Classifications

• • 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
  • C25D5/10—Electroplating with more than one layer of the same or of different metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K11/00—Resistance welding; Severing by resistance heating
  • B23K11/34—Preliminary treatment
• • 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
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
  • C23C14/14—Metallic material, boron or silicon
  • C23C14/16—Metallic material, boron or silicon on metallic substrates or on substrates of boron or silicon
• • 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
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
  • C23C2/06—Zinc or cadmium or alloys based thereon

Definitions

• the invention concerns a process for preparing a zinc coated ferrous metal substrate having improved resistance spot welding characteristics consisting of the steps of applying on a ferrous metal substrate separate layers of metallic zinc and of metallic iron, the outermost layer being a metallic iron layer which promotes the ease with which a plurality of said zinc coated ferrous metal substrates may be welded by resistance spot welding, the said outermost metallic iron layer being applied on a metallic zinc layer by electrodeposition from an aqueous iron plating solution or by vacuum deposition.
• the present invention relates to a process'for forming a zinc-iron coating on a steel substrate.
• Zinc coated or galvanised steel is widely used throughout industry, for example in the motor car industry.
• One problem found in the use of zinc coated sheet steel is apparent when such bodies have to be welded.
• zinc coated steel steets are normally welded by resistance spot welding where it is necessary to use higher welding currents than when welding uncoated steel.
• the life of the welding electrodes is consequently much reduced.
• iron has been introduced into the zinc coating, for example, see the article by H. A. Jahnle in the British Welding Journal 15 (3) 1968 at 1 l3-l 19.
• a process for preparing a zinc coated ferrous metal substrate having improved resistance spot welding characteristics consisting of the steps of applying on a ferrous metal substrate separate layers of metallic zinc and of metallic iron, the outermost layer being a metallic iron layer which promotes the ease with which a plurality of said zinc coated ferrous metal substrates may be welded by resistance spot welding, the said outermost metallic iron layer being applied on a metallic zinc layer by electrodeposition from an aqueous iron plating solution or by vacuum deposition.
• a process of welding comprising the step of welding a plurality of ferrous metal substrates by resistance spot welding, the said ferrous metal substrates having separate layers of metallic zinc and of metallic iron thereon, the outermost layer of the said separate layers of metallic zinc and metallic iron being a metallic iron layer which promotes the ease with which the said plurality of ferrous metal substrates may be welded by resistance spot welding.
• the layers of both zinc and iron may be produced by electrodeposition or by vacuum deposition.
• the layer or layers of zinc may be produced by hot dip galvanising.
• the outermost layer of iron which has substantial corrosion resistance, preferably has a thickness of between 1 and 4 microns, and preferably has a thickness of between 4% and of that of the metallic zinc layer.
• the zinc layer may be substantially twice as thick as the iron layer.
• the thickness of the metallic zinc layer is about 2 to 3 microns, that of the metallic iron layer is desirably 1 micron, while if a metallic zinc layer having a thickness of between 20 and 25 microns is applied to the ferrous metal substrate, e.g. by hot dipping, the metallic iron layer may be 3 microns in thickness.
• the layers may be constituted by one zinc and one iron layer only, or by a number of (normally alternately arranged) zinc and iron layers, the iron layer being outermost.
• the substrate is preferably cathodically polarised relative to a plating solution in which the substrate is immersed during the electrodeposition of each said layer.
• the pH value of the iron plating solution be maintained at a predetermined value to avoid the nodular formation of iron deposits and in general, the pH value should be below 2.
• the electrodeposition of zinc onto an iron substrate is a well known process but the converse process whereby iron is deposited electrolytically onto a zinc substrate or a Zinc coated substrate presents difficulties. Since zinc is cathodic relative to iron it is necessary to avoid the formation of an immersion coating of iron which tends to be non-uniform and poorly adherent so far as the zinc based substrate is concerned. In order to achieve this, it is necessary for the zinc based substrate to be cathodically polarised during the time that it is in contact with the iron plating solution.
• a composite coating can be built up which consists of any desired number of layers of zinc and iron, an iron layer being outermost.
• the thickness of each layer depends only upon the quantity of electricity passed in producing the layer and hence the composition of the coating is readily controllable.
• a coating plant of the type used at present for electrogalvanising is easily adapted to carry out this invention.
• EXAMPLE I Two plating tanks constructed from polyvinyl chloride and of similar size were used. 'One tank constituting a zinc plating bath has pure zinc anodes afiixed to the inner surface of its walls and the other tank constituting an iron plating bath had mild steel anodes affixed to the inner surfaces of its walls. The anodes were housed in porous polypropylene bags and each tank contained the appropriate plating solution which was maintained at 50 C.
• the zinc plating solution consisted of 1 M zinc sulphate and sufiicient sulphuric acid to give the solution a pH value of 2.
• the iron plating solution consisted of 1 M ferrous sulphate, 0.15 M ferrous chloride, 0.4 ml./l. of Teepol (registered trademark) and suflicient sulphuric acid to give the solution a pH value of 1.7.
• a source of electric power was provided to give an electrolytic plating current density in the order of 1000 a./m.
• the steel sheet to be treated was degreased and etched in 20% v./v. sulphuric acid at room temperature, then 4 rinsed with water and dipped in sulphuric acid of pH value 1.
• the steel sheet was immersed into the zinc plating tank and cathodically polarised therein.
• the steel was removed from the zinc plating tank, rinsed with water and dipped into the dilute sulphuric acid with a pH value of 1.
• the sheet was then placed into the iron plating tank and cathodically polarised therein.
• the sheet was maintained in the iron plating tank for a duration of time sufficient to produce a desired thickness of iron coating, again for example 30 seconds.
• the sheet was then removed from the iron plating solution, rinsed with water and dipped into the dilute sulphuric acid.
• the washed sheet was then cathodically polarised and re-immersed into the zinc plating solution. This process was repeated so that a number of alternate layers of zinc and iron were produced, the outermost layer being a metallic iron layer.
• Each metallic zinc layer was about 1.4 microns in thickness and each metallic iron layer was about 1 micron in thickness.
• EXAMPLE II A hot dipped galvanised steel sheet, having a metallic zinc layer about 25 microns in thickness, was etched by dipping, for a period of 5 to 10 seconds, in 20 v./v. sulphuric acid at room temperature. After rinsing in water, the sheet was dipped in a solution of sulphuric acid of pH 1. The zinc coated sheet was next immersed in an iron plating solution which consisted of 1 molar ferrous sulphate, 0.15 molar ferrous chloride, and 0.4 mL/Iitre of a wetting agent such as Teepol. The pH of the iron plating solution was 1.7. Plating was continued for 60 seconds at a current density of 1000 a./m. so as to produce an outermost metallic iron layer having a thickness of about 2.5 microns. After plating, the sheet was washed with water and dried.
• the iron could have been deposited from any known iron plating solution, e.g. a ferrous chloride solution.
• EXAMPLE III As illustrated in the accompanying drawing, a steel strip 1, having opposite surfaces 2, 3 was passed through an entry seal 4 into a vacuum chamber 5 and withdrawn therefrom through an exit seal 6. The pressure in the vacuum chamber 5 was maintained by the use of vacuum pumps (not shown) at l0- torr.
• the surface 2 passed above and adjacent to successively arranged zinc evaporation and iron evaporation crucibles 15, 16 respectively, while in travelling over the second horizontal run 14, the surface 3 passed above and adjacent to successively arranged zinc evaporation and iron evaporation crucibles 15, 16 respectively.
• each of the opposite sides of the strip 1 was coated successively with zinc and iron layers, the iron layer being outermost.
• the zinc in the crucibles 15 was heated by means of electrically heated immersion heaters (not shown), whilst the iron in the crucibles 16 was heated by an electron beam gun (not shown).
• the thicknesses of the zinc and iron layers which were for instance 2.5 microns and 1.5 microns respectively.
• EXAMPLE IV 3 The process was the same as in Example III above, except that the steel strip 1 already had zinc layers on its surfaces 2, 3 prior to entering the vacuum chamber 5 since it was a hot dipped galvanised steel strip. Accordingly, the zinc evaporation crucibles were omitted.
• spot welds were performed on a number of samples of hot dipped galvanised steel.
• One of the samples had no iron layers (i.e. was a conventional hot dipped galvanised steel), the other samples having outermost iron layers of varying thickness.
• the number of spot welds performed on each sample before there was a need to dressing the welding electrode was counted. The results are indicated in Table II below.
• a process for preparing a zinc coated ferrous metal substrate having increased corrosion resistance and imthe spot welding proved resistance spot welding characteristics consisting of the steps of applying on a ferrous metal substrate separate layers of metallic zinc and of metallic iron, the outermost layer being a substantially continuous metallic iron layer which increases the corrosion resistance and promotes the ease with which a plurality of said zinc coated ferrous metal substrates may be welded by resistance spot welding, the said outermost substantially continuous metallic iron layer being applied on a metallic zinc layer by electrodeposition from an aqueous iron plating solution or by vacuum deposition and being unalloyed with the metallic zinc layer, the said outermost metallic iron layer being applied in a thickness bet-ween 4% and of that of the metallic zinc layer and having a thickness of at least 0.5 micron, and the metallic zinc layer on which the said outermost metallic iron layer is applied being applied by vacuum deposition or hot dip galvanizing.
• a process as claimed in claim 1 comprising the sequential steps of washing the ferrous metal substrate, dipping the said substrate into a dilute acid, and immersing the said substrate in an electrolytic tank containing an iron plating solution with the said substrate cathodically polarised relative to said second plating solution.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrochemistry (AREA)
• Electroplating Methods And Accessories (AREA)

Applications Claiming Priority (1)

Publications (1)

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Cited By (2)

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• 1969
  • 1969-07-02 GB GB32155/68A patent/GB1281872A/en not_active Expired
  • 1969-07-03 FR FR6922523A patent/FR2012367A1/fr not_active Withdrawn
  • 1969-07-04 BE BE735685D patent/BE735685A/xx unknown
  • 1969-07-04 SE SE6909517A patent/SE374139B/xx unknown
  • 1969-07-04 NL NL6910295.A patent/NL164332C/xx not_active IP Right Cessation
• 1972
  • 1972-03-13 US US00234010A patent/US3843494A/en not_active Expired - Lifetime

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