A high-strength 7-series aluminum alloy and a method of making the same

Abstract

The application discloses a high-strength 7-series aluminum alloy and a preparation method thereof. The 7-series aluminum alloy is composed of the following components in percentage by mass: Zn 6.0-6.5%, Mg 2.1-2.5%, Cu 2.0-2.5%, Mn 0.20-0.30%, Ti 0.10-0.15%, Cr 0.10-0.20%, Zr 0.10-0.15%, rare earth elements 0.02-0.10%, wherein the rare earth elements are a mixture of La and Ce, and the balance is Al and inevitable impurities, wherein Fe < 0.15% and Si < 0.15%. By optimizing the main alloy components, adjusting the trace element ratio, and adopting multiple process means such as micro-alloying and deformation heat treatment, a high-strength aluminum alloy is prepared.

Description

Technical Field

[0001] This invention belongs to the field of 7-series aluminum alloy material preparation, specifically relating to a high-strength 7-series aluminum alloy and its preparation method. Background Technology

[0002] In recent years, with the increasing demands for lightweight and strength in motorcycle structural components, 7-series aluminum alloys (Al-Zn-Mg-Cu) have gradually become the preferred material for manufacturing motorcycle wheels. These alloys not only meet the requirements for lightweight and high strength but also offer an aesthetically pleasing appearance, making them particularly suitable for off-road and racing motorcycles. In these high-strength and high-performance motorcycle applications, the performance requirements for wheels are extremely stringent, especially under uncertain and extreme operating conditions, necessitating higher impact resistance, fatigue resistance, and high-temperature resistance. This places higher demands on the composition design and manufacturing processes of 7-series aluminum alloys and presents significant challenges to traditional production methods.

[0003] In motorcycle wheel applications, especially on high-performance off-road and racing motorcycles, wheels using 7-series aluminum alloys must not only meet lightweight requirements but also possess excellent strength and fatigue resistance. However, due to the internal deformation energy stored in 7-series aluminum alloys during hot working, coarse recrystallization can easily occur as this stored energy is released during subsequent heat treatment. This coarse-grained defect not only reduces the product's mechanical properties and fatigue resistance but may even affect the wheel's service life. Furthermore, if such defects appear on the outer surface of the wheel, they can also lead to color differences and mottling during the anodizing process. Therefore, this coarse-grained defect may prevent 7-series aluminum alloy motorcycle wheels from meeting the market's dual requirements for performance and aesthetics.

[0004] For example, CN113444940A discloses a method for preparing high-strength, high-toughness, and corrosion-resistant 7055 aluminum alloy medium-thick plates. By optimizing the alloy element formula and strictly controlling the casting process, the method ensures the uniformity of alloy composition and grain refinement, thereby improving the overall performance of the plate. However, with the continuous improvement of requirements for lightweight and high-performance structural materials, the aluminum alloy prepared by this patented method still has shortcomings and cannot meet the current cutting-edge application needs of the industry.

[0005] Currently, the traditional technical approach involves first forming the material through extrusion, then performing solution treatment, and finally artificial aging to achieve the desired performance standards. 7-series aluminum alloys, due to their high Zn and Mg content, exhibit very high strength because of the large number and density of precipitated phases after aging. However, the high content of these solid-solution elements also results in high deformation resistance during extrusion, making the process more difficult and reducing production efficiency. This is especially true for profiles with complex cross-sections, where the extrusion process becomes significantly more challenging and cannot meet the dual requirements of shape and strength in certain industrial applications.

[0006] The existing 7-series aluminum alloys are no longer strong enough to fully meet the performance requirements of current parts designs, especially in high-performance applications such as motorcycle wheels. Summary of the Invention

[0007] In existing technologies, 7-series aluminum alloys present a dual challenge: the difficulty in extrusion forming due to the pursuit of high strength, and the tendency for coarse recrystallization during subsequent heat treatment. This problem directly affects the forming efficiency, final mechanical properties, and surface quality of components. This invention provides a high-strength 7-series aluminum alloy and its preparation method. By optimizing the main alloy composition, adjusting the proportion of trace elements, and employing multiple processes such as micro-alloying and deformation heat treatment, a high-strength aluminum alloy is prepared. This results in a near-fibrous structure distributed along the extrusion direction within the wheel, effectively suppressing coarse recrystallization on the surface and significantly improving material strength. After anodizing, the wheel not only possesses excellent mechanical properties but also maintains a bright and glossy surface, achieving a balance between high strength and aesthetics.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A high-strength 7-series aluminum alloy, comprising the following composition by mass percentage: Zn 6.0%–6.5%, Mg 2.1%–2.5%, Cu 2.0%–2.5%, Mn 0.20%–0.30%, Ti 0.10%–0.15%, Cr 0.10%–0.20%, Zr 0.10%–0.15%, and rare earth elements 0.02%–0.10%, wherein the rare earth elements are a mixture of La and Ce; the balance is Al and unavoidable impurities, wherein Fe < 0.15% and Si < 0.15%.

[0009] Furthermore, the mass percentage of Zn to Mg satisfies 2.4 ≤ Zn / Mg ≤ 3.1; and the mass percentage of Cu to Mg satisfies 0.8 ≤ Cu / Mg ≤ 1.19.

[0010] The synergistic relationship of the "composition window ratio" in the Zn-Mg-Cu main strengthening system is explored. Zn is controlled at 6.0%–6.5%, Mg at 2.1%–2.5%, and Cu at 2.0%–2.5%, with the Zn / Mg ratio controlled at approximately 2.4–3.1 and the Cu / Mg ratio at 0.8–1.2. This is achieved through simultaneous constraints of "supersaturation, precipitation kinetics, and grain boundary stability." The synergistic effect of Zn and Mg ensures sufficient supersaturation after solid solution treatment, resulting in high number density and fine-scale dispersed precipitation, primarily η″ / η′, during aging, thus achieving high yield strength and high tensile strength. Within this window, Cu provides an "effective gain" in strengthening the solid solution and peak aged strength. Simultaneously, by imposing upper limit constraints, the significant amplification of quenching sensitivity and the tendency for grain boundary η-phase coarsening, precipitation depletion zone (PFZ) widening, and continuous grain boundary embrittlement are avoided, thereby simultaneously improving high strength and toughness. The suitable composition range of Zn-Mg-Cu reduces the nonlinear risk of "strength improvement leading to a sharp deterioration in reliability," enabling relatively stable aging response and surface quality under conditions of thick cross-section, fluctuating operating conditions, or fluctuating extrusion heat history. This composition window achieves simultaneous optimization of "high precipitation strengthening potential" and "grain boundary stability and process stability" by constraining the volume fraction, size distribution, and grain boundary precipitation continuity of the precipitated phase.

[0011] The addition of trace transition elements such as Mn and Cr can form fine, dispersed precipitates in aluminum alloys. These precipitates significantly refine the grain structure of the alloy by inhibiting recrystallization. During plastic deformation, these dispersed precipitates effectively increase the complexity of the deformation substructure within the grains, promoting the formation of intragranular fracture modes, thereby improving the toughness, tensile strength, and yield strength of the alloy. Especially during hot deformation, these dispersed phases not only enhance the strength of the material but also increase the recrystallization temperature of the alloy, preventing excessive recrystallization during subsequent quenching, thus ensuring the mechanical stability of the alloy at high temperatures. This is beneficial for the alloy to have better durability and resistance to plastic deformation under high stress and high temperature environments, which helps to improve the service life and reliability of the material.

[0012] Adding Zr to aluminum alloys allows it to combine with aluminum to form Al3Zr intermetallic compounds, which play important roles in aluminum alloys. Al3Zr intermetallic compounds exist in two main structural forms: one is the tetragonal Al3Zr precipitated from the melt, which can significantly refine the as-cast grains of aluminum alloys; the other is spherical particles precipitated during ingot homogenization, possessing an L12 structure, which can coherently integrate with the aluminum matrix and strongly inhibit recrystallization during hot working. Trace amounts of Zr can effectively improve the alloy's strength, fracture toughness, and stress corrosion resistance. This is because the presence of the Al3Zr phase inhibits excessive grain growth, improving the overall mechanical properties of the alloy. Furthermore, since zirconium has low quenching sensitivity, it can significantly improve the alloy's hardenability and optimize weldability, giving the alloy better operability in heat treatment and welding processes.

[0013] Adding Ti to aluminum alloys can significantly refine the as-cast grains and increase the recrystallization temperature, thereby improving their weldability. Ti reacts with Al to form the Al3Ti phase, which acts as a nucleation site for heterogeneous growth during solidification, promoting grain refinement. Furthermore, the Al3Ti phase, by dispersing in the matrix, hinders dislocation movement, thus enhancing the alloy's strength and hardness. The addition of Ti not only improves the alloy's strength but also effectively inhibits grain growth during hot deformation. Additionally, Ti reacts with B to form TiB2 particles, which promote nucleation during grain formation, a role particularly important during the casting stage. Excess Ti can also mitigate the effects of Zr addition on grain refiners, preventing the "poisoning" effect of the refiners and maintaining the grain refinement effect of the alloy.

[0014] The addition of rare earth elements La and Ce can induce compositional supercooling during aluminum alloy casting, further refining the grains and reducing secondary dendrite spacing. The addition of rare earth elements can also significantly reduce gases and inclusions in the alloy, promoting the transformation of inclusions into spherical shapes, thereby improving the purity and uniformity of the alloy. Simultaneously, the addition of rare earth elements reduces the surface tension of the alloy melt, effectively improving the fluidity of the aluminum alloy and giving it better filling and forming properties during casting.

[0015] Furthermore, the mass percentages of Zn and Mg satisfy 2.63 ≤ Zn / Mg ≤ 2.80. This ensures the synergistic effect of Zn and Mg in the alloy, promoting the formation of supersaturation after solid solution treatment, and thus generating high-density, fine η″ / η′ precipitates during artificial aging. This optimization effectively improves the yield strength and tensile strength of the alloy, while strictly controlling the Zn / Mg ratio avoids the problems of grain boundary η-phase coarsening and precipitation-depleted zone (PFZ) widening caused by excessive Zn, thereby maintaining the alloy's strength, toughness, and service reliability.

[0016] Furthermore, the mass percentages of Cu and Mg satisfy 0.91 ≤ Cu / Mg ≤ 1.00. This helps enhance the solid solution strengthening effect of the alloy and provides effective gains during peak aging. By limiting the Cu / Mg ratio, it is possible to ensure solid solution strengthening while avoiding excessive Cu that could lead to unstable precipitates or affect hot workability. This optimization can also improve the stability of precipitates during aging, thereby further enhancing the aged strength of the alloy.

[0017] Furthermore, by mass percentage, the sum of Ti and Zr contents satisfies 0.24% ≤ Ti + Zr ≤ 0.27%. Limiting the Ti and Zr contents within this range effectively refines the as-cast grains and improves the alloy's thermal stability. During homogenization and hot deformation, the dispersed phases formed by Ti and Zr act as dislocation pinning and grain boundary anchors, increasing the recrystallization temperature and inhibiting the formation of coarse grains, thereby enhancing the alloy's strength, ductility, and fatigue resistance.

[0018] Furthermore, the total content of the rare earth elements is preferably 0.04% to 0.08% by mass percentage. The appropriate addition of rare earth elements can significantly improve the microstructure uniformity of the aluminum alloy, refine the as-cast grains, increase the melt purity of the alloy, and reduce inclusions and porosity during the casting process. This optimization not only enhances the strength and toughness of the alloy but also improves its corrosion resistance and appearance quality, ensuring the reliability of high-strength aluminum alloys in high-strength applications such as motorcycle wheels.

[0019] The present invention also provides a method for preparing the above-mentioned high-strength 7-series aluminum alloy, the steps of which include melt treatment, gradient homogenization treatment, rounding, welding, multi-stage heat treatment and surface coloring treatment.

[0020] Furthermore, the gradient-level homogenization process optimizes the microstructure of the aluminum alloy through three stages of temperature control. The first stage is a low-temperature precipitation stage, where the cast ingot is heated from room temperature to 350–380°C and held for 2–5 hours, which helps promote the formation of precipitates, especially fine η″ / η′ precipitates. The second stage is a high-temperature holding stage, where the temperature is further increased to 440–475°C and held for 10–15 hours. Its main function is to further refine the precipitates and homogenize the dissolved substances in the alloy, optimizing the grain structure. The third stage involves cooling to 350–390°C and holding for 0.5–3 hours to ensure that the precipitates remain fine and uniformly distributed, preventing coarsening at high temperatures, thereby improving the strength and toughness of the alloy.

[0021] Furthermore, the multi-stage heat treatment involves solution treatment and aging to strengthen the welded wheels. This multi-stage heat treatment process combines solution treatment and artificial aging to further improve the mechanical properties of the alloy. The solution treatment stage is carried out at a temperature range of 440–480℃ for 0.5–2 hours, which helps to completely dissolve elements such as Cu and Mg into the aluminum matrix, forming a supersaturated solid solution and preparing for subsequent strengthening precipitation. Next, the artificial aging process is carried out at a temperature of 105–135℃ for 6–14 hours. By adjusting the aging temperature and time, the formation of precipitates such as η″ / η′ is promoted, thereby significantly improving the yield strength and tensile strength of the alloy and enhancing its service reliability.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By adjusting the amount of Zn, Mg and Cu elements added and the ratio of Zn / Mg and Cu / Mg elements, the strength of the 7 series alloy was effectively improved, realizing the requirement of high strength and high plasticity of aluminum alloy material for high-end motorcycle wheels; the Zn / Mg range was controlled at about 2.4 to 3.1 and the Cu / Mg range was controlled at 0.8 to 1.2, forming a synergistic effect of Zn and Mg to ensure sufficient supersaturation after solid solution, so that the dispersed precipitation mainly composed of η″ / η′ during aging process has high density and fine scale, thereby obtaining high yield and high tensile strength; Cu provides "effective gain" for solid solution strengthening and peak aging strength within this window, while avoiding significant amplification of quenching sensitivity and the tendency of grain boundary η phase coarsening, precipitation depletion zone (PFZ) widening and continuous grain boundary embrittlement through upper limit constraint, thereby simultaneously improving high strength and toughness.

[0023] (2) By controlling the content range and proportion of trace elements such as transition elements Mn, Cr, Zr and Ti, precipitate phase particles that inhibit recrystallization are precipitated, and the recrystallization temperature is increased. This ensures that the material does not undergo coarse recrystallization on the surface of the high-energy-storage product during hot working deformation and heat treatment strengthening. After anodizing, the surface is beautiful and bright, and its performance and appearance meet the aesthetic requirements of motorcycle wheels being thin, beautiful and cool.

[0024] (3) Adding rare earth elements can change the crystallization conditions of the alloy, refine the dendritic structure, inhibit the generation of coarse lamellar iron-rich phase in aluminum alloy, effectively inhibit the growth of columnar crystals and secondary dendrites, and promote the formation of fine equiaxed crystals; they exist in the form of compounds, form crystal nuclei, and are distributed in the grains or grain boundaries, which refines the grains and generates a large number of dislocations, thereby improving the strength of aluminum alloys to a certain extent.

[0025] (4) The profiles prepared by the novel aluminum alloy of the present invention have a tensile strength ≥570MPa, a yield strength ≥520MPa, and an elongation after fracture ≥12.5%. Attached Figure Description

[0026] Figure 1 This is a metallographic image of the aluminum alloy in Example 3. Detailed Implementation

[0027] The invention can be further understood through the specific embodiments and comparative embodiments given below. However, they are not intended to limit the invention.

[0028] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this invention can all be purchased commercially.

[0029] Example 1 The composition and mass percentage of a high-strength 7-series aluminum alloy are as follows: Zn 6.0%; Mg 2.5%; Cu 2.0%; Mn 0.20%; Ti 0.10%; Cr 0.13%; Zr 0.10%; La and Ce mixed rare earth 0.1%; and other unavoidable impurities, of which Fe 0.13%; Si 0.12% and the balance is Al.

[0030] The specific preparation method is as follows: (1) Weigh the required raw materials according to the alloy composition design requirements. Select 3.000 kg of zinc ingot with a purity of 99.95%, 1.253 kg of magnesium ingot with a purity of 99.8%, 1.003 kg of copper wire with a purity of 99.7%, 0.50 kg of Al-20Mn master alloy, 0.65 kg of Al-10Cr master alloy, 0.50 kg of Al-10Zr master alloy, 0.50 kg of Al-10Ti master alloy, 0.05 kg of La and Ce mixed rare earth, and 43.535 kg of aluminum ingot with a purity of 99.7% as raw materials for batching. When the temperature of the aluminum melt is in the range of 740 to 750℃, refine the melt and remove the slag inclusions. The melt is continuously degassed and filtered using online degassing and plate filtration equipment, and the hydrogen content of the melt is less than 0.15 ml / 100 g Al. Extrusion aluminum alloy rods are prepared by direct water-cooled semi-continuous casting.

[0031] (2) The new casting rod is homogenized by a gradient grade homogenization process. The first stage is the low temperature precipitation stage, in which the casting rod is heated from room temperature to 360°C and kept at that temperature for 3 hours. The second stage is the high temperature holding stage, in which the temperature is further increased to 460°C and held for 13 hours. The third stage is the rapid cooling to 360°C, in which the specific method is air cooling and holding for 1.5 hours.

[0032] (3) Heat the homogenized casting rod to 370°C and keep it at that temperature for 1 hour, then extrude it into a profile.

[0033] (4) The profile is rounded at room temperature using a rounding machine to give it the required shape and diameter of a wheel. The rounded profile is then welded together using resistance welding to form a complete wheel.

[0034] (5) The welded wheels are subjected to solution treatment and aging heat treatment. The solution treatment temperature is 460℃ and the time is 1h; then the wheels are subjected to aging heat treatment at 120℃ for 8h.

[0035] (6) The wheel surface is polished by mechanical grinding to remove the surface texture of the extruded material. The wheel surface is then anodized to present a uniform and bright anodized layer. The wheel has a uniform and bright color and is free from defects such as orange peel or spots.

[0036] The properties of the aluminum alloy profiles obtained in Example 1 are shown in Table 1.

[0037] Example 2 The composition and mass percentage of a high-strength 7-series aluminum alloy are as follows: Zn 6.5%; Mg 2.1%; Cu 2.5%; Mn 0.24%; Ti 0.15%; Cr 0.16%; Zr 0.15%; La and Ce mixed rare earth 0.02%; and other unavoidable impurities, of which Fe 0.13%; Si 0.13% and the balance is Al.

[0038] The following raw materials were selected for batching: 3.251 kg of zinc ingots with a purity of 99.95%, 1.052 kg of magnesium ingots with a purity of 99.8%, 1.253 kg of copper wire with a purity of 99.7%, 0.60 kg of Al-20Mn master alloy, 0.80 kg of Al-10Cr master alloy, 0.75 kg of Al-10Zr master alloy, 0.75 kg of Al-10Ti master alloy, 0.01 kg of mixed rare earth elements of La and Ce, and 43.535 kg of aluminum ingots with a purity of 99.7%.

[0039] The specific preparation method is the same as in Example 1. The properties of the aluminum alloy profiles obtained in Example 2 are shown in Table 1.

[0040] Example 3 The composition and mass percentage of a high-strength 7-series aluminum alloy are as follows: Zn 6.3%; Mg 2.4%; Cu 2.4%; Mn 0.27%; Ti 0.14%; Cr 0.18%; Zr 0.14%; La and Ce mixed rare earth 0.08%; and other unavoidable impurities, of which Fe 0.12%; Si 0.12% and the balance is Al.

[0041] The following raw materials were selected for batching: 3.151 kg of zinc ingots with a purity of 99.95%, 1.202 kg of magnesium ingots with a purity of 99.8%, 1.204 kg of copper wire with a purity of 99.7%, 0.675 kg of Al-20Mn master alloy, 0.90 kg of Al-10Cr master alloy, 0.70 kg of Al-10Zr master alloy, 0.70 kg of Al-10Ti master alloy, 0.04 kg of mixed rare earth elements of La and Ce, and 43.805 kg of aluminum ingots with a purity of 99.7%.

[0042] The specific preparation method is the same as in Example 1. The properties of the aluminum alloy profiles obtained in Example 3 are shown in Table 1.

[0043] Example 4 The composition and mass percentage of a high-strength 7-series aluminum alloy are as follows: Zn 6.2%; Mg 2.2%; Cu 2.3%; Mn 0.25%; Ti 0.11%; Cr 0.10%; Zr 0.11%; La and Ce mixed rare earth 0.06%; and other unavoidable impurities, of which Fe 0.13%; Si 0.13% and the balance is Al.

[0044] The following raw materials were selected for batching: 3.100 kg of zinc ingots with a purity of 99.95%, 1.102 kg of magnesium ingots with a purity of 99.8%, 1.154 kg of copper wire with a purity of 99.7%, 0.625 kg of Al-20Mn master alloy, 0.50 kg of Al-10Cr master alloy, 0.55 kg of Al-10Zr master alloy, 0.55 kg of Al-10Ti master alloy, 0.03 kg of mixed rare earth elements of La and Ce, and 43.835 kg of aluminum ingots with a purity of 99.7%.

[0045] The specific preparation method is the same as in Example 1. The properties of the aluminum alloy profiles obtained in Example 4 are shown in Table 1.

[0046] Example 5 The composition and mass percentage of a high-strength 7-series aluminum alloy are as follows: Zn 6.4%; Mg 2.3%; Cu 2.1%; Mn 0.30%; Ti 0.12%; Cr 0.20%; Zr 0.12%; La and Ce mixed rare earth 0.04%; and other unavoidable impurities, of which Fe 0.14%; Si 0.14% and the balance is Al.

[0047] The following raw materials were selected for batching: 3.200 kg of zinc ingots with a purity of 99.95%, 1.153 kg of magnesium ingots with a purity of 99.8%, 1.053 kg of copper wire with a purity of 99.7%, 0.75 kg of Al-20Mn master alloy, 1.00 kg of Al-10Cr master alloy, 0.60 kg of Al-10Zr master alloy, 0.60 kg of Al-10Ti master alloy, 0.02 kg of mixed rare earth elements of La and Ce, and 43.585 kg of aluminum ingots with a purity of 99.7%.

[0048] The specific preparation method is the same as in Example 1. The properties of the aluminum alloy profiles obtained in Example 5 are shown in Table 1.

[0049] Example 6 The composition and mass percentage of a high-strength 7-series aluminum alloy are as follows: Zn 6.3%; Mg 2.3%; Cu 2.3%; Mn 0.20%; Ti 0.10%; Cr 0.13%; Zr 0.10%; La and Ce mixed rare earth 0.1%; and other unavoidable impurities, of which Fe 0.13%; Si 0.14% and the balance is Al.

[0050] The following raw materials were selected for batching: 3.151 kg of zinc ingots with a purity of 99.95%, 1.153 kg of magnesium ingots with a purity of 99.8%, 1.154 kg of copper wire with a purity of 99.7%, 0.50 kg of Al-20Mn master alloy, 0.65 kg of Al-10Cr master alloy, 0.50 kg of Al-10Zr master alloy, 0.50 kg of Al-10Ti master alloy, 0.05 kg of mixed rare earth elements of La and Ce, and 43.685 kg of aluminum ingots with a purity of 99.7%.

[0051] The specific preparation method is the same as in Example 1. The properties of the aluminum alloy profiles obtained in Example 6 are shown in Table 1.

[0052] Example 7 The composition and mass percentage of a high-strength 7-series aluminum alloy are as follows: Zn 6.4%; Mg 2.4%; Cu 2.3%; Mn 0.24%; Ti 0.12%; Cr 0.14%; Zr 0.12%; La and Ce mixed rare earth 0.06%; and other unavoidable impurities, of which Fe 0.13%; Si 0.13% and the balance is Al.

[0053] The following raw materials were selected for batching: 3.200 kg of zinc ingots with a purity of 99.95%, 1.202 kg of magnesium ingots with a purity of 99.8%, 1.154 kg of copper wire with a purity of 99.7%, 0.60 kg of Al-20Mn master alloy, 0.70 kg of Al-10Cr master alloy, 0.60 kg of Al-10Zr master alloy, 0.60 kg of Al-10Ti master alloy, 0.03 kg of mixed rare earth elements of La and Ce, and 43.905 kg of aluminum ingots with a purity of 99.7%.

[0054] The specific preparation method is the same as in Example 1. The properties of the aluminum alloy profiles obtained in Example 7 are shown in Table 1.

[0055] Example 8 The composition and mass percentage of a high-strength 7-series aluminum alloy are as follows: Zn 6.2%; Mg 2.2%; Cu 2.4%; Mn 0.25%; Ti 0.13%; Cr 0.14%; Zr 0.11%; La and Ce mixed rare earth 0.05%; and other unavoidable impurities, of which Fe 0.13%; Si 0.14% and the balance is Al.

[0056] The following raw materials were selected for batching: 3.101 kg of zinc ingots with a purity of 99.95%, 1.102 kg of magnesium ingots with a purity of 99.8%, 1.204 kg of copper wire with a purity of 99.7%, 0.625 kg of Al-20Mn master alloy, 0.70 kg of Al-10Cr master alloy, 0.55 kg of Al-10Zr master alloy, 0.65 kg of Al-10Ti master alloy, 0.025 kg of mixed rare earth elements of La and Ce, and 43.835 kg of aluminum ingots with a purity of 99.7%.

[0057] The specific preparation method is the same as in Example 1. The properties of the aluminum alloy profiles obtained in Example 8 are shown in Table 1. Comparative Example 1 A high-strength 7-series aluminum alloy has the following composition by mass percentage: Zn 6.3%; Mg 2.3%; Cu 2.3%; Mn 0.26%; Cr 0.14%; Zr 0.13%; Ti 0.13%; and other unavoidable impurities, of which Fe 0.13%; Si 0.14% and the balance is Al.

[0058] The following raw materials were selected for batching: 3.151 kg of zinc ingots with a purity of 99.95%, 1.153 kg of magnesium ingots with a purity of 99.8%, 1.154 kg of copper wire with a purity of 99.7%, 0.65 kg of Al-20Mn master alloy, 0.70 kg of Al-10Cr master alloy, 0.65 kg of Al-10Zr master alloy, 0.65 kg of Al-10Ti master alloy, and 43.735 kg of aluminum ingots with a purity of 99.7%.

[0059] The specific preparation method is basically the same as that in Example 1; the properties of the aluminum alloy profiles obtained in Comparative Example 1 are shown in Table 1.

[0060] Comparative Example 2 A high-strength 7-series aluminum alloy has the following composition by mass percentage: Zn 6.4%; Mg 2.4%; Cu 2.3%; Mn 0.26%; Ti 0.13%; Zr 0.14%; Cr 0.16%; La and Ce mixed rare earth 0.18%; and other unavoidable impurities, of which Fe 0.14%; Si 0.14% and the balance is Al.

[0061] The following raw materials were selected for batching: 3.201 kg of zinc ingots with a purity of 99.95%, 1.202 kg of magnesium ingots with a purity of 99.8%, 1.154 kg of copper wire with a purity of 99.7%, 0.65 kg of Al-20Mn master alloy, 0.80 kg of Al-10Cr master alloy, 0.70 kg of Al-10Zr master alloy, 0.65 kg of Al-10Ti master alloy, 0.09 kg of mixed rare earth elements of La and Ce, and 43.835 kg of aluminum ingots with a purity of 99.7%.

[0062] The specific preparation method is basically the same as that in Example 1; the properties of the aluminum alloy profiles obtained in Comparative Example 2 are shown in Table 1.

[0063] Comparative Example 3 A high-strength 7-series aluminum alloy has the following composition by mass percentage: Zn 6.3%; Mg 2.3%; Cu 2.3%; Mn 0.06%; Ti 0.13%; Cr 0.04%; Zr 0.15%; La and Ce mixed rare earth 0.06%; and other unavoidable impurities, of which Fe 0.13%; Si 0.13% and the balance is Al.

[0064] The following raw materials were selected for batching: 3.151 kg of zinc ingots with a purity of 99.95%, 1.153 kg of magnesium ingots with a purity of 99.8%, 1.154 kg of copper wire with a purity of 99.7%, 0.15 kg of Al-20Mn master alloy, 0.20 kg of Al-10Cr master alloy, 0.75 kg of Al-10Zr master alloy, 0.65 kg of Al-10Ti master alloy, 0.03 kg of mixed rare earth elements of La and Ce, and 43.735 kg of aluminum ingots with a purity of 99.7%.

[0065] The specific preparation method is basically the same as that in Example 1; the properties of the aluminum alloy profiles obtained in Comparative Example 3 are shown in Table 1.

[0066] Comparative Example 4 A high-strength 7-series aluminum alloy has the following composition by mass percentage: Zn 6.3%; Mg 2.3%; Cu 2.3%; Mn 0.26%; Ti 0.20%; Cr 0.15%; Zr 0.17%; La and Ce mixed rare earth 0.06%; and other unavoidable impurities, of which Fe 0.13%; Si 0.13% and the balance is Al.

[0067] The following raw materials were selected for batching: 3.151 kg of zinc ingots with a purity of 99.95%, 1.153 kg of magnesium ingots with a purity of 99.8%, 1.154 kg of copper wire with a purity of 99.7%, 0.65 kg of Al-20Mn master alloy, 0.75 kg of Al-10Cr master alloy, 0.85 kg of Al-10Zr master alloy, 1.00 kg of Al-10Ti master alloy, 0.03 kg of mixed rare earth elements of La and Ce, and 43.685 kg of aluminum ingots with a purity of 99.7%.

[0068] The specific preparation method is basically the same as that in Example 1; the properties of the aluminum alloy profiles obtained in Comparative Example 4 are shown in Table 1.

[0069] Comparative Example 5 A high-strength 7-series aluminum alloy has the following composition by mass percentage: Zn 6.2%; Mg 2.2%; Cu 2.4%; Mn 0.29%; Ti 0.02%; Cr 0.15%; Zr 0.04%; La and Ce mixed rare earth 0.05%; and other unavoidable impurities, of which Fe 0.13%; Si 0.13% and the balance is Al.

[0070] The following raw materials were selected for batching: 3.101 kg of zinc ingots with a purity of 99.95%, 1.102 kg of magnesium ingots with a purity of 99.8%, 1.204 kg of copper wire with a purity of 99.7%, 0.725 kg of Al-20Mn master alloy, 0.75 kg of Al-10Cr master alloy, 0.20 kg of Al-10Zr master alloy, 0.10 kg of Al-10Ti master alloy, 0.025 kg of mixed rare earth elements of La and Ce, and 43.735 kg of aluminum ingots with a purity of 99.7%.

[0071] The specific preparation method is basically the same as that in Example 1; the properties of the aluminum alloy profiles obtained in Comparative Example 5 are shown in Table 1.

[0072] Comparative Example 6 A high-strength 7-series aluminum alloy has the following composition by mass percentage: Zn 6.6%; Mg 2%; Cu 2.6%; Mn 0.28%; Ti 0.13%; Cr 0.14%; Zr 0.14%; La and Ce mixed rare earth 0.06%; and other unavoidable impurities, of which Fe 0.13%; Si 0.13% and the balance is Al.

[0073] The following raw materials were selected for batching: 3.301 kg of zinc ingots with a purity of 99.95%, 1.002 kg of magnesium ingots with a purity of 99.8%, 1.303 kg of copper wire with a purity of 99.7%, 0.70 kg of Al-20Mn master alloy, 0.70 kg of Al-10Cr master alloy, 0.70 kg of Al-10Zr master alloy, 0.65 kg of Al-10Ti master alloy, 0.03 kg of mixed rare earth elements of La and Ce, and 43.765 kg of aluminum ingots with a purity of 99.7%.

[0074] The specific preparation method is basically the same as that in Example 1; the properties of the aluminum alloy profiles obtained in Comparative Example 6 are shown in Table 1.

[0075] Comparative Example 7 A high-strength 7-series aluminum alloy has the following composition by mass percentage: Zn 6.5%; Mg 2.8%; Cu 2.2%; Mn 0.30%; Ti 0.14%; Cr 0.15%; Zr 0.15%; La and Ce mixed rare earth 0.07%; and other unavoidable impurities, of which Fe 0.13%; Si 0.13% and the balance is Al.

[0076] The following raw materials were selected for batching: 3.251 kg of zinc ingots with a purity of 99.95%, 1.402 kg of magnesium ingots with a purity of 99.8%, 1.104 kg of copper wire with a purity of 99.7%, 0.75 kg of Al-20Mn master alloy, 0.75 kg of Al-10Cr master alloy, 0.75 kg of Al-10Zr master alloy, 0.70 kg of Al-10Ti master alloy, 0.035 kg of mixed rare earth elements of La and Ce, and 43.735 kg of aluminum ingots with a purity of 99.7%.

[0077] The specific preparation method is basically the same as that in Example 1; the properties of the aluminum alloy profiles obtained in Comparative Example 7 are shown in Table 1.

[0078] Table 1. Alloy properties of Examples 1-8 and Comparative Examples 1-7 Tensile strength Rm / MPa The specified plastic elongation strength is Rp 0.2 / MPa. Elongation after fracture A / % Example 1 572 523 12.7 Example 2 575 521 12.5 Example 3 585 536 13.5 Example 4 578 527 13.1 Example 5 583 535 13.3 Example 6 582 532 13.4 Example 7 584 535 13.2 Example 8 578 527 13.1 Comparative Example 1 513 482 10.4 Comparative Example 2 534 501 11.6 Comparative Example 3 533 503 11.8 Comparative Example 4 541 510 12.1 Comparative Example 5 539 507 11.9 Comparative Example 6 513 482 10.4 Comparative Example 7 516 486 10.1 As can be seen from the alloy properties of Examples 1-8 and Comparative Examples 1-7 in Table 1, the alloy materials in Examples 1-8 all meet the requirements of tensile strength ≥ 570 MPa, specified plastic elongation strength ≥ 520 MPa, and elongation after fracture ≥ 12.5%. The comprehensive mechanical properties of the examples are superior to those of the comparative examples.

[0079] The example constructs a microalloying system consisting of Zn-Mg-Cu main elements, a mixture of La and Ce rare earth elements, and an optimized ratio of Mn, Cr, Zr, and Ti. This system achieves the effects of rare earth purification of the melt, reduction of modified inclusions, and microalloying. Cr and Zr form thermally stable dispersed phases, pinning dislocations and grain boundaries. The addition of trace amounts of the La and Ce mixed rare earth elements effectively purifies the alloy melt, refines the grain boundary second phase, and improves its morphology and distribution. Simultaneously, specific amounts of Mn, Cr, Zr, and Ti form stable nanoscale dispersed phases, strongly pinning dislocations and grain boundaries, inhibiting recrystallization, and refining the substructure. The combined effect of rare earth elements and the dispersed phases of Mn, Cr, Zr, and Ti achieves multi-level and multi-dimensional microstructure refinement and purification from grain boundaries to the grain interior, thereby significantly improving strength while ensuring excellent plastic deformation capacity.

[0080] Figure 1 Metallographic microscopy images of Example 3 are shown, clearly revealing the near-fibrous microstructure distributed along the extrusion direction within the alloy, with fine and uniform grains. This image demonstrates that in the Zn-Mg-Cu main strengthening system, the synergistic effect of precisely optimized La and Ce mixed rare earth elements and microalloying elements Mn, Cr, Zr, and Ti significantly improves the alloy's microstructure. The dispersed phases formed by the rare earth elements and Mn, Cr, Zr, and Ti work together to refine and purify the microstructure at multiple levels and dimensions, from grain boundaries to the grain interior, thereby effectively improving the alloy's mechanical properties.

[0081] By controlling the composition and optimizing the precipitated phase composition in the microstructure, the material's strength is ensured while also maintaining its toughness, especially its corrosion resistance. Experimental results from adjusting various elements demonstrate that this invention exhibits excellent room-temperature mechanical properties in extruded products, possessing high strength, a refined internal microstructure, and good elongation. It can significantly improve strength and is widely applicable to high-strength 7-series aluminum alloys in extrusion molding.

[0082] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A high-strength 7-series aluminum alloy, characterized in that, The 7-series aluminum alloy is composed of the following components by mass percentage: Zn 6.0%–6.5%, Mg 2.1%–2.5%, Cu 2.0%–2.5%, Mn 0.20%–0.30%, Ti 0.10%–0.15%, Cr 0.10%–0.20%, Zr 0.10%–0.15%, and rare earth elements 0.02%–0.10%, wherein the rare earth elements are a mixture of La and Ce; the balance is Al and unavoidable impurities, wherein Fe < 0.15% and Si < 0.15%.

2. The 7-series aluminum alloy according to claim 1, characterized in that, The mass percentage of Zn to Mg satisfies 2.4 ≤ Zn / Mg ≤ 3.1; the mass percentage of Cu to Mg satisfies 0.8 ≤ Cu / Mg ≤ 1.

19.

3. The 7-series aluminum alloy according to claim 2, characterized in that, The mass percentage of Zn to Mg satisfies 2.63 ≤ Zn / Mg ≤ 2.

80.

4. The 7-series aluminum alloy according to claim 2, characterized in that, The mass percentage of Cu to Mg satisfies the condition that 0.91 ≤ Cu / Mg ≤ 1.

00.

5. The 7-series aluminum alloy according to claim 1, characterized in that, The sum of the contents of Ti and Zr, by mass percentage, satisfies the condition 0.24%≤Ti+Zr≤0.27%.

6. The 7-series aluminum alloy according to claim 1, characterized in that, The total content of the rare earth elements is 0.04% to 0.08% by mass percentage.

7. A method for preparing 7-series aluminum alloy according to any one of claims 1-6, comprising the steps of melt treatment, gradient homogenization treatment, rounding, welding, multi-stage heat treatment, and surface coloring treatment, characterized in that, The gradient grading homogenization treatment consists of three stages: the first stage is a low-temperature precipitation stage, in which the casting rod is heated from room temperature to 350-380°C and held for 2-5 hours; the second stage is a high-temperature holding stage, in which the temperature is further increased to 440-475°C and held for 10-15 hours; and the third stage is a cooling stage, in which the temperature is reduced to 350-390°C and held for 0.5-3 hours.

8. The method for preparing 7-series aluminum alloys according to claim 7, characterized in that, The multi-stage heat treatment involves strengthening the welded wheels through solution treatment and aging. The solution treatment temperature is 440–480℃ and the time is 0.5–2 hours. The artificial aging process is carried out at an aging temperature of 105–135℃ for 6–14 hours.

9. A motorcycle wheel, characterized in that, Made of any one of the 7-series aluminum alloys according to claims 1-6, or made of the 7-series aluminum alloys prepared by the preparation method described in claim 7 or 8.

10. A vehicle, characterized in that, Including the motorcycle wheel as described in claim 9.

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