Magnesium alloy with ultrahigh surface hardness and preparation method thereof

Abstract

The invention discloses a preparation method of a magnesium alloy with ultrahigh surface hardness, which relates to the technical field of magnesium alloy materials and comprises the following steps: step 1, smelting a pure magnesium ingot and an Mg-Gd intermediate alloy; a vacuum induction melting furnace is adopted, the pure magnesium ingot and the Mg-Gd intermediate alloy are put into the melting furnace according to the weight percentage, and an alloy cast ingot is obtained after vacuum induction melting; step 2, carrying out solution treatment on the alloy cast ingot; step 3, surface ultrasonic rolling; carrying out rolling treatment on the surface of the alloy ingot subjected to solution treatment by adopting ultrasonic rolling equipment of a high-carbon chromium bearing steel rolling head; 4, performing low-temperature aging treatment; according to the method, the processes of pure magnesium ingot and Mg-Gd intermediate alloy smelting, alloy cast ingot solution treatment, surface ultrasonic rolling and low-temperature aging treatment are adopted, water cooling is conducted after solution treatment, the stability of a supersaturated solid solution is guaranteed, and conditions are provided for aging strengthening; and through the synergistic effect of ultrasonic rolling and aging, the surface hardness is greatly improved, the process logic is clear, and industrialization is easy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnesium alloy materials, and particularly relates to a magnesium alloy with super-high surface hardness and a preparation method thereof. BACKGROUND

[0002] Magnesium alloys have an irreplaceable position in the field of lightweight manufacturing due to their low density, high specific strength, and good shock absorption. However, the low surface hardness and poor wear resistance of magnesium alloys at room temperature limit their application in frictional working conditions. Mg-Gd magnesium alloys become an important research direction of high-performance magnesium alloys due to the strengthening effect of rare earth element Gd. Among them, Mg-15wt.%Gd alloy has strong precipitation strengthening potential due to its high Gd content.

[0003] In the existing methods for improving the surface hardness of magnesium alloys, the surface coating is easy to fall off, the laser surface treatment has high cost and is prone to cracks, and the conventional heat treatment has limited effect on the improvement of the surface hardness of Mg-15wt.%Gd alloy. Therefore, it is of great significance to develop a preparation method with reasonable process and significant strengthening effect for promoting the engineering application of Mg-15wt.%Gd alloy. SUMMARY

[0004] The present application relates to the technical field of magnesium alloy materials, and particularly relates to a magnesium alloy with super-high surface hardness and a preparation method thereof.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical scheme: A magnesium alloy with super-high surface hardness, which comprises magnesium alloy components containing gadolinium at 15% by weight and the balance being magnesium and unavoidable impurity elements, with the content of impurity elements being less than or equal to 0.1%.

[0006] A preparation method of a magnesium alloy with super-high surface hardness, which is based on a magnesium alloy with super-high surface hardness and comprises the following steps: Step 1, melting of pure magnesium ingot and Mg-Gd intermediate alloy; The pure magnesium ingot and the Mg-Gd intermediate alloy are placed in the melting furnace according to the weight percentage, and the alloy ingot is obtained by pouring after vacuum induction melting; Step 2, solid solution treatment of the alloy ingot; The alloy ingot is kept at 500-520℃ for 8-12h to make the Gd element fully solid-solute in the Mg matrix, and then the alloy ingot is water-cooled to room temperature to obtain a supersaturated solid solution, thereby inhibiting the early precipitation of strengthening phases; Step 3, surface ultrasonic rolling; The surface of the solid-solution-treated alloy ingot is rolled by using an ultrasonic rolling equipment with a high-carbon chromium bearing steel rolling head; Step 4, low-temperature aging treatment; The ultrasonic rolled alloy ingot is placed in a low-temperature aging furnace, is kept at 100 DEG C for 12-24h, and is then water-cooled to room temperature.

[0007] Preferably, in the step 1, the purity of the pure magnesium ingot is greater than or equal to 99.95%, and the balance is inevitable impurity elements; the content of Gd in the Mg-Gd intermediate alloy is 30%, and the balance is magnesium and inevitable impurity elements.

[0008] Preferably, in the step 1, the pure magnesium ingot and the Mg-Gd intermediate alloy are placed in a graphite crucible, and then are placed in a vacuum induction melting furnace, wherein the vacuum degree in the vacuum induction melting furnace is less than or equal to 5*10 -3 Pa, high-purity argon is introduced for protection, and the purity of the argon is greater than or equal to 99.99%.

[0009] Preferably, in the step 1, the vacuum induction melting temperature is 720-750 DEG C, and the holding time is 30-40 min, so that the raw materials are completely melted and uniformly stirred, and then the melt is poured into a preheated metal mold at 200-250 DEG C, and is cooled to room temperature to obtain an alloy ingot.

[0010] Preferably, in the step 2, the alloy ingot is placed in a box-type resistance furnace for heat preservation, and is then water-cooled to room temperature at a water-cooling rate greater than or equal to 20 DEG C / s.

[0011] Preferably, in the step 3, the ultrasonic rolling equipment works at an ultrasonic frequency of 20-30 kHz, a rolling force of 70-160 N, a feeding speed of 800-1300 mm / min, and a rolling number of 5-30 times.

[0012] The present application has the following beneficial effects: 1. In the present application, the process of "melting of pure magnesium ingot and Mg-Gd intermediate alloy, solid solution treatment of alloy ingot, surface ultrasonic rolling, and low-temperature aging treatment" is adopted, the stability of the supersaturated solid solution after the solid solution treatment is ensured by water-cooling, and conditions for aging strengthening are provided; the synergistic effect of ultrasonic rolling and aging realizes a large increase in hardness, the process logic is clear, and industrialization is easy; and the surface hardness of the final alloy can reach 145-150 HV, the surface hardness of the Mg-15wt.%Gd alloy treated by the traditional process is 85-95 HV, the surface hardness of the Mg-15wt.%Gd alloy treated by the traditional process is increased by more than 60% compared with the Mg-15wt.%Gd alloy treated by the traditional process, and the requirement of high-end fields for surface hardness is met.

[0013] 2. In the present application, the surface of the alloy ingot after the solid solution treatment is subjected to ultrasonic rolling treatment, the surface is subjected to strong plastic deformation through the ultrasonic rolling, the grains are refined to the nanoscale, residual compressive stress is introduced, and the surface hardness is preliminarily increased. 3. In this invention, during the low-temperature aging process, the β' (Mg3Gd) strengthening phase precipitated in the supersaturated solid solution works synergistically with the fine-grained structure formed by ultrasonic rolling to further improve the surface hardness. The low-temperature aging process avoids the coarseness of the matrix grains. Attached Figure Description

[0014] Figure 1 This is a microstructure diagram of a cross-section of an ultra-high surface hardness magnesium alloy after ultrasonic rolling, according to the present invention. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0016] An ultra-high surface hardness magnesium alloy comprises, by weight percentage, gadolinium: 15%, with the balance being magnesium and unavoidable impurity elements, the impurity element content being ≤0.1%.

[0017] It is worth mentioning that Gd has a large solid solubility in magnesium, and after solid solution treatment, it can form a supersaturated solid solution, which lays the foundation for subsequent aging precipitation strengthening. At the same time, the atomic radius of Gd is much different from that of Mg, which can produce a significant solid solution strengthening effect.

[0018] Example 1: A method for preparing an ultra-high surface hardness magnesium alloy, comprising the following steps: Step 1: Smelting of pure magnesium ingots and Mg-Gd master alloy; The composition of the magnesium alloy by weight percentage is: gadolinium: 15%, with the balance being magnesium and unavoidable impurity elements, the impurity element content being ≤0.1%. Weigh the pure magnesium ingots and Mg-Gd master alloy by weight percentage, and place the pure magnesium ingots and Mg-Gd master alloy in a graphite crucible. The purity of the pure magnesium ingots is ≥99.95%, with the balance being unavoidable impurity elements. The Gd content in the Mg-Gd master alloy is 30%, with the balance being magnesium and unavoidable impurity elements. Then it is placed in a vacuum induction melting furnace, the vacuum degree of which is ≤5×10⁻⁶. -3 Pa, protected by high-purity argon gas with a purity ≥99.99%; The vacuum induction melting temperature is 730℃, and the holding time is 35 minutes to completely melt the raw materials and stir them evenly. Then the melt is poured into a metal mold preheated to 220℃ and cooled to room temperature to obtain an alloy ingot. Step 2: Solution treatment of alloy ingot; The alloy ingot is kept at 510℃ for 10h to allow Gd to fully dissolve into the Mg matrix. Then the alloy ingot is water-cooled to room temperature to obtain a supersaturated solid solution and inhibit the premature precipitation of the strengthening phase. The alloy ingot is placed in a box-type resistance furnace for heat preservation, and then water-cooled to room temperature at a water cooling rate of ≥20℃ / s; Step 3, surface ultrasonic rolling; the surface of the solid solution treated alloy ingot is rolled by using an ultrasonic rolling equipment with a high-carbon chromium bearing steel rolling head; The ultrasonic frequency of the ultrasonic rolling equipment is 35 kHz, the rolling force is 140 N, the feeding speed is 1300 mm / min, and the rolling times is 10 times; It is worth mentioning that in the surface ultrasonic rolling, the surface is subjected to strong plastic deformation by ultrasonic rolling, the grains are refined to nanoscale, and residual compressive stress is introduced, so that the surface hardness is initially improved. Figure 1 As shown in the cross-sectional microstructure diagram of the magnesium alloy after surface ultrasonic rolling, it can be seen that nanocrystalline structure is formed in the surface layer after ultrasonic rolling.

[0019] Step 4, low-temperature aging treatment; the alloy ingot after ultrasonic rolling is placed in a low-temperature aging furnace for heat preservation at 100℃ for 24h, and then water-cooled to room temperature.

[0020] It is worth mentioning that in the low-temperature aging treatment process, the β' (Mg3Gd) strengthening phase is precipitated and dispersed in the supersaturated solid solution, which cooperates with the fine-grained structure formed by ultrasonic rolling to further improve the surface hardness.

[0021] Embodiment 2, a preparation method of a magnesium alloy with ultrahigh surface hardness, comprising the following steps: Step 1, melting of pure magnesium ingot and Mg-Gd intermediate alloy; the magnesium alloy contains gadolinium 15% by weight, and the balance is magnesium and unavoidable impurity elements; the pure magnesium ingot and the Mg-Gd intermediate alloy are weighed according to the weight percentage, and then placed in a graphite crucible; the purity of the pure magnesium ingot is ≥99.95%, and the balance is unavoidable impurity elements; the content of Gd in the Mg-Gd intermediate alloy is 30%, and the balance is magnesium and unavoidable impurity elements; Then it is put into a vacuum induction melting furnace, and the vacuum degree in the furnace of the vacuum induction melting furnace is ≤5×10 -3 Pa, high-purity argon gas is introduced for protection, and the purity of argon is ≥99.99%; The vacuum induction melting temperature is 740℃, and the heat preservation time is 30min to completely melt and uniformly stir the raw materials, and then the melt is poured into a preheated 240℃ metal mold, and cooled to room temperature to obtain an alloy ingot; Step 2, solid solution treatment of alloy ingot; the alloy ingot is heat preserved at 520℃ for 8h to make the Gd element fully solid-solute into the Mg matrix, and then the alloy ingot is water-cooled to room temperature to obtain a supersaturated solid solution, and to inhibit the early precipitation of the strengthening phase; The alloy ingot is placed in a box-type resistance furnace for heat preservation, and then water-cooled to room temperature at a water cooling rate of ≥20℃ / s; Step 3, surface ultrasonic rolling; the surface of the alloy ingot after solid solution treatment is rolled by an ultrasonic rolling equipment with a high-carbon chromium bearing steel rolling head; The ultrasonic frequency of the ultrasonic rolling equipment is 35 kHz, the rolling force is 168 N, the feeding speed is 1300 mm / min, and the rolling times are 10 times. Step 4, low-temperature aging treatment; the alloy ingot after ultrasonic rolling is placed in a low-temperature aging furnace, and is kept at 100℃ for 24h, and then is water-cooled to room temperature.

[0022] Example 3, a preparation method of a magnesium alloy with ultrahigh surface hardness, comprising the following steps: Step 1, melting of pure magnesium ingot and Mg-Gd intermediate alloy; the magnesium alloy contains gadolinium 15% by weight, and the balance is magnesium and unavoidable impurity elements; the pure magnesium ingot and the Mg-Gd intermediate alloy are weighed according to the weight percentage, and are placed in a graphite crucible; the purity of the pure magnesium ingot is ≥99.95%, and the balance is unavoidable impurity elements; the content of Gd in the Mg-Gd intermediate alloy is 30%, and the balance is magnesium and unavoidable impurity elements; Then it is put into a vacuum induction melting furnace, the vacuum degree in the furnace of the vacuum induction melting furnace is ≤5×10 -3 Pa, high-purity argon gas is introduced for protection, and the purity of the argon gas is ≥99.99%; The vacuum induction melting temperature is 720℃, the holding time is 40min, so that the raw materials are completely melted and uniformly stirred, then the melt is poured into a preheated 200℃ metal mold, and cooled to room temperature to obtain an alloy ingot; Step 2, solid solution treatment of the alloy ingot; the alloy ingot is kept at 500℃ for 12h to make the Gd element fully solid-solute into the Mg matrix, and then the alloy ingot is water-cooled to room temperature to obtain a supersaturated solid solution and inhibit the early precipitation of the strengthening phase; The alloy ingot is placed in a box-type resistance furnace for heat preservation, and is water-cooled to room temperature after heat preservation at a water cooling rate of ≥20℃ / s; Step 3, surface ultrasonic rolling; the surface of the alloy ingot after solid solution treatment is rolled by an ultrasonic rolling equipment with a high-carbon chromium bearing steel rolling head; The ultrasonic frequency of the ultrasonic rolling equipment is 35 kHz, the rolling force is 112 N, the feeding speed is 1000 mm / min, and the rolling times are 30 times. Step 4, low-temperature aging treatment; the alloy ingot after ultrasonic rolling is placed in a low-temperature aging furnace, and is kept at 100℃ for 12h, and then is water-cooled to room temperature.

[0023] Comparative Example 1, a preparation method of a magnesium alloy, comprising the following steps: Step 1, pure magnesium ingot and Mg-Gd intermediate alloy smelting; the magnesium alloy composition contains gadolinium 15% by weight, and the balance is magnesium and unavoidable impurity elements; the pure magnesium ingot and the Mg-Gd intermediate alloy are weighed according to the weight percentage, the pure magnesium ingot is placed in a graphite crucible, the purity of the pure magnesium ingot is greater than or equal to 99.95%, and the balance is unavoidable impurity elements; the content of Gd in the Mg-Gd intermediate alloy is 30%, and the balance is magnesium and unavoidable impurity elements; Then put into a vacuum induction melting furnace, the vacuum degree in the furnace of the vacuum induction melting furnace is less than or equal to 5*10 -3 Pa, high-purity argon gas is introduced for protection, and the purity of the argon gas is greater than or equal to 99.99%; The vacuum induction melting temperature is 730 DEG C, the holding time is 35 min, the raw materials are completely melted and uniformly stirred, then the melt is poured into a preheated metal mold at 220 DEG C, and cooled to room temperature to obtain an alloy ingot; Step 2, solution treatment of the alloy ingot; the alloy ingot is heat treated at 510 DEG C for 10 h, so that the Gd element is fully dissolved into the Mg matrix, then the alloy ingot is water cooled to room temperature to obtain a supersaturated solid solution, and the precipitation of the strengthening phase is inhibited; The alloy ingot is placed in a box-type resistance furnace for heat preservation, and then air-cooled to room temperature after heat preservation, and the air-cooling cooling rate is less than or equal to 5 DEG C / s; Step 3, surface ultrasonic rolling; the surface of the solution-treated alloy ingot is rolled by using an ultrasonic rolling equipment with a high-carbon chromium bearing steel rolling head; The ultrasonic frequency of the ultrasonic rolling equipment is 35 kHz, the rolling force is 140 N, the feeding speed is 1300 mm / min, and the rolling times are 10.

[0024] Step 4, low-temperature aging treatment; the alloy ingot after ultrasonic rolling is placed in a low-temperature aging furnace, heat treated at 100 DEG C for 24 h, and then water cooled to room temperature.

[0025] Comparative example 2, a preparation method of a magnesium alloy with ultra-high surface hardness, comprising the following steps: Step 1, pure magnesium ingot and Mg-Gd intermediate alloy smelting; the magnesium alloy composition contains gadolinium 15% by weight, and the balance is magnesium and unavoidable impurity elements; the pure magnesium ingot and the Mg-Gd intermediate alloy are weighed according to the weight percentage, the pure magnesium ingot is placed in a graphite crucible, the purity of the pure magnesium ingot is greater than or equal to 99.95%, and the balance is unavoidable impurity elements; the content of Gd in the Mg-Gd intermediate alloy is 30%, and the balance is magnesium and unavoidable impurity elements; Then put into a vacuum induction melting furnace, the vacuum degree in the furnace of the vacuum induction melting furnace is less than or equal to 5*10 -3 Pa, high-purity argon gas is introduced for protection, and the purity of the argon gas is greater than or equal to 99.99%; Vacuum induction melting temperature is 730℃, holding time 35min to make the raw materials completely melted and stirred evenly, then the melt is cast into preheated 220℃ metal mold, cooled to room temperature to get alloy ingot; Step 2, alloy ingot solid solution treatment; the alloy ingot is kept at 510℃ for 10h to make Gd element fully solid solution into Mg matrix, then the alloy ingot is water cooled to room temperature to obtain supersaturated solid solution, inhibit the early precipitation of strengthening phase; The alloy ingot is put into the box resistance furnace for heat preservation, and then water cooled to room temperature after heat preservation, the water cooling rate is ≥20℃ / s; Step 3, surface ultrasonic rolling; the surface of the solid solution treated alloy ingot is rolled by ultrasonic rolling equipment with high carbon chromium bearing steel rolling head; The ultrasonic frequency of the ultrasonic rolling equipment is 35kHz, the rolling force is 140N, the feed speed is 1300mm / min, and the rolling times is 10 times; Step 4, low temperature aging treatment; the alloy ingot after ultrasonic rolling is placed in a low temperature aging furnace, kept at 130℃ for 24h, and then water cooled to room temperature.

[0026] Comparative example 3, a preparation method of ultrahigh surface hardness magnesium alloy, comprising the following steps: Step 1, pure magnesium ingot and Mg-Gd intermediate alloy melting; the magnesium alloy composition contains gadolinium 15% by weight, the balance is magnesium and unavoidable impurity elements, the pure magnesium ingot and the Mg-Gd intermediate alloy are weighed according to the weight percentage, the purity of the pure magnesium ingot is ≥99.95%, the balance is unavoidable impurity elements, the content of Gd in the Mg-Gd intermediate alloy is 30%, the balance is magnesium and unavoidable impurity elements; Then put into the vacuum induction melting furnace, the vacuum degree in the furnace of the vacuum induction melting furnace is ≤5×10 -3 Pa, high-purity argon gas is introduced for protection, the purity of argon is ≥99.99%; Vacuum induction melting temperature is 730℃, holding time 35min to make the raw materials completely melted and stirred evenly, then the melt is cast into preheated 220℃ metal mold, cooled to room temperature to get alloy ingot; Step 2, alloy ingot solid solution treatment; the alloy ingot is kept at 510℃ for 10h to make Gd element fully solid solution into Mg matrix, then the alloy ingot is water cooled to room temperature to obtain supersaturated solid solution, inhibit the early precipitation of strengthening phase; The alloy ingot is put into the box resistance furnace for heat preservation, and then water cooled to room temperature after heat preservation, the water cooling rate is ≥20℃ / s; Step 3, surface ultrasonic rolling; the surface of the solid solution treated alloy ingot is rolled by ultrasonic rolling equipment with high carbon chromium bearing steel rolling head; The ultrasonic frequency of the ultrasonic rolling equipment during operation is 35 kHz, the rolling force is 140 N, the feeding speed is 1300 mm / min, and the rolling times is 1.

[0027] Step 4, low-temperature aging treatment; the alloy ingot after ultrasonic rolling is placed in a low-temperature aging furnace, and is kept at 100 DEG C for 24 hours, and then is water-cooled to room temperature.

[0028] Table 1: surface hardness comparison of example 1, example 2, example 3 and comparative example 1, comparative example 2, comparative example 3; the surface hardness is tested by using a Vickers hardness tester (load 100 g, pressure maintaining 10 s), and the average value of 5 point values is taken as the test hardness; Sample name Surface hardness Example 1 145 HV Example 2 150 HV Example 3 142 HV Comparative Example 1 105 HV Comparative Example 2 132 HV Comparative Example 3 110 HV In summary, according to example 1, example 2 and example 3, the magnesium alloy with surface hardness of 142-150 HV can be stably obtained in the process range of the application. In comparative example 1, the solid solution treatment is cooled by air cooling, the cooling rate is less than or equal to 5 DEG C / s, and the other steps are the same as those in example 1; the surface hardness is 105 HV, part of the strengthening phase is precipitated in advance due to air cooling, the solid solubility is reduced, and the aging strengthening effect is weakened.

[0029] In comparative example 2, the aging temperature in the low-temperature aging treatment is 130 DEG C, and the other steps are the same as those in example 1; the surface hardness is 132 HV, the beta prime phase is coarsened due to the too high temperature, and the strengthening effect is reduced.

[0030] In comparative example 3, the surface ultrasonic rolling times is 1, and the other steps are the same as those in example 1; the surface hardness is 110 HV, the deformation is insufficient, the grain refinement effect is poor, and the residual compressive stress is small.

[0031] In summary, comparative example 1, comparative example 2 and comparative example 3 prove that the solid solution water cooling, aging temperature, ultrasonic rolling times and other parameters are crucial for hardness improvement, only by following the process flow and parameters of the application, can the ultrahigh surface hardness be realized.

[0032] The above is only the preferred specific embodiment of the application, but the protection scope of the application is not limited to this, any person skilled in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the application within the technical range disclosed by the application, which should be covered in the protection scope of the application.

Claims

1. A magnesium alloy with ultra-high surface hardness, characterized in that, The magnesium alloy composition contains, by weight percentage: gadolinium: 15%, with the balance being magnesium and unavoidable impurity elements, the impurity element content being ≤0.1%.

2. A method for preparing an ultra-high surface hardness magnesium alloy, the method being implemented based on the ultra-high surface hardness magnesium alloy according to claim 1, characterized in that, Includes the following steps: Step 1: Melting of pure magnesium ingots and Mg-Gd master alloy; Using a vacuum induction melting furnace, pure magnesium ingots and Mg-Gd master alloy are placed into the melting furnace according to the weight percentage, and after vacuum induction melting, alloy ingots are cast. Step 2: Solution treatment of alloy ingots; The alloy ingot is held at 500-520℃ for 8-12 hours to allow Gd to fully dissolve into the Mg matrix. Then the alloy ingot is water-cooled to room temperature to obtain a supersaturated solid solution, which inhibits the premature precipitation of the strengthening phase. Step 3: Surface ultrasonic rolling; An ultrasonic rolling device using a high-carbon chromium bearing steel rolling head is used to roll the surface of the alloy ingot after solution treatment. Step 4: Low-temperature aging treatment; The ultrasonically rolled alloy ingot is placed in a low-temperature aging furnace and held at 100℃ for 12-24 hours, then water-cooled to room temperature.

3. The method for preparing an ultra-high surface hardness magnesium alloy according to claim 2, characterized in that, In step 1, the purity of the pure magnesium ingot is ≥99.95%, with the balance being unavoidable impurity elements. The Gd content in the Mg-Gd master alloy is 30%, with the balance being magnesium and unavoidable impurity elements.

4. The method for preparing an ultra-high surface hardness magnesium alloy according to claim 3, characterized in that, In step 1, pure magnesium ingots and Mg-Gd master alloy are placed in a graphite crucible, and then placed into a vacuum induction melting furnace. The vacuum degree inside the vacuum induction melting furnace is ≤5×10⁻⁶. -3 Pa, with high-purity argon gas introduced for protection, and the argon gas purity ≥ 99.99%.

5. The method for preparing an ultra-high surface hardness magnesium alloy according to claim 4, characterized in that, In step 1, the vacuum induction melting temperature is 720-750℃, and the holding time is 30-40 minutes to completely melt the raw materials and stir them evenly. Then, the melt is poured into a metal mold preheated to 200-250℃ and cooled to room temperature to obtain an alloy ingot.

6. The method for preparing an ultra-high surface hardness magnesium alloy according to claim 2, characterized in that, In step 2, the alloy ingot is placed in a box-type resistance furnace for heat preservation, and then water-cooled to room temperature with a water cooling rate ≥20℃ / s.

7. The method for preparing an ultra-high surface hardness magnesium alloy according to claim 2, characterized in that, In step 3, the ultrasonic rolling equipment operates at an ultrasonic frequency of 20-30kHz, a rolling force of 70-160N, a feed speed of 800-1300mm / min, and 5-30 rolling cycles.

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