Ultrahigh-strength 7-series aluminum alloy for mobile phone middle frame and preparation method of ultrahigh-strength 7-series aluminum alloy

Abstract

The invention relates to the technical field of preparation of aluminum alloy profiles, and discloses an ultrahigh-strength 7-series aluminum alloy for a mobile phone middle frame and a preparation method of the ultrahigh-strength 7-series aluminum alloy, the tensile strength of the prepared aluminum alloy profile is larger than 660 MPa, the yield strength is larger than 620 MPa, compared with a traditional 6013 mobile phone middle frame material, the strength is improved by 70%, and the service life of the aluminum alloy profile is prolonged. The middle frame can be thinned by 40%, and the requirement for the light and thin design of a mobile phone is met; the ductility is larger than 8%, and the good ductility is achieved; the intergranular corrosion grade reaches level 3, the corrosion resistance is excellent, surface anodic oxidation treatment can be carried out after machining, and the requirements for the machining performance and the surface decoration effect of the mobile phone middle frame are met. In addition, the preparation process provided by the invention is relatively simple, adopts two-stage homogenization and two-stage aging heat treatment, does not need a complicated process flow, and is relatively high in production efficiency and controllable in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of aluminum alloys, and particularly relates to a super-high-strength 7-series aluminum alloy for mobile phone middle frames and a preparation method thereof. Background Art

[0002] With the development of smart phones towards being thinner, lighter and having larger screens, the strength requirements for mobile phone middle frame materials are getting higher and higher. The existing mobile phone middle frames widely use 6000-series aluminum alloys, such as 6013 aluminum alloy, whose yield strength is about 330 Mpa. The strength is relatively low, and it is difficult to meet the requirements of the middle frame thinning design. In order to improve the strength of the mobile phone middle frame and at the same time ensure good processing performance and surface decoration effects, new high-strength aluminum alloy materials need to be developed. The prior art usually improves the strength of aluminum alloys by increasing the content of alloying elements or complex heat treatment processes.

[0003] For example, the Chinese patent application with the publication number CN115354201A discloses a high-strength 7-series aluminum alloy for 3C electronic products and its processing technology. The 7-series aluminum alloy includes the following components in mass percentage: Zn 7.0 - 9.0 wt%, Mg 1.0 - 3.5 wt%, Cu 1.0 - 2.5 wt%, Mn ≤ 0.30 wt%, Si ≤ 0.30 wt%, Cr ≤ 0.15 wt%, Ti ≤ 0.15 wt%, Zr ≤ 0.25 wt%, Fe ≤ 0.15 wt%, and the remaining components are Al and inevitable impurities. The invention homogenizes and anneals the ingot of the above components, extrudes the material after homogenization, and performs aging treatment on the extruded material. Through the control of the composition content and the optimization of the process, the conductivity coefficient of the 7-series aluminum alloy material is ≥ 37 IACS%, the brightness after anodization is ≥ 602 Gu, and the yield strength is ≥ 610 MPa. The material has both a relatively high yield strength and good high-brightness anodizing effects and corrosion resistance. Summary of the Invention

[0004] The purpose of the present invention is to further optimize the alloy composition to improve the strength and anodic appearance effect of the aluminum alloy material, and thus to solve one or more technical problems existing in the prior art, and at least provide a beneficial choice or create conditions.

[0005] To achieve the above object, the present invention adopts the following technical solutions.

[0006] A super-high-strength 7-series aluminum alloy for mobile phone middle frames, and its preparation process is as follows:

[0007] 1) Alloy raw material configuration: By mass percentage, the aluminum alloy raw material contains 2.4%-3.0% Mg, 7.4%-8.0% Zn, the Zn / Mg ratio is 2.7-3.0, 0.4%-0.7% Cu, 0.05%-0.15% Mn, Fe less than 0.1%, the single content of other elements is less than 0.03%, the total content of other elements is less than 0.10%, and the balance is Al.

[0008] 2) Homogenization treatment: After the aluminum rod is cast, double-stage homogenization heat treatment is carried out. The first-stage homogenization temperature is 300°C-350°C, the first-stage homogenization holding time is 6h-12h, the second-stage homogenization temperature is 400°C-450°C, and the second-stage homogenization holding time is 14h-20h.

[0009] 3) Extrusion molding: After homogenization, extrusion processing is carried out. The extrusion rod temperature is 420°C-480°C, the extrusion discharge port temperature is greater than 500°C, and online quenching and cooling are carried out after extrusion. The cooling rate is greater than 200°C / min.

[0010] 4) Aging treatment: The extruded profiles are subjected to double-stage aging heat treatment. The first-stage aging temperature is 90°C-120°C, the first-stage aging holding time is 4h-8h, the second-stage aging temperature is 130°C-160°C, and the second-stage aging holding time is 15h-20h.

[0011] The present invention improves the mechanical properties and corrosion resistance of the product by controlling the Zn / Mg ratio; too high a Zn / Mg ratio will cause more strengthening phases to form in the alloy, such as η phase (MgZn2), etc., and will form more continuous corrosion channels, greatly reducing the corrosion resistance of the material. While too low a Zn / Mg ratio will result in insufficient number of strengthening phases formed, and the strengthening effect of the alloy is not obvious; and the precipitation phases at the grain boundaries of the material are unevenly distributed, easily forming continuous weak areas; under the combined action of stress and corrosive medium, cracks are likely to initiate and expand in these weak areas, resulting in a decrease in the stress corrosion resistance of the alloy.

[0012] The present invention improves the product performance by controlling the content of Cu element. Excessive Cu will cause the oxide film structure on the alloy surface to become loose, reducing the protective effect of the oxide film on the matrix, making the alloy more vulnerable to the erosion of corrosive media, which is very unfavorable for the middle frame products of mobile phones that need to frequently contact high-corrosion environments such as hand sweat.

[0013] In addition, for the middle frame products of mobile phones, the oxidation gloss of the 7-series alloy itself is lower than that of the 6-series alloy. If the trace elements are not properly controlled, other impurity phases will be formed in the oxide film to further expand the diffuse reflection effect, resulting in the oxidation surface quality of the final product not meeting the requirements. The present invention strictly controls the trace elements, does not include any rare earth elements, and has a reasonable alloy composition design for the aluminum alloy material. There is no need to significantly increase the content of alloy elements, avoiding a substantial increase in production costs.

[0014] After testing, the tensile strength of the aluminum alloy profile prepared by the present invention is greater than 660 MPa, and the yield strength is greater than 620 MPa. Compared with the traditional 6013 mobile phone middle frame material, the strength is increased by 70%, and the middle frame can be thinned by 40%, meeting the requirements of the thin and light design of mobile phones; the elongation is greater than 8%, having good ductility; the intergranular corrosion grade reaches level 3, with excellent corrosion resistance, and can be subjected to surface anodic oxidation treatment after processing, meeting the processing performance and surface decoration effect requirements of mobile phone middle frames.

[0015] In addition, the preparation process provided by the present invention is relatively simple. It adopts double-stage homogenization and double-stage aging heat treatment, without complex process flows, has a high production efficiency, and controllable costs.

[0016] In one embodiment, a preparation method of a super-high-strength 7-series aluminum alloy for mobile phone middle frames includes the following preparation steps: 1) Alloy raw material configuration: By mass percentage, the aluminum alloy raw material contains 2.53% Mg, 7.42% Zn, the Zn / Mg ratio is 2.9, 0.49% Cu, 0.12% Mn, 0.07% Fe, 0.03% Si, 0.01% Ti, and the balance is Al; 2) Homogenization treatment: After the aluminum rod is cast, double-stage homogenization heat treatment is carried out. The first-stage homogenization temperature is 310 °C, and the first-stage homogenization holding time is 12 h. The second-stage homogenization temperature is 410 °C, and the second-stage homogenization holding time is 20 h; 3) Extrusion forming: After homogenization, extrusion processing is carried out; 4) Aging treatment: The profile obtained by extrusion is subjected to double-stage aging heat treatment. The first-stage aging temperature is 95 °C, and the first-stage aging holding time is 8 h. The second-stage aging temperature is 135 °C, and the second-stage aging holding time is 20 h.

[0017] In one embodiment, a preparation method of a super-high-strength 7-series aluminum alloy for a mobile phone middle frame includes the following preparation steps: 1) Alloy raw material configuration: By mass percentage, the aluminum alloy raw material contains 2.64% Mg, 7.55% Zn, the Zn / Mg ratio is 2.9, 0.53% Cu, 0.12% Mn, 0.07% Fe, 0.03% Si, 0.01% Ti, and the balance is Al; 2) Homogenization treatment: After the aluminum rod is cast, double-stage homogenization heat treatment is carried out. The first-stage homogenization temperature is 320°C, and the first-stage homogenization holding time is 10 h. The second-stage homogenization temperature is 420°C, and the second-stage homogenization holding time is 18 h; 3) Extrusion molding: After homogenization, extrusion processing is carried out; 4) Aging treatment: The extruded profile is subjected to double-stage aging heat treatment. The first-stage aging temperature is 100°C, and the first-stage aging holding time is 7 h. The second-stage aging temperature is 140°C, and the second-stage aging holding time is 18 h.

[0018] In one embodiment, a preparation method of a super-high-strength 7-series aluminum alloy for a mobile phone middle frame includes the following preparation steps: 1) Alloy raw material configuration: By mass percentage, the aluminum alloy raw material contains 2.78% Mg, 7.69% Zn, the Zn / Mg ratio is 2.8, 0.51% Cu, 0.09% Mn, 0.07% Fe, 0.03% Si, 0.01% Ti, and the balance is Al; 2) Homogenization treatment: After the aluminum rod is cast, double-stage homogenization heat treatment is carried out. The first-stage homogenization temperature is 330°C, and the first-stage homogenization holding time is 8 h. The second-stage homogenization temperature is 430°C, and the second-stage homogenization holding time is 16 h; 3) Extrusion molding: After homogenization, extrusion processing is carried out; 4) Aging treatment: The extruded profile is subjected to double-stage aging heat treatment. The first-stage aging temperature is 105°C, and the first-stage aging holding time is 6 h. The second-stage aging temperature is 145°C, and the second-stage aging holding time is 16 h.

[0019] In one embodiment, a preparation method of a super-high-strength 7-series aluminum alloy for a mobile phone middle frame includes the following preparation steps: 1) Alloy raw material configuration: By mass percentage, the aluminum alloy raw material contains 2.92% Mg, 7.91% Zn, the Zn / Mg ratio is 2.8, 0.62% Cu, 0.11% Mn, 0.07% Fe, 0.03% Si, 0.01% Ti, and the balance is Al; 2) Homogenization treatment: After the aluminum rod is cast, double-stage homogenization heat treatment is carried out. The first-stage homogenization temperature is 340°C, and the first-stage homogenization holding time is 6 h. The second-stage homogenization temperature is 440°C, and the second-stage homogenization holding time is 14 h; 3) Extrusion molding: After homogenization, extrusion processing is carried out; 4) Aging treatment: The extruded profile is subjected to double-stage aging heat treatment. The first-stage aging temperature is 110°C, and the first-stage aging holding time is 5 h. The second-stage aging temperature is 150°C, and the second-stage aging holding time is 15 h.

[0020] In one embodiment, in the extrusion forming step, the temperature of the extrusion rod is 420°C - 480°C, and the temperature at the extrusion discharge port is greater than 500°C.

[0021] In one embodiment, online quenching and cooling is carried out after extrusion, and the cooling rate is greater than 200°C / min.

[0022] On the other hand, the present invention also provides a super-high-strength 7-series aluminum alloy for mobile phone middle frames, which is obtained by using the preparation method of a super-high-strength 7-series aluminum alloy for mobile phone middle frames as described above.

[0023] A super-high-strength 7-series aluminum alloy for mobile phone middle frames has a tensile strength greater than 660 MPa, a yield strength greater than 620 MPa, an elongation greater than 8%, and an intergranular corrosion grade above level 3.

[0024] Some other beneficial effects of the present invention will become more obvious in the following description or be understood in practice. Detailed Embodiments

[0025] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] A preparation process of a super-high-strength 7-series aluminum alloy for mobile phone middle frames is as follows:

[0027] 1) Alloy raw material configuration: By mass percentage, the aluminum alloy raw materials contain 2.4% - 3.0% Mg, 7.4% - 8.0% Zn, the Zn / Mg ratio is 2.7 - 3.0, 0.4% - 0.7% Cu, 0.05% - 0.15% Mn, Fe less than 0.1%, the individual content of other elements less than 0.03%, the total content of other elements less than 0.10%, and the balance is Al.

[0028] 2) Homogenization treatment: After the aluminum rod is cast, double-stage homogenization heat treatment is carried out. The first-stage homogenization temperature is 300°C - 350°C, the first-stage homogenization holding time is 6 h - 12 h, the second-stage homogenization temperature is 400°C - 450°C, and the second-stage homogenization holding time is 14 h - 20 h.

[0029] 3) Extrusion forming: After homogenization, extrusion processing is carried out. The temperature of the extrusion rod is 420°C - 480°C, the temperature at the extrusion discharge port is greater than 500°C, and after extrusion, online quenching and cooling is carried out, and the cooling rate is greater than 200°C / min.

[0030] 4) Aging treatment: The extruded profiles are subjected to two-stage aging heat treatment. The first-stage aging temperature is 90°C - 120°C, and the first-stage aging holding time is 4h - 8h. The second-stage aging temperature is 130°C - 160°C, and the second-stage aging holding time is 15h - 20h.

[0031] After testing, the tensile strength of the aluminum alloy profiles prepared by the present invention is greater than 660 MPa, the yield strength is greater than 620 MPa. Compared with the traditional 6013 mobile phone middle frame material, the strength is increased by 70%, and the middle frame can be thinned by 40%, meeting the requirements of the mobile phone for a thinner and lighter design; the elongation is greater than 8%, with good ductility; the intergranular corrosion grade reaches level 3, with excellent corrosion resistance, and surface anodic oxidation treatment can be carried out after processing, meeting the processing performance and surface decoration effect requirements of the mobile phone middle frame.

[0032] In addition, the preparation process provided by the present invention is relatively simple. By adopting two-stage homogenization and two-stage aging heat treatment, there is no need for complex process flows, the production efficiency is relatively high, and the cost is controllable.

[0033] To better reflect the progressiveness of the present invention, Examples 1 - 4 and Comparative Examples 1 - 6 are formed by adjusting the alloy raw material ratios and process parameters. The alloy raw material ratios of Examples 1 - 4 and Comparative Examples 1 - 6 are shown in Table 1, and the process parameters of Examples 1 - 4 and Comparative Examples 1 - 6 are shown in Table 2. The process parameters not listed in Table 2 are defaulted to be the same.

[0034] Table 1. Alloy raw material ratios of Examples 1 - 4 and Comparative Examples 1 - 6 Type Magnesium Zinc Zinc / Magnesium Iron Manganese Copper Silicon Titanium Example 1 2.53 7.42 2.9 0.07 0.12 0.49 0.03 0.01 Example 2 2.64 7.55 2.9 0.07 0.11 0.53 0.03 0.01 Example 3 2.78 7.69 2.8 0.07 0.09 0.51 0.03 0.01 Example 4 2.92 7.91 2.7 0.07 0.11 0.62 0.03 0.01 Comparative Example 1 1.89 7.56 4.0 0.08 0.12 0.6 0.03 0.01 Comparative Example 2 3.35 5.26 1.6 0.07 0.13 0.6 0.05 0.01 Comparative Example 3 2.68 7.85 2.9 0.17 0.2 0.01 0.03 0.01 Comparative Example 4 2.64 7.55 2.9 0.07 0.11 0.53 0.04 0.01 Comparative Example 5 2.64 7.55 2.9 0.07 0.11 0.53 0.04 0.01 Comparative Example 6 2.64 7.55 2.9 0.07 0.11 0.53 0.04 0.01

[0035] Table 2. Process parameters of Examples 1 - 4 and Comparative Examples 1 - 6 。

[0036] The aluminum alloy properties obtained in Examples 1 - 4 and Comparative Examples 1 - 6 are shown in Table 3.

[0037] Table 3. Aluminum alloy properties obtained in Examples 1 - 4 and Comparative Examples 1 - 6 Type Tensile Strength (MPa) Yield Strength (MPa) Elongation Rate (%) Intergranular Corrosion Grade Anodic Oxidation Effect Example 1 657 626 10.2 3 Qualified Example 2 662 631 9.9 3 Qualified Example 3 673 636 9.8 3 Qualified Example 4 681 641 9.5 3 Qualified Comparative Example 1 595 523 11.5 4 Corrosion Points Comparative Example 2 564 534 10.5 3 Low Gloss Comparative Example 3 592 554 11.9 4 Strip Corrosion Comparative Example 4 647 615 9.6 4 Pitting Comparative Example 5 625 584 12.1 3 Qualified Comparative Example 6 552 509 9.9 2 Qualified

[0038] As can be seen from Table 3, when the zinc / magnesium ratio exceeds the upper limit, the tensile strength, yield strength, intergranular corrosion grade and anodic oxidation effect of the finally prepared aluminum alloy product will all deteriorate significantly; when the zinc / magnesium ratio is lower than the lower limit, the tensile strength, yield strength and anodic oxidation effect of the finally prepared aluminum alloy product will all deteriorate significantly; when the contents of manganese and copper exceed the range, the tensile strength, yield strength, intergranular corrosion grade and anodic oxidation effect of the finally prepared aluminum alloy product will all deteriorate significantly; when the silicon content exceeds the range and the primary homogenization process is adopted, the tensile strength, yield strength, intergranular corrosion grade and anodic oxidation effect of the finally prepared aluminum alloy product will all deteriorate significantly; when the silicon content exceeds the range and the primary aging process is adopted, the tensile strength and yield strength of the finally prepared aluminum alloy product will deteriorate significantly; when the silicon content exceeds the range and the secondary aging temperature and duration are changed, the tensile strength and yield strength of the finally prepared aluminum alloy product will deteriorate significantly.

[0039] Thus, it can be seen that by optimizing the alloy raw material ratio and preparation process, the performance of the aluminum alloy product can be significantly improved in the present invention.

[0040] It should be noted that the technical features of the above embodiments can be combined arbitrarily. For the sake of brief description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0041] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these all belong to the protection scope of the present invention. The parts not described in the specific embodiments are all prior art or common general knowledge.

[0042] In addition, it should be noted that in the description of the present invention, the detailed description of the preferred implementation methods selected for the present invention and the included embodiments can more easily understand the content of the present invention. Unless otherwise defined, all the technologies and scientific terms used in the present invention have the same meaning as those commonly understood by those of ordinary skill in the art to which the present invention belongs. When there is a contradiction, the definition in this specification shall prevail.

[0043] In the present invention, the term "prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing" or any other variation thereof used in the present invention are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or device containing the listed elements does not necessarily only include those elements, but may include other elements not explicitly listed or elements inherent to such composition, step, method, article or device.

[0044] In the present invention, when an equivalent, a concentration, or other values or parameters are expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, it should be understood that all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value are specifically disclosed, regardless of whether the ranges are separately disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted as including ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described in the present invention, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0045] In addition, the indefinite articles "a" and "an" before an element or component of the present invention do not limit the quantity requirement (i.e., the number of occurrences) of the element or component. Therefore, "a" or "an" should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers to the singular form.

Claims

1. A method for preparing an ultra-high strength 7 series aluminum alloy for a mobile phone middle frame, characterized in that: The method comprises the following preparation steps: 1) Alloy raw material configuration: by mass percentage, the aluminum alloy raw material contains Mg 2.4%-3.0%, Zn 7.4%-8.0%, Zn / Mg ratio is 2.7-3.0, Cu 0.4%-0.7%, Mn 0.05%-0.15%, Fe less than 0.1%, other elements single content less than 0.03%, other elements total content less than 0.10%, and the balance is Al; 2) Homogenization treatment: after casting, the aluminum rod is subjected to double-stage homogenization heat treatment. The first-stage homogenization temperature is 300℃-350℃, the first-stage homogenization insulation time is 6h-12h, the second-stage homogenization temperature is 400℃-450℃, and the second-stage homogenization insulation time is 14h-20h; 3) Extrusion molding, extrusion processing after homogenization; 4) Aging treatment: the extruded profiles are subjected to a two-stage aging heat treatment, the first stage aging temperature is 90℃-120℃, the first stage aging insulation time is 4h-8h, the second stage aging temperature is 130℃-160℃, and the second stage aging insulation time is 15h-20h.

2. The method for preparing an ultra-high strength 7 series aluminum alloy for a mobile phone middle frame according to claim 1, characterized in that: The method comprises the following preparation steps: 1) Alloy raw material configuration: by mass percentage, the aluminum alloy raw material contains Mg 2.53%, Zn 7.42%, Zn / Mg ratio is 2.9, Cu 0.49%, Mn 0.12%, Fe 0.07%, Si 0.03%, Ti 0.01%, and the balance is Al; 2) Homogenization treatment: after casting, the aluminum bar is subjected to a two-stage homogenization heat treatment, with the first-stage homogenization temperature at 310°C and the first-stage homogenization holding time at 12h, and the second-stage homogenization temperature at 410°C and the second-stage homogenization holding time at 20h; 3) Extrusion molding, extrusion processing after homogenization; 4) Aging treatment: the extruded profiles are subjected to a two-stage aging heat treatment, with the first-stage aging temperature at 95°C and the first-stage aging insulation time at 8h, and the second-stage aging temperature at 135°C and the second-stage aging insulation time at 20h.

3. The method for preparing an ultra-high strength 7 series aluminum alloy for a mobile phone middle frame according to claim 1, characterized in that: The method comprises the following preparation steps: 1) Alloy raw material configuration: by mass percentage, the aluminum alloy raw material contains Mg 2.64%, Zn 7.55%, Zn / Mg ratio is 2.9, Cu 0.53%, Mn 0.12%, Fe 0.07%, Si 0.03%, Ti 0.01%, and the balance is Al; 2) Homogenization treatment: after casting, the aluminum bar is subjected to double-stage homogenization heat treatment, the first-stage homogenization temperature is 320°C, the first-stage homogenization holding time is 10h, the second-stage homogenization temperature is 420°C, and the second-stage homogenization holding time is 18h; 3) Extrusion molding, extrusion processing after homogenization; 4) Aging treatment: the extruded profiles are subjected to a two-stage aging heat treatment, with the first-stage aging temperature at 100°C and the first-stage aging insulation time at 7h, and the second-stage aging temperature at 140°C and the second-stage aging insulation time at 18h.

4. The method for preparing an ultra-high strength 7 series aluminum alloy for a mobile phone middle frame according to claim 1, characterized in that: The method comprises the following preparation steps: 1) Alloy raw material configuration: by mass percentage, the aluminum alloy raw material contains Mg 2.78%, Zn 7.69%, Zn / Mg ratio is 2.8, Cu 0.51%, Mn 0.09%, Fe 0.07%, Si 0.03%, Ti 0.01%, and the balance is Al; 2) Homogenization treatment: after casting, the aluminum bar is subjected to a two-stage homogenization heat treatment, with the first stage homogenization temperature at 330°C and the first stage homogenization holding time at 8h, and the second stage homogenization temperature at 430°C and the second stage homogenization holding time at 16h; 3) Extrusion molding, extrusion processing after homogenization; 4) Aging treatment: the extruded profiles are subjected to a two-stage aging heat treatment, with the first-stage aging temperature at 105°C and the first-stage aging insulation time at 6h, and the second-stage aging temperature at 145°C and the second-stage aging insulation time at 16h.

5. The method for preparing an ultra-high strength 7 series aluminum alloy for a mobile phone middle frame according to claim 1, characterized in that: The method comprises the following preparation steps: 1) Alloy raw material configuration: by mass percentage, the aluminum alloy raw material contains Mg 2.92%, Zn 7.91%, Zn / Mg ratio is 2.8, Cu 0.62%, Mn 0.11%, Fe 0.07%, Si 0.03%, Ti 0.01%, and the balance is Al; 2) Homogenization treatment: after casting, the aluminum bar is subjected to a two-stage homogenization heat treatment, with the first-stage homogenization temperature at 340°C and the first-stage homogenization holding time at 6h, and the second-stage homogenization temperature at 440°C and the second-stage homogenization holding time at 14h; 3) Extrusion molding, extrusion processing after homogenization; 4) Aging treatment: the extruded profiles are subjected to a two-stage aging heat treatment, with the first-stage aging temperature at 110°C and the first-stage aging insulation time at 5h, and the second-stage aging temperature at 150°C and the second-stage aging insulation time at 15h.

6. The method for preparing an ultra-high strength 7 series aluminum alloy for a mobile phone middle frame according to claim 1, characterized in that: In the extrusion molding step, the extrusion rod temperature is 420°C-480°C, and the extrusion outlet temperature is greater than 500°C.

7. The method for preparing an ultra-high strength 7 series aluminum alloy for a mobile phone middle frame according to claim 1, characterized in that: After extrusion, online quenching and cooling are carried out, and the cooling rate is greater than 200℃ / min.

8. An ultra-high strength 7 series aluminum alloy for a mobile phone middle frame, characterized in that: The alloy is prepared by using the method for preparing an ultra-high strength 7 series aluminum alloy for a mobile phone middle frame as described in any one of claims 1 to 7.

9. The ultra-high strength 7 series aluminum alloy for a mobile phone middle frame according to claim 8, characterized in that: The tensile strength of aluminum alloy is greater than 660MPa, the yield strength is greater than 620MPa, the elongation is greater than 8%, and the intergranular corrosion level is above level 3.