Thermomechanical treatment method of 2XXX series aluminum alloy

Abstract

The invention discloses a thermomechanical treatment method of a 2XXX series aluminum alloy. The method comprises the following steps: placing an alloy in a heating furnace for solution treatment; the alloy is immediately subjected to water quenching to 20-25 DEG C after being discharged from the furnace, and the quenching time is less than 15 seconds; after quenching, naturally aging the alloy at room temperature for 12 hours; the alloy subjected to natural aging is placed in a heating furnace to be heated to 175 + / -10 DEG C, taken out of the heating furnace and extruded in a Bc mode for four passes; and naturally cooling the extruded alloy in air. According to the 2XXX series aluminum alloy obtained through the method, the tensile strength can reach 490 MPa, the yield strength can reach 410 MPa, the hardness can reach 171 HV, and the mechanical property is obviously improved compared with the mechanical property obtained after artificial aging. The high-temperature ECAP technology is adopted, the situation that the aluminum-copper alloy is prone to breakage during normal-temperature extrusion is avoided, the method is suitable for machining treatment of small workpieces, and the mechanical property of the alloy is effectively improved.

Description

Technical Field

[0001] The invention discloses a heat treatment method, in particular, relates to a deformation heat treatment method of a 2XXX series aluminum alloy, belonging to the field of deformation heat treatment of aluminum alloys. Background Art

[0002] 2XXX series aluminum alloys have good anti-ballistic performance, welding performance and stress corrosion resistance, excellent mechanical properties and stress corrosion resistance. They are mainly used for structural parts of aircraft skins, rockets, ships, etc. and armor materials for amphibious armored assault vehicles, airdrop vehicles, etc.

[0003] 2XXX series aluminum alloy is a heat-treatable aluminum alloy, and its mechanical properties can be improved by heat treatment methods such as quenching and aging. Deformation heat treatment is an important means to improve the performance of 2XXX series aluminum alloy. With the increase of cold rolling deformation, the θ' phase in the alloy becomes more dispersed and finer after aging, and the strength and hardness of the alloy are also higher.

[0004] Equal Channel Angular Pressing (ECAP) technology is a plastic forming method that effectively refines the grains and obtains complete large-sized block specimens by introducing large strains during the deformation process. It indirectly controls the microstructure of the material during the deformation process by changing the deformation temperature, deformation path and deformation times, and can simultaneously obtain bulk nanomaterials with high strength and high plasticity.

[0005] In order to improve the mechanical properties of 2XXX series aluminum alloys, ECAP technology is used to refine the grains to microns and submicrons to obtain ultrafine grain materials. Through the excitation of a certain temperature, while the grains become finer, a large amount of precipitation phases precipitate to fill the vacancies, hindering the recrystallization behavior of the grains at high temperatures. For the traditional ECAP deformation process, it is extremely difficult for 2XXX series aluminum alloys to pass through the die during room temperature extrusion; high temperature extrusion is prone to recrystallization of grains, and the effect of grain refinement is weakened. The process cannot meet the high mechanical properties requirements of 2XXX series aluminum alloys. Summary of the invention

[0006] The purpose of the present invention is to provide a deformation heat treatment process for improving the mechanical properties of 2XXX series aluminum alloys, combining heat treatment with severe plastic deformation to simultaneously improve the fracture toughness and hardness of 2XXX series aluminum alloys.

[0007] To achieve the above object, the present invention provides the following technical solution: a thermomechanical treatment process for a 2XXX series aluminum alloy, comprising the following steps:

[0008] (1) placing the alloy in a heating furnace for solution treatment;

[0009] (2) The alloy is immediately quenched in water to 20℃~25℃ after being taken out of the furnace, and the quenching time is less than 15s;

[0010] (3) After quenching, the alloy was naturally aged at room temperature for 12 h;

[0011] (4) The naturally aged alloy is placed in a heating furnace and heated to 175±10°C, taken out of the heating furnace, and extruded in a Bc manner for a total of 4 passes;

[0012] (5) The extruded alloy is left in the air to cool naturally.

[0013] As a preferred technical solution of the present invention, in step (1), the element composition of the 2XXX series aluminum alloy is as follows in mass percentage: Cu 5.8%, Mn 0.3%, Mg 0.2%, Ti 0.05%, Zr 0.2%, Fe 0.2%, Si 0.1%, and the balance is Al. In addition to the elemental components indicated above, the total content of the remaining metal and non-metallic impurity elements does not exceed 0.1%.

[0014] As a preferred technical solution of the present invention, in step (1), the solution treatment is performed at 530±10°C and kept warm for 2.5 hours.

[0015] As a preferred technical solution of the present invention, in step (4), the extrusion speed during extrusion is 10 -2 ~10 -1 mm / s.

[0016] As a preferred technical solution of the present invention, in step (4), the extrusion method is Bc method: after each pass of the sample through the die, it is rotated 90° clockwise around the axis in sequence, and engine oil and graphite powder are used for lubrication during the extrusion process. The mold should be cleaned in time after each extrusion. The extruded sample is first placed on a hydraulic press to straighten it, and then ground with a grinding wheel machine. A total of 4 extrusions are performed.

[0017] Compared with the prior art, the thermomechanical treatment technology of the present invention is suitable for small 2XXX series aluminum alloy workpieces and has the following advantages:

[0018] (1) The present invention performs severe plastic deformation under certain temperature excitation to avoid cracking and failure of extrusion of the workpiece. For the 2XXX series aluminum alloy used in the present invention, the Bc method is used for 4-pass extrusion to achieve the highest degree of grain refinement.

[0019] (2) In the present invention, the precipitated phase is not completely precipitated during natural aging, but under certain temperature excitation, during the extrusion process, a large amount of precipitated phase that has not been precipitated before is precipitated, the vacancy concentration decreases, the high-density precipitated phase hinders the movement of the grain boundary, the recrystallization process is delayed, and the grains are still small. The grains are relatively fine, and the plastic deformation of the grains under external force can be dispersed in more grains. The plastic deformation is more uniform, the stress concentration is smaller, and the plasticity and hardness are higher.

[0020] (3) The 2XXX series aluminum alloy obtained by the present invention has a tensile strength of 490 MPa, a yield strength of 410 MPa, and a hardness of 171 HV, and its mechanical properties are significantly improved compared with those after artificial aging. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a process flow chart of a deformation heat treatment process for a 2XXX series aluminum alloy.

[0022] Figure 2 1 is a comparison diagram of the metallographic morphologies of the untreated 2XXX aluminum alloy and the 2XXX aluminum alloy of Example 1, wherein a is a T4 2XXX aluminum alloy that has not been deformed (step 4), and b is a T4 2XXX aluminum alloy that has undergone deformation heat treatment.

[0023] Figure 3 TEM morphologies of the precipitated phase of the 2XXX series aluminum alloy after the treatment in Example 1 at different magnifications.

[0024] Figure 4 2XXX series aluminum alloy stress-strain curve obtained after the heat treatment process in the embodiment.

[0025] Figure 5 This is a hardness test chart of 2XXX series aluminum alloy obtained after the heat treatment process in the embodiment. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Embodiment 1:

[0028] (1) The 2519A aluminum alloy is placed in a heating furnace for solution treatment; the solution treatment temperature is 530±10°C and the temperature is kept for 2.5 hours to allow the residual phase in the alloy matrix to be fully dissolved while avoiding the problem of overburning of the alloy.

[0029] (2) The alloy is immediately quenched to room temperature after being taken out of the furnace, and the quenching time is 10s;

[0030] (3) After quenching, the alloy was naturally aged at room temperature for 12 h;

[0031] (4) The naturally aged alloy is placed in a heating furnace and preheated to 175±10°C. It is then taken out of the heating furnace and placed in a NYL-2000D pressure testing machine for extrusion in the Bc method: the sample is rotated 90° clockwise around the axis after passing through the die each time. Engine oil and graphite powder are used for lubrication during the extrusion process. The mold should be cleaned in time after each extrusion. The extruded sample is first placed on a hydraulic press to straighten it, and then ground with a grinding wheel. A total of 4 extrusion passes are performed. The Bc pass does not change the cross-sectional area and cross-sectional shape of the material during its deformation process, so only a lower working pressure is required to achieve repeated directional and uniform shear deformation of the material, so that the material can obtain a uniform and significantly refined grain structure under particularly large deformation. Therefore, this deformation method is adopted. The extrusion speed of the pressure testing machine is 10 -2 ~10 -1 mm / s;

[0032] (5) The extruded alloy was placed in air to cool naturally, and the resulting sample was named T4Bc4p175℃.

[0033] Embodiment 2:

[0034] The difference between this embodiment and Example 1 is that the preheating temperature in step (4) is 200°C, and the other steps are the same as those in Implementation 1. The obtained sample is named T4Bc4p200°C.

[0035] Figure 2 (a) shows the sample obtained after heat treatment without deformation. Figure 2 (b) shows the metallographic morphology comparison diagram of the sample obtained in Example 1. Figure 2 In (a), it can be found that the original grain size is larger and the grain boundary is more obvious; Figure 2 In (b), it can be found that the grains on the surface of the alloy after ECAP treatment are obviously broken and the grains are very small, but it is difficult to see the size of a single grain after severe deformation.

[0036] Figure 3 The TEM morphology of the sample obtained in Example 1 is shown. Figure 3 In (a), we can see a large number of high-density dislocations and many fine grains. The material forms more dislocations during severe deformation. These dislocations are formed by the collapse of a large number of vacancies generated during severe plastic deformation, and they multiply in large numbers, greatly increasing the dislocation density. Figure 3As can be seen in (a), the distribution of dislocations is not uniform, but they are distributed in large numbers between crystals. These dislocations increase the strength and toughness of the material.

[0037] As dislocations increase in the crystal, Figure 3 In (b), we can clearly see many black spots, which are the second phase precipitation in the matrix. These precipitates are mostly dispersed coherent or semi-coherent phases, usually ranging from tens of nanometers to one hundred nanometers. It can be seen that the precipitates are distributed relatively evenly. These precipitated second phases can occupy the vacancies in the matrix metal lattice in the form of insertion and substitution, resulting in the alloy material having higher hardness, strength and wear resistance.

[0038] By comparison Figure 4 and Figure 5 From the data of each embodiment, it can be found that Example 1 can greatly improve the mechanical properties of 2XXX series aluminum alloys, with tensile strength reaching 490MPa, yield strength reaching 410MPa, and hardness reaching 171HV, effectively improving the mechanical properties of 2XXX series aluminum alloys. Moreover, the lower the preheating temperature before ECAP treatment, the better the mechanical properties of the aluminum alloy after treatment. The temperature selected by the present invention is the lowest temperature at which the alloy can be extruded from the die. It is difficult to extrude when the temperature is lower than 175°C; when the temperature is higher than 175°C, the higher the temperature, the easier it is for the grains to recrystallize under the stimulation of high temperature, the grain size will increase, and the mechanical properties will decrease instead.

[0039] Therefore, the present invention adopts a high-temperature ECAP process to avoid the aluminum-copper alloy from being easily fractured during extrusion at room temperature, is suitable for processing smaller workpieces, and effectively improves the mechanical properties of the alloy.

[0040] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific embodiments of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the present invention, which should be regarded as belonging to the present invention and the scope of patent protection determined by the submitted claims.

Claims

1. A thermomechanical treatment method for a 2XXX series aluminum alloy, characterized in that: The following steps are involved: (1) placing the alloy in a heating furnace for solution treatment; (2) The alloy is immediately quenched in water to 20℃~25℃ after being taken out of the furnace, and the quenching time is less than 15s; (3) After quenching, the alloy was naturally aged at room temperature for 12 h; (4) The naturally aged alloy is placed in a heating furnace and heated to 175±10°C, taken out of the heating furnace, and extruded in a Bc manner for a total of 4 passes; (5) The extruded alloy is placed in the air to cool naturally.

2. The method according to claim 1, characterized in that In step (1), the element composition of the 2XXX series aluminum alloy is as follows in terms of mass percentage: Cu 5.8%, Mn 0.3%, Mg 0.2%, Ti 0.05%, Zr 0.2%, Fe 0.2%, Si 0.1%, and the balance is Al.

3. The method according to claim 1, characterized in that In step (1), the solution treatment is performed at 530±10°C for 2.5 hours.

4. The method according to claim 1, characterized in that In step (4), the extrusion speed is 10 -2 ~10 - 1 mm / s.

5. The method according to claim 1, characterized in that In step (4), the extrusion method is Bc method: after each pass of the sample through the die, it is rotated 90° clockwise around the axis in sequence. During the extrusion process, engine oil and graphite powder are used for lubrication. After extrusion, the sample is first placed on a hydraulic press to straighten it, and then polished with a grinding wheel machine. A total of 4 extrusion passes are performed.

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