US2248062A - Method of treating electrolytic coatings on magnesium and its alloys - Google Patents

Description

Patented July 8, 1941 COATINGS ON MAGNESIUM AND ITS ALLOYS L Robert W. Buzzard, Remington, Md.

No Drawing.

Original application June 29,

1937, Serial No. 150,932. Divided and this application Apr-i126, 1938, Serial No. 204,387

(Granted under the act of March 3, 1883, as amended April 30, 1928; 870 0. G. 757) 6 Claims.

The invention disclosed and claimed herein is a division of my copending application, Serial No.

- 150,932 filed June '29, 1937, now Patent No.

2,203,670 of June 11, 1940. p

This invention relates to the treatment of eleccharacteristics of the electroylytic coating.

tr-olytically formed coatings on magnesium and its I alloys and one of its objects is to increase the durability and the protective characteristics of the film by sealing the coating.

,The method specifically relates to the treating of electrolytic coatings on magnesium and its alloys with a solution in the presence of heat so as to form a seal that not only increases the durability of the article coated to wear but also improves its resistance to corrosion.

The article to be treated in this manner, which has been coated electrolytically, is washed free of solution, providing the electrolytic bath is basically difl'erent from the solution used in my sealing method and is then immersed in a hot solution of sealing compounds, preferably at or above the boiling point of the solution, but below the fusion point of the metal.

The sealing solution should contain a corrosion inhibiting ion such as either a chromate or dichromate and a second salt as a reacting ion such as manganese or chromium or borate, phosphate, fluoride or a combination of any of the said second salts. The concentration of the salts is" limited only by their solubility, but may be varied to conform with'time of application and quality of seal. Good seals of'coated metal have been obtained by subjecting the coatings to treatment monobasic phosphate and the coating has been I washed free of anodizing solution, its corrosion resistance will be greatly improved if it is immersed in a solution of dichromate and manganous sulphate at .boiling temperature of water or above. The sealing solution may be varied to contain a trivalent chromium salt as chromium acetate or sulphate or fluoride. A chromate may be introduced or substituted in the solution or a phosphate may be substituted or added when the solution is of such composition not to cause detrimental intersolution reactions.

It should be understood that the protection obtained by my treatment is dependent on the presence of an electrolytic coating and is not a prime surface treatment.

In the sealing treatment herein set forth a chemical reaction is produced improving the This change is evinced by a corrosion test wherein two identical anodized articles, one sealed by my method and one unsealed, disclosed over a corrosion period that the sealed coating did not change in color, whereas the unsealed coating showed a radical change in color.

As further examples of compositions which will satisfactorily seal electrolytic coatings 0 magnesium, the following are cited: (a) 1 to 30 percent dichromate 0.25 to 10 percent chromium fluoride 10 percent sodium dichromate 1 percent chromium fluoride 10 percent sodium dichromate 10 percent monobasic sodium phosphate 1 percent chromium fluoride 10 percent sodium dichromate 1 percent zinc phosphate 1 percent magnesium phosphate 1 percent chromium fluoride 10 percent sodium dichromate 10 percent sodium phosphate 1 percent chromium sulphate 1 percent'zinc chromate 1 percent manganous sulphate 1 percent chromium fluoride 10 percent dichromate I 5 percent sodium fluoride .1 percent chromium fluoride 10 percent sodium phosphate 10 percent dichromate 1 percent chromium fluoride 1 percent zinc chromate 5 percent sodium dichromate 1 percent chromium fluoride A double dip may also be used such asfirst immersing the electrolytically coated article in a solution of dichromate and phosphates 'followed by an immersion in a solution of manganese and chromium sulphate. Ammonium and other salts may be substituted for the sodium and potassiumsalts.

The above mentioned substances used in the magnesium treatments are mentioned by way of illustration and not by limitation, since the invention comprehends treatments of the character indicated broadly above and is not to be limited except by the appended claims.

The invention described herein may be manufactured or used by or for the Government of the United'States of America for governmental pound selected from group consisting of chromate and dichromate.

2. The method of producing corrosion resistant coatings on' magnesium and magnesium alloys in. which magnesium predominates comprising forming on the metal an anodic coating produced by reaction with magnesium and subjecting said coating to a non-electrolytic treatment .in an aqueous solution containing chromium acetate 20 and a water soluble compound selected from group consisting of chromate and dichromate.

3. The method of producing corrosion-resistant magnesium or magnesium alloys comprising forming an anodic coating produced by reaction with magnesium on the metal and subjecting the coating to a non-electrolytic treatment in an aqueous solution containing a chromium salt 7 soluble in the solutionand a water soluble compound selected from the group consisting of chromate and dichromate, the pH of said solution being on the acid side.

4. The method of producing corrosion resistant.

coatings on magnesium and alloys thereof in which magnesium predominates comprising.

' forming on the metal an anodic coating produced by reaction with magnesium, and subjecting the coating to a non-electrolytic treatment in an aqueous solution containing chromium sulphate v and a water soluble compound selected from the group consisting of the chromates and dichromates, the pH of the solution being on the acid side.

, 5. The method 01' producing corrosion resistant coatings on magnesium and alloys thereof in which magnesium predominates comprising forming on th metal an anodic coating produced by reaction with magnesium, and subjecting the coating to a non-electrolytic treatment for 5 to minutes in an aqueous solution containing from 1 to 30 per cent of a water soluble dichromate and i'rom 0.25 to 10 per cent of chromium fluoride, and maintaining the temperature of the solution during treatment substantially equivalent to the boiling point of the solution.

6. The method of producing corrosion resistant coatings on magnesium and alloys thereof in which magnesium predominates comprising forming on' the metal an anodic coating produced by reaction with magnesium, and subjecting the coating to a non-electrolytic treatment {or 5 to 30 minutes in 'an'aqueous solution containing from 1 to 3 per cent of zinc chromate,

3 to '7 per cent of sodium dichromate, and 1 to 3 per cent of chromium fluoride-and maintaining the temperatureof the solution during treatment substantially equiifalent' to the boiling point of the solution. 1

4 ROBERT W. BUZZARD.