CN110004343B - High-strength high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting and preparation method thereof - Google Patents
High-strength high-toughness heat-resistant Mg-Gd-Er 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-Er alloy suitable for gravity casting and a preparation method thereof, wherein the alloy comprises the following elements in percentage by mass: 4.0-10.0% of RE, 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 the RE is Gd and Er, and the M is at least one element of Ti and B. After the high-strength high-toughness heat-resistant cast Mg-Gd-Er alloy is subjected to gravity casting, secondary solution treatment and artificial aging heat treatment, the room-temperature tensile strength is 298MPa, and the elongation is 17%; the tensile strength at high temperature of 200 ℃ is 217MPa, the elongation is 21 percent, and the high-end requirement of the industries of aerospace, war industry, automobiles and the like on light weight development is met.
Description
Technical Field
The invention relates to a high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting and a preparation method thereof, 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 earliest applications of Mg-Al magnesium alloys, the main alloys thereofThe element aluminum has larger atomic radius difference with magnesium and has larger solid solubility in magnesium, and plays 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- > 3803.) and thus 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. The invention of Chinese patent ZL200510025251.6 (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 (Chinese patent invention 201510333457.9 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.
Because Gd and Er have similar properties and atomic radii, researchers often add Y to Mg-Gd-based alloys to improve the properties of the alloys. The Mg-Gd-Y alloy is the most deeply and widely researched Mg-Gd series alloy, and has excellent high-temperature performance and creep resistance. The research shows that: as the content of Y is increased, the as-cast structure of the alloy of Mg-10Gd-xY-0.4Zr (x is 1,3 and 5 wt.%) is refined (the grain size is from 150 to 40 mu m), the precipitated phases distributed in a discrete way are gradually increased, the species are changed, and XRD and EDS analysis after solution aging treatment show that the rare earth-rich phase is changed from Mg5(Gd,Er)→Mg5(Gd,Er)→Mg24(Gd, Er) because the addition of Y reduces the solid solubility of Gd in the alloy, replaces the original partial lattice nodes of Gd and promotes the precipitation of rare earth phases (Materials Science and Engineering: A456 (1) (2007) 78-84.).
The addition of cheap Zn in Mg-RE alloy not only has a remarkable effect on regulating the aging precipitation structure of the alloy system, but also can form various strengthening phases under the conditions of different Zn/RE (RE is Gd and/or Er) ratios: when the Zn/RE atomic ratio in the alloy is more than or equal to 6.0, an icosahedral quasicrystal structure I phase (Mg) is easily formed3Zn6RE comprises Mg3Zn6Gd、Mg3Zn6Y and Mg3Zn6(Gd, Er)); the W phase (Mg) of face-centered cubic structure is easily formed when the Zn/RE atomic ratio in the alloy is between 1.5 and 6.03Zn3RE2Comprising Mg3Zn3Gd2、Mg3Zn3Y2And Mg3Zn3(Gd,Er)2) And phase I; the W phase and the LPSO phase (Mg) of the long-period stacking ordered structure are easily formed when the Zn/RE atomic ratio in the alloy is between 1.0 and 1.512ZnRE comprises Mg12ZnGd、Mg12ZnY and Mg12Zn (Gd, Er)); the LPSO phase is easily formed when the Zn/RE atomic ratio in the alloy is less than or equal to 1.0 (Materials Science and Engineering: A695 (2017) 135-; Journal of Alloys and Compounds 602(2014) 32-39; Acta materiala 68(0) (2014) 325-; 338). The Mg-Gd-Y-Zn strengthening phases can further improve the room temperature strength and the high temperature performance of the magnesium alloy, and the rare earth wrought magnesium alloy containing trace Al element reported in Chinese patent invention 201310597670.1 (the rare earth wrought magnesium alloy containing trace Al and the preparation method thereof) comprises the following components in percentage by weight: gd: 6.5-15.0%, Y: 3.0-5.5%, Zn: 2.0-4.0%, Nd: 0.3-1.5%, Zr: 0.3-0.9%, Al: 0.4-1.0% and the balance of Mg. The preparation method of the magnesium alloy comprises the steps of raw material preparation, alloy smelting, alloy semi-solid extrusion, homogenization treatment, re-deformation, cooling, pre-stretching treatment, aging strengthening treatment and the like. The technical problems of the invention are as follows: the Nd rare earth element added in the range of the alloy composition provided by the invention promotes the formation of coarse massive Mg5The (Gd, Y, Nd) phase, whose ternary strengthening phase number is reduced accordingly, results in performance degradation. The content of rare earth elements Gd, Y and Nd is too high, the price of the expensive rare earth elements and the complex preparation process cause that the invention is difficult to be applied to the industry on a large scale. The invention discloses a self-generated quasicrystal reinforced Mg-Zn-Y alloy reported by Chinese patent ZL201110155378.5 (a self-generated quasicrystal reinforced Mg-Zn-Y alloy and a smelting method thereof), which comprises the following chemical components in percentage by mass: 3.0-10.0% of Zn, 0.5-3.0% of Y, 0.05-1.0% of Al-Ti-C and the balance of Mg and inevitable impurities; the preparation method comprises smelting and casting, wherein when the temperature of a smelted melt is reduced to 700-720 ℃, Al-Ti-C intermediate alloy is added, ultrasonic waves are introduced into the melt, and the melt is cast after ultrasonic treatment; the tensile strength of the self-generated quasicrystal reinforced Mg-Zn-Y alloy can reach 260MPa, and the elongation is 10.6%. The technology of the invention still has the following problems: the alloy has an excessively high Zn/Y mass ratio content,the quasicrystal I phase is formed, the solidification interval is too large, only gravity casting can be carried out, the pressure casting is not suitable, ultrasonic treatment is introduced, the operation is too complicated, and large-scale industrial application is difficult. Under the conventional solidification condition, the Mg-Gd-Er-Zn alloy has coarse grains, precipitated phases are often in a coarse net structure, the mechanical property of the Mg-Gd-Er-Zn alloy is deteriorated, the size of the precipitated phases must be adjusted through thermal deformation or thermal treatment solid solution and aging so as to play the role of the reinforced phases of the Mg-Gd-Er-Zn alloy, the existing Mg-Gd-Er-Zn alloy is generally limited to gravity casting and hot working processes, a complex thermal treatment process is required, and no report is provided for die casting application.
The Mg-Gd-Er-Zn alloy is usually added with Zr as a grain refining element to refine the 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. The invention patent 201611133731.9 (a high-strength and toughness corrosion-resistant flame-proof Mg-Gd-Y-Zn-Zr alloy and a preparation method thereof) reports a high-strength and toughness corrosion-resistant flame-proof Mg-Gd-Y-Zn-Zr alloy and a preparation method thereof, wherein the Mg-Gd-Y-Zn-Zr alloy comprises the following components in percentage by mass: gd is between 3.0 and 9.0 percent, Y is between 1.0 and 6.0 percent, Zn is between 0.5 and 3.0 percent, Zr is between 0.2 and 1.5 percent, and the balance is Mg and inevitable impurities. The technology of the invention still has the following 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) Is easy to precipitate to the bottom of the crucibleIn part, the yield of Zr was low. Meanwhile, the alloy is a wrought magnesium alloy, the Zn content in the embodiment is 1.1% at most, the (Gd + Y) content exceeds 8.0%, Zr is added into the alloy, and Al and Mn are not added.
Chinese patent 201210107771.1 (a heat-resistant Mg alloy of MgAlZn series containing Nb) discloses a Mg alloy, which comprises (by weight) Al 1.5-25%, Zn 0.1-3.5%, Mn 0.1-2.2%, rare earth 0.0002-16%, Nb 0.0002-4%, Zr 0.001-2%, M0.001-2%, and Mg in balance; wherein, the M element is at least one of Ti, Sr, Ca, C and B; the rare earth is at least one of Gd, Y, Sc, Sm, Nd, Yb, Pr, La, Ce, Tb, Dy, Ho and Er. The technology of the invention still has the following problems: al preferentially reacts with rare earth, Nb, Zr and other elements to form stable phases such as Al2Gd, Al3Y, Al3Sc, Al3Nb and Al3 Zr. Not only excellent refining effect cannot be obtained due to the excessively high content of added aluminum, but also the stable phases are easily agglomerated and grown coarse, which is disadvantageous for obtaining excellent elongation and strength, and the structure and properties of the Al — X phases cannot be improved by means of heat treatment due to the high stability of the Al — X phases. Because the content of Zn is relatively less, the content of Al and rare earth elements is high, and the formed Mg-rare earth-Zn strengthening phase is less, the design idea of the alloy is opposite to that of the invention; when the content of the rare earth exceeds 5%, the content of the formed strengthening phase is too high, and agglomeration and coarsening are easily caused, so that the elongation rate is obviously reduced. The normal-temperature tensile strength of the rare earth alloy is 247-260 MPa, the elongation rate is not more than 7%, the maximum normal-temperature mechanical property is 280MPa, and the performance of rare earth is not fully exerted. In addition, the rare earth content is too high, so that the alloy cost is too high, and the industrial large-scale application and popularization are not facilitated.
Disclosure of Invention
The invention provides a high-strength-toughness heat-resistant Mg-Gd-Er 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, toughness and heat resistance, and the alloy has the room-temperature tensile strength of 298MPa and the elongation of 17 percent after the alloy is subjected to gravity casting heat treatment; the tensile strength at high temperature of 200 ℃ is 217MPa, and the elongation is 21%.
The purpose of the invention is realized by the following technical scheme:
in a first aspect, the invention provides a high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting, which comprises the following elements in percentage by mass: 4.0-10.0% of RE, 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 the RE is Gd and Er, and the M is at least one element of Ti and B.
Preferably, in the alloy composition elements, the mass ratio of Zn to RE is 0.2-0.6, wherein the mass ratio of Gd to Er in the RE composition is 0.25-4.
Preferably, in the alloy composition elements, the mass ratio of (Zn + Al)/RE is 0.3-0.8.
Preferably, the combined elements comprise the following elements in percentage by mass based on the total amount of all elements in the alloy: 0.01 to 0.05 percent of Ti and 0.01 to 0.03 percent of B.
One of the innovative ideas of the high-strength, high-toughness and heat-resistant Mg-Gd-Er alloy suitable for gravity casting provided by the invention is as follows: the alloy is designed by adopting cheap Zn element and rare earth RE element (RE is Gd and/or Er) and matrix Mg element to form a ternary Mg-RE-Zn strengthening phase, particularly the mass ratio of Zn to RE is 0.2-0.6, wherein the mass ratio of Gd to Er in the composition of RE is 0.25-4, on one hand, the alloy mainly forms long period stacking ordered structure LPSO phase (Mg12ZnRE comprises Mg12ZnGd, Mg12ZnEr and Mg12Zn (Gd, Er)) and face centered cubic structure W phase (Mg3Zn3RE2 comprises Mg3Zn3Gd2, Mg3Zn3Er2 and Mg3Zn3(Gd, Er)2), which are high melting point phases, compared with binary Mg-Y 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 the high-temperature property of the high-strength high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting, and particularly improves the high-temperature creep property at 300 ℃ by more than one order of magnitude; on the other hand, the invention overcomes the defect that the traditional Mg-Zn-RE 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 and heat-resistant Mg-Gd-Er alloy suitable for gravity casting, which is as follows: the RE element added into the high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting is mixed rare earth of Gd and Er, and does not adopt mixed rare earth of Gd or Er and commonly used Ce, La, Nd and Pr, and the reason is that: on one hand, if the alloy is added with common rare earth elements such as Ce, La, Nd and Pr, the solidification temperature range of the alloy is enlarged along with the increase of the content of the common rare earth elements such as Ce, so that the alloy segregation and the casting process performance are poor, and casting defects are easily formed; on the other hand, as the content of the common rare earth element such as Ce increases, the W, LPSO phase, which is the main strengthening phase precipitated from the alloy, gradually changes into the (Mg, Zn)12RE phase, and the W, LPSO strengthening phase, which is stable in composition in the alloy, rapidly decreases in number, thereby reducing the precipitation strengthening effect.
The invention provides the third innovative idea of the high-strength high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting, which is as follows:
the precipitated phases of Mg-Gd-Er-Zn alloy are often in a coarse network structure under the conventional solidification condition, the mechanical properties 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 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 Y alloy elements, and the elements are combined with Zr to form compounds such as Al3Zr and precipitate to the bottom of the crucible so that the crystal grain refinement effect of zirconium is not generated. On the other hand, researches show that the Mg-Gd-Er-Zn alloy added with Zr for refining 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 in low melt is added to replace Zr to form dispersed high melting point Al3Er, Al2Gd and Al4GdY phases, so that the structure of the alloy is refined, and the high temperature stability of the magnesium alloy structure is ensured together 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 four innovative ideas of the high-strength, high-toughness and heat-resistant Mg-Gd-Er alloy suitable for gravity casting, which are as follows: the mass ratio of Gd/Er is limited to be 0.25-4, the mass ratio of Zn/RE is 0.2-0.6, and the mass ratio of (Zn + Al)/RE is 0.3-0.8, so that the solidification interval of the alloy is ensured to be small, the hot cracking tendency of the Mg-Gd-Er-Zn alloy in the casting process is overcome, and the casting process performance of the alloy is improved.
In a second aspect, the invention provides a preparation method of high-strength, high-toughness and heat-resistant Mg-Gd-Er alloy suitable for gravity casting, which comprises the following steps:
(1) calculating the dosage of the required raw materials according to the components and the stoichiometric ratio of the Mg-Gd-Er alloy; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and Mg-hot and Mg-Mn intermediate alloys, and drying and preheating;
(2) after the industrial pure magnesium ingot is completely melted, adding industrial pure zinc and Mg-RE and Mg-Mn intermediate alloy, melting and preserving heat;
(3) sequentially adding the industrial pure aluminum ingot and the Al-M intermediate alloy into the molten aluminum ingot and adding a refining agent for refining 40-60 minutes before gravity casting, and then raising the temperature of the furnace to 750-760 ℃, keeping the temperature and standing for 10-20 minutes to promote the settlement of impurities to obtain a magnesium alloy melt;
(4) and cooling the magnesium alloy melt to 720-740 ℃, skimming surface scum, pouring the melt into a mold preheated to 220-250 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant cast Mg-Gd-Er alloy.
(5) And (4) sequentially carrying out secondary solution treatment and artificial aging treatment on the alloy cast in the step (5) to obtain the required high-strength-toughness heat-resistant Mg-Gd-Er alloy.
Preferably, the Mg-RE master alloy comprises a Mg-Gd master alloy and a Mg-Er master alloy; the Mg-Gd intermediate alloy is MgGd25 or MgGd30, and the Mg-Er intermediate alloy is MgEr25 or MgEr 30; the Mg-Mn intermediate alloy is MgMn 10; the Al-M intermediate alloy is at least one of AlTi5B1, AlB3, AlB8, AlTi5 or AlTi 10.
Preferably, the industrial pure magnesium ingot is melted at 680 ℃, and the industrial pure zinc and Mg-RE master alloy are added and melted at 720 ℃; the industrial pure aluminum ingot and the Al-M intermediate alloy are added and melted at 730 ℃.
Preferably, 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 is 720-730 ℃, and the stirring time of refining treatment is 10-15 min.
Preferably, the process parameters of the secondary solution treatment are as follows: the first-stage solid solution temperature is 480-490 ℃, and the time is 36-48 h; the temperature of the second-stage solid solution 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.
Preferably, the specific steps of the secondary solution treatment include:
putting the cast alloy into a solid solution furnace, heating to 200 ℃ at the speed of 5 ℃/min, introducing protective gas, continuing heating to 480-490 ℃ at the speed of 5 ℃/min until the first-stage solid solution temperature is reached, starting timing when the solid solution temperature is reached, and keeping the temperature for 36-48 h; and slowly heating to the second stage of solution treatment at the speed of 10 ℃/h, keeping the temperature at 535-545 ℃, preserving the heat for 1-2 h, and then quickly transferring the sample to a quenching device for water cooling quenching.
Preferably, the specific steps of performing the artificial aging treatment on the cast alloy comprise: and when the aging temperature is 185-215 ℃, timing, keeping the temperature for 12-36 h, and air-cooling to room temperature after discharging.
Preferably, the method for adding the industrial pure magnesium ingot comprises the following steps: firstly melting an industrial pure magnesium ingot accounting for 25% of the height of a crucible into a molten pool, introducing protective gas, and adding the rest magnesium ingot for melting;
the protective gas is argon or SF with 0.2% volume fraction6And CO2The mixed gas of (1).
The preparation method of the high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting has the beneficial effects that: (1) rare earth elements Mg-Gd and Mg-Er intermediate alloy which are easy to burn and lose are added at 720 ℃, and melting is carried out at low temperature, so that the yield of the rare earth Gd and Er is improved; (2) the refining treatment adopts a special refining agent without MgCl2, so that the burning loss of rare earth Gd and Er in the refining process is further reduced; (3) the heat treatment of the high-strength high-toughness heat-resistant cast Mg-Gd-Er 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, Er 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 ℃, preserving the temperature for 12-36 h, carrying out aging treatment, and finally precipitating a nano-grade and finely dispersed strengthening phase in the alloy crystal after long-time aging, 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 the high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting is subjected to gravity casting, secondary solution treatment and artificial aging heat treatment, the room-temperature tensile strength is 298MPa, and the elongation is 17%; the tensile strength at high temperature of 200 ℃ is 217MPa, the elongation is 21 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
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 a metallographic structure of the heat-treated state prepared by gravity casting in example 2.
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-Er alloy suitable for gravity casting comprises the following components in percentage by weight: according to the theoretical mixture ratio, 8.0% of Er, 2.0% 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) calculating the dosage of the required raw materials according to the components and the stoichiometric ratio of the Mg-Gd-Er alloy; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and intermediate alloys of MgGd30, MgEr30 and MgMn10, 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-;
(4) heating to 730 ℃ after 40-60 minutes before gravity 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 1% 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 750-760 ℃, preserving the heat and standing for 10 minutes to promote the settlement of impurities to obtain the magnesium alloyMelting the materials;
(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-Gd-Er alloy.
(6) And sequentially carrying out secondary solution treatment on the cast alloy, putting the cast alloy into a solution furnace, heating to 200 ℃ at a speed of 5 ℃/min, introducing protective gas, continuously heating to 480 ℃ of the primary solution temperature at a speed of 5 ℃/min, starting timing when the temperature reaches the solution temperature, keeping the temperature for 36h, slowly heating to the secondary solution treatment at a speed of 10 ℃/h, keeping the temperature at 535 ℃, keeping the temperature for 1h, 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 12h, and carrying out air cooling to room temperature after discharging to obtain the high-strength high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd-Er alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 292MPa, and the elongation is 21 percent; the tensile strength at high temperature of 200 ℃ is 211MPa, and the elongation is 25%.
Example 2
The high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting comprises the following components in percentage by weight: according to the theoretical mixture ratio, 2.0 percent of Er,8.0 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) calculating the dosage of the required raw materials according to the components and the stoichiometric ratio of the Mg-Gd-Er alloy; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and intermediate alloys of MgGd30, MgEr30 and MgMn10, 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) will occupy the height of the crucibleMelting 25% industrial pure magnesium ingot at 680 deg.C to form molten pool, introducing protective gas containing 0.2% SF by volume fraction6And CO2Adding the rest magnesium ingot into the mixed gas;
(3) after the magnesium ingot is completely melted, heating to 700-;
(4) heating to 730 ℃ after 40-60 minutes before gravity casting, sequentially adding the industrial pure aluminum ingot and the AlTi10 intermediate alloy to wait for complete melting, adding a refining agent accounting for 3.5 percent of the weight of the raw materials to refine at 730 ℃, and stirring for 10 minutes 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 750-760 ℃, preserving the heat and standing for 10 minutes to promote the settlement of impurities to obtain a 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-Gd-Er alloy.
(6) And sequentially carrying out secondary solution treatment on the cast alloy, putting the cast alloy into a solution furnace, heating to 200 ℃ at a speed of 5 ℃/min, introducing protective gas, continuously heating to 490 ℃ of the primary solution temperature at a speed of 5 ℃/min, starting timing when the temperature reaches the solution temperature, keeping the temperature for 48h, slowly heating to the secondary solution treatment at a speed of 10 ℃/h, keeping the temperature at 545 ℃ 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 215 ℃, starting timing when the aging temperature is reached, keeping the temperature for 36h, taking out the alloy from the furnace, and then cooling the alloy in air to room temperature to obtain the high-strength high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting, wherein the metallographic structure diagram of the heat treatment state of the alloy is shown in figure 1.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd-Er alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 298MPa, and the elongation is 17%; the tensile strength at high temperature of 200 ℃ is 217MPa, and the elongation is 21%.
Example 3
The high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting comprises the following components in percentage by weight: according to the theoretical mixture ratio, 1.0% of Er, 3.0% of Gd, 2.0% of Zn, 0.6% of Al, 0.2% of Mn, 0.05% of Ti, 0.01% 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 components and the stoichiometric ratio of the Mg-Gd-Er alloy; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and intermediate alloys of MgGd30, MgEr30 and MgMn10, 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-;
(4) heating to 730 ℃ after 40-60 minutes before gravity 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 2.5 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 750-760 ℃, preserving the heat and standing for 10 minutes to promote the settlement of impurities to obtain a magnesium alloy melt;
(5) and cooling the magnesium alloy melt to 730 ℃, skimming surface scum, pouring the melt into a metal mold preheated to 200 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant cast Mg-Gd-Er alloy.
(6) And sequentially carrying out secondary solution treatment on the cast alloy, putting the cast alloy into a solution furnace, heating to 200 ℃ at a speed of 5 ℃/min, introducing protective gas, continuously heating to the first-stage solution temperature of 485 ℃ at a speed of 5 ℃/min, starting timing when the solution temperature is reached, keeping the temperature for 42h, slowly heating to the second-stage solution treatment at a speed of 10 ℃/h, keeping the temperature at 540 ℃, keeping the temperature 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-Er alloy suitable for gravity casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd-Er alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. 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 24 percent; the tensile strength at high temperature of 200 ℃ is 187MPa, and the elongation is 31%.
Example 4
The high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting comprises the following components in percentage by weight: 4.0% of Er, 2.0% of Gd, 3.6% of Zn, 1.2% of Al, 0.2% of Mn, 0.08% of B and the balance of Mg and other inevitable impurities according to the theoretical proportion.
The preparation method comprises the following steps:
(1) calculating the dosage of the required raw materials according to the components and the stoichiometric ratio of the Mg-Gd-Er alloy; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and intermediate alloys of MgGd30, MgEr30 and MgMn10, 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 accounting for 25% of the height of the crucible into a molten pool at 680 ℃, and introducing SF containing 0.2% of volume fraction6And CO2Adding the rest magnesium ingot into the mixed protective gas;
(3) after the magnesium ingot is completely melted, heating to 700-;
(4) heating to 730 ℃ after 40-60 minutes before gravity casting, sequentially adding the industrial pure aluminum ingot, the AlB3 intermediate alloy and the AlB8 intermediate alloy to wait for complete melting, adding a refining agent accounting for 3.0 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 750-760 ℃, preserving the heat and standing for 10 minutes to promote the settlement of impurities to obtain a magnesium alloy melt;
(5) and cooling the magnesium alloy melt to 720 ℃, skimming surface scum, pouring the melt into a metal mold preheated to 220 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant cast Mg-Gd-Er alloy.
(6) And sequentially carrying out secondary solution treatment on the cast alloy, putting the cast alloy into a solution furnace, heating to 200 ℃ at a speed of 5 ℃/min, introducing protective gas, continuously heating to 480 ℃ of the primary solution temperature at a speed of 5 ℃/min, starting timing when the temperature reaches the solution temperature, keeping the temperature for 48h, slowly heating to the secondary solution treatment at a speed of 10 ℃/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-Er alloy suitable for gravity casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd-Er alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 287MPa, and the elongation is 22%; the tensile strength at high temperature of 200 ℃ is 205MPa, and the elongation is 26%.
Example 5
The high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting comprises the following components in percentage by weight: 3.5 percent of Er, 3.5 percent of Gd,3.5 percent of Zn, 0.5 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 according to the theoretical proportion.
The preparation method comprises the following steps:
(1) calculating the dosage of the required raw materials according to the components and the stoichiometric ratio of the Mg-Gd-Er alloy; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and intermediate alloys of MgGd30, MgEr30 and MgMn10, 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-;
(4) heating to 730 ℃ after 40-60 minutes before gravity casting, sequentially adding a refining agent accounting for 2.0 percent of the weight of the raw materials for refining after the industrial pure aluminum ingot, the AlTi5 intermediate alloy, the AlTi5B1 intermediate alloy and the AlB3 intermediate alloy are completely 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. Raising the temperature of the furnace to 750-760 ℃, preserving the heat and standing for 10 minutes to promote the settlement of impurities to obtain a 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-Gd-Er alloy.
(6) And sequentially carrying out secondary solution treatment on the cast alloy, putting the cast alloy into a solution furnace, heating to 200 ℃ at a speed of 5 ℃/min, introducing protective gas, continuously heating to 490 ℃ of the primary solution temperature at a speed of 5 ℃/min, starting timing when the temperature reaches the solution temperature, keeping the temperature for 36h, slowly heating to the secondary solution treatment at a speed of 10 ℃/h, keeping the temperature at 545 ℃ for 1h, 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 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-Er alloy suitable for gravity casting.
Respectively carrying out a-room temperature tensile test on the prepared high-strength high-toughness heat-resistant Mg-Gd-Er alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 284MPa, and the elongation is 21%; the tensile strength at high temperature of 200 ℃ is 199MPa, and the elongation is 24%.
Example 6
The high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting comprises the following components in percentage by weight: 9.0% of Er, 1.0% 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 according to the theoretical proportion.
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-Er alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 290MPa, and the elongation is 19 percent; the tensile strength at high temperature of 200 ℃ is 209MPa, and the elongation is 24%.
Example 7
The high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting comprises the following components in percentage by weight: according to the theoretical mixture ratio, 1.0 percent of Er,9.0 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 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-Er alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 298MPa, and the elongation is 16%; the tensile strength at high temperature of 200 ℃ is 216MPa, and the elongation is 19.2%.
Example 8
The high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting comprises the following components in percentage by weight: according to the theoretical mixture ratio, 2.5 percent of Er, 2.5 percent of Gd,5.5 percent of Zn, 0.5 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 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-Er alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. 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 7.2%; tensile strength at high temperature of 200 ℃ is 143MPa, and elongation is 13.2%.
Comparative example 1
The high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting comprises the following components in percentage by weight: according to the theoretical mixture ratio, 4.0 percent of Gd,2.0 percent of Zn, 0.6 percent of Al, 0.2 percent of Mn, 0.05 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-Er alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 268MPa, and the elongation is 20%; the tensile strength at high temperature of 200 ℃ is 186MPa, and the elongation is 30.3%.
Comparative example 2
The high-strength and high-toughness heat-resistant Mg-Gd-Nd alloy suitable for gravity casting comprises the following components in percentage by weight: according to the theoretical mixture ratio, 1.0% of Nd, 3.0% of Gd, 2.0% of Zn, 0.6% of Al, 0.2% of Mn, 0.05% of Ti, 0.01% 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-Nd alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 241MPa, and the elongation is 15%; the tensile strength at high temperature of 200 ℃ is 167MPa, and the elongation is 21%.
Comparative example 3
The high-strength and high-toughness heat-resistant Mg-Yb-Er alloy suitable for gravity casting comprises the following components in percentage by weight: according to the theoretical mixture ratio, 8.0 percent of Er,2.0 percent of Yb, 2.0 percent of Zn, 1.0 percent of Al, 0.3 percent of Mn, 0.04 percent of Ti, 0.04 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-Yb-Er alloy; b, performing high-temperature tensile property test at 200 ℃ after 200-hour heat exposure treatment at 200 ℃. In the example, the room-temperature tensile strength of the high-strength and high-toughness heat-resistant magnesium alloy is 271MPa, and the elongation is 14 percent; the tensile strength at high temperature of 200 ℃ is 188MPa, and the elongation is 17%.
The invention has many applications, and the above description is only a preferred embodiment of the invention. It should be noted that the above examples are only for illustrating the present invention, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various modifications can be made without departing from the principles of the invention and these modifications are to be considered within the scope of the invention.
Claims (8)
1. The high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting is characterized by comprising the following elements in percentage by mass: 4.0-10.0% of RE, 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 RE is Gd and Er, and M is at least one element of Ti and B;
in the alloy composition elements, the mass ratio of Zn to RE is 0.2-0.6, wherein the mass ratio of Gd to Er in the RE composition is 0.25-4;
in the alloy composition elements, the mass ratio of (Zn + Al)/RE is 0.3-0.8;
the preparation method of the Mg-Gd-Er alloy comprises the following steps:
(1) calculating the dosage of the required raw materials according to the components and the stoichiometric ratio of the Mg-Gd-Er alloy; removing oxide layers of industrial pure magnesium ingots, industrial pure zinc, industrial pure aluminum ingots and Mg-Gd, Mg-Er and Mg-Mn intermediate alloys, drying and preheating to 200 ℃;
(2) after the industrial pure magnesium ingot is completely melted, adding industrial pure zinc and Mg-RE and Mg-Mn intermediate alloy, melting and preserving heat;
(3) sequentially adding the industrial pure aluminum ingot and the Al-M intermediate alloy into the molten aluminum ingot and adding a refining agent for refining 40-60 minutes before gravity casting, and then raising the temperature of the furnace to 750-760 ℃, keeping the temperature and standing for 10-20 minutes to promote the settlement of impurities to obtain a magnesium alloy melt;
(4) cooling the magnesium alloy melt to 720-740 ℃, skimming surface scum, pouring the melt into a mold preheated to 220-250 ℃ through gravity casting, and cooling to obtain the high-strength-toughness heat-resistant cast Mg-Gd-Er alloy;
(5) sequentially carrying out secondary solution treatment and artificial aging treatment on the alloy cast in the step (5) to obtain the required high-strength high-toughness heat-resistant Mg-Gd-Er alloy; the technological parameters of the secondary solution treatment are as follows: the first-stage solid solution temperature is 480-490 ℃, and the time is 36-48 h; the temperature of the second-stage solid solution 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 high toughness, heat resistant Mg-Gd-Er alloy suitable for gravity casting according to claim 1, wherein M comprises the following elements in mass percent, based on the total of all elements in the alloy: 0.01 to 0.05 percent of Ti and 0.01 to 0.03 percent of B.
3. The high toughness, heat resistant Mg-Gd-Er alloy suitable for gravity casting according to claim 1, wherein said Mg-RE master alloy comprises a Mg-Gd master alloy and a Mg-Er master alloy; the Mg-Gd intermediate alloy is MgGd25 or MgGd30, and the Mg-Er intermediate alloy is MgEr25 or MgEr 30; the Mg-Mn intermediate alloy is MgMn 10; the Al-M intermediate alloy is at least one of AlTi5B1, AlB3, AlB8, AlTi5 or AlTi 10.
4. The high strength and toughness heat resistant Mg-Gd-Er alloy suitable for gravity casting of claim 1, wherein the commercial pure magnesium ingot is melted at 680 ℃, and the commercial pure zinc, Mg-RE master alloy is melted by addition at 720 ℃; the industrial pure aluminum ingot and the Al-M intermediate alloy are added and melted at 730 ℃.
5. The high-strength and high-toughness heat-resistant Mg-Gd-Er 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；
The addition amount of the refining agent 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.
6. The high toughness heat resistant Mg-Gd-Er alloy for gravity casting according to claim 1, wherein the secondary solution treatment comprises the specific steps of:
putting the cast alloy into a solid solution furnace, heating to 200 ℃ at the speed of 5 ℃/min, introducing protective gas, continuing heating to 480-490 ℃ at the speed of 5 ℃/min until the first-stage solid solution temperature is reached, starting timing when the solid solution temperature is reached, and keeping the temperature for 36-48 h; and slowly heating to the second stage of solution treatment at the speed of 10 ℃/h, keeping the temperature at 535-545 ℃, preserving the heat for 1-2 h, and then quickly transferring the sample to a quenching device for water cooling quenching.
7. The high strength and toughness heat resistant Mg-Gd-Er alloy of claim 6, suitable for gravity casting, wherein the specific steps of subjecting the cast alloy to said artificial aging comprises: and when the aging temperature is 185-215 ℃, timing, keeping the temperature for 12-36 h, and air-cooling to room temperature after discharging.
8. The high-strength and high-toughness heat-resistant Mg-Gd-Er alloy suitable for gravity casting according to claim 1, wherein the adding method of the industrial pure magnesium ingot is as follows: firstly melting an industrial pure magnesium ingot accounting for 25% of the height of a crucible into a molten pool, introducing protective gas, and adding the rest magnesium ingot for melting; the protective gas is argon or SF with 0.2% volume fraction6And CO2The mixed gas of (1).
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| CN102839308A (en) * | 2012-08-24 | 2012-12-26 | 中南大学 | High-strength high-modulus magnesium alloy and preparation method |
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| JP2008069418A (en) * | 2006-09-14 | 2008-03-27 | Kumamoto Univ | High strength magnesium alloy with excellent corrosion resistance |
| KR20120079638A (en) * | 2011-01-05 | 2012-07-13 | 강호길 | Mg alloy and the manufacturing method of the same |
| CN102618758A (en) * | 2012-04-13 | 2012-08-01 | 江汉大学 | Cast magnesium alloy of low linear shrinkage |
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