US3530048A

US3530048A - Bright anodized aluminum alloy

Info

Publication number: US3530048A
Application number: US703897A
Authority: US
Inventors: George Richard Darrow
Original assignee: Reynolds Metals Co
Current assignee: Reynolds Metals Co
Priority date: 1968-02-08
Filing date: 1968-02-08
Publication date: 1970-09-22
Anticipated expiration: 1987-09-22

Description

United States Patent 3,530,048 BRIGHT ANODIZED ALUMINUM ALLOY George Richard Darrow, Richmond, Va., assignor to Reynolds Metals (lompany, Richmond, Va., a corporation of Delaware No Drawing. Filed Feb. 8, 1968, Ser. No. 703,897 Int. (ll. C23b 9/02 US. Cl. 20433 11 Claims ABSTRACT OF THE DISCLOSURE A bright anodized article, such as a golf club shaft, of an aluminum alloy of the 7000 series, is produced by preconditioning the alloy prior to heat treatment, by subjecting the alloy to a cold mechanical work of at least 40%, followed by application of a deoxidizing bath. The alloy is then heat treated, the surface deoxidized again, chemically brightened by an aluminum phosphate bath at elevated temperature, and finally anodized and sealed.

BACKGROUND OF THE INVENTION The most widely used material for metal golf club shafts has been chromium-plated steel. This material has certain drawbacks, however, principally that of weight. Many efforts have been made in the past to adapt aluminum to golf club shaft requirements, since aluminum produces a lighter shaft under the same playing conditions and this enables the golf club designer to produce a club which will drive the golf ball further. Aluminum golf club shafts have not come into general use in the past, however, because until recently aluminum alloys having the requisite high strength and brightness approximating that of the conventional steel shafts were not available.

Aluminum alloy golf club shafts are in the form of hollow tubes made by extruding, drawing and tapering to get the desired shape. The length of the shaft ranges from 31 inches to 48 inches, the outside diameter from about 0.390 inch to 0.6 inch, and the wall thickness from about 0.032 inch to 0.065 inch.

Certain aluminum alloys of the 7000 series (Aluminum Association designation) have been found to be the most suitable for this purpose, particularly in regard to their favorable stress-corrosion resistance and high mechanical strength. The high strength alloys contain from 1.6 to 2.6 percent copper, 2.4 to 3.4 percent magnesium, 6.3 to 8.0 percent zinc, and small amounts of other elements such as silicon, iron, chromium and titanium.

The alloy of this series which is 'best suited for golf club shaft use because of its high strength and a minimumof stress-corrosion problems is alloy 7178, which has the nominal composition, in percentages by weight:

Copper 1.6-2.4 Magnesium 2.4-3.1 Zinc 6.3-7.3 Silicon 0.50 Iron 0.7 Manganese 0.30 Chromium 0 l80.40 Titanium 0.20 Other 0.05 Aluminum Balance For golf club shaft purposes the drawn and tapered shaft made from the 7000 series alloy must be subjected to solution heat treatment, quenching and aging suitable for the particular alloy, then mechanically or chemically polished, and finally anodized, to produce a bright finish on the outer surface.

Efforts to utilize alloys of the 7000 series in this way 353,048 Patented Sept. 22, 1970 ICC have been unsuccessful in the past because the color and appearance of the heat treated and anodized shaft were unsatisfactory. The finished shafts exhibited a greyish pewter color, with a broken surface. This condition was believed attributable to the high copper and zinc content of these alloys and to the effects of the heat treatment. Attempts to improve he appearance by chemical polishing of the heat treated surface were likewise unsuccessful, because usually slight etching of the surface rather than brightening took place, and this further impaired the appearance of the final product. Another drawback was that even after anodizing, the anodic coating would become grey and lose whatever brightness it originally had.

It was accordingly the principal object of the invention to produce an aluminum alloy shaft for golf clubs or the like (e.g., ski poles), Which could be heat treated, polished and anodized to a lasting bright finish.

Another object was to produce a bright finished golf club shaft from an alloy of the 7000 series, and particularly alloy 7178.

SUMMARY OF THE INVENTION In accordance with one aspect of the present invention, it has been found that adverse effects of heat treatment of aluminum alloys of the 7000 series can be avoided or minimized by subjecting the alloy to at least 40% cold Work from zero temper prior to the heat treatment. In the case of a golf club shaft, the extrusion is usually annealed to zero temper and then cold work is imparted by drawing and tapering the extrusiondown to final shape. Thus, for example, a 1 inch outside diameter tube drawn down to 0.6 inch outside diameter represents approximately a 40% reduction, which is typical for the large end of the shaft. Additional cold work may be imparted by tapering the small end of the shaft down to 0.39 inch outside diameter, representing a 60% reduction at the small end of the shaft. The shaft may have a straight or stepped taper, with progressively increased cold work. toward the small end of the shaft.

The foregoing cold work conditioning treatment permits the subsequent heat treatment to be performed so as to obtain the required minimum physical properties in the alloy, while at the same time imparting to the heat treated alloy the capability of accepting polishing treatment, and eventual anodizing to a. bright finish, free from discoloration and surface blemishes.

In accordance with a second aspect of the invention, it has been found advantageous to subject the cold worked alloy to a deoxidizing treatment prior to the heat treatment. This further conditions the shaft for heat treatment, and constitutes a surprising and unexpected improvement, because these alloys are normally susceptible to corrosion, and it was the prevailing practice to leave the natural oxide film on the alloy surface before heat treating to protect it from corrosion during the heating and quenching steps.

The deoxidizing treatment is performed by immersing the article in an acid bath containing a mineral acid, such as sulfuric acid, and either chromic acid, or an alkali metal chromate, or dichromate, or bisulfate. Suitable alkali metals include sodium and potassium. Thus, the range of concentration of the sulfuric acid may lie between about 7.5% and 9.0% by weight, and that of the chromic acid or equivalent constituent between about 2.5% and about 3.5%, the remainder of the bath being Water. A suitable deoxidizing bath is an aqueous solution of 3% CrO and 8% H by weight, which is applied at a temperature between about 70 F. and F. This bath dissolves the aluminum. oxide film. The dip is followed by a warm water F. or more) rinse to dry the metal surface prior to heat treatment. The heat treating step should be performed within about 6 hours of deoxiding.

Thus, in accordance with the invention, the preconditioning cold work treatment and the deoxidizing treatment cooperate to produce an unexpected improvement in the heat treatment and especially in the bright anodizing response of the alloy.

While the process of the present invention is applicable to the aluminum alloys of the 7000 series generally, such as, for example, alloys 7001, 7075, 7079, 7175 and 7178, it is particularly well adapted to the improvement of alloy 7178. Accordingly, the description of the process will be illustrated with respect to alloy 7178, but it is to be understood that the general sequence of steps is applicable to the other alloys of the series, with appropriate variations depending upon the particular alloy being treated.

The types of heat treatment for the individual alloys of the 7000 series are known and do not constitute a part of the present invention. Typically, solution heat treatment takes place at between 820 F. and 950 F. In the case of 7178 alloy, for example, the solution heat treatment is performed at a temperature between 860 F. and 930 F., preferably at 870 F.::l F. for about 20 minutes. This is followed by quenching in water at a temperature of about 90 F. or lower, within 1 to a maximum of 5 seconds. For best results, the 5 second limit is critical. The article is then aged at about 240 F. to about 260 F., preferably at 250 F.i5 F. for 24 hours.

Following the heat treatment, the article is again deoxidized to remove all naturally formed oxide and heat treatment scale. The deoxidizing step is performed with the same type of bath as employed in the previous deoxidizing treatment, and it greatly contributes to the clarity of the anodic film subsequently formed on the shaft.

The aluminum alloy article may thereafter be subjected to mechanical finishing, such as surface buffing or polishing, to impart an acceptable degree of surface luster.

In order to maintain and improve the final brightness of the anodized article, while allowing for cleaning of the surface, the shaft is then subjected to a chemical brightening treatment using an acid bath of specially selected type which will not diminish but improve the specularity of the surface, and which contains aluminum phosphate as an active chemical reaction limiting ingredient. Aluminum phosphate acid baths have been known in the prior art for the brightening of automotive trim. They contain about 6% to 7% by weight of aluminum phosphate or less, together with surfactants, and are conventionally applied at temperatures in the range of 190 F. to 210 F. These automotive type bathsproved unsuited for aluminum alloy golf club shaft treat ment.

In accordance with the present invention, it was found that by employing a special aluminum phosphate brightening bath, the specularity of the article would be improved, and the anodizing effect would be enhanced. The bath composition must be carefully controlled, the following ranges of composition being critical:

Aluminum phosphate Al (PO 910% by weight Nitric acid HNO 3-3.5 by weight Phosphoric acid H PO 65-70% by weight Copper added as sulfate: 0.00150.0025% by weight Water: 18-21% No surfactants are employed, and the bath is applied to the article at a temperature between about 225 F. and 230 F. for a period of time between about 1.3 and 1.7 minutes. The aluminum phosphate can be incorporated as such, or can be formed in situ by using aluminum hydroxide as an ingredient.

The article is then ready for anodizing. This step is performed in accordance with conventional practice, employing a mineral acid electrolyte, preferably sulfuric acid at a concentration between about 12% and 20% by weight, for example 15%. Anodizing temperature lies between about 70 F. and F., preferably 75 F.:1 F. Current density range from about 10 to 15, and preferably 12 amperes per square foot. Anodizing time is sufficient to produce an oxide film of 0.10 to 0.45 mil thickness, preferably 0.20 mil. After anodizing the anodic coating is sealed by treatment with hot water, preferably deionized water, at a temperature between about 206 F. and 211 F. for at least 15 minutes. The pH of the water should be adjusted to between 6.0 and 6.5, by addition of a small amount, e.g. 4 p.p.m. of a phosphate buffer, and 1000 ppm. of sodium acetate.

Thus, there is within contemplation of the present invention the preconditioning of the aluminum alloy article before heat treatment, and comprising the steps of subjecting the article to a cold mechanical size reduction of at least 40%, followed by deoxidizing the surface of the alloy. The invention also includes the entire sequence of bright anodizing an aluminum alloy article, such as a golf club shaft, by heat treating the previously cold worked and deoxidized alloy, followed by chemical brightening, anodizing, and optionally, sealing the anodized article.

DESCRIPTION OF THE PPREFERRED EMBODIMENT The following example illustrates a present preferred practice of the invention:

Example An extruded tube of 7178 aluminum alloy having an outside diameter of 1 inch was cold drawn down to 0.6 inch outside diameter, and further drawn down to 0.39 inch, representing a reduction of about 60%. The tube was then deoxidized by applying to the surface an aqueous solution containing 8% H SO and 3% CrO by weight to dissolve the oxide film. This treatment was followed by a warm water rinse at 160 F. and the metal surface was allowed to dry. The tube was then solution heat treated at 870 F.il0 F. for 20 minutes, then quenched in water at F. within 5 seconds after leaving heat treatment, and then aged for 24 hours at 250 Fi-5 F. The tube was again deoxidized with the same deoxidizing solution, and then mechanically buffed to a good surface luster. The article was then chemically brightened by immersion in a solution containing 9% Al (PO 3% HNO 18% H 0, 65% H PO and 0.0015% copper added as sulfate, at 225 F. for 1.5 minutes. The article was rinsed and anodized in 15% sulfuric acid at 75 F.:1 F. at 12 amperes per square foot current density until an oxide film of 0.14 mil thickness was obtained. The coating was then sealed with deionized water with 3 ppm. phosphate added and buffered to pH 6.0. The resulting coating was lustrous and attractive.

While present preferred embodiments of the invention have been described, and have been further illustrated by by an example, it will be recognized that the invention may be otherwise variously embodied and practiced within the scope of the following claims.

What is claimed is:

1. Process of producing a bright anodized article of an aluminum alloy of the 7000 series, comprising the steps of:

(a) subjecting said article to a cold mechanical size reduction of at least 40%;

(b) deoxidizing the surface of the alloy by applying to the article a bath containing a mineral acid and a member selected from the group consisting of chromic acid, an alkali metal chromate, an alkali metal dichromate, and an alkali metal bisulfate;

(c) solution heat treating, quenching, and aging the article;

(d) deoxidizing the surface of the heat treated alloy by applying to the article the bath recited in step (e) chemically brightening the surface of the article by applying thereto an aqueous solution of the composition: Al (PO 910%, HNO 3-3.5%, H PO 65-70%, H O 18-21%, copper added as sulfate 0.00l50.0025%, percentages being by weight, at a temperature between about 225 F. and 230 F.; and

(f) anodizing the article.

2. The process of claim 1 in which the alloy is 7178 alloy.

3. The process of claim 1 in which the article is a tubular extrusion.

4. The process of claim 1 in which the article is a golf club shaft.

5. The process of claim 1 in which the mechanical size reduction is made by cold drawing.

6. The process of claim 1 in which the deoxidizing bath consists essentially of sulfuric acid and chromic acid.

7. The process of claim 1 in which the article is memechanically finished to acceptable surface luster following the second deoxidizing step.

8. The process of claim 1 in which the anodized coating is sealed with hot Water.

9. A bright anodized 7178 aluminum alloy golf club shaft produced according to the process of claim 1.

10. Process of producing a bright anodized tubular article of an aluminum alloy of the 7000 series, comprising the steps of (a) forming a tubular extrusion of said alloy;

(b) annealing said tubular extrusion to zero temper;

(0) drawing and tapering said extrusion to effect a cold mechanical size reduction of at least 40%;

(d) deoxidizing the extrusion by applying to the surface a bath containign a mineral acid and a member selected from the group consisting of chromic acid,

an alkali metal chromate, an alkali metal dichromate, and an alkali metal bisulfate;

(e) solution heat treating the extrusion at a temperature between about 860 F. and about 930 F.;

(f) quenching at a temperature not above about 90 F. for a maximum of 5 seconds;

(g) aging at a temperature of about 240 F. to about (h) deoxidizing the article as in step (d);

(i) subjecting the article to mechanical polishing;

(j) chemically brightening the surface of the article by applying thereto an aqueous solution of the composition: Al (PO 9-10%, HNO 3-3.5%, H PO -70%, H O 18-21%, copper added as sulfate 0.00150.0025%, percentages being by weight, at a temperature between about F. and F. and at a current density from about 10 to 15 amperes per square foot.

11. The process of claim 10 in which the article is a golf club shaft.

References Cited UNITED STATES PATENTS Re. 26,216 5/1967 English 20458 XR 2,941,930 6/1960 Mostovych et al 204-29 3,180,806 4/ 1965 Hollingsworth 20429 3,351,442 11/1967 Hooper 204-29 XR FOREIGN PATENTS 763,549 12/ 1956 Great Britain.

DANIEL E. WYMAN, Primary Examiner P. E. KONOPKA, Assistant Examiner US. Cl. X.R..