Mg-Al-Mn-C grain refiner for refining magnesium-aluminum alloy and preparation method of Mg-Al-Mn-C grain refiner

Abstract

The invention discloses an Mg-Al-Mn-C grain refiner for refining magnesium-aluminum alloy, the Mg-Al-Mn-C grain refiner comprises the following components: Mg (5.3 x <-0.2 >) Al <-x > Mn <-0.01 > x C, x is equal to 0.9 to 1.5, and the balance is Mg. The invention further discloses a preparation method and application of the Mg-Al-Mn-C grain refiner for refining the magnesium-aluminum alloy. A matrix of the Mg-Al-Mn-C grain refiner is alpha-Mg, a second phase of the Mg-Al-Mn-C grain refiner is tau-MnAl-C, gamma2 (Al8Mn5) and Mg17Al12, and the Mg-Al-Mn-C grain refiner can be added into a magnesium-aluminum alloy melt in a blocky form for use; the tau-MnAl-C phase is an efficient nucleation substrate of alpha-Mg, and the refining effect is good; in the refining process of the Mg-Al-Mn-C grain refiner, the attenuation speed is low, and the stability is greatly improved; the adding amount of the magnesium alloy accounts for 1.0-1.5 wt.% of Mg-Al alloy melt, and the Mg-Al alloy contains Al element and a small amount of Mn impurities, so that the pollution to the alloy melt is low.

Description

Technical Field

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

[0002] Magnesium-aluminum alloys are widely used in the automotive industry, 3C products, aerospace and other fields due to their advantages such as light weight and high strength. However, their absolute strength and plasticity are still insufficient compared to competing aluminum alloys. Grain refinement is a recognized method that can simultaneously improve the strength and plasticity of alloys, and can also reduce defects such as hot cracking and looseness during alloy casting and improve the subsequent machinability of the alloy.

[0003] my country's patents on grain refinement of magnesium-aluminum alloys are mainly concentrated in various derivative versions of superheated melt treatment and carbon inoculation. In addition, patents CN 101481766 B, CN 101693969 B and CN 106062224 B all disclose the addition of Mn-Al alloy as a grain refiner. However, due to the high melting point of Mn-Al master alloy, it is difficult to add it directly to the magnesium-aluminum alloy melt in the form of a block. It needs to be added in the form of a powder after the casting alloy is mechanically crushed using a strip. Summary of the invention

[0004] 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 Mg-Al-Mn-C grain refiner for magnesium-aluminum alloy refinement, aiming to solve the problems of the Mn-Al grain refiner, such as the complicated preparation process, the need to add in the form of strips or powders, and the easy degradation of its refinement effect.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A Mg-Al-Mn-C grain refiner for magnesium-aluminum alloy refinement, wherein the composition of the Mg-Al-Mn-C grain refiner is Mg-(5.3x-0.2)Al-xMn-0.01xC, wherein x=0.9-1.5 and Mg is the balance.

[0007] In some specific embodiments, the matrix of the Mg-Al-Mn-C grain refiner is α-Mg, and the second phase is τ-MnAl-C, γ2(Al8Mn5) and Mg 17 Al 12 .

[0008] In some specific embodiments, the Mg-Al-Mn-C grain refiner is in block form, with a single volume of 3.3.3 mm 3-30·30·30mm 3 .

[0009] The present invention also provides a method for preparing a Mg-Al-Mn-C grain refiner for magnesium-aluminum alloy refinement, comprising the following steps:

[0010] 1) According to the formula requirements, Mg-Al-Mn-C master alloy is smelted to obtain Mg-Al-Mn-C alloy melt;

[0011] 2) casting the Mg-Al-Mn-C alloy melt by semi-continuous solidification to obtain a cast Mg-Al-Mn-C master alloy;

[0012] 3) Cutting the cast Mg-Al-Mn-C master alloy into blocks that meet the requirements to obtain the Mg-Al-Mn-C grain refiner.

[0013] In some specific embodiments, the smelting temperature in step 1) is 785-800°C.

[0014] In some specific embodiments, the process parameters of the semi-continuous solidification casting in step 2) are: water cooling and a casting speed of 5-10 cm / min.

[0015] The present invention also provides other preparation methods of Mg-Al-Mn-C grain refiner for magnesium and its alloy refinement, specifically, particles can be prepared by strip throwing and atomization method, and then sieved to obtain Mg-Al-Mn-C grain refiner.

[0016] The present invention also aims to provide an application of a Mg-Al-Mn-C grain refiner for magnesium-aluminum alloy refinement in magnesium-aluminum alloy.

[0017] In some specific embodiments, the addition amount of the Mg—Al—Mn—C grain refiner is 1-1.5 wt. % of the mass of the magnesium-aluminum alloy.

[0018] In some specific embodiments, the Mg-Al-Mn-C grain refiner can be directly added to a magnesium-aluminum alloy melt at 680-720° C., and the refinement time needs to be controlled within 5-60 min.

[0019] Compared with the prior art, the present invention has at least the following advantages:

[0020] 1) The refiner of the present invention effectively improves the stability of the τ-MnAl phase refiner by adding the C component; at the same time, the matrix of the Mg-Al-Mn-C grain refiner is α-Mg, and the second phase is τ-MnAl-C, γ2(Al8Mn5) and Mg 17Al 12 , can be added to the magnesium-aluminum alloy melt in the form of blocks, which is convenient and practical;

[0021] 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;

[0022] 3) The refiner provided by the present invention is mainly used for the refinement of magnesium-aluminum alloys. The refiner is added to the magnesium-aluminum alloy melt in the form of a Mg-Al-Mn-C intermediate alloy block containing a τ-MnAl-C phase, and the α-Mg matrix is ​​dissolved. At the same time, the τ-MnAl-C phase particles, which are efficient nucleation substrates, are released into the melt, thereby promoting the grain refinement of the Mg-Al alloy during the solidification process. The τ-MnAl-C phase is an efficient nucleation substrate for α-Mg, and has a good refinement effect; and the Mg-Al-Mn-C grain refiner has a slow decay rate during the refinement process, and its stability is greatly improved; the addition amount is 1.0-1.5wt.% of the Mg-Al alloy melt. The Mg-Al alloy itself contains Al elements and a small amount of Mn impurities, and the pollution to the alloy melt is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific embodiments of the present invention, the drawings required for use in the specific embodiments or the description of the prior art will be briefly introduced below.

[0024] Figure 1 The SEM image of the dendritic primary phase of the Mg-7.7Al-1.5Mn-0.02C (C is graphite addition) master alloy (a), the TEM image of the ion-thinned sample (b), the TEM magnified image of the dendrite part (c) and the selected area diffraction image of the middle part of the dendrite (d);

[0025] Figure 2 Polarized microscope photos of commercial AZ31 alloy samples at 720°C before refinement (a) and after adding 1wt.% Mg-7.7Al-1.5Mn-0.02C (C is activated carbon) master alloy block and keeping warm for 20min (b);

[0026] Figure 3 Polarized microscope photos of commercial AZ31 alloy samples at 720°C before refinement (a) and after adding 1wt.% Mg-7.7Al-1.5Mn-0.02C (C is graphite addition) master alloy block and keeping warm for 5 minutes (b);

[0027] Figure 4These are the grain size statistics of commercial AZ31 alloy samples with 1 wt.% C addition (activated carbon addition or graphite addition) of Mg-7.7Al-1.5Mn-0.02C master alloy blocks at 720°C for 0, 5, 10, 20, 30 and 60 min. 0 min represents no addition of master alloy powder. DETAILED DESCRIPTION

[0028] 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.

[0029] 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.

[0030] Unless otherwise indicated, all percentages, parts, ratios, etc. herein are by weight.

[0031] The materials, methods, and examples herein are illustrative and are not to be construed as limiting unless specifically stated.

[0032] In the following embodiments, refinement of commercial AZ31 alloy is used as an example for explanation;

[0033] Example 1

[0034] This embodiment provides a method for preparing a Mg-Al-Mn-C grain refiner for magnesium-aluminum alloy refinement, which comprises the following steps:

[0035] 1) using a resistance furnace to melt a Mg-Al-Mn-C master alloy to obtain a Mg-Al-Mn-C alloy melt; wherein the Mg-Al-Mn-C master alloy has, by mass fraction, 7.7% Al, 1.5% Mn, 0.02% C, and the remainder Mg; wherein Mn is added in the form of a Mg-5Mn master alloy, and C is pressed in in the form of aluminum foil coated activated carbon;

[0036] 2) performing semi-continuous solidification casting on the Mg-Al-Mn-C alloy melt under water cooling and a casting speed of 5 cm / min to obtain a cast Mg-Al-Mn-C master alloy;

[0037] 3) Cut the cast Mg-Al-Mn-C master alloy into 3.3.3 mm pieces by wire cutting. 3block to obtain Mg-Al-Mn-C grain refiner.

[0038] The microstructure of the prepared Mg-Al-Mn-C grain refiner was tested by SEM and TEM. Figure 1 As shown in ad, there is the SEM image of the dendritic primary phase of the Mg-Al-Mn-C grain refiner (a), the TEM image of the ion-thinned sample (b), the TEM enlarged image of the dendrite part (c) and the selected area diffraction image of the middle part of the dendrite (d), which is marked as τ-MnAl-C phase.

[0039] The Mg-Al-Mn-C grain refiner prepared in this application is used to refine the commercial AZ31 alloy, and the specific steps are as follows:

[0040] S1) melting commercial AZ31 alloy in a stainless steel crucible at 720° C. in a protective atmosphere of CO2+1 Vol.% SF6 to obtain an AZ31 alloy melt;

[0041] S2) a Mg-Al-Mn-C grain refiner equal to 1 wt.% of the mass of the AZ31 alloy melt is coated with aluminum foil and pressed into the magnesium-aluminum alloy melt, stirred for 30 seconds, and kept warm at 720°C;

[0042] 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;

[0043] In this embodiment, a casting sample without adding Mg-Al-Mn-C grain refiner is introduced as a control group to measure the grain size. Specifically, the AZ31 alloy melt prepared in step 1) is cast into the alloy. The casting mold used is a Φ20·Φ30·25mm preheated to 200°C. 3 Head-removing cone mold;

[0044] Take a sample 10 mm high from the middle of the casting sample, grind it metallographically, and then use picric acid solution to corrode it for 20 seconds.

[0045] The present application also applies the Mg-Al-Mn-C grain refiner to the commercial AZ31 alloy to obtain alloy structure photos of the cast alloy samples under a polarizing microscope, and uses the intercept method to measure the grain size of the cast alloy samples after being treated with different holding times; the optical microscope photos of the AZ31 alloy samples without adding the Mg-Al-Mn-C grain refiner and adding the Mg-Al-Mn-C grain refiner to hold for 20 minutes are shown as follows: Figure 2As shown in a and b, it can be seen that the grain size is significantly reduced from 356±40μm to 129±9μm. The statistical comparison results of grain size at different holding times after adding Mg-Al-Mn-C grain refiner are shown in Figure 4 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 intermediate alloy powder. The decreasing stage corresponds to the release of τ-MnAl-C phase particles caused by the dissolution of Mg-Al-Mn-C, and the increasing 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 1wt.% of Mg-Al-Mn-C (activated carbon) grain refiner is added, the grain size is reduced by about 227μm, which proves the refining effect of Mg-Al-Mn-C grain refiner on commercial AZ31 alloy.

[0046] Example 2

[0047] This embodiment provides a method for preparing a Mg-Al-Mn-C grain refiner for magnesium-aluminum alloy refinement, which is basically the same as the preparation method of Example 1, except that C is added in the form of graphite, specifically:

[0048] The Mg-Al-Mn-C master alloy is melted in a resistance furnace, and C is pressed in by means of aluminum foil wrapped graphite.

[0049] The Mg-Al-Mn-C (graphite) grain refiner prepared in this example is applied to commercial AZ31 alloy, and the application method is the same as that in Example 1.

[0050] The present application also applies the Mg-Al-Mn-C grain refiner to the commercial AZ31 alloy to obtain alloy structure photos of the cast alloy samples under a polarizing microscope, and uses the intercept method to measure the grain size of the cast alloy samples after different holding times; the optical microscope photos of the AZ31 alloy samples without adding the Mg-Al-Mn-C grain refiner and adding the Mg-Al-Mn-C grain refiner to hold for 5 minutes are shown as follows: Figure 3 As shown in a and b, it can be seen that the grain size is significantly reduced from 465±34μm to 154±18μm. The statistical comparison results of grain size at different holding times after adding Mg-Al-Mn-C grain refiner are shown in Figure 4 As shown, it can be observed that the grain size tends to decrease with the extension of the holding time after the addition of the master alloy powder, and the grain size does not fluctuate much after it decreases. The results show that when 1wt.% of Mg-Al-Mn-C (graphite) grain refiner is added, the grain size is reduced by about 311μm, which proves the refining effect of Mg-Al-Mn-C grain refiner on commercial AZ31 alloy.

[0051] 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 Mg-Al-Mn-C grain refiner for magnesium and its alloys, characterized in that: The composition of the Mg-Al-Mn-C grain refiner is Mg-(5.3x-0.2)Al-xMn-0.01xC, wherein x=0.9-1.5 and Mg is the balance.

2. The Mg-Al-Mn-C grain refiner for magnesium and its alloys according to claim 1, characterized in that: The matrix of the Mg-Al-Mn-C grain refiner is α-Mg, and the second phase is τ-MnAl-C, γ2(Al8Mn5) and Mg 17 Al 12 .

3. The Mg-Al-Mn-C grain refiner for magnesium and its alloys according to claim 1, characterized in that: The Mg-Al-Mn-C grain refiner is in block form, with a single volume of 3.3.3 mm 3 -30·30·30mm 3 .

4. A method for preparing a Mg-Al-Mn-C grain refiner for magnesium and its alloys according to any one of claims 1 to 3, characterized in that: The steps include: 1) According to the formula requirements, Mg-Al-Mn-C master alloy is smelted to obtain Mg-Al-Mn-C alloy melt; 2) casting the Mg-Al-Mn-C alloy melt by semi-continuous solidification to obtain a cast Mg-Al-Mn-C master alloy; 3) Cutting the cast Mg-Al-Mn-C master alloy into blocks that meet the requirements to obtain the Mg-Al-Mn-C grain refiner.

5. The method for preparing the Mg-Al-Mn-C grain refiner for magnesium-aluminum alloy refinement according to claim 4, characterized in that: The smelting temperature in step 1) is 785-800°C.

6. The method for preparing the Mg-Al-Mn-C grain refiner for magnesium-aluminum alloy refinement according to claim 4, characterized in that: The process parameters of the semi-continuous solidification casting in step 2) are: water cooling and a casting speed of 5-10 cm / min.

7. A method for preparing a Mg-Al-Mn-C grain refiner for magnesium and its alloy refinement according to any one of claims 1 to 3, characterized in that: The particles can also be prepared by strip throwing and atomization method, and then sieved to obtain Mg-Al-Mn-C grain refiner.

8. Use of the Mg-Al-Mn-C grain refiner for magnesium-aluminum alloy refinement according to any one of claims 1 to 3 or the Mg-Al-Mn-C grain refiner for magnesium-aluminum alloy refinement obtained by the preparation method according to any one of claims 4 to 7 in magnesium-aluminum alloy.

9. The use according to claim 8, characterized in that: The magnesium alloy includes a Mg-Al alloy.

10. The use according to claim 8 or 9, characterized in that: The addition amount of the Mg-Al-Mn-C grain refiner is 1-1.5wt.% of the mass of the magnesium-aluminum alloy.

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