KR20220057455A - LEAD-FREE Cu-Zn BASE ALLOY - Google Patents

Abstract

Provided is a lead-free Cu-Zn-based alloy which comprises: 57 - 59.3 wt% of Cu; 0.12 - 0.17 wt% of Fe (a first alternative example) or a maximum of 0.06 wt% of Fe; 0.3 - 0.7 wt% of Mn (a second alternative example); 0.03 - 0.1 wt% of P; a maximum of 1.0 wt% of Sn; a maximum of 0.1 wt% of Pb; a remnant consisting of unavoidable impurities which account for a maximum of 0.05 wt% for each element (a total of the unavoidable impurities is no greater than 0.15 wt%) and Zn; and the following elements, such as a maximum of 0.03 wt% of Ni, a maximum of 0.05 wt% of Al, a maximum of 0.01 wt% of Si, and a maximum of 0.01 wt% of Cr, wherein the lead-free Cu-Zn-based alloy has improved properties of machining, compared to CuZn42 alloy.

Description

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

An object of the present invention is a lead-free Cu-Zn alloy with improved machinability compared to CuZn42 alloy.

Due to the small number of elements included in the structure of the alloy, the CuZn42 alloy is a very simply structured brass alloy with a Cu content of 57.0 to 59.0% by weight. In principle, no other elements are included in these alloys. Up to 0.2 wt% of Pb, along 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 CuZn42 alloy is lead-free, it is also used, due to its α/β microstructure, 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 leeways. In this case, the machinability of these alloys is not satisfactory.

Although machinability for certain machining operations on workpieces made from these alloys is acceptable, unless the Pb and Bi elements commonly used in free cutting alloys are used to achieve the desired machinability, the It would be desirable for the machinability to be improved in this way, since these elements are classified as hazardous to health.

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 the elements Pb and Bi is provided by the Sn and Si inclusions 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. While silicides contained in the matrix are advantageous for some applications, particularly when wear resistance requirements exist, silicides can be notable for machinability due to increased tool wear.

JP H 03 253527 A discloses a Cu—Zn alloy for manufacturing an electric fuse. A number of alloys are disclosed in this prior art. One of the disclosed alloys comprises 25 to 40 wt % Zn, 0.01 to 0.1 wt % P, 0.02 to 0.50 wt % Fe, the balance Cu with unavoidable impurities. According to an alternative embodiment, the element Fe is replaced by the elements Co, Ni, or Mn, respectively, in equal proportions. Accordingly, such previously known alloys may have a Cu content of 59.4 to 75% by weight. Embodiments provided for Fe variants of these previously known alloys have an Fe content of 0.03 to 0.12% by weight. Except for unavoidable impurities, no other elements are allowed. This also applies to Co, Ni and Mn variants. In addition to the above-mentioned suitability as a material for making electric fuses, these materials also exhibit good strength and spring properties.

JP S 59153856 A discloses a Cu—Zn alloy with improved corrosion resistance for fabricating a heat exchanger. This alloy has the following composition: 25 to 40 wt % Zn, 0.005 to 0.070 wt % P, 0.05 to 1.0 wt % Sn, 0.005 to 1.3 wt %, total 0.005 to 1.0 wt % Fe and/or 0.005 to 0.3 wt % Pb , the remainder of copper plus inevitable impurities. These previously known Cu—Zn alloys also have a wide range, ie, 57.9 to 74.9, in Cu content. The grain size of this previously known alloy is controlled to be 15 μm or less. The P content is provided to achieve the desired properties. Alloy 12 of Table 1 has the following composition: 63.8 wt% Cu, 0.1 wt% Fe, 0.07 wt% P and 1.0 wt% Sn, balance Zn. Mn is not an approved alloying element in these previously known alloys.

Accordingly, on the basis of this prior art discussed in the introduction, the present invention is based on the object of presenting a lead-free Cu-Zn alloy with improved machinability properties compared to CuZn42 alloy, wherein this presented alloy is a simple It has a structure and does not require any special fabrication steps to achieve the desired good machinability.

1 shows a chip shape obtainable with an alloy according to the present invention.

According to the present invention, this object is a lead-free Cu-Zn alloy having improved machinability properties compared to CuZn42 alloy,

- Cu: 57 to 59.3%

- Fe: 0.12 to 0.17% (first alternative) or

Fe: at most 0.06% and Mn: 0.3 to 0.7% (second alternative)

-P: 0.03 to 0.1%

- Sn: up to 1.0%,

- Pb: max. 0.1%;

- consisting of the remainder consisting of Zn with unavoidable impurities (unavoidable impurities allow up to 0.05% per element, the sum of unavoidable impurities not exceeding 0.15%) (data are given in wt%);

- the following elements are achieved by a lead-free Cu-Zn alloy which allows up to the specified content:

Ni: 0.03% max;

Al: up to 0.05%;

Si: up to 0.01%;

Cr: 0.01% max.

An unavoidable impurity is allowed at 0.05% by weight per element, wherein the sum of the 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.

This alloy contains P such that iron phosphide or manganese phosphide is formed, depending on the design of the alloy under the first alternative or the second alternative. The addition of phosphorus in this proportion has a positive effect on casting, since phosphorus has a grain-reducing effect. This has a positive effect on the desired improved machinability. In this context, it is important that the workpiece produced from the alloy has a fine grain without requiring additional processing such as water quenching after pressing. Due to the composition of the claimed alloy, the extruded semi-finished product already has a sufficiently fine grain. In addition, the finely divided phosphide contained in the matrix has a chip breaking effect. The chips produced during machining of workpieces made of these alloys are significantly better than those produced during machining of CuZn42 alloys due to their chip shape (brittle chips or very short spiral chips), lead-containing machining Very similar to that produced during machining of CuZn39Pb3 alloy. Despite the addition of phosphorus to form phosphides, it is essential that the strength properties of articles made from these alloys match those of the comparative CuZn42 alloy. Besides improved chip fracture, the surface quality obtained by machining is similar to that obtained by machining the leaded alloy CuZn39Pb3. It is surprising to observe this, as low surface quality was actually expected due to the phosphides distributed in the matrix and thus due to the more heterogeneous matrix compared to the CuZn42 and CuZn39Pb3 alloys.

Likewise, phosphides may not be expected to act as inhibitors of recrystallization of microstructures, especially at elevated temperatures.

Accordingly, the P content is limited to 0.1% by weight. At higher P content, grain roughening of the phosphides occurs. This is disadvantageous not only for machining, but also for certain surface treatments such as polishing or coating. Although coarser phosphide improves the wear resistance of workpieces produced from the alloy, it does not compensate for the other disadvantages mentioned above. When the P content is less than 0.03% by weight, the above-mentioned advantageous properties occur only insufficiently or not at all.

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

Sn can be involved in alloying and support machinability. Sn is also advantageous in terms of the formation of a melt. The inclusion of P dilutes the melt. Sn works in the opposite way. In addition, Sn in the melt may have a deoxidizing effect. Sn is incorporated below the solubility limit in the mixed crystals in the alloy. Otherwise, there is a risk that a Sn-containing γ-phase is formed, which has a brittle effect on the alloy product. When Sn is used as the alloying element, the improved machinability is due, on the one hand, to the effect of the phosphides described above and, on the other hand, to the mechanism of action of Sn. Both mechanisms of action complement each other. The inclusion of Sn also aids in dry machining by forming Sn oxide, which reduces tool wear as the oxide moves protectively to the tool surface. Especially in the case where a simple alloy structure is desired, the working principle based on Sn favoring machining can be eliminated. In this embodiment, Sn is not used as an alloying element and is only allowed in a proportion of up to 0.1% by weight.

The permissible concomitant elements do not affect, 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 element P, which is essential for the invention and is generally not present when using customary recycled materials.

The zinc equivalent weight of the alloy according to the invention is approximately 39 to 42, so that the alloy product has an α/β structure. The zinc equivalent is typically slightly lower compared to the CuZn42 alloy and, consequently, the formation of the α-phase is favored over the comparative alloy. This has a positive effect on the cold formability of articles (workpieces) made from these alloys. This is taken into account because the elements Fe and/or Fe and Mn have reduced the zinc equivalent only to the extent that the cold formability is improved, but the good hot formability known from the CuZn42 alloy is still maintained, and also the phosphides already described above are formed. .

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 machinability properties are achieved without further processing steps, but, if desired, they increase again after extrusion through special treatment steps, for example chip breaking and thus cold forming to improve machinability. Needless to say it could be.

exam

From the alloys specified below (data given in weight %):

Specimens were prepared by casting and subsequent extrusion into bar stock, each having a diameter of 40 mm, stretched after extrusion. Machining tests were performed on specimen pieces. Alloys 1 to 3 are alloys according to the present invention.

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:

To illustrate the chip shape obtainable with the alloy according to the present invention, reference is made to Fig. 1 , which is a chip of comparative alloy CuZn39Pb3 (left) and alloy 1 according to the present invention (right) showing the desired chip fracture shape. A comparison of destruction is shown. This comparison illustrates that the alloy according to the present invention achieves a significantly improved chip shape compared to the lead-free comparative alloy CuZn42. The chip shapes of machined alloys 2 and 3 match those shown in FIG. 1 for alloy 1.

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, somewhat higher cutting forces can be tolerated compared to comparative alloys.

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 are given in the table below:

It is clear that these mechanical properties of the semi-finished product made from the alloy according to the invention, obtained from the specimen under pressure conditions, have significantly improved tensile strength and higher hardness compared to the comparative alloy. The elongation at break is similar to the elongation at break of the comparative alloy. This applies to the yield strength, which is significantly higher for alloy 3 than the yield strength determined for the comparative alloy. Accordingly, in spite of the improved machinability, it is not necessary to accept any disadvantages with respect to the mechanical strength values of the alloys according to the invention. Instead, these are even improved.

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 (5)

As a lead-free Cu-Zn alloy with improved machinability compared to CuZn42 alloy,
- Cu: 57 to 59.3%
- Fe: 0.12 to 0.17% (first alternative) or
Fe: at most 0.06% and Mn: 0.3 to 0.7% (second alternative)
-P: 0.03 to 0.1%
- Sn: up to 1.0%,
- Pb: max. 0.1%;
- consisting of the remainder consisting of Zn with unavoidable impurities (unavoidable impurities are allowed up to 0.05% per element, the sum of unavoidable impurities not exceeding 0.15%) (data are given in wt%);
- lead-free Cu-Zn alloys, in which the following elements are allowed up to a certain amount:
Ni: 0.03% max;
Al: up to 0.05%;
Si: up to 0.01%,
Cr: 0.01% max. The Cu-Zn alloy according to claim 1, characterized in that the Fe content in the alloy according to the first alternative is between 0.13 and 0.15%. The Cu-Zn alloy according to claim 1, characterized in that the Fe content in the alloy according to the second alternative is not more than 0.04% and the Mn content is 0.35 to 0.55%. 4. Cu-Zn alloy according to any one of the preceding claims, characterized in that the P content is between 0.05 and 0.08%. Cu-Zn alloy according to claim 1 or 2 according to the first alternative, characterized in that the alloy has a Sn content of 0.8 to 1.0%, and its P content is at most 0.04%.

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