BRASS ALLOY AND METHOD FOR PRODUCING A SEMI-FINISHED PRODUCT FROM THIS BRASS ALLOY

Description

[0001] The invention relates to a brass alloy for producing semi-finished products for machining and to a method for producing a semi-finished product intended for machining.

[0002] Brass is an alloy of copper and zinc. Zinc contents of 5–45 wt.% are common. To improve machinability, the alloy may contain lead, as well as other alloying elements such as aluminum, iron, manganese, nickel, silicon, or tin, which primarily serve to increase strength and improve sliding properties and corrosion resistance. The added alloying elements determine the processing options and manufacturing processes, with production as a wrought alloy being the most important form in practice. Typical processing involves primary forming in continuous or discontinuous casting plants, forming by extrusion or rolling and drawing, and subsequent thermal treatment. In this way, semi-finished products are manufactured in the form of bars, hollow rods, or strips, which are then further processed into various geometries, such as wires.With their specifically adjusted material properties, they are used to create products for applications such as plumbing, electrical applications, and mechanical and automotive engineering. Copper-zinc casting alloys are produced using sand, permanent mold, centrifugal, continuous, and pressure die casting processes.

[0003] Brass alloys with less than 37% zinc exhibit a homogeneous alpha microstructure with a face-centered cubic spatial lattice at room temperature. In alloys with more than 37 wt.% zinc, a beta microstructure also occurs as a second phase. In the beta phase, the atoms of the crystal lattice are arranged in a body-centered cubic spatial lattice. Body-centered cubic spatial lattices have fewer slip planes, so this structural component exhibits less plasticity. At 37-46 wt.% zinc, the brass material contains both alpha and beta phases. The proportion of the beta phase in the overall microstructure (alpha + beta microstructure) increases with the zinc content. The beta microstructure significantly alters the material properties of the brass alloy. The gamma phase can also occur, the brittleness of which must be taken into account when larger proportions are present in the microstructure.

[0004] The previously mentioned classification of microstructures also results when approximately 1.5 - 3.5 wt.% lead is added to the alloy. Lead in these quantities is insoluble in a copper-zinc alloy. Lead inclusions form, which act as chip breakers, thereby improving machinability. Brasses with higher zinc contents are influenced in terms of their material properties, in particular by the content of other alloying elements, such as the addition of aluminum, tin, nickel, iron, silicon and manganese. These additives shift the phase boundaries of the copper-zinc system with their alpha and beta components. They influence the composition and properties of the microstructure. In general, the alloying elements serve to improve strength, sliding and wear properties and corrosion resistance.

[0005] For environmental reasons, the lead content in brasses should be kept as low as possible. For example, the material CuZn21Si3 does not contain lead. Instead, silicon and the resulting silicides are used as chip breakers. This is a special brass with a low Zn content and a relatively high Si content. This creates a separate material class with a strictly separate material cycle. Processing these materials requires a modified manufacturing process and demonstrates improved machinability in further processing, but only with significant process adjustments.

[0006] Furthermore, the machinability of brass materials can be increased by adding bismuth (Bi). However, the addition of bismuth is viewed with skepticism in processing. Bismuth can lead to severe embrittlement. Even trace contamination in other wrought copper-zinc materials can lead to catastrophic failures. Therefore, the addition of bismuth is not accepted in Europe, and Bi-containing materials are rarely used.

[0007] It is known that tellurium acts as a chip breaker through the formation of high-melting tellurides in copper-zinc alloys, thus improving machining properties. However, tellurium is also a highly sought-after material in other technological areas, so it cannot be used economically to improve the machinability of brass materials.

[0008] DE 10 2009 038 657 A discloses a brass alloy that is essentially lead-free, but requires a mandatory combination of iron, nickel, and tin. The mandatory nickel content can lead to the most common form of contact allergy, the so-called nickel allergy, upon contact with the skin. Nickel allergy causes a rash, so alloys made from these materials cannot be used for applications where skin contact cannot be ruled out.

[0009] DE 10 2015 212 937 A1 discloses a brass alloy containing indium. This brass alloy is intended to achieve good machinability. The brass alloy is intended to provide sufficient mechanical properties and minimize wear on the tools used. Indium is intended to replace the previously used lead while achieving the same advantages, so that the lead content in the brass alloy can be reduced to zero in extreme cases, while the brass alloy still remains very easy to machine. The nickel content is preferably 0.2 to 0.3 wt.% to stabilize the alpha phase.

[0010] EP 3 529 389 B1 discloses a special brass alloy that is said to be particularly suitable for the production of electrically conductive components, such as contacts as parts of connectors, and is said to be characterized by improved mechanical properties and improved electronic conductivity. The alloy contains at least two silicide-forming elements from the group consisting of Mn, Fe, Ni, and Al, each containing a maximum of 0.15 wt.%, as well as a maximum lead content of 0.1 wt.%. With a maximum permitted content of 0.1 wt.%, this alloy is still considered lead-free.

[0011] The invention is based on the object of providing a brass alloy for the production of semi-finished products for machining, which possesses sufficient machinability and thus sufficient strength, sufficient ductility, and sufficient electrical conductivity. Said brass alloy should be economically producible and, despite its sufficient machinability, avoid high silicon contents and be as free from bismuth as possible so that the alloy does not lead to trace contamination in other copper-zinc wrought materials. Furthermore, it should comply with future environmental regulations, i.e., in particular, it should be lead-free or essentially lead-free (Pb < 0.1 wt%).

[0012] This object is achieved with a brass alloy according to the features of patent claim 1.

[0013] A method for producing a semi-finished product intended for machining is the subject of patent claim 12.

[0014] The respective subclaims relate to advantageous developments of the invention.

[0015] According to the invention, a brass alloy for the production of semi-finished products for machining is proposed, wherein the brass alloy consists of the following alloying elements in wt.%: Cu 54,0 - 59,0 Zn 40,5 - 46,0 Pb 0,02 - 0,10 Fe 0,10 - 0,50 Mn 0,10 - 0,50 Sn 0,10 - 0,60 P < 0,20 optional S 0,010 - 0,030 Si 0,020 - 0,20 Co ≤ 0,30 The < 0,50 and melting-related impurities below 0.20, with the proportion of Ni in the melting-related impurities being less than 0.080. It is a copper-zinc alloy with a copper content of 54-59% and a zinc content of 40.5-46% as the main alloying components. The material is essentially lead-free, as the lead content is limited to a maximum of 0.10 wt.%. The minimum content is 0.02 wt.%.

[0016] A further characteristic of the brass alloy according to the invention is the combination with small amounts of other alloying elements, which serve to simultaneously or optionally stabilize the beta microstructure, with the aim of promoting machinability. The beta microstructure is crucial for the strength and machinability of the material due to its body-centered cubic crystal structure, which has a chip-breaking effect and thus promotes machinability.

[0017] The addition of alloying elements utilizes both solid solution strengthening and precipitation hardening as strengthening mechanisms. Machinability is significantly improved compared to lead-free brass alloys without the addition of these alloying elements.

[0018] Stabilization of the beta phase is achieved by reducing the alpha-stabilizing nickel content. Nickel is avoided as much as possible and, due to unavoidable impurities resulting from the melting process, should not exceed a maximum of 0.08 wt.%, and is not deliberately added to the alloy. Stabilization of the beta phase can also be achieved through targeted temperature control during the first hot-forming process step. Reducing the nickel content also has the effect of preventing the alloy according to the invention from triggering a nickel allergy. This improves the handling and application-related benefits of the brass alloy.

[0019] The alloying elements iron and manganese are deliberately added to increase the basic strength values ​​of yield strength and tensile strength of the brass alloy according to the invention; furthermore, the material properties are determined by subsequent cold forming and heat treatments. Iron is used as a microstructure-refining element, which initially has a positive effect on a homogeneous, less coarse-grained structure. Furthermore, iron has a favorable influence on machinability, especially in combination with other effects. The minimum proportion of 0.10 wt.% should not be undercut in order to achieve a significant stability effect on the structure in combination with other alloying elements. Excessively high proportions of iron greater than 0.5 wt.% could, depending on the choice of thermal processing parameters, negatively lead to larger precipitations, especially in combination with manganese.

[0020] The brass alloy according to the invention optionally contains silicon, albeit in very limited proportions. Compared to the known brass alloys with a high silicon content of 2-3 wt.%, the Si content should be limited to 0.020 - 0.20 wt.%. This very small addition of silicon leads to the formation of a few silicides, particularly in the form of iron silicides. Iron silicides have a positive effect on machinability. However, it has surprisingly been shown that the combination with the other measures mentioned leads to relatively good machinability, even when the silicon content is limited to values ​​below 0.20. The alloying element manganese is completely soluble in copper due to its great similarity and contributes to increasing the strength of the brass alloy through the effect of solid solution formation. This is surprising in the absence of silicon, given the non-existent or very low silicon content of max.0.20% only very few manganese silicides can be formed.

[0021] By deliberately omitting nickel, a small amount of cobalt is optionally added, which is, however, limited to a maximum of 0.30 wt.% and preferably does not exceed 0.1 wt.% in order not to cause excessive inhibition of recrystallization in the interaction with manganese.

[0022] The brass alloy according to the invention contains tin. Tin is highly soluble in copper and zinc. Although tin is usually added to the alloy as an element that favorably influences corrosion behavior, this plays only a minor role in the brass alloy according to the invention. Rather, the addition of tin ensures that tin is absorbed into the solid solution, since the removal of nickel means fewer copper atoms are directly replaced in the crystal lattice. Therefore, the tin content is relatively high at up to 0.6 wt.%.

[0023] It is emphasized that the combination of manganese, iron and tin in particular has a strength-enhancing effect, which, due to the lack of larger silicide contents, was recognized as particularly favorable for the material properties to be adjusted later, especially in the concentration ranges claimed according to the invention of Fe with 0.10 - 0.50 wt.%, Mn with 0.10 - 0.50 wt.% and Sn with 0.10 - 0.60 wt.%.

[0024] Surprisingly, the absence of nickel in particular has increased the possibility that the three elements Mn, Fe, and Sn, in combination, have a positive effect on a relatively higher-strength alpha-beta microstructure. This higher microstructural strength can apparently replace, as an alternative, albeit not to quite the same extent, the machining effect otherwise induced by microstructural particles such as lead, nickel, or silicides.

[0025] For regulatory and environmental reasons, the lead content is limited to a maximum of 0.10 wt.%. Even at lower levels, lead has a relatively positive influence on machinability, although the influence decreases with decreasing lead content.

[0026] The alloy according to the invention contains phosphorus up to a maximum of 0.20 wt.%. Phosphorus has a beneficial effect on the molten liquid during the casting process and, in the absence of nickel and silicon, surprisingly plays a positive role by forming extremely fine phosphides, which, in addition to the effects of other alloying elements, have a positive additive effect on the machining behavior used to evaluate the alloy.

[0027] Arsenic is not used for environmental reasons.

[0028] The brass alloy according to the invention contains melting-related impurities or manufacturing-related admixtures in a total proportion of less than 0.20 wt.%, whereby the proportion of Ni is attributable to the melting-related impurities due to the special alloy composition and amounts to less than 0.080 wt.%. The melting-related impurities or manufacturing-related admixtures are present only in such small proportions that undesirable side effects are avoided.

[0029] All element concentrations of the brass alloy according to the invention are designed to be particularly environmentally and user-friendly. The compositions are roughly based on the values ​​specified in the DIN EN 12164-12168 series of standards, but the specified ranges of element combinations may also lie outside the ranges defined therein.

[0030] Due to the above-described effects of the alloying elements on the brass alloy according to the invention, the proportion of Zn is preferably in a range of 41.50 - 42.50 wt.%. The proportion of Fe is preferably in a range of 0.20 - 0.40 wt.%. The proportion of Sn is preferably in a range of 0.20 - 0.40 wt.%. The proportion of Mn is preferably in a range of 0.10 - 0.30 wt.%. The proportion of Si is preferably in a range of 0.080 - 0.150 wt.%. The proportion of Co is max. 0.1 wt.%.

[0031] It is considered particularly advantageous if the sum of Fe + Mn + Sn is at least 0.450 wt.%, since the combination of these alloying elements increases the strength of the alloys in particular and eliminates the need for silicide components. The brass alloy according to the invention has a beta solid solution content of more than 71% and less than 78%. Preferably, it is around 75%; with beta solid solution contents of up to 70%, the machining-promoting effect of this microstructure component is not sufficiently utilized given the then relatively higher alpha microstructure component. The brass alloy according to the invention preferably has a Ni content of 0 wt.%, i.e., is nickel-free.

[0032] A preferred brass alloy with the above-mentioned properties has the following composition (all data in weight percent): Cu 57,60 - 58,00 Zn 41,50 - 42,50 Pb 0,02 - 0,10 Fe 0,20 - 0,40 Mn 0,10 - 0,30 Sn 0,20 - 0,40 P < 0,20 optional S 0,010 - 0,030 Si 0,080 - 0,150 Co 0,10 - 0,30 The < 0,50 and melting-related impurities below 0.20, with the proportion of Ni in the melting-related impurities being less than 0.080.

[0033] Optionally, the brass alloy according to the invention has the following composition (all values ​​in weight percent): Cu 57,60 - 58,00 Zn 41,50 - 42,50 Pb 0,02 - 0,10 Fe 0,26 - 0,34 Mn 0,10 - 0,15 Sn 0,26 - 0,34 P < 0,20 Si 0,030 - 0,060 optional S 0,010 - 0,030 Co 0,10 - 0,30 The < 0,50 and melting-related impurities below 0.20, with the proportion of Ni in the melting-related impurities being less than 0.080.

[0034] All of the brass alloys mentioned above are binary alloys containing copper and zinc. The alloys do not contain any other deliberately added alloying elements. The mentioned alloying elements add up to 100 wt.%. The brass alloy therefore consists of the mentioned alloying elements in the sense of a conclusive list. The proportions of copper and zinc are selected within the specified limits so that, with the other mandatory and optional alloying elements, including melting-related impurities of less than 0.2 wt.%, the total amount of 100 wt.% is achieved. For low copper contents of, for example, 54 wt.%, the weight fraction of zinc closes the gap to 100 wt.%. The same applies to a higher copper content. In this case, the zinc content is selected accordingly lower so that the gap is closed to 100 wt.%.The respective residual proportions of copper and zinc are within the weight percentage ranges specified in the respective patent claims or in the respective exemplary embodiments. The alloy is fully quantitatively and qualitatively defined by the residual content, such as Zn. The sum of all specified weight proportions always equals 100 wt.%.

[0035] The invention further relates to a method for producing a semi-finished product intended for machining, using a brass alloy according to the above features, wherein the brass alloy is extruded at a temperature between 550°C and 750°C. Extrusion should generally not be followed by a prolonged holding time with stagnant heat or insufficient cooling, but rather by intensive cooling within a few minutes. Accelerated cooling to a temperature below 450°C within 3 seconds is achieved, for example, with an air / water mixture.

[0036] The additional cooling creates a more machinable microstructure, depending on the requirements of the subsequent machining process. The relatively high quenching rate, starting from the extrusion temperature, creates a microstructure with a high beta content of approximately 75%. The quenching rate induces both precipitation and solid solution strengthening, resulting in the desired, sufficiently machinable material.

[0037] The material according to the invention, for the first time, creates an environmentally friendly and user-friendly material through its simultaneous freedom from lead (Pb < 0.1 wt.%) and nickel (Ni < 0.080 wt.%) while maintaining relatively good machinability. The process according to the invention allows the production of geometries in particular in the form of rods, hollow rods, and profiles using the brass alloy according to the invention.

[0038] The Figure 1 shows an image of tangled chips from a binary brass alloy CW510L or CuZn42. They represent the starting point of the brass alloy according to the invention and demonstrate unfavorable chip formation, which leads to problems in chip removal and thus causes susceptibility to failure during machining if higher demands are placed on the machining performance.

[0039] Under the same machining parameters, the Figure 2 The behavior of the material according to the invention during machining, here using the example of external turning. Favorable, short-breaking chips are present, which, in this direct comparison, essentially positively demonstrate the pure material effect on machinability.

[0040] The material according to the invention was evaluated using the usual machining parameters. Machining with external turning of round bars as part of routine production is carried out exemplarily in the example of Figures 1 and 2 on the same machines, under the same conditions, without specific adjustments to the machining parameters such as tool material, geometries, and machining parameters, such as cutting depth, speed, and coolant / lubricant strategy. The comparison is intended only to enable a relative evaluation of the materials in the individual case shown, without making an absolute statement regarding machinability. The material according to the invention, which is lead-free and therefore more environmentally friendly and also easier to handle due to its nickel-free nature, is significantly better suited for machining than the comparison material.

Claims

1. Brass alloy for manufacturing of semi-finished products for machining, wherein the brass alloy consists of the following alloy elements in percent by weight: Cu54.0 -59.0Zn40.5 -46.0Pb0.02 -0.10Fe0.10 -0.50Mn0.10 -0.50Sn0.10 -0.60P<0.20 optionally S0.010 -0.030Si0.020 -0.20Co≤0.30Te<0.50 and melt-related impurities below 0.20, wherein the proportion of Ni in the melt-related impurities is less than 0.080.

2. The brass alloy according to claim 1, characterized in that the proportion of Zn is 41.50 - 42.50 percent by weight.

3. The brass alloy according to any one of claims 1 or 2, characterized in that the proportion of Fe is 0.20 - 0.40 percent by weight.

4. The brass alloy according to any one of claims 1 to 3, characterized in that the proportion of Sn is 0.20 - 0.40 percent by weight.

5. The brass alloy according to any one of claims 1 to 4, characterized in that the proportion of Mn is 0.10 - 0.30 percent by weight.

6. The brass alloy according to any one of claims 1 to 5, characterized in that the proportion of Si is 0.080 - 0.150 percent by weight.

7. The brass alloy according to any one of claims 1 to 6, characterized in that the proportion of Co is max. 0.1 percent by weight.

8. The brass alloy according to any one of claims 1 to 7, characterized in that the sum of Fe, Mn and Sn is at least 0.450 percent by weight.

9. The brass alloy according to any one of claims 1 to 8, characterized in that the proportion of beta-phase crystals is more than 71% and less than 78%.

10. The brass alloy according to any one of claims 1 to 6, 8 or 9, characterized in that the brass alloy consists of the following alloy elements in percent by weight: Cu57.60 -58.00Zn41.50 -42.50Pb0.02 -0.10Fe0.20 -0.40Mn0.10 -0.30Sn0.20 -0.40P<0.20 optionally S0.010 -0.030Si0.080 -0.150Co0.10 -0.30Te<0.50 as well as melt-related impurities below 0.20, wherein the proportion of Ni in the melt-related impurities is less than 0.080.

11. The brass alloy according to any one of claims 1 to 6 and 8 to 10, characterized in that the brass alloy consists of the following alloy elements in percent by weight: Cu57.60 -58.00Zn41.50 -42.50Pb0.02 -0.10Fe0.26 -0.34Mn0.10 -0.15Sn0.26 -0.34P<0.20Si0.030 -0.060 optionally S0.010 -0.030Co0.10 -0.30Te<0.50 as well as melt-related impurities below 0.20, wherein the proportion of Ni in the melt-related impurities is less than 0.080.

12. Method for manufacturing a semi-finished product, intended for machining, using a brass alloy according to the features of any one of claims 1 to 11, wherein the brass alloy is extruded at a temperature between 550°C and 750°C and is cooled with air / water mixtures using accelerated cooling within 3 seconds to a temperature below 450°C.