A method for pulse magnetic field heat treatment of A356 aluminum alloy

Abstract

The application belongs to the technical field of alloy, and particularly relates to a pulse magnetic field heat treatment method for A356 aluminum alloy. The heat treatment method provided by the application comprises the following steps: sequentially performing solid solution treatment and aging treatment on the aluminum alloy casting under the condition of a pulse magnetic field; the holding time of the solid solution treatment is 20-50 min, and the holding time of the aging treatment is 30-60 min. The pulse magnetic field is applied in the holding stage of the solid solution treatment, so as to improve the Gibbs free energy of the system, improve the dissolution and diffusion rate of strong elements such as Si and Mg in the matrix, and obtain a supersaturated solid solution in a short time. In the holding stage of the aging treatment, the pulse magnetic field reduces the thermodynamic energy barrier of the second phase precipitation of the alloy, improves the nucleation rate of the second phase, and accelerates the precipitation and growth of the second phase. The heat treatment in the pulse magnetic field greatly shortens the heat treatment time, and the heat treatment time of the A356 aluminum alloy is only 50-110 min.

Description

Technical Field

[0001] This invention belongs to the field of alloy technology, specifically relating to a pulsed magnetic field heat treatment method for A356 aluminum alloy. Background Technology

[0002] A356 aluminum alloy belongs to the Al-Si-Mg alloy system. It not only possesses excellent casting fluidity but also exhibits good corrosion resistance and mechanical properties, making it widely used in the automotive, shipbuilding, and aerospace industries. A356 aluminum alloy castings require T6 heat treatment, which imparts better microstructure and superior mechanical properties to the parts.

[0003] Conventional T6 heat treatment includes 3–7 hours of solution treatment and 2–5 hours of aging treatment. Solution treatment of A356 aluminum alloy allows the strengthening elements to dissolve fully and uniformly into the matrix, resulting in a supersaturated solid solution. During aging treatment, the second phase precipitates uniformly from the matrix, reducing the α-Al grain size, eutectic silicon size, and secondary dendrite arm spacing of the aluminum alloy. This improves the alloy's microstructure and enhances its properties.

[0004] Although T6 heat treatment can give A356 aluminum alloy good mechanical properties, the T6 heat treatment takes a long time, requiring 5 to 12 hours, which seriously restricts the production efficiency of A356 aluminum alloy castings. Summary of the Invention

[0005] In view of this, the present invention provides a pulsed magnetic field heat treatment method for A356 aluminum alloy. The heat treatment method provided by the present invention can greatly shorten the heat treatment time while ensuring the mechanical properties of A356 aluminum alloy.

[0006] To address the aforementioned technical problems, this invention provides a pulsed magnetic field heat treatment method for A356 aluminum alloy, comprising the following steps:

[0007] A356 aluminum alloy castings were subjected to solution treatment and aging treatment sequentially under pulsed magnetic field conditions.

[0008] The heat treatment time for the solution treatment is 20-50 min, and the heat treatment time for the aging treatment is 30-60 min.

[0009] Preferably, the intensity of the pulsed magnetic field is 10-50 mT, the duty cycle of the pulsed magnetic field is 10-60%, and the frequency of the pulsed magnetic field is 10-60 Hz.

[0010] Preferably, the solution treatment includes sequentially performing solution heating, solution holding, and post-solution cooling.

[0011] Preferably, the solution heat preservation temperature is 525–550°C.

[0012] Preferably, the heating rate of the solution heating is 10–20 °C / min.

[0013] Preferably, the aging process includes sequentially performing aging heating, aging heat preservation, and post-aging cooling.

[0014] Preferably, the temperature for the aging insulation is 155–195°C.

[0015] Preferably, the heating rate of the aging heating is 10-20°C / min.

[0016] Preferably, the aluminum alloy casting includes A356 aluminum alloy castings, including A356 aluminum alloy steering knuckle castings or A356 aluminum alloy wheel rim castings.

[0017] Preferably, the heat treatment apparatus includes a quartz tube 4, a ceramic plate 5 placed in the quartz tube, heating devices 3 located on both sides of the outer surface of the quartz tube, a pulsed magnetic field generator 2 adjacent to the heating devices, and a water cooling system 1 connected to the heating devices 3.

[0018] This invention provides a pulsed magnetic field heat treatment method for A356 aluminum alloy, comprising the following steps: A356 aluminum alloy castings are subjected to solution treatment and aging treatment sequentially under a pulsed magnetic field; the solution treatment time is 20–50 min, and the aging treatment time is 30–60 min. In the solution treatment heating stage, the pulsed magnetic field is applied to increase the Gibbs free energy of the system, thereby increasing the dissolution and diffusion rate of strengthening elements such as Si and Mg in the matrix, resulting in a supersaturated solid solution in a short time. In the aging treatment heating stage, the pulsed magnetic field lowers the thermodynamic energy barrier for the precipitation of the second phase in the alloy, increasing the nucleation rate of the second phase, thus accelerating its precipitation and growth. The heat treatment in the pulsed magnetic field promotes grain refinement in the aluminum alloy, reduces the spacing between secondary dendrite arms, and improves the spheroidization effect of eutectic silicon and Mg2Si, thereby enabling A356 aluminum to obtain good mechanical properties. The heat treatment under magnetothermal coupling significantly shortens the heat treatment time; the heat treatment time for A356 aluminum alloy is only 50–110 min. Attached Figure Description

[0019] Figure 1 The diagram shows the structure of the pulsed magnetic field heat treatment device used in the embodiment, where 1 is a water cooling system, 2 is a pulsed magnetic field generator, 3 is a heating device, 4 is a quartz tube, 5 is a ceramic plate, and 6 is the sample to be treated.

[0020] Figure 2 This is a SEM image of the heat-treated A356 aluminum alloy from Example 1;

[0021] Figure 3 The image shows a SEM image of the heat-treated A356 aluminum alloy in Comparative Example 1. Detailed Implementation

[0022] This invention provides a pulsed magnetic field heat treatment method for A356 aluminum alloy, comprising the following steps:

[0023] The A356 aluminum alloy casting was subjected to solution treatment and aging treatment in sequence under pulsed magnetic field conditions.

[0024] In this invention, the aluminum alloy casting preferably includes A356 aluminum alloy steering knuckle castings or A356 aluminum alloy wheel rim castings, more preferably A356 aluminum alloy steering knuckle castings. This invention does not impose special requirements on the processing method of the aluminum alloy castings; they can be prepared using conventional methods in the art.

[0025] In this invention, the intensity of the pulsed magnetic field is preferably 10–50 mT, more preferably 20–40 mT; the duty cycle of the pulsed magnetic field is preferably 10–60%, more preferably 20–40%; and the frequency of the pulsed magnetic field is preferably 10–60 Hz, more preferably 20–40 Hz. In this invention, the average current of the pulsed magnetic field is preferably 10–60 A, more preferably 20–40 A.

[0026] The present invention preferably involves heating to the temperature required for solution treatment and aging treatment under magnetic field conditions.

[0027] In this invention, the solution treatment preferably includes sequentially performing solution heating, solution holding, and post-solution cooling; the heating rate of the solution heating is preferably 10–20 °C / min, more preferably 12–16 °C / min; the solution holding temperature is preferably 525–550 °C, more preferably 535–545 °C; and the solution holding time is 20–50 min, preferably 30–40 min. Preferably, a pulsed magnetic field is applied during the solution holding stage.

[0028] In this invention, the cooling after solution treatment is preferably water cooling. Specifically, the water cooling is preferably achieved by immersing the sample after solution treatment and heat preservation in water; the water temperature is preferably 20–35°C, more preferably 25–30°C; and the immersion time is preferably 5–8 seconds, more preferably 6–7 seconds.

[0029] In this invention, the aging treatment preferably includes sequentially performing aging heating, aging holding, and post-aging cooling; the heating rate of the aging process is preferably 10–20 °C / min, more preferably 13–16 °C / min. In this invention, the aging holding temperature is preferably 155–195 °C, more preferably 160–190 °C; the aging holding time is 30–60 min, preferably 40–50 min. Preferably, a pulsed magnetic field is applied during the aging holding stage.

[0030] In this invention, the post-aging cooling is preferably water cooling or air cooling, more preferably air cooling; the post-aging cooling temperature is preferably 20-35°C, more preferably 25-30°C.

[0031] The present invention has no special requirements for the heat treatment device, as long as it can provide a pulsed magnetic field while heating.

[0032] In an embodiment of the present invention, the schematic diagram of the heat treatment apparatus is as follows: Figure 1 The heat treatment apparatus includes a quartz tube 4, a ceramic plate 5 placed inside the quartz tube, heating devices 3 located on both sides of the outer surface of the quartz tube, a pulsed magnetic field generator 2 adjacent to the heating devices 3, and a water cooling system 1 connected to the heating devices 3. In this invention, the sample 6 to be treated is placed on the surface of the ceramic plate 5. Preferably, this invention utilizes the heating devices 3 to control the heat treatment temperature, and utilizes the water cooling system 1 to prevent the magnetic field coil from overheating.

[0033] This invention incorporates a pulsed magnetic field during the solution treatment and aging processes of heat treatment. The coupling of the magnetic and thermal fields reduces the grain size and secondary dendrite arm spacing of the aluminum alloy, resulting in a uniform and fine distribution of eutectic silicon and a significant spheroidization effect. The pulsed magnetic field and thermal field coupling accelerate precipitate formation, significantly shortening the heat treatment time to no more than 1.5 hours for A356 aluminum alloy, greatly improving production efficiency. Simultaneously, it increases elongation without reducing alloy strength, thus improving the alloy's mechanical properties while shortening the heat treatment time.

[0034] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0035] Example 1

[0036] Turn on the heating device 3 and raise the temperature in the quartz tube 4 to 540℃ at a heating rate of 15℃ / min. Place the A356 aluminum alloy steering knuckle casting 6 on the surface of the ceramic plate 5 and then place the ceramic plate 5 in the quartz tube 4. Turn on the pulse magnetic field generator 2 and set the pulse magnetic field strength to 33mT, duty cycle to 20%, frequency to 20Hz, and average current to 20A. Maintain the temperature in the quartz tube at 540℃ and perform solution treatment for 30min. Immerse the sample after solution treatment in water at 30℃ for 7s.

[0037] The heating device 3 is turned on to raise the temperature in the quartz tube to 185°C. The water-cooled sample is then placed back on the surface of the ceramic plate 5. The pulse magnetic field generator 2, the heating device 3, and the water cooling system 1 are adjusted to allow the quartz tube to be aged for 50 minutes under the conditions of a pulse magnetic field strength of 33mT, a duty cycle of 20%, a frequency of 20Hz, an average current of 20A, and a temperature of 185°C. After aging, the sample is removed and cooled to 25°C in air to obtain the heat-treated A356 aluminum alloy steering knuckle casting.

[0038] Comparative Example 1

[0039] The A356 aluminum alloy steering knuckle casting was solution treated at 540℃ for 450 min and then water-cooled; the water-cooled sample was then aged at 175℃ for 250 min and then air-cooled to room temperature to obtain the heat-treated A356 aluminum alloy casting.

[0040] The heat-treated A356 aluminum alloy from Example 1 was examined using a scanning electron microscope (SEM), and the resulting SEM images are shown below. Figure 2 As shown; the heat-treated A356 aluminum alloy in Comparative Example 1 was examined by scanning electron microscopy (SEM), and the SEM images were obtained, as shown. Figure 3 As shown.

[0041] The secondary dendrite arm spacing, average diameter of eutectic silicon, average area of ​​eutectic silicon, and aspect ratio of eutectic silicon of A356 aluminum alloy after heat treatment in Example 1 and Comparative Example 1 were detected using Image-Pro Plus software. The results are listed in Table 1.

[0042] The tensile strength and elongation of the heat-treated A356 aluminum alloys in Example 1 and Comparative Example 1 were tested according to GB / T 228.1-2010, and the results are listed in Table 1.

[0043] Table 1. Microstructure and mechanical properties of A356 aluminum alloys after heat treatment in Example 1 and Comparative Example 1.

[0044]

[0045] Combining Table 1 and Figures 2-3It can be seen that under the influence of the pulsed magnetic field, the main morphology of eutectic silicon is elliptical, with small particles being the most abundant. The particles are evenly distributed and have a significant spheroidization effect, indicating that the pulsed magnetic field can reduce the size of eutectic silicon, increase the degree of spheroidization of eutectic silicon, and improve the microstructure of A356 aluminum alloy.

[0046] As can be seen from Table 1, although the heat treatment method provided by the present invention has less impact on the tensile strength of A356 aluminum alloy than conventional heat treatment methods, it significantly improves the elongation.

[0047] The heat treatment time in Example 1 was 80 min, and the heat treatment time in Comparative Example 1 was 700 min. The heat treatment method provided by the present invention significantly reduces the heat treatment time, while the microstructure of A356 aluminum alloy is more uniform and the eutectic silicon spheroidization degree is higher.

[0048] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A pulsed magnetic field heat treatment method for A356 aluminum alloy, comprising the following steps: The A356 aluminum alloy castings were subjected to solution treatment and aging treatment sequentially under a pulsed magnetic field; the aluminum alloy castings included A356 aluminum alloy steering knuckle castings; the intensity of the pulsed magnetic field was 10-50 mT. The solution treatment includes sequentially performing solution heating, solution holding, and post-solution cooling; the heating rate of the solution treatment is 10-20℃ / min, and the holding time of the solution treatment is 20-50min; the post-solution cooling is water cooling; the water cooling involves immersing the sample after solution holding in water; the water temperature is 30℃, and the immersion time is 7s. The aging treatment includes sequentially performing aging heating, aging heat preservation, and post-aging cooling; the temperature of the aging heat preservation is 155-195℃, and the heat preservation time of the aging treatment is 30-50 minutes.

2. The heat treatment method according to claim 1, characterized in that, The duty cycle of the pulsed magnetic field is 10-60%, and the frequency of the pulsed magnetic field is 10-60Hz.

3. The heat treatment method according to claim 1, characterized in that, The solution insulation temperature is 525–550℃.

4. The heat treatment method according to claim 1, characterized in that, The heating rate of the aging heating is 10-20℃ / min.

5. The heat treatment method according to claim 1, characterized in that, The heat treatment apparatus includes a quartz tube (4), a ceramic plate (5) placed in the quartz tube, heating devices (3) located on both sides of the outer surface of the quartz tube, a pulse magnetic field generator (2) adjacent to the heating devices, and a water cooling system (1) connected to the heating devices (3).

Images