Patent Application
20110064602
1. Field of the Invention
The present invention relates to dezincification-resistant copper alloys, and more particularly, to a dezincification-resistant low lead brass alloy.
2. Description of Related Art
Brass comprises copper and zinc, as major ingredients, usually at a ratio of about 7:3 or 6:4. If the zinc content of brass exceeds 20 wt %, corrosion (such as dezincification) is likely to occur. For example, when a brass alloy article is used in the environment, zinc on the alloy surface is preferentially melted and copper contained in the alloy remains on the base metal, thereby causing corrosion in the form of porous, brittle copper. Generally, if the zinc content is less than 15 wt %, dezincification is not likely to occur. However, as the zinc content increases, the sensitivity to dezincification is increased. If the zinc content exceeds 30 wt %, dezincification corrosion is more severe.
It has been reported in literatures that dezincification corrosion is associated with alloy compositions and environmental factors. In the context of alloy compositions, dezincification of brass with a single a phase and zinc content higher than 20 wt % gives porous copper, whereas dezincification of brass with double α+β phases begins initially in β phase and later expands to a phase when β phase is completely converted into loosely-structured copper (see Kuaiji Wang et al., Chinese Journal of Materials Research, Vol. 13, pages 1-8).
Since dezincification of brass severely damages the structures of brass alloys, the surface intensities of brass products produced from brass alloys are decreased such that porosity occurs on brass pipes. This significantly decreases the lifetimes of the brass products, and causes application problems. Therefore, standards like AS 2345 and ISO 6509 are used for testing the dezincification resistance of a brass product, i.e., the depth of a dezincification layer formed on the surface of a brass product shall not exceed 100 μm.
Regarding the formulations of dezincification resistant brass alloys, except for copper and zinc that are major ingredients, patents such as U.S. Pat. No. 4,417,929 discloses a formulation comprising iron, aluminum and silicon ingredients, U.S. Pat. No. 5,507,885 and U.S. Pat. No. 6,395,110 disclose formulations comprising phosphorus, tin and nickel ingredients, U.S. Pat. No. 5,653,827 discloses a formulation comprising iron, nickel and bismuth ingredients, U.S. Pat. No. 6,974,509 discloses a formulation comprising tin, bismuth, iron, nickel and phosphorus ingredients, U.S. Pat. No. 6,787,101 discloses a formulation comprising phosphorus, tin, nickel, iron, aluminum, silicon and arsenic ingredients at the same time, and U.S. Pat. No. 6,599,378 and U.S. Pat. No. 5,637,160 discloses adding selenium and phosphorus ingredients in a brass alloy to achieve a dezincifying effect. Alternatively, please refer to Kuaiji Wang et al., Chinese Journal of Materials Research, Vol. 13, pages 1-8, wherein a dezincifying effect is achieved by adding boron and selenium into a brass alloy.
Conventional dezincification-resistant brasses usually have higher lead contents (most in the range from 1 to 3 wt %), enabling cold/thermal processing of brass materials. However, as the awareness of environmental protection increases and the impacts of heavy metals on human health and issues like environmental pollutions become major focuses, it is a tendency to restrict the usage of lead-containing alloys. Various countries such as Japan, the United States of America, etc, have sequentially amended relevant regulations and put intensive efforts to lower lead contents in the environment by particularly demanding that no molten lead shall leak from the lead-containing alloy materials used in products such as household electronic appliances, automobiles and water systems to drinking water and lead contamination shall be avoided during processing. Thus, there exists an urgent need in the industry to develop a lead-free brass material, and find an alloy formulation that can substitute for lead-containing brasses while possessing desirable properties like good casting properties, machinability, corrosion resistance and mechanical properties.
The present invention provides a dezincification-resistant low lead brass alloy, comprising less than 0.3 wt % of lead (Pb), 0.02 to 0.15 wt % of antimony (Sb), 0.02 to 0.25 wt % of arsenic (As), 0.4 to 0.8 wt % of aluminum (Al), 1 to 20 ppm of boron (B), and more than 97 wt % of copper (Cu) and zinc (Zn), wherein copper is present in an amount ranging from 58 to 70 wt %.
The dezincification-resistant copper alloy of the present invention is a brass alloy, wherein the total amount of copper and zinc can be higher than 97 wt %. In an embodiment, copper is in an amount ranging from 58 to 70 wt % of the brass alloy. The amount allows copper to confer good toughness to the alloy, thereby facilitating subsequent processing of the alloy material. In a preferred embodiment, copper is in an amount ranging from 61 to 65 wt % of the alloy.
In the dezincification-resistant low lead brass alloy of the present invention, antimony is in an amount ranging from 0.02 to 0.15 wt %. In a preferred embodiment, antimony is in an amount ranging from 0.04 to 0.12 wt % of the alloy. Elements like copper and antimony form an intermetallic compound according to the alloy formulation of the present invention, thereby increasing the machinability of the alloy material without necessarily generating casting defects.
In the dezincification-resistant low lead brass alloy of the present invention, aluminum is in an amount ranging from 0.4 to 0.8 wt %. In a preferred embodiment, aluminum is in an amount ranging from 0.5 to 0.7 wt % of the alloy. Addition of an adequate amount of aluminum in the alloy can increase the fluidity of a copper liquid, and improve the casting properties of the alloy material.
In the dezincification-resistant copper alloy of the present invention, arsenic is in an amount ranging from 0.02 to 0.25 wt %. In a preferred embodiment, arsenic is in an amount ranging from 0.13 to 0.17 wt % of the alloy. Addition of an adequate amount of arsenic in the alloy can significantly increase the property of dezincification corrosion resistance of the alloy material.
In the dezincification-resistant copper alloy of the present invention, boron is in an amount ranging from 1 to 20 ppm. In a preferred embodiment, boron is in an amount ranging from 8 to 14 ppm of the alloy. Addition of an adequate amount of boron can refine the grains of the alloy material, and improve the properties of the alloy material.
The dezincification-resistant copper alloy of the present invention further comprises at least one of nickel and tin in an amount ranging from 0.2 to 1.25 wt %. In an embodiment, the dezincification-resistant copper alloy can comprise nickel and tin at the same time. In a preferred embodiment, tin is in an amount ranging from 0.1 to 1 wt % of the alloy. In another preferred embodiment, nickel is in an amount ranging from 0.1 to 0.25 wt % of the alloy.
The dezincification-resistant copper alloy of the present invention comprises extremely low lead content of less than 0.3 wt % in the alloy. In an embodiment, lead is in an amount ranging from 0.05 to 0.3 wt % of the alloy. The alloy can contain unavoidable impurities in an amount less than 0.1 wt %.
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.
In the specification of the present invention, the term “dezincification-resistant copper alloy/dezincification-resistant brass alloy” is a commonly used technological term in the field, and means an alloy having surfaces that are tolerant to corroding conditions in the environment and not likely to dezincify. AS 2345 regulations (Dezincification resistance of copper alloys) are used as a basis to define that the depth of the dezincification layer formed on the surface of a brass alloy product shall not exceed 100 μm.
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 %).
The dezincification-resistant copper alloy according to the present invention only contains 0.02 to 0.15 wt % of antimony and 0.02 to 0.25 wt % of arsenic to obtain the material properties (such as machinability) possessed by conventional lead brasses. Further, this type of dezincification-resistant low lead copper alloy material is not prone to generate product defects like cracks and slag inclusions, and complies with the dezincification requirement set forth in AS-2345. Also, the brass alloy formulation of the present invention is effective in lowering the production cost of the dezincification-resistant low lead copper alloy, and is extremely advantageous to commercial-scale productions and applications.
Moreover, the lead content in the dezincification-resistant copper alloy formulation of the present invention can be decreased to less than 0.3 wt %, and even less than 0.2 wt %. Therefore, the alloy formulation facilitates manufacturing of faucets and laboratory components, water pipelines for supplying tap water, water supply systems, etc.
In an embodiment, the dezincification-resistant low lead brass alloy of the present invention comprises 58 to 70 wt % of copper, 0.02 to 0.15 wt % of antimony, 0.02 to 0.25 wt % of arsenic, 0.4 to 0.8 wt % of aluminum, 1 to 20 ppm of boron, 0.05 to 0.3 wt % of lead, less than 0.1 wt % of unavoidable impurities, and zinc in balance.
In another embodiment, the dezincification-resistant low lead copper alloy of the present invention comprises 58 to 70 wt % of copper, 0.02 to 0.15 wt % of antimony, 0.02 to 0.25 wt % of arsenic, 0.4 to 0.8 wt % of aluminum, 1 to 20 ppm of boron, 0.2 to 1.25 wt % of nickel and/or tin, 0.05 to 0.3 wt % of lead, less than 1 wt % of unavoidable impurities, and zinc in balance.
In further embodiment, the dezincification-resistant low lead copper alloy of the present invention comprises 61 to 65 wt % of copper, 0.04 to 0.12 wt % of antimony, 0.13 to 0.17 wt % of arsenic, 0.5 to 0.7 wt % of aluminum, 8 to 14 ppm of boron, 0.1 to 1 wt % of tin, 0.1 to 0.25 wt % of nickel, 0.05 to 0.3 wt % of lead, less than 0.1 wt % of unavoidable impurities, and zinc in balance.
The present invention is illustrated by the following exemplary examples.
The ingredients of the dezincification-resistant 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. 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 foundry return were preheated for 15 minutes to reach a temperature higher than 400° C., and the two 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 was 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 to a range from 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 from 3 to 8 seconds.
After the molds were cooled, the molds were opened and the casting heads were cleaned. The mold temperatures were monitored so as to control the mold temperatures to a range from 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 were clean. A graphite liquid was spread on the surface of the molds following by cooling with immersion. The temperature of the graphite liquid for cooling the mold was preferably maintained at a range from 30 to 36° C., and the specific weight of the graphite liquid ranged from 1.05 to 1.06.
Self-checking was performed on the cooled casting parts, and the casting parts were sent in 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 cavity of the casting parts. A quality inspection analysis was performed and the total non-defectiveness in production was calculated by the following equation.
total non-defectiveness in production=the number of non-defective products/the total number of products×100%
Total non-defectiveness in production reflects the qualitative stability of production processes. High qualitative stability of production processes ensures normal production.
Moreover, conventional CW602N dezincification-resistant brass (which is sometimes abbreviated as DR brass, and certified as dezincification-resistant brass according to AS2345-2006) and conventional C85710 brass were used in comparative examples in which articles were produced by the same process as described above. The ingredients, processing characteristics and total non-defectiveness in production of each of the alloys are shown in
It is known from Table 1 that the dezincification-resistant low lead copper alloy of the present invention gave a yield higher than 90% when it was used a raw material. The yield of the alloy of the present invention was comparable to those of conventional C85710 brass and DR brass (i.e., CW602N), and can indeed be a substitute brass material. The dezincification-resistant low lead copper alloy of the present invention can significantly decrease the lead content in the alloy, effectively avoid the lead contamination occurred during processes, and decrease the amount of lead leached when using the casting parts. It is clear that the alloy of the present invention has material characteristics to meet the environmental requirements.
The measured values of the major ingredients of the alloy in examples 3 are as follows: Cu: 62.6%, Zn: 36.43%, Pb: 0.159%, Sb: 0.1137%, Al: 0.627% and As: 0.147%. The structural distribution of the alloy is shown in
As shown in
A dezincification test was performed on the brass alloys of example 3 and comparative examples 1 and 4 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 to make the exposed area of each of the specimens to be 100 mm2. The specimens were ground flat using a 600# metallographic abrasive paper, following by washing using distilled water. Then, the specimens were baked dry. The test solution was 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
It is corroborated from the above results that the dezincification-resistant low lead brass of the present invention meets the dezincification resistance standard set forth in AS2345-2006 (i.e., the depth of a dezincification layer not exceeding 100 μm), and has better dezincification resistance.
A test of mechanical properties was performed on the specimens in 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.
It is known from Table 2 that the tensile strength and the elongation (%) of dezincification-resistant low lead brass in the present invention were comparable to those of the conventional C85710 brass and CW602N, meaning that the dezincification-resistant low lead brass alloy of the present invention had mechanical properties comparable to those of the C85710 brass and CW602N. Further, the lead content of the dezincification-resistant low lead brass of the present invention was low, thereby complying with the environmental requirements. It appears that the dezincification-resistant low lead brass of the present invention can indeed replace the C85710 brass and CW602N brass in product manufacturing.
The 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.
As shown in
In conclusion, the dezincification-resistant low lead copper alloy material has excellent casting properties and good toughness and machinability, and it is thus not likely to generate defects like cracks and slag inclusions or casting defects. Therefore, the alloy material of the present invention can achieve the material characteristics possessed by lead brasses, and is suitable for applications to subsequent processes. Further, lead can readily precipitate from the dezincification-resistant low lead brass alloy material of the present invention without the need to perform a lead stripping treatment. This can lower the production costs, and is extremely advantageous in commercial-scale productions 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.
