High-strength and high-toughness wrought magnesium alloy with good extrudability

Abstract

The invention belongs to the technical field of wrought magnesium alloy preparation, and particularly relates to a high-strength and high-toughness wrought magnesium alloy with good extrudability. The high-strength and high-toughness wrought magnesium alloy comprises the following components in percentage by mass except Mg: 5.5 to 6.0 percent of Zn, 0.6 to 0.9 percent of Zr, 0.2 to 0.3 percent of RE and inevitable impurities, smelting and casting to form a metal casting rod; and after the outer skin of the metal casting rod is removed, the metal casting rod is prepared through homogenization treatment, extrusion treatment and heat treatment. The high-strength and high-toughness wrought magnesium alloy with better extrudability, prepared by the invention, has excellent ductility and extrudability under the condition of keeping reasonable strength and castability (blank casting before processing or extrusion), the extrusion speed can reach 1.1 mm / s, the yield strength of an extruded product can reach 275 MPa, the tensile strength can reach 335 MPa, and the ductility can reach 15%.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of wrought magnesium alloys, and more specifically relates to a high-strength and high-toughness wrought magnesium alloy with good extrudability. Background Art

[0002] Magnesium alloys are one of the lightest structural metals currently known to be applicable in the industrial field, with a density of 1.75 - 1.85 g / cm 3 , which is about 23% of that of steel and 64% of that of aluminum. Magnesium alloys have high specific strength and specific stiffness. Their specific strength is higher than that of aluminum alloys and steels, and their specific stiffness has a certain load-bearing capacity compared with aluminum alloy and steel materials.

[0003] ZK (Mg-Zn-Zr) series magnesium alloys are one of the most widely used high-strength wrought magnesium alloys at present and have been widely applied in the fields of aerospace, automotive, military, etc. However, this series of magnesium alloys belong to the HCP close-packed hexagonal crystal structure and have poor plasticity. During the extrusion process, the billet heating temperature is high and the extrusion speed is low, resulting in low production efficiency and high cost, which limits the wide application of this series of alloys. Therefore, developing a magnesium alloy that can be extruded into shape at a faster speed without reducing the current mechanical properties is of great significance for expanding the application channels of this product. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-strength and high-toughness wrought magnesium alloy with good extrudability to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above purpose, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention: Provide a high-strength and high-toughness wrought magnesium alloy with good extrudability. By mass percentage, except for Mg, the components include: 5.5 - 6.0% of Zn, 0.6 - 0.9% of Zr, 0.2 - 0.3% of RE, and inevitable impurities.

[0007] Further, by mass percentage, the components of the high-strength and high-toughness wrought magnesium alloy with good extrudability are: 5.5 - 6.0% of Zn, 0.6 - 0.9% of Zr, 0.2 - 0.3% of RE, and the balance is Mg and inevitable impurities.

[0008] The total amount of inevitable impurities in the present invention is less than 0.1 wt.%.

[0009] Optionally, by mass percentage, the components of the high-strength and high-toughness wrought magnesium alloy with good extrudability are: 5.8% of Zn, 0.6 - 0.9% of Zr, 0.2 - 0.3% of RE, and the balance is Mg and inevitable impurities.

[0010] Optionally, by mass percentage, the components of the high-strength and high-toughness wrought magnesium alloy with good extrudability are: Zn 5.5-6.0%, Zr 0.8%, and RE 0.2-0.3%, and the balance is Mg and inevitable impurities.

[0011] Optionally, by mass percentage, the components of the high-strength and high-toughness wrought magnesium alloy with good extrudability are: Zn 5.5-6.0%, Zr 0.6-0.9%, and RE 0.25%, and the balance is Mg and inevitable impurities.

[0012] Optionally, by mass percentage, the components of the high-strength and high-toughness wrought magnesium alloy with good extrudability are: Zn 5.8%, Zr 0.8%, and RE 0.25%, and the balance is Mg and inevitable impurities.

[0013] Further, the RE is at least one of Y, Ce, and Gd.

[0014] The second technical solution of the present invention: Provide a preparation method of a high-strength and high-toughness wrought magnesium alloy, and the steps include:

[0015] Prepare raw materials according to the components of the above high-strength and high-toughness wrought magnesium alloy, and melt and cast them into a metal mold casting rod;

[0016] After removing the outer skin of the metal mold casting rod, through homogenization treatment, extrusion treatment, and heat treatment, the high-strength and high-toughness wrought magnesium alloy is obtained.

[0017] Further, the raw materials include various ones among magnesium ingots, zinc ingots, magnesium-zirconium master alloy, magnesium-yttrium master alloy, magnesium-gadolinium master alloy, and magnesium-cerium master alloy.

[0018] Further, the melting and casting are: casting and forming in a mold preheated to 150°C at 700°C.

[0019] Further, the homogenization treatment is: heating to 420°C, holding for 10 h, and cooling with strong wind.

[0020] The homogenization treatment can improve the segregation problem inside the casting rod and improve the hot extrusion performance of the material. And the homogenization treatment makes the low-temperature phases in the casting rod dissolve into the matrix, playing a role in precipitation strengthening during the subsequent heat treatment process.

[0021] Further, the extrusion treatment is: preheating the metal mold casting rod after homogenization treatment to 355-360°C and holding for not less than 1 h; heating the mold to 390-400°C and holding for not less than 3 h; holding the extrusion cylinder at 370-375°C; using an extrusion rod to push the metal mold casting rod through the mold to obtain the extruded magnesium alloy.

[0022] Optionally, the pushing speed is 1.0 - 1.1 mm / s, and the breakthrough pressure is 130 - 150 Bar.

[0023] Hot extrusion treatment can improve the crystal structure of the cast rod and refine the grains. At the same time, it can also improve the defects such as porosity and gas holes inside the cast rod, and form the required profiles through the extrusion die.

[0024] Further, the heat treatment is: heating to 180 °C, holding for 12 h, and natural cooling.

[0025] Heat treatment can precipitate the second phase in the supersaturated solid solution. During the deformation process of the material, the second phase will hinder the movement of dislocations and play a strengthening role.

[0026] The present invention discloses the following technical effects:

[0027] The high-strength and high-toughness wrought magnesium alloy with good extrudability prepared by the present invention has excellent ductility and extrudability while maintaining reasonable strength and castability (billet casting before processing or extrusion). Its yield strength can reach 275 MPa, the tensile strength can reach 335 MPa, and the elongation can reach 15%.

[0028] Using the preparation method of the present invention to prepare the wrought magnesium alloy can improve the extrusion speed during the preparation process and improve the preparation efficiency of the wrought magnesium alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0030] Figure 1 It is a schematic diagram of the extrusion speed comparison under the methods of Example 1 - 3 and Comparative Example 1.

[0031] Figure 2 It is the metallographic structure diagram of the materials prepared in Example 1 and Comparative Example 1. Among them, a is Comparative Example 1, and b is Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0032] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation to the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0033] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0035] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are merely exemplary.

[0036] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0037] Currently, one of the wrought magnesium alloys that can simultaneously possess excellent strength and plasticity is ZK61M (a magnesium-based alloy named according to GB / T 5153 with approximately 6% by weight zinc, 1% by weight zirconium, and the balance of magnesium and impurities, generally represented by the formula: Mg - 6% by weight Zn - 1% by weight Zr), which provides excellent mechanical properties among the existing wrought magnesium alloys. However, compared with the existing aluminum extrusion alloys, the extrudability of all currently existing magnesium-based alloys is relatively poor.

[0038] In some specific embodiments, rare earths (Y, Ce, Gd) are included as one of the alloying elements. Adding rare earth elements to the ZK magnesium alloy can produce a solid solution strengthening effect, but the effect of solid solution strengthening is related to the crystal structure, atomic size, electronegativity difference, and electron concentration of the rare earth elements; adding rare earth elements to the ZK magnesium alloy will have an obvious grain refinement effect and can produce fine grain strengthening.

[0039] Rare earth elements will accumulate in front of the solid-liquid interface of the alloy, causing constitutional supercooling of the alloy and thus hindering the growth of dendrites and inhibiting growth. Secondly, the addition of rare earth elements will become new nucleation sites, promoting nucleation. Second-phase strengthening is another important strengthening mechanism when rare earth elements are added to ZK magnesium alloys. Adding rare earth element Ce will form the MgZn2Ce phase, which helps to improve the mechanical strength of the alloy. Rare earth elements Y and Gd have a large solid solubility in magnesium alloys. After heat treatment, a large number of intermetallic compounds containing Y and Gd precipitate in the alloy and are uniformly dispersed in the grains and grain boundaries, having a good strengthening effect.

[0040] The present invention provides a high-strength and high-toughness wrought magnesium alloy with good extrudability. By mass percentage, except for Mg, the components include: 5.5 - 6.0% of Zn, 0.6 - 0.9% of Zr, 0.2 - 0.3% of RE, and inevitable impurities.

[0041] In some specific embodiments, the Zn component in the high-strength and high-toughness wrought magnesium alloy is about 5.8 wt.%.

[0042] In some specific embodiments, the Zr component in the high-strength and high-toughness wrought magnesium alloy is about 0.8 wt.%.

[0043] In some specific embodiments, the RE component in the high-strength and high-toughness wrought magnesium alloy is about 0.25 wt.%.

[0044] In some specific embodiments, the RE is selected from at least one of Y, Ce, and Gd.

[0045] The total impurity content in the high-strength and high-toughness wrought magnesium alloy prepared by the present invention is not higher than 0.1 wt.%. Generally, the impurities include at least one of elements such as Al, Mn, Si, Fe, Cu, and Ni, and other impurities with a content lower than 0.01 wt.%. Among them, the content of Al as an impurity is not higher than 0.05 wt.%, the content of Mn as an impurity is not higher than 0.1 wt.%, the content of Si as an impurity is not higher than 0.05 wt.%, the content of Fe as an impurity is not higher than 0.05 wt.%, the content of Cu as an impurity is not higher than 0.05 wt.%, and the content of Ni as an impurity is not higher than 0.005 wt.%.

[0046] All raw materials used in the specific embodiments of the present invention are commercially available products.

[0047] Example 1

[0048] The preparation steps of the high-strength and high-toughness wrought magnesium alloy include:

[0049] S1. The composition of the high-strength and high-toughness wrought magnesium alloy is: 5.5 - 6.0% Zn, 0.6 - 0.9% Zr, and 0.2 - 0.3% RE, with the balance being Mg and inevitable impurities; where RE is Y;

[0050] Prepare the raw material magnesium ingots, zinc ingots, magnesium-zirconium master alloy, and magnesium-yttrium master alloy according to the above composition of the high-strength and high-toughness wrought magnesium alloy;

[0051] S2. Melt and cast the raw materials. At 700 °C, cast 300 kg of the melt into a metal mold casting rod die preheated to 150 °C to obtain a metal mold casting rod;

[0052] S3. Use a lathe to turn off the outer skin of the metal mold casting rod and process it into a casting rod; where the casting rod is obtained by turning off 5 mm from each side of the casting rod along the radial direction, and the proportion of the alloy components of the casting rod is shown in Table 1;

[0053] S4. Homogenization treatment: Heat the casting rod to 420 °C, hold for 10 hours, and cool it with strong wind to obtain a homogenized casting rod;

[0054] S5. Preheat the homogenized casting rod to 360 °C and hold for 1 h; heat the rod die to 390 °C and hold for 3 h; keep the extrusion cylinder at 370 °C; let the extrusion rod push the metal mold casting rod through the rod die at a certain pushing speed to obtain a 20-m long extruded magnesium alloy;

[0055] Among them, determine the maximum extrusion speed when the surface cracking of the rod starts. The maximum extrusion speed in this embodiment is 1.1 mm / s, and at this speed, the breakthrough pressure is 140 Bar;

[0056] S6. Heat the extruded magnesium alloy to 180 °C, hold for 12 h, and cool it naturally to obtain a high-strength and high-toughness wrought magnesium alloy rod.

[0057] Example 2

[0058] Compared with Example 1, the only difference is that RE is Ce.

[0059] Example 3

[0060] Compared with Example 1, the only difference is that RE is Gd.

[0061] Comparative Example 1

[0062] Compared with Example 1, the difference is that the raw materials are prepared according to the chemical composition of ZK61M.

[0063] Test Example

[0064] The ingot bar alloy compositions of Examples 1-3 and Comparative Example 1 are shown in Table 1 (excluding impurities and Mg).

[0065] Table 1 Composition Ratio of Blank (wt.%)

[0066] Zn Zr Y Ce Gd Example 1 6.00 0.75 0.25 -- -- Example 2 6.00 0.75 -- 0.25 -- Example 3 6.00 0.75 -- -- 0.25 Comparative Example 1 5.82 0.80 -- -- --

[0067] Each blank was heated to between 355 - 360 °C and extruded using a 630T extruder. Extrusion of the bar. For the alloys of Examples 1-3 and Comparative Example 1, the maximum extrusion speed was determined at the onset of surface cracking of the bar, and for each alloy, approximately 20 meters of alloy bars were manufactured at the maximum extrusion speed.

[0068] Figure 1 It is a schematic diagram for comparing the extrusion speeds under the methods of Examples 1-3 and Comparative Example 1. As can be seen from the figure, the extrusion speed in the method of Example 1 can reach 1.1 mm / s, and the extrusion speed in the method of Comparative Example 1 is 0.7 mm / s. The extrusion speed of the high-strength and high-toughness wrought magnesium alloy prepared by the present invention is approximately 57% faster than that of Comparative Example 1.

[0069] The mechanical properties of the obtained wrought magnesium alloy were tested at room temperature. The test standard refers to GB / T228.1-2021. Three specimens were tested for each example and comparative example, and the average value was calculated. The results are shown in Table 2.

[0070] Table 2

[0071]

[0072] The data in Table 2 show that the alloys prepared by the preparation methods of Examples 1-3 of the present invention have significantly improved tensile strength, yield strength and elongation compared with the alloys prepared by Comparative Example 1.

[0073] Figure 2 It is the metallographic structure diagram of the materials prepared in Example 1 and Comparative Example 1. Among them, a is Comparative Example 1 and b is Example 1. As can be seen from the figure, adding rare earth elements to the ZK magnesium alloy will have an obvious effect of refining grains and can produce fine grain strengthening.

[0074] In this specification, each example is described in a progressive manner. The key point of each example is to illustrate the differences from other examples. For the same and similar parts between each example, reference can be made to each other.

[0075] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-strength and high-toughness wrought magnesium alloy with good extrudability, characterized in that, By mass percentage, except for Mg, the components include: 5.5 - 6.0% of Zn, 0.6 - 0.9% of Zr, 0.2 - 0.3% of RE, and inevitable impurities.

2. The high-strength and high-toughness wrought magnesium alloy according to claim 1, wherein, By mass percentage, the components of the high-strength and high-toughness wrought magnesium alloy with good extrudability are: 5.5 - 6.0% of Zn, 0.6 - 3. The high-strength and high-toughness wrought magnesium alloy according to claim 1 or 2, characterized in that, ​ 4. A preparation method of a high-strength and high-toughness wrought magnesium alloy, characterized in that the steps ​ ​ ​ 5. The preparation method according to claim 4, characterized in that, ​ 6. The preparation method according to claim 4, characterized in that, ​ 7. The preparation method according to claim 4, wherein ​ 8. The preparation method according to claim 4, wherein ​ 9. The preparation method according to claim 8, wherein ​ 10. The preparation method according to claim 4, characterized in that, ​

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