US3634262A - Process and compositions for treating aluminum and aluminum alloys - Google Patents

Abstract

ALUMINUM AND ALUMINUM ALLOY SURFACES ARE PREPARED FOR METAL FINISHING OPERATIONS SUCH AS ANODIZING, PAINTING, BRIGHT DIPPING ETC., BY IMMERSING THEM FOR ABOUT 1 TO ABOUT 10 MINUTES AT A TEMPERATURE OF ABOUT 60* TO ABOUT 170*F. IN AND ACIDIC SOLUTION OF A PEROXYDIPHOSPHATE COMPOUND, SUCH AS POTASSIUM PEROXYDIPHOSPHATE. OPTIONALLY, THE SOLUTION MAY ALSO CONTAIN A FLUORIDE SALT.

Description

3,634,262 PROCESS AND COMPOSITEONS FOR TREATING ALUMINUM AND ALUMINUM ALLOYS John J. Grunwald, New Haven, and Edmund E. Homer,

Watertown, Conn., assignors to MacDermid, Incorporated, Waterbury, Conn. No Drawing. Filed May 13, 1970, Ser. No. 37,013 Int. Cl. (311d 7/54 U.S. Cl. 252-100 15 Claims ABSTRACT OF THE DISCLOSURE Aluminum and aluminum alloy surfaces are prepared for metal finishing operations such as anodizing, painting, bright dipping etc, by immersing them for about 1 to about 10 minutes at a temperature of about 60 to about 170 F. in an acidic solution of a peroxydiphosphate compound, such as potassium peroxydiphosphate. Optionally, the solution may also contain a fluoride salt.

This invention relates to the surface preparation of aluminum and aluminum alloys for subsequent metal finishing operations such as painting, anodizing, plating bright dipping, Welding, chromating, etc. More particularly, this invention relates to novel acidic compositions containing ammonium peroxydiphosphate or peroxydiphosphates of the alkali metals and the alkaline earth metals and to a process for deoxidizing and desmutting aluminum surfaces subsequent to the final metal finishing operation.

It is an important procedure in the aluminum finishing industry, prior to the finishing operations mentioned above, to remove the ever-present oxide film which forms on the surface of aluminum alloys on atmospheric exposure. A typical method employed in the past by which this is achieved is to immerse the previously degreased aluminum object in a suitable deoxidizing solution, which usually contains oxidizing agents such as chromic acid, chromates or dichromates, nitric acid or a mixture of these materials in Well defined proportions. Their function is to replace this tenacious oxide film on the aluminum alloy by another film more suitable for subsequent treatments.

The use of chromic acid or any other chrome base deoxidizing solution in the finishing industry creates waste disposal difficulties since these formulations must be treated chemically before they can be disposed of safely. Also the use of chromic acid in certain finishing shops may cause contamination of rinsing Waters, bright dips, anodizing and plating solutions. Furthermore, the use of nitric acid is always accompanied by obnoxious fumes which makes for uncomfortable and health hazardous conditions as well as corrosive action in many plating installations.

Another procedure frequently used heretofore in the aluminum finishing industry as a preparatory step, prior to the finishing treatments, consists of etching the aluminum alloy in a suitable alkaline solution, thereby removing substantial amounts of surface metal. During this etching process, certain alloying elements of the aluminum, which are insoluble in the etching solution, will cover the surface in the form of a loose coating forming an unsatisfactory basis for further treatment, and care must therefore be taken to see that this loose coating is completely removed. This phenomenon is known in the industry as smut formation, and removal of the smut is also covered by the term deoxidizing as it is used in practice and in the present specification and appended claims.

3,634,262 Patented Jan. 11, 1972 It is therefore a primary object of this invention to provide a novel deoxidizing solution which is free of waste treatment difliculties and wherein the ingredients are readily controllable at the room operating temperature of the solution; also to provide a solution compatible with bright dip and anodizing solutions. It is a further object of the invention to eliminate adherent films on the articles undergoing treatment and the production of offensive fumes and insoluble residues in the bath, which disadvantages have inherently characterized prior aluminum deoxidizing and desmutting operations. Among other advantages of the treatment herein disclosed is the fact that the bath components used are physiologically safe, Which makes them Well suited for treating aluminum objects to be used in the food industry. It is found that the deoxidizing action of the novel bath composition here disclosed is considerably faster than other existing proprietary deoxidizers. Other features and advantages of the invention will .be discussed as the description proceeds.

As previously pointed out, the novel deoxidizing and desmutting compositions of this invention contain at least one peroxydiphosphate compound which by itself in aqueous solution regardless of the concentration will not perform as a deoxidizer or deoxidizer-desmutter of aluminum or aluminum alloys. Surprisingly, the novel deoxidizing and desmutting solutions of this invention which comprise aqueous solutions of a peroxydiphosphate compound selected from the group consisting of ammonium peroxydiphosphate, an alkali metal peroxydiphosphate and an alkaline earth metal, and certain acids or acid salts thereof in sufficient amount to provide a solution pH of not over 3.0, are excellent deoxidizing and desmutting compositions. The concentration of the peroxydiphosphate compound which can be varied over a wide range generally will be from about 18 grams per liter up to saturation. Such solutions provide excellent deoxidizing and desmutting action on aluminum and all aluminum alloys with the exception of those alloys having a high silicon content. These novel aqueous solutions are especially useful in deoxidizing and desmutting wrought aluminum and Wrought aluminum alloys. Further, it has been found that casting alloys with silicon content not in excess of 1%, can be handled with these same solutions provided a fluoride anion is included as one of the ingredients.

In the deoxidizing-desmutting process of this invention, the peroxydiphosphates react with the aluminum or its alloying elements and are reduced to the orthophosphates. Thus, the bath after being exhausted, can be conveniently disposed of after neutralization as in the case of any other spent acid solution.

Furthermore, introduction of a suitable wetting agent such as any of the well-known surface tension depressing ionic or nonionic materials, is found to be of great assistance in removing oxide films from aluminum strip processed in continuous operation, wherein the aluminum strip is moved at high speed through a trough containing the deoxidizing solution and then through a rinsing trough. Large quantities of aluminum strip can be processed during short periods of time in such manner. Such treatments are impossible with chrome type deoxidizers which require very abundant rinsing that cannot .be provided in a continuous operation.

Another advantage of this formulation is that it will not dimensionall alter or aflect aluminum objects that are immersed, even for very prolonged periods of time.

Alkali metal peroxydiphosphates which can be employed in formulating the novel solutions of this invention include sodium, potassium and lithium peroxydiphosphates while the useful alkaline earth metal peroxydiphosphates include calcium and magnesium.

As previously pointed out it is sometimes advantageous add a fluoride anion to the novel solutions of this inention and this is especially true with regard to alumiium alloys which contain a considerable amount of silicon such as Type 6061, 6063, etc. A wide variety of soluble iuoride compounds canbe employed although it is preferred to utilize a fluoride compound selected from the group consisting of NaF, Natl-1P NH HF Na siF HF, FIBF KF, KHF NaHF NH P, K SiF Fel and mix- :ures thereof. Generally, 'sufiicient soluble fluoride comaound is added to provide a fluoride ion concentration in :he aqueous solution of from 0 to about 6 grams per liter.

Acids useful in preparing the novel compositions of his invention include sulfuric, phosphoric, sulfamic, and nixtures thereof; acid salts of these same acids, such as lOdlllIl'l bisulfate, potassium bisulfate and mixtures there- )f. Preferably, the acid used in preparing the novel dexidizing solutions is sulfuric acid. Sufiicient acid, acid .alt, or a mixture of these two materials is added to the iovel bath composition to provide a pH of not more than L0.

A complete deoxidizing process for aluminum and aluninum alloys utilizing the novel acidic aqueous peroxyliphosphate solutions of this invention together with the isual cleaning and etching steps is as follows:

PROCESS I '1) 3 to 5-minute immersion in a non-etch aluminum soak cleaner at a concentration of 8 to 10 oz./ gal. and at 160 to 180 F.,

:2) 30-second cold water rinse,

:3) 1 to 3-minute immersion in an alkaline etchant at a concentration of 8 to 10 oz./gal., temperature 160 to 180 F.,

4) 30-second cold water rinse,

5) l to 10-minute immersion in an acidic aqueous potassium peroxydiphosphate solution at a temperature about 60 to about 170 F. to desmut and deoxidize the aluminum,

16) 30-second cold water rinse, and

7) subsequent finishing operations such as: anodizing,

chromating, etc.

A similar process in which the etching step is not emloyed comprises the following steps:

PROCESS II 1) 3 to S-minutes immersion in an alkaline non-etch aluminum soak cleaner at a concentration of 8 to 10 02/ gal. and at a temperature of about 160 to 180 F.,

2) 30-second cold water rinse,

3) 1 to S-minute immersion in an acidic aqueous potassium peroxydiphosphate solution at a temperature of about 60 to about 170 F., to deoxidize the aluminum,

4) 30-second cold water rinse, and

5) subsequent finishing operations such as: anodizing,

chromating, etc.

Generally, the metal surface is immersed in the acidic ,queous peroxydiphosphate bath for about 1 to about 0 minutes or more and preferably for about 1 to about 1 minutes. A useful deoxidizer-desmutter solution not nly must remove smut and deoxidize the aluminum but .lllSt also not have a detrimental effect on the metal surace with extended immersion times. These requqirements re met in the novel acidic peroxydiphosphate solutions f this invention.

In another aspect, this invention relates to dry comositions which can be dissolved with mixing in water form deoxidizing and desmutting solutions of the type reviously described. The dry compositions of this inention comprise (l) a water soluble peroxydiphosphate alt selected from the group consisting of ammonium perxydiphosphate, an alkali metal peroxydiphosphate and n alkaline earth metal peroxydiphosphate, (2) an acid alt of sulfuric acid and, optionally, a soluble fluoride salt. Generally, the novel dry compositions of this invention will contain the following ingredients in approximate percentages indicated below:

Ingredients: Percent by weight Peroxydiphosphate salt 520 Acid salt of sulfuric acid 77-95 Fluoride salt 0-3 Any of the peroxydiphosphate salts, acid salts of sulfuric acid, and fluoride saltspreviously described in connection with the description of the novel deoxidizing and desmutting solutions of this invention can be employed in preparing the novel dry compositions.

The pH of the aqueous solution prepared from the dry compositions must be less than 3.0 if the resulting solution is to operate effectively as a deoxidizing and desmutting composition. However, if adjustment of the pH is required, it can be conveniently carried out through the addition of sulfuric acid in any needed amount.

Dry powder compositions offer a number of advantages over the liquid compositions especially with regard to easier handling and lower shipping weights. Further, the use of such dry compositions offers the additional advantage of elimination of the majority of the weighing out or measuring operations thus further reducing the possibility of faulty make-up.

The following examples illustrate various embodiments of this invention and are to be considered not limitative.

Example I An aqueous solution containing the following ingredients in the amounts indicated, in addition to water, was prepared:

Potassium peroxydiphosphate (K P O )--120 g./l. I Sulfuric acid (66 B.)40 ml./l. pH 3.0

Aluminum objects prepared from Type '7075 aluminum alloy (Analysis: 1.6% Cu, 2.5% Mg., 5.6% Zn,

7 0.2% Cr-balance Al plus impurities) were immersed in a non-etch aluminum soak cleaner having a concentration of 8 oz./ gal. at 170 F., rinsed in cold water, immersed in an alkaline etchant at a concentration of 10 oz./gal. at F. for 3 minutes during which time a heavy dark smut developed on the surface of the aluminum objects, again rinsed in cold water, immersed in the above-described solution of potassium peroxydiphosphate at a temperature of 70 F. for 3 minutes; and then rinsed for 30 seconds in cold water. The thus-treated aluminum objects exhibited light and smut-free surfaces which provide an excellent base for subsequent finishing operations such as painting, dyeing, chromating, etc.

Example II In this example an aqueous solution having the following composition is employed in treating the surfaces of aluminum objects:

Lithium peroxydiphosphate (Li P O )--lO5 g./1. Sulfuric acid (66 B.)60 ml./l. pH 3.0

Utilizing the same procedure and cleaning and etching solutions utilized in Example I, aluminum objects of Type 2024 alloy (Analysis: 4.5% Cu., 0.6% Mn, 1.5% Mgbalance Al plus impurities) are desmutted and deoxidized in the above-described lithium peroxydiphosphate solution. The resulting aluminum alloy objects possess light surfaces completely free of smut which are highly satisfactory for further finishing.

Example 111 In this example articles made of an aluminum alloy having a substantial silicon content are deoxidized and 6 desmutted using an aqueous solution of the following com- What is claimed is: position: 1. A composition for desmutting and deoxidizing aluminum and aluminum alloys consisting essentially of a mig i l g ggg g ZE g f f 140 dry admixture of from about to 20 weight percent of Sulfuric acid mL/L 5 a compound selected from the group consisting of an P alkali metal peroxydiphosphate, an alkallne earth metal peroxydiphosphate, and ammonium peroxydiphosphate; Aluminum articles maHllfamI edf1'm p 6061 alloy from about 77 to 95 weight percent of an acid salt of (Analysis: 0.25% Cu, 0.6% S1, 1.0% Mg and sulfuric acid and from 0 to about 3.0 weight percent of Crbalance vAl plus impurities) are first cleaned by im- 10 water-soluble fluoride alt,

mersion for 5 minutes at 160 F. in an alkaline non- The Composition of claim 1 wherein the Said etch aluminum soak cleaner at a concentration of 8.5 pound is potassium peroxydiphosphate. oz./gal., rinsed 1n cold water for 30 seconds, immersed 3. The composition of claim 1 wherein the Said acid in the peroxydiphosphate solution previously prepared in Salt of Sulfuric acid is sodium bisulfate a thls example for mmutes at 80 and "used agant for 4. The composition of claim 1 wherein the said fluoride about 30 seconds in cold water. The thus-treated articles salt is sodium fluoride.

exhibit aluminum surfaces which are of excellent appear- A composition according to claim 1 consisting s gq i g q gmshmg operatlons Such sentially of about 15.3 Weight percent of potassium peroxyas P osp a mg lppmg e diphosphate with the balance being sodium bisulfate.

E l 1V XII 6. A deoxidizing and desmutting solution for aluminum and aluminum alloys consisting essentially, in addition to water: (1) a soluble peroxydiphosphate compound selected from the group consisting of ammonium peroxydiphosphate, an alkali metal peroxydiphosphate and an In these examples articles prepared from Type 6061 and 6063 aluminum alloys which contain substantial quantities of silicon were cleaned, etched and then treated at a temperature of 72 F. in an acidic aqueous peroxydiphosphate solution in the same manner as described in alkaline earth metal p p p ill of Example I. Pertinent data relating to the acidic peroxyb011t 18 1 t0 SaturatlOIl; a Soluble flu ride Salt diphosphate compositions utilized in these examples is in amount sufficlent to provide a fluoride ion concentrashown in Table 1 which follows: tion in the solution of from 0 to about 6 -g./l. and (3) an TABLE 1 Example Number IV V VI VII VIII IX X XI XII Deoxidizing solution composition: 1

Potassium peroxydiphosphate (g./

1 Ingredients shown are in addition to water.

In each instance the surfaces of the resulting aluminum acid material selected from the group consisting of sul articles, which were smut-free and of light appearance, furic, phosphoric and sulfamic acid, the acid salts thereof, provided a highly satisfactory base for further finishing and mixtures of the said acids and acid salts, in amount operations. sufficient to provide a solution pH of not more than 3.0.

Example XIII 7. The solution of claim 6 wherein the said peroxydiphosphate compound is potassium peroxydiphosphate.

8. The solution of claim 6 wherein the said acid is sulfuric acid.

9. The solution of claim 6 wherein said fluoride salt is sodium fluoride.

10. A solution according to claim 6 consisting essentially, in addition to water, potassium peroxydiphosphate and sulfuric acid.

11. A process for deoxidizing and desmutting aluminum and aluminum alloy articles which comprises treating said articles by immersing them for a period of about 1 to about 10 minutes at a temperature of about 60 F. to about 170 F. in a solution consisting essentially, in addition to water: (1) a soluble peroxydiphosphate compound selected from the group consisting of ammonium peroxydiphosphate, an alkali metal peroxydiphosphate,

A dry mixture is prepared by admixing 100 g. of finelydivided sodium bisulfate and 19 g. of finely-divided sodium bisulfate and 18 g. of finely-divided potassium peroxydiphosphate. This composition, when thoroughly mixed, can be stored for long periods of time in appropriate shipping containers without hazard and without deterioration.

An aqueous solution is prepared containing 118 g. of the above-described dry mix per liter (pH about 1.6). This solution is employed in desmutting and deoxidizing articles prepared from Type 7075 aluminum alloy in the same manner as set forth in Example I. The thus-treated articles possess a light and smut-free surface highly suitable for further operations including anodizing, dyeing, painting, etc.

Example XIV and an alkaline earth metal peroxydiphosphate, in amount An acidic aqueous composition containing, in addition of about 18 g./l. up to saturation; (2) a soluble fluoride to water, 120 g./l. of potassium peroxydiphosphate and salt in amount sufiicient to provide a fluoride ion con- 40 mls. of sulfuric acid (66 B.) is prepared. centration in the solution of from 0 to about 6 .g./l. and Aluminum articles constructed of Type 2024 and 7075 (3) an acid material selected from the group consisting aluminum alloys are first alkaline cleaned, rinsed and of sulfuric, phosphoric and sulfamic acid, and the acid then immersed in the peroxydiphosphate solution of this salts thereof and mixtures of the said acid and acid salts,

example for 4 minutes at a temperature of 90 F. to give in amount suflicient to provide a solution pH of not more smut-free articles. than 3.0.

8 References Cited UNITED STATES PATENTS 7/1964 Grunwald 134-3 3/1968 Grunwald 252186 X MAYER WEINBLATI, Primary Examiner U.S. Cl. X.R.