EP2963134B1 - Low-lead brass alloy - Google Patents

Description

FIELD OF INVENTION
• The invention relates to a low-lead brass alloy.
BACKGROUND OF INVENTION
• Copper has excellent electrical conductivity and environmental friendliness, and bacteria harmful to the human can't survive on its surface. Other elements are added into copper, so as to improve its performance. For example, the addition of lead into the brass alloy containing copper and zinc significantly improves the cutting performance of the brass. However, lead has a destructive effect on the human health and ecological balance. It is also a trend around the world that there are increasing restrictions on the application of lead-containing alloy.
• In addition, the environmental problem is increasingly outstanding, and the working environment is becoming more serious. As a result, the surface strength of brass products is reduced, and the brass tube may even perforate. This greatly reduces the lifetime of brass products and causes problems in application.
• Therefore, there is a need to provide an alloy formula for solving the above problems, which can replace the brass with a high lead content, is dezincification corrosion resistant, and further has excellent casting performance, forgeability, cutting performance, corrosion resistance and mechanical properties.
• CN 101988164 A discloses a dezincification resistant brass alloy with low lead content, comprising less than 0.3 wt% of lead (Pb), 0.02 to 0.15 wt% of stibium (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 the copper content in the dezincification resistant brass alloy is 58 to 70 wt%.
SUMMARY OF INVENTION
• It is an object of the invention to provide a brass alloy which exhibits excellent performance like tensile strength, elongation rate, dezincification resistance and cutting performance, which is suitable for cutting processed products that require high strength, wear resistance and waterlogging resistance. The brass alloy of the invention can securely replace the alloy copper with a high lead content, and can completely meet the demands about restrictions on lead-containing products in the development of human society.
• To achieve the above object, the inventors have proposed the following low-lead brass alloy.
• A low-lead brass alloy (hereinafter referred to as the product 1), not in accordance with the present invention, comprises: by the total weight of the brass alloy, 62.5-63 wt% copper, 0.16-0.24 wt% lead, 0.55-0.7 wt% aluminum, and a balance of zinc.
• In the product 1, the content of lead is reduced to 0.24 wt% or less, the content of copper is maintained at 62.5-63 wt%, and a trace amount of aluminum is added to increase cutting performance of the brass alloy. Meanwhile, since aluminum has a higher tendency to be ionized on the surface of the alloy than zinc, and preferentially reacts with oxygen in a corrosive gas or solution to develop a dense protection film of aluminum oxide on the surface of the alloy, thus increasing corrosion resistance and dezincification resistance of the brass alloy in the severe environment. Besides, aluminum can increase cast flowability of the alloy, so that the alloy exhibits a significant improvement in strength and hardness. In order to make a better use of the above effects, the content of aluminum is 0.55-0.7 wt% by the total weight of the brass alloy.
• Preferably, the product 1, not in accordance with the present invention, further comprises: one or more elements selected from the group consisting of 0-0.02 wt% antimony, 0-0.2 wt% tin, 0-0.01 wt% magnesium, and 0.09-0.12 wt% arsenic by the total weight of the brass alloy. All of these elements can to a certain degree increase cutting performance of the brass alloy. The addition of antimony and tin can significantly increase strength of the alloy, and improve its plasticity and corrosion resistance. A trace amount of arsenic can increase dezincification resistance of the alloy. However, a high content of arsenic is not favorable, since it will decrease the thermal forgeability and squeezing performance of the alloy.
• More preferably, the above-mentioned product, not in accordance with the present invention, further comprises one or more elements selected from the group consisting of 0.0005-0.0009 wt% boron, 0.05-0.15 wt% iron, 0-0.15 wt% nickel, and 0-0.005 wt% zirconium by the total weight of the brass alloy. Boron can increase corrosion resistance of the brass alloy, and can also prevent dezincification. Iron can enhance toughness of the brass alloy. Nickel can not only prevent the brass alloy from rusting, but also can form intermetallic compounds among metals in the alloy, which uniformly precipitate in the matrix, thus increasing wear resistance and strength of the alloy. Zirconium can help to refine grains, thus increasing casting performance of the brass alloy.
• A low-lead brass alloy (hereinafter referred to as the product 2), not in accordance with the present invention, comprises: by the total weight of the brass alloy, 62.5-63 wt% copper, 0.16-0.24 wt% lead, two or more elements selected from the group consisting of 0.55-0.7 wt% aluminum, 0-0.02 wt% antimony, 0-0.2 wt% tin, and 0-0.01 wt% magnesium by the total weight of the brass alloy, and a balance of zinc. Aluminum, antimony, tin, and magnesium are added on basis of the same reasons as the inventive product 1, and are added according to actual needs.
• Preferably, the product 2 further comprises two or more elements selected from the group consisting of 0.09-0.12 wt% arsenic, 0.0005-0.0009 wt% boron, 0.05-0.15 wt% iron, 0-0.15 wt% nickel, and 0-0.005 wt% zirconium by the total weight of the brass alloy. Arsenic, boron, iron, nickel, and zirconium are added on basis of the same reasons as the inventive product 1, and are added according to actual needs.
• A low-lead brass alloy (hereinafter referred to as the inventive product 3), in accordance with the invention, comprises: by the total weight of the brass alloy, 62.5-63 wt% copper, 0.16-0.24 wt% lead, 0-0.02 wt% antimony, 0-0.01 wt% magnesium, 0-0.2 wt% tin, 0.0005-0.0009 wt% boron, 0.55-0.7 wt% aluminum, 0.05-0.15 wt% iron, 0-0.15 wt% nickel, 0.09-0.12 wt% arsenic, 0-0.005 wt% zirconium, 0-0.01 wt% impurities, and a balance of zinc. Antimony, magnesium, tin, boron, aluminum, iron, nickel, arsenic, and zirconium are added on basis of the same reasons as the product 1. In the inventive product 3, these elements are added simultaneously for the purpose of meeting needs for specific product performance.
DETAILED DESCRIPTION
• The technical solutions of the invention will be described expressly by referring to embodiments thereof.
• The dezincification corrosion resistant performance measurement, as used herein, is performed according to AS-2345-2006 specification in the cast state, in which 12.8 g copper chloride is added into 1000C.C deionized water, and the object to be measured is placed in the resulting solution for 24 hr to measure a dezincification depth.
• ⊚ indicates a dezincification depth of less than 300 µm; ○ indicates a dezincification depth between 300 µm and 400 µm; and × indicates a dezincification depth larger than 400 µm.
• The cutting performance measurement, as used herein, is performed in the cast state, in which the same cutting tool is adopted with the same cutting speed and feed amount. The cutting speed is 25 m/min (meter per minute), the feed amount is 0.2 mm/r (millimeter per number of cutting edge), the cutting depth is 0.5 mm, the measurement rod has a diameter of 20 mm, and C36000 alloy is taken as a reference. The relative cutting rate is derived by measuring the cutting resistance. $$\mathrm{The\; relative\; cutting\; rate}=\mathrm{cutting\; resistance\; of\; C36000\; alloy}/\mathrm{cutting\; resistance\; of\; the\; sample.}$$

  
• ⊚ indicates a relative cutting rate larger than 85%; and ○ indicates a relative cutting rate larger than 70%.
• Both the tensile strength measurement and the elongation rate measurement, as used herein, are performed in the cast state at room temperature as an elongation measurement. The elongation rate refers to a ratio between the total deformation of gauge section after elongation ΔL and the initial gauge length L of the sample in percentage: δ=ΔL/L×100%. The reference sample is a lead-containing brass with the same state and specification, i.e., C36000 alloy.
• As used herein, the performance for elements in alloy to dissolve in water is tested in accordance with GB/T5750-2006 "Standard examination methods for drinking water" and is judged in accordance with GB5749-2006 "Standards for drinking water quality".
• According to measurement, the proportions for constituents of C36000 alloy mentioned above are listed as follow, in the unit of weight percentage (wt%):

  Material No.	copper (Cu)	zinc (Zn)	bismuth (Bi)	antimon y (Sb)	mangane se (Mn)	aluminu m (Al)	tin (Sn)	lead (Pb)	iron (Fe)
  C36000 alloy	60.53	36.26	0	0	0	0	0.12	2.97	0.12

Embodiment
• Table 1 lists 15 different constituents for the low-lead brass alloy, each constituent being in the unit of weight percentage (wt%). In particular, no. 7 and 15 of the embodiments illustrated in Table 1 are in accordance with the scope of the present invention. The remaining embodiments illustrated in Table 1 are not in accordance with the scope of the present invention. Table 1

  No.	copper (Cu)	zinc (Zn)	lead (Pb)	magnes ium (Mg)	alumin um (Al)	antimo ny (Sb)	tin (Sn)	boron (B)	iron (Fe)	nickel (Ni)	arsenic (As)	zirconi um (Zr)
  1	63.000	36.233	0.215	--	0.550	--	--	--	--	--	--	--
  2	62.542	36.578	0.240	--	0.638	--	--	--	--	--	--	--
  3	62.500	36.638	0.160	--	0.700	--	--	--	--	--	--	--
  4	62.511	36.648	0.168	0.010	0.551	0.020	--	--	--	--	0.090	--
  5	62.780	36.136	0.179	0.009	0.589	--	0.200	--	--	--	0.105	--
  6	62.993	35.967	0.200	--	0.688	--	0.150	--	--	--	--	--
  7	62.567	36.541	0.161	--	0.560	--	--	0.0005	0.050	--	0.120	--
  8	62.874	36.123	0.187	0.007	0.653	--	--	--	--	0.150	--	0.004
  9	63.000	36.116	0.192	--	0.670	0.015	--	--	--	--	--	0.005
  10	62.510	36.416	0.167	--	0.689	0.018	0.198	--	--	--	--	--
  11	62.913	36.860	0.198	0.008	--	0.019	--	--	--	--	--	--
  12	62.780	36.250	0.201	0.009	0.580	--	0.178	--	--	--	--	--
  13	62.500	36.541	0.200	--	0.663	0.017	--	0.0007	0.076	--	--	--
  14	62.831	35.987	0.212	0.010	0.578	--	0.132	--	--	0.132	0.112	0.004
  15	62.670	35.845	0.198	0.008	0.674	0.017	0.188	0.0009	0.150	0.143	0.101	0.003

• Measurements about cutting performance, dezincification corrosion resistant performance, tensile strength, and elongation rate are performed on alloys with the above constituents in the cast state at room temperature, and the reference sample is a lead-containing brass with the same state and specification, i.e., C36000 alloy.
• Results of the measurements about tensile strength, elongation rate, cutting performance, and dezincification corrosion resistant performance are listed as follow:

  No.	TENSILE STRENGTH (N/mm2)	ELONGATION RATE (%)	DEZINCIFIC ATION LAYER	RELATIVE CUTTING RATE
  1	298	10	⊚	○
  2	301	10	⊚	⊚
  3	308	10	⊚	⊚
  4	305	11	⊚	⊚
  5	310	11	⊚	⊚
  6	315	12	⊚	⊚
  7	311	12	⊚	⊚
  8	317	12	⊚	⊚
  9	320	11	⊚	⊚
  10	310	11	⊚	⊚
  11	300	10	⊚	⊚
  12	307	11	⊚	⊚
  13	317	12	⊚	⊚
  14	335	13	⊚	⊚
  15	326	13	⊚	⊚
  C36000 alloy	394	9	×	⊚

• The performance for constituents in alloy to dissolve in water is tested, and the measurement results are listed as follow (in the unit of mg/L):

  No.	copper (Cu)	zinc (Zn)	lead (Pb)	aluminum (Al)	antimony (Sb)	boron (B)	iron (Fe)	nickel (Ni)	arsenic (As)
  1	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  2	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  3	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  4	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  5	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  6	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  7	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  8	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  9	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  10	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  11	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  12	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  13	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  14	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01
  15	<1.0	<1.0	<0.01	<0.2	<0.005	<0.5	<0.3	<0.02	<0.01

Claims (1)

1. A low-lead brass alloy, characterized by comprising: by the total weight of the brass alloy, 62.5-63 wt% copper, 0.16-0.24 wt% lead, 0-0.02 wt% antimony, 0-0.01 wt% magnesium, 0-0.2 wt% tin, 0.0005-0.0009 wt% boron, 0.55-0.7 wt% aluminum, 0.05-0.15 wt% iron, 0-0.15 wt% nickel, 0.09-0.12 wt% arsenic, 0-0.005 wt% zirconium, 0-0.01 wt% impurities, and a balance of zinc.