US2365208A - Manufacture of copper base alloy products - Google Patents

Description

Patented Dec. 19, 1944 MANUFACTURE OF COPPER BASE ALLOY PRODUCTS Alan Morris, Nichols, Conn., assignor to Bridgeport Brass Company, Bridgeport, Conn., a corporation of Connecticut No Drawing. Application July 15, 1942,

' Serial No. 451,009

12 Claims.

This invention relates to the manufacture of copper base alloy products. It relates especially to the manufacture-of products such as tubing, rods, etc.,-by operations including casting, cold working and annealing. I

This invention may be conveniently described in connection with the manufacture of brass tubing. In the manufacture of brasstubing it the metal into billets and then form lengths of tubing of larger cross section than desired by extrusion of the hot metal billets through a die of-suitab1e cross section. The extruded tubing thereafter is subjected to a series of drawing and annealing operations untilthe tubing is reduced to its desired finished dimensions. Drawing so as to reduce the cross section of the tubing by approximately 20 to 40% and then annealing has been usual practice. This operation has the advantage of being relatively inexpensive and rapid and is satisfactory for the production of many types of tubing.

' in the alloy as impurities.

' has heretofore been conventional practice to cast For the production of brass tubing from some alloys the conventional operations above referred to have proven to be unsatisfactory. Thus in the manufacture of aluminum brass tubing required for condenser installations and the like, the conventional methods above mentioned for the manufacture of tubing result in the occurrence of internal defects in the body of the tubing and likewise result in the occurrence of small surface cracks usually extending longitudinally of the tubing, which defects render the tubing unsatisfactory commercially for the purpose intended. These difliculties have long been very serious in the art and have prevented the commercial production of aluminum brass tubing by such tube making methods.

It is a purpose of this invention to overcome -or minimize difliculties of the character above referred to and to permit the successful manufacture, by casting and drawing methods, of tubing and other articles which are made of alumi- I have indirect experimental evidence that the precipitate is a silicide, probably of magnesium.

Both silicon and magnesium are usually present These weaknesses manifest themselves in two different ways. First,

they are likely to break in subsequent drawingoperations, causing fractures entirely within the wall of the tubing. Second, if ordinary drawing practice is followed wherein the tubing is an nealed after the first reduction by drawing following the extrusion, the intercrystalline weaknesses above referred to cause localized fire cracks to form in the outside surfaceof the tubing during the anneal. These fire cracks develop into fine surface cracks during subsequent processing. Both of these defects are causally related to the precipitation tendency above mentioned.

I have found that drastic mechanical working of aluminum brass tubing wherein there is heavy reduction of the cross section of the tubing and drawing of the tubing, instead of creating or aggravating the production of defects in the tubing. has the opposite effect and is highly effective in preventing such defects, especially defects in the form of cracks in the outer surface of the tubing.

.Moreover, I have found further that after the finishing of the tubing and bringing it to ultimate desired dimensions, there is no further tendency to develop and extend points of intercrystalline weakness such as occur in the absence of the num brass alloy and other copper base alloys. It

is a further purpose of this invention to afford commercial methods for making such articles that are both economical and rapid and that utilize ordinary tube drawing equipment;

My investigation of possible causes of the defects above referred to in aluminum brass tubing produced by conventional extrusion and drawing methods has indicated that during normal air cooling followin -extrusion particles of a secondary constituent are precipitated in the grain boundaries, causing intercrystalline weaknesses.

prior drastic treatment according to this invention.

1 have further found that internal defects n the metal of the tubing can be still further reduced by accelerating the cooling of the tubing after the extrusion stepas compared with ordinary air cooling of the tubing. Preferably the cooling is accomplished as rapidly as possible as by quenching the tubing in a liquid, e. g., water, which is maintained at approximately atmospheric temperature or thereabouts. In this manner tendency for metal components to precipitate with development of intercrystalline weaknesses is minimized. Such precipitation is most likely to occunbetween temperatures of about 200 C. and about 800 C. and acceleration of the cooling to a temperature below 200 C. is therefore desirable. When the cooling of the tubing after extrusion is accelerated and preferably is accomplished rapidly as by quenching and the tubing is thereafter subjected to drastic working of the character aforesaid wherein the tubing is drawn with heavy reduction in cross section, optimum results are obtained and the resultin tubing possesses in high degree not only freedom from surface defects but also freedom from internal points of weakness. My investigation of the possible causes of the defects above mentioned has indicated that by accelerating the'cooling. of the metal after hot extrusion, precipitation of impurities that tends to cause intercrystalline weaknesses is suspended. In other words, when the metal is cast, the cast metal contains impurities which are precipitatable at annealing temperatures of the range 200 C. to 800 C. and by accelerated cooling of the metal from a temperature above 800 C. the tendency for the impurities to precipitate is suspended. However, upon subse-- quent annealing in conventional drawing and annealing operations the impurities will tend to appear as precipitate and cause the intercrystalline weaknesses and defects above mentioned. Thus, for example, if aluminum brass tubing is cast, extruded, quenched, drawn to effect a reduction of about 20 to 40% (as is conventional), and thereafter is annealed, the impurities tend to form during the anneal and produce intercrystalline weaknesses in the metal. When the metal, at temperatures below annealing temperatures of the range above referred to, contains impurities which would be precipitated if the metal were heated to annealing temperatures, the impurities are in a condition of suspended precipitability as this term is used herein and in the claims.

In preferred practice of this invention, the drastic drawing step, wherein the metal is drawn so as to effect a very heavy reduction in cross section, is carried out while the metal contains precipitable impurities in a condition of suspended precipitability, and the drastic drawing step has the peculiar effect of modifying the metal so that subsequent percipitation of said impurities at annealing temperatures is minimized or eliminated.

Thus after tubing containing impurities in the condition of suspended precipitability has been subjected to the drastic drawing step, the tubing can thereafter be annealed without causing precipitation of impurities or development of other internal points of weaknesses in the metal and the tubing can be processed to ultimate dimensions by conventional methods comprising annealing and drawing without injury to the tubing or. development of defects therein.

In order that the amount of any impurities contained in the cast metal and'precipitable at annealing temperatures may be as much as possible maintained in the condition of suspended precipitability prior to the drastic drawing step, the metal, after it has been cast, is not subjected to substantial annealing at a temperature between about 200" C. and about 800 0., namely, is not subjected to sustained heating either constant or variant at such temperatures. Moreover, as aforesaid, it is preferable also to avoid gradual cooling such as air cooling through thistemperature range. When the article in question is extruded a recommended procedure consists in casting, extruding at a temperature above 800 0., quenching, and drastic drawing at a temperature below 200 0., followed by any further operationsthat maybe required and that may, if desired, include annealing and further drawin or other cold working.

1A aforesaid the drastic working and drawing appears to modify the metal of the tub g- 01 .81

during subsequent annealing or gradual cooling precipitation and development; of weaknesses do not take place. This phenomenon which takes place in practicing my inventionis not clearly understood as far as possible explanation is concerned, but from an operational standpoint it is the feature of my invention. that contributes chiefly to successful production of aluminum brass tubing or the like free from defects that occur during annealing and drawing operations.

The occurrence of surface cracks in tubing, if this defect occurs, is readily apparent particularly if the tubing is subjected to expansion by meansof a suitable implement, or if the tube is flattened. Thepresence of internal weaknesses in the metal may be ascertained by subjecting the tubing to a standard tensile test until rupture. Metal of good ductility and freedom from-internal weaknesses exhibits a smooth "silky fracture while a more crystalline type of fracture indicates that the tubing possesses these properties to a lesser' degree. Moreover, by photomicrographic methods the presence of intercrystalline precipitate of alloy components may be determined both in the finished tubing or prior to the drastic cold working and drawing step.

Having thus indicated in a general way the nature of my invention. the practice thereof may be illustrated in connection with certain typical examples.

Aluminum-brass metal, composed substantially of 77% copper, 2% aluminum, 21% zinc and containing traces of impurities, was cast in billet form and the metal while at a temperature of about 900 C. was extruded usin a conventional extruding apparatus to form tubing which, as extruded, was 2%; inches in outside diameter and inches in wall thickness. may be more briefly indicated as 2{%" x and this more brief indication of tubing dimensions will be employed hereinafter.) Promptly after the extrusion the tubing was quenched in water. The tubing thereafter, and without any intermediate annealing step, was subjected to drastic drawing so as to reduce the cross section to about 1 x .187", namely, a 65 /g% reduction in cross section from the cross section as extruded. The drawing was carried out cold and in three drawing steps of about equal extent. The tubing thereafter was annealed at about 750 C. for about 23 minutes and then was processed by successive drawing and annealing operations to a finished size of A" x .049". The finished tubing was entirely free of external cracks and was of good internal structure as exhibited by the fracture tests.

tubing that is free of defects.

In the foregoing example, steps of annealing and processing after the drastic cold drawing operation are not essential in the production of The inclusion of these steps in the foregoing example indicates, however, that after the drastic cold drawing step has been carried out, the tubing can thereafter be annealed, drawn and otherwise processed, with or without quenching after annealing, without weakening or otherwise causing defects in the tubing.

When the practice of this invention according to the foregoing example was carried out similarly but with air cooling of the extruded tubing (instead of quenching after extruding) the finished tubing did not exhibit surface cracks but, as mentioned hereinabove, internal ruptures have been found in such tubing, regardless of the use or non-use of the drastic drawing step.

(These dimensions effect a 65 reduction in cross section. Somewhat more generally it is preferable to effect a reduction in cross section by mechanical working and'drawing until the cross section of the tubing is not more than 40% of the cross section of the tubing as extruded, namely, to effect at least a 60% reduction of the tubing. However, such working until the cross section is not more than 50% of the cross section of the tubing as extruded affords a decided improvement and especially when the tubing is quenched after extrusion, satisfactory tubing can be made. according to this invention, but such working, namely, until the cross section is not more than 50% of the cross section of the tubing as extruded constitutes drastic treatment as compared with prior ing conventional equipment for cold drawing of brass tubing may be employed. This is ordinarily whether or not the operation includes an extruding step.

While this invention has been described in connection with certain illustrations of the practice thereof, it is to be understood that this has been done for exemplary purposes only and that the practice of this invention may be varied while utilizing the principles herein referred to and of the type wherein the tubing is pulled through the die. However, the drawing operation may be carried out using equipment of the pusher type,

. e. g., of the type wherein a mandrel is pushed through the die that causes reduction in the, diameter of the tubing and the resulting reduced tubing is buttered on the periphery of the mandrel. The drastic drawing of the tubing may be accomplished in any number of stages or draws. While three drawings are convenient a lesser or a greater number may be employed. The drawing is ordinarily carried out at atmospheric' temperature or slightly above but the drawing operation may be carried out at tem peratures up to about 200 C. or thereabouts, and

any such drawing operation, is regarded as cold drawing.

Aluminum brass tubing usually has the composition mentioned in connection with the foregoing example, namel'y, approximately 77% copper,

2% aluminum and 21 zinc, .03% arsenicwith less than about one-half-per cent. ofimpurities such as tin, lead, iron. silicon, magnesium, etc. However, tubing made from other similar alloys may advanta eously be manufactured according to this invention where the alloy contains impurities that are precipitable fromthe cast metal at annealing temperatures. Thus there are several other copper base alloys which contain aluminum as a major alloying element and which are used as condenser and heat exchanger tubing as well as for other purposes. For example, one such alloy contains 5 to 9% by weight of aluminum, the balance consisting essentially of copper. Such alloys contain essentially the same type of precipitable impurities that are found in 'the metal of aluminum brass tubing. Even the utility in connection with the manufacture of articles from copper base alloys containing impurities which are precipitable at annealing temperatures. Moreover, the practice of this invention is not limited to the production of tubing but may be availed of in the manufacture of other copper base alloy products such as rods, etc., by an operation wherein the metal is cast and .the cast metal is formed by steps including cold mechanical worklng and annealing and mechanical working wherein the alloy is drawn,

said drawing being effected while said impurities are in the condition of suspended precipitability and being such that the cross section of the metal is reduced to not more than of its cross section prior to the drawing, thereby inhibiting subsequentprecipitation of said impurities at annealing temperatures.

2. In the manufacture of articles from copper base alloy containing over 1% of aluminum wherein the alloy is cast and the cast metal is formed by steps including cold working and annealing, said alloy comprising impurities precipitable from the metal at annealing temperatures. the step comprising subjecting the alloy after casting to cold mechanical working wherein the alloy is drawn, said drawing being of a drastic character so that the cross section of the metal being drawn is reduced to less than 50% of its original cross section and said drawing being effected prior to substantial annealing after the casting step, thereby inhibiting subse-, quent precipitation of said impurities at annealin temperatures.

3. In the manufacture of articles from copper base alloy containing over 1% of aluminum wherein the alloy is cast and the cast metal is formed by hot extrusion followed by cold working and annealing, said alloy comprising impurities precipitable from the metal at annealing temperatures, the steps comprising quenching the metal after extrusion, and drawing the extruded and quenched metal until its cross section is resaid impurities are precipitated therefrom between the casting. step and completion of said drawing, thereby inhibiting subsequent precipi tation'of saidimpurities at annealing temperatures. 1

4. In the manufacture of articles from alumi- 'num brass alloy containing as the principal ingredients approximately 77% copper, approxi-' mately 2% aluminum and approximately 21%' zinc containing impurities precipitable therefrom at annealing temperatures,.the steps comprising forming a body of the metal with said impurities contained therein in the state of suspended precipitability, and then subjecting the body to cold working and drawing until the cross section of the body is reduced to less than 50 of its cross section prior to drawing, thereby inhibiting tendany of said impurities to precipitate upon subsequent exposure of said metal to annealing tempei'atures.

5. In the manufacture of articles from copper base alloy containing over 1% of aluminum, the

steps comprising forming a metal body by extrusion of the cast metal at a temperature above 800 C. and reducing the cross section of the extruded metal body by mechanical working wherein the tubing is drawn at a temperature below 200 C., the cross sectionof the body being reduced by the mechanical working to not more than 50%- of its cross section as extruded and the metal of said body not being subjected to annealing at a temperature between 200 C. and 800 C. after the extrusion step until said reduction has been completed.

6. The manufacture of articles of copper base alloy containing over 1% of aluminum comprising casting the metal and extruding it at a temperatureabove- 800 C. to form a metal body,

cooling the body from extrusion temperature with acceleration of cooling through the range from above about 800 C. to below about 200 C., and reducingthe cross section of the body by a cold drawing operation until the cross section of the body is not greater than about 50% of its cross section as extruded,*the metal of said body not being subjected to annealing at annealing temperatures of the range 200 C. to 800 C. after the ex- .trusion step until said reduction has been comhot extruded as tubing and the extruded tubing.

is subjected to cold working and annealing, said alloy containing impurities precipitable from the metal at annealing temperatures of the range 200 C. to 800 C., the steps comprising quenching the extruded tubing and drawing the extruded and quenched tubing until the cross section of the tubing has been reduced to not more than 40% of its cross section as extruded, the metal of said tubing after the casting thereof not being subjected to annealing at an annealing temperature of the range 200 C. to 800 C. between the casting step andcompletion of said drawing.

'9. In the manufacture of tubing from copper base alloy containing over 1% of aluminum wherein the alloy is cast and the tubing is extruded and is subjected to cold working and annealing, said alloy comprising impurities precipitable from the metal at annealing temperatures, the step comprising subjecting the tubing after extrusion to cold working and drawing until the cross section of the tubing has been reduced to less than of its cross section as extruded, the metal of said tubing not being subjected to substantial annealing at a temperature at which said impurities are precipitable therefrom bea tween the casting step and completion of the drawing.

10. In the manufacture of aluminum brass tubing, the steps comprising forming tubing by hot extrusion, cooling the tubing after extrusion by quenching, then subjecting the tubing to drawing without intervening annealing until the cross section of the tubing has been reduced to not more than 50% of the cross section of the tubing as extruded, and thereafter annealing the tubing and processing it to desired dimensions.

11'. In the manufacture of aluminum brass tubing. the steps comprising forming tubing by hot extrusion, cooling-the tubing, then subjecting the tubing to drawing without annealing until the cross sectionof the tubing has been reduced to not more than 50% of the cross section of the tubing as extruded, and thereafter annealing the tubing andprocessing it to desired dimensions.

12. In the manufacture of aluminum brass tubing according to the steps'recited in claim 10 wherein said drawingis conducted until the cross section of the tubing has been reduced to not more than 40% of the cross section of the tubing as extruded and wherein said aluminum brass tubing consists principally of approximately 77% copper, approximately 2% aluminum and approximately 21% zinc.

' ALAN MORRIS.