Aluminum alloy, application of aluminum alloy, structural component for motor vehicle and motor vehicle

Abstract

The invention relates to an aluminum alloy with enhanced ductility for structural casting. The aluminum alloy comprises aluminum and inevitable impurities, 7.5 to 11.5 weight percent of silicon; 0.25 to 0.6 weight percent of manganese; 0.03 to 0.06 weight percent of chromium; 0.001 to 0.048 weight percent of molybdenum; 0.04 to 0.095 weight percent of magnesium, in particular 0.06 to 0.095 weight percent of magnesium; 0.17 to 0.5 weight percent of iron; 0.03 to 0.5 weight percent of copper; a maximum of 0.35 weight percent of zinc; and 0.004 to 0.15 weight percent of titanium.

Description

Technical Field

[0001] This invention relates to an aluminum alloy with enhanced ductility for structural casting, the application of the aluminum alloy in die-cast structural components, structural components made of the aluminum alloy for motor vehicles, and motor vehicles. Background Technology

[0002] For high-load die-cast components in vehicle structures, solution-annealed alloys are primarily used. This is because solution annealing advantageously alters the structure, thereby achieving high ductility in addition to high strength, which is beneficial for component performance and the joining process.

[0003] On the other hand, using recycled aluminum can reduce costs, decrease energy input and thus reduce CO2 emissions (CO2 footprint) in vehicle manufacturing, and improve the durability of the aluminum used. Therefore, the use of recycled aluminum alloys is advantageous in terms of durability and climate protection. This is because using recycled alloys instead of virgin aluminum alloys to manufacture components can achieve CO2 emission reductions ranging from approximately 5 to 17 tons of CO2 equivalent per ton of aluminum alloy.

[0004] However, when using recycled aluminum or utilizing recycled waste to manufacture aluminum components, "impurity elements" are typically present in the alloy. Impurity elements refer to elements that are not essential for achieving the desired performance but are detrimental instead, yet cannot be avoided during the recycling process and are therefore present in the final product of the recycling process. Typical impurity elements are iron, copper, zinc, and titanium. A high proportion of recycled aluminum is chosen, which is associated with an increased proportion of these impurity elements in the alloy.

[0005] Furthermore, it is advantageous to use AlSi9Mn-type naturally hardening alloys, which do not harden due to their very low magnesium content, thus eliminating the need for subsequent heat treatment and, consequently, solution annealing. Therefore, components made from such alloys can be produced cost-effectively due to the lack of unnecessary heat treatment, and these alloys also enable the manufacture of very large, one-piece die-cast components. This trend makes it possible to manufacture vehicle bodies with the smallest possible body manufacturing area and equipment investment.

[0006] For example, document EP 1 443 122 A1 describes an aluminum alloy suitable for die-casting components with high elongation in the as-cast state, the aluminum alloy comprising: 8.5 to 10.5 wt% silicon; 0.3 to 0.8 wt% manganese; up to 0.06 wt% magnesium; up to 0.15 wt% iron; up to 0.03 wt% copper; up to 0.10 wt% zinc; up to 0.15 wt% titanium; 0.05 to 0.5 wt% molybdenum; 30 to 300 ppm strontium; or 5 to 30 ppm sodium; and / or 1 to 30 ppm calcium for continuous refining processes. Optionally, the alloy also contains: 0.05 to 0.3 wt% zirconium; gallium phosphide and / or indium phosphide in a content corresponding to 1 to 250 ppm phosphorus for grain refinement; titanium and boron, added by means of an aluminum master alloy comprising 1 to 2 wt% Ti and 1 to 2 wt% B for grain refinement; aluminum as the remainder and unavoidable impurities.

[0007] Furthermore, document EP 3 775 309 B1 (WO 2020 / 207 708 A1) describes an aluminum die-casting alloy having the following alloy composition: 7.5 to 11.5 wt% silicon; 0.25 to 0.6 wt% manganese; 0.03 to 0.06 wt% chromium; 0.001 to 0.048 wt%, particularly 0.001 to 0.043 wt%, particularly 0.024 to 0.043 wt% molybdenum; 0.001 to 0.08 wt% magnesium; optionally 0.001 to 0.15 wt% iron; optionally 0.004 to 0.15 wt% titanium; optionally 0.01 to 0.2 wt% zirconium; optionally 0.008 to 0.02 wt% strontium; optionally 0.001 to 0.1 wt% strontium. Vanadium by weight percentage; aluminum as the remainder and unavoidable impurities.

[0008] Furthermore, document EP 3 235 917 A1 describes an aluminum-silicon based die-casting alloy with the following composition: 8.5 to 11.5 wt% silicon; 0.1 to 0.5 wt% magnesium; 0.3 to 0.8 wt% manganese; 0.02 to 0.5 wt% iron; 0.005 to 0.5 wt% zinc; 0.02 to 0.3 wt% molybdenum; 0.1 to 0.5 wt% copper; 0.02 to 0.15 wt% titanium; 0.02 to 0.3 wt% zirconium; 5 to 250 ppm phosphorus; 10 to 200 ppm gallium; aluminum as the remainder; and unavoidable impurities. This alloy can be manufactured with a 50% recycling rate. Summary of the Invention

[0009] Therefore, the purpose of this invention is to provide a naturally hardened aluminum casting alloy that does not require subsequent heat treatment after casting, has good mechanical properties, and can reduce costs and CO2 footprint.

[0010] According to the invention, the objective is achieved by an aluminum alloy for structural casting having the features described in claim 1, which has enhanced ductility. Furthermore, the objective is achieved by the application of this aluminum alloy, as described in another independent claim, to die-cast structural components, structural components for motor vehicles made from this aluminum alloy, and motor vehicles having structural components. Advantageous improvements of the invention are given in the dependent claims.

[0011] The present invention is based on the following basic idea: to provide an aluminum alloy that can use a high proportion of recycled aluminum without degrading the mechanical properties of the aluminum alloy.

[0012] According to a first aspect, this disclosure provides an aluminum alloy with enhanced ductility for structural casting, the aluminum alloy comprising: 7.5 to 11.5 wt% silicon; 0.25 to 0.6 wt% manganese; 0.03 to 0.06 wt% chromium; 0.001 to 0.048 wt% molybdenum; 0.04 to 0.095 wt% magnesium, particularly 0.06 to 0.095 wt% magnesium; 0.17 to 0.5 wt% iron; 0.03 to 0.5 wt% copper; up to 0.35 wt% zinc; 0.004 to 0.15 wt% titanium; aluminum as the remainder; and unavoidable impurities.

[0013] It should be noted that there is a conflict of objectives when using aluminum die-cast components. Silicon-containing alloys are advantageous in aluminum die-cast components due to their casting properties. However, in applications where no heat treatment is performed, they are relatively brittle compared to annealed alloys because of the lack of a solution annealing process. This is because the eutectic silicon network restricts deformation capacity and promotes crack susceptibility in the brittle phase.

[0014] Here, solution annealing of alloys can often achieve better mechanical properties; however, it requires costly subsequent heat treatment processes. Due to these heat treatments, the size of the possible components is severely limited, or is only possible under conditions of high cost and high consumption, due to high space requirements, high energy consumption, and long heating and cooling times.

[0015] Naturally hardened alloys do not have this limitation and do not require costly subsequent processes, thus reducing the manufacturing cost of body components when using them. However, they are also relatively brittle.

[0016] Here, natural hardening refers to the situation where the required strength increase can only be achieved through solid solution strengthening and work hardening, without precipitation hardening. Therefore, naturally hardening alloys are also known as non-heat-treatable alloys. Conversely, the strength increase of heat-treatable alloys is achieved through precipitation hardening (a special heat treatment). For example, some silicon-containing aluminum alloys (AlSi alloys) are naturally hardening alloys.

[0017] The ever-increasing size of components necessitates the use of naturally hardened alloys that do not require heat treatment, as this makes it easier to meet the tolerance requirements of the vehicle body and avoids high manufacturing costs.

[0018] By skillfully selecting alloying elements, a naturally hardening alloy can be created. Despite its high potential for recycling (recycled aluminum) and high potential post-consumer scrap rate, this alloy still possesses good casting properties, excellent mechanical properties, and high elongation.

[0019] Here, a silicon content within the range of 7.5 to 11.5 wt% ensures a good balance between ductility and casting performance for different component sizes. Silicon expands upon solidification, thus compensating for shrinkage during the solidification process of the cast component. Furthermore, compared to other elements, silicon releases a very large amount of energy upon solidification; therefore, a high silicon content ensures good fluidity, resulting in excellent casting properties of the alloy. If the selected silicon content is below 7.5 wt%, good fluidity cannot be achieved, therefore a silicon content below 7.5 wt% is not preferred. On the other hand, aluminum with a silicon content above 11.5 wt% tends to become brittle, therefore a silicon content above 11.5 wt% is also not preferred.

[0020] A skillful combination of manganese, chromium, and molybdenum content enables smooth demolding performance, thus allowing for defect-free production. Choosing a high proportion of manganese, chromium, and molybdenum can lead to severe segregation, which severely limits the material's mechanical properties. Conversely, excessively low manganese, chromium, and molybdenum content can cause undesirable adhesion between the component and the mold. The given combination achieves the optimal balance between demolding performance and mechanical properties.

[0021] Furthermore, the alloy may include a copper content of 0.03 to 0.5% by weight. Preferably, the alloy may include 0.03 to 0.23% by weight of copper, more preferably 0.03 to 0.21% by weight of copper, and even more preferably 0.03 to 0.17% by weight of copper. This reduced copper content increases the product of the elongation at break of the resulting alloy and the ratio of the 0.2% yield strength in the as-cast state (F) to the 0.2% yield strength in the state after heat treatment at 150°C for 1000 hours (h) (peak aging state), thus yielding a particularly preferred alloy.

[0022] The alloy may include 0.25 to 0.60 weight percent of manganese. Preferably, the alloy may include 0.30 to 0.60 weight percent of manganese, more preferably 0.32 to 0.60 weight percent of manganese, and even more preferably 0.35 to 0.60 weight percent of manganese.

[0023] In addition, the alloy may include 0.03 to 0.060 weight percent chromium. Preferably, the alloy may include 0.03 to 0.057 weight percent chromium, more preferably 0.03 to 0.050 weight percent chromium.

[0024] Limiting chromium is used to prevent coarse sludge phases that can degrade elongation, which is detrimental. However, increasing Mn content can be advantageous to prevent die sticking (poor mold release) at limited Cr content. These combinations can achieve exceptionally good elongation, exceptionally high deformability, and / or exceptionally high ductility while maintaining good mold release. Ductility can be characterized by elongation at break and can be a measure of a material's impact resistance and deformability, while also providing suitability for riveting, i.e., applicability, making it suitable for one of the most important cold joining technologies: riveting.

[0025] The upper limit of 0.095 wt% for magnesium allows for the use of high proportions of recycled aluminum, while maintaining the natural hardening properties of the alloys disclosed herein. Increasing the magnesium proportion further beyond 0.095 wt% may lead to age hardening over time (and / or temperature), resulting in an unfavorable unstable strength state. Conversely, below 0.04 wt%, the hardening effect of solid solution strengthening is lost, potentially leading to lower alloy strength. Significant solid solution strengthening and a thermally stable state can only be observed within the aforementioned range of 0.04 to 0.095 wt% magnesium, particularly 0.06 to 0.095 wt%.

[0026] Furthermore, it is advantageous that after the coating process, including heat treatment, the yield strength does not exceed 160 MPa and / or the increase in yield strength does not exceed 30 MPa (the increase in yield strength does not exceed 30 MPa), because such an increase indicates thermal instability. For example, in such a coating process, it may be set to continue at 80°C to 250°C for 10 to 120 minutes, particularly at 150°C to 250°C for 25 to 120 minutes.

[0027] In other words, in heat treatment simulating the coating process, or in heat treatment simulating temperature stress during the service life of a component (e.g., by heat treatment with a temperature load of 150°C for 1000 hours), the yield strength should not exceed 160 MPa and / or the increase in yield strength should not exceed 30 MPa; otherwise, thermal instability is indicated. Furthermore, excessively low yield strength values ​​may lead to fatigue strength problems.

[0028] The proportions of iron, copper, zinc, and titanium in the alloy disclosed herein allow the alloy to be made from a mixture of primary and recycled aluminum, wherein the content of recycled aluminum is maintained at a high level. On the other hand, according to the invention, the contents are selected such that even if the contents of iron, copper, zinc, and titanium are increased, coarser phase aggregates are not formed, thereby avoiding adverse effects on mechanical properties. From the perspective of corrosion resistance, unfavorable properties (which may be mainly caused by the presence of copper) can be kept within a limited range by the given weight proportions. For the purpose of manufacturing components with high ductility and good corrosion resistance or low corrosion susceptibility from the obtained aluminum alloy, it is advantageous to select copper and iron contents that are not too high.

[0029] In particular, this can significantly reduce the CO2 footprint in demanding fields such as structural casting, i.e., manufacturing structural components such as thin-walled car body parts. For example, producing one kilogram of aluminum alloy can achieve a CO2 emission reduction of more than 6 kilograms of CO2 equivalent. This is extremely beneficial for reducing the CO2 footprint.

[0030] Furthermore, iron, for example, is almost insoluble in aluminum alloys, and therefore precipitates almost entirely as a coarse intermetallic phase. In silicon-containing aluminum alloys, the β-Al₅FeSi phase is particularly unfavorable because it is needle-like. This needle-like iron-containing phase reduces the ductility of components obtained from the aluminum alloy. Moreover, this iron-containing intermetallic phase is very brittle and prone to aggregation. When the iron content in the aluminum alloy is high, these needle-like iron-containing phases can become very large.

[0031] In particular, these large intermetallic ferrous phases have a strong tendency to initiate cracks and thus often lead to premature failure of components under mechanical stress. This is especially attributed to the low ductility of the component material due to the presence of acicular ferrous phases.

[0032] By adding manganese and / or molybdenum and / or chromium and / or vanadium, the formation of the unfavorable β-Al5FeSi phase can be particularly suppressed, and an iron-containing α phase is formed instead. This α phase, containing manganese and / or molybdenum and / or chromium and / or vanadium in addition to iron and aluminum, ensures a more favorable morphology for the phases containing these additives. In particular, it prevents the formation of large, acicular iron-containing phases. This can lead to improved mechanical properties of components made from the obtained aluminum alloy. Specifically, the ductility of components formed from the obtained aluminum alloy can be significantly improved in this way.

[0033] Furthermore, the present invention includes improvements that provide additional advantages.

[0034] In an advantageous improvement of the invention, the alloy may further comprise 0.01 to 0.2 weight percent zirconium. This improvement allows for an increase in the yield strength of the alloy without heat treatment. Zirconium forms a so-called trialuminate, or Al3Zr phase, which has a grain-refining effect and also increases strength. This effect cannot be determined at very low content, therefore a lower limit of 0.01 weight percent is preferred. On the other hand, if the content is too high, exceeding 0.2%, coarser Al3Zr acicular phases are formed, which in turn leads to an undesirable decrease in ductility.

[0035] In an advantageous improvement of the invention, the alloy may further comprise 0.001 to 0.1 weight percent vanadium. This improvement allows for an increase in the yield strength of the alloy without heat treatment. Furthermore, the vanadium content enables the easy use of recycled aluminum. Similar to manganese, vanadium can also suppress or reduce β-AlFeSi by adding it to α-AlFeSi. At lower vanadium contents, the beneficial effects of vanadium can no longer be determined. If the vanadium content is increased above the given limit of 0.1 weight percent, a coarse phase can be formed again, resulting in poor or low ductility.

[0036] In an advantageous improvement of the invention, the alloy may further comprise 0.002 to 0.030 wt% strontium. This improvement allows for an increase in the yield strength of the alloy without heat treatment. Strontium can modify the silicon phase, causing it to form a fine network structure. If the selected strontium proportion is too low, this effect cannot be determined. However, if the selected strontium proportion is too high, so-called over-modification occurs, leading to a re-coarsening of the silicon phase and an unfavorable decrease in ductility. Furthermore, when the strontium content exceeds 0.03 wt%, the hydrogen content of the melt may increase, thereby reducing the quality of the casting.

[0037] In an advantageous embodiment of the invention, the aluminum alloy may be specified to comprise 25% by weight or more of recycled aluminum, and / or 10% by weight or more of post-consumer recycled aluminum. This embodiment offers the advantage that a reduction in CO2 footprint can be achieved in a simple manner with this composition.

[0038] In an advantageous improvement of the invention, the NDS value of the aluminum alloy may be specified to be greater than 6, preferably greater than 10, and even more preferably greater than 12. Here, the NDS value of the aluminum alloy is the product of the following three factors: the total amount of impurity elements; the elongation at break as a percentage; and the ratio of the 0.2% yield strength in the as-cast state to the 0.2% yield strength in the peak aged state, wherein the total amount of impurity elements is the sum of the elemental contents of the impurity elements as a weight percentage, and iron content is included in the total amount of impurity elements with double weight.

[0039] In other words, the elemental contents of iron, copper, zinc, and titanium are added together for the total impurity elements, with iron being counted twice due to its strong influence on the ductility of the aluminum alloy. The obtained total impurity element content is then multiplied by the elongation at break (in percent) in the as-cast state F, and further multiplied by the ratio of the 0.2% yield strength in the as-cast state F to the 0.2% yield strength in the state after heat treatment at 150°C for 1000 hours (peak aging state) to obtain the NDS value.

[0040] The NDS value describes the "Sustainability-Ductility-Stability Factor" (NDS), which clearly reflects the comprehensive performance advantages of the alloy according to the present invention. The NDS value corresponding to the above description is derived from the following formula:

[0041] NDS = [ (2xFe) + Cu + Zn + Ti ] * A * [R p0.2 (F) / R p0.2 (T5)]

[0042] Where Fe, Cu, Zn, and Ti represent the elemental contents of iron, copper, zinc, and titanium, respectively, expressed as a weight percentage; A represents the elongation at break, expressed as a percentage; and R... p0.2 (F) represents the 0.2% yield strength at as-cast F in MPa, R p0.2 (T5) represents the 0.2% yield strength under peak aging condition in MPa.

[0043] As can be seen from the formula above, the higher the NDS value, the better the cumulative core performance suitable for naturally hardened recycled car body casting alloys. The reason is:

[0044] - The total amount of high-impurity elements enables the use of a large proportion of recycled aluminum.

[0045] - The high elongation at break of the alloy enables the manufactured components to have good deformability and good stamping and riveting properties, and

[0046] High thermal stability means, for example, that the alloy retains its favorable properties after the coating process and throughout the service life of the component (and does not undergo age hardening, and thus, for example, the yield strength is also increased). This high thermal stability is verified by the aforementioned heat treatment tests, and if the yield strength increases significantly by 0.20% after heat treatment (e.g., at 150°C for 1000 hours), the ratio R... p0.2 (F) / R p0.2 (T5) becomes smaller.

[0047] If the control alloys 1, 2 and 3 listed in Tables 1 and 2 are compared with the alloys according to the present invention, it can be found that the NDS factor of the alloys according to the present invention is more than twice that of the optimal control alloy (alloy 2).

[0048] Therefore, the aluminum alloy preferably has a large NDS value, and more preferably the aluminum alloy has an NDS value greater than 6, more preferably the aluminum alloy has an NDS value greater than 10, and even more preferably the aluminum alloy has an NDS value greater than 12.

[0049] Furthermore, according to one aspect of the invention, the above-described aluminum alloy is provided for use in die-casting structural components, particularly for die-casting structural components in automobile manufacturing. In other words, the above-described aluminum alloy can be used to manufacture structural components by means of die casting, which can be used, for example, as body components in automobile manufacturing.

[0050] Furthermore, according to one aspect of the invention, a structural member for a motor vehicle is provided, the structural member being made of an aluminum alloy according to the invention.

[0051] Specifically, the structural component can be a single-piece die-cast component. Single-piece die casting is described herein as a manufacturing method, preferably used, for example, in automobile manufacturing, where large components, such as those made of aluminum, can be manufactured in a single process step. Here, single-piece die casting enables the manufacture of parts with enormous dimensions and complex geometries that were previously impossible using conventional casting methods. For example, a single-piece die-cast component can weigh up to 300 kg and may also have an area exceeding one square meter.

[0052] For example, aluminum or aluminum alloys according to the invention can be used as materials, thereby achieving advantages in weight and strength in automobile manufacturing. By using aluminum alloys according to the invention, the overall weight of the vehicle can be reduced in this way, thereby achieving lower fuel consumption and lower emissions. Furthermore, the high rigidity of the integrally die-cast components due to their size and shape can contribute to stable driving performance and high handling performance. In addition, integral die-casting, for example, enables the manufacture of complex shapes, thereby enabling innovative structures with optimized performance. Moreover, the number of components in a motor vehicle can be reduced by means of integral die-casting, thereby simplifying the assembly process and reducing production costs.

[0053] This type of structural component can be used for a variety of different applications in motor vehicles because it possesses not only the required strength but also sufficiently high ductility and good mold release properties. High strength is advantageous because it allows for the manufacture of motor vehicles with thin-walled structural components, which in turn reduces the vehicle's weight. Sufficiently high ductility ensures, for example, that crack-free and fracture-free riveting connections can be formed during stamping and riveting. Good mold release properties are advantageous, for example, in manufacturing processes such as the die casting of structural components.

[0054] The aluminum alloy according to the invention is particularly suitable for such structural components; however, the aluminum alloy can also be used for other components. By eliminating the need for heat treatment of the structural components, geometric deformation of the structural components can be avoided, thereby achieving high geometric or shape accuracy of the structural components.

[0055] In an advantageous improvement of the invention, it can be specified that the aforementioned structural member, particularly the aforementioned integral die-cast member, possesses a predetermined thermal stability. In other words, it can be specified that the 0.2% yield strength obtained through heat treatment—for example, heating the structural member to 150°C for 1000 hours—is less than 160 MPa, and the increase in yield strength is less than 30 MPa.

[0056] Furthermore, it is advantageous that after temperature loading at 80°C to 250°C for 10 to 120 minutes, particularly after temperature loading at 150°C to 250°C for 25 to 120 minutes, the yield strength is less than 160 MPa and the increase in yield strength is less than 30 MPa, and / or after temperature loading at 150°C for 1000 hours, the yield strength is less than 160 MPa and the increase in yield strength is less than 30 MPa.

[0057] On the other hand, if the yield strength increases to above 160 MPa and / or by 30 MPa or more after loading at such a temperature, precipitation hardening has occurred, indicating the presence of thermal instability. This thermal instability is undesirable because it can lead to a decrease in elongation at break and thus reduce the load-bearing capacity of the component, or weaken its ability to absorb deformation energy in the event of an accident in a motor vehicle. An excessively low elongation at break can also cause problems with fatigue strength.

[0058] On the one hand, the heat treatment values ​​defined above are based on the fact that, advantageously, after a coating process including heat treatment, the yield strength does not exceed 160 MPa and / or the increase in yield strength does not exceed 30 MPa (an increase in yield strength not exceeding 30 MPa), because such an increase indicates thermal instability. For example, in such a coating process, it may be set to continue at 80°C to 250°C for 10 to 120 minutes, particularly at 150°C to 250°C for 25 to 120 minutes.

[0059] On the other hand, after heat treatment to simulate temperature stress during the service life of the component (e.g., by heat treatment with a temperature loading of 150°C for 1000 hours), the yield strength should not exceed 160 MPa and / or the increase in yield strength should not exceed 30 MPa (compared to the as-cast state), as this also indicates thermal instability.

[0060] Furthermore, according to another aspect of the invention, a motor vehicle having the aforementioned structural member is provided. In addition to the advantages described above, the use of the structural member eliminates the need for costly heat treatment, thus particularly achieving advantages in terms of cost and manufacturing time. Furthermore, if deformation due to heat treatment can be avoided, the dimensional stability of the motor vehicle according to the invention can be improved. Moreover, by using recycled aluminum, CO2 emissions during the manufacture of the motor vehicle according to the invention can be reduced, thus further reducing costs and improving durability.

[0061] The motor vehicle according to the present invention is preferably designed as an automobile, particularly as a passenger car or commercial vehicle, or as a bus or motorcycle.

[0062] The present invention also includes feature combinations of the described embodiments. Therefore, the present invention also includes the following implementations, each having a plurality of feature combinations of the described embodiments, provided that these implementations are not described as mutually exclusive. Attached Figure Description

[0063] Embodiments of the present invention are described below. This is illustrated in the following:

[0064] Figure 1A schematic diagram showing the relationship between yield strength and magnesium content.

[0065] List of reference numerals in the attached diagram:

[0066] 100 Yield Strength

[0067] 102. No solution hardening range.

[0068] 104. Scope of solid solution hardening

[0069] 106 Range of thermal instability

[0070] 108 x-axis

[0071] 110 y-axis

[0072] 112 Lower limit

[0073] 114 upper limit Detailed Implementation

[0074] Figure 1 A schematic diagram showing the relationship between the yield strength 100 of an aluminum alloy and its magnesium content.

[0075] The Mg content, expressed as a weight percentage, is recorded on the x-axis (108), while the yield strength Rp0.2, expressed in MPa, is recorded on the y-axis (110). Here, the 0.2% yield strength Rp0.2 is... p0.2 This refers to a (uniaxial) mechanical stress such that, after unloading, the permanent elongation (i.e., plastic deformation, hence with a subscript) calculated relative to the initial length of the specimen reaches 0.2%.

[0076] from Figure 1 As can be seen, the Mg content range of 104 selected in this disclosure is optimal, ranging from the lower limit of 0.04 wt% (112) to the upper limit of 0.095 wt% (114). Only within the lower limit of 112 and the upper limit of 114 can both the strengthening effect brought about by solid solution strengthening and the thermally stable state be achieved.

[0077] When the Mg content is less than 0.04% by weight, the strength of the aluminum alloy is very low (range 102); however, when the magnesium content is high (range 106), that is, exceeding the upper limit of 114, age hardening will occur over time, resulting in unfavorable thermal instability.

[0078] The composition of various alloys is further shown in Table 1 below, and their properties are listed in Table 2 below.

[0079] Table 1: Composition of various aluminum alloys

[0080]

[0081] Table 2: Properties of Various Aluminum Alloys

[0082]

[0083] The first column of Table 1 lists the various chemical elements, and their contents in the given alloys are listed in Table 1 as a weight percentage.

[0084] Reference alloy 1 is taken from document EP 1 443 122 B1, reference alloy 2 is taken from document EP 3 235 917 B1, and reference alloy 3 is taken from document EP 3 775 309 B1. Furthermore, alloys according to the invention are listed in the fifth column of Tables 1 and 2.

[0085] Here, 0.2% yield strength R p0.2 This refers to a uniaxial mechanical stress such that, after unloading, the permanent elongation (i.e., the subscript p indicates plastic deformation) calculated relative to the initial length of the specimen reaches 0.2%. Furthermore, R is used here... p0.2 (F) represents the 0.2% yield strength in MPa at the as-cast state without further heat treatment, and A(F) represents the elongation at break in the as-cast state without further heat treatment as a percentage. Furthermore, Rp0.2(T5) represents the 0.2% yield strength in MPa after heat treatment at 150°C for 1000 hours, and A(T5) represents the elongation at break as a percentage after heat treatment at 150°C for 1000 hours.

[0086] Here, a larger value is preferred for the 0.2% yield strength of the aluminum alloy in the as-cast state, because this allows for a smaller wall thickness of the component, which helps to reduce the weight of the component.

[0087] Elongation at break here refers to the permanent elongation of a tensile specimen after fracture in a fracture test, which is calculated relative to the initial length of the tensile specimen. It characterizes the material's deformability or ductility. Preferably, aluminum alloys have a high elongation at break because this enables good riveting and stitching connections.

[0088] The descriptions of thermal stability, riveting connection, and corrosion resistance involve tests performed on the alloy, whereby the alloy is evaluated relative to a pre-defined standard catalog. For example, thermal stability is tested by measuring the 0.2% yield strength and elongation at break on predefined samples, one hand without heat treatment and the other after heat treatment at 150°C for 1000 hours. If R p0.2 If the increase exceeds 30 MPa, thermal stability cannot be guaranteed.

[0089] Regarding the stamping and riveting joint performance, the experimental design involved inserting a stamped rivet (5.3 mm in diameter) into a specimen. The specimen consisted of a 2 mm thick 6000 series sheet on the stamping side, while the mating parts on the die side comprised a 3 mm thick sheet of die-cast alloy to be inspected. Following the stamping and riveting connection, the resulting rivet joints were inspected for cracks and anomalies, and the results were evaluated according to a pre-defined standard catalog.

[0090] In addition, corrosion resistance is evaluated in corrosion change tests according to a standardized testing procedure. This testing procedure involves cyclical alternation of different climatic loads and / or corrosion loads. One test cycle includes:

[0091] – 4-hour salt spray test, according to test method NSS of DIN EN ISO 9227;

[0092] – 4 hours of storage under standard climate conditions; and

[0093] – 16 hours of humid heat storage, tested according to the DIN EN ISO 6270-2 climate (CH).

[0094] After every 5 cycles, a 2-day resting phase is performed under standard climatic conditions. Therefore, the 15-cycle test lasts a total of 3 weeks. These test methods allow for the evaluation of corrosion behavior under static loads comprised of salt, humidity, and temperature.

[0095] High thermal stability, good riveting connection properties, and high corrosion resistance are preferred here to ensure the wide applicability of the aluminum alloy. High yield strength, high elongation at break, high thermal stability, good riveting connection properties, and high corrosion resistance are also referred to here as good mechanical properties.

[0096] The recycling rate indicates the percentage by weight of recycled aluminum in the entire alloy. Additionally, the post-consumer waste ratio indicates the proportion of recycled aluminum that has been used by the end user and then re-enters the recycling cycle. High recycling rates and high post-consumer waste ratios contribute to improved durability of the aluminum alloys used.

[0097] Comparative alloys 1 and 3 have low magnesium content and are therefore naturally hardened. They possess good mechanical, physical, and thermal properties, but due to their low Fe, Cu, Mg, and Zn content, they can only be manufactured from recycled materials to a limited extent. This can be derived from the recovery rate values ​​in Table 2. These values ​​are calculated from or derived from the iron and copper contents given in the literature.

[0098] Because the tolerance limits for impurity metals in alloys 1 and 3 are extremely low, post-consumer waste can only be used in very limited ways.

[0099] Although control alloy 2 achieved a very high recovery rate, it possessed only very limited mechanical and physical properties compared to control alloys 1 and 3, as evidenced by its poor thermal stability and riveting adhesion according to Table 2. Furthermore, its corrosion resistance was particularly poor. Moreover, due to the increased magnesium content of control alloy 2, it lacked natural hardening properties and therefore could not maintain thermal stability.

[0100] The alloy according to the invention is the only alloy in this comparison that combines all the advantages. By selecting the range of impurity elements (Fe, Cu, Zn, Ti), the alloy according to the invention can achieve a high recovery rate. This alloy achieves a recovery rate of 88% and a post-consumer waste ratio of 36%, which even exceeds the recovery rates of the aforementioned control alloys 1, 2, and 3.

[0101] Furthermore, by skillfully adjusting the element content in the alloy and the appropriate proportions between the elements, the alloy according to the invention is an alloy that is thermally stable on the one hand, has a high elongation on the other hand, and is also capable of achieving a high recycling rate.

[0102] Allowing for higher levels of impurity elements enables extremely high recovery rates. Furthermore, by setting specific elemental boundary conditions, the overall performance is made only slightly different from, or essentially equivalent to, that of a control alloy including primary aluminum. This results in an alternative alloy that still offers high recovery rates and thereby reduces the CO2 footprint, for example, in automotive manufacturing processes.

[0103] This is reflected in the NDS factor: in the alloy according to the invention, this factor is more than twice that of the best control alloy (alloy 2).

[0104] To obtain the sustainability-ductility-stability factor (NDS factor), the contents of impurity elements are summed, with iron content doubled in the sum due to its significant effect on the ductility of aluminum alloys. The determined sum is multiplied by the elongation at break as a percentage and a coefficient representing the 0.2% yield strength R at as-cast F in MPa. p0.2 (F) and the 0.2% yield strength R after heat treatment at 150°C for 1000 hours. p0.2 The ratio of (T5).

[0105] Overall, the examples demonstrate how to provide an aluminum alloy with enhanced ductility for structural casting, the application of the aluminum alloy in die-cast structural components, structural components made of the aluminum alloy for motor vehicles, and motor vehicles having the structural components.

Claims

1. An aluminum alloy with enhanced ductility for structural casting, the aluminum alloy comprising: - 7.5 to 11.5% by weight of silicon; - 0.25 to 0.6% manganese by weight; - 0.03 to 0.06 percent chromium by weight; - 0.001 to 0.048 wt% of molybdenum; - 0.04 to 0.095% by weight of magnesium, particularly 0.06 to 0.095% by weight of magnesium; - 0.17 to 0.5% by weight of iron; - 0.03 to 0.5% copper by weight; - Up to 0.35% by weight of zinc; - 0.004 to 0.15% by weight of titanium; - As a surplus of aluminum and unavoidable impurities.

2. The aluminum alloy according to claim 1, Its features are, The aluminum alloy includes 0.01 to 0.2% by weight zirconium.

3. The aluminum alloy according to claim 1 or 2, Its features are, The aluminum alloy comprises 0.001 to 0.1% by weight of vanadium.

4. The aluminum alloy according to any one of the preceding claims, Its features are, The aluminum alloy comprises 0.002 to 0.030 wt% strontium.

5. The aluminum alloy according to any one of the preceding claims, Its features are, The aluminum alloy comprises 25% by weight or more recycled aluminum content, and / or 10% by weight or more post-consumer recycled aluminum content.

6. The aluminum alloy according to any one of the preceding claims, Its features are, The NDS value of the aluminum alloy is greater than 6, preferably greater than 10, and more preferably greater than 12. The NDS value of aluminum alloy is the product of the following three factors: total impurity elements; elongation at break as a percentage; and the ratio of 0.2% yield strength in the as-cast state to 0.2% yield strength in the peak aged state. The total impurity elements is the sum of the content of impurity elements as a weight percentage, and the iron content is included in the total impurity elements with double weight.

7. The application of the aluminum alloy according to any one of the preceding claims for die-cast structural components, particularly for die-cast structural components in automobile manufacturing.

8. A structural component for motor vehicles, particularly an integrally die-cast component, made of an aluminum alloy according to any one of claims 1 to 6.

9. The structural member, particularly the unitary die cast member according to claim 8, characterized in that The structural components have a predetermined thermal stability.

10. A motor vehicle having a structural member according to claim 8 or 9.

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