EP2340318B1 - Copper-tin alloy, composite material and use thereof - Google Patents

Description

The invention relates to a copper-tin alloy, a composite material with such a copper-tin alloy and a use of the copper-tin alloy and the composite material. The copper-tin alloy and the comprehensive composite material is particularly suitable for fasteners in electrical engineering and electronics. The invention is particularly concerned with the problem of recyclability.

In general, copper alloys based on Cu-Zn, Cu-Sn and Cu-Fe are widely used today for connecting elements in electrical engineering and in electronics. In particular, such copper alloys are used for lead frames and connectors. Important criteria for the selection of materials are modulus of elasticity, yield strength, relaxation behavior and bendability. In addition to a sufficient mechanical strength, the electrical conductivity and corrosion resistance are important criteria for the safe function of the components over the life of the entire system. Often there is an overlap of property requirements, which in principle preclude each other, such as the combination of a good Conductivity with high corrosion resistance. On the one hand, alloying elements in copper, such as nickel and chromium, on the one hand improve the corrosion resistance, on the other hand, they considerably reduce the conductivity.

The topic of weldability, in particular laser welding, with other metallic materials is also gaining in importance. Against the background of the exorbitant increases in metal prices in recent years, the issue of the recyclability of the alloys used is becoming increasingly important.

Cu-Zn or brass alloys are solid solution hardening materials. They are binary alloys, which usually contain between 5 and 40 wt .-% of zinc. With increasing zinc content, tensile strength and hardness increase. The elongation reaches a maximum at 30% by weight of zinc. Higher strength and hardness values can only be achieved by cold forming.

For connectors in the form of spring bands, for example, a CuZn 30 or a CuZn 37 alloy, a Vickers hardness of Hv = 150 is usually required. In addition, compliance with a minimum bending radius r / s = 1 normalized to the sheet thickness s for a 90 ° rebate must be ensured. The disadvantage of the Cu-Zn alloys, however, lies in the relatively poor weldability, because the alloying element zinc has a relatively high vapor pressure. Pure zinc already boils at 1.013 bar at 907 ° C. Furthermore, Cu-Zn alloys have a low elastic modulus of about 110 KN / mm ² (SI unit: GPa). In addition, tinned brass bands can not be recycled well due to the tin included for corrosion protection reasons. The relaxation behavior of Cu-Zn alloys is also pronounced, limiting the operating temperature.

Cu-Sn alloys, ie tin bronzes, are among the oldest technically usable copper alloys. The Cu-Sn alloys are usually added some phosphorus, which is why these alloys are also referred to as phosphorus bronzes. The properties of these alloys are determined primarily by the tin content, which is usually between 4 and 8 wt .-%. Depending on the Sn content, the modulus of elasticity of phosphorus bronzes is between 115 and 120 kN / mm ² (SI unit: GPa). The bendability of tin bronzes is excellent. Rising Sn levels improve the flexibility for a given temper. Phosphor bronze bronze tapes can be readily consolidated to a hardness level of Vickers hardness of Hv = 200 and still have a bendability of r / s = 1 with a 90 ° fold. The laser weldability of tin or phosphorus bronzes is given, because these alloys have no volatile elements (especially zinc) and no disturbing second phases. The relaxation behavior of tin or phosphorus bronzes is better than that of brass alloys, although it does not reach the level of hardenable copper materials.

Cu-Sn alloys are used in the form of tapes for stampings and connectors, if a good to very good spring characteristic, a good electrical and thermal resilience, low stress relaxation, good bendability, good weldability and solderability are required. Even in tinned form, phosphorus bronzes are easy to recycle. Tin is already included in the alloy as such.

The low-alloyed copper materials include the Cu-Fe alloys. By small additions of iron and phosphorus, the material properties of pure copper, such as the strength, the softening or relaxation behavior can be improved. Widely used for stamped grids in automotive engineering is in particular a CuFe2P alloy in the heat setting FH. The material has a tensile strength of Rm = 420 to 500 N / mm ² (SI unit: MPa) in this heat treatment stage. The Vickers hardness is Hv = 130 to 150. The sharp-edged bendability is still present. Among the advantages of the CuFe2P alloy is that the modulus of elasticity is about 125 KN / mm ² (GPa), and thus the material has good spring properties. The electrical conductivity is between 60% and 70% IACS (I nternational Annealed C opper S tandard: 100% IACS correspond approximately to 58 MS / m). A tinning of the material for corrosion protection reasons is well possible.

One of the disadvantages of the CuFe2P alloy is that it does not form a homogeneous material but has Fe2P precipitates. In particular, this makes laser welding difficult. If the laser beam encounters coarser Fe2P precipitates during spot welding, it can be deflected, making the penetration result unsatisfactory. Another disadvantage is the poor recyclability of tin-plated scrap of CuFe2P alloy. The electrical conductivity of a CuFe2P alloy is reduced by 25% upon reflow by a dissolving tin of about 1% by weight. The tinned punching scrap, which usually make up 50% to 70% of the material used in the manufacture of stamped laths, can not be returned directly to the melting process, but rather must be smelted and electrochemically separated. The return to the material cycle is therefore as a cathode. This process is very energy intensive and thus very expensive compared to the direct melting of the scraps.

Out Fig. 1 For a CuFe2P alloy, the influence of a percentage of tin on the electrical conductivity is shown. The electrical conductivity drops drastically even from levels above 0.3 wt .-% tin. For example, a 0.4 mm thick band of a CuFe2P alloy for corrosion protection reasons Coated with about 3 μm tin on both sides, a CuFe2P alloy contaminated with about 1.5% by weight tin would result from direct recycling based on this scrap. In addition to drastic losses in the electrical conductivity, this tin content also has a strong negative effect on the solidification behavior.

From the JP 2007 039 735 A CuNiP alloys are known, which may optionally include Sn, Zn and Fe.

The object of the invention is to provide an alloy and a composite material which corresponds as far as possible in its physical and technological properties of a CuFe2P alloy, as well as possible laser weldable and can be recycled well. Another object is to provide a use for such an alloy and composite material.

With regard to the alloy, the above object is achieved by a copper-tin alloy having the composition according to claim 1. Accordingly, the copper-tin alloy comprises 0.2 to 0.8 wt .-% tin (Sn), 0.3 to 0.5 wt .-% nickel (Ni) and / or cobalt (Co), 0 to 0 , 05 wt .-% zinc (Zn), 0 to 0.02 wt .-% iron (Fe), 0.008 to 0.05 wt .-% phosphorus (P) and the balance copper (Cu).

The invention is based on the idea of specifying an alternative to the CuFe2P alloy, new alloy, which has comparable properties, but can be easily recycled even in tinned state. Pure Cu-Sn alloys, such as a CuSn0.15 alloy, undoubtedly have the potential to be used as such an alternative. Coated with tin, the scrap of such an alloy can be fed directly to the recycling cycle. The mechanical and technological properties correspond to those of a CuFe2P alloy relatively well. Significant weaknesses, however, occur in the softening behavior and the relaxation resistance.

Extensive investigations have now shown that a copper-tin alloy with a specific coordination of the alloying elements tin, nickel and / or cobalt and phosphorus both to a CuFe2P alloy comparable mechanical and technological properties as that for the respective Further processing and end use required property profile in the area of the softening behavior and the relaxation, ie the creep of the component under tension at elevated temperature achieved. In this case, either nickel or cobalt is included with the specified proportion. In this case, part of the nickel is preferably replaced by cobalt, in which case the sum of the two alloying elements together gives the stated proportion.

A comparison of the technological and physical properties of a Cu-Sn alloy with a CuFe2P alloy gives the following picture: CuFe2P CuSnNiCoP Tensile strength Rm [MPa] 450 438-440 Yield point 0.2% R _{p 0.2} [MPa] 420 405 - 430 Elongation at break A50 [%] 9 4-5 Young's modulus [GPa] 123 126 Conductivity [% IACS] 63 55 - 70 Thermal conductivity [W / mK] 260 250 Minimum bending radius [r / s, 90 °] 1 1 Thermal expansion coefficient [Rt-100 ° C] 17.7 x 10 ^-6 17.7 x 10 ^-6 Vickers hardness [Hv] 145 130-134 Softening temperature [° C (1h)] 350 350

The table shows that Cu-Sn alloys can meet the specified requirements in terms of technological and physical properties.

When using the Cu-Sn alloy according to the invention in tinned form, an alloy layer is formed between the base material and the tin coating. An adaptation of the production facilities is not required when converting to the new material.

In addition, the Cu-Sn alloy according to the invention exhibits a property profile which is comparable to the CuFe 2 P alloy in the area of the softening behavior and the relaxation.

The Cu-Sn alloy according to the invention is further distinguished in a special way by the direct traceability of tin-plated scrap from the individual stages of the value-added chain. The tin-coated scrap can be returned directly to the smelting process, so that the recycling costs are significantly lower than smelting. The smelting costs, for example, can quickly reach the level of manufacturing costs with a scrap content of 70% and put into question the economic efficiency. For this reason, even a consideration of the metal values between a copper-iron alloy such as the CuFe2P alloy and the Cu-Sn alloy given here does not change the fact that the stated alloy is economical and ecological (the additional use of electricity and acid for the electrolytic treatment of the scrap can be omitted) represents a reasonable alternative to tinned copper-iron alloys.

With regard to the required properties, it is advantageous if the stated copper-tin alloy contains a proportion of Sn between 0.3 and 0.7% by weight, in particular between 0.4 and 0.6% by weight the invention, the proportion of Ni and / or Co in the copper-tin alloy is between 0.3 and 0.5 wt .-%.

By a preferred amount of phosphorus between 0.008 and 0.03 wt .-%, in particular between 0.008 and 0.015 wt .-%, the strength can be improved.

In a preferred alloy composition, the copper-tin alloy has 0.3 to 0.7 wt% Sn, 0.3 to 0.5 wt% Ni and / or Co, 0 to 0.04 wt%. Zn, 0 to 0.015 wt .-% Fe, 0.08 to 0.03 wt .-% P, and the balance Cu on.

The copper-tin alloy is further improved when it contains 0.4 to 0.6% by weight Sn, 0.3 to 0.5% by weight Ni and / or Co, 0 to 0.03% by weight. % Zn, 0 to 0.01 wt .-% Fe, 0.008 to 0.015 wt .-% P, and the remainder comprises Cu.

A further advantageous precise adjustment of the properties of the copper-tin alloy can be carried out if there is a total of impurities and other admixtures of not more than 0.3% by weight.

As a concrete embodiment having excellent properties, mention is made of a copper-tin alloy containing 0.38 wt% Sn, 0.30 wt% Ni and / or Co, 0.003 wt% Zn, 0.008 wt%. % Fe, 0.014 wt .-% P, and the remainder comprises Cu.

The copper-tin alloy according to the invention is very good laser weldable, since no volatile elements are contained and the alloy is free of a second phase. In particular, the alloy does not exhibit NiP precipitates.

The alloy is ideal for a good laser weldable composite material, which can be used in particular for stamped grid. Such stamped grids are used today, for example in automotive technology for ABS and ESP systems. For this purpose, a base material of the aforementioned copper-tin alloy is provided with a tin layer or covered, which can be made in particular by the method of hot tinning. In this respect, there is a layer of pure or free tin on the base material of the specified copper-tin alloy. The composite material is characterized by a high relaxation resistance up to temperatures of 100 ° C. Inside, as the core, the specified copper-tin alloy with a composition according to the claims directed thereto. The outer coating or tin cover ensures high corrosion resistance. The thickness of the tin layer is preferably between 1 and 3 μm.

When tinning the copper-tin alloy according to the invention, a transition layer is formed between the base material and the tin layer. The tin layer is preferably applied in such a way that the transition layer comprises an intermetallic phase of Cu, Ni and / or Co and Sn. The formation of the transition layer is in particular designed such that it has a thickness between 0.1 and 1 micron. In this respect, the composite material in the interior or core of the specified copper-tin alloy with the corresponding proportions of nickel and / or cobalt and phosphorus. The alloy of the core transitions through the transition layer into a layer of pure tin. Via the formed transition or alloy layer, a good connection of the tin layer is achieved.

Considering a three-dimensional structure like a stamped grid made of composite material, the overall result is a five-layer structure. On one core of the specified copper-tin alloy as the base material sits on both sides of a layer of an intermetallic phase consisting of CuNiCoSn with a thickness between 0.1 and 1.0 microns. The composite material is finally covered for corrosion protection reasons with a layer of free or pure tin, which has a thickness of 1.0 to 3.0 microns. The layer composite material has a total thickness of 0.2 to 1 mm, preferably up to 2 mm, particularly preferably up to 3 mm.

The electrical conductivity of the specified composite material corresponds to that of the previously used comparison material CuFe2P. Thermal conductivity and other technological values of the composite are also fully comparable.

Both the copper-tin alloy according to the invention and the tinned composite material are outstandingly suitable for tapes, films, profiled strips, stampings or connectors, in particular for applications in electrical engineering or electronics.

Claims (12)

1. Copper-tin alloy, comprising:

   0.2 to 0.8% by weight Sn,

   0.3 to 0.5% by weight Ni and/or Co,

   0 to 0.05% by weight Zn,

   0 to 0.02% by weight Fe,

   0.008 to 0.05% by weight P,

   and also Cu as remainder.
2. Copper-tin alloy according to Claim 1,
   having an Sn content of between 0.3 and 0.7% by weight, in particular of between 0.4 and 0.6% by weight.
3. Copper-tin alloy according to either of the preceding claims,
   having a P content of between 0.008 and 0.03% by weight, in particular of between 0.008 and 0.015% by weight.
4. Copper-tin alloy according to Claim 1, comprising:

   0.3 to 0.7% by weight Sn,

   0.3 to 0.5% by weight Ni and/or Co,

   0 to 0.04% by weight Zn,

   0 to 0.015% by weight Fe,

   0.008 to 0.03% by weight P,

   and also Cu as remainder.
5. Copper-tin alloy according to Claim 4, comprising:

   0.4 to 0.6% by weight Sn,

   0.3 to 0.5% by weight Ni and/or Co,

   0 to 0.03% by weight Zn,

   0 to 0.01% by weight Fe,

   0.008 to 0.015% by weight P,

   and also Cu as remainder.
6. Copper-tin alloy according to one of the preceding claims,
   in which the sum of impurities and other admixtures is at most 0.3% by weight.
7. Composite material having a base material according to one of the preceding claims and a layer of tin applied thereto.
8. Composite material according to Claim 7,
   wherein the layer of tin has a thickness of between between 1 and 3 µm.
9. Composite material according to Claim 7 or 8, having a transition layer between the base material and the layer of tin, wherein the transition layer comprises an intermetallic phase of Cu, Ni and/or Co and also Sn.
10. Composite material according to Claim 9,
    wherein the transition layer has a thickness of between 0.1 and 1 µm.
11. Use of a copper-tin alloy according to one of Claims 1 to 6 for strips, wires, foils, profiled strips, stamped parts or plug-in connectors.
12. Use of a composite material according to one of Claims 7 to 10 for strips, wires, foils, profiled strips, stamped parts or plug-in connectors.

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