Copper-base alloys having resistance to dezincification

Abstract

Copper-base alloys are provided that maintain high hot forgeability and cuttability and low-cost feature and which still are improved in resistance to dezincification. The alloys comprise 57-69% of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, all percentages based on weight, with a Si/Sn value in the range of 0.051, and the balance being Zn and incidental impurities.

Description

[0001] This is a continuation-in-part application of U.S. Ser. No. 09/891,650 filed Jun. 26, 2001.

BACKGROUND OF THE INVENTION

[0002] This invention relates to copper-base alloys having high resistance to dezincification corrosion which would otherwise occur during use in corrosive aqueous solutions. The alloys also have good hot working and cutting properties.

[0003] Cu--Zn alloys, commonly called brasses, have good working properties, both cold and hot, so they have found extensive use from old times. Among the best known are forging brass bars (JIS C 3771), free-cutting brass bars (JIS C 3604) and high-strength brass bars (JIS C 6782). These copper-base alloys share the common feature of including a continuous .beta. phase for better workability.

[0004] Zinc in the .beta. phase has high ionization tendency, so in natural environment, particularly in the presence of a corrosive aqueous solution, it is selectively leached from the above-mentioned alloys. This is why those alloys are very poor in resistance to dezincification.

[0005] Various proposals have recently been made with a view to improving the resistance to dezincification of brasses that are typically used in parts that are brought into contact with water. According to Unexamined Japanese Patent Application (JPA) No. 183275/1998, Sn is added to Cu--Zn alloys and, after hot extruding, various heat treatments are performed to control the proportion of the .gamma. phase and the Sn level in the .gamma. phase, thereby improving resistance to dezincification.

[0006] According to Unexamined Published Japanese Patent Application (JPA) No. 108184/1994, Sn is added to Cu--Zn alloys and, after hot extruding, the alloys are subjected to a heat treatment so that they are solely composed of the a phase, thereby enhancing their resistance to dezincification.

[0007] The new alloys described above are characterized by having Sn added in larger amounts than the conventional brasses. However, the high inclusion of Sn in brasses has its own problems.

[0008] First, with the increase in the Sn level, the local solidification time of brasses increases and there occurs inverse segregation of Sn during casting, producing ingots with surface defects. At the same time, the adaptability to extrusion and other hot working processes is impaired, causing a significant drop in the yield of shaped products.

[0009] Secondly, in order to elicit the ability of Sn to improve resistance to dezincification, hot extruding must be followed by a heat treatment for generating a certain area of .gamma. phase at grain boundaries of the .alpha. phase and causing Sn to diffuse uniformly in the .gamma. phase. However, this adds to the overall production cost.

[0010] What is specifically taught in JPA No. 183275/1998 is as follows: a heat treatment is applied at between 500.degree. C. (inclusive) and 550.degree. C. (inclusive) for at least 30 seconds, then cooling to 350.degree. C. is done at a rate no faster than 0.4.degree. C./sec; alternatively, a heat treatment is applied at between 400.degree. C. (inclusive) and 500.degree. C. (inclusive) for at least 30 seconds, then cooling is done; or a heat treatment is applied at between 500.degree. C. (inclusive) and 550.degree. C. (inclusive) for at least 30 seconds, then cooling to 350.degree. C. is done at a rate between 0.4.degree. C./sec (inclusive) and 4.degree. C./sec (inclusive). The teaching of JPA No. 108184/1994 comprises hot extruding or drawing the alloy, followed by a heat treatment at 500-600.degree. C. for a period of 30 minutes to 3 hours.

[0011] These heat treatments involve various problems. For one thing, in order to ensure the appropriate conditions, costly equipment must be used. Secondly, depending on product size, the difference in heat pattern between the interior and exterior of the product can cause variations in microstructure, which makes the process less cost-effective due to lower yield. Thirdly, products of complex shape occasionally suffer from the problems of dimensional changes, residual stress and so forth.

[0012] A recent proposal worth particular mention is free-cutting copper alloys having Si added to Cu--Zn alloys (JPA Nos. 119774/2000 and 119775/2000). These alloys contain at least 1.8 wt % of Si with a large portion of Cu/Si .gamma. phase at grain boundaries of the a phase. Under environment of actual use, the Cu/Si .gamma. phase has better resistance to dezincification than the .beta. phase but is not as resistant as a Cu/Sn .gamma. phase. If the Si content is 1.8% or more, the thermal conductivity of the material drops considerably and the blade of a cutting tool becomes unduly hot during cutting to cause many problems such as a shorter life of the cutting tool, lower precision in cutting and limit on the cutting speed.

[0013] JPA 60-149740 proposes alloys having improved wear-resistance prepared by adding to Cu--Zn alloys elements such as Al, Fe, Sn, Si and Zr. These alloys are endowed with high strength and improved wear-resistance by precipitating therein intermetallic compounds of Sn, Si, Zr and Fe. However, because these alloys show a small elongation, there is a problem in that they show poor cold workability. Moreover, since they contain a large number of elements, it is complicated to control proportions of component elements in the course of casting. This is one of the important factors that adds to the cost of production.

SUMMARY OF THE INVENTION

[0014] The present invention has been accomplished under these circumstances and has as an object providing copper-base alloys that have outstanding resistance to dezincification, hot forgeability, cuttability and elongation and which still can be fabricated at reasonably low cost.

[0015] The present inventors conducted intensive studies in order to ensure that the addition of Sn would prove effective in preventing dezincification of copper-base alloys to the fullest extent and found the following: when Si as well as Sn were added and the weight percentage ratio of Si to Sn was adjusted to lie in an appropriate range, secondary dendrite arms grew sufficiently thinner and longer during solidification to suppress segregation of Sn; upon hot working, the .gamma. phase was dispersed uniformly between regions of a phase. This phenomenon made a great contribution to improvements in resistance to dezincification and hot working properties.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The stated object can be attained by any one of the following copper-base alloys having improved resistance to dezincification.

[0017] (1) A dezincification resistant copper-base alloy consisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si, and 0.5-3% of at least one of Pb and Bi, all percentages based on weight, with a Si/Sn wt % ratio value in the range of 0.05-1 and the balance being Zn and incidental impurities.

[0018] (2) A dezincification resistant copper-base alloy consisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of at least one of Pb and Bi, all percentages based on weight, with a Si/Sn wt % ratio value in the range of 0.05-1, further containing in a total amount of 0.02-0.2% at least one element selected from the group consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, all percentages based on weight, and the balance being Zn and incidental impurities.

[0019] (3) A dezincification resistant copper-base alloy consisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of at least one of Pb and Bi, all percentages based on weight, with a Si/Sn wt % ratio value in the range of 0.05-1, further containing in a total amount of 0.01-2% of at least one element selected from the group consisting of 0.01-0.3% of Fe, 0.01-0.5% of Ni, 0.01-0.5% of Cr, 0.01-0.5% of Be, 0.01-0.3% of Zr, 0.01-0.5% of Ce, 0.01-0.5% of Ag, 0.01-0.3% of Ti, 0.01-0.5 of Mg, 0.01-0.5% of Co, 0.01-0.5% of Te, 0.01-0.5% of Au, 0.01-0.5% of Y, 0.01-0.5% of La, 0.01-0.5% of Cd and 0.01-0.5% of Ca, all percentages based on weight, and the balance being Zn and incidental impurities.

[0020] (4) A dezincification resistant copper-base alloy consisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of at least one of Pb and Bi, all percentages based on weight, with a Si/Sn wt % ratio value in the range of 0.05-1, further containing in a total amount of 0.02-0.2% at least one element selected from the group consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, still further containing in a total amount of 0.01-3% of at least one element selected from the group consisting of 0.01-0.3% of Fe, 0.01-0.5% of Ni, 0.01-0.5% of Cr, 0.01-0.5% of Be, 0.01-0.3% of Zr, 0.01-0.5% of Ce, 0.01-0.5% of Ag, 0.01-0.3% of Ti, 0.01-0.5% of Mg, 0.01-0.5% of Co, 0.01-0.5% of Te, 0.01-0.5% of Au, 0.01-0.5% of Y, 0.01-0.5% of La, 0.01-0.5% of Cd and 0.01-0.5% of Ca, all percentages based on weight, and the balance being Zn and incidental impurities.

[0021] On the following pages, the criticality of the compositional ranges for the ingredients in the copper-base alloy of the invention is described in detail.

[0022] Cu:

[0023] An increase in the Cu content adds to the .alpha. phase and improves corrosion resistance but if its content exceeds 69%, there occurs a marked drop in hot forgeability. Since Cu is more expensive than Zn, the Cu content is desirably minimized from an economical viewpoint. If the Cu content is smaller than 57%, the proportion of the .beta. phase increases to improve forgeability at elevated temperature; on the other hand, resistance to dezincification decreases and so do the strength and elongation of the material. Considering these merits and demerits, the compositional range of Cu is specified to lie between 57 and 69%, preferably between 59 and 63%, on a weight basis.

[0024] Sn:

[0025] Adding at least 0.3% of Sn is effective in improving resistance to dezincification. What is more, the improvement in resistance to dezincification is marked if the addition of Sn is increased. However, adding Sn in excess of 3% not only induces deep defects in the surface of ingots being cast but also fails to bring out a corresponding improvement in the resistance to dezincification. In addition, Sn is more expensive than Zn and Cu, so it is a factor in increasing the production cost. For these reasons, the content of Sn in the copper-base alloy of the invention is specified to lie between 0.3 and 3%, preferably between 0.5 and 2%.

[0026] Si:

[0027] Silicon is added for the particular purpose of improving castability and eliciting the ability of Sn to improve resistance to dezincification. Adding a suitable amount of Si is effective in improving the fluidity of a melt during casting and suppressing the segregation of Sn. As a result, in the absence of any heat treatment after hot extruding and forging, the ability of Sn to improve resistance to dezincification is elicited to the fullest extent, thereby providing consistent and outstanding dezincification resistance and mechanical characteristics.

[0028] If the Si content exceeds 1.5%, an increased amount of Si/Cu .gamma., .kappa. or .beta. phase appears at grain boundaries of the a phase to deteriorate the resistance to dezincification. In addition, the increased amount of Si oxide is detrimental to castability and hot workability. If the Si content further increases to 1.8% or more, the thermal conductivity of the material drops considerably and the blade of a cutting tool becomes unduly hot during cutting to cause many problems such as a shorter life of the cutting tool, lower precision in cutting and limit on the cutting speed.

[0029] If the Si content is less than 0.02%, there is obtained no effect of improving castability or suppressing the segregation of Sn. For these reasons, the compositional range of Si is specified to lie between 0.02 and 1.5%, preferably between 0.06 and 0.6%.

[0030] Si/Sn:

[0031] The Si/Sn value is specified in the present invention since in order to maximize the ability of Sn to improve resistance to dezincification, Si must be added in an optimum amount that depends on the amount of Sn addition.

[0032] Generally, the 60/40 brass has a two-phase structure consisting of .alpha.-phase+.beta.-phase, wherein .beta.-phase has poorer resistance to dezincification than .alpha.-phase. Tin (Sn) dissolves more in .beta.-phase than in .alpha.-phase and enhances resistance to dezincification. If tin is added in an amount of 0.5% or more, however, precipitation of .gamma.-phase is observed. The .gamma.-phase is hard and brittle and so it makes the material more brittle. In addition, since the .gamma.-phase dissolves a larger amount of Sn, it impairs the ability of .alpha.- and .beta.-phases as a matrix to resist dezincification. On the other hand, since the zinc equivalent of Si is as high as 10, its addition is effective to decrease the precipitation of .gamma.-phase and increase the proportion of .beta.-phase. For this reason the addition of Si is effective in enhancing hot workability and in embrittling the material at ordinary temperatures. By controlling the Si/Sn ratio at an appropriate level, effect of Sn to resist dezincification can be obtained, retaining the (.alpha.+.beta.)-phase structure as it is.

[0033] Moreover, if Si is added under the condition that the Si/Sn ratio is controlled at an appropriate level, secondary dendrite arms grow in a sufficiently finer and longer form during solidification to suppress the segregation of Sn and, after hot working, the .gamma. phase is dispersed uniformly between regions of a phase to improve resistance to dezincification while assuring hot deformability. If the Si/Sn value is greater than 1, the volume of .beta.-phase increases, the Sn content in the .beta.-phase correlatively decreases. This makes it difficult to obtain sufficient effect of resisting dezincification. Since Si has a small molecular weight and strongly affects the formation of solid-solutions, an unduly large amount of addition of Si may be linked to room temperature enbrittlement of the material. If the Si/Sn ratio is smaller than 0.05, the intended effect of suppressing the segregation of Sn is not fully attained and the (.alpha.+.beta.+.gamma.) three-phase structure is easy to develop, which makes it difficult to obtain the effect of resisting dezincification. Therefore, the Si/Sn ratio is preferably in the range of 0.05-1, more preferably in the range of 0.1-0.5.

[0034] P, Sb, As:

[0035] These elements are effective in suppressing dezincification without impairing cuttability and forgeability. If their addition is less than 0.02%, the intended effect of suppressing dezincification is not obtained. If their addition exceeds 0.2%, boundary segregation occurs to reduce ductility while increasing stress corrosion cracking sensitivity. Hence, the contents of P, Sb and As are each specified to lie between 0.02 and 0.2%.

[0036] Pb, Bi:

[0037] At least one of lead and bismuth is added to improve the cuttability of the material. If its addition is less than 0.5%, the desired cuttability is not attained. If the Pb and/or Bi addition exceeds 3%, hot working such as extruding or forging is difficult to perform. If Pb and/or Bi is to be added, its compositional range, each or in total, is between 0.5 and 3%, preferably between 1.5 and 2.3%.

[0038] If desired, the copper-base alloy of the invention may further contain at least one element selected from the group consisting of 0.01-0.3% of Fe, 0.01-0.5% of Ni, 0.01-0.5% of Cr, 0.01-0.5% of Be, 0.01-0.3% of Zr, 0.01-0.5% of Ce, 0.01-0.5% of Ag, 0.01-0.3% of Ti, 0.01-0.5% of Mg, 0.01-0.5% of Co, 0.01-0.5% of Te, 0.01-0.5% of Au, 0.01-0.5% of Y, 0.01-0.5% of La, 0.01-0.5% of Cd and 0.01-0.5% of Ca; these elements may be contained in a total amount of 0.01-3%. If added in amounts within the specified ranges, these elements are effective in improving mechanical characteristics and cuttability without damaging resistance to dezincification and hot workability. Moreover, since the presence of the above-listed elements is allowable, scraps can be used easily. This fact contributes to the reduction of the production cost. However, if the contents of the above-listed elements exceed the ranges specified above, they form intermetallic compounds with Si and/or Sn, thereby hindering the effect of improving resistance to dezincification, and at the same time the elongation decreases due to the precipitation hardening.

[0039] If in a small amount the addition of Al or Mn neither impairs nor enhances characteristic properties such as resistance to dezincification, hot forgeability, cuttability and the like.

[0040] The meaning of the addition of Al or Mn is described below in detail.

[0041] Al:

[0042] Aluminum is not only effective in forming a solid-solution in the Cu--Zn alloy to enhance its strength but also upon being rubbed diffuses into the surface of the alloy to form there Al.sub.2O.sub.3 and contribute to improving its wear-resistance. However, increase in strength due to the formation of a solid-solution of Al is too big to keep good workability of the material. For example, JP-60149740 shows in Example 1 that the alloys disclosed therein have tensile strength of approximately 700 Mpa and elongation of 10-15%. This means that the alloys of JP-60149740 are inferior in their workability at room temperature to the alloys of the present invention that have elongation of not less than 20%.

[0043] Mn:

[0044] Manganese (Mn) forms an intermetallic compound with Si that precipitates uniformly in the form of fine dispersed particles to increase strength and wear-resistance of the material. However, silicon (Si) dissolves in the Cu--Zn matrix to impair the effect of enhancing resistance to dezinfication.

[0045] Both JPA 60-149740 and JPA 62-274036 relate to alloy materials whose strength and wear-resistance have been enhanced by precipitating therein the elements added thereto in the form of their intermetallic compounds. Accordingly, elements such as Fe and Zr that are easy to form intermetallic compounds are selectively used as requisite elements. In particular, elements such as Zr and Mn are easy to form intermetallic compounds with Sn and Si. Thus, the presence of these elements hinders Sn and Si to dissolve in the matrix to enhance resistance to dezincification. The alloys disclosed in JPA 11-1736 are out of the scope of the present invention because they contain neither Sn nor Si and the invention disclosed therein does not relate to the improvement of "resistance to corrosion" but relates to the improvement of "resistance to high temperature corrosion" which is quite different to "resistance to dezincification". The alloys shown in the working examples of JPA 11-1736 cannot satisfy the resistance to dezincification and hot forgeability desired and attained by the present inventors.

[0046] In summary, all the alloys disclosed in the JPA 60-149740, JPA 62-274036 and JPA 11-1736 have been developed bearing wear-resistance in mind. For this reason the elements added are precipitated in the resulting alloys in the form of intermetallic compounds so as to obtain high strength and high wear-resistance. Moreover, Al is added to obtain improved resistance to corrosion by marine water. The addition of Al is effective to improve resistance to corrosion by marine water and acid of the entire matrix of the alloy. But it is not very much effective to enhance the resistance to dezincification of the alloy. In contrast, in the present invention appropriate amounts of Sn and Si are added to dissolve in the matrix for the purpose of enhancing resistance to dezincification. The alloys of the present invention include the uses for which good cuttability at room temperature and good caulking ability are required. Therefore, the alloys are desired to possess superior parting properties as well as elongation of not less than 20%. Thus, it is evident that no alloys disclosed in the above references can satisfy all of the above-recited requirements in view of the known capabilities of the elements added to the alloys.

[0047] The copper-base alloy of the invention with its composition adjusted to the ranges set forth above has outstanding resistance to dezincification, hot forgeability and cuttability and still can be fabricated at reasonably low cost.

[0048] The mode for carrying out the present invention is described below with reference to examples.

EXAMPLES

[0049] Samples of the dezincification resistant copper-base alloy of the invention were prepared as described below. Comparative samples were also prepared. The chemical ingredients listed in Table 1 were melted in an induction furnace and cast semicontinuously into billets (80 mm.sup..phi.) at temperatures of the liquidus plus about 100.degree. C. The castability of each composition was evaluated by checking the depth of surface defects such as inclusions in the cast billets. The results are shown in Table 1 as evaluated by the following criteria: .circleincircle. (depth of surface defect<1 mm); .smallcircle. (1-3 mm); X (>3 mm).

1 Sample Chemical ingredients (wt %) No. Cu Zn Sn Si Si/Sn Pb Bi P Fe Al Zr Ni 1 Invention 61.3 bal. 1.50 0.71 0.473 1.7 -- -- -- -- -- -- 2 59.5 bal. 1.38 0.65 0.471 1.8 -- -- -- -- -- -- 3 60.2 bal. 1.40 0.63 0.450 1.9 -- 0.07 -- -- -- -- 4 58.5 bal. 2.50 0.24 0.096 2.0 -- -- -- -- -- -- 5 60.7 bal. 1.08 0.20 0.185 2.0 -- 0.04 0.11 0.02 -- -- 6 61.2 bal. 0.87 0.21 0.241 1.9 -- 0.05 0.13 -- 0.08 0.17 7 61.8 bal. 1.00 0.12 0.120 1.7 -- 0.05 0.10 0.11 -- 0.30 8 61.2 bal. 1.50 0.18 0.120 1.6 -- 0.07 0.17 -- -- -- 9 59.0 bal. 1.50 0.36 0.240 1.4 -- 0.08 0.23 -- -- 1 10 62.0 bal. 1.30 0.66 0.508 1.4 0.05 0.05 -- 11 60.2 bal. 1.10 0.45 0.409 1.8 0.03 0.23 -- -- 0.60 12 Comparison 62.0 bal. 1.50 -- -- 1.9 -- -- -- -- -- -- 13 60.6 bal. 0.46 1.00 2.174 2.0 -- 0.05 -- -- -- -- 14 59.0 bal. 0.20 0.01 0.050 -- -- 0.04 -- -- -- -- 15 58.0 bal. -- 2.5 -- 1.9 -- -- -- -- -- -- 16 61.0 bal. -- 3 -- -- -- -- -- -- -- -- 17 59.0 bal. 1.5 1.9 1.267 -- -- -- -- -- -- --

[0050] The 80-mm.sup..phi. billets were held at 800.degree. C. for 30 minutes and later hot extruded into bars having a diameter of 30 mm.

[0051] The as-extruded bars were evaluated for resistance to dezincification, resistance to hot deformation, hardness, tensile strength and elongation. The dezincification test was conducted by two methods under different conditions, one specified in JBMA T303-1988 and the other in ISO 6509-1981. Test samples as cut from the extruded bars were set so that the direction of corrosion coincided with the extruding direction. In order to investigate the extent of the change in resistance to dezincification that was caused by heat treatment, evaluation was also made for the resistance to dezincification of samples that were subjected to a heat treatment at 400.degree. C. for 3 hours.

[0052] To measure the resistance to hot deformation, cylindrical samples 15 mm in both diameter and height were cut on a lathe from the extruded bars and subjected to a drop-hammer test. The test temperature and the distortion rate were 750.degree. C. and 180 s.sup.-1, respectively.

[0053] The cutting test was performed by cutting on a lathe and chip fragmentation was evaluated by the following criteria: .smallcircle. (all chips were completely fragmented); X (chips were not fragmented). For sticking property, 10 cutting tests were conducted with a continuous feed of 100 mm and the results were evaluated by the following criteria: X (copper stuck to the tip of the blade); .smallcircle. (no copper stuck). The cutting conditions were as follows: rotating speed, 950 rpm; depth of cut, 0.5 mm; feed speed, 0.06 mm/rev.; feed, 100 mm; cutting oil, none; cutting tool material, superhard steel. The hardness of the copper-base alloy was Vickers hardness and measured according to JIS Z 2244 under a testing force of 49 N on a section perpendicular to the extruding direction. The tensile test was conducted in accordance with JIS Z 2241 on No. 4 specimens which were stretched in a direction parallel to the extruding direction. The results of the tests are shown in Table 2.

2 TABLE 2 Resistance Maximum depth of to hot Chip Hard- Tensile Elonga- dezincification Sample Cast- deformation fragment- ness strength tion after heat No. ability MPa ation Hv MPa % as-extruded treatment 1 Invention .circleincircle. 78 .smallcircle. 130 451 27 59 59 2 .circleincircle. 67 .smallcircle. 132 445 28 65 64 3 .circleincircle. 67 .smallcircle. 129 433 34 60 60 4 .smallcircle. 72 .smallcircle. 141 452 25 41 39 5 .circleincircle. 75 .smallcircle. 107 407 45 57 55 6 .circleincircle. 76 .smallcircle. 105 399 46 59 58 7 .circleincircle. 74 .smallcircle. 110 445 45 57 56 8 .circleincircle. 73 .smallcircle. 118 418 44 53 51 9 .circleincircle. 68 .smallcircle. 133 467 44 52 52 10 .circleincircle. 69 .smallcircle. 128 410 25 58 54 11 .circleincircle. 69 .smallcircle. 120 422 27 60 53 12 Comparison X 79 .smallcircle. 119 412 36 92 71 13 .circleincircle. 67 .smallcircle. 132 423 25 115 116 14 .circleincircle. 85 X 98 387 48 173 167 15 X 75 .smallcircle. 140 440 21 134 135 16 X 73 X 146 453 19 165 171 17 X 65 X 165 527 26 155 157

[0054] Sample Nos. 1-11 prepared in accordance with the alloy composition of the invention showed outstanding castability, mechanical characteristics and cuttability, as well as low resistance to hot deformation comparable to that of hot forging alloy C 3771 (deformation resistance, 70 MPa). They all had high resistance to dezincitication since the maximum depth of dezincification was no more than 65 .mu.m in JBMA T303-1988 and no more than 130 .mu.m in ISO 6509-1981.

[0055] What was particularly interesting about the samples of the invention was that the maximum depth of dezincification as measured by JBMA was little different between the as-extruded state and the heat-treated state. It was therefore clear that by adding suitable amounts of Si, the copper-base alloys were given consistent and outstanding resistance to dezincification even when they were just subjected to hot working without any subsequent special heat treatments.

[0056] Sample Nos. 12-17 were comparisons and had various defects. Sample No. 12 did not contain Si, so it was not only low in castability and resistance to dezincification but also characterized by considerable difference in the maximum depth of dezincification between the as-extruded state and the heat-treated state. Sample No. 13 had a Si/Sn value beyond the range specified by the invention, so an excessive .beta. phase surrounded the .alpha. phase, deteriorating the resistance to dezincification.

[0057] Sample No. 14 contained less Sn and Si than the lower limits specified by the invention, so the proportions of the .gamma. and .kappa. phases were insufficient to prevent marked drop in resistance to dezincification; what is more, the resistance to hot deformation was great and chips could not be fragmented. Sample Nos. 15 and 16 did not contain Sn, so they were poor in resistance to dezincification; in addition, they contained more Si than specified by the invention, so copper stuck to the tip of the cutting blade showing how poor the cuttability of the material was.

[0058] Sample No. 17 contained both Sn and Si but the Si/Sn value exceeded the range specified by the invention; what is more, the Si content was greater than 1.8%. Hence, the sample was poor in resistance to dezincification and castability and copper stuck to the tip of the cutting blade.

[0059] As described above, the present invention offers copper-base alloys that have outstanding resistance to dezincification, hot forgeability and cuttability and which still can be fabricated at reasonably low cost.

Claims

What is claimed is:

1. A dezincification resistant copper-base alloy consisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of at lest one of Pb and Bi, all percentages based on weight, with a Si/Sn value in the range of 0.05-1, and the balance being Zn and incidental impurities.

2. A dezincification resistant copper-base alloy consisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of at least one of Pb and Bi, with a Si/Sn value in the range of 0.05-1, further containing in a total amount of 0.02-0.2% at least one element selected from the group consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, all percentages based on weight, and the balance being Zn and incidental impurities.

3. A dezincification resistant copper-base alloy consisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of at least one of Pb and Bi, with a Si/Sn value in the range of 0.05-1, further containing in a total amount of 0.01-2% of at least one element selected from the group consisting of 0.01-0.3% of Fe, 0.01-0.5% of Ni, 0.01-0.5% of Cr, 0.01-0.5% of Be, 0.01-0.3% of Zr, 0.01-0.5% of Ce, 0.01-0.5% of Ag, 0.01-0.3% of Ti, 0.01-0.5% of Mg, 0.01-0.5% of Co, 0.01-0.5% of Te, 0.01-0.5% of Au, 0.01-0.5% of Y, 0.01-0.5% of La, 0.01-0.5% of Cd and 0.01-0.5% of Ca, all percentages based on weight, and the balance being Zn and incidental impurities.

4. A dezincification resistant copper-base alloy consisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of at least one of Pb and Bi, with a Si/Sn value in the range of 0.05-1, further containing in a total amount of 0.02-0.2% at least one element selected from the group consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, still further containing in a total amount of 0.01-3% of at least one element selected from the group consisting of 0.01-0.3% of Fe, 0.01-0.5 of Ni, 0.01-0.5% of Cr, 0.01-0.5% of Be, 0.01-0.3% of Zr, 0.01-0.5% of Ce, 0.01-0.5% of Ag, 0.01-0.3% of Ti, 0.01-0.5% of Mg, 0.01-0.5% of Co, 0.01-0.5% of Te, 0.01-0.5% of Au, 0.01-0.5% of Y, 0.01-0.5% of La, 0.01-0.5% of Cd and 0.01-0.5% of Ca, all percentages based on weight, and the balance being Zn and incidental impurities.