High-strength heat-resistant magnesium-rare earth alloy and preparation method thereof

Abstract

The invention discloses a high-strength heat-resistant magnesium rare earth alloy which comprises the following components in percentage by mass: 8.5%-9.5% of Gd, 2.5%-4.0% of Y, 1.0%-2.0% of Zn, 0.3%-0.5% of Zr, 0.2%-0.6% of La, 0.2%-0.5% of Ce, less than or equal to 0.2% of other impurity elements and the balance of Mg. The invention further discloses a preparation method of the magnesium-rare earth alloy. The preparation method comprises the following steps: (1) smelting; (2) casting; (3) carrying out homogenization treatment; (4) multidirectional free forging; and (5) aging treatment. According to the Mg-Gd-Y-Zn-La-Ce-Zr alloy and the preparation method thereof, the Mg-Gd-Y-Zn-La-Ce-Zr alloy with ultrahigh room-temperature strength and excellent high-temperature performance is prepared by utilizing the promoting effect of La and Ce on aging precipitation of Gd and Y and the segregation effect of La and Ce at the grain boundary and the phase boundary through trace addition of La and Ce.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth magnesium alloy materials, and in particular relates to a high-strength heat-resistant magnesium rare earth alloy and a preparation method thereof. Background Art

[0002] With the increasing global attention to resource and environmental issues, the manufacturing industry is pursuing the goals of lightweighting, energy conservation and emission reduction, and comprehensive resource utilization. In this context, magnesium alloys will play a very important role in the future field of metal materials. However, traditional magnesium alloys have weaknesses such as low strength, poor oxidation resistance, poor corrosion resistance, poor high-temperature creep resistance, and low high-temperature strength, which cannot meet the strict requirements of modern aerospace, transportation, 3C industry and other manufacturing industries. Therefore, magnesium alloy materials containing rare earths have emerged in recent years. Practice has proved that rare earth elements have special chemical activity and surface activity, and are the most effective and practical elements to improve the casting properties, high-temperature creep properties and corrosion resistance of magnesium alloys.

[0003] However, most of the current methods improve the mechanical properties of magnesium rare earth alloys by increasing the content of rare earth elements, which greatly increases the cost of the alloy and makes it difficult to promote and apply the alloy. In recent years, there have been many studies on improving the performance of magnesium rare earth alloys by microalloying. However, due to the unreasonable types and addition amounts of rare earth elements, magnesium rare earth alloys cannot meet the requirements of the modern fine chemical industry, especially the room temperature strength and high temperature strength of magnesium rare earth alloys. Summary of the invention

[0004] In view of the problems that existing magnesium alloys have low room temperature strength and insufficient high temperature resistance, which makes it difficult to meet product application requirements, the present invention provides a high-strength and heat-resistant magnesium rare earth alloy and a preparation method thereof through optimization of composition and process. By compositely adding rare earth elements, the high-temperature mechanical properties and organizational stability of the magnesium alloy are improved, solving the problem that the room temperature performance of the magnesium alloy in the prior art is low and the high temperature performance cannot meet the use requirements.

[0005] To achieve the above object, the technical solution of the present invention is:

[0006] A high-strength heat-resistant magnesium rare earth alloy comprises the following components in mass percentage: Gd: 8.5%-9.5%, Y: 2.5%-4.0%, Zn: 1.0%-2.0%, Zr: 0.3%-0.5%, La: 0.2%-0.6%, Ce: 0.2%-0.5%, other impurity elements total: ≤0.2%, and the rest is Mg.

[0007] Based on the same inventive concept, a method for preparing a high-strength heat-resistant magnesium rare earth alloy comprises the following steps:

[0008] S1: melting the raw materials and then casting to obtain a magnesium alloy ingot;

[0009] S2: homogenizing the magnesium alloy ingot obtained in step S1;

[0010] S3: After the homogenization treatment in step S2 is completed, preheating is performed at 465-480°C for 1.5-3h, and then multi-directional free forging is performed;

[0011] S4: performing aging treatment on the alloy ingot after multi-directional free forging to finally obtain a high-strength and heat-resistant magnesium rare earth alloy.

[0012] Preferably, the step S1 comprises:

[0013] S101: Smelting: pre-set the component requirements of each element, and prepare the ingredients required for the magnesium rare earth alloy according to the component requirements, the ingredients include: pure Mg, pure Zn, Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, Mg-La master alloy, Mg-Ce master alloy;

[0014] The ingredients are preheated at 140-160° C. for 30-80 min; then pure Mg is placed in a crucible, and the temperature in the crucible is raised to 740-760° C. under the protection of an inert gas to melt the pure Mg;

[0015] S102: Alloying: Control the temperature in the crucible to 680-720°C, add preheated pure Zn, Mg-Zn master alloy, Mg-Gd master alloy, Mg-Y master alloy, Mg-La master alloy, Mg-Ce master alloy, stir evenly to melt, then heat to 780°C, add Mg-Zr master alloy, let stand for 10-30 minutes, and salvage scum on the surface of the melt;

[0016] S103: Refining: baking the refining agent at 200-300℃, stirring while spreading the refining agent, refining time 5-8min, slagging, and standing for 120min;

[0017] S104: Pouring: Control the melt temperature to 660-680°C, pour the melt in the crucible into an iron mold at 200-300°C, allow the melt to flow in the mold and cool into an ingot, and obtain a magnesium rare earth alloy ingot.

[0018] The obtained alloy ingot needs to be inspected for cost. If the alloy composition is not within the required range or the alloy ingot has abnormal appearances such as inclusions, slag inclusions, gas inclusions, shrinkage cavities, shrinkage porosity, etc., step S1 needs to be repeated.

[0019] Preferably, the Mg purity in pure Mg is 99.95%, the Zn purity in pure Zn is 99.95%, the mass percentage of Gd in Mg-Gd alloy is 20-30%, the mass percentage of Y in Mg-Y master alloy is 20-30%, the mass percentage of Zr in Mg-Zr master alloy is 20-30%, the mass percentage of La in Mg-La master alloy is 20-30%, and the mass percentage of Ce in Mg-Ce master alloy is 20-30%.

[0020] Preferably, the homogenization treatment in step S2 is specifically: subjecting the magnesium-rare earth alloy ingot to homogenization treatment at 480-520° C. for a holding time of 10-20 hours.

[0021] Preferably, the multi-directional free forging in step S3 is firstly forging along the height direction of the ingot, and then forging alternately along the height direction and the width direction of the ingot;

[0022] The number of forging passes along the height direction of the ingot is 1-2 passes, and the deformation of a single forging pass along the height direction of the ingot is 40-45%. Then, the number of alternating forging passes along the length and width of the ingot is 2-6 passes, and the deformation of a single alternating forging pass is 20-30%.

[0023] Preferably, the multi-directional free forging is performed three times, and the speed of the three multi-directional free forgings is 10-25 mm / s.

[0024] Preferably, the aging treatment is performed at 180°C-210°C for 20-25h.

[0025] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art:

[0026] Light rare earth elements such as La and Ce have very low solid solubility in Mg, and trace addition can have a significant effect on the structure and performance of magnesium alloys. In the present invention, trace addition of La and Ce greatly improves the room temperature tensile strength and high temperature performance of Mg-Gd-Y-Zn-Zr alloy. Among them, the improvement of room temperature tensile strength is mainly attributed to: on the one hand, La and Ce are segregated at the recrystallization grain boundaries, inhibiting the growth of recrystallized grains, and the strength is improved due to grain refinement; on the other hand, La and Ce promote aging precipitation, increase the number density of β-phase, and increase its resistance to dislocation slip. The improvement of high temperature performance is mainly due to the fact that La and Ce improve the thermal stability of β' phase. La and Ce atoms replace part of Gd and Y atoms in β' phase, and La and Ce are easy to segregate at the interface between β' phase and Mg matrix. The above factors lead to the significant inhibition of coarsening of β' phase in high temperature environment.

[0027] La and Ce are high-abundance rare earth elements with relatively low prices. The present invention prepares a Mg-Gd-Y-Zn-La-Ce-Zr alloy having both ultra-high room temperature strength and excellent high temperature performance by adding La and Ce in trace amounts, only slightly increasing the alloy cost. DETAILED DESCRIPTION

[0028] The present invention utilizes the promoting effect of La and Ce on the aging precipitation of Gd and Y, as well as their segregation effect at grain boundaries and phase boundaries, and prepares a Mg-Gd-Y-Zn-La-Ce-Zr alloy with ultra-high room temperature strength and excellent high temperature performance by adding La and Ce in trace amounts.

[0029] It should be noted that the temperature field and deformation degree of different regions of large-sized magnesium alloys are different during thermal deformation, resulting in uneven microstructure and performance during thermal deformation. Therefore, the present invention adopts multi-directional free forging, and adopts three multi-directional free forgings to make the magnesium alloy as uniform as possible in terms of deformation degree, temperature field and microstructure and performance during thermal deformation, thereby making the present invention more suitable for the preparation of large-sized magnesium alloys.

[0030] The high-strength and heat-resistant magnesium-rare-earth alloy and its preparation method proposed by the present invention are further described in detail below in conjunction with specific embodiments. The advantages and features of the present invention will become more apparent from the following description.

[0031] Example 1

[0032] High-strength and heat-resistant magnesium rare earth alloy: Gd: 9.0%, Y: 3.0%, Zn: 2%, Zr: 0.4%, La: 0.6%, Ce: 0.5%, other impurity elements total: ≤ 0.2%, the rest is Mg. The mass ratio of Gd, Y, Zn, Zr, La, Ce is about 9:2.5:2:0.5:0.4:0.4.

[0033] Preparation method of the above high-strength heat-resistant magnesium rare earth alloy:

[0034] (1) Ingredient preparation: pre-set the component requirements of each element, and prepare the ingredients required for preparing the magnesium rare earth alloy according to the component requirements, the ingredients include: pure Mg, pure Zn, Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, Mg-La master alloy, Mg-Ce master alloy;

[0035] (2) Preheating ingredients: preheat the above ingredients at 150°C for 60 minutes;

[0036] (3) Melting: pure Mg is placed in a crucible and the temperature in the crucible is raised to 750°C under the protection of an inert gas to melt the pure Mg;

[0037] (4) Alloying: Control the temperature in the crucible to 700°C, add preheated pure Zn, Mg-Zn master alloy, Mg-Gd master alloy, Mg-Y master alloy, Mg-La master alloy, and Mg-Ce master alloy, stir evenly to melt, then heat to 780°C, add Mg-Zr master alloy, let stand for 25 min, and salvage scum on the surface of the melt;

[0038] (5) Refining: bake the refining agent at 300°C, sprinkle the refining agent and stir, refining time 7min, remove the slag, and let it stand for 120min;

[0039] (6) Pouring: Controlling the melt temperature to 670°C, pouring the melt in the crucible into an iron mold at 280°C, allowing the melt to flow in the mold and cool into an ingot, thereby obtaining a magnesium-rare earth alloy ingot;

[0040] (7) Homogenization treatment: The obtained magnesium rare earth alloy ingot is homogenized at 510° C. for 20 h;

[0041] (8) Multi-directional free forging: The ingot after homogenization treatment is preheated at 480°C for 3 h, and then subjected to three multi-directional free forging treatments, each of which has a speed of 10-25 mm / s;

[0042] A multi-directional free forging is to forge in the height direction of the ingot first, and then forge alternately in the height direction and width direction of the ingot;

[0043] The number of forging passes along the height direction of the ingot is 1-2, and the deformation of a single forging pass along the height direction of the ingot is 40-45%. Then, the number of alternate forging passes along the length and width of the ingot is 2-6, and the deformation of a single alternate forging pass is 20-30%.

[0044] (9) Aging treatment: The alloy ingot after multi-directional free forging is aged at 200°C for 23 hours to obtain a high-strength and heat-resistant magnesium rare earth alloy material.

[0045] Comparative Example 1

[0046] Magnesium rare earth alloy: Gd: 8.5%, Y: 2.5%, Zn: 1.5%, Zr: 0.4%, other impurity elements total: ≤ 0.2%, the rest is Mg.

[0047] The preparation method is the same as that of Example 1.

[0048] Comparative Example 2

[0049] Magnesium rare earth alloy: Gd: 8.5%, Y: 2.5%, Zn: 1.5%, Zr: 0.4%, La: 0.4%, other impurity elements total: ≤ 0.2%, the rest is Mg.

[0050] The preparation method is the same as that of Example 1.

[0051] Comparative Example 3

[0052] Magnesium rare earth alloy: Gd: 8.5%, Y: 2.5%, Zn: 1.5%, Zr: 0.4%, Ce: 0.4%, other impurity elements total: ≤ 0.2%, the rest is Mg.

[0053] The preparation method is the same as that of Example 1.

[0054] The specific compositions of the magnesium alloys of the embodiments and comparative examples are shown in the following table:

[0055] G Y Zn Zr La Ce Example 1 9 3.0 2.0 0.4 0.6 0.5 Comparative Example 1 8.5 2.5 1.5 0.4 - - Comparative Example 2 8.5 2.5 1.5 0.4 0.4 - Comparative Example 3 8.5 2.5 1.5 0.4 - 0.4

[0056] The tensile strength test was performed on the magnesium alloys of the embodiment and the comparative example. The test results are shown in the following table:

[0057]

[0058] As can be seen from Table 1, at room temperature and 300°C, the tensile strength of the rare earth magnesium alloys of Comparative Examples 1-3 is lower than that of the high-strength heat-resistant magnesium alloy of the present invention, and the tensile strength thereof is higher than 320MPa. The embodiments have high room temperature strength and high high temperature tensile strength, and stable high temperature performance. Moreover, compared with Comparative Examples 2-3, Example 1 can only achieve high tensile strength at 300°C by adding La and Ce at the same time. Therefore, the magnesium rare earth alloy of the present invention can meet the strength requirements of aerospace, military, automobile and other industries in a wide temperature range, especially when used at 200°C to 300°C.

[0059] The embodiments of the present invention are described in detail above in conjunction with the embodiments, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they still fall within the protection scope of the present invention.

Claims

1. A high-strength heat-resistant magnesium rare earth alloy, characterized in that: The invention comprises the following components in mass percentage: Gd: 8.5%-9.5%, Y: 2.5%-4.0%, Zn: 1.0%-2.0%, Zr: 0.3%-0.5%, La: 0.2%-0.6%, Ce: 0.2%-0.5%, other impurity elements total: ≤0.2%, and the rest is Mg.

2. A method for preparing a high-strength heat-resistant magnesium rare earth alloy as claimed in claim 1, characterized in that: The following steps are involved: S1: melting the raw materials and then casting to obtain a magnesium alloy ingot; S2: homogenizing the magnesium alloy ingot obtained in step S1; S3: After the homogenization treatment in step S2 is completed, preheating is performed at 465-480°C for 1.5-3h, and then multi-directional free forging is performed; S4: performing aging treatment on the alloy ingot after multi-directional free forging to finally obtain a high-strength and heat-resistant magnesium rare earth alloy.

3. The method for preparing a high-strength heat-resistant magnesium rare earth alloy according to claim 2, characterized in that: The step S1 comprises: S101: Smelting: pre-set the component requirements of each element, and prepare the ingredients required for the magnesium rare earth alloy according to the component requirements, the ingredients include: pure Mg, pure Zn, Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, Mg-La master alloy, Mg-Ce master alloy; The ingredients are preheated at 140-160° C. for 30-80 min; then pure Mg is placed in a crucible, and the temperature in the crucible is raised to 740-760° C. under the protection of an inert gas to melt the pure Mg; S102: Alloying: Control the temperature in the crucible to 680-720°C, add preheated pure Zn, Mg-Zn master alloy, Mg-Gd master alloy, Mg-Y master alloy, Mg-La master alloy, Mg-Ce master alloy, stir evenly to melt, then heat to 780°C, add Mg-Zr master alloy, let stand for 10-30 minutes, and salvage scum on the surface of the melt; S103: Refining: baking the refining agent at 200-300℃, stirring while spreading the refining agent, refining time 5-8min, slagging, and standing for 120min; S104: Pouring: Control the melt temperature to 660-680°C, pour the melt in the crucible into an iron mold at 200-300°C, allow the melt to flow in the mold and cool into an ingot, and obtain a magnesium rare earth alloy ingot.

4. The method for preparing a high-strength heat-resistant magnesium rare earth alloy according to claim 3, characterized in that: The purity of Mg in pure Mg is 99.95%, the purity of Zn in pure Zn is 99.95%, the mass percentage of Gd in Mg-Gd alloy is 20-30%, the mass percentage of Y in Mg-Y master alloy is 20-30%, the mass percentage of Zr in Mg-Zr master alloy is 20-30%, the mass percentage of La in Mg-La master alloy is 20-30%, and the mass percentage of Ce in Mg-Ce master alloy is 20-30%.

5. The method for preparing a high-strength heat-resistant magnesium rare earth alloy according to claim 2, characterized in that: The homogenization treatment in step S2 is specifically as follows: subjecting the magnesium rare earth alloy ingot to homogenization treatment at 480-520° C. for a holding time of 10-20 hours.

6. The method for preparing a high-strength heat-resistant magnesium rare earth alloy according to claim 2, characterized in that: In the step S3, the multi-directional free forging is firstly performed in the height direction of the ingot, and then alternately forged in the height direction and the width direction of the ingot; The number of forging passes along the height direction of the ingot is 1-2 passes, and the deformation of a single forging pass along the height direction of the ingot is 40-45%. Then, the number of alternating forging passes along the length and width of the ingot is 2-6 passes, and the deformation of a single alternating forging pass is 20-30%.

7. The method for preparing a high-strength heat-resistant magnesium rare earth alloy according to claim 2 or 6, characterized in that: The multi-directional free forging is performed three times, and the speed of the three multi-directional free forgings is 10-25 mm / s.

8. The method for preparing a high-strength heat-resistant magnesium rare earth alloy according to claim 2, characterized in that: The aging treatment is performed at 180° C.-210° C. for 20-25 hours.

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