CN109280829B - High-strength cast Mg-Zn-Cu-Zr alloy and preparation method thereof - Google Patents
High-strength cast Mg-Zn-Cu-Zr alloy and preparation method thereof Download PDFInfo
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- 239000000956 alloy Substances 0.000 title claims abstract description 101
- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 89
- REDXJYDRNCIFBQ-UHFFFAOYSA-N aluminium(3+) Chemical class [Al+3] REDXJYDRNCIFBQ-UHFFFAOYSA-N 0.000 title claims abstract description 88
- 229910017985 Cu—Zr Inorganic materials 0.000 title claims abstract description 37
- 238000002360 preparation method Methods 0.000 title claims abstract description 11
- 238000007711 solidification Methods 0.000 claims abstract description 29
- 229910052802 copper Inorganic materials 0.000 claims abstract description 16
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 15
- 239000012535 impurity Substances 0.000 claims abstract description 7
- 238000010438 heat treatment Methods 0.000 claims description 33
- 229910052751 metal Inorganic materials 0.000 claims description 18
- 239000002184 metal Substances 0.000 claims description 18
- 239000002994 raw material Substances 0.000 claims description 17
- OKTJSMMVPCPJKN-UHFFFAOYSA-N carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 14
- 229910002804 graphite Inorganic materials 0.000 claims description 14
- 239000010439 graphite Substances 0.000 claims description 14
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- 229910052582 BN Inorganic materials 0.000 claims description 8
- PZNSFCLAULLKQX-UHFFFAOYSA-N N#B Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 claims description 8
- 238000001816 cooling Methods 0.000 claims description 8
- 238000003723 Smelting Methods 0.000 claims description 6
- 238000000137 annealing Methods 0.000 claims description 6
- 238000005520 cutting process Methods 0.000 claims description 6
- 238000000265 homogenisation Methods 0.000 claims description 6
- 230000001681 protective Effects 0.000 claims description 6
- 238000003756 stirring Methods 0.000 claims description 6
- 239000007788 liquid Substances 0.000 claims description 5
- 238000004140 cleaning Methods 0.000 claims description 4
- 238000001035 drying Methods 0.000 claims description 4
- 240000004375 Petrea volubilis Species 0.000 claims description 2
- 101700073801 gpa-6 Proteins 0.000 claims description 2
- 238000004506 ultrasonic cleaning Methods 0.000 claims description 2
- 229910026551 ZrC Inorganic materials 0.000 claims 1
- 238000004519 manufacturing process Methods 0.000 claims 1
- 238000005266 casting Methods 0.000 abstract description 7
- 238000009826 distribution Methods 0.000 abstract description 4
- 238000007792 addition Methods 0.000 abstract description 3
- 239000007769 metal material Substances 0.000 abstract description 3
- 239000011777 magnesium Substances 0.000 description 41
- 239000012071 phase Substances 0.000 description 17
- 229910007565 Zn—Cu Inorganic materials 0.000 description 13
- 210000001787 Dendrites Anatomy 0.000 description 8
- 238000000034 method Methods 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 6
- 230000005496 eutectics Effects 0.000 description 6
- 238000005728 strengthening Methods 0.000 description 6
- 229910000636 Ce alloy Inorganic materials 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 4
- 238000001125 extrusion Methods 0.000 description 4
- 229910000861 Mg alloy Inorganic materials 0.000 description 3
- 239000000654 additive Substances 0.000 description 3
- 230000000996 additive Effects 0.000 description 2
- 230000032683 aging Effects 0.000 description 2
- 238000005275 alloying Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000009776 industrial production Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000000155 melt Substances 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C23/00—Alloys based on magnesium
- C22C23/04—Alloys based on magnesium with zinc or cadmium as the next major constituent
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
- C22C1/03—Making non-ferrous alloys by melting using master alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/02—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working in inert or controlled atmosphere or vacuum
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/06—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon
Abstract
The invention belongs to the technical field of metal material engineering, and provides a high-strength cast Mg-Zn-Cu-Zr alloy and a preparation method thereof. The weight percentages of the components are as follows: 4 to 10 percent of Zn, 0.1 to 1.0 percent of Cu, 0.1 to 0.5 percent of Zr and the balance of Mg. The addition of the low-cost element Zr can not only refine grains, but also reduce the damage of other impurity elements to the alloy structure and performance. The solidification of the conventional casting Mg-Zn-Cu-Zr alloy under a high GPa grade pressure refines the solidification structure of the alloy and improves Mg (Zn, Cu)2The form and distribution of the phases further expand the mechanical property and the high-temperature application range of the Mg-Zn-Cu-Zr alloy.
Description
Technical Field
The invention belongs to the technical field of metal material engineering, and relates to a high-strength cast Mg-Zn-Cu-Zr alloy and a preparation method thereof.
Background
The magnesium alloy has good specific strength, specific stiffness, thermal conductivity, shock resistance and machinability, is widely applied to light-weight industrial production of high-end automobiles, aerospace and the like, becomes the most attractive potential substitute in the aluminum alloy and steel industry, and is known as '21 st century green metal material'. However, the magnesium alloy has low strength, poor plasticity, expensive alloying additives and the like, so that the popularization and application of the magnesium alloy in industrial production are greatly limited.
The Mg-Zn-Cu alloy is a Mg-Zn heat-resistant alloy which is successfully applied commercially so far, has better high-temperature performance below 150 ℃, and is successfully applied to parts needing medium and high temperature resistance, such as automobile engine parts, propellers and the like. But because of casting Mg-Zn-Cu alloyCoarse texture and main strengthening phase Mg (Zn, Cu)2Eutectic phase is connected into a network and distributed among the dendrites, and not only Mg (Zn, Cu)2The strengthening effect of the phase cannot be sufficiently exerted and the mechanical properties of the cast Mg-Zn-Cu alloy are also degraded. In order to further improve the mechanical properties of Mg-Zn-Cu alloys, technicians try to develop research around alloying, heat treatment and extrusion processes, such as: patent CN 102071345a discloses a Mg-Zn-Cu alloy containing Zr, which comprises the following components by weight percent: 5-7% of Zn, 0.5-2% of Cu, 0.3-0.8% of Zr and the balance of Mg, wherein after full heat treatment, the maximum tensile strength, the yield strength and the elongation rate respectively reach 240-270 MPa, 160-190 MPa and 11-17%; buha researches the influence of aging treatment on the performance of Mg-6Zn-2Cu-0.1Mn alloy, and the maximum tensile strength, yield strength and elongation of the alloy reach 220-253 MPa, 121-168 MPa and 2.8-8.6% respectively (J.Buha, mechanical properties of naturallyagedMg-Zn-Cu-Mnalloy, Materials Science and engineering A, 2008, 489: 127-; the impact of an extrusion process on the performance of the Mg-Zn-Cu-Ce alloy is researched by Zhaochong, and the tensile strength, yield strength and elongation of the alloy treated by different extrusion processes reach 293-321 MPa, 215-282 MPa and 2.04-15.7% respectively (Zhaochi, research on the organization and performance of the Mg-Zn-Cu-Ce alloy, the university of Chongqing, Shuichi's academic thesis, 2012).
Although the method improves the mechanical property of the Mg-Zn-Cu alloy, the strengthening phase in the alloy is easy to grow into an overaging phase at high temperature, the strengthening effect is still not ideal, and the introduction of noble metal elements (such as Ce and the like) also increases the alloy cost. Research shows that the Mg-Zn-Cu alloy has better high-temperature performance and Cu exists in eutectic phase Mg (Zn, Cu)2In connection with this, the refining of the cast Mg-Zn-Cu alloy structure, the improvement of Mg (Zn, Cu)2The eutectic phase shape and distribution can obviously improve the mechanical property of the alloy, and the cost is lower.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a novel preparation process of a low-cost and high-performance Mg-Zn-Cu-Zr alloy, wherein the addition of a low-cost element Zr can not only refine grains, but also reduce the texture and the property of other impurity elements to the alloyEnergy is impaired. The solidification of the conventional casting Mg-Zn-Cu-Zr alloy under a high GPa grade pressure refines the solidification structure of the alloy and improves Mg (Zn, Cu)2The form and distribution of the phases further expand the mechanical property and the high-temperature application range of the Mg-Zn-Cu-Zr alloy.
The invention adopts the following technical scheme:
a high-strength cast Mg-Zn-Cu-Zr alloy comprises the following components in percentage by mass: 4 to 10 percent of Zn, 0.1 to 1.0 percent of Cu, 0.1 to 0.5 percent of Zr and the balance of Mg.
The preferable range of the mass percent of the alloy components is as follows: 7% of Zn, 0.5% of Cu, 0.2% of Zr and the balance of Mg.
The preparation method of the high-strength casting Mg-Zn-Cu-Zr alloy comprises the following steps:
(1) adopting an Mg ingot with the purity of 99.99 percent, a Zn ingot with the purity of 99.99 percent, brass with the Cu/Zn mass ratio of 7:3 and Mg-30 percent Zr intermediate alloy as raw materials, and calculating the required mass percent of each raw material according to the target alloy components;
(2) preheating the raw material in the step (1) at 250 ℃;
(3) setting the heating temperature of the crucible resistance furnace to 750-770 ℃, adding Mg ingots and Zn ingots when the crucible temperature reaches 300-350 ℃, and introducing CO in a volume ratio2/SF6Mixed gas of 99:1 is used as smelting protective gas; when Mg ingots and Zn ingots in the crucible are completely melted and the temperature of the crucible reaches 650-700 ℃, sequentially adding brass with the ratio of Cu/Zn being 7:3 and Mg-30% Zr intermediate alloy, and preserving heat for 2-5 min; stirring and removing dross on the surface of the molten liquid when the furnace temperature reaches 750-770 ℃, preserving the heat for 20-30 min, then pouring the molten metal into a preheated metal mold, wherein the preheating temperature of the metal mold is 450-500 ℃, and obtaining the required Mg-Zn-Cu-Zr as-cast alloy material;
(4) putting the prepared Mg-Zn-Cu-Zr as-cast alloy material into a vacuum resistance furnace for carrying out homogenization annealing, setting the temperature to be 240-300 ℃, keeping the temperature for 12-24 hours, and then carrying out wire cutting to obtain a sample for high pressure;
(5) putting the high-pressure sample obtained in the step (4) into a graphite assembly sleeve, putting the assembled graphite assembly sleeve into a cavity position of a high-pressure six-side top, and starting high-pressure solidification after aligning a hammer head: firstly, raising the pressure to a set solidification pressure of 2 GPa-6 GPa, simultaneously starting a temperature measuring device, rapidly heating to a preset heating temperature of 770 ℃ to 970 ℃, preserving heat and maintaining pressure at the temperature for 15min to 20min, turning off a power supply to stop heating, and relieving pressure and taking out after naturally cooling to room temperature to obtain a final alloy sample.
In the step (5), a CS-1B type high-pressure cubic press is used for carrying out a high-pressure solidification experiment, and compared with a two-side press system, the cubic press saves a pre-stressed die and a large frame, and the pressure field in a high-pressure cavity is more ideal.
In the step (5), before the sample for high pressure is loaded into the graphite assembly sleeve, in order to effectively avoid the introduction of impurity elements, the surface of the sample needs to be cleaned: firstly, removing impurities such as oil stains and oxide layers on the surfaces of samples by using 600-2000 # fine sand paper, then putting the samples into an ultrasonic cleaning machine for cleaning, and finally putting the samples into a drying oven at 110 ℃ for drying for more than 12 hours.
In the step (5), before the heating temperature is set, the liquidus temperature of each sample under the action of high pressure of GPa grade needs to be tested. According to the Clausius-Clapeyren equation, the melting point of a substance with pressure change is influenced by the volume change at the time of solid-liquid phase change. Since the melting process of Mg under high pressure is an expansion reaction, the melting point of Mg increases with increasing pressure. Heating and insulating the experimental sample at different temperatures under the action of high pressure of 2-6 GPa respectively, rapidly cooling to room temperature under the condition of pressure maintaining, and determining the liquidus temperature according to the solidification structure characteristics of the experimental sample; the set heating temperature is about the liquidus temperature +30 ℃ of each high-pressure sample.
In the step (5), the crucible for containing the high-pressure solidification sample is a boron nitride crucible, the service temperature of the boron nitride crucible in vacuum is 1800 ℃, the thermal shock resistance of the boron nitride crucible is good, and the boron nitride crucible is not easy to crack under rapid cooling; the size of the boron nitride crucible is selected or machined according to the size of a sample, and if the size of the boron nitride crucible is too large, the sample can be contained and heated, and if the size of the boron nitride crucible is too small, the crucible can be cracked due to thermal expansion in the metal heating process.
In the step (5), before the experiment, each hammer head of the CS-1B type high-pressure cubic press is strictly wiped and checked to determine whether cracks exist.
In the step (5), the CS-1B type high-pressure cubic press needs to be preheated for 30min in advance before being used; the change of an ammeter is concerned at any moment in the heating process, and the current is not suitable to be too large; during pressure relief, the pressure is relieved slowly to 20MPa and then is relieved quickly.
Compared with the prior art, the invention has the following advantages:
1. zr is a low-cost alloy additive element, and the addition of a proper amount of Zr in the Mg-Zn-Cu alloy not only can refine alloy grains, but also can reduce the damage of other impurity elements to the alloy structure and performance, improve the plasticity of the Mg-Zn-Cu alloy and improve the corrosion resistance.
2. The better high-temperature performance of the Mg-Zn-Cu alloy and the existence of Cu in eutectic phase Mg (Zn, Cu)2However, the cast Mg-Zn-Cu alloy has a relatively coarse as-cast structure and a main strengthening phase Mg (Zn, Cu)2Is eutectic phase and is mostly connected in a net shape and distributed among the dendrites. The high-pressure solidification technology can ensure that the Mg-Zn-Cu-Zr alloy obtains more crystal nucleus numbers and obviously refines the solidification structure on one hand, and Mg (Zn, Cu) is obtained in the high-pressure solidification process on the other hand2The eutectic phase network morphology is broken into a discontinuous distribution of granular or island-like morphology, which is more uniformly distributed. Therefore, the strength of the alloy is greatly improved.
3. The Mg-Zn-Cu alloy after aging treatment is easy to grow the strengthening phase in the alloy into an overaging phase when the alloy is in service in a higher temperature range, so that the mechanical property of the alloy is greatly reduced; the Mg-Zn-Cu-Zr alloy prepared by adopting the high-pressure solidification technology has the advantages that the strength and the hardness are obviously improved, the high-temperature performance is more stable, and the maximum compressive strength, the maximum yield strength and the maximum elongation are 320.6-430.3 MPa, 280.2-370.1 MPa and 16.3-21.3% respectively.
Drawings
FIG. 1 is a microstructure of a conventionally cast Mg-7Zn-0.5Cu-0.2Zr alloy at different magnifications;
FIG. 2 shows the microstructure (6GPa) of Mg-7Zn-0.5Cu-0.2Zr alloy prepared by high-pressure solidification under different magnifications.
Detailed Description
The present invention will be further described with reference to specific embodiments, but the present invention is not limited to the following examples.
Example 1: a high-strength cast Mg-Zn-Cu-Zr alloy comprises the following components in percentage by mass: 7% of Zn, 0.8% of Cu, 0.4% of Zr and the balance of Mg, wherein the total mass is 100%.
The preparation method comprises the following steps:
(1) taking Mg ingot and Zn ingot with the purity of 99.99 percent, brass with the Cu/Zn ratio of 7:3 and Mg-30 percent Zr intermediate alloy as raw materials, and proportioning the raw materials according to the alloy component proportion of 7 percent by mass of Zn, 0.8 percent by mass of Cu, 0.4 percent by mass of Zr and the balance of Mg;
(2) preheating the raw material in the step (1) at 250 ℃;
(3) setting the heating temperature of the crucible resistance furnace at 760 ℃, adding Mg ingots and Zn ingots when the crucible temperature reaches 350 ℃, and introducing CO2/SF6Mixed gas of 99:1 is used as smelting protective gas; sequentially adding brass with the ratio of Cu to Zn being 7:3 and Mg-30% Zr intermediate alloy when the Mg ingot and the Zn ingot in the crucible are completely melted and the temperature of the crucible reaches 670 ℃, and preserving the heat for 5 min; stirring when the furnace temperature reaches 760 ℃, removing dross on the surface of the molten liquid, preserving the heat for 20min, and then pouring the molten metal into a preheated metal mold (the preheating temperature of the metal mold is 500 ℃) to obtain the required Mg-Zn-Cu-Zr as-cast alloy material;
(4) putting the prepared Mg-Zn-Cu-Zr as-cast alloy material into a vacuum resistance furnace for carrying out homogenization annealing, setting the temperature at 280 ℃, keeping the temperature for 14 hours, and then carrying out wire cutting to obtain a sample for high pressure;
(5) putting the high-pressure sample obtained in the step (4) into a graphite assembly sleeve, putting the assembled graphite assembly sleeve into a cavity position of a high-pressure six-side top, and starting high-pressure solidification after aligning a hammer head: firstly, raising the pressure to a set solidification pressure of 2GPa, simultaneously starting a temperature measuring device, rapidly heating to a preset heating temperature of 800 ℃, preserving heat and maintaining pressure for 18min at the temperature, turning off a power supply to stop heating, naturally cooling to room temperature, releasing pressure and taking out to obtain a high-strength cast Mg-7Zn-0.8Cu-0.4Zr alloy sample.
Example 2: a high-strength cast Mg-Zn-Cu-Zr alloy comprises the following components in percentage by mass: 8% of Zn, 1% of Cu, 0.3% of Zr and the balance of Mg, wherein the total mass is 100%.
The preparation method comprises the following steps:
(1) taking Mg ingot and Zn ingot with the purity of 99.99 percent, brass with the Cu/Zn ratio of 7:3 and Mg-30 percent Zr intermediate alloy as raw materials, and proportioning according to the alloy component ratio of 8 percent of Zn, 1 percent of Cu, 0.3 percent of Zr and the balance of Mg by mass percent;
(2) preheating the raw material in the step (1) at 250 ℃;
(3) setting the heating temperature of the crucible resistance furnace at 770 ℃, adding Mg ingots and Zn ingots when the crucible temperature reaches 350 ℃, and introducing CO2/SF6Mixed gas of 99:1 is used as smelting protective gas; sequentially adding brass with the ratio of Cu to Zn being 7:3 and Mg-30% Zr intermediate alloy when the Mg ingot and the Zn ingot in the crucible are completely melted and the temperature of the crucible reaches 700 ℃, and preserving the heat for 4 min; stirring when the furnace temperature reaches 770 ℃, removing dross on the surface of the melt, preserving heat for 25min, then pouring the melt into a preheated metal mold (the preheating temperature of the metal mold is 450 ℃) to obtain the required Mg-Zn-Cu-Zr as-cast alloy material;
(4) putting the prepared Mg-Zn-Cu-Zr as-cast alloy material into a vacuum resistance furnace for carrying out homogenization annealing, setting the temperature at 260 ℃, keeping the temperature for 16 hours, and then carrying out wire cutting to obtain a sample for high pressure;
(5) putting the high-pressure sample obtained in the step (4) into a graphite assembly sleeve, putting the assembled graphite assembly sleeve into a cavity position of a high-pressure six-side top, and starting high-pressure solidification after aligning a hammer head: firstly, raising the pressure to a set solidification pressure of 4GPa, simultaneously starting a temperature measuring device, rapidly heating to a preset heating temperature of 850 ℃, preserving heat and maintaining pressure for 15min at the temperature, closing a power supply to stop heating, and releasing pressure and taking out after naturally cooling to room temperature to obtain a high-strength cast Mg-8Zn-1Cu-0.3Zr alloy sample.
Example 3: a high-strength cast Mg-Zn-Cu-Zr alloy comprises the following components in percentage by mass: zn 6%, Cu 1%, Zr 0.2%, and the balance Mg, the total mass being 100%.
The preparation method comprises the following steps:
(1) taking Mg ingot and Zn ingot with the purity of 99.99 percent, brass with the Cu/Zn ratio of 7:3 and Mg-30 percent Zr intermediate alloy as raw materials, and proportioning the raw materials according to the alloy component ratio of 6 percent of Zn, 1 percent of Cu, 0.2 percent of Zr and the balance of Mg;
(2) preheating the raw material in the step (1) at 250 ℃;
(3) setting the heating temperature of the crucible resistance furnace at 750 ℃, adding Mg ingots and Zn ingots when the crucible temperature reaches 300 ℃, and introducing CO2/SF6Mixed gas of 99:1 is used as smelting protective gas; sequentially adding brass with the ratio of Cu to Zn being 7:3 and Mg-30% Zr intermediate alloy when the Mg ingot and the Zn ingot in the crucible are completely melted and the temperature of the crucible reaches 660 ℃, and preserving the heat for 4 min; stirring when the furnace temperature reaches 750 ℃, removing dross on the surface of the molten liquid, preserving the heat for 20min, then pouring the molten metal into a preheated metal mold (the preheating temperature of the metal mold is 450 ℃) to obtain the required Mg-Zn-Cu-Zr as-cast alloy material;
(4) putting the prepared Mg-Zn-Cu-Zr as-cast alloy material into a vacuum resistance furnace for carrying out homogenization annealing, setting the temperature to be 250 ℃, keeping the temperature for 20 hours, and then carrying out wire cutting to obtain a sample for high pressure;
(5) putting the high-pressure sample obtained in the step (4) into a graphite assembly sleeve, putting the assembled graphite assembly sleeve into a cavity position of a high-pressure six-side top, and starting high-pressure solidification after aligning a hammer head: firstly, raising the pressure to the set solidification pressure of 5GPa, simultaneously starting a temperature measuring device, rapidly heating to the preset heating temperature of 900 ℃, preserving heat and maintaining pressure for 20min at the temperature, closing a power supply to stop heating, and releasing pressure and taking out after naturally cooling to the room temperature to obtain the high-strength cast Mg-6Zn-1Cu-0.2Zr alloy sample.
Example 4: a high-strength cast Mg-Zn-Cu-Zr alloy comprises the following components in percentage by mass: 7% of Zn, 0.5% of Cu, 0.2% of Zr and the balance of Mg, wherein the total mass is 100%.
The preparation method comprises the following steps:
(1) taking Mg ingot and Zn ingot with the purity of 99.99 percent, brass with the Cu/Zn ratio of 7:3 and Mg-30 percent Zr intermediate alloy as raw materials, and proportioning the raw materials according to the alloy component proportion of 7 percent by mass of Zn, 0.5 percent by mass of Cu, 0.2 percent by mass of Zr and the balance of Mg;
(2) preheating the raw material in the step (1) at 250 ℃;
(3) setting the heating temperature of the crucible resistance furnace at 760 ℃, adding Mg ingots and Zn ingots when the crucible temperature reaches 300 ℃, and introducing CO2/SF6Mixed gas of 99:1 is used as smelting protective gas; sequentially adding brass with the ratio of Cu/Zn being 7:3 and Mg-30% Zr intermediate alloy when the Mg ingot and the Zn ingot in the crucible are completely melted and the temperature of the crucible reaches 680 ℃, and preserving the heat for 3 min; stirring when the furnace temperature reaches 760 ℃, removing dross on the surface of the molten liquid, preserving the heat for 25min, and then pouring the molten metal into a preheated metal mold (the preheating temperature of the metal mold is 500 ℃) to obtain the required Mg-Zn-Cu-Zr as-cast alloy material;
(4) putting the prepared Mg-Zn-Cu-Zr as-cast alloy material into a vacuum resistance furnace for carrying out homogenization annealing, setting the temperature to be 250 ℃, keeping the temperature for 18 hours, and then carrying out wire cutting to obtain a sample for high pressure;
(5) putting the high-pressure sample obtained in the step (4) into a graphite assembly sleeve, putting the assembled graphite assembly sleeve into a cavity position of a high-pressure six-side top, and starting high-pressure solidification after aligning a hammer head: firstly, raising the pressure to the set solidification pressure of 6GPa, simultaneously starting a temperature measuring device, rapidly heating to the preset heating temperature of 950 ℃, preserving heat and maintaining pressure for 20min at the temperature, closing a power supply to stop heating, and releasing pressure and taking out after naturally cooling to the room temperature to obtain the high-strength cast Mg-7Zn-0.5Cu-0.2Zr alloy sample.
And (3) performance comparison:
the following table shows the room temperature tensile properties of the Mg-Zn-Cu-Zr alloys of the different compositions of the above examples, wherein the comparative alloy 1 and the comparative alloy 2 are respectively near-peak Mg-6Zn-2Cu-0.1Mn alloys (Materials Science and Engineering A2008, 489:127-, the comparative alloy 3 is Mg-Zn-Cu-Zr alloy obtained by casting and subsequent heat treatment of Zhuhongmei et al (patent CN 102071345A), comparative alloy 4 is the room temperature tensile property of Mg-Zn-Cu-Ce alloy obtained by the extrusion process in zhao chong (zhao chong, study on the organization and properties of Mg-Zn-Cu-Ce alloy, thesis in the university of chongqing, university of studios, 2012), and examples 1 to 4 are Mg-Zn-Cu-Zr alloy obtained by using the technology of the present invention.
As can be seen from the above table, the cast Mg-Zn-Cu-Zr alloy prepared by the high-pressure solidification technology has the maximum compressive strength of 320.6-430.3 MPa, the maximum yield strength of 280.2-370.1 MPa and the maximum elongation of 16.3-21.3%. Compared with the comparative alloys 1, 2 and 3, the invention has better compressive strength, yield strength and elongation percentage, better thermal stability and no over-aging phenomenon in the high-temperature long-term service process; compared with comparative alloy 4, the invention does not contain high-cost additive element (Ce), and the casting cost is lower.
FIG. 1 is a microstructure of a conventionally cast Mg-7Zn-0.5Cu-0.2Zr alloy showing that primary crystals of alpha-Mg are coarse dendrite structures, the average size of "dendrite clusters" is about 365 μm, and eutectic second phases of Mg (Zn, Cu) are continuously distributed among the alpha-Mg dendrites2。
FIG. 2 shows the microstructure of Mg-7Zn-0.5Cu-0.2Zr alloy prepared by 6GPa high-pressure solidification. Compared with the conventional casting experimental alloy solidification structure shown in the figure 1, most of primary crystals alpha-Mg in the experimental alloy solidification structure under the action of high pressure are fine equiaxial 'dendrite clusters', the dendrite form is regular and complete, the phenomenon of dissolution and fragmentation is less, the branches are undeveloped, and the average size of the 'dendrite clusters' is about 56 mu m; the network structure formed by the intercrystalline second phase is broken, and the intercrystalline second phase is mostly distributed among alpha-Mg dendrites in a long island shape or granular discontinuous way.
Claims (5)
1. The preparation method of the high-strength cast Mg-Zn-Cu-Zr alloy is characterized by comprising the following steps of:
(1) adopting an Mg ingot with the purity of 99.99 percent, a Zn ingot with the purity of 99.99 percent, brass with the Cu/Zn mass ratio of 7:3 and Mg-30 percent Zr intermediate alloy as raw materials, and calculating the required mass percent of each raw material according to the target alloy components; the weight percentages of the components are as follows: 4 to 10 percent of Zn, 0.1 to 1.0 percent of Cu, 0.1 to 0.5 percent of ZrC and the balance of Mg;
(2) preheating the raw material in the step (1) at 250 ℃;
(3) setting the heating temperature of the crucible resistance furnace to 750-770 ℃, adding Mg ingots and Zn ingots when the crucible temperature reaches 300-350 ℃, and introducing CO in a volume ratio2/SF6Mixed gas of 99:1 is used as smelting protective gas; when Mg ingots and Zn ingots in the crucible are completely melted and the temperature of the crucible reaches 650-700 ℃, sequentially adding brass with the ratio of Cu/Zn being 7:3 and Mg-30% Zr intermediate alloy, and preserving heat for 2-5 min; stirring and removing dross on the surface of the molten liquid when the furnace temperature reaches 750-770 ℃, preserving the heat for 20-30 min, then pouring the molten metal into a preheated metal mold, wherein the preheating temperature of the metal mold is 450-500 ℃, and obtaining the required Mg-Zn-Cu-Zr as-cast alloy material;
(4) putting the prepared Mg-Zn-Cu-Zr as-cast alloy material into a vacuum resistance furnace for carrying out homogenization annealing, setting the temperature to be 240-300 ℃, keeping the temperature for 12-24 hours, and then carrying out wire cutting to obtain a sample for high pressure;
(5) putting the high-pressure sample obtained in the step (4) into a graphite assembly sleeve, putting the assembled graphite assembly sleeve into a cavity position of a high-pressure six-side top, and starting high-pressure solidification after aligning a hammer head: firstly, raising the pressure to a set solidification pressure of 2 GPa-6 GPa, simultaneously starting a temperature measuring device, rapidly heating to a preset heating temperature of 770 ℃ to 970 ℃, preserving heat and maintaining pressure at the temperature for 15min to 20min, turning off a power supply to stop heating, and relieving pressure and taking out after naturally cooling to room temperature to obtain a final alloy sample.
2. The method for preparing the high-strength cast Mg-Zn-Cu-Zr alloy according to claim 1, wherein the mass percentages of the components are as follows: 7% of Zn, 0.5% of Cu, 0.2% of Zr and the balance of Mg.
3. The method for producing a high-strength cast Mg-Zn-Cu-Zr alloy according to claim 1, wherein in step (5), before the sample for high-pressure use is loaded into the graphite assembling sheath, in order to effectively avoid the introduction of impurity elements, the surface of the sample is cleaned: firstly, removing oil stains and oxide layer impurities on each surface of a sample by using 600-2000 # fine sand paper, then putting the sample into an ultrasonic cleaning machine for cleaning, and finally putting the sample into a drying oven at 110 ℃ for drying for more than 12 hours.
4. The method for preparing a high-strength cast Mg-Zn-Cu-Zr alloy according to claim 1, wherein in the step (5), the sample for high pressure is heated and kept at different temperatures under the action of high pressure of 2-6 GPa respectively, and is rapidly cooled to room temperature under the condition of pressure maintaining, and the liquidus temperature is determined according to the solidification structure characteristics; the set heating temperature was the liquidus temperature +30 ℃ for each high pressure sample.
5. The method of claim 1, wherein the crucible for holding the high pressure solidified sample is a boron nitride crucible.
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