US2731343A - Copper base alloy - Google Patents

Description

Jan. 17, 1956 E. J. DUNN 2,731,343

COPPER BASE ALLOY Filed July 25, 1952 2 Sheets-Sheet l 87,8 Cu, MAL, 4H 84.5 cu, 7.6m, 3.92m, 5.71% Ppww Ppafgou-GOW INVENTOR. :Ed-wurd LT. Dunn 7m9g ma; fpEA/T Jan. 17, 1956 E J, DUNN 2,731,343

COPPER BASE ALLOY Filed July 25, 1952 2 Sheets-Sheet 2 JNVENTOR. Edwurd T T. Dunn AGE/v1- N United States Patent O COPPER BASE ALLOY Edward J. Dunn, Arlington County, Va. Application July 25, 1952, Serial No. 301,009 6 Claims. (Cl. 75--162) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention herein described, if patented, may be manufactured and used by or for the Government of the United States for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to the production of new and useful alloys.

Objects ofthe invention include: the production of alloys useful as bearing metals; thepreparation of copper-base alloys containing aluminum, and having no appreciable tin content; the production of copper-base, tin free, aluminum-containing alloys having improved characteristics.

Copper-base alloys find conventional use in the bearings of automotive engines, such as a piston or wrist pin bushings. In manufacturing such bearings it is accepted practice to cast the metal in the shape of rods or bars, and to then subject the rods or bars to rolling, stamping, and annealing operations. In working metal alloys it is important that the materials to be worked possess characteristics that will enable them to undergo, without eX- tensive rupture, or cracking, the stresses and deformations that are incident to metal working.

For such purpose it has been customary to use copperbase alloys containing copper in preponderant proportion with lesser quantities of lead, tin, and zinc. Recently however inasmuch as tin has become a material of strategic importance, research has been directed to the development of alloys which will not be dependent upon the more or less uncertain supply of itin. In this View the i employment of aluminum as a replacement component to take the place of tin in copper-base alloy compositions, has been considered. i

Now it has been found that alloys containing aluminum as a replacement component, while exhibiting certain advantages are deficient in qualities valued as being desirable in a bearing alloy. Especially troublesome is the fact that` known compositions of copper-base aluminumcontaining alloys do not uniformly resist shear under the stresses and deformations incident to rolling and working operations.

I have found that copper-base aluminum-containing alloys may be produced which not only serve the important purpose of saving tin, but which are characterized by excellent physical properties as will become more fully evident from the ensuing description.

In order to illustrate characteristics that distinguish my invention from the prior art reference is had to the accompanying drawings which graphically set forth the nature of the invention in certain of its more specific aspects.

Figure l. is a photomicrograph, at a magnification of X 75, of the etched surface of an alloy of a prior art composition of 88 parts copper, 4 parts tin, 4 parts zinc, and 4 parts lead.

Figure 2 is a photomicrograph of the etched surface of the alloy of Figure l, at a magnification of X 500.

Figure 3 is a photomicrograph at a magnification of X 75, of the etched surface of a prior art alloy of compositiou 88 parts copper, 4 parts aluminum, 4 parts zinc, and 4 parts lead.

Figure 4 is a photomicrograph of the etched surface of the alloy of Figure 3, at a magnification of X 500.

Figure 5 is a photomicrograph at a magnification of X 75, of the etched surface of an alloy prepared according to the present invention and of composition 87.8 parts copper, 8.2 parts aluminum, and 4 parts lead.

Figure 6 is a photomicrograph of the etched surface of the alloy of Figure 5, at a magnification of X 500.

Figure 7 is a photomicrograph at a magnification of X 75, of the etched surface of an alloy prepared according to the present invention and of composition 84.8 copper, 7.6 aluminum, 3.9 zinc, and 3.7 lead.

Figure 8 is a photomicrograph of the etched surface of the alloy of Figure 7, at a magnification of X 500.

Figures 5 to 8 graphically display the grain structure of alloys corresponding to the present invention, and Figures l to 4, the grain structure of alloys corresponding to the prior'art.

in each of the Figures 1 to 8 there is shown a segregation of the lead component manifest by dark heavy markings. The identity of the lines in the figures which show the structures in lower (X 75) magnification, as consisting of a series of dots or particles, is well shown in Figure 3.

Figures l and 2 display the grain structure of a tincontaining copper-base alloy known to the art. Figures 3 and 4 display the grain structure of :a type of alloy wherein the tin component has been replaced, by aluminum. The alloy of Figures 3 and 4 corresponds to that described in Patent No. 2,492,786, issued December 27, l949, to Harry P. Croft, and Edward J. lDunn.

Figures 5 and 6, and Figures 7 and 8, respectively, illustrate different species or embodiments of the present invention, the compositions of which are as` follows:

nishes strong evidence of an existing correlation between the internal structure of the alloy and the physical properties exhibited thereby. In each case there is displayed a characteristic separation of the lead. In those alloys,

`which contain a relativelyminor amount of aluminum i. e. in Figures 3 and 4, the photomicrographs reveal the segregation of the lead to follow a preferential separation in the interstices between the matrix grains or crystals. This structure, which manifestly decreases the bonding area between crystals, or otherwise stated, interposes a separating wall between the contiguous interfaces, furnishes not only clear evidence of a critical difference in structure, but also a correspondence between this structure and the relative Weakness of the alloy in regard to its resistance to fracture and shear.

On the other hand the heterogeneous distribution of the lead particles in the alloys whose structure is indicated in Figures 5, 6, 7 and 8, furnishes graphic evidence that serves to account for the higher resistance to fracture and shear on the part of the alloys corresponding to the present invention.

The lead in the alloy shown in Figures 1 and 2 does not occur at the dendrite grain boundaries, but to a very large extent, is surrounded by a coring of the matrix, as can be seen when the alloy is lightly etched. On the other hand, in the alloy shown in Figures 3 and 4 the lead is much more highly concentrated at the grain and dendrite boundaries. In attempting to produce the alloy of the Figures 3 and 4 on a laboratory mill scale, difliculty was experienced with the formation of cracks in the material. The iigures lend conrmation to the theory that the tender quality of the alloy as developed on the cast breakdownV rolling, is ascribable to the relatively reduced boundary area due to the occupancy of the boundary areas by the lead.

In view of the results obtained with tin-containing aluminum-free alloys of known composition such as are shown in Figures l and 2 in relation to thhe aluminum-containing tin-free alloy shown in Figures 3 and 4 the suggestion to decrease the proportion of aluminum appeared as a logical solution. Likewise alteration in the content of zinc was suggested. These suggestions were put to test. However, these proposals in general did not lead to successful results.

It was found however, that the alloys of higher aluminum content exhibited unexpected improvement in working properties. Accompanying the improvement there has occurred in the alloys of the higher aluminum content a remarkable change in the lead distribution as shown in the photomicrographs, Figures 5', 6, 7 and 8 whether the Zinc is present or absent as an element in the composition. These high-aluminum content alloys when worked and annealed, exhibit an alpha structure. They take hot squashing in the laboratory tensile machine very satisfactorily, the compositions corresponding to Figures 7 and 8 being particularly outstanding in this respect. The alloys of Figures 7 and 8 took the first pass in hot rolling at 1550 F. without cracking. Both alloys have good hot and cold malleability, and when hot rolled, annealed, and cold rolled, display a yield strength up to 47,400 p. s. i. an ultimate tensile strength up to 60,000 p. s. i., an elongation of 4% and a hardness of R383. When further cold rolled, annealed, and cold rolled 27%, these alloys display a yield strength up to 62,000 p. s. i., an ultimate tensile strength up to 81,000 p. s. i., an elongation of 14% and a hardness of R392. Annealed at 1,250 F., these alloys display a yield strength as high as 33,000 p. s. i., an ultimate tensile strength up to 67,000 an elongation of 32% and a hardness of RB65.

The proportions of the composition may be varied within a range compatible with operability. In general it has been found desirable to establish the copper content within a range that does not depart significantly from 83.8 to 87.8 per cent, the aluminum content within a range of 6.6 to 8.6 percent, while zinc may be present in amount usually not higher than 5 per cent, i. e. the range being substantially 5.0 to 0.0 per cent. The lead component will usually remain within the range of 2.7 to 4.7 per cent although it has been found possible to increase the lead content considerably, without departing from a uniform cast lead distribution, and without adversely diminishing the aforesaid desirable physical properties. The lead content may in fact rise as high as 10%, provided the copper-aluminum ratio is maintained Within the functional range. In this respect it is of definite advantage to incorporate lead in such higher proportion, while keeping the ratio of copper to aluminum within a value of approximately 9.7 to 13.3. This higher lead content is of value when it is an object to produce an alloy having advantages for use as a cast bearing metal particularly for bearings that encounter sand and grit, and bearings subject to poor or inadequate lubrication, such as automobile spring shackles or steering mechanisms. As will be readily understood by those skilled in the art, the proportions of components of the alloy composition, in any case, must be correlated to the desired performance characteristics. y

It will also be understood that while the foregoing description has been given in terms of pure metals, the invention contemplates the use of metals from commercial sources, which may include traces of additional metals or other substances provided these inclusions are not in such quantity and quality as to interfere with the basic character of the alloys.

Having now fully disclosed the invention what I claim and desire to secure by Letters Patent is:

l. A copper base alloy consisting essentially of 8.2 per cent aluminum, 4 per cent lead and 87.8 per cent copper.

2. A copper base alloy consisting essentially of 7.6 per cent aluminum, 3.9 per cent Zinc, 3.7 per cent lead, and 84.8 per cent copper.

3. A copper base alloy consisting of 6.6 to 8.6 per cent aluminum, 2.7 to 10% lead and the balance copper.

4. A copper base alloy consisting of 6.6 to 8.5% aluminum, 2.7 to 4.7% lead and the balance copper.

5. A copper base alloy consisting of 6.6 to 8.6 per cent aluminum 2.7 to 10% lead, up to 5.0 per cent zinc and the balance copper.

6. A copper base alloy consisting of 6.6 to 8.6 per cent aluminum, 2.7 to 4.7 per cent lead, up to 5 .0 per cent zinc and the balance copper.

References Cited in the le of this patent UNITED STATES PATENTS 2,062,426 Pierson Dec. 1, 1936 2,245,459 Buhler June 10, 1941 2,271,969 Davis et al. Feb. 3, 1942 2,492,786 Croft et al. Dec. 27, 1949 2,494,736 Berwick Ian. 17, 1950 OTHER REFERENCES Aluminum Bronze, Copper Development Assn., Thames House, Millbank, London (1939), pages & 61.

Metallurgia, vol. 41, Issue 245, pages 242-243 relied on. March 1950.

Claims (1)

1. 3. A COPPER BASE ALLOY CONSISTING OF 6.6 TO 8.6 PER CENT ALUMINUM, 2.7 TO 10% LEAD AND THE BALANCE COPPER.

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