Method for producing high-toughness microalloyed magnesium alloy ingots and products thereof

Abstract

The application discloses a high-toughness micro-alloyed magnesium alloy ingot preparation method, and at least comprises the following steps: a semi-continuous casting stage: a pulse magnetic field and gradient cooling coupling process is adopted, a pulse magnetic field is applied and a gradient cooling system is matched: wherein the strength of the applied pulse magnetic field is 0.1T-0.3T, and the magnetic field frequency is 50Hz-100Hz; the gradient cooling system makes the cooling rate of the upper part of the ingot be 20℃-30℃ / s, and the cooling rate of the lower part be 40℃-50℃ / s; based on the dynamic synergistic regulation of the pulse magnetic field and the gradient cooling system, segregation and edge-first solidification are inhibited, and the ingot core and surface organization homogenization is realized. The application adopts the pulse magnetic field and gradient cooling coupling process to dynamically disturb and homogenize the regulation of the melt solidification process, effectively breaks the temperature field and composition field unevenness caused by the traditional static solidification, significantly inhibits the intracrystalline and intercrystalline segregation, refines the coarse columnar crystal organization, and makes the strengthening effect of the micro-alloying element fully play.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy ingot technology, and particularly relates to a method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots and their products. Background Technology

[0002] Magnesium alloys are widely used in many fields such as aerospace, automobile manufacturing, new energy, and 3C electronics, and are one of the core materials for achieving lightweight equipment and energy conservation.

[0003] Currently, the semi-continuous casting process for this type of magnesium alloy ingot often adopts the traditional method of static solidification and single cooling rate, which has the following technical defects: First, the melt solidification is in a static accumulation state, and the temperature field and composition field are unevenly distributed, which easily leads to intragranular or intergranular segregation, coarse columnar grain growth, and cannot give full play to the strengthening effect of microalloying; Second, the single cooling rate across the entire domain is not adapted to the difference in heat conduction between the upper and lower parts of the ingot, which easily leads to excessive grain growth in the upper part and excessively fast cooling rate in the lower part, resulting in microcracks or pores. At the same time, it induces preferential solidification at the edges, resulting in uneven structure between the surface and the core of the ingot and large differences in performance. Summary of the Invention

[0004] To address the problems in the prior art, the present invention proposes the following technical solution: This invention provides a method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots, comprising at least the following steps: Semi-continuous casting stage: Employing a pulsed magnetic field coupled with gradient cooling process, applying a pulsed magnetic field in conjunction with a gradient cooling system: The intensity of the applied pulsed magnetic field is 0.1T~0.3T, and the magnetic field frequency is 50Hz~100Hz. The gradient cooling system enables the upper part of the ingot to cool at a rate of 20℃~30℃ / s and the lower part to cool at a rate of 40℃~50℃ / s. By leveraging the synergistic regulation of pulsed magnetic field and gradient cooling system, segregation and edge-preferential solidification are suppressed, thereby achieving homogenization of the ingot core and surface microstructure.

[0005] As a preferred embodiment of the above technical solution, it includes at least the following steps: Online purification process: The melt passes through a ceramic filter and is purified by argon gas injection; The ceramic filter traps oxide inclusions, and argon gas is injected to generate microbubbles. The bubbles rise, adsorb and carry gaseous impurities to the surface of the melt and escape. Ceramic filters and argon gas injection work together to remove oxide inclusions and gaseous impurities from the melt.

[0006] As a preferred embodiment of the above technical solution, the following steps are included: S1: Raw material smelting: Magnesium ingots and microalloying elements are placed in a vacuum induction melting furnace for smelting; S2: Online purification treatment; S3: Semi-continuous casting; S4: Low-temperature homogenization treatment: The ingot undergoes segmented low-temperature homogenization treatment. S5: Cooling: Allow the homogenized magnesium alloy ingot to cool naturally to room temperature.

[0007] As a preferred embodiment of the above technical solution, in step S1, the microalloying elements include Ce and Mn, wherein the Ce content is 0.2wt%~0.5wt% and the Mn content is 0.1wt%~0.3wt%.

[0008] As a preferred embodiment of the above technical solution, in step S1, the melting vacuum degree is ≤5×10-3Pa and the melting temperature is 700℃~750℃.

[0009] As a preferred embodiment of the above technical solution, in step S2, the pore size of the ceramic filter is [missing information]. The argon gas injection flow rate is 5L / min~10L / min.

[0010] As a preferred embodiment of the above technical solution, in step S4, the low-temperature homogenization treatment parameters are: first, keep warm at 280℃~320℃ for 4 to 6 hours, and then keep warm at 380℃~420℃ for 8 to 10 hours.

[0011] This invention provides a high-strength and high-toughness microalloyed magnesium alloy ingot, which is prepared by any of the preparation methods described above.

[0012] The beneficial effects of this invention are as follows: This invention employs a pulsed magnetic field coupled with gradient cooling technology. Based on the synergistic control of the pulsed magnetic field and gradient cooling system, it suppresses segregation and edge-preferential solidification, thereby achieving homogenization of the microstructure of the ingot core and surface. By applying a pulsed magnetic field of 0.1T~0.3T and 50Hz~100Hz, the solidification process of the melt can be dynamically disturbed and homogenized, effectively breaking the temperature and composition field inhomogeneity caused by traditional static solidification, significantly suppressing intragranular and intergranular segregation, refining coarse columnar grain structure, and fully leveraging the strengthening effect of microalloying elements. At the same time, in conjunction with a gradient cooling system, the upper part of the ingot is cooled at 20℃~30℃ / s and the lower part at 40℃~50℃ / s, which conforms to the heat conduction law of the upper and lower parts of the ingot. This avoids problems such as excessive grain growth in the upper part and microcracks and porosity caused by excessive cooling rate in the lower part, fundamentally improving the microstructure inhomogeneity caused by edge preferential solidification.

[0013] In the purification stage, this invention employs a combined purification process of ceramic filtration and argon gas blowing to synergistically remove oxide inclusions and gaseous impurities from the melt. The ceramic filter efficiently traps oxide inclusions in the melt, preventing them from forming stress concentrations and crack sources inside the ingot. At the same time, argon gas injection generates uniform microbubbles, which fully adsorb gaseous impurities in the melt and carry them to the surface to escape, significantly reducing the incidence of defects such as porosity and looseness. The two work together to remove solid inclusions and gaseous impurities from the melt simultaneously, greatly improving the cleanliness of the melt and providing a high-purity melt base for subsequent semi-continuous casting. This results in a denser ingot structure with fewer internal defects, further improving the yield strength and elongation after fracture of the magnesium alloy ingot and ensuring stable performance of strength and toughness. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Example 1

[0015] The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots includes the following steps: S1: Raw material smelting: Pure magnesium ingots, Ce, and Mn are added to a vacuum induction melting furnace, wherein Mg is 99.7wt%, Ce is 0.2wt%, and Mn is 0.1wt%; the smelting vacuum degree is controlled. The melting temperature is 700℃, and the temperature is held until the alloy is completely melted and the composition is uniform to obtain magnesium alloy melt. S2: Online purification process: The above-mentioned magnesium alloy melt is sequentially passed through a hole with a diameter of [missing information]. The melt is filtered by a ceramic filter and purged with argon gas at a flow rate of 5 L / min. S3: Semi-continuous casting: The pulsed magnetic field-gradient cooling coupling process is adopted. A pulsed magnetic field with an intensity of 0.1T and a frequency of 50Hz is applied, and the cooling rate of the upper part of the ingot is controlled by the gradient cooling system to be 20℃ / s and the cooling rate of the lower part is 40℃ / s. During the cooling process, a low-flow atomized cooling water ring is directly sprayed onto the upper part of the ingot, while a high-flow atomized cooling water ring is used in conjunction with air cooling at the lower part. At the same time, the solidification temperature field of the upper and lower parts of the ingot is monitored in real time by a temperature sensor.

[0016] S4: Low-temperature homogenization treatment: The above magnesium alloy ingot is subjected to segmented low-temperature homogenization treatment: first, it is kept at 280℃ for 4 hours, and then kept at 380℃ for 8 hours to achieve homogenization of the ingot structure.

[0017] S5: Cooling: The homogenized magnesium alloy ingot is naturally cooled to room temperature to obtain a high-strength and high-toughness micro-alloyed magnesium alloy ingot. Example 2

[0018] The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots includes the following steps: S1: Raw material smelting: Pure magnesium ingots, Ce, and Mn are added to a vacuum induction melting furnace, wherein Mg is 99.55wt%, Ce is 0.30wt%, and Mn is 0.15wt%; the smelting vacuum degree is controlled. The melting temperature is 710℃, and the temperature is held until the alloy is completely melted and the composition is uniform to obtain magnesium alloy melt. S2: Online purification process: The above-mentioned magnesium alloy melt is sequentially passed through a hole with a diameter of [missing information]. The melt is filtered by a ceramic filter and simultaneously purged with argon gas at a flow rate of 6 L / min. S3: Semi-continuous casting: The pulsed magnetic field-gradient cooling coupling process is adopted. A pulsed magnetic field with an intensity of 0.15T and a frequency of 60Hz is applied, and the cooling rate of the upper part of the ingot is controlled by the gradient cooling system to be 22℃ / s and the cooling rate of the lower part is 42℃ / s. During the cooling process, a low-flow atomized cooling water ring is directly sprayed onto the upper part of the ingot, while a high-flow atomized cooling water ring is used in conjunction with air cooling at the lower part. At the same time, the solidification temperature field of the upper and lower parts of the ingot is monitored in real time by a temperature sensor.

[0019] S4: Low-temperature homogenization treatment: The above magnesium alloy ingot is subjected to segmented low-temperature homogenization treatment: first, it is kept at 290℃ for 4.5 hours, and then at 390℃ for 8.5 hours to achieve homogenization of the ingot structure.

[0020] S5: Cooling: The homogenized magnesium alloy ingot is naturally cooled to room temperature to obtain a high-strength and high-toughness micro-alloyed magnesium alloy ingot. Example 3

[0021] The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots includes the following steps: S1: Raw material smelting: Pure magnesium ingots, Ce, and Mn are added to a vacuum induction melting furnace, wherein Mg is 99.45wt%, Ce is 0.35wt%, and Mn is 0.20wt%; the smelting vacuum degree is controlled. The melting temperature is 720℃, and the temperature is held until the alloy is completely melted and the composition is uniform to obtain magnesium alloy melt. S2: Online purification process: The above-mentioned magnesium alloy melt is sequentially passed through a hole with a diameter of [missing information]. The melt is filtered by a ceramic filter and simultaneously purged with argon gas at a flow rate of 8 L / min. S3: Semi-continuous casting: The pulsed magnetic field-gradient cooling coupling process is adopted. A pulsed magnetic field with an intensity of 0.2T and a frequency of 75Hz is applied, and the cooling rate of the upper part of the ingot is controlled by the gradient cooling system to be 25℃ / s and the cooling rate of the lower part is 45℃ / s. During the cooling process, a low-flow atomized cooling water ring is directly sprayed onto the upper part of the ingot, while a high-flow atomized cooling water ring is used in conjunction with air cooling at the lower part. At the same time, the solidification temperature field of the upper and lower parts of the ingot is monitored in real time by a temperature sensor.

[0022] S4: Low-temperature homogenization treatment: The above magnesium alloy ingot is subjected to segmented low-temperature homogenization treatment: first, it is kept at 300℃ for 5 hours, and then kept at 400℃ for 9 hours to achieve homogenization of the ingot structure.

[0023] S5: Cooling: The homogenized magnesium alloy ingot is naturally cooled to room temperature to obtain a high-strength and high-toughness micro-alloyed magnesium alloy ingot. Example 4

[0024] The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots includes the following steps: S1: Raw material smelting: Pure magnesium ingots, Ce, and Mn are added to a vacuum induction melting furnace, wherein Mg is 99.3 wt%, Ce is 0.45 wt%, and Mn is 0.25 wt%; the smelting vacuum degree is controlled. The melting temperature is 740℃, and the temperature is held until the alloy is completely melted and the composition is uniform to obtain magnesium alloy melt. S2: Online purification process: The above-mentioned magnesium alloy melt is sequentially passed through a hole with a diameter of [missing information]. The melt is filtered by a ceramic filter and simultaneously purged with argon gas at a flow rate of 9 L / min. S3: Semi-continuous casting: The pulsed magnetic field-gradient cooling coupling process is adopted. A pulsed magnetic field with an intensity of 0.25T and a frequency of 90Hz is applied, and the cooling rate of the upper part of the ingot is controlled by the gradient cooling system to be 28℃ / s and the cooling rate of the lower part is 48℃ / s. During the cooling process, a low-flow atomized cooling water ring is directly sprayed onto the upper part of the ingot, while a high-flow atomized cooling water ring is used in conjunction with air cooling at the lower part. At the same time, the solidification temperature field of the upper and lower parts of the ingot is monitored in real time by a temperature sensor.

[0025] S4: Low-temperature homogenization treatment: The above magnesium alloy ingot is subjected to segmented low-temperature homogenization treatment: first, it is held at 310℃ for 5.5 hours, and then held at 410℃ for 9.5 hours to achieve homogenization of the ingot structure.

[0026] S5: Cooling: The homogenized magnesium alloy ingot is naturally cooled to room temperature to obtain a high-strength and high-toughness micro-alloyed magnesium alloy ingot. Example 5

[0027] The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots includes the following steps: S1: Raw material smelting: Pure magnesium ingots, Ce, and Mn are added to a vacuum induction melting furnace, wherein Mg is 99.2 wt%, Ce is 0.50 wt%, and Mn is 0.30 wt%; the smelting vacuum degree is controlled. The melting temperature is 750℃, and the temperature is held until the alloy is completely melted and the composition is uniform to obtain magnesium alloy melt. S2: Online purification process: The above-mentioned magnesium alloy melt is sequentially passed through a hole with a diameter of [missing information]. The melt is filtered by a ceramic filter and simultaneously purged with argon gas at a flow rate of 10 L / min. S3: Semi-continuous casting: The pulsed magnetic field-gradient cooling coupling process is adopted. A pulsed magnetic field with an intensity of 0.3T and a frequency of 100Hz is applied, and the cooling rate of the upper part of the ingot is controlled by the gradient cooling system to be 30℃ / s and the cooling rate of the lower part is 50℃ / s. During the cooling process, a low-flow atomized cooling water ring is directly sprayed onto the upper part of the ingot, while a high-flow atomized cooling water ring is used in conjunction with air cooling at the lower part. At the same time, the solidification temperature field of the upper and lower parts of the ingot is monitored in real time by a temperature sensor.

[0028] S4: Low-temperature homogenization treatment: The above magnesium alloy ingot is subjected to segmented low-temperature homogenization treatment: first, it is kept at 320℃ for 6 hours, and then kept at 420℃ for 10 hours to achieve homogenization of the ingot structure.

[0029] S5: Cooling: The homogenized magnesium alloy ingot is naturally cooled to room temperature to obtain a high-strength and high-toughness micro-alloyed magnesium alloy ingot.

[0030] Comparative Example The steps are as follows: S1: Add pure magnesium ingots, Ce, and Mn into a conventional smelting furnace, wherein Mg is 99.45wt%, Ce is 0.35wt%, Mn is 0.20wt%, the smelting temperature is 720℃, and the temperature is held until the alloy is completely melted and the composition is uniform to obtain magnesium alloy melt. S2: Pass the above magnesium alloy melt through a hole with a diameter of... The filter was a regular metal filter without argon gas blowing for degassing, and only large particles were simply removed. S3: Casting is carried out without applying a pulsed magnetic field, using a single cooling rate of 25℃ / s, and naturally solidifying to obtain magnesium alloy ingots. S4: After casting, the magnesium alloy is placed directly in a room temperature environment to cool.

[0031] Mechanical properties were tested on the magnesium alloy ingot samples from Examples 1 to 5 and the comparative examples. The tensile strength and elongation were tested according to the standard GB / T 16865-2013. The specific properties are shown in Table 1 below: Table 1 As can be seen from Table 1, the high-strength and high-toughness microalloyed magnesium alloy ingots prepared in Examples 1 to 5 of this invention are significantly superior to the comparative examples in terms of the three core mechanical properties: yield strength, tensile strength, and elongation after fracture. Specific analysis is as follows: The yield strength and elongation after fracture of Examples 1 to 2 showed a steady increasing trend, while the performance of Examples 3 to 5 showed a steady decreasing trend. The data of all examples were significantly higher than those of the comparative examples.

[0032] In step S2, a high-precision ceramic filter combined with a constant-flow argon gas injection online purification method is used. By gradient optimization of the filter pore size and argon gas flow rate, efficient and simultaneous removal of solid oxide inclusions and gaseous hydrogen impurities from the magnesium alloy melt is achieved. In Examples 1 and 2, the ceramic filter pore size and argon flow rate were matched to improve melt flow efficiency while ensuring purification accuracy. The purification accuracy and flow efficiency were optimally balanced. Adapting to changes in melt composition and flow rate enabled continuous optimization of the purification effect. It removed fine inclusions and porosity hazards in the melt, preventing impurities from becoming stress concentration points and crack initiation sources when the ingot is under stress. This laid a clean melt base for subsequent casting and homogenization treatment, ensuring the synergistic improvement of the plasticity and strength of the magnesium alloy ingot from the source. Although Examples 3 to 5 further increased the argon flow rate, the filter pore size reached the upper limit of the adaptation, and the marginal improvement effect of the purification effect weakened. The magnetic field strength and cooling rate approached the adaptation threshold of magnesium alloy solidification. Excessive external field control caused micro-thermal stress inside the ingot, and the large-pore filter caused a slight decrease in purification accuracy, which together led to a slight decline in performance.

[0033] In step S3, a semi-continuous casting process coupled with pulsed magnetic field and gradient cooling is adopted. By gradient-controlling the magnetic field strength, frequency, and differential cooling rates of the upper and lower parts of the ingot, precise control of the melt solidification process is achieved. In Examples 1 and 2, the magnetic field strength and frequency were gradually increased, and the cooling rate gradient was optimized, which continuously enhanced the stirring effect of the pulsed magnetic field on the melt, effectively breaking the static accumulation state of the melt solidification, making the temperature and composition fields more uniform, suppressing intragranular segregation and coarse columnar grain growth. At the same time, the gradient cooling was adapted to the heat conduction law of the ingot, avoiding structural defects caused by single cooling, and promoting the formation of finer and more uniform equiaxed grain structure in the ingot. The grain boundary bonding strength was continuously improved, which was directly reflected in the steady increase of yield strength and elongation after fracture. In Examples 3 to 5, the magnetic field strength, frequency, and cooling rate were close to the solidification adaptation threshold of magnesium alloy. Although the excessively high external field control and cooling rate further refined the grains, they easily caused small micro-stresses to be generated inside the ingot, which were difficult to completely eliminate through subsequent processes, resulting in a steady decline in performance. In contrast, the comparative example without pulsed magnetic field control and using a single cooling rate resulted in coarse grains, severe micro-segregation, more internal porosity and defects, and significantly deteriorated mechanical properties, highlighting the core role of the coupled casting process of this technology in improving performance.

[0034] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it.

Claims

1. A method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots, characterized in that, At least the following steps are included: Semi-continuous casting stage: Employing a pulsed magnetic field coupled with gradient cooling process, applying a pulsed magnetic field in conjunction with a gradient cooling system: The intensity of the applied pulsed magnetic field is 0.1T~0.3T, and the magnetic field frequency is 50Hz~100Hz. The gradient cooling system enables the upper part of the ingot to cool at a rate of 20℃~30℃ / s and the lower part to cool at a rate of 40℃~50℃ / s. By leveraging the synergistic regulation of pulsed magnetic field and gradient cooling system, segregation and edge-preferential solidification are suppressed, thereby achieving homogenization of the ingot core and surface microstructure.

2. The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots according to claim 1, characterized in that, At least the following steps are included: Online purification process: The melt passes through a ceramic filter and is purified by argon gas injection; The ceramic filter traps oxide inclusions, and argon gas is injected to generate microbubbles. The bubbles rise, adsorb and carry gaseous impurities to the surface of the melt and escape. Ceramic filters and argon gas injection work together to remove oxide inclusions and gaseous impurities from the melt.

3. The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots according to claim 1 or 2, characterized in that, Includes the following steps: S1: Raw material smelting: Magnesium ingots and microalloying elements are placed in a vacuum induction melting furnace for smelting; S2: Online purification treatment; S3: Semi-continuous casting; S4: Low-temperature homogenization treatment: The ingot undergoes segmented low-temperature homogenization treatment. S5: Cooling: Allow the homogenized magnesium alloy ingot to cool naturally to room temperature.

4. The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots according to claim 3, characterized in that, In step S1, the microalloying elements include Ce and Mn, wherein the Ce content is 0.2wt%~0.5wt% and the Mn content is 0.1wt%~0.3wt%.

5. The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots according to claim 3, characterized in that, In step S1, the melting vacuum degree The melting temperature is 700℃~750℃.

6. The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots according to claim 3, characterized in that, In step S2, the pore size of the ceramic filter is The argon gas injection flow rate is 5L / min~10L / min.

7. The method for preparing high-strength and high-toughness microalloyed magnesium alloy ingots according to claim 3, characterized in that, In step S4, the low-temperature homogenization treatment parameters are: first, keep at 280℃~320℃ for 4 to 6 hours, and then keep at 380℃~420℃ for 8 to 10 hours.

8. A high-strength, high-toughness microalloyed magnesium alloy ingot, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 7.

Images