Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • 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
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
  • C22C21/08—Alloys based on aluminium with magnesium as the next major constituent with silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/043—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with silicon as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/05—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys of the Al-Si-Mg type, i.e. containing silicon and magnesium in approximately equal proportions

Definitions

• the present invention relates to an aluminum alloy for components with increased heat stability.
• the components made from the alloy are characterized by a high strength and high hardness after exposure to high heat.
• the inventive aluminum alloy is particularly suitable for manufacturing components of the aforementioned type by extrusion, forging, or casting in permanent molds, as well as for further processing of the components thus prepared by means of thermal joining methods.
• the present invention further relates to components which are produced by means of the alloy, and to the use of this aluminum alloy for the production of components, in particular of components for the automotive industry.
• Extrusion and mold casting are two of the most economical methods of forming aluminum alloys.
• the design options are influenced and limited mainly by the type of alloy, the available process forces and the pressing direction.
• Another important parameter in forming by means of extrusion is the pressing temperature, the height of which is limited by the particular alloy composition, in particular by its resistance to heat application. Since local heating of the alloy may occur during the forming process, partial melting may occur, especially in the area of the die inlet edges, which affects the mechanical properties of the extruded product.
• the design limits are influenced mainly by the aspired simplest possible component geometry, since the method needs to be realized without the use of insertable cores.
• the quality of the extruded part depends not only on the machine setting and tool design (die geometry), but largely on the selected alloy system. Particularly, AlMn(Cu) and AlMgSi alloy systems are widely used for extruded products (F. Ostermann, “AnArchitectstechnologie Aluminium,” 3rd Edition, pp 456-457, Berlin 2014). In the permanent mold processes, in particular in die casting, also, the chemical composition and microstructure play a crucial role for the later component properties relevant in terms of application technologically.
• thermal joining processes such as welding or soldering/brazing
• the reliability of the material and its stability under the thermal stress conditions occurring in these thermal joining processes are essential.
• the resistance of the material to short-term thermal stress is important, both in the case of accidental heating and in the case of an intended heating of a structure, such as in soldering/brazing or welding.
• high-temperature strength is generally understood to mean the strength of the material at elevated temperatures. The highest values in terms of high-temperature strength are exhibited, inter alia, by the alloys of the 2xxx type (AlCu). High-temperature strength is achieved, among other things, by increased amounts of Si, Cu, Ni or Fe, whereby, however, a deterioration of the mechanical properties (e.g., fracture toughness) is caused (F. Ostermann, “Anthinkstechnologie Aluminium,” 3rd Edition, pp 300-303, Berlin 2014).
• the required mechanical properties are achieved by addition of copper or zinc to the alloys.
• these alloys are subjected to a heat treatment to achieve an improvement in mechanical properties due to the hardening effects.
• metastable phases are formed to counteract dislocation movements upon application of force.
• Al—Mn alloys are used.
• a prerequisite for the solderability/brazeability of an alloy is that the solidus temperature of the material is above the liquidus temperature of the solder.
• the working temperature is generally 440° C. to 600° C.
• soldering the working temperature is below 440° C.
• the temperature profile of the brazing process significantly affects the mechanical properties. Where temperatures near the solidus are used, this leads to a softening of the material. A gain in strength can only be achieved by subsequent natural or artificial age-hardening with rapid cooling of the structure.
• brazeable aluminum alloys are very limited. This is a result of the above-mentioned condition that the solidus temperature of the material must be above the liquidus temperature of the brazing solder.
• Prevalent Al—Mn alloys are less susceptible to the effects of heat, but at processing temperatures near solidus point they also exhibit deficits in hardness stability.
• aluminum alloys for high temperature applications which contain additions of alloying elements from the group of rare earth metals (e.g., Sc, Er). These rare earth metals form dispersoids in the aluminum matrix (e.g., of the Al 3 Er type), which is meant to improve the mechanical properties at elevated service temperatures.
• rare earth metals e.g., Sc, Er
• Such an alloy is known from EP 2 110 452 A1, and has a high Cu content (1.0 to 8.0 wt %) but contains no Zn.
• objectives of the present invention are to provide an aluminum alloy which is suitable for extrusion, forging and casting in permanent molds (in particular, high-pressure die casting), and which is readily castable and has a high hardness in the as-cast state and during brief application of high heat.
• the alloy is to have good joining properties, in particular good brazeability, and high corrosion resistance.
• the alloy is to be suitable for the production of components for the automotive industry, in particular components with increased high-temperature strength.
• inventive alloy composition it is possible to achieve a high heat stability not only in extruded sections, but also in forgings and pressure die castings in the as-fabricated or as-cast condition, at good hardness values.
• the alloy is therefore especially suitable for producing temperature-stressed parts for the automotive industry and/or for further processing by means of joining methods, in particular thermal joining processes such as brazing or welding. Due to the increased heat stability of the alloy, extrusion processes or other forming processes can be carried out at a higher process speed or at higher pressures, without local overheating occurring in the workpiece.
• the inventive aluminum alloy has the following composition:
• the aluminum alloy may optionally also contain one or more of the following elements in the proportions indicated below:
• the alloy may optionally contain a Ti and B-containing grain refiner in an amount of 0.01 to 0.2 wt %.
• the specified composition of the alloy remains unaffected.
• the grain refining agent is preferably added when preparing the alloy in the form of an aluminum master alloy containing the components mentioned.
• the balance consists of aluminum and unavoidable impurities.
• the proportion of these impurities is preferably a maximum of 0.05 wt % (individually) or a maximum of 0.15 wt % (in total).
• the limitation of the Cu content to a maximum of 0.05 wt % prevents the solidus point of the alloy from falling below 610° C.
• the Cu content is limited to a maximum of 0.03 wt %.
• the Mn content in the range of 0.3 to 2.5 wt %, preferably in the range of 0.8 to 1.5 wt % Mn, more preferably 1.2 to 1.5 wt % Mn, a high dimensional strength at elevated temperatures can be secured, so that during demolding very little or no warpage is to be expected. Furthermore, in the case of production by means of casting methods, especially pressure die casting, the Mn contents employed in accordance with the present invention prevent any sticking in the mold and ensure demoldability.
• the preferred silicon content is 0.6 to 0.8 wt %, in particular 0.7 wt %.
• Si content it has also been found that an adjustment of the Si/Mg ratio in the range of 0.9 to 1.1 has a favorable effect on the hardness of the alloy and on its castability. For optimum hardness and castability, a Si/Mg ratio of 1:1 should preferably be maintained.
• the Fe content is 0.2 to 1.5 wt %, preferably 0.2 to 1.0 wt %, in particular 0.2 to 0.8 wt %.
• the Fe content is preferably adjusted depending on the Fe content, as explained above (Fe/Mn ratio).
• the Mg content is in the range from 0.2 to 1.8 wt % Mg, preferably 0.2 to 1.2-.%, in particular 0.2 to 0.9 wt %, and is more preferably 0.7 wt %.
• the Mg content is preferably set depending on the Si content, as discussed above (Si/Mg ratio).
• the Ti content is in the range of 0.03 to 0.18 wt %, preferably in the range of 0.05 to 0.1 wt %.
• the Ti content is preferably set depending on the Zr content, as explained above (Ti/Zr ratio).
• the inventive alloy therefore contains erbium as a further alloying element.
• the desired effect is achieved by adding 0.02 to 0.5 wt % Er. Preferably, this proportion is in the range of 0.02 to 0.3 wt % Er.
• the alloy of the invention thus contains zinc as a further alloying element.
• the optional Zn content is in the range of 0.2 to 1.8 wt % of Zn; it is preferably 0.4 to 0.8 wt %, in particular 0.5 to 0.7 wt %.
• the Zn content is in the range of 0.4 to 1.2 wt %, preferably from 0.6 to 1.2 wt %, in particular 1 wt %.
• the alloying elements Zn and Er when used in combination, allow a further increase in heat stability.
• 0.02 wt % to 0.5 wt % Er, and 0.2 to 1.8 wt % Zn, preferably 0.4 to 0.8 wt % Zn such an increase can be achieved.
• the inventive alloy is subjected to a grain refinement wherein a Ti and B-containing grain refiner is used.
• the proportion of the grain refining agent in the inventive alloy is preferably 0.5 to 2 kg/t, more preferably 1.5 kg/t.
• an aluminum master alloy which contains Ti and B (balance: aluminum) and which during the production of the alloy is added in a proportion of preferably 0.5 to 2 kg/t, particularly preferably 1.5 kg/t, is used as a grain refiner.
• Ti and B are substantially contained in a crystalline or particulate form, which can serve as crystallization nuclei (e.g. TiB 2 , Al 3 Ti AlTi 5 B 1 , AlTi 6 ).
• the master alloy contains 2.7 to 3.2 wt % Ti, in particular 2.9 to 3.1 wt % Ti, and 0.6 to 1.1 wt % B, in particular 0.8 to 0.9 wt % B, in each case aluminum being the balance.
• the aluminum alloy of the present invention and the components produced therefrom are distinguished in that they have a Brinell hardness of at least 55 HBW5/250, preferably at least 65 HBW5/250, more preferably at least 80 HBW5/250.
• the aluminum alloy of the present invention and the components made therefrom are further distinguished by a solidus temperature of ⁇ 610° C., in particular ⁇ 630° C.
• the inventive alloy can optionally be subjected to a heat treatment.
• a heat treatment is preferably carried out for a time period of 2 to 42 hours, in particular 6 to 24 hours, at a temperature in the range of 325° C. to 425° C., in particular 350° C. to 400° C.
• a suitable gaseous e.g., air or inert gas
• liquid medium e.g., water or oil.
• the preferred heat treatment is carried out for 6 to 24 hours and a temperature of 350° C. to 400° C., followed by air cooling.
• the inventive alloy can be used for the production of components for different applications, preferably for applications in the automotive industry.
• the inventive alloy, in particular the heat-treated alloy (see above) is suitable for the production of components that are subjected to high operating temperatures, for example, up to 250° C. or up to 300° C. (e.g., engine components or gearbox components, such as pistons, cylinder heads, engine blocks, gearbox housings, heat exchanger).
• the alloy of the present invention is especially suitable for components which are further processed by means of thermal joining methods, such as soldering/brazing (in particular, brazing) or welding.
• the inventive alloy is suitable for the soldering/brazing of aluminum components using flux, for example in the automotive industry and in HVAC technology, as well as for processes in soldering/brazing furnaces, especially for the manufacture of heat exchangers.
• the present invention thus extends to components that are prepared from an alloy, as defined in more detail above.
• the components are manufactured by casting in permanent molds, in particular by high-pressure die casting, or by extruding, or by forging.
• the components can be further processed by means of other methods, in particular thermal joining methods (e.g., soldering/brazing, welding), or by forging, to obtain complex assemblies or components having complex geometries.
• the heat resistance of components made from the alloy of the present invention can, if desired, be further increased by subjecting the components to artificial ageing.
• an increase in the Brinell hardness can be achieved by such a heat treatment.
• the high hardness typically in the range of 50 to 70 HBW 5/250, present in the components produced with the inventive alloy in the condition as manufactured, can be increased even further by performing a heat treatment at 150° C. to 240° C., preferably 180° C. to 220° C., particularly preferably at 200° C., for a period of 4 to 72 hours, preferably 8 to 24 hours, more preferably 8 to 12 hours.
• the components After such heat treatment, the components have an increased Brinell value (HBWS/250) which typically corresponds to 1.1 to 1.5 times the initial value (prior to heat treatment). It is possible to increase hardness even further.
• components can be obtained which have a Brinell hardness (HBWS/250) of at least 70, preferably at least 80.
• the components thus prepared have a Brinell hardness in the range of 70 to 120, in particular in the range of 75 to 95.
• the alloys of the present invention and the components produced therefrom are distinguished by a high heat stability under exposure to high heat, even over prolonged periods. As a result, the mechanical properties, especially hardness, are largely stable under such temperature conditions.
• Another important and advantageous property of the alloy of the present invention is that the components thus produced can be temporarily exposed to a temperature that is close to the solidus point, without thereby causing a substantial deterioration of the hardness or other mechanical properties.
• This heat stability is of practical importance since components are exposed to such a thermal load when they are further processed, for example, by means of thermal joining methods (in particular, brazing or welding).
• the components produced using the inventive alloy can briefly ( ⁇ 30 minutes, preferably ⁇ 20 minutes, especially ⁇ 15 minutes) be subjected to a temperature of 400° C. to 650° C., preferably 400° C. to 620° C., especially 400° C. to 610° C., without thereby causing a relevant deterioration of their mechanical properties, particularly their hardness. After exposure to heat as indicated above, only a slight decrease in hardness is observed. In general, after such a brief exposure to heat, the Brinell hardness still amounts to 70-95% of the initial value (as-prepared condition).
• the alloy of the present invention and the components made therefrom thus fulfill the aforementioned requirements, particularly with regard to heat stability on exposure to high heat.
• the inventive aluminum alloy is above all suitable for the manufacture of components for the automotive industry by pressure die casting, forging or extrusion, wherein the components can optionally be further processed by joining processes, in particular by means of thermal joining processes.
• the inventive aluminum alloy can preferably be used for the production of components which, during their manufacture, their further processing or in subsequent use, are subject to increased requirements in terms of temperature, such as engine or gearbox components (e.g., pistons, cylinder heads, engine blocks, gearbox housings, etc.) or heat exchangers, as well as chassis components and body components.
• engine or gearbox components e.g., pistons, cylinder heads, engine blocks, gearbox housings, etc.
• heat exchangers e.g., heat exchangers, as well as chassis components and body components.
• the inventive aluminum alloy can be prepared by methods known to those skilled in the art, typically by preparing a melt having a composition corresponding to the above-mentioned alloy composition of the present invention.
• the alloying elements Ti and B are preferably added in the form of a master alloy during the production of the alloy, as explained above.
• the alloy of the present invention is preferably prepared using the vertical continuous casting method.
• a prior gas treatment of the melt with inert gases sufficient melt quality is ensured and a hydrogen-poor cast product is produced. This is also an important prerequisite for achieving a high hardness stability on exposure to heat.
• Methods for treating metal melts with inert gases are known in the art.
• the alloy after its preparation, is subjected to an optional heat treatment.
• This heat treatment is preferably carried out for a period of 2 to 42 hours, in particular 6 to 24 hours, at a temperature in the range of 325° C. to 425° C., in particular 350° C. to 400° C.
• This is followed by air cooling, or the heat-treated alloy is quenched in a suitable gaseous (e.g., air or inert gas) or liquid medium (e.g. water or oil).
• a suitable gaseous e.g., air or inert gas
• liquid medium e.g. water or oil
• components can also be fabricated by known methods, preferably by extrusion, casting in permanent molds (in particular, die-casting) and/or forging.
• the components can be subjected to further processing by means of joining methods (in particular, brazing or welding) or by means of forming processes.
• the components produced from an alloy of the present invention are subjected to an optional heat treatment (artificial aging) for the purpose of increasing their hardness.
• This heat treatment is performed at 150° C. to 240° C., preferably 180° C. to 220° C., particularly preferably at 200° C., during a period of 4 to 72 hours, preferably 8 to 24 hours, more preferably 8 to 12 hours.
• Al—Mn alloy based on EN AW-3103 which is known under the trade name “Aluman 16” (AlMn1,6; manufactured by Aluminium Rheinfelden GmbH) was used.
• This alloy can be brazed due to its high solidification point, and it is suitable for the die casting process.
• the alloy is used in the manufacture of coolers and in the food industry.
• composition of this alloy is given in below Table 1 (first row, “V”).
• this alloy Due to its relatively high Mn and Fe contents, this alloy is characterized by good heat stability at elevated temperatures. However, with the above-described new areas of application, particularly for applications in the automotive industry, this alloy has reached its limits. In particular, the hardness is no longer sufficient to meet the required component properties. Here, it was possible to achieve a significant improvement by using the alloy described in the present application, as is shown by the test results given in Tables 2, 3 and 4 shown below.
• L1, L2, L3, L4, L5, L6 and L7 relate to alloy variants according to the present invention.
• L8 corresponds to L7 with additional heat treatment as indicated above, and likewise constitutes an alloy of the present invention.
• L1, L2, L3, L4, L5, L6 and L7 of the present invention whose composition is given in Table 1, were prepared by melting.
• L8 corresponds to L7 with additional heat treatment as indicated above.
• a comparative alloy V (“Aluman-16”), the composition of which is also shown in Table 1, was smelted. Cylindrical test bodies ( ⁇ 40 mm; height 30 mm) were cast from all eight alloys.
• test specimens cast from the eight alloys were subjected to different heat applications.
• test specimens treated under the specified temperature conditions were cooled to room temperature (ca. 25° C.) in air, and then subjected to a Brinell hardness test (HBW5/250; tungsten carbide hard metal-test ball; ball diameter 5 mm).
• HBW5/250 tungsten carbide hard metal-test ball; ball diameter 5 mm.
• the arithmetic mean of the measured hardness values is listed in Tables 2, 3 and 4.
• the inventive alloy variants (L1 to L8) exhibit a markedly greater hardness compared to the comparative alloy V.
• the heat treatment at 200° C. (10 hours) it was even possible to increase hardness even further (see Table 2).

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