KR20110131272A - Lead-free brass alloy - Google Patents

Abstract

The present invention relates to a brass alloy that is substantially lead free. In the alloy of the present invention, lead is replaced by tellurium, thereby achieving an alloy with good machinability and conductivity.

Description

Lead-Free Brass Alloy {LEAD-FREE BRASS ALLOY}

The present invention relates to brass composites with very low lead content up to lead-free content. Brass composites have good machinability and strength similar to conventional leaded brass alloys without machining brass.

It was a common embodiment to add up to 4.5% lead to the brass composite to improve the machinability of the resulting product. However, lead is a toxic material and its use in the manufacture of alloys is surrounded by legislation and expensive control procedures. For example, a law adopted in California that limits the amount of lead in pipe connections to 2.5% or less came into force in 2010.

Moreover, the lead phase in copper lead alloys can be affected by the corrosive attack of hot organic or mineral oils. For example, when the temperature of such an alloy rises, the oil causes chemical changes to form peroxides and organic gases, which affect the degree of leaching of the lead phase in the alloy. If this leaching proceeds to any significant extent, the component (if it is a bearing or structural component) may ultimately malfunction or fail.

Thus, it can be quite advantageous to reduce or possibly eliminate the content of lead in powder metallurgy composites. To this end, various proposals have been made. In the past, significant proportions of lead incorporated into powder metallurgy materials resulted in the ease and durability of the machinability of the resulting product components. In the international application published as WO91 / 14012, it has been proposed to replace the lead portion with bismuth. As a result, the lead portion was successfully replaced without significant reduction in machinability. However, some reduction in the lateral strength of the material was involved. For many purposes, this reduction in lateral strength is not a serious problem.

Another approach is described in US Pat. No. 5,445,665. In this product, 0.1 to 1.5% graphite was added to the alloy to reduce lead to less than 2% of the alloy.

The aforementioned alloys result in substantially lead-free alloys, but the alloys do not have the same machinability as lead containing alloys. As a result, substantial modification of the equipment used to manufacture the final product, such as plumbing equipment, is required. In addition, scrap generated during the manufacture of lead products is often not easily reused by the end product manufacturer. Reuse can typically be done only by the manufacturer of the alloy. The cost of shipping scrap back to the original factory increases the overall product cost of the final product.

Accordingly, there remains a need for lead-free brass alloys that have similar machinability to lead-containing products and can be reused by customers.

The present invention typically includes a brass alloy containing from about 0.20% to 1.5% tellurium as a substitute for lead added to the brass composition. In one series of examples, the tellurium ranges from about 0.4% to about 1.0%. The resulting alloy has a lead content of less than about 0.025% to less than about 0.001%, which is typically considered "lead free".

Brass alloys of the present invention typically have a copper content of about 98% to about 57%, a zinc content of about 43% to about 2%, a tellurium content of about 1.0% to about 0.02%, and a lead of about 0.025% to about 0.001% Content, and a maximum phosphorus content of about 0.05%.

The resulting alloy has good machinability and conductivity. Depending on the composition of the alloy, the tensile strength will be between 240 MPa and 530 MPa and the yield strength will be between about 200 and about 450 MPa. The conductivity will be about 28% to about 49% IACS. The machinability of the novel alloy of the present invention is similar to the machinability of lead containing composites. This eliminates or reduces the amount of modification required to use the new alloy to produce finished products such as piping connectors.

The composition of the new alloy also allows the manufacturer of the final product to reuse the scrap from its manufacturing process. This eliminates the need to return the scrap to the alloy manufacturer for reuse. Another major feature of the present invention is that alloys containing less than about 15% zinc have good dezinc resistance.

The features and technical advantages of the present invention have been described broadly above in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. Those skilled in the art should appreciate that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It is also to be understood that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS The novel features which appear to be features of the invention with respect to their construction and method of operation together with other objects and advantages will be better understood from the following description when considered in conjunction with the accompanying drawings. However, it should be clearly understood that each figure is provided for illustration and description only and is not intended as a definition of the limits of the invention.

1 is a micrograph of the alloy used for Sample C1 after drawing.
2 is a micrograph of the alloy used for Sample C2 after drawing.
3 is a micrograph of the alloy used for Sample C3 after drawing.

The brass alloy of the present invention is prepared by first melting copper at a temperature of about 1050 ° C. Subsequently, zinc and tellurium are added to the molten copper. The brass alloy is then cast into billets using either horizontal or vertical casting.

The copper used to make the alloy is typically copper cathode or high quality, uncontaminated pure copper scrap containing 99.95% minimum copper and up to 0.05% impurities. Lead is a common impurity comprising less than 0.025% of the copper used. In forming the alloy of the present invention, copper comprises from about 57.00 to about 98.00% of the alloy.

Zinc is the next major component that makes up about 2.00% to about 43.00% of the alloy.

Tellurium is used as a substitute for lead. Like lead, tellurium is added to improve the machinability of the alloy without the negative contribution of lead. Tellurium is added in an amount of about 0.20% to about 1.5% of the alloy. In one series of examples, the tellurium ranges from about 0.4 to about 1.0%. In one embodiment, tellurium comprises about 0.5% of the alloy. The amount of tellurium used depends in part on the amount of copper used in the alloy since the copper level increases and decreases the amount of tellurium used. As with lead, the addition of tellurium to the alloy causes breaks in the copper and zinc phases of the alloy as shown in FIGS. Good dispersion of these breaks results in improved machinability of the alloy.

One advantage of the present invention is that the alloy has similar machinability to lead containing alloys while using significantly lower amounts of tellurium.

Other materials that can be added to the brass alloy include arsenic, nickel, manganese, silicon and phosphorus. When phosphorus is used, the amount present will typically be less than 0.05% of the alloy.

The resulting alloy exhibits excellent machinability and conductivity, as indicated by Ultimate Tensile Strength (UTS) of about 240 to about 530 MPa and yield strength of about 200 MPa to about 450 MPa as determined using ASTM method B140. You will usually have Actual tensile and yield strengths depend, in part, on the actual composition of the alloy. The conductivity of the alloy is about 28 to about 45% IACS.

A series of brass alloys was prepared in which the added lead (typically about 2%) was replaced with approximately 0.5% terrur. The composition of each alloy is shown in Table 1.

sample Cu Pb Zn Te P Sn A Remainder <0.01 5.10 0.5 0.011 ---- B Remainder 0.00 8.82 0.57 0.001 ---- C 83.03 0.06 Remainder 0.052 0.05 0.11 D 59.41 0.02 Remainder 0.17 0.05 ----

The billet is then ground to an extrusion press at a temperature of about 780 ° C to about 860 ° C. Billets are hot extruded at various pressures through various dies to create multiple sizes. Each shot is lubricated before extrusion and the extrusion die is preheated. The results are shown in Table 2.

sample Final draw size Shot temperature pressure Length A1 31.75 mm 808 ℃ 234 MPa 12 m A2 75.40 mm 822 ℃ 268 MPa 18.5 m A3 19.05 mm 803 ℃ 305 MPa 34 m B1 31.75 mm 794 ℃ 267 MPa 12 m B2 25.40 mm 800 ℃ 289 MPa 18.5 m B3 19.05 mm 806 ℃ 304 MPa 34 m B4 12.70 mm 870 ℃ 265 MPa 67 m C1a 25.40 mm 830 ℃ 298 MPa 18.4 m C1b 25.40 mm 867 ℃ 280 MPa 18.4 m C2a 50.80 mm 750 ℃ 230 MPa 21.5 m C3a 22.23 mm AF Hex 830 ℃ 312 MPa 21.5 m C3b 22.23 mm AF Hex 837 ℃ 324 MPa 21.5 m D1a 50.8 mm 640 ℃ 128 MPa 4.6 m D1b 50.80 mm 637 ℃ 142 MPa 4.6 m D2a 25.4 mm 650 ℃ 234 MPa 18.4 m D2b 25.4 mm 660 ℃ 214 MPa 18.4 m D3a 22.23 mm AF Hex 648 ℃ 235 MPa 21.5 m D3b 22.23 mm 621 ℃ 276 MPa 21.5 m

The bar is then passed through a sulfuric acid washing bath and then cold drawn to induce accurate mechanical properties and particle size requirements. This process ensures that the correct size tolerances are met. Cold drawing operations are accomplished effortlessly. The product was then tested for tensile strength, hardness, conductivity and machinability. The results are shown in Table 3.

sample Area reduction (%) Tensile strength (MPa) Yield strength (MPa) Elongation Hardness (Rb) A1 11.24 267.9 210.3 30% 56 A2 12.8 296.5 341.3 24% 57 A3 11.71 322 279.2 16% 60 B1 11.24 302.7 241.3 26% 59 B2 12.8 322 259.2 24% 63 B3 17.71 322.7 268.9 21% 64 B4 28.32 393.7 393 12% 69 C1 12.8 350.2 291.9 20% 51 C2 11.13 354.9 295.8 20% 52 C3 13 358.8 294.1 22% 53 D1 14.10 487.8 278.2 29% 75 D2 14.10 531.6 443 20% 78 D3 14.44 485.3 407.8 19% 76

Conductivity tests were performed on various samples. Conductivity decreases as the proportion of zinc content increases. The result is at least about 28% up to about 49%.

Photomicrographs of samples C1, C2 and C3 were taken after drawing and shown in FIGS. The microstructure of the alloy is uniform showing good dispersion of tellurium throughout the alloy.

While the invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made here without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the invention is not intended to be limited to the processes, machines, manufacture, compositions of matter, means, methods and steps described in the specification. Those skilled in the art from the present disclosure, presently or later developed processes, machines, manufacture, composition, means, methods of materials which perform substantially the same functions or achieve substantially the same results as the corresponding embodiments described herein. It will be readily appreciated that the steps may be used in accordance with the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods or steps.

Claims (19)

As a brass alloy,
Copper,
zinc,
Tellurium and
Wherein the lead comprises less than 0.25% of the alloy and tellurium comprises from about 0.025% to about 1% of the alloy. The brass alloy of claim 1, wherein the copper comprises about 57% to about 98% of the alloy. The brass alloy of claim 1, wherein the zinc comprises from about 2.0% to about 43% of the alloy. The brass alloy of claim 1, further comprising less than about 0.02% phosphorus. As a brass alloy,
About 57% to about 98% copper,
About 2% to about 43% zinc and
A brass alloy comprising from about 0.025% to about 1.0% tellurium. 6. The brass alloy of claim 5, further comprising less than about 0.025% lead. The brass alloy of claim 1 having a tensile strength of about 240 MPa to about 530 MPa. The brass alloy of claim 1 having a yield strength of about 200 MPa to about 450 MPa. The brass alloy of claim 1 having a conductivity of about 28% to about 49% IACS. The brass alloy of claim 1, wherein the zinc comprises about 5% of the alloy. The brass alloy of claim 1, wherein the zinc comprises about 10% of the alloy. The brass alloy of claim 1, wherein the zinc comprises about 15% of the alloy. The brass alloy of claim 1, wherein the zinc comprises about 40% of the alloy. As a brass alloy,
About 57% to about 98% copper,
About 43% to about 2% zinc,
About 0.025% to about 1.0% tellurium
Brass alloy comprising a. The brass alloy of claim 14 having a lead content of less than about 0.5%. The brass alloy of claim 14 having a lead content of less than about 0.01%. The brass alloy of claim 14 having a tensile strength of about 240 MPa to about 530 MPa. The brass alloy of claim 14 having a yield strength of about 200 MPa to about 450 MPa. The brass alloy of claim 14 having a conductivity of about 28% to about 49% IACS.

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