CN114892109B - Treatment method for improving performance of high-Zn light medium-entropy alloy - Google Patents
Treatment method for improving performance of high-Zn light medium-entropy alloy Download PDFInfo
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Abstract
Hair brushThe invention discloses a treatment method for improving the performance of a high-Zn light medium-entropy alloy, belonging to the technical field of rolling of entropy alloys. The treatment method is to utilize micro-droplets to rapidly cool and mold Al 78 Zn 13 Mg 5 Li 2 Cu 2 The high-Zn light medium-entropy alloy is subjected to sheath hot rolling treatment by keeping the temperature at 380 ℃ for 240 min; then completing solution treatment by combining with heat preservation for 15min-30min at the temperature of 420-450 ℃, placing the alloy after solution treatment in a heat treatment furnace, and performing heat preservation aging treatment for 22h-24h at the temperature of 100-140 ℃ to obtain the high-Zn light medium-entropy alloy with improved performance; the light medium-entropy alloy prepared by the method has uniform temperature, good stress state and uniform deformation, can effectively slow down or inhibit cracking, obviously reduces the number of second phases in the alloy, and solves the problems of difficult solid solution of the second phases and poor mechanical properties of the high-Zn light medium-entropy alloy.
Description
Technical Field
The invention belongs to the technical field of rolling of entropy alloys, and particularly relates to a treatment method for improving the performance of a high-Zn light medium-entropy alloy.
Background
Aluminum alloy is one of the most widely used lightweight materials in industry, and has been widely used for aircraft housings, automobile structural members, and the like. However, for the conventional aluminum alloy, although many trace elements are added to improve the mechanical properties, the composition design range is almost unchanged for many years, i.e., the mass fraction of Al is more than 90at.%, and the content of each alloying element does not exceed 5at.%. The mechanical properties of the aluminum alloy are limited by the composition design concept. Therefore, the search for new materials to replace traditional aluminum alloys is urgently needed, and a new material design concept is sought.
In recent years, high Entropy Alloys (HEA) have received much attention due to their unique structures. Elements in the high-entropy alloy are mixed in a nearly equal atomic ratio, and the high-entropy effect enables the alloy to form a stable solid solution phase structure more easily. The high-entropy alloy has a thermodynamic high-entropy effect, a structural lattice distortion effect, a kinetic delayed diffusion effect and a performance 'cocktail' effect. Compared with the traditional alloy, the high-entropy alloy has excellent mechanical property and corrosion resistance and wider component design space.
It follows that the concept of entropy increase is the developmentNovel light alloys offer promising approaches, so Medium Entropy Alloys (MEA) have become the focus of research for novel light alloys. The content of Al element is reduced, the content of Zn element is increased, the entropy value of an alloy system can be effectively improved, and more MgZn is promoted 2 And a precipitate phase is generated, so that the mechanical property of the alloy is improved.
The microdroplet fast cooling forming technology is one technological process of atomizing alloy liquid with high pressure inert gas into fine molten drops, flying and cooling in high speed gas flow and depositing in the blank before complete solidification. The prepared alloy has fine crystal grains, uniform structure and low macrosegregation, and is beneficial to improving the mechanical property of the alloy. The medium-entropy alloy prepared by the droplet rapid cooling forming technology can simultaneously show high MgZn 2 The phase content and the size of low alloy crystal grains greatly improve the mechanical property compared with the traditional aluminum alloy. On the one hand, however, excessive Zn element exceeds the maximum solid solution amount of the Al matrix, so that the Zn element is difficult to be solid-dissolved into the matrix, and the mechanical property is reduced; on the other hand, the conventional long-time heat treatment process can increase the size of alloy grains, so that the advantage of fine alloy grains prepared by droplet rapid cooling and forming is reduced. In order to solve this problem, it is necessary to increase the solubility of Zn by subsequent rolling and to limit the alloy grain size by short-time solution treatment.
Disclosure of Invention
In order to solve the problems, the invention provides a treatment method for improving the performance of a high-Zn light medium-entropy alloy, which comprises the following steps: carrying out sheath hot rolling treatment and short-time solid solution aging treatment on the high-Zn light medium-entropy alloy obtained by utilizing droplet rapid cooling forming;
the high-Zn light medium-entropy alloy is Al 78 Zn 13 Mg 5 Li 2 Cu 2 (at.%), its density ρ =2.8g/cm 3 ；
In order to reduce alloy grains and macro segregation and make an alloy structure uniform, the high-Zn light medium-entropy alloy is prepared by a microdroplet rapid cooling forming technology;
1) In order to facilitate rolling, 2-series aluminum alloy material with hardness slightly lower than that of the medium-entropy alloy is selected to manufacture a sheath die, and thenAl 78 Zn 13 Mg 5 Li 2 Cu 2 The medium-entropy alloy is cut into blanks matched with the cavity of the sheath die, the blanks are pressed into the sheath cavity, the alloy is tightly matched with the sheath cavity, and then the upper part of the cavity is covered with a metal cover and is welded to be dead, so that the blanks are tightly matched with the cavity wall of the die, the stress in the rolling process is more uniform, and the problem of alloy oxidation in the high-temperature heat preservation process is avoided;
2) Placing the sheath in a resistance furnace, preserving heat for 240min at 380 ℃, taking out, carrying out rolling treatment at the temperature, placing the blank with the sheath in a heating furnace after each pass is finished, returning to the furnace and preserving heat for 30min, and then carrying out rolling of the next pass for 10-12 times in total, wherein the rolling deformation of each pass is 5-10%;
3) After rolling is finished, removing the sheath material, and flattening the alloy in a vacuum furnace to obtain a hot-rolled alloy;
4) Determining the solid solution temperature of the hot-rolled alloy by using Differential Scanning Calorimetry (DSC), and sequentially carrying out solid solution treatment and aging treatment on the rolled alloy to obtain the high-Zn light medium-entropy alloy with improved performance;
the solution treatment process comprises the following steps: preserving heat for 15min-30min at 420-450 ℃, and placing in water for cooling; to avoid Al 78 Zn 13 Mg 5 Li 2 Cu 2 The crystal grain of the medium entropy alloy grows in the solid solution treatment stage, and a short-time solid solution treatment mode is selected.
The aging treatment process comprises the following steps: placing the alloy after the solution treatment in a heat treatment furnace, preserving the heat for 22-24 h at the temperature of 100-140 ℃, and placing in air for cooling;
5) By diffusion model
Calculating the correlation of the time required by the solution treatment under different hot rolling temperature conditions;
in the above formula: r is 0 The size of the second phase of the hot rolled alloy obtained in the step 3), namely the initial radius of the second phase; d is a diffusion coefficient; t is diffusion time；C 1 -C 0 ＝ΔX，C 2 -C 1 ＝ΔY，C 0 Is r 0 Concentration of Al element, C 1 Is r 1 In the concentration of Al element, C 2 Is r 2 The concentration of Al element.
For convenience of calculation, the second phase in the alloy is simplified into a spherical shape and is dispersed in an alpha-Al matrix, and a model schematic diagram is shown in FIG. 16.
In the solution treatment process of the alloy, the second phase and the matrix phase (alpha-Al) generate mutual diffusion of elements, and according to Fick diffusion law, the diffusion flux of the elements is as follows:
when the second phase and the matrix phase (alpha-Al) are subjected to element interdiffusion, al atoms in the matrix are diffused into the second phase through a diffusion interface, and solid solution of the second phase is promoted. At the boundary r of the second phase 1 In dt time, volume element
The amount of Al required for solid solution was:
at the same time, at the boundary r of the second phase 1 The amount of Al entering the volume element through the diffusion interface is:
according to the law of conservation of mass, the amount of Al required for solid solution of the second phase per unit time is equal to the amount of diffusion into it, and can be established at the second phase boundary r 1 Solid solution equation of (a):
the formula is arranged to obtain:
to simplify the calculation, C 1 -C 0 ＝ΔX，C 2 -C 1 ＝ΔY.
The equation (5) is integrated to obtain:
after completion of the solid solution, the second phase disappears completely, so r 1 =0, substituting the above equation yields:
in the above formulas: j is the diffusion flux, r 0 Is the initial radius of the second phase, r 1 For the second phase radius after a period of diffusion, r 2 Is the diffusion region radius, C 0 Is r 0 In the concentration of Al element, C 1 Is r 1 In the concentration of Al element, C 2 Is r 2 The concentration of Al element, D is diffusion coefficient and t is diffusion time.
Step 2) in the rolling process: the first rolling deformation is 5%, and the subsequent rolling deformation is 10%.
The heat preservation process in the resistance furnace in the step 2) is as follows: the heat preservation is carried out at 380 ℃, and 380 ℃ is the optimal heat treatment temperature. In order to ensure the experimental safety of the rolling process, the rolling deformation of the first pass is 5%, and then the rolling deformation is increased to 10%. The small deformation multi-pass rolling can reduce the stress concentration in the structure in the rolling process, avoid rolling fracture and refine grains. After each pass of rolling, the blank together with the sheath is placed in a heat treatment furnace for heat preservation for 30min, the internal attraction caused by the previous pass of rolling is released, and meanwhile, the blank is uniformly heated again, thereby creating favorable conditions for the next pass of rolling.
The rolling speed of the step 2) is 150r/min.
Preferably, the solution treatment process: the solid solution temperature is 450 ℃, the solid solution time is 30min, and then the mixture is taken out quickly and placed in water for cooling.
The aging process comprises the following steps: the ageing temperature is 125 ℃, the ageing time is 24 hours, and then the material is taken out and placed in the air for cooling.
The method of short-time solution treatment can reduce the problem of alloy grain growth caused by long-time heat preservation to the maximum extent. The peak value aging treatment is carried out at 125 ℃, which is higher than the aging treatment temperature (120 ℃) of the traditional aluminum alloy, and the high-Zn medium-entropy alloy MgZn can be accelerated 2 Formation of a dispersed phase.
The periphery of the sheathing die in the step 1) is cuboid, a die cavity for placing blanks is arranged in the middle of the sheathing die, and the sheathing die and the die cavity are equal in length and width; so as to obtain better sheath rolling effect, the stress is uniform during rolling, and the cracking is not easy to generate;
the length and the width of the die cavity are 35 to 50 percent of the peripheral length and the width of the sheath die; the height of the die cavity is 60-80% of the height of the periphery of the sheath die.
Preferably, the width of the cavity of the die in the step 1) is 41.2% of the peripheral width of the sheath die; the height of the die cavity is 50.0% of the height of the periphery of the sheath die.
The invention has the beneficial effects that:
1. the invention provides the components of the high-Zn light medium-entropy alloy, and the improvement of the entropy value of an alloy system is beneficial to the formation of a special solid solution structure of the alloy and the improvement of the plasticity of the alloy; increasing the Zn content can increase the MgZn content in the alloy 2 The phase content is favorable for improving the strength of the alloy, and the design and selection of the components can simultaneously ensure that the alloy has excellent plasticity and strength.
2. The invention provides a method for improving the performance of a light medium-entropy alloy obtained by utilizing droplet rapid cooling forming through sheath hot rolling and solid solution aging treatment. Wherein, in order to avoid the crystal grain growth of the alloy in the solution treatment stage, a treatment mode of firstly hot rolling and then solution treatment is selected. The hot rolling and the short-time solution treatment are sheathed, the solubility of Zn element in an Al matrix is improved, the alloy is ensured to maintain a lower grain size, and the research scheme of the experiment has guiding significance for the subsequent processing treatment of other medium-entropy and high-entropy alloys.
3. The invention is suitable for the structure optimization of the medium-entropy and high-entropy alloy in a sheath hot rolling mode, and can achieve the following effects: 1) The porosity of the alloy prepared by micro-droplet rapid forming is reduced; 2) Forming deformation texture and improving mechanical property; 3) The driving force of the alloy is increased, so that the second phase in the alloy can be dissolved into the matrix more easily.
Drawings
FIG. 1 is an as-cast alloy DSC curve;
FIG. 2 is a direct solid solution microstructure of an as-cast alloy;
FIGS. 3a and 3b are schematic diagrams illustrating the structure and dimensions of a sheathing die;
FIG. 4 is a diagram of a jacket object;
FIG. 5 is an electron backscatter diffraction pattern (EBSD) of the alloy product obtained in comparative example 2;
FIG. 6 is a microstructure profile of an alloy product obtained in comparative example 2;
FIG. 7 is a microstructure morphology of the alloy product obtained in comparative example 3;
FIG. 8 is a macroscopic photograph of the billet of example 1 after rolling;
FIG. 9 is XRD patterns of the billets of example 1 and comparative example 4 before rolling and after hot rolling at different temperatures;
FIG. 10 is a Scanning Electron Microscope (SEM) image of the alloy after hot rolling at 380 ℃ in example 1;
FIG. 11 is an Electron Back Scattering Diffraction (EBSD) pattern of grains of example 1 after hot rolling at 380 ℃;
FIG. 12 is a scanning electron micrograph of an alloy subjected to solution treatment at 450 ℃ in example 1;
FIG. 13 is a transmission electron micrograph of an alloy aged at 125 ℃ in example 1;
FIG. 14 is a chart of mechanical properties testing of the high Zn light medium entropy alloy raw material used in step 1 of example 1;
FIG. 15 is a chart of the mechanical properties of the high Zn light medium entropy alloy of example 1 after the properties thereof are improved;
FIG. 16 is a schematic view of a diffusion model;
FIG. 17 is a microstructure topography of the alloy product obtained in example 3;
wherein, 1-sheathing die, 2-die cavity and 3-cover body.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific examples:
a treatment method for improving the performance of high-Zn light medium-entropy alloy comprises the following steps: carrying out sheath hot rolling treatment and short-time solid solution aging treatment on the high-Zn light medium-entropy alloy obtained by utilizing droplet rapid cooling forming;
the high-Zn light medium-entropy alloy is Al 78 Zn 13 Mg 5 Li 2 Cu 2 (at.%), its density ρ =2.8g/cm 3 ；
In order to reduce alloy grains and macro segregation and make an alloy structure uniform, the high-Zn light medium-entropy alloy is prepared by a microdroplet rapid cooling forming technology;
1) In order to facilitate rolling, 2 series aluminum alloy material with hardness slightly lower than that of the medium entropy alloy is selected to manufacture a sheath die, and Al is added 78 Zn 13 Mg 5 Li 2 Cu 2 The medium-entropy alloy is cut into blanks matched with the cavity of the sheath die, the blanks are pressed into the sheath cavity, the alloy is tightly matched with the sheath cavity, and then the upper part of the cavity is covered with the metal cover body 3 and is welded to be dead, so that the blanks are tightly matched with the cavity wall of the die, the stress in the rolling process is more uniform, and the problem of alloy oxidation in the high-temperature heat preservation process is avoided;
the periphery of the sheathing die 1 is cuboid, a die cavity 2 for placing blanks is arranged in the middle of the sheathing die, and the length and the width of the sheathing die and the die cavity are equal, so that a better sheathing rolling effect is obtained, the stress is uniform during rolling, and cracking is not easy to generate; the length and the width of the die cavity are 35 to 50 percent of the peripheral length and the peripheral width of the sheath die; the height of the die cavity is 60-80% of the height of the periphery of the sheath die.
2) Placing the sheath in a resistance furnace, preserving heat for 240min at 380 ℃, taking out and carrying out rolling treatment at the temperature, placing the blank together with the sheath in a heating furnace after each pass is finished, returning to the furnace and preserving heat for 30min, then carrying out rolling of the next pass for 10-12 times in total, wherein the rolling deformation of each pass is 5-10%, and the rolling speed is 150r/min;
3) After rolling is finished, removing the jacket material, placing the rolled sample without the jacket in a heat treatment furnace, preserving heat for 15-60 min at 420-450 ℃, and then performing water quenching to obtain hot-rolled alloy;
4) Determining the solid solution temperature of the hot-rolled alloy by using Differential Scanning Calorimetry (DSC), and sequentially carrying out solid solution treatment and aging treatment on the rolled alloy to obtain the high-Zn light medium-entropy alloy with improved performance;
the solution treatment process comprises the following steps: preserving heat for 15min-30min at 420-450 ℃, and placing in water for cooling; in order to avoid Al 78 Zn 13 Mg 5 Li 2 Cu 2 The crystal grain of the medium entropy alloy grows in the solid solution treatment stage, and a short-time solid solution treatment mode is selected.
The aging treatment process comprises the following steps: placing the alloy after the solution treatment in a heat treatment furnace, preserving the heat for 22-24 h at the temperature of 100-140 ℃, and placing in air for cooling;
5) By diffusion model
The correlation of the time required by the solution treatment under different hot rolling temperature conditions is calculated, and the solution treatment time required under other hot rolling temperature conditions is calculated according to the known certain hot rolling temperature and the initial radius of the second phase at the temperature, so that the process flow is greatly simplified, and the economic benefit of actual production is improved.
The specific calculation process of the diffusion model is as follows:
for convenience of calculation, the second phase in the alloy is simplified into a spherical shape and is dispersed in an alpha-Al matrix, and a model schematic diagram is shown in FIG. 16.
In the solution treatment process of the alloy, the second phase and the matrix phase (alpha-Al) generate mutual diffusion of elements, and according to Fick diffusion law, the diffusion flux of the elements is as follows:
when the second phase and the matrix phase (alpha-Al) are subjected to element interdiffusion, al atoms in the matrix are diffused into the second phase through a diffusion interface, and solid solution of the second phase is promoted. At the boundary r of the second phase 1 In dt time, volume element
The amount of Al required for solid solution was:
at the same time, at the boundary r of the second phase 1 The amount of Al entering the volume element through the diffusion interface is:
according to the law of conservation of mass, the amount of Al required for solid solution of the second phase per unit time is equal to the amount of diffusion into it, and can be established at the second phase boundary r 1 Solid solution equation of (a):
the formula is arranged to obtain:
to simplify the calculation, C 1 -C 0 ＝ΔX，C 2 -C 1 ＝ΔY.
Integrating equation (5) can obtain:
after completion of the solid solution, the second phase disappears completely, so r 1 =0, substituting the above equation yields:
in the above formulas: j is the diffusion flux, r 0 Initial radius of second phase, r 1 For the second phase radius after a period of diffusion, r 2 Is the diffusion region radius, C 0 Is r 0 Concentration of Al element, C 1 Is r 1 Concentration of Al element, C 2 Is r 2 The concentration of Al element, D is diffusion coefficient and t is diffusion time.
Comparative example 1:
a treatment method for improving the performance of a high-Zn light medium-entropy alloy comprises the following components: al (aluminum) 78 Zn 13 Mg 5 Li 2 Cu 2 (at.%). The treatment method comprises the steps of droplet rapid cooling forming and solution treatment;
the method comprises the following specific steps:
1) And (3) preparing an alloy ingot by droplet rapid cooling forming.
2) The solution temperature of the hot-rolled alloy is determined by Differential Scanning Calorimetry (DSC), the temperature is determined according to DSC, the DSC curve is shown in figure 1, and the solution temperature is selected to be lower than 467 ℃ according to the DSC curve.
3) The test selects a water-cooling solid solution process after heat preservation for 30min at the temperature of 450 ℃, the microscopic morphology of the alloy after solid solution is shown in figure 2, the second phase in the alloy is not dissolved into the matrix, and the obvious growth phenomenon appears, which proves that the process is not suitable for the solid solution treatment of the alloy with the components.
Comparative example 2:
treatment method for improving performance of high-Zn light medium-entropy alloy and componentsComprises the following steps: al (Al) 78 Zn 13 Mg 5 Li 2 Cu 2 (at.%). The treatment method comprises droplet rapid cooling forming, sheath hot rolling treatment and solid solution treatment;
the method comprises the following specific steps:
1) And (3) preparing an alloy ingot by droplet rapid cooling forming.
And 2 series aluminum alloy is selected as a sheath material, the 2 series aluminum alloy is processed according to the drawings shown in fig. 3a and fig. 3b, and a cavity is processed in the middle. The periphery of the sheath die is square, a die cavity for placing a blank and a cover body cavity for placing a cover body are processed in the middle of the sheath die, and the sheath object is shown in figure 4.
Wherein, the peripheral dimension of the sheath mould is length, width and height =148 multiplied by 30mm; the cover size length width height =64 × 64 × 7.5mm; the length, width and height of the sample and the die cavity before rolling are =61 × 61 × 15mm, so that a better sheath rolling effect is obtained, the stress is uniform during rolling, and cracking is not easy to generate; the sample size after rolling was 5mm thick.
The width of the die cavity is 41.2% of the width of the periphery of the sheath die; the height of the die cavity is 50.0% of the height of the periphery of the sheath die.
Al prepared by quickly cooling and forming microdroplets 78 Zn 13 Mg 5 Li 2 Cu 2 The light medium-entropy alloy is processed in a linear cutting mode to obtain a blank matched with a die cavity and required by hot rolling.
And pressing the light medium-entropy alloy blank into the sheath cavity, enabling the alloy to be tightly matched with the sheath cavity, and then covering the upper part of the cavity with a metal cover body and welding the metal cover body to be dead.
2) And (2) putting the wrapped blank into a heat treatment furnace to heat along with the furnace, keeping the temperature at 400 ℃ for 240min, taking out the blank to be rolled, wherein the rolling speed is 150r/min, the first-pass rolling deformation is 5%, the subsequent rolling deformation of each pass is 10%, after each-pass rolling is finished, putting the blank into the heat treatment furnace, keeping the temperature at 400 ℃ for 30min, rolling for 10-12 passes in total, and the size of the rolled sample is 5mm.
The Electron Back Scattering Diffraction (EBSD) of the alloy grains at the hot rolling parameters is shown in fig. 5, which shows that the grains in the alloy are recrystallized to form equiaxed grains.
3) After the hot-rolled alloy obtained in the step 2) is subjected to solution treatment at 450 ℃ for 30min, a second phase is not dissolved in a matrix and grows up obviously (figure 6), and the micro morphology is not beneficial to improving the mechanical property of the alloy.
Comparative example 3:
a treatment method for improving the performance of a high-Zn light medium-entropy alloy comprises the following components: al (Al) 78 Zn 13 Mg 5 Li 2 Cu 2 (at.%). The treatment method comprises droplet rapid cooling forming, sheath hot rolling treatment and solid solution treatment;
the method comprises the following specific steps:
1) And (3) preparing an alloy ingot by droplet rapid cooling forming.
2) Selecting 2 series aluminum alloy as a jacket material, processing the 2 series aluminum alloy according to drawings shown in figures 3a and 3b, and processing a cavity in the middle. The periphery of the sheath die is square, a die cavity for placing a blank and a cover body cavity for placing a cover body are processed in the middle of the sheath die, and the sheath object is shown in figure 4.
Wherein, the peripheral dimension of the sheath mould is length, width and height =148 multiplied by 30mm; the cover size length width height =64 × 64 × 7.5mm; the length, width and height of the sample and the die cavity before rolling are =61 × 61 × 15mm, so that a better sheath rolling effect is obtained, the stress is uniform during rolling, and cracking is not easy to generate; the sample size after rolling was 5mm thick.
The width of the die cavity is 41.2% of the width of the periphery of the sheath die; the height of the die cavity is 50.0% of the height of the periphery of the sheath die.
Al prepared by quickly cooling and forming microdroplets 78 Zn 13 Mg 5 Li 2 Cu 2 The light medium-entropy alloy is processed in a linear cutting mode to obtain a blank matched with a die cavity and required by hot rolling.
And pressing the light medium-entropy alloy blank into the sheath cavity, enabling the alloy to be tightly matched with the sheath cavity, and then covering the upper part of the cavity with a metal cover body and welding the metal cover body to be dead.
3) And (2) putting the wrapped blank into a heat treatment furnace to heat along with the furnace, keeping the temperature at 400 ℃ for 240min, taking out the blank to be rolled, wherein the rolling speed is 150r/min, the first-pass rolling deformation is 5%, the subsequent rolling deformation of each pass is 10%, after each-pass rolling is finished, putting the blank into the heat treatment furnace, keeping the temperature at 360 ℃ for 30min, rolling for 10-12 passes in total, and the size of the rolled sample is 5mm.
4) After rolling solution treatment (450 ℃,30 min), the second phase is not dissolved in the matrix and grows up obviously (figure 7), and the micro-morphology is not beneficial to improving the mechanical property of the alloy.
Example 1
A treatment method for improving the performance of a high-Zn light medium-entropy alloy comprises the following components: al (Al) 78 Zn 13 Mg 5 Li 2 Cu 2 (at.%). The treatment method comprises droplet rapid cooling forming, sheath hot rolling treatment and solid solution aging treatment;
the method comprises the following specific steps:
1) Preparation of Al by droplet rapid cooling forming 78 Zn 13 Mg 5 Li 2 Cu 2 (at.%) alloy ingot.
And 2 series aluminum alloy is selected as a sheath material, the 2 series aluminum alloy is processed according to the drawings shown in fig. 3a and fig. 3b, and a cavity is processed in the middle. The periphery of the sheath die 1 is square, a die cavity 2 for placing a blank and a cover body cavity for placing a cover body 3 are processed in the middle of the sheath die, and the sheath object is shown in figure 4.
Wherein, the peripheral dimension of the sheath mould is the length, width and height =148 multiplied by 30mm; the cover size length width height =64 × 64 × 7.5mm; the length, width and height of the sample and the die cavity before rolling are =61 × 61 × 15mm, so that a better sheath rolling effect is obtained, the stress is uniform during rolling, and cracking is not easy to generate; the sample size after rolling was 5mm thick.
The width of the die cavity is 41.2% of the width of the periphery of the sheath die; the height of the die cavity is 50.0% of the height of the periphery of the sheath die.
Al prepared by quickly cooling and forming microdroplets 78 Zn 13 Mg 5 Li 2 Cu 2 (at.%) light medium-entropy alloy, adding by wire cuttingAnd obtaining the blank required by hot rolling matched with the cavity of the die.
The light medium-entropy alloy blank is pressed into the capsule cavity, the alloy is tightly matched with the capsule cavity, and then the upper part of the cavity is covered with the metal cover body and is welded to be dead.
2) Putting the wrapped blank into a heat treatment furnace to heat along with the furnace, preserving heat for 240min at 380 ℃, taking out the blank to be rolled, wherein the rolling speed is 150r/min, the first-pass rolling deformation is 5%, the subsequent rolling deformation of each pass is 10%, after each-pass rolling is finished, putting the blank into the heat treatment furnace, preserving heat for 30min at 380 ℃, rolling for 12 passes in total, and the size of the rolled sample is 5mm thick, and the real object is shown in FIG. 8;
after hot rolling at 380 ℃, the alloy forms a deformation texture, a Scanning Electron Microscope (SEM) is shown in figure 10, electron Back Scattering Diffraction (EBSD) of crystal grains is shown in figure 11, and fibrous crystal grains can improve the mechanical property of the alloy.
3) After rolling is finished, removing the sheath material, and flattening the alloy in a vacuum furnace to obtain a hot-rolled alloy;
4) The solution temperature of the hot rolled alloy was determined by Differential Scanning Calorimetry (DSC), which was determined by DSC, which is shown in FIG. 1, and was selected to be less than 467 deg.C.
Putting the rolled alloy into a heat treatment furnace, carrying out solution treatment at 450 ℃ and preserving heat for 15min, and then carrying out water quenching; the Scanning Electron Microscope (SEM) picture of the alloy after the solution treatment at 450 ℃ is shown in figure 12, and the second phase in the alloy after the solution treatment is basically dissolved in the matrix, so that the alloy after the rolling treatment is proved to be easier to achieve a good solution effect.
After the solution treatment is finished, the alloy is kept at the temperature of 125 ℃ for 24h, then is taken out for air cooling, and the transmission electron microscope of the alloy subjected to the aging treatment at the temperature of 125 ℃ is shown in figure 13, and as can be seen from figures a and b under different magnifications and a diffraction chart c, a large amount of dispersion strengthening MgZn is generated in the alloy 2 Phase (1); the high-Zn light medium-entropy alloy with improved performance is obtained.
After the rolling solution aging treatment, the tensile strength of the alloy is 618MPa, the elongation at break is 6 percent (figure 15), the tensile strength is far higher than that of the prepared high-Zn light medium-entropy alloy without any subsequent treatment (230MPa, 5 percent and figure 14), and the strength is improved by 10 percent compared with that of the 7 series aluminum alloy.
In the embodiment, al is solved by reasonably setting the rolling temperature, the rolling deformation of each pass, the solid solution temperature and the solid solution time 78 Zn 13 Mg 5 Li 2 Cu 2 The light medium-entropy alloy has the problems of low Zn solid solution amount, large crystal grains and low density, and greatly improves the mechanical property of the alloy.
Comparative example 4
The hot rolling temperature in the example 1 is changed to 360 ℃ and 400 ℃, and other conditions are not changed, so that the high-Zn light medium-entropy alloy is prepared.
Characterization test
The alloy sample before hot rolling in example 1 was designated as sample 0, the alloy of comparative example 2 having hot rolling temperatures of 360 ℃ and 400 ℃ was designated as sample 1 and sample 3, respectively, and the alloy obtained in example 1 was designated as sample 2, and XRD measurements were carried out.
Before and after hot rolling of sheath, al 78 Zn 13 Mg 5 Li 2 Cu 2 The change trend of the high-Zn light medium-entropy alloy structure is as follows:
in sample 1, after hot rolling at 360 ℃, a main peak 2 theta =44.702 corresponding to an alpha-Al (200) crystal face;
the bragg formula 2dsin θ = n λ can obtain, and α -Al lattice constants a of the alloy in four states are: 0.4052, 0.4054, 0.4060, 0.4054. The XRD results are shown in fig. 9. The larger the solid solution amount of Zn in the alpha-Al matrix is, the larger the lattice constant of the alpha-Al matrix is; the lattice constants of the hot-rolled samples are all larger than that of the original blank, and the results prove that Al is obtained after hot rolling 78 Zn 13 Mg 5 Li 2 Cu 2 The solid solution amount of Zn of the light medium entropy alloy is increased, and particularly after hot rolling at 380 ℃, the solid solution of Zn is increasedThe amount is maximal.
Example 2
A treatment method for improving the performance of a high-Zn light medium-entropy alloy comprises the following components: al (Al) 78 Zn 13 Mg 5 Li 2 Cu 2 (at.%). The other steps are the same as the embodiment 1, and the solid solution time required by the hot rolling temperature of different sheaths is calculated through an autonomously designed diffusion model.
The method comprises the following specific steps:
according to diffusion model equation (7):
the sizes of the second phases (i.e. initial sizes of solid solutions) in the alloy are respectively 1 μm (figure 10) and 4 μm (figure 7) at the hot rolling temperature of the sheath of 380 ℃ and 400 ℃, namely r in the formula 0 Respectively 1 and 4. When the temperature of the sheath hot rolling is 380 ℃ and 400 ℃, D, delta X and delta Y are equal in the formula. When the hot rolling temperature of the sheath is 380 ℃, the time for the second phase to be completely dissolved into the matrix is t 380 (ii) a When the hot rolling temperature of the sheath is 400 ℃, the time for the second phase to be completely dissolved into the matrix is t 400 (ii) a Therefore, t 380 Is only t 400 1/16 of the total amount of the molten steel, and long-time solid solution causes the grain size to grow, so that the advantage of rapid cooling and forming of microdroplets is reduced, and the hot rolling temperature of the sheath is 380 ℃ which is the optimal solid solution temperature.
Example 3
The hot rolling temperature in the example 1 is increased to 400 ℃, the Al is obtained after treatment under the conditions of the same solid solution temperature and solid solution time and the unchanged other treatment steps and parameters 78 Zn 13 Mg 5 Li 2 Cu 2 A large amount of incompletely solid-dissolved second phases exist in the light intermediate-entropy alloy.
According to the prediction result of the embodiment 2, the hot rolling temperature in the embodiment 1 is increased to 400 ℃, the heat preservation is carried out for 4h at the solid solution temperature of 450 ℃, and Al is obtained after the treatment under the condition that other treatment steps and parameters are not changed 78 Zn 13 Mg 5 Li 2 Cu 2 The solid solution condition of the second phase in the matrix in the light intermediate entropy alloy is good, and the result is shown in FIG. 17. Thereby is paired withThe comparative data prove that the diffusion model of the application can accurately predict the solid solution time required by different sheath hot rolling temperatures.
Claims (7)
1. A treatment method for improving the performance of a high-Zn light medium-entropy alloy is characterized by comprising the following steps: carrying out sheath hot rolling treatment and short-time solid solution aging matching on the high-Zn light medium-entropy alloy obtained by utilizing microdroplet rapid cooling forming;
the high-Zn light medium-entropy alloy is Al 78 Zn 13 Mg 5 Li 2 Cu 2 （at. %）；
1) Selecting 2 series aluminum alloy material to manufacture a sheath die, and adding Al 78 Zn 13 Mg 5 Li 2 Cu 2 Cutting the medium-entropy alloy into a blank matched with the cavity of the sheath die, pressing the blank into the sheath cavity, enabling the alloy to be tightly matched with the sheath cavity, covering a metal cover on the upper part of the cavity of the die, and welding the metal cover to ensure that the blank is tightly matched with the cavity wall of the die;
2) Placing the sheath in a resistance furnace, preserving heat for 240min at 380 ℃, taking out, carrying out rolling treatment at 380 ℃, placing the blank with the sheath in a heating furnace after each pass is finished, returning to the furnace and preserving heat for 30min, and then carrying out rolling of the next pass for 10-12 times in total, wherein the rolling deformation of each pass is 5-10%;
3) After rolling is finished, removing the sheath material, and flattening the alloy in a vacuum furnace to obtain a hot-rolled alloy;
4) Sequentially carrying out solid solution treatment and aging treatment on the rolled alloy to obtain the high-Zn light medium-entropy alloy with improved performance;
the solution treatment process comprises the following steps: preserving heat for 15min-30min at 420-450 ℃, and placing in water for cooling;
the aging treatment process comprises the following steps: and (3) placing the alloy subjected to the solution treatment in a heat treatment furnace, preserving the heat for 22-24 h at the temperature of 100-140 ℃, and placing in air for cooling.
2. The treatment method for improving the performance of the high-Zn light medium-entropy alloy is characterized in that in the step 2) rolling process: the first rolling deformation is 5%, and the subsequent rolling deformation is 10%.
3. The treatment method for improving the performance of the high-Zn light medium-entropy alloy in accordance with claim 2, wherein the rolling rate in the step 2) is 150r/min.
4. The treatment method for improving the performance of the high-Zn light medium-entropy alloy according to claim 1, characterized in that the solution treatment process comprises the following steps: the solid solution temperature is 450 ℃, the solid solution time is 30min, and then the mixture is taken out quickly and placed in water for cooling.
5. The treatment method for improving the performance of the high-Zn light medium-entropy alloy is characterized by comprising the following steps of: the ageing temperature is 125 ℃, the ageing time is 24 hours, and then the material is taken out and placed in the air for cooling.
6. The treatment method for improving the performance of the high-Zn light medium-entropy alloy according to claim 1, wherein the shape of the periphery of the sheath die in the step 1) is a cuboid, a die cavity for placing a blank is arranged in the middle of the sheath die, and the length and the width of the blank and the die cavity are equal;
the length and the width of the die cavity are 35 to 50 percent of the peripheral length and the width of the sheath die; the height of the die cavity is 60-80% of the height of the periphery of the sheath die.
7. The treatment method for improving the performance of the high-Zn light medium-entropy alloy is characterized in that the width of the cavity of the die in the step 1) is 41.2% of the peripheral width of the sheath die; the height of the die cavity is 50.0% of the height of the periphery of the sheath die.
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