Twin-crystal-enhanced and aging-strengthened magnesium alloy and preparation method thereof

Abstract

The invention discloses a magnesium alloy subjected to twin crystal reinforcement and aging strengthening and a preparation method thereof. The magnesium alloy comprises the following components in percentage by weight: 4.5%-6.5% of Er element, 0.65%-1.25% of La element, 0.85%-2.25% of Sr element, 0.55%-0.75% of Zr element and the balance of metal Mg and some inevitable impurity elements. Belongs to the technical field of material alloys. The magnesium alloy has excellent room-temperature and high-temperature mechanical properties and good plasticity, after twin crystal introduction and aging treatment are conducted on the twin-crystal-reinforced aging-strengthened magnesium alloy through compression deformation, the tensile strength and the elongation of the magnesium alloy at the room temperature and the temperature of 300 DEG C are 356 MPa and 5.3% respectively, and the tensile strength and the elongation of the magnesium alloy at the temperature of 300 DEG C are 304 MPa and 8.7% respectively. The magnesium alloy has excellent tensile strength, higher high-temperature mechanical property and good plasticity, and solves the technical problems of low tensile strength, poor high-temperature mechanical property and low plasticity of the existing magnesium alloy.

Description

Technical Field

[0001] The invention belongs to the technical field of material alloys, and in particular relates to a twin-enhanced aging-strengthened magnesium alloy and a preparation method thereof. Background Art

[0002] As the lightest metal structural material, magnesium alloy has the advantages of high specific strength, high specific stiffness, good damping and shock absorption performance, and light weight. It is an ideal lightweight structural material in the field of lightweight and energy saving and consumption reduction. Therefore, magnesium alloy has broad application prospects in aerospace, deep space exploration, drones, new energy vehicles, 5G communications, etc. However, the existing magnesium alloys have shortcomings such as low tensile strength, poor high-temperature mechanical properties, and low plasticity, which seriously hinder the development and application promotion of magnesium alloys.

[0003] Related art discloses a high-strength and high-plasticity rare earth magnesium alloy and its preparation method. Although the invented alloy has excellent room temperature mechanical properties, six rare earth elements are added, the alloy components are many and the cost is high, which is not conducive to the large-scale promotion of magnesium alloys. Related art discloses a rare earth magnesium alloy and its preparation method. The alloy is composed of 6%~12%Gd, 1%~4%Y, 0.01%~0.5%Er, 0.01%~0.25%Ho, 0.01%~0.25%Dy, 0.01%~0.5%La, 0.5%~1.3%Zn, 0.01~0.5%Bi, 0.3%~0.9%Zr. Although the alloy has excellent room temperature mechanical properties and good high temperature mechanical properties, the alloy design composition is complex, and the preparation process includes smelting, refining, two-stage solid solution, hot extrusion or hot forging treatment, which seriously increases the alloy production cycle, preparation cost and labor intensity. The related technology discloses a rare earth magnesium alloy and its aging treatment method and application. The method is suitable for binary or multi-component precipitation-strengthened magnesium alloys containing Ce, Nd, Y and Gd elements, and the pre-deformation rate is relatively fast. Since the magnesium alloy has a close-packed hexagonal crystal structure and few slip systems at room temperature, the method is not universal, and the improved alloy performance still cannot meet the market demand for a new type of magnesium alloy with high strength, heat resistance and good plasticity. Therefore, it is urgent to develop a new type of magnesium alloy with excellent tensile strength, high high-temperature mechanical properties and good plasticity. Summary of the invention

[0004] In order to overcome the above disadvantages, the present invention provides a twinning-reinforced aging-strengthened magnesium alloy and a preparation method thereof.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A twinning-enhanced aging-strengthened magnesium alloy, comprising the following components in weight percentage: 4.5% to 6.5% of Er element, 0.65% to 1.25% of La element, 0.85% to 2.25% of Sr element, 0.55% to 0.75% of Zr element, and the rest being metallic Mg and some inevitable impurity elements; The tensile strength and elongation of the magnesium alloy at room temperature are 356 MPa and 5.3% respectively, and the tensile strength and elongation at 300° C. are 304 MPa and 8.7% respectively.

[0006] Further optimization, the content of the unavoidable impurity elements does not exceed 0.04%.

[0007] A method for preparing a twinning-reinforced aging-strengthened magnesium alloy comprises the following steps: (1) Put the raw materials of industrial pure Mg, Mg-20Er and Mg-15La master alloy into a crucible in turn, use a mixed gas of CO2 and SF6 for protection, and melt to obtain alloy liquid A; (2) Raise the temperature of alloy liquid A to 765-785°C, add Mg-15Sr master alloy and Mg-20Zr master alloy, and keep the temperature for 10-20 minutes to obtain alloy liquid B; (3) Cooling the alloy liquid B to 725-745°C to obtain alloy liquid C, and pouring the alloy liquid C into a metal mold to obtain an alloy ingot; (4) homogenizing the alloy ingot obtained in step (3) at a temperature of 500-520° C. for a time of 6-12 h; (5) The alloy after homogenization treatment in step (4) is subjected to compression deformation treatment to form twins, the compression deformation temperature is 15~25°C, the compression deformation amount is 2.5~11.5%, and the compression rate is 0.005~0.01s -1 ; (6) The alloy after compression deformation in step (5) is subjected to aging treatment to obtain the prepared alloy. The aging temperature is 160-180° C. and the aging time is 12-18 h.

[0008] Further optimization, the pure Mg, Mg-20Er, and Mg-15La master alloys in step (1) and step (2) are descaled and dried before use.

[0009] Further optimization, in step (3), the mold is preheated to 190-210° C. before pouring.

[0010] For further optimization, the compression deformation in step (5) needs to be performed in three directions.

[0011] The beneficial effects of the present invention are: 1. The twinning-enhanced aging-strengthening magnesium alloy of the present invention comprises rare earth element Er as the main additive element, rare earth element La as a trace additive element, alkaline earth element Sr as an auxiliary additive element, and Zr as a grain refiner. Er has an HCP structure, and its maximum solid solubility in Mg is 32.7%. It is easy to precipitate Mg5Er phase in the magnesium alloy, which can greatly improve the alloy solid solution strengthening and aging strengthening effects. The addition of Er can increase the crystal axis of the magnesium matrix. a value, reducing the crystal axis c value, reduce the crystal axis ratio c / a The reduction of the crystal axis ratio is beneficial to coordinate the deformation between grains during the alloy plastic processing and stretching process, and improve the alloy plasticity; the reduction of the crystal axis ratio is beneficial to reduce the shear stress of the alloy basal plane and promote the activation of non-basal plane slip, so that the basal plane slip and non-basal plane slip are coordinated during room temperature stretching, diversifying the plastic deformation mode of the alloy, thereby improving the mechanical properties of the alloy; 2. The solid solubility of La in magnesium is low. The maximum solid solubility is 0.23% at 612℃. When the temperature drops to 400℃, the solid solubility decreases to 0.01%. Taking advantage of the large difference in the solid solubility of La and Er in magnesium alloys, a trace amount of La is added to the Mg-Er alloy to regulate the alloy structure, promote the aging precipitation of the Mg-Er alloy, and improve the mechanical properties of the alloy. La has a larger atomic radius and a smaller solid solubility. It is easy to segregate at the grain boundary and form more grain boundary second phase particles, resulting in a strong solute drag effect, which further improves the room temperature and high temperature mechanical properties of the alloy; 3. The addition of alkaline earth element Sr can not only refine the grains, but also modify the second phase in the magnesium alloy, making it finer and more evenly distributed, which is more conducive to strengthening the alloy and improving the mechanical properties; the addition of Sr can also generate heat-resistant phase Mg 17 Sr2, these heat-resistant phases can significantly improve the mechanical properties of magnesium alloys under high temperature conditions; 4. After the alloy is homogenized, it is subjected to three-dimensional compression to introduce a large number of twins. The presence of twins will form a large number of twin boundaries. As large-angle grain boundaries, twin boundaries will greatly hinder the movement of dislocations. Therefore, the presence of twins can improve the strength of the alloy. On the other hand, a dislocation pileup area will form around the twin boundaries, causing severe lattice distortion. The atomic diffusion coefficient in the lattice distortion area is greater than the diffusion coefficient inside the complete crystal. During the aging process, it is easier for Er, La, and Sr atoms to diffuse here, providing a favorable position for the heterogeneous nucleation of the precipitated phase, promoting the precipitation of the precipitated phase, and further improving the room temperature and high temperature mechanical properties of the alloy. 5. The twinning-enhanced aging-strengthened magnesium alloy of the present invention, by reasonably regulating the contents of the main added element Er, the trace element La and the auxiliary added element Sr, and combining compression deformation to introduce twinning and aging processes, gives full play to the mutual promotion of aging precipitation, modification treatment, grain refinement and strengthening and precipitation promotion of the elements, thereby improving the tensile strength of the alloy, enhancing the high-temperature mechanical properties of the alloy, improving the plasticity of the alloy, and broadening the application field of magnesium alloys. The tensile strength and elongation of the magnesium alloy of the present invention at room temperature can reach 356MPa and 5.3%, and the tensile strength and elongation at 300°C can reach 304MPa and 8.7%. The magnesium alloy of the present invention has excellent tensile strength, high high-temperature mechanical properties and good plasticity, and solves the technical problems of low tensile strength, poor high-temperature mechanical properties and low plasticity of existing magnesium alloys; In summary, compared with the prior art, the preparation method of the twin-reinforced age-strengthened magnesium alloy of the present invention has a simple alloy composition design, low preparation cost, and easy operation. The obtained alloy has excellent tensile strength, high high-temperature mechanical properties and good plasticity, and is suitable for large-scale promotion and application. DETAILED DESCRIPTION

[0012] In order to more clearly understand the above-mentioned purposes, features and advantages of the present invention, the present invention is described in detail below in conjunction with specific embodiments. The following embodiments are implemented based on the technical solutions of the present invention, and detailed implementation methods and specific operating procedures are given. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the following embodiments.

[0013] Example 1 The twin-reinforced age-hardened magnesium alloy of this embodiment is composed of the following components in mass percentage: 4.5% Er, 1.25% La, 2.25% Sr, 0.55% Zr, and the rest are Mg and some unavoidable impurity elements, and the content of impurity elements does not exceed 0.04%.

[0014] The method for preparing the twinning-enhanced age-hardened magnesium alloy of this embodiment comprises the following steps: (1) Put the raw materials, industrial pure Mg, Mg-20Er, and Mg-15La master alloy, into the crucible in turn. Using CO2 and SF6 mixed gas as protection, melting to obtain alloy liquid A; (2) Raise the temperature of alloy liquid A to 765°C and add Mg-15Sr master alloy and Mg-20Zr master alloy. Alloy, keep warm for 10min, and obtain alloy liquid B; (3) Cool down alloy liquid B to 725℃ to obtain alloy liquid C; pour alloy liquid C until it is preheated to In a metal mold at 210°C, an alloy ingot is obtained; (4) homogenizing the alloy ingot obtained in step (3); the homogenization temperature is 500℃, homogenization time is 12h; (5) The alloy homogenized in step (4) is subjected to compression deformation in three directions to introduce Twin, compression deformation temperature is 15℃, compression deformation is 2.5%, compression rate is 0.01s -1 ; (6) The alloy after compression deformation in step (5) is subjected to aging treatment at a temperature of 160°C. The time is 18 hours, and the prepared alloy is obtained.

[0015] Example 2 The twin-reinforced age-hardened magnesium alloy of this embodiment is composed of the following components in mass percentage: 5.5% Er, 0.95% La, 0.85% Sr, 0.65% Zr, and the rest are Mg and some unavoidable impurity elements, and the content of impurity elements does not exceed 0.04%.

[0016] The method for preparing the twinning-enhanced age-hardened magnesium alloy of this embodiment comprises the following steps: (1) Put the raw materials, industrial pure Mg, Mg-20Er, and Mg-15La master alloy, into the crucible in turn. Using CO2 and SF6 mixed gas as protection, melting to obtain alloy liquid A; (2) Raise the temperature of alloy liquid A to 775°C and add Mg-15Sr master alloy and Mg-20Zr master alloy. Alloy, keep warm for 1510min, obtain alloy liquid B; (3) Cool down alloy liquid B to 735℃ to obtain alloy liquid C; pour alloy liquid C until it is preheated to In a metal mold at 200°C, an alloy ingot is obtained; (4) homogenizing the alloy ingot obtained in step (3); the homogenization temperature is 510℃, homogenization time is 9h; (5) The alloy homogenized in step (4) is subjected to compression deformation in three directions to introduce Twin crystal, compression deformation temperature is 20℃, compression deformation is 7%, compression rate is 0.0075s -1 ; (6) The alloy after compression deformation in step (5) is subjected to aging treatment at a temperature of 170°C. The time is 16 hours, and the prepared alloy is obtained.

[0017] Example 3 The twin-reinforced age-hardened magnesium alloy of this embodiment is composed of the following components in mass percentage: 6.5% Er, 0.6% La, 0.85% Sr, 0.75% Zr, and the rest are Mg and some unavoidable impurity elements, and the content of impurity elements does not exceed 0.04%.

[0018] The method for preparing the twinning-enhanced age-hardened magnesium alloy of this embodiment comprises the following steps: (1) Put the raw materials, industrial pure Mg, Mg-20Er, and Mg-15La master alloy, into the crucible in turn. Using CO2 and SF6 mixed gas as protection, melting to obtain alloy liquid A; (2) Raise the temperature of alloy liquid A to 785°C and add Mg-15Sr intermediate alloy and Mg-20Zr intermediate alloy. Alloy, keep warm for 2010min, obtain alloy liquid B; (3) Cool down alloy liquid B to 745℃ to obtain alloy liquid C; pour alloy liquid C until it is preheated to In a metal mold at 190°C, an alloy ingot is obtained; (4) homogenizing the alloy ingot obtained in step (3); the homogenization temperature is 520℃, homogenization time is 6h; (5) The alloy homogenized in step (4) is subjected to compression deformation in three directions to introduce Twin, compression deformation temperature is 25℃, compression deformation is 11.5%, compression rate is 0.005s -1 ; (6) The alloy after compression deformation in step (5) is subjected to aging treatment at a temperature of 180°C. The time is 12 hours, and the prepared alloy is obtained.

[0019] The room temperature and high temperature tensile strength and elongation of the twinning enhanced aging strengthened magnesium alloy prepared in Examples 1-3 were tested. The room temperature tensile strength and elongation test method: According to the national standard GB / T228.1-2021 "Metallic Materials-Tensile Test-Part 1: Room Temperature Test Method", the Shimadzu precision universal electronic tensile testing machine was used for testing; the high temperature tensile strength and elongation test method: According to the national standard GB / T228.2-2015 "Metallic Materials-Tensile Test-Part 2: High Temperature Test Method", the Shimadzu precision universal electronic tensile testing machine was used for testing. The tensile strength and elongation test results are shown in Table 1.

[0020] Table 1 Test results of tensile strength and elongation of twinning-reinforced aging-hardened magnesium alloys prepared in Examples 1-3 The above shows and describes the main features, methods of use, basic principles and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements according to actual conditions, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A twinning-enhanced aging-hardened magnesium alloy, characterized in that: The composition includes the following weight percentages: Er element 4.5%~6.5%, La element 0.65%~1.25%, Sr element 0.85%~2.25%, Zr element 0.55%-0.75%, and the rest is metal Mg and some inevitable impurity elements; The tensile strength and elongation of the magnesium alloy at room temperature are 356 MPa and 5.3% respectively, and the tensile strength and elongation at 300° C. are 304 MPa and 8.7% respectively.

2. A twinning-enhanced age-hardened magnesium alloy as claimed in claim 1, characterized in that: The content of the unavoidable impurity elements does not exceed 0.04%.

3. The method for preparing a twinning-enhanced age-hardened magnesium alloy according to claim 1, characterized in that: The following steps are involved: (1) Put the raw materials of industrial pure Mg, Mg-20Er and Mg-15La master alloy into a crucible in turn, use a mixed gas of CO2 and SF6 for protection, and melt to obtain alloy liquid A; (2) Raise the temperature of alloy liquid A to 765-785°C, add Mg-15Sr master alloy and Mg-20Zr master alloy, and keep the temperature for 10-20 minutes to obtain alloy liquid B; (3) Cooling the alloy liquid B to 725-745°C to obtain alloy liquid C, and pouring the alloy liquid C into a metal mold to obtain an alloy ingot; (4) homogenizing the alloy ingot obtained in step (3) at a temperature of 500-520° C. for a time of 6-12 h; (5) The alloy after homogenization treatment in step (4) is subjected to compression deformation treatment to form twins, the compression deformation temperature is 15~25°C, the compression deformation amount is 2.5~11.5%, and the compression rate is 0.005~0.01s -1 ; (6) The alloy after compression deformation in step (5) is subjected to aging treatment to obtain the prepared alloy. The aging temperature is 160-180° C. and the aging time is 12-18 h.

4. The method for preparing a twinning-enhanced age-hardened magnesium alloy according to claim 3, characterized in that: The pure Mg, Mg-20Er, and Mg-15La master alloys in step (1) and step (2) are descaled and dried before use.

5. The method for preparing a twinning-enhanced age-hardened magnesium alloy according to claim 3, characterized in that: In the step (3), the mold is preheated to 190-210° C. before pouring.

6. The method for preparing a twinning-enhanced age-hardened magnesium alloy according to claim 3, characterized in that: The compression deformation in step (5) needs to be performed in three directions.

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