CN113755732B - Mg-Nd-Mn ternary heat-resistant magnesium alloy and preparation method thereof - Google Patents
Mg-Nd-Mn ternary heat-resistant magnesium alloy and preparation method thereof Download PDFInfo
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- C22C23/00—Alloys based on magnesium
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- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/06—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon
Abstract
The invention belongs to the field of non-ferrous metal materials and processing thereof, and particularly relates to a Mg-Nd-Mn ternary heat-resistant magnesium alloy and a preparation method thereof. The heat-resistant magnesium alloy comprises the following components in percentage by mass: 0.5-3.0 wt% of Nd, 0-3.0 wt% of Mn, and the balance of Mg and inevitable impurities, wherein the content of the impurities is less than or equal to 0.04 wt%. The heat-resistant magnesium alloy is prepared by a series of means such as melting, casting, solution treatment, low-temperature extrusion and the like. According to the invention, the wrought magnesium alloy with submicron grain size is obtained by compositely adding Nd and Mn elements and combining a low-temperature extrusion process. Dynamic precipitation of high density Mg during extrusion 12 The Nd nanometer precipitated phase has higher thermal stability and still plays a role in strengthening at high temperature; and a large amount of solute atoms are segregated near the grain boundary and the dislocation, so that the movement of the grain boundary and the dislocation is strongly inhibited, and the high-temperature mechanical property of the alloy is further improved.
Description
The technical field is as follows:
the invention belongs to the field of non-ferrous metal materials and processing thereof, and particularly relates to a Mg-Nd-Mn ternary heat-resistant magnesium alloy and a preparation method thereof.
Background art:
as the lightest metal structural material, magnesium and magnesium alloy are the third most metal structural materials with more potential after steel and aluminum alloy, are known as 'green engineering metal in the 21 st century', and are widely applied to key equipment and major engineering in China. Especially in the fields of transportation and aerospace, the popularization and application of magnesium and magnesium alloy can obviously reduce the weight of parts, improve the fuel efficiency and save energy, thereby relieving the increasingly severe environmental and energy crisis in China.
However, the magnesium alloy has low strength, and the strength is sharply reduced particularly at high temperature, which severely limits the application of the magnesium alloy in the high temperature field. At present, researches are started from limiting dislocation movement and strengthening a grain boundary, and the aim of improving the high-temperature performance of the magnesium alloy is achieved by means of introducing a second phase with higher thermal stability, reducing the diffusion rate of alloy elements in a magnesium matrix, improving the structural state of the grain boundary and the like through proper alloying. However, the effect of improving the high-temperature performance of Mg — Al alloys, which are most widely used, is extremely limited when the combination of various elements such as Si, Ca, Ba, Sr, and rare earth elements (REs) is changed to 1.
In order to eliminate the negative effect of Al element, alloy systems such as Mg-RE, Mg-Sn and Mg-Sr-Mn appear in succession, wherein the high-temperature performance of the Mg-RE alloy is the most excellent. Among the rare earth elements, Nd, Y and Gd have more obvious solid solution and precipitation strengthening effects, and the precipitated phase also has higher thermal stability, so that the dislocation and the movement of a crystal boundary can be inhibited at high temperature, and the high-temperature mechanical property of the alloy is greatly improved. However, the current commercial heat-resistant magnesium alloy such as WE54 is difficult to be applied in the fields of military, aerospace, transportation and the like on a large scale due to its rapid strength reduction at high temperature and high cost. Therefore, the development of a magnesium alloy material with high strength, heat resistance and low cost has important significance for the practical application of magnesium alloy.
The invention content is as follows:
the invention aims to provide an Nd and Mn composite reinforced Mg-Nd-Mn ternary heat-resistant magnesium alloy and a preparation method thereof. The deformed magnesium alloy with submicron grain size is obtained by compositely adding elements such as Nd, Mn and the like and combining a low-temperature extrusion process. Dynamic precipitation of high density Mg during extrusion 12 The Nd nanometer precipitated phase has higher thermal stability and still plays a role in strengthening at high temperature; and a large amount of solute atoms are segregated near the grain boundary and the dislocation, so that the movement of the grain boundary and the dislocation is strongly inhibited, and the high-temperature mechanical property of the alloy is further improved.
The purpose of the invention can be realized by the following technical scheme:
a Mg-Nd-Mn ternary heat-resistant magnesium alloy comprises Nd and Mn, wherein the content of Nd is 0.5-3.0 wt%.
The Mg-Nd-Mn ternary heat-resistant magnesium alloy comprises the following components in percentage by mass: 0.5-3.0 wt% of Nd; 0-3.0 wt% of Mn, and the balance of Mg and inevitable impurities, wherein the content of the impurities is less than or equal to 0.04 wt%.
The yield strength of the Mg-Nd-Mn ternary heat-resistant magnesium alloy at room temperature is 380-400 MPa, the tensile strength is 410-430 MPa, and the elongation is 2-10%.
The yield strength of the Mg-Nd-Mn ternary heat-resistant magnesium alloy at a high temperature of 250 ℃ is 240-270 MPa, the tensile strength is 260-280 MPa, and the elongation is 4-16%.
The preparation method of the Mg-Nd-Mn ternary heat-resistant magnesium alloy comprises the following steps:
preheating an industrial pure magnesium ingot, an Mg-25% Nd intermediate alloy and an Mg-10% Mn intermediate alloy at 100-200 ℃ for 30-60 min;
step two, melting the preheated industrial pure magnesium ingot in a protective atmosphere at the temperature of 760 +/-10 ℃; sequentially putting the preheated Mg-25% Nd intermediate alloy and the preheated Mg-10% Mn intermediate alloy into the completely molten pure magnesium melt, and preserving the heat for 10-30 min; after the Mg-25% Nd intermediate alloy and the Mg-10% Mn intermediate alloy are completely melted, mechanically stirring for 1-3 min; then, reducing the temperature to 730 +/-10 ℃, introducing argon to promote the uniform mixing of the melt and achieve degassing of the melt, and standing for 5-15 min at the temperature to enable impurities in the melt to float or settle; finally, cooling the melt to 710 +/-10 ℃, skimming dross, and pouring to obtain a magnesium alloy ingot;
step three, carrying out solid solution treatment on the obtained magnesium alloy ingot;
and step four, performing low-temperature extrusion on the magnesium alloy ingot subjected to the solution treatment.
The preparation method of the Mg-Nd-Mn ternary heat-resistant magnesium alloy comprises the second step of adopting the protective atmosphere of SF 6 And CO 2 And mixed gas of (1), and SF 6 The volume percentage content of (A) is 0.5-0.7 vt％。
The preparation method of the Mg-Nd-Mn ternary heat-resistant magnesium alloy comprises the third step of water quenching, wherein the temperature of solution treatment is 520-550 ℃, the heat preservation time is 10-30 h.
In the fourth step, the extrusion temperature of low-temperature extrusion is not higher than 300 ℃, the extrusion rate is 0.3-0.5 mm/s, and the extrusion ratio is 20-30.
The invention has the advantages and beneficial effects that:
1. according to the invention, 0.5-3.0 wt% of Nd element and 0-1.2 wt% of Mn element are added into the magnesium alloy, the addition of the Nd element can not only refine the matrix, but also dynamically precipitate high-melting-point Mg in the crystal grains and on the crystal boundary in the extrusion process 12 Nd nanometer precipitated phase can obviously improve the high-temperature mechanical property of the alloy; the addition of the Mn element can not only form compounds with Fe or other heavy metal elements in impurities, but also be discharged as slag; can promote Mg in the extrusion process 12 Dynamic precipitation of Nd phase, refining the size of the phase.
2. The Nd element and the Mn element which are added into the magnesium alloy in a compounding way can be deviated on crystal boundaries and dislocation lines, so that the solute dragging effect is generated on the dislocations and the crystal boundaries, the movement of the dislocations and the crystal boundaries is effectively blocked, and the boundaries and phase interfaces are strengthened, thereby improving the high-temperature mechanical property of the alloy.
3. The high-strength heat-resistant magnesium alloy prepared by the invention is a ternary system, is prepared by a series of means such as melting, casting, solution treatment, low-temperature extrusion and the like, is simple and easy to industrialize, realizes the unification of high strength and heat resistance, and has excellent performance, fewer alloy principal elements, more uniform alloy components, lower cost and good industrial application value compared with the existing heat-resistant alloy system.
Description of the drawings:
FIG. 1 is a microstructure diagram of an extruded Mg-1.0Nd-0.3Mn alloy according to example 1 of the present invention.
FIGS. 2 to 3 are microstructure diagrams of an extruded Mg-2.0Nd-0.5Mn alloy according to example 2 of the present invention; fig. 2 is an annular bright field scanning transmission photograph, and fig. 3 is a high-angle annular dark field scanning transmission photograph.
FIGS. 4 to 5 are microstructure views of an extruded Mg-3.0Nd-0.8Mn alloy according to example 3 of the present invention; wherein, fig. 4 is a ring bright field scanning transmission photograph, and fig. 5 is a result of energy spectrum analysis of a transmission electron microscope.
FIG. 6 is a microstructure comparison of the alloys in the extruded state of examples 4, 5 and 6 according to the invention; wherein (a) is a microstructure diagram of the as-extruded Mg-3.0Nd-3.0Mn alloy of example 4, (b) is a microstructure diagram of the as-extruded Mg-2.0Nd alloy of example 5, (c) is a microstructure diagram of the as-extruded Mg-1.0Nd alloy of example 6, and (d) is a microstructure enlarged view of the as-extruded Mg-1.0Nd alloy of example 6.
FIG. 7 is a tensile engineering stress-strain curve of the alloys of examples 1, 2 and 3 of the present invention at room temperature.
FIG. 8 is a tensile engineering stress-strain curve at 250 ℃ for the alloys of examples 1, 2 and 3 of the present invention.
FIG. 9 is a tensile engineering stress-strain curve at room temperature for the alloys of examples 4, 5 and 6 of the present invention.
FIG. 10 is a tensile engineering stress-strain curve at 250 ℃ for the alloys of examples 4, 5 and 6 of the present invention.
The specific implementation mode is as follows:
in the specific implementation process, the Nd and Mn composite reinforced heat-resistant magnesium alloy comprises Nd and Mn elements, wherein the mass percentage content of the Nd element and the mass percentage content of the Mn element are 0.5-3.0 wt% and 0-1.2 wt% respectively. The added Mn element forms an alpha-Mn phase during extrusion, which can act as Mg 12 Heterogeneous nucleation core of Nd phase promoting Mg 12 Dynamic precipitation of Nd phase, refining the size of the phase; and Mn element can also form a compound with Fe or other heavy metal elements in impurities, and the compound is discharged as slag, so that the aim of purifying the melt is fulfilled. The added Nd and Mn elements can be partially gathered on crystal boundaries and dislocation lines, so that a solute dragging effect is generated on the dislocations and the crystal boundaries, the movement of the dislocations and the crystal boundaries is effectively blocked, and the high-temperature mechanical property of the alloy is improved.
Preferably, the magnesium alloy comprises the following components in percentage by mass: nd0.5-2.0 wt%; mn 0-1.2 wt%, and the balance of Mg and inevitable impurities, wherein the content of the impurities is less than or equal to 0.04 wt%.
The yield strength of the magnesium alloy at room temperature is 380-400 MPa, the tensile strength is 400-440 MPa, and the elongation is 2-10% (preferably 2-4%). The yield strength of the magnesium alloy at a high temperature of 250 ℃ is 240-270 MPa, the tensile strength is 260-290 MPa, and the elongation is 4-16% (preferably 13-15%).
The preparation method of the Nd and Mn composite reinforced heat-resistant magnesium alloy comprises the following steps:
preheating an industrial pure magnesium ingot, an Mg-25% Nd intermediate alloy (Nd 25% and the balance of Mg according to the mass percentage content) and an Mg-10% Mn intermediate alloy (Mn 10% and the balance of Mg according to the mass percentage content) for 1h at 150 ℃;
step two, melting the preheated industrial pure magnesium ingot in a protective atmosphere at the temperature of 760 ℃; sequentially putting the preheated Mg-25% Nd intermediate alloy and the preheated Mg-10% Mn intermediate alloy into the completely molten pure magnesium melt, and preserving the heat for 20 min; after the Mg-25% Nd intermediate alloy and the Mg-10% Mn intermediate alloy are completely melted, mechanically stirring for 2 min; then introducing argon to promote the uniform mixing of the melt and achieve the effect of melt degassing, and standing for 10min at the temperature to enable impurities in the melt to float upwards or settle; finally, cooling the melt to 710 ℃, skimming dross, and pouring to obtain a magnesium alloy ingot;
preferably, the protective atmosphere in the second step is SF 6 And CO 2 And mixed gas of (1), and SF 6 The percentage content by volume of (B) was 0.6 vt%.
Step three, carrying out solid solution treatment on the obtained magnesium alloy ingot;
preferably, in the third step, the temperature of the solution treatment is 520-550 ℃, the heat preservation time is 10-30 h, and water quenching is carried out. On one hand, the step can lead elements in the alloy to carry out solid diffusion, eliminate or reduce the intragranular segregation caused by the unbalanced solidification of the magnesium alloy, and promote the homogenization of the chemical components and the structure of the alloy, thereby improving the performance of the magnesium alloy; on the other hand, the coarse second phase can be fully dissolved in the magnesium matrix, and the supersaturated solid solution is obtained by rapid cooling, so that preparation is provided for dynamically precipitating the high-density nano second phase in the extrusion process.
And step four, performing low-temperature extrusion on the magnesium alloy ingot subjected to the solution treatment.
Preferably, in the fourth step, the extrusion temperature of the low-temperature extrusion is not higher than 300 ℃ (preferably 200-300 ℃), the extrusion rate is 0.3-0.5 mm/s, and the extrusion ratio is 25. Firstly, the extrusion can improve the structural defects (such as shrinkage porosity, shrinkage cavity, air holes and the like) generated in the casting process and increase the compactness of the alloy. Secondly, the temperature rise in the deformation process can be reduced to the greatest extent by using the temperature lower than 300 ℃ and matching with the lower speed for extrusion, so that the recrystallized grains and the dynamically precipitated second phase are not too coarse, the dynamic recovery of dislocation can be effectively inhibited, and the storage of dislocation in the dynamic deformation process is facilitated.
The invention will now be further illustrated by reference to the following examples:
example 1:
in the embodiment, the Nd and Mn composite reinforced heat-resistant magnesium alloy comprises the following components in percentage by mass: 1.0 wt% of Nd, 0.3 wt% of Mn, and the balance of Mg and inevitable impurities, wherein the content of the impurities is less than or equal to 0.04 wt%.
In this embodiment, the preparation method of the Nd and Mn composite reinforced heat-resistant magnesium alloy includes the following steps:
1) preheating an industrial pure magnesium ingot, Mg-25% of Nd intermediate alloy and Mg-10% of Mn intermediate alloy for 1h at 150 ℃;
2) putting the preheated industrial pure magnesium ingot in SF 6 /CO 2 Melting in protective atmosphere at 760 ℃; sequentially putting the preheated Mg-25% Nd intermediate alloy and the preheated Mg-10% Mn intermediate alloy into the completely molten pure magnesium melt, and preserving the heat for 20 min; after the Mg-25% Nd intermediate alloy and the Mg-10% Mn intermediate alloy are completely melted, mechanically stirring for 2 min; then, reducing the temperature to 730 ℃, introducing argon to promote the uniform mixing of the melt and achieve the effect of melt degassing, and standing for 10min at the temperature to enable impurities in the melt to float or settle; finally, cooling the melt to 710 ℃, skimming dross, and pouring to obtain a magnesium alloy ingot;
3) carrying out solution treatment on the obtained magnesium alloy ingot at the temperature of 530 ℃ for 20h, and then carrying out water quenching;
4) and (3) carrying out low-temperature extrusion on the magnesium alloy ingot subjected to solution treatment under the conditions that the extrusion temperature is 290 ℃, the extrusion rate is 0.45mm/s and the extrusion ratio is 25.
The yield strength of the magnesium alloy at room temperature is 382MPa, the tensile strength is 400MPa, and the elongation is 3.6 percent; the yield strength of the magnesium alloy at the high temperature of 250 ℃ is 243MPa, the tensile strength is 266MPa, and the elongation is 11.3%.
Example 2:
in the embodiment, the Nd and Mn composite reinforced heat-resistant magnesium alloy comprises the following components in percentage by mass: 2.0 wt% of Nd, 0.5 wt% of Mn, and the balance of Mg and inevitable impurities, wherein the content of the impurities is less than or equal to 0.04 wt%.
In this embodiment, the preparation method of the Nd and Mn composite reinforced heat-resistant magnesium alloy includes the following steps:
1) preheating an industrial pure magnesium ingot, Mg-25% of Nd intermediate alloy and Mg-10% of Mn intermediate alloy for 1h at 150 ℃;
2) putting the preheated industrial pure magnesium ingot in SF 6 /CO 2 Melting in protective atmosphere at 760 ℃; sequentially putting the preheated Mg-25% Nd intermediate alloy and the preheated Mg-10% Mn intermediate alloy into the completely molten pure magnesium melt, and preserving the heat for 20 min; after the Mg-25% Nd intermediate alloy and the Mg-10% Mn intermediate alloy are completely melted, mechanically stirring for 2 min; then, reducing the temperature to 730 ℃, introducing argon to promote the uniform mixing of the melt and achieve the effect of melt degassing, and standing for 10min at the temperature to enable impurities in the melt to float or settle; finally, cooling the melt to 710 ℃, skimming dross, and pouring to obtain a magnesium alloy ingot;
3) carrying out solution treatment on the obtained magnesium alloy ingot at the temperature of 540 ℃ for 22h, and then carrying out water quenching;
4) and (3) carrying out low-temperature extrusion on the magnesium alloy ingot subjected to the solution treatment under the conditions that the extrusion temperature is 280 ℃, the extrusion rate is 0.4mm/s and the extrusion ratio is 25.
The yield strength of the magnesium alloy at room temperature is 395MPa, the tensile strength is 408MPa, and the elongation is 3.2%; the yield strength of the magnesium alloy at the high temperature of 250 ℃ is 249MPa, the tensile strength is 271MPa, and the elongation is 9.8 percent
Example 3:
in the embodiment, the Nd and Mn composite reinforced heat-resistant magnesium alloy comprises the following components in percentage by mass: nd 3.0 wt%, Mn 0.8 wt%, Mg and inevitable impurity for the rest, and the impurity content is less than or equal to 0.04 wt%.
In this embodiment, the preparation method of the Nd and Mn composite reinforced heat-resistant magnesium alloy includes the following steps:
1) preheating an industrial pure magnesium ingot, Mg-25% of Nd intermediate alloy and Mg-10% of Mn intermediate alloy for 1h at 150 ℃;
2) putting the preheated industrial pure magnesium ingot in SF 6 /CO 2 Melting in protective atmosphere at 760 ℃; sequentially putting the preheated Mg-25% Nd intermediate alloy and the preheated Mg-10% Mn intermediate alloy into the completely molten pure magnesium melt, and preserving the heat for 20 min; after the Mg-25% Nd intermediate alloy and the Mg-10% Mn intermediate alloy are completely melted, mechanically stirring for 2 min; then, reducing the temperature to 730 ℃, introducing argon to promote the uniform mixing of the melt and achieve the effect of melt degassing, and standing for 10min at the temperature to enable impurities in the melt to float or settle; finally, cooling the melt to 710 ℃, skimming dross, and pouring to obtain a magnesium alloy ingot;
3) carrying out solution treatment on the obtained magnesium alloy ingot at the temperature of 550 ℃ for 24h, and then carrying out water quenching;
4) and (3) extruding the magnesium alloy ingot subjected to solution treatment at a low temperature under the conditions that the extrusion temperature is 270 ℃, the extrusion rate is 0.3mm/s and the extrusion ratio is 25.
The yield strength of the magnesium alloy at room temperature is 398MPa, the tensile strength is 430MPa, and the elongation is 2.5 percent; the yield strength of the magnesium alloy at the high temperature of 250 ℃ is 269MPa, the tensile strength is 288MPa, and the elongation is 4.2%.
Example 4:
in the embodiment, the Nd and Mn composite reinforced heat-resistant magnesium alloy comprises the following components in percentage by mass: 3.0 wt% of Nd, 3.0 wt% of Mn, and the balance of Mg and inevitable impurities, wherein the content of the impurities is less than or equal to 0.04 wt%.
In this embodiment, the preparation method of the Nd and Mn composite reinforced heat-resistant magnesium alloy includes the following steps:
1) preheating an industrial pure magnesium ingot, Mg-25% of Nd intermediate alloy and Mg-10% of Mn intermediate alloy for 1h at 150 ℃;
2) putting the preheated industrial pure magnesium ingot in SF 6 /CO 2 Melting in protective atmosphere at 760 ℃; sequentially putting the preheated Mg-25% Nd intermediate alloy and the preheated Mg-10% Mn intermediate alloy into the completely molten pure magnesium melt, and preserving the heat for 20 min; after the Mg-25% Nd intermediate alloy and the Mg-10% Mn intermediate alloy are completely melted, mechanically stirring for 2 min; then, reducing the temperature to 730 ℃, introducing argon to promote the uniform mixing of the melt and achieve the effect of melt degassing, and standing for 10min at the temperature to enable impurities in the melt to float or settle; finally, cooling the melt to 710 ℃, skimming dross, and pouring to obtain a magnesium alloy ingot;
3) carrying out solution treatment on the obtained magnesium alloy ingot at the temperature of 550 ℃ for 24h, and then carrying out water quenching;
4) and (3) carrying out low-temperature extrusion on the magnesium alloy ingot subjected to solution treatment under the conditions that the extrusion temperature is 280 ℃, the extrusion rate is 0.4mm/s and the extrusion ratio is 25.
The yield strength of the magnesium alloy at room temperature is 400MPa, the tensile strength is 440MPa, and the elongation is 2.0%; the yield strength of the magnesium alloy at the high temperature of 250 ℃ is 269MPa, the tensile strength is 289MPa, and the elongation is 8.5%.
Example 5:
in the embodiment, the Nd and Mn composite reinforced heat-resistant magnesium alloy comprises the following components in percentage by mass: 2.0 wt% of Nd, and the balance of Mg and inevitable impurities, wherein the content of the impurities is less than or equal to 0.04 wt%.
In this embodiment, the preparation method of the Nd and Mn composite reinforced heat-resistant magnesium alloy includes the following steps:
1) preheating an industrial pure magnesium ingot, Mg-25% of Nd intermediate alloy and Mg-10% of Mn intermediate alloy for 1h at 150 ℃;
2) putting the preheated industrial pure magnesium ingot in SF 6 /CO 2 Protection ofMelting in atmosphere at 760 ℃; sequentially putting the preheated Mg-25% Nd intermediate alloy and the preheated Mg-10% Mn intermediate alloy into the completely molten pure magnesium melt, and preserving the heat for 20 min; after the Mg-25% Nd intermediate alloy and the Mg-10% Mn intermediate alloy are completely melted, mechanically stirring for 2 min; then, reducing the temperature to 730 ℃, introducing argon to promote the uniform mixing of the melt and achieve the effect of melt degassing, and standing for 10min at the temperature to enable impurities in the melt to float or settle; finally, cooling the melt to 710 ℃, skimming dross, and pouring to obtain a magnesium alloy ingot;
3) carrying out solution treatment on the obtained magnesium alloy ingot at the temperature of 550 ℃ for 24h, and then carrying out water quenching;
4) and (3) carrying out low-temperature extrusion on the magnesium alloy ingot subjected to solution treatment under the conditions that the extrusion temperature is 280 ℃, the extrusion rate is 0.4mm/s and the extrusion ratio is 25.
The yield strength of the magnesium alloy at room temperature is 398MPa, the tensile strength is 425MPa, and the elongation is 3.8%; the yield strength of the magnesium alloy at the high temperature of 250 ℃ is 262MPa, the tensile strength is 279MPa, and the elongation is 11.2%.
Example 6:
in the embodiment, the Nd and Mn composite reinforced heat-resistant magnesium alloy comprises the following components in percentage by mass: nd1.0 wt%, and the balance of Mg and inevitable impurities, wherein the content of the impurities is less than or equal to 0.04 wt%.
In this embodiment, the preparation method of the Nd and Mn composite reinforced heat-resistant magnesium alloy includes the following steps:
1) preheating an industrial pure magnesium ingot, Mg-25% of Nd intermediate alloy and Mg-10% of Mn intermediate alloy for 1h at 150 ℃;
2) putting the preheated industrial pure magnesium ingot in SF 6 /CO 2 Melting in protective atmosphere at 760 ℃; sequentially putting the preheated Mg-25% Nd intermediate alloy and the preheated Mg-10% Mn intermediate alloy into the completely molten pure magnesium melt, and preserving the heat for 20 min; after the Mg-25% Nd intermediate alloy and the Mg-10% Mn intermediate alloy are completely melted, mechanically stirring for 2 min; then, the temperature is reduced to 730 ℃, argon is introduced to promote the uniform mixing of the melt and achieve the effect of melt degassing, and the mixture is kept stand for 10min at the temperature to ensure that impurities in the melt float or settle(ii) a Finally, cooling the melt to 710 ℃, skimming dross, and pouring to obtain a magnesium alloy ingot;
3) carrying out solution treatment on the obtained magnesium alloy ingot at the temperature of 550 ℃ for 24h, and then carrying out water quenching;
4) and (3) carrying out low-temperature extrusion on the magnesium alloy ingot subjected to solution treatment under the conditions that the extrusion temperature is 280 ℃, the extrusion rate is 0.4mm/s and the extrusion ratio is 25.
The yield strength of the magnesium alloy at room temperature is 386MPa, the tensile strength is 417MPa, and the elongation is 5.0%; the yield strength of the magnesium alloy at the high temperature of 250 ℃ is 257MPa, the tensile strength is 272MPa, and the elongation is 15.8%.
As shown in FIG. 1, it can be seen from the microstructure of the extruded Mg-1.0Nd-0.3Mn alloy of example 1 of the present invention that the alloy undergoes incomplete dynamic recrystallization during the extrusion process, and the integral number of recrystallized grains is calculated to be about 74.5%, and the grain size is calculated to be about 0.64 + -0.20 μm, so that the fine grain strengthening effect can be greatly improved.
As shown in FIGS. 2 to 3, from the microstructure of the extruded Mg-2.0Nd-0.5Mn alloy of example 2 of the present invention, it can be seen that the alloy dynamically precipitates a high number density of nano-precipitates having a size of about 350. + -.89 nm during the extrusion process.
As shown in fig. 4 to 5, it can be seen from the microstructure diagrams of the extruded Mg-3.0Nd-0.8Mn alloy of example 3 of the present invention that a large amount of nano precipitated phases are precipitated along the grain boundaries of the alloy, and the grain boundaries show bright white color under a high-angle toroidal dark field, which indicates that a large amount of solute atoms are segregated near the grain boundaries, and both of them can effectively inhibit grain boundary sliding at high temperature, and improve the high-temperature mechanical properties of the alloy.
As shown in FIG. 6, from the microstructure comparison of the extruded alloys of examples 4, 5 and 6 of the present invention, it can be seen that the dynamic recrystallization fraction of the alloy increased from 54.7% to 62.5% and the grain size increased from 0.64. + -. 0.16 μm to 0.96. + -. 0.17 μm with the decrease in Nd element.
As shown in FIG. 7, it can be seen from the tensile engineering stress-strain curves of the alloys of examples 1, 2 and 3 of the present invention at room temperature that the yield strength of the alloy increases from 382MPa to 398MPa and the elongation decreases from 3.6% to 2.5% as the extrusion temperature decreases.
As shown in fig. 8, it can be seen from the tensile engineering stress-strain curves of the alloys of example 1, example 2 and example 3 of the present invention at 250 ℃, that the yield strength of the alloy increases from 243MPa to 269MPa and the elongation decreases from 11.3% to 4.2% as the extrusion temperature decreases.
As shown in fig. 9, it can be seen from the tensile engineering stress-strain curves of the alloys of example 4, example 5 and example 6 of the present invention at room temperature that as the Nd content is decreased, the yield strength of the alloy is decreased from 400MPa to 386MPa, and the elongation is increased from 2.0% to 5.0%.
As shown in fig. 10, it can be seen from the tensile engineering stress-strain curves at 250 ℃ of the alloys of example 4, example 5 and example 6 of the present invention that as the Nd content is reduced, the yield strength of the alloy is reduced from 269MPa to 257MPa, and the elongation is increased from 8.5% to 15.8%.
The above embodiments are implemented on the premise of the technical solution of the present invention, and detailed embodiments and specific operation procedures are given, but the scope of the present invention is not limited to the above embodiments. Those skilled in the art, having the benefit of the teachings of this invention, may effect numerous modifications thereto and changes may be made without departing from the scope and spirit of the invention as set forth in the claims. Therefore, all equivalent technical solutions also belong to the protection of the present invention.
Claims (5)
1. The Mg-Nd-Mn ternary heat-resistant magnesium alloy is characterized by comprising Nd and Mn elements, wherein the magnesium alloy comprises the following components in percentage by mass: nd 3.0 wt%; 0.8-3.0 wt% of Mn, and the balance of Mg and inevitable impurities, wherein the content of impurities is less than or equal to 0.04 wt%, the yield strength of the magnesium alloy at room temperature is 380-400 MPa, the tensile strength is 400-440 MPa, and the elongation is 2-4%;
the preparation method of the Mg-Nd-Mn ternary heat-resistant magnesium alloy comprises the following steps:
preheating an industrial pure magnesium ingot, an Mg-25% Nd intermediate alloy and an Mg-10% Mn intermediate alloy at 100-200 ℃ for 30-60 min;
step two, melting the preheated industrial pure magnesium ingot in a protective atmosphere at the temperature of 760 +/-10 ℃; sequentially putting the preheated Mg-25% Nd intermediate alloy and the preheated Mg-10% Mn intermediate alloy into the completely molten pure magnesium melt, and preserving the heat for 10-30 min; after the Mg-25% Nd intermediate alloy and the Mg-10% Mn intermediate alloy are completely melted, mechanically stirring for 1-3 min; then, reducing the temperature to 730 +/-10 ℃, introducing argon to promote the uniform mixing of the melt and achieve degassing of the melt, and standing for 5-15 min at the temperature to enable impurities in the melt to float or settle; finally, cooling the melt to 710 +/-10 ℃, skimming dross, and pouring to obtain a magnesium alloy ingot;
step three, carrying out solid solution treatment on the obtained magnesium alloy ingot;
and step four, extruding the magnesium alloy ingot subjected to the solution treatment at low temperature.
2. The Mg-Nd-Mn ternary heat-resistant magnesium alloy according to claim 1, wherein the yield strength of the magnesium alloy at a high temperature of 250 ℃ is 240-270 MPa, the tensile strength is 260-280 MPa, and the elongation is 4-16%.
3. A method for preparing a Mg-Nd-Mn ternary heat resistant magnesium alloy according to any of claims 1 to 2, comprising the steps of:
preheating an industrial pure magnesium ingot, an Mg-25% Nd intermediate alloy and an Mg-10% Mn intermediate alloy at 100-200 ℃ for 30-60 min;
step two, melting the preheated industrial pure magnesium ingot in a protective atmosphere at the temperature of 760 +/-10 ℃; sequentially putting the preheated Mg-25% Nd intermediate alloy and the preheated Mg-10% Mn intermediate alloy into the completely molten pure magnesium melt, and preserving the heat for 10-30 min; after the Mg-25% Nd intermediate alloy and the Mg-10% Mn intermediate alloy are completely melted, mechanically stirring for 1-3 min; then, reducing the temperature to 730 +/-10 ℃, introducing argon to promote the uniform mixing of the melt and achieve degassing of the melt, and standing for 5-15 min at the temperature to enable impurities in the melt to float or settle; finally, cooling the melt to 710 +/-10 ℃, skimming dross, and pouring to obtain a magnesium alloy ingot;
performing solid solution treatment on the obtained magnesium alloy ingot, performing water quenching at the temperature of 520-550 ℃ for 10-30 h;
and step four, performing low-temperature extrusion on the magnesium alloy ingot subjected to the solution treatment.
4. The method for preparing the Mg-Nd-Mn ternary heat-resistant magnesium alloy according to claim 3, wherein in the second step, the protective atmosphere is SF 6 And CO 2 And mixed gas of (1), and SF 6 The percentage content by volume of the composition is 0.5-0.7 vt%.
5. The preparation method of the Mg-Nd-Mn ternary heat-resistant magnesium alloy according to claim 3, wherein in the fourth step, the extrusion temperature of low-temperature extrusion is not higher than 300 ℃, the extrusion rate is 0.3-0.5 mm/s, and the extrusion ratio is 20-30.
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