High-strength plastic heat-resistant magnesium alloy and preparation method thereof

Abstract

The invention provides a high-strength plastic heat-resistant magnesium alloy and a preparation method thereof, and the high-strength plastic heat-resistant magnesium alloy comprises the following components in percentage by mass: 9-18% of Gd element, 0-4% of Y element, 0-0.5% of Zr element and the balance of Mg element. The interior of crystal grains of the high-strength plastic heat-resistant magnesium alloy contains a prismatic precipitated phase and a needle-shaped precipitated phase, and a crystal boundary contains Gd element segregation. The high-strength and high-plasticity heat-resistant magnesium alloy has high strength and high plasticity at the room temperature and the high temperature, and at the room temperature, the yield strength is larger than or equal to 300 MPa, the tensile strength is larger than or equal to 380 MPa, and the ductility is larger than or equal to 10%; at the temperature of 250 DEG C, the yield strength is larger than or equal to 250 MPa, the tensile strength is larger than or equal to 320 MPa, the ductility is larger than or equal to 20%, and the steel can be applied to the industrial fields of aerospace and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-ferrous metal materials and processing, and relates to a high-strength, high-plasticity and heat-resistant magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloy is the lightest metal structural material available at present, and its products have been widely used in many industrial fields. Among them, the demand for lightweight of large-sized complex structural parts in the aerospace industry has given magnesium alloy a broader application prospect and a more urgent application demand. Facing the eager expectation of double weight reduction of aerospace structural parts and carried fuel, as well as the strict requirements of the aerospace service environment for the stability of mechanical properties, the cast magnesium alloy with high strength, high plasticity and high heat resistance has become the development core of technical personnel in this field. Excellent casting fluidity is an important basis for complex structural parts to have uniform mechanical properties. Elements such as Al, Mn and Sn have long been used to enhance fluidity, but the strength of Mg-Al, Mg-Mn and Mg-Sn alloys is severely damaged in a heated environment. When the temperature reaches 200 °C or above, the tensile strength of such magnesium alloys is less than 200 MPa, which cannot meet the minimum requirements of aerospace structural parts for high-temperature mechanical strength. Adding rare earth elements such as Gd, Er, Nd, Sm and Y has been proven to effectively improve the high-temperature strength of cast magnesium alloys, and adding multiple rare earth elements or compound adding rare earth and non-rare earth elements and subjecting to aging treatment can further strengthen the magnesium alloy, which has been gradually applied to small-sized regular-shaped secondary load-bearing structural parts. However, multi-element cast magnesium alloys still cannot form effective filling and feeding during the casting process of complex-shaped structural parts, resulting in passive safety problems such as uneven performance, poor heat resistance and short lifespan frequently occurring in large-sized load-bearing parts. With the birth, improvement and popularization of low-pressure casting technology, preparing a cast / die-cast magnesium alloy that meets the requirements of variable temperatures in the aerospace service environment and has a high standard of strength and plasticity matching is the key to achieving a technological breakthrough. Therefore, it is necessary to find a magnesium alloy with synchronous improvement of high strength and plasticity at room temperature and high temperature, so that its high strength and plasticity and heat resistance meet the application standards of industrial fields such as aerospace. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a high-strength, high-plasticity and heat-resistant magnesium alloy and a preparation method thereof.

[0004] To solve the above technical problem, the present invention adopts the following technical solutions.

[0005] A high-strength, high-plasticity and heat-resistant magnesium alloy, by mass percentage, comprises the following components: 9% to 18% of Gd element, 0 to 4% of Y element, 0 to 0.5% of Zr element, and the balance is Mg element; the grain interior of the high-strength, high-plasticity and heat-resistant magnesium alloy contains prismatic precipitates and needle-shaped precipitates, and the grain boundary of the high-strength, high-plasticity and heat-resistant magnesium alloy contains Gd element segregation.

[0006] For the above-mentioned high-strength, plastic and heat-resistant magnesium alloy, further improved, the grain size in the high-strength, plastic and heat-resistant magnesium alloy is ≤ 40 μm.

[0007] For the above-mentioned high-strength, plastic and heat-resistant magnesium alloy, further improved, the quantity ratio of the prismatic precipitates to the needle-shaped precipitates is 0.5 - 2:1; the grain size in the high-strength, plastic and heat-resistant magnesium alloy is ≤ 30 μm.

[0008] For the above-mentioned high-strength, plastic and heat-resistant magnesium alloy, further improved, by mass percentage, it comprises the following components: 12% - 18% of Gd element, 0 - 3% of Y element, 0.2% - 0.5% of Zr element, and the balance is Mg element; the total content of the Gd element and the Y element is ≤ 18%.

[0009] For the above-mentioned high-strength, plastic and heat-resistant magnesium alloy, further improved, the high-strength, plastic and heat-resistant magnesium alloy further comprises the following component: 0 - 2% of Zn element;

[0010] When the content of the Zn element is not 0, the grain boundary of the magnesium alloy contains Zn element segregation.

[0011] For the above-mentioned high-strength, plastic and heat-resistant magnesium alloy, further improved, the high-strength, plastic and heat-resistant magnesium alloy further comprises the following components: 0 - 1% of A element, 0 - 0.5% of B element; the A element is any one of Er element, Nd element, Sm element, La element and Ce element, and the B element is any one of Ni element, Cu element and Co element;

[0012] When the content of the A element is not 0, the grain boundary of the magnesium alloy contains A element segregation.

[0013] For the above-mentioned high-strength, plastic and heat-resistant magnesium alloy, further improved, in the high-strength, plastic and heat-resistant magnesium alloy, one side or both sides of the grain boundary contain a precipitate-free zone; the width of the precipitate-free zone is 0.4 μm - 2 μm.

[0014] For the above-mentioned high-strength, plastic and heat-resistant magnesium alloy, further improved, in the high-strength, plastic and heat-resistant magnesium alloy, the grain boundary contains massive precipitates, and the massive precipitates and the precipitate-free zone exist simultaneously.

[0015] As a general technical concept, the present invention also provides a preparation method of the above-mentioned high-strength, plastic and heat-resistant magnesium alloy, and any one of the following methods is used to prepare the high-strength, plastic and heat-resistant magnesium alloy;

[0016] Method 1 includes the following steps:

[0017] S1. According to the mass percentages of the components in the magnesium alloy, weigh the required raw materials, melt and cast them to obtain an ingot;

[0018] S2. Solution treatment is carried out on the ingot; the temperature of the solution treatment is 420°C to 520°C, and the time is 6h to 24h;

[0019] S3. Aging treatment is carried out on the material after solution treatment to obtain a high-strength, high-plasticity and heat-resistant magnesium alloy; the temperature of the aging treatment is 160°C to 240°C, and the time is 6h to 72h;

[0020] Method 2 includes the following steps:

[0021] S1. Weigh the required raw materials according to the mass percentages of the components in the magnesium alloy, melt and cast to obtain an ingot;

[0022] S2. Gradient solution treatment is carried out on the ingot; the specific process of the gradient solution treatment is: keep warm at 420°C to 460°C for 0.5h to 12h, and then keep warm at 460°C to 520°C for 6h to 12h;

[0023] S3. Gradient aging treatment is carried out on the material after solution treatment to obtain a high-strength, high-plasticity and heat-resistant magnesium alloy; the specific process of the gradient aging treatment is: keep warm at 160°C to 200°C for 3h to 36h, and then keep warm at 200°C to 240°C for 6h to 18h;

[0024] Method 3 includes the following steps:

[0025] S1. Weigh the required raw materials according to the mass percentages of the components in the magnesium alloy, melt and cast to obtain an ingot;

[0026] S2. Gradient solution treatment is carried out on the ingot; the specific process of the gradient solution treatment is: keep warm at 420°C to 460°C for 0.5h to 12h, and then keep warm at 460°C to 520°C for 6h to 12h;

[0027] S3. Aging treatment is carried out on the material after solution treatment to obtain a high-strength, high-plasticity and heat-resistant magnesium alloy; the temperature of the aging treatment is 160°C to 240°C, and the time is 6h to 72h;

[0028] Method 4 includes the following steps:

[0029] S1. Weigh the required raw materials according to the mass percentages of the components in the magnesium alloy, melt and cast to obtain an ingot;

[0030] S2. Solution treatment is carried out on the ingot; the temperature of the solution treatment is 420°C to 520°C, and the time is 6h to 24h;

[0031] S3. Perform stepwise aging treatment on the solution-treated material to obtain a high-strength, high-ductility and heat-resistant magnesium alloy. The specific process of the stepwise aging treatment is as follows: keep it at 160°C - 200°C for 3h - 36h, and then keep it at 200°C - 240°C for 6h - 18h.

[0032] In the above preparation method, further improved, in step S1, the melting temperature is 680°C - 750°C, the casting temperature is 680°C - 750°C, the casting is semi-continuous casting or low-pressure casting, and the pressure of the low-pressure casting is 0.02MPa - 0.2MPa.

[0033] Compared with the prior art, the advantages of the present invention are as follows:

[0034] (1) Aiming at the problems existing in the existing Mg-Gd-Y series cast magnesium alloys, such as large grain size, uneven intragranular precipitation, easy coarsening of the precipitation phase, serious loss of rare-earth solute atoms, and low grain boundary strength during high-temperature plastic deformation, the present invention creatively proposes a high-strength, high-ductility and heat-resistant magnesium alloy. The added Gd element enables Gd solute atoms to accumulate at the grain boundaries of the magnesium alloy, which can not only avoid the solute loss and coarsening of the intragranular precipitation phase caused by excessive precipitation of Gd elements in the grains, but also make full use of the Gd element to form additional grain boundary segregation strengthening, enhance the high-temperature stability of the grain boundaries, and significantly reduce the degree of strength decrease during high-temperature plastic deformation; based on the fact that the types of binary precipitation phases of MgY are single and it is not easy to form a strong precipitation strengthening effect, the content of the added Y element is significantly lower than that of the Gd element, so that the Y element still exists in the form of solid solution atoms after aging treatment, thereby being able to give full play to the advantage of good solid solution strengthening effect of the Y element; the added Zr element can refine the casting structure, improve the melt fluidity, and reduce the ingot defects; more importantly, there are two precipitation phases in the grain interior of the magnesium alloy, namely prism-shaped precipitation phases growing along the second-order cone plane and needle-shaped precipitation phases growing along the first-order cone plane. The precipitation phases with the same habit plane form an angle of 60° or 120°, and the precipitation phases with different habit planes form an angle of 30° or 90°, which can effectively hinder the cross-slip of basal dislocations to adjacent prism planes, improve the strength, and can also induce independent prism plane dislocations, promote plastic deformation, and achieve the purpose of simultaneous improvement of strength and plasticity. The high-strength, high-ductility and heat-resistant magnesium alloy of the present invention has high strength and high ductility at both room temperature and high temperature. At room temperature, its yield strength ≥ 300MPa, tensile strength ≥ 380MPa, and elongation ≥ 10%; at 250°C, its yield strength ≥ 250MPa, tensile strength ≥ 320MPa, and elongation ≥ 20%.

[0035] (2) For the high-strength, high-ductility and heat-resistant magnesium alloy of the present invention, its grain size ≤ 40μm. According to the Hall-Petch relationship, the smaller the grain size, the higher the strength, and the fine grain strengthening effect is significant; more preferably, its grain size ≤ 30μm, which is beneficial to further promoting the fine grain strengthening and improving the strength of the magnesium alloy.

[0036] (3) For the high-strength, plastic and heat-resistant magnesium alloy of the present invention, by optimizing the quantity ratio of prismatic precipitates to acicular precipitates to be 0.5 - 2:1, it is beneficial to weaken the local stress concentration caused by incoherent precipitation, thereby maintaining the plastic deformation ability of the magnesium alloy.

[0037] (4) For the high-strength, plastic and heat-resistant magnesium alloy of the present invention, by optimizing the mass percentages of the components of the magnesium alloy, namely 12% - 18% of Gd element, 0 - 3% of Y element, and 0.2% - 0.5% of Zr element, increasing the ratio of Gd to Y content can accelerate the diffusion of Gd element, which is beneficial to simultaneously promoting intragranular precipitation strengthening, grain boundary segregation strengthening, grain boundary precipitation to enhance grain boundary heat resistance, and widening of grain boundary precipitate-free zones to enhance plasticity; by optimizing the total amount of Gd and Y elements in the magnesium alloy ≤ 18%, it can avoid the serious lattice distortion caused by three or more intragranular precipitates, and is also beneficial to reducing the weight of magnesium alloy structural parts.

[0038] (5) For the high-strength, plastic and heat-resistant magnesium alloy of the present invention, by adding 0 - 2% of Zn element, it can further enhance the solid solution strengthening effect, and can also co-segregate with Gd at the grain boundary, strengthening the grain boundary segregation strengthening and grain boundary thermal stability, and reducing the degree of high-temperature strength decline.

[0039] (6) Aiming at the problem that existing heat-resistant magnesium alloys mostly use long-range ordered stacking phases (LPSO phases) as strengthening means, which requires adding a large amount of rare earth elements and transition group elements at the same time, resulting in poor fluidity during the casting process, excessive dendritic numbers in the obtained ingots, and being unable to be completely eliminated by solution treatment, and finally only high strength can be obtained, while the plasticity at room temperature and high temperature is seriously insufficient. The high-strength, plastic and heat-resistant magnesium alloy of the present invention only adds any one subgroup element of 0 - 0.5% of Ni, Co, and Cu. Using such subgroup elements can accelerate the simultaneous generation of grain boundary precipitates and precipitate-free zones during aging, not only will not damage the melt fluidity during the casting process, but also can promote grain boundary precipitation and enhance grain boundary strength; adding any one rare earth element of 0 - 1% of Er, Nd, Sm, La, and Ce can further enhance the solid solution strengthening effect, and can also co-segregate with Gd at the grain boundary to further enhance the grain boundary segregation strengthening effect.

[0040] (7) For the high-strength, plastic and heat-resistant magnesium alloy of the present invention, it is further defined that one side or both sides of the grain boundary contain precipitate-free zones, and the width of the precipitate-free zones is 0.4 μm - 2 μm. Controlling the width of the precipitate-free zones can make the proportion of the precipitate-free zones relative to the grain size be 1% - 10%, which can not only release stress concentration and enhance plasticity, but also will not damage the strength.

[0041] (8) The high-strength, high-plasticity and heat-resistant magnesium alloy of the present invention is further defined in that blocky precipitates are included at the grain boundaries, and the blocky precipitates and the precipitate-free zone coexist. On the one hand, the grain boundary strength is increased to avoid significant grain boundary slip during high-temperature plastic deformation and loss of strength. On the other hand, the precipitate-free zone and the blocky precipitates are generated simultaneously, rather than the blocky precipitates at the grain boundaries being generated alone, which can effectively avoid stress concentration at the grain boundary precipitates during room-temperature deformation.

[0042] (9) The present invention also correspondingly provides a preparation method of a high-strength, high-plasticity and heat-resistant magnesium alloy. According to the mass percentages of the components in the magnesium alloy, the required raw materials are weighed and melted and cast. The ingot is subjected to solution treatment. Through high-temperature (420°C to 520°C) solution treatment, all the added elements exist in the form of solid solution atoms, reducing the impurities inside the magnesium alloy and purifying the matrix. And short-time (6h to 24h) solution treatment can avoid grain coarsening and texture strengthening. Then the material after solution treatment is subjected to aging treatment. The aging treatment temperature is relatively high (160°C to 240°C) and the time is relatively short (6h to 72h), so that the prismatic precipitates and needle-like precipitates will not rapidly coarsen during subsequent aging, nor will they shear and fracture during high-temperature plastic deformation, thus avoiding damaging the plasticity of the magnesium alloy. For the high-strength, high-plasticity and heat-resistant magnesium alloy prepared by the present invention, the precipitate-free zone at the grain boundaries can provide an additional stress release region to generate high plasticity, and the grain boundary element segregation and the blocky precipitates at the grain boundaries can improve the grain boundary thermal stability and are not prone to generating intergranular cracks during high-temperature deformation. That is, by using the multi-stage coupling effects of element segregation, intragranular prismatic precipitates and needle-like precipitates, precipitate-free zones at the grain boundaries and blocky precipitates at the grain boundaries, the room-temperature and high-temperature strength and plasticity of the magnesium alloy are synergistically improved, so that its strength, plasticity and heat resistance meet the application standards in industrial fields such as aerospace.

[0043] The preparation method of the present invention adopts stepwise solution treatment, that is, it is held at 420°C to 460°C for 0.5 to 12h, and then held at 460°C to 520°C for 6h to 12h. The low-temperature and long-time solution treatment in the first stage can avoid grain coarsening. Finer grains can enhance the fine-grain strengthening effect and provide more grain boundaries to facilitate the formation of precipitate-free zones and blocky precipitates at the grain boundaries. The high-temperature and short-time solution treatment in the second stage can make the Gd element and trace rare earth elements tend to segregate at the grain boundaries more, increasing the segregation strengthening effect.

[0044] The preparation method of the present invention adopts step aging treatment, that is, it is held at 160°C to 200°C for 3h to 36h, and then held at 200°C to 240°C for 6h to 18h. The low-temperature and long-time aging treatment in the first stage enables more nucleation sites of Gd element to form in the crystal grains, increasing the number of precipitation phases and the strengthening effect of precipitation phases; the high-temperature and short-time aging treatment in the second stage can avoid the adverse effects of precipitation phase coarsening on mechanical properties; in addition, prismatic precipitation phases tend to form preferentially on the secondary prism planes, while needle-like precipitation phases are generated by the continuous evolution of prismatic precipitation phases during high-temperature aging and on the primary prism planes. The high-temperature and short-time aging treatment enables the coexistence of the two precipitation phases, forming precipitation strengthening along the primary and secondary prism planes simultaneously, avoiding the dissolution of precipitation phases during high-temperature plastic deformation, and ensuring that the magnesium alloy has excellent heat resistance.

[0045] (10) By optimizing the melting temperature to 680°C to 750°C and the casting temperature to 680°C to 750°C, the preparation method of the present invention can ensure that all raw materials are completely melted, evenly mixed, and have a low burn-up rate, reducing the loss of raw materials and the deviation of components; at the same time, its melt has good fluidity and strong filling ability, is suitable for the low-pressure casting method, and can be applied to the preparation of large-size and complex-shaped structural parts in the aerospace industry. Description of the Drawings

[0046] Figure 1 It is the microstructure diagram of the high-strength, plastic and heat-resistant magnesium alloy prepared in Example 1 of the present invention.

[0047] Figure 2 It is the microstructure diagram of the magnesium alloy prepared in Comparative Example 1. Detailed Embodiments

[0048] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby. The materials and instruments used in the following embodiments are all commercially available.

[0049] Example 1

[0050] A high-strength, plastic and heat-resistant magnesium alloy of the present invention contains the following components by mass percentage: 12% Gd element, 3% Y element, 0.2% Zr element, and the balance is Mg element.

[0051] A preparation method of the high-strength, plastic and heat-resistant magnesium alloy of this example includes the following steps:

[0052] S1. Weigh the required raw materials according to the mass percentages of the components in the above magnesium alloy;

[0053] S2. Melting and Casting: Mix the above raw materials evenly, then melt and perform low-pressure casting. The melting temperature is 710°C - 720°C, the low-pressure casting temperature is 680°C - 690°C, and the pressure is 0.02 MPa to obtain an ingot.

[0054] S3. Solution Treatment: Perform solution treatment on the ingot. The solution treatment temperature is 460°C and the time is 24 h.

[0055] S4. Aging Treatment: Perform stepwise aging treatment on the material after solution treatment. Specifically: Keep it at 200°C for 12 h, then at 240°C for 6 h to obtain a high-strength, high-ductility and heat-resistant magnesium alloy, abbreviated as Mg-12Gd-3Y-0.2Zr alloy, marked as Sample No. 1.

[0056] Figure 1 This is the microstructure diagram of the high-strength, high-ductility and heat-resistant magnesium alloy prepared in Example 1 of the present invention. Figure 1 In it, (a) is the metallographic structure, (b) is the bright-field TEM image of the intragranular precipitates of the magnesium alloy, (c) is the dark-field TEM image of the elemental aggregation state at the grain boundary of the magnesium alloy, and (d) is the bright-field TEM image of the massive grain boundary precipitates and the precipitate-free zone at the grain boundary of the magnesium alloy. As Figure 1 shown, for the high-strength, high-ductility and heat-resistant magnesium alloy prepared in this example, its grain size is all less than 25 μm. The intragranular part contains both prismatic precipitates and needle-like precipitates, and the quantity ratio of prismatic precipitates to needle-like precipitates is 1.5:1. The grain boundary contains Gd element segregation, and the grain boundary also contains a precipitate-free zone and massive grain boundary precipitates. The width of the precipitate-free zone is 0.6 μm.

[0057] Comparative Example 1

[0058] A magnesium alloy, by mass percentage, contains the following components: 20% Gd element and 0.2% Zr element, and the balance is Mg element.

[0059] The preparation method of this magnesium alloy is basically the same as that of the high-strength, high-ductility and heat-resistant magnesium alloy in Example 1, except that: the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-20Gd-0.2Zr alloy, marked as Sample No. 2.

[0060] As Figure 2 shown, its grain size is all less than 20 μm. The intragranular part only contains needle-like precipitates, the grain boundary has no Gd element segregation, and the grain boundary contains a precipitate-free zone with a width of 2.8 μm and massive precipitates.

[0061] Figure 2 This is the microstructure diagram of the magnesium alloy prepared in Comparative Example 1. Figure 1Among them, (a) is the metallographic structure, (b) is the bright-field TEM image of the precipitates within the grains of the magnesium alloy, (c) is the dark-field TEM image of the elemental aggregation state at the grain boundaries of the magnesium alloy, and (d) is the bright-field TEM image of the massive grain-boundary precipitates and the precipitate-free zone at the grain boundaries of the magnesium alloy. As Figure 2 shown, for the magnesium alloy prepared in Comparative Example 1, its grain size is less than 20 μm, only acicular precipitates are contained within the grains, there is no segregation of Gd element at the grain boundaries, and the grain boundaries contain a precipitate-free zone with a width of 2.8 μm and massive precipitates.

[0062] Comparative Example 2

[0063] A magnesium alloy, whose components are the same as those of the high-strength, high-plasticity, and heat-resistant magnesium alloy in Example 1.

[0064] The preparation method of this magnesium alloy is basically the same as that of the high-strength, high-plasticity, and heat-resistant magnesium alloy in Example 1, with the only difference being that: in step S4, the step of stepwise aging treatment is replaced by a single aging treatment, the temperature of the single aging treatment is 150 °C, and the time is 96 h; the magnesium alloy obtained is simply referred to as the Mg-12Gd-3Y-0.2Zr alloy and is labeled as Sample No. 3.

[0065] For the magnesium alloy prepared in Comparative Example 2, its grain size is less than 25 μm, only prismatic precipitates are contained within the grains, the grain boundaries contain segregation of Gd element, and the grain boundaries also contain a grain-boundary precipitate-free zone with a width of 0.2 μm.

[0066] Uniaxial tensile tests were respectively carried out on the three magnesium alloys obtained in Example 1 and Comparative Examples 1-2 at room temperature (25 °C) and 250 °C to test the mechanical properties at room temperature and high temperature, and the results are shown in Table 1.

[0067] Table 1 Performance test results of magnesium alloys

[0068]

[0069]

[0070] As can be seen from Table 1, Sample No. 1 has both high strength and high plasticity at room temperature and high temperature; for Sample No. 2, due to the excessive Gd content, all the prismatic precipitates are transformed into acicular precipitates, resulting in obvious stress concentration near the precipitates and a decrease in plasticity, and the precipitate-free zone is too wide, causing a synchronous decrease in strength; for Sample No. 3, due to the low aging temperature, even long-term aging cannot transform the prismatic precipitates into acicular precipitates, resulting in a synchronous decrease in strength and plasticity.

[0071] Example 2

[0072] A high-strength, high-plasticity, and heat-resistant magnesium alloy of the present invention contains the following components by mass percentage: 13% Gd element, 1% Sm element, 0.1% Ni element, 0.1% Zr element, and the balance is Mg element.

[0073] A preparation method of a high-strength, plastic and heat-resistant magnesium alloy according to this embodiment includes the following steps:

[0074] S1. Weigh the required raw materials according to the mass percentages of the components in the above magnesium alloy;

[0075] S2. Melting and casting: Mix the above raw materials evenly, conduct melting and low-pressure casting. The melting temperature is 730°C to 740°C, the low-pressure casting temperature is 710°C to 720°C, and the pressure is 0.1 MPa to obtain an ingot;

[0076] S3. Solution treatment: Conduct solution treatment on the ingot. The solution treatment temperature is 520°C and the time is 6 h;

[0077] S4. Aging treatment: Conduct step-by-step aging treatment on the material after solution treatment. Specifically: Keep it at 160°C for 12 h, and then keep it at 200°C for 12 h to obtain a high-strength, plastic and heat-resistant magnesium alloy, abbreviated as Mg-13Gd-1Sm-0.1Ni-0.1Zr alloy, marked as sample No. 4.

[0078] For the high-strength, plastic and heat-resistant magnesium alloy prepared in this embodiment, its grain size is less than 30 μm. The intragranular part simultaneously contains prismatic precipitates and needle-like precipitates, and the quantity ratio of prismatic precipitates to needle-like precipitates is 0.6∶1. The grain boundary contains segregation of Gd and Sm elements, and the grain boundary also contains a precipitate-free zone and massive precipitates. The width of the precipitate-free zone is 1.8 μm.

[0079] Comparative Example 3

[0080] A magnesium alloy contains the following components by mass percentage: 13% Gd element, 2% Sm element, 0.1% Ni element, 0.1% Zr element, and the balance is Mg element.

[0081] The preparation method of this magnesium alloy is basically the same as that of the high-strength, plastic and heat-resistant magnesium alloy in Example 2, except that: the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-13Gd-2Sm-0.1Ni-0.1Zr alloy, marked as sample No. 5.

[0082] For the magnesium alloy prepared in Comparative Example 3, its grain size is less than 20 μm. The intragranular part simultaneously contains prismatic precipitates and needle-like precipitates and the quantity ratio of the two is 0.1∶1. The grain boundary only contains segregation of Sm element, and the grain boundary also contains a precipitate-free zone with a width of 3.2 μm and massive precipitates.

[0083] Comparative Example 4

[0084] A magnesium alloy, by mass percentage, contains the following components: 13% Gd element, 1% Sm element, 1% Ni element, 0.1% Zr element, and the balance is Mg element.

[0085] The preparation method of this magnesium alloy is basically the same as that of the high-strength, high-plasticity and heat-resistant magnesium alloy in Example 2, with the only difference being that the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-13Gd-1Sm-1Ni-0.1Zr alloy and is marked as Sample No. 6.

[0086] For the magnesium alloy prepared in Comparative Example 4, its grain size is less than 30 μm, the intragranular part only contains prismatic precipitates, the grain boundary does not contain Gd element segregation, and the grain boundary does not contain a precipitate-free zone but contains massive precipitates.

[0087] Comparative Example 5

[0088] A magnesium alloy, by mass percentage, contains the following components: 13% Gd element, 0.5% La element, 0.5% Ce element, 0.1% Ni element, 0.1% Zr element, and the balance is Mg element.

[0089] The preparation method of this magnesium alloy is basically the same as that of the high-strength, high-plasticity and heat-resistant magnesium alloy in Example 2, with the only difference being that the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-13Gd-0.5La-0.5Ce-0.1Ni-0.1Zr alloy and is marked as Sample No. 7.

[0090] For the magnesium alloy prepared in Comparative Example 5, its grain size is less than 20 μm, the intragranular part only contains prismatic precipitates, the grain boundary only contains Gd element segregation, and the grain boundary also contains a precipitate-free zone with a width of 2.8 μm.

[0091] Uniaxial tensile tests were carried out on the four magnesium alloys obtained in Example 2 and Comparative Examples 3-5 at room temperature (25 °C) and 250 °C respectively to test the mechanical properties at room temperature and high temperature, and the results are shown in Table 2.

[0092] Table 2 Performance test results of magnesium alloys

[0093]

[0094] As can be seen from Table 2, Sample 4 has both high strength and plasticity at room temperature and high temperature; for Sample 5, due to the excessive Sm content, although the grain size is further refined, the excessive Sm occupies the original positions of the Gd solute atoms, forcing the Gd atoms to accelerate diffusion and precipitation, resulting in the transformation of a large number of prismatic precipitation phases into needle-like precipitation phases, leading to no segregation of Gd elements at the grain boundaries and an overly wide precipitate-free zone, and finally only high plasticity can be obtained but not high strength; for Sample 6, due to the excessive Ni element content, the diffusion of the Gd element is hindered, resulting in an excessive amount of MgGdNi massive precipitates at the grain boundaries, which is extremely likely to cause stress concentration at the grain boundaries and seriously damage the strength and plasticity of the sample; for Sample 7, due to the simultaneous presence of La and Ce elements, the diffusion of the Gd element is hindered, lacking the strengthening effect of needle-like precipitates in the grains, resulting in insufficient strength.

[0095] Example 3

[0096] A high-strength and plastic heat-resistant magnesium alloy of the present invention contains the following components by mass percentage: 18% Gd element and 0.5% Co element, with the balance being Mg element.

[0097] A preparation method of the high-strength and plastic heat-resistant magnesium alloy of this example includes the following steps:

[0098] S1. Weigh the required raw materials according to the mass percentages of the components in the above magnesium alloy.

[0099] S2. Melting and casting: Mix the above raw materials evenly, conduct melting and low-pressure casting. The melting temperature is 740 °C - 750 °C, the low-pressure casting temperature is 710 °C - 720 °C, and the pressure is 0.2 MPa to obtain an ingot.

[0100] S3. Solution treatment: Conduct stepwise solution treatment on the ingot, specifically: hold at 420 °C for 12 h, and then hold at 480 °C for 12 h.

[0101] S4 Aging treatment: Conduct stepwise aging treatment on the material after solution treatment, specifically: hold at 160 °C for 12 h, and then hold at 220 °C for 6 h to obtain a high-strength and plastic heat-resistant magnesium alloy, abbreviated as Mg-18Gd-0.5Co alloy, marked as Sample 8.

[0102] The high-strength and plastic heat-resistant magnesium alloy prepared in this example has a grain size of less than 25 μm, both prismatic precipitation phases and needle-like precipitation phases are contained in the grains, and the quantity ratio of prismatic precipitation phases to needle-like precipitates is 0.6:1. The grain boundaries contain Gd element segregation, and the grain boundaries also contain a precipitate-free zone and massive precipitates. The width of the precipitate-free zone is 1.4 μm.

[0103] Example 4

[0104] A high-strength, plastic and heat-resistant magnesium alloy of the present invention contains the following components by mass percentage: 18% Gd element, and the balance is Mg element.

[0105] A preparation method of the high-strength, plastic and heat-resistant magnesium alloy of this embodiment is basically the same as that of the high-strength, plastic and heat-resistant magnesium alloy in Embodiment 3, except that: the components of the magnesium alloy are different; the obtained high-strength, plastic and heat-resistant magnesium alloy is abbreviated as Mg-18Gd alloy and marked as Sample No. 9.

[0106] The high-strength, plastic and heat-resistant magnesium alloy prepared in this embodiment has a grain size of less than 35 μm. The crystal interior contains both prismatic precipitates and needle-like precipitates, and the quantity ratio of prismatic precipitates to needle-like precipitates is 0.4:1. The grain boundary contains Gd element segregation and also contains a precipitate-free zone with a width of 1 μm.

[0107] Embodiment 5

[0108] A high-strength, plastic and heat-resistant magnesium alloy of the present invention contains the following components by mass percentage: 18% Gd element, 2% Y element, 0.5% Co element, and the balance is Mg element.

[0109] A preparation method of the high-strength, plastic and heat-resistant magnesium alloy of this embodiment is basically the same as that of the high-strength, plastic and heat-resistant magnesium alloy in Embodiment 3, except that: the components of the magnesium alloy are different; the obtained high-strength, plastic and heat-resistant magnesium alloy is abbreviated as Mg-18Gd-2Y-0.5Co alloy and marked as Sample No. 10.

[0110] The high-strength, plastic and heat-resistant magnesium alloy prepared in this embodiment has a grain size of less than 20 μm. The crystal interior contains both prismatic precipitates and needle-like precipitates, and the quantity ratio of prismatic precipitates to needle-like precipitates is 0.2:1. The crystal interior also contains MgGdY ternary lamellar precipitates. The grain boundary contains Gd element segregation, and also contains a precipitate-free zone and a large number of massive precipitates. The width of the precipitate-free zone is 1.6 μm.

[0111] Embodiment 6

[0112] A high-strength, plastic and heat-resistant magnesium alloy has the same components as the high-strength, plastic and heat-resistant magnesium alloy in Embodiment 3.

[0113] A preparation method of the high-strength, plastic and heat-resistant magnesium alloy of this embodiment is basically the same as that of the high-strength, plastic and heat-resistant magnesium alloy in Embodiment 2, except that: in step S2, low-pressure casting is replaced by semi-continuous casting, and the temperature of semi-continuous casting is 720°C to 730°C; the obtained high-strength, plastic and heat-resistant magnesium alloy is abbreviated as Mg-18Gd-0.5Co alloy and marked as Sample No. 11.

[0114] The high-strength, plastic and heat-resistant magnesium alloy prepared in this example has a grain size of less than 40 μm. The intragranular part contains both prismatic precipitates and needle-like precipitates, and the quantity ratio of prismatic precipitates to needle-like precipitates is 0.2∶1. The grain boundary contains Gd element segregation, and also contains a precipitate-free zone and massive precipitates. The width of the precipitate-free zone is 2.2 μm.

[0115] Comparative Example 6

[0116] A magnesium alloy has the same components as the high-strength, plastic and heat-resistant magnesium alloy in Example 3.

[0117] The preparation method of this magnesium alloy is basically the same as that of the high-strength, plastic and heat-resistant magnesium alloy in Example 3, with the only difference being that in step S3, the fractional solution treatment is different. Specifically, it is held at 400 °C for 12 h and then at 480 °C for 12 h. The obtained magnesium alloy is abbreviated as Mg-18Gd-0.5Co alloy and marked as Sample No. 12.

[0118] For the magnesium alloy prepared in Comparative Example 6, its grain size is less than 45 μm. The intragranular part only contains prismatic precipitates. The grain boundary does not contain Gd element segregation, and contains a precipitate-free zone and massive precipitates, and the width of the precipitate-free zone is 0.05 μm.

[0119] Comparative Example 7

[0120] A magnesium alloy contains the following components by mass percentage: 18% Gd element, 0.5% Co element, 1% Zr element, and the balance is Mg element.

[0121] The preparation method of this magnesium alloy is basically the same as that of the high-strength, plastic and heat-resistant magnesium alloy in Example 3, with the only difference being that the components of the magnesium alloy are different. The obtained magnesium alloy is abbreviated as Mg-18Gd-0.5Co-1Zr alloy and marked as Sample No. 13.

[0122] For the magnesium alloy prepared in Comparative Example 7, the size of some grains is greater than 50 μm. The intragranular part contains both prismatic precipitates and needle-like precipitates, and the quantity ratio of prismatic precipitates to needle-like precipitates is 1.2∶1. The grain boundary contains Gd element segregation, and contains a precipitate-free zone and massive precipitates, and the width of the precipitate-free zone is 1.4 μm.

[0123] Uniaxial tensile tests were carried out on the 6 magnesium alloys obtained from Examples 3 to 6 and Comparative Examples 6 to 7 at room temperature (25 °C) and 250 °C respectively to test the mechanical properties at room temperature and high temperature. The results are shown in Table 3.

[0124] Table 3 Performance test results of magnesium alloys

[0125]

[0126] As can be seen from Table 3, Sample No. 8 has high strength and plasticity at both room temperature and high temperature; Sample No. 9 lacks Co element and no grain boundary precipitation phase is formed, resulting in a decrease in strength; for Sample No. 10, since the total content of Gd and Y is higher than 18%, the intragranular MgGdY ternary lamellar precipitation phase is also included, which exacerbates the lattice distortion, reduces the plasticity, and fails to reach the expected higher level after solid solution strengthening; Sample No. 11 uses the semi-continuous casting method, and its tissue compactness and uniformity are inferior to those of Sample No. 8 prepared by the low-pressure casting method, resulting in a decrease in both the strength and plasticity of Sample No. 11; for Sample No. 12, due to the low solution temperature, Gd and Co elements fail to fully dissolve into the magnesium matrix and remain at the grain boundary, seriously damaging the plasticity and strength; for Sample No. 13, due to the excessive Zr content, the excess Zr element cannot dissolve into the magnesium matrix and is unevenly distributed in the grains and grain boundaries, seriously damaging the plasticity and strength.

[0127] Example 7

[0128] A high-strength, plastic and heat-resistant magnesium alloy of the present invention contains the following components by mass percentage: 9% Gd element, 2% Zn element, and the balance is Mg element.

[0129] A preparation method of the high-strength, plastic and heat-resistant magnesium alloy of this example includes the following steps:

[0130] S1. Weigh the required raw materials according to the mass percentages of the components in the above magnesium alloy.

[0131] S2. Melting and casting: Mix the above raw materials evenly, conduct melting and semi-continuous casting. The melting temperature is 730°C - 740°C, and the semi-continuous casting temperature is 700°C - 710°C to obtain an ingot.

[0132] S3. Solution treatment: Perform stepwise solution treatment on the ingot, specifically: keep it at 440°C for 6 hours, and then at 520°C for 12 hours.

[0133] S4. Aging treatment: Perform aging treatment on the material after solution treatment. The aging treatment temperature is 240°C and the time is 6 hours to obtain a high-strength, plastic and heat-resistant magnesium alloy, abbreviated as Mg-9Gd-2Zn alloy, marked as Sample No. 14.

[0134] The high-strength, plastic and heat-resistant magnesium alloy prepared in this example has a grain size of less than 30 μm. The intragranular part simultaneously contains prismatic precipitation phase and needle-like precipitation phase, and the quantity ratio of the prismatic precipitation phase to the needle-like precipitation phase is 2:1. The grain boundary contains segregation of Gd and Zn elements, and also contains a precipitation-free zone and massive precipitation phase. The width of the precipitation-free zone is 0.6 μm.

[0135] Example 8

[0136] A high-strength, plastic and heat-resistant magnesium alloy of the present invention contains the following components by mass percentage: 9% Gd element, and the balance is Mg element.

[0137] A preparation method of the high-strength, plastic and heat-resistant magnesium alloy of this embodiment is basically the same as the preparation method of the high-strength, plastic and heat-resistant magnesium alloy in Example 7, except that: the components of the magnesium alloy are different; the obtained high-strength, plastic and heat-resistant magnesium alloy is abbreviated as Mg-9Gd alloy and marked as Sample No. 15.

[0138] The high-strength, plastic and heat-resistant magnesium alloy obtained in this embodiment has a grain size of less than 35 μm. The crystal interior contains both prismatic precipitates and needle-shaped precipitates, and the quantity ratio of prismatic precipitates to needle-shaped precipitates is 2.5:1. The grain boundary contains Gd element segregation, and the grain boundary also contains a precipitate-free zone and massive precipitates. The width of the precipitate-free zone is 0.6 μm.

[0139] Comparative Example 8

[0140] A magnesium alloy contains the following components by mass percentage: 9% Gd element, 3% Zn element, and the balance is Mg element.

[0141] The preparation method of this magnesium alloy is basically the same as the preparation method of the high-strength, plastic and heat-resistant magnesium alloy in Example 7, except that: the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-9Gd-3Zn alloy and marked as Sample No. 16.

[0142] The magnesium alloy obtained in Comparative Example 8 has a grain size of less than 20 μm. The crystal interior contains both prismatic precipitates and needle-shaped precipitates, and the quantity ratio of prismatic precipitates to needle-shaped precipitates is 1.8:1. The grain boundary does not contain element segregation, and the grain boundary does not contain a precipitate-free zone but contains a large amount of massive MgGdZn precipitates.

[0143] Comparative Example 9

[0144] A magnesium alloy has the same components as the high-strength, plastic and heat-resistant magnesium alloy in Example 7.

[0145] The preparation method of this magnesium alloy is basically the same as the preparation method of the high-strength, plastic and heat-resistant magnesium alloy in Example 7, except that: aging treatment is not carried out; the obtained magnesium alloy is abbreviated as Mg-9Gd-3Zn alloy and marked as Sample No. 17.

[0146] The magnesium alloy obtained in Comparative Example 9 has a grain size of less than 30 μm. The crystal interior does not contain any precipitates. The grain boundary contains Gd and Zn element segregation. The grain boundary does not contain a precipitate-free zone and does not contain massive precipitates either.

[0147] Comparative Example 10

[0148] A magnesium alloy, by mass percentage, contains the following components: 6% Gd element, 3% Y element, 2% Zn element, and the balance is Mg element.

[0149] The preparation method of this magnesium alloy is basically the same as that of the high-strength and high-plasticity heat-resistant magnesium alloy in Example 7, with the only difference being that the components of the magnesium alloy are different; the prepared magnesium alloy is abbreviated as Mg-6Gd-3Y-2Zn alloy and is marked as Sample No. 18.

[0150] For the magnesium alloy prepared in Comparative Example 10, the size of some grains is greater than 50 μm. The intragranular part only contains prismatic precipitates, and the grain boundary only contains Zn element segregation, without a precipitate-free zone or massive precipitates at the grain boundary.

[0151] The five magnesium alloys obtained in Examples 7 - 8 and Comparative Examples 8 - 10 were respectively subjected to uniaxial tensile tests at room temperature (25 °C) and 250 °C to test the mechanical properties at room temperature and high temperature. The results are shown in Table 4.

[0152] Table 4 Performance test results of magnesium alloys

[0153]

[0154] As can be seen from Table 4, Sample No. 14 has both high strength and high plasticity at room temperature and high temperature; Sample No. 15 does not contain Zn element, and the grain boundary segregation strengthening effect is weakened, resulting in a decrease in high-temperature strength; in Sample No. 16, due to excessive Zn content, Gd atoms are attracted to precipitate at the grain boundary together to form a large number of massive precipitates, and stress concentration accumulates continuously during plastic deformation, seriously damaging plasticity; in Sample No. 17, due to the lack of aging treatment, the precipitation strengthening is insufficient and the strength drops severely; in Sample No. 18, due to too little Gd content, the degree of grain refinement is low, the precipitation strengthening effect is weak, and there is a lack of grain boundary segregation strengthening, so only high plasticity can be obtained.

[0155] As described above, it is only a preferred embodiment of the present invention and does not impose any formal limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes, without departing from the spirit and technical solution of the present invention. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A high-strength, plastic and heat-resistant magnesium alloy, characterized in that, By mass percentage, it contains the following components: 9% - 18% of Gd element, 0 - 4% of Y element, 0 - 0.5% of Zr element, and the balance is Mg element; the interior of the grains of the high-strength and high-plasticity heat-resistant magnesium alloy contains prismatic precipitates and needle-like precipitates, and the grain boundaries of the high-strength and high-plasticity heat-resistant magnesium alloy contain Gd element segregation.

2. The high-strength and heat-resistant magnesium alloy according to claim 1, characterized in that, The grain size in the high-strength and high-plasticity heat-resistant magnesium alloy is ≤ 40 μm.

3. The high-strength and heat-resistant magnesium alloy according to claim 2, characterized in that, The quantity ratio of the prismatic precipitates to the needle-like precipitates is 0.5 - 2:1; the grain size in the high-strength and high-plasticity heat-resistant magnesium alloy is ≤ 30 μm.

4. The high-strength and heat-resistant magnesium alloy according to any one of claims 1 to 3, characterized in that By mass percentage, it contains the following components: 12% - 18% of Gd element, 0 - 3% of Y element, 0.2% - 0.5% of Zr element, and the balance is Mg element; the total content of the Gd element and the Y element is ≤ 18%.

5. The high-strength and heat-resistant magnesium alloy according to any one of claims 1 to 3, characterized in that The high-strength and high-plasticity heat-resistant magnesium alloy further contains the following component: 0 - 2% of Zn element; When the content of the Zn element is not 0, the grain boundaries of the magnesium alloy contain Zn element segregation.

6. The high-strength and heat-resistant magnesium alloy according to any one of claims 1 to 3, characterized in that The high-strength and high-plasticity heat-resistant magnesium alloy further contains the following components: 0 - 1% of A element, 0 - 0.5% of B element; the A element is any one of Er element, Nd element, Sm element, La element and Ce element, and the B element is any one of Ni element, Cu element and Co element; When the content of the A element is not 0, the grain boundaries of the magnesium alloy contain A element segregation.

7. The high-strength and heat-resistant magnesium alloy according to any one of claims 1 to 3, characterized in that, In the high-strength and high-plasticity heat-resistant magnesium alloy, one side or both sides of the grain boundaries contain precipitate-free zones; the width of the precipitate-free zones is 0.4 μm - 2 μm.

8. The high-strength and heat-resistant magnesium alloy according to claim 7, characterized in that, In the high-strength and high-plasticity heat-resistant magnesium alloy, blocky precipitates are contained at the grain boundaries, and the blocky precipitates and the precipitate-free zones exist simultaneously.

9. A method for preparing a high-strength and plastic heat-resistant magnesium alloy according to any one of claims 1 to 8, characterized in that, The high-strength and high-plasticity heat-resistant magnesium alloy is prepared by any one of the following methods; Method 1 includes the following steps: S1. According to the mass percentages of the components in the magnesium alloy, weigh the required raw materials, melt and cast them to obtain an ingot; S2. Perform solution treatment on the ingot; the temperature of the solution treatment is 420°C - 520°C and the time is 6 h - 24 h; S3. Perform aging treatment on the material after solution treatment to obtain the high-strength and high-plasticity heat-resistant magnesium alloy; the temperature of the aging treatment is 160°C - 240°C and the time is 6 h - 72 h; Method 2 includes the following steps: S1. According to the mass percentages of the components in the magnesium alloy, weigh the required raw materials, melt and cast them to obtain an ingot; S2. Perform stepwise solution treatment on the ingot; the specific process of the stepwise solution treatment is: keep it at 420°C - 460°C for 0.5 h - 12 h, and then keep it at 460°C - 520°C for 6 h - 12 h; S3. Perform stepwise aging treatment on the material after solution treatment to obtain the high-strength and high-plasticity heat-resistant magnesium alloy; the specific process of the stepwise aging treatment is: keep it at 160°C - 200°C for 3 h - 36 h, and then keep it at 200°C - 240°C for 6 h - 18 h; Method 3 includes the following steps: S1. According to the mass percentages of the components in the magnesium alloy, weigh the required raw materials, melt and cast them to obtain an ingot; S2. Perform stepwise solution heat treatment on the ingot; the specific process of the stepwise solution heat treatment is: keep the temperature at 420°C to 460°C for 0.5 h to 12 h, and then keep the temperature at 460°C to 520°C for 6 h to 12 h; S3. Perform aging treatment on the solution heat-treated material to obtain a high-strength, high-ductility and heat-resistant magnesium alloy; the temperature of the aging treatment is 160°C to 240°C and the time is 6 h to 72 h; Method 4 includes the following steps: S1. Weigh the required raw materials according to the mass percentages of the components in the magnesium alloy, melt and cast to obtain an ingot; S2. Perform solution heat treatment on the ingot; the temperature of the solution heat treatment is 420°C to 520°C and the time is 6 h to 24 h; S3. Perform stepwise aging treatment on the solution heat-treated material to obtain a high-strength, high-ductility and heat-resistant magnesium alloy; the specific process of the stepwise aging treatment is: keep the temperature at 160°C to 200°C for 3 h to 36 h, and then keep the temperature at 200°C to 240°C for 6 h to 18 h.

10. The preparation method of the high-strength and plastic heat-resistant magnesium alloy according to claim 9, characterized in that, In step S1, the temperature of the melting is 680°C to 750°C, the temperature of the casting is 680°C to 750°C, the casting is semi-continuous casting or low-pressure casting, and the pressure of the low-pressure casting is 0.02 MPa to 0.2 MPa.

Images