Copper base alloy that contains intermetallic constituents rich in calcium and/or magnesium

Abstract

An alloy is provided containing by weight about 1 to 7% bismuth, up to 45% zinc, up to 20% tin, up to 30% nickel, up to 3% selenium, up to 2% aluminum, up to 2% antimony, up to 1% iron, up to 1% lead, up to 2% phosphorus, up to 2% carbon, and calcium and magnesium, singularly or in combination, from 0.02 to 2.0%, and the remainder copper and incidental impurities. The method for producing such an alloy is also provided.

Description

BACKGROUND OF THE INVENTION

[0002] This invention relates to a new copper based alloy intended for, but not limited to, use in the production of components suitable for potable water plumbing service.

[0003] Brass plumbing components are typically machined, forged or cast to shape and traditionally contain from 1 to 9% by weight of lead. The presence of lead in these components enhances machining and improves pressure tightness. Yet, these benefits are rapidly being outweighed by concern over the potential toxicological effects of human exposure to lead. Human exposure is reportedly linked directly to lead leaching from such plumbing components into drinking water. In addition, hazards may arise during manufacturing of leaded brass from exposure to airborne lead particulate released by melting, machining, and cleaning operations.

[0004] Bismuth substituted for lead, alone or in combination with other elements, provides the basis for a majority of the “lead-free” alloy developmental work to date. Both bismuth and lead have relatively low melting points and limited solid solubility with respect to copper based alloys. Upon solidification of these alloys, these characteristics promote a segregation of each element into isolated pockets throughout the alloy matrix. These segregated pools act as chip-breakers during machining and fill the micro-porosity voids left in certain cast alloys by solidification shrinkage. It is preferable that these discrete pools be uniformly distributed throughout the matrix. In general, replacing lead with bismuth does not benefit the mechanical properties of brass. Elongation of bismuth brasses at ambient temperature is lower than that of leaded brass. Also, bismuth brasses tend to lose mechanical strength, undergo hot-shortness, at lower elevated temperature than leaded brasses due to lower melting point. Other alloys that have been tried as a replacement for leaded brass contain particles of graphite, thermally stable dispersoids, or inter-metallic compounds.

[0005] In recent years, a preferred form and distribution of bismuth within “no-lead” brasses has been demonstrated by the use of grain refining techniques. These techniques include the use of grain refining melt additives including boron, phosphorus, and rare earth elements such as lanthanum and cerium. As noted, these additives do not change the nature of the bismuth segregate but rather only affect its size and distribution.

[0006] Yet another approach to modification of grain microstructure within “no-lead” bismuth brasses requires there to be an addition of selenium to the alloy. Selenium is introduced to the melt as selenide particles, which are claimed to have a synergistic effect on the bismuth. It is claimed that these particles improve free-machining characteristics by adding an additional component to interrupt and break continuously formed machine chips.

[0007] U.S. Pat. No. 4,879,094 is directed to an alloy for the manufacture of cast components intended for potable water supply installations. This alloy is comprised in weight percent of 1.5 to 7% bismuth by weight, 5 to 15% zinc, 1 to 12% tin, with the balance, excepting impurities and minor additives, being copper.

[0008] U.S. Pat. No. 5,137,685 discloses an alpha-beta (yellow) brass containing bismuth in place of lead. The brass is comprised of about 30 to 58 wt. % zinc, up to 5 wt. % bismuth, and the balance copper. In one embodiment of the invention, the alloy contains sulfur, tellurium, and selenium, in the respective forms of sulfides, tellurides, and selenides, as combined with zirconium, manganese, iron, nickel or mischmetal (rare earth elements). Another embodiment described calls for the use of bismuth spheroidizing agents, such as phosphorous, antimony, and tin.

[0009] A further “lead-free” brass is disclosed in U.S. Pat. No. 5,330,712. That patent describes an alloy that contains mischmetal as a grain refiner to more uniformly distribute segregated bismuth particles.

[0010] U.S. Pat. No. 5,879,477, describes brasses used in plumbing applications that contain either reduced lead alloys or bismuth yellow brasses. These brasses contain 55 to 70 wt. % copper, 30 to 45 wt. % zinc, and 0.2 to 1.5 wt. % bismuth and are rendered dezincification resistant by use of aluminum and antimony additions or grain refiners including boron, indium, silver, titanium, cobalt, zirconium, niobium, tantalum, molybdenum, and vanadium.

[0011] Dispersed particle brasses are a recent approach to “lead-free” brass, as disclosed in U.S. Pat. No. 5,766,377. These brasses contain no lead or bismuth to enhance machining through dispersion of either high-melt point or intermetallic compound particles. This patent describes a group of copper-zinc alloys that contain one or more of the thermally stable dispersoids: Cr2Ta, Dy2O3, Er2O3, MoB, Mo2C, NbC, Nd2O3, Sm2O3, WS2, WSi2, Yb2O3, and ZrC, or the inter-metallic compounds: CeAl2, LaAl2, La3Sb, LaSb, La2Sb, Ni3Al, NiAl, and Ni3Nb.

[0012] U.S. Pat. No. 4,859,417 discloses the presence of intermetallic compounds of CaP, CuMg, and CuP. The primary composition of the alloy includes the following elements, in percent by weight: magnesium 0.05 to 1.0%, phosphorus 0.03 to 0.9%, and calcium 0.002 and 0.04%. The remainder of the alloy is copper with other alloying elements such as tin, zirconium, manganese, and lithium.

[0013] U.S. Pat. No. 5,624,506 discloses a copper alloy in which calcium is added to combine with and separate out sulfur from the melt. The amount of calcium added to the molten bath is between 0.0001 and 0.01%, by weight.

[0014] European Patent Application No. 93301814.5 focuses on combining bismuth and mischmetal in brass. This application explains the formation and non-formation of certain intermetallic compounds with copper and zinc. Calcium is identified as having potential for intermetallic compound formation with these elements.

[0015] U.S. Pat. No. 5,026,433 discloses grain refinement of a copper based alloy using calcium.

[0016] Yet another approach to “lead-free” brass combines relatively high levels of selenium and bismuth. The ratio of selenium to bismuth is generally represented to be 1 to 2 parts. These alloys are claimed to impart free-machining characteristics by forming chip-breaking selenide particles.

SUMMARY OF THE INVENTION

[0017] The current invention presents an alloy that uses target compositions to achieve enhanced machinability and/or improved pressure tightness for lead-free plumbing components. The invention utilizes intermediate compounds to modify the form and distribution of the segregate bismuth phase.

[0018] One aspect of the present invention is an alloy comprising bismuth in an amount of about 1.0% to about 7.0% by weight of the alloy, zinc in an amount of 0.0% to about 45.0% by weight of the alloy, tin in an amount of 0.0% to about 20.0% by weight of the alloy, calcium and magnesium in an amount combined from about 0.02% to about 2.0% by weight of the alloy, and copper in an amount of 27.0% to about 98.8% by weight of the alloy.

[0019] Another aspect of the present invention is a method for producing a pre-alloy comprising the steps of melting and superheating bismuth, placing granular calcium carbide on top of the molten bismuth, replenishing the calcium carbide until saturation is reached, and plunging magnesium into the bismuth melt.

[0020] Yet another aspect of the present invention is a plumbing component made of an alloy comprising bismuth in an amount of about 1.0% to about 7.0% by weight of the alloy, zinc in an amount of 0.0% to about 45.0% by weight of the alloy, tin in an amount of 0.0% to about 20.0% by weight of the alloy, calcium and magnesium in an amount combined from about 0.02% to about 2.0% by weight of the alloy, and copper in an amount of 27.0% to about 98.8% by weight of the alloy.

[0021] Still another aspect of the present invention is a no-lead alloy comprising about 68% copper by weight of the alloy, about 28% zinc by weight of the alloy, about 2% bismuth by weight of the alloy, about 1% tin by weight of the alloy, about 0.5% magnesium by weight of the alloy, and about 0.5% calcium by weight of the alloy.

[0022] These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a high magnification SEM view of the distribution of Mg—Bi, Ca—Mg—Bi, and Bi agglomeration particles;

[0024] FIG. 2 is a high magnification SEM view of bismuth rich intermetallic particles;

[0025] FIG. 3 is a high magnification SEM view of bismuth rich intermetallic particles;

[0026] FIG. 4 is a microscopic photograph of non-treated yellow brass with bismuth therein;

[0027] FIG. 5 is a microscopic photograph of calcium carbide treated yellow brass;

[0028] FIG. 6 is a microscopic photograph of pure bismuth;

[0029] FIG. 7 is a microscopic photograph of calcium;

[0030] FIG. 8 is a microscopic photograph of calcium;

[0031] FIG. 9 is a microscopic photograph of magnesium rich bismuth saturated with calcium;

[0032] FIG. 10 is a microscopic photograph of magnesium rich bismuth saturated with calcium;

[0033] FIG. 11 is a microscopic photograph of the alloy of the present invention;

[0034] FIG. 12 is a microscopic photograph of the alloy of the present invention; and

[0035] FIG. 13 is an elevational view of a plumbing fitting elbow that can be made from the alloy of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The present invention is an alloy containing by weight about 1 to 7% bismuth, up to 45% zinc, up to 20% tin, up to 30% nickel, up to 3% selenium, up to 2% aluminum, up to 2% antimony, up to 1% iron, up to 1% lead, up to 2% phosphorus, up to 2% carbon, and calcium and magnesium, singularly or in combination, from 0.02% to 2.0%, and the remainder copper and incidental impurities.

[0037] The basis for this invention is a recognition that it is beneficial to add to (or create within) copper based alloys a uniform distribution of discrete intermetallic compounds. These compounds are primarily intended to influence the distribution and required amount of specific non-soluble segregate phases within an alloy. This invention utilizes intermetallic compounds of magnesium-bismuth, magnesium-calcium-bismuth, and calcium-carbon as modifiers of the segregate phase of bismuth within “no-lead” brass.

[0038] One facet of this invention relates to the creation of nucleation sites within bismuth yellow brass. These nucleation sites change the solidification pattern (i.e. dendrite structure) of the freezing alloy, causing grain refinement and ultimately a redistribution of the low-melt point bismuth phase. In order to achieve such nucleation, discrete particles must be introduced into the molten alloy and, upon cooling, be held within the matrix beyond solidification. The nucleating particles must remain wholly or partially insoluble in the alloy and be uniformly distributed throughout the matrix. It is a further advantage to have these particles act in unison with the bismuth phase to improve the alloy. In particular, the segregation of any such constituents within a bismuth brass would preferably, and does in practice, reduce the amount of bismuth required to achieve good machining properties.

[0039] Selection of the appropriate intermetallic compounds for this invention is based on the following considerations:

[0040] The tendency for compounds to remain active within the molten bath and not be consumed or removed during melting.

[0041] The potential for compounds to interact with or influence the bismuth phase.

[0042] The proven compatibility of compounds and the chosen base copper alloy.

[0043] One aspect of the current invention provides to the copper based alloy an intermetallic compound of calcium carbide powder as a late melt addition. The calcium component of the intermetallic compound assists in modification of the bismuth phase of the alloy. Calcium is a known grain refiner and increases fluidity of certain copper based alloys. Calcium plays a role, singularly or in combination with other elements, in deoxidizing copper alloys. For example, calcium boride is used to deoxidize certain copper alloys. In this process, a calcium boron compound is plunged into the molten bath and reacts with the oxygen to form a B2O2 slag.

[0044] The second component of the intermetallic compound is carbon. It provides a non-soluble particle that further enhances grain refinement by introducing additional nucleation sites. Carbon as an individual element is non-wetting and less dense in relationship to a copper based alloy and naturally tends to float out of the melt due to relative specific gravity differences. Calcium presents itself as a wetting agent that inhibits the flotation of the combined carbon from the liquid metal. Thus, the non-soluble carbon tends to remain more uniformly distributed throughout the melt providing nucleation sites for grain refinement and improved bismuth distribution.

[0045] It was discovered that an addition to brass of a relatively small amount of calcium carbide, less than 0.1%, into the furnace melt provided no appreciable modification to the bismuth phase. Calcium carbide was apparently largely being given up as a slag. It was demonstrated that a change in dendrite spacing and correspondingly a more uniform distribution of segregate bismuth pools was possible with the late addition of calcium carbide. (See FIGS. 4 and 5.)

[0046] The intent was to create a separate intermetallic compound, combined with or largely replacing the segregate bismuth phase of “no-lead” brass. The investigative work was expanded to include consideration of the possibility of forming intermetallic compounds containing magnesium, phosphorus and/or calcium.

[0047] Phosphorus was selected because of its demonstrated ability to refine grain structure and form intermetallic compounds within copper based alloys. The late addition of phosphorus to these alloys did not change the form and distribution of the bismuth phase, most notably through spheroidizing and grain refinement. Nevertheless, this modification did not include the creation of a substantive intermetallic compound within the bismuth phase itself. In fact, the addition of phosphorus to cast yellow brass alloys containing by weight 2% bismuth, 0.5% magnesium, and 0.5% calcium resulted in high scrap due to entrapped inclusions and porosity.

[0048] The addition of magnesium to a series of yellow brass alloys containing bismuth and calcium achieved the intended outcome sought by this invention, development of intermetallic compounds of magnesium-bismuth and magnesium-calcium-bismuth. (See FIGS. 1, 2, and 3.) Magnesium and calcium were both separately added to the alloy melt. These elements segregated out of the alloy matrix upon cooling along with the bismuth phase.

[0049] A more preferred technique for producing this invention calls for the melt addition of prepared additive mixtures containing target percentages of bismuth, calcium, carbon, and magnesium.

[0050] The following examples illustrate the invention.

EXAMPLE 1

[0051] A “no-lead” version of an alloy, analogous to C85400 leaded yellow brass, contains the composition given in Table 1.

TABLE 1
“No-Lead” Bismuth Yellow Brass with Calcium and Magnesium
Overall Weight Percent
Component	Target	Actual
Copper	about 68	Balance
Zinc	about 28	27.62
Bismuth	about 2	2.12
Tin	about 1	1.02
Magnesium	about 0.5	0.32
Calcium	about 0.5	0.64

[0052] The alloy presented in Example 1 was selected from a series of casting trials investigating the effects of variation in chemical composition and foundry practice. The alloy of Table 1 was enriched with calcium by placing and maintaining a granular calcium carbide cover layer on the brass melt. Calcium was visibly taken up by the molten bath. The cover was replenished until the bath appeared to reach a level of calcium saturation; that is, the cover remained intact without further addition. Magnesium was plunged into the melt batch directly prior to pouring.

[0053] After magnesium treatment, the molten brass developed a somewhat stringy magnesium oxide skin. The pouring temperature of the alloy did not change appreciably from that expected for a comparable traditional leaded brass.

[0054] Sample plumbing components were cast in bonded sand molds without modification of the existing pressurized gating system used for leaded brass. An example of such a plumbing component is shown in FIG. 13. The castings poured from this alloy were machined without encountering any difficulty.

[0055] Microstructure evaluation of the alloy of Example 1 revealed intermetallic compounds combined with the expected bismuth segregate. These combined agglomerations were well distributed throughout the matrix as shown in the high magnification SEM view of FIG. 1. Separate constituents of individual agglomeration sites are shown under higher magnification in FIGS. 2 and 3. The agglomeration phase contains three distinct constituents that can be distinguished as follows:

[0056] Constituent 1—White Irregular Shaped Bismuth-Rich Phase

[0057] Constituent 2—Grayish Segregate of Mg—Bi—Cu

[0058] Constituent 3—White Rounded Segregate of Ca—Mg—Bi—Cu

[0059] Semiquantitative EDX elemental analysis of the individual constituents is provided in Table 2.

TABLE 2
Bi-Rich Pool Constituent Composition
Weight Percent Element Per Constituent
Constituent	Mg	Ca	Bi	Zn	Sn	Cu
1	0.02	0.14	95.42	0.00	0.00	Balance
2	5.46	0.00	75.39	0.00	0.00	Balance
3	3.97	3.87	88.76	0.00	0.00	Balance

[0060] The tensile strength of the alloy was checked using machined test bars with an average ultimate tensile strength (UTS) of 36,000 pounds per inch2 and elongation of 40%. This compares favorably with the typical UTS of 34,000 pounds per inch2 and 35% elongation for the leaded C85400.

[0061] It was originally thought that corrosion resistance might be adversely affected by introducing calcium and/or magnesium into certain brasses. A series of samples, including the Example 1 alloy, were subjected to 24-hour copper chloride exposure corrosion testing. The exemplar alloy was compared with a C85400 yellow brass tested in a like manner. The invention alloy compared favorably with the standard yellow brass with only a third of the dezincification corrosion loss.

EXAMPLE 2

[0062] This example is another embodiment of the invention with chemical composition by weight (of the alloy) of 26.76% zinc, 3.20% bismuth, 1.23% tin, 0.65% nickel, 0.083% antimony, 0.098% aluminum, 0.1% calcium, and 0.07% carbon. This example demonstrates the base technique used for bismuth phase modification and redistribution by the late melt addition of calcium carbide powder. (See FIGS. 4 and 5.) It is intended that magnesium and/or calcium be added in varying percentages to this late melt addition to achieve intermetallic phase segregation.

EXAMPLE 3

[0063] This example is from foundry trials that were conducted on several preferred embodiments of this invention, and alpha-beta brass (DZR yellow brass) was selected based on the dual requirement of the alloy for grain refinement in regards to provision of a uniform distribution of bismuth and the need for enhancement of DZ resistance. The chemical composition of this alloy is as follows:

26.76% Zinc
3.20%  Bismuth
1.23%  Tin
0.65%  Nickel
0.083% Antimony
0.098% Aluminum
0.1%   Calcium
0.07%  Carbon

[0064] where all percentages are weight percentages based on the total weight of the alloy.

EXAMPLE 4

[0065] Another run where items were cast using a bismuth/calcium/magnesium alloy addition had the following composition:

28.51% zinc
1.68%  bismuth
1.04%  tin
0.005% calcium, and
0.015% magnesium

[0066] A weight percent target of 2.20% of the melt bath was used for the bismuth-rich additive. This additive contained 73.40% bismuth, 0.95% calcium and 25.65% magnesium. After melting in the additive, the furnace melt was held at a temperature greater than 2100° F. for nearly three hours. The magnesium content was reduced considerably by this extended holding at temperature; however, the calcium content remained reasonably stable. This demonstrated retention of calcium confirmed previous study findings. The castings produced by this demonstration were machined, assembled and pressure tested without difficulty.

[0067] The addition of calcium to the bismuth provides an alloy with a distinct segregate pattern of calcium. The microstructure of pure bismuth is shown in FIG. 6. In contrast, the sharp acicular form of the calcium segregate is depicted in FIGS. 7 and 8. The further addition of magnesium to bismuth saturated with calcium provides a microstructure as shown in FIGS. 9 and 10. Magnesium is revealed as a dark component within the acicular calcium form. FIGS. 11 and 12 show the microstructure of the final copper base alloy containing 2% by weight of the bismuth/calcium/magnesium additive. This alloy also contains about 38% zinc and about 1% tin by weight with the balance being copper. It is contemplated that the bismuth alloy may include other elements such as antimony, lead, and tin.

[0068] The following process is used to create a bismuth/calcium or bismuth/calcium/magnesium pre-alloy. Bismuth is melted and superheated with an electric coreless furnace to about 2,000° F. Granular calcium carbide is then placed on top of the molten bismuth bath as a cover material. The calcium carbide cover is replenished to make up for any loss. By doing this, calcium is taken into the melt and carbon is released as fumes. The calcium carbide cover is replenished until a point of saturation is reached when the cover remains largely intact. After the calcium carbide cover is maintained without further additions, a predetermined amount of magnesium is plunged into the alloy. To create the no-lead brass alloy, copper is melted in an induction furnace, tin is optionally added, and then zinc is added. The pre-made bismuth/calcium/magnesium or bismuth/calcium alloy is then added to form the alloy. Other components such as antimony, selenium, aluminum, and phosphorus can be added, as desired.

[0069] The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention.

Claims

1. An alloy comprising: bismuth in an amount of about 1% to about 7% by weight of the alloy; zinc in an amount of 0 to about 45% by weight of the alloy; tin in an amount of 0 to about 20% by weight of the alloy; calcium and magnesium, in an amount combined from about 0.02% to about 2.0% by weight of the alloy; and copper in an amount of 27% to about 98.8% by weight of the alloy.

2. The alloy defined in claim 1, further including antimony.

3. The alloy defined in claim 1, further including lead.

4. The alloy defined in claim 1, where said bismuth, calcium, and magnesium are melt added to the remaining components of the alloy.

5. A method for producing a pre-alloy comprising the steps of: (a) melting and superheating bismuth; (b) placing granular calcium carbide on top of the molten bismuth; (c) replenishing the calcium carbide until saturation is reached; and (d) plunging magnesium into the bismuth melt.

6. The method defined in claim 5, wherein said bismuth is melted and superheated at a temperature of about 2000° F.

7. A plumbing component made of an alloy comprising: bismuth in an amount of about 1% to about 7% by weight of the alloy; zinc in an amount of 0 to about 45% by weight of the alloy; tin in an amount of 0 to about 20% by weight of the alloy; calcium and magnesium, in an amount combined from about 0.01% to about 2.0% by weight of the alloy; and copper in an amount of 27% to about 98.9% by weight of the alloy.

8. The plumbing component of claim 7, further including antimony.

9. The plumbing component of claim 7, further including lead.

10. The plumbing component of claim 7, where said bismuth, calcium, and magnesium are melt added to the remaining components of the alloy.

11. A method of producing a no-lead alloy comprising the steps of: (a) melting and superheating bismuth; (b) placing granular calcium carbide on top of the molten bismuth; (c) replenishing the calcium carbide until saturation is reached; (d) plunging magnesium into the bismuth melt to form a pre-alloy; (e) melting copper; (f) adding zinc to the copper; and (g) adding said pre-alloy to said melted copper and zinc.

12. The method defined in claim 11, further including the step of adding tin to said melted copper before the addition of zinc.

13. The method defined in claim 11, wherein said bismuth is melted and superheated at about 2000° F.

14. The method defined in claim 13, wherein said bismuth is melted in an electric coreless furnace.

15. The method defined in claim 11, further including the step of adding antimony to the alloy.

16. A no-lead alloy comprising: about 68% copper by weight of the alloy; about 28% zinc by weight of the alloy; about 2% bismuth by weight of the alloy; about 1% tin by weight of the alloy; about 0.5% magnesium by weight of the alloy; and about 0.5% calcium by weight of the alloy.