US2101625A - High strength corrosion resistant copper alloy - Google Patents

Description

Dec. 7, 1937.

E. L. MUNSQN 2,101,625

HIGH STRENGTH CORROSION RESISTANT COPPER ALLOY Filed June 1, 1937 2 Sheets-Sheet l ATTORNEYS Dec. 7, 1937. E. L. MUNSON 2,101,625

HIGH STRENGTH CORROSION RESISTANT COPPER ALLOY Filed June 1, 1937 2 Sheets-Sheet 2 INVENTOR PW ZZMKM o ATTORNEYS Patented Dec. 7, 1937 PATENT OFFICE HTGH STRENGTH CORROSION RESISTANT COPPER ALLOY Elmer L. MunsomNaugatuck, Connuassignor' to The American Brass Company, Waterbury, Conn., a corporation of Connecticut Application June 1. 1937, Serial No. 145,744

'1 Claims. (01. 1415-32) This invention relates to an improvement in non-ferrous alloys and particularly to an alloy whose principal constituentis copper plus various amounts of nickel and zinc, to which has I been added in the present invention small but essential amounts of aluminum, whereby increased strength, corrosion resistance, resistance to softening at elevated temperatures and other valuable characteristics are secured.

This application is a continuation in part of. my

prior application Serial Number 750,019, filed October 25,1934.

This application involves the alloys of copper, nickel, zinc and aluminum within the following ranges of the elements, 48% to 65% copper, 13.5% to 31% nickel, 1.0% to 21% zinc, 0.5% to 3% aluminum, which are single phase type (alpha solid solution) when heated to tempera- ;tures ranging from about 800 to 900 C. and quenched. These comprise the alloys in which the copper content maybe decreased progressively from 65% at 13.5% nickel down to 48% at 31% nickel when the aluminum content is 0.5%. and as the aluminum content is increased the copper decreases from the broadest range at the minimum of 0.5% aluminum down to the narrowest range at the maximum of 3% aluminum for these'commercial alpha alloys. The broadening of the alpha range is accomplished by the addition of increasing amounts of nickel,

in which case the copper may be correspondingly decreased for a given aluminum content. Ap-

parently copper and nickel are equivalents in obtaining the alpha solid solution noted herein,

that is, each added percentage of nickel may displace approximately an equal percentage of copper.

I have discovered.- that when small amounts of aluminum (from about 0.5% to about 3%) are added to the single phase type (alphasolid solution) copper-nickel-zinc alloys, new and valuable characteristics are obtained not heretofore found in said alloys. This addition of aluminum in amount from 0.5% to 3% to the coppernickel-zinc alloys involved causes a change from may be present in the alloy. In other words at temperatures below this line the structure is composed'of alpha plus precipitate or compound. At temperatures above 600 C. and up to about 750 C. the hardeningconstituent coalesces to such a degree that the precipitate or compound is renderedless effective as a hardening agent. The preferred hardening range extends from about 400 C. to 600 C. for periods-of about two hours. Below 400 C. some hardening occurs 10 in this length of time, but the precipitate is more or less submicroscopic and greater hardening may be secured by heating for longer periods. The maximum hardening temperature for the several annealed alloys in general gradually in- 1 creases as the nickel or aluminum is increased from about 450 C. to about 650 C. and for work hardened alloys from about 400 C. to about 600 C. Likewise there is a phase change when there is materially more than about 3% alumi- 20 num present in the alloy, and with aluminum contents above about this percent we again have a duplex structure.

In the accompanying drawinga which form a part of this specification, Fig. 1 is a graph show 25 mg the composition limits for cold workable alloys for an aluminum range of 0.5% to 3%.

Fig. 2 shows the portion of Fig. 1 in which the alloys or compositions show a remarkable resistance to softening when heated at elevated 30 temperatures. This chart shows the zones for three diiferent percentages of aluminum, from which the eflect of intermediate percentages of aluminum may-be'determined.

Fig. 3 is a composite plot for a series of alloys 35 containing 1.5% aluminum and shows the softening resistant zone shown in Fig. 2 and the softening zone, which zones together comprise the zone shown in Fig. l for this aluminum content.

Fig. 4 shows the range of alloys involved in the invention of this application. The diagrams of Figs. 1, 2 and 3 not only show the composition range involved in this application but also those involved in the prior application noted of which this application is a continuation in part. The curves are presented in full in order thatone skilled in the art may have a clearer and more concise'view of the entire range than would be given by the numerical limits of the present application.

Referring to Fig. 1, this shows the composition limits for cold workable copper-nickel-zincaluminum alloys for an aluminum range of 0.5%

to 3%. The maximum. and minimum copper content for alloys containing 0.5%, 1.5% and 3% aluminum, with nickel as indicated, and the remainder zinc, are shown by the curves in thisdrawing. Alloys falling within the ranges indicated were found to cold work satisfactorily. It was also found that alloys lying within these useful composition ranges were of the alpha solid solution or single phase type when heated at temperatures in the neighborhood of 850 C. and quenched. The limits for alloys containing intermediate amounts of aluminum may be obtained by interpolation. These curves also show that the addition of increasing amounts of aluminum up to 3% decreases the useful composition range for a given nickel content. That is to say, the minimum copper content must be increased progressively to compensate for the increase in aluminum content. The area bounded by lines A and HI indicates the broadest range, namely that for the alloys containing 0.5% aluminum. Lines C and DE bound the area representing the narrowest range, namely for the alloys containing 3% aluminum. Similarly the area bounded by lines B and FG represents as an example the range of alloys containing an intermediate amount of aluminum, namely 1.5%.

Figure 2 was prepared to show that portion of the total range shown in Figure 1, in which the alloys show a remarkable resistance to softening when heated at temperatures as high as 900 C. This chart shows the zones for given percentages of aluminum, namely 0.5%, 1.5% and 3%. The greatest resistance to softening, of course, is obtained with the lowest copper content indicated. These new alloys, though resistant to softening at elevated temperatures, are malleable at room temperature and can be cold forged, rolled, drawn, etc. to a limited though commercial extent, although considerable pressure is required to effect reduction thereof.

Most copper-base alloys can be softened by annealing at temperatures up to about 700 0.,- whereas some of the new alloys indicated do not soften at temperatures up to 900 C. Noteworthy is the fact that these alloys are composed of one single phase and yet resist softening-at 900 C. Other alloys containing from 8% to 10% aluminum, 2% nickel and 1% iron, are known to resist softening at temperatures up to about 800 C. but are dependent upon the presence of the beta phase to resist softening. This duplex structure lacks ductility and its resistance to corrosive attack is somewhat impaired by the presence of the additional phase. The resistance to corrosive attack of my new alloy is excellent because it is a single phase solid solution alloy at temperatures up to its melting point.

The area NPI represents the softening resistant range for alloys containing 0.5% aluminum, while the area between lines HP and A represents the'softening alloys (when heated at temperatures up to 900 C. and quenched) containing the same amount of aluminum. Similarly the area JKE represents the softening resistant range for alloys containing 3% aluminum, while the area between line DK and line C represents the softening alloys containing this amount of aluminum. A third or intermediate example is also shown, in which lines LMG represents the softening resistant range for alloys containing 1.5% aluminum, while the area between line FM and line B represents the softening range. The area LMG is cross hatched to show clearly the softening resistant range for the intermediate example containing 1.5% aluminum and to avoid confusion because this area overlaps a portion of the areas for the maximum (3%) and minimum (0.5%) aluminum contents. These alloys have a nickel content of from 17% to 31%.

Figure 3 was prepared to show by itself a specific example indicating the two zones for an alloy containing 1.5% aluminum, with I copper and nickel as indicated, and the balance zinc. The first zone represented by area above line FM and below line B contains those alloys richer in copper and which can be softened by heating in the neighborhood of 750 C. to .900 C. followed by quenching. (This solution temperature gradually increases from about 750 C. to 900 C. as the nickel and/or aluminum is increased.) The second zone, represented by the lines LMG indicates those alloys which do not soften materially when heated at temperatures up to 900 C. and quenched.

The precipitation hardening effect, however, takes place throughout both zones but is less noticeable in the second zone in alloys that have been heated up to 900 C. and quenched. It is probable that the hardness of the alpha solid solution approaches that of the nickel-aluminum compound or precipitate in'these alloys. For example, an alloy containing 64% copper, 21% nickel, 1.5% aluminum, the remainder zinc plus impurities, has a Rockwell G hardness of 69 after heating for two hours at 900 C. and quenching. The same alloy when heated for two hours at 500 C. has a Rockwell G hardness of 77. The annealed alloy was rolled 2 B. 8; 8. numbers hard and found to have a Rockwell "G hardness of '72 which was increased to 89 after a two hour heat treatment at 500 C.

The alloys involved in this application are within the rangesof limits as follows:

but are in the area bounded by the lines XYI of Fig. 4 for alloys containing the minimum aluminum content of 0.5% and by area ZYE for alloys containing the maximum aluminum content of 3%. For intermediate aluminum contents the areas would be approximately as indicated. In all cases the zinc content should be at least 1% to secure the desired characteristics.

The maximum and minimum amounts of copper, nickel and aluminum are shown in this figure and the following table is taken therefrom and shows some of the zinc values which are not indicated in Fig. 4 in detail.

Tapas: I

. Zinc Group Copper Nickel Aluminum impurities 65 max. 31 max .5 min. 3 5min.

1 65 max. 13.5 min. 5 min. 21 max.

48 min. 31 max 5 min. 20. 5 max 65 max. 31 max. 1 3 min.

2 65 max. 16 min. 1 18 max. 50. 5 min. 81 max. 1 17.5 max.

65 max. 31 max. 1. 5 2. 5 min.

3 65 max. 18 min. 1. 5 15.5 max. 52.5 min. 31 max. 1. 5 15 max.

65 max. 31 max. 2 2 min.

4 65 max. 19. 5 min. 2 13. 5 max 54 min. 31 max. 2 13 max.

65 max. 31 max. 2. 5 l. 5 min.

5 65 max. 21. 5 min. 2. 5 11 max. 55. 5 min. 31 max. 2. 5 11 max.

65 max. 31 max. 3 max. 1 min.

6 65 max. 22. 5 min. 3 max. 9. 5 max.

.56. 5 min. 31 max. 3 max. 9. 5 max The remainder is essentially zinc plus impurities.

- ing the minimum of 0.5% aluminum, may contain a maximum of 65% copper with all nickel contents from 13.5% to 31% inclusive, but the minimum copper content decreases progressively as the nickel is increased from 13.5% to 31% at which point the minimum copper content is 48%. Thus the sum total of the elements with maximum copperand nickel for alloys containing the minimum of 0.5% aluminum is 96.5% leaving a minimum of 3.5% zinc plus impurities.

. Likewise the sum total of the elements with maximum copper and minimum nickel for this group of alloys is 79% which leaves a balance of 21% zinc (plus impurities) as the maximum.

Another example, in the area ZYE representing the maximum of 3% aluminum will contain a maximum of 65% copper with all nickel contents of 22.5% to3l% inclusive, but the minimum copper content decreases progressively as the nickel is increased from 22.5% to 31% at which point the minimum copper content is Thus the sum total of the elements with maximum copper and nickel for alloys containing the maximum of 3% aluminum is 99% leaving aminimum of 1% zinc (plus impurities). Likewise the sum total of the elements with maximum copper and minimum nickel for this group amount of nickel with copper willcontain.

1% zinc.

As a further example, an alloy containing 25% nickel, 0.5% aluminum, and 8.5% zinc will contain a maximum of 65% copper, while an alloy containing the same amount of nickel with 3%, aluminum and 9.5% zinc will have a minimum copper content of 62.5%..

. Thus it may be seen that the minimum amount of zinc that can be present in these alloys is 1% and maximum zinc is 21%.

It is also apparent that the aluminum content governs the size of the area of useful compositions. Those alloys with lowest aluminum content have the largest composition area while those with the largest aluminum content have the narrowest range.

Microscopic examination of the precipitate or compound formed with heat treatment from 400 C. to 600 C. reveals that the particle size ofthe same is very minute and considerably smaller than that observed in several other known precipitation hardening alloys. This may account for the satisfactory elongation and corresponding high strength obtained with the present alloy.

An alloy or alloys ade in accordance with the present invention are suitable for the same uses as the previously commonly used ternary copper-nickel-zinc alloys, and in addition have several new uses hereinafter mentioned. A considerable improvement in corrosion resistance,

, and especially resistance to oxidation at temperatures below 500 C. is obtained with my improved alloy or alloys.- Also, an important fea-.

ture is the softening resistant characteristic previously described.

Avery important advantage of an alloy embodying the essential features of'the present invention is the great increase in hardness that may be obtained by heat treatment at low temperatures. For example, an alloy composedoi about 63% copper, 30% nickel, 5% zinc and 1.5% aluminum that had been cold rolled showed a Rockwell'G hardness value of 65 (G scale ball, 150 kg. load). After being heat treated in an electric mullle furnace for 2 hours at approxi mately 500 C. the hardnessvalue of this same sample increased to 79. When the said alloy was annealed at approximately 900 C. for 1 hour and quenched, the G" hardness value was somewhat less than minus 10 which, after the specimen was heat treated for 2 hours at about 500 C. was

raised to "G" 41. This softening after quenching is in marked contrast to the alloy above noted containing 64% copper, 21% nickel, 1.5% aluminum and remainder zinc'plus impurities which showed a Rockwell G hardness value of 69 after heating at 900 C. and quenching.

The corresponding copper-nickel-zinc alloys containing no aluminum are not capable of being successfully hardened by heat treatment at ,low 1 temperatures. The importance of this age hard-' ening or precipitation hardening is readily apparent. Articles may be fabricated from the annealed or wrought alloy, and when finished may be hardened by low temperature heat treatment.

Because the alloy is not susceptible to softening at temperatures up to about 500 C., it is suitable for condenser tubes, parts for internal combustion engines and other uses subject to operating temperatures below 500 C. The resistance 01 this alloy to wear, when hardened, is very good. A further advantage of an alloy or alloys made in accordance with the present invention is the great increase in tensile strength which is obtained by heat treatment at low temperature.

Thisincrease in strength, is accompanied by an unusual eifect, namely an increase in elongation; This increase in elongation means an increase in ductility and indicates greater resistance to fatigue of the hardened alloy made according to my invention as opposed to low percentage elongation or brittleness which is found in some age hardened alloys.

After annealing my improved alloys, the presence of a greenish-gray film was noted on the surcloth. After drying, the presence of a thin, dull gray film was again noted on the surface of the metal. This film appears to afford some protection against intererystalline attack and corrosion.

Many of these improved alloys containing aluminum, particularly those having the higher nickel content, have shown very good resistance to attack by corrosion when immersed in concentrated and dilute nitric acid at room temperature, and at 86 C. I have also found that the resistance of these alloys to corrosive attack by several other oxidizing agents is increased considerably.

These alloys have also shown good resistance against attack in sea water. This characteristic together with the high strength and ductility as well as high elastic limit makes the alloy especially adapted for use in contact with this medium and particularly propeller shafts, propeller blades, and so forth.

There are other advantages secured by the addition of aluminum to these alloys. Thus, for example, loss of zinc during casting is reduced by the protective film produced by the aluminum on the metal.

With the aluminum addition, pickling is more or less unnecessary for heavy gauges, and there is no heavy scale with thin gauge metal. Overhauling is very light as it is required to remove surface only. Pot annealing is unnecessary.

In short these new alloys are suitable for the operations and uses peculiar to the brass and copper industries. Thus, for example, they are adapted for cold rolling and drawing.

To total one hundred percent, the "Remainder" in the range above noted ls most advantageously zinc, but in practice elements other than zinc may be present in slight amounts without injury to the resultant product. Thus, for example, it is common practice to add a small amount of manganese to copper-nickel-zinc alloys, and this metal (up to 0.5%).may be added to my alloy. Because it cannot be avoided without too much expense in refining the constituent metals, there may be and usually are some lead and iron present. The great increase in hardness is only obtained when nickel and aluminum are present together in the alloy.

In view of the fact that my improvement applies to a great number of commercially produced copper-nickel-zinc alloys, it is impossible to state all of the commercially useful alloys in the group. However, for informative purposes I am listing a few of the most important alloys "which have been greatly improved by my invention:

Nickel Aluminum Copper Zinc 18 l 64 17 25 1 64 10 30. 1 64 5 20 l 5 64 14.6 25 1 60 14 30 l 55 i4 30 2 60 8 Improved alloys that are indicated in the respective copper-rich softening zones between lines A and HP, lines B and FM, and lines C and DK for the three examples given in Fig. 2, that have be readily fabricated into the finished product and then hardened by heat treatment at a low temperature. It can, if desired, be further work hardened after the low temperature heat treatment. This hardening by low temperature heat treatment after fabrication is especiallysuitable for such articles as nuts, bolts, fuse bodies, primers, nipples, valves, springs, wire screens, hinges, chains, jewelry, tableware, coins, keys, clock parts, and the like.

They have also been found to be corrosion resistant and characterized by the presence of a protective surface film, and can be hardened by heat treatment at low temperatures (approximately 300 C. to 600 C. for periods of about two hours or less), but they can also be hardened by heat treating for longer periods of time at lower temperatures.

These new alloys are also very satisfactory for certain uses when not hardened by low temperature heat treatment as they are corrosion resistant, have good strength and elongation and can be readily-fabricated into various articles.

The alloy is alsouseful for welding and for welding rods, and may be brazed. In addition to its workability and adaptability to be drawn into wire, as previously noted, it may be drawn into rods, tubes, sheets and shapes, and also drawn, stamped, or spun into cups, cartridge cases and other metal articles.

Having thus set forth the nature of my invention, what I claim is:

1.' An alloy composed of copper, nickel, zinc, and aluminum within the following ranges:

- Percent Copper 48 to 65 Nickel 13.5to31 Aluminum 0.5 to 3 Zinc (plus impurities) '1 to21 and in which the copper range for a given aluminum content is increased progressively as the nickel is increased.

2. A heat hardened alloy composed of copper, nickel, zinc, and aluminum in the following 3. An alloy composed of copper, nickel, zinc and aluminum within the following ranges:

Percent Copper 48 to 65 Nickel e 1'7 to31 Aluminum 0.5 to 3 Zinc (plus impurities) remainder which is characterized by being resistant to softening when heated at temperatures below 900 C. and quenched.

4. An alloy composed of copper, nickel, zinc and aluminum within the following ranges:

Percent Copper 48 to'65 Nickel 13.5 to 31 Aluminum 0.5 to 3 Zinc (plus impurities) 1 to 21 copper, 30% nickel, 1% aluminum, and 14% zinc.

ELMER L. MUNSON.

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