Classifications

• • 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
  • C22F1/053—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 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
  • C22C21/00—Alloys based on aluminium
  • C22C21/10—Alloys based on aluminium with zinc as the next major constituent

Definitions

• the present invention relates to an extruded structural component for a motor vehicle according to the features of claim 1.
• the invention further relates to a method for producing a structural component for a motor vehicle according to the features of claim 14.
• Aluminum alloys are known to be used as a material for the production of extruded structural components for motor vehicles due to their low weight, high strength, and good corrosion resistance.
• aluminum alloys of the 7000 series whose main alloying element is zinc, are widely used in vehicle construction due to their high strength, rigidity, and dynamic load-bearing capacity.
• Stress corrosion cracking is the formation of transcrystalline or intergranular cracks in materials under the simultaneous influence of a purely static load and a specific corrosion medium.
• the object of the present invention is to provide an extruded structural component for a motor vehicle which is made of an aluminum alloy of the 7000 series and has improved stress corrosion cracking resistance.
• a further object of the invention is to provide a method for producing a corresponding structural component for a motor vehicle.
• the objective part of the problem is solved by an extruded structural component for a motor vehicle according to the features of claim 1.
• the process-related part of the problem is solved by a method for producing a structural component for a motor vehicle according to the features of claim 14.
• the structural component for a motor vehicle according to the invention is extruded and made of a 7000 series aluminum alloy.
• This is an aluminum alloy that, in addition to aluminum, contains zinc, magnesium, and copper as the main alloying elements.
• Zn and Mg are present in the aluminum alloy in a weight ratio of 4.8 to 6.6, preferably less than or equal to 6.0, particularly preferably less than or equal to 5.5.
• a weight ratio of 4.8 to 6.6 preferably less than or equal to 6.0, particularly preferably less than or equal to 5.5.
• the weight ratio according to the invention has proven advantageous in that a comparatively high zinc content has a negative impact on corrosion resistance. An excessively high magnesium content increases the flow resistance and thus reduces productivity.
• W-temper is an intermediate state defined in EN 515 and means that the component has been subjected to a solution treatment after extrusion and then quenched. In this state, the material is not yet stable and can be soft-formed for a short time. Since natural aging occurs rapidly immediately after quenching and diminishes over time, forming takes place within 30 minutes of quenching to achieve reproducible results.
• the T5 temper is defined as cooling after a forming process at elevated temperature followed by artificial aging. Since the standard does not specify the actual "elevated" temperature, it cannot be lower than the solution annealing temperature. However, this is not necessary. Cooling can also be rapid enough to produce the best possible solid solution. Artificial aging is synonymous with a final heat treatment to ensure the subsequent stability of the microstructure and properties.
• T5x are modified versions of the T5 temper, with additional process steps or process variations. Details are specified in EN 515.
• the T6 temper comprises a solution treatment, in particular solution annealing, followed by artificial aging.
• solution treatment the aluminum alloy material is heated to a high temperature, in particular below the recrystallization temperature, preferably to 450°C to 560°C, to dissolve the alloying elements such as zinc, magnesium, and copper.
• the aluminum alloy material is then cooled in water or another quenching agent to obtain the solution of alloying elements in the aluminum matrix. This is done in particular to a temperature of 200°C at a cooling rate of 5 to 100°C/min.
• the aluminum alloy material is heated in particular to a temperature between 90°C and 210°C, preferably between 120°C and 190°C, and held for a specified time. This can be done in a single-step or multi-step process. This artificial aging leads to the formation of fine precipitates that significantly increase the strength of the alloy. In the T6 temper, the structural component exhibits high strength.
• the T6x temper refers to a modified version of the T6 temper with additional process steps or process variations. Details are specified in EN 515.
• the T7 temper is similar to the T6 temper, but with a longer and more intensive artificial aging after solution treatment, also known as overaging. Instead of a normal aging period, the alloy in the T7 treatment is held at a specific temperature for a longer period. In the overaged condition, 7000 series alloys generally exhibit slightly lower strength compared to the T6 temper, but higher toughness, fracture toughness, and corrosion resistance.
• the T7x condition refers to a modified version of the T7 condition with additional process steps or process variations. Details are specified in EN 515.
• the structural component according to the invention is hollow.
• High-strength aluminum alloys of the 7000 series are generally difficult to extrude. Such alloys are therefore usually only used for simple, open, and thick extruded profiles.
• the composition according to the invention ensures improved corrosion resistance while simultaneously providing high extrudability without compromising the mechanical properties of the manufactured structural component.
• the structural component has single-, double-, or multi-chamber profiles with local wall thicknesses of up to 2.5 mm for the higher-alloyed variants and up to 2 mm for the lower-alloyed variants, which can be extruded with good productivity.
• the structural component has an elastic limit Rp02 greater than 270 MPa. This applies in particular to parts of the structural component that are intended to be crash-proof in the extrusion direction.
• the elastic limit of the structural component describes the point up to which the material can be elastically, and therefore reversibly, loaded before it is permanently plastically deformed. Crash-proof within the meaning of the invention are areas that deform largely plastically when loaded and, upon reaching the elastic limit of the material and/or the geometric design, are Shear off the rest of the component.
• Parts of the structural component that are subjected to transverse bending and compression loads with respect to the extrusion direction preferably have an elastic limit Rp02 greater than 320 MPa, and structural parts without specific crash requirements have an elastic limit Rp02 of more than 360 MPa.
• the structural component has at least partially recrystallized outer layers, each of which has a thickness corresponding to no more than 15%, preferably less than 12%, particularly preferably less than 8% of a wall thickness of the structural component at the respective location.
• the structural component preferably has a fibrous microstructure, i.e. thin, long grains in the extrusion direction.
• the inventive formation of the structural component by the heat treatment after extrusion can relate to the entire structural component or selected profile sections of the structural component.
• the features of the extruded structural component essential to the invention complement each other synergistically and, in combination, form a structural component which has a high and, compared to structural components made of aluminum alloys of the 7000 series known in the prior art, improved stress corrosion cracking resistance.
• the structural component in the T6 and T6x state has a critical stress intensity factor KISCC (Stress Corrosion Cracking Fracture Toughness) of greater than 7 MPa ⁇ m and in the T7 and T7x state a critical stress intensity factor KISCC of greater 25 MPa ⁇ m
• KISCC Stress Corrosion Cracking Fracture Toughness
• KISCC Stress Corrosion Cracking Fracture Toughness
• DCB Double Cantilever Beam
• the structural component according to the invention preferably has a crack propagation rate DCD (Delayed Cracking Detection) of less than 0.03 mm/h in the T6 and T6x states and a crack propagation rate DCD of less than 0.001 mm/h in the T7 and T7x states.
• the crack propagation rate indicates how quickly a crack propagates under the test conditions described in the previous paragraph.
• it has been shown that the crack propagation rate of the structural components according to the invention could be significantly reduced compared to components known from the prior art.
• structural components known from the prior art have crack propagation rates DCD of approximately 0.6 mm/h in the T6 state and approximately 0.004 mm/h in the T7 state.
• the high stress corrosion cracking resistance of the structural component according to the invention was also confirmed by realistic tests with a special corrosion medium based on the test standard VW PV 1210.
• Tests conducted directly on the structural components according to the invention have shown that they remain corrosion-free in both the T6 and T7 tempers even after 72 days of testing.
• State-of-the-art components made of standard 7108 (EN 573) alloys in the T6 and T7 tempers exhibited corrosion-induced cracks after 63 days of testing at the latest.
• Zn and Mg are present in the aluminum alloy in a weight ratio of 5.0 to 5.5.
• the aluminum alloy has a Mg content of 0.5 to 1.2 wt.%, preferably 0.5 to 1.0 wt.%.
• the aluminum alloy has a Si content of 0.50 to 1.2 wt.%, preferably 0.05 to 1.0 wt.%.
• the aluminum alloy is made from 25 to 100 wt.% secondary material.
• the secondary material is, in particular, recycled aluminum, which is preferably obtained from production scrap and end-user scrap.
• the aluminum alloy is made from 10 to 100 wt.% end-user scrap. This use of scrap saves resources, reduces waste, and lowers emissions, as only a fraction of the energy required to produce the primary materials is used.
• CO2 emissions can be reduced to 3 kg CO2 equivalent/kg of 7000 series alloy, preferably to less than 2 kg CO2 equivalent/kg of 7000 series alloy, compared to more than 8 kg CO2 equivalent/kg of 7000 series alloy, which is considered typical today.
• the structural component preferably has a wall thickness of less than 5 mm, preferably less than 4 mm, and particularly preferably less than 3 mm. These wall thicknesses have proven advantageous for the formation of the recrystallized outer layers.
• the thicknesses of the recrystallized outer layers on both sides correspond to a maximum of 5% of the respective local wall thickness of the structural component.
• the recrystallized outer layers have, in particular, an average grain size of less than or equal to 300 ⁇ m, preferably less than or equal to 250 ⁇ m, or a maximum grain size of less than or equal to 300 ⁇ m.
• an average grain size of less than or equal to 300 ⁇ m, preferably less than or equal to 250 ⁇ m, or a maximum grain size of less than or equal to 300 ⁇ m.
• Corresponding grain boundaries in conjunction with the recrystallized outer layers, can increase the material's tensile strength and hardness. Furthermore, improved stress corrosion cracking resistance can be achieved.
• the structural component preferably has a recrystallization-free core between the recrystallized outer layers. This further improves the mechanical properties, crushability, and corrosion resistance of the component.
• the structural component is manufactured with a local degree of deformation greater than 10%, preferably greater than 15%, particularly preferably greater than or equal to 20%, very particularly preferably greater than or equal to 25%.
• the combination of the specific chemical composition, the microstructure, and the processing, in particular the low recrystallization during extrusion and the repeated solution annealing and quenching without recrystallization before forming, as provided for in this invention, is very advantageous for the complex local downstream forming.
• the local degree of deformation can be derived from a forming simulation, which is carried out using a suitable material card and is checked on the corresponding component by checking the geometry before and after forming.
• the forming of the solution-annealed and quenched extruded profile in the W-temper condition can be carried out within 1 h, preferably within 0.5 h after extrusion.
• the forming of the structural component is carried out with a local degree of deformation greater than 10%, preferably greater than 15%, particularly preferably greater than 20%, most particularly preferably greater than 25%.
• the structural component is formed in at least one tool under at least one press.
• the structural component can also be cut and/or punched in at least one tool under at least one press.
• the forming process to produce the finished extruded component can involve bending or stretch bending within two or three spatial directions, or a compression or compression-tension forming process.
• the recrystallized outer layers according to the invention are subsequently determined using the Figure 1 illustrated microscopic image of a cross-section of a wall of a structural component according to the invention.
• FIG. 1a shows a microscopic image of a cross-section of a wall 1 of a structural component according to the invention, taken transversely to the extrusion direction.
• Wall 1 has a wall thickness D of approximately 2.4 mm and has recrystallized outer layers 2, 3 on both sides.
• the recrystallized outer layers are in the Figures 1b and 1c Enlarged detailed views.
• the upper recrystallized outer layer 2 has a thickness D2 of approximately 109 ⁇ m
• the lower recrystallized outer layer 3 has a thickness D3 of approximately 64 ⁇ m.
• the thicknesses D2 and D3 each refer to a single measurement point and are naturally subject to slight fluctuations.
• the thickness D2 of the upper outer layer 2 thus corresponds to approximately 4.5% of the wall thickness D of wall 1 of the structural component.
• the thickness D3 of the lower outer layer 3, in this exemplary embodiment, corresponds to approximately 2.7% of the wall thickness D of wall 1 of the structural component.
• the wall 1 of the structural component has a recrystallization-free core 4.
• the Figure 2 shows a test setup 5 for determining a critical stress intensity factor and a crack propagation velocity.
• the sample body 6 is taken from a structural component according to the invention and has a V-shaped recess 7 at its end.
• the tip 8 of the V-shaped recess 7 points towards the nearby sample end.
• a free space 9 is formed between an upper section 10 and a lower section 11 of the sample body 6.
• the V-shaped recess 7 and the free space 9 each have a height h1 of 2.5 mm.
• This is also shown in the Figure 2d shown detailed view DA of the Figure 2b can be seen.
• the detailed view also shows that the V-shaped recess 7 has a V-shaped indentation 12 extending toward the rest of the specimen 6.
• An angle ⁇ of 60° is formed between the legs 13 of the V-shaped indentation 12.
• the V-shaped recess 7 and indentation 12 serve as the initial crack for a double cantilever beam test to initiate crack propagation.
• the upper section 10 of the specimen 6 has a through-hole 14 with a thread in which a screw 15 is arranged.
• the screw 15 has a ball 16 at its lower end, which is in contact with the lower section 11 of the specimen 6.
• a distance a1 of 6.4 mm is formed between the recess-side end of the specimen and the longitudinal axis LA of the screw 15.
• a distance a2 of 5 mm is formed between the longitudinal axis LA of the screw 15 and the tip 8 of the V-shaped recess 7.
• the V-shaped recess 7 extends with a length l2 of 15 mm in the longitudinal direction LR of the specimen 6.
• the test can first determine the critical stress intensity factor (KISCC). This is the stress intensity at which the first crack formation occurs. This is also the case in the Figure 3 This can be seen in the graph shown, which shows an example of the crack growth rate as a function of stress intensity.
• the crack growth rate itself is determined by measuring the crack length over time.
• the tests have shown that the structural component in the T6 and T6x state has a critical stress intensity factor KISCC of greater than 7 MPa ⁇ m and in the T7 and T7x condition a critical stress intensity factor KISCC of greater than 25 MPa ⁇ m
• the crack propagation velocity DCD is less than 0.03 mm/h in the T6 and T6x states and less than 0.001 mm/h in the T7 and T7x states.

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• Crystallography & Structural Chemistry (AREA)
• Extrusion Of Metal (AREA)

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Citations (3)

• 2025
  • 2025-03-10 EP EP25162651.1A patent/EP4610389A1/fr active Pending

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