Creep-resistant Mg-Y-Ca magnesium alloy and preparation method thereof

Abstract

The invention discloses a creep-resistant Mg-Y-Ca magnesium alloy and a preparation method thereof, and relates to the technical field of magnesium alloy materials, the creep-resistant Mg-Y-Ca magnesium alloy comprises the following components in percentage by mass: 4-7% of Y, 0.4-0.8% of Ca, 0.3-0.5% of X and the balance of Mg and inevitable impurities, and X is Mn or Zr; the invention also provides a preparation method of the creep-resistant Mg-Y-Ca magnesium alloy, which comprises the following steps: S1, smelting and casting the raw materials to obtain an as-cast magnesium alloy; s2, the as-cast magnesium alloy obtained in the step S1 is subjected to homogenizing heat treatment; and S3, the magnesium alloy obtained after homogenization heat treatment in the S2 is subjected to solid-state phase change stable particle generation heat treatment, and the creep-resistant Mg-Y-Ca magnesium alloy is obtained. The Mg-Y-Ca series magnesium alloy prepared by the preparation method disclosed by the invention has good high temperature resistance and creep resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloy materials, and particularly relates to a creep-resistant Mg-Y-Ca series magnesium alloy and a preparation method thereof. Background Art

[0002] As the lightest metal structural material, magnesium alloys have irreplaceable advantages in lightweight applications in fields such as automobiles, aerospace, and consumer electronics due to their high specific strength, excellent damping performance, and easy machinability. However, in a service environment at high temperatures (>250°C), due to the thermodynamic instability of metastable precipitated phases in traditional magnesium alloys, coarsening or re-dissolution easily occurs, resulting in a sharp decline in strength and creep resistance, severely restricting their application in key high-temperature scenarios such as engine blocks and transmission components. To solve the above problems, in the prior art, improvements are basically made through alloying and process optimization.

[0003] In the literature (T Sato, et al, Precipitation structure of Mg-Y alloys, Jornal of Japan Institute of Light Metals, 1992(42):804-809), it is confirmed that the Mg-10Y binary alloy has outstanding age hardening ability. However, at 250°C, the strengthening second phase formed at low and medium temperatures in the Mg-Y binary alloy will re-dissolve, resulting in a significant decrease in the strength and creep resistance of the alloy; in the patent with the publication number CN107739947A - A Mg-Y-Mn-Sc heat-resistant magnesium alloy and a preparation method thereof, as a typical precious metal, the addition of Sc greatly increases the alloy cost. At the same time, the alloy composition forms a complex multi-element system, and the preparation process is complex; in the patent with the authorization announcement number CN103757512B - A creep-resistant rare-earth magnesium alloy, a five-element alloy system is prepared, with great difficulty in composition control and a relatively complex alloy preparation process.

[0004] In the three patents of CN108866410A - A high-strength and high yield ratio Mg-Al-Ca-Y-Mn series alloy and a preparation method thereof, CN170236886A - A medical degradable high-strength, tough and corrosion-resistant multi-element Mg-Zn-Y-Ca-Zr alloy and a preparation method thereof, and CN115233060A - A high-strength, plastic, weak texture and low alloy content Mg-Zn-Y-Ca-Zr alloy and a preparation method thereof, these three patents focus on room-temperature strengthening, biocompatibility, and plasticity optimization respectively. None of the three patents involve the structural regulation of high-temperature stable phases, so the problem of the high-temperature performance short board of magnesium alloys cannot be solved either. Summary of the Invention

[0005] Aiming at the deficiencies existing in the prior art, the purpose of the present invention is to provide a creep-resistant Mg-Y-Ca series magnesium alloy and its preparation method to solve the problems of insufficient performance of existing magnesium alloys under high-temperature conditions and high preparation costs.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A creep-resistant Mg-Y-Ca series magnesium alloy, in terms of mass fraction, includes 4-7% of Y, 0.4-0.8% of Ca, and 0.3-0.5% of X, with the balance being Mg and inevitable impurities, where X is Mn or Zr.

[0008] The present invention also provides a preparation method of a creep-resistant Mg-Y-Ca series magnesium alloy, including the following steps:

[0009] S1. After melting and casting each component raw material, a as-cast magnesium alloy is obtained;

[0010] S2. The as-cast magnesium alloy obtained in step S1 is subjected to homogenization heat treatment;

[0011] S3. The magnesium alloy after homogenization heat treatment in S2 is subjected to solid-state phase transformation stable particle generation heat treatment to obtain a creep-resistant Mg-Y-Ca series magnesium alloy.

[0012] Preferably, in step S2, the magnesium alloy after homogenization heat treatment is hot extruded and then subjected to solid-state phase transformation stable particle generation heat treatment.

[0013] Preferably, in step S1, the melting method is specifically:

[0014] S11. Under a protective atmosphere, pure Mg is heated and melted to obtain a Mg melt;

[0015] S12. The Mg-Y master alloy is added to the Mg melt and melted to obtain a Mg-Y melt;

[0016] S13. The Mg-Ca master alloy is added to the Mg-Y melt and melted to obtain a Mg-Y-Ca melt;

[0017] S14. The Mg-Mn master alloy or Mg-Zr master alloy is added to the Mg-Y-Ca melt and melted to obtain a Mg-Y-Ca-Mn or Mg-Y-Ca-Zr melt;

[0018] S15. The Mg-Y-Ca-Mn or Mg-Y-Ca-Zr melt obtained in S14 is subjected to standing-stirring-standing-refining-casting to obtain an as-cast magnesium alloy.

[0019] Preferably, in step S11, the heating temperature is 670 - 700 °C and the heating time is 110 - 130 min;

[0020] In step S12, the heating temperature is 730 - 750 °C and the heating time is 8 - 15 min;

[0021] In step S13, the heating temperature is 690 - 710 °C and the heating time is 8 - 15 min;

[0022] In step S14, the heating temperature is 760 - 780 °C and the heating time is 8 - 15 min;

[0023] In step S15, the static temperature is 750 - 780 °C, the time for each static state is 8 - 12 min, and the stirring time is 2 - 5 min.

[0024] Preferably, in step S15, the specific refining operation is: adding a refining agent to the Mg - Y - Ca - Mn or Mg - Y - Ca - Zr melt, stirring at 750 - 770 °C, and then standing for 10 - 15 min, where the mass ratio of the refining agent to the Mg - Y - Ca - Mn or Mg - Y - Ca - Zr melt is 15:1000.

[0025] Preferably, in step S15, the casting temperature is 700 - 730 °C.

[0026] Preferably, in step S2, the homogenization heat treatment temperature is 500 - 520 °C and the time is 4 - 24 h.

[0027] Preferably, before the hot extrusion treatment, the magnesium alloy after the homogenization heat treatment needs to be preheated at 300 - 350 °C for 15 - 30 min, and then hot - extruded under the conditions of 300 - 350 °C and an extrusion ratio of 16 - 30.

[0028] Preferably, the heat treatment temperature for generating stable solid - state phase transformation particles is 300 - 350 °C and the time is 2 - 20 h.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The Mg-Y-Ca series magnesium alloy prepared by the present invention has good high-temperature resistance and creep resistance. The reason is based on the crystallographic characteristics of the second-phase particles formed by the coupling of Y and Ca. Since the second-phase particles are formed under conditions higher than the service temperature of the material and used under conditions lower than the phase transformation temperature, they naturally have thermodynamic stability. And these second-phase particles are distributed on the Mg matrix cylinder planes with triple crystallographic equivalence through solid-state phase transformation, rather than a single basal plane. As a result, the second-phase particles form a skeletonized configuration in three-dimensional space, generating a three-dimensional obstacle network for dislocation slip and increasing the kinetic blocking effect of the second-phase particles on dislocation movement. Moreover, the strengthening effect of the cylinder plane of the magnesium alloy is more significant than that of the basal plane strengthening. Therefore, the second-phase particles distributed on the cylinder plane have a stronger blocking effect on dislocations than the second-phase particles distributed on the basal plane and are a more ideal strengthening phase type. At the same time, the second-phase particles also have the advantages of being pollution-free and crystal matching, and will not form brittle stress concentration interfaces, resulting in the alloy being prone to cracking and failure at high temperatures.

[0031] 2. Through the coupling of two elements, Y and Ca, the alloy obtained in the present invention forms intermetallic compound particles rich in Y and Ca in the high-temperature range of 300 - 350 °C, generating a high-temperature precipitation strengthening effect and breaking through the bottleneck that traditional age-hardening Mg alloys have no precipitation strengthening ability in this temperature range, thereby effectively improving the thermodynamic stability of magnesium alloys in high-temperature applications.

[0032] 3. The addition content of Y is lower than that of traditional age-hardening Mg-Y alloys (Y content ≥ 10 wt.%). At the same time, Ca is an alloying element with extremely low cost in Mg alloys. The addition cost of alloying elements is low. Moreover, the second-phase particles formed by the coupling of Y and Ca have a short formation time. Compared with the conventional aging process, which usually takes 32 - 128 h to form strengthening phases inside the grains, the second-phase particles of the present invention can be formed within 2 - 20 h. The preparation process is simple, the equipment requirements are ordinary, and it has good application and promotion prospects.

[0033] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. Description of the Drawings

[0034] Figure 1 It is a schematic diagram of the melting process of the creep-resistant Mg-Y-Ca series magnesium alloy in Example 1.

[0035] Figure 2 It is a grain microstructure diagram of the creep-resistant Mg-Y-Ca series magnesium alloy in Example 1.

[0036] Figure 3 It is a precipitation phase microstructure diagram of the creep-resistant Mg-Y-Ca series magnesium alloy in Example 1.

[0037] Figure 4 It is the creep curve of the creep-resistant Mg-Y-Ca series magnesium alloy in Example 1. Detailed implementation mode

[0038] In order to make the technical means, creative features, achieved purposes and functions of the present invention clearer and easier to understand, the present invention will be further described below in conjunction with the drawings and specific implementation modes:

[0039] Example 1

[0040] X is Mn. By mass fraction, the Mg-Y-Ca series magnesium alloy includes 7% of Y, 0.6% of Ca, 0.5% of Mn, and the rest is Mg and inevitable impurities. The specific preparation method includes the following steps:

[0041] S1. Using a mixed gas of CO2 and SF6 as the protective atmosphere, pure Mg is melted by heating at 670°C for 130 min, the temperature is raised to 750°C, the Mg-Y master alloy is added, and melted by heating for 15 min. The temperature is lowered to 710°C, the Mg-Ca master alloy is added, and melted by heating for 15 min. Then the temperature is raised to 760°C, the Mg-Mn master alloy is added, and melted by heating for 15 min. Then at 770°C, static - stirring - static is carried out, with each static time of 12 min and the stirring time of 5 min. Subsequently, at 770°C, a refining agent is added while stirring, and then left standing for 10 min, where the mass ratio of the refining agent to the Mg-Y-Ca-Mn melt is 15:1000. Finally, casting is carried out at 730°C to obtain the as-cast magnesium alloy;

[0042] S2. The as-cast magnesium alloy prepared in S1 is subjected to homogenization heat treatment at 520°C for 24 h;

[0043] S3. For the magnesium alloy after homogenization heat treatment in S2, it is first preheated at 350°C for 30 min, and then hot extruded at 350°C with an extrusion ratio of 16;

[0044] S4. The magnesium alloy after hot extrusion in S3 is subjected to solid-state phase transformation and stable particle formation heat treatment at 350°C for 20 h to obtain the creep-resistant Mg-Y-Ca series magnesium alloy.

[0045] Example 2

[0046] X is Mn. By mass fraction, the Mg-Y-Ca series magnesium alloy includes 6% of Y, 0.4% of Ca, 0.3% of Mn, and the rest is Mg and inevitable impurities. The specific preparation method includes the following steps:

[0047] S1. Using a mixed gas of CO2 and SF6 as the protective atmosphere, pure Mg is melted by heating at 690 °C for 120 min, then the temperature is raised to 740 °C, Mg-Y master alloy is added, and melted by heating for 12 min. The temperature is lowered to 700 °C, Mg-Ca master alloy is added, and melted by heating for 12 min. Then the temperature is raised to 770 °C, Mg-Mn master alloy is added, and melted by heating for 12 min. Then at 760 °C, static-stir-static treatment is carried out, with each static time of 10 min and the stirring time of 4 min. Subsequently, at 750 °C, a refining agent is added while stirring, and then left standing for 12 min, where the mass ratio of the refining agent to the Mg-Y-Ca-Mn melt is 15:1000. Finally, casting is carried out at 720 °C to obtain as-cast magnesium alloy;

[0048] S2. The as-cast magnesium alloy prepared in S1 is subjected to homogenization heat treatment at 510 °C for 8 h;

[0049] S3. For the magnesium alloy after homogenization heat treatment in S2, it is first preheated at 330 °C for 20 min, and then hot extruded at 330 °C with an extrusion ratio of 24;

[0050] S4. The magnesium alloy after hot extrusion in S3 is subjected to solid-state phase transformation and stable particle formation heat treatment at 320 °C for 10 h to obtain creep-resistant Mg-Y-Ca series magnesium alloy.

[0051] Example 3

[0052] X is Zr. By mass fraction, the Mg-Y-Ca series magnesium alloy includes 4% of Y, 0.8% of Ca, 0.4% of Zr, and the rest is Mg and unavoidable impurities. The specific preparation method includes the following steps:

[0053] S1. Using a mixed gas of CO2 and SF6 as the protective atmosphere, pure Mg is melted by heating at 700 °C for 110 min, then the temperature is raised to 730 °C, Mg-Y master alloy is added, and melted by heating for 8 min. The temperature is lowered to 710 °C, Mg-Ca master alloy is added, and melted by heating for 8 min. Then the temperature is raised to 780 °C, Mg-Mn master alloy is added, and melted by heating for 8 min. Then at 750 °C, static-stir-static treatment is carried out, with each static time of 8 min and the stirring time of 2 min. Subsequently, at 760 °C, a refining agent is added while stirring, and then left standing for 15 min, where the mass ratio of the refining agent to the Mg-Y-Ca-Zr melt is 15:1000. Finally, casting is carried out at 700 °C to obtain as-cast magnesium alloy;

[0054] S2. The as-cast magnesium alloy prepared in S1 is subjected to homogenization heat treatment at 500 °C for 4 h;

[0055] S3. For the magnesium alloy after homogenization heat treatment in S2, first preheat it at 300 °C for 15 min, and then perform hot extrusion at 300 °C with an extrusion ratio of 30.

[0056] S4. For the magnesium alloy after hot extrusion in S3, conduct heat treatment for 2 h at 300 °C to generate stable particles for solid-state phase transformation, obtaining a creep-resistant Mg-Y-Ca series magnesium alloy.

[0057] Example 4

[0058] Compared with Example 1, without performing the hot extrusion operation, after the as-cast magnesium alloy undergoes homogenization heat treatment, directly conduct heat treatment for generating stable particles for solid-state phase transformation.

[0059] Calculate the steady-state creep rates of the creep-resistant Mg-Y-Ca series magnesium alloys prepared in Examples 1-4. The results are shown in Table 1:

[0060] Example 1 Example 2 Example 3 Example 4 Steady-state creep rate <![CDATA[7.8×10 -6 s -1 > <![CDATA[5.6×10 -7 s -1 > <![CDATA[9.1×10 -9 s -1 > <![CDATA[9.7×10 -6 s -1 >

[0061] Table 1 Steady-state creep rates of each example

[0062] As can be seen from the above table, the creep-resistant Mg-Y-Ca series magnesium alloys prepared in Examples 1-4 all have good high-temperature resistance and creep resistance, and among them, Example 3 has the best creep resistance.

[0063] Moreover, according to the steady-state creep rates of Example 1 and Example 4, it can be seen that after undergoing the hot extrusion treatment, the creep resistance of the creep-resistant Mg-Y-Ca series magnesium alloy can be made more excellent.

[0064] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not intended to limit. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A creep-resistant Mg-Y-Ca series magnesium alloy, characterized in that, By mass fraction, it includes 4-7% of Y, 0.4-0.8% of Ca, and 0.3-0.5% of X, with the balance being Mg and inevitable impurities, where X is Mn or Zr.

2. The preparation method of an anti-creep Mg-Y-Ca series magnesium alloy according to claim 1, characterized in that, It includes the following steps: S1. After melting and casting each component raw material, an as-cast magnesium alloy is obtained. S2. The as-cast magnesium alloy obtained in step S1 is subjected to homogenization heat treatment. S3. The magnesium alloy after homogenization heat treatment in S2 is subjected to solid-state phase transformation stable particle generation heat treatment to obtain a creep-resistant Mg-Y-Ca series magnesium alloy.

3. The preparation method of a creep-resistant Mg-Y-Ca series magnesium alloy according to claim 2, characterized in that, In step S2, after hot extrusion of the magnesium alloy after homogenization heat treatment, solid-state phase transformation stable particle generation heat treatment is carried out.

4. The preparation method of an anti-creep Mg-Y-Ca series magnesium alloy according to claim 2, characterized in that, In step S1, the melting method is specifically as follows: S11. Under a protective atmosphere, pure Mg is heated and melted to obtain a Mg melt. S12. The Mg-Y master alloy is added to the Mg melt and melted to obtain a Mg-Y melt. S13. The Mg-Ca master alloy is added to the Mg-Y melt and melted to obtain a Mg-Y-Ca melt. S14. The Mg-Mn master alloy or Mg-Zr master alloy is added to the Mg-Y-Ca melt and melted to obtain a Mg-Y-Ca-Mn or Mg-Y-Ca-Zr melt. S15. After standing-stirring-standing-refining-casting of the Mg-Y-Ca-Mn or Mg-Y-Ca-Zr melt obtained in S14, an as-cast magnesium alloy is obtained.

5. According to the preparation method of a creep-resistant Mg-Y-Ca series magnesium alloy described in claim 4, it is characterized in that In step S11, the heating temperature is 670-700 °C, and the heating time is 110-130 min. In step S12, the heating temperature is 730-750 °C, and the heating time is 8-15 min. In step S13, the heating temperature is 690-710 °C, and the heating time is 8-15 min. In step S14, the heating temperature is 760-780 °C, and the heating time is 8-15 min. In step S15, the standing temperature is 750-780 °C, the standing time for each time is 8-12 min, and the stirring time is 2-5 min.

6. The preparation method of a creep-resistant Mg-Y-Ca series magnesium alloy according to claim 4, characterized in that, In step S15, the refining operation is specifically: adding a refining agent to the Mg-Y-Ca-Mn or Mg-Y-Ca-Zr melt, stirring at 750-770 °C, and then standing for 10-15 min, where the mass ratio of the refining agent to the Mg-Y-Ca-Mn or Mg-Y-Ca-Zr melt is 15:1000.

7. The preparation method of a creep-resistant Mg-Y-Ca series magnesium alloy according to claim 4, characterized in that, In step S15, the casting temperature is 700-730 °C.

8. The preparation method of an anti-creep Mg-Y-Ca series magnesium alloy according to claim 2, characterized in that, In step S2, the homogenization heat treatment temperature is 500-520 °C, and the time is 4-24 h.

9. The preparation method of an anti-creep Mg-Y-Ca series magnesium alloy according to claim 3, characterized in that, Before hot extrusion treatment, the magnesium alloy after homogenization heat treatment needs to be preheated at 300-350 °C for 15-30 min, and then hot extrusion is carried out at 300-350 °C with an extrusion ratio of 16-30.

10. The preparation method of an anti-creep Mg-Y-Ca series magnesium alloy according to claim 2, characterized in that, The solid-state phase transformation stable particle generation heat treatment temperature is 300-350 °C, and the time is 2-20 h.

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