Structural components made of an aluminium alloy, starting material and production method

Abstract

The invention relates to a method for producing starting material for forged structural components made of aluminium. The method comprises producing an aluminium alloy containing 0.7 to 1.8 wt.% silicon, 0.5 to 1.4 wt.% magnesium, 0.3 to 1.2 wt.% manganese, 0.005 to 0.5 wt.% zirconium, 0.001 to 0.1 wt.% titanium and at most 0.3 wt.% iron by means of direct-quenching continuous casting. The melt is guided in such a way that it does not come into contact with a solid surface during quenching.

Description

[0001] Structural components made of an aluminum alloy, raw material and process for manufacturing

[0002] The invention relates to structural components made of an aluminum alloy, in particular structural components for automobiles, a precursor material for such structural components and associated methods for producing the same.

[0003] It is known to produce bars made of aluminum alloys, which are used, for example, to manufacture structural components for vehicles, using the continuous casting process.

[0004] In a continuous casting process, a material - e.g., an aluminum alloy - is converted from a molten to a solidified state by continuously feeding the alloyed or unalloyed melt into a short, water-cooled annular mold. The annular mold is closed off by a lowerable base block on a casting table. By lowering the casting table, the cast ingot is created while water is continuously fed into the mold chamber. The annular mold and the solidified cast product are cooled using water. In addition to annular molds, molds with a ceramic structure on the mold ("hot top") are also used, which reduces the temperature gradient in the solidifying melt, which can lead to a more uniform structure in the ingot cross-section and a thinner edge shell with improved surface quality. Casting lengths are usually between 3 and 7 meters. (F. Ostermann "Application Technology Aluminum", Springer, 2007, 2.Edition, pp. 419f.).

[0005] Pre-material produced by continuous casting is typically extruded to appropriate pre-dimensions prior to the actual forming step to achieve the final shape. In addition to changing the dimensions of the resulting forging pre-material, the grain structure of the material also changes. While the as-cast grain structure is more globulitic, the extrusion process transforms this into a fiber structure oriented in the direction of extrusion (F. Ostermann, "Application Technology for Aluminum," Springer, 2007, 2nd edition, p. 482).

[0006] Extrusion and forging are two of the most economical forming processes for aluminum. The design limits of extrusion and forging are influenced, among other things, by the alloy and the available process forces. In addition to machine settings and tool design, the quality of a formed part depends significantly on the selected alloy system. AlMn(Cu) and AlMgSi alloy systems are particularly widely used for extruded products. (F. Ostermann "Application Technology for Aluminum," Springer, 2007, 2nd edition, pp. 435-444). In principle, all wrought and cast aluminum alloys can be used for hot forming by forging. For technical and economic reasons, however, selected wrought alloys of the 2xxx, 5xxx, 6xxx and 7xxx series according to DIN EN 573-4 and DIN EN 586-3 are mainly used (F. Ostermann “Application Technology Aluminium”, Springer, 2007, 2nd edition, p. 481 f.).

[0007] The general heat treatment cycle for age-hardenable wrought aluminum alloys is shown in Figure 1 and consists of the steps of solution annealing, quenching, and age-hardening.

[0008] Since the hot forming temperatures during forming are in the range of the solution annealing temperature, solution annealing can be omitted for low- to medium-strength materials. For high-strength materials, the forging material is subjected to solution annealing after forming in order to exploit the full potential of the alloys. Too short a solution annealing time results in reduced strength and reduced ductility after hardening. A further annealing after forming serves to homogenize the forged structure. For high-alloy materials, precise control of the quenching rate after the solution annealing process is not insignificant in order to counteract premature demixing. As an example, Figure 2 shows the C-curve of a pressed profile made of EN AW-6060.

[0009] Following quenching of the structural component after hot forming, an alloy-specific single- or multi-stage cold and / or artificial ageing is typically performed on the formed component. This serves to achieve the required mechanical properties (Source: F. Ostermann "Application Technology Aluminium", Springer, 2007, 2nd edition, pp. 157-166).

[0010] In the past, increasing attention has been paid to the development of aluminum alloys with improved corrosion resistance and simultaneous enhancement of mechanical properties. This is particularly true given the growing demand, particularly in the automotive industry, for materials that offer a benefit in the CO2 balance over the vehicle's life cycle through weight savings through reduced wall thickness.

[0011] At the same time, there are demands for wear resistance, low density and thermal expansion, as well as good formability. These requirements have so far been met predominantly by alloys from the 6xxx series according to DIN EN 573-4, for example, 6082 alloys.

[0012] The demands for the highest mechanical properties can currently only be met by precipitation sequences with copper (Cu) additions to the alloy. However, this increasingly leads to a conflict of objectives, as Cu-containing 6xxx alloys are reaching their limits in terms of corrosion resistance, especially with regard to intergranular corrosion.

[0013] Efforts to replace Cu additives with rare earth metal alloying elements have shown some positive results. However, the limited availability of rare earth metal alloying elements and the associated high prices make such variants unattractive in industrial applications.

[0014] Aluminum alloys for the production of structural components are described in EP 2 644 727 A2 or EP 2 81 1 042 B1. Known aluminum alloys according to AA 6182 have the following composition:

[0015] Aluminium, AI 95 - 97.85% Chromium, Cr <= 0.25% Copper, Cu <= 0.10% Iron, Fe <= 0.50% Magnesium, Mg 0.70 - 1.2% Manganese, Mn 0.50 - 1.0% Silicon, Si 0.90 - 1.3% Titanium, Ti <= 0.10% Zinc, Zn <= 0.20% Zirconium, Zr 0.05 - 0.20% Others, each <= 0.05% Others, total <= 0.15%

[0016] The invention is based on the object of creating a structural component which has both high strength and good corrosion resistance and is also economical to produce, as well as an associated manufacturing method.

[0017] According to a first aspect of the invention, this object is achieved by a method for producing pre-material for forged structural components made of aluminum, which comprises the following steps:

[0018] Creating a melt with the components.

[0019] 1.2 to 1.4 wt% silicon,

[0020] 0.8 to 1.2 wt% magnesium,

[0021] 0.3 to 1.2 wt% manganese,

[0022] 0.1 to 0.2 wt% zirconium,

[0023] 0.01 to 0.05 wt% titanium,

[0024] 0.08 to 0.3 wt% iron,

[0025] 0.08 to 0.2 wt.% chromium max. 0.04 wt.% zinc, max. 0.02 wt.% copper and

[0026] The remainder being aluminium and unavoidable impurities, the ratio of silicon to magnesium being at least 1 : 0.8, and the melt containing less than 0.5 and preferably less than 0.25 ml of H2 per 100g of aluminium, and

[0027] Continuous casting of the melt of the aluminum alloy, in which the melt is guided in such a way that it has no contact with a solid surface during solidification, to produce an ingot which preferably has an electrical conductivity between 16 MS / m and 18 MS / m.

[0028] Preferably, the melt is liquid-cooled as it passes through a mold, so that it solidifies without contact with the wall. The coolant temperature and the mass flow of the coolant (e.g., water) are preferably adjusted so that the maximum cooling rate of the melt is more than -25 K / s. Suitable cooling rates are, for example, between -15 K / s and -35 K / s for a billet with a diameter between 90 mm and 100 mm, measured at a lateral distance of approximately 20 mm from a central longitudinal axis of the billet. The coolant is preferably water with a maximum temperature of 80°C.At a casting speed between 100 mm / min and 500 mm / min, the cooling water volume flow for a billet with a diameter between 90 mm and 100 mm is preferably between 40 l / min and 80 l / min. The cooling water volume flow is preferably 20 to 50 times greater than the volume flow of the cast aluminum alloy, whereby the cooling water volume flow for billet diameters on the order of 50 mm is preferably about 25 times greater than the volume flow of the cast aluminum alloy and for billet diameters on the order of 100 mm is preferably about 40 times greater than the volume flow of the cast aluminum alloy. The cooling capacity can be determined and adjusted as a function of the flow, return flow temperature and volume flow.

[0029] The preferred mold is a water-cooled ring mold, which is designed so that the molten aluminum alloy is separated from the solid components of the ring mold by a water film and thus does not touch any solid components of the mold during solidification. The water serves for the described liquid cooling of the cast strand.

[0030] Preferably, the melt passing through the mold is completely exposed from the outside to a gas mixture containing oxygen, preferably as pure as possible, to promote the formation of a solidified surface layer of oxidized aluminum alloy. The oxygen is applied before water is applied for liquid cooling. Only after the solidified surface layer has formed is the cast strand (ingot), which initially still consists of liquid melt on the inside, cooled with water as mentioned above. The aforementioned water film thus comes into contact not with the melt, but with the already solidified surface layer of the cast strand. Beforehand, the melt is separated from the mold by the gas mixture during the solidification of the surface layer.

[0031] The gas mixture preferably contains between 10% and 80% or between 20% and 70% oxygen (O2).

[0032] In further variants, the melt of the aluminum alloy can optionally contain one or more of the following elements in the following proportions: max. 0.2 wt.% chromium max. 0.04 wt.% zinc max. 0.02 wt.% copper

[0033] In comparison with standard continuous casting processes, the use of a direct quenching continuous casting process, avoiding contact between melt and solid surfaces (e.g. the mold), allows for the achievement of a directly formable pre-material quality that is characterized by sufficiently homogeneous surface quality, sufficiently fine microstructure and sufficiently low recrystallization tendency.

[0034] The inventive starting material has a significantly reduced tendency toward secondary recrystallization compared to the prior art, so that, for example, the circumferential coarse grain seam typical of forged parts is eliminated (see also Figures 3 and 4). The electrical conductivity is significantly lower than in comparable extruded material, namely approximately 16 to 18 megasiemens per meter (MS / m) compared to approximately 25 MS / m in the prior art. This is advantageous when the inventive starting material is used to manufacture components of electrical machines, because the lower conductivity reduces harmful eddy currents.

[0035] The inventive starting material exhibits increased corrosion resistance compared to the prior art. Furthermore, products made from the inventive starting material offer greater pressure resistance than cast aluminum, for example, due to the absence of porosity.

[0036] The aluminum alloy used in the invention is easily castable and formable and exhibits good mechanical properties. The achieved mechanical properties include, for example, a tensile strength Rm>375 MPa, a yield strength Rp02>345 MPa, an elongation A>10%, and a hardness>100 HB. Furthermore, the aluminum alloy possesses good machinability and high corrosion resistance.

[0037] The components made from the aluminum alloy are characterized by high strength and elongation properties as well as excellent corrosion resistance.

[0038] The aluminum alloy used according to the invention is particularly suitable for producing structural components, in particular automotive components, by means of forming processes.

[0039] Preferably, the weight ratio of titanium to zirconium (Ti:Zr) in the melt of the aluminum alloy is between 1:4 and 1:6, particularly preferably at least approximately 1:5.

[0040] Preferably, the weight ratio of iron to chromium to manganese (Fe:Cr:Mn) in the melt of the aluminum alloy is at least approximately 1:1:4.

[0041] The aluminum alloy preferably contains up to a maximum of 0.3 wt.% of one or more so-called rare earth elements, preferably Sc, Er, La, Ce, Y and / or Yb, to form further finely divided dispersoids.

[0042] Grain refinement is preferably carried out in the aluminum alloy according to the invention.

[0043] For this purpose, the alloy can contain Ti and B for grain refinement, with the addition of titanium and boron to the melt via a master alloy containing 2.7 to 3.2 wt.% Ti and 0.6 to 1.1 wt.% B, the remainder being aluminum. According to one variant, the aluminum master alloy contains 2.9 to 3.1 wt.% Ti and 0.8 to 0.9 wt.% B and has a Ti:B weight ratio of approximately 3:1. Preference is given to a master alloy having a Ti:B weight ratio of between approximately 5:1 and 5:0.6. In this case, the titanium content is preferably between 4.5 and 5.5 wt.%, for example between 4.8 and 5.2 wt.%.

[0044] The content of the master alloy in the alloy according to the invention is preferably set to 0.02 to 0.3 wt.%.

[0045] The manufacturing process according to the invention accordingly preferably additionally comprises the following steps:

[0046] Producing an aluminium master alloy with 4.8 to 5.2 wt% Ti and 0.8 to 1.2 wt% B and the remainder being aluminium and unavoidable impurities and

[0047] Adding the aluminum master alloy to the melt of the aluminum alloy with the components:

[0048] 1.2 to 1.4 wt% silicon,

[0049] 0.8 to 1.2 wt% magnesium,

[0050] 0.3 to 1.2 wt% manganese,

[0051] 0.1 to 0.2 wt% zirconium,

[0052] 0.01 to 0.05 wt% titanium,

[0053] 0.08 to 0.3 wt% iron,

[0054] 0.08 to 0.2 wt.% chromium, max. 0.04 wt.% zinc, max. 0.02 wt.% copper and

[0055] Rest aluminum and unavoidable impurities.

[0056] Using the aluminum master alloy, Ti and B are added to the aluminum alloy for grain refinement.

[0057] In the preferred manufacturing process for a pre-material made of the aluminum alloy, the aluminum pre-alloy containing titanium and boron is preferably added to the melt in the form of a wire immediately before the mold.

[0058] The precursor material produced by the process according to the invention is preferably forged into a structural component immediately after continuous casting. A further aspect of the invention is a manufacturing process for the aluminum alloy according to the invention, which achieves the required component properties.

[0059] A further aspect is a structural component made of the aluminum alloy according to the invention, in particular a structural component for a vehicle, for example an aircraft or an automobile.

[0060] A further aspect is a method for producing a structural component, in which the primary material produced as described above is hot-formed, in particular forged, to form a structural component immediately after continuous casting, without any treatment for homogenizing the primary material taking place between continuous casting and hot forming.

[0061] Quenching of the forged structural component can be performed directly after hot forming, without requiring a further solution annealing. The forged structural component can then be artificially aged.

[0062] Alternatively, the forged structural component can be solution-annealed, quenched, and artificially aged after hot forming. The solution-annealing temperature is approximately the same as the forging temperature, i.e., between 400°C and 570°C.

[0063] After hot forming, in particular after forging, the structural component is preferably subjected to artificial aging followed by air cooling. The artificial aging preferably takes place for 2 to 7 hours at 180°C to 210°C.

[0064] Due to the material properties, crash- and deformation-relevant parts or fail-safe parts made from the inventive precursor material are particularly preferred. Examples of preferred structural components are the following vehicle parts: anti-roll bars, battery boxes, nodes, engine mounts, pivot bearings, and wishbones.

[0065] Accordingly, a further aspect is the use of the aluminum alloy according to the invention for producing a structural component for a vehicle, for example an aircraft or an automobile, in particular for producing deformation-relevant parts or fail-safe parts, especially for producing slip wedges, battery boxes, body nodes, engine mounts, pivot bearings, and wishbones for vehicles. The invention includes the finding that to achieve the required mechanical properties, in particular a high yield strength Rp0.2, copper or zinc must usually be added to a 6xxx alloy. However, this procedure conflicts with the equally required corrosion resistance. To achieve this, the permissible Cu and Zn contents in the alloy must be severely limited, since otherwise precipitations would occur, particularly at the grain boundaries, which would have a negative impact on the corrosion resistance of the alloy.The required properties can therefore be achieved through other suitable measures, such as adjusting the Si:Mg ratio to at least 1:0.8 and preferably the Fe:Mn:Cr ratio to at least approximately 1:1:4, or the addition of dispersoid formers. Furthermore, a suitable heat treatment strategy is a proven means of achieving the required objectives. This involves the formation of phases that counteract dislocation movements when subjected to force.

[0066] The invention also includes the finding that known EN AW-6082 aluminum alloys lack sufficient strength while offering adequate corrosion resistance. On the other hand, known EN AW-6056 aluminum alloys, while offering sufficient mechanical properties, fail to meet the required corrosion properties. Other EN AW-6xxx alloys and the other wrought alloy groups also fail to meet the required properties.

[0067] Furthermore, the invention includes the finding that only a few wrought alloys are actually used for forging, although in principle all aluminum and wrought alloys can be formed using hot forging. This is due to the high demands regarding strength and component safety in the typical applications of forged aluminum parts, namely automotive and mechanical engineering. A common application for aluminum forgings is chassis safety parts, which, due to their exposed location, can be permanently exposed to corrosion attack; cf. F. Ostermann, Application Technology Aluminum, London, Heidelberg: Springer, 2007.

[0068] It is generally known that pure aluminum is highly resistant to corrosion. Its susceptibility only arises with the addition of appropriate alloying elements. F. Uyma writes that increasing magnesium content improves corrosion properties. Manganese influences recrystallization and precipitation behavior, leading to the increased occurrence of the so-called "Chinese script" (binary eutectic of Al and Mg2Si), which in turn causes intergranular corrosion. Additions of zinc and scandium are said to increase resistance to intergranular corrosion; cf. F. Uyma, Investigations in the field of Al-Mg-Si and Al / Mg2Si in-situ alloys, Freiberg: Technische Universität Bergakademie Freiberg, 2007. JP Wloka states that a continuous corrosion-active pathway through the metal is responsible for the occurrence of intergranular corrosion.This occurs primarily in artificially aged materials, which exhibit pearl-like grain boundary precipitations. This phenomenon is not observed in over-aged structures; cf. JP Wloka, Corrosion investigations on scandium-containing AlZnMgCu alloys with special consideration of the influence of intermetallic phases, Erlangen: University of Erlangen-Nuremberg, 2007. Furthermore, it is known that the susceptibility to intergranular corrosion is increased by insufficient quenching rates after solution annealing. This applies particularly to age-hardenable alloys. Intergranular corrosion is therefore almost impossible to avoid in thick-walled semi-finished products; cf. F. Ostermann, Application Technology Aluminium, London, Heidelberg: Springer, 2007. G. Svenningsen et al. investigated the influence of copper content in AlMgSi alloys. The susceptibility to intergranular corrosion is therefore largely due to the copper content of an alloy.In addition, the quenching rate has a significant influence on the intergranular corrosion resistance of an alloy. Cooling with water is therefore preferable to cooling in air. Most recently, as also described in JP Wloka's Corrosion Investigations on Scandium-Containing AlZnMgCu Alloys with Special Consideration of the Influence of Intermetallic Phases (Erlangen: University of Erlangen-Nuremberg, 2007), it was shown that overaging has a positive influence on resistance to intergranular corrosion. The so-called Q phase (Al4Mg8Si7Cu2) was identified as the phase primarily responsible for intergranular corrosion (G. Svenningsen et al., "Effect of Low Copper Content and Heat Treatment on Intergranular Corrosion of Model AlMgSi Alloys," Corrosion Science, Vol. 1, No. 48, pp. 226-242, 2006). In this context, the ratio of magnesium to silicon is hotly debated.However, there is no consensus on the best ratio, partly because no direct evidence of its influence has been provided so far. G. Svenningsen et al. set the ratio at Mg / Si ~ 0.87. Altenpohl suggests a ratio of Mg / Si ~ 1 (G. Svenningsen et al., "Effect of low copper content and heat treatment on intergranular corrosion of model AIMgSi alloys," Corrosion Science, Vol. 1, No. 48, pp. 226-242, 2006), (D. Altenpohl, Aluminium and Aluminium Alloys, London, Heidelberg: Springer, 1965).

[0069] With the alloy composition according to the invention, significantly improved corrosion properties can be achieved in bulk-formed components with at least the same high strength values ​​and at least the same low recrystallization tendency. Surprisingly, it has been shown that this also enables a more stable casting process and a more moderate use of grain refiners.

[0070] The invention will now be explained in more detail using exemplary embodiments and in comparison to other aluminum alloys. The figures show:

[0071] Figure 1 : the general heat treatment cycle for age-hardenable wrought aluminium alloys;

[0072] Figure 2: C-curves for profiles made of alloy EN AW-6060 (AIMgSi);

[0073] Figure 3: a schematic representation of the coarse grain development on a

[0074] Forged part using the usual extruded material;

[0075] Figure 4: a schematic representation of the coarse grain development on a

[0076] Forged part using the material according to the invention; and

[0077] Figure 5: a schematic sketch to explain the production of the intermediate product according to the invention.

[0078] Figure 1, already mentioned in the introduction to the description (source: F. Ostermann "Application Technology Aluminium", Springer, 2007, 2nd edition, p. 174), shows the general heat treatment cycle for age-hardening aluminum alloys. I illustrates the non-critical heating rate during solution annealing, II illustrates the critical cooling rate during quenching after solution annealing, III illustrates the critical heating rate during artificial ageing (this depends on the alloy), and IV illustrates the non-critical cooling rate after artificial ageing. "RT" denotes room temperature.

[0079] For the process presented in this description, the following deviations from the general description in Figure 1 arise: explicit cold aging is not required. Rather, there is only an intermediate aging process prior to artificial aging. Artificial aging is a single-stage process. A particular advantage of the process described here is that the billets produced by continuous casting can be cold formed after continuous casting without extended aging. Following continuous casting, after cooling, artificial aging can be performed for a period of 2 to 7 hours at 180°C to 210°C.

[0080] The C-curves shown in Figure 2 illustrate the influence of the quenching rate on the formation of phases and unwanted precipitates during extrusion. The quenching rate must be selected so that unwanted precipitates do not occur. The principles applicable to extrusion are intended to illustrate the influence of the quenching rate on the formation of precipitates. According to the process described here, strand pressing is preferably avoided, but rather the billets are forged. Solution annealing can be performed after forging if necessary.

[0081] An advantage of the aluminum alloy according to the invention, which is explained in more detail below, is that it requires no heat treatment or only a short artificial ageing if a precursor product is produced in the manner described here using the direct quenching continuous casting process.

[0082] A preferred aluminum alloy for this purpose has the following components:

[0083] The preferred silicon content is 0.7 to 1.8 wt.%, particularly preferably 1.0 to 1.6 wt.%, in particular 1.2 to 1.4 wt.%.

[0084] The preferred magnesium content is 0.5 to 1.4 wt.%, particularly preferably 0.6 to 1.2 wt.%, in particular 0.8 to 1.0 wt.%.

[0085] The preferred copper content is max. 0.1 wt.%.

[0086] The preferred manganese content is 0.4 to 0.8 wt%, particularly preferably 0.5 to 0.7 wt%.

[0087] The preferred zirconium content is 0.005 to 0.5 wt%, particularly preferably 0.005 to 0.1 wt%.

[0088] In addition, the alloy may optionally contain one or more of the following elements in the proportions specified below: The preferred chromium content is max. 0.2 wt.%.

[0089] The preferred iron content is max. 0.3 wt%.

[0090] The preferred titanium content is 0.001 to 0.05 wt%.

[0091] The preferred zinc content is max. 0.04 wt.%, preferably max. 0.01 wt.%.

[0092] The following ratios of the alloy components to each other are preferred:

[0093] • Si:Mg - between 1:0.5 and 1:0.75

[0094] An appropriately adjusted silicon excess causes the strength to increase significantly

[0095] • Fe:Cr:Mn - between approximately 1:1:4 and 1:1:5, with the iron to chromium ratio Fe:Cr preferably being 1:1 and between 0.8:1 and 1:0.8. The preferred ratio of iron to chromium to manganese serves to avoid needle-like AlFeSi phases, which negatively impact ductility. Manganese forms these phases into less problematic AlFeMnSi phases. The chromium content is limited due to its high affinity for free silicon, which can also negatively impact mechanical properties.

[0096] • Ti:Zr - 1:5 (TiZr compound / recrystallization topic, also RE metals see below, grain refinement)

[0097] The ratio of titanium to zirconium serves to form a sufficient number of AI3Zr phases with an L12 structure, which, as dispersoids, positively influence the mechanical properties and recrystallization behavior.

[0098] • Cu<0.02, preferably Cu<0.01

[0099] Copper serves to inhibit the tendency to corrosion, especially with regard to intergranular corrosion Zn<0.04, preferably Zn<0.01

[0100] Zinc serves to inhibit the tendency to corrosion, especially with regard to stress corrosion cracking

[0101] • Rare earths

[0102] Rare earths act as additional dispersoid formers to increase mechanical properties, especially hardness, and to influence the tendency to recrystallization during hot forming.

[0103] Description of an example:

[0104] The aluminum alloy can be produced by methods known to those skilled in the art, usually by producing a melt having a composition corresponding to the alloy composition specified above.

[0105] 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.

[0106] The precursor material made of the aluminum alloy according to the invention is preferably produced using a horizontal continuous casting (HCM) process. Prior gas treatment of the melt with a suitable inert gas or several inert gases ensures sufficient melt quality and produces a low-H2 cast product, which represents an important step toward achieving the required properties in the final product. Methods for treating metal melts with inert gases are known to those skilled in the art. To obtain a low-H2 cast product, the maximum value for hydrogen (H2) in the melt is preferably between 0.05 and 0.5 ml H2 per 100 g aluminum. A maximum value for hydrogen of less than 0.25 ml H2 / 100 g Al and in particular less than 0.15 ml H2 / 100 g Al is particularly preferred.

[0107] Structural components using the aluminum alloy according to the invention are manufactured by hot forming, preferably by drop forging, of precursor material preferably produced as described here. Heating to a forming temperature between 400°C and 570°C can be carried out in any desired manner, preferably using a heating furnace or induction. Intermediate heating steps can be performed between individual forming steps. The forged structural component can be quenched directly from the forming heat—i.e., immediately after hot forming. The forged structural component can then be artificially aged.

[0108] Alternatively, the forged structural component can be solution-annealed, quenched, and artificially aged. The temperature during solution-annealing roughly corresponds to the forming temperature for forging, i.e., between 400°C and 570°C.

[0109] Depending on the application or requirements profile, the starting material can be subjected to heat treatment before hot forming or the structural component obtained by hot forming. However, heat treatment is not absolutely necessary because the continuously cast starting material already possesses excellent properties for the production of structural components using the forging process. The aluminum alloy according to the invention can, for example, be heat-treated for 0.25 to 24 hours at 150°C to 260°C and then quenched in a suitable gaseous medium, e.g., air or inert gas, or in a suitable liquid medium, e.g., water or oil. The preferred heat treatment is between 1 and 10 hours at 170°C to 220°C, particularly preferably between 2 and 7 hours at 180°C to 210°C, followed by air cooling.

[0110] However, homogenization and / or extrusion of the precursor material is not required. In particular, the precursor material can be hot-formed, for example, forged, immediately after continuous casting. Otherwise, conventional process steps such as homogenization following continuous casting and extrusion following homogenization can be omitted.

[0111] The heat-treated precursor material is suitable for the production of structural components used in highly stressed and safety-critical areas, such as automotive engineering. This requires high strength and high ductility.

[0112] The production of the raw material includes, for example, the following process steps:

[0113] • Melting of the alloy components

[0114] • Adjusting the alloy

[0115] Melt purification direct quenching continuous casting of an ingot Production of billets as starting material by sawing the ingot

[0116] The subsequent forging of a structural component includes, for example, the following process steps:

[0117] • Heating the bolt

[0118] • Preforms

[0119] • optional: intermediate heating

[0120] • Forging

[0121] • optional: solution annealing

[0122] • Quenching

[0123] • Artificial aging

[0124] It has been shown that forged parts made from the inventive starting material exhibit significantly reduced coarse grain formation. This is illustrated in Figures 3 and 4.

[0125] Figure 3 shows a schematic cross-section through a hot-formed structural component 30 made from a conventional precursor material. A pronounced coarse-grained seam 32 and a similarly pronounced burr area 34 can be seen.

[0126] Figure 3 illustrates the typical coarse grain development on a forged part using the usual extruded material.

[0127] In contrast, Figure 4 shows the significantly lower coarse grain development on a forged part 30' using the inventive starting material, because the tendency toward secondary recrystallization is significantly reduced with the inventive starting material. The circumferential coarse grain seam 32 typical of forged parts (see Figure 3) is eliminated (see Figure 4). This results in a high surface quality of the forged parts.

[0128] The following tables show examples of various alloys tested for comparison with the claimed alloy.

[0129]

[0130] By definition, AA6182 alloys are composed as follows: The precursor material suitable for forging, for example, is produced from the aluminum alloy according to the invention by producing a melt 10 with the following components:

[0131] 1.2 to 1.4 wt% silicon,

[0132] 0.8 to 1.2 wt% magnesium, 0.3 to 1.2 wt% manganese,

[0133] 0.1 to 0.2 wt% zirconium,

[0134] 0.01 to 0.05 wt% titanium,

[0135] 0.08 to 0.3 wt% iron,

[0136] 0.08 to 0.2 wt.% chromium, max. 0.04 wt.% zinc, max. 0.02 wt.% copper and

[0137] Rest aluminum and unavoidable impurities.

[0138] In addition, a wire 12 made of an aluminum master alloy containing 4.8 to 5.2 wt.% Ti and 0.8 to 1.2 wt.% B, the remainder being aluminum and unavoidable impurities, is provided and added to the melt immediately before it passes through a water-cooled annular mold 14; see Figure 5. The annular mold 14 is designed such that the melt of the aluminum alloy is spaced from the solid components of the annular mold by a water film and thus does not come into contact with any solid components of the mold during solidification. In addition, the melt passing through the annular mold 14 is fully exposed from the outside with oxygen O2 of the purest possible in order to promote the formation of a surface layer of oxidized aluminum alloy. The oxygen is applied before the water is applied for liquid cooling.

[0139] For example, when continuously casting an ingot with a diameter between 90 mm and 100 mm, the casting speed is between 150 mm / min and 200 mm / min.

[0140] The cooling water 16 for cooling the melt 10 as it passes through the annular mold 14 is guided in the circuit 18 such that the temperature and volume flow of the cooling water result in a maximum cooling rate of the melt during solidification of more than -25 K / s. Suitable cooling rates are, for example, between -15 K / s and -35 K / s for an ingot with a diameter between 90 mm and 100 mm, measured at a lateral distance of approximately 20 mm from a central longitudinal axis of the ingot.

[0141] The water 16 used as coolant has a temperature of between 20°C and 80°C. When continuously casting an ingot with a diameter of between 90 mm and 100 mm at a casting speed of between 150 mm / min and 200 mm / min, the cooling water volume flow is, for example, between 40 l / min and 80 l / min. The cooling water volume flow is preferably 20 to 50 times greater than the volume flow of the cast aluminum alloy, whereby the cooling water volume flow for ingot diameters of the order of 50 mm is preferably about 25 times greater than the volume flow of the cast aluminum alloy and for ingot diameters of the order of 100 mm is preferably about 40 times greater than the volume flow of the cast aluminum alloy. Using an annular mold 14, for example, a cast strand 20 for ingots 22 with an outer diameter of 60 mm to 110 mm can be produced. At a melt temperature of approx.650°C and a continuous casting speed VG between 150 mm / min and 200 mm / min, the cooling water temperature TK is preferably between 20°C and 80°C and the cooling water flow is preferably greater than 30 l / min.

[0142] After solidification, the ingot 20 is separated into individual billets 22, which can then be cold-formed or forged. Preferably, the diameter and cross-sectional shape—for example, circular or oval—of the ingot 20 are selected such that the billets obtained from the ingot 20 have a volume that exceeds the volume of the cold-formed finished part as little as possible. The diameter and cross-sectional shape of the ingot 20 can be adjusted by selecting a suitable annular mold 14.

[0143] A bolt 22 manufactured from the aluminum alloy described here using the continuous casting process also described here has properties that make the bolt 22 suitable as a starting material for forging resilient structural components with high strength, low corrosion susceptibility, and high surface quality. Typical values ​​achieved for this starting material are a tensile strength Rm>375 MPa, a yield strength Rp02>345 MPa, an elongation A>10%, and a hardness>100 HB.

[0144] Structural components forged from the raw material can be deformation-relevant parts or fail-safe parts for motor vehicles, for example sliding wedges, battery boxes, nodes, engine mounts, pivot bearings or wishbones.

[0145] Due to its reduced electrical conductivity, the raw material is also suitable for components of electrical machines in which eddy currents and associated losses need to be reduced.

[0146] 10 melt

[0147] 12 wire

[0148] 14 Ring mold 16 Cooling water

[0149] 18 Circulation

[0150] 20 bars

[0151] 22 bolts

[0152] 30 Structural component 32 Coarse grain seam

[0153] 34 Ridge area

Claims

Patent claims 1. Method for producing pre-material for forged structural components made of aluminium, comprising the steps: To prepare a melt with the components. 0.7 to 1.8 wt.%, preferably 1.2 to 1.4 wt.% silicon, 0.5 to 1.4 wt.%, preferably 0.8 to 1.2 wt.% magnesium, 0.3 to 1.2 wt.%, preferably 0.4 to 0.8 wt.% manganese, 0.005 to 0.2 wt.%, preferably 0.05 to 0.2 wt.% zirconium, 0.01 to 0.05 wt% titanium, 0.08 to 0.3 wt% iron, 0.08 to 0.2 wt.% chromium, max. 0.04 wt.% zinc, max. 0.1 wt.%, preferably max. 0.02 wt.% copper and Residual aluminum and unavoidable impurities, wherein the ratio of silicon to magnesium is at least 1 : 0.8, and the melt contains less than 0.5 and preferably less than 0.25 ml H2 per 100g aluminum Continuous casting of the aluminum alloy, whereby the molten metal is guided in such a way that it has no contact with a solid surface when it solidifies.

2. Method according to claim 1, wherein the production of the aluminium alloy comprises adding a master alloy containing titanium and boron for grain refinement, wherein the master alloy is preferably added to the melt immediately before it passes through a water-cooled ring mold (14).

3. Method according to claim 2, wherein the aluminium master alloy contains 4.5 to 5.5 wt.% titanium and 0.8 to 1.2 wt.% boron, with aluminium and unavoidable impurities as the remainder.

4. Method according to at least one of claims 1 to 3, wherein a bar with an electrical conductivity between 16 MS / m and 18 MS / m is produced by continuous casting.

5. Method according to at least one of claims 1 to 4, wherein the weight ratio of titanium to zirconium (Ti:Zr) in the aluminium alloy is between 1 :4 and 1 :6, preferably at least approximately 1 :

5.

6. Method according to at least one of claims 1 to 5, wherein the weight ratio of iron to chromium to manganese (Fe:Cr:Mn) in the aluminium alloy is at least approximately 1 :1 :

4.

7. Method according to at least one of claims 1 to 6, wherein the aluminium alloy contains between 0.05 and 0.3 wt. % of one or more elements of the so-called rare earths, preferably Sc, Er, La, Ce, Y and / or Yb, for the formation of further finely divided dispersoids.

8. Method according to at least one of claims 1 to 7, wherein the weight ratio of silicon to magnesium (Si:Mg) in the aluminium alloy is between 1 :0.7 and 1 :0.8, preferably at least approximately 1 :0.

75.

9. Method according to at least one of claims 1 to 8, wherein during the solidification of the melt in continuous casting, contact between the melt and a solidified surface layer with a solid surface of the mold is prevented and liquid cooling of the melt is effected during its passage through a mold.

10. Method according to claim 9, wherein the melt is liquid-cooled during passage through the mold such that the cooling rate of the solidifying aluminium alloy is greater than 25 Kelvin per second.

11. Method according to claim 9 or 10, wherein the melt is exposed to an oxygen-containing gas mixture during its passage through the mold before and during the solidification of the surface layer.

12. Method for producing a structural component, wherein the pre-material produced by the method according to one of claims 1 to 11 is hot-formed, in particular forged, into a structural component immediately following continuous casting, without any treatment for homogenizing the pre-material taking place between continuous casting and hot forming.

13. Method for producing a structural component according to claim 12, comprising a hot aging process and subsequent air cooling of the hot-formed structural component.

14. Method according to claim 13, wherein the heat aging is carried out for 2h to 7h at 180°C to 210°C.

15. Use of a pre-material produced by a method according to at least one of claims 1 to 11 for extrusion of forging pre-material for the vehicle industry.

16. Use of a pre-material produced by a method according to at least one of claims 1 to 11 for forging components for the automotive industry.

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