Heat-resistant high-plasticity cast rare earth magnesium alloy and preparation method thereof

Abstract

The invention provides a cast rare earth magnesium alloy. The cast rare earth magnesium alloy comprises the following components in percentage by mass: 12-18% of Gd; 0.5%-4% of Ag; 0.1% to 1.0% of Zr; 1%-10% of a second heavy rare earth element; 0.5-3% of a light rare earth element; and the balance magnesium. The prepared heat-resistant high-plasticity cast rare earth magnesium alloy material has excellent room-temperature and high-temperature mechanical properties, the room-temperature mechanical properties are obviously improved, the strength performance index is improved to different extents on the premise that the total amount of rare earth is not increased, good plasticity is reserved, and the heat-resistant high-plasticity cast rare earth magnesium alloy material has good heat-resistant and high-temperature mechanical properties on the premise that the strength exceeds 400 MPa. And the elongation of the alloy finally reaches 6% or above and is obviously higher than that of a traditional cast magnesium alloy with the high rare earth content, engineering application is easy to achieve, the high-temperature mechanical property is excellent, and the requirements for the mechanical property of a light structural material in the high-temperature environment in the current fields of aerospace, missile military industry, rail transit and the like can be met.

Description

Technical Field

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

[0002] As the lightest structural metal material (density is 2 / 3 of aluminum and 1 / 4 of steel), magnesium alloy has significantly higher specific strength than aluminum alloy and steel. Although its specific stiffness is comparable to that of aluminum alloy and steel, it is much higher than that of engineering plastics. At present, automobiles, rail transportation, aviation industry, etc. have become the largest application areas of magnesium alloys. The application in automobiles alone has increased at a high rate of 30% per year. However, when the temperature exceeds 120°C, the high temperature strength of general magnesium alloys will drop significantly, which limits the application of magnesium alloys in transportation and aerospace fields such as automobile engines, transmission parts (such as gearbox housings, cylinder blocks, cylinder heads, intake / exhaust pipes), and aircraft engine casings. For this reason, scientific research institutions around the world have carried out a lot of research work to study and develop heat-resistant magnesium alloys. Heat-resistant magnesium alloys refer to magnesium alloy materials that can serve at high temperatures (above 200°C) for a long time and are widely used in aerospace, national defense and military industries. Rare earth elements can improve the room temperature and high temperature properties of magnesium alloys. The mixed addition of light and heavy rare earth elements can better strengthen rare earth magnesium alloys. This is because rare earth elements in different groups can reduce each other's solubility in the magnesium matrix, increase the density of aging precipitation phases, and can also dissolve into each other's precipitation phases, further strengthening the precipitation phases, thereby strengthening the magnesium alloy.

[0003] At present, most heat-resistant magnesium alloys contain rare earths. According to the different contents of rare earths in heat-resistant magnesium alloys, heat-resistant magnesium alloys containing rare earths can be divided into the following three categories: (1) Low rare earth heat-resistant magnesium alloys (total amount of RE <2wt%). Representative alloys include AE41, ZE41, QE21, ZE10A and other alloys. In addition, it also includes improving the high-temperature performance of alloy systems such as AZ, AS, and AM by adding a small amount of rare earth elements Ce, Y, etc., which can also meet some needs in the civilian field. (2) Medium rare earth heat-resistant magnesium alloys (2wt% ≤ total amount of RE <6wt%). There are many alloys in this range, and representative ones include AE42, AE44, ACM522, ZE33, ZE63, EQ21, QE22, QE22A, EK30, EK31, EK41 and other series. (3) High rare earth heat-resistant magnesium alloys (total amount of RE ≥6wt%). The alloys include WE33, WE43, WE54, and the currently developed Mg-Gd alloys such as Mg-6Sc-1Mn, Mg-15Sc-1Mn and Mg-9Gd-4Y-Zr. This series of alloys has excellent high temperature performance and can be used for a long time at a temperature of 250-300°C. In general, with the increase of rare earth content, the high temperature performance of heat-resistant magnesium alloys improves.

[0004] However, although adding high contents of rare earths to improve the room temperature and high temperature mechanical properties of cast magnesium alloys is a common method in the field of magnesium alloy research and industrial application, traditional high rare earth content cast magnesium alloys still have the problem of low plasticity.

[0005] Therefore, how to design a more suitable casting magnesium alloy to solve the above-mentioned problem of low plasticity of existing casting magnesium alloys has become one of the urgent problems to be solved by many forward-looking researchers in the industry. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a cast rare earth magnesium alloy and a preparation method thereof, in particular, a heat-resistant and high-plasticity cast rare earth magnesium alloy and a preparation method thereof. The cast magnesium alloy provided by the present invention, on the basis of a high content of heavy rare earth Gd, adds a small amount of heavy rare earth elements such as Er and light rare earth elements such as Ce, improves the mechanical properties of the magnesium alloy through the synergistic effect of several rare earth elements, combines the Ag element's effect of promoting aging precipitation, and cooperates with the heat treatment process to improve the strength and plasticity at the same time. At the same time, the preparation method is simple, the conditions are mild, the controllability is good, and the stability is strong, which is more suitable for the promotion and application of industrial large-scale production.

[0007] The present invention provides a cast rare earth magnesium alloy, which comprises, by mass percentage:

[0008] Gd: 12%~18%;

[0009] Ag: 0.5%~4%;

[0010] Zr: 0.1%~1.0%;

[0011] The second rare earth element: 1% to 10%;

[0012] Light rare earth elements: 0.5-3%;

[0013] The balance is magnesium.

[0014] Preferably, the cast rare earth magnesium alloy also includes trace amounts of unavoidable impurity elements;

[0015] The impurity elements include one or more of Fe, Ni, Cu, Cl, Zn and Al;

[0016] Among the impurity elements, Fe is ≤ 0.01% by mass;

[0017] Ni≤0.01%;

[0018] Cu≤0.005%;

[0019] Cl≤0.03%;

[0020] Zn≤0.01%;

[0021] Al≤0.1%.

[0022] Preferably, the casting includes one or more of gravity casting, differential pressure casting and die casting;

[0023] The second heavy rare earth element includes one or more of Er, Y, Ho, Yb, Dy, Tm, Tb, Lu and Sc;

[0024] The light rare earth element includes one or more of La, Ce, Pr, Nd and Sm.

[0025] The present invention also provides a method for preparing a cast rare earth magnesium alloy as described in any one of the above technical solutions, comprising the following steps:

[0026] 1) Mixing and melting the rare earth magnesium alloy raw materials, casting them into a mold, and obtaining an alloy ingot after cooling;

[0027] 2) The alloy ingot obtained in the above steps is subjected to solid solution treatment and aging treatment to obtain a cast rare earth magnesium alloy.

[0028] Preferably, the rare earth magnesium alloy raw material is a preheated rare earth magnesium alloy raw material;

[0029] The preheating temperature is 350-500°C;

[0030] The mixed melting is specifically carried out under protective gas conditions.

[0031] Preferably, the mixing and melting step comprises the following steps:

[0032] Under protective gas conditions, a magnesium ingot, a Mg-Gd master alloy, a Mg-second heavy rare earth element master alloy and a Mg-light rare earth element master alloy are heated and melted, and then a Mg-Zr master alloy is added to continue melting, and then Ag is added to mix, and then the temperature is lowered and allowed to stand;

[0033] The heating and melting temperature is 710-740°C.

[0034] Preferably, the temperature of the continued melting is 740-780°C;

[0035] The mixing time is 10 to 15 minutes;

[0036] The temperature after cooling is 700-720°C;

[0037] The standing time is 15 to 40 minutes.

[0038] Preferably, the solution treatment comprises a staged solution treatment;

[0039] The solution treatment further includes a quenching step;

[0040] The quenching step is specifically performed in hot water at 80-100°C.

[0041] Preferably, the solution temperature of the first stage of the solution treatment is 450-500°C;

[0042] The holding time of the first stage of the solution treatment is 10 to 30 hours;

[0043] The solution temperature of the second stage of the solution treatment is 500-550°C;

[0044] The holding time of the second stage of the solution treatment is 5 to 15 hours.

[0045] Preferably, the aging treatment includes isothermal aging treatment;

[0046] The temperature of the aging treatment is 175-250°C;

[0047] The aging treatment time is 10 to 50 hours;

[0048] The aging treatment is specifically performed in an air atmosphere.

[0049] The present invention provides a cast rare earth magnesium alloy, which includes, by mass percentage: Gd: 12% to 18%; Ag: 0.5% to 4%; Zr: 0.1% to 1.0%; the second heaviest rare earth element: 1% to 10%; light rare earth element: 0.5 to 3%; and the balance of magnesium. Compared with the prior art, the present invention believes that adding a small amount of light rare earth can reduce the solid solubility of Gd in the Mg matrix, but has limited effect on improving the mechanical properties and heat resistance of the alloy. Among the added light rare earth elements, Nd has a better effect, followed by Ce and La. The added heavy rare earth elements Ho, Er, Y and Dy have a large solid solubility in the magnesium alloy, easily replace the position of Gd in the matrix, and are conducive to improving the aging hardening effect of Gd, thereby improving the mechanical properties and heat resistance of the alloy. Among the heavy rare earths, Y and Dy have a better effect, followed by Ho and Er. The addition of combined rare earths can improve the aging hardening characteristics of the alloy and improve the mechanical properties of the alloy. Although adding rare earth elements to the existing solutions can improve the heat resistance of magnesium alloys and solve the problem of serious performance degradation of magnesium alloys in high temperature environments. At present, among the alloy systems with the highest rare earth content, Mg-Gd rare earth magnesium alloy is more common, and its mass percentage is as high as more than 15%. This alloy system has great application prospects in the aerospace field, but the elongation of this casting alloy is usually low, only about 2-3%, which greatly limits its depth and breadth in practical applications.

[0050] Based on this, the present invention achieves a synergistic effect by rationally selecting and proportioning alloy elements, adding a small amount of heavy rare earth elements such as Er and light rare earth elements such as Ce, and combines the Ag element to improve the high-temperature mechanical properties of the magnesium alloy. Subsequently, by optimizing the heat treatment process, selecting appropriate solid solution treatment and aging treatment to regulate the microstructure of the alloy, the strength and elongation of the alloy are improved at the same time. Under the premise of a strength of more than 400MPa, the elongation of the alloy finally reaches more than 6%, which is significantly higher than traditional high rare earth content cast magnesium alloys.

[0051] The present invention optimizes the high-temperature mechanical properties of magnesium alloys by designing rare earth elements with high Gd content and low Er and Ce content, and promotes aging through the Ag element. The combined effect of several elements simultaneously improves the strength and plasticity of the magnesium alloy. Furthermore, the present invention can precipitate a large amount of nano rare earth compounds in the casting alloy by adding a high content of rare earth Gd element and a small amount of rare earth elements such as Er and Ce, combined with the "solid solution + aging" T6 heat treatment. Due to the promoting effect of the Ag element and the simultaneous presence of elements such as Gd, Er, Ce, the superposition of the dual effects significantly increases the number of nano compound precipitations in the alloy compared to traditional magnesium alloys with similar rare earth content. The strength and plasticity of the alloy are significantly improved at the same time. This phenomenon is caused by the aging precipitation strengthening of rare earth (RE) intermetallic compounds as the main strengthening mechanism, and by adding non-rare earth elements Ag, RE-Ag fine high-temperature stable phase and Mg-RE-Ag eutectic are formed. The newly formed phase has the characteristics of fine dispersion and high-temperature stability, which significantly improves the heat treatment aging hardening effect and heat resistance of the material of the present invention.

[0052] The heat-resistant high-plasticity cast rare earth magnesium alloy material prepared by the present invention has excellent room temperature and high temperature mechanical properties, and its room temperature mechanical properties are significantly improved. Under the premise of not increasing the total amount of rare earth, the strength performance index is improved to varying degrees, and good plasticity is retained, which is easy to realize engineering application. The high-temperature mechanical properties of the magnesium alloy material are excellent, and can meet the current aerospace, missile military, rail transportation and other fields for the mechanical properties of lightweight structural materials in high temperature environments. Moreover, the present invention uses the precipitation strengthening of rare earth metal intermetallic compounds as the main strengthening mechanism, and can obtain excellent high-temperature mechanical properties by adding a small amount of heavy rare earth elements (such as Er) and a small amount of light rare earth elements (such as Ce), and improves the aging hardening effect by adding non-rare earth elements Ag, thereby optimizing the diversified components of such alloys.

[0053] The high rare earth content cast heat-resistant magnesium alloy provided by the present invention has a significantly improved elongation while ensuring the strength of the alloy, compared with the traditional high rare earth content heat-resistant magnesium alloy, so that the alloy has greater application advantages compared with the traditional high rare earth content magnesium alloy. The present invention also provides a preparation method of the alloy, the production process is simple and easy, and the process performance is stable and good. Due to the good plasticity, the processing performance of the alloy of the present invention is significantly improved, the practicality is enhanced, and it has a good application prospect in aerospace and other high-tech industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The metallographic diagram of the cast alloy of the rare earth magnesium alloy prepared in Example 1 of the present invention;

[0055] Figure 2This is a SEM photograph of the cast alloy of the rare earth magnesium alloy prepared in Example 1 of the present invention;

[0056] Figure 3 The metallographic diagram of the solid solution alloy of the rare earth magnesium alloy prepared in Example 1 of the present invention;

[0057] Figure 4 This is a TEM photograph of the rare earth magnesium alloy prepared in Example 1 of the present invention after aging treatment for 32 hours. DETAILED DESCRIPTION

[0058] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention.

[0059] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0060] There is no particular restriction on the purity of all raw materials in the present invention. The present invention preferably adopts analytically pure materials or materials with conventional purity requirements in the field of casting rare earth magnesium alloy preparation.

[0061] All the raw materials of the present invention, their brands and abbreviations are conventional brands and abbreviations in the field, and each brand and abbreviation is clear and definite in the field of its related use. Those skilled in the art can purchase them from the market or prepare them by conventional methods according to the brands, abbreviations and corresponding uses.

[0062] The abbreviations of the processes used in the present invention are all conventional abbreviations in the field. The specific steps and conventional parameters of each abbreviation are clear and definite in its relevant field. Those skilled in the art can implement them in a conventional manner based on the abbreviations.

[0063] The present invention provides a cast rare earth magnesium alloy, which comprises, by mass percentage:

[0064] Gd: 12%~18%;

[0065] Ag: 0.5%~4%;

[0066] Zr: 0.1%~1.0%;

[0067] The second rare earth element: 1% to 10%;

[0068] Light rare earth elements: 0.5-3%;

[0069] The balance is magnesium.

[0070] In the present invention, the added amount of Gd is 12% to 18%, may be 13% to 17%, or may be 14% to 16%.

[0071] In the present invention, the added amount of Ag is 0.5% to 4%, can be 1% to 3.5%, can be 1.5% to 3%, or can be 2% to 2.5%.

[0072] In the present invention, the added amount of Zr is 0.1% to 1.0%, can be 0.3% to 0.8%, or can be 0.5% to 0.6%.

[0073] In the present invention, the added amount of the second heavy rare earth element is 1% to 10%, can be 3% to 8%, or can be 5% to 6%.

[0074] In the present invention, the added amount of the light rare earth element is 0.5-3%, can be 1%-2.5%, or can be 1.5%-2%.

[0075] In the present invention, the cast rare earth magnesium alloy preferably further includes trace amounts of unavoidable impurity elements.

[0076] In the present invention, the impurity elements preferably include one or more of Fe, Ni, Cu, Cl, Zn and Al.

[0077] Among the impurity elements, Fe is ≤ 0.01% by mass;

[0078] Ni≤0.01%;

[0079] Cu≤0.005%;

[0080] Cl≤0.03%;

[0081] Zn≤0.01%;

[0082] Al≤0.1%.

[0083] The specific requirements for impurity content are preferably as follows:

[0084] In the present invention, among the impurity elements, Fe is preferably ≤ 0.01%, more preferably Fe is ≤ 0.008%, and more preferably Fe is ≤ 0.005%.

[0085] In the present invention, among the impurity elements, Ni is preferably ≤ 0.01%, more preferably Ni is ≤ 0.008%, and more preferably Ni is ≤ 0.005%.

[0086] In the present invention, among the impurity elements, Cu is preferably ≤ 0.005%, more preferably Cu is ≤ 0.004%, and even more preferably Cu is ≤ 0.003%.

[0087] In the present invention, among the impurity elements, Cl is preferably ≤ 0.03%, more preferably Cl is ≤ 0.02%, and more preferably Cl is ≤ 0.01%.

[0088] In the present invention, among the impurity elements, Zn≤0.01% is preferred, Zn≤0.008% is more preferred, and Zn≤0.005% is further preferred.

[0089] In the present invention, among the impurity elements, Al≤0.1% is preferred, Al≤0.08% is more preferred, and Al≤0.05% is further preferred.

[0090] In the present invention, the casting preferably includes one or more of gravity casting, differential pressure casting and die casting, and more preferably gravity casting, differential pressure casting or die casting.

[0091] In the present invention, the second heavy rare earth element preferably includes one or more of Er, Y, Ho, Yb, Dy, Tm, Tb, Lu and Sc, and more preferably Er, Y, Ho, Yb, Dy, Tm, Tb, Lu or Sc.

[0092] In the present invention, the light rare earth element preferably includes one or more of La, Ce, Pr, Nd and Sm, and more preferably La, Ce, Pr, Nd or Sm.

[0093] In the present invention, the cast rare earth magnesium alloy is preferably a heat-resistant and high-plasticity cast rare earth magnesium alloy.

[0094] The present invention provides a method for preparing a cast rare earth magnesium alloy as described in any one of the above technical solutions, comprising the following steps:

[0095] 1) Mixing and melting the rare earth magnesium alloy raw materials, casting them into a mold, and obtaining an alloy ingot after cooling;

[0096] 2) The alloy ingot obtained in the above steps is subjected to solid solution treatment and aging treatment to obtain a cast rare earth magnesium alloy.

[0097] The invention firstly mixes and melts rare earth magnesium alloy raw materials, casts them into a mold, and obtains alloy ingots after cooling.

[0098] In the present invention, the rare earth magnesium alloy raw material is preferably a preheated rare earth magnesium alloy raw material.

[0099] In the present invention, the preheating temperature is preferably 350-500°C, more preferably 370-480°C, and more preferably 400-450°C. Specifically, it may be 400°C.

[0100] In the present invention, the mixed melting is preferably carried out under protective gas conditions.

[0101] In the present invention, the step of mixing and melting preferably includes the following steps:

[0102] Under protective gas conditions, a magnesium ingot, a Mg-Gd master alloy, a Mg-second heavy rare earth element master alloy and a Mg-light rare earth element master alloy are heated and melted, and then a Mg-Zr master alloy is added to continue melting, and then Ag is added to mix, and then the temperature is lowered and allowed to stand;

[0103] In the present invention, the heating and melting temperature is preferably 710 to 740°C, more preferably 720 to 730°C.

[0104] In the present invention, the temperature of the continued melting is preferably 740 to 780°C, more preferably 750 to 770°C, and specifically 750°C.

[0105] In the present invention, the mixing time is preferably 10 to 15 minutes, more preferably 11 to 14 minutes, and more preferably 12 to 13 minutes.

[0106] In the present invention, the temperature after cooling is preferably 700-720°C, more preferably 704-716°C, and more preferably 708-712°C.

[0107] In the present invention, the standing time is preferably 15 to 40 minutes, more preferably 20 to 35 minutes, and specifically 30 minutes.

[0108] In the present invention, the alloy ingot obtained in the above steps is finally subjected to solid solution treatment and aging treatment to obtain a cast rare earth magnesium alloy.

[0109] In the present invention, the solution treatment preferably includes a staged solution treatment.

[0110] In the present invention, the solution treatment further includes a quenching step;

[0111] In the present invention, the quenching step is preferably performed in hot water at 80 to 100°C, more preferably 84 to 96°C, and even more preferably 88 to 92°C.

[0112] In the present invention, the solution temperature of the first stage of the solution treatment is preferably 450 to 500°C, more preferably 460 to 490°C, and even more preferably 470 to 480°C.

[0113] In the present invention, the holding time of the first stage of the solution treatment is preferably 10 to 30 hours, more preferably 14 to 28 hours, and even more preferably 18 to 24 hours.

[0114] In the present invention, the solution temperature of the second stage of the solution treatment is preferably 500 to 550°C, more preferably 510 to 540°C, and even more preferably 520 to 530°C.

[0115] In the present invention, the holding time of the second stage of the solution treatment is preferably 5 to 15 hours, more preferably 7 to 13 hours, and even more preferably 9 to 11 hours.

[0116] In the present invention, the aging treatment preferably includes isothermal aging treatment.

[0117] In the present invention, the temperature of the aging treatment is preferably 175-250°C, more preferably 190-235°C, and more preferably 205-220°C.

[0118] In the present invention, the aging treatment time is preferably 10 to 50 hours, more preferably 15 to 40 hours, more preferably 20 to 35 hours, and more preferably 25 to 30 hours.

[0119] In the present invention, the aging treatment is preferably performed in an air atmosphere.

[0120] The present invention is to complete and refine the overall technical solution, better ensure the composition and microstructure of the cast rare earth magnesium alloy, and further improve the strength and plasticity of the cast rare earth magnesium alloy. The above-mentioned heat-resistant high-plasticity cast rare earth magnesium alloy and its preparation method may specifically include the following contents:

[0121] A heat-resistant rare earth magnesium alloy and a preparation method thereof utilize the synergistic effect of heavy rare earth element Gd and other light and heavy rare earth elements to promote the precipitation of high-density nano-sized compounds in the alloy, thereby significantly improving the strength and plasticity of the alloy.

[0122] The heat-resistant rare earth magnesium alloy of the present invention has the following mass percentages of components: Gd: 12-18%; other heavy rare earth elements: 1-10%; other light rare earth elements: 0.5-3%; Ag: 0.5-4%; Zr: 0.1-1%. Except for trace inevitable impurity elements, the rest is Mg.

[0123] Specifically, other heavy rare earth elements may be one or a mixture of more than one of Er, Y, Ho, Yb, Dy, Tm, Tb, Lu, and Sc.

[0124] Specifically, other light rare earth elements may be one or a mixture of more than one of La, Ce, Pr, Nd, and Sm.

[0125] Specifically, the heat-resistant rare earth magnesium alloy can be prepared by gravity casting; can be prepared by differential pressure casting; can be prepared by die casting.

[0126] Specifically, the preparation method of the heat-resistant rare earth magnesium alloy has a stepwise solution treatment, wherein the solution treatment temperature of the first stage is in the range of 450 to 500°C, and the holding time is 10 to 30 hours; the solution treatment temperature of the second stage is in the range of 500 to 550°C, and the holding time is 5 to 15 hours. The aging treatment temperature range is 150 to 275°C.

[0127] Furthermore, the present invention also provides a specific preparation method of the heat-resistant cast rare earth magnesium alloy, and the specific implementation method is as follows:

[0128] The present invention weighs the ingredients according to the mass ratio of the alloy, and the raw materials used are pure Mg (purity>99%), Mg-25wt.%Gd, Mg-30wt.%Zr, Mg-20wt.%Er, Mg-20wt.%Ce (or other heavy rare earth elements), and pure Ag (purity>99%). The smelting equipment used is a medium-frequency pit-type resistance furnace, and the crucible is an ordinary low-carbon steel crucible.

[0129] The specific process steps are as follows:

[0130] (1) First, clean the crucible, stirring tools, casting mold, etc., then prepare the ingredients according to the predetermined alloy composition, and remove the oxide layer on the surface of the raw materials. It should be noted that the loss should be calculated in advance during the batching process. For example, Er (or other heavy rare earth elements) and Zr elements generally have large burnout, so they can be calculated as three times when preparing the ingredients.

[0131] (2) Dry and preheat the prepared materials. After the crucible is preheated to 400°C, pure magnesium ingot, Mg-25wt.% Gd, Mg-20wt.% Er, Mg-20wt.% Ce magnesium rare earth master alloy are placed in the crucible, protective gas (CO2 and 1vol.% SF6 mixed gas) is introduced, and then the temperature is raised to 730°C.

[0132] (3) After the magnesium ingot and the magnesium-rare earth master alloy are completely melted, the crucible temperature is further increased to 750°C, and then the Mg-Zr master alloy is added. After melting, the surface scum is skimmed off.

[0133] (4) Add pure Ag, stir the molten alloy for 10-15 minutes after melting, then cool to 700-720°C and let stand for 30 minutes.

[0134] (5) After standing, remove the surface scum again, then take it out of the furnace and cast it into a water-cooled mold. During the pouring process, ensure that the flow rate is uniform until the riser is filled. After the mold cools to room temperature, take out the ingot.

[0135] (6) The heat treatment process adopted in the present invention mainly includes: solution treatment (T4), solution + aging treatment (T6), aging treatment (T5). The purpose of solution treatment is to dissolve the eutectic second phase of the cast alloy into the matrix and eliminate segregation, which is beneficial to the subsequent aging process. The ingot solution treatment process is carried out in a muffle furnace. First, the ingot is placed in a muffle furnace, and then heated to 480°C at 5°C / min with the furnace and kept warm for 18 hours, and then heated to 500°C at 5°C / min with the furnace and kept warm for 10 hours, and then immediately placed in 80-100°C hot water for quenching.

[0136] (7) In order to improve the strength of the cast alloy, an aging process is also an indispensable process. In the present invention, the aging treatment is an isothermal aging treatment at 175-250°C, and the aging device is a muffle furnace, and the heat is kept in an air atmosphere.

[0137] The above content of the present invention provides a heat-resistant and highly plastic cast rare earth magnesium alloy and a preparation method thereof. The present invention achieves a synergistic effect by rationally selecting and proportioning alloy elements, adding a small amount of heavy rare earth elements such as Er and light rare earth elements such as Ce, and combines the Ag element to improve the high-temperature mechanical properties of the magnesium alloy. Subsequently, by optimizing the heat treatment process, selecting appropriate solid solution treatment and aging treatment to regulate the microstructure of the alloy, the strength and elongation of the alloy are simultaneously improved. Under the premise of a strength exceeding 400MPa, the elongation of the alloy finally reaches more than 6%, which is significantly higher than that of traditional cast magnesium alloys with high rare earth content.

[0138] The present invention optimizes the high-temperature mechanical properties of magnesium alloys by designing rare earth elements with high Gd content and low Er and Ce content, and promotes aging through the Ag element. The combined effect of several elements simultaneously improves the strength and plasticity of the magnesium alloy. Furthermore, the present invention can precipitate a large amount of nano rare earth compounds in the casting alloy by adding a high content of rare earth Gd element and a small amount of rare earth elements such as Er and Ce, combined with the "solid solution + aging" T6 heat treatment. Due to the promoting effect of the Ag element and the simultaneous presence of elements such as Gd, Er, Ce, the superposition of the dual effects significantly increases the number of nano compound precipitations in the alloy compared to traditional magnesium alloys with similar rare earth content. The strength and plasticity of the alloy are significantly improved at the same time. This phenomenon is caused by the aging precipitation strengthening of rare earth (RE) intermetallic compounds as the main strengthening mechanism, and by adding non-rare earth elements Ag, RE-Ag fine high-temperature stable phase and Mg-RE-Ag eutectic are formed. The newly formed phase has the characteristics of fine dispersion and high-temperature stability, which significantly improves the heat treatment aging hardening effect and heat resistance of the material of the present invention.

[0139] The heat-resistant high-plasticity cast rare earth magnesium alloy material prepared by the present invention has excellent room temperature and high temperature mechanical properties, and its room temperature mechanical properties are significantly improved. Under the premise of not increasing the total amount of rare earth, the strength performance index is improved to varying degrees, and good plasticity is retained, which is easy to realize engineering application. The high-temperature mechanical properties of the magnesium alloy material are excellent, and can meet the current aerospace, missile military, rail transportation and other fields for the mechanical properties of lightweight structural materials in high temperature environments. Moreover, the present invention uses the precipitation strengthening of rare earth metal intermetallic compounds as the main strengthening mechanism, and can obtain excellent high-temperature mechanical properties by adding a small amount of heavy rare earth elements (such as Er) and a small amount of light rare earth elements (such as Ce), and improves the aging hardening effect by adding non-rare earth elements Ag, thereby optimizing the diversified components of such alloys.

[0140] The high rare earth content cast heat-resistant magnesium alloy provided by the present invention has a significantly improved elongation while ensuring the strength of the alloy, compared with the traditional high rare earth content heat-resistant magnesium alloy, so that the alloy has greater application advantages compared with the traditional high rare earth content magnesium alloy. The present invention also provides a preparation method of the alloy, the production process is simple and easy, and the process performance is stable and good. Due to the good plasticity, the processing performance of the alloy of the present invention is significantly improved, the practicality is enhanced, and it has a good application prospect in aerospace and other high-tech industries.

[0141] In order to further illustrate the present invention, a cast rare earth magnesium alloy and a preparation method thereof provided by the present invention are described in detail in combination with embodiments below. However, it should be understood that these embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. The protection scope of the present invention is not limited to the following embodiments.

[0142] Example 1

[0143] 1) First, clean the crucible, stirring tools, casting mold, etc., remove the oxide layer on the surface of the raw materials, and then prepare the alloy composition according to Gd: 14wt%, Ag: 2wt%, Er: 1wt%, Ce: 1wt%, Zr: 0.5wt%.

[0144] 2) Dry and preheat the prepared materials. After the crucible is preheated to 400°C, put the pure magnesium ingot and magnesium rare earth master alloy into the crucible, introduce protective gas (CO2 and 1vol.% SF6 mixed gas), and then raise the temperature to 730°C.

[0145] 3) After the magnesium ingot and the magnesium-rare earth master alloy are completely melted, the crucible temperature is further increased to 750°C, and then the Mg-Zr master alloy is added, and the surface scum is skimmed off after melting.

[0146] 4) Add pure Ag, stir the molten alloy for 10-15 minutes after melting, then cool to 700-720°C and let stand for 30 minutes.

[0147] 5) After standing, remove the surface scum again, then take it out of the furnace and cast it into a water-cooled mold. During the pouring process, ensure that the flow rate is uniform until the riser is filled. After the mold cools to room temperature, take out the ingot.

[0148] See also Figure 1 , Figure 1 This is a metallographic diagram of the cast alloy of the rare earth magnesium alloy prepared in Example 1 of the present invention.

[0149] See also Figure 2 , Figure 2 This is a SEM photograph of the cast alloy of the rare earth magnesium alloy prepared in Example 1 of the present invention.

[0150] 6) First, place the ingot in a muffle furnace, then heat it to 480°C at 5°C / min and keep it for 18 hours, then heat it to 500°C at 5°C / min and keep it for 10 hours, and then immediately quench it in 80-100°C hot water.

[0151] See also Figure 3 , Figure 3 This is a metallographic diagram of the solid solution alloy of the rare earth magnesium alloy prepared in Example 1 of the present invention.

[0152] 7) The ingot after the solution treatment is placed in a muffle furnace, and then heated to 200°C at 5°C / min with the furnace, and kept warm for 32 hours in an air atmosphere for isothermal aging treatment.

[0153] See also Figure 4 , Figure 4 This is a TEM photograph of the rare earth magnesium alloy prepared in Example 1 of the present invention after aging treatment for 32 hours.

[0154] Example 2

[0155] 1) First, clean the crucible, stirring tools, casting mold, etc., remove the oxide layer on the surface of the raw material, and then prepare the alloy composition according to Gd: 14wt%, Ag: 2wt%, Er: 2wt%, Ce: 0.5wt%, Zr: 0.5wt%.

[0156] 2) Dry and preheat the prepared materials. After the crucible is preheated to 400°C, put the pure magnesium ingot and magnesium rare earth master alloy into the crucible, introduce protective gas (CO2 and 1vol.% SF6 mixed gas), and then raise the temperature to 730°C.

[0157] 3) After the magnesium ingot and the magnesium-rare earth master alloy are completely melted, the crucible temperature is further increased to 750°C, and then the Mg-Zr master alloy is added, and the surface scum is skimmed off after melting.

[0158] 4) Add pure Ag, stir the molten alloy for 10-15 minutes after melting, then cool to 700-720°C and let stand for 30 minutes.

[0159] 5) After standing, remove the surface scum again, then take it out of the furnace and cast it into a water-cooled mold. During the pouring process, ensure that the flow rate is uniform until the riser is filled. After the mold cools to room temperature, take out the ingot.

[0160] 6) First, place the ingot in a muffle furnace, then heat it to 480°C at 5°C / min and keep it for 18 hours, then heat it to 500°C at 5°C / min and keep it for 10 hours, and then immediately quench it in 80-100°C hot water.

[0161] 7) The ingot after the solution treatment is placed in a muffle furnace, and then heated to 200°C at 5°C / min with the furnace, and kept warm for 32 hours in an air atmosphere for isothermal aging treatment.

[0162] Example 3

[0163] 1) First, clean the crucible, stirring tools, casting mold, etc., remove the oxide layer on the surface of the raw materials, and then prepare the alloy composition according to Gd: 14wt%, Ag: 2wt%, Er: 3wt%, La: 0.5wt%, Zr: 0.5wt%.

[0164] 2) Dry and preheat the prepared materials. After the crucible is preheated to 400°C, put the pure magnesium ingot and magnesium rare earth master alloy into the crucible, introduce protective gas (CO2 and 1vol.% SF6 mixed gas), and then raise the temperature to 730°C.

[0165] 3) After the magnesium ingot and the magnesium-rare earth master alloy are completely melted, the crucible temperature is further increased to 750°C, and then the Mg-Zr master alloy is added, and the surface scum is skimmed off after melting.

[0166] 4) Add pure Ag, stir the molten alloy for 10-15 minutes after melting, then cool to 700-720°C and let stand for 30 minutes.

[0167] 5) After standing, remove the surface scum again, then take it out of the furnace and cast it into a water-cooled mold. During the pouring process, ensure that the flow rate is uniform until the riser is filled. After the mold cools to room temperature, take out the ingot.

[0168] 6) First, place the ingot in a muffle furnace, then heat it to 480°C at 5°C / min and keep it for 18 hours, then heat it to 500°C at 5°C / min and keep it for 10 hours, and then immediately quench it in 80-100°C hot water.

[0169] 7) The ingot after solution treatment is placed in a muffle furnace, and then heated to 225°C at 5°C / min with the furnace, and kept warm for 8 hours in an air atmosphere for isothermal aging treatment.

[0170] Example 4

[0171] 1) First, clean the crucible, stirring tools, casting mold, etc., remove the oxide layer on the surface of the raw material, and then prepare the alloy composition according to Gd: 14wt%, Ag: 2wt%, Er: 4wt%, Ce: 1.5wt%, Zr: 0.5wt%.

[0172] 2) Dry and preheat the prepared materials. After the crucible is preheated to 400°C, put the pure magnesium ingot and magnesium rare earth master alloy into the crucible, introduce protective gas (CO2 and 1vol.% SF6 mixed gas), and then raise the temperature to 730°C.

[0173] 3) After the magnesium ingot and the magnesium-rare earth master alloy are completely melted, the crucible temperature is further increased to 750°C, and then the Mg-Zr master alloy is added, and the surface scum is skimmed off after melting.

[0174] 4) Add pure Ag, stir the molten alloy for 10-15 minutes after melting, then cool to 700-720°C and let stand for 30 minutes.

[0175] 5) After standing, remove the surface scum again, then take it out of the furnace and cast it into a water-cooled mold. During the pouring process, ensure that the flow rate is uniform until the riser is filled. After the mold cools to room temperature, take out the ingot.

[0176] 6) First, place the ingot in a muffle furnace, then heat it to 480°C at 5°C / min and keep it for 18 hours, then heat it to 500°C at 5°C / min and keep it for 10 hours, and then immediately quench it in 80-100°C hot water.

[0177] 7) The ingot after the solution treatment is placed in a muffle furnace, and then heated to 250°C at 5°C / min with the furnace, and kept warm for 6 hours in an air atmosphere for isothermal aging treatment.

[0178] Example 5

[0179] 1) First, clean the crucible, stirring tools, casting mold, etc., remove the oxide layer on the surface of the raw material, and then prepare the alloy composition according to Gd: 14wt%, Ag: 2wt%, Er: 5wt%, Nd: 0.5wt%, Zr: 0.5wt%.

[0180] 2) Dry and preheat the prepared materials. After the crucible is preheated to 400°C, put the pure magnesium ingot and magnesium rare earth master alloy into the crucible, introduce protective gas (CO2 and 1vol.% SF6 mixed gas), and then raise the temperature to 730°C.

[0181] 3) After the magnesium ingot and the magnesium-rare earth master alloy are completely melted, the crucible temperature is further increased to 750°C, and then the Mg-Zr master alloy is added, and the surface scum is skimmed off after melting.

[0182] 4) Add pure Ag, stir the molten alloy for 10-15 minutes after melting, then cool to 700-720°C and let stand for 30 minutes.

[0183] 5) After standing, remove the surface scum again, then take it out of the furnace and cast it into a water-cooled mold. During the pouring process, ensure that the flow rate is uniform until the riser is filled. After the mold cools to room temperature, take out the ingot.

[0184] 6) First, place the ingot in a muffle furnace, then heat it to 480°C at 5°C / min and keep it for 18 hours, then heat it to 500°C at 5°C / min and keep it for 10 hours, and then immediately quench it in 80-100°C hot water.

[0185] 7) The ingot after the solution treatment is placed in a muffle furnace, and then heated to 200°C at 5°C / min with the furnace, and kept warm for 32 hours in an air atmosphere for isothermal aging treatment.

[0186] See Table 1, which shows the performance data of the cast rare earth magnesium alloys prepared in Examples 1 to 5 of the present invention.

[0187] Table 1

[0188]

[0189] See Table 2, which shows the performance data of cast rare earth magnesium alloys in existing research.

[0190] Table 2

[0191]

[0192] Among them, S is sand casting; PM is metal mold casting; T6 is the state after solution treatment and then artificial aging.

[0193] [1]CHEN X,LIU W,WU G,et al.High-Temperature Tensile and CompressiveBehavior of Peak-Aged Sand-Cast Mg–10Gd–3Y–0.5Zr Alloy[J].NationalEngineering Research Center of Light Alloy Net Forming,Key State Laboratoryof Metal Matrix Composite,School of Materials Science and Engineering,Shanghai Jiao Tong University,Shanghai,200240,China Shanghai2016,Vol.18(No.4):671-7.

[0194] [2]NODOOSHAN H,WU G,LIU W,et al.Effect of Gd content on hightemperature mechanical properties of Mg-Gd-Y-Zr alloy(Article)[J].State KeyLaboratory of Rare Earth Resource Utilization,Changchun Institute of AppliedChemistry,Chinese Academy of Sciences,Changchun,130022,China;University ofChinese Academy of Sciences,Beijing,100049,Chi,2016,Vol.651(No.0):840-7.

[0195] [3]LU J,YIN D,REN L,et al.Tensile and compressive deformationbehavior of peak-aged cast Mg–-11Y–-5Gd–-2Zn–-0.5Zr(wt%)alloy at elevatedtemperatures(Article)[J].Key Laboratory of Advanced Technologies ofMaterials,Ministry of Education,Southwest Jiaotong University,Chengdu,Sichuan610031,China;School of Materials Science and Engineering,Southwest Jiaotong University,Chengdu,,2016,Vol.51(No.23):10464-77.

[0196] The above is a detailed introduction to a heat-resistant high-plasticity cast rare earth magnesium alloy and a preparation method thereof provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enables any technician in the field to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements that are not different from the text of the claims, or if they include equivalent structural elements that are not substantially different from the text of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A cast rare earth magnesium alloy, characterized in that: Included by mass percentage: Gd: 12%~18%; Ag: 0.5%~4%; Zr：0.1％～1.0％； The second rare earth element: 1% to 10%; Light rare earth elements: 0.5-3%; The balance is magnesium.

2. The cast rare earth magnesium alloy according to claim 1, characterized in that: The cast rare earth magnesium alloy also includes trace amounts of unavoidable impurity elements; The impurity elements include one or more of Fe, Ni, Cu, Cl, Zn and Al; Among the impurity elements, Fe is ≤ 0.01% by mass; Ni≤0.01%; Cu≤0.005%; Cl≤0.03％； Zn≤0.01%; Al≤0.1％。 3. The cast rare earth magnesium alloy according to claim 1, characterized in that: The casting includes one or more of gravity casting, differential pressure casting and die casting; The second heavy rare earth element includes one or more of Er, Y, Ho, Yb, Dy, Tm, Tb, Lu and Sc; The light rare earth element includes one or more of La, Ce, Pr, Nd and Sm.

4. A method for preparing a cast rare earth magnesium alloy according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1) Mixing and melting the rare earth magnesium alloy raw materials, casting them into a mold, and obtaining an alloy ingot after cooling; 2) The alloy ingot obtained in the above steps is subjected to solid solution treatment and aging treatment to obtain a cast rare earth magnesium alloy.

5. The preparation method according to claim 4, characterized in that: The rare earth magnesium alloy raw material is specifically a preheated rare earth magnesium alloy raw material; The preheating temperature is 350-500°C; The mixed melting is specifically carried out under protective gas conditions.

6. The preparation method according to claim 4, characterized in that: The step of mixing and melting comprises the following steps: Under protective gas conditions, a magnesium ingot, a Mg-Gd master alloy, a Mg-second heavy rare earth element master alloy and a Mg-light rare earth element master alloy are heated and melted, and then a Mg-Zr master alloy is added to continue melting, and then Ag is added to mix, and then the temperature is lowered and allowed to stand; The heating and melting temperature is 710-740°C.

7. The preparation method according to claim 6, characterized in that: The temperature of the continued melting is 740-780°C; The mixing time is 10 to 15 minutes; The temperature after cooling is 700-720°C; The standing time is 15 to 40 minutes.

8. The preparation method according to claim 4, characterized in that: The solution treatment includes staged solution treatment; The solution treatment further includes a quenching step; The quenching step is specifically performed in hot water at 80-100°C.

9. The preparation method according to claim 8, characterized in that: The solution temperature of the first stage of the solution treatment is 450-500°C; The holding time of the first stage of the solution treatment is 10 to 30 hours; The solution temperature of the second stage of the solution treatment is 500-550°C; The holding time of the second stage of the solution treatment is 5 to 15 hours.

10. The preparation method according to claim 4, characterized in that: The aging treatment includes isothermal aging treatment; The temperature of the aging treatment is 175-250°C; The aging treatment time is 10 to 50 hours; The aging treatment is specifically performed in an air atmosphere.

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