EP0586197A2

EP0586197A2 - Machinable lead-free forging copper-containing alloys

Info

Publication number: EP0586197A2
Application number: EP93306792A
Authority: EP
Inventors: John Travis Plewes
Original assignee: American Telephone and Telegraph Co Inc; AT&T Corp
Current assignee: AT&T Corp
Priority date: 1992-09-01
Filing date: 1993-08-26
Publication date: 1994-03-09
Also published as: JPH06200340A; MX9305206A; EP0586197A3

Abstract

Two-phase, α+β, brasses are rendered lead-free while retaining properties - notably, hot working properties. Supplementing bismuth, as substituted for lead with either of the elements phosphorus or indium, assures retention of the hot working properties associated with the conventional, lead-containing "forging" and "architectural" brasses.

Description

Background of the Invention

The invention relates to copper-containing, lead-free alloys which retain the properties associated with the prototypical lead-containing "forging brasses" and/or "architectural bronzes". Of particular importance, alloys of the invention evidence the freedom from embrittlement sufficient to permit hot working at the low pressures characteristic of the prototype materials.

Description of the Prior Art

There is a long history of copper-containing alloys - of the many "brass" and "bronze" alloys. Included compositions for serving various uses are based on long experience, and are set forth, for example, in Copper Development Association Handbook, 8th ed., Part 2-Alloy Data (1985).
Regardless of fundamental purpose, many industry-accepted copper-containing alloys are designed, inter alia, to permit machining, e.g. threading, likely to be required in expected use. Virtually without exception, machinability is imparted by inclusion of lead to compensate for the "gummy" nature of copper. Choice of lead over fundamentally equivalent selenium or tellurium is largely on basis of cost.
Recently, health and environmental concerns have focused on lead toxicity. For example, legislation to severely limit the level of lead acceptable in potable water is being introduced in many countries. In August 1988 the U.S. Environmental Protection Agency (USEPA) proposed a rule designed to minimize lead level in drinking water which explicitly limits the use of lead in piping and fittings. See, Journal American Water Works Association, R. G. Lee, et al, p. 51 (July 1989). There are other objectives which suggest limitations on lead content in alloys. For example, there have been legislative proposals which would minimize atmospheric lead, as resulting from volatilization due to high temperature processing.
Bismuth, an element next to lead in the periodic table, shares many of the properties of lead, and does impart machinability to copper-containing alloys. See, Copper, A. Butts, ed., p. 704 (1954). Significantly, a variety of studies lead to the conclusion that bismuth shares none of the toxicity problems of lead. Consultation with EPA indicates that bismuth, in amounts likely encountered, is no problem in drinking water, nor generally in inhalation or ingestion. Bismuth has not been found to have any harmful effect on the human nervous system, or on health in general. In fact, a common indigestion remedy contains bismuth as a major ingredient.
Work reflected by specification and claims in co-pending application SN 07/523774 is responsive to such concerns. It addresses acknowledged unacceptability of bismuth in lieu of lead for use in an important class of copper alloys to be subjected to working, e.g. by extrusion. As noted in ASM Metals Handbook, pp. 907, 916 (1948), "Bismuth creates brittleness in amounts greater than 0.001%. Tolerance for bismuth under commercial processing is virtually nil." Text and other literature references address harmful effect of bismuth - e.g. emphasize deleterious effect on workability at levels as low as 0.0004%. See, Bureau of Mines Circular 9033, p. 6, (1985). The co-pending application claims inclusion of a third element, phosphorus or indium as avoiding the embrittlement associated with bismuth, while retaining machinability in the nominally single-phase alloys - the alpha phase alloys - exemplified by the CDA-designated "360 brasses".
The two-phase alloys - α + β alloys - exemplified by "377 forging brass" and "385 architectural bronze" - are, of course, contemplated by all such pending legislation to the extent relevant to the objective of the legislation. Nonetheless, there is an absence of reported work on removal of lead from such alloys. Absence is explainable on the basis of work exemplified by C. S. Smith, TAIMC 175, pp. 15-51 (1948) and by W. Price, Trans. AIME, vol. 147, pp. 136-143, (1946). Price suggests that substitution of bismuth for lead is a solution for two-phase alloys. The Price reference reports that the representative composition, Cu 60, Zn 37, Bi 3, evidences useful working properties, explicitly hot working and forging properties. For this reason, the relevant two-phase compositions - generally those containing 54-60% copper - were not specifically addressed in the co-pending application. (Consistent with usage throughout this disclosure, alloy compositions whether or not expressly in %, are invariably in weight % unless otherwise noted.)
Experimental work conducted by the named inventors has established, contrary to the general view, that bismuth substitution in fact results in embrittlement at a level sufficient to interfere with hot working properties of α + β brasses. In initial experimentation, inclusion of 2% bismuth to result in the alloy, Cu 59, Bi 2, Zn remainder resulted in extensive cracking when hot upset 75% within the temperature range of 625-800°C. The terminology "hot upset" has the well-known assigned meaning in this technology of describing compression of a specimen, in this instance, a specimen 1.0 inches in height hot compressed to 0.25 inches in height to result in 75% thickness reduction, e.g. resulting in a disk of 1/4 inch final thickness. In accordance with one industry standard, acceptance of these two-phase alloys requires one-step hot working - at a temperature in the range of 600°C to 825°C, exemplified by hot upsetting, to a thickness reduction of at least 50%. The same criterion establishes satisfaction of industry requirement for other contemplated forms of hot working including extrusion and rolling.

Summary of the Invention

The invention is directed to retention of hot working properties of lead-free, two-phase copper-containing alloys including the "forging brasses" and "architectural bronzes". Included compositions may be substituted for lead-containing materials without altering processing conditions - most importantly without constraint on hot rolling or other contemplated hot working. Compositionally, alloys of the invention depend for workability only upon phosphorus and/or indium inclusion together with lead-replacing bismuth. Required concentrations of the third elements, phosphorus and indium are quite small. Further, qualities resulting in needed machinability are often attained with lower bismuth content - perhaps half that of lead. Accordingly, desired characteristics are attained at reasonable cost. The same cost consideration leads to a pronounced preference for phosphorus over relatively expensive indium. Required ingredients are typically: 0.5-2.0 Bi together with as little as 0.1 P, 0.25 In or appropriate lesser amounts of both if included in combination.
The inventive teaching relies on avoidance of the now-observed bismuth-associated embrittlement - on attainment of noted hot working characteristics - and, accordingly, description as well as claims are in terms of processing requiring such characteristics. These characteristics are, in the following description, referred to as "forging" characteristics. As stated, a class of alloy compositions of concern are variously designated, as "forging brasses" or "architectural bronzes". Use of the term, "forging", has reference to hot working properties as retained in accordance with the inventive teaching, and is not to be considered limiting with respect to alloys, however designated, which otherwise meet stated compositional and workability properties.

Detailed Description

The Drawing

FIG. 1

This figure is a plot on coordinates of temperature and composition in terms of weight percent zinc as based on the binary alloy of copper and zinc (without regard either to lead in the prototypical material or to bismuth plus third element addition in the lead-free material). Plotted lines constitute the conventional phase diagram, e.g. as shown in Constitution of Binary Alloys, M. Hansen, p. 650 (1958). From the standpoint of the present invention, the consequential portion of the phase diagram is that showing: the single-phase, α-phase, copper-rich material, in region 1, to the left of phase boundary 2-3; the single-phase, β-phase - material in region 4 on the zinc-rich side of phase boundary 5-6, and the two-phase - α + β-phase - material in region 7 as bounded by boundaries 2-3 and 5-6. The three blocked regions 8, 9 and 10 designate those compositions, which, for the leaded materials, are the regions of primary consequence with regard to the invention. These three regions identify the α + β, two-phase regions of CDA-designated leaded compositions 360, 377 and 385, respectively (corresponding in that order with regions 8, 9, 10). The identical composition regions, in which lead is replaced by bismuth plus third element addition, identify, as well, primary regions of consequence in the present context. Variation to result in selection of compositions outside these regions is, at least initially, unlikely if only by reason of familiarity with the working properties of the prototypical compositions. The blocked regions, however, are nominal in that they both encompass minor areas corresponding with single-phase composition not meeting the inventive requirements and exclude minor areas of two-phase composition meeting the inventive requirements.
The precise compositional range of consequence - that defining equilibrium two-phase structure over the designated 600-825°C - is that encompassed within broken line 11. The broken line traces the portion of the composition shown as bounded by isothermal lines at 600°C and 825°C, and by phase boundaries 2-3 and 5-6.

FIG. 2

This figure is on the same coordinates of temperature and composition. In this instance, plotted data shows the relationship between composition and normalized force required for deformation. The latter, often in terms of "K" factor, is, consequently, a measure of required pressure to bring about such deformation. The term is discussed in the context of extrusion in the following section of this description. K factor values are meaningful only for the explicit type of working contemplated. Accordingly, while K values accurately define comparative pressures for explicit working as well as working conditions and measurement techniques, they are in no sense fundamental. Iso-pressure lines 20 through 27 represent mean deformation resistance K values in Newton's per square millimeter quantifying force required for forging. Plotted data, while measured on leaded prototypical material (see, Extrusion, K. Lane and H. Stenger, p. 169, ISBN 0-87170-094-8, A.S.M., Metals Park, Ohio) is of the same form for the lead-free materials under discussion. The plotted data is included for showing the relative hot working ease realized for two-phase materials. It also shows reduction in needed force for increasing temperature.
The included part of the 360 brasses is of particular consequence. For the most part, materials of this designated class are regarded as single-phase, and, consequently, not candidates for significant hot working. In fact, this nominal characterization is true for the major part of the 360 materials. Only that region shown on the figure meets the inventive requirements. At hot working temperatures in the 600-825°C range, materials are properly regarded as being of their equilibrium two-phase structure during working. In the instance of the 360 materials, the single-phase α structure transforms to the required two-phase structure in a period of no more than seconds - well within the usual working period.

General

The invention is directed to retention of properties associated with the two-phase system - with the α + β brasses. Properties of particular consequence are concerned with "hot workability" - for purposes of the invention, largely workability within the temperature range of 600-825°C. The temperature relationship of such properties is well-known. As contrasted with the nominally single-phase materials, workability of the two-phase materials is facilitated for higher temperatures, however, at the expense of loss of workability at lower temperatures. Cold workability is impaired - e.g. usage entailing substantial cold rolling is prohibited. On the other hand, hot workability is improved to the extent that the extrusion of which single-phase material is capable is permitted at substantially decreased pressures for the two-phase materials. An α + β brass chosen for use not requiring low temperature working, e.g. cold ductility, may permit a given degree of extrusion at a given temperature with a pressure substantially less than that required for another composition which is α.
Figure 1 depicts compositional and temperature ranges of particular consequence with regard to hot working. Ranges corresponding with the CDA-designated 377 and 385 lead-containing alloys, for temperatures of consequence, are clearly within the two-phase range. These compositions may be extruded to much greater extrusion ratios than the α brasses for given pressure. A measure of the relative pressures required is given by the alloy's "K" factor which is defined as the equilibrium constant which relates pressure to deformation - in the instance of extrusion to relate pressure to extrusion ratio. The relationship between required pressure and extrusion ratio may be expressed by: $P=Kln(A₁/A₂)$

in which
P = applied pressure (applied force as normalized for the initial surface area to which applied)
A₁ = cross-sectional area of the body before reduction due to extrusion
A₂ = cross-sectional area after extrusion
and
K is a constant sometimes referred to as the "K" factor
K factors for the two-phase brasses are generally no more than half that for single-phase materials of the same composition (e.g. for 360 brasses of such composition as to be two-phase only above a specific temperature). On the other hand, for a given hot working temperature, it is seen that K factor is dependent solely on composition. The improved workability for the two-phase materials, as with corresponding lead-containing materials, may serve in attainment of a desired extrusion ratio at decreased pressure, with consequent saving in equipment and/or processing cost.
Facilitated workability - permitted use of lower pressures in working of two-phase materials - is clearly shown in FIG. 2. FIG. 2 on coordinates of temperature and composition includes iso-pressure (K-factor) lines - each showing needed temperature and composition for attainment of the indicated pressures (K factors). It is clear from this figure, that at any given temperature, T, the K factor drops rapidly as the zinc content is increased above about 37% (K factor drops as a continuum immediately before, at, and after the onset of the β-phase boundary).
As noted in the figure description, specific K factor values may not be carried over from one process to another. Accordingly, while extrusion K values are of the same form as that of the iso-pressure lines for forging as shown on FIG. 2, explicit pressure values will differ.
As shown in FIG. 1, change in properties is, however, continuous from the nominal single-phase to the nominal two-phase materials. In fact, extreme compositions ordinarily considered as single-phase show hot workability - albeit at relatively high pressures - as associated with a minor content of β-phase material. Compositions addressed by the invention include these CDA-designated 360 brasses, as worked at temperatures at which the two phases are in equilibrium.
A small matter - use of the terminology "architectural bronze" is of historical significance. Reference to such materials as "bronzes" rather than "brasses" has reference to their "bronze" coloration which occurs as the zinc content is increased to levels of approximately 41% and greater. This abrupt color change from yellow to bronze is caused by the presence of β-phase in the alloy, the same β-phase whose presence causes the abrupt decrease in K factor. This pleasant red coloration often gives rise to selection of such material for its appearance. General reference to two-phase brasses is intended to include all such materials.

Composition

Compositional requirements here set forth are discussed in considerable detail with regard to specific CDA classifications with reference to the figures. Contemplated materials are all α + β brasses at working temperatures specified. At such elevated temperatures, generally within the 600-825°C range, materials attain their equilibrium (two-phase) state essentially instantaneously. Hot working characteristics of consequence correspond with two-phase materials containing at least five volume percent β-phase, the remainder essentially α-phase.
All compositions contemplated by the invention correspond with compositions included within the far larger classes of lead-containing materials within the CDA-designated 360, 377 and 385 brass/bronze classes as set forth in the CDA Handbook of Wrought Products, eighth edition, 1985, published by Copper Development Association Inc., Greenwich, Conn. Compositional considerations are largely identical as regards copper/zinc ratio. While bismuth may replace lead on a one-to-one basis, as noted, there is experimental evidence which suggests that this replacement element may be somewhat more effective so that desired machinability may be attained with lesser amounts - perhaps 50% of corresponding lead content. Third element additions, of far lesser content, are: phosphorus - 0.1-0.5 and/or indium - 0.25-1.0 (or in appropriately reduced amounts).
Precise compositions, in terms of copper and zinc content, are those depicted on FIG. 1. While all inclusive, they may contain tolerable contaminants in accordance with art-accepted practice, as well as additional elements intended to serve specific purposes perhaps unrelated to the thrust of the invention. (Such additional elements whether intentional or merely tolerable are not likely to total as much as 5%.)
Freedom from lead is quantified primarily to satisfy statutory or other health-related requirements. With regard to hot workability which is the thrust of the invention, greater amounts of lead may, of course, be tolerated - such greater amounts only continue to serve to impart machinability. In fact, it has been experimentally proven that lead continues to serve its traditional purposes unimpaired by partial substitution by bismuth plus third element addition. This finding will likely serve in recycling of lead-containing material, e.g. in which lead content is reduced perhaps to 50% so that but half is replaced to result in retention of properties in accordance with the invention. Ultimately, the inventive advance may take the form of truly lead-free compositions, e.g. compositions containing only contaminant levels of less than 0.1%, or even compositions in which additional processing has served to still further reduce lead content.
While included compositions are best specified in terms of FIG. 1, they may be set forth as: Cu 54-64, Bi 0.5-3, P 0.1-0.5 or In 0.25-1, remainder Zn (or appropriate lesser amounts of P and In if both are included). Narrowing of the indicated range is in accordance with hot working temperature with the constraint that all included materials include at least 5 vol.% of β-phase at such temperature.
Compositions as so defined were found to satisfy inventive requirements on the basis of test procedures described. In general, compositional ranges define bismuth-containing compositions having machining as well as forging characteristics similar to those of the corresponding lead-containing compositions. Compositions of the invention, like the corresponding lead-containing compositions, evidence a machinability of 40% or greater in accordance with usual criteria. In accordance with conventional practice, machinability is expressed as a percentage relative to the prototypical CDA series lead-containing C360 alloy. This percentage is referred to as "machinability index". Workability sufficient for intended purposes also varies, but all compositions on which claims are based, permit 5:1 extrusion ratio, or more generally, reduction of some dimension by a minimum of 50% for any form of hot working - e.g. by forging or rolling, as well as by extrusion. Pressures in all instances are those associated - as good or better than - hot working characteristics of the prototypical compositions within the noted range of 600-825°C.
It is inherent in the above that two-phase nature is unaffected by substitution for lead, and, indeed, experimentation substantiates this conclusion. There is a vast body of art suggesting modifications of compositions by addition of a variety of elements other than those named. Such additions, always in kind and amount as to result in retention of the two-phase nature of the alloy, may be introduced for any of a number of purposes: to affect appearance as by changing color; to improve corrosion behavior in specific contemplated environments, etc. Such addition may be for the purpose of further promoting the two-phase nature of the material, e.g. at lower zinc content than in accordance with the binary phase diagram of FIG. 1. In all such instances, substitution for lead in accordance with the invention does not affect the two-phase nature. Substitution of bismuth plus third element addition continues to assure the hot workability and machinability which is the thrust of the inventive teaching. In all such instances, such properties as associated with the leaded compositions are retained.
All compositional ranges are in terms of the inventive advance, one aspect of which, simply stated, permits attainment of copper-containing forging alloy characteristics while replacing lead with a combination of bismuth together with one or both of the third element additions. Experimental results demonstrate bismuth to be more effective than lead in terms of consequent machinability. While composition ranges are as expressed, bismuth inclusion is characteristically less than that of replaced lead for equivalent properties - experimental results suggest that about 50% as much bismuth imparts the same machinability. In terms of prototypical lead-containing alloys, the inventive contribution translates into a large variety of compositions which often contain elements designed to serve functions unrelated to the inventive thrust - unrelated to machinability or workability. In accordance with the generic inventive teaching, all such alloys containing such additional elements may be rendered lead-free while continuing to serve intended functions with little or no change in processing.
All alloys within the inventive scope are classified as two-phase alloys - as "α + β" alloys - at the working temperature. Associated properties - in particular forging properties - depend upon this two-phase nature. Contemplated substitution for lead has little effect on the two-phase nature of the alloy, which is primarily dependent upon the binary, copper-lead composition and on processing conditions. Specification of the latter, since essentially unchanged by the inventive substitution, is outside the scope of this description.

Processing

Workability, here of consequence, has been variously referred to in terms of "hot workability" and workability characteristic of two-phase systems. The distinguishing factor - the consideration of commercial significance - concerns ease of working. Workability for contemplated α + β brasses, as contrasted with that associated with the α brasses, requires far less force. Improvement is seen in the extreme low zinc compositions - the compositions which upon heating to the hot working range are converted from α to α + β brass. Referring to FIG. 1, the alloys of maximum copper content - alloy of composition 62% Cu, 2% Bi + third element addition, remainder Zn - the composition corresponding with those in the vicinity of the lefthand border of the hot working 360 brass, shows this improvement in K factor upon heating from, e.g. 600°C at which it is single-phase to an increased temperature at which it is two-phase. As noted, materials satisfying the inventive requirements must be two-phase within the specified composition/temperature range of working. Not all materials are two-phase within the entirety of the composition or temperature range considered alone, and to the extent they are single-phase - to the extent they are not two-phase at some temperature or composition - they are excluded.

Experimental Conditions

The relative hot workability for these alloys was measured by hot upsetting billets, 0.75" diam. x 1" height, to 75% thickness reduction in a 60 ton press. The billets were preheated in air for one hour at temperature, were rapidly transferred to the press, and were reduced in height from 1" to 0.25" (i.e. to result in 75% thickness reduction) at a strain rate of 0.15"/sec. All samples were worked at temperatures within the 600-825°C range. The degree of hot workability was determined by comparing the relative degree of edge cracking observed in the experimental alloys with respect to that observed in CDA 377 leaded forging brass tested under the same conditions. CDA 377 alloys are generally recognized as exhibiting good hot working characteristics - considered exemplary as among the leaded two-phase brasses for forging.
Representative lead-free two-phase brasses, still within the CDA 377 compositional range were extruded - sometimes supplemental to forging. Experimental procedures resulted in a variety of end products, both round and square in reduced cross-section. In one set of experiments the starting material was in the form of a billet, six inches in diameter and ten inches in length. Extrusion ratios of up to 150/1, always for extrusion as carried out with two-phase material at a temperature within the 600-825°C range, showed no evidence of surface defects.

Machinability Index

Machinability of the claimed alloys has not been extensively discussed. The reason is that machinability is assured by bismuth for lead substitution without resort to the third element addition of the inventive advance. Alloys of the invention retain machinability to the extent satisfying usual industry requirements.
Compositions of the invention are characterized as manifesting a machinability index of at least 40%. This level, corresponding with lower bismuth substitutions within the specified ranges, is expressed as a percentage relative to CDA 360.

Test Procedures

For comparison purposes, experimental work directed both to machinability and workability were based on samples produced in accordance with a uniform procedure. While the procedure used is commercially acceptable for many purposes, other procedures may be better adapted for particular use depending for example on size and shape of the final article. Processing conditions are not critical, the primary requirement being essential compositional uniformity.
Sufficient experimentation has established applicability of the inventive teaching to result in lead-free, free-machining alloys to replace lead-containing compositions. Experimentation has been extensive - sufficient basis for the terms in which the invention is described.

Sample Preparation

Sample preparation, for some experimental procedures including those of the numbered examples, is outlined. Oxygen-free high conductivity copper was melted under a controlled atmosphere - under argon at a pressure of 1 atmosphere. Once molten, appropriate quantity of zinc was added, and after five minutes of homogenization at a temperature of ∼ 1050°C bismuth and third element addition were introduced. Dissolution was essentially immediate at the melt temperature of ∼ 1050°C. Molten alloy was poured into a 0.75 inch diameter split steel mold, and castings were air cooled. "OFHC" copper, standard in the industry, is ∼ 99.99% pure, and while unnecessary for most purposes implicit in this teaching was employed consistent with good experimental procedure. In further extrusion trials, commercial grade scrap of lead-free 70/30 copper/zinc brass was used together with additional zinc. There was no observed contaminant-related problem upon working. For commercial purposes, tolerable contaminant levels, are specified in accordance with the intended function. Except where otherwise noted, contaminants in usual kind and amount are tolerable, as well, in the lead-free composition of the invention.

Example 1

A Cu-41%, Zn-2%, Bi alloy (no third element addition) was melted as previously described and poured into a 0.75 inch split steel mold. For comparison, a sample of commercial CDA 377, the related leaded composition, was melted as above and was cast in the same or an identical mold.
The castings were sectioned into one inch length (or height) billets. Billets were heated to a variety of temperatures in the 600-825°C range, were held at such temperature for one hour in air, and were hot upset in a 60 ton press at 0.15 inch/sec to a final thickness (height) of 0.25 inch. The outside diameter was unconstrained during forging. The leaded CDA 377 alloy exhibited good hot workability up to 750°C - minimal edge cracking was observed. At temperatures in excess of 775°C, edge tearing and hot shortness was evident. The Cu-41,Zn-2Bi alloy exhibited significant edge tearing (up to 1/4 inch in depth) over the entire temperature range. While the degree of edge tearing lessened as the temperature was reduced, even at the lowest temperature tested, (625°C) only moderate hot workability was observed.

Example 2

The unleaded composition of Example 1 but with third element addition - explicitly an alloy of composition Cu-41%,1Zn-2%Bi-0.15%P was melted and poured into a 0.75 inch diameter split steel mold. For comparison, a sample of commercial CDA 377 was melted as above and cast into the same dimensioned mold.
The castings were sectioned into one inch length billets, billets were heated to a variety of temperatures spaced at 50°C intervals within the temperature range of 625-825°C, and were held at temperature for one hour in air. Billets were hot upset as in Example 1 to a final thickness of 0.25 inch. The Cu-41,Zn-2,Bi-0.15P alloy exhibited hot workability at least equivalent to that of the leaded alloy for samples worked over the entirety of the temperature range. At temperatures below 675 and above 775°C, the experimental alloys were clearly superior to CDA 377 in their hot workability.

Example 3

An 800 lb. melt of Cu-1.8%Bi-0.14%P-39%Zn alloy was prepared from scrap charge. The melt was cast in a six inch diameter steel mold and the casting was air cooled. The casting was sectioned into ten inch length billets which were satisfactorily extruded over a temperature range of 680-825°C. Extrusion ratios of 36-150/1 were achieved. Optimum extrusion temperatures appeared to be in the region of 700-750°C. A variety of strain rates within the 0.5-5 inch/sec range were explored. The alloy did not appear to be strain rate sensitive within this temperature regime.

Claims

Fabrication of an article entailing forming at least a portion from a lead-free copper-containing composition in which bismuth replaces lead, such composition having hot working characteristics in its two-phase, alpha + beta, structure which in corresponding lead-containing composition are associated with lead content,
characterized in that said lead-free composition additionally contains at least one third element selected from the group consisting of phosphorus and indium,
such composition having a machinability index of at least 40% and hot working characteristics both to permit extrusion to a ratio of at least 5:1 and otherwise at least comparable to those of the corresponding lead-containing composition at a temperature within the range of from 600-825°C, such lead-free composition being two-phase within such range with a minimum of five volume percent of β phase,
and hot working at least a fraction of said portion, at temperature within such temperature range at which it is two-phase, alpha + beta to result in a thickness reduction of at least 50%.
Fabrication of claim 1 in which said lead-free copper-containing composition is selected from compositions within the region defining alpha + beta two-phase structure as bounded by the α and the β composition lines on the phase diagram and by the 600°C and 825°C isotherms.
Fabrication of claim 2 in which such lead-free copper-containing composition is essentially of a stoichiometry of prototypical lead-containing composition within the CDA-designated ranges 360, 377 and 385 in accordance with the eighth edition of the CDA Handbook of Wrought Products except that lead is replaced essentially in its entirety by bismuth plus said at least one third element addition.
Fabrication of claim 1 in which working includes extrusion and in which said fraction is extruded to a ratio of at least 5:1.
Fabrication of claim 1 in which working includes forging.
Fabrication of claim 1 in which such composition contains from 54 wt.% to 61 wt.% copper.
Fabrication of claim 1 in which such composition contains Bi in the range of from 0.5 to 3.0 wt.%.
Fabrication of claim 1 in which such composition contains Bi in the range of from 0.75 to 1.5 wt.%.
Fabrication of claim 1 in which such composition contains at least one of the following elements in the amount indicated: Zn 36% to 42%, maximum 11% Al, maximum 2 Fe, maximum 26 Ni, maximum 1 Co, maximum 4 Si, maximum 2 Be, maximum 3.5 Mn, maximum 0.8 As.