Light and heavy rare earth composite reinforced high-strength heat-resistant magnesium alloy and preparation method thereof

Abstract

The invention provides a light and heavy rare earth composite reinforced high-strength heat-resistant magnesium alloy and a preparation method thereof, and belongs to the field of metal material processing, the magnesium alloy comprises the following components by mass: 6.5-7.1 wt.% of Gd, 2.0-2.6 wt.% of Sm, 0.2-2.0 wt.% of Zn, 0.1-0.5 wt.% of Zr, 0-0.3 wt.% of Ho, and the balance Mg, and the content of unavoidable impurities is less than or equal to 0.05 wt.%. The preparation method is short in process flow and mainly comprises the steps of smelting and pouring, solution treatment and extrusion treatment. The magnesium alloy obtained through the method has a high thermal stability phase, a solute enrichment layer fault structure, an ultra-fine grain structure smaller than or equal to 0.9 mu m and excellent high-strength heat resistance, wherein the room-temperature yield strength is larger than or equal to 340 MPa; the high-temperature yield strength at 200-210 DEG C is greater than or equal to 300MPa; the high-temperature performance attenuation is less than or equal to 11.7% and is superior to that of The method has important significance for promoting the application of the magnesium alloy in the high-tech fields of aerospace, national defense and military industry and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of metal material processing, and particularly relates to a light-heavy rare earth composite strengthened high-strength heat-resistant magnesium alloy and a preparation method thereof. BACKGROUND

[0002] As the lightest metal structural material at present, magnesium alloy has high specific strength, specific stiffness, good cutting performance, electromagnetic shielding performance, damping and shock absorption performance, is rich in resources and easy to recycle, and therefore has wide application prospects in the fields of aerospace, automobiles, electronic consumer goods and military industry.

[0003] Mg-Al series alloy is one of the most widely used systems in traditional magnesium alloys, and has significant advantages in room temperature scenarios (such as automobile panels and seat supports) due to the good strength and casting performance brought by Al element. However, its core shortcoming is the deterioration of high-temperature performance, especially when the temperature exceeds 120℃, the main strengthening phase Mg 17 Al 12 Due to poor thermal stability, coarse aggregation easily occurs, resulting in serious attenuation of high-temperature performance, which restricts its application in high-tech fields, especially in high-temperature service environments such as aerospace engines and missile shells. At present, the main measures to solve the technical problem of poor high-strength heat resistance of traditional Mg-Al series alloy are: (1) by optimizing the alloy composition, adding Si, Ca and other elements, realizing the inhibition or replacement of Mg 17 Al 12 phase; (2) by complex processes such as reciprocating multi-pass large deformation and multi-stage high-temperature long-time heat treatment to improve the room temperature and high-temperature performance of the alloy. However, the complex process is often difficult to realize industrial application, and more importantly, the improved Mg-Al series alloy is difficult to balance the room temperature and high-temperature strength, that is, when the room temperature strength is improved, the high-temperature strength usually decreases significantly (>27%), and the higher the temperature, the more serious the performance attenuation of the alloy, which leads to the difficulty of improving the highest service temperature of Mg-Al series alloy to 175℃ and above, and the difficulty of meeting the performance index of some special structural parts in the field of aerospace.

[0004] Therefore, how to simultaneously improve the room temperature and high-temperature strength of magnesium alloy and reduce the high-temperature mechanical performance attenuation under the condition of simplifying the process flow is a technical problem to be solved at present. SUMMARY

[0005] In order to solve the above technical problems, the application provides a light and heavy rare earth composite reinforced high-strength heat-resistant magnesium alloy, and the magnesium alloy composition is as follows in terms of mass percentage: Gd: 6.5-7.1 wt.%, Sm: 2.0-2.6 wt.%, Zn: 0.2-2.0 wt.%, Zr: 0.1-0.5 wt.%, Ho: 0-0.3 wt.%, the balance of Mg, and inevitable impurities ≤0.05 wt.%.

[0006] The preparation method of the magnesium alloy comprises the following steps:

[0007] (1) under the protection of a mixed gas of CO2 and SF6 in a volume ratio of 97-99:3-1, melting pure Mg, Mg-Gd, Mg-Sm, Mg-Zr, Mg-Ho intermediate alloy and pure Zn at 700-720 DEG C, stirring for 15-20 min, and then blowing argon for gas refining, and after standing for 25-40 min, pouring into a preheated mold at 200-250 DEG C by using gravity casting to obtain a magnesium alloy ingot;

[0008] (2) the magnesium alloy ingot obtained in step (1) is subjected to solid solution treatment at 500-520 DEG C for 6-8 h, and then subjected to turning processing to obtain a magnesium alloy blank;

[0009] (3) the magnesium alloy blank obtained in step (2) and an extrusion die are subjected to heat preservation at 350-370 DEG C for 1-3 h, and then subjected to extrusion treatment at 350-370 DEG C to obtain a light and heavy rare earth composite reinforced high-strength heat-resistant magnesium alloy, wherein the extrusion treatment is carried out at an extrusion speed of 0.5-0.9 mm / s and an extrusion ratio of 5-9:1; the obtained high-strength heat-resistant magnesium alloy has a high thermal stability phase, a solute enrichment layer structure and an ultra-fine crystal structure with a size of ≤0.9 μm, and has a relatively high strength at room temperature and high temperature: the yield strength at room temperature is ≥340 MPa; the high-temperature yield strength at 200-210 DEG C is ≥300 MPa; and the high-temperature performance attenuation is ≤11.7%.

[0010] Further, the magnesium alloy composition is as follows in terms of mass percentage: Gd: 6.8-7.0 wt.%, Sm: 2.3-2.5 wt.%, Zn: 0.4-1.8 wt.%, Zr: 0.2-0.4 wt.%, Ho: 0.1-0.2 wt.%, the balance of Mg, and inevitable impurities ≤0.04 wt.%.

[0011] Further, the magnesium alloy ingot in step (2) is subjected to solid solution treatment at 505-515 DEG C for 6.5-7.5 h.

[0012] Further, the magnesium alloy blank and the extrusion die in step (3) are kept at 355-365℃ for 1.5-2.5h, and then the high-strength heat-resistant magnesium alloy of light and heavy rare earth composite strengthening is obtained after extrusion treatment at 355-365℃, wherein the extrusion speed is 0.6-0.8mm / s, and the extrusion ratio is 6-8:1.

[0013] Compared with the prior art, the alloy has low service temperature, poor high-strength heat resistance, significant high-temperature strength attenuation, difficult to simultaneously improve room temperature and high-temperature strength, and complex process, etc. The present application realizes the following beneficial effects through the synergistic regulation of element interaction, ratio, process and process parameters:

[0014] (1) The improved Mg-Al alloy is difficult to simultaneously improve room temperature and high-temperature strength, that is, when the room temperature strength is improved, the high-temperature strength usually significantly attenuates (>27%), and the higher the temperature, the more serious the alloy performance attenuation, which leads to that the highest service temperature of the Mg-Al alloy is difficult to be improved to 175℃ and above, and it is difficult to meet the performance index of some special structural parts in the field of aerospace, etc. The present application is based on light and heavy rare earth composite strengthening, and a large number of high-thermal-stability phases (melting point: ~700℃) are formed in the alloy to replace the Mg 17 Al 12 phases (melting point: ~460℃) in the traditional Mg-Al alloy, and the solute-rich dislocation structure is introduced to effectively hinder the movement of non-basal plane dislocations. These stable strengthening effects simultaneously improve the mechanical properties of the alloy in room temperature and high-temperature environments, and significantly reduce the high-temperature attenuation rate of the alloy.

[0015] (2) The magnesium alloy obtained by the prior art is mainly improved in room temperature and high-temperature performance through complex processes such as reciprocating multi-pass large deformation and multi-stage high-temperature long-time heat treatment, which is not conducive to engineering and industrialization application. The process flow of the present application is short, and the high-strength heat-resistant magnesium alloy obtained has high-thermal-stability phases, solute-rich dislocation structures and ultra-fine crystal structures with a size of ≤0.9μm, and maintains high strength in room temperature and high-temperature conditions, and significantly reduces the high-temperature strength attenuation rate: the room temperature yield strength is ≥340MPa; the high-temperature yield strength at 200-210℃ is ≥300MPa; and the high-temperature performance attenuation is ≤11.7%. DETAILED DESCRIPTION

[0016] Example 1

[0017] The Mg-6.8Gd-2.5Sm-0.2Zr-0.12Ho-0.5Zn alloy has the following magnesium alloy components in terms of mass percentage: Gd: 6.8wt.%, Sm: 2.5wt.%, Zn: 0.5wt.%, Zr: 0.2wt.%, Ho: 0.12wt.%, and the balance of Mg, and the unavoidable impurity content is ≤0.04wt.%, and its preparation method comprises the following steps:

[0018] (1) Melting pure Mg, Mg-Gd, Mg-Sm, Mg-Zr, Mg-Ho intermediate alloy and pure Zn under the protection of mixed gas of CO2 and SF6 with volume ratio of 97:3 at 700°C, stirring for 15 min, and then argon blowing refining, standing for 25 min, and then pouring into a preheated mold at 200°C by gravity casting to obtain a magnesium alloy ingot;

[0019] (2) Solution treating the magnesium alloy ingot obtained in step (1) at 505°C for 6.5 h, and then turning to obtain a magnesium alloy blank;

[0020] (3) After standing the magnesium alloy blank obtained in step (2) and an extrusion die at 355°C for 1.5 h, performing extrusion treatment at 355°C to obtain a Mg-6.8Gd-2.5Sm-0.2Zr-0.12Ho-0.5Zn alloy, wherein the extrusion treatment is performed at an extrusion speed of 0.6 mm / s and an extrusion ratio of 6:1; the obtained Mg-6.8Gd-2.5Sm-0.2Zr-0.12Ho-0.5Zn alloy has a high thermal stability phase, a solute-rich stacking fault structure, and a super-fine crystal structure with a size of about 0.9 μm, and has a high strength at room temperature and at high temperature: the tensile yield strength at room temperature can reach 340 MPa; the high-temperature tensile yield strength at 200°C can reach 300 MPa; the high-temperature performance attenuation is 11.7%.

[0021] Example 2

[0022] A Mg-6.9Gd-2.4Sm-0.3Zr-0.14Ho-1Zn alloy, wherein the magnesium alloy components are as follows in terms of mass percentage: Gd: 6.9 wt.%, Sm: 2.4 wt.%, Zn: 1.0 wt.%, Zr: 0.3 wt.%, Ho: 0.14 wt.%, and the balance of Mg, and unavoidable impurities ≤0.03 wt.%; the preparation method comprises the following steps:

[0023] (1) Melting pure Mg, Mg-Gd, Mg-Sm, Mg-Zr, Mg-Ho intermediate alloy and pure Zn under the protection of mixed gas of CO2 and SF6 with volume ratio of 98:2 at 710°C, stirring for 18 min, and then argon blowing refining, standing for 30 min, and then pouring into a preheated mold at 220°C by gravity casting to obtain a magnesium alloy ingot;

[0024] (2) Solution treating the magnesium alloy ingot obtained in step (1) at 510°C for 7 h, and then turning to obtain a magnesium alloy blank;

[0025] (3) the magnesium alloy blank obtained in step (2) and an extrusion die are kept at 360°C for 2 hours, and then the Mg-6.9Gd-2.4Sm-0.3Zr-0.14Ho-1Zn alloy is obtained after extrusion treatment at 360°C, wherein the extrusion speed is 0.7 mm / s and the extrusion ratio is 7:1; the obtained Mg-6.9Gd-2.4Sm-0.3Zr-0.14Ho-1Zn alloy has high thermal stable phase, solute-rich stacking fault structure and ultra-fine grain structure with a size of about 0.7 μm, and maintains high strength at room temperature and high temperature; the tensile yield strength at room temperature can reach 358 MPa; the high-temperature tensile yield strength at 205°C can reach 320 MPa; the high-temperature performance attenuation is 10.6%.

[0026] Example 3

[0027] The Mg-7Gd-2.3Sm-0.4Zr-0.18Ho-1.5Zn alloy has the following magnesium alloy components in terms of mass percentage: Gd: 7.0 wt.%, Sm: 2.3 wt.%, Zn: 1.5 wt.%, Zr: 0.4 wt.%, Ho: 0.18 wt.%, and the balance of Mg, with the unavoidable impurity content being ≤0.02 wt.%; the preparation method comprises the following steps:

[0028] (1) under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 99:1, pure Mg, Mg-Gd, Mg-Sm, Mg-Zr, Mg-Ho intermediate alloy and pure Zn are melted at 720°C, stirred for 20 min, and then argon is introduced for gas refining; after standing for 35 min, the magnesium alloy ingot is obtained by gravity casting into a preheated mold at 240°C;

[0029] (2) the magnesium alloy ingot obtained in step (1) is kept at 515°C for 7.5 h for solid solution treatment, and then turned into a magnesium alloy blank;

[0030] (3) the magnesium alloy blank obtained in step (2) and an extrusion die are kept at 365°C for 2.5 h, and then the Mg-7Gd-2.3Sm-0.4Zr-0.18Ho-1.5Zn alloy is obtained after extrusion treatment at 365°C, wherein the extrusion speed is 0.8 mm / s and the extrusion ratio is 8:1; the obtained Mg-7Gd-2.3Sm-0.4Zr-0.18Ho-1.5Zn alloy has high thermal stable phase, solute-rich stacking fault structure and ultra-fine grain structure with a size of about 0.8 μm, and maintains high strength at room temperature and high temperature; the tensile yield strength at room temperature can reach 345 MPa; the high-temperature tensile yield strength at 210°C can reach 305 MPa; the high-temperature performance attenuation is 11.6%.

[0031] In summary, compared with the conventional magnesium alloy, the application simplifies the process while having the following advantages: (1) in terms of performance, the service temperature (≥200℃) of all the alloy embodiments of the application is higher than that of the conventional magnesium alloy (difficult to exceed 175℃); the application simultaneously improves the room temperature and high temperature strength of the alloy (excellent high-strength heat resistance) and has a lower high-temperature performance decay rate: the room temperature yield strength is ≥340MPa; the high-temperature yield strength at 200-210℃ is ≥300MPa; the high-temperature performance decay is ≤11.7%, which is superior to that of the conventional magnesium alloy; (2) in terms of structure, compared with the low-thermal-stability phase Mg 17 Al 12 The alloy obtained by the application has a large number of high-thermal-stability phases, solute-rich stacking structures and ultra-fine crystal structures with a size of ≤0.9μm, which can comprehensively improve the room temperature and high-temperature mechanical properties of the alloy. In addition, it can be seen from the embodiments of the application that the component allocation ratio, process parameters and obtained performance of each group of embodiments are different, among which the ratio used in embodiment 2 is not the highest, but the performance is the most excellent. Therefore, it is illustrated that the excellent effect obtained by the application is not determined by a certain component, ratio, process or process parameter, but is realized through the synergistic regulation of component interaction, ratio, process and process parameter, and only within the protection scope of the claims of the application, the most excellent technical effect can be realized. The application shows excellent industrial application prospects and has important significance for promoting the application of magnesium alloy in high-tech fields such as aerospace, national defense and military industry.

Claims

1. A light-heavy rare earth composite strengthened high-strength heat-resistant magnesium alloy, characterized in that: The magnesium alloy composition is: Gd: 6.5-7.1wt.%, Sm: 2.0-2.6wt.%, Zn: 0.2-2.0wt.%, Zr: 0.1-0.5wt.%, Ho: 0-0.3wt.%, the balance of Mg, and inevitable impurities ≤0.05wt.%. ​ The preparation method of the magnesium alloy comprises the following steps: (1) melting pure Mg, Mg-Gd, Mg-Sm, Mg-Zr, Mg-Ho intermediate alloy and pure Zn under the protection of a mixed gas of CO2 and SF6 in a volume ratio of 97-99:3-1 at 700-720℃, stirring for 15-20min, and then argon blowing refining, standing for 25-40min, and then pouring into a preheated mold at 200-250℃ by gravity casting to obtain a magnesium alloy ingot; (2) the magnesium alloy ingot obtained in step (1) is subjected to solid solution treatment at 500-520℃ for 6-8h, and then subjected to turning processing to obtain a magnesium alloy blank; (3) the magnesium alloy blank obtained in step (2) and an extrusion die are subjected to heat preservation at 350-370℃ for 1-3h, and then subjected to extrusion treatment at 350-370℃ to obtain a light and heavy rare earth composite reinforced high-strength heat-resistant magnesium alloy, wherein the extrusion treatment has an extrusion speed of 0.5-0.9mm / s and an extrusion ratio of 5-9:1; the obtained high-strength heat-resistant magnesium alloy has a high thermal stability phase, a solute enrichment fault structure and an ultra-fine crystal structure with a size of ≤0.9μm, and maintains a high strength at room temperature and high temperature: the room temperature yield strength is ≥340MPa; the high temperature yield strength at 200-210℃ is ≥300MPa; the high temperature performance attenuation is ≤11.7%.

2. The high-strength heat-resistant magnesium alloy of claim 1, wherein the alloy is a light and heavy rare earth composite strengthened high-strength heat-resistant magnesium alloy. The magnesium alloy composition is: Gd: 6.8-7.0wt.%, Sm: 2.3-2.5wt.%, Zn: 0.4-1.8wt.%, Zr: 0.2-0.4wt.%, Ho: 0.1-0.2wt.%, the balance of Mg, and inevitable impurities ≤0.04wt.%.

3. The high-strength heat-resistant magnesium alloy of claim 1 or 2, wherein the alloy is a light and heavy rare earth composite strengthened high-strength heat-resistant magnesium alloy. The magnesium alloy ingot in step (2) is subjected to solid solution treatment at 505-515℃ for 6.5-7.5h.

4. The high-strength heat-resistant magnesium alloy of claim 3, wherein the alloy is a light and heavy rare earth composite strengthened high-strength heat-resistant magnesium alloy. The magnesium alloy blank in step (3) and the extrusion die are subjected to heat preservation at 355-365℃ for 1.5-2.5h, and then subjected to extrusion treatment at 355-365℃ to obtain a light and heavy rare earth composite reinforced high-strength heat-resistant magnesium alloy, wherein the extrusion treatment has an extrusion speed of 0.6-0.8mm / s and an extrusion ratio of 6-8:1.