A low-cost high-strength and high-toughness squeeze casting magnesium alloy and its preparation method

Abstract

The present invention provides a low-cost high-strength and high-toughness squeeze-cast magnesium alloy and a preparation method thereof, belonging to the field of metal materials. The cast magnesium alloy is composed of the following components by mass percentage: Zn: 1.3-2%, La: 0.6-1.1%, Ti: 0.1-0.3%, Gd: 0.3-0.7%, Dy: 0.3-0.8%; the content of inevitable impurities ≤ 0.1%; the balance is magnesium. The preparation method includes steps such as alloy melting, solidification under external pressure, secondary solution treatment, secondary aging treatment, etc. The present invention not only has a lower alloy content, but also significantly refines the alloy grains, changes the morphology of the coarse eutectic phase distributed along the grain boundaries in the alloy. After solution treatment, the sub-phase is almost completely dissolved into the matrix, and in the subsequent aging precipitation, the precipitated second phase is finer and more uniform, finally enabling the comprehensive mechanical and plastic properties of the alloy to be significantly improved synchronously.

Description

Technical Field

[0001] The present invention belongs to the field of material processing, and particularly relates to a low-cost high-strength and high-toughness squeeze-cast magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium and its alloys are currently the lightest metal structural materials applicable in industry, having advantages such as low density (about 2 / 3 of aluminum and 1 / 4 of steel), high specific strength and specific stiffness, good damping property, machinability, and casting performance, and have been widely used in fields such as automobiles, communication electronics, aerospace, and military. In recent years, with the rapid development of aerospace and transportation tools, the power required for operation is getting larger and larger, so higher requirements are put forward for the strength, toughness, and anti-elastic strain ability of material components. However, the relatively low absolute strength, plasticity, and elastic modulus of magnesium alloys restrict their further popularization and application in these fields. In actual applications, due to the difficulty of plastic processing of magnesium alloys, magnesium alloy products are mainly produced by casting. The magnesium alloys of the prior art improve their mechanical properties by increasing the alloy addition amount (addition amount > 12%) and performing heat treatment at high temperature for a long time. However, this will lead to a relatively high production cost of the alloy. In addition, while improving the mechanical properties of the alloy, the plasticity will be reduced, and it cannot be used for the production of large-size and thin-wall parts. With the continuous expansion of the application fields and the continuous improvement of the comprehensive performance requirements for magnesium alloys, higher requirements are put forward for the economy, mechanical properties, and plasticity of the materials. Therefore, how to design and develop high-strength and high-toughness cast magnesium alloys with higher strength, better plasticity, and lower cost has become a technical problem to be solved urgently at present. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides a low-cost high-strength and high-toughness squeeze-cast magnesium alloy. By mass percentage, the composition of the magnesium alloy includes: Zn: 1.3 - 2%, La: 0.6 - 1.1%, Ti: 0.1 - 0.3%, Gd: 0.3 - 0.7%, Dy: 0.3 - 0.8%; the content of inevitable impurities ≤ 0.1%, and the balance is magnesium. Its preparation method includes the following steps:

[0004] 1. Preheat pure Mg, pure Zn, Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; wherein, the preheating temperature is 250 - 300°C, the preheating time is 1 - 3 hours, and then melt in a protective atmosphere; add preheated pure Zn at 665 - 685°C; when the temperature rises to 700 - 720°C, add preheated Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; after the master alloy and pure magnesium are completely melted, stir for 1 - 3 min, then blow in argon and skim the slag; keep the melt at 670 - 680°C for 10 - 30 min to obtain a magnesium alloy melt;

[0005] 2. Extrusion casting is performed on the magnesium alloy melt in Step 1. Under the conditions that the extrusion pressure ranges from 100 MPa to 220 MPa and the pressure holding time is 1 to 60 s, and at the same time, metal casting is completed at 220°C to 300°C to obtain a magnesium alloy ingot;

[0006] 3. The magnesium alloy ingot obtained in Step 2 is successively subjected to secondary solution treatment, water quenching, secondary aging treatment, and water quenching to obtain a low-cost high-strength and high-toughness extrusion-cast magnesium alloy.

[0007] Furthermore, the protective atmosphere in Step 1 is a mixed gas of SF6 and CO2, where the volume ratio of SF6 to CO2 is 1 - 5:90 - 99.

[0008] Furthermore, the secondary solution treatment in Step 3 is: holding at 480 - 490°C for 2 - 6 h; then holding at 515 - 530°C for 1 - 3 h; the water quenching is: at a temperature of 10 - 60°C and a time of 1 - 6 s.

[0009] Furthermore, the secondary aging treatment in Step 3 is: holding at 70 - 80°C for 1 - 3 h; then holding at 200 - 230°C for 6 - 16 h; the water quenching is: at a temperature of 10 - 60°C and a time of 1 - 6 s.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0011] Through the synergistic effect of components, ratios, processes, and parameters, the present invention provides a high-strength and high-toughness extrusion-cast magnesium alloy. By controlling the precipitation morphology and proportion of the reinforcing phase, the alloy simultaneously has high strength and high toughness at room temperature, and can meet the requirements for manufacturing high-strength and high-toughness lightweight materials and / or components. The specific advantages are as follows:

[0012] 1. Compared with the prior art, the present invention reduces the addition amount of alloys and rare earths. Through the synergistic effect of alloy components, ratios, processes, and process parameters, the grains are significantly refined, and a eutectic phase with good thermal stability is formed;

[0013] 2. The prior art discloses that after solution treatment of magnesium alloy, there is a phase separation structure in the alloy matrix (i.e., the phase is not completely solid-solved in the matrix), and it is difficult to simultaneously improve the mechanical and plastic properties of the alloy. The present invention first realizes the transformation of the eutectic phase in the as-cast matrix from continuous intergranular network distribution to massive uniform distribution. Finally, the eutectic phase in the alloy can fully dissolve back into the matrix, and the phase separation structure basically disappears. And in the subsequent aging precipitation, compared with the prior art, the precipitated second phase is finer and more uniform, and finally the mechanical and plastic comprehensiveness of the alloy can be significantly improved synchronously.

[0014] The process flow of the present invention is simple. The alloy addition content is controlled below 5%, and the rare earth element addition amount is controlled below 3%, which controls the cost. At room temperature, through the synergistic effect of components, ratios, processes and parameters, the mechanical properties and plasticity of the alloy are improved synchronously. The obtained alloy has a tensile strength of 273 - 312 MPa and an elongation of 14.8 - 17.6%. Description of the Drawings

[0015] Figure 1 It is the SEM image of the Mg-8Gd-3Y-1.5Zn-0.6Zr magnesium alloy after solution treatment at 500°C for 10 h and quenching by Tian Kaikai et al. in Comparative Example 2;

[0016] Figure 2 It is the SEM image of the Mg-1.7Zn-0.9La-0.1Ti-0.55Gd-0.75Dy magnesium alloy obtained after the secondary solution treatment and quenching in Step 3 of Example 2. Detailed Embodiments

[0017] Example 1

[0018] Mg-1.8Zn-0.9La-0.15Ti-0.45Gd-0.4Dy. By mass percentage, the composition of the magnesium alloy includes: Zn: 1.8%, La: 0.9%, Ti: 0.15%, Gd: 0.45%, Dy: 0.4%; the content of inevitable impurities ≤ 0.1%; the balance is magnesium. The preparation method of the magnesium alloy includes the following steps:

[0019] 1: Preheat pure Mg, pure Zn, Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; wherein, the preheating temperature is 280°C and the preheating time is 1 hour; then melt in a protective atmosphere; add preheated pure Zn at 678°C; when the temperature rises to 713°C, add the preheated Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; stir for 2 min after the master alloy and pure metal are completely melted, then blow in argon and skim the slag; cool the melt to 676°C and then hold for 15 min to obtain a magnesium alloy melt;

[0020] 2: Perform squeeze casting on the magnesium alloy melt in Step 1. Under the conditions of an extrusion pressure of 108 MPa and a holding time of 25 s, complete the metal casting at a metal mold temperature of 220°C to obtain a magnesium alloy ingot;

[0021] 3: Solutionize the alloy ingot obtained in step 2 at 486 °C for 4 hours, then raise the temperature to 515 °C for solution treatment for 2 h, and then quench in water at 20 °C for 2 s; then age at 74 °C for 2 h, then age at 215 °C for 8 h, and quench in water at 18 °C for 1 s to obtain a low-cost high-strength and tough squeeze-cast magnesium alloy 1.

[0022] The room-temperature mechanical property test results of Example 1 of the present invention are shown in Table 1.

[0023] Example 2

[0024] Mg-2Zn-1La-0.2Ti-0.4Gd-0.45Dy, by mass percentage, the composition of the magnesium alloy includes: Zn: 2%, La: 1%, Ti: 0.2%, Gd: 0.4%, Dy: 0.45%; the content of inevitable impurities ≤ 0.1%; the balance is magnesium; the preparation method of the magnesium alloy includes the following steps:

[0025] 1: Preheat pure Mg, pure Zn, Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; wherein, the preheating temperature is 275 °C and the preheating time is 2 hours; then melt in a protective atmosphere; add preheated pure Zn at 665 °C; when the temperature rises to 710 °C, add preheated Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; stir for 2 min after the master alloy and pure metal are completely melted, then blow in argon and skim the slag; cool the melt to 677 °C and then hold for 20 min to obtain a magnesium alloy melt;

[0026] 2: Perform squeeze casting on the magnesium alloy melt in step 1. Under the condition that the extrusion pressure is within 120 MPa and the pressure holding time is 30 s, complete the metal casting at the metal mold temperature of 240 °C to obtain a magnesium alloy ingot;

[0027] 3: Solutionize the alloy ingot obtained in step 2 at 483 °C for 3 hours, then raise the temperature to 525 °C for solution treatment for 2.5 h, and then quench in water at 12 °C for 2 s; then age at 75 °C for 1.5 h, then age at 220 °C for 12 h, and quench in water at 12 °C for 3 s to obtain a low-cost high-strength and tough squeeze-cast magnesium alloy 2.

[0028] The room-temperature mechanical property test results of Example 2 of the present invention are shown in Table 1.

[0029] Example 3

[0030] Mg-2Zn-0.8La-0.25Ti-0.45Gd-0.6Dy. By mass percentage, the composition of the magnesium alloy includes: Zn: 2%, La: 0.8%, Ti: 0.25%, Gd: 0.45%, Dy: 0.6%; the content of inevitable impurities ≤ 0.1%; the balance is magnesium; the preparation method of the magnesium alloy includes the following steps:

[0031] 1: Preheat pure Mg, pure Zn, Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; wherein, the preheating temperature is 260°C and the preheating time is 2.5 hours; then melt in a protective atmosphere; add preheated pure Zn at 680°C; when the temperature rises to 720°C, add preheated Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; after the master alloy and pure metal are completely melted, stir for 3 min, then blow in argon and skim the slag; cool the melt to 678°C and then hold for 25 min to obtain a magnesium alloy melt;

[0032] 2: Perform squeeze casting on the magnesium alloy melt in step 1. Under the conditions of an extrusion pressure of 145 MPa and a holding time of 20 s, and at the same time complete metal casting at a metal mold temperature of 250°C to obtain a magnesium alloy ingot;

[0033] 3: Solution-treat the alloy ingot obtained in step 2 at 494°C for 5 hours, then raise the temperature to 530°C for solution treatment for 1.5 h, and then quench in water at 19°C for 3 s; then age at 70°C for 2 h, then age at 215°C for 16 h, and quench in water at 19°C for 1 s to obtain a low-cost high-strength and tough squeeze-cast magnesium alloy 3.

[0034] The room-temperature mechanical property test results of Example 3 of the present invention are shown in Table 1.

[0035] Example 4

[0036] Mg-1.9Zn-1.1La-0.2Ti-0.7Gd-0.7Dy. By mass percentage, the composition of the magnesium alloy includes: Zn: 1.9%, La: 1.1%, Ti: 0.2%, Gd: 0.7%, Dy: 0.7%; the content of inevitable impurities ≤ 0.1%; the balance is magnesium; the preparation method of the magnesium alloy includes the following steps:

[0037] 1: Preheat pure Mg, pure Zn, Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; among them, the preheating temperature is 300 °C and the preheating time is 3 hours; then melt in a protective atmosphere; add preheated pure Zn at 667 °C; when the temperature rises to 716 °C, add the preheated Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; after the master alloy and pure metal are completely melted, stir for 1.5 min, then blow in argon and skim the slag; cool the melt to 677 °C and then hold for 27 min to obtain a magnesium alloy melt;

[0038] 2: Perform squeeze casting on the magnesium alloy melt in step 1. Under the conditions of an extrusion pressure of 163 MPa and a holding time of 35 s, complete metal casting at a metal mold temperature of 245 °C to obtain a magnesium alloy ingot;

[0039] 3: Solution treat the alloy ingot obtained in step 2 at 480 °C for 5 hours, then raise the temperature to 520 °C and solution treat for 2.5 h, then quench in water at 25 °C for 2 s; then perform aging treatment at 80 °C for 2 h, then perform aging treatment at 220 °C for 13.5 h, and quench in water at 30 °C for 2 s to obtain a low-cost high-strength and tough squeeze-cast magnesium alloy 4.

[0040] The room-temperature mechanical property test results of Example 4 of the present invention are shown in Table 1.

[0041] Example 5 [[ID=,14]]

[0042] Mg-1.7Zn-0.9La-0.1Ti-0.55Gd-0.75Dy, by mass percentage, the composition of the magnesium alloy includes: Zn: 1.7%, La: 0.9%, Ti: 0.1%, Gd: 0.55%, Dy: 0.75%; the content of inevitable impurities ≤ 0.1%; the balance is magnesium; the preparation method of the magnesium alloy includes the following steps:

[0043] 1: Preheat pure Mg, pure Zn, Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; among them, the preheating temperature is 290 °C and the preheating time is 1.5 hours; then melt in a protective atmosphere; add preheated pure Zn at 677 °C; when the temperature rises to 712 °C, add the preheated Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; after the master alloy and pure metal are completely melted, stir for 1.5 min, then blow in argon and skim the slag; cool the melt to 673 °C and then hold for 19 min to obtain a magnesium alloy melt;

[0044] 2: The magnesium alloy melt in step 1 is subjected to squeeze casting. Under the conditions that the extrusion pressure is within 205 MPa and the holding time is 15 s, and at the same time, the metal casting is completed at the metal mold temperature of 250 °C to obtain a magnesium alloy ingot.

[0045] 3: The alloy ingot obtained in step 2 is solution-treated at 485 °C for 5.5 hours and then heated to 525 °C for solution treatment for 2 h, and then quenched in water at 30 °C for 1 s; then aged at 70 °C for 1 h, then aged at 225 °C for 15 h, and quenched in water at 20 °C for 2 s to obtain a low-cost high-strength and tough squeeze-cast magnesium alloy 5.

[0046] The room temperature mechanical property test results of Example 5 of the present invention are shown in Table 1.

[0047] Example 6

[0048] Mg-1.85Zn-1La-0.15Ti-0.6Gd-0.8Dy. By mass percentage, the composition of the magnesium alloy includes: Zn: 1.85%, La: 1%, Ti: 0.15%, Gd: 0.6%, Dy: 0.8%; the content of inevitable impurities ≤ 0.1%; the balance is magnesium; the preparation method of the magnesium alloy includes the following steps:

[0049] 1: Preheat pure Mg, pure Zn, Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; among them, the preheating temperature is 255 °C and the preheating time is 2 hours; then melt in a protective atmosphere; add preheated pure Zn at 674 °C; when the temperature rises to 713 °C, add preheated Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; after the master alloy and pure metal are completely melted, stir for 1 min, then blow in argon and skim the slag; cool the melt to 675 °C and then hold for 20 min to obtain a magnesium alloy melt.

[0050] 2: The magnesium alloy melt in step 1 is subjected to squeeze casting. Under the conditions that the extrusion pressure is 220 MPa and the holding time is 30 s, and at the same time, the metal casting is completed at the metal mold temperature of 245 °C to obtain a magnesium alloy ingot.

[0051] 3: The alloy ingot obtained in step 2 is solution-treated at 490 °C for 6 hours and then heated to 510 °C for solution treatment for 3 h, and then quenched in water at 18 °C for 3 s; then aged at 76 °C for 2 h, then aged at 224 °C for 13 h, and quenched in water at 25 °C for 2 s to obtain a low-cost high-strength and tough squeeze-cast magnesium alloy 6.

[0052] The room temperature mechanical property test results of Example 6 of the present invention are shown in Table 1.

[0053] Comparative Example 1

[0054] Zhang Qi et al. mentioned a Mg-10Gd-2Y-1Zn-0.6Mn magnesium alloy in the article "Study on the Microstructure and Mechanical Properties of Mg-10Gd-xY-(Zn)-0.6Mn Cast Magnesium Alloys" published in Chongqing University of Technology in 2022. Its main preparation method is through conventional melting and casting, pouring, and then solution treatment at 520°C / 24h + aging treatment at 225°C / 24h. There is still an obvious phase separation phenomenon after solution treatment. Its room temperature tensile strength is 213 MPa, and the elongation is 9.8%.

[0055] Comparative Example 2

[0056] Tian Kaikai et al. mentioned a Mg-8Gd-3Y-1.5Zn-0.6Zr magnesium alloy in the article "Effect of Heat Treatment on the Microstructure and Mechanical Properties of Mg-8Gd-Three Y-1.5Zn-0.6Zr Alloy" published in Volume 47, Issue 11, Pages 54 - 58 of the journal "Heat Treatment of Metals" in 2022. Its main preparation method is through conventional melting and casting, pouring, and then solution treatment at 500°C / 10h + aging treatment at 225°C / 12h. Its room temperature tensile strength is 242 MPa, and the elongation is 13.9%.

[0057] Table 1 Mechanical and Plasticity Conditions of Alloys Obtained in Examples 1 - 6 and Comparative Examples 1 - 2

[0058] Tensile strength / MPa Elongation / % Example 1 273 14.9 Example 2 277 15.3 Example 3 280 14.8 Example 4 298 15.5 Example 5 312 17.6 Example 6 301 16.1 Comparative Example 1 213 9.8 Comparative Example 2 242 13.9

[0059] The total alloy addition amount in Comparative Examples 1 and 2 exceeds 13%, and the rare earth addition amount exceeds 10%. The alloy and rare earth addition amounts in the comparative examples far exceed those of the alloy and rare earth in the present invention. However, as can be seen from Table 1, the mechanical properties and elongation of the alloys obtained in Examples 1 - 6 exceed those of the alloys obtained in Comparative Examples 1 - 2. In addition, compared with Comparative Example 2 in the appendix Figure 1 compared, from the appendix Figure 2 it can be seen that: the second phase of the present invention is completely dissolved into the matrix, while there are a large number of precipitated phases around the matrix in Comparative Example 2. Therefore, compared with the comparative examples, the present invention has achieved an unexpectedly significant improvement in technical effects. In addition, it can be seen from Examples 1 - 6 that the alloy components and process parameters used are all different. The alloy obtained in Example 5 has the best mechanical and plastic properties, but its alloy and rare earth addition amounts are not the highest among the examples. Thus, it can be concluded that: compared with the prior art, the present invention has achieved a simultaneous improvement in the excellent mechanical properties and plasticity of the alloy. The best comprehensive properties of the alloy obtained in the present invention are achieved by the synergistic effect of components, ratios, processes, and parameters.

Claims

1. A low-cost, high-strength and tough squeeze casting magnesium alloy, characterized in that: By mass percentage, the composition of the magnesium alloy includes: Zn: 1.3 - 2%, La: 0.6 - 1.1%, Ti: 0.1 - 0.3%, Gd: 0.3 - 0.7%, Dy: 0.3 - 0.8%; the content of inevitable impurities ≤ 0.1%; the balance is magnesium. The preparation method of the magnesium alloy includes the following steps: S1: Preheat pure Mg, pure Zn, Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; wherein, the preheating temperature is 250 - 300°C, and the preheating time is 1 - 3 hours; then melt in a protective atmosphere; add preheated pure Zn at 665 - 685°C; when the temperature rises to 700 - 720°C, add preheated Mg-La master alloy, Mg-Ti master alloy, Mg-Gd master alloy, and Mg-Dy master alloy; stir for 1 - 3 min after the master alloy and pure magnesium are completely melted, then blow in argon and skim the slag; keep the melt at 670 - 680°C for 10 - 30 min to obtain a magnesium alloy melt; S2: Perform squeeze casting on the magnesium alloy melt in step S1. Under the conditions that the extrusion pressure is in the range of 100 MPa - 220 MPa and the holding pressure time is 1 - 60 s, and at the same time complete metal casting at 220°C - 300°C to obtain a magnesium alloy ingot; S3: Subject the magnesium alloy ingot obtained in step S2 to secondary solution treatment, water quenching, secondary aging treatment, and water quenching in sequence to obtain a low-cost high-strength and tough squeeze-cast magnesium alloy.

2. A low-cost high-strength and high-toughness squeeze-cast magnesium alloy according to claim 1, characterized in that, The protective atmosphere in step S1 is a mixed gas of SF6 and CO2, and the volume ratio of SF6 to CO2 is 1 - 5:90 - 99.

3. The low-cost high-strength and high-toughness squeeze-cast magnesium alloy according to claim 1, wherein The secondary solution treatment in step S3 is: hold at 480 - 490°C for 2 - 6 h; then hold at 515 - 530°C for 1 - 3 h; the water quenching is: the temperature is 10 - 60°C, and the time is 1 - 6 s.

4. The low-cost high-strength and high-toughness squeeze-cast magnesium alloy according to claim 1, wherein The secondary aging treatment in step S3 is: hold at 70 - 80°C for 1 - 3 h; then hold at 200 - 230°C for 6 - 16 h, and the water quenching is: the temperature is 10 - 60°C, and the time is 1 - 6 s.

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