CN106435417B - A kind of multistage deformation aging process for improving 7xxx line aluminium alloy comprehensive performances - Google Patents

Abstract

The invention discloses a multi-stage deformation aging method for improving the comprehensive performance of 7xxx series aluminum alloys. Firstly, the aluminum alloy is subjected to enhanced solid solution treatment and then water-cooled and quenched to room temperature. First-level low-temperature aging treatment, and immediately water-cooled to room temperature, so that the aluminum alloy material is close to the state of peak aging, and then the treated aluminum alloy material is subjected to second-level high-temperature regression aging treatment, immediately water-cooled to room temperature, and the treated aluminum alloy is subjected to secondary aging treatment. After sub-room temperature tensile deformation and low-temperature storage, three-stage low-temperature aging treatment is carried out, and water cooling to room temperature is sufficient. The method of the invention can effectively improve the strength and corrosion resistance of the aluminum alloy, and has simple technological process, low operation difficulty, low cost and good generalization.

Description

A Multi-stage Deformation Aging Method for Improving the Comprehensive Properties of 7xxx Series Aluminum Alloys

technical field

The invention belongs to the technical field of material processing, and in particular relates to a multi-stage deformation aging method for improving the comprehensive performance of 7xxx series aluminum alloys.

Background technique

The increasingly serious energy and environmental crisis has promoted the development of lightweight structures, and it has become a major trend to replace steel materials with high-strength aluminum alloys in various structural products. The 7xxx series aluminum alloys are ultra-high-strength aluminum alloys, which are widely used in aerospace and modern transportation fields due to their higher specific strength. However, since the 7xxx series aluminum alloys are mostly used in the structural parts of airplanes and trains and other vehicles, their service environment is complex, and they are easily affected by stress, temperature, weather, corrosive media, scouring, heterogeneous structures, etc., often making aluminum alloy components fail. Therefore, the low corrosion resistance of 7xxx series aluminum alloys greatly limits its application.

With the rapid development of aviation technology, new requirements have been put forward for the comprehensive performance of 7xxx series aluminum alloy components. In addition to high strength, many key components also have high requirements for their toughness and corrosion resistance. The traditional isothermal heat treatment technology is only limited to the simple aging strengthening of aluminum alloy, and the fine control of the microstructure of aluminum alloy grain characteristics, precipitated phase size and distribution is far from enough. At the same time, a large number of studies have shown that the strength and corrosion resistance of aluminum alloys are contradictory. Increasing the strength of 7xxx series aluminum alloys often leads to a decrease in its corrosion performance. For example, the traditional T6 aging state has high strength but poor corrosion performance, while The corrosion performance of the T7 aging state is better than that of the T6 state, but the strength of the alloy is reduced. Therefore, the traditional aging process has been difficult to meet the high comprehensive performance requirements of the 7xxx series aluminum alloy sheets in the future. At present, most studies mainly focus on the aging process, and improve the properties of 7xxx series aluminum alloys by optimizing the aging process. In 7xxx series aluminum alloys, different types and sizes of precipitates will be precipitated during the entire aging process, and the type, size and distribution of precipitates have an important impact on the mechanical properties and corrosion properties of the alloy. However, due to the small controllable parameters in the aging process of 7xxx series aluminum alloys, the improvement of the strength of aluminum alloys only through the aging process is very limited, and it is usually not easy to exceed the ultimate tensile strength of 600MPa, and it is easy to sacrifice its corrosion performance. cost. Some scholars have achieved a substantial increase in the strength of 7xxx series aluminum alloys through some unusual methods, such as the method of obtaining fine-grained materials by severe plastic deformation (equal channel extrusion, high-pressure torsion, etc.), but this method requires aluminum alloys to produce Huge amount of deformation, high technical difficulty, it is difficult to manufacture large-sized products, and there is a big gap with the processing capacity that can be achieved by current industrial production equipment, the processing cost is high, and it is difficult to popularize and apply. Therefore, it is very meaningful to find a method that can improve the comprehensive performance of 7xxx series aluminum alloys, adapt to the use of modern industrial equipment, and reduce production costs at the same time.

Pre-stretching is a common and mature work hardening process for aluminum alloys. The stacking fault energy of aluminum alloy is high, and more dislocations and higher distortion energy will be obtained after tensile deformation at room temperature, and a large number of dislocations and high distortion energy are exactly what is expected in the subsequent processing of 7xxx series aluminum alloys of. Since the high-density dislocations formed after stretching have a strong driving effect on the recovery and recrystallization of the material, recovery and partial recrystallization occur during re-aging to obtain fine equiaxed grains, and the high-density dislocations promote the precipitation of the GP region The transition to η″, and then obtain the dispersed η″ phase, which is the ideal microstructural feature that takes into account the strength, plasticity and corrosion resistance of the alloy. However, after stretching, due to the existence of work hardening, the high strength will inevitably sacrifice the plasticity of the alloy, and the elongated grains will also damage the exfoliation corrosion resistance of the alloy, which cannot be tolerated in actual production. In addition, the deformation of the alloy with too large amount of tensile deformation is significantly reduced and the processing is laborious, and the deformation amount is too small to obtain sufficient deformation storage energy to promote precipitation. The aging temperature also has an important influence on the microstructure after aging. If the aging temperature is too high, coarse grains and η″ phases will be obtained, and the η″ phase density will also decrease. This microstructure is unfavorable to the mechanical properties. ; The aging temperature is low, only atomic clusters with weak strengthening effect can be precipitated, and it is difficult to precipitate the β″ phase, and the aging strengthening effect is poor. It is necessary to further control the type, size and distribution of zirconium and precipitates.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a multi-stage deformation aging method for improving the comprehensive performance of 7xxx series aluminum alloys, which can better control the precipitated phase of the aluminum alloy matrix and the precipitation on the grain boundary The size and distribution of phases can improve the strength and corrosion resistance of aluminum alloy, and the method is simple and easy to operate.

To achieve the above object, the present invention adopts the following technical solutions:

A multi-stage deformation aging method for improving the comprehensive performance of 7xxx series aluminum alloys, comprising the steps of:

1) Enhanced solution treatment: heat the aluminum alloy at 460~480°C for 45~120 minutes for enhanced solution treatment;

2) Quenching: quickly water-cool and quench the aluminum alloy material after solid solution in step 1) to room temperature;

3) Pre-stretch deformation: Stretch the aluminum alloy material treated in step 2) at room temperature with a deformation amount of 3-8%, then soak it in ice water for 20-60min, and store it at 3-8°C ;

4) First-level low-temperature aging treatment: the aluminum alloy stretched in step 3) is subjected to low-temperature aging treatment at 100-130°C for 10-30 h, and then immediately quenched and cooled with ice water;

5) Secondary regression aging treatment: the aluminum alloy material after step 4) primary aging treatment is subjected to high temperature regression aging treatment at 190~240°C for 10~60min;

6) Secondary tensile deformation: the aluminum alloy material treated in step 5) is stretched at room temperature with a deformation amount of 3~8%, and then soaked in ice water for 20~60min, and then heated at 3~8℃. Save under;

7) Three-stage low-temperature aging treatment: the aluminum alloy material after the secondary stretching in step 6) is subjected to low-temperature re-aging treatment at 80-100°C for 20-30 h, and then water-cooled to room temperature.

In the present invention, the aluminum alloy is first heated to a temperature near the solubility curve for enhanced solid solution treatment, so that the alloy elements in the aluminum alloy can be fully dissolved into the aluminum matrix to achieve uniform distribution; The alloy elements in the matrix are retained without time to diffuse, forming a structure similar to the high-temperature state, that is, a supersaturated solid solution; after a low-temperature stretch, the material is subjected to a low-temperature aging treatment, which is beneficial to refine the grain and form a strengthened The strengthening phase with greater effect can strengthen the aluminum alloy; and then through the high temperature regression aging treatment, the fine and dispersed precipitates in the grain can be dissolved back into the matrix, and then the distribution of the coarse precipitates at the grain boundary can be adjusted, and the deformed alloy can also be deformed at high temperature. Fine equiaxed grains are obtained by recovering and re-aging to further improve the corrosion resistance of aluminum alloys; finally, the material after secondary low-temperature stretching is subjected to three-stage low-temperature aging treatment, which can further promote grain refinement and form a stronger strengthening effect. Strengthening phase, the alloy is further strengthened.

In the process of the present invention, strengthening solid solution + deformation aging treatment is a key step. Firstly, enhanced solid solution can fully dissolve the alloying elements in the aluminum alloy into the matrix to form a supersaturated solid solution; then a large number of dispersed GP regions can be pre-formed in the matrix through the first-order deformation and low-temperature aging. Pinning dislocations can increase the number of dislocations generated by deformation; and during secondary high-temperature regression aging, the high-density dislocations promote the occurrence of recovery and recrystallization, and the GP regions generated by pre-aging can be directly converted into fine and diffuse η″ phase, and obtain the ideal microstructure, so that the aluminum alloy has very high strength and plasticity. Therefore, the treatment methods of solid solution, quenching, pre-aging, low-temperature stretching and re-aging can be used in the present invention to make the aluminum alloy obtain excellent Mechanical properties. After testing, the tensile strength of the treated aluminum alloy can reach 650MPa, the yield strength can reach 500MPa, and the fracture toughness can reach 42 MPa/m ^1/2 , which can be applied to large structural parts such as carrier-based aircraft, large ship On structural parts such as ships, on the basis of ensuring the mechanical strength, the corrosion resistance of aluminum alloy is also improved, which can give full play to the advantages of aluminum alloy.

The 7xxx series aluminum alloys treated by the method of the present invention have ideal precipitated structure morphology, content and distribution, which can not only improve the comprehensive mechanical properties including strength and corrosion resistance, but also have simple technological process and easy operation. The difficulty is low, ordinary industrial production equipment can carry out related processing, the processing cost is low, and it has good scalability.

Description of drawings

Fig. 1 is process flow chart of the present invention.

Fig. 2 is the SEM image of the fracture morphology of 7050 aluminum alloy after the treatment of the present invention.

Fig. 3 is a room temperature tensile curve of aluminum alloy samples obtained by different processes.

Figure 4 shows the stress corrosion slow tensile curves of aluminum alloy samples treated with different processes in 3.5% NaCl solution.

Figure 5 is the surface topography of the aluminum alloy samples treated by different processes after soaking in seawater for 72 hours.

Detailed ways

In order to make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

Example 1

A multi-stage deformation aging method for improving the comprehensive performance of aluminum alloys, comprising the following steps:

1) Enhanced solid solution treatment: heat the 7050 aluminum alloy in a salt bath furnace at 470°C for 60 minutes for enhanced solid solution treatment;

2) Quenching: quickly water-cool and quench the aluminum alloy material after solid solution in step 1) to room temperature, and the transfer time should be less than 15s;

3) Pre-stretching deformation: the aluminum alloy material treated in step 2) is subjected to uniaxial stretching at room temperature, and the tensile deformation amount is 5%, and then soaked in ice water for 20 minutes, at 3-8°C Save under;

4) First-level low-temperature aging treatment: the aluminum alloy material stretched in step 3) is subjected to low-temperature aging treatment at 120°C for 24 h, and then immediately quenched and cooled with ice water, so that the alloy is close to the peak aging state and the strength of the aluminum alloy is improved;

5) Secondary regression aging treatment: perform high temperature regression aging treatment on the aluminum alloy material after step 4) primary aging treatment at 200°C for 30 minutes;

6) Secondary tensile deformation: stretch the aluminum alloy material treated in step 5) at room temperature with a deformation amount of 5%, then soak it in ice water for 30 minutes, and store it at 5°C;

7) Three-stage low-temperature aging treatment: The aluminum alloy material after the secondary stretching in step 6) is subjected to low-temperature re-aging treatment at 90°C for 24 h, and then water-cooled to room temperature.

Fig. 2 is a SEM image of the fracture morphology of 7050 aluminum alloy after treatment in this embodiment. It can be seen from Figure 2 that the fracture of the treated 7050 aluminum alloy has many fine dimples, that is, it has good fracture ductility, and its fracture is plastic fracture.

Example 2

A multi-stage deformation aging method for improving the comprehensive performance of aluminum alloys, comprising the following steps:

1) Enhanced solid solution treatment: heat the 7050 aluminum alloy in a salt bath furnace at 480°C for 45 minutes for enhanced solid solution treatment;

2) Quenching: quickly water-cool and quench the aluminum alloy material after solid solution in step 1) to room temperature, and the transfer time should be less than 15s;

3) Pre-stretch deformation: the aluminum alloy material treated in step 2) is uniaxially stretched at room temperature, and the tensile deformation is 3%, and then soaked in ice water for 30 minutes, and then heated at 3-8°C Save under;

4) First-level low-temperature aging treatment: the aluminum alloy material stretched in step 3) is subjected to low-temperature aging treatment at 100°C for 30 h, and then immediately quenched and cooled with ice water, so that the alloy is close to the peak aging state and the strength of the aluminum alloy is improved;

5) Secondary regression aging treatment: perform high temperature regression aging treatment on the aluminum alloy material after step 4) primary aging treatment at 240°C for 10 minutes;

6) Secondary tensile deformation: stretch the aluminum alloy material treated in step 5) at room temperature with a deformation amount of 3%, then soak it in ice water for 20 minutes, and store it at 3°C;

7) Three-stage low-temperature aging treatment: The aluminum alloy material after the secondary stretching in step 6) was subjected to low-temperature re-aging treatment at 100°C for 20 h, and then water-cooled to room temperature.

Example 3

A multi-stage deformation aging method for improving the comprehensive performance of aluminum alloys, comprising the following steps:

1) Enhanced solid solution treatment: heat the 7050 aluminum alloy in a salt bath furnace at 460°C for 120 min for enhanced solid solution treatment;

2) Quenching: quickly water-cool and quench the aluminum alloy material after solid solution in step 1) to room temperature, and the transfer time should be less than 15s;

3) Pre-stretching deformation: the aluminum alloy material treated in step 2) is subjected to uniaxial stretching at room temperature, and the tensile deformation amount is 8%, and then soaked in ice water for 60 minutes, and then heated at 3-8°C Save under;

4) First-level low-temperature aging treatment: The aluminum alloy material stretched in step 3) is subjected to low-temperature aging treatment at 130°C for 10 h, and then immediately quenched and cooled with ice water, so that the alloy is close to the peak aging state and the strength of the aluminum alloy is improved;

5) Secondary regression aging treatment: perform high temperature regression aging treatment at 190°C for 60 minutes on the aluminum alloy material after step 4) primary aging treatment;

6) Secondary tensile deformation: stretch the aluminum alloy material treated in step 5) at room temperature with a deformation amount of 8%, then soak it in ice water for 60 minutes, and store it at 8°C;

7) Three-stage low-temperature aging treatment: the aluminum alloy material after the secondary stretching in step 6) was subjected to low-temperature re-aging treatment at 80°C for 30 h, and then water-cooled to room temperature.

Comparative example 1

The 7050 aluminum alloy was heat-preserved in a 470°C salt bath furnace for 60 minutes for solution treatment, then quenched in water to room temperature, and then carried out artificial aging commonly used in industry, that is, after 100°C primary aging treatment for 6 hours, then at 160°C After the second aging treatment for 20 h, the overaged state is reached, which is recorded as T7.

Comparative example 2

The 7050 aluminum alloy was heat-preserved in an air furnace at 470°C for 60 min for solution treatment, then quenched in water to room temperature, followed by primary aging treatment at 80°C for 6 h, and then secondary aging treatment at 120°C for 30 h to reach the peak In the aging state, a high aging strength is obtained, which is recorded as T6.

Using the method of GB/T 288.1-2010, the aluminum alloy samples obtained in Examples 1-3, Comparative Example 1 and Comparative Example 2 were subjected to tensile tests at room temperature, stress corrosion slow tension in 3.5% NaCl solution and simulated seawater corrosion conditions Under soaking for 72h, the results are shown in Figures 3, 4 and 5, respectively.

Fig. 3 is the tensile curves of the aluminum alloy samples obtained in Examples 1-3, Comparative Example 1 and Comparative Example 2 at room temperature. It can be seen from the figure that the yield strength and tensile strength of the aluminum alloy samples obtained in Examples 1-3 are higher than those of Comparative Examples 1 and 2, and the elongation is also better. Among them, the aluminum alloy obtained in Example 1 has the best tensile comprehensive mechanical properties at room temperature, with a yield strength of 610 MPa, a tensile strength of 670 MPa, and a total elongation of 13.8%.

Figure 4 shows the slow tensile curves of the aluminum alloy samples obtained in Examples 1-3, Comparative Example 1 and Comparative Example 2 in 3.5% NaCl solution, and the tensile strain rate is 10 ^-6 /s ^-1 . It can be clearly seen from Fig. 4 that in 3.5% NaCl solution, the tensile strength and elongation of the aluminum alloy samples obtained in Examples 1-3 are better than those of Comparative Example 1 and Comparative Example 2; wherein the aluminum alloy samples obtained in Example 1 have Maintain a yield strength of 460MPa, a tensile strength of 480MPa, and a total elongation of 11%. This shows that the present invention can effectively improve the stress corrosion resistance of aluminum alloy compared with the traditional process.

Fig. 5 shows the surface morphology of the aluminum alloy samples obtained in Examples 1-3, Comparative Example 1 and Comparative Example 2 after soaking in seawater for 72 hours. It can be seen from Figure 5 that after the aluminum alloy samples obtained in Comparative Example 1 and Comparative Example 2 were soaked in seawater for 72 hours, obvious corrosion damage appeared on the edge of the alloy, while the surface corrosion of the aluminum alloy samples obtained in Examples 1-3 was relatively light , but there are some uneven surfaces formed by corrosion salts on the surface of Example 2.

The above test results prove that the treatment method of the present invention can improve the corrosion resistance of the aluminum alloy to a certain extent while improving the strength of the alloy, and is an ideal treatment method.

It should be noted that although the present invention only selects the aluminum alloy with the grade of 7050 for testing, the strengthening form, precipitation type, and precipitation law of the 7xxx series aluminum alloys are basically the same. Therefore, the present invention can also be applied to other grades of 7xxx series aluminum alloys by properly adjusting the deformation heat treatment process parameters within the range of process parameters disclosed in the present invention.

Claims (1)

1. a kind of multistage deformation aging process for improving 7xxx line aluminium alloy comprehensive performances, it is characterised in that：Include the following steps：

1）Strengthened solution：7050 aluminium alloys are kept the temperature into 120 min in 460 DEG C of salt bath furnaces and carry out strengthened solution；

2）Quenching：By step 1）The rapid water hardening of aluminum alloy materials after solid solution is to room temperature；

3）Pre-tension deformation：By step 2）Treated, and aluminum alloy materials carry out simple tension at room temperature, and stretcher strain amount is 8%, after it then is impregnated 60min in ice water, preserved under the conditions of 3 ~ 8 DEG C；

4）The processing of level-one low temperature aging：By step 3）Aluminum alloy materials after stretching carry out low temperature aging at 130 DEG C and handle 10 h, It is cooled down immediately with ice water quenching again；

5）Two level returns ageing treatment：By step 4）Aluminum alloy materials after level-one ageing treatment carry out high temperature recurrence at 190 DEG C Ageing treatment 60min；

6）Succeeding stretch deforms：By step 5）Treated, and aluminum alloy materials carry out the room temperature tensile of deflection 8% again, then will After it impregnates 60min in ice water, preserved under the conditions of 8 DEG C；

7）The processing of three-level low temperature aging：By step 6）Aluminum alloy materials after succeeding stretch carry out low temperature ageing treatment again at 80 DEG C 30 h, then water cooling to room temperature.