Novel copper-free high-strength 7-series aluminum alloy and preparation method thereof

Abstract

The invention provides a novel copper-free high-strength 7-series aluminum alloy and a preparation method thereof, and relates to the technical field of aluminum alloy design and processing. The alloy comprises the following chemical components in percentage by mass: 6.00-7.80% of Zn, 1.80-2.60% of Mg, 0.05-0.30% of Mn and the balance of Fe, Si and other impurity elements, 0.05%, and the balance being Al. The final-state novel copper-free high-strength 7-series aluminum alloy material is prepared through aluminum alloy element content selection and weighing, casting, two-stage heating and heat preservation treatment, hot extrusion machining, two-stage solution treatment and single-stage aging treatment. The novel alloy obtained through the method is few in element variety, low in total content, beneficial to recycling of the alloy, simple and easy to operate, environmentally friendly, low in cost, short in process, high in efficiency and beneficial to industrial large-scale production and popularization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum alloy design and processing, in particular to a new type of copper-free high-strength 7-series aluminum alloy and a preparation method, which can meet the demand for high mechanical properties, excellent appearance and excellent processing performance of aluminum alloys in the fields of consumer electronics and transportation. BACKGROUND

[0002] Aluminum alloys are widely used in transportation, aerospace, computers, communications and consumer electronics (3C) and many other key fields due to their excellent specific strength, corrosion resistance and good processing performance, becoming one of the core materials for realizing lightweight structures and long service life of equipment. Especially in the field of 3C products, with the rapid development of electronic devices towards ultra-thin, lightweight and high performance, the demand for high-performance aluminum alloys continues to grow, showing a broad application prospect.

[0003] Currently, the shells and structural parts of 3C products are mainly made of 6xxx-series aluminum alloys, but the existing 6xxx-series alloys generally have insufficient strength (the tensile strength is usually lower than 350 MPa). In order to meet the basic structural strength requirements, the cross-sectional size such as wall thickness has to be increased, which is difficult to meet the increasingly stringent lightweight design requirements. Al-Zn-Mg-(Cu) series (7xxx series) aluminum alloys have higher tensile strength, but they are prone to form banded structures during alloy preparation and processing, and have poor anodic oxidation coloring performance, which limits their application in high-end 3C fields.

[0004] For example, Chinese patent CN113564434A discloses a 7-series aluminum alloy and a preparation method thereof, which has multiple alloying elements in the composition, resulting in high cost. The homogenization heat treatment in the adopted heat treatment method is in a ladder type, including three stages, which is complicated and difficult to operate. The tensile strength of the prepared aluminum alloy is lower than 530 MPa, and the strength increase is not large.

[0005] Chinese patent CN116694968A discloses a 7-series high-strength corrosion-resistant aluminum alloy and a preparation method thereof. The Cu element in the composition will form red Cu2O during anodic oxidation, resulting in the appearance of mixed colors in the oxidation film and affecting the anodic oxidation effect. At the same time, the Cu element is prone to form micron-sized second phases, affecting the surface quality of the alloy. The preparation method has a total of ten steps, which is complex. Just the preparation of the ingot requires seven complex steps, and there may be an additional two steps later, resulting in high cost and low efficiency.

[0006] Chinese patent CN114941094A discloses a high-strength 7-series aluminum alloy profile and its processing method and application. The method improves the mechanical properties of the alloy material by controlling the contents of zinc, magnesium, copper and silicon. However, the alloy element types are numerous, and the production cost is high and the efficiency is low due to the need for controlled cooling and natural aging and two-stage artificial aging treatment. Moreover, the prepared material has low tensile strength, high elongation and narrow application range.

[0007] Therefore, developing a new type of aluminum alloy material with high strength, excellent surface processing performance, good anodic oxidation adaptability and corrosion resistance has become a major requirement for lightweight design of 3C products and high-end transportation equipment. SUMMARY

[0008] To solve the technical problems of the prior art that the excellent mechanical properties, anodic oxidation adaptability, corrosion resistance and surface finish of high-strength 7-series aluminum alloys cannot be achieved simultaneously, the present application provides a new copper-free high-strength 7-series aluminum alloy and a preparation method. The technical solution is as follows:

[0009] A new copper-free high-strength 7-series aluminum alloy, the chemical composition of the new copper-free high-strength 7-series aluminum alloy is as follows: Zn 6.00-7.80%, Mg 1.80-2.60%, Mn 0.05-0.30%, total of impurity elements such as Fe and Si <0.05%, and the balance is Al.

[0010] Optionally, the microstructure of the new copper-free high-strength 7-series aluminum alloy is surface finish, the volume fraction of micron-level second phase is less than 0.001%, equiaxed crystal structure, and the average grain size is less than 100μm; there are Al6Mn dispersed phases with sizes of several tens to several hundred nanometers; GP zone and η' phase, volume fraction is greater than 5%, size range is 2-10nm.

[0011] Optionally, the density of the new copper-free high-strength 7-series aluminum alloy is 2.75-2.85g / cm 3 , the hardness is higher than 165HV, the tensile strength is higher than 530MPa, the yield strength is higher than 500MPa, the yield ratio is 0.92-0.96, the elongation after fracture is higher than 8%, the anodic oxidation film thickness is 10-25μm, the anodic gloss is 80-100GU, and the anti-exfoliation corrosion grade is not lower than EB grade.

[0012] A preparation method based on the new copper-free high-strength 7-series aluminum alloy, the preparation method of the new copper-free high-strength 7-series aluminum alloy is as follows:

[0013] S1, raw material selection and weighing: high-purity aluminum, industrial pure zinc, industrial pure magnesium and aluminum-manganese intermediate alloy are used as raw materials, and the required alloy raw materials are obtained by weighing according to the alloy composition:

[0014] S2, ingot preparation: after the alloy raw material is smelted and the melt is purified, mold casting or semi-continuous casting is carried out, and an aluminum alloy ingot is obtained;

[0015] S3, two-stage temperature rising and holding treatment: the aluminum alloy ingot of S2 is subjected to two-stage temperature rising and holding treatment, and is air-cooled to room temperature after discharging, so that an aluminum alloy ingot with uniform structure is obtained;

[0016] S4, hot extrusion processing: the aluminum alloy ingot with uniform structure of S3 is subjected to hot extrusion processing, and an aluminum alloy blank is obtained;

[0017] S5, double-stage solid solution treatment: the aluminum alloy blank of S4 is subjected to double-stage solid solution treatment, and a solid-solution-treated aluminum alloy blank is obtained;

[0018] S6, single-stage aging treatment: the solid-solution-treated aluminum alloy blank of S5 is subjected to single-stage aging treatment, and a final-state novel copper-free high-strength 7-series aluminum alloy material is obtained.

[0019] Optionally, in S1, the purity of the high-purity aluminum is ≥99.95wt%, the purity of the industrial pure zinc is ≥99.99wt%, the purity of the industrial pure magnesium is ≥99.99wt%, and the manganese content in the aluminum-manganese intermediate alloy is ≥10wt%.

[0020] Optionally, in S2, the smelting temperature is 700-750℃, the smelting time is 30-60min, the pouring temperature is 680-700℃, and the shape of the ingot is a cylindrical ingot with a size of 75-90mm in diameter and 300-600mm in length.

[0021] Optionally, in S3, the two-stage temperature rising and holding treatment is first rising to 380-420℃ and holding for 10-30h, and then rising to 450-480℃ and holding for 10-30h.

[0022] Optionally, in S4, the temperature of the hot extrusion processing is 380-420℃, and the heating time is 2-4h; the extrusion ratio is 7-50 during extrusion.

[0023] Optionally, in S5, the double-stage solid solution treatment is first rising to 420-440℃ and holding for 0.5-2h, and then rising to 460-480℃ and holding for 0.5-2h, and then quenching in room temperature water.

[0024] Optionally, in S6, the single-stage aging treatment is rising the blank to 110-130℃ and holding for 15-30h.

[0025] The technical principle of the application is as follows:

[0026] 1. Zn and Mg are the main strengthening elements in the novel high-strength aluminum alloy Al-Zn-Mg-Mn, and can produce η-phase (MgZn2) and T-phase (Al2Mg2Zn3) precipitates. When the mass ratio of Zn to Mg is greater than 2.2, the main precipitate in the alloy is the η-phase, which can produce a better strengthening effect. Since Zn and Mg have high solid solubility in the aluminum matrix, appropriately increasing the Zn and Mg content can obtain a higher volume fraction of precipitates without producing a micron-sized second phase. In this invention, the total content of Zn and Mg added is greater than 8 wt%, and the mass ratio of Zn to Mg is maintained at greater than 2.2, which significantly improves the strength of the alloy.

[0027] 2. Mn has low solid solubility in aluminum. The addition of a small amount of Mn in this invention can form an Al6Mn phase during casting / homogenization. During subsequent hot extrusion and solution treatment, it pins subgrain boundaries and dislocations, which can refine grains, inhibit grain growth and promote dispersion strengthening. This helps prevent the formation of extruded strip structures and improves the mechanical properties and corrosion resistance of the alloy.

[0028] 3. Fe and Si are impurity elements that are difficult to completely remove from high-strength aluminum alloys. They typically form coarse, brittle phases larger than 1 μm, such as Al7Cu2Fe, Al3Fe, and Mg2Si. These phases cause stress concentration at the matrix interface, initiating microcracks and reducing the alloy's strength and plasticity. Simultaneously, the brittle phases create a potential difference with the aluminum matrix, inducing pitting corrosion. Furthermore, micron-sized brittle phases also reduce the alloy's surface quality. This invention strictly controls the Fe and Si content to less than 0.05%, reducing the impact of impurity elements on the alloy's mechanical properties, corrosion resistance, and surface quality.

[0029] 4. Cu forms red Cu₂O during the anodizing process, causing discoloration in the oxide film and affecting the anodizing effect. Simultaneously, Cu readily forms a micron-sized second phase, impacting the alloy's surface quality. This invention does not add Cu; through a reasonable matching of Zn, Mg, and Mn elements, it achieves high strength, high plasticity, and excellent surface quality, anodizing effect, processability, and recyclability.

[0030] 5. The present invention adopts a two-stage solution treatment system. Compared with the single-stage solution treatment system, the slow heating process in the two-stage solution treatment system can make the temperature exceed the multiphase eutectic temperature without producing overburnt structure, improve the solubility of the residual soluble second phase, increase the supersaturation of the solid solution after quenching, improve the age hardening effect of the alloy, thereby improving the mechanical properties, corrosion resistance and surface quality of the alloy.

[0031] 6. The present invention adopts a single-stage aging treatment, which is simple in process and can obtain high-density GP region and η′ phase, which helps to improve strength.

[0032] Compared with the prior art, the technical scheme has at least the following beneficial effects:

[0033] The scheme provides a new copper-free high-strength 7-series aluminum alloy and a preparation method, which can solve the technical problems of the prior art, such as the problem that the excellent mechanical properties, anodic oxidation adaptability, corrosion resistance and surface finish of the high-strength 7-series aluminum alloy cannot be achieved at the same time, and the like, and can significantly improve the strength of the alloy while achieving excellent surface processing quality, oxidation coloring effect, processing performance, recycling performance and excellent corrosion resistance.

[0034] The present application can ensure the surface processing finish, excellent oxidation coloring effect and corrosion resistance by reasonably matching the contents of Zn and Mg elements, so that the micron-sized second phase is almost completely absent in the alloy, and the same level as 7003 and 7N01 aluminum alloys is achieved.

[0035] The present application can prevent the formation of extrusion strip structure and surface material lines by selecting Mn element as a micro-alloying element to refine the grain and form equiaxed crystal structure.

[0036] The present application can fully transform the multi-phase eutectic structure in the ingot, improve the uniformity of the structure, reduce the low-melting-point brittle phase, and provide a good structure basis for subsequent processing by two-stage heating and holding treatment.

[0037] The present application can further refine the alloy structure, improve the texture orientation, improve the mechanical properties and obtain a dense and continuous surface quality by hot extrusion processing, which is beneficial to the subsequent anodic oxidation effect.

[0038] The present application can fully dissolve the residual Zn and Mg-rich phase, improve the solid solubility, strengthen the subsequent aging precipitation behavior, and significantly improve the strength and corrosion resistance of the alloy by two-stage solid solution treatment.

[0039] The present application can form a uniformly distributed GP zone and η' phase with stable size in the alloy by single-stage aging treatment, which can simplify the process flow and facilitate industrial application while ensuring the mechanical properties.

[0040] The new copper-free high-strength 7-series aluminum alloy prepared by the present application has a tensile strength UTS> 530 MPa, which is much higher than that of 7003, 7N01 and other aluminum alloys. High strength is of great significance for the lightweight of 3C products and high-end transportation equipment.

[0041] The new copper-free high-strength 7-series aluminum alloy prepared by the present application has a density of 2.75-2.85 g / cm 3The hardness is higher than 165HV, the tensile strength is higher than 530MPa, the yield strength is higher than 500MPa, the yield strength ratio is 0.92-0.96, the elongation after fracture is higher than 8%, the anodic oxidation film thickness is 10-25 mu m, the anodic gloss is 80-100GU, and the anti-exfoliation corrosion grade is not lower than EB grade.

[0042] In summary, the method of the present application is used to prepare the final state new type copper-free high-strength 7 series aluminum alloy material through the selection and weighing of aluminum alloy alloying element content, melting and casting, two-stage temperature rising and holding treatment, hot extrusion processing, double-stage solid solution treatment and single-stage aging treatment. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0044] Figure 1a is a micron-level second phase distribution diagram of a new type copper-free high-strength 7 series aluminum alloy Al-Zn-Mg-Mn aluminum alloy of embodiment 1 of the present application;

[0045] Figure 1b is an EBSD diagram of a new type copper-free high-strength 7 series aluminum alloy Al-Zn-Mg-Mn aluminum alloy of embodiment 1 of the present application;

[0046] Figure 2a is a nanometer-level dispersed phase distribution diagram of a new type copper-free high-strength 7 series aluminum alloy Al-Zn-Mg-Mn aluminum alloy of embodiment 1 of the present application, with a scale of 1 mu m;

[0047] Figure 2b is an Al6Mn dispersed phase distribution diagram of a new type copper-free high-strength 7 series aluminum alloy Al-Zn-Mg-Mn aluminum alloy of embodiment 1 of the present application, with a scale of 250 nm;

[0048] Figure 3a is a grain boundary precipitated phase morphology distribution diagram of a new type copper-free high-strength 7 series aluminum alloy Al-Zn-Mg-Mn aluminum alloy of embodiment 1 of the present application;

[0049] Figure 3b is a matrix precipitated phase morphology distribution diagram of a new type copper-free high-strength 7 series aluminum alloy Al-Zn-Mg-Mn aluminum alloy of embodiment 1 of the present application. DETAILED DESCRIPTION

[0050] The technical solutions in the present application will be described below with reference to the drawings.

[0051] In the embodiments of the present application, the words "exemplary", "for example", and the like are used solely to indicate examples, instances, or illustrations. Any embodiment or design described as "exemplary" in the present application should not be construed as being preferred or superior over other embodiments or designs. In fact, the word "exemplary" is used to present concepts in a concrete manner. In addition, in the embodiments of the present application, the meaning expressed by "and / or" can be both, or can be either one of the two.

[0052] In the embodiments of the present application, "image" and "picture" can be used interchangeably at times. It should be pointed out that when the distinction is not emphasized, the meanings expressed are consistent.

[0053] In the embodiments of the present application, sometimes the subscript such as W1 can be written in the form of non-subscript such as W1. When the distinction is not emphasized, the meanings expressed are consistent.

[0054] To make the technical problems, technical solutions and advantages of the present application clearer, the following will be described in detail with reference to the drawings and specific embodiments.

[0055] A new copper-free high-strength 7-series aluminum alloy, the chemical composition of the new copper-free high-strength 7-series aluminum alloy is as follows in terms of mass percentage: Zn 6.00-7.80%, Mg 1.80-2.60%, Mn 0.05-0.30%, total of impurity elements such as Fe and Si <0.05%, and the balance being Al.

[0056] In particular, the microstructure of the new copper-free high-strength 7-series aluminum alloy is as follows: surface finish, volume fraction of micron-level second phase <0.001%, equiaxed crystal structure, average grain size <100 μm; Al6Mn dispersed phase with size of tens to hundreds of nanometers; GP zone and η' phase, volume fraction >5%, size range 2-10 nm.

[0057] In particular, the density of the new copper-free high-strength 7-series aluminum alloy is 2.75-2.85 g / cm 3 , the hardness is higher than 165 HV, the tensile strength is higher than 530 MPa, the yield strength is higher than 500 MPa, the yield strength ratio is 0.92-0.96, the elongation after fracture is higher than 8%, the anodic oxidation film thickness is 10-25 μm, the anodic gloss is 80-100 GU, and the anti-exfoliation corrosion grade is not lower than EB grade.

[0058] A preparation method of the new copper-free high-strength 7-series aluminum alloy, the preparation method of the new copper-free high-strength 7-series aluminum alloy comprises the following steps:

[0059] S1, raw material selection and weighing: high-purity aluminum, industrial pure zinc, industrial pure magnesium and aluminum-manganese intermediate alloy are used as raw materials, and the required alloy raw materials are obtained by weighing according to the alloy composition:

[0060] S2, ingot preparation: after the alloy raw materials are melted and the melt is purified, mold casting or semi-continuous casting is performed to obtain aluminum alloy ingots;

[0061] S3, two-stage temperature rising and holding treatment: the aluminum alloy ingots of S2 are subjected to two-stage temperature rising and holding treatment, and after discharging, air cooling to room temperature is performed to obtain aluminum alloy ingots with uniform structure;

[0062] S4, hot extrusion processing: the aluminum alloy ingots with uniform structure of S3 are subjected to hot extrusion processing to obtain aluminum alloy billets;

[0063] S5, double-stage solid solution treatment: the aluminum alloy billets of S4 are subjected to double-stage solid solution treatment to obtain solid-solution-treated aluminum alloy billets;

[0064] S6, single-stage aging treatment: the solid-solution-treated aluminum alloy billets of S5 are subjected to single-stage aging treatment to obtain a final-state novel copper-free high-strength 7-series aluminum alloy material.

[0065] In particular, in S1, the purity of high-purity aluminum is ≥ 99.95wt%, the purity of industrial pure zinc is ≥ 99.99wt%, the purity of industrial pure magnesium is ≥ 99.99wt%, and the manganese content in aluminum-manganese intermediate alloy is ≥ 10wt%.

[0066] In particular, in S2, the melting temperature is 700-750℃, the melting time is 30-60min, the pouring temperature is 680-700℃, and the shape of the ingot is a cylindrical ingot with a size of 75-90mm in diameter x 300-600mm in length.

[0067] In particular, in S3, the two-stage temperature rising and holding treatment is first rising to 380-420℃ for 10-30h, and then rising to 450-480℃ for 10-30h.

[0068] In particular, in S4, the temperature of hot extrusion processing is 380-420℃, and the heating time is 2-4h; the extrusion ratio is 7-50 during extrusion.

[0069] In particular, in S5, the double-stage solid solution treatment is first rising to 420-440℃ for 0.5-2h, and then rising to 460-480℃ for 0.5-2h, and then quenching in room temperature water.

[0070] In particular, in S6, the single-stage aging treatment is rising the billet to 110-130℃ for 15-30h.

[0071] Example 1

[0072] A new copper-free high-strength 7-series aluminum alloy, the chemical composition of the new copper-free high-strength 7-series aluminum alloy is as follows: Zn 6.84%, Mg 2.49%, Mn 0.17%, Fe 0.01%, Si 0.015%, and the balance is Al.

[0073] A preparation method of the new copper-free high-strength 7-series aluminum alloy, the preparation method of the new copper-free high-strength 7-series aluminum alloy comprises the following steps:

[0074] S1, raw material selection and weighing: taking high-purity aluminum, industrial pure zinc, industrial pure magnesium and aluminum-manganese intermediate alloy as raw materials, and weighing the alloy raw materials according to the alloy composition to obtain the required alloy raw materials: wherein the purity of high-purity aluminum is ≥99.95wt%, the purity of industrial pure zinc is ≥99.99wt%, the purity of industrial pure magnesium is ≥99.99wt%, and the content of manganese in aluminum-manganese intermediate alloy is ≥10wt%;

[0075] S2, ingot preparation: the alloy raw materials are subjected to melting, melt purification, the melting temperature is 704-738℃, the melting time is 40min, and the melt purification adopts N2 refining; mold casting or semi-continuous casting is carried out, the pouring temperature is 680-700℃, and the aluminum alloy ingot is obtained; the shape of the ingot is cylindrical, and the size is 81mm in diameter x 546mm in length;

[0076] S3, two-stage temperature rising and holding treatment: the aluminum alloy ingot of S2 is subjected to two-stage temperature rising and holding treatment, which is first heated to 400℃ and held for 20h, and then heated to 465℃ and held for 26h, and then air-cooled to room temperature after discharging, to obtain an aluminum alloy ingot with uniform structure;

[0077] S4, hot extrusion processing: the aluminum alloy ingot with uniform structure of S3 is subjected to hot extrusion processing, the temperature of the hot extrusion processing is 390-405℃, and the heating time is 2.5h; the temperature of the extrusion cylinder, die and pad is 410-430℃, and the heating time is 12h, and the extrusion ratio is 9, to obtain an aluminum alloy blank;

[0078] S5, double-stage solid solution treatment: the aluminum alloy blank of S4 is subjected to double-stage solid solution treatment, which is first heated to 425℃ and held for 1h, then heated to 470℃ for 1h and held for 0.5h, and then quenched in room temperature water, to obtain a solid-solution-treated aluminum alloy blank;

[0079] S6, single-stage aging treatment: the solid-solution-treated aluminum alloy blank of S5 is subjected to single-stage aging treatment, which is heated to 120℃ and held for 24h, to obtain a final new copper-free high-strength 7-series aluminum alloy material.

[0080] As Figure 1a andFigure 1b As shown in the microstructure of the new type of copper-free high-strength 7-series aluminum alloy prepared in this embodiment is surface finish, the volume fraction of micron-sized second phase is less than 0.001%, equiaxed crystal structure, and the average grain size is 96 μm; as shown in Figure 2a and Figure 2b As shown, there are Al6Mn dispersed phases with sizes of tens to hundreds of nanometers; as shown in Figure 3a and Figure 3b As shown, the volume fraction of GP zones and η' phases is 5.4%, and the size range is 2-8 nm.

[0081] The density of the new type of copper-free high-strength 7-series aluminum alloy prepared in this embodiment is 2.77 g / cm 3 , the hardness is 166.6 ± 2.5 HV, the tensile strength is UTS = 540 ± 2 MPa, the yield strength is 504 ± 4 MPa, the yield strength ratio is 0.93, the elongation after fracture is 10.3 ± 0.5%, the anodic oxidation film thickness is 13 μm, the anodic gloss is 84 GU, and the anti-flaking corrosion resistance grade is EA grade.

[0082] Embodiment 2

[0083] A new type of copper-free high-strength 7-series aluminum alloy, the chemical composition of the new type of copper-free high-strength 7-series aluminum alloy is as follows: Zn 7.45%, Mg 2.03%, Mn 0.11%, Fe 0.013%, Si 0.015%, and the balance is Al.

[0084] A preparation method of the new type of copper-free high-strength 7-series aluminum alloy, the preparation method of the new type of copper-free high-strength 7-series aluminum alloy comprises the following steps:

[0085] S1, raw material selection and weighing: taking high-purity aluminum, industrial pure zinc, industrial pure magnesium and aluminum-manganese intermediate alloy as raw materials, and weighing the alloy raw materials according to the alloy composition to obtain the required alloy raw materials: the purity of high-purity aluminum is ≥ 99.95wt%, the purity of industrial pure zinc is ≥ 99.99wt%, the purity of industrial pure magnesium is ≥ 99.99wt%, and the manganese content in aluminum-manganese intermediate alloy is ≥ 10wt%;

[0086] S2, ingot preparation: the alloy raw materials are melted, the melt is purified, the melting temperature is 710-740℃, the melting time is 48 min, and the melt is purified by N2 refining; mold casting or semi-continuous casting is carried out, the pouring temperature is 694-705℃, and the aluminum alloy ingot is obtained; the shape of the ingot is cylindrical, and the size is 85mm in diameter × 498mm in length;

[0087] S3, two-stage temperature rising and holding treatment: the aluminum alloy ingot of S2 is subjected to two-stage temperature rising and holding treatment, the two-stage temperature rising and holding treatment is first rising to 400 DEG C, holding for 24h, then rising to 470 DEG C, holding for 25h, after discharging, air cooling to room temperature, obtaining the aluminum alloy ingot with uniform structure;

[0088] S4, hot extrusion processing: the aluminum alloy ingot with uniform structure of S3 is subjected to hot extrusion processing, the temperature of hot extrusion processing is 395-415 DEG C, heating time is 3h; the temperature of extrusion cylinder, die and pad is 415-430 DEG C, heating time is 12h, extrusion ratio is 25, obtaining the aluminum alloy blank;

[0089] S5, double-stage solid solution treatment: the aluminum alloy blank of S4 is subjected to double-stage solid solution treatment, the double-stage solid solution treatment is first rising to 440 DEG C, holding for 1h; then spending 1h to rise to 472 DEG C, holding for 0.5h, then quenching in room temperature water, obtaining the solid solution treated aluminum alloy blank;

[0090] S6, single-stage aging treatment: the solid solution treated aluminum alloy blank of S5 is subjected to single-stage aging treatment, the single-stage aging treatment is rising the blank to 125 DEG C, holding for 23h, obtaining the final state new type copper-free high strength 7 series aluminum alloy material.

[0091] The microstructure of the new type copper-free high strength 7 series aluminum alloy prepared in the embodiment is surface smooth, the volume fraction of micron level second phase is less than 0.001%, equiaxed crystal structure, the average grain size is 82 mu m; there is Al6Mn dispersed phase with size of dozens to hundreds of nanometers; the volume fraction of GP zone and η' phase is 5.8%, the size range is 2-9 nm.

[0092] The density of the new type copper-free high strength 7 series aluminum alloy prepared in the embodiment is 2.80 g / cm 3 , the hardness is 168.5±1.6HV, the tensile strength is UTS=563±7 MPa, the yield strength is 535±8 MPa, the yield strength ratio is 0.95, the elongation after fracture is 9.1±0.6%, the anodic oxidation film thickness is 17 mu m, the anodic gloss is 89GU, and the anti-exfoliation corrosion grade is EA grade.

[0093] Example 3

[0094] A new type copper-free high strength 7 series aluminum alloy, the chemical composition of the new type copper-free high strength 7 series aluminum alloy is as follows in terms of mass percentage: Zn 7.70%, Mg 2.22%, Mn 0.18%, Fe 0.01%, Si 0.01%, the balance being Al.

[0095] A preparation method of the new type copper-free high strength 7 series aluminum alloy, the preparation method of the new type copper-free high strength 7 series aluminum alloy is as follows:

[0096] S1, raw material selection and weighing: high-purity aluminum, industrial pure zinc, industrial pure magnesium and aluminum-manganese intermediate alloy are used as raw materials, and the required alloy raw materials are obtained by weighing according to the alloy composition: the purity of high-purity aluminum is ≥99.95wt%, the purity of industrial pure zinc is ≥99.99wt%, the purity of industrial pure magnesium is ≥99.99wt%, and the manganese content in aluminum-manganese intermediate alloy is ≥10wt%;

[0097] S2, ingot preparation: the alloy raw materials are subjected to melting, melt purification, the melting temperature is 720-740℃, the melting time is 55min, and N2refining is used for melt purification; mold casting or semi-continuous casting is carried out, the pouring temperature is 702-715℃, and the aluminum alloy ingot is obtained; the shape of the ingot is cylindrical, and the size is 77mm in diameter x 553mm in length;

[0098] S3, two-stage temperature rising and holding treatment: the aluminum alloy ingot of S2 is subjected to two-stage temperature rising and holding treatment, which is first raised to 410℃ and held for 20h, and then raised to 470℃ and held for 24h, and then air-cooled to room temperature after discharging, to obtain an aluminum alloy ingot with uniform structure;

[0099] S4, hot extrusion processing: the aluminum alloy ingot with uniform structure of S3 is subjected to hot extrusion processing, the temperature of hot extrusion processing is 410-420℃, and the heating time is 4h; the temperature of extrusion cylinder, mold and pad is 420-430℃, and the heating time is 12h, the extrusion ratio is 16, and the aluminum alloy blank is obtained;

[0100] S5, double-stage solid solution treatment: the aluminum alloy blank of S4 is subjected to double-stage solid solution treatment, which is first raised to 440℃ and held for 1h, and then raised to 475℃ and held for 0.5h, and then quenched in room temperature water, to obtain the solid-solution-treated aluminum alloy blank;

[0101] S6, single-stage aging treatment: the solid-solution-treated aluminum alloy blank of S5 is subjected to single-stage aging treatment, which is raised to 120℃ and held for 26h, to obtain the final state new copper-free high-strength 7-series aluminum alloy material.

[0102] The microstructure of the new copper-free high-strength 7-series aluminum alloy prepared in this embodiment is surface smooth, the volume fraction of micron-sized second phase is less than 0.001%, equiaxed crystal structure, the average grain size is 86μm; there are Al6Mn dispersed phases with sizes of tens to hundreds of nanometers; the volume fraction of GP zone and η' phase is 6.1%, and the size range is 2-10nm.

[0103] The density of the new copper-free high-strength 7-series aluminum alloy prepared in this embodiment is 2.82g / cm 3, hardness of 174.6 ± 3.2 HV, tensile strength of UTS = 582 ± 8 MPa, yield strength of 557 ± 5 MPa, yield ratio of 0.96, elongation of 8.6 ± 0.2%, anodic oxidation film thickness of 18 μm, anodic gloss of 93 GU, and exfoliation corrosion resistance grade of EA.

[0104] Comparative Example 1

[0105] The chemical composition of Comparative Example 1 is as follows in terms of mass percentage: Zn 5.14%, Mg 2.01%, Cu 0.04%, Fe 0.09%, Si 0.14%, and the balance being Al.

[0106] The preparation method of Comparative Example 1 is as follows:

[0107] S1, raw material selection and weighing: high-purity aluminum, industrial pure zinc, industrial pure magnesium, and aluminum-copper intermediate alloy are used as raw materials, and the alloy components are weighed to obtain the required alloy raw materials: the purity of high-purity aluminum is ≥ 99.95 wt%, the purity of industrial pure zinc is ≥ 99.99 wt%, the purity of industrial pure magnesium is ≥ 99.99 wt%, and the copper content in the aluminum-copper intermediate alloy is ≥ 5 wt%;

[0108] S2, ingot preparation: the alloy raw materials are subjected to melting, melt purification, the melting temperature is 700-720℃, the melting time is 38 min, and the melt purification is performed by N2 refining; mold casting or semi-continuous casting is performed at a pouring temperature of 685-697℃ to obtain an aluminum alloy ingot; the shape of the ingot is cylindrical, and the size is 75 mm in diameter x 504 mm in length;

[0109] S3, two-stage temperature rising and holding treatment: the aluminum alloy ingot of S2 is subjected to two-stage temperature rising and holding treatment, which is first raised to 405℃ and held for 22 h, and then raised to 468℃ and held for 23 h, and then air-cooled to room temperature after discharging to obtain an aluminum alloy ingot with uniform structure;

[0110] S4, hot extrusion processing: the aluminum alloy ingot with uniform structure of S3 is subjected to hot extrusion processing, the temperature of the hot extrusion processing is 405-410℃, and the heating time is 4 h; the temperature of the extrusion cylinder, mold, and pad is 415-425℃, and the heating time is 12 h, and the extrusion ratio is 9, to obtain an aluminum alloy blank;

[0111] S5, double-stage solid solution treatment: the aluminum alloy blank of S4 is subjected to double-stage solid solution treatment, which is first raised to 430℃ and held for 1 h, and then raised to 473℃ and held for 0.5 h, and then quenched in room temperature water to obtain a solid-solution-treated aluminum alloy blank;

[0112] S6, single-stage aging treatment: the solid-solution-treated aluminum alloy blank of S5 is subjected to single-stage aging treatment, the single-stage aging treatment is to heat the blank to 121 ℃ and keep for 26 h, to obtain the final 7N01 aluminum alloy material.

[0113] The microstructure of the alloy prepared in the present comparative example is a small amount of Fe-rich second phase, equiaxed crystal structure, and the average grain size is 132 μm; the volume fraction of GP zone and η' phase is 3.0%, and the size range is 4-10 nm.

[0114] The density of the alloy prepared in the present comparative example is 2.76 g / cm 3 , the hardness is 137.6±2.9 HV, the tensile strength is UTS=382±4 MPa, the yield strength is 322±5 MPa, the yield strength ratio is 0.84, the elongation after fracture is 12.8±0.3%, the anodic oxidation film thickness is 13 μm, the anodic gloss is 81 GU, and the anti-exfoliation corrosion grade is EB grade.

[0115] Comparative Example 2

[0116] The chemical composition of Comparative Example 2 is as follows in terms of mass percentage: Zn 8.10%, Mg 2.20%, Cu 2.24%, Zr 0.10%, Fe 0.11%, Si 0.09%, and the balance being Al.

[0117] The preparation method of Comparative Example 2 is as follows:

[0118] S1, raw material selection and weighing: high-purity aluminum, industrial pure zinc, industrial pure magnesium, aluminum-copper intermediate alloy and aluminum-zirconium intermediate alloy are used as raw materials, and the alloy raw materials required are weighed according to the alloy composition: the purity of high-purity aluminum is ≥99.95wt%, the purity of industrial pure zinc is ≥99.99wt%, the purity of industrial pure magnesium is ≥99.99wt%, the copper content in the aluminum-copper intermediate alloy is ≥10wt%, and the zirconium content in the aluminum-zirconium intermediate alloy is ≥5wt%;

[0119] S2, ingot preparation: the alloy raw materials are subjected to melting, melt purification, the melting temperature is 706-717 ℃, the melting time is 47 min, and the melt purification adopts N2 refining; mold casting or semi-continuous casting is carried out, the pouring temperature is 693-703 ℃, to obtain an aluminum alloy ingot; the shape of the ingot is cylindrical, and the size is 74 mm in diameter x 525 mm in length;

[0120] S3, two-stage temperature rising and holding treatment: the aluminum alloy ingot of S2 is subjected to two-stage temperature rising and holding treatment, the two-stage temperature rising and holding treatment is to first heat to 415 ℃ and keep for 24 h, then heat to 470 ℃ and keep for 24 h, and then air cool to room temperature after discharging, to obtain an aluminum alloy ingot with uniform structure;

[0121] S4, hot extrusion: the aluminum alloy ingot with uniform structure of S3 is subjected to hot extrusion, the temperature of hot extrusion is 405-410℃, the heating time is 4h; the temperature of extrusion cylinder, die and pad is 420-427℃, the heating time is 12h, the extrusion ratio is 9, to obtain an aluminum alloy blank;

[0122] S5, double-stage solid solution treatment: the aluminum alloy blank of S4 is subjected to double-stage solid solution treatment, the double-stage solid solution treatment is first heated to 435℃, and then heated to 478℃ for 1h, and then quenched in room temperature water, to obtain a solid-solution-treated aluminum alloy blank;

[0123] S6, single-stage aging treatment: the solid-solution-treated aluminum alloy blank of S5 is subjected to single-stage aging treatment, the single-stage aging treatment is heating the blank to 120℃, and then holding for 23h, to obtain a final 7055 aluminum alloy material.

[0124] The microstructure of the alloy prepared in the comparative example is that a large number of Cu-rich micron-sized second phases exist, the surface finish is poor, the columnar crystal structure, and the average grain size is 12μm; the volume fraction of GP zone and η' phase is 6.0%, and the size range is 2-10nm.

[0125] The density of the alloy prepared in the comparative example is 2.85g / cm 3 , the hardness is 196.6±3.6HV, the tensile strength is UTS=674±2MPa, the yield strength is 629±4MPa, the yield strength ratio is 0.92, the elongation after fracture is 7.8±0.3%, the anodic oxidation film thickness is 12μm, the anodic gloss is 58GU, and the anti-exfoliation corrosion grade is EB grade.

[0126] Comparative Example 3

[0127] The chemical composition of the comparative example is the same as that of the alloy used in Example 2, specifically, in mass percent: Zn 7.45%, Mg 2.03%, Mn 0.11%, Fe 0.013%, Si 0.015%, and the balance being Al.

[0128] The difference is that the heat treatment system is adjusted, as follows:

[0129] S1, raw material selection and weighing: high-purity aluminum, industrial pure zinc, industrial pure magnesium and aluminum-manganese intermediate alloy are used as raw materials, and the required alloy raw materials are weighed according to the alloy composition: the purity of high-purity aluminum is ≥99.95wt%, the purity of industrial pure zinc is ≥99.99wt%, the purity of industrial pure magnesium is ≥99.99wt%, and the content of manganese in aluminum-manganese intermediate alloy is ≥10wt%;

[0130] S2, ingot preparation: the alloy raw material is subjected to melting, melt purification, the melting temperature is 710-740 °C, the melting time is 48 min, the melt purification adopts N2 refining; mold casting or semi-continuous casting is carried out, the pouring temperature is 694-705 °C, and an aluminum alloy ingot is obtained; the shape of the ingot is cylindrical, and the size is 85 mm in diameter x 498 mm in length;

[0131] S3, two-stage temperature rising and holding treatment: the aluminum alloy ingot of S2 is subjected to two-stage temperature rising and holding treatment, which is first raised to 400 °C and held for 24 h, and then raised to 470 °C and held for 25 h, and then air-cooled to room temperature after discharging, to obtain an aluminum alloy ingot with uniform structure;

[0132] S4, hot extrusion processing: the aluminum alloy ingot with uniform structure of S3 is subjected to hot extrusion processing, the temperature of the hot extrusion processing is 395-415 °C, and the heating time is 3 h; the temperature of the extrusion cylinder, die and pad is 415-430 °C, and the heating time is 12 h, and the extrusion ratio is 25, to obtain an aluminum alloy blank;

[0133] S5, single-stage solid solution treatment: the aluminum alloy blank of S4 is subjected to single-stage solid solution treatment, the solid solution temperature is 460 °C, and the holding time is 1.5 h, and then quenched in room temperature water, to obtain a solid-solution-treated aluminum alloy blank;

[0134] S6, single-stage aging treatment: the solid-solution-treated aluminum alloy blank of S5 is subjected to single-stage aging treatment, the single-stage aging treatment is to raise the blank to 125 °C and hold for 23 h, to obtain a final-state aluminum alloy material.

[0135] The aluminum alloy prepared in the comparative example has a rough surface, the volume fraction of the micron-sized second phase is greater than 0.5%, the equiaxed crystal structure and the average grain size are 95 μm; there are Al6Mn dispersed phases with a size of tens to hundreds of nanometers; the volume fraction of GP zones and η' phases is 4.6%, and the size range is 4-15 nm.

[0136] The density of the alloy prepared in the comparative example is 2.82 g / cm 3 , the hardness is 160.5±1.6 HV, the tensile strength is UTS=514±6 MPa, the yield strength is 472±5 MPa, the yield strength ratio is 0.93, the elongation after fracture is 8.4±0.5%, the anodic oxidation film thickness is 18 μm, the anodic gloss is 73 GU, and the anti-exfoliation corrosion grade is EC grade.

[0137] As can be seen from the comparison of Comparative Examples 1-3 and Example 1-3, the new copper-free high-strength 7-series aluminum alloy (Example 1-3) exhibits excellent comprehensive mechanical properties, corrosion resistance and anodizing adaptability under the synergistic regulation of optimized alloy composition design, microstructure control and heat treatment system. By increasing the contents of Zn and Mg and introducing an appropriate amount of Mn element, good strengthening phase precipitation behavior and microstructure stability are achieved without adding Cu, the dispersed Al6Mn phase effectively inhibits the growth of recrystallized grains, so that the alloy grain size is maintained within a relatively fine range, and the formation of micron-sized second phases is significantly reduced. Combined with two-stage solid solution treatment and precise control of the aging system, the formation and uniform distribution of a large number of GP zones and η' phases are promoted, the volume fraction of the strengthening phase reaches 5.4-6.1%, and the size is stable within 2-10 nm, achieving high strength, high hardness and good yield ratio. At the same time, since the alloy does not introduce Cu element which is easy to cause grain boundary corrosion, combined with fine equiaxed structure and pure matrix structure, it has excellent resistance to exfoliation corrosion and good anodizing appearance, and the anodic film thickness and gloss are significantly better than those of the comparative alloy, showing excellent comprehensive performance level, especially suitable for high-strength and high-corrosion-resistant aviation, rail transportation and high-end structural application fields.

[0138] The above scheme, the present application provides a new type of copper-free high-strength 7-series aluminum alloy and a preparation method, which can solve the technical problems of the prior art that the excellent mechanical properties, anodizing adaptability, corrosion resistance and surface finish of high-strength 7-series aluminum alloys cannot be achieved at the same time, etc. While significantly improving the strength of the alloy, excellent surface processing quality, oxidation coloring effect, processing performance, recycling performance and excellent corrosion resistance are obtained.

[0139] The present application matches the contents of Zn and Mg elements reasonably, so that there is almost no micron-sized second phase in the alloy, ensuring the surface processing finish, excellent oxidation coloring effect and corrosion resistance, reaching the same level as 7003 and 7N01 aluminum alloys.

[0140] The present application selects Mn element as a micro-alloying element to refine the grains, form equiaxed crystal structure, prevent the formation of extrusion strip structure and surface texture.

[0141] The present application can fully transform the multi-phase eutectic structure in the ingot through two-stage temperature rising and holding treatment, improve the uniformity of the structure, reduce the low-melting-point brittle phase, and provide a good structure basis for subsequent processing.

[0142] The present application can further refine the alloy structure through hot extrusion processing, improve the texture orientation, improve the mechanical properties and obtain a dense and continuous surface quality, which is beneficial to the subsequent anodizing effect.

[0143] The application can make residual Zn and Mg rich phase fully dissolve, improve solid solubility, strengthen subsequent aging precipitation behavior, and significantly improve alloy strength and corrosion resistance through double-stage solid solution treatment.

[0144] The application can form GP zone and eta prime phase with uniform distribution and stable size in the alloy through single-stage aging treatment, simplify the process flow while ensuring mechanical properties, and facilitate industrial application.

[0145] The new type of copper-free high-strength 7-series aluminum alloy prepared by the application has a tensile strength UTS of more than 530 MPa, which is much higher than that of 7003, 7N01 and other aluminum alloys. High strength is of great significance to the lightweight of 3C products and high-end transportation equipment.

[0146] The new type of copper-free high-strength 7-series aluminum alloy prepared by the application has a density of 2.75-2.85 g / cm 3 , a hardness of more than 165 HV, a tensile strength of more than 530 MPa, a yield strength of more than 500 MPa, a yield strength ratio of 0.92-0.96, an elongation after fracture of more than 8%, an anodized film thickness of 10-25 mu m, an anodized gloss of 80-100 GU, and a peeling corrosion resistance grade of no less than EB grade.

[0147] In summary, the method of the application prepares a final state new type of copper-free high-strength 7-series aluminum alloy material through aluminum alloy element content selection and weighing, melting and casting, two-stage temperature rising and holding treatment, hot extrusion processing, double-stage solid solution treatment and single-stage aging treatment. The method has fewer types and lower total content of elements in the new alloy, is beneficial to recycling of the alloy, is simple and easy to operate, is green and environmentally friendly, has low cost, short process, high efficiency, and is beneficial to industrial large-scale production and promotion.

[0148] It should be understood that the term "and / or" herein merely describes an association relationship of associated objects, and can represent three relationships, for example, A and / or B can represent three cases of A alone, A and B together, and B alone, wherein A and B can be singular or plural. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects, but can also represent an "and / or" relationship, which can be understood according to the context before and after.

[0149] In the application, "at least one" means one or more, and "a plurality of" means two or more. "At least one of the following" or the like means any combination of the items, including any combination of single item or multiple items. For example, at least one of a, b, or c can represent a, b, c, a-b, a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple.

[0150] It should be understood that the magnitude of the sequence number of the above-mentioned processes does not mean the order of execution, and the execution order of the processes should be determined according to their functions and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0151] The above description is merely a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A novel copper-free, high-strength 7-series aluminum alloy, characterized in that, The chemical composition of the novel copper-free high-strength 7-series aluminum alloy, by mass percentage, is: Zn 6.00-7.80%, Mg 1.80-2.60%, Mn 0.05-0.30%, total impurity elements such as Fe and Si <0.05%, with the balance being Al.

2. The novel copper-free high-strength 7-series aluminum alloy according to claim 1, characterized in that, The microstructure of the novel copper-free high-strength 7-series aluminum alloy is characterized by a smooth surface, a volume fraction of less than 0.001% of the micron-sized second phase, an equiaxed crystal structure, and an average grain size of less than 100 μm. The presence of Al6Mn dispersed phases with sizes ranging from tens to hundreds of nanometers; GP region and η′ phase, with a volume fraction greater than 5% and a size range of 2-10 nm.

3. The novel copper-free high-strength 7-series aluminum alloy according to claim 1, characterized in that, The density of the novel copper-free high-strength 7-series aluminum alloy is 2.75-2.85 g / cm³. 3 The hardness is higher than 165HV, the tensile strength is higher than 530MPa, the yield strength is higher than 500MPa, the yield strength ratio is 0.92-0.96, the elongation after fracture is higher than 8%, the thickness of the anodic oxide film is 10-25μm, the anodic gloss is 80-100GU, and the resistance to exfoliation corrosion is not lower than EB grade.

4. A method for preparing a novel copper-free high-strength 7-series aluminum alloy according to any one of claims 1-3, characterized in that, The preparation method of the novel copper-free high-strength 7-series aluminum alloy is as follows: S1. Raw material selection and weighing: High-purity aluminum, industrial-pure zinc, industrial-pure magnesium, and aluminum-manganese master alloy are used as raw materials, and the required alloy raw materials are weighed according to the alloy composition. S2. Ingot preparation: After the alloy raw materials are smelted and purified, they are molded or semi-continuously cast to obtain aluminum alloy ingots. S3. Two-stage heating and heat preservation treatment: The aluminum alloy ingot of S2 is subjected to two-stage heating and heat preservation treatment, and after being taken out of the furnace, it is air-cooled to room temperature to obtain an aluminum alloy ingot with uniform structure. S4. Hot extrusion: The aluminum alloy ingot with uniform microstructure of S3 is hot extruded to obtain aluminum alloy billet. S5, Two-stage solution treatment: The aluminum alloy billet of S4 is subjected to two-stage solution treatment to obtain the solution-treated aluminum alloy billet. S6. Single-stage aging treatment: The solution-treated aluminum alloy billet of S5 is subjected to a single-stage aging treatment to obtain a new copper-free high-strength 7-series aluminum alloy material in its final state.

5. The method for preparing the novel copper-free high-strength 7-series aluminum alloy according to claim 4, characterized in that, S1 has a high purity aluminum content ≥99.95wt%, an industrial pure zinc content ≥99.99wt%, an industrial pure magnesium content ≥99.99wt%, and a manganese content ≥10wt% in the aluminum-manganese master alloy.

6. The method for preparing the novel copper-free high-strength 7-series aluminum alloy according to claim 4, characterized in that, The S2 melting temperature is 700-750℃, the melting time is 30-60min, the casting temperature is 680-700℃, and the ingot shape is a cylindrical ingot with a diameter of 75-90mm × a length of 300-600mm.

7. The method for preparing the novel copper-free high-strength 7-series aluminum alloy according to claim 4, characterized in that, The two-stage heating and holding process in S3 involves first heating to 380-420℃ and holding for 10-30 hours, then heating to 450-480℃ and holding for 10-30 hours.

8. The method for preparing the novel copper-free high-strength 7-series aluminum alloy according to claim 4, characterized in that, The hot extrusion temperature in S4 is 380-420℃, and the heating time is 2-4h; the extrusion ratio is 7-50 during extrusion.

9. The method for preparing the novel copper-free high-strength 7-series aluminum alloy according to claim 4, characterized in that, The two-stage solution treatment in S5 involves first heating to 420-440℃ and holding for 0.5-2 hours; then heating to 460-480℃ for 0.5-2 hours and holding for 0.5-2 hours, followed by quenching in water at room temperature.

10. The method for preparing the novel copper-free high-strength 7-series aluminum alloy according to claim 4, characterized in that, In S6, the single-stage aging treatment involves heating the billet to 110-130℃ and holding it for 15-30 hours.

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