Mn-Al-C grain refiner for refining magnesium and magnesium alloy as well as preparation method and application of Mn-Al-C grain refiner

Abstract

The invention discloses a Mn-Al-C grain refiner for refining magnesium and alloy thereof, the Mn-Al-C grain refiner comprises the following components in percentage by mass: 68-72% of Mn, 0.6-0.8% of C and the balance of Al, and further, the phase of the Mn-Al-C grain refiner is a tau-MnAl-C phase or an epsilon-MnAl-C phase. The invention further discloses a preparation method and application of the Mn-Al-C grain refiner for refining the magnesium and the magnesium alloy. By adding the C component, the stability of the Mn-Al alloy refiner is effectively improved; the refining agent is added into magnesium and magnesium alloy melt in the form of tau-MnAl-C phase precursor phase epsilon-MnAl-C phase single-phase intermediate alloy, the refining agent can be completely converted into a single-phase tau-MnAl-C phase within 10 min in the metal melt, and then the refining agent of the tau-MnAl-C phase serves as an efficient nucleation substrate to refine magnesium and magnesium alloy. The refining agent is an epsilon-MnAl-C single phase, so that a very good refining effect can be achieved by adding a small amount of the refining agent, and in the refining process of the refining agent, the attenuation speed is low, and the stability is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material preparation, and in particular relates to a Mn-Al-C grain refiner for magnesium and its alloy refinement, and a preparation method and application thereof. Background Art

[0002] Magnesium alloys have the advantages of low density, high specific strength and good damping performance. They are widely used in automotive parts, electronic products and rail transportation. Mg-Al alloy is the most widely used alloy among magnesium alloys. However, the absolute strength and plasticity of the alloy are still relatively low, which limits the application scenarios and scope of Mg-Al alloys. Grain refinement is one of the methods to improve strength and plasticity at the same time, and can also improve the casting performance, structural uniformity and machinability of the alloy.

[0003] Existing Mg-Al alloy refinement technologies mainly include superheated melt grain refinement, carbon inoculation, and FeCl3 addition. However, these methods still have some disadvantages: the superheated melt method consumes too much energy, is only applicable to small-mass parts, and has poor aging resistance; the carbon inoculation method produces harmful gases or introduces C elements that are detrimental to the corrosion performance of Mg alloys; the FeCl3 method easily introduces Fe elements that accelerate the corrosion rate of Mg alloys. Currently, there is still a lack of a suitable commercially available Mg-Al alloy grain refinement method on the market.

[0004] The refiner currently used for magnesium-aluminum alloy is a master alloy based on manganese-aluminum alloy. For example, patent number CN101693969A discloses an aluminum-manganese grain refiner for Mg-Al-based alloy, and its preparation method and use method. The composition of the grain refiner is 25-35% Al and 65-75% Mn by weight. The preparation method is carried out according to the following steps: (1) according to the composition of the grain refiner, add an excess of metallic manganese to obtain a mixed metal; (2) clean the mixed metal; (3) place the mixed metal in an arc furnace, evacuate it, fill it with argon, and perform four smelting; (4) place the mixed metal in a closed container, evacuate it, fill it with argon, heat and keep it warm for 24-72 hours, and take it out for water quenching. The use method is to add the aluminum-manganese grain refiner to the Mg-Al-based alloy melt at 700-750°C, stir it evenly, and then let it stand for 20-60 minutes. The addition amount of the product of the present invention is 0.5-2.5% of the Mg-Al based alloy solution, and the refinement effect does not degrade within 1 hour. However, the refiner has the problems of complex preparation process, large addition amount during use, and poor refinement effect. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the main purpose of the present invention is to provide a Mn-Al-C grain refiner for magnesium and its alloy refinement, aiming to solve the problems of the Mn-Al grain refiner having a complex preparation process, a large amount of addition during use, and poor refinement effect. The present invention also discloses a preparation method of the Mn-Al-C grain refiner for magnesium and its alloy refinement.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A Mn-Al-C grain refiner for magnesium and its alloy refinement comprises the following components by mass ratio: 68-72% of Mn, 0.6-0.8% of C and the balance of Al.

[0008] In some specific embodiments, the phase of the Mn—Al—C grain refiner is a τ-MnAl—C phase or an ε-MnAl—C phase.

[0009] In some specific embodiments, the atomic ratio of Al / Mn in the Mn-Al-C grain refiner is 0.77-0.94.

[0010] The present invention also provides a method for preparing a Mn-Al-C grain refiner for magnesium and its alloy refinement, comprising the following steps:

[0011] 1) According to the formula requirements, smelting and casting the Mn-Al-C master alloy to obtain a cast Mn-Al-C master alloy;

[0012] 2) homogenizing the cast Mn-Al-C master alloy, and then quenching it to obtain a homogenized Mn-Al-C master alloy;

[0013] 3) The homogenized Mn-Al-C master alloy is mechanically crushed, mechanically crushed and subjected to a suitable ball milling process, and sieving to obtain a Mn-Al-C grain refiner.

[0014] In some specific embodiments, the process parameters of the homogenization treatment in step 2) are: maintaining the temperature at 950-1100° C. for 0.5-3 h.

[0015] In some specific embodiments, the particle size of the Mn—Al—C grain refiner is ≤250 μm.

[0016] In another specific embodiment, the present application provides another method for preparing a Mn-Al-C grain refiner for magnesium and its alloy refinement, specifically, it also includes preparing particles by spinning strips or its ground powder, atomizing, and screening to obtain a Mn-Al-C grain refiner.

[0017] The present invention also aims to provide the use of a Mn-Al-C grain refiner for refining magnesium and its alloys in magnesium / magnesium alloys.

[0018] In some specific embodiments, the magnesium alloy includes Mg-Al, Mg-Si and Mg-Mn alloys.

[0019] In some specific embodiments, the added amount of the Mn—Al—C grain refiner is 0.1-0.4 wt. % of the mass of the magnesium / magnesium alloy.

[0020] In some specific embodiments, the Mn-Al-C grain refiner can be directly added to the magnesium and its alloy melt at 680-720°C, and the added amount is 0.1-0.3wt.% of the melt mass, and the refinement time needs to be controlled within 10-60min.

[0021] Compared with the prior art, the present invention has at least the following advantages:

[0022] 1) The refiner of the present invention effectively improves the stability of the Mn-Al alloy refiner by adding the C component; at the same time, the inventors have found and verified that the phase that acts as a nucleation substrate after the magnesium of the Mn-Al alloy and its alloy refiner are added to the melt is the τ-MnAl-C phase, so a refiner containing only a single phase of the ε-MnAl-C phase, which is the precursor phase of the τ-MnAl-C phase, is prepared;

[0023] 2) The preparation method provided by the present invention has the characteristics of readily available raw materials, simple process, high repeatability, etc., and is suitable for large-scale promotion and application.

[0024] 3) The refiner provided by the present invention is mainly used for the refinement of magnesium and its alloys. The refiner is added to the magnesium and its alloy melt in the form of a single phase ε-MnAl-C phase, a precursor phase of the τ-MnAl-C phase. The refiner can be completely transformed into a single phase τ-MnAl-C phase in the metal melt within 10 minutes, and then the refiner of the τ-MnAl-C phase acts as an efficient nucleation substrate to refine magnesium and its alloys. Since the refiner is a single phase of the ε-MnAl-C phase, it can achieve a good refinement effect even if it is added in a small amount, and the refiner has a slow decay rate during the refinement process and greatly improved stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific implementation of the present invention, the drawings required for use in the specific implementation or the description of the prior art will be briefly introduced below.

[0026] Figure 1The ε-MnAl-C and γ2(Al8Mn5) phase microstructures of the cast Mn-Al-C master alloy (a), the ε-MnAl-C phase microstructure of the homogenized Mn-Al-C master alloy after heat treatment at 950℃ for 2h (b), the τ-MnAl-C phase microstructure of the homogenized Mn-Al-C master alloy after aging at 700℃ for 10min (c) and its corresponding XRD pattern (d);

[0027] Figure 2 Optical microscopic photographs of Mg-9wt.%Al sample after solution treatment at 700℃ before refinement (a) and after adding 0.2wt.% Mn-Al-C grain refiner (particle size ≤ 250μm) and keeping warm for 10min (b);

[0028] Figure 3 Optical microscopic photographs of Mg-9wt.%Al sample after solution treatment at 700℃ before refinement (a) and after adding 0.2wt.% Mn-Al-C grain refiner (particle size ≤ 74μm) and keeping warm for 30min (b);

[0029] Figure 4 Photos of pure Mg samples at 720°C before refinement (a) and after adding 0.2wt.% Mn-Al-C grain refiner (particle size ≤ 74μm) and keeping warm for 10min (b);

[0030] Figure 5 These are the statistical results of grain size after solution treatment of Mg-9wt.% Al samples at 700°C with 0.2wt.% Mn-Al-C grain refiner of different particle sizes (particle size ≤ 250μm or 74μm) added and kept warm for 0, 5, 10, 20, 30 and 60min. 0min represents no addition of intermediate alloy powder. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0032] When a certain amount, concentration or other value or parameter is expressed in the form of a range, a preferred range, or a preferred upper and lower numerical limit, it should be understood that it is equivalent to specifically revealing any range by combining any pair of upper range limits or preferred numerical values ​​with any lower range limit or preferred numerical value, regardless of whether the range is specifically disclosed. Unless otherwise indicated, the numerical range values ​​listed herein include the endpoints of the range, and all integers and fractions within the range.

[0033] Unless otherwise indicated, all percentages, parts, ratios, etc. herein are by weight.

[0034] The materials, methods, and examples herein are illustrative and are not to be construed as limiting unless specifically stated.

[0035] In the following embodiments, the magnesium alloy used may be Mg-Al, Mg-Si and Mg-Mn alloys. Furthermore, the following embodiments are described by taking Mg and Mg-Al alloys as examples.

[0036] Example 1

[0037] This embodiment provides a method for preparing a Mn-Al-C grain refiner for magnesium and its alloy refinement, which comprises the following steps:

[0038] 1) using a medium frequency melting furnace to melt a Mn-Al-C master alloy and casting it, wherein the Mn content is 70.2%, the Al content is 29.2%, and the C content is 0.6% by mass, to obtain a cast Mn-Al-C master alloy;

[0039] 2) heat treating the cast Mn-Al-C master alloy at 950° C. for 2 h for homogenization, and then quenching to obtain a homogenized Mn-Al-C master alloy;

[0040] 3) The homogenized Mn-Al-C master alloy is mechanically crushed, and then the master alloy powder with a particle diameter of ≤250 μm is screened through a sample sieve to obtain a Mn-Al-C grain refiner.

[0041] The present application performs SEM phase diagram and XRD tests on the microstructures of the cast Mn-Al-C master alloy prepared in step 1) and the homogenized Mn-Al-C master alloy prepared in step 2). The results are as follows: Figure 1 ab and Figure 1 As shown in d, it can be seen from the figure that the cast Mn-Al-C master alloy contains ε-MnAl-C and γ2(Al8Mn5) phases ( Figure 1 a), while the homogenized Mn-Al-C master alloy is ε-MnAl-C phase ( Figure 1 b), that is, the cast Mn-Al-C master alloy is converted into ε-MnAl-C single phase after homogenization treatment.

[0042] The present application also performs metallographic scanning on the homogenized Mn-Al-C master alloy prepared in step 2) after heat treatment at 700°C for 10 minutes. The SEM results are as follows: Figure 1As shown in Figure c, it can be seen from the figure that the phase after holding for 10 minutes is τ-MnAl-C phase. This test shows that after the homogenized Mn-Al-C master alloy is heat-treated at 700°C for 10 minutes, it transforms from ε-MnAl-C phase to τ-MnAl-C phase; its heat treatment at 700°C for 10 minutes is equivalent to the Mn-Al-C grain refiner in the present application being held in the Mg-Al alloy melt for 10 minutes.

[0043] The Mn-Al-C grain refiner prepared in this application is used to refine Mg-Al alloy, and the specific steps are as follows:

[0044] S1) melting Mg-9wt.%Al alloy in a stainless steel crucible at 700°C in a protective atmosphere of CO2+1Vol.%SF6 to obtain a magnesium-aluminum alloy melt;

[0045] S2) a Mn-Al-C grain refiner equal to 0.2 wt.% of the mass of the magnesium-aluminum alloy melt is coated with aluminum foil and then pressed into the alloy melt, stirred for 30 seconds, and continued to be kept at 700° C.;

[0046] S3) The alloy was cast after keeping warm for 5, 10, 20, 30 and 60 min respectively. The alloy was stirred for 10 s before casting. The mold used for casting was Φ20·Φ30·25 mm preheated to 200 °C. 3 Head-removing cone mold;

[0047] In this embodiment, a casting sample without adding Mn-Al-C grain refiner is introduced as a control group to measure the grain size. Specifically, the magnesium-aluminum alloy melt prepared in step S1) is used to prepare a casting alloy. The casting mold used is a Φ20·Φ30·25mm preheated to 200°C. 3 Head-removing cone mold;

[0048] The sample at a height of 10 mm in the middle of the casting sample was taken, and the casting sample was solution treated at 420°C for 12 h and then quenched. The solution sample was metallographically polished and then corroded with nitric acid alcohol solution and picric acid solution for 20 s each.

[0049] The present application also applies the Mn-Al-C grain refiner to the Mg-Al alloy to obtain the cast alloy sample after solution treatment under an optical microscope to obtain alloy microstructure photos, and uses the intercept method to measure the grain size of the alloy sample after solution treatment for different holding times; the optical microscope photos of the Mg-9wt.%Al alloy solution sample without adding the Mn-Al-C grain refiner and adding the Mn-Al-C grain refiner to hold for 10 minutes are as follows: Figure 2As shown in a and b, it can be seen that the grain size is significantly reduced from 198±8μm to 130±5μm. The statistical comparison results of grain size at different holding times after adding Mn-Al-C grain refiner are shown in Figure 5 As shown, it can be observed that the grain size decreases first and then increases with the extension of the holding time after the addition of the master alloy powder, but the refinement decay rate is not large. The reduction stage corresponds to the transformation of the ε-MnAl-C phase to the τ-MnAl-C phase, and the increase stage corresponds to the gradual decomposition of the τ-MnAl-C phase to the equilibrium phase γ2 (Al8Mn5) and β-Mn. The results show that when 0.2wt.% of the MnAl-C master alloy powder grain refiner (powder particle size ≤250μm) is added, the grain size is reduced by about 68μm, which proves the refinement effect of τ-MnAl-C on the Mg-9wt.%Al alloy.

[0050] Example 2

[0051] This embodiment provides a method for preparing a Mn-Al-C grain refiner for magnesium and its alloy refinement, wherein the components and proportions thereof are the same as those in embodiment 1, and the preparation steps and parameters thereof are substantially the same as those in embodiment 1, except that the particle size of the screened particles of the Mn-Al-C grain refiner is different, specifically:

[0052] The quenched master alloy is mechanically crushed, and then the master alloy powder with a particle diameter of ≤74 μm is screened through a sample sieve to obtain a Mn-Al-C grain refiner with a particle diameter of ≤74 μm.

[0053] The Mn-Al-C grain refiner with a particle size of ≤74 μm prepared in this embodiment is applied to Mg-Al alloy, and the application method is the same as that in embodiment 1;

[0054] The present application also obtains alloy microstructure photos of the cast alloy sample obtained by applying the Mn-Al-C grain refiner in this embodiment to the Mg-Al alloy after solution treatment under an optical microscope, and uses the intercept method to measure the grain size of the alloy sample after solution treatment for different holding times; the optical microscopic photos of the Mg-9wt.%Al alloy solution sample without adding the intermediate alloy and after adding the intermediate alloy and holding for 30 minutes are shown as follows: Figure 3 As shown in a and b, it can be seen that the grain size has decreased significantly from 186±6μm to 113±4μm. The statistical comparison results of grain size are shown in Figure 5As shown, it can be observed that the grain size after the addition of the master alloy powder shows a trend similar to that of Example 1. The results show that when 0.2wt.% of Mn-Al-C master alloy powder (powder particle size ≤ 74μm) is added, the grain size is reduced by about 73μm, which once again proves the refinement effect of τ-MnAl-C relative to Mg-9wt.%Al alloy.

[0055] Example 3

[0056] This embodiment provides a method for preparing a Mn-Al-C grain refiner for magnesium and its alloy refinement, wherein the components and proportions thereof are the same as those in embodiment 1, and the preparation steps and parameters thereof are substantially the same as those in embodiment 1, except that the particle size of the screened particles of the Mn-Al-C grain refiner is different, specifically:

[0057] The quenched master alloy is mechanically crushed, and then the master alloy powder with a particle diameter of ≤74 μm is screened through a sample sieve to obtain a Mn-Al-C grain refiner with a particle diameter of ≤74 μm.

[0058] The Mn-Al-C grain refiner with a particle size of ≤74 μm prepared in this embodiment is applied to pure magnesium. The application method is basically the same as that in Example 1, except that the casting samples are only cast without adding the Mn-Al-C grain refiner and the samples are kept warm for 10 minutes after adding the Mn-Al-C grain refiner. The metallographic sample is directly taken from the cross section at 10 mm without solution treatment. After grinding, it is corroded with a picric acid solution, specifically:

[0059] The master alloy powder equal to 0.2wt.% of the melt mass was coated with aluminum foil and pressed into the pure magnesium melt, stirred for 30s, and then kept at 700℃ for 10min. The alloy was cast after being stirred for 10s before casting.

[0060] Take the cross-section sample at a height of 10 mm of the casting sample, metallographically polish the solid solution sample, and then use picric acid solution to corrode for 20 seconds.

[0061] The present application applies the Mn-Al-C grain refiner in this embodiment to pure magnesium, and uses the intercept method to measure the grain size of the casting sample before and after 10 minutes of refinement. The results are as follows: Figure 4 As shown in the figure, it can be seen that the grain size of pure magnesium before refinement in the present application is 648 μm, and it is 309 μm after refinement for 10 minutes, indicating that the Mn-Al-C grain refiner also has a refining effect on pure Mg.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A Mn-Al-C grain refiner for magnesium and its alloys, characterized in that: The composition includes the following components by mass ratio: Mn 68-72%, C 0.6-0.8%, and Al as the balance.

2. The Mn-Al-C grain refiner for magnesium and its alloys according to claim 1, characterized in that: The phase of the Mn-Al-C grain refiner is τ-MnAl-C phase or ε-MnAl-C phase.

3. The Mn-Al-C grain refiner for magnesium and its alloys according to claim 1, characterized in that: The atomic ratio of Al / Mn in the Mn-Al-C grain refiner is 0.77-0.

94.

4. A method for preparing a Mn-Al-C grain refiner for magnesium and its alloy refinement according to any one of claims 1 to 3, characterized in that: The steps include: 1) According to the formula requirements, smelting and casting the Mn-Al-C master alloy to obtain a cast Mn-Al-C master alloy; 2) homogenizing the cast Mn-Al-C master alloy, and then quenching it to obtain a homogenized Mn-Al-C master alloy; 3) The homogenized Mn-Al-C master alloy is subjected to mechanical crushing, mechanical crushing plus a suitable ball milling process, and screening to obtain a Mn-Al-C grain refiner.

5. The method for preparing the Mn-Al-C grain refiner for magnesium and its alloy refinement according to claim 4, characterized in that: The process parameters of the homogenization treatment in step 2) are: maintaining the temperature at 950-1100° C. for 0.5-3 h.

6. The method for preparing the Mn-Al-C grain refiner for magnesium and its alloy refinement according to claim 4, characterized in that: The particle size of the Mn-Al-C grain refiner is ≤250 μm.

7. A method for preparing a Mn-Al-C grain refiner for magnesium and its alloy refinement according to any one of claims 1 to 3, characterized in that: It also includes the use of spinning strips or grinding powders or atomization methods to prepare particles.

8. Use of the Mn-Al-C grain refiner for magnesium and its alloy refinement according to any one of claims 1 to 3 or the Mn-Al-C grain refiner for magnesium and its alloy refinement prepared by the preparation method according to any one of claims 4 to 7 in magnesium / magnesium alloys.

9. The use according to claim 8, characterized in that: The magnesium alloy includes Mg-Al, Mg-Si and Mg-Mn alloys.

10. The use according to claim 8 or 9, characterized in that: The addition amount of the Mn-Al-C grain refiner is 0.1-0.4wt.% of the mass of the magnesium / magnesium alloy.

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