Heat treatment method for preventing overaging of Al-Cu alloy

Abstract

The invention discloses a heat treatment method for preventing overaging of Al-Cu alloy. The method comprises the following steps: firstly adding trace rare earth elements into the Al-Cu alloy, then carrying out ultrasonic low-temperature aging treatment, then carrying out plastic deformation, and finally carrying out secondary aging treatment. Alloy elements are gathered in a small range through rare earth elements, long-distance diffusion of the alloy elements is avoided, nucleation of atomic clusters (GP regions) is improved through ultrasonic waves and plastic deformation, a large number of plastic deformation dislocations are formed in an Al matrix, growth and coarsening of the sizes of the atomic clusters are restrained, theta ''is kept, phase change does not occur, and the alloy elements are prevented from being dispersed in the Al matrix. The problem that when the Al-Cu alloy is subjected to artificial aging, the maintenance time of the peak aging state is short, and the Al-Cu alloy easily enters the overaging state, so that the mechanical property of the alloy is reduced is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy aging heat treatment, and more specifically, relates to a heat treatment method for preventing Al-Cu alloy from over-aging. Background Art

[0002] Al-Cu alloy is an extremely important type of aluminum alloy material. Its main alloying element is Cu, which is widely used in aviation, aerospace, automobile and machinery manufacturing. Al-Cu alloy is a heat-treated aluminum alloy. The general heat treatment process is as follows: Figure 1 As shown, it includes the steps of solid solution, quenching, artificial aging, etc., wherein the purpose of solid solution is to make the alloy elements dissolve evenly in the Al matrix, the purpose of quenching is to form supersaturated solid solution and supersaturated quenching vacancies of the alloy elements in the Al matrix by rapid cooling, and the purpose of artificial aging is to make the supersaturated atoms of the alloy elements re-aggregate and precipitate to form nano-reinforced phase particles, so as to obtain high strength of the alloy.

[0003] The main process parameters of artificial aging include aging heating temperature and holding time. After aging and holding, the hardness and strength of the alloy material change. In the early stage of aging, the hardness increases rapidly with the increase of aging time, and then reaches the maximum value and can maintain a horizontal state for a period of time, that is, the hardness of the material does not change or changes very little with the increase of aging time, which is also called the peak aging platform. Then the hardness of the material decreases rapidly with the increase of aging time. These three stages are called under-aging stage, peak aging stage, and over-aging stage. The strength of the alloy material in the under-aging state is low and the plasticity is good. In the peak aging state, the strength and plasticity can reach the optimal combination, while in the over-aging state, not only the strength is reduced but also its plasticity is significantly reduced. The reason for over-aging is that the further diffusion of alloy element atoms increases the size and quantity of the precipitation strengthening phase particles formed, and the strengthening effect is weakened. Usually, Al-Cu alloy parts or raw materials adopt the peak aging state, and reach the peak aging hardness through solid solution-quenching-artificial aging to avoid under-aging or over-aging. In addition, in Al-Cu alloys, artificial aging treatment is related to the type of precipitation strengthening phase in the alloy. When under-aging or over-aging occurs, the θ″ phase with small size, high number density and best strengthening effect cannot be achieved or maintained. Therefore, aging treatment of Al-Cu alloys is an important means to strengthen the performance of the alloy. Different elements in aluminum alloys have different effects on aging. How to control the alloy to be in the peak aging state is a major problem.

[0004] In CN109023178A, a 7075 aluminum alloy low-temperature ultrasonic aging treatment method is disclosed. During the aging process, an ultrasonic field with a certain vibration frequency and power is introduced into the aluminum alloy solid to reduce the temperature required for aging, accelerate the precipitation rate of the precipitated phase, and improve efficiency. At the same time, under high-frequency vibration conditions, the atomic diffusion movement speed in the aluminum alloy structure is accelerated, the grain boundary movement is strengthened, the number of precipitated phases is increased, the size is reduced, and the precipitated phase is more dispersed. However, although the patent shortens the aging time and reduces the aging temperature, and uses ultrasound to increase the dispersion of the precipitated phase, the performance of the aluminum alloy is improved. However, for multi-element alloys, such as those containing Mg, Ni, Ti, Co, Mn, Cr, Zr and other elements, the diffusion of alloy elements during artificial aging of Al-Cu alloys will be aggravated, so the precipitation reaction rate of its artificial aging process is increased, the phase transformation and growth rate of the precipitated phase are significantly increased, the time required for the alloy to reach the peak aging state is significantly reduced, and the time for the peak platform to exist is very short, and it may even cause the peak platform to disappear. That is, the Al-Cu alloy containing multiple complex alloy elements takes a shorter time to reach the peak aging state after artificial aging. After reaching the peak aging, the material enters the over-aging state in a very short time, making it difficult to control the alloy in the peak aging stage, which will lead to a decrease in mechanical properties after aging. Summary of the invention

[0005] The present invention provides a heat treatment method for preventing Al-Cu alloy from over-aging in order to overcome the problems that the peak aging state is short during the aging of the existing copper-aluminum alloy, which easily leads to the degradation of alloy performance due to the aging entering the over-aging state.

[0006] The present invention is achieved through the following technical solutions:

[0007] A heat treatment method for preventing Al-Cu alloy from overaging, the preparation steps comprising:

[0008] S1. Adding rare earth element Re to Al-Cu alloy and performing solid solution and quenching;

[0009] S2. The quenched Al-Cu alloy is subjected to a low temperature aging treatment at an ultrasonic power of 300 to 1500 W for 2 to 12 h, and the temperature is controlled to be maintained in the range of 50 to 90 ° C;

[0010] S3. Plastic deformation of the ultrasonically treated Al-Cu alloy followed by secondary aging treatment;

[0011] S4. After cooling, the Al-Cu alloy heat treatment is completed.

[0012] Furthermore, the Al-Cu alloy in step S1 includes one or more of AlCu5Ni2CoZr alloy, AlCu5MnCdV, AlCu4MnMg and the like.

[0013] Furthermore, the rare earth element Re in step S1 includes one or more of erbium (Sc), scandium (Er), and yttrium (Y).

[0014] Furthermore, the amount of rare earth element Re added in step S1 is not greater than 0.05%.

[0015] Furthermore, the solid solution in step S1 is to heat to 480° C. to 550° C. and keep the temperature for 0.5 h to 2.0 h, so that the alloy elements are uniformly dissolved in the Al matrix.

[0016] Furthermore, the quenching in step S1 is to use water or an organic aqueous solution as a cooling medium to quickly cool the alloy from the solution temperature to room temperature.

[0017] Furthermore, in step S2, the ultrasonic power is 300 to 1500 W, and the treatment time is 2 to 12 hours.

[0018] Furthermore, the plastic deformation in step S3 includes one or more of rolling and drawing deformation. Specifically, plate parts can be subjected to a certain rolling deformation in the normal direction of the plate by rolling; sheet metal parts can be subjected to plastic deformation while being formed by stamping or drawing; forged parts can be subjected to a certain amount of deformation by forging; extruded parts can be subjected to a certain amount of plastic deformation by stretching and straightening after hot extrusion.

[0019] Furthermore, the amount of plastic deformation in step S3 is 2-10%.

[0020] Furthermore, the temperature of the secondary aging treatment in step S3 is 155° C. to 185° C., and the time is 10 h to 30 h, so that the supersaturated atoms of the alloy elements re-aggregate and precipitate to form nano-reinforced phase particles, thereby improving the high strength of the alloy.

[0021] Compared with the prior art, the beneficial effects are:

[0022] The present invention adds a trace amount of rare earth elements, utilizes the characteristics of rare earth elements such as large diameter, slow diffusion, strong adsorption force on small diameter atoms, and the ability to form dispersed particles at the triangular grain boundaries of the aluminum matrix, etc., and can form atomic "Coriolis gas clusters" around the rare earth atoms, dispersed particles, triangular grain boundaries, etc. dissolved in the Al matrix, so that the alloy elements can be gathered in a small range to avoid long-distance diffusion, thereby reducing the speed of precipitation of alloy strengthening elements to form strengthening phases, which is beneficial to slowing down the violent growth of strengthening phases and obtaining fine precipitation strengthening phases, and can also improve mechanical properties. In addition, after the Al-Cu alloy is quenched, the material is in a state of high concentration of supersaturated solute atoms and quenching vacancies. At this time, heating to a lower temperature or using ultrasonic treatment increases the short-range diffusion capacity of solute atoms to a certain extent, greatly improves the nucleation of precipitation strengthening phase atomic clusters (GP zones), can significantly increase their number density, but will not make their size grow excessively, can form a large number of θ" phase nucleation points for subsequent secondary aging, and their size will not be too coarse.

[0023] After ultrasonic treatment, the present invention utilizes plastic deformation to form a large number of plastic deformation dislocations in the Al matrix, and the deformation dislocations will become pinning points of supersaturated solid solution atoms and vacancies. When heated again for secondary aging, the atoms of the alloy elements are constrained and are not easy to diffuse quickly and over long distances. The atomic clusters with high number density will undergo a phase transformation into a θ″ phase, and at the same time, the size of the atomic clusters is not easy to grow and coarsen, and the phase transformation into a θ′ phase or a θ phase with a worse strengthening effect will not occur.

[0024] The method of the present invention can avoid the problem that multiple elements in the Al-Cu alloy cause the alloy to quickly enter an over-aging state during the aging process, and the precipitated phase that can be obtained has a smaller size and a higher number density, and the strengthening effect of the aging treatment is better, thereby improving the strength and toughness of the alloy material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the TEM image of Al-Cu alloy after a low temperature aging treatment;

[0026] Figure 2 It is the TEM image of Al-Cu alloy treated by plastic tensile deformation;

[0027] Figure 3 It is the age hardening curve of alloy with elongation of 3% and 6%;

[0028] Figure 4 TEM images of the precipitation strengthening phase with a stretching amount of 3% and secondary aging of 30h and 200h respectively, where (a) is the diffraction signal image of the 30h treatment, (a) is the morphology image of the 30h treatment, (a) is the diffraction signal image of the 200h treatment, and (a) is the morphology image of the 200h treatment;

[0029] Figure 5 is an age hardening curve diagram in the comparative example;

[0030] Figure 6 The peak aging time is 160℃ and 20h in the comparative example. <100> TEM image of T precipitation strengthening phase in the direction, (a) is the diffraction signal image, (b) is the morphology image;

[0031] Figure 7 For the comparative example, 160℃, 50h peak aging <100> Direction detection diagram, (a) is the diffraction signal diagram, (b) is the TEM morphology diagram;

[0032] Figure 8 1. The uniaxial tensile stress-strain curves of the Al-Cu alloys prepared in Example 1, Example 2 and the comparative example. DETAILED DESCRIPTION

[0033] The following is further explained and illustrated in conjunction with the examples, but the specific examples do not limit the present invention in any form. If not specifically stated, the methods and equipment used in the examples are conventional methods and equipment in the art, and the raw materials used are all conventional commercially available raw materials.

[0034] Example 1

[0035] This embodiment provides a heat treatment method for preventing Al-Cu alloy from overaging based on AlCu5Ni2CoZr alloy, and the preparation steps include:

[0036] S1. Add Sc element to AlCu5Ni2CoZr alloy to obtain Al-Cu alloy with the composition:

[0037] element Cu Ti Mn Sb Ni Co Zr Fe Si Sc Al content 4.51 0.15 0.24 0.20 1.34 0.24 0.14 0.11 0.076 0.04 margin

[0038] S2. The Al-Cu alloy in step S1 is heated to 540°C and then maintained for solution treatment for 1 hour, and then transferred to room temperature water for cooling and quenching within a period of no more than 2 seconds;

[0039] S3. The quenched Al-Cu alloy was subjected to a low-temperature aging treatment at an ultrasonic power of 800 W for 6 h, and the temperature was maintained at 60 ° C;

[0040] S4. The ultrasonically treated Al-Cu alloy was subjected to tensile deformation, and the deformation amount was 6% of the unidirectional dimension of the sample in the tensile direction;

[0041] S5. Then heated to 160 ° C for 20 hours for secondary aging treatment;

[0042] S4. After cooling, the Al-Cu alloy heat treatment is completed.

[0043] Example 2

[0044] This embodiment provides a heat treatment method for preventing Al-Cu alloy from overaging based on AlCu5Ni2CoZr alloy, and the preparation steps include:

[0045] S1. Add Sc element to AlCu5Ni2CoZr alloy to obtain Al-Cu alloy with the composition:

[0046] element Cu Ti Mn Sb Ni Co Zr Fe Si Sc Al content 4.51 0.15 0.24 0.20 1.34 0.24 0.14 0.11 0.076 0.04 margin

[0047] S2. The Al-Cu alloy in step S1 is heated to 540°C and then maintained for solution treatment for 1 hour, and then transferred to room temperature water for cooling and quenching within a period of no more than 2 seconds;

[0048] S3. The quenched Al-Cu alloy was subjected to a low-temperature aging treatment at an ultrasonic power of 800 W for 6 h, and the temperature was maintained at 60 ° C;

[0049] S4. The ultrasonically treated Al-Cu alloy is subjected to tensile deformation, and the deformation amount is 3% of the unidirectional dimension of the sample in the tensile direction;

[0050] S5. Then heated to 160 ° C for 20 hours for secondary aging treatment;

[0051] S4. After cooling, the Al-Cu alloy is heat treated. The Al-Cu alloy subjected to low temperature aging treatment in step S3 of Example 1 is tested. Figure 1 As shown in FIG. 1 , after the ultrasonic and low temperature aging treatment, a large number of fine atomic clusters (GP regions) are formed in the Al matrix, and the state of the clustered solute atoms is as follows. The Al-Cu alloy after the stretching in step S4 is tested. Figure 2 As shown, a large number of deformation dislocations are formed inside the Al-Cu alloy. Many dislocation lines can be observed and atomic clusters gather near the dislocation lines, that is, the dislocations pin the atomic clusters.

[0052] The hardness test of the aging hardening performance of different secondary aging treatment time in Example 1 and Example 2 was carried out respectively. The results are as follows: Figure 3 As shown in the figure, secondary aging is carried out. After the under-aging stage, the alloy reaches the peak hardness on the aging hardening curve, and an obvious peak hardness platform appears, which lasts for about 100 to 110 hours. Then the hardness decreases and enters the over-aging state.

[0053] The TEM microstructures of the alloys subjected to secondary aging treatment for 30 h and 200 h in Example 2 were tested respectively. Figure 4As shown in the figure, after 3% tensile plastic deformation and secondary aging for 30h, the strengthening phase of the AlCu5Ni2CoZr alloy is composed of θ″ phase and θ′ phase, mainly θ″ phase; after 200h of secondary aging, the θ″ phase is greatly reduced, while the amount of θ′ phase increases significantly. From the peak platform to the over-aging process, the θ″ phase transforms to the θ′ phase, resulting in a decrease in over-aging hardness, but it is difficult to observe the size change of the θ″ phase.

[0054] Comparative Example 1

[0055] This embodiment provides a heat treatment method for preventing Al-Cu alloy from overaging, and the preparation steps include:

[0056] S1. Heating at 540°C for 1 hour in AlCu5Ni2CoZr alloy, water-quenching S2. Then heating to 160°C, 180°C, and 200°C for aging treatment;

[0057] S3. After cooling, the Al-Cu alloy heat treatment is completed.

[0058] The aging hardening curves of Al-Cu alloys aged at different temperatures are obtained, such as Figure 5 As shown in the figure, after aging at 160℃, 180℃ and 200℃, the hardness of the alloy reaches its peak after under-aging. After that, with the increase of artificial aging time, its hardness decreases rapidly and the alloy enters the over-aging state.

[0059] Specifically, the alloys aged at 160°C for 20 h and 50 h were tested. Figures 6-7 It can be seen that the AlCu5Ni2CoZr alloy reaches the peak aging state after artificial aging at 160℃ for 20h, and the precipitation strengthening phase is mainly θ″ phase, containing a small amount of θ′ phase. After the AlCu5Ni2CoZr alloy is aged at 160℃ for 50h, the alloy is in an over-aged state, and the main strengthening phase transforms from the θ″ phase of peak aging to the θ′ phase. After the hardness reaches the peak hardness, continuous aging treatment causes the θ″ phase to gradually transform into the θ′ phase. The strengthening effect of the θ′ phase is weaker than that of the θ″ phase, and the θ′ phase grows further, the inter-particle spacing becomes larger, and the strengthening effect decreases, so the hardness is lower.

[0060] The Al-Cu alloys of Example 1, Example 2 and Comparative Example 1 were subjected to uniaxial tensile tests. The results are as follows: Figure 8 As shown in Table 1, the aging hardening curves show that all three are in the peak aging state. Compared with the existing aging heat treatment method, the present invention can improve the comprehensive mechanical properties of the Al-Cu alloy by adding ultrasonic low-temperature primary aging treatment and plastic deformation treatment after quenching.

[0061] Table 1

[0062] Example 1 Example 2 Comparative Example 1 Yield strength(MPa) 379 391 382 Tensile strength(MPa) 301 278 322 Elongation at break (%) 2.3 2.1 1.36

[0063] Example 3

[0064] This embodiment provides a heat treatment method for preventing Al-Cu alloy from overaging, and the preparation steps include:

[0065] S1. Add 0.02% Y element to AlCu5MnCdV alloy.

[0066] S2. The Al-Cu alloy in step S1 is heated to 480°C and then maintained for solution treatment for 2 hours, and then transferred to room temperature water for cooling and quenching within a period of no more than 2 seconds;

[0067] S3. The quenched Al-Cu alloy was subjected to a low-temperature aging treatment at an ultrasonic power of 300 W for 12 h, and the temperature was maintained at 60 to 90 ° C;

[0068] S4. The ultrasonically treated Al-Cu alloy was subjected to tensile deformation, and the deformation amount was 2% of the unidirectional dimension of the sample in the tensile direction;

[0069] S5. Then heated to 155 ° C for 30 hours for secondary aging treatment;

[0070] S4. After cooling, the Al-Cu alloy heat treatment is completed.

[0071] Example 4

[0072] This embodiment provides a heat treatment method for preventing Al-Cu alloy from overaging, and the preparation steps include:

[0073] S1. Add 0.05% Er element to AlCu5MnCdV alloy.

[0074] S2. The Al-Cu alloy in step S1 is heated to 550°C and then maintained for solution treatment for 0.5h, and then transferred to room temperature water for cooling and quenching within a period of no more than 2s;

[0075] S3. The quenched Al-Cu alloy was subjected to a low-temperature aging treatment at an ultrasonic power of 1500W for 2h, and the temperature was controlled to be maintained at 50 to 60°C;

[0076] S4. The ultrasonically treated Al-Cu alloy is subjected to tensile deformation, and the deformation amount is 10% of the unidirectional dimension of the sample in the tensile direction;

[0077] S5. Then heated to 185 ° C for 10 hours for secondary aging treatment;

[0078] S4. After cooling, the Al-Cu alloy heat treatment is completed.

[0079] Example 5

[0080] This embodiment provides a heat treatment method for preventing Al-Cu alloy from overaging, and the preparation steps include:

[0081] S1. Add 0.03% Sc element to AlCu4MnMg alloy.

[0082] S2. The Al-Cu alloy in step S1 is heated to 520°C and then maintained for solution treatment for 1.5 hours, and then transferred to room temperature water for cooling and quenching within a period of no more than 2 seconds;

[0083] S3. The quenched Al-Cu alloy was subjected to a low-temperature aging treatment at an ultrasonic power of 1000 W for 10 h, and the temperature was maintained at 50 to 60 ° C;

[0084] S4. The ultrasonically treated Al-Cu alloy was subjected to tensile deformation, and the deformation amount was 8% of the unidirectional dimension of the sample in the tensile direction;

[0085] S5. Then heated to 175 ° C for 18 hours for secondary aging treatment;

[0086] S4. After cooling, the Al-Cu alloy heat treatment is completed.

[0087] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A heat treatment method for preventing Al-Cu alloy from overaging, characterized in that: The preparation steps include: S1. Adding rare earth element Re to Al-Cu alloy for solid solution and quenching; S2. The quenched Al-Cu alloy is subjected to a low temperature aging treatment at an ultrasonic power of 300 to 1500 W for 2 to 12 h, and the temperature is controlled to be maintained in the range of 50 to 90 ° C; S3. Plastic deformation of the ultrasonically treated Al-Cu alloy followed by secondary aging treatment; S4. After cooling, the Al-Cu alloy heat treatment is completed.

2. The heat treatment method for preventing Al-Cu alloy from overaging according to claim 1, characterized in that: The Al-Cu alloy in step S1 includes one or more of AlCu5Ni2CoZr alloy, AlCu5MnCdV alloy, and AlCu4MnMg alloy.

3. The heat treatment method for preventing Al-Cu alloy from overaging according to claim 1, characterized in that: The rare earth element Re in step S1 includes one or more of erbium, scandium and yttrium.

4. The heat treatment method for preventing Al-Cu alloy from overaging according to claim 1, characterized in that: The amount of rare earth element added in step S1 is not more than 0.05%.

5. The heat treatment method for preventing Al-Cu alloy from overaging according to claim 1, characterized in that: The solution treatment temperature in step S1 is 480° C. to 550° C., and the holding time is 0.5 h to 2.0 h.

6. The heat treatment method for preventing Al-Cu alloy from overaging according to claim 1, characterized in that: The quenching in step S1 is to cool the alloy after the solution treatment in room temperature water or an organic aqueous solution.

7. The heat treatment method for preventing Al-Cu alloy from overaging according to claim 1, characterized in that: The ultrasonic power in step S2 is 300 to 1500 W, and the treatment time is 2 to 12 hours.

8. The heat treatment method for preventing Al-Cu alloy from overaging according to claim 1, characterized in that: The plastic deformation in step S3 includes one or more of rolling and drawing deformation.

9. The heat treatment method for preventing Al-Cu alloy from overaging according to claim 1, characterized in that: The amount of plastic deformation in step S3 is 2-10%.

10. The heat treatment method for preventing Al-Cu alloy from overaging according to claim 1, characterized in that: The temperature of the secondary aging treatment in step S3 is 155° C. to 185° C., and the time is 10 h to 30 h.

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