Patent Application
20110081272
1. Field of the Invention
The present invention relates to copper alloys, and more particularly, to a low-lead brass alloy.
2. Description of Related Art
Brass comprises copper and zinc, as major ingredients, usually in a ratio of about 7:3 or 6:4. In addition, brass usually comprises a small amount of impurities. In the context of improving the properties of brass, a conventional brass contains lead (mostly in the range of 1 to 3 wt %) to achieve the desired mechanical properties for use in the industry, thereby becoming an important industrial material that is widely applicable to metallic devices and valves for use in pipelines, faucets and water supply and discharge systems.
However, as awareness of the importance of environmental protection increases and the impact of heavy metals on human health becomes better understood, there is a tendency to restrict the use of lead-containing alloys. Various countries, such as Japan and the United States, have progressively amended relevant regulations in an intensive effort to lower the lead content in the environment by particularly requiring that no lead shall leach from lead-containing alloys used in products ranging from household appliances and automobiles to residential water pipes and municipal water systems, while also requiring that lead contamination shall be avoided during processing.
As mentioned, brass, by definition, contains zinc. However, if the zinc content of brass exceeds 20 wt %, corrosion (such as dezincification) is likely to occur. Because dezincification seriously damages the structure of brass, the surface integrity of brass products is lowered and even pores may be formed in brass pipes. This significantly decreases the lifespan of brass products, thereby causing application problems.
Regarding the above issues of high lead content and dezincification, the industry continues to develop copper alloy formulations. For example, in addition to copper and zinc as essential and primary ingredients, U.S. Pat. Nos. 6,413,330 and 7,354,489, and US Patent Application Publication Nos. 20070062615, 20060078458 and 2004023441 disclose lead-free copper alloys with other components to address the above concerns. However, these alloys have poor machinability, low processing efficiencies, unsuitability for large-scale productions and susceptibility to defects like cracks and slag inclusions. In addition, U.S. Pat. Nos. 7,297,215, 6,974,509, 6,955,378, 6,149,739, 5,942,056, 5,637,160, 5,653,827, 5,487,867 and 5,330,712, and US Patent Application Publication Nos. 20060005901, 20040094243 and US20070039667, etc., disclose lead-free or low-lead bismuth-containing brass alloy formulations, wherein the bismuth content of the formulations ranges from 0.5 wt % to 7 wt %. However, high bismuth content is likely to lead to defects like cracks and slag inclusions, leading to low processing efficiencies.
Furthermore, regarding formulations designed to combat dezincification, in addition to copper and zinc as essential ingredients, U.S. Pat. No. 4,417,929 discloses a formulation comprising iron, aluminum and silicon, U.S. Pat. Nos. 5,507,885 and 6,395,110 disclose formulations comprising phosphorus, tin and nickel, U.S. Pat. No. 5,653,827 discloses a formulation comprising iron, nickel and bismuth, U.S. Pat. No. 6,974,509 discloses a formulation comprising tin, bismuth, iron, nickel and phosphorus, U.S. Pat. No. 6,787,101 discloses a formulation comprising phosphorus, tin, nickel, iron, aluminum, silicon and arsenic, all at the same time, and U.S. Pat. Nos. 6,599,378 and 5,637,160 disclose adding selenium and phosphorus in a brass alloy, all of these formulations aimed at addressing the dezincification problem. Conventional dezincification-resistant brasses usually have higher lead contents (most in the range of 1 to 3 wt %), which facilitates cold/thermal processing of brass materials. However, these brasses do not meet environmental demands, because lead leaching is high and lead contamination is likely to occur during processes.
Thus, the industry continues to develop brass materials, and to seek an alloy formulation that can substitute for lead-containing brasses and achieve dezincification corrosion resistance, while possessing desirable properties such as good casting characteristics, machinability, corrosion-resistance as well as mechanical properties.
In order to attain the above and other objectives, the present invention provides a low-lead copper alloy, comprising: 0.05 to 0.3 wt % of lead (Pb), 0.3 to 0.8 wt % of aluminum (Al), 0.01 to 0.4 wt % of bismuth (Bi), 0.1 to 2 wt % of nickel (Ni), and more than 96.5 wt % of copper (Cu) and zinc (Zn), wherein copper is present in an amount ranging from 58 to 70 wt %.
The low-lead copper alloy of the present invention is a brass alloy. The total amount of copper and zinc can be higher than 96.5 wt %. In an embodiment, copper is in an amount ranging from 58 to 70 wt %. A copper content in this range can provide excellent toughness for the alloy, facilitating subsequent processing of the alloy material. In a preferred embodiment, the copper content ranges from 62 to 65 wt %.
In the copper alloy of the present invention, the aluminum content ranges from 0.3 to 0.8 wt %. In a preferred embodiment, the aluminum content ranges from 0.4 to 0.7 wt %, and preferably 0.5 to 0.65 wt %. Addition of an appropriate amount of aluminum can increase the fluidity of a copper liquid and improve the casting properties of the alloy material.
In the copper alloy of the present invention, the bismuth content is less than 0.4 wt %. In a preferred embodiment, the bismuth content ranges from 0.01 to 4 wt %, preferably 0.05 to 0.3 wt %, and more preferably 0.1 to 0.2 wt %.
In the copper alloy of the present invention, the nickel content ranges from 0.1 to 2 wt %. In a preferred embodiment, the bismuth content ranges from 0.5 to 1 wt %. Nickel used in an appropriate amount in the copper alloy can result in a copper alloy having a high melting point. Nickel acts as heterogeneous nucleus formed in non-spontaneous nucleation when the alloy crystallizes, so that the number of nucleation sites is increased, thereby refining the alloy grains. Further, nickel can purify the copper matrix and the grain boundary, thereby increasing the kinetic properties and corrosion resistance of the copper alloy.
The copper alloy of the present invention comprises extremely low lead content, i.e., less than 0.3 wt %. In an embodiment, the lead content ranges from 0.05 to 0.3 wt %, preferably 0.1 to 0.25 wt %, and more preferably 0.15 to 0.20 wt %. The alloy may possibly contain impurities. The amount of unavoidable impurities is less than 0.1 wt %.
The copper alloy of the present invention can substitute for conventional lead-containing brasses, and is more likely to meet environmental demands and lower the effects of lead contamination. Further, the alloy has advantages like having dezincification corrosion resistance, desirable casting properties, machinability and mechanical properties possessed by conventional lead-containing brasses.
The detailed description of the present invention is illustrated by the following specific examples. Persons skilled in the art can conceive the other advantages and effects of the present invention based on the disclosure contained in the specification of the present invention.
Unless otherwise specified, the ingredients comprised in the dezincification-resistant copper alloy of the present invention, as discussed herein, are all based on the total weight of the alloy, and are expressed in weight percentages (wt %).
When a conventional high amount of bismuth (i.e., more than 1 wt %) is added to a brass alloy, at the micro level, a liquid-state bismuth film is likely to be first formed in the brass alloy, and then continuously flaky bismuth is formed on the grain boundary to shield the grain boundary, disrupting the mechanical integrity of the alloy and then increasing the hot shortness and cold shortness of the alloy, thereby causing material cracking. Nevertheless, the low-lead brass alloy formulation according to the present invention only needs to use less than 0.4 wt % of bismuth. This not only facilitates elimination of defects like material cracking, but also allows for desirable material properties (such as machinability) of lead brasses (such as conventional C85710 lead brasses). Further, defects like cracks or slag inclusions are unlikely to occur. Hence, the low-lead brass alloy of the present invention can substantially lower the amount of bismuth used, thereby effectively lowering the production cost thereof. This is extremely advantageous to commercial-scale productions and applications.
Moreover, the low-lead brass alloy formulation according to the present invention can lower the lead content to a range of 0.05 to 3 wt %, to comply with the international standards for lead content in pipeline materials in contact with water. Therefore, the low-lead brass alloy of the present invention is suitable for applications to faucets and lavatory components, pipelines for tap water, water supply systems, etc.
In an embodiment, the low-lead brass alloy of the present invention comprises 0.05 to 0.3 wt % of lead, 0.3 to 0.8 wt % of aluminum, 0.01 to 0.4 wt % of bismuth, 0.1 to 2 wt % of bismuth, and 96.5 to 99.54 wt % of copper and zinc, wherein copper is in an amount ranging from 58 to 70 wt %.
In another embodiment, the nickel-containing low-lead brass alloy of the present invention comprises 0.1 to 0.25 wt % of lead, 0.4 to 0.7 wt % of aluminum, 0.05 to 0.3 wt % of bismuth, 0.5 to 1 wt % of nickel, 58 to 70 wt % of copper, and zinc in balance, wherein unavoidable impurities are less than 0.1 wt %.
In a further embodiment, the nickel-containing low-lead brass alloy of the present invention comprises 0.15 to 0.20 wt % of lead, 0.5 to 0.65 wt % of aluminum, 0.1 to 0.2 wt % of bismuth, 0.5 to 1 wt % of nickel, 62 to 65 wt % of copper, and zinc in balance, wherein unavoidable impurities are less than 0.1 wt %.
The present invention is illustrated in detail by the following exemplary examples.
The ingredients of the low-lead copper alloy of the present invention used in the following test examples are described below, wherein each of the ingredients is added at a proportion based on the total weight of the alloy.
Rounded sand, a urea formaldehyde resin, a furan resin and a curing agent were used as raw materials to prepare sand core using a core shooter, and the gas evolutions of the resins were measured using a testing machine for testing gas evolutions. The obtained sand core must be completely used within 5 hours, or it needs to be baked dry.
The dezincification-resistant low-lead brass alloy of the present invention and scrap returns were preheated for 15 minutes to reach a temperature higher than 400° C. Then, the alloy of the present invention and the scrap returns were mixed at a weight ratio of 7:1, along with addition of 0.2 wt % of refining slag, for melting in an induction furnace until the brass alloy reached a certain molten state (hereinafter referred to as “molten copper liquid”). A metallic gravity casting machine coupled with the sand core and the gravity casting molds to perform casting, and a temperature monitoring system further controlled temperatures so as to maintain the casting temperature at a range of 1010 to 1060° C. In each casting, the feed amount was preferably 1 to 2 kilograms, and the casting time was controlled to a range of 3 to 8 seconds.
After the molds were cooled, the molds were opened and the casting head was cleaned. The mold temperatures were monitored so as to control the mold temperatures in the range of 200 to 220° C. to form casting parts. Then, the casting parts were released from the molds. Then, the molds were cleaned to ensure that the site of the core head was clean. A graphite liquid was spread on the surfaces of the molds followed by cooling by immersion. The temperature of the graphite liquid for cooling the mold was preferably maintained at a range of 30 to 36° C., and the specific weight of the graphite liquid ranged from 1.05 to 1.06.
Inspection was performed on the cooled casting parts, and the casting parts were sent into a sand cleaning drum for cleaning. Then, an as-cast treatment was performed, wherein a thermal treatment for distressing annealing was performed on as-casts to eliminate the internal stress generated by casting. The as-casts were subsequently mechanically processed and polished, so that no sand, metal powder or other impurities adhered to the cavities of the casting parts. A quality analysis was performed and the overall production yield was calculated by the following equation:
O.P. Yield=Number of Non-Defective Products/Total Number of Products×100%
The overall production yield (O. P. Yield) reflects the qualitative stability of production processes. High qualitative stability of production processes ensures normal production.
Moreover, a lead-free high nickel brass and a conventional lead brass were used as comparative examples to produce products by the same process as described above. The ingredients, processing characteristics and overall production yield of each of the alloys are shown in
The lead-free high nickel brass had higher degrees of hardness. Thus, it was difficult to perform mechanical processing on the lead-free high nickel brass. When the same feeding amount and cutting speed were applied on the above three copper materials, cuts were likely to be found on the surfaces of the lead-free high nickel brass product, and the roughness of the surfaces could not meet requirements (i.e., an Ra value of 3.2 μm). Hence, the production yield of the lead-free high nickel was lower.
As for the test group in which the low-lead brass of the present invention was used as a raw material, the production yield was as high as 85 wt %. This was comparable to that of the conventional C85710 lead bass. Thus, the low-lead brass of the present invention can indeed be used as a substitute brass material. Further, the low-lead brass of the present invention can have substantially lowered lead content, thereby effectively avoiding the lead contamination that arose during processing and lowering lead leaching when using the casting product. As such, desirable material properties are achieved while meeting environmental demands at the same time.
The measured values of the ingredients of the bismuth-containing low-lead brass of Example 1 are as follows: Cu: 61.54 wt %, Al: 0.457 wt %, Pb: 0.144 wt %, Bi: 0.197 wt % and Ni: 0.584 wt %.
The measured values of the ingredients of the lead-free high nickel brass of Comparative Example 1 are as follows: Cu: 61.01 wt %, Al: 0.574 wt %, Pb: 0.0067 wt %, Bi: 0.134 wt % and Ni: 2.324 wt %.
The measured values of the major ingredients of the C85710 lead brass of Comparative Example 3 are as follows: Cu: 59.7 wt %, Al: 0.521 wt %, Pb: 2.16 wt %, Bi: 0.0074 wt % and Ni: 0.0103 wt %.
The measured values of the major ingredients of the lead-free low bismuth brass of Comparative Example 5 are as follows: Cu: 63.28 wt %, Al: 0.597 wt %, Pb: 0.037 wt %, Bi: 0.114 wt % and Ni: 0.063 wt %.
A dezincification test was performed on the brass alloys of Example 3 and Comparative Example 3 to test the corrosion resistance of the brasses. The dezincification test was performed according to the Australian standard AS2345-2006 “Dezincification resistance of copper alloys.” Before a corrosion experiment was performed, a novolak resin was used for inlaying to make the exposed area of each of the specimens to be 100 mm2. All the specimens were ground flat using a 600# metallographic abrasive paper, followed by washing using distilled water. Then, the specimens were baked dry. The test solution was a 1% CuCl2 solution prepared before use, and the test temperature was 75±2° C. The specimens and the CuCl2 solution were placed in a temperature-controlled water bath to react for 24±0.5 hours. The specimens were removed from the water bath, and cut along the vertical direction. The cross-sections of the specimens were polished, and then the depths of corrosion of the specimens were measured and observed under a digital metallographic electronic microscope. Results are shown in
As shown in
A test of the mechanical properties was performed on specimens of the examples according to the standard set forth in ISO6998-1998 “Tensile experiments on metallic materials at room temperature.” Results are shown in Table 2.
As shown in Table 2, the tensile strength and elongation for Example 1 were comparable to that of the conventional C85710 lead brass for Example 3, indicating that the low-lead brass alloy of the present invention had mechanical properties comparable to those of the C85710 lead brass. However, the low-lead brass of the present invention had lower lead content, thereby better complying with environmental demands. Thus, the low-lead bass of the present invention can indeed substitute for the C85710 lead brass in manufacturing of products.
Although the intensity and degrees of hardness of the lead-free high nickel brass of Comparative Example 1 were higher, the high degrees of hardness were detrimental to machining processing. The level of difficulty in cold processing and production costs were increased, such that the lead-free high nickel brass of Comparative Example 1 was not suitable for use in manufacturing lavatory components.
A test was performed according to the standard set forth in NSF 61-2007a SPAC for the allowable precipitation amounts of metals in products, to examine the precipitation amounts of the metals of the brass alloys in an aqueous environment. Results are shown in Table 3.
The lead content of the material of Comparative Example 3 exceeded the upper limit of the standard value before a lead stripping treatment was performed. Only the material of Example 1 reached the standard value without the need to perform a lead stripping treatment. Further, the precipitation amount of the heavy metal, lead, of the low-lead brass alloy of the present invention was still significantly lower than that of the C85710 lead brass that underwent a lead-stripping treatment. Hence, the low-lead brass alloy of the present invention was more environmentally friendly and reducing risks to human health.
In light of the above, the low-lead brass alloy of the present invention has a refined grain structure and good alloy integrity and toughness, such that it is not likely to cause defects like cracks and slag inclusions or even casting defects, thereby achieving the desirable properties possessed by lead brasses. This facilitates the application of the alloy material to subsequent processes. The low-lead brass alloy of the present invention can have a low-lead precipitation amount without experiencing a lead-stripping treatment, thereby decreasing the production costs of the process. This is extremely advantageous to commercial-scale production and applications.
The invention has been described using exemplary preferred embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation, so as to encompass all such modifications and similar arrangements.
