A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy

Abstract

A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy, which sequentially performs solid solution treatment, high temperature insulation, first water cooling to room temperature, and artificial aging on the 7xxx aluminum alloy, wherein the temperature T of the high temperature insulation is T1<T<T2, T2 is the lowest temperature of the solid solution treatment, and the method for determining T1 is to first measure the curve of the conductivity of the 7xxx aluminum alloy after the solid solution treatment and the temperature at which the conductivity decreases rapidly and tends to be flat is taken as T1. The present invention can improve the corrosion resistance and shorten the process time, saving energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloy materials, and specifically relates to a heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy, which is suitable for improving the corrosion resistance while shortening the process time and saving energy consumption. Background Art

[0002] 7xxx high-strength aluminum alloys are often used in structural parts in the aerospace field due to their high strength. However, with the rapid development of these industries, higher and higher requirements have been placed on the performance, molding difficulty and low-cost control of aluminum alloy materials, which has also promoted the development of special aluminum alloy materials. 7xxx series aluminum alloys have the best performance due to their complex composition and high alloying characteristics, but they also have the problem of poor corrosion resistance. The existing technology has the following heat treatment processes to improve the corrosion resistance of 7xxx aluminum alloys:

[0003] 1. Two-stage aging: solution treatment at 470℃ / 1h→immediately water-cooled to room temperature→120℃ / 6h→immediately water-cooled to room temperature→160℃ / 24h;

[0004] 2. RRA (regression re-aging): solution treatment at 470℃ / 1h→immediately water-cooled to room temperature→120℃ / 24h→immediately water-cooled to room temperature→180℃ / 1h→immediately water-cooled to room temperature→120℃ / 24h;

[0005] 3. T6I6 (interrupted aging): solution treatment at 470℃ / 1h→immediately water-cooled to room temperature→120℃ / 15min→immediately water-cooled to room temperature→65℃ / 12d→immediately water-cooled to room temperature→120℃ / 26h;

[0006] However, the above heat treatment processes generally have problems such as long process, high energy consumption and low production efficiency. Summary of the invention

[0007] The purpose of the present invention is to provide a heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy, which can improve the corrosion resistance while shortening the process time and saving energy consumption in order to solve the above problems existing in the prior art.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A heat treatment method for improving the corrosion resistance of a 7xxx aluminum alloy, the heat treatment method comprising: performing a solid solution treatment, high temperature insulation, a first water cooling to room temperature, and artificial aging on the 7xxx aluminum alloy in sequence, wherein the temperature T of the high temperature insulation is T1<T<T2, T2 is the lowest temperature of the solid solution treatment, and the method for determining T1 is: measuring a curve of the change in electrical conductivity of the 7xxx aluminum alloy with temperature after the solid solution treatment, and taking the temperature at which the electrical conductivity rapidly decreases and then tends to be flat as T1.

[0010] The method for measuring the conductivity-temperature curve of the 7xxx aluminum alloy after solution treatment is as follows: the 7xxx aluminum alloy after solution treatment is heated at 10°C / min, and from the time the temperature is raised to 200°C, a sample is taken at every 20°C interval to measure its conductivity, thereby obtaining a conductivity-temperature curve.

[0011] The high temperature insulation time is 30-60 minutes.

[0012] The high temperature insulation time is 45 minutes.

[0013] The solution treatment is carried out at 450-480°C for 1 hour.

[0014] The solution treatment is carried out at 470° C. for 1 hour.

[0015] The T1 is 420°C, and the high temperature insulation temperature T is 445°C.

[0016] The artificial aging is carried out by keeping the temperature at 120°C for 12-48 hours.

[0017] The artificial aging is carried out at 120°C for 24 hours.

[0018] The transfer time of the first water cooling and the second water cooling is less than 3s.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention discloses a heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy, which sequentially performs solution treatment, high temperature insulation, first water cooling to room temperature, and artificial aging on the 7xxx aluminum alloy, wherein the temperature T of the high temperature insulation is T1<T<T2, T2 is the lowest temperature of the solution treatment, and the method for determining T1 is to first measure the conductivity-temperature curve of the 7xxx aluminum alloy after the solution treatment, and take the temperature at which the conductivity rapidly decreases and tends to be flat as T1; this design can also shorten the process time and save energy consumption while improving the corrosion resistance. Therefore, the present invention can shorten the process time and save energy consumption while improving the corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of the heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy according to the present invention.

[0022] Figure 2 7055 aluminum alloy conductivity versus temperature curve in the embodiment.

[0023] Figure 3 This is a cross-sectional metallographic image of Test Example 1 in the embodiment.

[0024] Figure 4 This is a cross-sectional metallographic image of Test Example 2 in the embodiment.

[0025] Figure 5 This is a cross-sectional metallographic image of Test Example 3 in the embodiment.

[0026] Figure 6 This is a cross-sectional metallographic image of Test Example 4 in the embodiment.

[0027] Figure 7 This is a cross-sectional metallographic image of Test Example 5 in the embodiment.

[0028] Figure 8 It is the cross-sectional metallographic image of comparative example 1 in the embodiment.

[0029] Fig. 9 It is the cross-sectional metallographic image of comparative example 2 in the embodiment.

[0030] Fig.10 It is the cross-sectional metallographic image of comparative example 3 in the embodiment.

[0031] Fig.11 It is the cross-sectional metallographic image of comparative example 4 in the embodiment.

[0032] Fig.12 It is the cross-sectional metallographic image of comparative example 5 in the embodiment.

[0033] Fig.13 It is the cross-sectional metallographic image of comparative example 6 in the embodiment. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with specific implementations and drawings.

[0035] See also Figure 1 A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy, the heat treatment method is to sequentially perform solid solution treatment, high temperature insulation, first water cooling to room temperature, and artificial aging on the 7xxx aluminum alloy, wherein the temperature T of the high temperature insulation is T1<T<T2, T2 is the lowest temperature of the solid solution treatment, and the method for determining T1 is: measuring the curve of the change of electrical conductivity with temperature of the 7xxx aluminum alloy after solid solution treatment, and taking the temperature at which the electrical conductivity tends to be flat after a rapid decrease as T1.

[0036] The method for measuring the conductivity-temperature curve of the 7xxx aluminum alloy after solution treatment is as follows: the 7xxx aluminum alloy after solution treatment is heated at 10°C / min, and from the time the temperature is raised to 200°C, a sample is taken at every 20°C interval to measure its conductivity, thereby obtaining a conductivity-temperature curve.

[0037] The high temperature insulation time is 30-60 minutes.

[0038] The high temperature insulation time is 45 minutes.

[0039] The solution treatment is carried out at 450-480°C for 1 hour.

[0040] The solution treatment is carried out at 470° C. for 1 hour.

[0041] The T1 is 420°C, and the high temperature insulation temperature T is 445°C.

[0042] The artificial aging is carried out by keeping the temperature at 120°C for 12-48 hours.

[0043] The artificial aging is carried out at 120°C for 24 hours.

[0044] The transfer time of the first water cooling and the second water cooling is less than 3s.

[0045] Example:

[0046] See also Figure 1 A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy is carried out in the following steps:

[0047] 1. Solution treatment: keep at 450-480℃ for 1h;

[0048] 2. High temperature insulation: Insulate at temperature T for 30-60 minutes, T1<T<T2, T2 is the lowest temperature of solution treatment, 450°C, and T1 is determined by heating the 7xxx aluminum alloy after solution treatment at 10°C / min with the furnace. From the time the temperature is raised to 200°C, a sample is taken at every 20°C interval to measure its conductivity, and a curve of conductivity changing with temperature is obtained. The temperature at which the conductivity decreases rapidly and then tends to be flat is taken as T1;

[0049] 3. The first water cooling to room temperature, the transfer time is less than 3s;

[0050] 4. Artificial aging: keep warm at 120℃ for 12-48h;

[0051] 5. Cool to room temperature for the second time with water, and the transfer time should be less than 3s.

[0052] In order to verify the effectiveness of the heat treatment method for improving the corrosion resistance of 7xxx aluminum alloys according to the present invention, 7055 aluminum alloy was used as a test object. The composition of the 7055 aluminum alloy is: 8.31wt% Zn, 2.07wt% Mg, 2.46wt% Cu, 0.12wt% Zr, 0.078wt% Fe, 0.056wt% Si, and the balance is Al. The commonly used minimum solution temperature T2 of the 7055 aluminum alloy is 450°C. After solution at 470°C / 1h, the conductivity of the 7055 aluminum alloy is tested as a function of temperature. Figure 2 As shown, according to Figure 2 It can be determined that T1 is 420°C, 420°C<T<450°C, and since the high temperature holding time decreases as T increases, T is preferably 445°C; referring to Table 1, the 7055 aluminum alloy is treated according to the heat treatment method of the present invention to obtain test examples 1-5, referring to Table 2, the 7055 aluminum alloy is treated according to other heat treatment methods to obtain comparative examples 1-6;

[0053] Table 1 Heat treatment methods used in test examples 1-9

[0054] Serial number Heat Treatment Test Example 1 Solution 470℃ / 1h→445℃ / 30min→water cooling to room temperature→120℃ / 24h→water cooling to room temperature Test Example 2 Solution 470℃ / 1h→445℃ / 30min→water cooling to room temperature→120℃ / 48h→water cooling to room temperature Test Example 3 Solution 470℃ / 1h→445℃ / 45min→water cooling to room temperature→120℃ / 12h→water cooling to room temperature Test Example 4 Solution 470℃ / 1h→445℃ / 45min→Water cooling to room temperature→120℃ / 24h→Water cooling to room temperature Test Example 5 Solution 470℃ / 1h→445℃ / 60min→water cooling to room temperature→120℃ / 12h→water cooling to room temperature

[0055] Table 2 Heat treatment methods used in comparative examples 1-6

[0056]

[0057] Performance Testing:

[0058] 1. Test Examples 1-5 and Comparative Examples 1-6 were tested for corrosion resistance. The corrosion resistance test was specifically as follows: three parallel samples were taken, and then the three parallel samples were placed in a solution of 57 g / L NaCl + 10 ml / L H2O2 (1.1 g / ml) and immersed for 6 hours. After washing with clean water, the cross-section metallographic observation of the alloy after the corrosion test was performed; the metallographic observation results of Test Examples 1-9 were as follows: Figure 3-Figure 7 As shown, the metallographic observation results of the comparative examples 1-6 are respectively as follows Figure 8-Figure 13 The surface corrosion conditions are shown in Table 3;

[0059] Table 3 Surface corrosion of all test examples and comparative examples

[0060]

[0061]

[0062] As can be seen from Table 3, by comparing test examples 1-5 with comparative examples 1-3, it can be seen that the high-temperature insulation in the temperature range determined by the present invention can significantly improve the corrosion resistance of 7055 aluminum alloy compared with no high-temperature insulation treatment; by comparing test examples 1-5 with comparative examples 4-6, it can be seen that the method of the present invention can significantly shorten the process flow when the corrosion resistance is improved to a considerable extent compared with the traditional heat treatment process, and the treatment process is simple.

[0063] 2. Mechanical properties tests were performed on test examples 1-5 and comparative examples 1-6, respectively. The mechanical properties tests included tensile strength, yield strength, and elongation. The mechanical properties test results are shown in Table 4:

[0064] Table 4 Mechanical properties test results of all test examples and comparative examples

[0065] Serial number Tensile strength / MPa Yield strength / MPa Elongation / % Test Example 1 650 620 7.1 Test Example 2 639 616 7.3 Test Example 3 654 629 7.3 Test Example 4 672 652 7.2 Test Example 5 642 612 7.1 Comparative Example 1 718 697 7.2 Comparative Example 2 730 712 7.2 Comparative Example 3 701 688 7.3 Comparative Example 4 661 638 7.3 Comparative Example 5 668 642 7.2 Comparative Example 6 675 650 7.2

[0066] By comprehensively analyzing the above-mentioned mechanical properties test results and corrosion resistance test results, the heat treatment parameters of Test Example 4 for improving the corrosion resistance of 7055 aluminum alloy in a short time and economically are preferred: solid solution at 470℃ / 1h→445℃ / 45min→water cooling to room temperature→120℃ / 24h→water cooling to room temperature; in summary, the heat treatment method of the present invention can provide a guiding basis for improving the corrosion resistance of 7xxx series aluminum alloys.

Claims

1. A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy, characterized in that: The heat treatment method is to sequentially perform solution treatment, high temperature insulation, first water cooling to room temperature, and artificial aging on the 7xxx aluminum alloy, wherein the temperature T of the high temperature insulation is T1<T<T2, T2 is the lowest temperature of the solution treatment, and the method for determining T1 is: measuring the curve of the change of electrical conductivity of the 7xxx aluminum alloy with temperature after the solution treatment, and taking the temperature at which the electrical conductivity tends to be flat after a rapid decrease as T1; The method for measuring the conductivity-temperature curve of the 7xxx aluminum alloy after solution treatment is as follows: the 7xxx aluminum alloy after solution treatment is heated at 10°C / min, and from the time the temperature is raised to 200°C, a sample is taken at every 20°C interval to measure its conductivity, thereby obtaining a conductivity-temperature curve.

2. A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy according to claim 1, characterized in that: The high temperature insulation time is 30-60 minutes.

3. A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy according to claim 2, characterized in that: The high temperature insulation time is 45 minutes.

4. A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy according to claim 1, characterized in that: The solution treatment is carried out at 450-480°C for 1 hour.

5. A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy according to claim 4, characterized in that: The solution treatment is carried out at 470° C. for 1 hour.

6. A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy according to claim 4, characterized in that: The T1 is 420°C, and the high temperature insulation temperature T is 445°C.

7. A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy according to claim 1, characterized in that: The artificial aging is carried out by keeping the temperature at 120°C for 12-48 hours.

8. A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy according to claim 7, characterized in that: The artificial aging is carried out at 120°C for 24 hours.

9. A heat treatment method for improving the corrosion resistance of 7xxx aluminum alloy according to claim 7, characterized in that: The transfer time of the first water cooling and the second water cooling is less than 3s.

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