Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper
  • C22C9/04—Alloys based on copper with zinc as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
  • C22C1/03—Making non-ferrous alloys by melting using master alloys

Definitions

• the invention relates to a process for the melt-metallurgical production of a high-strength brass alloy comprising at least one special alloying element bound in a precipitation phase with other metals of the alloy composition, which is insoluble or only sparingly soluble in a brass alloy melt.
• the invention further relates to a melt-metallurgically produced brass alloy comprising such a special alloying element.
• Brass alloys that contain several accompanying elements in addition to Cu and Zn are also referred to as special brass alloys.
• the selection and proportion of the accompanying element(s) can be used to adjust the properties of the brass alloy, particularly mechanical properties, physical properties such as electrical or thermal conductivity, machining properties, corrosion resistance, and the like.
• EP 4 801 794 A1 discloses a high-strength, hot-formable special brass alloy, particularly for a highly stressed component.
• This special brass alloy known from this prior art, combines numerous requirements. It is subject to higher loads, especially in conjunction with low-viscosity, synthetic oils, and is also cost-effectively formable, both cold and hot, and exhibits good machinability.
• This known alloy has the following composition (data in wt.%): Cu: 50 to 58%, Mn: 1.5 to 3.1%, Ni: 3.2 to 5.85%, Al: 2.8 to 5.6%, Si: 0.5 to 2.5%, Sn: 0.05 to 0.5%, Cr: 0.05 to 1%, P: 0.01 to 0.1%, Fe: max. 0.3%, Pb: max. 0.1%, Zn: remainder plus unavoidable impurities.
• brass alloys can also be produced by powder metallurgy (sintering).
• powder metallurgy sining
• the individual particles are welded together. Homogenization processes of the chemical composition distribution are therefore limited to the size scales of the particles and their neighboring grains, which is why powder metallurgically produced brass alloys only exhibit a lower degree of homogeneity.
• the resulting shorter transport routes compared to a well-mixed melt lead, even in the worst case, to a reduction in the number of resulting mixing and compound phases relative to the existing alloy system.
• the powder metallurgical production route can introduce elements or compounds into the brass alloy that are insoluble or only very poorly soluble in a brass alloy melt (Cu-Zn melt). Such elements are typically those with high melting points or simply elements that tend to form slag in a brass melt and are therefore insoluble.
• Another disadvantage at such temperatures can be a coarsening of the microstructure due to the elimination of grain-refining nuclei in the Other disadvantages must also be taken into account, such as an uneven solidification front during cooling of the casting and the resulting stresses, as well as the risk of a break in the edge solidification shell.
• Mo and W which are listed together with Al, Ta, Nb, and V in an element group, are listed in this prior art as optional alloying elements.
• the high-entropy alloy precipitates contain one or more of the elements Cr, Mn, Fe, Co, and Ni. This state of the art does not provide any information regarding melt-metallurgical production, in particular how insoluble or only slightly soluble elements in a brass alloy are to be introduced by melt-metallurgy.
• phase boundaries between the matrix and the particles embedded therein which may well be agglomerates, represent potential weak points in the structure, as these phase boundaries can initiate cracks or promote crack growth.
• a lead- and antimony-free brass alloy is described. It contains 56-66% Cu, 0.1-1.5% Mg, less than 0.1% Pb, the remainder Zn, and unavoidable impurities. This alloy is not a high-strength special brass alloy. It lacks the necessary accompanying elements in the appropriate proportions. This previously known alloy may contain As and P with less than 0.15% and Al and Sn with less than 0.1% as accompanying elements.
• the above-mentioned low solubility of certain elements in a Cu-Zn alloy melt can be further reduced due to interactions if the alloy melt contains the accompanying elements typical of a high-strength special brass alloy, such as Al, Ni, Si, Mn, and the like, in corresponding proportions, which can range between 4 and 7% for Al, between 4 and 8% for Ni, between 1 and 2.5% for Si, and between 2 and 5.5% for Mn. Furthermore, the accompanying elements can interact with the low-solubility element to cause lattice distortion and affect phase stability, thus further reducing the solubility of the alloy element in question.
• a high-strength special brass alloy such as Al, Ni, Si, Mn, and the like
• the object of the invention is to propose a method for the melt-metallurgical production of a high-strength brass alloy with at least one special alloying element bound in a precipitation phase with other metals of the alloy composition and which is insoluble or only sparingly soluble in a brass alloy melt.
• a special feature of this process is that the special alloying element(s) that are insoluble or only very slightly soluble in a Cu-Zn alloy melt are provided in one or more master alloys, with this master alloy being a Zn master alloy.
• Such a special alloying element can certainly be used as a component of a master alloy.
• Typical examples are Al master alloys that contain the special alloying element(s). The master alloy containing a special alloying element is melted together with Zn to form a Zn master alloy and then cast.
• the new master alloy produced in this way is then introduced into a molten Cu master alloy to create a brass alloy melt, from which the casting is then carried out.
• the special alloying element that is insoluble or only slightly soluble in a Cu-Zn alloy melt is dissolved in the Zn master alloy, so that the special alloying element(s) are dissolved in the Cu-Zn alloy by melt metallurgy and introduced into the Cu-Zn alloy.
• the persons involved in the creation of the invention were surprised to discover that special alloying elements or master alloys containing such an element, as are commercially available and which slag in a brass alloy melt, can be melted in a Zn master alloy.
• the alloying elements required for the brass alloy to be produced and not contained in the Zn master alloy are contained in the Cu master alloy, into which the Zn master alloy is introduced to create the brass alloy melt.
• a Zn master alloy contains no or only a minor amount of the complementary Zn element Cu.
• the Cu master alloy can contain Zn without this being detrimental to the formation of the Cu master alloy.
• the Zn required for the brass alloy or the brass alloy melt to be produced comes at least in part from the Zn master alloy.
• the Zn content of the brass alloy melt is readjusted, thus introducing the missing amount of Zn.
• the proportions of other elements contained in the Zn master alloy in the brass alloy melt can be readjusted in the same way.
• the proportion of the at least one special alloying element in the Zn alloy in relation to the amount of Zn master alloy successively introduced into the Cu master alloy can be set up in such a way that the successive introduction of the Zn master alloy with the at least one special alloying element leads to that its solubility in the Cu-Zn alloy melt is exceeded, and at least one precipitation phase, in which at least one special alloying element is bound, forms in this melt.
• this process takes advantage of the insolubility or poor solubility of the special alloying elements in question in a Cu-Zn alloy melt by binding precipitation phases early on by adding the Zn alloy melt with the special alloying element. Since at least one special alloying element was previously melted, homogeneous chemical compounds in the form of precipitates are formed, but not solid solutions.
• Another advantage of this process is that lower temperatures are required to melt the Zn master alloy and prepare the resulting casting compared to the temperatures required for the Cu-Zn alloy melt.
• the advantages lie, on the one hand, in the fact that the solubility of the special alloying element also increases at the correspondingly high casting temperature of the Zn master alloy compared to an Al master alloy.
• the advantage compared to a Cu master alloy with these special alloying elements is lower energy consumption due to the lower melting and casting temperatures. For example, while the solidus temperature of the element Ca in a Cu melt is around 1,085 °C, the solidus temperature of Ca in a zinc-rich melt - the Zn master alloy - is around 840 °C. The same applies to the other special alloying elements.
• the precipitate phases in the brass alloy containing one or more special alloying elements can contain these in proportions between 20 and 70 wt.%.
• This process now expands the design freedom for constructing a brass alloy (special brass alloy) to include the possibility of incorporating elements into the alloy by melt metallurgy, particularly in significant proportions, thus influencing the properties of the brass alloy or brass alloy product that could not previously be incorporated into such an alloy by melt metallurgy.
• these elements can be used to form precipitate phases that would not form without such a special alloying element. This is advantageous for the brass alloy or the product manufactured with it, since the different properties of the precipitates allow the brass alloy product to be equipped with corresponding properties.
• one precipitation phase may have a positive effect on machinability, while another phase may have a positive effect on tribology when the brass alloy is used in an oil environment.
• the properties of the brass alloy or brass alloy product can be adjusted by selecting one or more special alloying elements.
• Such a special brass alloy typically contains, in addition to a precipitation phase containing at least one special alloying element, other intermetallic precipitation phases that occur in special brass alloys. These are also taken into account when designing the brass alloy to meet the requirements of its subsequent use.
• the formation of different Precipitation phases in the brass alloy increase its application and use possibilities, as the different precipitation phases support or positively influence different aspects of later use.
• Such a brass alloy can be used for different load ranges due to its different precipitation phases, which include silicides and aluminides, among other precipitation phases, and where the various precipitation phases can be present in different sizes. If precipitates of different sizes are present, smaller precipitates are typically responsible for the strength of the brass alloy, while larger ones can improve wear resistance and tribological behavior.
• precipitation phases include silicides and aluminides, among other precipitation phases, and where the various precipitation phases can be present in different sizes. If precipitates of different sizes are present, smaller precipitates are typically responsible for the strength of the brass alloy, while larger ones can improve wear resistance and tribological behavior.
• the element Mo which can be introduced into a brass alloy using this melt-metallurgical process, can improve the properties of the brass alloy product, for example, with regard to its thermal expansion, electrical conductivity, hardness, or even its machining properties.
• Mo as a special alloying element, for example, reduces the thermal expansion of the special brass alloy.
• the nest-like formation of the precipitation phase containing at least one Mo within the matrix has a positive effect.
• Mo also exhibits very good thermal conductivity, so that the special brass alloy or the special brass alloy product produced from it also exhibits very good thermal conductivity. This special property results from the fact that this special alloying element is introduced into the brass alloy melt using melt-metallurgical methods and not merely as an unmelted component of a metal matrix composite material.
• the special alloying element W promotes mechanical wear resistance in the precipitation phase caused by it and otherwise acts similarly to the element Mo.
• Mg and Ca have a precipitation-forming effect, are due to the precipitation thus increasing strength.
• temperature resistance and relaxation behavior are improved.
• Mg and Ca are also considered suitable as solid lubricants in brass alloy products.
• these elements are biocompatible and therefore have no adverse effects on humans, which is why alloys containing such elements are also suitable for medical applications.
• the Zn content in the Zn master alloy is typically greater than the sum of the other elements contained in the Zn master alloy.
• the Zn content in the master alloy is preferably 65 to 90 wt.%.
• the remainder is made up of the special alloying element(s) alone or together with the other element(s) of the master alloy containing the special alloying element, such as Al.
• a high-strength brass alloy typically contains Al. Therefore, the special alloying element(s) are preferably used as part of an Al master alloy to provide the Zn master alloy. This master alloy then does not introduce any elements into the brass alloy that are actually not required.
• the use of an Al master alloy containing the special alloying element(s) also has the advantage that Al master alloys have a relatively low melting temperature. Should the amount of Zn and/or Al in the Zn master alloy be insufficient to represent the desired proportions of these elements in the brass alloy melt, the brass alloy melt can be readjusted with regard to these elements. These elements can therefore be subsequently introduced into the brass alloy melt without impairing the solubility of the special alloying element(s).
• special alloying elements are those that form silicide precipitates with the Si present in a special brass alloy, typically with other alloying elements.
• a special alloying element can also be used as a Si scavenger, The result is that other metals that would otherwise be present in silicide precipitates are now available for the formation of aluminides.
• the special alloying element(s) also influences the formation and chemical composition of the precipitate phases.
• the unavoidable impurities mentioned in this statement comprise a maximum of 0.05 wt.% per element and do not exceed a total of 0.15 wt.%.
• Brass alloys according to the invention with different compositions were investigated. These alloys contain Mo as a special alloying element.
• the following description of the inventive process for producing the inventive brass alloy with Mo as a special alloying element also applies analogously to other elements that are insoluble or only sparingly soluble in a Cu-Zn alloy melt, or even to those that can only be dissolved in such a melt at very high temperatures.
• a Zn master alloy is first produced.
• Zn and Mo, which were introduced into the Zn master alloy as a component of an Al master alloy, are melted in this alloy.
• the Zn master alloy is a 3-component alloy comprising the elements Zn, Al, and Mo.
• additional elements can be components of the Zn master alloy, in particular those elements that, like Mo, are considered special alloying elements.
• the Zn master alloy melt is cast at a temperature of slightly more than 1,100°C to create the Zn master alloy.
• a Cu master alloy is prepared and prepared. This contains the Cu content intended for the brass alloy melt, as well as the other alloying elements that contribute to the structure of the brass alloy.
• the elements contained in the Zn master alloy are not included in the composition of the Cu master alloy. If the proportions of one or more elements in the Zn master alloy, with the exception of the special alloying element(s), are insufficient for the proportions of these elements in the Cu-Zn alloy, these elements can be readjusted in the Cu-Zn alloy melt by introducing the shortfalls accordingly. This is the case, for example, if the Al content contained in the master alloy is insufficient in relation to the amount introduced into the Cu master alloy via the Zn master alloy to provide the Al content intended for the brass alloy.
• the Zn master alloy is introduced into the molten Cu master alloy.
• the total amount of Zn master alloy to be introduced into the Cu master alloy is introduced successively, i.e., gradually, into the Cu master alloy so that the introduced Zn master alloy particles can melt quickly and be homogeneously distributed in the Cu master alloy.
• This successive addition of Zn master alloy into the Cu master alloy melt can be used to form precipitation phases in this alloy melt, which contain the special alloying element, in this case: Mo.
• the special alloying element in this case: Mo.
• the precipitation phases form with the special alloying element Mo, which has been dissolved by melting metallurgy.
• the brass alloy melt has been completed in terms of its composition by sufficient addition of Zn master alloy to the Cu master alloy, casting takes place.
• the temperature of the brass alloy melt is higher than that of the Zn master alloy melt. Consequently, the casting temperature of the brass alloy melt is also higher and, in the illustrated embodiment, lies between 1,150°C and 1,250°C.
• micrographs were taken to visualize the microstructure.
• the images of the Figures 2 and 3 show images of the brass alloy according to sample 1.
• Figure 4 shows a micrograph of sample 2.
• the images of the Figures 5 to 7 are recordings from sample 3.
• Figure 8 shows a micrograph of sample 4.
• the microstructure contains no refractory (non-melted) components. The same was observed for samples 9 to 12, which, unlike samples 1 to 8, are Co-free.
• sample 1 ( Figure 2 ) characterizes this brass alloy as a fine-grained, homogeneous brass alloy. This homogeneous structure and the fine grain with the precipitates it contains give this brass alloy good wear resistance, good machinability, and good formability. The hardness of this brass alloy is approximately 192 HBW 2.5/62.5.
• the brass alloy of sample 3 ( Figure 4 ) is relatively fine-grained.
• the needle-shaped silicide precipitates, which stabilize the microstructure and are located without any preferred orientation, are clearly visible.
• the brass alloy of sample 3 exhibits similar properties to sample 1, but has a significantly higher hardness of 296 HBW 2.5/62.5.
• Ni aluminides spectra 7 to 9
• silicides spectra 13 to 18
• the aluminides were investigated using spectrum 6, the silicides in spectra 7 to 10.
• Mo was introduced into the brass alloy melt as a special alloying element using melt metallurgy, as it is expected that this element has a particularly positive effect on machining, thus forming short chips.
• the Mo in the precipitate phases also ensures that these brass alloys have a low coefficient of thermal expansion by interlocking the precipitate phases with the matrix, resulting in a high thermal conductivity. This property is advantageous in the context of machining the brass alloy, as the heat generated during machining can be dissipated quickly and effectively.
• brass alloys can be produced by melt metallurgy in a simple, cost-effective process that can readily be used on an industrial scale. These alloys, through the introduction of their special alloying elements, exhibit additional properties that cannot be achieved using conventional methods or only with disproportionate effort. This is not only, but primarily, about imparting additional properties to the brass alloy through the special alloying element(s).
• Machining tests were carried out on cylindrical specimens of the alloys according to the invention by turning. The tests were carried out at a sample rotation speed of 1,300 rpm and a feed rate of 0.21 mm/rev. Segmented, spiral-shaped chips were consistently generated in the samples of the alloy according to the invention. In such chips, the individual segments within a chip section adhere less strongly to one another, so that short chips are ultimately generated during the machining process. Fraying, if present at all, is on the inside due to its curvature. The diameter of the chips is generally no more than 10 mm, but in many cases is less. Chip length of the curved chips is 10 to 20 mm. The chip shape and chip size of the inventive sample 2 is exemplary for all inventive samples in the Figure 9 shown.
• the chips are shown as a heap.
• two individual chip segments are shown in an enlarged view.
• the chip shape which is particularly favorable for a machining process, is clearly visible. It is worth emphasizing that the fraying is arranged on the inside with respect to the curvature of the chips. Therefore, entanglement with other chips is either absent or reduced to a minimum due to these fraying.
• Figure 10 shows for comparison a sample of the state of the art EP 4 108 794 A1 described special brass alloy.
• the positive properties of this special brass alloy have already been mentioned.
• machining tests show that this previously known alloy, into which none of the special alloying elements according to the invention have been introduced in the manner described, forms long chips.
• the reason for the greater length of these chips is that the individual chip segments adhere more closely to one another and the chips do not break apart into smaller chip segments through the machining process alone. This is undesirable for a machining process.
• the fraying on the chips is located on the outside of their chip curvature, which is why these chips tend to entangle with each other.
• Figure 10 The chip pile shown (left) as well as the enlarged view of individual chips (right) make it clear that these chips are undesirable for a machining process.

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• 2024
  • 2024-03-21 EP EP24165214.8A patent/EP4621084A1/fr active Pending

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