Extruded structural component for a motor vehicle and method for producing same

Abstract

The invention relates to an extruded structural component for a motor vehicle, which is made of an aluminum alloy of the 7000 series, wherein the aluminum alloy has the following composition in addition to Al and unavoidable impurities: • 4.50 to 6.60 wt.% Zn, • 0.50 to 1.7 wt.% Mg, • 0.10 to 0.20 wt.% Zr, • 0.12 to 0.35 wt.% Cu, • 0.02 to 0.16 wt.% Si, • 0.00 to 0.30 wt.% Fe, • and 0.00 to 0.10 wt.% Mn and 0.05 wt.% Cr and / or Ti, wherein Zn and Mg are present in a weight ratio of 4.8 to 6.6, wherein the structural component is formed after extrusion in the W-temper and has one of the tempering states T5, T5x, T6, T6x, T7 or T7x, wherein the structural component is hollow and has an elastic limit Rp0.2 > 250 MPa, wherein the structural component has recrystallized outer layers (2, 3) which each have a thickness (D2, D3) corresponding to less than 15% of a wall thickness (D) of the structural component.The invention further comprises a method for producing a structural component for a motor vehicle.

Description

[0001] The present invention relates to an extruded structural component for a motor vehicle according to the features of claim 1.

[0002] The invention further relates to a method for producing a structural component for a motor vehicle according to the features of claim 14.

[0003] 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. In particular, 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.

[0004] However, structural components made of 7000 series aluminum alloys are susceptible to stress corrosion cracking. 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.

[0005] Against this background, 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.

[0006] A further object of the invention is to provide a method for producing a corresponding structural component for a motor vehicle.

[0007] 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.

[0008] Advantageous embodiments of the invention are the subject of the dependent claims.

[0009] 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.

[0010] According to the invention, the aluminum alloy has the following composition in addition to aluminum and unavoidable impurities: 4.50 to 6.60 wt.% Zn (zinc). By adding zinc together with magnesium and copper, the strength of the structural component made from the aluminum alloy can be increased. However, within the scope of the invention, it has been found that adding more than 6.60 wt.% Zn can reduce extrudability. The use of less than 4.8 wt.% Zn, on the other hand, leads to low strength. 0.50 to 1.7 wt.% Mg (magnesium). The magnesium content also influences the strength, extrudability, and corrosion resistance of the structural component made from the aluminum alloy. If too much magnesium is added to the alloy, this can lead to poor extrudability of the alloy material. Within the scope of the invention, an upper limit of 1.7 wt.% Mg has proven advantageous here. If the amount of magnesium added is too small, this can lead to reduced strength.Therefore, according to the invention, the aluminum alloy contains at least 0.50 wt.% Mg. 0.10 to 0.20 wt.% Zr (zirconium). Zirconium is added to the aluminum alloy to improve the microstructure of the alloy. Too low a zirconium content can lead to impaired toughness, formability, joinability, and corrosion resistance. Therefore, according to the invention, at least 0.1 wt.% Zr is added to the alloy. An excessive zirconium content can lead to embrittlement of the alloy or cause problems in the production of cast alloys as a basis for later extrusion. Therefore, a maximum value of 0.20 wt.% has proven appropriate within the scope of the invention. 0.12 to 0.35 wt.% Cu (copper). Copper is a precipitation-hardening element and contributes to the strength of the alloy through the formation of stable Zn-Mg-Cu precipitates.These precipitates also have a lower electrochemical potential, thus reducing the alloy's sensitivity to stress corrosion. However, too high a copper content can impair the alloy's corrosion resistance and extrudability. In the context of the invention, a maximum value of 0.35 wt.% Cu has proven advantageous. However, too low a copper content can lead to reduced strength, so that according to the invention the alloy contains at least 0.12 wt.% Cu, 0.02 to 0.16 wt.% Si (silicon), 0.00 to 0.30 wt.% Fe (iron), 0.00 to 0.10 wt.% Mn (manganese), and 0.05 wt.% Cr (chromium) and / or Ti (titanium). The addition of appropriate amounts of the elements Si, Fe, Mn, Cr, and / or Ti serves to improve the alloy's microstructure and mechanical properties such as strength, toughness, corrosion resistance, and machinability.Within the scope of the invention, it has been found that these effects are particularly advantageous within the specified intervals. The effects are particularly advantageous when Si is less than 0.15 wt.% and Fe is less than 0.25 wt.%. The elements Si, Fe, Mn, Cr, and Ti are particularly attributable to the use of secondary material. Surprisingly, it was found within the scope of the invention that improved corrosion resistance can be achieved despite the presence of corresponding amounts of the elements Si, Fe, Mn, Cr, and / or Ti.

[0011] It is essential to the invention that 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. Within the scope of the invention, it has been shown that only in this ratio of zinc to magnesium does the desired shape and number of precipitates form, without an undesirable excess of one of these elements occurring. The precipitates determine the strength of the alloy on the one hand and its stress corrosion resistance on the other. 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.

[0012] The structural component is formed after extrusion in the W-temper. 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.

[0013] The structural component has one of the temper states T5, T5x, T6, T6x, T7, or T7x according to EN 515. The temper states refer to the specific heat treatment that the aluminum alloy or structural component has undergone after extrusion. The temper states influence the mechanical properties of the structural component, such as strength, toughness, crash behavior, and corrosion resistance.

[0014] 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.

[0015] T5x are modified versions of the T5 temper, with additional process steps or process variations. Details are specified in EN 515.

[0016] The T6 temper comprises a solution treatment, in particular solution annealing, followed by artificial aging. During 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, in order 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 carried out in particular to a temperature of 200°C at a cooling rate of 5 to 100°C / min. After quenching and an optional intermediate storage during which the material ages naturally, 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 there for a specified time.This can be done in a single-stage or multi-stage 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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. However, 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. In particular, 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.

[0021] 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 undergoes permanent plastic deformation. Crash-proof within the meaning of the invention are regions that largely deform plastically under load and shear off from the rest of the component when the elastic limit of the material and / or the geometric design is reached. Parts of the structural component that are exposed 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.

[0022] Since corrosion reactions occur at the grain boundaries and spread where the difference in electrochemical potential between precipitates and the surrounding depleted zones is greatest, it is advantageous if as many grain boundaries as possible are present across the entire thickness of the profile. A fibrous microstructure ensures this. Within the scope of the present invention, it is therefore important that the component has only a thin recrystallized layer. Therefore, it is essential within the scope of the invention that 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. Between the recrystallized outer layers, the structural component preferably has a fibrous microstructure, i.e. thin, long grains in the extrusion direction.

[0023] 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.

[0024] 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.

[0025] Preferably, 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 The critical stress intensity factor (KISCC) indicates the value above which crack growth is expected. The critical stress intensity factor is calculated as follows: KISCC = Δ Eh 3 h a + 0 , 6 h 2 + h 3 0 , 5 4 a + 0 , 6 h 3 + h 2 a

[0026] To determine the critical stress intensity factor, screw-loaded and pre-cracked DCB (Double Cantilever Beam) specimens were used in accordance with ASTM G168-17. These specimens were wetted with a 3.5 wt.% NaCl solution and exposed to a humid atmosphere (82% relative humidity, 40 °C). The DCB specimens were taken from a structural component according to the invention. Δ is the deflection of the specimen at the loading point caused by the screw, E is the elastic modulus, h is half the length of the specimen height, and a is the crack length. The crack length is measured with a light microscope from the crack tip to the load line. The structural components according to the invention have a significantly higher stress intensity factor than comparable components known from the prior art. For known components in the T6 state, this is typically approximately 3 MPa. m and for known components in T7 condition approx. 16 MPa ⋅ m .

[0027] 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. Within the scope of the invention, 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. Thus, 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.

[0028] 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.

[0029] The test cycle is cyclical and consists of three phases that repeat: 1. Salt spray phase: Duration: 4 hours Conditions: Salt spray according to DIN 50021-SS Purpose: Simulates the influence of a salty atmosphere, such as that found in coastal regions or on winter roads. 2. Normal climate phase: Duration: 4 hours Conditions: 23 °C and 50% relative humidity according to DIN 50014-23 / 50-2 Purpose: Represents typical ambient conditions for evaluating material behavior under normal climatic conditions. 3. Humid climate phase: Duration: 16 hours Conditions: 40 ± 3 °C and 100% relative humidity according to DIN 50017-KK Purpose: Simulates high humidity conditions to test the effects of condensation on corrosion resistance.

[0030] After five of these cycles, a two-day rest period follows to evaluate the results under more realistic conditions. This procedure allows the corrosion behavior of materials and coatings to be investigated under changing climatic conditions.

[0031] 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.

[0032] Preferably, Zn and Mg are present in the aluminum alloy in a weight ratio of 5.0 to 5.5.

[0033] The aluminum alloy preferably has a Zn content of 4.5 to 6 wt.%, preferably 4.5 to 5.5 wt.%.

[0034] It has also proven advantageous if the aluminum alloy has a Mg content of 0.5 to 1.2 wt.%, preferably 0.5 to 1.0 wt.%.

[0035] In particular, the aluminum alloy has a Si content of 0.50 to 1.2 wt.%, preferably 0.05 to 1.0 wt.%.

[0036] In a particularly advantageous embodiment of the invention, 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 particularly preferably made from 10 to 100 wt.% end-user scrap. This use of scrap saves resources, reduces waste, and reduces emissions, as only a fraction of the energy required to produce the primary materials is used. Depending on the content and type of secondary material and the type of energy 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.

[0037] 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.

[0038] Preferably, 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.

[0039] The recrystallized outer layers have, in particular, an average grain size of less than or equal to 300 µm, preferably less than or equal to 250 µm, or a maximum grain size of less than or equal to 300 µm. Within the scope of the invention, it has been found that corresponding grain boundaries in conjunction with the recrystallized outer layers lead to an increase in the tensile strength and hardness of the material. Furthermore, improved stress corrosion cracking resistance can be achieved.

[0040] 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.

[0041] It has also proven advantageous if 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.

[0042] The method according to the invention for producing a structural component for a motor vehicle, in particular a structural component according to one of claims 1 to 13, comprises the following method steps: Providing an aluminum alloy material which, in addition to Al and unavoidable impurities, has the following composition: 4.50 to 6.60 wt% Zn, 0.50 to 1.7 wt% Mg, 0.10 to 0.20 wt% Zr, 0.12 to 0.35 wt% Cu, 0.02 to 0.16 wt% Si, 0.00 to 0.30 wt% Fe, 0.00 to 0.10 wt% Mn, and less than 0.05 wt% Cr and / or Ti, wherein Zn and Mg are present in a weight ratio of 4.8 to 6.6. Extruding the aluminum alloy material to form a hollow extruded profile. Solution annealing the extruded profile below the recrystallization temperature, in particular at 450°C to 560°C. Solution annealing achieves a homogeneous microstructure in which the elements contained in the alloy are evenly distributed. The solution-annealed extruded profile is then quenched, using a cooling rate of 5 to 100 °C / min up to a temperature of 200 °C.Quenching is carried out in particular using a liquid medium such as water or oil. The cooling rate according to the invention can particularly advantageously prevent the dissolution of the alloying elements after solution annealing. Forming the solution-annealed and quenched extruded profile to form the structural component in the W-tempered state within 2 hours of extrusion. Within the scope of the invention, it has been found that forming more than 2 hours after extrusion has a detrimental effect on formability. Artificial aging of the structural component so that the structural component has one of the temper states T5, T5x, T6, T6x, T7, or T7x.

[0043] 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.

[0044] In particular, 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%.

[0045] Preferably, 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.

[0046] 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.

[0047] All features of the structural component can be combined with the process for manufacturing a structural component.

[0048] Further properties and features of the invention are explained in more detail in the following description of the figures. They show: Figure 1 shows recrystallized outer layers according to the invention, Figure 2 shows sample design and test arrangement for determining a stress intensity factor and a crack propagation rate, and Figure 3 shows a schematic representation of the effect of stress intensity on the crack growth rate.

[0049] 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.

[0050] The Figure 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.

[0051] The recrystallized outer layers are in the Figures 1b and 1cEnlarged detailed views. The upper recrystallized outer layer 2 has a thickness D2 of approximately 109 µm, and the lower recrystallized outer layer 3 has a thickness D3 of approximately 64 µm. 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.

[0052] Between the recrystallized outer layers 2, 3, the wall 1 of the structural component has a recrystallization-free core 4.

[0053] The Figure 2 shows a test setup 5 for determining a critical stress intensity factor and a crack propagation velocity.

[0054] In the Figures 2a to 2cThe test setup 5 is shown in a top view, a side view, and a front view. The test setup 5 comprises a specimen 6 with a width b of 25.4 mm, a height 2h of 25.4 mm, and a length l of 127 mm.

[0055] 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. Between the tip 8 of the V-shaped recess 7 and the end of the sample body 6, 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 2bcan 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 α 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.

[0056] 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.

[0057] 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.

[0058] During the test, a defined constant force is applied to the specimen 6 by rotating the screw 15, which pushes the upper section 10 and the lower section 11 apart. During the test, the specimen is wetted with a 3.5 wt.% NaCl solution, and the test takes place in a humid atmosphere with 82% relative humidity at 40 °C.

[0059] 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.

[0060] 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. These values ​​represent a significant improvement over prior art components, which exhibit significantly lower critical stress intensity factors and higher crack propagation velocities. Reference symbol:

[0061] 1 - wall 2 - recrystallized outer layer 3 - recrystallized outer layer 4 - recrystallization-free core 5 - test arrangement 6 - specimen 7 - recess 8 - tip of 7 9 - free space 10 - upper section 11 - lower section 12 - indentation 13 - leg 14 - bore 15 - screw 16 - ball D -Wall thickness of 1 D2 -Thickness of 2 D3 -Thickness of 3 b -Width of 6 h -Height of 6 l -Length of 6 DA -Detail view α -Angle LA -Longitudinal axis of 15 LR -Longitudinal direction of 6 a1 -Distance a2 -Distance l2 -Length h1 -Height of 7 and 9

Claims

1. Extruded structural component for a motor vehicle, which is made of an aluminum alloy of the 7000 series, wherein the aluminum alloy has the following composition in addition to Al and unavoidable impurities: • 4.50 to 6.60 wt.% Zn, • 0.50 to 1.7 wt.% Mg, • 0.10 to 0.20 wt.% Zr, • 0.12 to 0.35 wt.% Cu, • 0.02 to 0.16 wt.% Si, • 0.00 to 0.30 wt.% Fe, • and 0.00 to 0.10 wt.% Mn and 0.05 wt.% Cr and / or Ti, wherein Zn and Mg are present in a weight ratio of 4.8 to 6.6, wherein the structural component is formed after extrusion in the W-temper and has one of the tempering states T5, T5x, T6, T6x, T7 or T7x, wherein the structural component is hollow and has an elastic limit Rp0.2 > 250 MPa, wherein the structural component has recrystallized outer layers (2, 3) which each have a thickness (D2, D3) corresponding to less than 15% of a wall thickness (D) of the structural component.

2. Structural component according to claim 1, characterized in that the structural component in the T6 and T6x state has a critical stress intensity factor KISCC of greater 7 MPa ⋅ m and in the T7 and T7x state a critical stress intensity factor KISCC of greater 25 MPa ⋅ m has.

3. Structural component according to claim 1 or 2, characterized in that the structural component has a crack propagation velocity DCD of less than 0.03 mm / h in the T6 and T6x states and a crack propagation velocity DCD of less than 0.001 mm / h in the T7 and T7x states.

4. Structural component according to one of claims 1 to 3, characterized in that in the aluminum alloy Zn and Mg are present in a weight ratio of 5.0 to 5.8, in particular from 5.0 to 5.5, preferably less than 6.0, particularly preferably less than 5.

5.

5. Structural component according to one of claims 1 to 4, characterized in thatthe aluminum alloy has a Zn content of 4.50 to 6.0 wt.%, preferably 4.50 to 5.5 wt.%.

6. Structural component according to one of claims 1 to 5, characterized in that the aluminum alloy has a Mg content of 0.50 to 1.2 wt.%, preferably 0.05 to 1.0 wt.%.

7. Structural component according to one of claims 1 to 6, characterized in that the aluminum alloy has a Si content of 0.05 to 0.16 wt.%, in particular 0.08 to 0.15 wt.%.

8. Structural component according to one of claims 1 to 7, characterized in that the aluminum alloy is made of 25 to 100 wt.% secondary material.

9. Structural component according to one of claims 1 to 8, characterized in that the aluminum alloy is made from 10 to 100 wt.% end-user scrap.

10. Structural component according to one of claims 1 to 9, characterized in that the structural component has a wall thickness (D) < 5 mm, preferably < 4 mm, particularly preferably < 3 mm.

11. Structural component according to one of claims 1 to 10, characterized in that the recrystallized outer layers (2, 3) have an average grain size < 300 µm or a maximum grain size ≤ 300 µm.

12. Structural component according to one of claims 1 to 11, characterized in that the structural component has a recrystallization-free core (4) between the recrystallized outer layers (2, 3).

13. Structural component according to one of claims 1 to 12, characterized in that the structural component is manufactured with a local degree of deformation > 10%, preferably > 15%, particularly preferably ≥ 20%, most particularly preferably ≥ 25%.

14. Method for producing a structural component for a motor vehicle with the following steps: • Providing an aluminum alloy material which, in addition to Al and unavoidable impurities, has the following composition: - 4.50 to 6.60 wt.% Zn, - 0.50 to 1.7 wt.% Mg, - 0.10 to 0.20 wt.% Zr, - 0.12 to 0.35 wt.% Cu, - 0.02 to 0.16 wt.% Si, - 0.00 to 0.30 wt.% Fe, - and 0.00 to 0.10 wt.% Mn and at least 0.05 wt.-% Cr and / or Ti, where Zn and Mg are present in a weight ratio of 4.8 to 6.6, • Extruding the aluminum alloy material to form a hollow extruded profile, • Solution annealing the extruded profile below the recrystallization temperature, in particular at 450°C to 560°C, • Quenching the solution annealed extruded profile, using a cooling rate of 5 to 100°C / min up to a temperature of 200°C, • Shaping the solution annealed and quenched extruded profile to form the structural component in the W-temper state within 2 hours after extrusion, • Artificially aging the structural component so that the structural component has one of the temper states T5, T5x, T6, T6x, T7 or T7x.

15. Method according to claim 14, characterized in that the forming of the solution-annealed and quenched extruded profile in the W-tempered state is carried out within 1 h, preferably within 0.5 h after extrusion.

16. Method according to claim 14 or 15, characterized in that the forming of the solution-annealed and quenched extruded profile in the W-tempered state is carried out within 5 minutes in at least one tool under at least one press.

17. Method according to one of claims 14 to 16, characterized in that the forming of the solution-annealed and quenched extruded profile into the structural component is carried out with a local degree of deformation > 10%, preferably > 15%, particularly preferably ≥ 20%, most particularly preferably ≥ 25%.

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