CN115896509B - Preparation method for constructing superfine crystal structure in magnesium alloy - Google Patents
Preparation method for constructing superfine crystal structure in magnesium alloy Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 30
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- 238000012545 processing Methods 0.000 claims abstract description 87
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims abstract description 38
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Abstract
A preparation method for constructing an ultrafine grain structure in magnesium alloy relates to the field of metal material processing, and comprises the following steps: preparing and batching intermediate alloy in the step (1): proportioning according to the component range; and (2) casting: putting a pure Mg ingot into a crucible of a smelting furnace for melting, adding an Mg-20Ca intermediate alloy into a melt, adding pure Al after the Mg-20Ca intermediate alloy is melted, sequentially adding an Mg-50Bi intermediate alloy and an Mg-40Sn intermediate alloy into the magnesium melt after the Mg-20Ca intermediate alloy is dissolved, and finally pouring the Mg-20Ca intermediate alloy into a metal mold to prepare an alloy cast ingot; and (3) solution treatment: carrying out solution treatment on the alloy cast ingot; step (4) pre-extrusion processing: pre-extruding the blank after solution treatment, and air-cooling to room temperature; and (5) room temperature ECAP processing: and (3) coating the surface of the extruded wrought alloy blank obtained in the step (4) with a lubricant, and placing the alloy blank into a die at room temperature to perform room temperature equal channel angular extrusion forming.
Description
Technical Field
The invention relates to the field of metal material processing, in particular to a preparation technology for constructing an ultrafine grain structure in magnesium alloy.
Background
Along with the increasing severity of energy conservation and emission reduction, the development and utilization of high-performance light metal materials are increasingly urgent. As the lightest metal structural material at present, the magnesium alloy has excellent damping performance, biocompatibility, thermal conductivity, electromagnetic shielding performance, large hydrogen storage capacity and good recyclability, and is known as a green engineering material in the 21 st century. However, the current magnesium alloy has poor mechanical properties, plastic workability and corrosion resistance, and severely restricts its wide application as engineering material. In general, the microstructure of an ultrafine grain (grain size is less than 1 micron) structure is introduced into a metal material, so that excellent mechanical property and corrosion resistance can be given to the material. The strong plastic deformation processing is an effective way for refining grain structures and second phases of metal materials such as magnesium alloy, but most magnesium alloy has a special crystal structure (HCP, c/a is about 1.624), and the slip system which can be started under the low temperature condition (less than 200 ℃) is insufficient, so that the magnesium alloy has poor low-temperature processing formability. In high-temperature plastic processing, the grain growth of recrystallized grains is easy to cause, the grain refinement degree is limited, and even though the alloy is subjected to strong plastic deformation processing at high temperature, most of recrystallized grains in the alloy are still more than 1 micron in size, and the grain is difficult to refine to be below the micron level. Currently, only less than 15% of magnesium alloy products are manufactured by deformation processing. In view of the above, if the poor low-temperature forming property of the magnesium alloy can be overcome, and the strong plastic deformation processing under the conditions of low temperature and even room temperature is realized, the growth of recrystallized grains is expected to be obviously restrained, and the grain size is reduced, so that a superfine grain structure with a larger proportion fraction can be constructed in the magnesium alloy; meanwhile, the size of the dynamic precipitated phase can be reduced, the fraction of the fine dynamic precipitated phase is increased, and the performance of the alloy is cooperatively improved.
The equal-diameter angular Extrusion (ECAP) technology with good industrialized application prospect can accumulate larger strain without changing the macroscopic size of a sample, and is an effective means for constructing ultrafine grain structures in metal materials such as aluminum (Al) alloy, copper (Cu) alloy and the like and optimizing the morphology and distribution of a second phase in the metal materials. In recent years, low-temperature or even room-temperature multi-pass ECAP processing has been successfully used as a front processing technology for constructing ultrafine grain or even nanocrystalline structures in alloy materials such as Al, cu and the like, and has great technical potential. In order to introduce ultrafine grain structures into magnesium alloys, plastic working techniques related to ECAP working of magnesium alloys have been proposed in recent years for development of high-strength and high-toughness magnesium alloys.
Patent 1 (patent publication number: CN 101406906A) discloses a method for preparing a magnesium alloy section by extrusion shaping with continuous corner shearing, which comprises the following steps: (1) homogenizing the magnesium alloy blank; (2) Preheating a die of an extrusion die with multiple corner forming, and uniformly coating lubricant in a die channel; (3) heating the extrusion cylinder to 175-325 ℃; (4) The homogenized blank is heated to 200-350 ℃, the extrusion rate of the extrusion die is 4-100, and the extrusion speed of 3-6 m/min is used for carrying out unidirectional extrusion on the magnesium alloy blank, so that the magnesium alloy blank is subjected to compression extrusion with high extrusion rate and then subjected to equal channel extrusion with multiple corners. The method of the invention realizes equal channel extrusion of magnesium alloy under lower temperature condition. However, this technique has the following disadvantages: (1) The extrusion method with continuous corner shearing can realize limited equal channel extrusion passes, generally not more than 2 passes, and the required extrusion force can be rapidly increased and cannot be carried out after the number of corners is increased; (2) The method has the advantages that the adopted die structure is complex, the lubricant needs to be additionally and uniformly smeared in the die channel in the specific operation process, the operation is complex, the processing efficiency is low, and the industrialized application is difficult; (3) The minimum extrusion temperature of the technology is still higher (200 ℃), excessive growth of recrystallized grains is difficult to effectively inhibit, the grain size of the finally prepared alloy is still larger, and the effect of constructing an ultrafine grain structure in the magnesium alloy is far from being achieved at more than 5 microns.
Patent 2 (patent publication No. CN 103215531A) discloses a continuous and severe plastic deformation preparation method of nanocrystalline magnesium alloy, which comprises the steps of firstly smelting and casting a prepared magnesium alloy raw material into a round bar ingot, then hot extruding the round bar into bars with phi of 9-12 mm at 340-460 ℃, cutting and segmenting the extruded round bar, performing equal channel angular extrusion for 4-8 times at 200-325 ℃, cutting the bars into disc samples with the thickness of 0.8-1 mm, and performing high-pressure torsion at room temperature under the pressure of 4-6 Gpa for 2-10 circles. The invention combines the conventional hot extrusion, equal channel angular extrusion belonging to the severe plastic deformation process and room temperature high pressure torsion, can easily prepare the magnesium alloy with the average grain size below 100nm and uniform structure, greatly improves the mechanical properties of the magnesium alloy, but has more defects: (1) Although ECAP processing is performed, the subsequent strong plastic deformation processing of high-pressure torsion at room temperature is needed to introduce the superfine crystal structure into the magnesium alloy, the preparation process is long, the process is long and complex, the processing efficiency is low, high cost is necessarily caused, and mass production is difficult to realize; (2) The bulk nanocrystalline magnesium alloy is prepared by combining ECAP with high-pressure torsion at room temperature, but the size and specification of alloy blanks are greatly limited, and the bulk production is difficult due to the fact that the alloy blanks are only 9-12 mm in diameter and 0.8-1 mm in thickness.
Patent 3 (patent publication number: CN 1792487A) discloses a two-step equal channel angular extrusion method of magnesium alloy, which specifically comprises the following steps: (1) designing an equal channel extrusion die; (2) According to the initial performance of the material, the deformation rate and the deformation temperature are adjusted, and the lowest temperature of 1 pass of crack-free deformation is found; (3) Performing multi-pass equal channel angular extrusion deformation on the alloy at the minimum temperature of crack-free deformation, and rotating the sample according to one of equal channel extrusion routes among deformation passes; (4) After the alloy is subjected to equal channel angular extrusion deformation for 2-4 times, the equal channel angular extrusion deformation temperature is reduced to 180-330 ℃, and one of equal channel extrusion routes is continuously adopted to carry out equal channel angular extrusion deformation for 4-8 times on the magnesium alloy. The invention reduces the processing temperature in the subsequent processing step, but has the following disadvantages: (1) The equal channel deformation temperature is still above 180 ℃, ECAP processing under the room temperature condition still cannot be realized, the growth of recrystallized grains is still facilitated, and the growth inhibition effect on the recrystallized grains is limited; (2) The blank and the die still need to be additionally heated to more than 180 ℃ in the ECAP processing process, and the ECAP die needs to be additionally heated due to energy consumption; (3) In the ECAP processing process, repeated temperature regulation and control are needed, needed ECAP processing passes are needed for 6-8 times, the temperature regulation and control of the die can be realized by an extra process or a longer time, the processing process is complex, the efficiency is low, and the processing cost is high.
Patent 4 (patent publication No. CN 107988536A) discloses a Mg-Mn-Sn-Ti magnesium alloy material and a preparation method thereof, wherein after corresponding magnesium alloy blanks are prepared by smelting, the Mg-Mn-Sn-Ti magnesium alloy material is prepared by carrying out one-time equal channel extrusion at a high temperature of more than 350 ℃ with the assistance of ultrasound. The invention combines ultrasonic vibration and equal channel extrusion technology and is simultaneously applied to plastic forming of magnesium alloy, and alloy materials can be obtained by only one extrusion, but low-temperature ECAP processing of magnesium alloy cannot be realized; and no information on the grain structure of the material is given in the relevant documents; the mechanical properties of the obtained alloy are relatively low, the tensile strength is 180-253MPa, and the elongation is 10.1-27%; in addition, an ultrasonic auxiliary process is additionally introduced, so that the equipment and process complexity of alloy processing are increased, and the energy consumption and the cost are high.
Therefore, the advanced processing preparation technology suitable for ECAP processing at low temperature and even at room temperature of the magnesium alloy needs to be further developed, the effect of constructing the superfine crystal structure in the magnesium alloy is achieved by applying a simple scheme, and the high-quality magnesium alloy material containing the superfine crystal structure can be obtained at lower cost. The method can better meet the requirements of the fields of aerospace, weaponry, biomedical use, solid hydrogen storage and the like on low cost, easy processing and high performance of high-quality magnesium alloy.
Disclosure of Invention
The invention aims to provide a preparation method for constructing an ultrafine grain structure in magnesium alloy.
The invention relates to a preparation method for constructing an ultrafine grain structure in magnesium alloy, which comprises the following alloy components in percentage by mass: 0.5-3 wt% of Al, 0.6-3.5 wt% of Bi, 0.3-2.0 wt% of Sn and 0.005-0.1 wt% of Ca, wherein the mass ratio of the element content Bi in the alloy is as follows: sn=1.7-2.0:1, the balance Mg and unavoidable impurities, the steps of:
preparing and batching intermediate alloy in the step (1): firstly, preparing an Mg-50Bi intermediate alloy and an Mg-40Sn intermediate alloy, then preparing a commercial Mg-20Ca intermediate alloy, a commercial pure magnesium with the purity of 99.95 wt% and a pure aluminum with the purity of 99.99 wt% as raw materials by using the Mg-50Bi intermediate alloy, the Mg-40Sn intermediate alloy and the commercial Mg-20Ca intermediate alloy, and mixing according to the component range;
and (2) casting: placing a pure Mg ingot into a crucible of a smelting furnace, setting the furnace temperature to be 710-760 ℃ and keeping, adding the Mg-20Ca intermediate alloy preheated to 100-200 ℃ into a melt after the pure magnesium is melted, adding the pure Al preheated to 100-200 ℃ after the pure Mg ingot is melted, and sequentially adding the Mg-50Bi intermediate alloy and the Mg-40Sn intermediate alloy preheated to 100-180 ℃ into the magnesium melt after the pure Mg ingot is dissolved; preserving heat for 10-30 minutes, mechanically stirring for 1-3 minutes, preserving heat for 5-10 minutes, and skimming surface scum; finally pouring into a metal mold to prepare an alloy cast ingot; the casting process is that CO 2 And SF (sulfur hexafluoride) 6 Is carried out under the protection of the mixed gas of the (2);
and (3) solution treatment: carrying out solution treatment on the alloy ingot obtained in the previous step, firstly preserving heat for 5-12h at 400-420 ℃, then introducing Ar gas, raising the temperature of a hearth to 450-490 ℃ under the atmosphere of Ar, preserving heat for 2-5 h, taking out, cooling, and closing an Ar gas valve;
step (4) pre-extrusion processing: pre-extruding the blank after solution treatment, firstly heating the blank to be extruded to 270-400 ℃, putting the blank into an extrusion die for pre-extruding, wherein the extrusion deformation speed is 10-20 m/min, the extrusion ratio is 10-40:1, the extrusion temperature is 270-400 ℃, and cooling the blank to room temperature in air after extrusion processing to obtain the blank with fine grain structure;
and (5) room temperature ECAP processing: coating lubricant on the surface of the extruded wrought alloy blank obtained in the step (4), placing the alloy blank into a die at room temperature, and performing equal channel angular extrusion forming at room temperature; finally, the wrought magnesium alloy material with the superfine crystal structure is obtained.
The beneficial effects of the invention are as follows: (1) The alloy blank in the technical scheme of the invention has excellent room temperature processing performance, can realize room temperature multi-pass ECAP processing at 20-35 ℃, and can be processed in the room temperature ECAP processing processDynamic recrystallization occurs, which is closely related to microstructure characteristics of a second phase type, matrix solid solution elements, grain sizes and the like in the alloy, and the second phase in the alloy is Mg 2 (SnBi) phase, which is significantly different from Mg in the existing alloy 3 Bi 2 Phase and Mg 2 Sn phase, and in addition, a certain amount of Al, ca, bi, sn, etc. elements are dissolved in the alloy matrix, which gives the alloy good low-temperature workability;
(2) The intermediate alloy is adopted for preparation, the precipitation of elements with different specific gravities in the melt is restrained, the uniform smelting is ensured, the Sn and Bi elements in the alloy are uniformly distributed, the uneven material performance caused by gravity segregation is reduced, the smelting efficiency and the ingot blank metallurgical quality are improved, the homogenization difficulty and the insufficient processing performance caused by uneven components are reduced, and the Mg in the alloy is promoted 2 The formation of (SnBi) phase can raise the low-temp. plastic working deformability of alloy.
(3) The double-stage solid solution heat treatment can avoid the over-burning caused by the melting of the low-melting-point second phase generated by unbalanced solidification in the alloy under the high-temperature condition, and can fully realize the homogenization of the alloy. In addition, protective gas is not required to be introduced when the low-temperature heat treatment of the first stage is carried out below 420 ℃, so that the cost is saved.
(4) Because the deformation is carried out at room temperature, the blank does not need to be heated, the heating process can be reduced, the energy is saved, and the process is extremely simple. The ECAP processing process does not need to heat magnesium alloy blanks and dies, the deformation process is simpler, the control is convenient, the alloy preparation efficiency can be improved, the alloy preparation cost is saved, and the commercialization popularization and application are convenient.
(5) Compared with the existing ECAP processing under most high temperature conditions, the method for processing the ECAP at room temperature can effectively inhibit the growth of recrystallized grains due to the fact that the temperature at which dynamic recrystallization occurs is at room temperature, and Mg which is further precipitated in the ECAP processing process at room temperature 2 The (SnBi) phase is also finer and combines with Mg 2 (SnBi) has a retarding effect on the growth of recrystallized grains, and effectively inhibits the growth of the recrystallized grains by synergistic effect, so that an ultrafine grain structure is constructed in the magnesium alloy.
(6) The invention provides a new path for regulating and controlling superfine crystal magnesium tissue by room temperature ECAP processing of magnesium alloy, the obtained high-strength and high-toughness magnesium alloy material has excellent performance, the alloy elongation can reach more than 50%, the yield strength reaches more than 190MPa, and excellent strong plastic matching is realized.
Drawings
Fig. 1 is a TEM microstructure of the alloy material obtained after the 5 th step of processing in example 1, fig. 2 is a SEM microstructure of the alloy material obtained after the 5 th step of processing in example 2, fig. 3 is a partially enlarged view of fig. 2, fig. 4 is a TEM microstructure of the alloy material obtained after the 5 th step of processing in example 2, fig. 5 is a partially enlarged view of fig. 4, fig. 6 is a SEM microstructure of the pre-extrusion billet obtained after the 4 th step of processing in example 3, fig. 7 is a partially enlarged view of fig. 6, fig. 8 is a SEM microstructure of the alloy material obtained after the 5 th step of processing in example 3, and fig. 9 is a partially enlarged view of fig. 8.
Detailed Description
The invention relates to a preparation method for constructing an ultrafine grain structure in magnesium alloy, which comprises the following alloy components in percentage by mass: 0.5-3 wt% of Al, 0.6-3.5 wt% of Bi, 0.3-2.0 wt% of Sn and 0.005-0.1 wt% of Ca, wherein the mass ratio of the element content Bi in the alloy is as follows: sn=1.7-2.0:1, the balance Mg and unavoidable impurities, the steps of:
preparing and batching intermediate alloy in the step (1): firstly, preparing an Mg-50Bi intermediate alloy and an Mg-40Sn intermediate alloy, then preparing a commercial Mg-20Ca intermediate alloy, a commercial pure magnesium with the purity of 99.95 wt% and a pure aluminum with the purity of 99.99 wt% as raw materials by using the Mg-50Bi intermediate alloy, the Mg-40Sn intermediate alloy and the commercial Mg-20Ca intermediate alloy, and mixing according to the component range;
and (2) casting: placing a pure Mg ingot into a crucible of a smelting furnace, setting the furnace temperature to be 710-760 ℃ and keeping, adding the Mg-20Ca intermediate alloy preheated to 100-200 ℃ into a melt after the pure magnesium is melted, adding the pure Al preheated to 100-200 ℃ after the pure Mg ingot is melted, and sequentially adding the Mg-50Bi intermediate alloy and the Mg-40Sn intermediate alloy preheated to 100-180 ℃ into the magnesium melt after the pure Mg ingot is dissolved; preserving heat for 10-30 minutes, mechanically stirring for 1-3 minutes, preserving heat for 5-10 minutes, and skimming surface scum; finally, pouring the mixture into a metal mold,preparing an alloy cast ingot; the casting process is that CO 2 And SF (sulfur hexafluoride) 6 Is carried out under the protection of the mixed gas of the (2);
and (3) solution treatment: carrying out solution treatment on the alloy ingot obtained in the previous step, firstly preserving heat for 5-12h at 400-420 ℃, then introducing Ar gas, raising the temperature of a hearth to 450-490 ℃ under the atmosphere of Ar, preserving heat for 2-5 h, taking out, cooling, and closing an Ar gas valve;
step (4) pre-extrusion processing: pre-extruding the blank after solution treatment, firstly heating the blank to be extruded to 270-400 ℃, putting the blank into an extrusion die for pre-extruding, wherein the extrusion deformation speed is 10-20 m/min, the extrusion ratio is 10-40:1, the extrusion temperature is 270-400 ℃, and cooling the blank to room temperature in air after extrusion processing to obtain the blank with fine grain structure;
and (5) room temperature ECAP processing: coating lubricant on the surface of the extruded wrought alloy blank obtained in the step (4), placing the alloy blank into a die at room temperature, and performing equal channel angular extrusion forming at room temperature; finally, the wrought magnesium alloy material with the superfine crystal structure is obtained.
In the preparation method, mg-50Bi intermediate alloy is prepared in the step (1): pure magnesium with commercial purity of 99.95 and wt percent and pure Bi with purity of 99.95 and wt percent are taken as raw materials, pure Mg ingots are placed into a crucible of a smelting furnace, the furnace temperature is set to 710 ℃ and kept, after the pure Bi ingots are melted, pure Bi blocks preheated to 50-70 ℃ are added into magnesium melt, the temperature is kept for 10-30 minutes, stirring is carried out for 1-3 minutes after the melting, the temperature is kept for 5-10 minutes, and Mg-50Bi intermediate alloy is obtained after casting into a die; the Mg-50Bi intermediate alloy is prepared by the following steps of 2 And SF (sulfur hexafluoride) 6 Is carried out under the protection of the mixed gas.
In the preparation method, mg-40Sn intermediate alloy is prepared in the step (1): pure magnesium with commercial purity of 99.95 wt% and pure Sn with purity of 99.95 wt% are taken as raw materials, pure Mg ingots are put into a crucible of a smelting furnace, the furnace temperature is set to 710 ℃ and kept, after the pure Mg ingots are melted, pure Sn blocks preheated to 50-70 ℃ are added into magnesium melt, the temperature is kept for 10-30 minutes, stirring is carried out for 1-3 minutes after the melting, the temperature is kept for 5-10 minutes, and Mg-4 is obtained after the melting, and the materials are poured into a die0Sn master alloy; the process for preparing the intermediate alloy is that CO 2 And SF (sulfur hexafluoride) 6 Is carried out under the protection of the mixed gas of the (2);
the preparation method comprises the step (1) of mixing CO in the gas 2 Volume: SF (sulfur hexafluoride) 6 The volume is not less than 95:5.
In the preparation method, the cooling process in the step (3) is quenching and cooling in warm water at 50-100 ℃.
In the preparation method, the extrusion processing technology in the step (4) may be either forward extrusion or backward extrusion.
According to the preparation method, in the step (5), the temperature range of room temperature ECAP processing is 20-35 ℃, the extrusion speed is 10-15mm/s, the channel angle is 110-160 degrees, the channel is Bc channel or C channel, the extrusion passes are 1-4 times, the sample extrusion process does not need to apply pressure, the blank does not need to be sheathed, only the surface of the blank is coated with lubricant, and the equal channel extrusion die does not need to be lubricated.
The technical content of the present invention is further developed by the following examples, which are all implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation procedures are given, but the protection scope of the present invention is not limited to the following examples.
Example 1: designing an alloy component of Mg-2.5Al-1.14Bi-0.6Sn-0.008Ca (wt%) (mass ratio: bi: sn=1.9:1), and constructing an ultrafine grain structure through the following processing and preparation steps:
preparing intermediate alloy in the step (1): commercial pure Mg (99.95%) and pure Bi (99.95%) are taken as raw materials, pure Mg ingot is put into a crucible of a smelting furnace, and CO is added into the crucible 2 And SF (sulfur hexafluoride) 6 Is mixed with the mixed gas (volume ratio CO) 2 ：SF 6 =100: 5) Under the protection, setting the furnace temperature at 710 ℃, starting heating, adding pure Bi blocks preheated to 60 ℃ into the magnesium melt after the Mg ingot is melted, preserving heat for 20 minutes, stirring for 1.5 minutes after melting, preserving heat for 6 minutes, and pouring into a mould to obtain Mg-50Bi intermediate alloy for later use; commercial pure magnesium (99.95%) and pure Sn (99.95%) are taken as raw materials, pure Mg ingot is put into a crucible of a smelting furnace, and CO is added 2 And SF (sulfur hexafluoride) 6 Is mixed with the mixed gas (volume ratio CO) 2 ：SF 6 =100: 5) Under the protection, setting the furnace temperature at 710 ℃, starting heating, adding pure Sn blocks preheated to 60 ℃ into the magnesium melt after the pure Sn blocks are melted, preserving the heat for 20 minutes, stirring for 1.5 minutes after the pure Sn blocks are melted, preserving the heat for 8 minutes, and pouring the mixed solution into a die to obtain Mg-40Sn intermediate alloy for later use; the Mg-50Bi master alloy, the Mg-40Sn master alloy, the commercial Mg-20Ca master alloy, the commercial pure magnesium (99.95%) and the pure aluminum (99.99%) prepared by the method are taken as raw materials, and the weight percentage of the Mg-2.5Al-1.14Bi-0.6Sn-0.008Ca (wt%) (the mass ratio: bi: sn=1.9:1) alloy components are taken as target components for proportioning;
and (2) casting: placing pure Mg ingot into a crucible of a smelting furnace, setting the furnace temperature at 730 ℃ and keeping, adding Mg-20Ca intermediate alloy preheated to 150 ℃ into a melt after pure magnesium is melted, adding pure Al preheated to 150 ℃ after the pure Mg ingot is melted, and sequentially adding Mg-50Bi intermediate alloy and Mg-40Sn intermediate alloy preheated to 150 ℃ into the magnesium melt after the pure Mg ingot is melted; preserving heat at 730 ℃ for 12 minutes, mechanically stirring for 1.5 minutes, preserving heat for 10 minutes, and skimming surface scum; finally pouring the alloy ingot into a metal mould to prepare an alloy ingot, wherein the casting temperature is 730 ℃, and the mould is preheated to 200 ℃; the whole casting process is that CO 2 ：SF 6 =100:1 (volume ratio) under mixed gas protection;
and (3) solution treatment: carrying out solution treatment on the alloy ingot obtained in the previous step, firstly preserving heat at 400 ℃ for 6 hours, then introducing Ar gas, raising the furnace temperature to 450 ℃ under the Ar atmosphere, preserving heat for 3 hours, taking out a blank, putting the blank into 60 ℃ for quenching in warm water, and closing an Ar gas valve;
step (4) pre-extrusion processing: the blank after solution treatment is skidded and is used as a pre-extrusion blank, the pre-extrusion blank is heated to 300 ℃, and is put into an extrusion die for forward extrusion processing, the temperature of an extrusion cylinder is 300 ℃, the die temperature is 300 ℃, the extrusion speed is 15m/min, and the extrusion ratio is 25:1, cooling the material obtained after extrusion processing in air to room temperature to obtain an extrusion state material, wherein the extrusion temperature is 300 ℃;
and (5) room temperature ECAP processing: the extrusion state alloy blank obtained through pre-extrusion processing is processed into a blank with the diameter of 12mm and the length of 70mm, the surface of the blank is coated with lubricant, the lubricant is not needed in an equal-channel angular extrusion die, the alloy blank is put into the die at room temperature, 2-pass equal-channel angular Extrusion (ECAP) processing at room temperature is carried out, the temperature measured during the ECAP processing at room temperature is 25 ℃, the extrusion speed is 15mm/s, the channel angular is 120 degrees, the path is a C path, the pressure is not needed to be applied during the sample extrusion process, and the blank does not need to be externally coated with a sheath.
FIG. 1 is a TEM structure diagram of the alloy material obtained after the 5 th step of processing in example 1, in which a large number of ultra-fine crystal grains (shown by black arrows in FIG. 1) with grain sizes below 1 μm (100-500 nm) appear, and it is illustrated that the technical scheme of the present invention can simply and efficiently construct an ultra-fine crystal structure in a magnesium alloy under the combined action of a low-cost material component design method and a simple preparation process. In addition, a small amount of nano-scale Mg is also contained in the alloy 2 The (SnBi) phase (indicated by the white arrow in fig. 1) shows that although the elemental content of the alloy is low and most of the alloying elements are solid-dissolved in the matrix, there is still a small amount of dynamic precipitation of the second phase due to ECAP processing at room temperature. These ultra-fine grain structures, nano-scale Mg 2 The (SnBi) precipitated phase and the solid solution element synergistically improve the mechanical properties of the alloy. The room temperature tensile mechanical properties of the finally obtained alloy are as follows: the elongation is 52 percent, the yield strength is 192MPa, the tensile strength is 236MPa, and excellent strong plastic matching is shown.
Example 2: designing an alloy component of Mg-2.0Al-2.0Bi-1.0Sn-0.05Ca (weight percent) (mass ratio: bi: sn=2.0:1), and constructing an ultrafine grain structure through the following processing preparation steps:
preparing intermediate alloy in the step (1): commercial pure Mg (99.95%) and pure Bi (99.95%) are taken as raw materials, pure Mg ingot is put into a crucible of a smelting furnace, and CO is added into the crucible 2 And SF (sulfur hexafluoride) 6 Is mixed with the mixed gas (volume ratio CO) 2 ：SF 6 =100: 5) Under the protection, setting the furnace temperature at 710 ℃, starting heating, adding pure Bi blocks preheated to 60 ℃ into the magnesium melt after the Mg ingot is melted, preserving heat for 20 minutes, stirring for 1.5 minutes after the melting, preserving heat for 6 minutes, and pouring into a mould to obtain the Mg-50Bi intermediate alloyUsing; commercial pure magnesium (99.95%) and pure Sn (99.95%) are taken as raw materials, pure Mg ingot is put into a crucible of a smelting furnace, and CO is added 2 And SF (sulfur hexafluoride) 6 Is mixed with the mixed gas (volume ratio CO) 2 ：SF 6 =100: 5) Under the protection, setting the furnace temperature at 710 ℃, starting heating, adding pure Sn blocks preheated to 60 ℃ into the magnesium melt after the pure Sn blocks are melted, preserving the heat for 20 minutes, stirring for 1.5 minutes after the pure Sn blocks are melted, preserving the heat for 8 minutes, and pouring the mixed solution into a die to obtain Mg-40Sn intermediate alloy for later use; the Mg-50Bi master alloy, the Mg-40Sn master alloy, the commercial Mg-20Ca master alloy, the commercial pure magnesium (99.95%) and the pure aluminum (99.99%) prepared by the method are taken as raw materials, and the weight percentage of the alloy components of Mg-2.0Al-2.0Bi-1.0Sn-0.05Ca (wt%) (the mass ratio: bi: sn=2.0:1) is taken as a target component for proportioning;
and (2) casting: placing pure Mg ingot into a crucible of a smelting furnace, setting the furnace temperature at 730 ℃ and keeping, adding Mg-20Ca intermediate alloy preheated to 150 ℃ into a melt after pure magnesium is melted, adding pure Al preheated to 150 ℃ after the pure Mg ingot is melted, and sequentially adding Mg-50Bi intermediate alloy and Mg-40Sn intermediate alloy preheated to 150 ℃ into the magnesium melt after the pure Mg ingot is melted; preserving heat at 730 ℃ for 14 minutes, mechanically stirring for 1.5 minutes, preserving heat for 10 minutes, and skimming surface scum; finally pouring the alloy ingot into a metal mould to prepare an alloy ingot, wherein the casting temperature is 730 ℃, and the mould is preheated to 200 ℃; the whole casting process is that CO 2 ：SF 6 =100:1 (volume ratio) under mixed gas protection;
and (3) solution treatment: carrying out solution treatment on the alloy ingot obtained in the previous step, firstly preserving heat at 400 ℃ for 6 hours, then introducing Ar gas, raising the furnace temperature to 460 ℃ under the atmosphere of Ar, preserving heat for 3.5 hours, taking out a blank, putting the blank into 60 ℃ of warm water for quenching, and closing an Ar gas valve;
step (4) pre-extrusion processing: the blank after solution treatment is skidded and is used as a pre-extrusion blank, the pre-extrusion blank is heated to 310 ℃, and is put into an extrusion die for forward extrusion processing, the temperature of an extrusion cylinder is 310 ℃, the temperature of the die is 310 ℃, the extrusion speed is 14m/min, and the extrusion ratio is 25:1, the extrusion temperature is 310 ℃, and the material obtained after extrusion processing is cooled to room temperature in the air to obtain an extrusion state material;
and (5) room temperature ECAP processing: the extrusion state alloy blank obtained through pre-extrusion processing is processed into a blank with the diameter of 12mm and the length of 72mm, the surface of the blank is coated with lubricant, the lubricant is not needed in an equal channel angular extrusion die, the alloy blank is placed into the die at room temperature, 4-pass room temperature ECAP processing is carried out, the temperature measured during the room temperature ECAP processing is 28 ℃, the extrusion speed is 12mm/s, the channel angular rotation is 120 DEG, the path is a Bc path, the pressure is not needed to be applied in the sample extrusion process, and the blank does not need to be externally coated with sheath treatment.
Fig. 2 and 3 are SEM microscopic structure diagrams of the alloy material obtained after the 5 th step of processing in example 2, from which it can be seen that there are a large number of ultra-fine crystal grains with grain size below 1 μm (700-nm) in the alloy, which illustrates that the technical scheme of the invention can simply and efficiently construct ultra-fine crystal structure in magnesium alloy under the combined action of low-cost material component design method and simple preparation process, and the proportion fraction of the ultra-fine crystal structure is higher, can reach more than 60%, and the ultra-fine crystal structure is uniformly distributed. Further, the microstructure of the alloy is detected by a TEM, and fig. 4 and 5 are TEM structure diagrams of the alloy material obtained after the processing in the step 5 in the embodiment 2, and ultrafine crystal grains (shown by white arrows in fig. 4) with the grain size of less than 1 μm (800-nm) in the alloy can be found, so that the technical scheme of the invention can be further verified to construct an ultrafine crystal structure in the magnesium alloy; in addition, a large amount of submicron-order Mg was found near the grain boundaries of the ultra-fine grain grains 2 (SnBi) precipitated phase particles (shown by black arrows in FIG. 4) having a size of about 200nm, and these fine precipitated phase particles may be formed by pinning grain boundaries of recrystallized grains to inhibit the growth of the recrystallized grains. The method shows that the superfine crystal structure is obtained as a result of the mutual matching comprehensive effect of the material component design and the preparation method. These ultra-fine grain structures, nano-scale Mg 2 The (SnBi) precipitated phase and the solid solution element system improve the mechanical properties of the alloy. The room temperature tensile mechanical properties of the finally obtained alloy are as follows: the elongation is 48-48%, the yield strength is 203-245 MPa, and the tensile strength is 245MPa, so that the excellent strong plastic matching is also shown.
Example 3: designing an alloy component of Mg-1.5Al-3.4Bi-2.0Sn-0.08Ca (wt%) (mass ratio: bi: sn=1.7:1), and constructing an ultrafine grain structure through the following processing and preparation steps:
preparing intermediate alloy in the step (1): commercial pure Mg (99.95%) and pure Bi (99.95%) are taken as raw materials, pure Mg ingot is put into a crucible of a smelting furnace, and CO is added into the crucible 2 And SF (sulfur hexafluoride) 6 Is mixed with the mixed gas (volume ratio CO) 2 ：SF 6 =100: 5) Under the protection, setting the furnace temperature at 710 ℃, starting heating, adding pure Bi blocks preheated to 60 ℃ into the magnesium melt after the Mg ingot is melted, preserving heat for 20 minutes, stirring for 1.5 minutes after melting, preserving heat for 6 minutes, and pouring into a mould to obtain Mg-50Bi intermediate alloy for later use; commercial pure magnesium (99.95%) and pure Sn (99.95%) are taken as raw materials, pure Mg ingot is put into a crucible of a smelting furnace, and CO is added 2 And SF (sulfur hexafluoride) 6 Is mixed with the mixed gas (volume ratio CO) 2 ：SF 6 =100: 5) Under the protection, setting the furnace temperature at 710 ℃, starting heating, adding pure Sn blocks preheated to 60 ℃ into the magnesium melt after the pure Sn blocks are melted, preserving the heat for 20 minutes, stirring for 1.5 minutes after the pure Sn blocks are melted, preserving the heat for 8 minutes, and pouring the mixed solution into a die to obtain Mg-40Sn intermediate alloy for later use; the Mg-50Bi master alloy, the Mg-40Sn master alloy, the commercial Mg-20Ca master alloy, the commercial pure magnesium (99.95%) and the pure aluminum (99.99%) prepared by the method are taken as raw materials, and the weight percentage of the Mg-1.5Al-3.4Bi-2.0Sn-0.08Ca (wt%) (the mass ratio: bi: sn=1.7:1) alloy components are taken as target components for proportioning;
placing pure Mg ingot into a crucible of a smelting furnace, setting the furnace temperature at 730 ℃ and keeping, adding Mg-20Ca intermediate alloy preheated to 150 ℃ into a melt after pure magnesium is melted, adding pure Al preheated to 150 ℃ after the pure Mg ingot is melted, and sequentially adding Mg-50Bi intermediate alloy and Mg-40Sn intermediate alloy preheated to 150 ℃ into the magnesium melt after the pure Mg ingot is melted; preserving heat at 730 ℃ for 15 minutes, mechanically stirring for 1.5 minutes, preserving heat for 10 minutes, and skimming surface scum; finally pouring the alloy ingot into a metal mould to prepare an alloy ingot, wherein the casting temperature is 730 ℃, and the mould is preheated to 200 ℃; the whole casting process is that CO 2 ：SF 6 =100:1 (volume ratio) under mixed gas protection;
and (3) solution treatment: carrying out solution treatment on the alloy ingot obtained in the previous step, firstly preserving heat at 400 ℃ for 6 hours, then introducing Ar gas, raising the furnace temperature to 460 ℃ under the Ar atmosphere, preserving heat for 4 hours, taking out a blank, putting the blank into 60 ℃ for quenching in warm water, and closing an Ar gas valve;
step (4) pre-extrusion processing: the blank after solution treatment is skidded and is used as a pre-extrusion blank, the pre-extrusion blank is heated to 330 ℃, and is put into an extrusion die for forward extrusion processing, the temperature of an extrusion cylinder is 330 ℃, the die temperature is 330 ℃, the extrusion speed is 16m/min, and the extrusion ratio is 30:1, cooling the material obtained after extrusion processing in air to room temperature to obtain an extrusion state material, wherein the extrusion temperature is 330 ℃;
and (5) room temperature ECAP processing: the extrusion state alloy blank obtained through pre-extrusion processing is processed into a blank with the diameter of 12mm and the length of 70mm, the surface of the blank is coated with lubricant, the lubricant is not needed in an equal channel angular extrusion die, the alloy blank is placed into the die at room temperature, 4-pass room temperature ECAP processing is carried out, the temperature measured during the room temperature ECAP processing is 30 ℃, the extrusion speed is 10mm/s, the channel angular rotation is 120 DEG, the path is a Bc path, the pressure is not needed to be applied in the sample extrusion process, and the blank does not need to be externally coated with sheath treatment.
FIGS. 6 and 7 are SEM micrograph of the pre-extruded billet obtained after the 4 th step of the process of example 3, from which it can be seen that the grain size in the alloy after the pre-extrusion is relatively small (3-10 μm) but does not reach submicron order. After the 5 th processing, the structure of the alloy is further refined on the basis of the extruded fine grain structure. Fig. 8 and 9 are SEM microstructure diagrams of the alloy material obtained after the 5 th step of processing in example 3, in which a large number of ultra-fine crystal grains (shown by black arrows in fig. 9) with grain sizes below 1 μm (100-500 nm) appear, and it is illustrated that the technical scheme of the present invention can simply and efficiently construct an ultra-fine crystal structure in a magnesium alloy under the combined actions of a low-cost material component design method and a simple preparation process. In addition, a large amount of submicron-order Mg was found near the grain boundaries of the ultra-fine grain grains 2 (SnBi) precipitated phase particles (white particles in FIG. 9)The size is around 200nm, and the particles of these dynamic precipitated phases are significantly increased, significantly more than the second phase fraction in the extruded structure (FIG. 7), and these fine precipitated phase particles can inhibit the growth of recrystallized grains by pinning the grain boundaries of the recrystallized grains. Also shows that the superfine crystal structure in the technical proposal is obtained as a result of the mutual matching comprehensive effect of the material composition design and the preparation method. These ultra-fine grain structures, nano-scale Mg 2 The (SnBi) precipitated phase and the solid solution element in the matrix synergistically improve the mechanical properties of the alloy. The room temperature tensile mechanical properties of the finally obtained alloy are as follows: the elongation is 47-47%, the yield strength is 215-MPa, the tensile strength is 258-MPa, and excellent strong plastic matching is shown.
In conclusion, the technical scheme of the invention gives excellent processing performance to the magnesium alloy under the combined action of a simple material component design method and a high-efficiency preparation process, breaks through the limitation that the magnesium alloy is difficult to be processed at room temperature ECAP, and introduces submicron-level Mg into the magnesium alloy 2 The (SnBi) phase can simply and efficiently construct an ultrafine grain structure in the magnesium alloy, and can prepare the magnesium alloy material with excellent toughness.
The starting materials and equipment used in the above examples were all obtained by known means and the operating procedures used are within the skills of a person skilled in the art. The invention is not a matter of the known technology.
Claims (7)
1. A preparation method for constructing an ultrafine grain structure in magnesium alloy is characterized by comprising the following alloy components in percentage by mass: 0.5-3 wt% of Al, 0.6-3.5 wt% of Bi, 0.3-2.0 wt% of Sn and 0.005-0.1 wt% of Ca, wherein the mass ratio of the element content Bi in the alloy is as follows: sn=1.7-2.0:1, the balance Mg and unavoidable impurities, the steps of:
preparing and batching intermediate alloy in the step (1): firstly, preparing an Mg-50Bi intermediate alloy and an Mg-40Sn intermediate alloy, then preparing a commercial Mg-20Ca intermediate alloy, a commercial pure magnesium with the purity of 99.95 wt% and a pure aluminum with the purity of 99.99 wt% as raw materials by using the Mg-50Bi intermediate alloy, the Mg-40Sn intermediate alloy and the commercial Mg-20Ca intermediate alloy, and mixing according to the component range;
step (2) casting: placing a pure Mg ingot into a crucible of a smelting furnace, setting the furnace temperature to be 710-760 ℃ and keeping, adding the Mg-20Ca intermediate alloy preheated to 100-200 ℃ into a melt after the pure magnesium is melted, adding the pure Al preheated to 100-200 ℃ after the pure Mg ingot is melted, and sequentially adding the Mg-50Bi intermediate alloy and the Mg-40Sn intermediate alloy preheated to 100-180 ℃ into the magnesium melt after the pure Mg ingot is melted; preserving heat for 10-30 minutes, mechanically stirring for 1-3 minutes, preserving heat for 5-10 minutes, and skimming surface scum; finally pouring into a metal mold to prepare an alloy cast ingot; the casting process is that CO 2 And SF (sulfur hexafluoride) 6 Is carried out under the protection of the mixed gas of the (2);
and (3) solution treatment: carrying out solution treatment on the alloy ingot obtained in the previous step, firstly preserving heat for 5-12h at 400-420 ℃, then introducing Ar gas, raising the temperature of a hearth to 450-490 ℃ under the atmosphere of Ar, preserving heat for 2-5 h, taking out, cooling, and closing an Ar gas valve;
step (4) pre-extrusion processing: pre-extruding the blank after solution treatment, firstly heating the blank to be extruded to 270-400 ℃, putting the blank into an extrusion die for pre-extruding, wherein the extrusion deformation speed is 10-20 m/min, the extrusion ratio is 10-40:1, the extrusion temperature is 270-400 ℃, and cooling the blank to room temperature in air after extrusion processing to obtain the blank with fine grain structure;
and (5) room temperature ECAP processing: coating lubricant on the surface of the extruded wrought alloy blank obtained in the step (4), placing the alloy blank into a die at room temperature, and performing equal channel angular extrusion forming at room temperature; finally, the wrought magnesium alloy material with the superfine crystal structure is obtained.
2. The method for producing an ultrafine grain structure in a magnesium alloy according to claim 1, wherein: preparing an Mg-50Bi intermediate alloy in the step (1): pure magnesium with commercial purity of 99.95 and wt percent and pure Bi with purity of 99.95 and wt percent are taken as raw materials, pure Mg ingots are put into a crucible of a smelting furnace, the furnace temperature is set to 710 ℃ and kept, after the pure Mg ingots are melted, pure Bi blocks preheated to 50-70 ℃ are added into magnesium melt, the temperature is kept for 10-30 minutes, stirring is carried out for 1-3 minutes after the melting, the temperature is kept for 5-10 minutes, and the pure Bi blocks are poured into a die to obtain the magnesium alloyMg-50Bi master alloy; the Mg-50Bi intermediate alloy is prepared by the following steps of 2 And SF (sulfur hexafluoride) 6 Is carried out under the protection of the mixed gas.
3. The method for producing an ultrafine grain structure in a magnesium alloy according to claim 1, wherein: preparing an Mg-40Sn intermediate alloy in the step (1): pure magnesium with commercial purity of 99.95 wt% and pure Sn with purity of 99.95 wt% are used as raw materials, pure Mg ingots are placed into a crucible of a smelting furnace, the furnace temperature is set to 710 ℃ and kept, after the pure Mg ingots are melted, pure Sn blocks preheated to 50-70 ℃ are added into magnesium melt, the temperature is kept for 10-30 minutes, stirring is carried out for 1-3 minutes after the melting, the temperature is kept for 5-10 minutes, and Mg-40Sn intermediate alloy is obtained after casting into a die; the process for preparing the intermediate alloy is that CO 2 And SF (sulfur hexafluoride) 6 Is carried out under the protection of the mixed gas.
4. The method for producing an ultrafine grain structure in a magnesium alloy according to claim 1, wherein: CO in the mixed gas in the step (1) 2 Volume: SF (sulfur hexafluoride) 6 The volume is not less than 95:5.
5. The method for producing an ultrafine grain structure in a magnesium alloy according to claim 1, wherein: and (3) quenching and cooling in water at the temperature of 50-100 ℃ in the cooling process.
6. The method for producing an ultrafine grain structure in a magnesium alloy according to claim 1, wherein: and (3) the extrusion processing technology in the step (4) is forward extrusion or backward extrusion.
7. The method for producing an ultrafine grain structure in a magnesium alloy according to claim 1, wherein: in the step (5), the temperature range of room temperature ECAP processing is 20-35 ℃, the extrusion speed is 10-15mm/s, the channel angle is 110-160 degrees, the path is a Bc path or a C path, and the extrusion passes are 1-4 times.
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Effective date of registration: 20240329 Address after: 458030 sL-5, Beixin Village, Dabai Line, Jinshan Office, Qibin District, Hebi City, Henan Province Patentee after: Hebi Magnesium Technology Co.,Ltd. Country or region after: China Address before: 730050, No. 287 Lan Ping Road, Qilihe District, Gansu, Lanzhou Patentee before: LANZHOU University OF TECHNOLOGY Country or region before: China |