KR20220057454A - LEAD-FREE Cu-Zn BASE ALLOY - Google Patents

Abstract

The present invention relates to a lead-free-based alloy which comprises: 58 - 64 wt% of Cu; 0.4 - 1.4 wt% of Fe; 0.4 - 2.3 wt% of Mn; 1.5 - 3.5 wt% of Ni; 0.1 - 4.4 wt% of Al; 0.5 - 1.8 wt% of Si; an alloy substance promoting destruction of a chip, which includes 0.65 - 1.2 wt% of Sn (in this case, P accounts for a maximum of 0.025% in an alloy structure) or 0.03 - 0.1 wt% of P(Sn is allowed to account for a maximum of 0.25%); a remnant consisting of unavoidable impurities and Zn (in this case, the unavoidable impurities accounts for a maximum of 0.05% for each element and a total of the unavoidable impurities is no greater than 0.15%); a maximum of 0.1 wt% of Pb; and a maximum of 0.035 wt% of Cr. According to the present invention, properties of machining can be ensured without a need for any special manufacturing step.

Description

Lead-free Cu-Zn based alloy {LEAD-FREE Cu-Zn BASE ALLOY}

The present invention relates to lead-free Cu-Zn based alloys with good machinability properties.

Due to the small number of elements included in the structure of the alloy, the alloy CuZn42 is a very simply structured brass alloy with a Cu content of 57.0 to 59.0% by weight. In principle, these alloys do not contain other elements. Up to 0.2 wt% of Pb with unavoidable impurities is allowed, up to 0.03 wt% of Sn, up to 0.3 wt% of Fe, up to 0.02 wt% of Ni, and up to 0.05 wt% of Al. These alloys are lead-free alloys which can be hot-worked very easily, in particular for the production of profiles as semi-finished products. This alloy is a lead-free variant of the commonly used alloy CuZn39Pb3. In the case of the CuZn39Pb3 alloy, elemental lead is mainly used to improve machinability. Although the alloy CuZn42 is lead-free, it is also, due to its α/β microstructure, used for machining, such as in the production of turned parts. However, the machinability of workpieces made from these alloys is limited. This means that the machining disadvantages caused by the alloy cannot be compensated for by the appropriate process parameters of the machine tool. This applies, for example, to machining processes with forming tools where the limits of the process parameters do not allow for any individual leeway. In this case, the machinability of these alloys is not satisfactory.

While the machinability for certain machining operations in workpieces made from these alloys is acceptable, it is possible to achieve the desired machinability without the use of the Pb and Bi elements commonly used in free cutting alloys. It would be desirable if the machinability could be improved, since these elements are classified as hazardous to health.

The above applies likewise to special brass alloys, optimized for specific properties by including other elements, such as Fe, Mn, Ni, Al and/or Si. The alloys CuZn28Al4Ni3Si1Mn and CuZn35Mn2Ni2FeSi may be provided herein as examples. The first alloy mentioned is characterized by high wear resistance and high strength together with good running and sliding properties. Accordingly, these alloys and workpieces made therefrom are suitable for applications with oil lubrication under boundary friction conditions. These alloys are also suitable for use in biolubricants. The second alloy mentioned is suitable for bearing and sliding applications, in particular also for bearing shafts or journals made of aluminum material. In this special brass alloy, special attention was paid to its corrosion resistance.

Cu-Zn alloys with improved machinability properties are known from EP 3 690 069 C1. This alloy contains 58 to 70% by weight Cu, 0.5 to 2.0% by weight Sn, 0.1 to 2.0% by weight Si, the balance zinc and unavoidable impurities, the sum of the elements Sn and Si being 1.0% by weight and 3.0% by weight, respectively. The improvement of machinability without the use of elements Pb and Bi is provided by the Sn and Si contents in these alloys. In certain proportions, these elements are responsible for the formation of the ε phase, which is distributed as a microstructure in the alloy, thus promoting chip fracture. The Si contained in the alloy also forms silicides, specifically with Mn and/or the elements Al and Ni allowed in the alloy, which are regularly found in alloys due to the general use of recycled materials. The Si content in this conventionally known alloy may be 2.0% by weight. It is true that the silicides contained in the matrix are advantageous for some applications, especially when requirements for abrasion resistance exist.

JP S 56 127741 A1 discloses a Cu—Zn alloy with improved wear resistance under more extreme sliding conditions. This alloy comprises 54 to 66 wt% Cu, 1.0 to 5.0 wt% Al, 1.0 to 5.0 wt% Mn, 0.2 to 1.5 wt% Si, 0.5 to 4.0 wt% Ni, 0.1 to 2.0 wt% Fe, 0.2 to 2.0 wt% It has a composition of the remainder Zn together with Sn and unavoidable impurities. These alloys have special Ni and Fe inclusions to form manganese silicides. Sn inclusions are used to improve the strength and toughness of the raw product. No other elements are allowed in these alloys. No information is provided on the machining behavior of these alloys.

WO 2015/117972 A2 discloses in weight percentages 54 to 65% Cu, 2.5 to 5.0% Al, 1.0 to 3.0% Si, 2.0 to 4.0% Ni, 0.1 to 1.5% Fe, up to 1.5% Mn, up to 1.5% A lubricant-compatible copper alloy is disclosed having a composition of Sn, up to 1.5% Cr, up to 0.8% Pb, the balance Zn with unavoidable impurities. The composition of these previously known Cu—Zn alloys is chosen such that at least 0.4% free Si is present. As such silicon is not bound to a silicide, it may also be contained in a silicon-containing non-silicide phase. Also, no other elements are allowed in these alloys. In these alloys, through the use of different oils in different tribological systems, the emphasis is placed on the use of components made therefrom in an oil environment, ... in a synchronizer ring. No information on machinability is provided in relation to this prior art.

DE 10 2017 007 138 B3 relates to aquaculture material, in particular a wire material and a net made therefrom or a breeding cage made therefrom. Information on machining behavior is of course not provided due to the intended use. Exemplary embodiments described in this document have the following composition: 63.8 to 65.5 wt% Cu, 0.9 to 1.1 wt% Sn, 0.2 to 0.3 wt% Fe, 0.15 to 0.2 wt% P, balance Zn, and in one sphere In, 0.6 wt% Al. In this composition, the wire material should have, for aquaculture resistance, a first oxide layer partially covering the metallic material, and a second oxide layer covering the metallic material in areas not covered by the first oxide layer. do.

Based on the prior art discussed above, the present invention can be used as a lead-free Cu—Zn alloy, in particular a base alloy, with improved machinability properties and does not require any special fabrication steps to form the desired machining properties. It is based on the purpose of proposing a lead-free Cu-Zn alloy that does not

1 is a table showing the composition of the specimen tested in the present invention.

According to the present invention, this object is

- Cu: 58 to 64%

- Fe: 0.4 to 1.4%

- Mn: 0.4 to 2.3%

- Ni: 1.5 to 3.5%

- Al: 0.1 to 4.4%

- Si: 0.5 to 1.8%

- the following alloying elements to promote chip breakage:

Sn 0.65 to 1.2%, wherein the structure of the alloy contains up to 0.025% P, or

P 0.03 to 0.1% (wherein Sn inclusions up to 0.25% are allowed)

- the remainder consisting of Zn with unavoidable impurities (a maximum of 0.05% per element is allowed for unavoidable impurities, and the sum of unavoidable impurities does not exceed 0.15%);

- Pb: consists of up to 0.1% (data given in wt%)

- achieved by lead-free Cu-Zn based alloys, where up to 0.035% of Cr is allowed.

In the context of this description, alloys are referred to as base alloys, wherein alloy products with different properties can be provided by varying the alloying elements in one and the same fabrication process. These alloys have the advantage that contamination is minimized when the alloy is melted when alloy products with different properties are manufactured.

An unavoidable impurity is allowed at 0.05% by weight per element, whereby the sum of unavoidable impurities does not exceed 0.15% by weight.

In the context of the claimed invention an alloy is considered lead-free if its Pb content does not exceed 0.1% by weight.

These alloys may contain P to achieve the desired improved machinability properties. When the alloy contains P, manganese and iron phosphides are formed at grain boundaries, which significantly improve the machinability compared to the alloys CuZn28Al4Ni3Si1Mn and CuZn35Mn2Ni2FeSi. Since the alloy also contains Si, silicides are also formed in the matrix, usually with the inclusion of the elements Fe, Mn, and also Ni and Al. Silicides contribute to abrasion resistance, but together with phosphides, they also promote machinability. The grain sizes of phosphides and silicides are relatively small, so tool wear can be kept low during machining.

When P is contained as an alloying component that promotes chip breakage, it is contained in a proportion of 0.03 to 0.1% by weight. Accordingly, the P content is limited to 0.1% by weight. When the P content is high, coarser phosphides are formed, which also presents disadvantages in machinability and surface processing, such as polishing or coating the surface of the workpiece after the machining process. These disadvantages are not compensated for by improved wear resistance when the manufactured alloys focus on optimization of machinability. The P-containing Cu-Zn based alloy is a first variant of the alloy according to the invention.

According to the second variant of this alloy, as an alloy component that promotes chip fracture, Sn is included in the structure of the alloy in a proportion of 0.65 to 1.2 wt%. Sn is incorporated into the mixed crystal below the solubility limit. The Sn content in this alloy is limited to 1.2% by weight, since otherwise there is a risk of Sn-containing γ phase formation. These have a brittle effect. This increases work hardening and strength, and thus has a beneficial effect on chip fracture and thus the machinability of workpieces made from these alloys. Also, Sn tends to form Sn oxides during dry machining, which migrate to the tool surface and thereby reduce tool wear. The Sn content preferably coincides with the Fe content ± 20%.

In one embodiment of the present invention, P and Sn are jointly included in the structure of the alloy. When using P, it is advantageous for the melt to solidify in a fine-grained manner. However, P has the disadvantage of making the melt less viscous. Sn counteracts this behavior without adversely affecting the positive structure-forming properties of P in the melt. Sn can also have a deoxidizing effect in the melt, which is advantageous for both P and no P alloys.

When machining workpieces made from these alloys, the broken chips usually have the desired chip shape (broken chips or very small spiral chips). Accordingly, the chip shape is consistent with that found in machining operations of CuZn39Pb3 alloys, which are considered particularly good for machining.

Surprisingly, it has been found that in these alloys, phosphides act as oxidation inhibitors of the structure, especially at elevated temperatures.

The contents of the elements Fe and Mn are limited to the stated contents. If more Fe or Mn is used, this results in coarsening of the grains. Below the stated limits, the desired phosphides do not develop to a sufficient extent to achieve machinability-improving properties.

The permissible concomitant elements do not, at least insignificantly, affect the improvement of the machinability of the workpiece produced from the alloy according to the invention. Accordingly, recycled materials can be used to make these alloys without accepting any disadvantages. For this purpose, preferably recycled material from a closed cycle is used, ie a single-type recycled material is used. For example, with respect to its composition, if one or more elements are not present, or if a recycled material is used which is not present in an appropriate proportion, these elements may be added to the recycled material. This applies in particular to the element P essential for the invention, which is not normally present when using conventional recycled materials.

A special feature of the alloy according to the invention is that the improved machinability is based solely on the specific composition of the alloy and no further measures such as specific fabrication or processing steps are required. Accordingly, the semi-finished product (workpiece) manufactured from the alloy can be manufactured using a general manufacturing process. It also has the advantage that individual processing steps can be carried out to set specific strength and/or structural properties in order to process the semi-finished product to produce the final product. Accordingly, they are not yet consumed by the manufacturing process for producing semi-finished products. In this context, improved machining properties are achieved without further process steps, but it goes without saying that if desired these can be increased again after extrusion via special treatment steps. Machining properties can be improved, for example, by cold deformation and associated work hardening, since this improves chip breakage and thus machinability. This may be followed by a stress relief annealing to reduce the internal stress. This process step can also be carried out in order to influence the microstructure, for example, by setting the α/β microstructure as fine and heterogeneous as possible or in the precipitation phase, for example very fine silicides or α in the β-matrix. -Can be used to create a precipitate.

A first variant of the alloy according to the invention has the specified elements in the following amounts:

- Cu: 59 to 63% by weight, in particular 59.5 to 61% by weight

- Fe: 0.4 to 1.1% by weight, in particular 0.6 to 1.1% by weight

- Mn: 0.4 to 1.1% by weight, in particular 0.6 to 1.0% by weight

- Ni: 2.5 to 3.7% by weight, in particular 2.6 to 3.3% by weight

- Al: 3.3 to 4.2% by weight, in particular 3.5 to 4.1% by weight

- Si: 1.0 to 1.8% by weight, in particular 1.1 to 1.7% by weight

This variant of the alloy according to the invention is designed for high strength values in the workpiece. Accordingly, these alloys have relatively high Si content and higher elemental Ni and Al content.

According to a second variant of the alloy according to the invention, the alloy contains the following elements in the specified proportions:

- Cu: 60 to 62.5 wt%

- Fe: 0.8 to 1.4% by weight, in particular 0.85 to 1.25% by weight

- Mn: 1.4 to 2.3% by weight, in particular 1.5 to 2.1% by weight

- Ni: 1.5 to 2.5% by weight, in particular 1.7 to 2.35% by weight

- Al: 0.1 to 0.7% by weight, in particular 0.2 to 0.5% by weight

- Si: 0.5 to 1.2% by weight, in particular 0.6 to 1.0% by weight

Ultimately, using the same alloying elements as the first variant, these alloys are significantly softer and have lower strength properties and, therefore, are suitable for other applications.

These two variants already exemplify the scope of the base alloy according to the present invention, in which workpieces with different strength properties can be manufactured simply by changing the elements and without changing the fabrication process.

The deformation of the elements also affects the structure, since they have different zinc equivalents and therefore both workpieces with predominantly β-phases and structures with α-phases embedded in β-phases. can be made from these alloys. The former is also characterized by good hot formability and also by a specific cold formability depending on the α-component, whereas the latter is more suitable for cold forming.

exam

Specimens from the alloys provided in Table 1 were formed into rods by continuous casting and subsequent extrusion, then straighten, and then subsequently thermally relaxed. Alloys 1 to 6 are alloys according to the present invention, alloys 1 to 3 belong to the first variant, and alloys 4 to 6 belong to the second variant.

Specimens were cut from semi-finished products having a cylindrical outer surface. Machining tests were performed uniformly on all specimens by external longitudinal turning at a cutting speed of 200 m/min with a cutting depth of 1 mm and a feed of 0.1 mm.

The test results were evaluated in the form of an index from 0 to 100. In this system, the comparative alloy CuZn42 has an index of 50 for various cut indices. The higher the index, the better the result.

Chip shape, cutting force, tool wear, and surface quality due to cut were tested.

The test results are provided in the table below:

A somewhat higher cutting force is required to cut the alloy according to the invention. The reason is that the alloy contains phosphides, but this contributes to better chip breakage and thus overall improved machinability. With regard to the machinability, the chip shape is a relevant factor and therefore, in this regard, a somewhat higher cutting force can be tolerated compared to the Pb-containing comparative alloy.

It is important that the alloy according to the invention has an improved tool wear index compared to the CuZn42 alloy. This was unexpected.

The surface quality of the alloy according to the invention is substantially consistent with that achieved with the two comparative alloys, and therefore no disadvantages, at least notable disadvantages, should be tolerated in this regard.

The mechanical strength values of the alloys according to the invention prepared by the above-described processes, i.e., continuous casting, extrusion, straightening, thermal stress relaxation, are shown as examples for alloy 1 and alloy 4 in the table below, and comparison The strength values of the alloys were compared:

The mechanical properties listed in the table above of the alloys according to the invention in comparison with alloys from the prior art make it clear that the improved machinability of the alloys according to the invention does not adversely affect the mechanical strength values. In principle, these correspond to the values of the individual reference alloys.

Due to the positive structural properties already established during pressing, semi-finished products made from alloys can be used for a wide variety of applications.

Claims (9)

- Cu: 58 to 64%
- Fe: 0.4 to 1.4%
- Mn: 0.4 to 2.3%
- Ni: 1.5 to 3.5%
- Al: 0.1 to 4.4%
- Si: 0.5 to 1.8%
- the following alloying components to promote chip breaking:
Sn 0.65 to 1.2% (wherein the structure of the alloy contains P, i.e., up to 0.025%), or
P 0.03 to 0.1% (here, up to 0.25% Sn inclusion is allowed)
- the remainder consisting of Zn together with unavoidable impurities (unavoidable impurities are allowed up to 0.05% per element, and the sum of unavoidable impurities does not exceed 0.15%);
- Pb: consists of up to 0.1% (data given in wt%)
- Lead-free Cu-Zn based alloys with up to 0.035% Cr allowed. The alloy of claim 1 , wherein the alloy
- Cu: 59.5 to 61 wt%
- Fe: 0.4 to 1.1 wt%
- Mn: 0.4 to 1.1 wt%
- Ni: 2.5 to 3.7 wt%
- Al: 3.3 to 4.2% by weight
- Si: Cu-Zn-based alloy, characterized in that it contains 1.0 to 1.8 wt%. 3. The method of claim 2,
- Fe: 0.6 to 1.1 wt%
- Mn: 0.6 to 1.0% by weight
- Ni: 2.6 to 3.3 wt%
- Al: 3.5 to 4.1 wt%
- Si: from 1.1 to 1.7% by weight of an alloy based on Cu—Zn. The alloy of claim 1 , wherein the alloy
- Cu: 60 to 62.5 wt%
- Fe: 0.8 to 1.4% by weight
- Mn: 1.4 to 2.3 wt%
- Ni: 1.5 to 2.5 wt%
- Al: 0.1 to 0.7 wt%
- Si: Cu-Zn-based alloy, characterized in that it contains 0.5 to 1.2% by weight. 5. The method of claim 4,
- Fe: 0.85 to 1.25 wt%
- Mn: 1.5 to 2.1% by weight
- Ni: 1.7 to 2.35 wt%
- Al: 0.2 to 0.5 wt%
- Si: from 0.6 to 1.0% by weight, a Cu-Zn based alloy. 6 . The Cu-Zn based alloy according to claim 2 , characterized in that the alloy contains from 0.03 to 0.1% by weight P and a maximum of 0.25% by weight of Sn is allowed. The Cu-Zn based alloy according to claim 6, characterized in that the alloy contains from 0.05 to 0.08% by weight of P. 6 . The Cu-Zn based alloy according to claim 2 , characterized in that the alloy contains from 0.65 to 1.2% by weight Sn and a maximum of 0.02% by weight P is allowed. The Cu-Zn based alloy according to claim 8, characterized in that the alloy contains 0.7 to 1.1 wt% Sn.

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