diecast aluminum alloy (Federal, A 13, Si 12%) having dimensions of 10 mm. thick, 75 mm. wide and 150 mm. long.
• the sample was washed with petroleum benzene and then degreased by dipping it in acetone for one minute. Then the sample was dipped in a mixture of 360 cc. of 63% nitric acid and 40 cc. of 46% hydrofluoric acid for 30 seconds at room temperature.
• the sample was immediately dipped in acetone and washed with it while being moved slowly for 5 seconds to completely remove the acids remaining on the sample. While still wetted with acetone, the sample was dipped in a plating bath consisting of 60 mol percent of aluminum chloride anhydride, 25 mol percent of sodium chloride and 15 mol percent of potassium chloride and maintained at a temperature of 160 C. The surface of the sample was activated in the same manner as in Example 1. Then the sample was plated with aluminum by connecting the sample to act as the cathode and the aluminum plates as the anode. For the first minutes the current density was maintained at about 0.4 a./dm. while in a subsequent stage the current density was increased to 2 a./dm. This current was passed for 90 minutes.
• the sample was taken out from the plating bath, thoroughly washed with a large quantity of running water and then rinsed with water under supersonic vibrations. After rinsing the sample was dried with hot air.
• the resulted aluminum plating had a thickness of about 25 microns and purely white appearance.
• the plated layer was adhered uniformly and did not peel off by washing under supersonic vibrations.
• Example 12 Sample: plated aluminum of Example 11. Treatment: after degreasing and pickling the sample was washed with acetone and then plated without drying.
• Example 11 After degreasing the sample by dipping it in petroleum benzene and acetone, the sample was again dipped for seconds in an identical mixture of nitric acid and hydrofiuoric acid to that employed in Example 11.
• Example 11 Thereafter, the sample was washed with acetone to completely remove the remaining acids, and then immersed at once in the plating bath while wetted with acetone to apply an additional aluminum layer by the same plating steps as in Example 11.
• Example 13 Sample: aluminum foil Treatment: after degreasing and pickling, the sample was rinsed with acetone and then immediately plated with out drying.
• Example 11 For example, five plating operations were repeatedly applied for an aluminum foil of 100 microns thick under the same conditions as in Example 11 and the thickness of the resulted aluminum film was determined to be 120 microns by measuring it with a micrometer.
• Example 14 Sample: diecast aluminum alloy, (Federal A 380 containing 8.5% of Si and 3.5% of copper) having dimensions of 10 mm. thick, 75 mm. wide and 150 mm. long.
• Example 11 The sample was treated in the same manner as in Example 11. After electroplating, a pure aluminum coating was obtained having a thickness of 25 microns, strong bonding strength and beautiful appearance.
• Examples 15 through 17 show the application of this invention wherein fasteners of chromium steel and titanium alloy were electroplated with aluminum by using a molten aluminum salt bath.
• Example 15 Sample: a fastener of chromium steel Treatment: after degreasing and pickling, the sample was washed twice with acetone and then immediately plated without drying.
• fasteners made of A181 HH steel were contained in a wire net bag of Saran (Vinylidene Chloride, registered trade name) and dipped in acetone to degrease them. Then the fasteners contained in the Saran bag were immersed in a mixture of 4% boric acid and hydrofluoric acid contained in a polyethylene beaker. Ultrasonic waves of 29 kc., 300 w. were applied through the bottom of the beaker to wash the fasteners for 2 minutes at room temperature.
• the plating bath consisted of 60 mol percent of aluminum chloride anhydride and 40 mol percent of sodium chloride, and was maintained at a temperature of 160 C.
• the operation of the plating apparatus was started by passing an alternating current for 2 minutes between aluminum plates and fasteners. Thereafter, the flow of the alternating current was interrupted and immediately thereafter a DC current of 40 a. was passed with the fasteners connected to act as the cathodes and aluminum plates as the anodes. After 45 minutes the flow of DC current was interrupted to stop the plating operation.
• the plated fasteners were taken out of the plating bath, thoroughly washed with a large quantity of running water to remove remaining molten salt and then rinsed with distilled water for one minute under ultrasonic wave vibrations. Finally the plated fasteners were dried under heat by a centrifugal drier.
• the plated fasteners were then subjected to a peening treatment for 5 minutes with glass beads (having diameters of about microns) to obtain silver white and beautiful aluminum films of 10 to 12 microns thick and having a metallic luster.
• Example 16 Sample: fasteners of chromuim steel Treatment: after degreasing and pickling, the sample was washed twice with acetone, dried with hot nitrogen gas and then plated.
• the fasteners in the acid solution were transferred into a basket of stainless steel and then dipped in acetone so as to remove remaining acid by moving the basket. This washing operation was repeated with fresh acetone.
• Fasteners washed with acetone were then dried by a hot nitrogen atmosphere and then placed in an aluminum plating bath consisting of 60 mol percent of aluminum chloride anhydride and 40 mol percent of sodium chloride and maintained at a temperature of 160 C.
• the plating apparatus was started by passing an alternating current of 50 a. for two minutes between the fasteners to be plated and aluminum plates.
• the plated fasteners were taken out of the plating bath, thoroughly washed with water for 10 minutes, and then rinsed with distilled water under ultrasonic vibrations to completely remove chloride remaining on the fasteners. Thereafter the plated fasteners were heat dried in a centrifugal drier.
• the plated fasteners were subjected to a peening treatment with glass beads of the diameter of about 100 microns in a peening barrel.
• glass beads of the diameter of about 100 microns in a peening barrel.
• Fasteners plated with aluminum as above described were treated with a chromium sulphate solution, then treated with a chromate treating solution, washed with Water and dried.
• the platings had an apperance of yellow to orange colour and improved weather proofness and resistance to brine.
• Example 17 Sample: fasteners of titanium alloy Treatment: after degreasing and pickling, the sample was washed twice with acetone, dried with nitrogen gas and then plated.
• the molten plating bath used comprised 60 mol percent of aluminum chloride (anhydrous) and 40 mol percent of sodium chloride. It was maintained at a temperature of 160 C.
• the plating device was started by passing an alternating current of 50 a. between the fasteners and aluminum plates for 5 minutes. After interrupting the flow of alternating current, a DC current of a. was passed for 5 minutes by connecting the aluminum plates to the positive pole and the fasteners to the negative pole of the DC source and thereafter current was increased to 40 a. This current was passed for 45 minutes. Thereafter the operation of the plating device was stopped and plated fasteners were taken out of the plating device, washed with a large quantity of water and rinsed twice with distilled water under supersonic wave vibrations.
• the fasteners were dried by a centrifugal drier and then subjected to a peening treatment utilizing glass beads to obtain beautiful silver white aluminum platings of 11 to 12 microns thick which did not peel off or swell.
• Examples 18 to 20 show the application of this invention to aluminum plating on stainless steel substrates by using a molten aluminum salt bath.
• Example 18 Sample stainless steel A151 304 containing 18% of chromium and 10% of nickel and having dimensions of 1.0 mm. thick, 25 mm. wide and mm. long.
• the sample was washed with a mixture of 450 cc. of concentrated nitric acid and 66 cc. of 49% hydrofluoric acid for 2 minutes .at room temperature followed by washing with a running water for 20 seconds. Immediately thereafter, the sample was put into an evacuated vessel to remove water remaining on the surface of the sample. Then the vacuum was broken by the admission of nitrogen gas to dip the sample in the plating bath without exposing it to the atmosphere.
• the plating bath consisted of 60 mol. percent of an hydrous aluminum chloride, 25 mol percent of sodium chloride and 15 mol percent of potassium chloride. It was maintained at a temperature of C.
• Two pure aluminum rods were placed in the aluminum bath in parallel with the sample on the opposite side thereof and an alternating current of one a. (50 cycles) was passed for three minutes between aluminum rods and the sample to clean the surface of the sample.
• the sample was taken out of the plating bath, immediately washed with a large quantity of water, rinsed with water under ultrasonic wave vibrations and finally dried with hot air.
• the aluminum layer plated on the surface of the stainless steel sample had a thickness of about 8 microns and pure white smooth surface.
• Example 19 Sample: stainless steel Treatment: after degreasing and pickling, the sample was washed with water, rinsed with methyl alcohol, dried in vacuum and then plated.
• the degreasing and pickling steps for the sample were the same as those of Example 18. After pickling, the sample was washed with water for 10 seconds, washed with methyl alcohol for 20 seconds for the purpose of accelerating drying and dried in an evacuated vessel. Then the vacuum was broken by introducing nitrogen into the vessel, and then the sample was dipped in the plating bath While preventing it from being exposed to the atmosphere.
• composition of the plating bath and the conditions of electrolysis were the same as those of Example 18.
• the aluminum layer plated in this manner on the surface of the stainless steel sample had a thickness of about 8 microns and strong bonding force similar to that of Example 18.
• the sample was washed with water for 6 seconds, rinsed with acetone for 18 seconds, and then immediately put in an evacuated vessel to remove the acetone remaining on the surface of the sample.
• the vacuum was then broken by admitting nitrogen gas into the vessel and dipping the vessel in a plating bath while preventing the sample from being exposed to the atmosphere.
• composition of the plating bath and the conditions of electrolysis were the same as those of Example 18.
• Example 21 shows the application of this invention to the electroplating of an aluminum layer on a substrate of metallic chromium by using a molten bath of aluminum salt.
• Example 21 Sample: metallic chromium (steel stock, 1.0 mm. thick,
• the sample was dipped in an aqueous solution of 50% caustic potassium for 4 minutes at a temperature of 80 C. After washing with water, the sample was pickled with the same mixture of nitric acid and hydrofluoric acid as that used in Example 18, for 15 seconds at room temperature. Then the sample was washed with water for 30 seconds, rinsed with acetone to remove moisture and then plated with aluminum under the same conditions and with the identical plating bath as those of Example 18.
• this invention provides a novel method of electroplating metals or alloys readily oxidizable in the air under clean conditions of the surface quite free from oxides. For this reason, it is possible to directly electroplate dense metal layers without using any intermediate layer, on metals which have been considered diflicult to be applied with plated layers by the prior techniques or even when plated layers are applied these layers tend to peel off readily. For this reason, this invention finds many applications in wide fiields with satisfactory results.
• titanium alloys and chromium steel of high tensile strength are also used in a large quantity, and the corrosion proof property of these metals can also be increased by plating them with aluminum 12 coatings by the method of this invention.
• Especially such coatings are efiicient when they are used in contact with aluminum alloys. In this manner, this invention is expected to be used extensively in the airplane industry.
• a method of electroplating a substrate with aluminum said substrate being selected from the group consisting of a metal and a metal alloy which is readily oxidized in the air to form a dense oxidized film on the surface thereof, comprising the sequential operations of (a) pickling said substrate with a mixture of nitric acid and hydrofluoric acid or a mixture of boric acid and hydrofluoric acid,

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
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• Electrochemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Electroplating Methods And Accessories (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

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• 1969
  • 1969-08-26 JP JP44067048A patent/JPS4928572B1/ja active Pending
• 1970
  • 1970-08-13 GB GB3901170A patent/GB1312723A/en not_active Expired
  • 1970-08-14 US US63938A patent/US3699013A/en not_active Expired - Lifetime
  • 1970-08-22 DE DE19702041728 patent/DE2041728A1/de active Pending
  • 1970-08-24 SE SE11474/70A patent/SE367658B/xx unknown
  • 1970-08-25 FR FR7031052A patent/FR2059685B1/fr not_active Expired
  • 1970-08-26 CH CH1276970A patent/CH538547A/fr not_active IP Right Cessation
  • 1970-08-26 SU SU1475034A patent/SU368762A3/ru active

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