A semi-solid alloy with high wear resistance and its preparation method

Abstract

The present invention relates to a semi-solid alloy with high wear resistance and a preparation method thereof. The preparation method includes the following steps: placing a porous graphite rod in a molten salt containing magnesium element and zirconium element as a cathode for electrolysis reaction, with the electrolysis time being 10 - 30 min and the voltage being 2.7 - 3 V; obtaining a melt of the alloy in a first container, allowing an inert gas to enter the melt through the porous graphite rod, with the flow rate of the inert gas being 5 - 20 L / min, applying ultrasound to the melt through an ultrasonic probe inserted into the melt, with the ultrasonic power being 2 - 4 kW and the ultrasonic frequency being 10 - 30 kHz, and when the solid content of the melt is 10 - 30%, removing the porous graphite rod and the ultrasonic probe; transferring the melt to a second container for casting, thus obtaining the semi-solid alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of semi-solid alloy materials, and particularly relates to a semi-solid alloy with high wear resistance and a preparation method thereof. Background Art

[0002] Zirconium is widely used as a grain refiner in various alloy systems, such as magnesium alloys. The crystal structure of zirconium is the same as that of magnesium alloys, both being close-packed hexagonal, and the lattice parameters are very close, meeting the conditions for serving as a heterogeneous nucleation core. Zirconium can serve as the crystallization core of α-Mg, thereby producing refined grains and improving the wear resistance of magnesium alloys. However, the solubility of zirconium in magnesium is less than 0.7%. In magnesium alloys, zirconium mainly exists in the form of simple substances, which is prone to aggregation, resulting in composition segregation and precipitation. Therefore, it is necessary to strictly control the addition amount of zirconium. Generally, a large amount of zirconium is added to solve the problem of zircon precipitation loss. However, as a rare earth element, the large addition of zirconium will lead to a significant increase in cost and difficulty in industrialization. Therefore, there are certain challenges in preparing high-wear-resistance alloys using zirconium as a grain refiner. Existing technologies generally improve the utilization rate of zirconium by preparing zirconium-magnesium alloys with finer particle sizes. However, the low solubility of zirconium makes it easy for zirconium-magnesium alloys with finer particle sizes to aggregate during the process of adding them to the melt. Therefore, it is difficult to significantly improve the utilization rate (or actual yield) of zirconium by this method. ZK60A magnesium alloy is a Mg-Zn-Zr magnesium alloy containing a relatively high content of zirconium. Due to the low utilization rate of zirconium and the loss of zirconium during the preparation process, it is often necessary to add 6-7 times the amount of Zr in the raw materials to achieve an ideal grain refinement effect.

[0003] In the patent CN118497545B previously applied for by the applicant, a preparation method of a graphene-reinforced magnesium alloy casting is disclosed. It generates graphene by electrochemically stripping a porous graphite rod under ultrasonic action, so that graphene is uniformly dispersed in the melt, thereby improving the tensile properties and yield properties of the casting. However, the improvement of the casting properties mainly depends on the strengthening effect of graphene. Although graphene has a certain grain refinement effect, its refinement effect is not as good as that of traditional grain refiners. When this method is directly used to prepare ZK60A alloy, it is still necessary to add 6-7 times the amount of Zr in the raw materials to achieve an ideal grain refinement effect, so as to obtain a semi-solid alloy with high wear resistance.

[0004] Therefore, it is necessary to provide a semi-solid alloy with high wear resistance and a preparation method thereof. Summary of the Invention

[0005] In order to solve the problem of low Zr utilization rate of ZK series alloys, it is necessary to provide a semi-solid alloy with high wear resistance and a preparation method thereof.

[0006] Place a porous graphite rod in a molten salt containing magnesium and zirconium elements as the cathode for electrolysis reaction. The electrolysis time is 10 - 30 min and the voltage is 2.7 - 3 V;

[0007] Obtain the melt of the alloy in the first container, and let an inert gas enter the melt through the porous graphite rod. The flow rate of the inert gas is 5 - 20 L / min. Apply ultrasonic waves to the melt through an ultrasonic probe inserted into the melt. The ultrasonic power is 2 - 4 kW and the ultrasonic frequency is 10 - 30 kHz. When the solid content of the melt is 10 - 30%, remove the porous graphite rod and the ultrasonic probe;

[0008] Transfer the melt to the second container for casting to obtain the semi - solid alloy.

[0009] In this solution, MgZr alloy is formed on the surface and in the gaps of the porous graphite rod by molten salt electrolysis. At the same time, the precipitated MgZr alloy inserted into the gaps of the porous graphite rod can promote the peeling of the porous graphite rod. The narrow gaps and short electrolysis time of the porous graphite rod limit the growth of the MgZr alloy, so that the peeled MgZr alloy has a large specific surface area. When the treated porous graphite rod is used for the preparation of semi - solid magnesium alloy, under the action of bubbles and ultrasonic waves, the MgZr alloy attached to the surface and in the gaps of the porous graphite rod peels off with the graphite. The high - surface - area MgZr produced by peeling is not easy to settle under the action of bubbles and dissolves in the magnesium alloy melt as it enters the magnesium alloy melt with the bubbles. Therefore, the concentration of Zr around the bubbles is relatively high, and the magnesium alloy melt nucleates around the bubbles. The precipitated Zr can serve as the crystallization core of α - Mg to promote the formation of crystal nuclei, thus obtaining a refined magnesium alloy and finally forming a semi - solid alloy with high wear resistance.

[0010] Further, the molten salt contains MgCl 2 、KCl and K 2 ZrF 6 。

[0011] Further, by mass fraction, the molten salt contains 20 - 40 parts of MgCl 2 、35 - 60 parts of KCl, 4 - 8 parts of KF, 15 - 25 parts of K 2 ZrF 6 。 By increasing the proportion of K 2 ZrF 6 , the content of Zr in the deposited MgZr is increased, and finally the content of Zr in the melt is increased to achieve an ideal refinement effect.

[0012] Further, the voltage is 2.7 - 2.8V. The reduction potential of Zr is -0.8V and -1.2V. At this voltage, Zr can be rapidly deposited, while the reduction potential of Mg is -2.67V. When the voltage is 2.7 - 2.8V, the deposition rate of Mg is slow, thereby increasing the content of Zr in the deposited MgZr. When the voltage exceeds 2.8V or even 2.9V, Mg will be rapidly deposited, resulting in a decrease in the Zr content in MgZr and segregation.

[0013] Further, the current density of the electrolysis reaction is (2 - 5) / (A·cm -2 ). At a low current density, the deposition rate of Mg ions is slow, which is beneficial to increasing the Zr content in MgZr.

[0014] Further, the pore diameter of the porous graphite rod is 50 - 100nm. In order to facilitate the peeling of MgZr, a porous graphite rod with a larger pore diameter is required; however, the pore diameter of the porous graphite rod should not be too large, otherwise the surface area of the porous graphite rod is too small, resulting in an excessive reduction in the peeling efficiency of MgZr.

[0015] Further, the mass of Zr in the molten salt is 2 - 3 times the designed value of Zr in the melt. Considering that Zr in the molten salt cannot be completely converted into MgZr and deposited on the porous graphite rod, an excessive amount of Zr needs to be set in the molten salt. The excessive Zr will not cause waste and can be supplemented with MgCl 2 and K 2 ZrF 6 to continue the electrolysis.

[0016] Further, the alloy is a ZK series alloy. The ZK series alloy requires a high concentration of Zr. Applying this method to the preparation of the ZK series alloy helps to reduce the cost of the ZK series alloy and improve its performance. Further, the ZK series alloy is ZK60A. Specifically, the composition of ZK60A includes: by weight fraction, zinc 5 - 6%, zirconium 0.3 - 0.9%, manganese 0.10%, the content of each other impurity is less than 0.05%, and the balance is magnesium.

[0017] Further, the material of the porous graphite rod is expanded graphite. Expanded graphite is a worm-like graphite material formed by intercalation, water washing, drying, and high-temperature expansion. Expanded graphite has a larger interlayer distance, can accommodate more MgZr during electrolysis, and is more likely to be peeled under external force.

[0018] The second aspect of the present invention provides a semi-solid alloy with high wear resistance, and the semi-solid alloy is prepared by the above preparation method.

[0019] The above semi-solid alloy has improved wear resistance. Brief Description of the Drawings

[0020] Figure 1 It is a schematic flow chart of the preparation method of an embodiment of this solution.

[0021] Figure 2 It is a metallographic diagram of Example 1.

[0022] Figure 3 It is a metallographic diagram of Comparative Example 1.

[0023] Figure 4 It is a metallographic diagram of Comparative Example 2. Detailed Embodiments

[0024] To facilitate the understanding of this application, the following will provide a more comprehensive description of this application. This application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosed content of this application more thorough and comprehensive.

[0025] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the application, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the description of this application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application in this specification are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0027] In this application, among the technically characterized features described in an open-ended manner, there are included closed technical solutions composed of the listed features, as well as open technical solutions including the listed features.

[0028] In this application, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of this range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of this range. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0029] In this application, the percentage content involved, unless otherwise specified, refers to the mass percentage for solid-liquid mixing and solid-solid mixing, and refers to the volume percentage for liquid-liquid mixing.

[0030] In this application, the percentage concentration involved, unless otherwise specified, refers to the final concentration. The final concentration refers to the proportion of the added component in the system after adding the component.

[0031] In this application, the temperature parameter, unless otherwise specified, allows both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument.

[0032] The "particles" mentioned in this application, or substances with a defined particle size distribution, do not necessarily have a spherical shape and may also be irregular. They can be primary particles or secondary particles. The particle size of irregular particles is calculated as the average of their maximum diameter and minimum diameter.

[0033] As Figure 1 shown, a schematic diagram of the preparation method of an embodiment of this solution mainly includes: placing a porous graphite rod in a molten salt containing magnesium and zirconium as the cathode for electrolysis, using the electrolyzed porous graphite rod for gas-induced semi-solid slurry preparation, applying ultrasonic action to the melt while preparing the slurry, and using the semi-solid slurry for casting.

[0034] Example 1: Prepare a molten salt. Place 126 g of MgCl 2 , 189 g of KCl, 25.2 g of KF, 84 g of K 2 ZrF 6 (the mass of Zr element is about 27 g) in a crucible and heat it to 800 °C to form a molten salt. All the above materials have been dried before heating.

[0035] Place a porous graphite rod (cathode) with a diameter of 26 mm, a length of 165 mm, and a pore size of 50 nm and a Pt electrode (anode) of the same size in the molten salt, and assemble them with a DC power supply to form a circuit. Electrolyze at a constant voltage of 2.75 V for 10 min, take out the porous graphite rod, dry it, and connect it to an argon gas source. The material of the porous graphite rod is expanded graphite.

[0036] Preparation of ZK60A (design values: 5% zinc, 0.9% zirconium, 0.1% manganese, and 94% magnesium): Weigh 53 g of zinc and 1050 g of magnesium, place them in a resistance furnace, stir and heat to 740 °C. After removing the slag, transfer them to a reaction vessel, cool down to 20 °C above the liquidus to form a melt. Place a porous graphite rod in the melt, with the bottom of the porous graphite rod 2 mm away from the bottom of the container. Place an ultrasonic probe in the container, make the ultrasonic probe parallel to the porous graphite rod and the distance between them is 2 cm. Start the argon gas flow, control the gas flow rate at 10 L / min, and at the same time start the ultrasonic wave, with the ultrasonic power of 4 kW and the ultrasonic frequency of 30 kHz. When the solid content of the melt is 10% (the solid content at the end of cooling), remove the porous graphite rod and the ultrasonic probe, transfer the melt to a mold for casting, and the time from removing the porous graphite rod to the melt completely entering the mold is 20 seconds (melt transfer time).

[0037] Squeeze casting: Use a squeeze casting machine to perform die casting on the above-mentioned semi-solid magnesium alloy melt, with the filling speed of 100 mm / s, the holding pressure of 180 MPa, the holding time of 10 s, and the mold temperature of 300 °C, then obtain a semi-solid magnesium alloy casting (gear).

[0038] Hardness test method: Refer to the national standard GB / T 7997-2014 "Test Method for Vickers Hardness of Cemented Carbides" for testing.

[0039] The experimental conditions of Examples 1-6 and Comparative Examples 1-3 are shown in Table 1. Among them, in Comparative Example 1, no electrolysis reaction is carried out, but the MgZr30 master alloy is directly added in twice the design value in the raw materials of the melt; in Comparative Example 2, a longer electrolysis time is used; in Comparative Example 3, 5 parts of K 2 ZrF 6 is used in the molten salt raw material.

[0040] Table 1 Experimental conditions of Examples 1-6 and Comparative Examples 1-3.

[0041]

[0042] Table 2 Performance test results of Examples 1-6 and Comparative Examples 1-3.

[0043]

[0044] According to the data in Table 2, it can be seen that the hardness of Examples 1-6 is significantly higher than that of Comparative Examples 1-3, and the average particle size of the corresponding Examples 1-6 is lower than that of Comparative Examples 1-3. This is because in this solution, MgZr alloy is formed on the surface and in the gaps of the porous graphite rod by molten salt electrolysis. At the same time, the precipitated MgZr alloy inserted into the gaps of the porous graphite rod can promote the peeling of the porous graphite rod. The narrow gaps and short electrolysis time of the porous graphite rod limit the growth of the MgZr alloy, resulting in a large specific surface area of the peeled MgZr alloy. When the treated porous graphite rod is used for the preparation of semi-solid magnesium alloy, under the action of bubbles and ultrasound, the MgZr alloy attached to the surface and in the gaps of the porous graphite rod peels off with the graphite. The high-surface-area MgZr produced by peeling is not easily sedimented under the action of bubbles and dissolves in the magnesium alloy melt as it enters the magnesium alloy melt with the bubbles. Therefore, the concentration of Zr around the bubbles is relatively high, and the magnesium alloy melt nucleates around the bubbles. The high concentration of Zr re-precipitates under the cooling effect provided by the bubbles, and the precipitated Zr can serve as the crystallization core of α-Mg to promote nucleation, thereby obtaining a refined magnesium alloy and finally forming a semi-solid alloy with high wear resistance. In Comparative Example 1, Zr with a design value twice that was added to the melt. However, this added amount of Zr could not achieve the ideal refinement effect, and most of the Zr directly precipitated, formed oxides, or was consumed through other channels, such as Figures 2 - 3 shown, the grain size of Comparative Example 1 increased significantly compared to Example 1 and was difficult to apply; in Comparative Example 2, a longer electrolysis time was used. On the one hand, the too-long electrolysis time might cause peeling on the surface of the graphite rod, resulting in the Zr content not reaching the expected value. On the other hand, it might cause excessive growth of MgZr particles, which rapidly precipitated during the process of mixing into the melt and could not achieve the utilization rate of Example 1. Therefore Figure 4 the grain size was coarsened; in Comparative Example 3, too little K 2 ZrF 6 was used, and the Zr content in the MgZr particles was too low and was further diluted after dissolving in the melt, making it difficult to play a refinement role.

[0045] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0046] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed. However, it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A method for preparing a semi-solid alloy with high wear resistance, characterized in that: The method comprises the following steps: placing a porous graphite rod in a molten salt containing magnesium and zirconium as a cathode for electrolysis reaction, wherein the molten salt contains 20-40 parts of MgCl2, 35-60 parts of KCl, 4-8 parts of KF, and 15-25 parts of K2ZrF6 by mass, the electrolysis time is 10-30 minutes, and the voltage is 2.7-2.8V; obtaining a melt of the alloy in a first container, allowing an inert gas to enter the melt through the porous graphite rod, the flow rate of the inert gas is 5-20L / min, applying ultrasound to the melt through an ultrasonic probe inserted into the melt, the ultrasonic power is 2-4kW, and the ultrasonic frequency is 10-30kHz, and when the solid content of the melt is 10-30%, removing the porous graphite rod and the ultrasonic probe; transferring the melt to a second container for casting, so as to obtain the semi-solid alloy.

2. The preparation method according to claim 1, characterized in that: The current density of the electrolysis reaction is 2A·cm -2 -5A cm -2 .

3. The preparation method according to claim 1, characterized in that: The pore size of the porous graphite rod is 50-100 nm.

4. The preparation method according to claim 1, characterized in that: The mass of Zr in the molten salt is 2-3 times the designed value of Zr in the melt.

5. The preparation method according to claim 1, characterized in that: The alloy is a ZK alloy.

6. The preparation method according to claim 5, characterized in that: The ZK alloy is ZK60A.

7. A semi-solid alloy with high wear resistance, characterized in that: The semi-solid alloy is prepared using the preparation method described in any one of claims 1 to 6.

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