CN109930046B - Magnesium rare earth alloy with room-temperature high-plasticity directional solidification and preparation method thereof - Google Patents
Magnesium rare earth alloy with room-temperature high-plasticity directional solidification and preparation method thereof Download PDFInfo
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Abstract
The invention provides a magnesium rare earth alloy with room temperature high plasticity directional solidification and a preparation method thereof, belonging to the technical field of alloy materials.The method utilizes a directional solidification technology to directionally solidify Mg-6.00-6.60 Gd-0.50-0.56Y wt.% alloy at a temperature gradient of 400K/cm and a solidification rate of 70 mu m/s, and prepares the alloy with the crystal growth orientation of
Has a columnar crystal structure with a cellular substructure primary arm spacing of about 120 μm. The room-temperature tensile strength of the directionally solidified magnesium rare earth alloy prepared by the invention is 102MPa, and the elongation after fracture is 35.66%.
Description
Technical Field
The invention belongs to the technical field of alloy materials, and particularly relates to a magnesium rare earth alloy with room-temperature high-plasticity directional solidification and a preparation method thereof.
Background
The Mg-Gd-Y alloy is usually applied to the fields of aerospace and the like as a balanced solid solubility of up to 23.49 wt.% (548 ℃) of Gd in magnesium, but as a metal structure material, the Mg-Gd-Y alloy has more than enough strength but insufficient plasticity, people have conducted intentional research and exploration on the aspects of technology and theory for improving the plasticity of the magnesium alloy, and mainly focus on the following two research directions, namely, 1) activating and providing < c + a > conical surface slippage of 5 independent slippage systems, such as increasing deformation temperature, adding rare earth elements and L i, refining grains and the like, 2) changing the plastic forming path of the magnesium alloy, introducing appropriate shear deformation to change orientation distribution of a basal plane, improving the plasticity and the like, such as deformation processes of ECAP (large plastic deformation), asynchronous rolling, repeated multi-crystal rolling and the like.
The columnar crystal structure has the geometric characteristics similar to bicrystals (according to a partial constraint model, constraint conditions at the grain boundary are reduced to 3 during deformation), the grain boundary constraint conditions are less than those of a common polycrystalline structure, and the coordination of grain boundary deformation is facilitated. Xie (XieXin, Wangyu, Huanghaiyou, continuous columnar crystal tissue copper and copper alloy hyper-extension deformation behavior and plasticity improvement mechanism [ J ] China non ferrous metals academic report 2011,21(10): 2324-. However, the FCC structure of Cu has 12 independent slip systems at room temperature. Therefore, theoretically, the columnar crystal structure for reducing the constraint condition of the grain boundary is expected to have more profound significance for improving the plasticity of the HCP structure magnesium alloy with only 2 independent slip systems at room temperature.
Disclosure of Invention
The invention aims to provide a magnesium rare earth alloy with room-temperature high plasticity directional solidification and a preparation method thereof, so as to improve the performance of the magnesium alloy.
The technical scheme of the invention is as follows:
the magnesium rare earth alloy is prepared by using pure magnesium, Mg-30Gd and Mg-30Y intermediate alloy as raw materials according to the mass percentage of 6.00-6.60 percent of Gd, 0.50-0.56 percent of Y and the balance of magnesium by adopting a directional solidification technology.
A preparation method of magnesium rare earth alloy with room temperature high plasticity directional solidification comprises the following specific steps:
(1) preparing raw materials: pure magnesium with a purity of 99.99%, Mg-30Gd (wt.%) and Mg-30Y (wt.%) master alloy; wherein the raw materials comprise the following components in percentage by mass: 6.00-6.60% of Gd, 0.50-0.56% of Y and the balance of magnesium;
(2) cutting the raw materials into small blocks, placing the blocked raw materials into a graphite crucible of a medium-frequency induction heating furnace, vacuumizing, filling protective gas, starting a smelting system and a heat preservation system, and smelting to obtain alloy liquid;
(3) pouring the obtained alloy liquid into a graphite sleeve provided with a water cooling system and a pull-down system, wherein the graphite sleeve is completely arranged in a heat insulation system, a servo motor of the pull-down system is started after the graphite sleeve is completely poured, the alloy liquid starts to solidify from a copper quenching table connected with the water cooling system from the bottom end of the graphite sleeve, and the servo motor drives the graphite sleeve to be pulled out of the heat insulation system at a constant speed; the temperature gradient of the front edge of a solid/liquid interface is adjusted by adjusting the thickness of a hot baffle, the liquid level of a cooling liquid to the position of a quenching table and a cooling medium, so that the alloy liquid is directionally solidified from bottom to top, the solidification speed is controlled by controlling the pull-down speed of a servo motor, crystal grains with specific orientation preferentially grow, and finally the magnesium-rare earth alloy with a columnar crystal structure is obtained.
In the step (2), the vacuum degree is 0.05Pa, and the protective gas is Ar.
In the step (3), the temperature of the chilling table is constant at 2 ℃.
In the step (3), the temperature gradient at the front edge of the solid/liquid interface is 400K/cm; the solidification rate was 70 μm/s.
In the step (3), the crystal growth orientation is
Has a columnar crystal structure with a cellular substructure and a primary arm spacing of 120 mu m.
Performance testing of the alloy: tensile specimens were cut along the longitudinal section of the directionally solidified specimens using wire cutting. Adopting a WDW3100 model universal tester to perform uniaxial tensile property experiment on the directionally solidified alloy sample under the condition that the strain rate is 0.0001s-1And a data recorder attached to the universal tester automatically collects data such as stress, strain and the like in the stretching process. A DMI 5000M type optical metallographic microscope is used for observing the microstructure of the directionally solidified alloy, an Nordlys Nano high-speed EBSD system is used for collecting EBSD data, and the experimental alloy is subjected to orientation analysis.
The invention has the beneficial effects that: the invention provides a high-strength-ductility directionally solidified magnesium rare earth alloy product. Mg-6.40Gd-0.54Y (wt.%) alloy with plasticity up to 35.66% is successfully prepared by adopting a directional solidification technology, and the grain orientation of the alloy is mainly concentrated on
In the process of room temperature uniaxial deformation, basal plane slippage is started by crystal grains, the mutual coordination deformability is good, the deformation mechanism mainly comprises basal plane slippage and stretching twin crystal, and the plasticity is extremely high.
Drawings
Fig. 1 is a drawing of the dimensions of a tensile specimen.
FIG. 2 shows the metallographic structure (OM) of the longitudinal section of the alloy to be tested.
FIG. 3 is a directional crystal growth orientation diagram of directionally solidified Mg-Gd-Y alloy columnar crystals. Wherein (a) is Mg-6.00 Gd-0.50Y; (b) mg-6.20 Gd-0.52Y; (c) is Mg-6.40 Gd-0.54Y.
FIG. 4 is an engineering stress-strain curve of the alloy of example 1.
FIG. 5 is an engineering stress-strain curve of the alloy of example 2.
FIG. 6 is an engineering stress-strain curve of the alloy of example 3.
FIG. 7 is an engineering stress-strain curve of the alloy of example 4.
Detailed Description
The technical solution of the present invention will be further described with reference to specific examples.
The experimental conditions are as follows: the corresponding relation between the power supply power and the time of the smelting system and the heat preservation system is shown in the table 1:
TABLE 1
| Time t/s | Thermal insulation power P/Kw | Smelting power P/ |
| 0 | 1.0 | 1.0 |
| 54.2 | 2.5 | 1.0 |
| 215 | 5.0 | 1.5 |
| 247 | 7.5 | 1.5 |
| 350 | 7.5 | 2.0 |
| 560 | 7.5 | 3.0 |
| 590 | 7.5 | 4.0 |
| 608 | 5.0 | 4.0 |
| 700 | 3.0 | 2.0 |
| 720 | 1.0 | 0 |
Example 1
A high-strength-ductility directionally solidified magnesium rare earth alloy is prepared by the following steps: the ingredients are as follows by mass percent: gd6.00 percent, Y0.50 percent and the balance of magnesium. 99.9 wt.% of pure magnesium ingot, Mg-30Gd (wt.%) and Mg-30Y (wt.%), which are divided into small blocks, are placed in a graphite crucible of an intermediate frequency induction heating furnace, the graphite crucible is vacuumized to 0.05Pa, Ar protective gas is filled, a power supply of a smelting and heat-insulating system is started, and alloy liquid is obtained by smelting. The alloy liquid is poured into a graphite sleeve which is provided with a water cooling system and a pull-down system, the graphite sleeve is completely arranged in a heat insulation system, the temperature gradient of the front edge of a solid/liquid interface is adjusted to 400K/cm by adjusting the thickness of a heat baffle, the liquid level position of cooling liquid, cooling medium and the like, and the solidification speed is 70 mu m/s. The crystal grains with specific orientation preferentially grow to finally obtain the magnesium alloy ingot with columnar crystal structure. The alloy obtained is tested by a tensile test of a WDW3100 electronic universal tester, and has the yield strength of 33MPa, the tensile strength of 75MPa, the room-temperature elongation of 22.27 percent and the product of strength and elongation of 1670MPa percent.
Example 2
A high-strength-ductility directionally solidified magnesium rare earth alloy is prepared by the following steps: the ingredients are as follows by mass percent: gd6.20%, Y0.52%, and the balance magnesium. 99.9 wt.% of pure magnesium ingot, Mg-30Gd (wt.%), Mg-30Y (wt.%) and Mg-10Er which are divided into small blocks are placed in a graphite crucible of a medium-frequency induction heating furnace, the graphite crucible is vacuumized to 0.05Pa, Ar protective gas is filled, a power supply of a smelting and heat-preserving system is started, and alloy liquid is obtained by smelting. The alloy liquid is poured into a graphite sleeve which is provided with a water cooling system and a pull-down system, the graphite sleeve is completely arranged in a heat insulation system, the temperature gradient of the front edge of a solid/liquid interface is adjusted to 400K/cm by adjusting the thickness of a heat baffle, the liquid level position of cooling liquid, cooling medium and the like, and the solidification speed is 70 mu m/s. The crystal grains with specific orientation preferentially grow to finally obtain the magnesium alloy ingot with columnar crystal structure. The obtained alloy cast ingot is tested by a tensile test of a WDW3100 electronic universal testing machine, and has 47MPa of yield strength, 89MPa of tensile strength, 20.27 percent of room-temperature elongation and 1804MPa of product of strength and elongation.
Example 3
A high-strength-ductility directionally solidified magnesium rare earth alloy is prepared by the following steps: the ingredients are as follows by mass percent: gd6.40%, Y0.54%, and the balance of magnesium. 99.9 wt.% of pure magnesium ingot, Mg-30Gd (wt.%), Mg-30Y (wt.%) and Mg-10Er which are divided into small blocks are placed in a graphite crucible of a medium-frequency induction heating furnace, the graphite crucible is vacuumized to 0.05Pa, Ar protective gas is filled, a power supply of a smelting and heat-preserving system is started, and alloy liquid is obtained by smelting. The alloy liquid is poured into a graphite sleeve which is provided with a water cooling system and a pull-down system, the graphite sleeve is completely arranged in a heat insulation system, the temperature gradient of the front edge of a solid/liquid interface is adjusted to 400K/cm by adjusting the thickness of a heat baffle, the liquid level position of cooling liquid, cooling medium and the like, and the solidification speed is 70 mu m/s. The crystal grains with specific orientation preferentially grow to finally obtain the magnesium alloy ingot with columnar crystal structure. The alloy ingot is tested by a WDW3100 electronic universal tester tensile test, and has the yield strength of 52MPa, the tensile strength of 102MPa, the room-temperature elongation of 35.66 percent and the product of strength and elongation of 3637MPa percent
Example 4
A high-strength-ductility directionally solidified magnesium rare earth alloy is prepared by the following steps: the ingredients are as follows by mass percent: gd6.60%, Y0.56%, and the balance magnesium. 99.9 wt.% of pure magnesium ingot, Mg-30Gd (wt.%), Mg-30Y (wt.%) and Mg-10Er which are divided into small blocks are placed in a graphite crucible of a medium-frequency induction heating furnace, the graphite crucible is vacuumized to 0.05Pa, Ar protective gas is filled, a power supply of a smelting and heat-preserving system is started, and alloy liquid is obtained by smelting. The alloy liquid is poured into a graphite sleeve which is provided with a water cooling system and a pull-down system, the graphite sleeve is completely arranged in a heat insulation system, the temperature gradient of the front edge of a solid/liquid interface is adjusted to 400K/cm by adjusting the thickness of a heat baffle, the liquid level position of cooling liquid, cooling medium and the like, and the solidification speed is 70 mu m/s. The crystal grains with specific orientation preferentially grow to finally obtain the magnesium alloy ingot with columnar crystal structure. The obtained alloy cast ingot is tested by a WDW3100 electronic universal testing machine, and has the yield strength of 53MPa, the tensile strength of 88MPa, the room-temperature elongation of 20.00 percent and the product of strength and elongation of 1760MPa percent.
Claims (3)
1. A preparation method of magnesium rare earth alloy with room temperature high plasticity directional solidification is characterized by comprising the following specific steps:
(1) preparing raw materials: pure magnesium with the purity of 99.99 percent, Mg-30Gd and Mg-30Y intermediate alloy; wherein the raw materials comprise the following components in percentage by mass: 6.00-6.60% of Gd, 0.50-0.56% of Y and the balance of magnesium;
(2) cutting the raw materials into small blocks, placing the blocked raw materials into a graphite crucible of a medium-frequency induction heating furnace, vacuumizing, filling protective gas, starting a smelting system and a heat preservation system, and smelting to obtain alloy liquid;
(3) pouring the obtained alloy liquid into a graphite sleeve provided with a water cooling system and a pull-down system, wherein the graphite sleeve is completely arranged in a heat insulation system, a servo motor of the pull-down system is started after the graphite sleeve is completely poured, the alloy liquid starts to solidify from a copper quenching table connected with the water cooling system from the bottom end of the graphite sleeve, and the servo motor drives the graphite sleeve to be pulled out of the heat insulation system at a constant speed; adjusting the temperature gradient of the front edge of a solid/liquid interface to 400K/cm by adjusting the thickness of a heat baffle, the liquid level of a cooling liquid to the position of a quenching table and a cooling medium to ensure that the alloy liquid is directionally solidified from bottom to top, controlling the solidification speed to be 70 mu m/s by controlling the pull-down speed of a servo motor to ensure that crystal grains with specific orientation preferentially grow to finally obtain the magnesium-rare earth alloy with the columnar crystal structure, wherein the crystal growth orientation of the columnar crystal structure is that
The primary arm spacing with the cellular substructure was 120. mu.m.
2. The method for preparing the magnesium rare earth alloy with room temperature high plasticity directional solidification according to claim 1, wherein in the step (2), the vacuum degree is 0.05Pa, and the shielding gas is Ar.
3. The method for preparing the magnesium rare earth alloy with room-temperature high plasticity directional solidification according to claim 1 or 2, wherein in the step (3), the chilling stage temperature is constant at 2 ℃.
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