A kind of extrusion production process of 7 series aluminum alloy special-shaped profiles

Abstract

This invention discloses an extrusion production process for 7-series aluminum alloy profiles, comprising the following steps: S1: heating an aluminum rod, extrusion cylinder, and extrusion die, placing the aluminum rod in the extrusion cylinder; S2: extruding the aluminum rod at a constant speed, heating the profile exiting the extrusion die to the solution temperature, and performing online solution treatment; S3: online quenching of the solution-treated profile obtained in S2; S4: double-stage aging heat treatment of the quenched profile obtained in S3; S5: shaping to obtain the finished profile. In this extrusion production process for 7-series aluminum alloy profiles, the profile exiting the extrusion die is heated to the solution temperature. Based on the residual heat of the extruded profile, the area with the smallest wall thickness has a large heating area and a rapid temperature rise; the area with a larger wall thickness heats up more slowly. Online solution treatment improves the plasticity and elongation of the aluminum alloy, eliminates internal stress, reduces the probability of crack formation, and thus improves the yield of the extruded profiles.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy production, and in particular to an extrusion production process for 7 series aluminum alloy special-shaped profiles. Background Art

[0002] 7 series aluminum alloy is the most widely used component material in the aerospace field, such as 7A09 aluminum alloy for rockets and 7075 aluminum alloy for aircraft wings. Taking 7075 aluminum alloy profile production as an example, 7075 aluminum alloy is a cold-treated forging alloy, mainly composed of aluminum, zinc, magnesium, copper and other elements, of which the zinc content is as high as about 6%. The high zinc content makes 7075 aluminum alloy have excellent strength and hardness; but the toughness and ductility are poor, the processing difficulty is relatively large, and the response to machining is poor.

[0003] The target special-shaped profiles produced by extrusion of 7075 aluminum alloy have different wall thicknesses, with the minimum wall thickness being about 1mm and the maximum wall thickness being about 6mm. The minimum wall thickness is connected to the maximum wall thickness to form an angle, and the fold width at the minimum wall thickness is 4 to 5 times the fold width at the maximum wall thickness. In the actual production of the target special-shaped profiles, intermittent cracks are prone to occur at the angles. The main reasons for the cracks are: the difference between the metal flow rate at the center of the billet and the metal flow rate at the outer layer during the extrusion process; as the extrusion continues, the profile intermittently experiences a periodic phenomenon along its own extension direction, in which the outer metal is subjected to an additional tensile stress that gradually increases, cracks occur due to the additional tensile stress reaching the actual fracture strength limit of the metal, and the cracks cause the additional tensile stress to decrease.

[0004] Increasing the extrusion speed of the profile can easily cause cracking of the edges, especially at the edges of thick walls, which leads to ineffective extrusion. Based on the same aluminum alloy bar, the slower the extrusion speed, the longer the aluminum alloy bar stays in the extrusion die, and the greater the temperature difference of the aluminum alloy bar when being extruded, which means that the high temperature during extrusion cannot be used for solid solution, and offline solid solution and quenching must be adaptively selected. However, offline quenching can easily cause deformation of the thinner wall of the aluminum profile, and consumes more energy and labor. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects in the prior art and provide an extrusion production process for 7 series aluminum alloy special-shaped profiles, which reduces the probability of cracks and improves the yield of profile extrusion production by real-time heating of the profile discharged from the extrusion die for online solid solution.

[0006] In order to achieve the above technical effects, the technical solution of the present invention is: an extrusion production process of 7 series aluminum alloy special-shaped profiles, comprising the following steps:

[0007] S1: heating the aluminum rod, the extrusion cylinder and the extrusion die, and placing the aluminum rod in the extrusion cylinder;

[0008] S2: Extruding aluminum bars at a constant speed, heating the profile discharged from the extrusion die outlet to the solution temperature, and performing online solution;

[0009] S3: profiles obtained by online quenching S2 through solid solution treatment;

[0010] S4: profile quenched by double-stage aging heat treatment S3;

[0011] S5: The finished product of special-shaped profile is obtained by shaping.

[0012] Furthermore, the heating temperature of the aluminum rod and the extrusion barrel is lower than the solid solution temperature of the aluminum alloy.

[0013] The preferred technical solution is that, by mass percentage, the element composition of the aluminum rod includes: Fe: 0.14% to 0.25%, Cu: 1.2% to 2.0%, Mn: 0.07% to 0.3%, Mg: 2.3% to 2.9%, Zn: 5.1% to 6.1%; a single impurity is ≤0.05%, the total impurities are ≤0.15%, and the balance is Al.

[0014] Further, by mass percentage, the elemental composition of the aluminum rod includes: Fe: 0.14% to 0.23%, Cu: 1.3% to 1.9%, Mn: 0.08% to 0.24%, Mg: 2.3% to 2.9%, Zn: 5.1% to 6.1%; individual impurities ≤ 0.05%, total impurities ≤ 0.15%, the balance is Al. Further, further, by mass percentage, the elemental composition of the aluminum rod includes: Fe: 0.15% to 0.21%, Cu: 1.3% to 1.9%, Mn: 0.09% to 0.17%, Mg: 2.3% to 2.9%, Zn: 5.1% to 6.1%; individual impurities ≤ 0.05%, total impurities ≤ 0.15%, the balance is Al.

[0015] The preferred technical solution is that the heating temperature of the aluminum rod in S1 is 345-360°C; the heating temperature of the extrusion barrel is 410-430°C, and the temperature of the extrusion die is 460-480°C.

[0016] The heating temperature of the aluminum rod in S1 can be selected as 345℃, 347℃, 349℃, 351℃, 353℃, 355℃, 357℃, 360℃ or an interval value with two points as endpoints; the heating temperature of the extrusion barrel is 410℃, 415℃, 420℃, 425℃, 430℃ or an interval value with two points as endpoints; the extrusion die temperature is 460-480℃, specifically 460℃, 462℃, 464℃, 466℃, 468℃, 470℃, 472℃, 474℃, 475℃, 478℃, 480℃ or an interval value with two points as endpoints.

[0017] Furthermore, the heating temperature of the aluminum rod is 345-355°C, the heating temperature of the extrusion barrel is 415-425°C, and the temperature of the extrusion die is 465-480°C.

[0018] The preferred technical solution is that the 7 series aluminum alloy is 7075 aluminum alloy, and the solid solution temperature is 460-480°C, which can be specifically selected as 460°C, 462°C, 464°C, 466°C, 468°C, 470°C, 472°C, 474°C, 475°C, 478°C, 480°C or an interval value with two points as endpoints; further, the solid solution temperature is 470-480°C.

[0019] The preferred technical solution is that the extrusion speed of the S2 profile is 0.7-1.8 m / min, specifically 0.7 m / min, 1 m / min, 1.2 m / min, 1.4 m / min, 1.6 m / min, 1.8 m / min or an interval value with two point values ​​as endpoints, and the further extrusion speed is 0.8-1.5 m / min, and further 0.85-1.25 m / min.

[0020] The preferred technical solution is that the online quenching is water mist cooling, the average cooling rate of the online quenching is 14-20°C / s, and the profile is quenched online to below 50°C. The average cooling rate can be specifically selected as 14°C / s, 16°C / s, 18°C / s, 20°C / s, or an interval value with two points as endpoints.

[0021] The preferred technical solution is that the profile channel length of the heating device at the outlet of the extrusion die is 0.7-1.5m, and the channel temperature is 485-500°C. The profile channel length can be specifically selected as 0.7m, 0.9m, 1.1m, 1.3m, 1.5m point value or an interval value with two point values ​​as endpoints, and the channel temperature is 485°C, 490°C, 495°C, 500°C point value or an interval value with two point values ​​as endpoints.

[0022] The preferred technical solution is that the two-stage aging heat treatment includes:

[0023] The temperature of the primary aging heat treatment is 110-125°C, and the insulation time is 4-8 hours;

[0024] The temperature of the secondary aging heat treatment is 142-157°C, and the insulation time is 8-15h.

[0025] The temperature of the primary aging heat treatment can be specifically selected as 110°C, 115°C, 120°C, 125°C, or an interval value with two points as endpoints, and the insulation time can be specifically selected as 4 h, 5 h, 6 h, 7 h, 8h, or an interval value with two points as endpoints. It is further preferred that the temperature of the primary aging heat treatment is 115-125°C;

[0026] The temperature of the secondary aging heat treatment can be specifically selected as 142°C, 145°C, 150°C, 153°C, 155°C, 157°C or an interval value with two points as endpoints, and the insulation time is 8h, 10h, 12h, 14h, 15h or an interval value with two points as endpoints; more preferably, the temperature of the secondary aging heat treatment is 145-155°C.

[0027] The preferred technical solution is that the extrusion ratio of the constant speed extrusion in S2 is 30-40, and more preferably 32-37.

[0028] A preferred technical solution is that the aluminum alloy special-shaped profile has a first wall and a second wall connected at corners, the thickness of the first wall is at least 2.5 times the thickness of the second wall, and the thickness of the second wall is 0.8-2 mm.

[0029] The thickness of the first wall is 2.5 times, 3.5 times, 4.4 times or even more than the thickness of the second wall; the thickness of the second wall can be 0.8 mm, 1 mm, 1.3 mm, 1.5 mm, 1.7 mm, 2 mm. Furthermore, the thickness of the second wall is 0.8-1.4 mm.

[0030] The advantages and beneficial effects of the present invention are:

[0031] In the extrusion production process of the 7 series aluminum alloy special-shaped profile, the profile discharged from the extrusion die outlet is heated to the solid solution temperature; based on the residual temperature of the extruded profile itself, the heating area at the minimum wall thickness is large and the temperature rises quickly; the temperature rises slowly at the thicker wall thickness, and the online solid solution improves the plasticity and elongation of the aluminum alloy, eliminates internal stress, reduces the probability of cracks, and thus improves the yield rate of special-shaped profile extrusion production;

[0032] Heating the profile at the exit of the extrusion die replaces the high-temperature solid solution method during extrusion, which relieves the strict restrictions on the extrusion speed caused by high-temperature solid solution; the combination of die exit heating and online quenching is conducive to reducing the overall energy consumption and labor of the heat treatment process;

[0033] Furthermore, by optimizing the elemental composition of the aluminum rod and the process parameters of the extrusion, solution, aging and other steps, the strength parameters such as tensile strength and elongation strength of the special-shaped profiles are improved, while the toughness parameters such as elongation after fracture are optimized;

[0034] Solution dissolution is carried out immediately after extrusion, and the extrusion production process makes full use of the waste heat of profile extrusion, which is beneficial to reducing the energy consumption of profile production and eliminating the workload of profile transportation for offline solution dissolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a cross-sectional view of a special-shaped aluminum profile;

[0036] Figure 2 is the stress-strain curve of the profile sample of comparative example 1;

[0037] Figure 3 It is the stress-strain curve of the profile sample of Example 2. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0039] Aluminum rods, extrusion barrels and extrusion dies

[0040] The extrusion cylinder is used to place the aluminum rod, the extrusion die has a die hole with the cross section of the aluminum alloy profile, and the extrusion cylinder includes an extrusion rod, which pushes the aluminum rod toward the die, and the profile is extruded through the die hole.

[0041] It is understood that the 7 series aluminum alloy aluminum rod with a predetermined element content is cast and homogenized to adapt to the extrusion production of profiles.

[0042] The extrusion speed determines the profile discharge speed at the outlet of the heated extrusion die, and the profile discharge speed further determines the maximum temperature of the profile in the profile channel of the heating equipment. The maximum temperature must meet the solution temperature range. Example

[0043] The aluminum profiles produced in the embodiment are as follows Figure 1 As shown, the aluminum alloy profile has a first wall and a second wall connected at an angle, the thickness L1 of the first wall is 1.02±0.15 mm, the thickness L2 of the second wall is 6±0.2 mm, and the cross-sectional area of ​​the profile is 0.0785-0.0802 cm 2 (The cross-sectional area of ​​the sample is subject to error within a predetermined range).

[0044] 1. Solution treatment method and cracking of extruded profiles

[0045] Example 1

[0046] Example 1 The extrusion production process of 7 series aluminum alloy special-shaped profiles comprises the following steps:

[0047] 7 series aluminum alloy is 7075 aluminum alloy.

[0048] S0: The element composition of the aluminum rod includes: Fe: 0.134%, Cu: 1.64%, Mn: 0.025%, Mg: 2.58%, Zn: 5.81%; individual impurities ≤ 0.05%, total impurities ≤ 0.15%, the balance is Al;

[0049] S1: Heat the aluminum rod, extrusion barrel and extrusion die, place the aluminum rod in the extrusion barrel, the heating temperature of the aluminum rod is 350±3℃; the heating temperature of the extrusion barrel is 420±3℃, and the temperature of the extrusion die is 470±3℃.

[0050] S2: Extruding aluminum bars at a constant extrusion speed of 1m / min, with an extrusion ratio of 35.2; a profile channel is set at the outlet of the online heating extrusion die, with a profile channel length of 0.8m and a set temperature of 500℃. The profile temperature in the profile channel is heated to the solution temperature (470-480℃) at the highest, and the online solution is tested. The temperature of the profile out of the channel is 472±2℃;

[0051] S3: The profile obtained by the solution treatment in S2 is quenched online by water mist. The average cooling rate of the online quenching is 17°C / s, and the profile is quenched online to below 50°C.

[0052] S4: Aging treatment of the quenched profile obtained in S3; the temperature of the first aging heat treatment is 120°C, and the insulation time is 6 hours; the temperature of the second aging heat treatment is 150°C, and the insulation time is 10 hours.

[0053] S5: The finished product of special-shaped profile is obtained by shaping.

[0054] Comparative Example 1

[0055] The element composition of the aluminum rods in Comparative Example 1 is the same as that in Example 1, except that S2 and S3 are:

[0056] S2: extruding an aluminum rod at a constant extrusion speed of 1 m / min, the extrusion die is the same as that in Example 1, and the extrusion ratio is the same; the aluminum alloy profile exiting the extrusion die is air-cooled to room temperature;

[0057] S3: The aluminum alloy profile obtained in S2 is placed in a heating device and heated to 472±2°C. The solid solution treated profile obtained in S2 is quenched online by water mist cooling. The average cooling rate of the online quenching is 18°C / s. The profile is quenched online to below 50°C.

[0058] Performance test of aluminum alloy profile samples obtained in the embodiments and comparative examples:

[0059] 1. Use a workbench (test temperature 20°C) to obtain the stress-strain curve of the aluminum alloy profile specimen; based on the stress-strain curve, obtain the profile's maximum force (Fm), tensile strength (Rm), tensile modulus (E), specified plastic extension strength (Rp0.2) and elongation after fracture (A);

[0060] 2. Evaluation of appearance cracks on aluminum profiles.

[0061] The stress-strain curve of comparative example 1 is as follows: Figure 2 shown.

[0062] 2. Element composition of aluminum bars and mechanical properties of profiles

[0063] Example 2-3

[0064] The element composition of the aluminum rod of Example 2 includes: Fe: 0.179%, Cu: 1.69%, Mn: 0.128%, Mg: 2.65%, Zn: 5.9%; individual impurities ≤ 0.05%, total impurities ≤ 0.15%, and the balance is Al; the Mn element content of the aluminum alloy of Example 2 is increased, but within the Mn element content range of 7075 aluminum alloy (0.1% to 0.3%), the solid solution channel temperature setting and the profile channel length are the same as those in Example 1.

[0065] The element composition of the aluminum rod of Example 3 includes: Fe: 0.152%, Cu: 1.67%, Mn: 0.084%, Mg: 2.60%, Zn: 5.85%; individual impurities ≤ 0.05%, total impurities ≤ 0.15%, and the balance is Al; the Mn element content of the aluminum alloy is higher than that of Example 2, but within the Mn element content range of 7075 aluminum alloy (0.1% to 0.3%), the solution temperature setting and the profile channel length are the same as those of Example 1.

[0066] The stress-strain curve of Example 2 is as follows: Figure 3 shown.

[0067] The maximum force (Fm), tensile strength (Rm), tensile modulus (E), specified plastic extension strength (Rp0.2) and elongation after fracture (A) of Examples 1-3 and Comparative Example 1 are shown in the following table:

[0068] Sample Fm / kN Rm / MPa E / MPa Rp0.2 / MPa A / % Appearance evaluation Example 1 46.26 585.30 73917.31 528.36 9.97 No obvious cracks on the surface Comparative Example 1 46.59 581.46 73868.50 523.97 9.64 There are many cracks on the surface Example 2 47.35 602.69 74980.28 534.55 11.22 No obvious cracks on the surface Example 3 46.86 595.35 73927.13 531.27 10.56 No obvious cracks on the surface

[0069] Example 1 and Comparative Example 1 show that, compared with offline solutionizing, online solutionizing is beneficial to eliminating profile cracks and improving tensile strength, tensile modulus, plastic extension strength and elongation after fracture; Figure 1 As shown, the cracks of Comparative Example 1 mostly appear at locations A and B.

[0070] Examples 1, 2 and 3 show that based on the production process of continuous extrusion and heating solution treatment, the Mn content in the 7075 aluminum alloy raw material has a significant effect on the mechanical properties of the profile, among which the Mn content in Example 2 is the best.

[0071] In addition, compared with Comparative Example 1, the production process of Example 2 reduces labor consumption by about 60% and reduces electricity consumption per ton by about 400 kilowatts.

[0072] 3. Extrusion speed and mechanical properties of profiles

[0073] Embodiment 4-5

[0074] The extrusion production process of the 7 series aluminum alloy special-shaped profile of Example 4 is based on the aluminum bar of Example 2, except that:

[0075] S2: Aluminum bars are extruded at a constant extrusion speed of 0.8 m / min, with an extrusion ratio of 35.2. A profile channel is set at the outlet of the online heating extrusion die. The profile channel length is 0.8 m, and the set temperature is 500 °C. The profile temperature in the profile channel is heated to the solution temperature (470-480 °C) at the highest, and the solution is performed online.

[0076] The extrusion production process of the 7 series aluminum alloy special-shaped profile in Example 5 is based on the aluminum bar in Example 2, except that:

[0077] S2: Aluminum bars are extruded at a constant extrusion speed of 1.3 m / min, with an extrusion ratio of 35.2. A profile channel is set at the outlet of the online heating extrusion die. The profile channel length is 0.8 m, and the set temperature is 500 °C. The profile temperature in the profile channel is heated to the solution temperature (460-470 °C) at the highest, and the solution is performed online.

[0078] The mechanical properties of the profiles of Examples 4-5 are shown in the following table:

[0079] Sample Fm / kN Rm / MPa E / MPa Rp0.2 / MPa A / % Appearance evaluation Example 4 47.01 586.53 74376.39 532.84 11.03 No obvious cracks on the surface Example 5 46.82 588.60 74125.61 530.77 10.43 No obvious cracks on the surface

[0080] Compared with Example 2, the extrusion speed of Example 4 is lower, and the temperature of the profile discharged into the profile channel is lower; the conveying speed in the profile channel is low, and the profile temperature is heated to a higher solid solution temperature at the same channel temperature; the solid solution temperature of the profile in Example 5 is lower than that in Example 4;

[0081] Compared with Example 5, the extrusion speed of Example 4 and the higher temperature (470-480° C.) within the solid solution temperature range of the sample profile are more conducive to improving the tensile strength, tensile modulus and other mechanical parameters of the profile.

[0082] 4. Heat treatment process parameters and mechanical properties of profiles

[0083] Embodiment 6-8 is based on embodiment 2, and the difference is:

[0084] S2 of Example 6: The profile channel length is 1.8 m, the temperature is set to 490° C., the profiles in the profile channel are heated to 470-480° C., and solid solution is performed online;

[0085] S2 of Example 7: The profile channel length is 0.8 m, the set temperature is 506° C., the profile temperature in the profile channel is heated to a maximum of 470-480° C., and solid solution is performed online;

[0086] S3 of Example 8: forced air cooling and online quenching of the solution treated profile obtained in S2, the average cooling rate of the online quenching is 10°C / s, and the profile is online quenched to below 50°C;

[0087] Sample Fm / kN Rm / MPa E / MPa Rp0.2 / MPa A / % Appearance evaluation Example 6 47.12 591.07 74205.86 529.06 10.22 No obvious cracks on the surface Example 7 47.03 596 73608.94 525.87 10.31 No obvious cracks on the surface Example 8 46.83 585.08 73472.03 530.26 10.76 Fewer cracks on the surface

[0088] The length of the profile channel, the temperature and the extrusion speed of the profile jointly determine the solid solution heating rate of the profile. Based on the same profile extrusion speed, the heating rate of Example 6 is less than that of Example 7. The data in the above table show that the heating rate of the profile sample is too fast, which is not conducive to improving the mechanical properties of the profile.

[0089] The cracks of Example 8 also appeared at A and B. Example 8 and Example 2 show that the cross-sectional shape of the profile must match the quenching cooling method, and the example sample (the ratio of L2 to L1 is 5.9, and L1 is 1.02±0.15 mm) is more suitable for water mist cooling.

[0090] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An extrusion production process for 7 series aluminum alloy special-shaped profiles, characterized in that: The following steps are involved: S1: heating the aluminum rod, the extrusion cylinder and the extrusion die, and placing the aluminum rod in the extrusion cylinder; S2: Extruding aluminum bars at a constant speed, heating the profile discharged from the extrusion die outlet to the solution temperature, and performing online solution; S3: profiles obtained by online quenching S2 through solid solution treatment; S4: profile quenched by double-stage aging heat treatment S3; S5: shaping to obtain the finished product of special-shaped profile; The aluminum alloy profile has a first wall and a second wall connected at corners, the thickness of the first wall is at least 2.5 times the thickness of the second wall, and the thickness of the second wall is 0.8-2 mm; The element composition of the aluminum rod includes, by mass percentage, Fe: 0.15% to 0.21%, Cu: 1.3% to 1.9%, Mn: 0.09% to 0.17%, Mg: 2.3% to 2.9%, Zn: 5.1% to 6.1%; individual impurities ≤ 0.05%, total impurities ≤ 0.15%, and the balance is Al; The extrusion speed of S2 medium profile is 0.85~1.25m / min; The online quenching is water mist cooling, the average cooling rate of the online quenching is 14-20°C / s, and the profile is quenched online to below 50°C; The profile channel length of the heating device at the outlet of the extrusion die is 0.7-1.5m, and the channel temperature is 485-500°C.

2. The extrusion production process of 7 series aluminum alloy special-shaped profiles according to claim 1 is characterized in that: In S1, the heating temperature of the aluminum rod is 345-355°C, the heating temperature of the extrusion barrel is 415-425°C, and the temperature of the extrusion die is 465-480°C.

3. The extrusion production process of 7 series aluminum alloy special-shaped profiles according to claim 1 is characterized in that: The two-stage aging heat treatment comprises: The temperature of the primary aging heat treatment is 110-125°C, and the insulation time is 4-8 hours; The temperature of the secondary aging heat treatment is 142-157°C, and the insulation time is 8-15h.

4. The extrusion production process of 7 series aluminum alloy special-shaped profiles according to claim 1 is characterized in that: The extrusion ratio of constant speed extrusion in S2 is 30-40.

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