CN109881066B - High-strength-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting and preparation method thereof - Google Patents
High-strength-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting and a preparation method thereof, wherein the alloy comprises the following chemical components in percentage by mass: 4.0-8.0% of Gd, 1.2-4.8% 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 at least one element of Ti and B. After the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting is subjected to low-pressure casting, secondary solution treatment and artificial aging heat treatment, the room-temperature tensile strength is more than 280MPa, and the elongation is more than 16%; the tensile strength at high temperature of 200 ℃ is more than 190MPa, the elongation is more than 16%, and the high-end requirement of aerospace, military industry, automobile and other industries on light weight development is met.
Description
Technical Field
The invention belongs to the field of industrial magnesium alloy and manufacturing thereof, and particularly relates to a high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting and a preparation method thereof.
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. The low-pressure casting is a casting method in which dry compressed air or inert gas is introduced into a sealed crucible, liquid alloy is smoothly pressed into a metal mold or sand mold cavity from bottom to top through a pouring channel along a riser tube by means of pressure acting on the metal liquid level, and the liquid alloy is solidified under the action of the pressure to obtain a casting. Compared with the alloy die casting process which is generally adopted at present, the low-pressure casting is a method for producing large castings with complex shapes and high density.
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 alloy is improved by adding alloy elements to improve the characteristics (crystal structure, form and thermal stability) of precipitated phases, but the normal-temperature and high-temperature mechanical properties of the Mg-Al alloy still can not reach the level of cast aluminum alloy, so that the application development of the Mg-Al alloy is severely limited.
Zn is an important alloy element in magnesium alloy, the maximum solid solubility in Mg is as high as 6.2 wt%, and the Zn can play a role in solid solution strengthening and aging strengthening. 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, but the elongation after fracture thereof decreases, and the castability, process plasticity and weldability deteriorate, particularly the tendency to hot crack is extremely severe due to 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 to 3803), and thus the alloy cannot be used for die casting.
The beneficial effect of rare earth elements on the strength performance of magnesium alloy and the grain refinement effect of zirconium on the magnesium alloy are discovered in the thirties of the twentieth century, and EK31 in Mg-RE-Zr series (EK30, EK31 and EK41) becomes the earliest successfully developed high-temperature cast magnesium alloy in Mg-Zr series. 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. Chinese invention patent 201410564817.1 (high thermal conductivity die-casting Mg-Y-Zr series multi-element magnesium alloy and preparation method thereof) reports a high thermal conductivity die-casting corrosion-resistant magnesium alloy, the component content of the magnesium alloy is that the content of Y is 1.5-4 wt.%, the content of Mn is 0.001-1 wt.%, the content of Zn is 0.001-2 wt.%, the content of Ca is 0.001-1 wt.%, the content of Zr is 0.4-0.8 wt.%, and the rest is Mg; the addition of Ca element in the alloy sharply increases the solidification temperature range of the alloy, increases the hot cracking tendency, and the tensile strength of the die-casting ingot is only 140-190 MPa.
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; w-phase and long period stacking ordered structure LPS are easily formed when the mass ratio of Zn/Gd in the alloy is between 0.42 and 0.62 (the atomic ratio is between 1.0 and 1.5)O phase (Mg)12ZnGd); LPSO phase is easily formed when the Zn/Gd mass ratio in the alloy is less than or equal to 0.42 (atomic ratio is less than or equal to 1.0) (Materials Science and Engineering: A695 (2017) 135-143). The room temperature strength and the high temperature performance of the magnesium alloy can be further improved by multiple Mg-Gd-Zn reinforcing phases, the multi-nano-phase composite reinforced wrought magnesium alloy reported in Chinese patent 201610056992.9 (a multi-nano-phase composite reinforced magnesium alloy and a preparation method thereof) comprises the components of Mg-Gd-Zn alloy, wherein the Gd content is 10-25 wt%, the Zn content is 1-5 wt%, and the balance is Mg, and the difference between the mass percentage content of Gd and the mass percentage content of Zn is not less 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. Chinese invention patent 201310105667.3 (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 as follows: 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. No Al and Mn, etc. to refine the grains, althoughThe alloy can be refined by Ag and Zr, but the crystal grains are coarse under the conventional solidification condition, the Mg-Gd-Zn precipitated phase is often in a coarse net structure, the mechanical property of the alloy is deteriorated, the size of the precipitated phase must be adjusted by thermal deformation or thermal treatment solid solution and aging so as to play a role of a strengthening phase, and the existing Mg-Gd-Zn alloy is generally limited to gravity casting and hot working processes, and a complex heat treatment process is required, so that the Mg-Gd-Zn alloy has no report for die casting application.
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. There are still many 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 high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure 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, toughness and heat resistance, and the alloy has the room-temperature tensile strength of more than 280MPa and the elongation of more than 16 percent after the alloy is subjected to low-pressure casting heat treatment; the tensile strength at high temperature of 200 ℃ is more than 190MPa, and the elongation is more than 16%.
In order to solve the technical problems, the invention adopts the following technical scheme:
in a first aspect, the invention relates to a high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting, which comprises the following elements in percentage by mass: 4.0-8.0% of Gd, 1.2-4.8% 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 at least one element of Ti and B.
Preferably, the mass ratio of Zn to Gd is 0.2-0.6: 1.
Preferably, the mass ratio of (Zn + Al)/Gd is 0.3-0.7: 1.
Preferably, when M is a combined element of Ti and B, the mass fraction of Ti is 0.01-0.08%, and the mass fraction of B is 0.01-0.08%, based on the total weight of the Mg-Gd alloy.
Compared with the prior art, one of the innovative ideas of the high-strength-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting provided by the invention is as follows: the alloy design adopts cheap Zn element and rare earth Gd element to form a ternary Mg-Gd-Zn strengthening phase with matrix Mg element. Particularly, in the mass ratio of Zn to Gd of 0.2-0.6, 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) The high-melting-point phases are adopted, and compared with binary Mg-Gd strengthening, the ternary strengthening phase has better high-temperature stability in a magnesium matrix, avoids performance reduction caused by dissolution of a precipitation strengthening phase, effectively enhances the room-temperature mechanical property and high-temperature property of high-strength-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting, and particularly doubles the room-temperature yield strength; on the other hand, the invention overcomes the defect that the traditional Mg-Zn-Gd alloy is easy to generate heat crack due to overlarge solidification interval caused by overhigh Zn content, and can not ensure the toughness and the die-casting performance of the alloy.
The invention provides the second innovative idea of the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting, which is as follows: the precipitated phases of Mg-Gd-Zn alloy are often coarse and coarse in network structure under the conventional solidification condition, the mechanical properties of the Mg-Gd-Zn alloy are deteriorated, and the Mg-Gd-Zn alloy is required to be subjected to heat deformation or heat deformationThe heat treatment solid solution and aging adjust the size of the precipitated phase to play the role of the strengthening phase. 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 crystal grains are rapidly coarsened when the temperature is kept at 550 ℃, so that the high-temperature performance is greatly reduced. In the alloy, 0.5-1.2% of Al of low melt is added 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.
The invention provides the third innovative idea of the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting, which is as follows: the mass ratio of Zn to Gd is limited to be 0.2-0.6 and the mass ratio of (Zn + Al)/Gd is limited to be 0.3-0.7, so that the solidification interval of the alloy is ensured to be small, the hot cracking tendency of the Mg-Gd-Zn alloy in the die casting process is overcome, and the die casting process performance of the alloy is improved.
In a second aspect, the invention relates to a preparation method of high-strength, high-toughness and heat-resistant Mg-Gd alloy suitable for low-pressure casting, which comprises the following steps:
s1, removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots, Mg-Gd intermediate alloy and Mg-Mn intermediate alloy, and drying and preheating to 200 ℃ of 180-; calculating the dosage of the required raw materials according to the components and the stoichiometric ratio of the Mg-Gd alloy;
s2, melting the industrial pure magnesium ingot which accounts for 20-25% of the height of the crucible at 675-685 ℃ under the condition of introducing protective gas;
s3, after the magnesium ingot is completely melted, heating to 700-710 ℃, adding the pure zinc, the Mg-Gd intermediate alloy and the Mg-Mn intermediate alloy for 2-4 times, keeping the temperature constant at 700-710 ℃, stirring until the pure zinc, the Mg-Gd intermediate alloy and the Mg-Mn intermediate alloy are melted, and keeping the temperature for 30-40 minutes;
s4, heating to 740 ℃ before low-pressure casting for 40-60 minutes, adding the aluminum ingot and the Al-M intermediate alloy, melting, refining, heating to 750-760 ℃, preserving heat and standing for 10-20 minutes to obtain a magnesium alloy melt;
s5, cooling the magnesium alloy melt to 720-740 ℃, skimming surface scum, and preheating a sand mold casting temperature to 25-150 ℃ or a metal mold casting temperature to 180-250 ℃; in the low-pressure casting process, the pressure in the liquid lifting stage is uniformly increased to 0.02-0.05 MPa, the pressurization time is controlled to 5-8 s, the pressure in the mold filling stage is uniformly increased to 0.07-0.08MPa, the metal liquid is filled in a casting mold cavity under the pressure, the pressure in the pressurization stage is uniformly increased to 0.1-0.15MPa, the pressurization time is controlled to 10-15 s, the pressure maintaining time in the pressure maintaining stage is controlled to 200-300 s, and the Mg-Gd casting alloy low-pressure casting is obtained after pressure relief;
s6, sequentially carrying out secondary solution treatment and artificial aging treatment on the Mg-Gd cast alloy low-pressure casting to obtain the high-strength high-toughness heat-resistant Mg-Gd alloy.
Preferably, the Mg-Gd intermediate alloy is MgGd25 or MgGd30, the Mg-Mn intermediate alloy is MgMn10, and the Al-M intermediate alloy is one or more of AlTiB intermediate alloy, AlB intermediate alloy and AlTi intermediate alloy. More preferably, the Al-M intermediate alloy is one or more of AlTi5B1, AlB3, AlB8, AlTi5 and AlTi 10.
Preferably, the refining agent used for refining comprises the following components in percentage by weight: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2。
Preferably, the dosage of the refining agent added for refining is 1.0-3.5% of the total weight of the raw materials.
Preferably, the refining temperature is 720-730 ℃, and the stirring time of the refining treatment is 10-15 min.
Preferably, the process parameters of the secondary solution treatment are as follows: in the first stage, the temperature is 480-490 ℃, and the time is 36-48 h; and in the second stage, the temperature is 535-545 ℃ and the time is 1-2 h.
Preferably, the secondary solution treatment of the high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting comprises the following steps: putting the cast alloy into a solid solution furnace, heating to 200-plus-250 ℃ at the speed of 5-8 ℃/min, introducing protective gas, continuing heating to 480-490 ℃ at the speed of 5-8 ℃/min until the first-stage solid solution temperature is 480-490 ℃, starting timing when the solid solution temperature is reached, keeping the temperature for 36-48 h, then slowly heating to the second-stage solid solution treatment at the speed of 6-10 ℃/h, keeping the temperature at 535-545 ℃, keeping the temperature for 1-2 h, and then quickly transferring the sample to a quenching device for water cooling quenching.
Preferably, the process parameters of the artificial aging treatment are as follows: the temperature is 185-215 ℃, and the time is 12-36 h.
Preferably, the artificial aging treatment of the high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting is carried out, the artificial aging treatment is carried out on the cast alloy, the furnace temperature is kept at 185-215 ℃, the timing is started when the aging temperature is reached, the temperature is kept for 12-36 h, and the high-strength and high-toughness heat-resistant Mg-Gd alloy is discharged from the furnace and then cooled to the room temperature in air.
Preferably, the protective gas is argon; or SF6And CO2Of mixed gas of (1), wherein SF6Is 0.2% by volume.
The preparation method of the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting, provided by the invention, has the advantages that: (1) rare earth element Mg-Gd intermediate alloy which is easy to burn and lose is added at 720 ℃, and melting is carried out at low temperature, 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 and the like are eliminated; the first-stage temperature 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 ℃ and keeping the temperature for 12h toAnd aging treatment is carried out for 36h, and long-time aging is carried out to finally precipitate a nano-grade and finely dispersed strengthening phase in the alloy crystal, so that the alloy has excellent room temperature and high temperature performances. The heat treatment of the invention has the advantages of stable alloy components, no obvious growth of crystal grains, obvious improvement of alloy performance, simple method, safety, reliability and convenient operation.
Compared with the prior art, the invention has the following beneficial effects:
after low-pressure casting, secondary solution treatment and artificial aging heat treatment are carried out on the high-strength high-toughness heat-resistant cast Mg-Gd alloy, the room-temperature tensile strength is more than 280MPa, and the elongation is more than 16%; the tensile strength at high temperature of 200 ℃ is more than 190MPa, the elongation is more than 16%, and the comprehensive performance reaches the performance of A380 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
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is an as-cast metallographic structure chart of the die-cast magnesium alloy prepared in example 4.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
Example 1
The high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting comprises the following components in percentage by weight: according to the theoretical mixture ratio, 4.0 percent of Gd, 1.2 percent of Zn, 1.2 percent of Al, 0.3 percent of Mn, 0.05 percent of Ti, 0.03 percent of B, and the balance of Mg and other inevitable impurities.
The preparation method comprises the following steps: (1) calculating the dosage of the required raw materials according to the Mg-Gd alloy components 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 ℃; calculating the consumption of the required raw materials according to the components and the stoichiometric ratio of the alloy; (2) melting an 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 and intermediate alloy of MgGd30 and MgMn10 for 2 times, keeping the temperature constant at 700 ℃, stirring until the intermediate alloy is completely melted, and keeping the temperature for 30 minutes; (4) heating to 730 ℃ 40 minutes before low-pressure casting, sequentially adding the industrial pure aluminum ingot, the AlTi5B1 intermediate alloy and the AlB3 intermediate alloy to wait for complete melting, adding a refining agent accounting for 1 percent of the weight of the raw materials to refine at 730 ℃, stirring for 10min during refining treatment, wherein the refining agent comprises the following components in percentage by mass: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2. Raising the temperature of the furnace to 750 ℃, preserving the heat and standing for 10 minutes to promote the settlement of impurities, and obtaining a magnesium alloy melt; (5) cooling the magnesium alloy melt to 720 ℃, skimming surface scum, preheating the temperature of a sand mold to 20 ℃, controlling and pressurizing in a grading way in a low-pressure casting process through a proportional valve, and comprising the following steps of: liquid lifting, mold filling, pressure increasing, pressure maintaining and pressure relief. Wherein the pressure in the liquid lifting stage is uniformly increased to 0.02MPa, and the pressurizing time is controlled to be 5 s; the pressure in the mold filling stage is uniformly increased to 0.08MPa, and the metal liquid is filled in the mold cavity of the casting mold under the pressure; the pressure in the pressurization stage is uniformly increased to 0.1MPa, and the pressurization time is controlled to be 10 s; the dwell time of the dwell phase was controlled at 220 s. And releasing the pressure to obtain the high-strength high-toughness heat-resistant cast Mg-Gd alloy low-pressure casting. (6) Sequentially carrying out secondary solution treatment on the low-pressure casting, putting the casting alloy into a solution furnace, heating to 200 ℃ at the speed of 5 ℃/min, introducing protective gas, continuously heating to 480 ℃ of the primary solution temperature at the speed of 5 ℃/min, starting timing when the temperature reaches the solution temperature, keeping the temperature for 36h, then slowly heating to the secondary solution treatment at the speed of 10 ℃/h, keeping the temperature at 535 ℃, keeping the temperature for 1h, and then carrying out the secondary solution treatment on the low-pressure castingAnd then quickly transferring the sample to a quenching device for water-cooling quenching. (7) And (3) carrying out artificial aging treatment on the cast alloy after the solution treatment, keeping the furnace temperature at 185 ℃, starting timing when the aging temperature is reached, keeping the temperature for 12h, and carrying out air cooling to room temperature after discharging to obtain the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 280MPa, and the elongation is 21 percent; the tensile strength at high temperature of 200 ℃ is 190MPa, and the elongation is 28%.
Example 2
The high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting comprises the following components in percentage by weight: according to theoretical proportion, 8.0 percent of Gd, 4.8 percent of Zn, 0.8 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) calculating the dosage of the required raw materials according to the Mg-Gd alloy components 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 180 ℃; calculating the consumption of the required raw materials according to the components and the stoichiometric ratio of the alloy; (2) melting industrial pure magnesium ingot 20% of crucible height at 685 deg.C to form molten pool, introducing SF containing 0.2% volume fraction6And CO2Adding the rest magnesium ingot into the mixed gas; (3) after the magnesium ingot is completely melted, heating to 710 ℃, adding industrial pure zinc, MgGd30 and MgMn10 intermediate alloy for 4 times, keeping the temperature constant at 710 ℃, stirring until the industrial pure zinc, the MgGd30 and the MgMn10 intermediate alloy are completely melted, and keeping the temperature for 40 minutes; (4) 60 minutes before low-pressure casting, heating to 730 ℃, adding refining agents with the weight of 3.5 percent of that of the raw materials for refining after the industrial pure aluminum ingot and the AlTi10 intermediate alloy are sequentially added for waiting for complete melting, wherein the refining temperature is 730 ℃, the stirring time of the refining treatment is 10 minutes, and the refining agents comprise the following components in percentage by mass: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2. Raising the temperature of the furnace to 760 ℃, preserving the heat, standing for 10 minutes and promoting the settlement of impurities to obtain a magnesium alloy melt; (5) cooling the magnesium alloy melt to 720 ℃, skimming surface scum, preheating the temperature of a sand mold to 150 ℃, controlling and pressurizing in a grading way in a low-pressure casting process through a proportional valve, and comprising the following steps of: liquid lifting, mold filling, pressure increasing, pressure maintaining and pressure relief. Wherein the pressure in the liquid lifting stage is uniformly increased to 0.05MPa, and the pressurizing time is controlled to be 8 s; the pressure in the mold filling stage is uniformly increased to 0.07MPa, and the metal liquid is filled in the mold cavity of the casting mold under the pressure; the pressure in the pressurization stage is uniformly increased to 0.15MPa, and the pressurization time is controlled to be 15 s; the dwell time of the dwell phase was controlled at 300 s. And releasing the pressure to obtain the high-strength high-toughness heat-resistant cast Mg-Gd alloy low-pressure casting. (6) And sequentially carrying out secondary solution treatment on the low-pressure castings, putting the cast alloy into a solution furnace, heating to 250 ℃ at 8 ℃/min, introducing protective gas, continuously heating to 490 ℃ of the primary solution temperature at 8 ℃/min, starting timing when the temperature reaches the solution temperature, keeping the temperature for 48h, slowly heating to the secondary solution treatment at 6 ℃/h, keeping the temperature at 545 ℃, keeping the temperature for 2h, and then quickly transferring the samples to a quenching device for water-cooling quenching. (7) And (3) carrying out artificial aging treatment on the cast alloy after the solution treatment, keeping the furnace temperature at 215 ℃, starting timing when the aging temperature is reached, keeping the temperature for 36h, and carrying out air cooling to room temperature after discharging to obtain the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 309MPa, and the elongation is 16%; the tensile strength at high temperature of 200 ℃ is 218MPa, and the elongation is 16%.
Example 3
The high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting comprises the following components in percentage by weight: according to theoretical proportion, 7.0 percent of Gd, 3.0 percent of Zn, 0.5 percent of Al, 0.2 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) calculating the dosage of the required raw materials according to the Mg-Gd alloy components 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 ℃; calculating the consumption of the required raw materials according to the components and the stoichiometric ratio of the alloy; (2) melting an industrial pure magnesium ingot which accounts for 20 percent of the height of the crucible into a molten pool at 675 ℃, 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 and intermediate alloy of MgGd30 and MgMn10 for 3 times, keeping the temperature constant at 700 ℃, stirring until the intermediate alloy is completely melted, and keeping the temperature for 30 minutes; (4) heating to 730 ℃ 40 minutes before low-pressure casting, sequentially adding the industrial pure aluminum ingot, the AlTi5 intermediate alloy and the AlB3 intermediate alloy to wait for complete melting, adding a refining agent accounting for 2.5 percent of the weight of the raw materials to refine at 720 ℃, stirring for 15min, wherein the refining agent comprises the following components in percentage by mass: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2. Raising the temperature of the furnace to 750 ℃, preserving the heat and standing for 10 minutes to promote the settlement of impurities, and obtaining a magnesium alloy melt; (5) cooling the magnesium alloy melt to 730 ℃, skimming surface scum, controlling and pressurizing in a low-pressure casting process by a proportional valve in a grading manner, wherein the temperature of the preheated metal mold is 180 ℃, and the method comprises the following steps: liquid lifting, mold filling, pressure increasing, pressure maintaining and pressure relief. Wherein the pressure in the liquid lifting stage is uniformly increased to 0.03MPa, and the pressurizing time is controlled to be 5 s; the pressure in the mold filling stage is uniformly increased to 0.08MPa, and the metal liquid is filled in the mold cavity of the casting mold under the pressure; the pressure in the pressurization stage is uniformly increased to 0.15MPa, and the pressurization time is controlled to be 12 s; the dwell time of the dwell phase was controlled at 260 s. And releasing the pressure to obtain the high-strength high-toughness heat-resistant cast Mg-Gd alloy low-pressure casting. (6) Sequentially carrying out secondary solution treatment on the low-pressure casting, putting the casting alloy into a solution furnace, heating to 250 ℃ at the speed of 5 ℃/min, introducing protective gas, continuously heating to 485 ℃ at the speed of 5 ℃/min until the first-stage solution temperature is reached, starting timing when the first-stage solution temperature is reached, keeping the temperature for 42h, and then carrying out heat preservation on the cast alloySlowly heating to the second stage solution treatment at the speed of 10 ℃/h, keeping the temperature at 540 ℃, preserving the heat for 1.5h, and then quickly transferring the sample to a quenching device for water-cooling quenching. (7) And (3) carrying out artificial aging treatment on the cast alloy after the solution treatment, keeping the furnace temperature at 200 ℃, starting timing when the aging temperature is reached, keeping the temperature for 24 hours, and carrying out air cooling to room temperature after discharging to obtain the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 302MPa, and the elongation is 17%; the tensile strength at high temperature of 200 ℃ is 215MPa, and the elongation is 21%.
Example 4
The high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting comprises the following components in percentage by weight: according to theoretical proportion, 5.0 percent of Gd, 2.5 percent of Zn, 1.0 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) calculating the dosage of the required raw materials according to the Mg-Gd alloy components 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 ℃; calculating the consumption of the required raw materials according to the components and the stoichiometric ratio of the alloy; (2) melting industrial pure magnesium ingot 22% of the height of the crucible into a molten pool at 680 ℃, and introducing SF containing 0.2% volume fraction6And CO2Adding the rest magnesium ingot into the mixed protective gas; (3) after the magnesium ingot is completely melted, heating to 705 ℃, adding industrial pure zinc and MgGd30 and MgMn10 intermediate alloy for 4 times, keeping the temperature constant at 705 ℃, stirring until the industrial pure zinc and the MgGd30 and the MgMn10 intermediate alloy are completely melted, and keeping the temperature for 30 minutes; (4) heating to 730 ℃ 50 minutes before low-pressure casting, sequentially adding a refining agent accounting for 3.0 percent of the weight of the raw materials for refining when the industrial pure aluminum ingot and the AlB8 intermediate alloy are completely melted, wherein the refining temperature is 720 ℃, and the refining position isThe stirring time is 15min, and the refining agent comprises the following components in percentage by mass: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2. Raising the temperature of the furnace to 755 ℃, preserving the temperature and standing for 10 minutes to promote the settlement of inclusions to obtain a magnesium alloy melt; (5) cooling the magnesium alloy melt to 740 ℃, skimming surface scum, preheating the temperature of a metal mold to 250 ℃, controlling and pressurizing in a grading way through a proportional valve in the low-pressure casting process, and comprising the following steps: liquid lifting, mold filling, pressure increasing, pressure maintaining and pressure relief. Wherein the pressure in the liquid lifting stage is uniformly increased to 0.04MPa, and the pressurizing time is controlled to be 8 s; the pressure in the mold filling stage is uniformly increased to 0.07MPa, and the metal liquid is filled in the mold cavity of the casting mold under the pressure; the pressure in the pressurization stage is uniformly increased to 0.1MPa, and the pressurization time is controlled to be 10 s; the dwell time of the dwell phase was controlled at 220 s. And releasing the pressure to obtain the high-strength high-toughness heat-resistant cast Mg-Gd alloy low-pressure casting. (6) And sequentially carrying out secondary solution treatment on the low-pressure casting, putting the casting alloy into a solution furnace, heating to 220 ℃ at 6 ℃/min, introducing protective gas, continuously heating to 480 ℃ of the primary solution temperature at 6 ℃/min, starting timing when the temperature reaches the solution temperature, keeping the temperature for 48h, slowly heating to the secondary solution treatment at 8 ℃/h, keeping the temperature at 535 ℃, keeping the temperature for 2h, and then quickly transferring the sample to a quenching device for water-cooling quenching. (7) And (3) carrying out artificial aging treatment on the cast alloy after the solution treatment, keeping the furnace temperature at 185 ℃, starting timing when the aging temperature is reached, keeping the temperature for 36h, and carrying out air cooling to room temperature after discharging to obtain the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting.
The cast metallographic structure of the die-cast magnesium alloy prepared in the embodiment is shown in fig. 1. Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 295MPa, and the elongation is 19 percent; the tensile strength at high temperature of 200 ℃ is 208MPa, and the elongation is 19%.
Example 5
The high-strength and high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting comprises the following components in percentage by weight: according to the theoretical mixture ratio, 6.0 percent of Gd, 1.2 percent of Zn, 0.6 percent of Al, 0.3 percent of Mn, 0.04 percent of Ti, 0.02 percent of B, and the balance of Mg and other inevitable impurities.
The preparation method comprises the following steps: (1) calculating the dosage of the required raw materials according to the Mg-Gd alloy components 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 ℃; calculating the consumption of the required raw materials according to the components and the stoichiometric ratio of the alloy; (2) melting an 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 710 ℃, adding industrial pure zinc and intermediate alloy of MgGd30 and MgMn10 for 4 times, keeping the temperature constant at 710 ℃, stirring until the intermediate alloy is completely melted, and keeping the temperature for 30 minutes; (4) heating to 730 ℃ 50 minutes before low-pressure casting, sequentially adding the industrial pure aluminum ingot, the AlTi10 intermediate alloy and the AlB8 intermediate alloy to wait for complete melting, adding a refining agent accounting for 2.0 percent of the weight of the raw materials to refine at 730 ℃, stirring for 10min during refining treatment, wherein the refining agent comprises the following components in percentage by mass: 55% KCl and 25% CaCl2、5％CaF2、15％BaCl2. Raising the temperature of the furnace to 760 ℃, preserving the heat, standing for 10 minutes and promoting the settlement of impurities to obtain a magnesium alloy melt; (5) cooling the magnesium alloy melt to 720 ℃, skimming surface scum, preheating the temperature of a sand mold to 100 ℃, controlling and pressurizing in a grading way in a low-pressure casting process through a proportional valve, and comprising the following steps of: liquid lifting, mold filling, pressure increasing, pressure maintaining and pressure relief. Wherein the pressure in the liquid lifting stage is uniformly increased to 0.05MPa, and the pressurizing time is controlled to be 5 s; the pressure in the mold filling stage is uniformly increased to 0.08MPa, and the metal liquid is filled in the mold cavity of the casting mold under the pressure; the pressure in the pressurization stage is uniformly increased to 0.1MPa, and the pressurization time is controlled to be 15 s; the dwell time of the dwell phase was controlled at 300 s. And releasing the pressure to obtain the high-strength high-toughness heat-resistant cast Mg-Gd alloy low-pressure casting. (6) The low-pressure casting is sequentially subjected to secondary solution treatment, casting alloy is put into a solution furnace at the temperature of 5 DEG CHeating to 200 ℃ in min, introducing protective gas, continuously heating to 490 ℃ at 5 ℃/min until the first-stage solid solution temperature is reached, timing when the solid solution temperature is reached, keeping the temperature for 36h, slowly heating to the second-stage solid solution treatment at 10 ℃/h, keeping the temperature at 545 ℃ for 1h, and quickly transferring the sample to a quenching device for water-cooling quenching. (7) And (3) carrying out artificial aging treatment on the cast alloy after the solution treatment, keeping the furnace temperature at 215 ℃, starting timing when the aging temperature is reached, keeping the temperature for 12h, and carrying out air cooling to room temperature after discharging to obtain the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant Mg-Gd alloy is 290MPa, and the elongation is 18 percent; the tensile strength at high temperature of 200 ℃ is 202MPa, and the elongation is 24%.
Comparative example 1
The high-strength and high-toughness heat-resistant Mg-Gd alloy comprises the following components in percentage by weight: according to the theoretical mixture ratio, 0.25 percent of Gd, 3.0 percent of Zn, 0.5 percent of Al, 0.2 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 is the same as in example 3.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 142MPa, and the elongation is 3.5%; the tensile strength at high temperature of 200 ℃ is 110MPa, and the elongation is 13%.
Comparative example 2
The high-strength and high-toughness heat-resistant Mg-Gd alloy comprises the following components in percentage by weight: according to the theoretical mixture ratio, 4.0 percent of Gd, 1.2 percent of Zn, 1.5 percent of Al, 0.3 percent of Mn, 0.05 percent of Ti, 0.03 percent of B, and the balance of Mg and other inevitable impurities.
The preparation method is the same as that of example 1.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 270MPa, and the elongation is 16%; the tensile strength at high temperature of 200 ℃ is 175MPa, and the elongation is 21%.
Comparative example 3
The high-strength and high-toughness heat-resistant Mg-Gd alloy comprises the following components in percentage by weight: according to the theoretical mixture ratio, 6.0 percent of Gd, 0.8 percent of Zn, 0.6 percent of Al, 0.3 percent of Mn, 0.04 percent of Ti, 0.02 percent of B, and the balance of Mg and other inevitable impurities.
The preparation method is the same as in example 5.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 277MPa, and the elongation is 14 percent; the tensile strength at high temperature of 200 ℃ is 176MPa, and the elongation is 19%.
Comparative example 4
The high-strength and high-toughness heat-resistant Mg-Gd alloy comprises the following components in percentage by weight: according to theoretical proportion, 8.0 percent of Gd, 5.2 percent of Zn, 0.8 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 is the same as that of example 2.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 241MPa, and the elongation is8.3 percent; the tensile strength at high temperature of 200 ℃ is 149MPa, and the elongation is 12%.
Comparative example 5
The high-strength and high-toughness heat-resistant Mg-Gd alloy comprises the following components in percentage by weight: according to theoretical proportion, 7.0 percent of Gd, 3.0 percent of Zn, 0.5 percent of Al, 0.5 percent of Zr, 0.2 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 is the same as that of example 3; in the step (4), the MgZr30 intermediate alloy is added into the magnesium alloy melt after the industrial pure aluminum ingot, the AlTi5 intermediate alloy and the AlB3 intermediate alloy are added, and the magnesium alloy melt is completely melted.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 282MPa, and the elongation is 13%; the tensile strength at high temperature of 200 ℃ is 185MPa, and the elongation is 17.5%.
Comparative example 6
The high-strength and high-toughness heat-resistant Mg-Gd alloy comprises the following components in percentage by weight: according to the theoretical mixture ratio, 6.0 percent of Gd, 1.2 percent of Zn, 0.3 percent of Al, 0.3 percent of Mn, 0.04 percent of Ti, 0.02 percent of B, and the balance of Mg and other inevitable impurities.
The preparation method is the same as in example 5.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 275MPa, and the elongation is 13 percent; the tensile strength at high temperature of 200 ℃ is 172MPa, and the elongation is 16.5%.
Comparative example 7
The high-strength and high-toughness heat-resistant Mg-Gd alloy comprises the following components in percentage by weight: according to theoretical proportion, 3.5 percent of Gd, 2.5 percent of Zn, 1.0 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 is the same as in example 4.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd alloy; b.200 ℃ and 200 hours of heat exposure treatment, and then carrying out a high-temperature tensile property test at 200 ℃, wherein the strain rate of the tensile test is 10-5s-1Static stretching of (2). In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 248MPa, and the elongation is 8.5%; the tensile strength at high temperature of 200 ℃ is 135MPa, and the elongation is 12%.
The above description is a detailed description of specific embodiments of the present invention. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.
Claims (5)
1. The preparation method of the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting is characterized in that the Mg-Gd alloy consists of the following elements in percentage by mass: 4.0-8.0% of Gd, 1.2-4.8% 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 at least one element of Ti and B; the mass ratio of Zn to Gd is 0.2-0.6: 1; the mass ratio of the total mass of Zn and Al to Gd is 0.3-0.7: 1; the method comprises the following steps:
s1, removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots, Mg-Gd intermediate alloy and Mg-Mn intermediate alloy, and drying and preheating to 200 ℃ of 180-; calculating the dosage of the required raw materials according to the components and the stoichiometric ratio of the Mg-Gd alloy;
s2, melting the industrial pure magnesium ingot which accounts for 20-25% of the height of the crucible at 675-685 ℃ under the condition of introducing protective gas;
s3, after the magnesium ingot is completely melted, heating to 700-710 ℃, adding the pure zinc, the Mg-Gd intermediate alloy and the Mg-Mn intermediate alloy for 2-4 times, keeping the temperature constant at 700-710 ℃, stirring until the pure zinc, the Mg-Gd intermediate alloy and the Mg-Mn intermediate alloy are melted, and keeping the temperature for 30-40 minutes;
s4, heating to 740 ℃ before low-pressure casting for 40-60 minutes, adding the aluminum ingot and the Al-M intermediate alloy, melting, refining, heating to 750-760 ℃, preserving heat and standing for 10-20 minutes to obtain a magnesium alloy melt;
s5, cooling the magnesium alloy melt to 720-740 ℃, skimming surface scum, and preheating a sand mold casting temperature to 25-150 ℃ or a metal mold casting temperature to 180-250 ℃; in the low-pressure casting process, the pressure of a liquid lifting stage is increased to 0.02-0.05 MPa, the pressurization time is controlled to 5-8 s, the pressure of a mold filling stage is increased to 0.07-0.08MPa, molten metal is filled in a mold cavity of a casting mold under the pressure, the pressure of a pressurization stage is increased to 0.1-0.15MPa, the pressurization time is controlled to 10-15 s, the pressure maintaining time of the pressure maintaining stage is controlled to 200-300 s, and a Mg-Gd casting alloy low-pressure casting is obtained after pressure relief;
s6, sequentially carrying out secondary solution treatment and artificial aging treatment on the Mg-Gd cast alloy low-pressure casting to obtain the high-strength high-toughness heat-resistant Mg-Gd alloy; the technological parameters of the secondary solution treatment are as follows: in the first stage, the temperature is 480-490 ℃, and the time is 36-48 h; in the second stage, the temperature is 535-545 ℃ and the time is 1-2 h; the technological parameters of the artificial aging treatment are as follows: the temperature is 185-215 ℃, and the time is 12-36 h.
2. The method for preparing the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting according to claim 1, wherein when M is a combined element of Ti and B, the mass fraction of Ti is 0.01-0.05%, and the mass fraction of B is 0.01-0.03%, based on the total weight of the Mg-Gd alloy.
3. The preparation method of the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting according to claim 1, wherein the Mg-Gd intermediate alloy is MgGd25 or MgGd30, the Mg-Mn intermediate alloy is MgMn10, and the Al-M intermediate alloy is one or more of AlTi5B1, AlB3, AlB8, AlTi5 and AlTi 10.
4. Adapted for low die casting as claimed in claim 1The preparation method of the high-strength and high-toughness heat-resistant Mg-Gd alloy is characterized in that the refining agent adopted by the refining comprises the following components in percentage by weight: 55% KCl and 25% CaCl2、5% CaF2、15% BaCl2。
5. The preparation method of the high-strength high-toughness heat-resistant Mg-Gd alloy suitable for low-pressure casting according to claim 1, wherein the amount of the refining agent added for refining is 1.0-3.5% of the total weight of the raw materials; the refining temperature is 720-730 ℃, and the stirring time of refining treatment is 10-15 min.
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| CN101693971A (en) * | 2009-10-27 | 2010-04-14 | 上海交通大学 | Low-pressure casting preparation method of heat resistant rare earth-magnesium alloy engine pistons |
| CN102994834A (en) * | 2011-09-09 | 2013-03-27 | 江汉大学 | Heatproof magnesium alloy containing Nb |
| JP2012197515A (en) * | 2012-04-27 | 2012-10-18 | Kumamoto Univ | High strength magnesium alloy having high corrosion resistance and method for producing the same |
| CN105648370A (en) * | 2016-02-03 | 2016-06-08 | 中南大学 | Heat treatment technology for improving mechanical properties of rare earth magnesium alloy castings |
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