A heat treatment process for a metal alloy after severe plastic deformation

Abstract

The application discloses a heat treatment process for a metal alloy after large plastic deformation and relates to the technical field of metallurgy. The process is de-energization treatment before solid solution treatment. The de-energization treatment is heat preservation for 12 hours or more under the condition that the solid solution temperature of the metal alloy is 1 / 3 or less. The application realizes the transformation of the structure from a metastable state to a stable state based on the dissipation of the energy of the alloy structure after deformation, and then realizes the regulation and optimization of the second phase while inhibiting the grain growth.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and more specifically to a heat treatment process for metal alloys after large plastic deformation. Background Technology

[0002] Grain refinement, as the most important strengthening method for metallic materials, has always been a research hotspot in the field of metals. However, traditional manufacturing processes such as casting, extrusion, and rolling are difficult to achieve ultrafine or nano-sized grains in metallic materials. At present, the important way to achieve significant grain refinement in metallic materials is through large plastic deformation, which mainly includes high-pressure torsion, die pressing, equal-diameter angular extrusion, reciprocating extrusion, cumulative rolling, and multi-directional forging. These large plastic deformation methods can all achieve significant microstructure refinement effects.

[0003] However, the refined microstructure obtained after large plastic deformation, due to its high dislocation density and significant matrix lattice distortion, transforms internal energy storage into a driving force for grain growth during heating, leading to abnormal grain growth. For example, in highly alloyed materials like 7-series aluminum alloys, the dispersion strengthening effect is greatly weakened after large plastic deformation due to the dissolution of the strengthening phase. Therefore, highly alloyed aluminum alloys after large plastic deformation require subsequent heat treatment to control the second phase and optimize alloy strength. The current problem is that existing heat treatment regimes for high-strength aluminum alloys, including peak aging and reversion aging, all require holding at a high temperature to achieve the dissolution of the second phase and subsequent dispersion precipitation of the nano-second phase during aging. During high-temperature heat treatment, traditional cast or extruded materials do not grow rapidly due to their relatively large grain size and low internal energy storage. However, the microstructure of materials after large plastic deformation will grow rapidly at the solution temperature due to their high internal energy storage, thus completely consuming the refining effect of large plastic deformation on high-strength aluminum alloys.

[0004] Therefore, in order to resolve the contradiction between grain refinement during large plastic deformation and second-phase control during heat treatment, providing a heat treatment process for metal alloys after large plastic deformation is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to propose a heat treatment process for metal alloys after large plastic deformation. This invention is based on the dissipation of energy in the microstructure of the deformed alloy to achieve the transformation of the microstructure from a metastable state to a stable state, thereby suppressing grain growth while controlling and optimizing the second phase.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A heat treatment process for metal alloys after large plastic deformation, wherein the process involves energy removal treatment before solution treatment;

[0008] The deenergizing treatment involves holding the metal alloy at a temperature below 1 / 3 of its solution temperature for 12 hours or more.

[0009] The purpose of deenergizing heat treatment is to increase the high-temperature thermal stability of crystal defects through dislocation rearrangement, thereby preserving as much of the high-density crystal defects (dislocations, dislocation cells, and small-angle grain boundaries, etc.) formed in the matrix after large plastic deformation as possible during the solution treatment stage. Because the material after large plastic deformation contains a high amount of deformation energy, abnormal grain growth will occur at relatively low temperatures. While holding at even lower temperatures can prevent grain growth, the deenergizing effect will be significantly weakened. Therefore, the deenergizing temperature and time specified in this invention are crucial. During the deenergizing process, the billet after large plastic deformation will undergo deenergizing treatment at a relatively low temperature, approximately one-third of the solution temperature (e.g., for 7-series aluminum alloys, the solution temperature is around 450℃, therefore the deenergizing temperature is around 150℃), for 12 hours or more. This treatment can achieve dislocation rearrangement within the matrix, thereby reducing lattice distortion and deformation energy storage, ultimately achieving the transformation of the material microstructure from a metastable to a stable state.

[0010] In the solution treatment process of this invention, the energy-removing heat treatment achieves the transformation of the material from a metastable to a stable structure after large plastic deformation, thus improving the high-temperature stability of the microstructure. The substructures formed after large plastic deformation are also retained during high-temperature heat treatment. These substructures serve as channels for the migration of alloying elements from the second phase to the matrix, thereby promoting the re-dissolution of the second phase. Furthermore, during the aging stage, the high-temperature stable substructures also serve as migration channels for solid solution atoms, further promoting the precipitation of the second phase.

[0011] Preferably, the metal alloy is an aluminum alloy.

[0012] Preferably, the deenergizing treatment is performed for 12 hours at 1 / 3 of the solution temperature of the metal alloy.

[0013] Preferably, the solution treatment temperature is 20-70°C lower than the solution temperature of the metal alloy, and the holding time is 2 hours.

[0014] Compared to the solution temperature of existing heat treatments, the solution temperature of the material subjected to large plastic deformation and energy removal treatment in the process of this invention can be correspondingly reduced. The degree of reduction in solution temperature varies from approximately 20°C to 70°C depending on the amount of deformation energy stored. When the deformation energy is low, a reduction of about 20°C in solution temperature can achieve a good solution recovery effect; while when the deformation energy is high, the solution temperature can be reduced by about 70°C, while the aging parameters are close to the traditional peak aging temperature.

[0015] Preferably, the process further includes an aging treatment.

[0016] Preferably, the aging treatment involves holding the product at 135°C for 16 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The heat treatment process of this invention can preserve the fine structure of aluminum alloy after large plastic deformation and control the second phase, solving the problem of rapid growth of metastable structure in existing heat treatment processes, and has good prospects for industrial application. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings in this description are merely embodiments of the present invention.

[0020] Figure 1 This invention presents the microstructure and corresponding KAM diagrams of samples subjected to different solutions at different times after large plastic deformation at the solution temperature.

[0021] Figure 2 This is the microstructure and corresponding KAM diagram of the sheet metal after large plastic deformation of the present invention after being kept at different temperatures for 2 hours;

[0022] Figure 3 This is the microstructure and corresponding KAM diagram of the sample after large plastic deformation of the present invention after being kept at different temperatures for 2 hours;

[0023] Figure 4 This is the microstructure and corresponding KAM diagram of the sample after large plastic deformation of the present invention after 12 hours at 150°C;

[0024] Figure 5 This is a diagram showing the orientation difference distribution of the samples after 24 PUC deformations and under different heat treatments according to the present invention.

[0025] Figure 6 These are material microstructure diagrams after large plastic deformation in Embodiment 1 and the comparative example of the present invention;

[0026] Figure 7 These are high deformation energy storage diagrams of the materials after large plastic deformation in Embodiment 1 and the comparative example of the present invention;

[0027] Figure 8 This is a microstructure diagram of the material after treatment in Comparative Example 1 of the present invention;

[0028] Figure 9 This is a diagram of the microstructure of the material after processing in Example 1 of the present invention;

[0029] Figure 10 The diagram shows the second phase distribution after heat treatment in Embodiment 1 and the comparative example of the present invention. Detailed Implementation

[0030] Embodiments of the present invention are described below, examples of which are shown in the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0031] Example 1

[0032] A heat treatment process for metal alloys after large plastic deformation specifically includes the following steps:

[0033] (1) Heat treatment to remove energy: Select aluminum alloy after large plastic deformation by 24-pass wave molding process at 350℃, and keep the billet after large plastic deformation at 150℃ for 12h.

[0034] (2) Solution heat treatment: Hold at 400℃ for 2 hours;

[0035] (3) Aging treatment: Keep warm at 135℃ for 16 hours.

[0036] Comparative Example

[0037] The aluminum alloy after large plastic deformation was directly subjected to the traditional peak aging process of solution treatment at 473℃ for 2 hours and aging at 135℃ for 16 hours using a 24-pass waveform molding process at 350℃.

[0038] Figure 6 These are microstructure diagrams of the materials after large plastic deformation in Example 1 and the comparative example. Figure 7 These are high deformation energy storage diagrams of the materials after large plastic deformation in Example 1 and the comparative example. Figure 8 The image shows the microstructure of the material after conventional peak aging (Comparative Example 1). The image reveals abnormal grain growth. Figure 9 This is a microstructure diagram of the material after treatment with the present invention in Example 1. As can be seen from the diagram, the refined grains are retained.

[0039] Figure 10 The figures show the distribution of the second phase after heat treatment in Example 1 and the comparative example, where (a) is the comparative example and (b) is Example 1. As can be seen from the figures, the second phase of Example 1 is finer and more dispersed than that of the comparative example. That is, after heat treatment by the present invention, the material after large plastic deformation can not only retain the fine-grained structure, but also achieve further optimization of the morphology of the second phase.

[0040] Conditional exploration experiment

[0041] 1) The samples after large plastic deformation were solution-treated at 473℃ for different times. The relevant microstructures and corresponding KAM diagrams after solution treatment are shown in [reference needed]. Figure 1In the figure, (a) and (b) are solutions dissolved for 0.5 h, (c) and (d) are solutions dissolved for 1 h, (e) and (f) are solutions dissolved for 1.5 h, (i) and (j) are solutions dissolved for 2 h, (g) and (h) are magnified views of (e) and (f) in the same position, and (k) and (l) are magnified views of (i) and (j) in the same position. As can be seen from the figure, after large plastic deformation, the billet will undergo significant grain growth after being held at the solution temperature for a very short time (15 min).

[0042] 2) The samples after large plastic deformation were subjected to solution treatment at different solution temperatures for 2 hours. The relevant microstructures and corresponding KAM diagrams after solution treatment are shown in [reference needed]. Figure 2 and 3 , Figure 2 In the middle, (a) and (e) are 250℃, (b) and (f) are 300℃, (c) and (g) are 350℃, and (d) and (h) are 400℃; Figure 3 In Figures (a) and (b), the temperature is 200℃, and in Figures (c) and (d), the temperature is 150℃. As can be seen from the figure, only by lowering the temperature to below 1 / 3 of the solution temperature can the microstructure in the billet be prevented from growing.

[0043] Figure 4 The microstructure (a) and corresponding KAM (b) images of the sample after large plastic deformation at 150℃ for 12 hours are shown. Figure 5 The figures show the orientation difference distribution of the samples after 24 PUC deformations and different heat treatments, where (a) no heat treatment; (b) heat treatment at 150℃ for 2h; (c) heat treatment at 150℃ for 12h; and (d) heat treatment at 400℃ for 2h. As can be seen from the figures, only at a suitable energy removal temperature can the ideal energy removal effect be achieved by heat treatment for a long time (12h).

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A heat treatment process for metal alloys after large plastic deformation, characterized in that, Specifically, the following steps are included: (1) Heat treatment to remove energy: aluminum alloys after large plastic deformation are selected by 24-pass wave molding process at 350℃, and the blanks after large plastic deformation are kept at 150℃ for 12h. (2) Solution heat treatment: hold at 400℃ for 2 hours; (3) Aging treatment: Keep warm at 135℃ for 16 hours.

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