Patent Application
20160053348
The present invention relates to a brass alloy, and more particularly to a low shrinkage corrosion-resistant brass alloy.
Major components of brasses are copper, zinc and a small amount of impurities, wherein copper and zinc are usually present at a ratio of about 7:3 or 6:4. It is known that brasses contain lead (mainly ranging from 1 to 3 wt %) to improve the properties thereof by achieving the desirable mechanical property at the industrial level, and thus the become important industrial materials which are widely applicable to products such as metallic devices or valves used in pipelines, faucets and water supply/drainage systems.
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 amend relevant regulations, putting 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 having desirable properties like the casting property, machinability, corrosion resistance and mechanical properties.
Conventionally, bismuth (Bi) is added in brass alloys as a major component to replace lead so as to have casting, machining polishing, and plating process efficiently. However, the high bismuth content is likely to cause defects like cracks and slag inclusions, and bismuth has radioactivity which is harmful to human.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.
The primary object of the present invention is to provide a low shrinkage corrosion-resistant brass alloy which is capable of overcoming the shortcomings of the conventional brass alloy.
To obtain the above objectives, a low shrinkage corrosion-resistant brass alloy contains: 58 to 64 wt % of copper; 0.3 to 1.0 wt % of tin; less than 0.25 wt % of lead; 0.01 to 0.15 wt % of phosphorus; at least two of nickel, niobium, zirconium and aluminum being an amount ranging from 0.01 to 0.4 wt %; zinc and unavoidable impurities; whereon copper and zinc is in an amount ranging more than 98 wt %.
In a preferred embodiment, the niobium is in an amount ranging from 0.07 to 0.15 wt %.
In a preferred embodiment, the nickel is in an amount ranging from 0.07 to 0.15 wt %.
In a preferred embodiment, the lead is in an amount ranging from 0.08 to 0.2 wt %.
In a preferred embodiment, the tin is in an amount ranging from 0.5 to 0.9 wt %.
In a preferred embodiment, the phosphorus is in an amount ranging from 0.08 to 0.15 wt %.
In a preferred embodiment, the zirconium is in an amount ranging from 0.07 to 0.15 wt %.
In a preferred embodiment, the aluminum is in an amount ranging from 0.07 to 0.25 wt %.
Thereby, the low shrinkage corrosion-resistant brass alloy of the present invention has the following advantages:
1. The niobium is added to the low shrinkage corrosion-resistant brass alloy so as to enhance the fluidity of the brass and to lower shrinkage of the brass in the casting process. In addition, the corrosion resistance of the brass is increased.
2. By adding less lead, insoluble solid solution forms in the copper and evenly disperses between two phases, thereby enhancing machinability.
3. The low shrinkage corrosion-resistant brass alloy increases mechanical property and the corrosion resistance of the brass and enhances strength, hardness, and machinability of the alloy material, thus improving machining performance of the brass.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
Compositions of a low shrinkage corrosion-resistant brass alloy according to the present invention is on the basis of total alloy weight and are presented are calculated by weight percent (wt %).
The present inventors found that when a high tin content (i.e., more than 2 wt % of Sn) is added to the brass alloy conventionally, at the micro level, a γ phase will generate to corrode workpiece or increase hardness, thus machining the workpiece difficultly.
The low shrinkage corrosion-resistant brass alloy of the present invention has added niobium, so in the high-temperature melting process, the niobium is covered in the brass pipe so that intermediate of the niobium and the brass is dissolved into the brass.
From (b) of
It can be learned from (c) of
Furthermore, the low shrinkage corrosion-resistant brass alloy with the niobium comprises less than 0.25% of lead calculated based on percentage by weight. Since the lead does not melt in the brass, so the machinability of the copper is enhanced.
Because excessive lead will pollute the environment and harm human bodies, the tin is limited in an amount ranging from 0.08 to 0.25 wt % to enhance the machinability of the brass.
Generally speaking, the chips broking from the brass includes rolled chips, C-shaped short chips, and flakes chips, wherein the rolled chips attach on the blade easily to lower machinability, the C-shaped short chips generate from a better machining process, and the flakes chips results from a best machining process.
The niobium can avoid workpiece material from crack and impurity and has machinability like lead brass (such as H-59 lead brass). Thereby, the low shrinkage corrosion-resistant brass alloy of the present invention lowers lead content and production cost and enhances machinability.
Moreover, according to the low shrinkage corrosion-resistant brass alloy of the present invention, the lead content of the alloy can be lowered to a range less than 0.2 wt %, so as to conform to the stipulated international requirement for the leads contents in water pipelines. Hence, the low shrinkage corrosion-resistant brass alloy according to the present invention is applicable to applications to manufacturing of faucets and bathroom accessories, water pipelines and water supply systems.
The present invention is illustrated in details by the exemplary examples below. Test example 1:
Under the same producing and operating conditions, the low shrinkage corrosion-resistant brass alloy (examples 1 to 8) of the present invention, lead-free bismuth brass alloy (comparative examples 1 to 2), and H-59 lead brass (comparative examples 3 and 4) were used as materials to cast the same product. The processing characteristics of each of the alloys and the yield rate in production at each stage were compared, wherein the yield rate is defined as follows:
yield rate in production=the number of non-defective products/the total number of products×100%
The yield rate in production reflects the qualitative stability of the production. High qualitative stability ensures normal production.
As shown in Table 1, when lead-free bismuth brass is used as a material for product casting, more casting defects are found in the obtained casting part. Thus, the total yield rate in production is lower than 60%. The higher the bismuth content is, the lower the yield rate obtains. The major defects observed in the casting part in which lead-free bismuth brass is used as material are voids, slag inclusions, cracks, misrun and shrinkage. The defective products with the above defects comprise 71% of the total number of defective products. Specifically, the fluidity of the molten copper liquid of the lead-free bismuth brass is low and the filling of the mold is poor, such that the casting part is prone to misrun. Cracking is likely to occur in the casting part, and some minor cracks are not found until the final polishing step. Slag inclusions and voids are likely to occur in the casting part. Further, the machinability of lead-free bismuth brass is poor, such that problems like vibration and adhesion are likely to occur, thereby causing low yield rate during subsequent mechanical processing.
Moreover, when the low shrinkage corrosion-resistant brass alloy of the present invention is used as a raw material in the test group, the yield rate is the best (i.e., higher than 90%), and the material fluidity of the low lead brass is close to that of the conventional H59 lead brass. After performing optimization of the casting art, an equiaxed dendritic crystal phase structure with low occurrence of embrittlement is obtained after the casting part solidifies. While ensuring the machinability, the above structure ensures that defects like cracking is not prone to occur, so that the entire material can suffice the production requirements.
Specimens of brass materials of the third embodiment, the comparative example 1, and the comparative example 4 were placed under a metallographic microscope to examine the structural distribution of the material. The results magnified at 100-fold is shown in
The measured values of the ingredients of the low shrinkage corrosion-resistant brass alloy in the third embodiment are Cu: 62.13 wt %, Bi: 0.0061 wt %, Al: 0.03 wt %, Pb: 0.11 wt %, Mg: 0.002 wt %, Zr 0.003 wt %, Ni: 0.048 wt %, Sn: 0.220 wt %, Sb: 0.06 wt %, Nb: 0.2 wt %, P: 0.12 wt %.
The structural distribution of the low shrinkage corrosion-resistant brass alloy of the third embodiment is shown in
The measured values of the ingredients of the lead-free bismuth brass in in the comparative example 1 are Cu: 62.48 wt %, Bi: 0.762 wt %, Al: 0.513 wt %, Pb: 0.0075 wt %, Mn: 0.0047 wt %, Ni: 0.210 wt %, Sn: 0.364 wt %, and Sb: 0.0028 wt %.
The measured values of the ingredients of the H-59 lead brass in the comparative example 4 were Cu: 61.1 wt %, Bi: 0.0089 wt %, Al: 0.589, Pb: 1.54 wt %, Mn: 0.0009 wt %, Ni: 0.147 wt %, Sn: 0.342 wt %, and Sb: 0.0010 wt %.
A test was performed according to the standards 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 aqueous environments. Results are shown in Table 2.
As shown in Table 2, various metal precipitation amounts of the low shrinkage corrosion-resistant brass alloy of the present invention are lower than the upper limits of the standard values, and therefore, the low shrinkage corrosion-resistant brass alloy of the present invention conforms to NSF 61-2007a SPAC.
Further, the low shrinkage corrosion-resistant brass alloy of the present invention clearly had a lower precipitation amount of the heavy metal lead than that of the H-59 lead brass. Thus, the low shrinkage corrosion-resistant brass alloy of the present invention conforms to the standards set forth in NSF 61-2007a SPAC and is more environmentally friendly, and more beneficial to human health.
A dezincification test was performed on the brass alloys in the third embodiment and comparative example 2 to examine the corrosion resistance of brass. The dezincification test was performed according to the standards set forth in Australian AS2345-2006 “Anti-dezincification of copper alloys”. Before a corrosion experiment was performed, a novolak resin was used to make the exposed area of each of the brasses to be 100 mm2, the specimens were ground flat using a 600# metallographic abrasive paper following by washing using distilled water, and 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, and 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 thereof were measured and observed under a digital metallographic microscope.
A mechanical property test was performed on the brass alloys according to the standards set forth in ASTM E8-08 “Standard Test Methods for Tension Testing of Metallic Materials”. Results are shown in Table 3.
As shown in Table 3, the tensile strength of the low shrinkage corrosion-resistant brass alloy of the present invention is higher than the H-59 lead brass in the fourth embodiment and the lead-free bismuth brass alloy in the comparative example 1, and the elongation of the low shrinkage corrosion-resistant brass alloy of the present invention is similar to the H-59 lead brass in the fourth embodiment. This means that the low shrinkage corrosion-resistant brass alloy of the present invention has better mechanical property than the H-59 lead brass and the lead-free bismuth brass alloy.
A shrinkage test was performed on the brass alloys in the embodiments and comparative examples to examine the solidification shrinkage values of brass. A measuring method of the shrinkage is listed as follows:
pouring 43 grams of high-temperature brass liquid into a mold and observing casting property, wherein because atom shrinks and fills into a casting head of the mold in a cooling process, so a volume is 5×1×1 cm3, and the shrinkage is estimated.
A plastic head dropper is applied to hold pure water, and 0.05 ml of water drop is dropped into a shrinkage hole, wherein a dropping amount of the pure water is calculated and is exchanged to a shrink percentage according to the following formula:
Shrinkage=dropped water volume/a volume of casting head×100%
As shown in Table 4, the solidification shrinkage of brass alloy of the low shrinkage corrosion-resistant brass alloy of the present invention is lower than lead-free bismuth brass in the comparative examples 1, 2 and the H-59 lead brass in the comparative examples 3 and 4. This means that the low shrinkage corrosion-resistant brass alloy of the present invention improves the casting property of the alloy material.
In sixth, seventh and eighth embodiments, a tin content is added to the brass alloys and its result is illustrated as follows:
Three specimens of the low shrinkage corrosion-resistant brass alloy are measured by a Vickers hardness tester, wherein the low shrinkage corrosion-resistant brass alloys of the sixth, the seventh and the eighth embodiments are cut into a 1 cm cube, and a hardness of one surface of the 1 cm cube is tested to obtain testing result as listed in Table 5. Furthermore, a cuboid at 100 mm length, 30 mm width, and 30 m height is made in the sixth, the seventh and the eighth embodiments, then a titanium edged cutting tool at 12 mm diameter mills the cuboid, wherein a cutting X axis is 2 mm, a cutting Z axis is 6 mm, a rotating speed is 2000 rpm, and a traverse speed is 300 mm/min. The cutting condition is shown in
From above Table 5, the more the Sn content is added, the more the hardness increases, for example, a maximum hardness Hv 183.2 is tested in the eighth embodiment; the more the Sn content is added, the more the chip length decreases (as illustrated in
While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.
