CN109930045B - High-strength-toughness heat-resistant Mg-Gd alloy suitable for gravity casting and preparation method thereof - Google Patents
High-strength-toughness heat-resistant Mg-Gd alloy suitable for gravity casting and preparation method thereof Download PDFInfo
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Abstract
The invention provides a high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting and a preparation method thereof, wherein the alloy comprises the following chemical components in percentage by mass: 4.0-10.0% of Gd, 2.0-6.0% of Zn, 0.5-1.2% of Al, 0.1-0.3% of Mn, 0.01-0.08% of M and the balance of Mg; wherein M is Ti, and B is one or two elements. The preparation method comprises the following steps: (1) preparing materials according to the components of Mg-Gd alloy; (2) melting an industrial pure magnesium ingot; (3) heating to 700 ℃, and melting the industrial pure zinc and the Mg-Gd and Mg-Mn intermediate alloy; (4) heating to 730 ℃, adding industrial pure aluminum ingots, Al-Ti and Al-Ti-B, Al-B intermediate alloys, completely melting, and refining to obtain a magnesium alloy melt; (5) gravity casting; (6) secondary solid solution and artificial aging treatment. After the alloy is subjected to gravity casting, secondary solution treatment and artificial aging heat treatment, the tensile strength at room temperature is 300MPa, and the elongation is 15%; the tensile strength at high temperature of 200 ℃ is 218MPa, the elongation is 20%, and the high-end requirement of the industries of aerospace, automobiles, telecommunication and the like on light weight development is met.
Description
Technical Field
The invention relates to a high-strength, high-toughness and heat-resistant Mg-Gd alloy suitable for gravity casting, which meets the high-end requirement of industries such as aerospace, automobiles, telecommunication and the like on light weight development. The invention also relates to a preparation method of the high-strength-toughness heat-resistant Mg-Gd alloy suitable for gravity casting, belonging to the field of industrial magnesium alloy and manufacturing.
Background
The magnesium alloy is used as the lightest engineering metal material (the density of magnesium is 2/3 of aluminum and 1/4 of steel), the specific strength of the magnesium alloy is obviously higher than that of aluminum alloy and steel, the specific stiffness of the magnesium alloy is equivalent to that of the aluminum alloy and the steel but far higher than that of engineering plastics, and the magnesium alloy has a series of advantages of good castability, good cutting processability, good thermal conductivity, strong damping property and electromagnetic shielding capability, easy recovery and the like, and has wide application prospects in the fields of aviation, aerospace, automobiles, electronics, national defense war industry and the like. Magnesium alloys have become ideal materials to replace aluminum alloys, steel and engineering plastics to achieve light weight, with the most promising replacement potential being aluminum alloys. The cast aluminum alloy has the necessary toughness and thermal stability, and is widely used for producing parts such as engine cylinder blocks, cylinder covers, wheel hubs and the like at present, and the representative alloys are A354, A356 and A380. If magnesium alloy is substituted for cast aluminum alloy, it must have equivalent toughness and be inexpensive and easy to cast. Gravity casting refers to a casting method for injecting molten metal into a casting mold under the action of earth gravity, and comprises sand casting, investment casting, metal mold casting and the like. Compared with the alloy die casting process which is generally adopted at present, the investment cost of gravity casting is greatly reduced, and the method is a main method for producing castings with complicated geometric shapes.
The Mg-Al magnesium alloy is applied earliest, and the main alloy elements of the Mg-Al magnesium alloy have larger atomic radius difference between aluminum and magnesium and larger solid solubility in magnesium, and play the roles of solid solution strengthening and precipitation strengthening in the alloy. After a small amount of Mn is found in 1925 to remarkably improve the corrosion resistance of Mg-Al-Zn magnesium alloy, AZ (such as AZ91) and AM magnesium alloy (such as AM60 and AM50) are developed into commercial magnesium alloy which is most widely applied at present. However, AZ and AM magnesium alloys have very poor high temperature creep properties, more than an order of magnitude lower than conventional alloys, and rapidly decrease in tensile strength at temperatures above 150 ℃ due to the supersaturated alpha-Mg matrix Mg at grain boundaries during high temperature creep17Al12The phases are separated out discontinuously. The heat resistance of Mg-Al alloys is improved by adding alloying elements to improve the properties (crystal structure, morphology and thermal stability) of the precipitated phaseHowever, the mechanical properties at normal temperature and high temperature still can not reach the level of cast aluminum alloy, and the application development of the aluminum alloy is severely limited. For example, patent document CN109136701A (a sand gravity casting magnesium alloy material and a method for producing the same) discloses magnesium alloy with the following components: 3.5-4.5 wt.% of Al, 0.5-4.5 wt.% of one or more of La, Ce and Pr, 0.2-0.5 wt.% of Mn, 0.01-2.5 wt.% of one or more of Gd, Y, Sm, Nd, Er, Eu, Ho, Tm, Lu, Dy and Yb, and the balance of Mg; the reported best normal temperature mechanical properties of the alloy: the tensile strength is 231MPa, and the elongation is 11.4%.
The maximum solid solubility of Zn in Mg is up to 6.2 wt%, which is an important alloying element of high-strength magnesium alloy. Typical Mg-Zn-based cast magnesium alloys include ZK51A and ZK60A, and wrought alloys include ZK21A, ZK31, ZK40A, ZK60A, and ZK61, and the like. As the Zn content increases, the tensile strength and yield strength of the alloy increase, the elongation after fracture slightly decreases, but the casting properties, process plasticity and welding properties deteriorate, and the tendency to hot crack is very severe, particularly because of the excessively wide solidification range (for example, the solidification range of ZK60 is as high as 265 ℃, Journal of Materials Science,45(14) (2010) 3797-. The beneficial effect of rare earth element RE (rare earth element) on the strength performance of magnesium alloy and the grain refining effect of zirconium on the magnesium alloy are discovered in the thirties of the twentieth century, and in the Mg-RE-Zr system (EK30, EK31 and EK41), EK31 becomes the highest-developed high-temperature casting magnesium alloy in the Mg-Zr system. Magnesium rare earth alloys based on rare earth RE elements have excellent age hardening effect, and various novel magnesium alloys taking RE as a main element, such as WE54 and WE43 alloys of Mg-Y series, are developed in sequence. Patent document with application publication number CN1676646A (high-strength heat-resistant magnesium alloy and preparation method thereof) discloses a preparation method of high-strength heat-resistant magnesium alloy, and the invented Mg-Gd-Y-Zr (-Ca) rare earth magnesium alloy comprises the following components by weight percent: 6-15% of Gd, 1-6% of Y, 0.35-0.8% of Zr, 0-1.5% of Ca, less than 0.02% of the total amount of impurity elements Si, Fe, Cu and Ni and the balance of Mg. However, when the alloy is used for sand casting, the grain size reaches 90 μm, and the tensile strength, yield strength and elongation of the cast T6 alloy are only 295MPa, 212MPa and 2.2% respectively (the patent document with the application publication number of CN104928548A discloses a high-strength heat-resistant magnesium alloy suitable for sand casting and a preparation method thereof); meanwhile, the addition of Ca increases the yield strength and high-temperature strength of the alloy, also sharply increases the solidification temperature range of the alloy, increases the hot cracking tendency, and reduces the processing performance of the alloy.
The solid solubility (25 wt%) of heavy rare earth element Gd in the magnesium alloy is high, the heavy rare earth element Gd has strong solid solution strengthening and aging strengthening effects, and the compactness, the casting performance, the three-temperature (low temperature, room temperature and high temperature), the creep resistance and the corrosion resistance of the magnesium alloy can be greatly improved by adding Gd. Researchers have discovered as early as 1974 that Mg-15 wt% Gd alloys that were extruded, quenched and aged had higher tensile strength at both high and low temperatures. Although the density and the cost of the alloy are increased due to the high Gd content, researchers aim to keep the mechanical property advantages of gadolinium-containing magnesium alloy and reduce negative effects as much as possible by coordinately adding alloying elements such as Sc, Mn, Nd, Y and Zr, and develop a plurality of multi-element gadolinium-containing magnesium alloys with development prospect such as Mg-Gd-Y-Mn, Mg-Gd-Y-Zr, Mg-Gd-Nd-Zr, Mg-Gd-Sc-Mn and the like.
The Mg-Gd alloy is added with cheap Zn, which not only has more remarkable effect on regulating and controlling the aging precipitation structure of the alloy system, but also can form a plurality of strengthening phases under the conditions of different Zn/Gd ratios: when the mass ratio of Zn to Gd in the alloy is more than or equal to 2.49 (the atomic ratio is more than or equal to 6.0), an icosahedral quasicrystal structure I phase (Mg) is easily formed3Zn6Gd); the face-centered cubic structure W phase (Mg) is easily formed when the Zn/Gd mass ratio in the alloy is between 0.62 and 2.49 (atomic ratio between 1.5 and 6.0)3Zn3Gd2) And phase I; the W phase and the LPSO phase (Mg) of the long period stacking ordered structure are easily formed when the Zn/Gd mass ratio in the alloy is between 0.42 and 0.62 (the atomic ratio is between 1.0 and 1.5)12ZnGd); the LPSO phase is easily formed when the Zn/Gd mass ratio in the alloy is less than or equal to 0.42 (atomic ratio less than or equal to 1.0) (Materials Science and Engineering A,695(2017) 135-. The room temperature strength and the high temperature performance of the magnesium alloy can be further improved by various Mg-Gd-Zn strengthening phases, and the elastic modulus and the microhardness of the LPSO phase except the strengthening phase W are both higher than those of pure magnesiumThe strength and the plasticity of the magnesium alloy can be obviously improved, so that the alloy shows excellent comprehensive mechanical properties. It was found that LPSO structures can be formed only when the rare earth elements are Y, Gd, Er, Dy, Ho, Tb, Tm in the Mg-RE-Zn system (Materials transformations, 48(11) (2007) 2986-. The patent document with the application publication number of CN105506426A (a multi-nano-phase composite reinforced magnesium alloy and a preparation method thereof) discloses a multi-nano-phase composite reinforced wrought magnesium alloy, wherein the Mg-Gd-Zn alloy comprises the following components in percentage by mass: 10-25% of Gd, 1-5% of Zn and the balance of Mg, wherein the mass percentage content difference of Gd and Zn is not lower than 8; the preparation method comprises the steps of obtaining a wrought magnesium alloy material with excellent mechanical properties through a step extrusion and multistage heat treatment process, wherein the heat treatment temperature range is 200-550 ℃, the solid solution treatment temperature range is 520-550 ℃, and the heat preservation time is 5-15 hours; the temperature range of the high-temperature phase precipitation treatment is 450-520 ℃, and the heat preservation time is 10-120 h; the temperature range of the low-temperature phase precipitation treatment is 200-350 ℃, and the heat preservation time is 15-100 h. Patent document with application publication number CN103184379A (biodegradable Mg-Gd-Zn-Ag-Zr magnesium alloy and preparation method thereof) reports a biodegradable Mg-Gd-Zn-Ag-Zr magnesium alloy and preparation method thereof, wherein the alloy consists of Gd, Zn, Ag, Zr and Mg, and the weight percentage of each component is: 5-10% of Gd, 0.5-3% of Zn, 0.1-1% of Ag, 0.1-1% of Zr and the balance of Mg. The preparation method of the alloy comprises the following steps: "(1) melting: adding the following raw materials into a smelting furnace for smelting: gd adopts Mg-Gd intermediate alloy, Zn adopts pure zinc, Ag adopts pure silver, Zr adopts Mg-Zr intermediate alloy, and the balance of Mg adopts pure magnesium; after the raw materials are smelted in a protective gas environment, casting the smelted raw materials into Mg-Gd-Zn-Ag-Zr series magnesium alloy cast ingots; (2) homogenizing: preserving the heat of the Mg-Gd-Zn-Ag-Zr magnesium alloy cast ingot obtained in the step (1) for 6-24 hours at 480-550 ℃; (3) and (3) carrying out extrusion or rolling deformation on the homogenized Mg-Gd-Zn-Ag-Zr magnesium alloy after heat preservation for 1-3 hours at 250-350 ℃. "the technical problem existing in the invention is as follows: the rare earth element Gd is too high in content to cause too high density, and the expensive price of the rare earth element causes the invention to be difficult to be applied to the large scale in industry. The alloy may be added throughZr is added for structure refinement, but crystal grains under the conventional solidification condition are coarse, and an Mg-Gd-Zn precipitation phase often takes a coarse network structure, so that the mechanical property is deteriorated, and the size of the precipitation phase must be adjusted through thermal deformation or heat treatment solid solution and aging so as to play a role of a strengthening phase.
The Mg-Gd-Zn alloys usually incorporate Zr as a grain refining element to refine their coarse microstructure. The currently reported Zr adding modes comprise sponge Zr, halogen salt of Zr, Zn-Zr intermediate alloy, Mg-Zr intermediate alloy and the like, wherein the Mg-Zr intermediate alloy has the advantages of convenient use, less inclusion, good refining effect and the like, and is the currently main mode for adding Zr. For example: in the preparation method of Mg-Gd-Y-Ag-Zr (B) rare earth magnesium alloy disclosed in patent document with application publication number CN104928548A (a high-strength heat-resistant magnesium alloy suitable for sand casting and a preparation method thereof), K containing 0.2-0.6% of Zr is added2ZrF6Mixed salt (K)2ZrF6-NaCl-KCl) and B2O3And the crystal grain growth of the alloy in sand casting and later solid solution processes is inhibited. At present, Zr-added grain refinement still has a plurality of problems: firstly, the preparation process of the Mg-Zr intermediate alloy is complex and has high energy consumption, so that the price of the Mg-Zr intermediate alloy is high, and the product cost can be increased by refining the crystal grains by using the Mg-Zr intermediate alloy; secondly, Zr has strong chemical activity and is easy to react with atmosphere and furnace gas at high temperature, and when a steel crucible is used and the temperature of a melt is higher than 750 ℃, Zr is easy to react with Fe in the crucible to generate a stable intermetallic compound Fe2Zr, all of which result in high Zr loss; much Zr in Mg-Zr intermediate alloy exists in the form of large-size simple substance Zr particles, the Zr particles are difficult to dissolve in the melt due to the high melting point (1852 ℃) of Zr, and the density of Zr is far higher than that of magnesium melt (the density of Zr is 6.52 g/cm)3The density of the pure magnesium melt was 1.58g/cm3) And is liable to precipitate to the bottom of the crucible, resulting in a low yield of Zr.
Disclosure of Invention
The invention provides a high-strength-toughness heat-resistant Mg-Gd alloy suitable for gravity casting and a preparation method thereof, aiming at solving the industrial problem that the application of the existing cast magnesium alloy is greatly limited because the performance of the cast aluminum alloy such as A380 and the like cannot be achieved due to insufficient strength and heat resistance, and the room-temperature tensile strength of the alloy is 300MPa and the elongation percentage is 15 percent after the alloy is subjected to gravity casting heat treatment; the tensile strength at high temperature of 200 ℃ is 218MPa, and the elongation is 20%.
In order to solve the technical problems, the invention adopts the following technical scheme:
the high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting comprises the following elements in percentage by mass: 4.0-10.0% of Gd, 2.0-6.0% of Zn, 0.5-1.2% of Al, 0.1-0.3% of Mn, 0.01-0.08% of M, and the balance of Mg and other inevitable impurities; wherein M is one or two of Ti and B.
The invention provides a high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting, which has the following innovation points:
(1) in the alloy design, except common metals of Zn, Al and Mn and a small amount of Ti and B elements, the invention selects heavy rare earth element Gd as an alloying element, and the Mg-Gd intermediate alloy is easy to prepare because Gd has extremely high corrosion resistance. The alloying elements Gd and Zn and the matrix Mg element form a ternary Mg-Gd-Zn strengthening phase. Particularly, in the mass ratio of Zn to Gd of 0.2-0.7, on the one hand, the alloy mainly forms a long-period stacking ordered structure LPSO phase (Mg)12ZnGd) and face-centered cubic W phase (Mg)3Zn3Gd2) All are high melting point phases; compared with binary Mg-Gd strengthening, the ternary Mg-RE-Zn strengthening phases LPSO and W have better high-temperature stability in a magnesium matrix, avoid performance reduction caused by dissolution of a precipitation strengthening phase, effectively enhance the room-temperature mechanical property and the high-temperature property of the high-strength-toughness heat-resistant Mg-Gd alloy suitable for gravity casting, and particularly improve the room-temperature yield strength by one time. On the other hand, the invention solves the technical problems that the traditional Mg-Zn-Gd alloy has overlarge solidification interval due to overhigh Zn content, is easy to generate hot cracking defect and can not ensure the toughness and the casting performance of the alloy.
(2) The precipitated phases of Mg-Gd-Zn alloy are often in a coarse network structure under the conventional solidification condition, the mechanical properties of the Mg-Gd-Zn alloy are deteriorated, and the size of the precipitated phases is usually adjusted by hot deformation or heat treatment solid solution and aging so as to exert the strengthening phaseAnd (4) acting. Zr is usually added into the alloy as a grain refining element, the alloy element of the invention contains Al, Mn and rare earth Gd alloy elements, and the elements are combined with Zr to form Al3Zr and the like are precipitated on the bottom of the crucible to prevent the crystal grain refinement of zirconium. On the other hand, researches show that the Mg-Gd-Zn alloy refined by adding Zr has poor structure thermal stability, and grains are rapidly coarsened when the temperature is kept at 550 ℃, so that the high-temperature performance is greatly reduced. The alloy of the invention is added with 0.5-1.2% of Al to replace Zr to form dispersed high melting point Al2The Gd phase not only refines the structure of the alloy, but also ensures the high-temperature stability of the magnesium alloy structure with high-temperature phases such as LPSO and the like. Meanwhile, Al and a small amount of Ti and B play a role in composite grain refinement, the alloy structure is further refined, and the toughness of the alloy is improved. The alloy element of the invention is added with a small amount of Mn, which not only can promote the formation of LPSO phase, improve the high-temperature stability of the alloy, but also can improve the corrosion resistance of the magnesium alloy.
(3) In order to reduce the hot cracking tendency in the casting process of the Mg-Gd-Zn alloy, the mass ratio of Zn to Gd is limited to be 0.2-0.7, and the mass ratio of (Zn + Al)/Gd is limited to be 0.3-0.8. Under the condition of the mass ratio, the alloy of the invention obtains a narrower solidification interval, thereby overcoming the hot cracking tendency in the casting process of the Mg-Gd-Zn alloy and improving the casting process performance of the alloy.
The preparation method of the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting comprises the following steps:
(1) after the burning loss is properly considered, calculating the consumption of required raw materials (industrial pure magnesium ingot, industrial pure zinc, industrial pure aluminum ingot, Mg-Gd intermediate alloy, Mg-Mn intermediate alloy, Al-Ti-B intermediate alloy and Al-B intermediate alloy) according to the components and the stoichiometric ratio of the Mg-Gd alloy; removing oxide layers from industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots, Mg-Gd intermediate alloy and Mg-Mn intermediate alloy, drying and preheating to 200 ℃.
(2) Melting industrial pure magnesium ingot accounting for 25% of the height of the crucible into a molten pool at 680 ℃, introducing protective gas, and adding the rest magnesium ingot. The protective gas is argon or SF with volume fraction of 0.2%6And CO2Mixed gas (i.e. SF)6Volume fraction of 0.2%, CO299.8% by volume).
(3) After the magnesium ingot is completely melted, heating to 700 ℃, adding industrial pure zinc, Mg-Gd and Mg-Mn intermediate alloy for 2-4 times, keeping the temperature constant at 700 ℃, stirring until the industrial pure zinc, Mg-Gd and Mg-Mn intermediate alloy are completely melted, and keeping the temperature for 30 min. Preferably, the Mg-Gd intermediate alloy is MgGd25 or MgGd30, and the Mg-Mn intermediate alloy is MgMn 10.
(4) Heating to 730 ℃ after 40-60 min before gravity casting, adding a refining agent for refining after all the industrial pure aluminum ingot, the Al-Ti intermediate alloy, the Al-Ti-B intermediate alloy and the Al-B intermediate alloy which are sequentially added are melted, heating the furnace to 750 ℃, keeping the temperature and standing for 10-20 min, and promoting the settlement of impurities to obtain the magnesium alloy melt. The Al-Ti-B intermediate alloy is AlTi5B1, the Al-B intermediate alloy is AlB3 or AlB8, and the Al-Ti intermediate alloy is AlTi5 or AlTi 10. The refining agent comprises the following components in percentage by mass: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2. The addition amount of the refining agent is 1.0-3.5% of the total weight of the raw materials, the refining temperature when the refining agent is added for refining is 720-730 ℃, and the stirring time of refining treatment is 10-15 min.
(5) And cooling the magnesium alloy melt to 720-740 ℃ for deslagging, pouring the melt into a sand mold casting mold or a 180-250 ℃ metal mold preheated to 25-150 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant cast Mg-Gd alloy.
(6) And sequentially carrying out secondary solution treatment and artificial aging treatment on the obtained as-cast alloy to obtain the required high-strength-toughness heat-resistant cast Mg-Gd alloy.
The secondary solution treatment step of the high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting comprises the following steps: putting the as-cast alloy into a solid solution furnace, heating to 200 ℃ at the speed of 5 ℃/min, and introducing protective gas (the protective gas is argon or SF with the volume fraction of 0.2 percent)6And CO2Mixed gas (i.e. SF)6Volume fraction of 0.2%, CO2The volume fraction of the solution is 99.8 percent)), continuously heating to 480-490 ℃ of the first-stage solid solution temperature at the speed of 5 ℃/min, and keeping the temperature for 3 percent6-48 h; and then slowly raising the temperature to 535-545 ℃ of the second-stage solution treatment at a speed of 10 ℃/h, preserving the temperature for 1-2 h, and then quickly transferring to a quenching device for water-cooling quenching.
The artificial aging treatment process of the high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting comprises the following steps: and (3) putting the quenched alloy into an aging furnace, heating to 185-215 ℃ at the temperature of artificial aging treatment at the speed of 5 ℃/min, keeping the temperature for 12-36 h, discharging from the furnace, and air cooling to room temperature.
The secondary solution treatment process parameters are as follows: the primary solid solution temperature is 480-490 ℃, and the heat preservation time is 36-48 h; the temperature of the second-stage solid solution is 535-545 ℃, and the heat preservation time is 1-2 h;
the technological parameters of the artificial aging treatment are as follows: the aging temperature is 185-215 ℃, and the heat preservation time is 12-36 h.
The preparation method of the high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting has the innovation points that: (1) Mg-Gd intermediate alloy which is easy to burn is added at 700 ℃, and is melted in the low-temperature melt in a heat preservation way, so that the yield of rare earth Gd is improved; (2) the refining treatment adopts MgCl-free2The special refining agent further reduces the burning loss of rare earth Gd in the refining process; (3) the heat treatment of the high-strength high-toughness heat-resistant cast Mg-Gd alloy comprises two working procedures of solution treatment and aging treatment. The first-stage temperature of the secondary solution treatment is 480-490 ℃, the time is 36-48 h, the solubility of Gd and Zn in a magnesium matrix is fully promoted, and coarse precipitated phases such as LPSO are eliminated; the temperature of the first stage of the secondary solution treatment is 535-545 ℃ for 1-2 h, the short-time heat preservation further eliminates undissolved coarse phases such as LPSO and the like, eliminates zone segregation and intragranular segregation existing in the casting, homogenizes the components of the alloy, improves the performance of the alloy and prevents the phenomenon of overburning caused by heat treatment. Keeping the furnace temperature at 185-215 ℃, preserving the temperature for 12-36 h, carrying out aging treatment, and finally precipitating a nano-grade and finely dispersed strengthening phase in alloy crystal after long-time aging, so that the alloy has excellent room temperature and high temperature performances. The heat treatment of the present invention has stable alloy components, no obvious growth of crystal grains, obviously improved alloy performance, simple process, high safety and reliability and other advantagesIt is convenient to use.
The invention has the following beneficial effects:
after the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting is subjected to gravity casting, secondary solution treatment and artificial aging heat treatment, the room-temperature tensile strength is 300MPa, and the elongation is 15%; the tensile strength at high temperature of 200 ℃ is 218MPa, the elongation is 20 percent, and the comprehensive performance reaches the performance of cast aluminum alloy; the preparation method has the advantages of simple process, high efficiency, suitability for large-scale production and the like, and meets the high-end requirements of the industries of aerospace, war industry, automobiles and the like on light weight development.
Drawings
FIG. 1 is a metallographic structure diagram of an alloy obtained in example 2.
Detailed Description
Example 1
The weight percentage of the high-strength, high-toughness and heat-resistant Mg-Gd alloy suitable for gravity casting is as follows: according to the theoretical mixture ratio, 4.0 percent of Gd, 2.0 percent of Zn, 0.6 percent of Al, 0.3 percent of Mn, 0.01 percent of Ti, 0.01 percent of B, and the balance of Mg and other inevitable impurities.
The preparation method comprises the following steps: (1) properly considering the burning loss, calculating the dosage of the required raw materials according to the components of the Mg-Gd alloy and the stoichiometric ratio; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and MgGd30 and MgMn10 intermediate alloys, drying and preheating to 200 ℃.
(2) Melting industrial pure magnesium ingot accounting for 25% of the height of the crucible into a molten pool at 680 ℃, introducing protective gas argon, and adding the rest magnesium ingot.
(3) After the magnesium ingot is completely melted, heating to 700 ℃, adding industrial pure zinc, MgGd30 and MgMn10 intermediate alloy for 2-4 times, keeping the temperature constant at 700 ℃, stirring until the intermediate alloy is completely melted, and keeping the temperature for 30 min.
(4) Heating to 730 ℃ after 40-60 min before gravity casting, adding a refining agent accounting for 1% of the weight of the raw materials for refining after all the industrial pure aluminum ingot, the AlTi10 intermediate alloy and the AlB3 intermediate alloy which are sequentially added are melted, wherein the refining temperature is 730 ℃, the stirring time of refining treatment is 10min, and the refining agent comprises the following components in percentage by mass: 55% KCl, 25％CaCl2、5％CaF2、15％BaCl2. And (4) raising the temperature of the furnace to 750 ℃, preserving the temperature and standing for 10 minutes to promote the settlement of impurities, thereby obtaining the magnesium alloy melt.
(5) And cooling the magnesium alloy melt to 720 ℃, skimming surface scum, pouring the melt into a sand mold casting mold at the room temperature of 25 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant casting Mg-Y alloy.
(6) Sequentially carrying out secondary solution treatment on the obtained as-cast alloy, putting the cast alloy into a solution furnace, heating to 200 ℃ at the speed of 5 ℃/min, and introducing SF containing 0.2% of volume fraction6And CO2The mixed gas is continuously heated to 480 ℃ of the first-stage solid solution temperature at the speed of 5 ℃/min, the temperature is kept for 36h, then the mixed gas is slowly heated to 535 ℃ of the second-stage solid solution temperature at the speed of 10 ℃/h, and the mixed gas is quickly transferred to a quenching device for water cooling quenching after the temperature is kept for 1 h.
(7) And (3) carrying out artificial aging treatment on the cast alloy after the solution treatment, putting the quenched alloy into an aging furnace, heating to 185 ℃ of the artificial aging treatment at the speed of 5 ℃/min, keeping the temperature for 12h, discharging from the furnace, and carrying out air cooling to room temperature to obtain the high-strength high-toughness heat-resistant Mg-Y alloy suitable for gravity casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. The high-strength and high-toughness heat-resistant magnesium alloy obtained in the embodiment has the room-temperature tensile strength of 270MPa and the elongation of 20 percent; the tensile strength at high temperature of 200 ℃ is 188MPa, and the elongation is 31%.
Example 2
The weight percentage of the high-strength, high-toughness and heat-resistant Mg-Gd alloy suitable for gravity casting is as follows: according to the theoretical mixture ratio, 10.0 percent of Gd, 6.0 percent of Zn, 1.2 percent of Al, 0.1 percent of Mn, 0.08 percent of Ti, and the balance of Mg and other inevitable impurities.
The preparation method comprises the following steps: (1) properly considering the burning loss, calculating the dosage of the required raw materials according to the components of the Mg-Gd alloy and the stoichiometric ratio; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and MgGd30 and MgMn10 intermediate alloys, drying and preheating to 200 ℃.
(2) Will occupy the crucibleMelting industrial pure magnesium ingot with height of 25% into a molten pool at 680 ℃, and introducing SF with volume fraction of 0.2%6And CO2The remaining magnesium ingot is added to the mixed gas of (1).
(3) After the magnesium ingot is completely melted, heating to 700 ℃, adding industrial pure zinc, MgGd30 and MgMn10 intermediate alloy for 2-4 times, keeping the temperature constant at 700 ℃, stirring until the intermediate alloy is completely melted, and keeping the temperature for 30 min.
(4) Heating to 730 ℃ after 40-60 min before gravity casting, adding a refining agent accounting for 3.5% of the weight of the raw materials for refining after all the industrial pure aluminum ingot and the AlTi10 intermediate alloy which are sequentially added are melted, wherein the refining temperature is 730 ℃, the stirring time of the refining treatment is 10min, and the refining agent comprises the following components in percentage by mass: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2. And (4) raising the temperature of the furnace to 750 ℃, preserving the temperature and standing for 10 minutes to promote the settlement of impurities, thereby obtaining the magnesium alloy melt.
(5) And (3) cooling the magnesium alloy melt to 740 ℃, skimming surface scum, pouring the melt into a metal mold preheated to 215 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant cast Mg-Y alloy.
(6) And sequentially carrying out secondary solution treatment on the obtained as-cast alloy, putting the cast alloy into a solution furnace, heating to 200 ℃ at the speed of 5 ℃/min, introducing protective gas argon, continuously heating to 490 ℃ of the first-stage solution temperature at the speed of 5 ℃/min, preserving heat for 48h, slowly heating to 545 ℃ of the second-stage solution temperature at the speed of 10 ℃/h, preserving heat for 2h, and quickly transferring to a quenching device for water-cooling quenching.
(7) And (3) carrying out artificial aging treatment on the cast alloy after the solution treatment, putting the quenched alloy into an aging furnace, heating to the artificial aging treatment temperature of 215 ℃ at the speed of 5 ℃/min, keeping the temperature for 36h, discharging from the furnace, and carrying out air cooling to room temperature to obtain the high-strength high-toughness heat-resistant Mg-Y alloy suitable for gravity casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. The high-strength and high-toughness heat-resistant magnesium alloy obtained in the embodiment has the room-temperature tensile strength of 300MPa and the elongation of 15 percent; the tensile strength at high temperature of 200 ℃ is 218MPa, and the elongation is 20%. The as-cast metallographic structure of the magnesium alloy obtained in the example is shown in fig. 1.
Example 3
The weight percentage of the high-strength, high-toughness and heat-resistant Mg-Gd alloy suitable for gravity casting is as follows: 7.0% of Gd, 3.5% of Zn, 0.5% of Al, 0.2% of Mn, 0.05% of Ti, 0.03% of B and the balance of Mg and other inevitable impurities according to the theoretical proportion.
The preparation method comprises the following steps: (1) properly considering the burning loss, calculating the dosage of the required raw materials according to the components of the Mg-Gd alloy and the stoichiometric ratio; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and MgGd30 and MgMn10 intermediate alloys, drying and preheating to 200 ℃.
(2) Melting industrial pure magnesium ingot accounting for 25% of the height of the crucible into a molten pool at 680 ℃, introducing protective gas argon, and adding the rest magnesium ingot.
(3) After the magnesium ingot is completely melted, heating to 700 ℃, adding industrial pure zinc, MgGd30 and MgMn10 intermediate alloy for 2-4 times, keeping the temperature constant at 700 ℃, stirring until the intermediate alloy is completely melted, and keeping the temperature for 30 min.
(4) Heating to 730 ℃ after 40-60 min before gravity casting, adding a refining agent accounting for 2.5 percent of the weight of the raw materials for refining after all the industrial pure aluminum ingot, the AlTi5B1 intermediate alloy and the AlB3 intermediate alloy which are sequentially added are melted, wherein the refining temperature is 720 ℃, the stirring time of refining treatment is 15min, and the refining agent comprises the following components in percentage by mass: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2. And (4) raising the temperature of the furnace to 750 ℃, preserving the temperature and standing for 10 minutes to promote the settlement of impurities, thereby obtaining the magnesium alloy melt.
(5) And cooling the magnesium alloy melt to 730 ℃, skimming surface scum, pouring the melt into a sand mold casting mould preheated to 150 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant cast Mg-Y alloy.
(6) And sequentially carrying out secondary solution treatment on the obtained as-cast alloy, putting the cast alloy into a solution furnace, heating to 200 ℃ at the speed of 5 ℃/min, introducing protective gas argon, continuously heating to the first-stage solution temperature of 485 ℃ at the speed of 5 ℃/min, preserving heat for 42h, slowly heating to the second-stage solution temperature of 540 ℃ at the speed of 10 ℃/h, preserving heat for 1.5h, and quickly transferring to a quenching device for water-cooling quenching.
(7) And (3) carrying out artificial aging treatment on the cast alloy after the solution treatment, putting the quenched alloy into an aging furnace, heating to the artificial aging treatment temperature of 200 ℃ at the speed of 5 ℃/min, keeping the temperature for 24h, discharging from the furnace, and carrying out air cooling to room temperature to obtain the high-strength high-toughness heat-resistant Mg-Y alloy suitable for gravity casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. The high-strength and high-toughness heat-resistant magnesium alloy obtained in the embodiment has the room-temperature tensile strength of 285MPa and the elongation of 17 percent; the tensile strength at high temperature of 200 ℃ is 200MPa, and the elongation is 25%.
Example 4
The weight percentage of the high-strength, high-toughness and heat-resistant Mg-Gd alloy suitable for gravity casting is as follows: according to the theoretical mixture ratio, 6.0 percent of Gd, 4.2 percent of Zn, 0.6 percent of Al, 0.2 percent of Mn, 0.08 percent of B, and the balance of Mg and other inevitable impurities.
The preparation method comprises the following steps: (1) properly considering the burning loss, calculating the dosage of the required raw materials according to the components of the Mg-Gd alloy and the stoichiometric ratio; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and MgGd30 and MgMn10 intermediate alloys, drying and preheating to 200 ℃.
(2) Melting industrial pure magnesium ingot accounting for 25% of the height of the crucible into a molten pool at 680 ℃, and introducing SF containing 0.2% of volume fraction6And CO2The remaining magnesium ingot is added to the mixed protective gas of (1).
(3) After the magnesium ingot is completely melted, heating to 700 ℃, adding industrial pure zinc, MgGd30 and MgMn10 intermediate alloy for 2-4 times, keeping the temperature constant at 700 ℃, stirring until the intermediate alloy is completely melted, and keeping the temperature for 30 min.
(4) Heating to 730 ℃ after 40-60 min before gravity casting, adding a refining agent accounting for 3.0 percent of the weight of the raw materials for refining after all the industrial pure aluminum ingot and the AlB8 intermediate alloy which are sequentially added are melted, wherein the refining temperature is 720 ℃, the stirring time of the refining treatment is 15min, and the refining is carried outThe refining agent comprises the following components in percentage by mass: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2. And (4) raising the temperature of the furnace to 750 ℃, preserving the temperature and standing for 10 minutes to promote the settlement of impurities, thereby obtaining the magnesium alloy melt.
(5) And cooling the magnesium alloy melt to 720 ℃, skimming surface scum, pouring the melt into a metal mold preheated to 180 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant cast Mg-Y alloy.
(6) Sequentially carrying out secondary solution treatment on the obtained as-cast alloy, putting the cast alloy into a solution furnace, heating to 200 ℃ at the speed of 5 ℃/min, and introducing SF containing 0.2% of volume fraction6And CO2The mixed protective gas is continuously heated to 480 ℃ of the first-stage solid solution temperature at the speed of 5 ℃/min, the temperature is kept for 48 hours, then the temperature is slowly heated to 535 ℃ of the second-stage solid solution temperature at the speed of 10 ℃/h, and the temperature is kept for 2 hours and then the steel plate is quickly transferred to a quenching device for water cooling quenching.
(7) And (3) carrying out artificial aging treatment on the cast alloy after the solution treatment, putting the quenched alloy into an aging furnace, heating to 185 ℃ at the temperature of the artificial aging treatment at the speed of 5 ℃/min, keeping the temperature for 36h, discharging from the furnace, and carrying out air cooling to room temperature to obtain the high-strength high-toughness heat-resistant Mg-Y alloy suitable for gravity casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. The high-strength and high-toughness heat-resistant magnesium alloy obtained in the embodiment has the room-temperature tensile strength of 290MPa and the elongation of 19 percent; the tensile strength at high temperature of 200 ℃ is 207MPa, and the elongation is 27%.
Example 5
The weight percentage of the high-strength, high-toughness and heat-resistant Mg-Gd alloy suitable for gravity casting is as follows: according to the theoretical mixture ratio, 10.0% of Gd, 2.0% of Zn, 1.0% of Al, 0.3% of Mn, 0.04% of Ti, 0.04% of B, and the balance of Mg and other inevitable impurities.
The preparation method comprises the following steps: (1) properly considering the burning loss, calculating the dosage of the required raw materials according to the components of the Mg-Gd alloy and the stoichiometric ratio; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and MgGd30 and MgMn10 intermediate alloys, drying and preheating to 200 ℃.
(2) Melting industrial pure magnesium ingot accounting for 25% of the height of the crucible into a molten pool at 680 ℃, introducing protective gas argon, and adding the rest magnesium ingot.
(3) After the magnesium ingot is completely melted, heating to 700 ℃, adding industrial pure zinc, MgGd30 and MgMn10 intermediate alloy for 2-4 times, keeping the temperature constant at 700 ℃, stirring until the intermediate alloy is completely melted, and keeping the temperature for 30 min.
(4) Heating to 730 ℃ after 40-60 min before gravity casting, adding a refining agent accounting for 2.0 percent of the weight of the raw materials for refining after all the industrial pure aluminum ingot, the AlTi5B1 intermediate alloy and the AlB8 intermediate alloy which are sequentially added are melted, wherein the refining temperature is 730 ℃, the stirring time of refining treatment is 10min, and the refining agent comprises the following components in percentage by mass: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2. And (4) raising the temperature of the furnace to 750 ℃, preserving the temperature and standing for 10 minutes to promote the settlement of impurities, thereby obtaining the magnesium alloy melt.
(5) And cooling the magnesium alloy melt to 740 ℃, skimming surface scum, pouring the melt into a metal mold preheated to 250 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant cast Mg-Y alloy.
(6) Sequentially carrying out secondary solution treatment on the obtained as-cast alloy, putting the cast alloy into a solution furnace, heating to 200 ℃ at the speed of 5 ℃/min, and introducing SF containing 0.2% of volume fraction6And CO2The mixed protective gas is continuously heated to the first-stage solid solution temperature of 490 ℃ at the speed of 5 ℃/min, the temperature is kept for 36h, then the temperature is slowly heated to the second-stage solid solution temperature of 545 ℃ at the speed of 10 ℃/h, and the temperature is kept for 1h and then the steel plate is quickly transferred to a quenching device for water-cooling quenching.
(7) And (3) carrying out artificial aging treatment on the cast alloy after the solution treatment, putting the quenched alloy into an aging furnace, heating to the artificial aging treatment temperature of 215 ℃ at the speed of 5 ℃/min, keeping the temperature for 12h, discharging from the furnace, and carrying out air cooling to room temperature to obtain the high-strength high-toughness heat-resistant Mg-Y alloy suitable for gravity casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. The room-temperature tensile strength of the high-strength and high-toughness heat-resistant Mg-Gd alloy obtained by the embodiment is 296MPa, and the elongation is 18 percent; the tensile strength at high temperature of 200 ℃ is 213MPa, and the elongation is 23%.
The above embodiments do not limit the present invention in any way, and all technical solutions obtained by means of equivalent substitution or equivalent transformation fall within the protection scope of the present invention.
Claims (8)
1. The high-strength high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting is characterized by comprising the following elements in percentage by mass: 4.0-10.0% of Gd, 2.0-6.0% of Zn, 0.5-1.2% of Al, 0.1-0.3% of Mn, 0.01-0.08% of M, and the balance of Mg and other inevitable impurities; wherein M is one or two of Ti and B; the mass ratio of Zn to Gd is 0.2-0.7; the mass ratio of (Zn + Al)/Gd is 0.3-0.8;
the preparation method of the high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting is characterized by comprising the following steps:
(1) calculating the use amounts of an industrial pure magnesium ingot, an industrial pure zinc ingot, an industrial pure aluminum ingot, an Mg-Gd intermediate alloy, an Mg-Mn intermediate alloy, an Al-Ti-B intermediate alloy and an Al-B intermediate alloy according to the components of the Mg-Gd alloy and the stoichiometric ratio; removing oxide layers of an industrial pure magnesium ingot, an industrial pure zinc ingot, an industrial pure aluminum ingot, a Mg-Gd intermediate alloy and a Mg-Mn intermediate alloy, drying and preheating to 200 ℃;
(2) melting an industrial pure magnesium ingot accounting for 25% of the height of the crucible into a molten pool, introducing protective gas, and adding the rest magnesium ingot;
(3) after the magnesium ingot is completely melted, heating to 700 ℃, adding industrial pure zinc and Mg-Gd and Mg-Mn intermediate alloy for multiple times, keeping the temperature constant at 700 ℃, stirring until the industrial pure zinc and the Mg-Gd and Mg-Mn intermediate alloy are completely melted, and keeping the temperature for 30 min;
(4) heating to 730 ℃ after 40-60 min before gravity casting, adding a refining agent for refining after all the industrial pure aluminum ingot, the Al-Ti intermediate alloy, the Al-Ti-B intermediate alloy and the Al-B intermediate alloy which are sequentially added are melted, heating the furnace to 750 ℃, keeping the temperature and standing for 10-20 min, and promoting the settlement of impurities to obtain a magnesium alloy melt;
(5) cooling the magnesium alloy melt to 720-740 ℃ for deslagging, pouring the melt into a sand mold casting mold or a 180-250 ℃ metal mold preheated to 25-150 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant cast Mg-Gd alloy;
(6) sequentially carrying out secondary solution treatment and artificial aging treatment on the obtained as-cast alloy to obtain the required high-strength high-toughness heat-resistant cast Mg-Gd alloy;
the secondary solution treatment process parameters are as follows: the primary solid solution temperature is 480-490 ℃, and the heat preservation time is 36-48 h; the temperature of the second-stage solid solution is 535-545 ℃, and the heat preservation time is 1-2 h;
the technological parameters of the artificial aging treatment are as follows: the aging temperature is 185-215 ℃, and the heat preservation time is 12-36 h.
2. The high toughness, heat resistant Mg-Gd alloy suitable for gravity casting according to claim 1, wherein: the Mg-Gd intermediate alloy is MgGd25 or MgGd30, the Mg-Mn intermediate alloy is MgMn10, the Al-Ti-B intermediate alloy is AlTi5B1, the Al-B intermediate alloy is AlB3 or AlB8, and the Al-Ti intermediate alloy is AlTi5 or AlTi 10.
3. The high toughness, heat resistant Mg-Gd alloy suitable for gravity casting according to claim 1, wherein: the refining agent comprises the following components in percentage by mass: 55% KCl and 25% CaCl2、5% CaF2、15% BaCl2。
4. The high-strength high-toughness heat-resistant Mg-Gd alloy suitable for gravity casting according to claim 1, wherein the addition amount of the refining agent is 1.0-3.5% of the total weight of the raw materials.
5. The high toughness, heat resistant Mg-Gd alloy suitable for gravity casting according to claim 1, wherein: the refining temperature when the refining agent is added for refining is 720-730 ℃, and the stirring time of the refining treatment is 10-15 min.
6. The high toughness, heat resistant Mg-Gd alloy suitable for gravity casting according to claim 1, wherein: the secondary solution treatment process comprises the following steps: putting the as-cast alloy into a solid solution furnace, heating to 200 ℃ at the speed of 5 ℃/min, introducing protective gas, continuously heating to 480-490 ℃ at the speed of 5 ℃/min for the first-stage solid solution temperature, and keeping the temperature for 36-48 h; and then slowly raising the temperature to 535-545 ℃ of the second-stage solution treatment at a speed of 10 ℃/h, preserving the temperature for 1-2 h, and then quickly transferring to a quenching device for water-cooling quenching.
7. The high toughness, heat resistant Mg-Gd alloy suitable for gravity casting of claim 1 or 6, wherein: the protective gas is argon or SF with the volume fraction of 0.2 percent6And CO2The mixed gas of (1).
8. The high toughness, heat resistant Mg-Gd alloy suitable for gravity casting according to claim 1, wherein: the artificial aging treatment process comprises the following steps: and (3) putting the quenched alloy into an aging furnace, heating to 185-215 ℃ at the temperature of artificial aging treatment at the speed of 5 ℃/min, keeping the temperature for 12-36 h, discharging from the furnace, and air cooling to room temperature.
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