CA1209947A - Chromate composition and process for treating zinc- nickel alloys - Google Patents
Chromate composition and process for treating zinc- nickel alloysInfo
- Publication number
- CA1209947A CA1209947A CA000419161A CA419161A CA1209947A CA 1209947 A CA1209947 A CA 1209947A CA 000419161 A CA000419161 A CA 000419161A CA 419161 A CA419161 A CA 419161A CA 1209947 A CA1209947 A CA 1209947A
- Authority
- CA
- Canada
- Prior art keywords
- zinc
- nickel alloy
- solution
- chromating
- nickel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 229910000990 Ni alloy Inorganic materials 0.000 title claims abstract description 55
- QELJHCBNGDEXLD-UHFFFAOYSA-N nickel zinc Chemical compound [Ni].[Zn] QELJHCBNGDEXLD-UHFFFAOYSA-N 0.000 title claims abstract description 55
- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical compound [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 title claims abstract description 49
- 238000000034 method Methods 0.000 title claims description 17
- 230000008569 process Effects 0.000 title claims description 11
- 239000000203 mixture Substances 0.000 title description 7
- 238000004532 chromating Methods 0.000 claims abstract description 51
- 239000002659 electrodeposit Substances 0.000 claims abstract description 45
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims abstract description 36
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 18
- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 claims abstract description 17
- 238000000576 coating method Methods 0.000 claims abstract description 15
- 239000011248 coating agent Substances 0.000 claims abstract description 8
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims abstract description 6
- 230000002378 acidificating effect Effects 0.000 claims abstract description 5
- 238000005868 electrolysis reaction Methods 0.000 claims abstract description 4
- 239000000243 solution Substances 0.000 description 50
- 238000005260 corrosion Methods 0.000 description 33
- 230000007797 corrosion Effects 0.000 description 33
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 15
- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 description 15
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 description 15
- 239000011701 zinc Substances 0.000 description 15
- 229910052725 zinc Inorganic materials 0.000 description 15
- 229910000831 Steel Inorganic materials 0.000 description 13
- 239000010959 steel Substances 0.000 description 13
- 238000012360 testing method Methods 0.000 description 13
- 239000000758 substrate Substances 0.000 description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 12
- 229910045601 alloy Inorganic materials 0.000 description 10
- 239000000956 alloy Substances 0.000 description 10
- 238000011282 treatment Methods 0.000 description 10
- 239000011651 chromium Substances 0.000 description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 8
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 8
- 230000001976 improved effect Effects 0.000 description 8
- 230000015572 biosynthetic process Effects 0.000 description 7
- 238000005755 formation reaction Methods 0.000 description 7
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 6
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 6
- 229910052804 chromium Inorganic materials 0.000 description 5
- 229910052742 iron Inorganic materials 0.000 description 4
- 150000003839 salts Chemical class 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- 241001163841 Albugo ipomoeae-panduratae Species 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- GRWVQDDAKZFPFI-UHFFFAOYSA-H chromium(III) sulfate Chemical compound [Cr+3].[Cr+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O GRWVQDDAKZFPFI-UHFFFAOYSA-H 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 238000005562 fading Methods 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- 229910002651 NO3 Inorganic materials 0.000 description 2
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 239000003929 acidic solution Substances 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000012141 concentrate Substances 0.000 description 2
- 238000007654 immersion Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 230000007935 neutral effect Effects 0.000 description 2
- 235000021317 phosphate Nutrition 0.000 description 2
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- 150000003467 sulfuric acid derivatives Chemical class 0.000 description 2
- NWONKYPBYAMBJT-UHFFFAOYSA-L zinc sulfate Chemical compound [Zn+2].[O-]S([O-])(=O)=O NWONKYPBYAMBJT-UHFFFAOYSA-L 0.000 description 2
- JHWIEAWILPSRMU-UHFFFAOYSA-N 2-methyl-3-pyrimidin-4-ylpropanoic acid Chemical compound OC(=O)C(C)CC1=CC=NC=N1 JHWIEAWILPSRMU-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- FMRLDPWIRHBCCC-UHFFFAOYSA-L Zinc carbonate Chemical compound [Zn+2].[O-]C([O-])=O FMRLDPWIRHBCCC-UHFFFAOYSA-L 0.000 description 1
- 229910001297 Zn alloy Inorganic materials 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000001464 adherent effect Effects 0.000 description 1
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- -1 alkali metal chromates Chemical class 0.000 description 1
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 1
- 229910000318 alkali metal phosphate Inorganic materials 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 238000001479 atomic absorption spectroscopy Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 150000001735 carboxylic acids Chemical class 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- MCWXGJITAZMZEV-UHFFFAOYSA-N dimethoate Chemical compound CNC(=O)CSP(=S)(OC)OC MCWXGJITAZMZEV-UHFFFAOYSA-N 0.000 description 1
- 229910000397 disodium phosphate Inorganic materials 0.000 description 1
- 238000004070 electrodeposition Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 229910000008 nickel(II) carbonate Inorganic materials 0.000 description 1
- ZULUUIKRFGGGTL-UHFFFAOYSA-L nickel(ii) carbonate Chemical compound [Ni+2].[O-]C([O-])=O ZULUUIKRFGGGTL-UHFFFAOYSA-L 0.000 description 1
- BFDHFSHZJLFAMC-UHFFFAOYSA-L nickel(ii) hydroxide Chemical compound [OH-].[OH-].[Ni+2] BFDHFSHZJLFAMC-UHFFFAOYSA-L 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- HLBBKKJFGFRGMU-UHFFFAOYSA-M sodium formate Chemical compound [Na+].[O-]C=O HLBBKKJFGFRGMU-UHFFFAOYSA-M 0.000 description 1
- 235000019254 sodium formate Nutrition 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- 239000011667 zinc carbonate Substances 0.000 description 1
- 235000004416 zinc carbonate Nutrition 0.000 description 1
- 229910000010 zinc carbonate Inorganic materials 0.000 description 1
- UGZADUVQMDAIAO-UHFFFAOYSA-L zinc hydroxide Chemical compound [OH-].[OH-].[Zn+2] UGZADUVQMDAIAO-UHFFFAOYSA-L 0.000 description 1
- 229910021511 zinc hydroxide Inorganic materials 0.000 description 1
- 229940007718 zinc hydroxide Drugs 0.000 description 1
- 239000011787 zinc oxide Substances 0.000 description 1
- 229960001763 zinc sulfate Drugs 0.000 description 1
- 229910000368 zinc sulfate Inorganic materials 0.000 description 1
- 239000011686 zinc sulphate Substances 0.000 description 1
- 235000009529 zinc sulphate Nutrition 0.000 description 1
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
- C25D5/48—After-treatment of electroplated surfaces
-
- 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
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/24—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/38—Chromatising
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention includes an aqueous acidic chromate solution, suitable for forming colored chromate coatings on zinc-nickel alloy electrodeposits containing up to about 15% by weight nickel, which solutions have a pH
within the range of about 1.3 to about 2.7, a hexavalent chromium concentration of at least 0.5 grams per liter, and preferably about 0.5 to 100 grams per liter, and which con-tain sulfate in a weight ratio of SO4:Cr+6 of about 0.025-1.5:1. The zinc-nickel alloy electrodeposits are preferably immersed in the chromating solution for a period sufficient to form the desired colored chromate coating. Alterna-tively, the zinc-nickel alloy electrodeposit may be immer-sed in the chromating solution and the solution electroly-zed, with the zinc-nickel alloy surface as the anode, at low current densities for a short period of time, after which, the electrolysis is discontinued and the zinc-nickel alloy surface is maintained in the chromating solution until the desired colored chromate film is formed.
The present invention includes an aqueous acidic chromate solution, suitable for forming colored chromate coatings on zinc-nickel alloy electrodeposits containing up to about 15% by weight nickel, which solutions have a pH
within the range of about 1.3 to about 2.7, a hexavalent chromium concentration of at least 0.5 grams per liter, and preferably about 0.5 to 100 grams per liter, and which con-tain sulfate in a weight ratio of SO4:Cr+6 of about 0.025-1.5:1. The zinc-nickel alloy electrodeposits are preferably immersed in the chromating solution for a period sufficient to form the desired colored chromate coating. Alterna-tively, the zinc-nickel alloy electrodeposit may be immer-sed in the chromating solution and the solution electroly-zed, with the zinc-nickel alloy surface as the anode, at low current densities for a short period of time, after which, the electrolysis is discontinued and the zinc-nickel alloy surface is maintained in the chromating solution until the desired colored chromate film is formed.
Description
This invention relates to a composition and process for forming colored chromate coatings on zinc-nickel alloy surfaces an~, more particularly, relates to composit;ons and proccsses for forming colored chromate coatings on electrodeposited zinc-nicke1 alloy surfaces to provide a composite coating having improved corrosion resistanse as compared to that obtained with zinc electrodeposits.
The use of zinc electrodeposits on iron or steel substrates to provide improved corrosion protection has long been practiced. Although such zinc 1~ electrodeposits greatly enhance the corrosion resistance oF the iron or steel substrate, the zinc itself forms white "rust" or corrosion ~hich, ultimately, can result in the corrosion of the iron or ; steel substrate itself with the consequent ~ormation of red rust. To minimize this and impro~e the corrosion ;~
' resistance of the zinc electroplated substrates, it has commonly been the practice to treat such surfaces ~lith an acidic, hexavalent chromium containing solution to form a visible or colored chromate passivating film on the surface. Typical compositions and process for forming such chromate passivating films are disclosed in U.S. patents 2~021,592; 27106,904; 2,288,007;
The use of zinc electrodeposits on iron or steel substrates to provide improved corrosion protection has long been practiced. Although such zinc 1~ electrodeposits greatly enhance the corrosion resistance oF the iron or steel substrate, the zinc itself forms white "rust" or corrosion ~hich, ultimately, can result in the corrosion of the iron or ; steel substrate itself with the consequent ~ormation of red rust. To minimize this and impro~e the corrosion ;~
' resistance of the zinc electroplated substrates, it has commonly been the practice to treat such surfaces ~lith an acidic, hexavalent chromium containing solution to form a visible or colored chromate passivating film on the surface. Typical compositions and process for forming such chromate passivating films are disclosed in U.S. patents 2~021,592; 27106,904; 2,288,007;
2,376,1~8; 2,9399664; 29610,133; 2,7~0,891; 3,090,710;
3,404,046; and 3,895,969.
Recently, considerable work has been done to improve the corrosion resistance of zinc electroplated substrates by the substitution of zinc alloy electrodeposits for the substantially pure zinc electrodeposits which have heretofor-e been used.
Although various different metals have been used with the zinc in such alloy electrodeposits, particularly good results, in terms of the improvements in corrosion resistance and the brightness or gloss of the surface, have been obtained with zinc-nickel alloy electrodeposits. Depending upon the nickel content of such zinc-nickel alloy electrodeposits~ the time for ; the formation of red rust in salt spray testing can be as much as five to ten times greater than the time for such red rust formation with zinc electrodeposits.- In spite of this, the formation of white rust or corrosion ' . ~
Recently, considerable work has been done to improve the corrosion resistance of zinc electroplated substrates by the substitution of zinc alloy electrodeposits for the substantially pure zinc electrodeposits which have heretofor-e been used.
Although various different metals have been used with the zinc in such alloy electrodeposits, particularly good results, in terms of the improvements in corrosion resistance and the brightness or gloss of the surface, have been obtained with zinc-nickel alloy electrodeposits. Depending upon the nickel content of such zinc-nickel alloy electrodeposits~ the time for ; the formation of red rust in salt spray testing can be as much as five to ten times greater than the time for such red rust formation with zinc electrodeposits.- In spite of this, the formation of white rust or corrosion ' . ~
4~
on such zinc-nickel alloy deposits is still a problem which must be minimized by the application of a chromate or other passivating film.
It has been found, however, that the formation of a colored or visible chromate film having high corrosion resistance on such z;nc-n;ckel alloy electrodeposits is much more difficult than on zinc ; electrodeposits. In the various patents disclosed hereinabove~ there is no specific disclosure of the treatment of zinc-nickel alloy electrodeposits, although the treatment of 7inc alloy deposits, broadly, i mentioned. Generally, the chromating compositions of these patents have not been effective in producing a satisfactory corrosion resistant chromate film on zinc-nickel alloy electrodeposits. For example, in U.S.
patent 2,106,904, there is disclosed a chromic acid/sulfuric acid solution which contains from about 13 to 104 g/l hexavalent chromium and from about 1.8 to 144 gtl S04, with a weight ratio of hexavlaent chromium:S04 of 0.09-Sg:1. This solution is specified as having a pH which is not in excess of 1.0, and when used for the treatment of zinc-nickel alloy electrodeposits, the resulting chromate film has relatively poor corrosion resistance. This difflculty ..,~
.
. , ~2~ 7 in forming colored chromate film with high corrosion resistance on the zinc-nickel alloy electrodeposits is one reason why such deposits have not been more widely adopted as a replacement for zinc electrodeposits for the production of decorative and corrosion resistant coatings on iron and steel sùbstrates.
The present invention provides an improved chromating composition which will produce excellent colored, corrosion resistant coatings on zinc-nickel alloy electrodeposits~
The present invention also provides an impro-ved process for the forma-tion of colored, corrosion resis-tant chromate films on zinc-nickel alloy electro-deposits.
.
: ~ :
- , According -to the present invention there is provided an aqueous acidic chroma-ting solution suitable for forming colored chromate Eilms on zinc-nickel alloy electrodeposi-ts containing up to about 15~ by weight nickel, which solution has a pH of Erom about 1.3 to about 2.7 and comprises hexa-valent chromium in an amount of at least 0.5 grams per liter and sulEate in a weight ratio of S04-2:Cr 6 of abou-t 0.025-1.5:1.
Typically, such zinc-nickel alloy electrodeposits are immersed in this aqueous acidic chromating solution for a period of time sufficient to form the desired corrosion re-sistant chromate fllm on the alloy surface. Alternatively, the improved corrosion resistant colored chroma-te film may be formed by electrolysis of the zinc-nickel alloy electro-deposit in the chromating solution, using a rela-tively weak electric current with the zinc-nickel alloy surface as the anode prior to the immersion treatment.
on such zinc-nickel alloy deposits is still a problem which must be minimized by the application of a chromate or other passivating film.
It has been found, however, that the formation of a colored or visible chromate film having high corrosion resistance on such z;nc-n;ckel alloy electrodeposits is much more difficult than on zinc ; electrodeposits. In the various patents disclosed hereinabove~ there is no specific disclosure of the treatment of zinc-nickel alloy electrodeposits, although the treatment of 7inc alloy deposits, broadly, i mentioned. Generally, the chromating compositions of these patents have not been effective in producing a satisfactory corrosion resistant chromate film on zinc-nickel alloy electrodeposits. For example, in U.S.
patent 2,106,904, there is disclosed a chromic acid/sulfuric acid solution which contains from about 13 to 104 g/l hexavalent chromium and from about 1.8 to 144 gtl S04, with a weight ratio of hexavlaent chromium:S04 of 0.09-Sg:1. This solution is specified as having a pH which is not in excess of 1.0, and when used for the treatment of zinc-nickel alloy electrodeposits, the resulting chromate film has relatively poor corrosion resistance. This difflculty ..,~
.
. , ~2~ 7 in forming colored chromate film with high corrosion resistance on the zinc-nickel alloy electrodeposits is one reason why such deposits have not been more widely adopted as a replacement for zinc electrodeposits for the production of decorative and corrosion resistant coatings on iron and steel sùbstrates.
The present invention provides an improved chromating composition which will produce excellent colored, corrosion resistant coatings on zinc-nickel alloy electrodeposits~
The present invention also provides an impro-ved process for the forma-tion of colored, corrosion resis-tant chromate films on zinc-nickel alloy electro-deposits.
.
: ~ :
- , According -to the present invention there is provided an aqueous acidic chroma-ting solution suitable for forming colored chromate Eilms on zinc-nickel alloy electrodeposi-ts containing up to about 15~ by weight nickel, which solution has a pH of Erom about 1.3 to about 2.7 and comprises hexa-valent chromium in an amount of at least 0.5 grams per liter and sulEate in a weight ratio of S04-2:Cr 6 of abou-t 0.025-1.5:1.
Typically, such zinc-nickel alloy electrodeposits are immersed in this aqueous acidic chromating solution for a period of time sufficient to form the desired corrosion re-sistant chromate fllm on the alloy surface. Alternatively, the improved corrosion resistant colored chroma-te film may be formed by electrolysis of the zinc-nickel alloy electro-deposit in the chromating solution, using a rela-tively weak electric current with the zinc-nickel alloy surface as the anode prior to the immersion treatment.
- 5 -~ ."
. . , ~l2~9~
The thus-formed chromated coatings are found to provide excellent corro5ion resistance to both white rust and red rust on zinc-nickel alloy electroplated substrates. Additionally, it has been found that the heat resistance to color fading of such films has also been increased.
The improved chromating solutions of the present invention are aqueous acidic solutions having a pH of from about 1.3 to about 2.7 and comprising hexavalent chromium (Cr+6) in an amount of at least 0.5 g/l and sulfate (S04~ in a weight ratio of S04oCr~6 of . about 0 . 025-1 . 5 :1 . Although the maximum concentration of the hexavalent chromium in this solution has not been found to be critical~
amounts up to the maximum saturation of hexavalent chromium in the solution being suitable, where high hexavalent chromium concentraitons are used, the cost of the process is increased and additional treatment of the waste or rinse water is often necessary in order to meet environmental standards. In general, it has been found that the use of hexavalent chromium concentrations in excess o~ about 100 g/l does not provide any significant and further improvement in the corrosion resistance of the chromate ilm.
Accordingly, ~rom the standpoint o practical considerations, hexavalent chromium concentrations in the present chromating solutions of from about 0.5 to about 100 g/l are pre~erred. Where hexavalent chromium concentrations below about 0.5 g/l are used, the resulting chromate film becomes relatively thin and sufficient corrosion resistance is, generally, not obtained.
It has been found to be important in the improved chromating solutions o the present invention, to maintain the weight ratio o S04:Cr+6 within the specified range of from 0.025-1.5:1, preerably 0005-l.0:1.
Where the sulfate to hexavalent chromium ratio is below about 0.025, the desired colored chromate film is not completely formed on the zinc-nickel alloy electrodeposit. Moreover, where the ral-io of sulfate to hexavalent chromium is in excess o about 1.5/
the resulting chromate film is relatively thin and its corrosion resistance is undesirably low.
Similarly, it is important to maintain the pH of the present chromating solution within the prescribed range of about 1.3 to 2.7 preferably 1.4 to 2.2. It has been ` ~L2~47 found that where the pH of the solution is below about 1.3, the resulting chromate film contains a relatively small amount of adherent chromium and, thus, has undesirably low corrosion resistance and an unsat;sfactory color. This finding is somewhat surprising in that with the treatment of zinc electrodeposits, rather than zinc-nickel alloy electrodeposits, using a conventional chromate solution containing 100 g/l CrO3 and 5 g/l H2S0~ with a pH
of 0.5, a colored chromate film having good appearance and corrosion resistance is formed. It has further been found that when the pH of the present chromating solutions is in excess of about 2.73 the reactivity of the chromating solution is reduced and a colored chromate film having good appearance and corrosion resistance is not formed on the zinc-nickel alloy electrodeposit.
The improved chromating solutions of the present invention may be formulated using any bath soluble hexavalent chromium and sulphate compounds, thP
anions or cations of which are not detrimental to the chromating solution or the chromate ~ilm subsequently forrned on the zinc-nickel alloy surface. Typical of 2~ the compounds which may be used are chromic acid, ' sulfuric acid, the alkali metal chromates and dichromates, metallic sulfates, such as zinc sulphate and chromium sulphate, and the like. In this latter regard, it has been found that in some instances, the inclusion of trivalent chromium, typically added as chromium sulphate, may be beneficial in the formation of the desired corrosion resistant chromate film. Even where trivalent chromium is not added to the bath as it is initially made up, it will typically be formed in the bath by reduction of the hexavalent chromium during use~
To adjust the pH of the present chromating solutions, acids, such as chromic acid or sulfuric acid, are typically used where a reduction in the pH is desired. Where the pH is to be raised, alkaline compounds are typically added~ such as the alkali metal hydroxides, zinc oxide, zinc carbonate, zinc hydroxide, nickel carbonate, nickel hydroxide, and the like.
- -In addition to the components which have been noted hereinabove, the chromating baths of the present invention may also contain other components which are typically present in such chromating solutions~ as is known in the art. Exemplary of such other components are phosphates, which may be added as phosphoric acid, or in ~he form of the alkali metal phosphates and acid phosphates and lower carboxylic acids, such as acetic acid or its bath soluble salts. It has been found, however, that the presence of nitrate in the chromating bath or on the surface of the zinc-nickel ailoys to be treated tends to inhibit the formation of the desired chromate film on such alloy electrodeposit surfaces.
Accordingly, in the practice of the present invention~
nitrate-containing compounds are not used in formulating the chromating solutions and the substrates on which the zinc-nickel alloy electrdeposit is formed should not be treated with a nitric acid solution prior to the present chromate treatment.
- The present chromating solutions may be applied to the zinc-nickel alloy electrodeposits containing up to about 15% by weight nickel.
Generally, such alloy deposits will contain at least about 1% nickel, with nickel contents of from about 5-12% by weight being particularly preferred.
Typically, the chromating solutions are applied by immersion of ~he zinc-nickel alloy electrodeposit in the solution, although other application techniques, such as spraying, flooding, and the like, may also be used. When using such application techniques, the zinc-nickel alloy electrodeposit is maintained in contact with the chromating solution for a period of time sufficient to form the desired chromate film on the surface. In many instances, contact times of from about 10 to about 30 seconds are typical 7 although this time may be varied in each instance and both shorter and longer contact times may be used to obtain the desired chromate ~ilm. The temperature of the chromating bath may be from room temperature, e.gO, - about 20C, up to temperatures which approach the boiling point of the solution. Typically, the solution is used at a temperature of from about 25 to about 60C.
It has been found that the surface of the zinc nickel alloy electrodeposit may become inactive or inert if it is exposed to the atmosphere for any significant period of time before being subjected to the chromating treatment. In such instances, it has been found desirable to utilize the chromating solutions at higher temperatures, such as about 35 to 55C, in order to form the desired chromate film.
Where the zinc-nickel alloy electrodeposit is treated with the chromating solutions immediately after electrodeposition of the alloy, the lower solution t~mperatures of 25 to 35~C may be used to satisfactorily obtain the chromate coating.
In this regard, it has further been found that activation of the zinc-nickel alloy electrodeposit surface may also be accomplished by making the zinc-nickel alloy substrate the anode and electrolyzing the substrate in the chromate solution at a relatively low current density. Typically, the electrolysis, with the zinc-nickel alloy electrodeposit surface as the anode, is carried out at a current density of from about 0.01 to about 0.2 A/dm2 for a period of up to about ten (10) seconds. Thereafter, the zinc-nickel alloy's substrate is retained in the chromatiny so!ution, without the application of current, until.the desired chromate film is formed on the surface.
.
~` ` `.
., .
~L2(~ 7 By means of -the process described hereinabove, zinc-nickel alloy electrodeposi-ts containing up to about 15%
by weight nickel are provided with a chromate film having a -thickness of at leas-t about lO0 mg/m2. These films impart a pleasing color -to the alloy surface and provide good corro-sion resis-tance of a magnitude which has heretofore not been possible on zinc-nickel alloy electrodeposi-ts. Moreover, the zinc-nickel alloy electrodeposits containing these chro-mate films are found to have a corrosion resistance which is superior to that of zinc electrodeposits which have been subject to conventional chromating treatments.
: 1 :
~2~ 7 Specific Examples of the Invention In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given:
Example I
An aqueous chromating bath was formulated by dissolving the following components in water in the amounts indicated:
Na2Cr207 2~20 lO g/l ~Cr+~ = 3.43 g/l) ~2S04 2 g/l (S04-2 = l.96 g/l) (SO4~2/Cr+6 = 0.56) pH 1.8 . . .
A steel sheetg electroplated to a thickness of 3 ~m with a zinc-nickel alloy containing 8% by weight nickel was chromated with this solution by immersing the sheet in the solution For fifteen (15) seconds at a temperature of 35~C.
-l4-4~
Example II
An aqueous chromating bath was formulated by dissolving the following components in water in the amounts indicated:
Na2Cr207;2H20 20 9/1 (Cr+6 = 6.g8 9/1) Cr2(S04)2-aqueous solution T 9/1 3 S04-2 = 0-75 9/1) (Cr2 (504)3 content 40% (S04-2/Cr+6 = 0.11) pH 2.1 (adjusted with CrO3) A steel sheet, electroplated to a thickness of lJum with a zinc-nickel alloy containing 8% by weight nickel was chromated in thîs solution by immersing the sheet in the solution for 2~ seconds at 50C.
Example I II
A chromating bath was fcrmulated by dissolving the following components in water in the amounts indicated:
CrO3 2 9/1 (Cr+6 = 1.04 g/l ) H2S04 0.1 9/l (S04-2 = 0.098 9/l ) (S04~2/Cr+5 = 0.094) pH 1.8 ~ 1 5 - ' lZ~ 7 5 A steel sheet, electroplated to a thickness of 3 ~m with a zinc-nickel alloy containing 8% by weight nickel was chromated by immersing the sheet in the solution for fifteen (15) seconds at a temperature of 40C.
Example IV
An aqueous chromating bath was formulated by dissolving the following components in water in the amounts indicated:
Na2Cr207 2H20 30 g/l (Cr+6 = ll.82 g/l) Cr2(S04)3aqueous solut;on T 9ll (S04-2 = 0-96 g/l) (Crz(s04)340% content) (S04~Z/Cr+6 = O~O~TJ
pH 2~0 ~ A steel sheet, electroplated to a thickness of 2 ~m : \ with a zinc-nickel alloy containing 12% by weight nickel ~as chromated by immersing the sheet in the 25 solution while the solution-was electrolyzed at a current density of 0.1 A/dm2 for 5 (five) seconds ::
:.
~ -l6-`, :
' ' ' -: :
~ , : ~ :
with the sheet as the anode. After five (5) seconds, the passage of electric current was discontinued and the sheet was retained in the solution for an additional twenty (20) seconds. The temperature of the 5 chromating solution during the entire treatment was 50-C.
Example V
An aqueous chromating solution was formulated by dissolving the following components in water in the amounts indicated:
CrO3 50 g71~(Cr+6 = 26~0 9/1) lS H2S04 (S04~2/Cr+6 = 0.38) Na2HP04 2 9/1 pH T.~ (adjusted with NaOH) A steel sheet, electroplated to a thickness of 6 ~m with a zinc-nicke1 alloy having a nickel content of 10X
by weight was chromated by immersing the sheet in the chromating bath for ten (10) seconds at a bath temperature of 30C.
, Example VI
An aqueous chromating bath was formulated by dissolving the following components in water in the amounts indicated:
Na2Cr207~2H20~50 g/l (Cr+6 = 52.4 g/l) ~2S4 lO g/l (S04-2 = 9.8 g/l) (S0~~2/Cr~6 = 0.~9 10 HCOONa l.5 g/l pH - - 1.6 A steel sheet, electroplated to a thickness of 3 ~m with a zinc-nickel alloy having a nickel content of 12%
by weight, to which had been applied a flash electrodeposit of zinc having a thickness of 0.1 ~m was chromated by immersing it in this solution for fifteen (15) seconds at a bath temperature of 30C.
23 By way of comparison, the following Examples VII through IX were run:
;
-l8-, , :
..... . ' ., Example VII
!
An aqueous chromating bath was formulated by dissolv;ng the following components in water in the amounts indicated:
CrO3 .~00 9/l (Cr+6 = 52.0 g/l) 4 lO g/l (S04-2 9.8 g/l) pH . 0.6 (S04~2tCr+6 = OI9) A steel sheet, electroplated to a thickness of 3 ~m with a zinc-nickel alloy having a nickel content of 10%
: by weight, was chromated by immersing the sheet in the chromating bath for ten (10) seconds at a bath temperature ~f 30C.
Example VIII
An aqueous chromating bath was formulated by dissolving the following components in water in the amounts indicated: .
_l g_ ~i!LZ~ 7 CrO3 To g/l (Cr+6 5.2 g/1) H2S04 l g/l (S04~Z/Cr+6 = 0.98 9/l) pH l.2 (S04~2/Cr+6 = 0.19) A steel sheet, electroplated to a thickness of 3 ym with a zinc-nickel alloy having a nickel con-tent of 10%
by weight, was chromated by immersing the sheet in the chromating solution for 30 seconds at a bath temperature of 30DC.
:
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The chromated samples prepared in accordance ; with the preceding Examples I through IX were analyzed to determine the chromium content of the chromate coating and were tested for corrosion resistance using the 5% neutral salt spray test and for heat resistance of the chromate coating. The analytical methods and test methods used were as follows:
(1~ Analysis of Cr in the chromate film:
Each test specimen was immersed in an aqueous acidic solution containing 100 gll HCl. The chromate film was oompletely dissolved from the test specimen and the eluted Cr portion was quantitatively analyzed by atomic absorption spectroscopy. The amount of chrom;um determined was expressed in terms of the surface area of the test specimen (miligrams per square meter).
(2) Corrosion resistance test:
Each test specimen was subjected to the 5% neutral salt spray test in accordance with the procedure ASTM-8117 and the time was noted for the .
development of white corrosion products on the surface of the specimen (white rust) and for the development of red corrosion products (red rust) in accordance with ; this procedure.
(3) Heat resistance test:
. Each test specimen was placed in a . thermostated oven and maintained in the oven for twenty-four hours at fixed temperatures of 100p 150, 200, and 250C. Thereafter, each test speciment was removed from the oven and the failure or fading of the chromate film due to the heat was visually observed.
Using thes~ procedures, the test results as shown in the following Table I were obtained:
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a~ . . ~ I s ~I) Vl -- C
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Vl ~ ~1 (L) -- O ~ V) - = = O C ~ = = 3 a~ C ~ =
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~xample X
.
A concentrate composition was formulated containing the following components in the amounts indicated:
sodium dichromate (Na2Cr~07.2H20) 300 971 .
zinc sulfate (ZnS0~7H?aT 15 9/1 chromium sulfate ~Cr2(~04)3 . . . 40% sol.) 30 ml~l chromic acid ~CrO3) 40 9/1 water balance .
A chromating solution was formulated by add;ng the foregoing concentrate solution to water in an amount of SO mililiters per liter. The pH ol this chromating soluton was 1.8 and steel sheets9 electroplated to a thic~ness of 4 ~m with a zinc-nickel alloy containing B.4X by weight nickel, were chromated by immersing the sheets in the chromating solution for 15 seconds while maintaining the bath temperature within the range of 45 - 55C. The results of the testing of the chromate coating produced in accordance with this procedure are found to correspond to the results obtained for Example III.
_z5, t '`
~ , During the operation of ~he process of this Example, the chromating solution is replenished using a replenishing composition containing the following components in the amounts indicated:
chromic acid (CrO3) 300 g/l ! sulfuric acid (H2S04 50 wt. ~) . lQO ml/l Sp. Gr. = 1.4 water balance The pH and CrO3 concentration of the chromating bath is periodically measured and the above replenishing solution is added in amounts necessary to reestablish the pH and CrO3 content of the bath at the levels originally formulated~
. . .
From the foregoing results, it is apparent that the chromating solutions of the present invention provide a colored chromate coating of high quality on 2a 2inc-nickel alloy electrodeposits, which chromate coatings have excellent corrosion resistance, as well as heat r`esistance to color fading. Moreover, the corrosion resistance of the substrates plated with the : zinc-nickel alloy electrodepGsits and chromated in accordance with the present invention is signi~icantly greater than that of substrates plated with zinc electrodeposits which had been chromated using conventional processes.
, .
. . , ~l2~9~
The thus-formed chromated coatings are found to provide excellent corro5ion resistance to both white rust and red rust on zinc-nickel alloy electroplated substrates. Additionally, it has been found that the heat resistance to color fading of such films has also been increased.
The improved chromating solutions of the present invention are aqueous acidic solutions having a pH of from about 1.3 to about 2.7 and comprising hexavalent chromium (Cr+6) in an amount of at least 0.5 g/l and sulfate (S04~ in a weight ratio of S04oCr~6 of . about 0 . 025-1 . 5 :1 . Although the maximum concentration of the hexavalent chromium in this solution has not been found to be critical~
amounts up to the maximum saturation of hexavalent chromium in the solution being suitable, where high hexavalent chromium concentraitons are used, the cost of the process is increased and additional treatment of the waste or rinse water is often necessary in order to meet environmental standards. In general, it has been found that the use of hexavalent chromium concentrations in excess o~ about 100 g/l does not provide any significant and further improvement in the corrosion resistance of the chromate ilm.
Accordingly, ~rom the standpoint o practical considerations, hexavalent chromium concentrations in the present chromating solutions of from about 0.5 to about 100 g/l are pre~erred. Where hexavalent chromium concentrations below about 0.5 g/l are used, the resulting chromate film becomes relatively thin and sufficient corrosion resistance is, generally, not obtained.
It has been found to be important in the improved chromating solutions o the present invention, to maintain the weight ratio o S04:Cr+6 within the specified range of from 0.025-1.5:1, preerably 0005-l.0:1.
Where the sulfate to hexavalent chromium ratio is below about 0.025, the desired colored chromate film is not completely formed on the zinc-nickel alloy electrodeposit. Moreover, where the ral-io of sulfate to hexavalent chromium is in excess o about 1.5/
the resulting chromate film is relatively thin and its corrosion resistance is undesirably low.
Similarly, it is important to maintain the pH of the present chromating solution within the prescribed range of about 1.3 to 2.7 preferably 1.4 to 2.2. It has been ` ~L2~47 found that where the pH of the solution is below about 1.3, the resulting chromate film contains a relatively small amount of adherent chromium and, thus, has undesirably low corrosion resistance and an unsat;sfactory color. This finding is somewhat surprising in that with the treatment of zinc electrodeposits, rather than zinc-nickel alloy electrodeposits, using a conventional chromate solution containing 100 g/l CrO3 and 5 g/l H2S0~ with a pH
of 0.5, a colored chromate film having good appearance and corrosion resistance is formed. It has further been found that when the pH of the present chromating solutions is in excess of about 2.73 the reactivity of the chromating solution is reduced and a colored chromate film having good appearance and corrosion resistance is not formed on the zinc-nickel alloy electrodeposit.
The improved chromating solutions of the present invention may be formulated using any bath soluble hexavalent chromium and sulphate compounds, thP
anions or cations of which are not detrimental to the chromating solution or the chromate ~ilm subsequently forrned on the zinc-nickel alloy surface. Typical of 2~ the compounds which may be used are chromic acid, ' sulfuric acid, the alkali metal chromates and dichromates, metallic sulfates, such as zinc sulphate and chromium sulphate, and the like. In this latter regard, it has been found that in some instances, the inclusion of trivalent chromium, typically added as chromium sulphate, may be beneficial in the formation of the desired corrosion resistant chromate film. Even where trivalent chromium is not added to the bath as it is initially made up, it will typically be formed in the bath by reduction of the hexavalent chromium during use~
To adjust the pH of the present chromating solutions, acids, such as chromic acid or sulfuric acid, are typically used where a reduction in the pH is desired. Where the pH is to be raised, alkaline compounds are typically added~ such as the alkali metal hydroxides, zinc oxide, zinc carbonate, zinc hydroxide, nickel carbonate, nickel hydroxide, and the like.
- -In addition to the components which have been noted hereinabove, the chromating baths of the present invention may also contain other components which are typically present in such chromating solutions~ as is known in the art. Exemplary of such other components are phosphates, which may be added as phosphoric acid, or in ~he form of the alkali metal phosphates and acid phosphates and lower carboxylic acids, such as acetic acid or its bath soluble salts. It has been found, however, that the presence of nitrate in the chromating bath or on the surface of the zinc-nickel ailoys to be treated tends to inhibit the formation of the desired chromate film on such alloy electrodeposit surfaces.
Accordingly, in the practice of the present invention~
nitrate-containing compounds are not used in formulating the chromating solutions and the substrates on which the zinc-nickel alloy electrdeposit is formed should not be treated with a nitric acid solution prior to the present chromate treatment.
- The present chromating solutions may be applied to the zinc-nickel alloy electrodeposits containing up to about 15% by weight nickel.
Generally, such alloy deposits will contain at least about 1% nickel, with nickel contents of from about 5-12% by weight being particularly preferred.
Typically, the chromating solutions are applied by immersion of ~he zinc-nickel alloy electrodeposit in the solution, although other application techniques, such as spraying, flooding, and the like, may also be used. When using such application techniques, the zinc-nickel alloy electrodeposit is maintained in contact with the chromating solution for a period of time sufficient to form the desired chromate film on the surface. In many instances, contact times of from about 10 to about 30 seconds are typical 7 although this time may be varied in each instance and both shorter and longer contact times may be used to obtain the desired chromate ~ilm. The temperature of the chromating bath may be from room temperature, e.gO, - about 20C, up to temperatures which approach the boiling point of the solution. Typically, the solution is used at a temperature of from about 25 to about 60C.
It has been found that the surface of the zinc nickel alloy electrodeposit may become inactive or inert if it is exposed to the atmosphere for any significant period of time before being subjected to the chromating treatment. In such instances, it has been found desirable to utilize the chromating solutions at higher temperatures, such as about 35 to 55C, in order to form the desired chromate film.
Where the zinc-nickel alloy electrodeposit is treated with the chromating solutions immediately after electrodeposition of the alloy, the lower solution t~mperatures of 25 to 35~C may be used to satisfactorily obtain the chromate coating.
In this regard, it has further been found that activation of the zinc-nickel alloy electrodeposit surface may also be accomplished by making the zinc-nickel alloy substrate the anode and electrolyzing the substrate in the chromate solution at a relatively low current density. Typically, the electrolysis, with the zinc-nickel alloy electrodeposit surface as the anode, is carried out at a current density of from about 0.01 to about 0.2 A/dm2 for a period of up to about ten (10) seconds. Thereafter, the zinc-nickel alloy's substrate is retained in the chromatiny so!ution, without the application of current, until.the desired chromate film is formed on the surface.
.
~` ` `.
., .
~L2(~ 7 By means of -the process described hereinabove, zinc-nickel alloy electrodeposi-ts containing up to about 15%
by weight nickel are provided with a chromate film having a -thickness of at leas-t about lO0 mg/m2. These films impart a pleasing color -to the alloy surface and provide good corro-sion resis-tance of a magnitude which has heretofore not been possible on zinc-nickel alloy electrodeposi-ts. Moreover, the zinc-nickel alloy electrodeposits containing these chro-mate films are found to have a corrosion resistance which is superior to that of zinc electrodeposits which have been subject to conventional chromating treatments.
: 1 :
~2~ 7 Specific Examples of the Invention In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given:
Example I
An aqueous chromating bath was formulated by dissolving the following components in water in the amounts indicated:
Na2Cr207 2~20 lO g/l ~Cr+~ = 3.43 g/l) ~2S04 2 g/l (S04-2 = l.96 g/l) (SO4~2/Cr+6 = 0.56) pH 1.8 . . .
A steel sheetg electroplated to a thickness of 3 ~m with a zinc-nickel alloy containing 8% by weight nickel was chromated with this solution by immersing the sheet in the solution For fifteen (15) seconds at a temperature of 35~C.
-l4-4~
Example II
An aqueous chromating bath was formulated by dissolving the following components in water in the amounts indicated:
Na2Cr207;2H20 20 9/1 (Cr+6 = 6.g8 9/1) Cr2(S04)2-aqueous solution T 9/1 3 S04-2 = 0-75 9/1) (Cr2 (504)3 content 40% (S04-2/Cr+6 = 0.11) pH 2.1 (adjusted with CrO3) A steel sheet, electroplated to a thickness of lJum with a zinc-nickel alloy containing 8% by weight nickel was chromated in thîs solution by immersing the sheet in the solution for 2~ seconds at 50C.
Example I II
A chromating bath was fcrmulated by dissolving the following components in water in the amounts indicated:
CrO3 2 9/1 (Cr+6 = 1.04 g/l ) H2S04 0.1 9/l (S04-2 = 0.098 9/l ) (S04~2/Cr+5 = 0.094) pH 1.8 ~ 1 5 - ' lZ~ 7 5 A steel sheet, electroplated to a thickness of 3 ~m with a zinc-nickel alloy containing 8% by weight nickel was chromated by immersing the sheet in the solution for fifteen (15) seconds at a temperature of 40C.
Example IV
An aqueous chromating bath was formulated by dissolving the following components in water in the amounts indicated:
Na2Cr207 2H20 30 g/l (Cr+6 = ll.82 g/l) Cr2(S04)3aqueous solut;on T 9ll (S04-2 = 0-96 g/l) (Crz(s04)340% content) (S04~Z/Cr+6 = O~O~TJ
pH 2~0 ~ A steel sheet, electroplated to a thickness of 2 ~m : \ with a zinc-nickel alloy containing 12% by weight nickel ~as chromated by immersing the sheet in the 25 solution while the solution-was electrolyzed at a current density of 0.1 A/dm2 for 5 (five) seconds ::
:.
~ -l6-`, :
' ' ' -: :
~ , : ~ :
with the sheet as the anode. After five (5) seconds, the passage of electric current was discontinued and the sheet was retained in the solution for an additional twenty (20) seconds. The temperature of the 5 chromating solution during the entire treatment was 50-C.
Example V
An aqueous chromating solution was formulated by dissolving the following components in water in the amounts indicated:
CrO3 50 g71~(Cr+6 = 26~0 9/1) lS H2S04 (S04~2/Cr+6 = 0.38) Na2HP04 2 9/1 pH T.~ (adjusted with NaOH) A steel sheet, electroplated to a thickness of 6 ~m with a zinc-nicke1 alloy having a nickel content of 10X
by weight was chromated by immersing the sheet in the chromating bath for ten (10) seconds at a bath temperature of 30C.
, Example VI
An aqueous chromating bath was formulated by dissolving the following components in water in the amounts indicated:
Na2Cr207~2H20~50 g/l (Cr+6 = 52.4 g/l) ~2S4 lO g/l (S04-2 = 9.8 g/l) (S0~~2/Cr~6 = 0.~9 10 HCOONa l.5 g/l pH - - 1.6 A steel sheet, electroplated to a thickness of 3 ~m with a zinc-nickel alloy having a nickel content of 12%
by weight, to which had been applied a flash electrodeposit of zinc having a thickness of 0.1 ~m was chromated by immersing it in this solution for fifteen (15) seconds at a bath temperature of 30C.
23 By way of comparison, the following Examples VII through IX were run:
;
-l8-, , :
..... . ' ., Example VII
!
An aqueous chromating bath was formulated by dissolv;ng the following components in water in the amounts indicated:
CrO3 .~00 9/l (Cr+6 = 52.0 g/l) 4 lO g/l (S04-2 9.8 g/l) pH . 0.6 (S04~2tCr+6 = OI9) A steel sheet, electroplated to a thickness of 3 ~m with a zinc-nickel alloy having a nickel content of 10%
: by weight, was chromated by immersing the sheet in the chromating bath for ten (10) seconds at a bath temperature ~f 30C.
Example VIII
An aqueous chromating bath was formulated by dissolving the following components in water in the amounts indicated: .
_l g_ ~i!LZ~ 7 CrO3 To g/l (Cr+6 5.2 g/1) H2S04 l g/l (S04~Z/Cr+6 = 0.98 9/l) pH l.2 (S04~2/Cr+6 = 0.19) A steel sheet, electroplated to a thickness of 3 ym with a zinc-nickel alloy having a nickel con-tent of 10%
by weight, was chromated by immersing the sheet in the chromating solution for 30 seconds at a bath temperature of 30DC.
:
I
:: ; ~
::; :
: :: -20- : ~
, : ~
The chromated samples prepared in accordance ; with the preceding Examples I through IX were analyzed to determine the chromium content of the chromate coating and were tested for corrosion resistance using the 5% neutral salt spray test and for heat resistance of the chromate coating. The analytical methods and test methods used were as follows:
(1~ Analysis of Cr in the chromate film:
Each test specimen was immersed in an aqueous acidic solution containing 100 gll HCl. The chromate film was oompletely dissolved from the test specimen and the eluted Cr portion was quantitatively analyzed by atomic absorption spectroscopy. The amount of chrom;um determined was expressed in terms of the surface area of the test specimen (miligrams per square meter).
(2) Corrosion resistance test:
Each test specimen was subjected to the 5% neutral salt spray test in accordance with the procedure ASTM-8117 and the time was noted for the .
development of white corrosion products on the surface of the specimen (white rust) and for the development of red corrosion products (red rust) in accordance with ; this procedure.
(3) Heat resistance test:
. Each test specimen was placed in a . thermostated oven and maintained in the oven for twenty-four hours at fixed temperatures of 100p 150, 200, and 250C. Thereafter, each test speciment was removed from the oven and the failure or fading of the chromate film due to the heat was visually observed.
Using thes~ procedures, the test results as shown in the following Table I were obtained:
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~ r- aJ ~ s o = _ = = = o In ~ ~ ~ C~J ~
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._ E aJ ~ c ~ ~ ~t LLI ~ ~3 ~ _ . ~ _ .
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C t ~ O ~ O O . I~ Ln ) ~ o~ t = r~ r O_ ~) N
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Vl ~ ~1 (L) -- O ~ V) - = = O C ~ = = 3 a~ C ~ =
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~'~
~J ~ ~I) a~ a) a E v~
E E E E
~ .
. .
,-C
Q>
,~
~ o .~ In s. O s ~
1~ (1) 3 o a) ~ O I:
c a~ o o u~
aJ aJ ~ O U~
s U~ E ~n V
q) ~ .
q~
+~ cn .r~ 3 ~n ~) Q O ~_ c C
1~ 1~
V) ~ _C S
O W ~ t~
C '-a~ O o u. u Cl ~ ~r-'~
~n ~ ~ E ~ ~. ~ 3 3 ~ ~ ~ ~ ~ s_ L~ a~
.,_ ., aJ c ~ ~ ~.
H ~' ~ ~ c,--.
q~ E ~ ~ +~ ~ c O O
,~
S ~ =~' ~ r~ .
V~
..
a >~
~ ~ ~ o qJ ~ ~ __ us l -=~ . o o o o +, ~ o ~n o u, O S ~ ~ ~ N N
Q I 1--.
O
~n ~
E ~
V ~
. ~2 ~ .~
~ v~ E \_ _ E V~ X
o c L~ O
: :
~.`. . : `:
,~,s,~, .
. ,, ~
~xample X
.
A concentrate composition was formulated containing the following components in the amounts indicated:
sodium dichromate (Na2Cr~07.2H20) 300 971 .
zinc sulfate (ZnS0~7H?aT 15 9/1 chromium sulfate ~Cr2(~04)3 . . . 40% sol.) 30 ml~l chromic acid ~CrO3) 40 9/1 water balance .
A chromating solution was formulated by add;ng the foregoing concentrate solution to water in an amount of SO mililiters per liter. The pH ol this chromating soluton was 1.8 and steel sheets9 electroplated to a thic~ness of 4 ~m with a zinc-nickel alloy containing B.4X by weight nickel, were chromated by immersing the sheets in the chromating solution for 15 seconds while maintaining the bath temperature within the range of 45 - 55C. The results of the testing of the chromate coating produced in accordance with this procedure are found to correspond to the results obtained for Example III.
_z5, t '`
~ , During the operation of ~he process of this Example, the chromating solution is replenished using a replenishing composition containing the following components in the amounts indicated:
chromic acid (CrO3) 300 g/l ! sulfuric acid (H2S04 50 wt. ~) . lQO ml/l Sp. Gr. = 1.4 water balance The pH and CrO3 concentration of the chromating bath is periodically measured and the above replenishing solution is added in amounts necessary to reestablish the pH and CrO3 content of the bath at the levels originally formulated~
. . .
From the foregoing results, it is apparent that the chromating solutions of the present invention provide a colored chromate coating of high quality on 2a 2inc-nickel alloy electrodeposits, which chromate coatings have excellent corrosion resistance, as well as heat r`esistance to color fading. Moreover, the corrosion resistance of the substrates plated with the : zinc-nickel alloy electrodepGsits and chromated in accordance with the present invention is signi~icantly greater than that of substrates plated with zinc electrodeposits which had been chromated using conventional processes.
, .
Claims (3)
1. A process For forming a colored chromate film on zinc-nickel alloy electrodeposits containing up to about 15% by weight nickel which comprises contacting the said zinc-nickel alloy with an aqueous acidic chromating solution suitable for forming colored chromate films on zinc-nickel alloy electrodeposits containing up to about 15% by weight nickel, which solution has a pH of from about 1.3 to about 2.7 and comprises hexavalent chromium in an amount of at least 0.5 grams per liter and sulfate in a weight ratio of SO4-2: Cr+6 of about 0.025-1.5:1, and maintaining the solution in contact with the zinc-nickel alloy for a period of time sufficient to form the desired colored chromate film.
2. The process as claimed in claim 1, wherein the zinc-nickel alloy electrodeposit is immersed in the chromating solution, the solution is electrolyzed, with the zinc-nickel alloy electrodeposit as the anode, for a period of up to about ten seconds at a current density of from about 0.01 to about 0.2 amps per square decimeter, and, there-after, electrolysis is discontinued and the zinc-nickel alloy electrodeposit is maintained in the chromating solution until the desired colored chromate coating is formed.
3. The process as claimed in claim 1 or 2, wherein the hexavalent chromium content of the chromating solution is from about 0.5 to about 100 grams per liter.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1745/1982 | 1982-01-11 | ||
| JP57001745A JPS6020467B2 (en) | 1982-01-11 | 1982-01-11 | Colored chromate treatment method for zinc-nickel alloy plated products |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1209947A true CA1209947A (en) | 1986-08-19 |
Family
ID=11510095
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000419161A Expired CA1209947A (en) | 1982-01-11 | 1983-01-10 | Chromate composition and process for treating zinc- nickel alloys |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS6020467B2 (en) |
| AU (1) | AU546541B2 (en) |
| BR (1) | BR8300076A (en) |
| CA (1) | CA1209947A (en) |
| DE (1) | DE3300543A1 (en) |
| FR (1) | FR2519655B1 (en) |
| GB (1) | GB2113721B (en) |
| NL (1) | NL8300090A (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2167449B (en) * | 1984-11-23 | 1988-06-02 | Omi Int Corp | Passivation |
| GB8507181D0 (en) * | 1985-03-20 | 1985-04-24 | Omi International Benelux Bv | Passivation |
| US4707415A (en) * | 1985-03-30 | 1987-11-17 | Sumitomo Metal Industries, Ltd. | Steel strips with corrosion resistant surface layers having good appearance |
| JP2717406B2 (en) * | 1987-12-23 | 1998-02-18 | ディップソール株式会社 | Blackening method of zinc alloy plating |
| JPH01283381A (en) * | 1988-05-10 | 1989-11-14 | Nippon Hyomen Kagaku Kk | Treating solution for chemically forming green chromate film on zinc-nickel alloy plating film |
| JPH0257447A (en) * | 1988-08-19 | 1990-02-27 | Suzuki Motor Co Ltd | Installation structure for pillar garnish of vehicle |
| JPH0730456B2 (en) * | 1988-10-05 | 1995-04-05 | 日本表面化学株式会社 | Treatment liquid for forming black chromate film on zinc / nickel alloy plating |
| JP2750710B2 (en) * | 1988-10-29 | 1998-05-13 | 臼井国際産業株式会社 | Heat-resistant and corrosion-resistant steel with multi-layer plating |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2293779A (en) * | 1940-02-14 | 1942-08-25 | Parker Rust Proof Co | Metal coating method and article produced thereby |
| US2469015A (en) * | 1943-02-20 | 1949-05-03 | United Chromium Inc | Method and compositions for producing surface conversion coatings on zinc |
| GB869395A (en) * | 1959-05-27 | 1961-05-31 | Pyrene Co Ltd | Improvements relating to the production of chemical coatings on zinc and zinc alloys |
| US3121032A (en) * | 1960-09-27 | 1964-02-11 | M & T Chemicals Inc | Process for applying a protective transparent coating to zinc and cadmium and composition therefor |
| JPS52106334A (en) * | 1976-03-04 | 1977-09-06 | Sumitomo Metal Ind | Surface treatment of zinc plated steel |
| JPS5554588A (en) * | 1978-10-13 | 1980-04-21 | Nippon Steel Corp | Production of high corrosion-resistant electroplated steel plate |
| JPS55110792A (en) * | 1979-02-15 | 1980-08-26 | Sumitomo Metal Ind Ltd | Surface treated steel plate |
| JPS5698496A (en) * | 1980-01-10 | 1981-08-07 | Nippon Kokan Kk <Nkk> | Chromate treating method of zinc alloy-electroplated steel plate |
| JPS56130477A (en) * | 1980-03-13 | 1981-10-13 | Sumitomo Metal Ind Ltd | Surface treated steel plate |
| JPS6033192B2 (en) * | 1980-12-24 | 1985-08-01 | 日本鋼管株式会社 | Composite coated steel sheet with excellent corrosion resistance, paint adhesion, and paint corrosion resistance |
-
1982
- 1982-01-11 JP JP57001745A patent/JPS6020467B2/en not_active Expired
-
1983
- 1983-01-04 AU AU10025/83A patent/AU546541B2/en not_active Ceased
- 1983-01-10 DE DE19833300543 patent/DE3300543A1/en not_active Ceased
- 1983-01-10 CA CA000419161A patent/CA1209947A/en not_active Expired
- 1983-01-10 BR BR8300076A patent/BR8300076A/en unknown
- 1983-01-10 FR FR8300283A patent/FR2519655B1/en not_active Expired
- 1983-01-11 NL NL8300090A patent/NL8300090A/en not_active Application Discontinuation
- 1983-01-11 GB GB08300676A patent/GB2113721B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2519655B1 (en) | 1986-05-16 |
| GB8300676D0 (en) | 1983-02-09 |
| JPS58120785A (en) | 1983-07-18 |
| AU1002583A (en) | 1983-07-21 |
| JPS6020467B2 (en) | 1985-05-22 |
| AU546541B2 (en) | 1985-09-05 |
| DE3300543A1 (en) | 1983-07-28 |
| FR2519655A1 (en) | 1983-07-18 |
| GB2113721B (en) | 1986-06-11 |
| GB2113721A (en) | 1983-08-10 |
| NL8300090A (en) | 1983-08-01 |
| BR8300076A (en) | 1983-09-20 |
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