KR20140042942A - Machinable copper-based alloy and method for producing the same - Google Patents

Abstract

The present invention is an alloy, the alloy contains 1 to 20% by weight of Ni, 1 to 20% by weight of Sn, and 0.5 to 3% by weight of Pb in Cu corresponding to 50% by weight or more of the alloy, The alloy relates to an alloy characterized in that it further contains 0.01 to 5% by weight of P or B alone or as a blend. The invention also relates to metal products having improved mechanical resistance and good machinability at intermediate temperatures (300-700 ° C.). The metal products of the present invention can be usefully used in the manufacture of connectors, electromechanical or micromechanical pieces.

Description

Machinable copper-based alloy and method for producing same

The present invention relates to alloys based on copper, nickel, tin, lead and methods for their preparation. In particular, although not exclusively, the present invention relates to alloys based on copper, nickel, tin, and lead that are readily processed by turning, slicing or milling.

Alloys based on copper, nickel and tin are known and widely used. They provide excellent mechanical properties and exhibit strong hardening in the strain-hardening process. Their mechanical properties are further improved by known heat-aging treatments such as spinodal decomposition. For alloys containing 15% by weight nickel and 8% by weight tin (standard alloy ASTM C72900) the mechanical resistance can reach 1500 MPa. These alloys also provide good stress relaxation resistance and high air corrosion resistance.

Another advantage of these materials is their good formability, combined with the useful elastic properties provided by their high yield stress. Moreover, these alloys provide good resistance to corrosion and good resistance to thermal relaxation. For this reason, Cu-Ni-Sn springs do not lose their compressive force by aging even under vibration and high heat or large stresses.

These useful properties, combined with good thermal and electrical conductivity, mean that these materials are widely used to make connectors that are highly reliable for the telecommunications and automotive industries. These alloys are also used in switches and electrical or electromechanical devices, or as a support for electronic components, or to produce bearing friction surfaces that are subject to high charges.

Good machinability in these alloys is usually obtained by adding lead distributed in the alloy matrix as a fine dispersion of inclusions. Unfortunately, the addition of lead also significantly increases the warm shortness of the alloy, which can lead to problems both in processing and in use.

Ductility loss of Cu-based alloys at intermediate temperatures (300-700 ° C.) has long been a known problem, see RV Foulger and E. Nicholls, “Metals Technology” 3, pages 366-369 (1976). and V. Laporte and A. Mortensen, "International Materials Reviews", in press (2009). The onset of grain boundary sliding in this temperature range forms voids and cavities in the grain boundaries and changes the conventional ductile failure of copper and its alloys to intergranular brittle failure. This phenomenon is observed for pure copper, but even more pronounced when embrittlement of the alloy or impurity elements is present in the alloy. At higher temperatures, above the critical range, dynamic recrystallization can restore ductility.

The presence of molten Pb inclusions in the Cu-alloy can lead to liquid metal embrittlement (LME) at very high strain rates. At the same time, lead contents as low as 18 ppm have been reported to embrittle the grain boundaries of Cu—Ni alloys, and alloys exposed to lead gas at 800 ° C. are damaged in a brittle fashion, indicating that lead may also cause solid-phase grain embrittlement. To show; That is, in contrast to LME, it is more severe at low strain rates. Other elements known to cause grain embrittlement in Cu-alloys are sulfur and oxygen.

Accordingly, one object of the present invention is to propose a metal product composed of a Cu—Ni—Sn—Pb based alloy that at least overcomes some limitations of the prior art.

Another object of the present invention is to provide a metal product composed of a Cu—Ni—Sn—Pb based alloy having improved tensile properties and good machinability.

According to the invention, these objects are achieved by a system and a method comprising the features of the independent claims, preferred embodiments of which are set forth in the dependent claims and the description.

These objects are also alloys, wherein the alloy contains 1 to 20% by weight of Ni, 1 to 20% by weight of Sn, and 0.5 to 3% by weight of Pb in Cu corresponding to at least 50% by weight of the alloy. And the alloy further contains 0.01 to 5% by weight of P or B alone or as a blend.

In one embodiment of the invention, the alloy further contains 0.01 to 0.5% by weight of P or B, alone or in combination.

In a preferred embodiment of the invention, the alloy comprises 9% by weight Ni, 6% by weight Sn, and 1% by weight Pb.

The alloy of the present invention was subjected to heat treatment at 800 ° C. for about 1 hour, and then quenched in water or air and then measured at 400 ° C., yield strength R _{p 0.2} and maximum stress R _m were essentially 180 MPa and 333, respectively. It is characterized by exceeding MPa. The alloy is also characterized by an Hv hardness of essentially greater than 190 after heat treatment at 800 ° C. for about 1 hour and then aging at 320 ° C. for about 12 hours.

These objects are also achieved by a method for producing a metal product composed of the alloy of the present invention, the method comprising: obtaining a first slug of the alloy having a homogeneous structure; Annealing the alloy at a temperature of 690-880 ° C. for homogenization and improvement of alloy cold forming properties; Cooling at a cooling rate of 50 to 50000 ° C./min depending on the transversal dimension of the product and the composition of the alloy; And cold forming.

The invention also comprises a metal product composed of the alloy of the invention and produced by the process of the invention, which product, in relation to standard ASTM C36000 brass, has a mechanical resistance of 700 to 1500 N / mm 2 and a Hv hardness of 250 to 400, the machinability index is greater than 70%.

The machinable metal product can be prepared without cracks and has good mechanical and tensile properties at intermediate temperatures (300-700 ° C.).

In the description of the present invention, all percentages are expressed in weight percent, even if not specifically mentioned in the text.

The invention will be better understood by reading the detailed description presented by the appended claims and examples and presented by the accompanying drawings.
1 shows a metal microscope section of a B-containing Cu-Ni-Sn-Pb alloy according to the present invention.
Figure 2 shows a metal microscope section of a P-containing Cu-Ni-Sn-Pb alloy according to the present invention.

In one embodiment of the invention, the Cu-based alloy comprises 1 to 20 weight percent Ni, 1 to 20 weight percent Sn, and a ratio of Pb that can vary from 0.1 to 4 weight percent, with the remainder being essentially Cu Unavoidable impurities are usually contained in an amount of 500 ppm or less.

Lead is essentially insoluble in the remaining metals of the alloy and the resulting product will include lead particles dispersed in a Cu—Ni—Sn matrix. In the machining operation, lead has a lubricating effect and facilitates silver fragmentation.

The amount of lead introduced into the alloy depends on the degree of machinability to be achieved. In general, amounts of lead up to several weight percent can be introduced without modifying the mechanical properties of the alloy at room temperature. However, above the lead melting point (327 ° C.), liquid lead strongly weakens the alloy. Therefore, alloys containing lead are difficult to manufacture because, on the one hand, the alloys tend to be very strong against cracks, and on the other hand, the alloys contain unwanted weak phases. This is because the crystallographic structure of -phase can be represented. As a result, in the alloy of the present invention, the lead content is preferably 0.5 to 3% by weight or 0.5 to 2% by weight, even more preferably 0.5 to 1.5% by weight.

The alloy composition may optionally further comprise 0.1 to 1% of an element, such as Mn, introduced into the composition as a deoxidant. The Cu alloy may also comprise other elements such as Al, Mg, Zr, Fe, or a combination of two or more of these elements, in addition to or in addition to Mn. The presence of these elements can also improve the spinodal cure of the Cu alloy. Alternatively, a device may be used to prevent the Cu alloy from oxidizing.

In another embodiment, a portion of the Cu content in the alloy of the present invention may be replaced by other elements, such as Fe or Zn, for example in a ratio of up to 10%.

In another embodiment of the present invention, the Cu-based alloy contains at least 0.01% by weight of an alloying element of an addition selected from Al, Mn, Zr, P (phosphorus) or B (boron). In addition, the Cu-based alloy of the present invention contains at least 0.01% by weight of a mixture of two or more additive elements selected from Al, Mn, Zr, P or B.

In a preferred embodiment of the present invention, the Cu-based alloy contains 0.01 to 5% by weight of P or B.

In a more preferred embodiment of the invention, the Cu-based alloy contains 9 weight percent Ni, 6 weight percent Sn, 1 weight percent Pb, and 0.02 to 0.5 weight percent P or B.

Further influences of P and / or B on the mechanical properties at the intermediate temperatures of the Cu—Ni—Sn—Pb alloys were investigated. For this reason, a semi-continuous casting of a metal product composed of Cu-based alloy containing about 9 wt% Ni, 6 wt% Sn, 1 wt% Pb and about 0.02 to 0.5 wt% P or B under argon cover In the casting unit (capacity: 30 kg), pure components (pre-alloy Cu3P and CuZr: 99.5 wt%, Al: 99.9 wt%, all others: 99.99 wt%) were prepared.

The compositions of the different alloys investigated, as determined by inductively coupled plasma (ICP) analysis, are shown in Table 1, where the compositions are reported in weight percent and the balance is Cu. Zr values are not detected by the ICP method.

[Table 1]

The metal product was cast into a cylindrical bar with a diameter of 12 mm and then swaged in three stages with a diameter of 7.5 mm. Cylindrical tensile test samples of gauge length 30 mm and diameter 4 mm were machined from these bars. Samples were homogenized at 800 ° C. for 1 hour in air and quenched in water.

Alloys C1 and C2 were added to the list to see if the addition of lower amounts of alloy could likewise reach properties for machinability and high strength. In contrast to the alloy marked B, samples of alloys C1 and C2 were annealed at 800 ° C. for 1 hour and then cooled in air.

1 and 2 show SEM micrographs of metal microscope sections of B-containing (B4) and P-containing (B5) alloys according to the present invention, respectively. Alloys B4 and B5 both represent Ni, Sn, and hard second phase particles 1 rich in Ni, Sn, and B or P, which are formed when B or P is added to a Cu-based alloy, respectively. Hard second phase particles 1 rich in Ni, Sn and Zr are also formed when Zr is added to the Cu-based alloy (not shown). The second phase 1 is harder than the rest of the Cu-based alloy matrix. Alloys B4 and B5 are also characterized by a grain size of essentially 35 μm in average diameter, which is almost as much as factor 2 smaller than the grain size of other alloys containing no B or P. In addition, alloys C1 and C2 having a lower B or P content, respectively, show the second phase particles 1 in spite of the reduced amounts (micrographs not shown). The second phase particles 1 are evenly distributed in a microstructure and are several micrometers in size. Pb inclusions 2 appear white in FIGS. 1 and 2.

Table 2 reports Vickers hardness (HV10) test values measured for alloys B1 to B5 after heat treatment at 800 ° C. for about 1 hour and then aged at 320 ° C. for about 10 hours and 12 hours. The test values are compared with the values obtained for alloy A2. The highest increase in hardness was found for the alloys B4 and B5 according to the invention.

[Table 2]

In Table 3, yield strength (R _{p 0.2} ) and maximum stress (R _m ) values are reported for A1 to B5 alloy samples. These values were obtained by heat treatment at 800 ° C. for about 1 hour, followed by quenching in water or air, followed by high temperature tensile test. Tensile testing was performed by a servo-hydraulic tester (MFL 100 kN) at 400 ° C. at a strain rate of 10 ⁻² s ⁻¹ . These samples are rapidly heated using a lamp furnace (Research Inc., Model 4068-12-10), which reaches a stabilized test temperature within less than 2 minutes, thereby minimizing the occurrence of phase strain during the heating period. Due to the rapid heating and high strain rate, breakage of the sample is obtained after holding at 400 ° C. for up to 3 minutes.

[Table 3]

Lead added to the CuNi9Sn6 alloy significantly embrittles the alloy. Improved yield strength (R _{p 0.2} ) and maximum stress (R _m ) values are compared with those obtained for other Pb-containing alloys A2 to B3 without P and / or B addition, and thus alloys B4 and Obtained for B5. The yield strength and maximum stress values obtained for alloys C1 and C2 with reduced amounts of B (0.03 wt.%) And P (0.1 wt.%), Respectively, at 400 ° C., are 160 MPa and about 300 MPa, respectively. It was improved when compared with the values of alloys A2 to B3 at temperature.

After breakage in the above high temperature tensile test, SEM studies (not shown) of the longitudinal cuts of the broken samples of alloys C1 and C2 indicate that the second phase particles 1 are often located adjacent to the Pb inclusions 2 ( 1 and 2) The breakage indicates presence at the grain boundary, suggesting that the breakage does not gather in the larger second phase particle 1.

Table 3 qualitatively reports the susceptibility to quench-crack formation of alloys A2 to B5. In Table 3, the indication "+" indicates the presence of cracks, from "+" to "+++" as the number and depth increase, and "0" indicates the absence of any cracks. The quenching experiment was conducted by first casting the alloy A2 to B5 samples at 800 ° C. for 1 hour and then dropping the samples into a water bath at room temperature or by dropping them into an oil bath maintained at 80 ° C. or 180 ° C. A2 to B5 samples were performed. The alloy sample surfaces were then optically inspected for cracks. Table 3 shows that alloys B4 and B5 according to the invention are not easy to quench-crack.

[Table 3]

The machining properties of alloys B4 to C2 according to the invention, tested by drilling taking into account cutting speed, feed and chip length, were found to be similar to the machining properties of other alloys containing no P or B. Alloy B5 has been found to have the best machinability properties compared to other alloys of groups A1 to C2.

The results suggest that the hard second phase particles 1 do not exhibit a desired nucleating site for intergranular voiding in the alloy, but rather interfere with grain boundary slip, which is nucleation. Without nucleating voids, it is one of the main reasons for embrittlement of intermediate temperatures (300-700 ° C.) in copper alloys. Moreover, in the Zr, B- and P-containing alloys (B3, B4, B5, C1, C2) of the present invention, the Pb inclusion 2 is adjacent to the solid B- or P-containing second phase precipitate 1 It shows a pronounced tendency to locate, but rather has an irregular complex shape. This may create a low energy interface between the molten lead inclusion 2 and the hard second phase 1 at an intermediate temperature so that Pb may “wet” the second phase particles 1. This increases the applied stress required to achieve the instability of the molten Pb inclusions 3, delaying the breakdown of the B- and P-containing alloys that make the alloy stronger and more ductile, and improved tension at intermediate temperatures. Properties are possibly obtained. In other words, additional elements such as P, B or Zr in the Cu-based alloy may be used to stabilize the particles against morphological changes under the application of stress when in contact with the hard second phase 1 (the molten Pb). Low interfacial energy). The higher tensile properties of B4 and B5 compared to A2 and the remaining B-series alloys (Table 2) also indicate that B and P both act as grain refiners and are less soft second phases. This can be explained by the difference in grain size in the case of load-bearing by (1).

Certainly, the alloys B4, B5, C1 and C2 of the present invention solve to a considerable extent the intermediate temperature embrittlement caused by the addition of lead to improve the machinability of CuNi9Sn6 alloys. Leaded B3-C2 alloys retain their attractive free-machining characteristics.

In one embodiment of the present invention, the machinable metal product composed of the Cu-based alloy of the present invention is obtained by a method comprising a continuous or semi-continuous casting process. In this method, the first metal mass is extruded to a diameter, for example, which may typically comprise 25 to 1 mm. The alloy is then, as discussed below, for example to limit the formation of a second phase that is cooled by a compressed air stream, or by water spray, or preferably fragilizing. Cooling is by any other suitable means that is high enough and can reach a suitable cooling rate fast enough to prevent cracking.

The first metal mass material is then subjected to one or several cold forming operations, for example by rolling, wire-drawing, stretching-forming, hammering or any other cold deformation process. Do this. After the cold forming step, the second metal mass is annealed, typically in a through-type furnace or a removable cover furnace, at an annealing temperature at which the alloy should be within the range of one phase. . In the case of the Cu alloy of the present invention having one of the compositions described above, the annealing temperature is comprised between 690 and 880 ° C. Among others, an annealing step or a heat homogenization step is used to induce ductility, to refine the structure by making the structure homogeneous, and to improve the cold forming properties of the alloy.

With the transformation of the above aspect, the second metal mass can be subjected to an annealing or heat homogenization treatment step before the cold forming process.

In the course of the annealing step, at least partial recrystallization occurs to the second metal mass, where new particles without deformation form nuclei, grow and replace those deformed by internal stresses. After the annealing step, the second metal mass is cooled again at an appropriate cooling rate, preferably high enough to limit the formation of the weakened second phase and fast enough to prevent cracking.

One or several successive steps of the cold forming process may be performed, followed by each cold forming step, followed by annealing and cooling steps to obtain continuous metal ingots of the desired diameter and shape.

After successive cold forming, annealing and cooling steps, the final metal mass can be wire-drawn or stretch-molded to the final diameter and / or shape to obtain a machinable product. Spinoidal decomposition heat treatment or curing may then be finally performed on the machinable product or machined piece to obtain optimum mechanical properties. The latter heat treatment can take place either before or after final machining.

The cooling step after the extrusion and / or annealing treatment is slow enough to prevent cracking of the alloy due to internal constraints created by the temperature difference during cooling, but fast enough to limit the formation of the two-phase structure. You must wake up. If the speed is too slow, a significant amount of second phase may appear. The second phase is very fragile, significantly reducing the deformation of the alloy. The critical cooling rate required to avoid forming too much of the second phase depends on the chemistry of the alloy and is greater for larger amounts of nickel and tin.

Moreover, during the cooling process, temporary internal constraints are created in the alloy. They are linked to the temperature difference between the metal mass or the surface and the center of the product. If these restraints exceed the resistance of the alloy, the alloy cracks and can no longer be used. The internal constraints due to cooling are all higher the larger the diameter of the product. Thus, the critical cooling rate to prevent cracking depends on the diameter of the product. In the process of the invention, cooling after the extrusion and / or annealing steps is carried out at a cooling rate of 50 to 50000 ° C./min.

Copper-nickel-tin alloys have long solidification intervals that lead to significant segregation during casting operations. In the course of the continuous or semi-continuous casting process, the molten alloy can be stirred to obtain greater regularity for the casting metal in terms of its surface state and its internal properties (eg segregation and shrinkage). Moreover, when the molten alloy is melted and cast, a dendrite structure is produced and a micro-crystalline alloy cannot be obtained.

The copper alloy may be electromagnetically stirred for stirring the melt. The magnetic force can produce agitation of the metal mass sufficient to allow a reduction in the number of segregation centers and to obtain a Cu-based alloy with fine equiaxed crystals having an average grain size of essentially less than 5 mm.

Alternatively, the molten Cu alloy in the metal mass may be mechanically agitated using ultrasonic energy to generate cavitation and acoustic streaming in the molten material. Other forms of mechanical stirring, such as forced gas mixing and physical mixing (eg, vibration or shaking of the molten alloy), or mechanical devices (eg, rotors, propellers, or stirred pulsing jets) may also be used. Alternatively, the electromagnetic agitation can be used with mechanical agitation, and ultrasonic agitation can be used with mechanical agitation.

In another aspect of the invention, the first metal mass of a Cu-based alloy having a diameter of 320 mm or less is known as a sprayforming process, for example the "Osprey" method and described in patent EP 0225732. Using the prepared process. At this time, using atomized particle sizes ranging in size from 1 to 500 microns, an alloy with an average grain size of less than 200 microns can be obtained. The spray molding method makes it possible to obtain an almost homogeneous microstructure exhibiting a minimum degree of segregation. Other forms of metal ingots (eg ingots, discs or bars) with rectangular portions can also be produced by the spray molding process. Spraying of the molten metal or metal alloy particles is carried out under a preferred atmosphere, preferably under an inert atmosphere (eg nitrogen or argon).

Alternatively, the metal product may be obtained by a static billet casting method or other suitable method.

The Cu-based alloy product has a tensile strength of 700 to 1500 N / mm 2 (700 to 1500 MPa) measured at room temperature after the annealing and cooling step, and a Vickers hardness (HV10) of 250 to 400 measured after the annealing and cooling step. , With respect to standard ASTM C36000 brass, is characterized by a machinability index of greater than 70%. Moreover, the Cu-based alloy product can be easily machined due to the easy removal of chips produced during the turning process, in particular the turning or free-cutting step, stamping step, bending step, drilling It can be usefully used for machining operations that require steps.

The Cu-based alloy products of the present invention are advantageously used to obtain products in the form of wires, strips (eg, rolled strips), slabs, ingots, sheets, etc. in the form of rods, circles or any other profile. Can be used. The Cu-based alloy product may also be an electrically conductive piece (e.g., a connector), an electromechanical piece, a telephone, a spring, etc., or a micromechanical, horology, having a high elasticity limit in excess of 700 N / mm 2, for example. It may be advantageously used in the manufacture of all or part of a machined piece, such as micromechanical pieces in applications such as tribology, aeronautics, or the like, or other pieces in various applications.

The process of the present invention is a machinable Cu-Ni-Sn-based system containing up to several percent by weight of Pb and 0.01 to 0.5 percent by weight of P and / or B, with excellent mechanical and tensile properties without cracking during the production process. Allow the product to be prepared.

1 second phase particles
2 Pb inclusions
R _{p 0.2} Yield Strength
R _m maximum stress

Claims (17)

As an alloy,
The alloy contains 1 to 20% by weight of Ni, 1 to 20% by weight of Sn, and 0.5 to 3% by weight of Pb in Cu corresponding to 50% by weight or more of the alloy,
The alloy is characterized in that it further contains 0.01 to 5% by weight of P or B alone or in combination. The alloy of claim 1, wherein the alloy further contains 0.01 to 0.5% by weight of P or B, alone or as a blend. The alloy of claim 1, wherein the alloy comprises 9 weight percent Ni, 6 weight percent Sn, and 1 weight percent Pb. 4. The alloy of claim 3 wherein the alloy is heat treated at 800 ° C. for about 1 hour and then quenched in water or air and the yield strength R _{p 0.2} measured at 400 ° C. is essentially greater than 180 MPa. alloy. The method according to claim 3 or 4, wherein the alloy is heat treated at 800 ° C. for about 1 hour and then quenched in water or air, and the maximum stress R _m measured at 400 ° C. is essentially greater than 333 MPa. alloy. 6. The Hv hardness of claim 3, wherein the alloy is heat treated at 800 ° C. for about 1 hour and then aged at 320 ° C. for about 12 hours. Made, alloy. The agent according to any one of claims 1 to 6, wherein the alloy contains Ni, Sn, and B or P, respectively, after heat treatment at 800 ° C. for about 1 hour and then quenched in water or air. Alloy comprising a second phase (1). A method for producing a metal product composed of an alloy characterized by any of claims 1 to 7, wherein the method is
a) obtaining a first slug of the alloy having a homogeneous structure;
b) annealing the alloy at a temperature of 690-880 ° C. for homogenization and improvement of alloy cold forming properties;
c) cooling at a cooling rate of 50 to 50000 ° C./min depending on the transversal dimension of the product and the composition of the alloy; And
d) cold forming. The method of claim 8, wherein step a) of 8 is a continuous casting process for extruding the first metal mass of the alloy having a diameter of 25 to 1 mm. 10. The method of claim 8 or 9, wherein the alloy in the first metal mass is subjected to electromagnetic or mechanical stirring to obtain an alloy having fine equiaxed crystals having an average grain size of essentially less than 5 mm. , Way. The method of claim 8, wherein step a) of claim 8 is a spray molding process, wherein the first metal mass is formed with a diameter of 320 mm or less and an average grain size of less than 200 microns. The method of claim 8, wherein the cold forming step comprises a rolling, wire-drawing, elongation-molding, hammering process. The metal product obtained from the process characterized by any one of claims 8-12, wherein the tensile strength measured at room temperature after the annealing step b) and cooling step c) of claim 8 is 700-1500 MPa. The product of claim 13, wherein the Hv hardness after annealing step b) and cooling step c) of claim 8 is 250 to 400. 15. The product of claim 13, wherein the product has a machinability index of greater than 70% with respect to standard ASTM C36000 brass. The product according to claim 13, wherein the product is in the form of rods, wires, strips, slabs, ingots and sheets. 17. The product according to any one of claims 13 to 16, wherein the product is used in the manufacture of all or part of a machined electrically conductive piece or a mechanical or micromechanical piece.

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