Special brass alloys and special brass alloy products

Abstract

The invention relates to a special brass alloy having 62.5 to 65 wt% Cu, 2.0 to 2.4 wt% Mn, 0.7 to 0.9 wt% Ni, 1.9 to 2.3 wt% Al, 0.35 to 0.65 wt% Si, 0.3 to 0.6 wt% Fe, 0.18 to 0.4 wt% each of Sn and Cr, ≤0.1 wt% Pb and the balance Zn and unavoidable impurities.

Description

[0001] This application is a divisional application of an earlier application filed on October 29, 2018, with application number 201880098633.7 and invention title "Special Brass Alloy and Special Brass Alloy Products". Technical Field

[0002] This invention relates to a special brass alloy and products made from this special brass alloy. Background Technology

[0003] For friction applications typically conducted in lubricated environments, alloys with low coefficients of friction are generally required. Furthermore, these coefficients should be adjustable within a predetermined range depending on the application, particularly the friction pair, the lubricating material used, and friction conditions such as pressure and relative velocity. This is especially true for piston sleeves, which are subjected to high static and dynamic loads. Additionally, applications with high relative velocity friction pairs, such as those involving axial bearings in turbochargers, require alloys that, in addition to ensuring lower heat generation, also guarantee good heat dissipation from the friction surfaces.

[0004] Frictional power and oil contact form a friction layer on the bearing surface, resulting in an accumulation of lubricant components. This requires a uniform and high accumulation rate of the lubricant components and their decomposition products to achieve a sufficiently stable adsorption layer on the sliding surface.

[0005] Furthermore, suitable bearing materials excel in broad oil compatibility, making the structure of the lubricating layer essentially insensitive to the selection of specific oil additives. Another objective is to provide alloys with excellent emergency operating properties for friction applications, thereby ensuring sufficient service life under dry friction conditions.

[0006] For components subjected to friction loading, it is important that the alloy used possesses sufficient strength. Accordingly, a high yield strength of 0.2 should be present to minimize plastic deformation under load. Furthermore, a particularly hard and tensile alloy is required to enhance its resistance to wear and adhesive loads. Sufficient toughness is also necessary to prevent impact loads. In this case, it is required to reduce the number of micro-defects and slow down the resulting defect growth. This necessitates providing an alloy with the highest possible fracture toughness, essentially free of internal stress.

[0007] Alloys suitable for components subjected to frictional loads are various special brasses, which, in addition to copper and zinc as the main components, contain at least one of the following elements as alloying additives: nickel, iron, manganese, aluminum, silicon, titanium, or chromium. Silicon brass, in particular, meets the above-mentioned requirements, wherein CuZn... 31 Si1 represents a standard alloy used in friction applications, such as piston sleeves. Furthermore, tin bronze is known to contain nickel, zinc, iron, and manganese in addition to tin and copper, and is used in friction applications or even in the mining industry.

[0008] An example of a copper-zinc alloy is disclosed in document CH223580A, suitable for machine parts subjected to sliding loads, such as bearings, turbines, gears, sliders, etc. It discloses an alloying element composition of 50-70 wt% copper, 2-8 wt% aluminum, 0.05-3 wt% silicon, and 0.5-10 wt% manganese, with the balance being zinc. Furthermore, the alloy may contain up to 10 wt% lead and 0.1-5 wt% of one or more elements from the group consisting of iron, nickel, and cobalt. Additionally, a special brass alloy is known from document EP 0407 596 B1, which, in addition to copper, zinc, manganese, aluminum, and silicon, contains iron, nickel, and cobalt as optional alloying components. Furthermore, 0.03-1 wt% oxygen is specified. Furthermore, document DE1558467A discloses another special brass alloy designed for objects subjected to sliding and frictional loads. In addition to the requirement of copper and zinc components not exceeding 45%, alloying elements such as manganese, silicon, and tellurium are also present. Furthermore, Fe, Ni, Al, and Be are other optional alloying components. Moreover, documents DE 15 58 817 B2 and DE 59 949 C1 disclose copper alloys with a wide range of compositions that constitute wear-reducing bearing materials.

[0009] To meet the specific properties of products made from special brass alloys, multiple alloys with different alloying elements are used. Therefore, for this type of component, it is necessary to stockpile correspondingly different products, and, most importantly, to control the processing of these various alloys.

[0010] JP2001355029 A discloses a synchronizing ring and thereby a component designed for time-varying frictional loads. The component is manufactured through the following steps: casting a blank, hot extruding into a tube, cutting into a ring, hot forging, and subsequent machining. The synchronizing ring is made of a special brass alloy comprising 62.46% Cu, 30.8% Cn, and 0.053% Cr, with the balance being Zn.

[0011] Weber et al.: "Neuer Pb-freier Kupferwerkstoff für Gleitlageranwendungenin Verbrennungsmotoren und Getrieben", Metall: Fachzeitschrift für Metallurgie; Technik, Wissenschaft, Wirtschaft, GDMB-Verlag, Vol. 63, No. 11, pp. 564-567 (November 1, 2009) discloses a sliding bearing made of a special brass alloy having the following composition: 58% Cu, 0.5% Pb, 1% Si, 2% Mn, 0.5% Ni, 0.5% Fe, 2% Al, balance Zn.

[0012] Another special brass alloy is known from document EP 3 269 835 B1, characterized by high strength, better wear resistance under frictional loads, and good emergency operating properties (or self-lubricating properties) under insufficient lubrication. This special brass alloy is an alloy containing 60-62 wt% Cu, 2.1-2.5 wt% Mn, 0.2-0.6 wt% Ni, 2.9-3.1 wt% Al, 0.35-0.65 wt% Si, ≤0.1 wt% Fe, ≤0.1 wt% Sn, ≤0.1 wt% Pb, the balance Zn, and unavoidable impurities. Products made from this special brass alloy are characterized by long intermetallic phases in the microstructure, which impart high mechanical wear resistance to the alloy. These intermetallic phases readily achieve good longitudinal orientation during extrusion processing. Here, the longitudinally elongated structure of the intermetallic phases, primarily manganese silicide, functions to protect the matrix from wear loads. The particle size formed by the β phase or a matrix dominated by the β phase is between 100 and 300 μm. As a result, products made from this alloy have relatively coarse particles; however, this may be advantageous for breakage during machining of semi-finished products made from the alloy.

[0013] Even though this known alloy possesses advantageous properties, the relatively coarse grains formed are sometimes considered detrimental because grain boundary cracks can occur during cold forming. Even if the semi-finished products made from this alloy are well machinable, it is still desirable to retain a lower surface roughness after machining, especially cutting, so as to avoid the additional processing costs associated with subsequent polishing or similar surface treatments when the special brass alloy product should only have a low surface roughness. Furthermore, it has been found that the special brass alloy products or semi-finished products are subject to relatively strong thermal relaxation. This results in the fact that, in some cases, the process window to be followed may have to be kept extremely narrow for thermal relaxation. In addition, the thermal relaxation process of the alloy can also lead to a reduction in strength when using products subjected to high temperatures and, especially, high temperature fluctuations. Summary of the Invention

[0014] Therefore, based on the prior art discussed above, the technical problem to be solved by the present invention is to provide a special brass alloy and a special brass alloy product made from said alloy, which is similar in type to the alloy known from document EP 3 269835 B1, but with improvements in grain size and thermal relaxation characteristics.

[0015] According to the present invention, the technical problem is solved by a special brass alloy, which has

[0016] 62.5 to 65% Cu by weight

[0017] 2.0 to 2.4 wt% Mn,

[0018] 0.7 to 0.9% by weight of Ni,

[0019] 1.9 to 2.3% by weight of Al,

[0020] 0.35 to 0.65 wt% Si,

[0021] 0.3 to 0.6% by weight of Fe,

[0022] Sn and Cr, individually or collectively, 0.18 to 0.4% by weight.

[0023] ≤0.1% by weight of Pb

[0024] And the balance of Zn and unavoidable impurities.

[0025] The special brass alloy is characterized by a very uniform and fine-grained microstructure, which is already formed in the initially formed semi-finished product—cast preform or extruded preform. The average grain size is 40 to 150 µm. Casting of the alloy achieves an even finer grain size. Another feature is that the special brass alloy already possesses an α-β microstructure in the semi-finished product, wherein the α phase is embedded in or penetrates the β phase in a mesh-like or banded manner. In this way, the α phase grains are connected to the grains of the β matrix, resulting in a grain bond (or grain network) densely penetrated by the α phase, and thus maintained even under cold forming loads. The alloy is characterized by the formation of this microstructure even in extruded preforms without a preferred orientation, and thus the same or somewhat identical microstructure (or microstructure) should be observed in both the longitudinal and transverse directions of the extruded nozzle. Therefore, unlike the alloys known in document EP 3 269 835 B1 (which have a microstructure with an α phase typically comprising less than 10% and a far more dominant β phase, with the α phase mostly located in the grain boundary region or within the β phase), the grain boundaries in the microstructure of the special brass alloy products, or even semi-finished products, made from this special brass alloy do not exhibit weak points. This also makes this new alloy less prone to grain boundary cracking during cold forming. Furthermore, this avoids, or significantly reduces, the strength degradation when using this type of special brass alloy product at higher temperatures or under the influence of temperature variations compared to known alloys, and in fact achieves a fine grain size.

[0026] Surprisingly, it was recognized that such a significant difference in microstructure and thus the advantages of the alloy could be achieved through relatively small changes in the alloy composition compared to that known from EP 3 269 835 B1. Unexpectedly, a small change in the zinc equivalent of the special brass alloy, compared to that known from EP 3 269 835 B1, resulted in this significant change in the special brass alloy product in order to achieve a slightly more α phase. The unexpected consequence is that the elements participating in the alloy composition already act in combination during forming—casting or extrusion—achieving the advantageous properties of the special brass alloy or the products or semi-finished products made from it. This also includes lower thermal relaxation, thus allowing for a relatively wide process window for thermal relaxation.

[0027] It is noteworthy that, in this special brass alloy, as described above, when the special brass alloy is extruded to manufacture a semi-finished product, no microstructural differences are identifiable between the core and edge regions of the extruded product. Interestingly, the α phase, which permeates the β phase in a grid-like pattern, is constructed indistinguishably, or at least not significantly, in its longitudinal axis orientation in both the longitudinal and transverse extensions of the extruded product, thus making the α phase permeating the β phase without a preferred orientation in the extruded product. Therefore, such extruded preforms can be processed without considering the preferred microstructural extension. Consequently, sections of the extruded nozzle designed for forging can be formed regardless of the extrusion direction. Furthermore, it is particularly advantageous that the intermetallic compounds—silicides—embedded in the α-β matrix have a more rounded, near-spherical, at most slightly elongated habit compared to the longitudinal elongation habit of special brass alloys known from EP 3269 835 B1, and similarly also do not have a preferred orientation, at most having only a slight elongation. And therefore it will not break during molding.

[0028] The elements Sn and Cr, which affect grain fineness, individually or jointly comprise 0.18 to 0.4% by weight of the alloy. According to one embodiment, the alloy contains only Sn and no Cr. The Sn content is preferably 0.2 to 0.3% by weight. In another design, the alloy does not contain Sn, but contains 0.2 to 0.27% by weight of Cr. A content exceeding 0.4% by weight of the aforementioned elements does not result in significant improvement. Besides Sn and Cr, the Fe content also benefits grain fineness. Furthermore, the use of Sn has a positive effect on forming a passivation layer on the surface of special brass alloy products made from the alloy, thereby improving the tribological properties of the special brass alloy products.

[0029] The semi-finished products made from the aforementioned special brass alloy are characterized by good cold formability. Therefore, the special brass alloy can also be used to manufacture products such as sliders, for which a considerably high forming rate is required. In sliders, for example, it is necessary for the semi-finished product to be rolled after forging to form a shoulder. Although the material has good cold formability, it is still hard enough to meet the requirements of such sliders in application, along with the desired settling time.

[0030] Thermal relaxation tolerance is achieved through the fine-grained structure and the aforementioned α-β matrix. Correspondingly, the matrix grains are not subject to regulation and therefore do not have a preferred orientation.

[0031] It is also noteworthy that this alloy exhibits approximately 10% lower electrical conductivity compared to alloys known from EP 3 269 835 B1. The correspondingly lower corrosion current allows for the flow of this lower current, thereby further improving corrosion resistance.

[0032] The α phase comprises approximately 40% to 60% in cast or extruded preforms. This proportion of the α phase in cast or extruded preforms is unpredictable because, in the comparative alloy according to EP 3 269835 B1, the α phase in this alloy state comprises only a maximum of 10%, and is typically significantly lower than 10%. Within the aforementioned range, approximately equal proportions of the α and β phases provide a good starting point, allowing the α phase proportion to be reduced or increased by heat treatment steps, such as annealing, depending on the desired microstructure in the final product. The α phase proportion can be significantly reduced, specifically by 20% to 25%, by heat treatment of the alloy product at lower temperatures, typically between 270°C and 290°C, for 4.5 to 6 hours. Heat treatment at higher temperatures, for example between 435°C and 460°C, for approximately 2.5 to 3.5 hours, results in an increase in the α phase proportion. This method enables the manufacture of specialty brass alloy products having a 70-75% α phase content. In this regard, the actual desired α phase content in the final product can be adjusted individually and independently of the molding process.

[0033] The advantageous wear resistance of products made from the alloy is already evident in their hardness. After extrusion molding, the semi-finished product has a hardness of 135 to 145 HB [2.5 / 62.5]. By heat treatment after molding, when the workpiece is heat-treated at the aforementioned higher temperature and for a shorter treatment time, the hardness can be increased to a value of over 160 HB.

[0034] The special brass alloy preferably contains 63 to 64% by weight of Cu, 2.1 to 2.2% by weight of Mn, 2.0 to 2.2% by weight of Al and 0.4 to 0.5% by weight of Fe. Attached Figure Description

[0035] The present invention will now be described with reference to the accompanying drawings and embodiments. In the drawings:

[0036] Figures 1a to 1d The image shows a microscopic image of an extruded sample of the first special brass alloy according to the present invention in the extruded state.

[0037] Figure 2 The image shows a comparison of the longitudinal and transverse microscopic images of the alloy sample according to Figure 1 with the microscopic image of the second special brass alloy according to the present invention.

[0038] Figure 3 This image shows a detailed longitudinal section of the first special brass alloy according to the present invention, compared with a comparative sample.

[0039] Figure 4 This image shows a detailed longitudinal section of the second special brass alloy according to the present invention, compared with a comparative sample.

[0040] Figure 5 : A microscopic image showing a slider made of a first special brass alloy according to the present invention,

[0041] Figure 6 : A microscopic image showing a rotating sleeve made of a first special brass alloy according to the invention.

[0042] Figure 7 The diagram shows the microstructure of the retaining section formed by forging the first special brass alloy according to the invention after forging.

[0043] Figure 8 The image shows the microstructure of the retaining section formed by forging from the first special brass alloy according to the invention, after heat treatment (annealing) following forging.

[0044] Figure 9 The diagram shows the microstructure of a slider formed by forging a first special brass alloy according to the invention after forging.

[0045] Figure 10 The image shows the microstructure of a slide block formed by forging from the first special brass alloy according to the present invention after heat treatment (annealing) following forging. Detailed Implementation

[0046] Multiple samples were manufactured from two special brass alloys according to the invention and a comparative alloy, and subsequently extruded at approximately 700°C. The composition of sample V of the comparative alloy and the compositions of two samples E1 and E2 made from the special brass alloys according to the invention are shown below (in weight %):

[0047]

[0048] The comparative alloy is the special brass alloy described in the examples of EP 3 269 835 B1. Sample E1 is a first special brass alloy according to the invention, which represents a Sn-containing scheme of the special brass alloy according to the invention. Figure 1 shows the alloy in the extruded state along the longitudinal direction of the extruded nozzle ( Figure 1a and Figure 1b ) and horizontal ( Figure 1c , Figure 1d The microscopic images obtained. Figure 1a and Figure 1c Shot from the core, Figure 1b and Figure 1dImages were taken from the radial edge region. Samples 1a and 1b were photographed longitudinally along the extruded nozzle, while samples 1c and 1d were photographed transversely along the nozzle. Notably, the microstructure is uniform both from the core to the edge and along both the longitudinal and transverse directions. Furthermore, the micrographs also reveal the typical α-β microstructure of the alloy, where the α phase (bright grains) extends through the β grains in a grid-like or banded pattern.

[0049] The special microstructure in the extruded nozzle is also composed of... Figure 2 The microscopic images shown are at a slightly lower magnification. In the views, sample E1 is shown on the left, while sample E2 is shown on the right. Sample E2 is a Cr-containing scheme of a special brass alloy according to the invention. The respective upper images show the microstructure along the longitudinal extension of the extruded nozzle (extruded preform). Figure 2 The image below shows the tissue along the transverse direction. The microscopic images also reveal interestingly homogeneous tissue structures along the longitudinal and transverse directions of samples E1 and E2. The α phase is also the brighter portion in the microscopic images.

[0050] Figure 3 and Figure 4 The microscopic images of sample E1 and sample V are shown in comparison. Figure 3 ), and a comparison of the microscopic image of the second sample E2 according to the present invention with the microscopic image of the comparative alloy sample V ( Figure 4 The comparison reveals a microstructure of the special brass alloy according to the invention that is significantly different from that of the comparative alloy. The comparative alloy, in its "extruded nozzle" processing state, shows only the β phase, while in the alloy according to the invention, the β phase is identified as being penetrated by the α phase, wherein the α phase grains extend beyond the grain boundaries of adjacent β phase grains.

[0051] Semi-finished products formed from the special brass alloy according to the invention, for example as extruded nozzles, have an α-phase content of about 35% to 55%, particularly about 40% to about 50%. In samples E1 and E2 according to the invention, the α-phase content is approximately 45%, respectively. The β-phase constitutes the remainder. The intermetallic phase content is approximately 3%.

[0052] For the special brass alloys according to the invention, the above-described microstructure associated with the alloy is not merely for the stated thermal and mechanical purposes. In fact, this microstructure, with its uniformly distributed α and β phases, is suitable for adjusting the proportion of the α phase according to the requirements of the finished product. This can be accomplished by heat treatment (annealing). If the semi-finished product undergoes annealing at a lower temperature but for a longer processing time, the proportion of the α phase decreases. To achieve this, the semi-finished product is treated at a temperature between 260°C and 300°C for 4 to 6 hours, particularly at approximately 280°C for 5 hours. When heat treatment is performed using these parameters, the proportion of the α phase decreases to 30% or even lower.

[0053] Conversely, if the heat treatment is performed at a higher temperature for a shorter time, the proportion of the α phase is higher than that in the extruded nozzle. This heat treatment is performed at temperatures between 430°C and 470°C for 2.5 to 4 hours, and particularly at approximately 450°C for 3 hours. The proportion of the α phase can then be increased to 65% or even higher.

[0054] The decrease in the α phase content leads to a certain increase in the content of the intermetallic phase, which can have a share of 4.5 to 5.5% in this annealed product.

[0055] The special brass alloy according to the invention is particularly suitable for forming extruded pipe sections by forging, and the uniform extrusion structure also contributes to this. Figure 7 The retaining section forged from sample E1 is shown. Forging was performed at 700°C. Figure 7 As shown in the microstructure images, the original tissue structure can still be largely identified and thus preserved after forging.

[0056] Figure 8 The retaining section is shown after a 5-hour heat treatment at 280°C. The heat treatment contributes to further homogenization of the microstructure. With respect to this heat treatment, the α-phase content decreases from approximately 40% after forging to approximately 29%. Furthermore, the hardness increases from approximately 140 HB [HBW 2.5 / 62.5] to approximately 148 HB.

[0057] In addition, a slider was made from sample E1 by forging. Figure 9 The microstructure is shown after the forging step, which was performed at 710°C. For the sample in question, the microstructure formed in the extruded nozzle is essentially retained despite the forging process. The forged slide block was then heat-treated at 450°C for 3 hours. Figure 10As shown, the annealing step increases the α-phase content, specifically from approximately 50% (the same as in the extruded nozzle after forging) to approximately 68%. The hardness HB is increased only slightly by annealing compared to the forged state, specifically from 155HB [HBW 2.5 / 62.5] to 159HB.

[0058] In the comparative alloy sample V, the matrix of the extruded nozzle contained <1% of the α phase.

[0059] Of particular interest in the special brass alloy according to the invention is its conductivity, which is more than 10% lower than that of the comparative alloy sample V. The conductivity in the comparative alloy is 10.4 to 10.7 MS / m, while in the alloy E1 according to the invention it is only 8.8 MS / m. This improves the corrosion resistance of the special brass alloy.

[0060] The mechanical characteristic values ​​of samples E1 and E2 are shown in the table below:

[0061]

Claims

1. A special brass alloy product, said special brass alloy product being composed of the following components: 62.5 to 65% Cu by weight 2.0 to 2.4 wt% Mn, 0.7 to 0.9% by weight of Ni, 1.9 to 2.3% by weight of Al, 0.35 to 0.65 wt% Si, 0.3 to 0.6% by weight of Fe, Total 0.18 to 0.4% by weight of Sn and / or Cr, individually or collectively, ≤0.1% by weight of Pb And the balance of Zn and unavoidable impurities, The special brass alloy product is a hot forging, wherein the special brass alloy product has: an α-β mixed crystal matrix containing α phase and β phase, the α-β mixed crystal matrix having a 35-55% α phase share and a 2-5% intermetallic phase share, wherein the α phase is surrounded in the β phase or the α phase passes through the β phase, thereby providing a grain network penetrated by the α phase.

2. The special brass alloy product according to claim 1, characterized in that, The special brass alloy contains 63 to 64% by weight of Cu.

3. The special brass alloy product according to claim 1, characterized in that, The special brass alloy contains 2.1 to 2.2% by weight of Mn.

4. The special brass alloy product according to claim 1, characterized in that, The special brass alloy contains 2.0 to 2.2% by weight of Al.

5. The special brass alloy product according to claim 1, characterized in that, The special brass alloy contains 0.4 to 0.5% by weight of Fe.

6. The special brass alloy product according to claim 1, characterized in that, The special brass alloy contains 0.2 to 0.3% by weight Sn or 0.2 to 0.27% by weight Cr.

7. The special brass alloy product according to claim 1, characterized in that, The special brass alloy products are sliders or bearing sleeves.

8. The special brass alloy product according to claim 1, characterized in that, The special brass alloy product includes: 63 to 64% Cu by weight 2.1 to 2.2 wt% Mn, 2.0 to 2.2 wt% Al, and 0.4 to 0.5% by weight of Fe.

9. The special brass alloy product according to claim 8, characterized in that, The special brass alloy product contains 0.2 to 0.3% by weight Sn or 0.2 to 0.27% by weight Cr.

10. The special brass alloy product according to claim 1, characterized in that, The α phase accounts for 40 to 50% of the α-β mixed crystal matrix.

11. The special brass alloy product according to claim 1, characterized in that, The special brass alloy product contains intermetallic compounds with circular or spherical habits embedded in the α-β mixed crystal matrix.

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