Method for preparing microalloyed AZ31 magnesium alloy through ultrasonic treatment

Abstract

The invention belongs to the field of material processing, and discloses a method for preparing microalloyed AZ31 magnesium alloy by ultrasonic treatment, which comprises the following steps: melting magnesium at 715-725 DEG C, keeping the temperature for 5-8 minutes, then heating to 725-735 DEG C, then adding Mg-50% Al intermediate alloy, after Mg-50% Al is completely melted, keeping the temperature for 8-12 minutes, slagging off, stirring to completely dissolve Mg-50% Al, continuously keeping the temperature at 725-735 DEG C, adding pure zinc, and stirring to obtain the microalloyed AZ31 magnesium alloy. After the pure zinc is completely molten, carrying out heat preservation for 8-12 minutes, then carrying out slagging-off and stirring to completely dissolve the pure zinc, finally adding Mg-30% Ca and Mg-30% Ce intermediate alloys, carrying out heat preservation for 8-12 minutes, and carrying out stirring to completely dissolve the Mg-30% Ca and Mg-30% Ce intermediate alloys to obtain an alloy melt; the alloy melt is cooled to 655-665 DEG C, heat preservation is conducted for 20-25 minutes, then an ultrasonic treatment tool head stretches into the position 18-22 mm below the liquid level of the alloy melt for ultrasonic treatment, the ultrasonic treatment power is 300-700 W, and the treatment time is 60-120 seconds; and casting and molding under a protective atmosphere to obtain a casting blank. According to the method, the problem of slow diffusion in the casting process is solved through ultrasonic treatment, the structure is homogenized, and the strength of the structure is obviously enhanced.

Description

Technical Field

[0001] The invention belongs to the field of material processing and relates to a method for preparing a microalloyed AZ31 magnesium alloy by utilizing ultrasonic treatment. Background Art

[0002] As a lightweight, high-strength metal material, magnesium alloys are widely used in aerospace, automobiles, electronic products, etc. However, as the most widely used commercial magnesium alloy, the mechanical properties of Mg-Al alloys are still insufficient in the application of large load-bearing components.

[0003] Adding trace elements for microalloying is a key means to improve the strength and toughness of magnesium alloys. This involves the synergistic effect of multiple trace elements and mechanisms. Trace elements affect the microstructures of magnesium alloys, such as grain boundaries, phase changes, and dislocations, and optimize the properties of the alloy. Trace elements such as rare earth elements, transition elements, carbon, and nitrogen interact with matrix elements, affect atomic arrangement and crystal structure, stabilize the matrix phase, change phase composition or induce new phase changes, and achieve microstructural optimization. Trace elements change the crystallization process during solidification, affect the nucleation and growth of grains, and thus control grain size and phase composition. During deformation, trace elements interact with dislocations to hinder dislocation movement, improve the tensile strength and elongation of the material, and pin dislocations by forming second phase particles, thereby enhancing the strength and toughness of the alloy.

[0004] In the microalloying research of magnesium alloys, rare earth elements and Ca elements have received extensive attention due to their unique properties. Heavy rare earth elements have a high solid solubility in magnesium alloys, but their high price limits their large-scale use. Relatively speaking, light rare earth elements such as Ce have received more attention due to their low cost and only a small amount of addition can significantly improve the performance of magnesium alloys. Studies have shown that the effect of a small amount of Ca on the texture of magnesium alloy rolled plates exhibits similar characteristics to rare earth elements, which provides a new idea for the development of low-cost, high-performance magnesium alloys.

[0005] However, the alloying elements and their compounds diffuse slowly during the melting and casting process, causing the alloying elements to produce coarse particles and intermetallic compounds in the grains and grain boundaries before the saturated solid solubility. These coarse compounds are difficult to improve by heat treatment. Only a small part of the alloying elements enters the α-Mg matrix, and most of them remain at the grain boundaries, presenting needle-like phases and discontinuous network phases, resulting in uneven distribution of tissues, which seriously affects the mechanical properties. Therefore, improving the dissolution and distribution of alloying elements in AZ31 magnesium alloy is crucial to improving the overall performance. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing microalloyed AZ31 magnesium alloy by ultrasonic treatment. The present invention aims to overcome the problem of slow diffusion of elements and their compounds in the microalloyed AZ31 magnesium alloy during the melting and casting process through ultrasonic treatment, resulting in poor room temperature forming performance and insufficient extrusion speed.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A method for preparing microalloyed AZ31 magnesium alloy by ultrasonic treatment comprises the following steps: Melting process: melt magnesium at 715-725℃, keep it warm for 5-8min, then heat it to 725-735℃, add Mg-50%Al master alloy, keep it warm for 8-12min, then skim off the slag, stir to make the Mg-50%Al master alloy completely dissolved, keep the temperature at 725-735℃, add pure zinc, keep it warm for 8-12min, then skim off the slag, stir to make the pure zinc completely dissolved, finally add Mg-30%Ca and Mg-30%Ce master alloy, keep it warm for 8-12min, stir to make the Mg-30%Ca and Mg-30%Ce master alloy completely dissolved, and obtain alloy melt; Ultrasonic treatment: cool the alloy melt to 655-665°C and keep it warm for 20-25 minutes, then insert the ultrasonic treatment tool head into the alloy melt 18-22mm below the liquid surface for ultrasonic treatment. The ultrasonic treatment power is 300-700W and the treatment time is 60-120 seconds. Casting process: Casting is carried out under a protective atmosphere to obtain a casting.

[0008] Preferably, 5-8 minutes after the casting is completed, the mold is opened to take out the ingot and the ingot is water-cooled.

[0009] Preferably, before casting, the casting mold is heated to 245-255° C., and then casting is performed under a protective atmosphere.

[0010] Preferably, the process of pre-treating the raw materials is also included before the smelting process: the oxide layer on the surface of all raw materials is polished off to make the surface silvery white; The pre-treated raw materials are weighed and used for smelting.

[0011] Preferably, the protective atmosphere during the casting process is a mixed protective atmosphere of CO2 and SF6.

[0012] Preferably, in the mixed protective atmosphere, the volume ratio of CO2 and SF6 is 97:3~99:1.

[0013] The present invention also provides a microalloyed AZ31 magnesium alloy prepared by the preparation method of the present invention as described above, wherein the components thereof, measured by mass percentage, include: Al: 2.5%~3.5%, Zn: 0.5%~1.5%, Ca: 0-0.2%, Ce: 0-0.12%, the balance is magnesium and inevitable impurities, and the contents of Ca and Ce are not zero at the same time.

[0014] Preferably, the impurity content is ≤0.1%.

[0015] Preferably, the microalloyed AZ31 magnesium alloy has a tensile strength of 125-245 MPa and an elongation of 6.8%-15.5%.

[0016] The microalloyed AZ31 magnesium alloy of the present invention as described above is used to prepare industrial fan profiles and track ventilation grille profiles, and the average extrusion speed thereof is not less than 4 m / min.

[0017] Compared with the prior art, the beneficial effects of the present invention include: The present invention solves the problem of slow diffusion of alloying elements and their compounds added during the melting and casting process of microalloyed AZ31 magnesium alloy through ultrasonic treatment, and significantly improves the diffusion efficiency. The room temperature forming performance of the magnesium alloy is improved, and the problem of poor forming performance in traditional processes is overcome, so that the magnesium alloy can also have good processing performance at room temperature. The proposed low-cost, high-performance magnesium alloy preparation process solves the problem of insufficient extrusion speed in the prior art, and greatly improves production efficiency. The AZ31 magnesium alloy prepared by the process of the present invention has a refined and uniform grain structure, which significantly improves the comprehensive performance of the material. The preparation process of the present invention has the advantage of low cost while maintaining high performance, and is suitable for large-scale industrial production. It solves the problem of single strengthening method (such as β-Mg 17 Al 12 The limitations of phase or precipitation strengthening) are overcome, and the comprehensive properties of magnesium alloys, especially high temperature mechanical properties and creep resistance, are improved. The magnesium alloy material of the present invention is suitable for manufacturing parts requiring higher load-bearing capacity, and broadens the application field of magnesium alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of an ultrasonic device used in the present invention; FIG2 (a) is a grain size photograph of AZ31-0.2Ca-0.12Ce in comparative example 3 without ultrasonic treatment; FIG2 (b) is a grain size photograph of AZ31-0.2Ca-0.12Ce in example 5 of the present invention after ultrasonic treatment at 500W for 90s; FIG3 (a) is a scanning image of the second phase distribution of AZ31-0.2Ca-0.12Ce without ultrasonic treatment in comparative example 3; FIG3 (b) is a scanning image of the second phase distribution of AZ31-0.2Ca-0.12Ce after ultrasonic treatment at 500W for 90s in Example 5 of the present invention; FIG4 (a) is a graph showing the mechanical properties test results of magnesium alloys of Example 3, Example 4, Example 5, Example 10, Example 11, Example 12, and Example 13 of the present invention; FIG4( b ) is an enlarged view of portion A of FIG4( a ).

[0019] In the figure, 1-ultrasonic generator; 2-crucible; 3-horn; 4-resistance furnace; 5-furnace cover; 6-thermocouple; 7-SF6 and CO2 inlet pipe; 8-bracket; 9-ultrasonic transducer. DETAILED DESCRIPTION

[0020] According to the technical solution of the present invention, without changing the essential spirit of the present invention, a person skilled in the art can propose a variety of interchangeable structures and implementations. Therefore, the following specific implementation methods and drawings are only examples of the technical solution of the present invention and should not be regarded as the entirety of the present invention or the limitation of its technical solution.

[0021] The invention proposes a low-cost, high-performance magnesium alloy preparation process, thereby improving the quality of AZ31 magnesium alloy and obtaining a grain-refined, uniform ingot structure. Specifically, it is a method for improving the mechanical properties of Ca and Ce-containing microalloyed AZ31 magnesium alloy by ultrasonic treatment.

[0022] Specifically, the present invention takes AZ31 cast magnesium alloy as the object, uses Ca and Ce for microalloying treatment, and applies ultrasonic treatment process during smelting to study its influence on alloy structure and mechanical properties. Ultrasonic treatment can give full play to the strengthening effect of microalloying elements to obtain microalloyed AZ31 magnesium alloy with excellent mechanical properties.

[0023] The microalloyed AZ31 magnesium alloy of the present invention comprises, by weight percentage, aluminum: 2.5% to 3.5%, zinc: 0.5% to 1.5%, Ca: 0-0.2%, Ce: 0-0.12%, the remainder being magnesium and unavoidable impurities, and the impurity content is ≤0.1%. The sum of the contents of Ca and Ce is not greater than 0.4%, and the contents of Ca and Ce are not zero at the same time.

[0024] Combination Figure 1 The preparation process of the microalloyed AZ31 magnesium alloy of the present invention is as follows: Ingredients: Considering the burning and volatilization of alloy elements in the actual smelting process, the addition amount of alloy elements is adjusted according to a certain yield. The yields of aluminum, zinc, Ca and Ce are 95%~97%, 96%~98%, 75%~90% and 75%~90% respectively. 99.9% pure magnesium, Mg-50%Al, 99.9% pure zinc, Mg-30%Ca and Mg-30%Ce master alloys are squeezed into pieces by a 300-ton hydraulic press for weighing and unloading.

[0025] Polishing: Polish off the oxide layer on the surface of all raw materials to make the surface silvery white. After polishing, weigh them strictly according to the calculated mass and put them into the sample bag marked with numbers to prevent the raw materials from being mixed up.

[0026] Preheating: Preheat and dry all smelting tools and raw materials before use to prevent moisture from entering and avoid explosions and other hazards during the smelting process.

[0027] Melting: First heat the melting furnace crucible to 720±5℃, then put the weighed 99.9% magnesium in, heat to 720±5℃, wait for it to be completely melted, raise the temperature to 730±5℃ after 5~8 minutes, add Mg-50% aluminum master alloy, wait for it to be completely melted, keep warm for 8 minutes, carefully skim the slag, and then stir quickly to completely dissolve the Mg-50% aluminum master alloy. Keep the temperature at 730±5℃, add 99.9% pure zinc, repeat the above operation, and finally add Mg-30%Ca and Mg-30%Ce master alloys, keep warm for 8~12 minutes, and stir quickly to fully dissolve the Mg-30%Ca and Mg-30%Ce master alloys to avoid burning caused by excessive temperature. Carefully skim the slag and stir before each discharge to prevent impurities from mixing into the melt.

[0028] Ultrasonic treatment: After smelting, cool the melt to 660±5℃ and keep it warm for 20-25 minutes. After the alloy melt is stable, insert the ultrasonic treatment tool head from the top of the crucible into the alloy liquid 18-22mm below the surface for ultrasonic treatment. The selected ultrasonic treatment power is 300~700W, and the treatment time is 60~120 seconds.

[0029] Casting: Preheat the forming mold to 250±5℃ before casting, then cast the alloy liquid steadily at the casting port of the mold after standing and cooling, and use a mixed protective atmosphere of CO2 and SF6 to prevent the alloy from oxidizing. 5-8 minutes after the casting is completed, open the mold to take out the ingot and immediately water-cool it to obtain a magnesium alloy ingot. If a metal cylindrical mold is used, a magnesium alloy ingot rod is obtained after molding. A mixed gas of CO2 and SF6 is always introduced during the casting process, with a volume ratio of 97:3~99:1.

[0030] Ingot treatment: Mark the solidified ingot, and consider the precipitation of impurities. Use a saw to cut off the tail and discard it. Grind a small amount of metal powder from each alloy component with a knife and put it into a sample bag for chemical composition testing.

[0031] In the above scheme, ultrasonic treatment is a pollution-free and efficient grain refinement technology that can significantly refine the solidification structure of the alloy without introducing impurities. Due to the cavitation effect and acoustic streaming effect, ultrasonic treatment forms a series of ultrasonic cavitation bubbles inside the melt. The cavitation bubbles absorb energy from the melt, resulting in local supercooling and nucleation of the intermetallic phase on the bubble surface. When the cavitation bubbles burst, the surrounding melt instantly generates high temperature and high pressure, which disperses the nucleation particles and promotes a more uniform distribution of the intermetallic phase.

[0032] In the above scheme, the temperature deviation of the heating device is ±5°C. In the following embodiments of the present invention, only the set value of the corresponding temperature is given, but in actual operation, the actual temperature is within the range of ±5°C of the design value. In the ultrasonic treatment process, the ultrasonic treatment tool head is inserted from the top of the crucible into the alloy liquid surface 20mm below the surface for ultrasonic treatment. Due to the fluctuation of the liquid surface, there will be a deviation of ±2mm during the actual experiment. Therefore, the actual position of the ultrasonic treatment tool head below the alloy liquid surface is 18-22mm. In the following embodiments of the present invention, only the set value of 20mm of the ultrasonic treatment tool head below the alloy liquid surface is given, but it is actually 18-22mm.

[0033] Example 1 This embodiment provides a Ca-containing microalloyed AZ31 magnesium alloy, the preparation process of which is as follows: S1. Weigh the raw materials, which include 99.9% pure magnesium, 99.9% pure zinc, Mg-30% Ca master alloy, and Mg-50% Al master alloy.

[0034] S2. Carry out surface treatment on the raw materials, weigh them twice, and seal them in numbered sample bags for storage.

[0035] S3. Place the smelting tools and raw materials into a heated smelting furnace for preheating and drying.

[0036] S4. Heat the smelting furnace to 720℃, put the weighed 99.9%Mg into the smelting furnace and heat it to 720℃. After Mg is completely melted, keep it warm for 8 minutes and then heat it to 730℃, put in Mg-50%Al intermediate alloy, after Mg-50%Al intermediate alloy is completely melted, keep it warm for 10 minutes and then skim off the slag, and stir to completely dissolve the Mg-50%Al intermediate alloy, continue to keep the temperature at 730℃, put in 99.9%Zn pure zinc, repeat the above operation, and finally add Mg-30%Ca intermediate alloy, keep it warm for 10 minutes, and stir to completely dissolve the Mg-30%Ca intermediate alloy.

[0037] S5. After smelting, cool the melt to 660°C and keep it warm for 20 minutes. After the alloy melt stabilizes, insert the ultrasonic treatment tool head from the top of the crucible into the alloy liquid 20mm below the surface for ultrasonic treatment. The selected ultrasonic treatment power is 300W and the treatment time is 60s.

[0038] S6. Under a protective gas atmosphere, the alloy liquid after standing and cooling is steadily poured into a molding mold preheated to 250°C at the casting port of the casting mold. After waiting for 5 minutes, the mold is opened to take out the formed alloy and immediately water-cool it to obtain a magnesium alloy ingot; wherein, the protective gas is a mixed gas of CO2 and SF6, and the volume ratio of CO2 to SF6 is 99:1.

[0039] S7. Perform tail cutting on the magnesium alloy ingot and mark and take samples for chemical composition testing.

[0040] Example 2 This embodiment provides a Ce-containing microalloyed AZ31 magnesium alloy, the preparation process of which is as follows: S1. Weigh the raw materials, which include 99.9% pure zinc, 99.9% Zn pure zinc, Mg-30% Ce master alloy, and Mg-50% Al master alloy.

[0041] S2. Carry out surface treatment on the raw materials, weigh them twice, and seal them in numbered sample bags for storage.

[0042] S3. Place the smelting tools and raw materials into a heated smelting furnace for preheating and drying.

[0043] S4. Heat the smelting furnace to 720℃, put the weighed 99.9%Mg into the smelting furnace and heat it to 720℃. After Mg is completely melted, keep it warm for 5 minutes and then heat it to 730℃. Put in Mg-50%Al intermediate alloy. After the Mg-50%Al intermediate alloy is completely melted, keep it warm for 8 minutes and then remove the slag. Stir it again to make the Mg-50%Al intermediate alloy completely dissolved. Keep the temperature at 730℃, put in 99.9%Zn pure zinc, repeat the above operation, and finally add Mg-30%Ce intermediate alloy. Keep it warm for 8 minutes and stir it to make the Mg-30%Ce intermediate alloy completely dissolved.

[0044] S5. After smelting, cool the melt to 660°C and keep it warm for 20 minutes. After the alloy melt stabilizes, insert the ultrasonic treatment tool head from the top of the crucible into the alloy liquid 20mm below the surface for ultrasonic treatment. The selected ultrasonic treatment power is 300W and the treatment time is 90s.

[0045] S6. Under a protective gas atmosphere, the alloy liquid after being allowed to cool down is steadily poured into a molding mold preheated to 250°C at the casting port of the casting mold. After waiting for 5 minutes, the mold is opened to take out the formed alloy and immediately water-cool it to obtain a magnesium alloy ingot; wherein, the protective gas is a mixed gas of CO2 and SF6, and the volume ratio of CO2 to SF6 is 98:2.

[0046] S7. Perform tail cutting on the magnesium alloy ingot and mark and take samples for chemical composition testing.

[0047] Example 3 This embodiment provides a microalloyed AZ31 magnesium alloy containing Ca and Ce, and the preparation process thereof is as follows: S1. Weigh the raw materials, which include 99.9% pure zinc, 99.9% Zn pure zinc, Mg-30% Ca master alloy, Mg-30% Ce master alloy, and Mg-50% Al master alloy.

[0048] S2. Carry out surface treatment on the raw materials, weigh them twice, and seal them in numbered sample bags for storage.

[0049] S3. Place the smelting tools and raw materials into a heated smelting furnace for preheating and drying.

[0050] S4. Heat the smelting furnace to 720℃, put the weighed 99.9%Mg into the smelting furnace and heat it to 720℃. After Mg is completely melted, keep it warm for 7min and then heat it to 730℃. Put in Mg-50%Al intermediate alloy. After Mg-50%Al intermediate alloy is completely melted, keep it warm for 12min and then skim off the slag. Stir again to make the Mg-50%Al intermediate alloy completely dissolved. Keep the temperature at 730℃, put in 99.9%Zn pure zinc, repeat the above operation, finally add Mg-30%Ca and Mg-30%Ce intermediate alloys, keep it warm for 12min and stir to make the Mg-30%Ca and Mg-30%Ce intermediate alloys completely dissolved.

[0051] S5. After smelting, cool the melt to 660°C and keep it warm for 20 minutes. After the alloy melt stabilizes, insert the ultrasonic treatment tool head from the top of the crucible into the alloy liquid 20mm below the surface for ultrasonic treatment. The selected ultrasonic treatment power is 300W and the treatment time is 90s.

[0052] S6. Under a protective gas atmosphere, the alloy liquid after being allowed to cool down is steadily poured into a molding mold preheated to 250°C at the casting port of the casting mold. After waiting for 5 minutes, the mold is opened to take out the formed alloy and immediately water-cool it to obtain a magnesium alloy ingot; wherein, the protective gas is a mixed gas of CO2 and SF6, and the volume ratio of CO2 to SF6 is 97:3.

[0053] S7. Perform tail cutting on the magnesium alloy ingot and mark and take samples for chemical composition testing.

[0054] Example 4 This embodiment provides a Ce-containing microalloyed AZ31 magnesium alloy. The preparation processes S1-S4 and S6-S7 are the same as those in Example 2, and the ultrasonic power of the preparation process S5 is 500 W and the processing time is 60 s.

[0055] Example 5 This embodiment provides a microalloyed AZ31 magnesium alloy containing Ca and Ce. The preparation processes S1-S4 and S6-S7 are the same as those in Example 3. The ultrasonic power of the preparation process S5 is 500 W and the processing time is 90 s.

[0056] Example 6 This embodiment provides a Ca-containing microalloyed AZ31 magnesium alloy. The preparation processes S1-S4 and S6-S7 are the same as those in Example 1, and the ultrasonic power of the preparation process S5 is 500 W and the processing time is 120 s.

[0057] Example 7 This embodiment provides a microalloyed AZ31 magnesium alloy containing Ca and Ce. The preparation process S1-S4 and S6-S7 are the same as those in Example 3. The ultrasonic power of the preparation process S5 is 700 W and the processing time is 60 s.

[0058] Example 8 This embodiment provides a Ca-containing microalloyed AZ31 magnesium alloy. The preparation processes S1-S4 and S6-S7 are the same as those in Example 1. The ultrasonic power of the preparation process S5 is 700 W and the processing time is 90 s.

[0059] Example 9 This embodiment provides a Ce-containing microalloyed AZ31 magnesium alloy. The preparation processes S1-S4 and S6-S7 are the same as those in Example 2, and the ultrasonic power of the preparation process S5 is 700 W and the processing time is 120 s.

[0060] Example 10 This embodiment provides a microalloyed AZ31 magnesium alloy containing Ca and Ce. The preparation processes S1-S4 and S6-S7 are the same as those in Example 3, and the ultrasonic power of the preparation process S5 is 300 W and the processing time is 90 s.

[0061] Embodiment 11 This embodiment provides a microalloyed AZ31 magnesium alloy containing Ca and Ce. The preparation processes S1-S4 and S6-S7 are the same as those in Example 1, and the ultrasonic power of the preparation process S5 is 700 W and the processing time is 90 s.

[0062] Example 12 This embodiment provides a microalloyed AZ31 magnesium alloy containing Ca and Ce. The preparation processes S1-S4 and S6-S7 are the same as those in Example 1, and the ultrasonic power of the preparation process S5 is 500 W and the processing time is 60 s.

[0063] Embodiment 13 This embodiment provides a microalloyed AZ31 magnesium alloy containing Ca and Ce. The preparation processes S1-S4 and S6-S7 are the same as those in Example 1, and the ultrasonic power of the preparation process S5 is 500 W and the processing time is 120 s.

[0064] Comparative Example 1 This comparative example provides a Ca-containing microalloyed AZ31 magnesium alloy, the preparation processes S1-S4 and S6-S7 of which are the same as those in Example 1, and there is no preparation process S5.

[0065] Comparative Example 2 This comparative example provides a Ce-containing microalloyed AZ31 magnesium alloy. The preparation processes S1-S4, S6-S7 are the same as those in Example 2, and the preparation process is S5.

[0066] Comparative Example 3 This comparative example provides a microalloyed AZ31 magnesium alloy containing Ca and Ce. The preparation processes S1-S4 and S6-S7 are the same as those in Example 1, and there is no preparation process S5.

[0067] Comparative Example 4 This comparative example provides an AZ31 magnesium alloy without any treatment, and the preparation process thereof comprises: S1. Weigh the raw materials, which include 99.9% pure zinc, 99.9% Zn pure zinc, and Mg-50% Al master alloy.

[0068] S2. Carry out surface treatment on the raw materials, weigh them twice, and seal them in numbered sample bags for storage.

[0069] S3. Place the smelting tools and raw materials into a heated smelting furnace for preheating and drying.

[0070] S4. Heat the smelting furnace to 720℃, put the weighed 99.9%Mg into the smelting furnace and heat it to 720℃. After Mg is completely melted, keep it warm for 6 minutes and then heat it to 730℃. Put in Mg-50%Al intermediate alloy. After Mg-50%Al intermediate alloy is completely melted, keep it warm for 10 minutes and then skim off the slag. Stir again to make the Mg-50%Al intermediate alloy completely dissolved. Keep the temperature at 730℃ and put in 99.9%Zn pure zinc. Repeat the above operation to make the zinc completely dissolved.

[0071] S5. Under a protective gas atmosphere, the alloy liquid after standing and cooling is steadily poured into a molding mold preheated to 250°C at the casting port of the casting mold. After waiting for 5 minutes, the mold is opened to take out the formed alloy and immediately water-cool it to obtain a magnesium alloy ingot; wherein, the protective gas is a mixed gas of CO2 and SF6, and the volume ratio of CO2 to SF6 is 99:1.

[0072] S6. Perform tail cutting on the magnesium alloy ingot and mark and take samples for chemical composition testing.

[0073] It should be noted that the comparative examples are microalloyed AZ31-0.04Ca magnesium alloy, AZ31-0.08Ce, magnesium alloy AZ31-0.2Ca-0.12Ce magnesium alloy, and AZ31 magnesium alloy, all of which have no ultrasonic treatment process.

[0074] In summary, the ultrasonic treatment process parameters and component detection (wt.%) of Examples 1 to 13 and Comparative Examples 1 to 4 are shown in Table 1: Table 1 Experiment number Ultrasonic power / W Processing time / s Mg Al Zn Ca Ce Fe C Example 1 300 60 Bal. 3.00 1.00 0.04 - 0.004 0.001 Example 2 300 90 Bal. 3.00 1.00 - 0.08 0.006 0.001 Example 3 300 120 Bal. 3.00 1.00 0.20 0.12 0.006 0.003 Example 4 500 60 Bal. 3.00 1.00 - 0.08 0.006 0.002 Example 5 500 90 Bal. 3.00 1.00 0.20 0.12 0.007 0.002 Example 6 500 120 Bal. 3.00 1.00 0.04 - 0.002 0.001 Example 7 700 60 Bal. 3.00 1.00 0.20 0.12 0.004 0.002 Example 8 700 90 Bal. 3.00 1.00 0.04 - 0.005 0.002 Example 9 700 120 Bal. 3.00 1.00 - 0.08 0.006 0.003 Example 10 300 90 Bal. 3.00 1.00 0.20 0.12 0.004 0.003 Embodiment 11 700 90 Bal. 3.00 1.00 0.20 0.12 0.006 0.002 Example 12 500 60 Bal. 3.00 1.00 0.20 0.12 0.006 0.002 Embodiment 13 500 120 Bal. 3.00 1.00 0.20 0.12 0.005 0.002 Comparative Example 1 - - Bal. 3.00 1.00 0.04Ca - 0.005 0.002 Comparative Example 2 - - Bal. 3.00 1.00 - 0.08Ce 0.006 0.001 Comparative Example 3 - - Bal. 3.00 1.00 0.20 0.12 0.007 0.002 Comparative Example 4 - - Bal. 3.00 1.00 - - 0.008 0.001 An X-ray fluorescence spectrometer (XRF) was used to analyze the components of Examples 1 to 5 and the comparative materials to ensure that the component content met the requirements within the error range. Subsequently, the electric spark cutting method was used to take samples to obtain tensile specimens, and the electric spark cutting affected layer was removed with sandpaper. The samples were polished with 400 mesh, 600 mesh, 800 mesh, 1200 mesh and 2000 mesh sandpaper in turn, and polished. Next, a microcomputer-controlled electronic universal testing machine was used to test the tensile strength and elongation at a speed of 0.5 mm / min. The tensile strength and elongation data of each embodiment and comparative example are shown in Table 2: Table 2 NO. Ultrasonic power / W Processing time / s ω(Ca-Ce)% Tensile strength (MPa) Elongation (%) Example 1 300 60 0.04Ca 125.48 6.81% Example 2 300 90 0.08Ce 193.56 14.88% Example 3 300 120 0.2Ca-0.12Ce 164.52 11.48% Example 4 500 60 0.08Ce 230.57 9.73% Example 5 500 90 0.2Ca-0.12Ce 217.89 11.44% Example 6 500 120 0.04Ca 242.11 12.08% Example 7 700 60 0.2Ca-0.12Ce 244.84 12.91％ Example 8 700 90 0.04Ca 235.67 15.28％ Example 9 700 120 0.08Ce 178.31 10.64％ Example 10 300 90 0.2Ca-0.12Ce 160.6 9.97% Embodiment 11 700 90 0.2Ca-0.12Ce 204 15.14% Example 12 500 60 0.2Ca-0.12Ce 162 9.9% Embodiment 13 500 120 0.2Ca-0.12Ce 161.2 9.6% Comparative Example 1 - - 0.04Ca 147 6.0% Comparative Example 2 - - 0.08Ce 155 6.0% Comparative Example 3 - - 0.2Ca-0.12Ce 150.2 7.8% Comparative Example 4 - - - 122.98 6.8% Through the above analysis, we know that in terms of strength index, the order of priority of each factor is: ultrasonic power → ultrasonic time → micro-alloy element content; and the optimal solution is: 0.2Ca-0.12Ce, ultrasonic treatment power 500w, ultrasonic treatment time 90s.

[0075] As can be seen from Table 2, the effects of ultrasonic treatment time, ultrasonic power and microalloy content on the properties of the alloy were systematically studied. The elongation of Examples 1-9 was compared and analyzed. The experimental results showed that the average elongation was 12.943% under the influence of 700W ultrasonic power; the average elongation was 13.867% under the influence of 90s ultrasonic time; the average elongation was 11.943% under the influence of microalloying element content of 0.2Ca-0.12Ce; Through the above analysis, we know that in terms of strength index, the order of priority of each factor is: ultrasonic time → ultrasonic power → micro-alloy element content; and the optimal solution is: 0.2Ca-0.12Ce, ultrasonic treatment power 700w, ultrasonic treatment time 90s.

[0076] By comparing Example 5, Example 12 and Example 13, the effect of ultrasonic time on tensile strength and elongation was analyzed.

[0077] As for the ultrasonic treatment time, under 500 W ultrasonic power, the tensile strength reaches a maximum value of 217 MPa at a treatment time of 90 seconds, and is 162 MPa and 161.2 MPa at 60 and 120 seconds, respectively. The elongation reaches a maximum value of 10.75% at a treatment time of 90 seconds, and is 9.9% and 9.6% at 60 and 120 seconds, respectively.

[0078] By comparing Example 5, Example 10 and Example 11, the effect of ultrasonic power on tensile strength and elongation was analyzed.

[0079] For ultrasonic power, under 90 seconds of treatment time, the tensile strength reaches a maximum value of 217 MPa at 500 W ultrasonic power, and is 160.6 MPa and 204 MPa at 300 W and 700 W ultrasonic powers, respectively. The elongation increases with the increase of ultrasonic power, reaching a maximum value of 15.14% at 700 W.

[0080] In summary, the combination of appropriate ultrasonic power and treatment time (such as 500W, 90s) can significantly improve the mechanical properties of 0.2Ca-0.12Ce alloy, which is specifically manifested in the significant improvement of tensile strength and compressive strength. At the same time, the elongation reaches the maximum value when the ultrasonic power is higher (700W). Optimizing ultrasonic treatment parameters is of great significance for improving the performance of alloy materials.

[0081] Compare Example 4 with Comparative Example 1 and Comparative Example 4.

[0082] Ultrasonic treatment increased the tensile strength of AZ31-0.04Ca by 64.7% and the elongation by 101%. Compared with the untreated AZ31, the tensile strength increased by 96.8% and the elongation increased by 77.6%.

[0083] Compare Example 6 with Example 2 and Example 4.

[0084] Ultrasonic treatment increased the tensile strength of AZ31-0.08Ce by 48.7% and the elongation by 62.1%. Compared with the untreated AZ31, the tensile strength increased by 87.4% and the elongation increased by 43.08%.

[0085] Compare Example 7 with Example 3 and Example 4.

[0086] Ultrasonic treatment increased the tensile strength of AZ31-0.2Ca-0.12Ce by 63% and the elongation by 65.5%. Compared with the untreated AZ31, the tensile strength increased by 99% and the elongation increased by 89.8%.

[0087] Figure 2 (a) is a grain size photo of AZ31-0.2Ca-0.12Ce in comparative example 3 without ultrasonic treatment, and Figure 2 (b) is a grain size photo of Example 5 after ultrasonic treatment at 500W and 90s. The grain size without ultrasonic treatment is 76μm, and the average grain size after ultrasonic treatment is 46μm. Figure 3 (a) is a second phase distribution scan of AZ31-0.2Ca-0.12Ce in comparative example 3 without ultrasonic treatment, and Figure 3 (b) is a second phase distribution scan of Example 5 after ultrasonic treatment at 500W and 90s. The composite treatment shows the finest grain structure, the grains are highly uniform and equiaxed, and the secondary phase is well distributed. Figures 4 (a) and 4 (b) are the results of mechanical property tests. According to the metal material tensile test standard GB / T228.1, the mechanical property tests of the seven groups of magnesium alloys of Example 5, Example 10, Example 11, Example 12, Example 13, Example 3 and Example 4 were carried out, and the tensile test strain rate was 1x10 -3 s -1 , the stretching rate is 0.5mm / min.

[0088] It can be proved from the results of the above embodiments and comparative examples that Ca and Ce elements have different effects on the performance and organization of AZ31 magnesium alloy. The addition of Ca element improves the strength and corrosion resistance of magnesium alloy, and improves its heat treatment process performance. The addition of Ce element improves the high temperature strength of the alloy. However, Ca and Ce elements and their compounds diffuse slowly during the melting and casting process. Therefore, it is necessary to balance these effects in the alloy design and preparation process to obtain optimal performance and organization. These effects can be regulated by the ultrasonic treatment process of the present invention to meet the requirements of specific applications. In terms of preparation process, traditional smelting, casting and other processes have problems such as uneven organization and unstable performance. Therefore, the preparation process provided by the present invention has important practical application value for the precision molding and performance regulation of magnesium alloys.

[0089] In summary, the ultrasonically treated microalloyed AZ31 magnesium alloy material provided by the present invention has significantly improved strength, corrosion resistance and heat resistance while ensuring plasticity and impact toughness, and is suitable for manufacturing parts requiring higher load-bearing capacity, and can achieve an average extrusion speed of not less than 4 m / min within the equipment capacity. Statistics show that the raw material cost of the magnesium alloy casting rod used in the present invention is not more than 1,200 yuan / ton compared with the existing AZ31.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing microalloyed AZ31 magnesium alloy by ultrasonic treatment, characterized in that: The process includes the following: Melting process: melt magnesium at 715-725℃, keep it warm for 5-8min, then heat it to 725-735℃, add Mg-50%Al master alloy, keep it warm for 8-12min, then skim off the slag, stir to make the Mg-50%Al master alloy completely dissolved, keep the temperature at 725-735℃, add pure zinc, keep it warm for 8-12min, then skim off the slag, stir to make the pure zinc completely dissolved, finally add Mg-30%Ca and Mg-30%Ce master alloy, keep it warm for 8-12min, stir to make the Mg-30%Ca and Mg-30%Ce master alloy completely dissolved, and obtain alloy melt; Ultrasonic treatment: cool the alloy melt to 655-665°C and keep it warm for 20-25 minutes, then insert the ultrasonic treatment tool head into the alloy melt 18-22mm below the liquid surface for ultrasonic treatment. The ultrasonic treatment power is 300-700W and the treatment time is 60-120 seconds. Casting process: Casting is carried out under a protective atmosphere to obtain a casting.

2. The method for preparing microalloyed AZ31 magnesium alloy by ultrasonic treatment according to claim 1, characterized in that: 5-8 minutes after the casting is completed, the mold is opened, the ingot is taken out and the ingot is water-cooled.

3. The method for preparing microalloyed AZ31 magnesium alloy by ultrasonic treatment according to claim 1, characterized in that: Before casting, the casting mold is heated to 245-255°C, and then casting is carried out under a protective atmosphere.

4. The method for preparing microalloyed AZ31 magnesium alloy by ultrasonic treatment according to claim 1, characterized in that: Before the smelting process, the raw materials are also pre-treated: the oxide layer on the surface of all raw materials is polished off to make the surface silvery white; The pre-treated raw materials are weighed and used for smelting.

5. The method for preparing microalloyed AZ31 magnesium alloy by ultrasonic treatment according to claim 1, characterized in that: The protective atmosphere during the casting process adopts a mixed protective atmosphere of CO2 and SF6.

6. The method for preparing microalloyed AZ31 magnesium alloy by ultrasonic treatment according to claim 5, characterized in that: In the mixed protective atmosphere, the volume ratio of CO2 and SF6 is 97:3~99:

1.

7. A microalloyed AZ31 magnesium alloy prepared by the preparation method according to any one of claims 1 to 6, characterized in that: In terms of mass percentage, its components include: Al: 2.5%~3.5%, Zn: 0.5%~1.5%, Ca: 0-0.2%, Ce: 0-0.12%, the balance is magnesium and inevitable impurities, and the contents of Ca and Ce are not zero at the same time.

8. The microalloyed AZ31 magnesium alloy according to claim 7, characterized in that: Impurity content ≤0.1%.

9. The microalloyed AZ31 magnesium alloy according to claim 7, characterized in that: The microalloyed AZ31 magnesium alloy has a tensile strength of 125-245 MPa and an elongation of 6.8%-15.5%.

10. The use of the microalloyed AZ31 magnesium alloy according to any one of claims 7 to 9, characterized in that: The microalloyed AZ31 magnesium alloy is used to prepare industrial fan profiles and track ventilation grille profiles, and the average extrusion speed thereof is not less than 4 m / min.

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