DE102017006970A1 - Copper casting alloy and casting process - Google Patents

Abstract

The invention relates to a copper casting alloy having the following composition: P: 50-190 ppm by weight Mg: 20-350 ppm by weight Cu: balance and unavoidable impurities. The invention further relates to a casting method for producing a cast component from a copper alloy.

Description

The invention relates to a copper casting alloy and a casting method for producing cast components from a copper alloy.

There is a need for electrically highly conductive components of complex geometric shape. Because of its high electrical conductivity, pure or low alloyed copper is the preferred material for such devices. In principle, such components can be produced from semi-finished products by machining and, if necessary, by joining. The semi-finished product itself is produced by forming steps from a cast format. Alternatively, the components may be manufactured by casting. The components are in this case essentially already in the casting process. The components are not reshaped after casting. Cutting steps, such as drilling holes, or surface treatment steps, such as grinding, polishing or coating, may, in special cases, follow the casting process. The production of a component by a casting process in the sense of this invention means that the shape of the component is essentially already achieved by the casting process. The component is produced by the casting process so near net shape. In particular, the component is subjected to the casting process no forming and no heat treatment. The material of the finished component is therefore in the cast state.

It depends on various factors whether it is more advantageous to produce a component from a semifinished product by a casting process or by machining. One of these factors is the size of the component. The larger the component, the cheaper it will be to produce the component by a casting process. For copper materials, it may be more advantageous from a component dimension of 50 mm or from a component weight of 100 g to produce the component by a casting process. Furthermore, the shape of the component plays a role: the more complex the shape of the component, the more effort it is to produce such a component by machining. Casting processes are a promising method for manufacturing complex components.

Producing components from almost pure copper by casting is demanding. Special difficulties prepares the production of such components in the lost foam process. One of the reasons is that copper can dissolve large amounts of gas when molten. In the lost-foam process, a positive model of hydrocarbon-containing polymer foam is decomposed by the melt. This creates a large gas volume and it comes to a turbulent melt flow. As a result, the problem of pore formation is more critical in components made by the lost foam process than in components made by other casting methods.

To reduce the oxygen content in copper melts deoxidizing agents are added. For pure copper varieties in the literature the elements P, Li, Zn, Sn, Be, Cd, Ca, Al and Mn and Borkupfer (CuB ₂ ), calcium boride and boron carbide are called. In practice, phosphorus has prevailed as a deoxidizer for copper. However, it should be noted that the electrical conductivity of the alloy is significantly reduced by dissolved phosphorus: additions of less than 0.05% by weight P are sufficient to reduce the electrical conductivity from 100% IACS to values below 65% IACS. For components with high demands on the electrical conductivity, therefore, copper wafers with a P content of less than 50 ppm by weight are used if these components are produced from a semifinished product.

From the publication JP 57089448 A For example, a Mg-containing copper alloy for wires is known. The Mg content is between 5 and 100 ppm, the P content is at most 1 ppm. Magnesium causes a lowering of the recrystallization temperature of the alloy and thus makes it possible, by lowering the annealing temperature, to avoid the problem of gluing wires together during annealing.

The invention has for its object to provide an improved copper casting alloy and an improved casting process for the production of cast components. In particular, the cast component should have an electrical conductivity of at least 49 MS / m (corresponding to 85% IACS) and a porosity of less than 1.5% by volume.

The invention is reproduced with respect to a cast copper alloy by the features of claim 1 and with respect to a casting method by the features of claim 7. The other dependent claims relate to advantageous embodiments and further developments of the invention.

The invention includes a copper casting alloy having the following composition: P: 50-190 ppm by weight mg: 20-350 ppm by weight Cu: Rest and unavoidable impurities.

The invention is based on the consideration that small amounts of deoxidizing agents added to the copper alloy have an effect on the electrical conductivity of the alloy and on the mold filling and the porosity of the cast product. Phosphorus has a positive effect on the casting behavior of the alloy and thus on the mold filling of the cast product. Therefore, the alloy should contain at least 50 ppm by weight of phosphorus. Consequently, as the phosphorus content increases, so does the porosity of the cast product. On the other hand, phosphorus significantly reduces the electrical conductivity of the alloy. In order to achieve an electrical conductivity of at least 49 MS / m (corresponds to 85% IACS), therefore, the phosphorus content in the alloy must not exceed 190 ppm by weight. Experiments show that a further improvement of the porosity of the cast product by the addition of even small amounts of magnesium can be achieved. In order to achieve a significant improvement in the porosity of the cast product, at least 20 ppm by weight of Mg must be added to the alloy. The addition of magnesium affects the electrical conductivity of the alloy significantly less than the addition of phosphorus, so that the proportion of magnesium in a relatively large range can be varied. If more than 350 ppm by weight of Mg is added to the alloy, the electrical conductivity drops to values below 49 MS / m. Thus, at most 350 ppm by weight of Mg should be added to the alloy.

The particular advantage of the copper casting alloy according to the invention is that a cast product with good mold filling, low porosity and high electrical conductivity can be produced by the special combination of phosphorus and magnesium. Phosphorus basically ensures good casting behavior and therefore good mold filling. The amount of phosphorus is limited upwards in order to keep the electrical conductivity at a high level. The addition of magnesium then ensures a low porosity in the cast material even with a relatively low proportion of phosphorus. The electrical conductivity is at least 49 MS / m and the porosity is below 1.5 vol .-%.

The casting alloy may contain unavoidable impurities. The impurities can have an influence on the properties of the alloy. In particular, by impurities, the electrical conductivity of the alloy can be reduced. The amount of impurities should be such that the copper content in the alloy is at least 99.92% by weight, preferably at least 99.95% by weight. With large proportions of P and Mg, the total proportion of all impurities must be smaller than with small proportions of P and Mg. The sum of all impurities should preferably be at most 150 ppm by weight, particularly preferably at most 90 ppm by weight.

In a preferred embodiment of the invention, the weight proportions of phosphorus P and magnesium Mg may be such that the following relation applies to them: $$\text{P}+\text{0}\text{15}\cdot \text{mg}\le \text{220 wt}\text{. Ppm}\text{,}$$

The sum of phosphorus content and 0.15 times the magnesium content should therefore preferably not exceed 220 ppm by weight. This additional limitation allows an electrical conductivity of at least 49 MS / m to be achieved with greater safety. Particularly preferably, the weight proportions of phosphorus P and magnesium Mg can be such that the sum of phosphorus content and 0.15 times the magnesium content does not exceed 175 ppm by weight. This can be achieved that the electrical conductivity of the alloy is at least 52 MS / m.

Advantageously, the P content of the alloy can be at least 80 ppm by weight. As a result, a very good castability of the alloy and excellent mold filling is achieved even with complex shapes of the cast component.

Furthermore, in an advantageous embodiment of the invention, the Mg content may be at least 40 ppm by weight. This achieves a reduction of the porosity to 1% by volume and less. In a particularly preferred combination of such a Mg content with a P content of at least 80 ppm by weight, a copper casting alloy with particularly good mold filling capacity can be achieved.

In an advantageous embodiment of the invention, the P content may amount to at most 170 ppm by weight. As a result, the electrical conductivity can be increased to 52 MS / m.

In a further advantageous embodiment of the invention, the Mg content may amount to at most 200 ppm by weight. Surprisingly, no further improvement in the porosity of the cast material occurs at Mg contents above 200 ppm by weight. The porosity remains at Mg levels above 200 ppm by weight at a level between 1.0 and 1.5 vol .-%. In contrast, even a decrease in porosity to levels below 1.0% by volume is observed when the Mg content is reduced from 200 ppm by weight to approximately 100 ppm by weight. Therefore, the content of Mg may preferably be at most 150 ppm by weight, more preferably at most 120 ppm by weight, and most preferably at most 80 ppm by weight. Further, if the P content of the alloy is limited to 170 ppm by weight at a content of Mg of the alloy of at most 80 ppm by weight, the properties of the alloy are particularly favorable. With approximately 53 MS / m, a very high electrical conductivity can be achieved and at the same time the porosity of the casting material is below 0.75 vol .-%. Preferably, the Mg content of the alloy may be at least 40 ppm by weight and the P content may be at least 80 ppm by weight.

Another aspect of the invention includes a casting process for producing a cast component from a copper alloy. According to the invention, the copper alloy has a composition as described above.

The inventive casting method includes the use of a copper alloy having the following composition: P: 50-190 ppm by weight mg: 20-350 ppm by weight Cu: Rest and unavoidable impurities.

By using such a copper alloy, a cast component of good quality and high electrical conductivity can be produced by means of a casting process. The cast component has a porosity of less than 1.5% by volume. The electrical conductivity is at least 49 MS / m.

In a preferred embodiment of the invention, in the alloy used in the casting process, the proportions by weight of phosphorus P and magnesium Mg may be so dimensioned that they have the following relation: $$\text{P}+\text{0}\text{15}\cdot \text{mg}\le \text{220 wt}\text{. Ppm}\text{,}$$

In a particularly preferred embodiment of the invention, in the alloy used in the casting process, the proportions by weight of phosphorus P and magnesium Mg may be such that they have the following relation: $$\text{P}+\text{0}\text{15}\cdot \text{mg}\le \text{175 wt}\text{. Ppm}\text{,}$$

Advantageously, the P content of the alloy used in the casting process may be at least 80 ppm by weight. Furthermore, in an advantageous embodiment of the invention, the Mg content of the alloy used in the casting process can be at least 40 ppm by weight. Particularly preferred is the combination of such Mg content with a P content of at least 80 ppm by weight. As a result, a porosity in the cast component of less than 0.75% by volume is achieved.

In an advantageous embodiment of the invention, the P content of the alloy used in the casting process may be at most 170 ppm by weight. In a further advantageous embodiment of the invention, the Mg content of the alloy used in the casting process may be at most 200 ppm by weight. The Mg content may preferably be at most 150 ppm by weight, particularly preferably at most 120 ppm by weight and in particular at most 80 ppm by weight. An extremely high electrical conductivity of at least 53 MS / m can be achieved if the Mg content of the alloy is limited to at most 80 ppm by weight and at the same time the P content of the alloy is limited to 170 ppm by weight.

In an advantageous embodiment of the inventive casting method, a lost shape can be used for shaping the cast component. Both sand molds and ceramic molds can be used. Cast components with complex shapes are often produced by such casting methods. The good shape filling behavior of the described copper alloy is therefore particularly suitable for these casting methods.

Advantageously, in a lost-mold inventive casting method, a lost model can be used as a model of the cast component. Lost-model casting techniques include lost-wax casting, cast-molding, and the lost-foam process. On components that are produced by these casting processes, high demands are made with respect to the absence of pores. Therefore, the copper alloys described above are particularly suitable for the production of cast components with such casting methods.

In a particularly preferred embodiment, in the inventive casting method, the lost model may be a model evaporating during the casting process. The casting methods with evaporating model include full-mold casting and the lost-foam process. In these processes, a positive model of the cast component is produced from a thermally decomposable material, usually a hydrocarbon-containing polymer foam. The positive model is coated with a size and after drying the size in a molding material, such as sand, embedded. The molding material is then compressed and thus forms the lost form. A sprue system enables the delivery of molten metal to the embedded positive model. In the process step of casting, molten metal is brought into contact with the thermally decomposable material, so that this material is decomposed by the introduced heat into gaseous products. The resulting cavity is filled with the molten metal. The gases formed must escape through the molding material or against the inflow direction of the molten metal. Compared with other casting methods, the casting methods with evaporating model are consequently burdened by the problem of gas formation. When casting copper, it adds that molten copper can dissipate large amounts of gas. The formation of large amounts of gas directly at the front of the molten metal makes it difficult to form a defect-free material. Thus, there is an increased risk of pore formation in the cast component in these methods. In the casting method according to the invention, the alloy used, because of its composition, ensures that, despite this problem, a largely pore-free cast material is formed. The porosity of the cast component is less than 1.5% by volume. By using alloys having the preferred compositions described above, the porosity can be reduced to below 1.0% by volume and below 0.75% by volume, respectively. At the same time, the selective selection of the proportions of the elements phosphorus and magnesium ensures a low electrical resistance of the cast component.

It may be particularly advantageous to apply a coating to the surface of a cast component which has been produced by a method described above. The coating can be applied over the entire surface or partially on the component. The coating can serve to improve the electrical contact. Tin or silver based coatings are particularly suitable for this purpose. Alternatively, the coating can serve to improve the corrosion and / or tarnish resistance of the component. For this purpose, coatings of ceramic or organoceramic materials, such as oxides, sulfides or carbides are suitable.

The invention will be explained in more detail with reference to the embodiments shown in Table 1. Test samples were poured with the lost foam method. The samples are designed as components with complex geometry and each weigh about 0.6 kg. The composition of the copper alloys used was varied as documented in Table 1. Table 1: Composition, conductivity and porosity of the samples Sample No. P-component Mg content Cu content and impurities electric conductivity porosity Ppm Ppm Ppm MS / m Vol .-% 1 0 0 rest 58 20 2 0 58.6 rest 57.5 4.6 3 164 58.2 rest 57 0.55 4 50 84 rest 56.3 0.9 5 104 48.4 rest 56 0.65 6 105 7.5 rest 55.2 1.3 7 156 74 rest 52.5 0.71 8th 114 215 rest 52.4 1.4 9 127 51.8 rest 52 0.49 10 182 200 rest 50.6 0.87 11 167 348 rest 50.1 0.96 12 183 25.6 rest 49 1.05 13 236 506 rest 48 1.05 14 312 47.8 rest 47 0.63 15 265 266 rest 46 1 16 251 393 rest 44.9 1.1 17 214 275 rest 39.2 1.03 18 208 253 rest 39.2 1.03 19 695 <1 rest 38.4 1.4 20 895 <1 rest 36.6 1.5

Table 1 shows the chemical composition, in particular the P content and the Mg content, of 20 test samples as well as the values of conductivity and porosity determined on the samples. In the table, the samples are sorted by decreasing electrical conductivity.

Sample No. 1 consists of pure copper without the addition of P and Mg. The conductivity is 58 MS / m. The porosity of the pure copper cast component is unacceptable at 20% by volume. Sample No. 2 is made of copper with an addition of about 60 ppm by weight Mg, but without the addition of P. Compared with pure copper (sample No. 1) is the addition of Mg, the electrical conductivity is only slightly reduced However, porosity is significantly improved. However, a porosity of almost 5% by volume is not sufficiently good. The cause of the poor porosity is the lack of phosphorus in the alloy.

Samples Nos. 19 and 20 are samples containing 700 and 900 ppm by weight phosphorus, respectively, but with no detectable Mg content. The addition of phosphorus achieves a porosity of approximately 1.5% by volume, but the electrical conductivity is at a level corresponding to approximately 65% IACS. By adding sufficiently large amounts of phosphorus, while an acceptable porosity can be achieved, the electrical conductivity then drops to a low level.

Sample Nos. 3 to 18 contain both phosphorus and magnesium. In this case, samples Nos. 3 to 12 have P contents of 50 to 190 ppm by weight and an electrical conductivity of at least 49 MS / m, while samples Nos. 13 to 18 have P contents of more than 190% by weight. ppm and an electrical conductivity of less than 49 MS / m. The two samples No. 17 and No. 18 also have a relatively high level of contamination with aluminum and silicon, so that the Cu content in the alloy in these two samples is below 99.90 wt%. In addition to the high doping with P and Mg, the high proportion of impurities is another reason for the low electrical conductivity of these two samples.

Within samples Nos. 3 to 12, the content of Mg varies between 7.5 ppm by weight (Sample No. 6) and 348 ppm by weight (Sample No. 11). In particular, the comparison of Samples Nos. 11 and 12 shows that magnesium has an indifferent and at most only a very weak influence on the electrical conductivity of the alloy over a wide range compared to phosphorus.

Within samples Nos. 3 to 12, the porosity varies between 0.49 and 1.4% by volume. It is noticeable that the two samples with the lowest Mg content (samples no. 6 and no. 12) and the two samples with the highest Mg content (Sample Nos. 8 and 11) have the highest porosity values within this group of samples. In terms of porosity, therefore, there is an optimum range for the Mg content in the alloy.

The most favorable property combinations are achieved with Samples No. 3, No. 5, No. 7, and No. 9. For these samples, the electrical conductivity is between 52 and 57 MS / m and the porosity is below 0.75% by volume. It is striking that in these samples, the P content is between 100 and 170 ppm by weight and the Mg content is between 40 and 80 ppm by weight.

In addition, sample No. 4 has excellent electrical conductivity and 0.9% by volume has very good porosity. The good conductivity is attributable to the very low proportion of phosphorus at 50 ppm by weight. The Mg content was set at 84 ppm by weight in a range favorable for the porosity.

Further, Sample No. 14 has a very low porosity at 0.63% by volume. Also in this sample, the addition of about 50 ppm by weight of Mg proves to be advantageous for the porosity. The electrical conductivity in this sample is only 47 MS / m, which is due to the relatively high proportion of phosphorus (over 300 ppm by weight).

The results of the investigation thus show that a targeted selection of the proportions of phosphorus and magnesium can achieve a copper casting material with excellent properties in terms of electrical conductivity, mold filling capacity and porosity in the cast state.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• JP 57089448 A [0006]

Claims (10)

Copper casting alloy with the following composition: P: 50-190 ppm by weight mg: 20-350 ppm by weight Cu: Rest and unavoidable impurities. Copper casting alloy after Claim 1 , characterized in that the following relation applies to the proportions by weight of P and Mg: $$\text{P}+\text{0}\text{15}\cdot \text{mg}\le \text{220 wt}\text{. Ppm}\text{,}$$

Copper casting alloy after Claim 1 or 2 , characterized in that the P content is at least 80 ppm by weight. Copper casting alloy according to one of the preceding claims, characterized in that the Mg content is at least 40 ppm by weight. Copper casting alloy according to one of the preceding claims, characterized in that the P content is at most 170 ppm by weight. Copper casting alloy according to one of the preceding claims, characterized in that the Mg content is at most 200 ppm by weight. Casting method for producing a cast component from a copper alloy, wherein the copper alloy has a composition according to any one of the preceding claims. Casting after Claim 7 , characterized in that a lost shape is used for shaping the cast component. Casting after Claim 8 , characterized in that a lost model is used as a model for the cast component. Casting after Claim 9 , characterized in that the lost model is a model evaporating during the casting process.