Thin-wall cavity 7-series aluminum alloy and processing method thereof

Abstract

The invention relates to the field of aluminum alloy material processing, in particular to a thin-wall cavity 7-series aluminum alloy and a processing method of the thin-wall cavity 7-series aluminum alloy. The content of Mg is 1.7 to 1.8 percent; the content of Cu is 0.5 to 0.6 percent; the content of Mn is 0.4 to 0.6 percent; the content of Zr ranges from 0.11% to 0.12%; the content of Ti is less than or equal to 0.03%; the content of Si is less than or equal to 0.05%; the content of Fe is smaller than or equal to 0.15%; the total content of other impurity elements is less than or equal to 0.05%; and the balance of Al. The thin-wall cavity 7-series aluminum alloy meets the requirements for the performance and the size, the thin-wall cavity 7-series aluminum alloy with the performance and the size meeting the requirements can be produced through the machining method, and the service life of a mold is prolonged.

Description

Technical Field

[0001] The invention relates to the field of aluminum alloy material processing, and in particular to a thin-wall cavity 7 series aluminum alloy and a processing method thereof. Background Art

[0002] Aluminum alloy is a metal material widely used in aviation, automobile, construction and electronics. Among them, 7 series aluminum alloy is widely used in industrial production and manufacturing due to its good mechanical properties and processing performance. The alloying degree of 7 series aluminum alloy is high, especially the Zn content is very high. The melting and casting process leads to macroscopic segregation in the material and the tendency of hot cracks in the ingot, which seriously affects the yield rate of the ingot and the corrosion, fatigue and other performance of the material. In addition, when producing profiles with a wall thickness of 2-5mm, due to the excessive extrusion resistance, the mold is subjected to the simultaneous action of cold and heat during the extrusion process, and the combined mold is very easy to break, and the service life is too short, resulting in poor mechanical properties of thin-walled cavity 7 series aluminum alloy, low production efficiency, high cost, and lack of market competitiveness.

[0003] Therefore, there is an urgent need for a thin-walled cavity 7 series aluminum alloy that can produce mechanical properties and dimensions that meet the requirements, as well as a processing method for producing the above-mentioned thin-walled cavity 7 series aluminum alloy and improving the service life of the mold. Summary of the invention

[0004] The present invention aims to solve the problems that thin-walled cavity 7 series aluminum alloy is difficult to meet the requirements of mechanical properties and size, and the processing method of thin-walled cavity 7 series aluminum alloy is not easy to produce thin-walled cavity 7 series aluminum alloy with performance and size meeting the requirements, and the mold service life is low.

[0005] In order to achieve the above-mentioned object, the first aspect of the present invention provides a thin-walled cavity 7 series aluminum alloy, wherein the components and their weight percentages in the aluminum alloy are:

[0006] Zn content is 7.0-7.2%;

[0007] Mg content is 1.7-1.8%;

[0008] Cu content is 0.5-0.6%;

[0009] Mn content is 0.4-0.6%;

[0010] Zr content is 0.11-0.12%;

[0011] Ti content ≤ 0.03%;

[0012] Si content ≤ 0.05%;

[0013] Fe content ≤ 0.15%;

[0014] The total content of other impurity elements is ≤0.05%;

[0015] The balance is Al.

[0016] A second aspect of the present invention provides a method for processing the above-mentioned thin-walled cavity 7 series aluminum alloy, wherein the processing method comprises:

[0017] Casting, homogenization, extrusion, quenching, stretching and straightening, aging treatment;

[0018] The extrusion conditions include: the heating temperature of the extrusion die is 480-490°C, the heating temperature of the extrusion barrel is 400-410°C, the extrusion speed is 1.4-2.0m / min, the length of the profile after extrusion is 990-1010mm, the temperature is 440-470°C, the working band length is 3.8mm-7mm, the processing accuracy is 0.01mm, the cast rod length is 190-210mm, and the extrusion ratio is 12-13.

[0019] A third aspect of the present invention provides a thin-walled cavity 7 series aluminum alloy produced by the above processing method.

[0020] The beneficial effects of the present invention are:

[0021] By controlling the alloy composition and specific extrusion process, the thin-walled cavity 7 series aluminum alloy provided by the present invention meets the requirements of mechanical properties and size, with a yield strength greater than 550MPa, a tensile strength greater than 600MPa, and an elongation of 12%. Furthermore, specific homogenization treatment and stretching straightening processes make the aluminum alloy performance even better.

[0022] The processing method provided by the present invention can also increase the service life of the mold, thereby improving the performance of the aluminum alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A cross-sectional view of a thin-walled cavity 7 series aluminum alloy profile provided by the present invention;

[0024] Figure 2 The structural diagram of the mold used in the present invention;

[0025] Figure 3 It is a schematic diagram of the inclined surface of the sizing belt and the outlet belt;

[0026] Figure 4 It is the working belt distribution and size diagram;

[0027] Figure 5 This is a high-magnification tissue observation image of Example 1;

[0028] Figure 6 This is a high-magnification structural observation diagram of Comparative Example 3. DETAILED DESCRIPTION

[0029] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0030] The thin-walled cavity 7 series aluminum alloy referred to in the present invention is an aluminum alloy profile with a wall thickness of 2-5 mm.

[0031] When the existing technology is used to produce thin-walled cavity 7 series aluminum alloys, due to the excessive extrusion resistance, the mold is subjected to simultaneous effects of cold and heat during the extrusion process, the combined mold is very easy to break, and the service life is too short, resulting in low production efficiency and high cost. The mechanical properties and dimensions of the produced thin-walled cavity 7 series aluminum alloys are difficult to meet the requirements.

[0032] In the present invention, the inventors found that by controlling the alloy composition and adjusting the processing technology, the performance and size of the thin-walled cavity 7 series aluminum alloy can meet the requirements, have excellent mechanical properties, and extend the service life of the mold.

[0033] To achieve this goal, the inventors tried to optimize the component composition and processing technology of thin-walled cavity 7 series aluminum alloy. The inventors found that the above purpose can be achieved through specific component composition and extrusion technology. Furthermore, specific homogenization treatment and stretching straightening technology make the performance of aluminum alloy even better.

[0034] The first aspect of the present invention provides a thin-walled cavity 7 series aluminum alloy, wherein the components and their weight percentages in the aluminum alloy are:

[0035] Zn content is 7.0-7.2%;

[0036] Mg content is 1.7-1.8%;

[0037] Cu content is 0.5-0.6%;

[0038] Mn content is 0.4-0.6%;

[0039] Zr content is 0.11-0.12%;

[0040] Ti content ≤ 0.03%;

[0041] Si content ≤ 0.05%;

[0042] Fe content ≤ 0.15%;

[0043] The total content of other impurity elements is ≤0.05%;

[0044] The balance is Al.

[0045] In the present invention, the inventors found that the alloy contains Mg, Mn and Zr elements at the same time, forming the main strengthening phase, MgZn2 and fine Al3Zr and Al6Mn particles. Under suitable process conditions combined with a reasonable heat treatment system, Mn and Zr increase the recrystallization temperature, and preferentially nucleate as nucleation points of the strengthening phase, refine the grains, and solve the problem of high Zn content, macro segregation in the material and increased tendency of hot cracks in the ingot caused by the melting and casting process.

[0046] A second aspect of the present invention provides a method for processing the above-mentioned thin-walled cavity 7 series aluminum alloy, wherein the processing method comprises:

[0047] Casting, homogenization, extrusion, quenching, stretching and straightening, aging treatment;

[0048] The extrusion conditions include: the heating temperature of the extrusion die is 480-490°C, the heating temperature of the extrusion barrel is 400-410°C, the extrusion speed is 1.4-2.0m / min, the length of the profile after extrusion is 990-1010mm, the temperature is 440-470°C, the working band length is 3.8mm-7mm, the processing accuracy is 0.01mm, the cast rod length is 190-210mm, and the extrusion ratio is 12-13.

[0049] In the present invention, under the non-lubricated extrusion process, unequal length working zones are designed according to the difference in wall thickness, and the particle flow velocity of the cross section is controlled to be as similar as possible; at the same time, the working zone is shortened to the greatest extent, the length of the cast rod is controlled, the breakthrough pressure is reduced, and the extrusion force consumed to overcome the friction force is reduced. At the same time, it is ensured that the profile will not be overburned due to friction and the residual material or tail shrinkage is minimized, thereby improving the mechanical properties of the material and improving production efficiency.

[0050] In the present invention, the size of the cast rod for extrusion is 190-210 mm, which is to control the heat generated by friction during the extrusion process. As the length of the cast rod increases, the friction heat generated increases. If the heat is too high, overburning is likely to occur. If the cast rod is too short, more metal residues are generated during extrusion or tail shrinkage occurs, and production efficiency decreases. In addition, the size of the cast rod is controlled, the liquid nitrogen cooling process of the mold is reduced, and the mold avoids the simultaneous effects of cold and heat, which can increase the service life of the mold, reduce the metal extrusion force at each position, ensure its formability and increase the service life of the mold.

[0051] In the present invention, a 2750T extruder is selected, and an extrusion barrel with a diameter of 160 mm is matched.

[0052] According to the present invention, the homogenization treatment conditions include: 470-480°C×20-30h, cooling to 20-30°C.

[0053] In the present invention, the above-mentioned specific homogenization process is adopted to precipitate MgZn2 phase and fine Al3Zr particles, thereby solving the problem of high Zn content, macroscopic segregation in the material and increased tendency of hot cracks in the ingot caused by the melting and casting process.

[0054] According to the present invention, the stretching and straightening conditions include: the extruded profile completes stretching and straightening within 1 hour.

[0055] In the present invention, the alloy undergoes natural aging, the strength increases, and the stretching difficulty increases, so the stretching straightening is performed within 1 hour. After extrusion quenching, the 7 series aluminum alloy will produce a parking effect, and the aging is performed immediately. The strength of the profile is the highest. The strength fluctuates after parking for 1-2 days. The strength is stable after parking for more than 3 days, but it is lower than the strength of the profile that is immediately aged.

[0056] According to the present invention, the melting and casting conditions include: electromagnetic stirring frequency of 15-20Hz, crystallizer height of 123-127mm, melting temperature of 740-750℃, electromagnetic stirring after melting for 20min, refining temperature of 735-745℃, refining for 30-40min, and casting temperature of 700-710℃.

[0057] In the present invention, a semi-continuous casting technology combining hot top casting and low-frequency electromagnetic casting is adopted. The low-frequency electromagnetic casting ensures that the axial temperature distribution of the melt in the crystallizer is uniform, and the melt temperature is lower than the liquidus temperature, so that the nucleation matrix such as oxides and intermetallic compounds in the melt is activated and the survival rate of the formed crystal nuclei is increased, and the grains are difficult to grow dendrites; at the same time, the height of the crystallizer is reduced to a specific range, so that the cooling intensity of the ingot is increased, the growth of the crystal nuclei is further prevented, and finally a uniform and fine equiaxed crystal structure is obtained.

[0058] According to the present invention, the aging treatment conditions include: aging within 1 hour after stretching and straightening, 120-130°C×12h.

[0059] In the present invention, specific alloy components need to be subjected to specific low-temperature and long-term aging treatment, which has the advantage of clustering Mg and Zn atoms to form GP zones and fully transforming into Mg2Zn phases; and the formed Al3Zr and Al6Mn phases further promote the precipitation of Mg2Zn phases.

[0060] According to the present invention, the extrusion conditions also include: the extrusion die is a conical combination die, provided with 8 diversion holes and a guide pit, the diversion bridge slope α is 24-26°, and a slope of 9.95-10.05° is provided between the sizing belt and the outlet belt.

[0061] In the present invention, the purpose of die optimization is to control the metal flow performance, reduce the extrusion dead corner area, make the flow rate of each extrusion hole profile uniform, reduce the extrusion pressure, increase the shear resistance of the sizing belt, ensure the formability of the profile and reduce the force on the die, and further improve the service life of the die.

[0062] According to the present invention, the quenching conditions include: the quenching temperature is 460-470° C., and the quenching medium is PAG quenching liquid.

[0063] In the present invention, the above-mentioned quenching conditions can prevent the 7 series aluminum alloy from being deformed during quenching.

[0064] A third aspect of the present invention provides a thin-walled cavity 7 series aluminum alloy produced by the above processing method.

[0065] Test Method

[0066] The test method for aluminum alloy profile composition is in accordance with GB / T7999-2015, and the test equipment is direct reading spectrometer ARL-3460.

[0067] The mechanical properties test method is in accordance with GB / T228.1-2021, and the testing equipment is the electronic universal testing machine AG-X100kNH.

[0068] The high-magnification microstructure observation of cast rods is in accordance with GB / T3246.1-2012, and the testing equipment is material microscope GX51.

[0069] The technical scheme of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments implemented by ordinary technicians in this field without making creative improvements belong to the protection scope of the present invention.

[0070] Example 1

[0071] A. Melting and casting: Prepare 7 series aluminum alloy raw materials according to the following weight ratio: Zn: 7.15%, Mg: 1.71%, Cu: 0.54%, Mn: 0.44%, Zr: 0.12%, Ti: ≤0.03%, Si: ≤0.05%, Fe: ≤0.15%, the total content of other impurity elements ≤0.05%, and the balance Al. Add the prepared aluminum alloy raw materials into a melting furnace, the melting temperature is 750°C, and electromagnetic stirring is turned on 20 minutes after the start of melting. The refining temperature is 745°C, and the refining is 20 minutes. After uniform mixing, it is melted into liquid aluminum alloy, and the liquid aluminum alloy is melted and cast into aluminum alloy casting rods. The casting temperature is 710°C. Hot top casting and low-frequency electromagnetic casting technology are used during casting. The frequency is 20Hz, and the height of the crystallizer is optimized to be 125mm.

[0072] B. Homogenization: heating the aluminum alloy cast rod obtained by molten casting to 480° C., keeping the temperature for 24 hours, and cooling to 20° C. to obtain a homogenized aluminum alloy cast rod, wherein the length of the homogenized aluminum alloy cast rod is 200 mm;

[0073] C. Extrusion: Use 2750T extruder with φ160mm extrusion barrel; send the homogenized aluminum alloy cast rod into the extrusion barrel of the extruder for extrusion, select a conical combination die with 8 diversion holes and diversion pits, and a diversion bridge slope α of 25°. The heating temperature of the extrusion die is 490℃, the heating temperature of the extrusion barrel is 400℃, the extrusion speed is 1.7m / min, the extrusion ratio is 12.5, the length of the aluminum alloy profile after extrusion is 1000mm, the working belt length is 3.8mm-7mm, and a 10° slope is set between the sizing belt and the outlet belt. ;

[0074] D. Offline quenching: The stretched aluminum alloy profile is placed in a quenching device for quenching, and PAG quenching liquid is used as the quenching medium. The quenching temperature is 465°C and the quenching time is 120 minutes.

[0075] E. Stretching and straightening: clamp the extruded aluminum alloy profile into the stretching device and stretch it within 1 hour;

[0076] F. Aging: The stretched aluminum alloy profile is aged within 1 hour, the aging temperature is 120℃, and the aging time is 12h

[0077] A thin-walled cavity 7 series aluminum alloy A1 was produced.

[0078] Example 2

[0079] A thin-walled cavity 7 series aluminum alloy is prepared according to the processing method of Example 1, except that the aluminum alloy composition is Zn: 7%, Mg: 1.7%, Cu: 0.5%, Mn: 0.4%, and Zr: 0.11%.

[0080] A thin-walled cavity 7 series aluminum alloy A2 was produced.

[0081] Example 3

[0082] A thin-walled cavity 7 series aluminum alloy is prepared according to the processing method of Example 1, except that the aluminum alloy components are Zn: 7.2%, Mg: 1.8%, Cu: 0.6%, Mn: 0.6%, and Zr: 0.12%.

[0083] A thin-walled cavity 7 series aluminum alloy A3 was produced.

[0084] Example 4

[0085] A thin-walled cavity 7 series aluminum alloy was prepared according to the processing method of Example 1, except that the length of the cast rod in the extrusion process was 190 mm.

[0086] A thin-walled cavity 7 series aluminum alloy A4 was produced.

[0087] Example 5

[0088] A thin-walled cavity 7 series aluminum alloy was prepared according to the processing method of Example 1, except that the length of the cast rod in the extrusion process was 210 mm.

[0089] A thin-walled cavity 7 series aluminum alloy A5 was produced.

[0090] Example 6

[0091] A thin-walled cavity 7 series aluminum alloy was prepared according to the processing method of Example 1, except that the heating temperature of the extrusion die was 480°C, the heating temperature of the extrusion barrel was 410°C, the extrusion speed was 1.4m / min, the extrusion ratio was controlled at 12, and the length of the aluminum alloy profile after extrusion was 1002mm.

[0092] A thin-walled cavity 7 series aluminum alloy A6 was produced.

[0093] Comparative Example 1

[0094] A thin-walled cavity 7 series aluminum alloy is prepared according to the processing method of Example 1, except that the extrusion die is a conventional die.

[0095] A thin-walled cavity 7 series aluminum alloy DA1 was produced.

[0096] Comparative Example 2

[0097] A thin-walled cavity 7 series aluminum alloy was prepared according to the processing method of Example 1, except that the homogenization treatment was performed at 490° C.×30 h.

[0098] A thin-walled cavity 7 series aluminum alloy DA2 was produced.

[0099] Comparative Example 3

[0100] A thin-walled cavity 7 series aluminum alloy is prepared according to the processing method of Example 1, except that conventional hot top casting and a conventional crystallizer are used, and the crystallizer height is 150 mm.

[0101] A thin-walled cavity 7 series aluminum alloy DA3 was produced.

[0102] Comparative Example 4

[0103] A thin-walled cavity 7 series aluminum alloy was prepared according to the processing method of Example 1, except that the heating temperature of the aluminum extrusion die was 470°C, the heating temperature of the extrusion barrel was 400°C, the extrusion speed was 13.5 m / min, the length of the profile after extrusion was 1010 mm, and the temperature was 460°C.

[0104] A thin-walled cavity 7 series aluminum alloy DA4 was produced.

[0105] Performance tests were performed on A1-A6 and DA1-DA4, as shown in Table 1.

[0106] Table 1

[0107]

[0108] By comparing the examples with the comparative examples, it can be seen that the thin-walled cavity 7 series aluminum alloy provided by the present invention has excellent mechanical properties.

[0109] Figure 5 This is a high-magnification microstructure observation diagram of Example 1, which shows the edge, R / 2 and core from top to bottom. R / 2 is half of the radius of the cast rod. It can be seen from the figure that the grain size from the core to the edge is relatively uniform and the grains are fine.

[0110] Figure 6 This is a high-magnification microstructure observation diagram of comparative example 3, which shows the edge, R / 2 and core from top to bottom. R / 2 is half of the radius of the cast rod. It can be seen from the figure that the grain size from the core to the edge of the cast rod is also relatively uniform, but the average grain is relatively coarse, which has a greater impact on subsequent processing.

[0111] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A thin-walled cavity 7 series aluminum alloy, characterized in that: The components and their weight percentages in the aluminum alloy are: Zn content is 7.0-7.2%; Mg content is 1.7-1.8%; Cu content is 0.5-0.6%; Mn content is 0.4-0.6%; Zr content is 0.11-0.12%; Ti content ≤ 0.03%; Si content ≤ 0.05%; Fe content ≤ 0.15%; The total content of other impurity elements is ≤0.05%; The balance is Al.

2. A method for processing the thin-walled cavity 7 series aluminum alloy according to claim 1, characterized in that: The processing method comprises: Casting, homogenization, extrusion, quenching, stretching and straightening, aging treatment; The extrusion conditions include: the heating temperature of the extrusion die is 480-490°C, the heating temperature of the extrusion barrel is 400-410°C, the extrusion speed is 1.4-2.0m / min, the length of the profile after extrusion is 990-1010mm, the temperature is 440-470°C, the working band length is 3.8mm-7mm, the processing accuracy is 0.01mm, the cast rod length is 190-210mm, and the extrusion ratio is 12-13.

3. The processing method according to claim 2, characterized in that: The homogenization treatment conditions include: 470-480°C×20-30h, cooling to 20-30°C.

4. The processing method according to claim 2, characterized in that: The stretching and straightening conditions include: the extruded profile is stretched and straightened within 1 hour.

5. The processing method according to claim 2, characterized in that: The melting and casting conditions include: electromagnetic stirring frequency of 15-20 Hz, crystallizer height of 123-127 mm, melting temperature of 740-750° C., electromagnetic stirring after melting for 20 minutes, refining temperature of 735-745° C., refining for 30-40 minutes, and casting temperature of 700-710° C.

6. The processing method according to claim 2, characterized in that: The aging treatment conditions include: aging within 1 hour after stretching and straightening, 120-130°C×12 hours.

7. The processing method according to claim 2, characterized in that: The extrusion conditions also include: the extrusion die is a conical combined die, provided with 8 diversion holes and a diversion pit, the diversion bridge slope α is 24-26°, and a slope of 9.95-10.05° is provided between the sizing belt and the outlet belt.

8. The processing method according to claim 2, characterized in that: The quenching conditions include: the quenching temperature is 460-470°C, and the quenching medium is PAG quenching liquid.

9. A thin-walled cavity 7 series aluminum alloy produced by the processing method described in any one of claims 2 to 8.

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