US3301719A - Chemical conversion coating for magnesium - Google Patents

Chemical conversion coating for magnesium Download PDF

Info

Publication number
US3301719A
US3301719A US230669A US23066962A US3301719A US 3301719 A US3301719 A US 3301719A US 230669 A US230669 A US 230669A US 23066962 A US23066962 A US 23066962A US 3301719 A US3301719 A US 3301719A
Authority
US
United States
Prior art keywords
magnesium
coating
solution
chemical conversion
conversion coating
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 - Lifetime
Application number
US230669A
Inventor
Earl C Groshart
James B Mohler
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Boeing Co
Original Assignee
Boeing Co
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Boeing Co filed Critical Boeing Co
Priority to US230669A priority Critical patent/US3301719A/en
Application granted granted Critical
Publication of US3301719A publication Critical patent/US3301719A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

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
    • 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

Definitions

  • This invention relates in general to a coating for magnesium and magnesium alloys, and in particular to an initial immersion coating for magnesium and magnesium alloys which facilitates and enhances subsequent priming and painting coatings for these materials.
  • a chemical conversion coating or an electrochemical coating is necessary as a paint base for magnesium.
  • Current chemical conversion coatings commonly employ some means other' than immersion for contacting the surface of the magnesium material.
  • the current methods of coating involve a surface spray, electrochemical application or manual application. In addition to being costly methods of application, these chemical conversion coatings do not produce uniform results.
  • the coatings can be marred by pitting in electrochemical applications.
  • the coatings can be powdery or of erratic thicknesses when spraying or manual methods of application are employed.
  • One method of immersion coating magnesium materials although using a solid Vaseline instead of a liquid solution, is given in Patent 2,671,736 by Zoeller. This process involves a costly heating step in order to obtain an impregnated petroleum coating. From this discussion, there is evident in the prior art an absence of a liquid immersion solution to serve as a chemical conversion coating for magnesium materials.
  • a further object of this invention is a chemical conversion coating with uniform, powder-free surfaces on magnesium and magnesium alloys.
  • a further object of this invention is a less reactive and more easily controlled chemical conversion coating.
  • this invention is a method of promoting reaction on the surfaces of magnesium and magnesium alloys with a resultant compound formation which promotes subsequent decorative or protective coatings.
  • This compound formation on the surfaces of magnesium materials is uniform, powder-free and pit-free, and it consists of a magnesium dichromate compound as formed by soluble dichrom-ate ions contacting magnesium material while being catalyzed -by soluble sulfate ions in an adjustable defined pH range.
  • This chemical conversion coating was devised specifically for rare-earth magnesium alloys.
  • An example of of such an aloy is HK31A.
  • the development of the coating solution was specifically for rare-earth magnesium alloys, the solution works adequately for all magnesium and magnesium alloy materials.
  • the aqueous solution range is as follows:
  • the proportionate remainder is water.
  • the immersion time is 2 to 10 minutes
  • the temperature is ambient or room temperature
  • the mild agitation of the solution is done by filtered air.
  • Example 1 This example is provided as being typical and illustrative and in no manner shall serve to limit our coating process to this specific instance.
  • the magnesium material (HK31A, for instance) is first degreased in trichloroethylene.
  • a cleaning solution is employed to remove foreign substances from the surface of the magnesium material.
  • the magnesium material is immersed in the following aqueous chemical conversion coating solution:
  • the solution should be mildly agitated with filtered air.
  • the time of immersion is 3 to 10 minutes if the solution is agitated as described above.
  • the solution is used at ambient temperatures. When the solution becomes saturated with magnesium, usually around three ounces per gallon, it is no longer effective.
  • the pH is adjusted to the lower limit on synthesis of the solution and maintained within the above stated range by chromic acid additions.
  • the magnesium material is rinsed as given above and allowed to dry, completing the chemical conversion coating. Storage of the conversion coated magnesium material is important as it should be a kept as clean and dry as possible until primed and painted.
  • a coating process for magnesium and magnesium alloys in preparation for subsequent applications of coatings comprising the steps of deg-reasing, cleaning, pickling in a solution comprised of:
  • a coating process for magnesium and magnesium alloys in preparation for subsequent applications of coatings comprising the steps of degreasing, cleaning, pickling in a solution comprised initially of:

Landscapes

  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)

Description

United States Patent 3,301,719 CHEMICAL CONVERSION COATING FOR MAGNESIUM Earl C. Groshart and James B. Mohler, Seattle, Wash, assignors to The Boeing Company, Seattle, Wash., a corporation of Delaware No Drawing. Filed Oct. 15, 1962, Ser. No. 230,669
2 Claims. (Cl. 148-6.21)
This invention relates in general to a coating for magnesium and magnesium alloys, and in particular to an initial immersion coating for magnesium and magnesium alloys which facilitates and enhances subsequent priming and painting coatings for these materials.
A chemical conversion coating or an electrochemical coating is necessary as a paint base for magnesium. Current chemical conversion coatings commonly employ some means other' than immersion for contacting the surface of the magnesium material. The current methods of coating involve a surface spray, electrochemical application or manual application. In addition to being costly methods of application, these chemical conversion coatings do not produce uniform results. The coatings can be marred by pitting in electrochemical applications. The coatings can be powdery or of erratic thicknesses when spraying or manual methods of application are employed. One method of immersion coating magnesium materials, although using a solid Vaseline instead of a liquid solution, is given in Patent 2,671,736 by Zoeller. This process involves a costly heating step in order to obtain an impregnated petroleum coating. From this discussion, there is evident in the prior art an absence of a liquid immersion solution to serve as a chemical conversion coating for magnesium materials.
Therefore it is an object of this invention to provide a liquid immersion solution to serve as a chemical conversion coating for magnesium and magnesium alloys.
A further object of this invention is a chemical conversion coating with uniform, powder-free surfaces on magnesium and magnesium alloys.
A further object of this invention is a less reactive and more easily controlled chemical conversion coating.
Further objects and advantages of this invention as well as its use and operation will be apparent from the following descriptions and claims.
In its most common usage, this invention is a method of promoting reaction on the surfaces of magnesium and magnesium alloys with a resultant compound formation which promotes subsequent decorative or protective coatings. This compound formation on the surfaces of magnesium materials is uniform, powder-free and pit-free, and it consists of a magnesium dichromate compound as formed by soluble dichrom-ate ions contacting magnesium material while being catalyzed -by soluble sulfate ions in an adjustable defined pH range.
This chemical conversion coating was devised specifically for rare-earth magnesium alloys. An example of of such an aloy is HK31A. Although the development of the coating solution was specifically for rare-earth magnesium alloys, the solution works adequately for all magnesium and magnesium alloy materials.
The aqueous solution range is as follows:
Sodium dichromate dihydrate, ounces/gallon 4 to 8 Sodium sulfate, ounces/ gallon 0.5 to 0.8 pH 1.6 to 1.9
The proportionate remainder is water. With this solution, the immersion time is 2 to 10 minutes, the temperature is ambient or room temperature, and the mild agitation of the solution is done by filtered air.
We have found that a broad variable range of concentrations of dichromate dihydrate ions and sulfate ions "ice with some permissible variations in the pH range are possible in producing an effective coating solution. However the above solution has been found to operate efiectively as a magnesium coating medium. Therefore the operating characteristics of the full range of constituents have not been determined as a matter of economy. The operating characteristics of the above defined range have been fully determined for our uses.
The following is a description of the procedure used to coat magnesium and magnesium alloys. After fabrication and trimming of the material, the part is degreased and allowed to dry. An alkaline cleaner, a mediumduty phosphate-silicate cleaner, follows, as improperly cleaned areas will not be coated. After cleaning, the magnesium material is pickled (i.e., corroded surface areas are removed). Rinsing in warm water (130 F. to 150 F.) prepares the magnesium material for immersion in the coating solution. Rinsing and drying the material after coating completes the application of the chemical conversion coating. Storage of the coated parts is very important as the magnesium material should be kept as clean as possible until priming and painting are complete.
Example This example is provided as being typical and illustrative and in no manner shall serve to limit our coating process to this specific instance.
The magnesium material (HK31A, for instance) is first degreased in trichloroethylene.
A cleaning solution is employed to remove foreign substances from the surface of the magnesium material.
- The best cleaning solutions that we have found are medium-duty phosphate-silicate cleaners, but aluminum cleaners and heavy-duty silicate caustic cleaners also function properly.
Picking accomplishes removal of the heavily corroded areas of the magnesium material and contributes greatly to successful and reliable coatings.
The following aqueous chrome-nitrate pickle is used:
Chromic acid, ounces/ gallon 40 to 50 Sodium nitrate, ounces/ gallon 3.5 to 4.5 Sodium chloride (chloride ion), parts per million, maximum 10 Temperature, F. Time, minutes in solution 5 to9 Rinsing insures proper uniform action of the coating solution and for this reason the magnesium material should be rinsed prior to contact with the coating solution. A rinse in warm water (130 F. to F.) for three minutes immersion or 8 to 10 minutes in a water spray is suflicient.
The magnesium material is immersed in the following aqueous chemical conversion coating solution:
Sodium dichromate dihydrate, ounces/gallon 6 Sodium sulfate, ounce/ gallon 0.65 pH 1.6 to 1.9
For effective operation the solution should be mildly agitated with filtered air. The time of immersion is 3 to 10 minutes if the solution is agitated as described above. The solution is used at ambient temperatures. When the solution becomes saturated with magnesium, usually around three ounces per gallon, it is no longer effective. The pH is adjusted to the lower limit on synthesis of the solution and maintained within the above stated range by chromic acid additions.
Following the coating, the magnesium material is rinsed as given above and allowed to dry, completing the chemical conversion coating. Storage of the conversion coated magnesium material is important as it should be a kept as clean and dry as possible until primed and painted.
We claim:
1. A coating process for magnesium and magnesium alloys in preparation for subsequent applications of coatings comprising the steps of deg-reasing, cleaning, pickling in a solution comprised of:
Chromic acid, ounces per gallon 40 to 50 Sodium nitrate, ounces per gallon 3.5 to 4.5 Sodium chloride (or chloride ion), parts per million, maximum 10 Water, balance rinsing, contacting with a coating solution of:
Sodium dichromate dihydrate 4 to 8 ounces per gallon Sodium sulfate 0.5 to 0.8 ounce per gallon Chromic acid Sufiicient to maintain the pH within 1.6 to 1.9
Water, balance and thereafter rinsing the part.
2. A coating process for magnesium and magnesium alloys in preparation for subsequent applications of coatings comprising the steps of degreasing, cleaning, pickling in a solution comprised initially of:
Chromic acid, ounces per gallon 50 Sodium nitrate, ounces per gallon 4.5 Sodium chloride (or chloride ion), parts per million,
maximum Water, balance 4 rinsing, contacting with a coating solution comprised initially of: 7
Sodium dichromate dihydrate 6 ounces per gallon Sodium sulfate 0.65 ounce per gallon Chromic acid Suflicient to maintain the pH Within 1.6 to 1.9 Water, balance and thereafter rinsing the part.
References Cited by the Examiner OTHER REFERENCES A.P.C., application of Seibel et al., Ser. No. 3,151,184, published May 11, 1943.
ALFR-ED L. LEAVITT, Primary Examiner.
WILLIAM D. MA RTIN, RALPH S. KENDALL,
Examiners.

Claims (1)

1. A COATING PROCESS FOR MAGNESIUM AND MAGNESIUM ALLOYS IN PREPARATION FOR SUBSEQUENT APPLICATIONS OF COATINGS COMPRISING THE STEPS OF DEGREASING, CLEANING, PICKLING IN A SOLUTION COMPRISED OF:
US230669A 1962-10-15 1962-10-15 Chemical conversion coating for magnesium Expired - Lifetime US3301719A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US230669A US3301719A (en) 1962-10-15 1962-10-15 Chemical conversion coating for magnesium

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US230669A US3301719A (en) 1962-10-15 1962-10-15 Chemical conversion coating for magnesium

Publications (1)

Publication Number Publication Date
US3301719A true US3301719A (en) 1967-01-31

Family

ID=22866123

Family Applications (1)

Application Number Title Priority Date Filing Date
US230669A Expired - Lifetime US3301719A (en) 1962-10-15 1962-10-15 Chemical conversion coating for magnesium

Country Status (1)

Country Link
US (1) US3301719A (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4070193A (en) * 1975-09-19 1978-01-24 Kaddis Mfg. Co. Corrosion resistant metal sealing formulation
US4592854A (en) * 1985-01-09 1986-06-03 Mcdonnell Douglas Corporation Steel etchant
US4915782A (en) * 1988-12-21 1990-04-10 Mcdonnell Douglas Corporation Aluminum lithium etchant

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1747776A (en) * 1929-04-19 1930-02-18 Firm Dr Otto Sprenger Patentve Production of dark oxidic coatings on magnesium and magnesium alloys
US2154451A (en) * 1934-12-17 1939-04-18 Du Pont Bright dip
US2224528A (en) * 1937-12-23 1940-12-10 Sutton Hubert Protection of magnesium and magnesium alloys
US2454799A (en) * 1944-12-09 1948-11-30 Hart David Method of producing protective coatings on magnesium powder
US2480448A (en) * 1943-04-28 1949-08-30 Permanente Metals Corp Protective surface treatment of magnesium base alloys
US2483510A (en) * 1945-04-14 1949-10-04 United Chromium Inc Composition for dip coating solution and dip process for coloring zinc
US2796372A (en) * 1953-05-07 1957-06-18 Poor & Co Corrosion protecting metal finishing composition
US2854371A (en) * 1956-02-01 1958-09-30 Shwayder Bros Inc Method and solution for treatment of magnesium articles
US2861019A (en) * 1956-06-07 1958-11-18 Dow Chemical Co Chromate-coating magnesium and its alloys
US3094489A (en) * 1959-08-31 1963-06-18 Monsanto Chemicals Method and composition for brightening aluminum

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1747776A (en) * 1929-04-19 1930-02-18 Firm Dr Otto Sprenger Patentve Production of dark oxidic coatings on magnesium and magnesium alloys
US2154451A (en) * 1934-12-17 1939-04-18 Du Pont Bright dip
US2224528A (en) * 1937-12-23 1940-12-10 Sutton Hubert Protection of magnesium and magnesium alloys
US2480448A (en) * 1943-04-28 1949-08-30 Permanente Metals Corp Protective surface treatment of magnesium base alloys
US2454799A (en) * 1944-12-09 1948-11-30 Hart David Method of producing protective coatings on magnesium powder
US2483510A (en) * 1945-04-14 1949-10-04 United Chromium Inc Composition for dip coating solution and dip process for coloring zinc
US2796372A (en) * 1953-05-07 1957-06-18 Poor & Co Corrosion protecting metal finishing composition
US2854371A (en) * 1956-02-01 1958-09-30 Shwayder Bros Inc Method and solution for treatment of magnesium articles
US2861019A (en) * 1956-06-07 1958-11-18 Dow Chemical Co Chromate-coating magnesium and its alloys
US3094489A (en) * 1959-08-31 1963-06-18 Monsanto Chemicals Method and composition for brightening aluminum

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4070193A (en) * 1975-09-19 1978-01-24 Kaddis Mfg. Co. Corrosion resistant metal sealing formulation
US4592854A (en) * 1985-01-09 1986-06-03 Mcdonnell Douglas Corporation Steel etchant
US4915782A (en) * 1988-12-21 1990-04-10 Mcdonnell Douglas Corporation Aluminum lithium etchant

Similar Documents

Publication Publication Date Title
US2851385A (en) Process and composition for coating aluminum surfaces
US3696498A (en) Pretreatment of metal sheets which are coated after a forming operation
US2164042A (en) Art of producing phosphate coatings on surfaces of iron, zinc, or alloys thereof
US2904413A (en) Process of bright dipping zinc base alloys
USRE32661E (en) Cleaning aluminum at low temperatures
US3140203A (en) Method of and composition for treating aluminum and aluminum alloys
US2535794A (en) Method of preparing ferrous metal objects for the application of synthetic resins
US2303242A (en) Metal coating
US2548420A (en) Method of producing lustrous zinc
US3895969A (en) Composition and process for inhibiting corrosion of non-ferrous metal surfaced articles and providing surface for synthetic resin coating compositions
US3301719A (en) Chemical conversion coating for magnesium
US3081238A (en) Electrolytic treatment of metal surfaces
US2620265A (en) Composition for treating aluminum and aluminum alloys
JPS5983775A (en) Chemical conversion of metal surface
US2288995A (en) Surface treatment of magnesium and its alloys
US3664887A (en) Process for increasing corrosion resistance of conversion coated metal
US2272216A (en) Method of coating copper and its alloys
US2760890A (en) Composition for and method of producing corrosion resistant metal coating
US2961358A (en) Method of forming a chromate conversion coating on magnesium
US2431728A (en) Treatment of ferrous metals to improve resistance to rusting
US3524817A (en) Method and compositions for chemically polishing zinc
US3493441A (en) Detoxification of hexavalent chromium containing coating on a metal surface
US2628925A (en) Bright corrosion resistant coating of metals
US2200615A (en) Method of and composition for cleaning and rendering metal surfaces immune from rust
US1549411A (en) Material and process for preparing metal for painting