A heat-resistant magnesium alloy strengthened by multiple precipitated phases and its preparation method

Abstract

The present invention provides a high-strength heat-resistant magnesium alloy with multiple precipitation phases and a preparation method thereof. The magnesium alloy is an Mg-A-B alloy, and the composition expression of the multiple precipitation phases is A x MgB y (where x and y are equal to 1 or 2), where both A and B are alloy element sets; according to the elements contained in the element sets and the precipitation phases of different lattice types formed by them, it can be specifically divided into face-centered cubic A2MgB type, face-centered cubic AMgB2 type, orthorhombic lattice AMgB type, hexagonal lattice AMgB type, and tetragonal lattice A2MgB2 type multiple precipitation phase strengthened magnesium alloys. The designed Mg-A-B alloy contains at least 5 elements; its microstructure has the following characteristics: (1) Nano-scale A x MgB y multiple precipitation phases are formed in the Mg matrix, and the average equivalent size is ≤20 nm; (2) A x MgB y multiple precipitation phases are not easily coarsened in a high-temperature environment, and the thermal stability of the alloy microstructure is strong. The room-temperature yield strength of the age-hardened peak-state magnesium alloy of the present invention is 300-550 MPa, the tensile strength is 350-600 MPa, and the elongation after fracture is 5-40%.

Description

Technical Field

[0001] The present invention belongs to the field of magnesium alloy design, preparation and processing, and particularly relates to a heat-resistant magnesium alloy strengthened by multiple precipitated phases and a preparation method thereof. Background Art

[0002] Magnesium alloys are the lightest structural materials in current engineering applications, and have advantages such as low density, high specific strength and specific stiffness, good damping and vibration reduction and noise reduction capabilities, good electromagnetic shielding performance, and easy recycling. However, poor heat resistance limits the popularization and application of magnesium alloys. Typical Mg-Al-Zn (AZ) series and Mg-Al-Mn (AM) series magnesium alloys are the most widely used commercial magnesium alloys, such as AZ91 (Mg-9Al-0.7Zn), AZ61 (Mg-6Al-0.7Zn), AM50 (Mg-5Al-0.4Mn), and AM60 (Mg-6Al-0.4Mn). Although they have good mechanical properties at room temperature, their heat resistance is not high, their creep resistance is poor, and the long-term service temperature does not exceed 130°C.

[0003] The heat resistance of magnesium alloys is determined by the thermal stability of the alloy microstructure. In AZ series and AM series magnesium alloys, the main second phase Mg 17 Al 12 has a melting point (T m ) of 458°C, and the eutectic temperature (T etc ) of the Mg-Al eutectic at the Mg-rich end is 437°C. Calculated in absolute temperature K, 130°C reaches 0.55T m and 0.57T etc , resulting in tissue softening. In addition, Al solute segregates along the grain boundaries of magnesium grains, reducing the melting point of the grain boundaries, making the grain boundaries prone to thermal softening, and resulting in a decrease in the creep resistance of the alloy.

[0004] Currently, alloying with rare earth elements (RE) is the main idea to improve the heat resistance of magnesium alloys. Some RE (such as Gd, Y, etc.) have a large solid solubility in Mg, and the solid solubility decreases rapidly with the decrease of temperature, which is easy to form Mg-RE compounds with high melting point and good thermal stability, improving the creep resistance of the alloy. Typical commercial heat-resistant Mg-RE series magnesium alloys are WE43 and WE54, and their total RE element content is greater than 7 wt.%. In recent years, a series of heat-resistant Mg-RE series magnesium alloys have been developed, such as Mg-Gd-Y-Zr-Ca (ZL200510025251.6), Mg-Gd-Y-Er (ZL201210467993.4), Mg-Y-Mn-Sc (ZL201711003938.9), Mg-Y-Nd-Zn (ZL201810607488.2), Mg-Y-Nd-Gd-Ag-Zr (ZL201810966108.4), Mg-Sm-Gd-Zn-Zr (ZL201310295995.4), Mg-Sm-Sn-Zn-V (ZL201810169383.3) and Mg-Sm-Y-La-Ce-Zn-Zr (ZL201910725285.8), etc.

[0005] Currently, the common feature of the second phase used to improve the heat resistance of magnesium alloys is that the types of elements contained in the second phase are few, and most of them do not exceed 3 kinds, such as Mg 2 Sn, Mg 3 Gd, Mg 12 Ce and Mg 12 NdY, etc. Their coarsening tendency in a high-temperature environment may be further reduced, achieving further improvement of heat resistance. Therefore, it is necessary to adopt a new design idea to regulate the microstructure of magnesium alloys to achieve the above purpose. Summary of the Invention

[0006] The present invention designs and prepares a new type of magnesium alloy that improves strength and heat resistance with multiple precipitation phases. The expression of the composition of the magnesium alloy is Mg-A-B, where both A and B are alloy element sets, and the Mg-A-B magnesium alloy is at least a 5-element alloy, that is, it contains at least 5 elements including the Mg element. According to the elements contained in the above "element set", the lattice type of the multiple precipitation phases, and the composition expression of the multiple precipitation phases, the Mg-A-B alloy of the present invention is specifically divided into the following 5 types:

[0007] ① Type 1: The A element set only contains Li element, with a content of 0.001 - 30 at.%; the B element set contains a combination of at least 3 elements among Al, Zn, Sn, Bi, Ga, In, Si, Ag, Au, Cd, Ge, Hg, Pb, Sb, Tl. Among them, the contents of Al, Zn, Sn, Bi, Ga, In elements are all 0.001 - 12 at.%, and the contents of Si, Ag, Au, Cd, Ge, Hg, Pb, Sb, Tl elements are all 0.001 - 5 at.%; and the atomic percentage satisfies A ≥ 2B. In this type of magnesium alloy, the A that forms a face-centered cubic structure 2 MgB precipitation phase;

[0008] ② Type 2: The A element set contains a combination of at least 2 elements among Tb, Dy, Ho, Er, Tm. Among them, the contents of Tb, Dy, Ho elements are all 0.001 - 10 at.%, and the contents of Er, Tm elements are all 0.001 - 30 at.%; the B element set contains Ag and Cu elements, with a content of 0.001 - 12 at.% each; and the atomic percentage satisfies 2A ≥ B. In this type of magnesium alloy, the AMgB 2 precipitation phase;

[0009] ③ Type 3: The A element set contains a combination of at least 2 elements among Ca, Sr, Eu, Yb, and the content of each element is 0.001 - 30 at.%; the B element set contains a combination of at least 2 elements among Sn, Ge, Si, Ag, Au, Pt, Pb. Among them, the contents of Sn, Ge, Si elements are all 0.001 - 12 at.%, and the contents of Ag, Au, Pt, Pb elements are all 0.001 - 5 at.%; and the atomic percentage satisfies A ≥ B. In this type of magnesium alloy, the AMgB precipitation phase with an orthorhombic lattice structure is formed;

[0010] ④ Type 4: The A element set contains a combination of at least 2 elements among La, Pr, Nd, and the content of each element is 0.001 - 30 at.%; the B element set contains a combination of at least 2 elements among Ga, In, Ag, Au, Pt, Tl. Among them, the contents of Ga, In elements are all 0.001 - 12 at.%, and the contents of Ag, Au, Pt, Tl elements are all 0.001 - 5 at.%; and the atomic percentage satisfies A ≥ B. In this type of magnesium alloy, the AMgB precipitation phase with a hexagonal lattice structure is formed;

[0011] ⑤ Type 5: The A element set contains a combination of at least two elements among Tb, Dy, Ho, Er, and Tm, where the contents of Tb, Dy, and Ho elements are all 0.001 - 10 at.%, and the contents of Er and Tm elements are all 0.001 - 30 at.%; the B element set contains Ge and Si elements, and the contents are both 0.001 - 12 at.%; and the atomic percentages satisfy A ≥ B. In this type of magnesium alloy, A that forms a tetragonal lattice structure 2 MgB 2 precipitation phase.

[0012] The microstructures of the above 5 types of Mg-A-B alloys have the following characteristics: (1) It contains multi-element precipitation phases with a size (i.e., equivalent diameter) ≤ 20 nm, and the general formula for its composition expression is A x MgB y (x, y are equal to 1 or 2); (2) The A x MgB y precipitation phase contains 5 or more elements. When held at a temperature of 250 - 300 °C for 60 - 90 days, the size increment of the precipitation phase < 10%, the hardness decrease amplitude < 10 HV, and the alloy has high thermal stability.

[0013] The preparation process of the Mg-A-B alloy of the present invention is any one of the following 2 types:

[0014] Process 1: Rapid cooling casting → Severe plastic deformation → Solution treatment → Quenching → Aging;

[0015] Process 2: Powder making → 3D printing → Aging.

[0016] Furthermore, Process 1 includes: S11. After mixing the elements, perform rapid cooling casting to obtain an alloy ingot; S12. Perform severe plastic deformation on the ingot to obtain an alloy bar; S13. Perform solution treatment on the bar to obtain a supersaturated solid solution; S14. Quench; S15. Perform aging heat treatment on the quenched solid solution to obtain the alloy.

[0017] Process 2 includes: S21. Melt and mix the bulk raw materials of the elements and then make powder to obtain alloy powder; S22. Use 3D printing to prepare a bulk sample from the powder; S23. Quench; S24. Perform aging heat treatment on the quenched sample to obtain the alloy.

[0018] In Process 1, further, the device for rapid cooling casting uses the device in the invention patent authorized to the first author of this application, "A Solidification Method and Device for Refining the Second Phase in Fe-containing Zinc Alloys" (Authorization Number: ZL 202010287273.4). The specific operation process is as follows: Using high-purity metal or commercial master alloy as raw materials, after proportioning according to the designed composition, put them into the crucible of the above device. Under argon protection, heat up to 680 - 780 °C to make the raw materials become a melt, refine and keep warm for 10 - 30 min, and then use the bottom circulating liquid cooling function of the rapid cooling casting device. The circulating liquid uses 15 °C circulating cooling water or calcium chloride solution to obtain Mg-A-B alloy ingots.

[0019] Further, the severe plastic deformation includes at least one or any combination of 2 - 4 techniques among equal-channel angular pressing, high-pressure torsion, equal-channel angular rolling, and accumulative roll bonding, including single-pass deformation and multi-pass deformation. The internal die angle of equal-channel angular pressing is 90 - 160 °, the external die angle is 10 - 50 °, the temperature is 500 - -25 °C, and it decreases by 25 - 100 °C successively after each pass, and it is pressed for 1 - 10 passes; the temperature of high-pressure torsion is 20 - 250 °C, the pressure is 2 - 10 GPa, the number of torsion turns is 1 / 8 turn - 20 turns, and the friction coefficient is 0.5 - 1.5; the die temperature of equal-channel angular rolling is 20 - 400 °C, the channel gap is 1.0 - 1.8 mm, the included angle of the die channel is 100 - 125 °, the number of rolling passes is 1 - 10 times, and the reduction per pass is 5 - 30%; the temperature of accumulative roll bonding is 20 - 450 °C, it is rolled for 3 - 15 passes, and the deformation per pass > 50%.

[0020] Further, the temperature of the solution heat treatment is 300 - 600 °C, and the holding time is 1 min - 5 min; quenching is carried out in water or mineral quenching oil at room temperature; the aging temperature is 150 - 200 °C, and the aging time is 5 min - 10 h.

[0021] In Process 2, further, the method for powder making is the plasma rotating electrode method or the argon gas atomization method; the technology used for 3D printing is any one of laser metal deposition technology (LDM), direct metal laser sintering technology (DMLS), electron beam selective melting technology (EBSM), and selective laser melting technology (SLM).

[0022] In the matrix of the magnesium alloy of the present invention prepared by process routes 1 to 2, in the rapidly solidified as-cast state, the average size of the second-phase particles is 10 to 25 μm; then the alloy after severe plastic deformation is solution heat-treated at 300 to 600 °C for a holding time of 1 min to 5 min to obtain a supersaturated solid solution; aging is carried out at 150 to 200 °C for 20 min to 5 h to reach the aging peak; the hardness in the aging peak state is 80 to 200 HV, and the hardness increment is 40 to 130 HV compared with the solution state or the non-aged 3D printing state; the room-temperature yield strength of the alloy in the aging peak state is 300 to 550 MPa, the tensile strength is 350 to 600 MPa, and the elongation after fracture is 5 to 40%; the yield strength at 150 to 250 °C is 150 to 420 MPa, the tensile strength is 175 to 480 MPa, and the elongation after fracture is 10 to 40%; the steady-state creep rate under the conditions of 150 to 300 °C and an applied load of 30 to 100 MPa < 5×10 -9 s -1 .

[0023] The significant differences and advantages of the present invention compared with the prior art literature are as follows:

[0024] (1) In the magnesium alloy of the present invention, multiple nano-precipitation phases precipitate during aging, and the number of element types is ≥5. They are not prone to coarsening during long-term holding at high temperatures, and the alloy has high tissue stability and excellent heat resistance;

[0025] (2) The creep rate of the magnesium alloy of the present invention is much lower than that of the commercial AZ91 magnesium alloy (2.5×10 -6 s -1 );

[0026] (3) The aging reaction of the magnesium alloy of the present invention is fast, and the aging peak is reached after aging for 30 min to 5 h, which is significantly faster than the time (24 h) for the commercial AZ91 magnesium alloy to reach the aging peak;

[0027] (4) The magnesium alloy of the present invention prepared by the above process 1 has good plasticity in the aging peak state, and the elongation after fracture at room temperature is ≥10%, which is better than most magnesium alloys. For example, the elongation after fracture at room temperature of the commercial AZ91 magnesium alloy in the aging peak state is only 2%;

[0028] The magnesium alloy of the present invention can be used to prepare load-bearing structural devices and heat-resistant devices, including but not limited to automobile wheels, engine casings, aircraft wing skins, electronic device housings, soluble bridge plugs for oil exploration, etc.; it can also be used to prepare implantable medical devices, including but not limited to cardiovascular stents, bone nails, bone plates, etc. Description of the Drawings

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0030] Figure 1 It is the TEM image of the microstructure of Alloy 5 in Example 1.

[0031] Figure 2 It is the EDS spectrum of the precipitated phase in Alloy 5 of Example 1. Specific Embodiments

[0032] The effects of the present invention will be specifically described below through examples and comparative examples. In addition, the present invention is not limited to the following examples and can be appropriately modified and implemented within the scope of the unchanged gist.

[0033] Unless otherwise specified, the following alloy compositions are defaulted to atomic percentages (at.%). The sizes of the grains and the second phase refer to their equivalent diameters.

[0034] Example 1: Face-centered cubic A 2 MgB type multi-precipitated phase strengthened magnesium alloy

[0035] The alloying elements added in Inventive Alloys 1 to 9 are shown in Table 1-1, and the balance is Mg; the preparation process is: rapid solidification casting → severe plastic deformation → solution treatment → quenching → aging. Using the rapid solidification casting device in "A Solidification Method and Device for Refining the Second Phase in a Zinc Alloy Containing Fe" (Authorization Number: ZL 202010287273.4), prepare the raw materials according to the element ratio in Table 1-1. The addition of Li is in the form of a commercial Mg-10Li (wt.%) master alloy, and the addition of the remaining elements is in the form of high-purity metals. Cut the high-purity metal and master alloy ingots into small pieces and put them into the crucible of the above device, and melt under argon protection. The specific process parameters are shown in Table 1-2. Then use the bottom circulating liquid cooling function of the rapid solidification casting device, and the circulating liquid uses 15°C circulating cooling water to obtain a rapid solidification ingot with a diameter of 100 mm and a height of 120 mm. The grain size of the magnesium matrix is 15 - 25 μm, and the size of the micron-scale second phase < 8 μm.

[0036] Table 1-1

[0037]

[0038] Then, the equal-channel angular pressing technology was adopted to perform large plastic deformation on the ingots of Invention Examples 1-9 alloys. The extruded samples were processed into bars with a diameter of 10 mm and a length of 70 mm. The die angle inside the extrusion equipment channel was 120°, the die angle outside was 20°, the channel diameter was 11 mm, the channel length was 100 mm, and the extrusion parameters were as shown in Table 1-2. The extrusion temperature of each pass was 25 °C lower than that of the previous pass. Finally, the alloy bars of Invention Examples after large plastic deformation were obtained.

[0039] Table 1-2

[0040]

[0041] Then, solution heat treatment was carried out at 500 °C for 5 min to obtain a supersaturated solid solution. After the solution was completed, it was quickly transferred to room-temperature water for quenching, and then aging heat treatment was carried out at different temperatures. The temperature parameters and the time to reach the peak aging hardness are shown in Table 1-2.

[0042] Round bar room-temperature tensile samples were prepared in accordance with the national standard GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", and tensile tests were carried out at room temperature using a universal material testing machine. The tensile strain rate was 10 -3 / s. Round bar high-temperature tensile samples were prepared in accordance with the national standard GB / T 37783-2019 "Metallic materials - High strain rate tensile testing at elevated temperature", and tensile tests were carried out at high temperature using a WDW-100 microcomputer-controlled electronic universal testing machine. The test temperature was 150-250 °C. Round bar creep samples were prepared in accordance with the national standard GB / T2039-2012 "Metallic materials - Uniaxial tensile creep testing method", and high-temperature creep properties were tested on an electronic high-temperature creep and rupture strength testing machine. The test parameters were: temperature 150-300 °C, load 30-100 MPa.

[0043] Instruments such as a metallographic microscope, an electron microscope (SEM) equipped with an EDS system, a time-of-flight secondary ion mass spectrometer (TOF-SIMS), and a transmission electron microscope (TEM) were used to observe the microstructure of Invention Examples 1-9 alloys in the peak aging state, and the characteristics were as follows:

[0044] (1) The grain size of the magnesium matrix < 5 μm;

[0045] (2) The size of the micron-scale second phase < 2 μm, and more than 80% of the second phase consists of at least 5 elements. For example, the second phase of Invention Example 5 alloy contains elements such as Li, Al, Zn, Sn, Ga, In, and Mg;

[0046] (3) There are high-density nano-scale precipitates in the magnesium matrix grains, with an average size ≤ 20 nm, and its composition expression is A 2MgB, as shown in Table 1-1, A is Li, and B is composed of at least three elements among Al, Zn, Sn, Bi, Ga, In, and Ge; the precipitated phase in Invention Example Alloy 1 is Li 2 Mg(Al, Zn, Sn); the precipitated phase in Invention Example Alloy 2 is Li 2 Mg(Al, Zn, Ga); the precipitated phase in Invention Example Alloy 3 is Li 2 Mg(Al, Zn, Ga, In); the precipitated phase in Invention Example Alloy 4 is Li 2 Mg(Al, Zn, Sn, Ge); the precipitated phase in Invention Example Alloy 5 is Li 2 Mg(Al, Zn, Sn, Ga, In), as Figure 1 shown; Figure 2 is the EDS energy spectrum diagram of the multi-component precipitated phase; the precipitated phase in Invention Example Alloy 6 is Li 2 Mg(Al, Zn, Sn, In, Ge); the precipitated phase in Invention Example Alloy 7 is Li 2 Mg(Al, Zn, Sn, In); the precipitated phase in Invention Example Alloy 8 is Li 2 Mg(Al, Zn, Sn, Bi, Ga, Ge); the precipitated phase in Invention Example Alloy 9 is Li 2 Mg(Al, Zn, Sn, Bi, Ga, In, Ge).

[0047] The peak aging hardness of the Invention Example Alloys 1-9 is 100-150 HV. Compared with the solution state, the hardness increment is 50-100 HV. The room temperature yield strength of the Invention Example Alloys 1-9 in the peak aging state is measured to be 300-550 MPa, the tensile strength is 350-600 MPa, and the elongation after fracture is 10-30%; the yield strength at 150-250 °C is 150-420 MPa, the tensile strength is 175-480 MPa, and the elongation after fracture is 15-40%; after heat preservation at 150-300 °C for 60-90 days, the average size increment of the nano-precipitated phase in the Invention Example Alloys is <10%; the steady-state creep rate at 150-300 °C and 30-100 MPa is <5×10 -9 s -1 , for example, the steady-state creep rate of Invention Example Alloy 5 at 200 °C and 50 MPa is 3.8×10 -9 s -1 , and the steady-state creep rate of Invention Example Alloy 9 at 177 °C and 60 MPa is 1.1×10 -9 s -1 . These multi-component nano-scale precipitated phases have a slow coarsening rate and can effectively hinder dislocation slip, thus significantly improving the thermal stability and high-temperature creep strength of the alloy.

[0048] Example 2: Face-centered cubic AMgB 2 Type of multi-precipitation phase strengthened magnesium alloy

[0049] The alloying elements added in Invention Example Alloys 10 - 18 are shown in Table 2-1. According to the element ratio, high-purity bulk materials are used as raw materials, and the rest is Mg. The preparation process is: powder making → 3D printing → aging. The weighed and proportioned bulk raw materials are placed in a crucible, melted and mixed thoroughly, and powder is made by argon gas atomization method. The metal liquid flow is blown and cooled by the jet force of high-pressure argon to form metal particles. The particle size of the prepared magnesium alloy powder is 10 - 100 μm. Then, a 15mm×15mm×100mm bulk specimen is printed using selective laser melting technology (SLM), and the specific preparation process parameters are shown in Table 2-2. After printing, the specimen is quickly transferred to room-temperature water for quenching. A 10mm×10mm×10mm small cube specimen is cut by electrical discharge machining technology, and then aging heat treatment is carried out at different temperatures. The temperature parameters and the time to reach the aging peak hardness are shown in Table 2-2.

[0050] Table 2-1

[0051]

[0052] Table 2-2

[0053]

[0054] Due to the high cooling rate of SLM, the specimen is in a non-equilibrium solidification state, and the second phase has no time to grow and coarsen. The size of the magnesium matrix grains in the aging peak state of Invention Example Alloys 10 - 18 is <10 μm; the size of the micron-scale second phase is <3 μm, and more than 70% of the second phase consists of at least 5 elements. For example, the second phase of Invention Example Alloy 13 contains multiple elements such as Tb, Dy, Ho, Er, Ag, Cu, and Mg; there are high-density nano-scale precipitation phases in the magnesium matrix grains, with an average size ≤20 nm, and its composition expression is AMgB 2 , as shown in Table 2-1, A consists of at least 2 elements among Tb, Dy, Ho, Er, and Tm, and B is Ag and Cu; the precipitation phase of Invention Example Alloy 10 is (Tb,Dy)Mg(Ag,Cu) 2 , the precipitation phase of Invention Example Alloy 11 is (Tb,Dy,Er)Mg(Ag,Cu) 2 , the precipitation phase of Invention Example Alloy 12 is (Tb,Dy,Ho)Mg(Ag,Cu) 2 , the precipitation phases of Invention Example Alloy 13 and Invention Example Alloy 14 are both (Tb,Dy,Ho,Er)Mg(Ag,Cu) 2 , the precipitation phase of Invention Example Alloy 15 is (Tb,Dy,Ho,Er,Tm)Mg(Ag,Cu)2 The precipitation phase in the inventive alloy 16 is (Tb, Dy, Ho, Tm)Mg(Ag, Cu) 2 The precipitation phase in the inventive alloy 17 is (Tb, Er, Tm)Mg(Ag, Cu) 2 The precipitation phase in the inventive alloy 18 is (Tb, Dy, Er, Tm)Mg(Ag, Cu) 2 .

[0055] The peak aging hardness of the inventive alloys 10 - 18 is 120 - 200 HV. Compared with the non-aged state, the hardness increment is 60 - 120 HV. The room temperature tensile yield strength of the inventive alloys 10 - 18 at the peak aging state is 300 - 500 MPa, the tensile strength is 350 - 550 MPa, and the elongation after fracture is 5 - 20%; the yield strength at 150 - 250 °C is 200 - 380 MPa, the tensile strength is 225 - 420 MPa, and the elongation after fracture is 10 - 25%; after heat preservation for 60 - 90 days at 150 - 300 °C, the average size increment of the multi-precipitation phase in the inventive alloy is < 10%; the steady-state creep rate under the conditions of 150 - 300 °C and 30 - 100 MPa applied load is < 1×10 -9 s -1 For example, the steady-state creep rate of the inventive alloy 12 at 200 °C and 50 MPa is 3.5×10 -10 s -1 The steady-state creep rate of the inventive alloy 17 at 300 °C and 30 MPa is 9.2×10 -10 s -1 . These multi-nano-scale precipitation phases have a slow coarsening rate and can effectively hinder dislocation slip, thus significantly improving the thermal stability and high-temperature creep strength of the alloy.

[0056] Example 3: Orthorhombic lattice AMgB type multi-precipitation phase strengthened magnesium alloy

[0057] The alloying elements added to Invention Examples 19 - 27 are shown in Table 3 - 1. According to the element ratio, high - purity metals are used as raw materials, and the rest is Mg. The preparation process is: rapid solidification casting → severe plastic deformation → solution treatment → quenching → aging. The rapid solidification casting process is carried out in the same manner as described in Example 1, and the specific process parameters are shown in Table 3 - 2. In the obtained rapidly solidified ingot, the grain size of the magnesium matrix is 15 - 25 μm, and the size of the micron - scale second phase is <8 μm. Then, accumulative roll - bonding severe plastic deformation is carried out. Two plates with dimensions of 100 mm×80 mm×2 mm are cut from the obtained rapidly solidified ingot. The surfaces of the plates are polished with a wire brush to expose the fresh metallic luster, and then rinsed with acetone until clean. The specific parameters of the rolling process are shown in Table 3 - 2. Then, under argon protection, solution heat treatment is carried out at 500 °C for 5 min, and it is quickly transferred to room - temperature water for quenching. Then, aging heat treatment is carried out at different temperatures. The temperature parameters and the time to reach the peak aging hardness are shown in Table 3 - 2.

[0058] Table 3 - 1

[0059]

[0060] Table 3 - 2

[0061]

[0062]

[0063] In the invention example alloys 19 - 27 in the peak-aged state, the size of the magnesium matrix grains is <8 μm; the size of the micron-scale second phase is <2 μm, and more than 80% of the second phase consists of at least 5 elements. For example, the second phase in the invention example alloy 25 contains elements such as Ca, Eu, Yb, Sn, Si, Ag, and Mg; there are high-density nano-scale precipitates in the magnesium matrix grains, with an average size ≤20 nm, and its composition expression is AMgB, as shown in Table 3-1. A consists of at least 2 elements among Ca, Sr, Eu, and Yb, and B consists of at least 2 elements among Sn, Ge, Si, and Ag; among them, the precipitate in the invention example alloy 19 is (Ca,Sr)Mg(Sn,Ge), the precipitate in the invention example alloy 20 is (Ca,Sr)Mg(Sn,Ge,Si), the precipitate in the invention example alloy 21 is (Ca,Sr,Eu,Yb)Mg(Sn,Ge,Si,Ag), the precipitate in the invention example alloy 22 is (Ca,Sr,Eu)Mg(Sn,Ge), the precipitate in the invention example alloy 23 is (Ca,Eu)Mg(Sn,Si,Ag), the precipitate in the invention example alloy 24 is (Ca,Sr,Yb)Mg(Ge,Ag), the precipitate in the invention example alloy 25 is (Ca,Eu,Yb)Mg(Sn,Si,Ag), the precipitate in the invention example alloy 26 is (Ca,Sr,Yb)Mg(Sn,Ge,Si), and the precipitate in the invention example alloy 27 is (Ca,Sr,Yb)Mg(Sn,Ge,Si,Ag).

[0064] The peak-aged hardness of the invention example alloys 19 - 27 is 80 - 120 HV. Compared with the solution-treated state, the hardness increment is 40 - 80 HV. The measured room-temperature yield strength of the invention example alloys 19 - 27 in the peak-aged state is 300 - 520 MPa, the tensile strength is 350 - 580 MPa, and the elongation after fracture is 12 - 30%; the yield strength at 150 - 250 °C is 220 - 350 MPa, the tensile strength is 250 - 420 MPa, and the elongation after fracture is 15 - 35%; after holding at 150 - 300 °C for 60 - 90 days, the average size increment of the multi-element precipitates in the invention example alloys is <10%; the steady-state creep rate under the conditions of 150 - 300 °C and 30 - 100 MPa applied load is <5×10 -9 s -1 , for example, the steady-state creep rate of the invention example alloy 20 at 200 °C and 50 MPa is 8.0×10 -10 s -1 , and the steady-state creep rate of the invention example alloy 26 at 300 °C and 100 MPa is 4.3×10 -9 s -1These multi-element nano-scale precipitates have a slow coarsening rate and can effectively hinder dislocation slip, thus significantly improving the thermal stability and high-temperature creep strength of the alloy.

[0065] Example 4: Hexagonal lattice AMgB type multi-element precipitate strengthened magnesium alloy

[0066] The alloying elements added in Invention Example Alloys 28 to 36 are shown in Table 4-1. According to the element ratio, high-purity bulk is used as the raw material, and the rest is Mg. The preparation process is: powder making → 3D printing → aging. The powder making and 3D printing processes of the alloy are carried out in the same manner as described in Example 2, and the preparation process parameters of 3D printing are shown in Table 4-2. After printing, the specimens are quickly transferred to room temperature water for quenching, and then aged heat treatment is carried out at different temperatures. The temperature parameters and the time to reach the peak aging hardness are shown in Table 4-2.

[0067] Table 4-1

[0068]

[0069] Table 4-2

[0070]

[0071] Due to the high cooling rate of SLM, the specimen is in a non-equilibrium solidification state, and the second phase does not have enough time to grow and coarsen. The size of the magnesium matrix grains in the peak-aged invention example alloys 28 - 36 is <5 μm; the size of the submicron second phase is <1 μm, and more than 80% of the second phase consists of at least 5 elements. For example, the second phase in invention example alloy 34 contains elements such as La, Pr, Nd, Ga, In, Au, Tl, and Mg; there are high-density nano-scale precipitates in the magnesium matrix grains, with an average size ≤20 nm, and its composition expression is AMgB, as shown in Table 4-1. A consists of at least 2 elements among La, Pr, and Nd, and B consists of at least 2 elements among Ga, In, Ag, Au, Pt, and Tl; among them, the precipitate in invention example alloy 28 is (La,Nd)Mg(Ga,Ag,Pt), the precipitate in invention example alloy 29 is (La,Pr)Mg(Ga,In,Ag,Au,Tl), the precipitate in invention example alloy 30 is (La,Pr,Nd)Mg(Ga,Au,Pt), the precipitate in invention example alloy 31 is (La,Nd)Mg(Ga,In,Ag,Au,Tl), the precipitate in invention example alloy 32 is (La,Pr,Nd)Mg(Ga,In,Au,Pt,Tl), the precipitate in invention example alloy 33 is (La,Pr,Nd)Mg(In,Ag,Au,Pt,Tl), the precipitate in invention example alloy 34 is (La,Pr,Nd)Mg(Ga,In,Au,Tl), the precipitate in invention example alloy 35 is (La,Pr,Nd)Mg(Ga,In,Au,Pt), and the precipitate in invention example alloy 36 is (La,Nd)Mg(In,Ag,Pt).

[0072] The peak-aged hardness of the invention example alloys 28 - 36 is 120 - 200 HV. Compared with the non-aged state, the hardness increment is 60 - 130 HV. The measured room temperature yield strength of the invention example alloys 28 - 36 in the peak-aged state is 300 - 400 MPa, the tensile strength is 320 - 480 MPa, and the elongation after fracture is 5 - 10%; the yield strength at 150 - 250 °C is 180 - 300 MPa, the tensile strength is 220 - 350 MPa, and the elongation after fracture is 10 - 20%; after holding at 150 - 300 °C for 60 - 90 days, the average size increment of the multi-element precipitates in the invention example alloys is <10%; the steady-state creep rate under the conditions of 150 - 300 °C and 30 - 100 MPa applied load is <5×10 -9 s -1 , for example, the steady-state creep rate of invention example alloy 30 at 150 °C and 100 MPa is 2.5×10 -10 s -1 , and the steady-state creep rate of invention example alloy 34 at 300 °C and 60 MPa is 7.2×10-10 s -1 These multi - element nano - scale precipitation phases have a slow coarsening rate and can effectively hinder dislocation slip, thereby significantly improving the thermal stability and high - temperature creep strength of the alloy.

[0073] Example 5: Tetragonal lattice A 2 MgB 2 type multi - precipitation - strengthened magnesium alloy

[0074] The alloying elements added in Invention Example Alloys 37 - 45 are shown in Table 5 - 1. According to the element ratio, high - purity bulk materials are used as raw materials, and the rest is Mg. The preparation process is: rapid solidification casting → severe plastic deformation → solution treatment → quenching → aging. The rapid solidification casting process of the alloy is carried out in the same manner as described in Example 1. Two initial plates with a cross - section of 80 mm × 10 mm and a thickness of 1.5 mm are cut from the obtained rapid solidification casting ingot, and then equal - channel angular rolling technology is used to complete severe plastic deformation. The specific preparation process parameters of the rapid solidification casting and equal - channel angular rolling are shown in Table 5 - 2. Subsequently, the obtained rolled plates are solution - heat - treated at 600 °C for 1 min, quickly transferred to room - temperature water for quenching, and then aged heat - treated at different temperatures. The temperature parameters and the time to reach the peak aging hardness are shown in Table 5 - 2.

[0075] Table 5 - 1

[0076]

[0077] Table 5 - 2

[0078]

[0079] In the grain interior of the Invention Example Alloys 37 - 45 in the peak aging state, there are many compressive twins, and a small amount of fine grains surround the coarse grains to form a typical bimodal microstructure, with an average size < 4 μm; the average size of the sub - micron - scale second phase is < 1 μm, and more than 80% of the second phase consists of at least 5 elements. For example, the second phase of the alloy in Invention Example 41 contains elements such as Tb, Dy, Er, Tm, Ge, Si, and Mg; there are high - density nano - scale precipitation phases in the magnesium matrix grains, with an average size ≤ 20 nm, and its composition formula is A 2 MgB 2 , as shown in Table 5 - 1, A consists of at least 2 elements selected from Er, Tm, Tb, Dy, and Ho, and B consists of Ge and Si; among them, the precipitation phase in Invention Example Alloy 37 is (Er,Tm,Dy) 2 Mg(Ge,Si) 2 , the precipitation phase in Invention Example Alloy 38 is (Er,Tb,Ho) 2 Mg(Ge,Si) 2, the precipitated phase in the alloy of Invention Example 39 is (Er, Tm, Tb, Dy, Ho) 2 Mg(Ge, Si) 2 , the precipitated phase in the alloy of Invention Example 40 is (Er, Dy, Ho) 2 Mg(Ge, Si) 2 , the precipitated phase in the alloy of Invention Example 41 is (Er, Tm, Tb, Dy) 2 Mg(Ge, Si) 2 , the precipitated phase in the alloy of Invention Example 42 is (Er, Tm, Tb, Ho) 2 Mg(Ge, Si) 2 , the precipitated phase in the alloy of Invention Example 43 is (Er, Tb, Dy, Ho) 2 Mg(Ge, Si) 2 , the precipitated phase in the alloy of Invention Example 44 is (Tm, Tb, Dy, Ho) 2 Mg(Ge, Si) 2 , the precipitated phase in the alloy of Invention Example 45 is (Er, Tm, Ho) 2 Mg(Ge, Si) 2 .

[0080] The peak aging hardness of the alloys of Invention Examples 37-45 is 80-140 HV, and the hardness increment is 40-100 HV compared with the solution state. The room temperature tensile yield strength of the alloys of Invention Examples 37-45 in the peak aging state is 300-520 MPa, the tensile strength is 350-560 MPa, and the elongation after fracture is 15-30%; the yield strength at 150-250 °C is 220-350 MPa, the tensile strength is 250-400 MPa, and the elongation after fracture is 20-40%; after heat preservation at 150-300 °C for 60-90 days, the average size increment of the multi-component precipitated phase in the alloys of Invention Examples is <10%; the steady-state creep rate under the conditions of 150-300 °C and 30-100 MPa applied load is <5×10 -9 s -1 , for example, the steady-state creep rate of the alloy of Invention Example 39 at 250 °C and 100 MPa is 6.2×10 -10 s -1 , the steady-state creep rate of the alloy of Invention Example 44 at 177 °C and 60 MPa is 1.1×10 -10 s -1 . These multi-component nano-scale precipitated phases have a slow coarsening rate and can effectively hinder dislocation slip, thus significantly improving the thermal stability and high-temperature creep strength of the alloy.

[0081] Comparative Example 1: Alloys of Type 1 and Type 4 only contain elements in the Mg and B sets

[0082] The alloying elements added in Comparative Alloys 1 to 18 are shown in Table 6-1. Among them, the alloying elements added in Comparative Alloys 1 to 9 are selected from the elements in Set B of Type 1, and the balance is Mg; the preparation process and parameters, the form of raw material addition, and the performance test method are the same as those in Invention Example 1. The alloying elements added in Comparative Alloys 10 to 18 are selected from the elements in Set B of Type 4, and the balance is Mg; the preparation process and parameters, the form of raw material addition, and the performance test method are the same as those in Invention Example 4.

[0083] For the said Comparative Alloys 1 to 9, they are subjected to aging heat treatment at 150 - 200 °C for heat preservation, and the aging hardness is reached after 20 - 50 h. Compared with Invention Alloys 1 to 9, the peak aging hardness decreases by 15% - 30%.

[0084] For the said Comparative Alloys 10 to 18, they are subjected to aging heat treatment at 150 - 200 °C for heat preservation, and the aging hardness is reached after 30 - 80 h. Compared with Invention Alloys 28 to 36, the peak aging hardness decreases by 20% - 35%.

[0085] The grain size of the magnesium matrix of Comparative Alloys 1 to 9 in the peak aging state is 10 - 20 μm, and the size of the micron-sized second phase is 2 - 5 μm; the grain size of the magnesium matrix of Comparative Alloys 10 to 18 in the peak aging state is 10 - 15 μm, and the size of the micron-sized second phase is 2 - 8 μm. The coarser grains and second phases result in the mechanical properties and high-temperature resistance of the Comparative Alloys being lower than those of the Invention Alloys.

[0086] In the peak aging state, compared with Invention Alloys 1 to 9, the room-temperature yield strength of Comparative Alloys 1 to 9 decreases by 20% - 35%, and the tensile strength decreases by 30% - 50%; when performing high-temperature tension at 150 - 250 °C, the high-temperature yield strength of Comparative Alloys 1 to 9 decreases by 10% - 30%, and the tensile strength decreases by 10% - 30%. In the peak aging state, compared with Invention Alloys 28 to 36, the room-temperature yield strength of Comparative Alloys 10 to 18 decreases by 20% - 30%, and the tensile strength decreases by 30% - 45%; when performing high-temperature tension at 150 - 250 °C, the high-temperature yield strength of Comparative Alloys 1 to 9 decreases by 15% - 35%, and the tensile strength decreases by 10% - 30%.

[0087] Table 6-1

[0088]

[0089] Comparative Example 2: Alloy Types 2 and 3 only contain Mg and the elements in Set A

[0090] The alloying elements added to Comparative Alloy 19 - 36 are shown in Table 7 - 1. Among them, the alloying elements added to Comparative Alloy 19 - 27 are selected from the elements in Set A of Type 2, and the balance is Mg; the preparation process and parameters, the form of raw material addition, and the performance testing methods are the same as those in Invention Example 2. The alloying elements added to Comparative Alloy 28 - 37 are selected from the elements in Set A of Type 3, and the balance is Mg; the preparation process and parameters, the form of raw material addition, and the performance testing methods are the same as those in Invention Example 3.

[0091] For the said Comparative Alloy 19 - 27, it is subjected to isothermal aging heat treatment at 150 - 200 °C and reaches the aging hardness after 30 - 80 h. Compared with Invention Alloy 10 - 18, the peak aging hardness decreases by 10% - 25%.

[0092] For the said Comparative Alloy 28 - 36, it is subjected to isothermal aging heat treatment at 150 - 200 °C and reaches the aging hardness after 25 - 50 h. Compared with Invention Alloy 19 - 27, the peak aging hardness decreases by 15% - 30%.

[0093] The grain size of the magnesium matrix of Comparative Alloy 19 - 27 in the peak aging state is 15 - 30 μm, and the size of the micron - scale second phase is 2 - 5 μm; the grain size of the magnesium matrix of Comparative Alloy 28 - 36 in the peak aging state is 10 - 25 μm, and the size of the micron - scale second phase is 2 - 5 μm; the coarser grains and second phases result in the mechanical properties and high - temperature resistance of the comparative alloys being lower than those of the invention alloys.

[0094] In the peak aging state, compared with Invention Alloy 10 - 18, the room - temperature yield strength of Comparative Alloy 19 - 27 decreases by 15% - 30%, and the tensile strength decreases by 30% - 60%; when performing high - temperature tension at 150 - 250 °C, the high - temperature yield strength of Comparative Alloy 10 - 18 decreases by 10% - 35%, and the tensile strength decreases by 15% - 40%. In the peak aging state, compared with Invention Alloy 19 - 27, the room - temperature yield strength of Comparative Alloy 28 - 36 decreases by 12% - 25%, and the tensile strength decreases by 20% - 50%; when performing high - temperature tension at 150 - 250 °C, the high - temperature yield strength of Comparative Alloy 28 - 36 decreases by 12% - 35%, and the tensile strength decreases by 10% - 40%.

[0095] Table 7 - 1

[0096]

[0097]

[0098] Comparative Example 3: Preparation of a Type 5 multi - precipitation - phase - strengthened magnesium alloy by a conventional casting process route

[0099] The above-mentioned alloy 37-45 of the invention example was prepared according to the following process: ordinary casting → severe plastic deformation → solution treatment → quenching → aging, to obtain the alloy 37-45 of the comparative example with the same composition. The ordinary casting was carried out in a vacuum induction heating furnace, and the addition method of alloying elements was the same as that of the invention example, and it was also protected by inert gas. The refining temperature was 680 °C, and the holding time was 5 min, and then it was poured into a graphite mold and cooled naturally to room temperature. The severe plastic deformation, solution treatment, quenching, and aging were all carried out according to the parameters provided in Example 5.

[0100] The alloy 37-45 of the comparative example was subjected to aging heat treatment at 150-200 °C and reached the aging hardness after 10-25 h. Compared with the corresponding alloy of the invention example, the peak aging hardness decreased by 15%-35%. There were still high-density nano-scale multi-component precipitates in the alloy 37-45 of the comparative example in the peak aging state, and the average size was still ≤20 nm. In the peak aging state, compared with the alloy 37-45 of the invention example with the same composition, the room temperature yield strength of the alloy 37-45 of the comparative example decreased by 15%-20%, and the tensile strength decreased by 25%-35%; when high-temperature tensile was carried out at 150-250 °C, the high-temperature yield strength of the alloy 37-45 of the comparative example decreased by 15%-30%, and the tensile strength decreased by 10%-25%.

[0101] The above is only a part of the embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A heat-resistant magnesium alloy strengthened by multiple precipitation phases, characterized in that, the composition expression of the magnesium alloy is Mg-A-B, where both A and B are alloy element sets, and the Mg-A-B magnesium alloy contains at least 5 elements; there are the following 5 categories of Mg-A-B alloys, and the composition is expressed in atomic percentage: ①Type 1: The A element set only contains Li element, with a content of 0.001 - 30 at.%; the B element set contains a combination of at least 3 elements among Al, Zn, Sn, Bi, Ga, In, and Ge, where the contents of Al, Zn, Sn, Bi, Ga, and In elements are all 0.001 - 12 at.%, and the content of Ge element is 0.001 - 5 at.%; and the atomic percentage satisfies A ≥ 2B, and the A that forms a face-centered cubic structure in this type of magnesium alloy 2 MgB precipitation phase; ②Type 2: The A element set contains a combination of at least two elements among Tb, Dy, Ho, Er, and Tm, where the contents of Tb, Dy, and Ho elements are all 0.001 - 10 at.%, and the contents of Er and Tm elements are all 0.001 - 30 at.%; the B element set contains Ag and Cu elements, with the contents all being 0.001 - 12 at.%; and the atomic percentages satisfy 2A ≥ B. In this type of magnesium alloy, a face-centered cubic structure AMgB 2 precipitation phase; ③ Type 3: The A element set contains at least 2 element combinations selected from Ca, Sr, Eu, and Yb, and the content of each element is 0.001~30 at.%; the B element set contains at least 2 element combinations selected from Sn, Ge, Si, and Ag, where the content of Sn, Ge, and Si elements is 0.001~12 at.%, and the content of Ag element is 0.001~5 at.%; and the atomic percentage satisfies A≥B, and an orthorhombic lattice structure AMgB precipitation phase is formed in this type of magnesium alloy; ④ Type 4: The A element set contains at least 2 element combinations selected from La, Pr, and Nd, and the content of each element is 0.001~30 at.%; the B element set contains at least 2 element combinations selected from Ga, In, Ag, Au, Pt, and Tl, where the content of Ga and In elements is 0.001~12 at.%, and the content of Ag, Au, Pt, and Tl elements is 0.001~5 at.%; and the atomic percentage satisfies A≥B, and a hexagonal lattice structure AMgB precipitation phase is formed in this type of magnesium alloy; ⑤Type 5: The set of element A contains a combination of at least two elements among Tb, Dy, Ho, Er, and Tm, where the contents of Tb, Dy, and Ho elements are all 0.001 - 10 at.%, and the contents of Er and Tm elements are all 0.001 - 30 at.%; the set of element B contains Ge and Si elements, and the contents are all 0.001 - 12 at.%; and the atomic percentages satisfy A≥B. In this type of magnesium alloy, A that forms a tetragonal lattice structure 2 MgB 2 precipitation phase; The microstructures of the above five types of Mg-A-B alloys have the following characteristics: (1) They contain multi-element precipitation phases with a size ≤ 20 nm, and the general formula for their composition expression is A x MgB y , x and y equals 1 or 2; (2) The A x MgB y precipitation phases contain 5 or more elements. When held at a temperature of 250 - 300 °C for 60 - 90 days, the size increment of the precipitation phases is < 10%, the hardness decrease is < 10 HV, and the alloy has high thermal stability.

2. The preparation method of the heat-resistant magnesium alloy strengthened by multiple precipitation phases according to claim 1, characterized in that, the preparation process of the Mg-A-B alloy is any one of the following 2: Process 1: S11. After mixing the elements, rapid cooling casting is carried out to obtain an alloy ingot; S12. Perform large plastic deformation on the ingot to obtain an alloy bar; S13. Perform solution treatment on the bar to obtain a supersaturated solid solution; S14. Quench; S15. Perform aging heat treatment on the quenched solid solution to obtain the alloy; Process 2: S21. Melt and mix the bulk raw materials of the elements and then make powder to obtain alloy powder; S22. Use 3D printing to prepare a bulk sample from the powder; S23. Quench; S24. Perform aging heat treatment on the quenched sample to obtain the alloy.

3. The preparation method of the heat-resistant magnesium alloy strengthened by multiple precipitation phases according to claim 2, characterized in that, in Process 1, the melting temperature range of the inner crucible of the device used for rapid cooling casting is 680~780 °C, the refining and heat preservation time range is 10~30 min, and the liquid used during the bottom circulating liquid solidification process is circulating water at 15 °C.

4. The preparation method of the heat-resistant magnesium alloy strengthened by multiple precipitation phases according to claim 3, characterized in that, after rapid cooling casting, the grain size of the magnesium matrix is 15~25 μm, and the size of the micron-scale second phase <8 μm.

5. The preparation method of the heat-resistant magnesium alloy strengthened by multiple precipitation phases according to claim 2, characterized in that, in Process 1, the temperature of the solution treatment is 300~600 °C, and the heat preservation time is 1 min~5 min.

6. The preparation method of the heat-resistant magnesium alloy strengthened by multiple precipitation phases according to claim 2, characterized in that, in Process 1 and Process 2, the aging temperature is 150~200 °C, and the aging time is 5 min~10 h.

7. The preparation method of the heat-resistant magnesium alloy strengthened by multiple precipitation phases according to claim 2, characterized in that, The microstructure and properties of the magnesium alloy prepared by Process 1 and Process 2 are characterized as follows: Aging at 150 - 200 °C for 20 min - 5 h reaches the aging peak; The hardness in the aging peak state is 80 - 200 HV, and the hardness increment is 40 - 130 HV compared with the solution state or the non-aged 3D printing state; The room temperature yield strength of the alloy in the aging peak state is 300 - 550 MPa, the tensile strength is 350 - 600 MPa, and the elongation after fracture is 5 - 40%; The yield strength at 150 - 250 °C is 150 - 420 MPa, the tensile strength is 175 - 480 MPa, and the elongation after fracture is 10 - 40%; The steady-state creep rate under the conditions of 150 - 300 °C and an applied load of 30 - 100 MPa is < 5×10 -9 s -1 .

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