1. The Mg-Gd alloy with low Gd content is characterized by comprising the following chemical components in percentage by mass: gd: 2-5%, Li: 2-5%, Y: 1-3%, Nd: 1-2%, Zr: 0.2-0.6%, and the balance of magnesium and inevitable impurities.

2. The low Gd-containing Mg-Gd alloy according to claim 1, wherein the mass percent of Li is 2 to 3%.

3. The low Gd containing Mg-Gd alloy of claim 1 wherein the atomic ratio of Li to Gd is greater than 10: 1.

4. A preparation method of a low Gd-content Mg-Gd alloy is characterized by comprising the following steps:

s1, preparing the Mg-Gd alloy with low Gd content according to the proportion of any one of the claims 1 to 3;

s2 at SF₆ + CO₂Under the protection of gas, the alloy material is melted in a resistance furnace, refined for 2-4 min, kept stand in the resistance furnace for 25-30 min and then cast into a metal mold to obtain a casting.

5. The method for preparing a low Gd-content Mg-Gd alloy according to claim 4, wherein in step S2, the alloy materials are Mg-20Gd intermediate alloy, Mg-20Y intermediate alloy, Mg-10Li intermediate alloy, Mg-20Nd intermediate alloy and Mg-30Zr intermediate alloy.

6. A heat treatment method of a low Gd content Mg-Gd alloy is characterized in that a casting prepared according to claim 4 is placed into a crucible, the crucible is placed into a muffle furnace, the temperature is raised to 480-500 ℃, and then heat preservation is carried out for 2-4 h; wherein the heating rate is 1-2 ℃/min; and taking out the crucible after heat preservation is finished, and immediately quenching the crucible in water to finish heat treatment.

7. The method for heat-treating a low Gd containing Mg-Gd alloy in accordance with claim 6, wherein the casting is embedded in graphite and placed in a crucible.

Background

As the structural material with the minimum density at present, the magnesium alloy has the advantages of high specific strength and specific rigidity, good heat dissipation and shock absorption, rich raw materials, recyclability and the like, and has great development potential. In the high-strength magnesium alloys developed at present, the proportion of the Mg-Gd-based alloy is high. The strengthening effect of Gd element in magnesium alloy is mainly realized by forming MgGd strengthening phase. As can be seen from the phase diagram of the Mg-Gd binary alloy, the maximum solid solubility of Gd element in the magnesium matrix can reach 23.3 percent (mass percent). In the Mg-Gd binary alloy, the Gd content is usually more than 10 percent (mass percentage), so that an MgGd strengthening phase can be formed, and an ideal strengthening effect is obtained.

However, the higher content of Gd increases the cost first, which is not favorable for the popularization and application of magnesium alloy; secondly, segregation is easy to occur in the preparation process, the mechanical property of the alloy is reduced, the density of the magnesium alloy is increased, and the low density of the magnesium alloy is reduced.

At present, Mg-Gd alloy mainly reduces the content of Gd element by adding other alloy elements and obtains MgGd strengthening phase at the same time, and the common elements comprise Y, Nd, Sm, Ag, Zn and the like. From the data reported in the publication, the content of Gd element still reaches 6-15% (mass percent), and the defects still exist.

Therefore, it is an object of the present invention to provide a magnesium alloy containing a MgGd strengthening phase with a low Gd content.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to solve the problems that the existing Mg-Gd alloy has high Gd content, is easy to segregate, increases the density of the magnesium alloy and has high cost, and provides the Mg-Gd alloy with low Gd content.

In order to solve the technical problems, the invention adopts the following technical scheme:

the Mg-Gd alloy with low Gd content comprises the following chemical components in percentage by mass: gd: 2-5%, Li: 2-5%, Y: 1-3%, Nd: 1-2%, Zr: 0.2-0.6%, and the balance of magnesium and inevitable impurities.

Preferably, the mass percentage of the Li is 2-3%. Thus, Li can be entirely dissolved in the Mg matrix.

Preferably, the atomic ratio of Li to Gd is greater than 10:1, such that the atomic percentage of Li is an order of magnitude higher than Gd, and the MgGd strengthening phase is more likely to form within the magnesium alloy matrix.

The invention also provides a preparation method of the low Gd content Mg-Gd alloy, which comprises the following steps:

s1, preparing materials according to the proportion of the low-Gd-content Mg-Gd alloy;

s2 at SF₆ + CO₂Under the protection of gas, the alloy material is melted in a resistance furnace, refined for 2-4 min, kept stand in the resistance furnace for 25-30 min and then cast into a metal mold to obtain a casting.

In step S2, the alloy material is Mg-20Gd intermediate alloy, Mg-20Y intermediate alloy, Mg-10Li intermediate alloy, Mg-20Nd intermediate alloy and Mg-30Zr intermediate alloy.

The invention also provides a heat treatment method of the low-Gd-content Mg-Gd alloy, the prepared casting is placed into a crucible, the crucible is placed into a muffle furnace, the temperature is raised to 480-500 ℃, and then heat preservation treatment is carried out, wherein the heat preservation time is 2-4 hours; wherein the heating rate is 1-2 ℃/min; and taking out the crucible after heat preservation is finished, and immediately quenching the crucible in water to finish heat treatment.

Preferably, the casting is embedded in graphite and then placed in a crucible.

Compared with the prior art, the invention has the following advantages:

1. according to the magnesium alloy, the lithium element is added, and lithium and magnesium do not form a compound and can be completely dissolved in the magnesium matrix when the lithium content is lower than 5.5%, so that the solid solubility of Gd in the magnesium alloy is reduced and the generation of an MgGd phase is promoted by adding lithium, namely the solid-solution Li is used for promoting the formation of the MgGd phase at a low alloy content, so that the magnesium alloy provided by the invention has the advantages that the main strengthening phase is the MgGd phase, but the Gd content is not more than 5%, the Gd content in the Mg-Gd alloy is reduced, the cost of the magnesium alloy is reduced, the magnesium alloy is not easy to segregate in the preparation process, and the mechanical property of the alloy is improved. In addition, the density of lithium is small (about 0.5 g/cm)³) Further reducing the density of the magnesium alloy and fully playing the advantage of low density of the magnesium alloy. The Mg-Gd wrought alloy exhibits age-hardening capabilities.

2. No compound is formed between lithium and zirconium, and at the same time, no solid solubility exists, so that the Mg-Gd alloy containing lithium can use zirconium to refine grains, and fine grain strengthening is realized, thereby improving the comprehensive mechanical property of the magnesium alloy.

3. Because the relative atomic weight of lithium is small (about 6.9), the atomic percent of lithium in the alloy can be improved by adding lithium with lower mass percent, thereby playing a role in promoting the formation of MgGd phase by using a small amount of Li element and being beneficial to reducing the cost of magnesium alloy. In the invention, the atomic ratio of Li to Gd is controlled to be more than 10:1, so that the atomic percentage content of Li is higher than that of Gd by one order of magnitude, and an MgGd strengthening phase is easier to form in the magnesium alloy matrix, thereby improving the mechanical property of the magnesium alloy.

4. The preparation method provided by the invention is simple and easy to operate, and the Li and other elements are added in the form of intermediate alloy, so that the burning loss of the added alloy elements is reduced, and the control of the alloy components is facilitated.

5. The heat treatment method provided by the invention has simple steps and adopts conventional experimental equipment. The solid solution temperature is 480-500 ℃ lower than the traditional 500-525 ℃, and the energy consumption is reduced.

Drawings

FIG. 1 is the original as-cast metallographic structure of the Mg-Gd alloy prepared in example 1 of the present invention.

FIG. 2 is an X-ray diffraction pattern of the Mg-Gd alloy prepared in example 1 of the present invention.

FIG. 3 is an age hardening curve (200 ℃ C. ageing temperature) for Mg-Gd wrought magnesium alloy prepared in accordance with example 1 of the present invention.

FIG. 4 is a stress-strain curve of the Mg-Gd wrought magnesium alloy prepared in example 1 of the present invention.

FIG. 5 is the original as-cast metallographic structure of the Mg-Gd alloy prepared in example 2 of the present invention.

FIG. 6 is a metallographic structure diagram of an extruded Mg-Gd alloy prepared in example 2 of the present invention.

FIG. 7 is the original as-cast metallographic structure of the Mg-Gd alloy prepared in example 3 of the present invention.

FIG. 8 is a metallographic structure diagram of an extruded Mg-Gd alloy prepared in example 3 of the present invention.

Detailed Description

The present invention will be further described with reference to the following examples and accompanying drawings.

Example 1

1. Preparation of Mg-Gd alloy

Mixing the raw materials according to the mass fraction of Mg-3% Gd-3% Li-2% Y-1% Nd-0.4% Zr, polishing the surface, adding the mixture into a preheated resistance furnace, and introducing SF₆ + CO₂The mixed gas is used as protection, and the temperature is gradually increased to 760 ℃. And refining for 2-4 min after furnace burden in the crucible is completely melted. Controlling the temperature at 720 ℃, standing the alloy in a furnace for 25-30 min, and then pouring. And opening the mold and taking out the cast ingot after the cast ingot is cooled in the mold.

The metallographic structure of the as-cast magnesium alloy obtained in this example is shown in fig. 1. In FIG. 1, the bright portion is the matrix Mg phase, the grains are in a dendritic state, the contrast at the grain boundary is relatively dark, and the grains are the second phase. The sample was subjected to X-ray diffraction analysis, and as a result, referring to FIG. 2, it was found that the phase composition of the alloy was Mg + Mg₅Gd, i.e. thThe two-phase structure is Mg₅A Gd phase. It can be seen that with the addition of Li, Mg is still formed even if the Gd content is reduced to 3%₅A Gd phase.

2. Heat treatment of Mg-Gd alloys

Embedding the prepared graphite for the magnesium alloy in a stainless steel crucible, putting the crucible into a muffle furnace, heating the crucible to 500 ℃ from room temperature at a heating rate of 1 ℃/min, performing heat preservation treatment after the temperature reaches 500 ℃, keeping the temperature for 2 h, turning off a power supply after the heat preservation is finished, taking out the crucible, immediately quenching the crucible in water, and finishing the heat treatment.

3. Performance testing of Mg-Gd alloys

Cutting the sample after the heat treatment, putting the sample into a muffle furnace at 380 ℃ for heat preservation, wherein the heat preservation time is 15 min, controlling the temperature of an extrusion cylinder of an extruder at 380 ℃, putting the sample into the extruder after the heat preservation, and extruding the sample at an extrusion ratio of 25: 1, obtaining an extruded bar, and aging a part of the bar at 200 ℃.

In this example, the age hardening curve of the as-extruded Mg-Gd alloy is shown in FIG. 3. As can be seen from FIG. 3, the Mg-Gd alloy prepared in this example exhibited age-hardening ability, indicating that the alloy had age-hardening ability and achieved precipitation strengthening. This is demonstrated in the stress-strain diagram of fig. 4.

Example 2

1. Preparation of Mg-Gd alloy

Proportioning according to the mass fraction of Mg-4% Gd-3% Li-3% Y-2% Nd-0.4%, polishing the surface, adding into a preheated resistance furnace, introducing SF₆ + CO₂The mixed gas is used as protection, and the temperature is gradually increased to 760 ℃. And refining for 2-4 min after furnace burden in the crucible is completely melted. Controlling the temperature at 720 ℃, standing the alloy in a furnace for 25-30 min, and then pouring. And opening the mold and taking out the cast ingot after the cast ingot is cooled in the mold.

2. Heat treatment of Mg-Gd alloys

Embedding the prepared graphite for the magnesium alloy in a stainless steel crucible, putting the crucible into a muffle furnace, heating the crucible to 500 ℃ from room temperature at a heating rate of 1 ℃/min, performing heat preservation treatment after the temperature reaches 500 ℃, keeping the temperature for 4 h, turning off a power supply after the heat preservation is finished, taking out the crucible, immediately quenching the crucible in water, and finishing the heat treatment.

3. Performance testing of Mg-Gd alloys

After the heat treatment is finished, the sample is placed into a 400 ℃ muffle furnace for heat preservation treatment, the heat preservation time is 15 min, the temperature of an extrusion cylinder of an extruder is controlled at 400 ℃, the sample is placed into the extruder for extrusion after the heat preservation is finished, and the extrusion ratio is 25: 1, obtaining an extruded bar, and aging a part of the bar at 200 ℃.

The as-cast structure of the Mg-Gd alloy prepared in this example is shown in fig. 5, and the metallographic structure of the extruded Mg-Gd alloy is shown in fig. 6. As can be seen from FIGS. 5 and 6, the matrix is transformed into an equiaxed crystal structure from the original cast dendritic structure after heat treatment and extrusion, and the average grain size is thinned to 12 +/-8 μm of the extruded state from 88 +/-25 μm of the original cast state, so that fine grain strengthening is realized. In the original as-cast alloy, the second phase is continuously distributed at the grain boundary of the matrix, and a crack source is easily formed in the stretching process; in the extruded alloy, the second phase is extruded and crushed and is dispersed and distributed in the matrix, and the mechanical property of the alloy is improved through dispersion strengthening.

Example 3

1. Preparation of Mg-Gd alloy

Mixing the raw materials according to the mass fraction of Mg-3% Gd-2% Li-2% Y-2% Nd-0.3%, polishing the surface, adding the polished surface into a preheated resistance furnace, and introducing SF₆ + CO₂The mixed gas is used as protection, and the temperature is gradually increased to 760 ℃. And refining for 2-4 min after furnace burden in the crucible is completely melted. Controlling the temperature at 720 ℃, standing the alloy in a furnace for 25-30 min, and then pouring. And opening the mold and taking out the cast ingot after the cast ingot is cooled in the mold.

2. Heat treatment of Mg-Gd alloys

Embedding the prepared graphite for the magnesium alloy in a stainless steel crucible, putting the crucible into a muffle furnace, heating the crucible to 500 ℃ from room temperature at a heating rate of 1 ℃/min, performing heat preservation treatment after the temperature reaches 500 ℃, keeping the temperature for 3 h, turning off a power supply after the heat preservation is finished, taking out the crucible, immediately quenching the crucible in water, and finishing the heat treatment.

3. Performance testing of Mg-Gd alloys

After the heat treatment is finished, the sample is placed into a muffle furnace at 390 ℃ for heat preservation treatment, the heat preservation time is 15 min, the temperature of an extrusion cylinder of an extruder is controlled at 390 ℃, the sample is placed into the extruder for extrusion after the heat preservation is finished, and the extrusion ratio is 25: 1, obtaining an extruded bar, and aging a part of the bar at 200 ℃.

The solid solution metallographic structure of the Mg-Gd alloy prepared in this example is shown in fig. 7, and the metallographic structure of the extruded alloy is shown in fig. 8. As can be seen from FIGS. 7 and 8, the matrix is transformed into an equiaxed crystal structure from the original cast dendritic structure after heat treatment and extrusion, and the average grain size is thinned from 85 + -25 μm of the original cast state to 11 + -7 μm of the extruded state, thereby realizing fine grain strengthening. A small amount of incompletely recrystallized shear band appears in the wrought alloy due to the reduction in extrusion temperature. In the original as-cast alloy, the second phase is continuously distributed at the grain boundary of the matrix, and a crack source is easily formed in the stretching process; in the extruded alloy, the second phase is extruded and crushed and is dispersed and distributed in the matrix, and the mechanical property of the alloy is improved through dispersion strengthening.

TABLE 1 Mass percents to atomic ratios of Li to Gd in examples 1-3

	Mass percent of Li and Gd	Atomic ratio of Li to Gd
			Example 1	3:3	95.77:4.23≈22.6:1
Example 2	3:4	94.44:5.56≈16.98:1
			Example 3	2:3	98.79:6.21≈15.9:1

In the Mg-Gd alloy provided by the invention, the mass percent of Li and Gd is less than 5 percent. As can be seen from Table 1, the atomic ratios of Li to Gd were all greater than 10:1 in examples 1-3. The main strengthening phase in the Mg-Gd alloy is Mg₅A Gd phase. Due to the addition of Li, the solid solubility of Gd in the magnesium alloy is reduced, and the generation of an MgGd phase is promoted, so that the main strengthening phase in the prepared magnesium alloy is the MgGd phase, the cost of the magnesium alloy is reduced, the segregation is not easy to occur in the preparation process, the Mg-Gd deformation alloy shows age hardening capacity, and the mechanical property of the alloy is improved.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the technical solutions, and those skilled in the art should understand that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all that should be covered by the claims of the present invention.