A method for rapid homogenization of as-cast rare earth magnesium alloys

Abstract

This invention provides a method for rapid homogenization of as-cast rare-earth magnesium alloys, belonging to the field of magnesium alloy heat treatment technology. The method includes: applying a pulsed current to the as-cast rare-earth magnesium alloy until a stable temperature is reached, then continuously applying the current, followed by disconnecting the current and cooling, to obtain a homogenized rare-earth magnesium alloy; the stable temperature is 300–520℃; the continuous energizing time is 1–300 min; the frequency of the pulsed current is 1–10000 Hz; the pulse width of the pulsed current is 1–500 μs; and the current density of the pulsed current is 1–1000 A / mm². 2 The input voltage of the preceding stage of the pulse current is 50–500V. The pulse current homogenization process described in this invention has a low temperature and a short time, which can significantly avoid coarsening of magnesium alloy grains and surface oxidation and burning, greatly reduce energy and material consumption, shorten processing time, and improve production efficiency.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy heat treatment technology, and in particular to a method for rapid homogenization treatment of cast rare earth magnesium alloys. Background Technology

[0002] Rare earth magnesium alloys generally refer to magnesium alloys containing rare earth elements. Most rare earth elements have atomic radii within ±15% of magnesium and exhibit high solid solubility in magnesium, resulting in good solid solution strengthening and precipitation strengthening effects. However, rare earth elements have high chemical reactivity, and magnesium has a low melting point, making rare earth magnesium alloys highly susceptible to burn-off during heat treatment. Currently, traditional homogenization heat treatment of as-cast rare earth magnesium alloys typically involves 12–35 hours at 510–520℃ to ensure a uniform distribution of alloying elements, suitable microstructure, and adjustment of phase composition and distribution, ultimately achieving good processing and performance characteristics. This homogenization process is not only energy-intensive and time-consuming but also leads to grain coarsening, severely affecting the alloy's plasticity. Furthermore, it results in severe surface oxidation and element burn-off (oxidation burn-off rate reaches 20%), failing to guarantee the desired performance of the rare earth magnesium alloy.

[0003] Therefore, there is an urgent need to provide a method for rapid homogenization of as-cast rare earth magnesium alloys, which can ensure that rare earth magnesium alloys have good plasticity. Summary of the Invention

[0004] The purpose of this invention is to provide a method for rapid homogenization of cast rare earth magnesium alloys. The homogenized rare earth magnesium alloy obtained by the method of this invention has fine grains and good plasticity.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for rapid homogenization of as-cast rare-earth magnesium alloys, comprising: applying a pulsed current to the as-cast rare-earth magnesium alloy until a stable temperature is reached, then continuously applying the current, followed by disconnecting the current and cooling, to obtain a homogenized rare-earth magnesium alloy; wherein the stable temperature is 350–500°C; the continuous energizing time is 1–300 min; the frequency of the pulsed current is 1–10000 Hz; the pulse width of the pulsed current is 1–500 μs; and the current density of the pulsed current is 1–1000 A / mm². 2 The input voltage of the preceding stage of the pulse current is 50–500V.

[0007] Preferably, the as-cast rare earth magnesium alloy is a Mg-Gd-Y-Zn-Zr as-cast rare earth magnesium alloy.

[0008] Preferably, the stable temperature is 350–500°C; and the continuous power-on time is 10–50 min.

[0009] Preferably, the frequency of the pulse current is 100–900 Hz.

[0010] Preferably, the pulse width of the pulse current is 10–90 μs.

[0011] Preferably, the current density of the pulse current is 50–800 A / mm². 2 .

[0012] Preferably, the input voltage of the preceding stage of the pulse current is 100–300V.

[0013] Preferably, the cooling method is air cooling to room temperature.

[0014] This invention utilizes the difference in resistivity between the second phase and the magnesium matrix in rare-earth magnesium alloys. By applying a pulsed current, both electrothermal and non-electrothermal effects are generated. The combined effect of these two factors promotes the diffusion of the second phase, making it easier for it to enter the magnesium matrix. This achieves homogenization of the rare-earth magnesium alloy and improves its plasticity. Simultaneously, by applying a pulsed current to the as-cast rare-earth magnesium alloy at a lower temperature and for a shorter time, this invention avoids problems such as grain coarsening and oxidation loss of the magnesium alloy matrix, resulting in a rare-earth magnesium alloy with uniform internal and external composition and properties that meet the target specifications. Furthermore, the method provided by this invention significantly reduces energy consumption, shortens processing time, and improves production efficiency.

[0015] The results of the examples show that the average oxide layer thickness of the homogenized rare earth magnesium alloy prepared by the method provided by the present invention is 1 / 3 of that of the traditional homogenization treatment, the second phase is small in size, the structure is uniform, and the elongation is 6.2%, which is a significant improvement compared to the initial rare earth magnesium alloy in the as-cast state. Attached Figure Description

[0016] Figure 1 This is a SEM image of the as-cast rare-earth magnesium alloy in Comparative Example 1 of this invention.

[0017] Figure 2 This is a SEM image of the rare earth magnesium alloy treated with a conventional homogenization process in Comparative Example 2 of this invention.

[0018] Figure 3 This is a SEM image of the rare earth magnesium alloy treated with pulsed current in Example 1 of the present invention;

[0019] Figure 4 This is a SEM image of the rare earth magnesium alloy treated with pulsed current in Example 2 of the present invention;

[0020] Figure 5 This is a SEM image of the rare earth magnesium alloy treated with pulsed current in Example 3 of the present invention;

[0021] Figure 6 This is a SEM image of the rare earth magnesium alloy treated with pulsed current in Example 4 of the present invention;

[0022] Figure 7 This is a SEM image of the rare earth magnesium alloy treated with pulsed current in Example 5 of the present invention;

[0023] Figure 8 This is a test image of the surface oxide layer thickness of the rare earth magnesium alloy treated by the conventional homogenization process in Comparative Example 2 of the present invention.

[0024] Figure 9 This is a test image of the oxide layer thickness of a rare earth magnesium alloy treated with pulsed current in Example 2 of the present invention;

[0025] Figure 10 The figures show the stress-strain curves of rare earth magnesium alloys in various states in Examples 1-3, Comparative Examples 1 and 2 of the present invention. Detailed Implementation

[0026] This invention provides a method for rapid homogenization of as-cast rare-earth magnesium alloys, comprising: applying a pulsed current to the as-cast rare-earth magnesium alloy until a stable temperature is reached, then continuously applying the current, followed by disconnecting the current and cooling, to obtain a homogenized rare-earth magnesium alloy; wherein the stable temperature is 300–520°C; the continuous energizing time is 1–300 min; the frequency of the pulsed current is 1–10000 Hz; the pulse width of the pulsed current is 1–500 μs; and the current density of the pulsed current is 1–1000 A / mm². 2 The input voltage of the preceding stage of the pulse current is 50–500V.

[0027] This invention involves applying a pulsed current to a stabilized temperature and then cooling the as-cast rare-earth magnesium alloy to obtain a homogenized rare-earth magnesium alloy. This invention utilizes the resistivity difference between the second phase in the rare-earth magnesium alloy and the magnesium matrix. By applying a pulsed current, both electrothermal and non-electrothermal effects are generated. Under the combined effect of these two factors, the diffusion of the second phase is promoted, making it easier for the second phase to enter the magnesium matrix, thereby achieving homogenization of the rare-earth magnesium alloy and improving its plasticity.

[0028] The method for rapid homogenization treatment of as-cast rare-earth magnesium alloys provided by this invention is applicable to all types of rare-earth magnesium alloys. In this invention, the as-cast rare-earth magnesium alloy is preferably a Mg-Gd-Y-Zn-Zr as-cast rare-earth magnesium alloy, more preferably a Mg-13Gd-4Y-2Zn-0.5Zr as-cast rare-earth magnesium alloy. When the as-cast rare-earth magnesium alloy is of the above type, the magnesium alloy matrix has a more suitable second phase, which is more conducive to obtaining a homogenized rare-earth magnesium alloy with good performance through pulsed current homogenization treatment.

[0029] In this invention, the stable temperature is 300–520°C, preferably 350–500°C; the continuous energizing time is 1–300 min, preferably 10–50 min. By controlling the stable temperature and time of the pulsed current within the above ranges, this invention can ensure that the composition and microstructure of the cast rare-earth magnesium alloy are fully homogenized, while avoiding abnormal grain growth and surface oxidation problems.

[0030] In this invention, the current density of the pulse current is 1–1000 A / mm². 2 Preferably, it is 50–800 A / mm 2 More preferably, it is 100–500 A / mm 2 This invention, by controlling the pulse current density within the aforementioned range, facilitates the rapid attainment of a stable temperature in the magnesium alloy matrix, thereby better promoting the diffusion of the second phase and making it easier for the second phase to enter the magnesium matrix. This achieves homogenization of the rare earth magnesium alloy and improves its plasticity.

[0031] In this invention, the frequency of the pulse current is 1–10000 Hz, preferably 100–900 Hz, and more preferably 300–600 Hz. By controlling the frequency of the pulse current within the above range, this invention is more conducive to achieving homogenization of rare earth magnesium alloys and improving their plasticity.

[0032] In this invention, the pulse width of the pulse current is 1–500 μs, preferably 10–90 μs, and more preferably 40–80 μs. By controlling the pulse width of the pulse current within the above range, this invention is more conducive to achieving homogenization of rare earth magnesium alloys and improving their plasticity.

[0033] In this invention, the input voltage of the preceding stage of the pulse current is 50–500V, preferably 100–300V, and more preferably 150–200V. By controlling the output voltage of the pulse current within the above range, this invention facilitates the rapid attainment of a stable temperature in the magnesium alloy substrate, preventing the stable temperature from exceeding the suitable range.

[0034] By controlling the parameters of the pulse current within the above-mentioned range, this invention can ensure that the magnesium alloy reaches its highest temperature within a stable temperature range after the pulse current is applied.

[0035] In this invention, the as-cast rare earth magnesium alloy can achieve homogenization by performing a single pulse current treatment, which has high processing efficiency.

[0036] In this invention, thermocouples are preferably used for temperature measurement during the continuous energization process. By using thermocouples for temperature measurement, this invention can monitor the stable temperature in real time and ensure that the error of the stable temperature does not exceed ±5℃.

[0037] In this invention, the preferred cooling method is air cooling to room temperature. By employing the above-mentioned cooling method, this invention can reduce stress during the cooling process while ensuring that the treated rare earth magnesium alloy quickly reaches room temperature, thus avoiding grain growth caused by residual heat during the cooling process.

[0038] The homogenized rare earth magnesium alloy obtained by the method provided by this invention has no oxidation on the surface, fine grain size, uniform structure, and good plasticity; moreover, the method provided by this invention greatly reduces energy consumption, shortens processing time, and improves production efficiency.

[0039] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] Example 1

[0041] A method for rapid homogenization of as-cast rare-earth magnesium alloys involves applying a pulsed current to the as-cast rare-earth magnesium alloy until it reaches a stable temperature, then continuously applying the current, followed by de-energizing and cooling to room temperature to obtain a homogenized rare-earth magnesium alloy. Thermocouples are used for temperature measurement during the continuous energizing process. The as-cast rare-earth magnesium alloy is Mg-13Gd-4Y-2Zn-0.5Zr as-cast rare-earth magnesium alloy. The stable temperature is 422℃. The continuous energizing time is 1 minute. The pulsed current density is 122 A / mm². 2 The frequency of the pulse current is 400Hz, the pulse width of the pulse current is 60μs, and the input voltage of the pulse current stage is 300V; the cooling method is air cooling to room temperature.

[0042] Example 2

[0043] A method for rapid homogenization of as-cast rare-earth magnesium alloys involves applying a pulsed current to the as-cast rare-earth magnesium alloy until it reaches a stable temperature, then continuously applying the current, followed by de-energizing and cooling to room temperature to obtain a homogenized rare-earth magnesium alloy. Thermocouples are used for temperature measurement during the continuous energizing process. The as-cast rare-earth magnesium alloy is a Mg-13Gd-4Y-2Zn-0.5Zr as-cast rare-earth magnesium alloy (from the same batch as the as-cast rare-earth magnesium alloy in Example 1). The stable temperature is 422℃. The energizing time is 10 minutes. The pulsed current density is 122 A / mm². 2 The frequency of the pulse current is 400Hz, the pulse width of the pulse current is 60μs, and the input voltage of the pulse current stage is 300V; the cooling method is air cooling to room temperature.

[0044] Example 3

[0045] A method for rapid homogenization of as-cast rare-earth magnesium alloys involves applying a pulsed current to the as-cast rare-earth magnesium alloy until it reaches a stable temperature, then continuously applying the current, followed by de-energizing and cooling to room temperature to obtain a homogenized rare-earth magnesium alloy. Thermocouples are used for temperature measurement during the continuous energizing process. The as-cast rare-earth magnesium alloy is a Mg-13Gd-4Y-2Zn-0.5Zr as-cast rare-earth magnesium alloy (from the same batch as the as-cast rare-earth magnesium alloy in Example 1). The stable temperature is 422℃. The continuous energizing time is 30 minutes. The pulsed current density is 122 A / mm². 2 The frequency of the pulse current is 400Hz, the pulse width of the pulse current is 60μs, and the input voltage of the pulse current stage is 300V; the cooling method is air cooling to room temperature.

[0046] Example 4

[0047] A method for rapid homogenization of as-cast rare-earth magnesium alloys involves applying a pulsed current to the as-cast rare-earth magnesium alloy until it reaches a stable temperature, then continuously applying the current, followed by de-energizing and cooling to room temperature to obtain a homogenized rare-earth magnesium alloy. Thermocouples are used for temperature measurement during the continuous energizing process. The as-cast rare-earth magnesium alloy is a Mg-13Gd-4Y-2Zn-0.5Zr as-cast rare-earth magnesium alloy (from the same batch as the as-cast rare-earth magnesium alloy in Example 1). The stable temperature is 350℃. The continuous energizing time is 300 min. The pulsed current density is 82 A / mm². 2 The frequency of the pulse current is 50Hz, the pulse width of the pulse current is 500μs, and the input voltage of the pulse current stage is 200V; the cooling method is air cooling to room temperature.

[0048] Example 5

[0049] A method for rapid homogenization of as-cast rare-earth magnesium alloys involves applying a pulsed current to the as-cast rare-earth magnesium alloy until it reaches a stable temperature, then continuously applying the current, followed by de-energizing and cooling to room temperature to obtain a homogenized rare-earth magnesium alloy. Thermocouples are used for temperature measurement during the continuous energizing process. The as-cast rare-earth magnesium alloy is a Mg-13Gd-4Y-2Zn-0.5Zr as-cast rare-earth magnesium alloy (from the same batch as the as-cast rare-earth magnesium alloy in Example 1). The stable temperature is 520℃. The continuous energizing time is 200 min. The pulsed current density is 1000 A / mm². 2 The frequency of the pulse current is 10000Hz, the pulse width of the pulse current is 2μs, and the input voltage of the pulse current is 300V; the cooling method is air cooling to room temperature.

[0050] Comparative Example 1

[0051] Untreated Mg-13Gd-4Y-2Zn-0.5Zr as-cast rare earth magnesium alloy (from the same source batch as the as-cast rare earth magnesium alloy in Example 1).

[0052] Comparative Example 2

[0053] The as-cast rare earth magnesium alloy Mg-13Gd-4Y-2Zn-0.5Zr (from the same batch as the as-cast rare earth magnesium alloy in Example 1) was homogenized using a traditional homogenization treatment method. The homogenization treatment temperature was 520℃ and the homogenization treatment time was 12h. The homogenization treatment was cooled to room temperature by air cooling.

[0054] The microstructures of the following alloys of the present invention were observed using scanning electron microscopy: Comparative Example 1 (untreated Mg-13Gd-4Y-2Zn-0.5Zr as-cast rare earth magnesium alloy), Comparative Example 2 (homogenized rare earth magnesium alloy prepared by conventional homogenization treatment), the homogenized rare earth magnesium alloy prepared in Example 1, the homogenized rare earth magnesium alloy prepared in Example 2, and the homogenized rare earth magnesium alloy prepared in Example 3. The observed microstructures are as follows: Figures 1-7 As shown; where, Figure 1 This is a SEM image of the as-cast rare-earth magnesium alloy used in Comparative Example 1 of this invention. Figure 2 SEM image of the homogenized rare earth magnesium alloy prepared by conventional homogenization treatment in Comparative Example 2. Figure 3 This is a SEM image of the homogenized rare-earth magnesium alloy prepared in Example 1 of the present invention. Figure 4 This is a SEM image of the homogenized rare-earth magnesium alloy prepared in Example 2 of the present invention;

[0055] Figure 5 This is a SEM image of the homogenized rare-earth magnesium alloy prepared in Example 3 of the present invention. Figure 6 This is a SEM image of the homogenized rare earth magnesium alloy prepared in Example 4 of the present invention. Figure 7 This is a SEM image of the homogenized rare earth magnesium alloy prepared in Example 5 of the present invention.

[0056] Depend on Figures 1-7 It can be seen that the microstructure of the cast rare earth magnesium alloy used in Comparative Example 1 has relatively coarse grains, and the precipitated phases are large in size and unevenly distributed. In contrast, the rare earth magnesium alloy prepared by the traditional homogenization treatment in Comparative Example 2 has a certain degree of improvement in the unevenness of the microstructure. The rare earth magnesium alloys prepared in Examples 2 to 5 have finer second phases and more uniform microstructures, and can exhibit better plasticity.

[0057] The thickness of the surface oxide layer of the rare earth magnesium alloy treated with the conventional homogenization process in Comparative Example 2 of this invention was tested, and the obtained surface oxide layer thickness is shown in the figure below. Figure 8As shown in the figure. The oxide layer thickness of the rare earth magnesium alloy treated with pulsed current in Example 2 of the present invention was tested, and the surface oxide layer thickness obtained by the test is shown in the figure. Figure 9 As shown.

[0058] Depend on Figures 8-9 It can be seen that the oxide layer thickness of the rare earth magnesium alloy prepared by conventional homogenization treatment in Comparative Example 2 (123 μm) is much higher than that of the rare earth magnesium alloy in Example 2 (40 μm). This demonstrates that the method provided by the present invention can avoid excessive oxidation of the surface of rare earth magnesium alloys.

[0059] Room temperature tensile tests were conducted on rare earth magnesium alloys in each state of Examples 1-3, Comparative Examples 1 and 2 of the present invention, and the stress-strain curves obtained are shown below. Figure 10 As shown. By Figure 10 It is known that the homogenized rare-earth magnesium alloy prepared by the method described in this invention has nearly the same strength (tensile strength up to 200 MPa) and ductility (elongation up to 6%) as traditional homogenized rare-earth magnesium alloys, and can even surpass traditional homogenized alloys if the parameters are properly controlled. The main reason is that under the action of a pulsed electric field, the large number of coarse and non-uniform blocky precipitates in the rare-earth magnesium alloy affect the current distribution within the material, generating a large number of high current density regions around the blocky phases. These high current density regions enhance local atomic diffusion and accelerate the dissolution of the precipitates, thereby obtaining a rare-earth magnesium alloy with good homogenization in a shorter time.

[0060] In summary, the method provided by this invention produces homogenized rare earth magnesium alloys with fine-sized second phases, uniform microstructure, and superior plasticity.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for rapid homogenization treatment of cast rare earth magnesium alloys, characterized in that, include: The pulse current is applied to the as-cast rare earth magnesium alloy to a stable temperature, then the current is continuously supplied, then the current is turned off and the alloy is cooled to obtain a homogenized rare earth magnesium alloy; the stable temperature is 422 DEG C; the time of continuously supplying the current is 10-30 min; the frequency of the pulse current is 400 Hz; the pulse width of the pulse current is 60 mu s; the current density of the pulse current is 122 A / mm 2 ; the input voltage of the pulse current is 300 V; The cast rare earth magnesium alloy is a Mg-13Gd-4Y-2Zn-0.5Zr cast rare earth magnesium alloy; The cooling method is air cooling to room temperature.

Images