High-toughness Mg-Zn-Sn-Sm alloy and texture control method thereof

Abstract

The application discloses a high-toughness Mg-Zn-Sn-Sm alloy and a texture control method thereof, and belongs to the technical field of alloy materials. The chemical composition of the magnesium alloy is as follows: Zn: 2-4%, Sn: 2-4%, Sm: 0.2-0.4%, and the rest is magnesium and trace additive elements, wherein the trace additive elements are one or more of Sc, Ca and Ag. The preparation method comprises four steps of alloy smelting, step-by-step solid solution treatment, differential temperature and differential speed rolling and recrystallization annealing. The application starts from the control of the recrystallization mechanism of the magnesium alloy, and a high-toughness magnesium alloy sheet with base texture components and non-base texture components is prepared through alloy composition design and process parameter control, so that the magnesium alloy sheet with high strength and plasticity is obtained. Compared with the prior art, the sheet has high yield strength and excellent elongation, the yield strength of the obtained alloy is greater than or equal to 320 MPa, the elongation is greater than or equal to 25%, and the performance is more excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alloy materials, in particular to a high-strength and high-toughness Mg-Zn-Sn-Sm alloy and a texture control method thereof. BACKGROUND

[0002] Magnesium alloy is the lightest engineering structural metal material, has high specific strength and specific stiffness, good electromagnetic shielding property and other advantages, and has broad application prospects in the fields of aerospace, automobile lightweight and electronic communication.

[0003] However, since magnesium has a hexagonal close-packed structure, strong basal plane texture is easily formed after hot rolling or hot extrusion, which reduces the plastic deformation capacity of the magnesium plate and greatly limits its popularization and application.

[0004] As reported in the journal paper Influence of rolling temperature on microstructural evolution and mechanical behavior of AZ31 alloy with accumulative roll bonding by Rao et al. published in Materials Science and Engineering: A, Vol. 754, pp. 112-120, an AZ31 magnesium alloy with strong basal plane texture has a yield strength of 215 MPa at room temperature, but the elongation is only 5.5%. The main reason for this phenomenon is that the AZ31 alloy forms strong basal plane texture after rolling annealing, which increases the yield strength but also leads to a significant decrease in plasticity. Adding alloying elements such as Ca, Gd and Y can weaken the texture and improve the plasticity, but it inevitably leads to a loss of strength.

[0005] As reported in the paper Texture and stretch formability of a rolled Mg-Zn alloy containing dilute content of Y by Chino et al. published in Materials Science and Engineering: A, Vol. 513-514, pp. 394-400, a weak-textured Mg-1.5Zn-0.Y alloy sheet prepared by multi-pass hot rolling and annealing has an elongation of 23% at room temperature, but the yield strength is only 139 MPa, which is difficult to meet the actual service requirements.

[0006] Therefore, how to control the texture composition of deformed magnesium alloy to obtain magnesium alloy sheet with high strength and high plasticity is a technical problem that needs to be solved at present. SUMMARY

[0007] In order to solve the above problems, the application provides a high-toughness Mg-Zn-Sn-Sm alloy and a texture control method thereof.

[0008] The application is realized by the following technical solutions.

[0009] The high-toughness Mg-Zn-Sn-Sm alloy comprises the following chemical components in percentage by mass: Zn: 2-4%, Sn: 2-4%, Sm: 0.2-0.4%, and the rest is magnesium and trace additive elements, wherein the trace additive elements are one or more of Sc, Ca and Ag, and the addition amount of the trace additive elements is 0.05-0.5%.

[0010] Preferably, the trace additive elements are added in percentage by mass as follows: Sc: 0.1-0.2%, Ca: 0.05-0.1%, and Ag: 0.05-0.1%.

[0011] The application further provides a texture control method of the high-toughness Mg-Zn-Sn-Sm alloy, which comprises the following steps.

[0012] Step one: alloy smelting

[0013] The magnesium ingot is melted under the protection of argon gas or mixed gas of SF6 and CO2, and after refining, gas blowing and slag removal treatment, the pure magnesium melt is obtained by standing and keeping warm at 650-750°C for 20-30 minutes; then pure Zn, pure Sn and Mg-Sm intermediate alloy are added, and then one or more of Mg-Sc intermediate alloy, Mg-Ca intermediate alloy and pure Ag are added in sequence, and after melting, stirring, refining and impurity removal treatment, the magnesium alloy melt is obtained; the magnesium alloy melt is kept standing and warm at 660-670°C for 20-30 minutes, and then poured into a mold to obtain a magnesium alloy ingot;

[0014] Step two: step-by-step solid solution treatment

[0015] The magnesium alloy ingot obtained in step one is placed in an argon gas atmosphere protection heat treatment furnace for step-by-step solid solution treatment, kept warm at 350-400°C for 2-6 hours, heated to 440-500°C and kept warm for 6-10 hours, and then quenched to obtain a solid solution magnesium alloy ingot;

[0016] Step three: differential temperature and speed rolling

[0017] The solid solution state magnesium alloy ingot obtained in step two is subjected to differential temperature differential speed rolling to obtain a magnesium alloy sheet, the differential temperature differential speed rolling is as follows: a total of 6-8 passes are required, the reduction of each of the first 4 passes is 30-48%, each pass requires 20-25 minutes of heat preservation in a heating box at 400-440°C, the rotating speed of the upper roller is 8-15 meters / minute and the temperature is 150-250°C, the rotating speed of the lower roller is 5-10 meters / minute and the temperature is 50-100°C; the reduction of each of the last 2-4 passes is 10-25%, each pass requires 6-12 minutes of heat preservation in a heating box at 175-250°C, the rotating speed of the upper roller is 10-15 meters / minute and the temperature is 50-80°C, the rotating speed of the lower roller is 15-25 meters / minute and the temperature is 100-150°C;

[0018] Step four: recrystallization annealing treatment

[0019] The magnesium alloy sheet obtained in step three is placed in an argon atmosphere protection heat treatment furnace, heat preserved at 250-400°C for 10-30 minutes, and quenched to obtain a high strength and toughness Mg-Zn-Sn-Sm alloy sheet.

[0020] Preferably, the high strength and toughness Mg-Zn-Sn-Sm alloy sheet in step four, wherein the basal plane texture component is a component with a deflection angle of ≤25º between the basal axis and the normal direction of the sheet, and the proportion is 25-40%; the non-basal plane texture component is a component with a deflection angle of ≥25º between the basal axis and the normal direction of the sheet, and the proportion is 60-75%.

[0021] Preferably, the high strength and toughness Mg-Zn-Sn-Sm alloy sheet in step four has a yield strength of ≥320 MPa and an elongation of ≥25%.

[0022] Preferably, the Mg-Sm intermediate alloy used in step one is Mg-20Sm, the Mg-Sc intermediate alloy used is Mg-20Sc, and the Mg-Ca intermediate alloy used is Mg-25Ca.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] The present application starts from the control of the recrystallization mechanism of magnesium alloy, and through alloy composition design and process parameter adjustment, a high strength and toughness magnesium alloy sheet with basal plane texture component and non-basal plane texture component is prepared, and a magnesium alloy sheet with high strength and plasticity is obtained; compared with the prior art, the sheet has high yield strength and excellent elongation, and the obtained alloy has a yield strength of ≥320 MPa and an elongation of ≥25%, and the performance is more excellent. DETAILED DESCRIPTION

[0025] The present application will be further described below in conjunction with examples: Example One

[0026] For example, the Mg-4Zn-4Sn-0.4Sm-0.2Sc-0.1Ca alloy, in terms of mass percentage, contains 4% Zn, 4% Sn, 0.4% Sm, 0.2% Sc, and 0.1% Ca, and the rest is Mg. The preparation method of the alloy comprises the following steps:

[0027] (1) The magnesium ingot is melted under the protection of argon gas or a mixed gas of SF6 and CO2. After refining, gas blowing and slag removal, the pure magnesium melt is obtained by standing at 690°C for 30 minutes. Then, pure Zn, pure Sn, and Mg-20Sm master alloy are added, followed by the addition of Mg-20Sc master alloy and Mg-25Ca master alloy. After melting, stirring, refining and impurity removal, the magnesium alloy melt is obtained. After standing at 670°C for 30 minutes, the magnesium alloy melt is poured into a mold to obtain a magnesium alloy ingot;

[0028] (2) The magnesium alloy ingot obtained in step (1) is placed in an argon gas atmosphere protection heat treatment furnace for step-by-step solid solution treatment. After standing at 400°C for 2 hours and heating to 500°C for 10 hours, the solid solution state magnesium alloy ingot is obtained after quenching in water;

[0029] (3) The solid solution state magnesium alloy ingot obtained in step (2) is subjected to differential temperature and differential speed rolling to obtain a magnesium alloy sheet. The differential temperature and differential speed rolling comprises a total of 8 passes, with a pass reduction of 48%, 35%, 30%, and 30% for the first 4 passes. Each pass requires 25 minutes of heat preservation in a heating box at 440°C. The upper roller speed is 15 meters / minute at a temperature of 250°C, and the lower roller speed is 10 meters / minute at a temperature of 100°C. For the last 4 passes, the pass reduction is 25%, 15%, 12%, and 10%. Each pass requires 12 minutes of heat preservation in a heating box at 250°C. The upper roller speed is 15 meters / minute at a temperature of 80°C, and the lower roller speed is 25 meters / minute at a temperature of 150°C;

[0030] (4) The magnesium alloy sheet obtained in step (3) is placed in an argon gas atmosphere protection heat treatment furnace and heat treated at 400°C for 20 minutes, and then quenched in water to obtain a high strength and toughness Mg-4Zn-4Sn-0.4Mn-0.2Sc-0.1Ca alloy sheet.

[0031] The obtained high strength and toughness Mg-4Zn-4Sn-0.4Mn-0.2Sc-0.1Ca alloy sheet has a basal plane texture component of 30% and a non-basal plane texture component of 70%. The yield strength and elongation at room temperature are 350 MPa and 25%, respectively. Example Two

[0032] For example, the Mg-2.5Zn-2Sn-0.2Sm-0.1Ag alloy, in terms of mass percentage, contains 2.5% of Zn, 2% of Sn, 0.2% of Sm, 0.1% of Ag, and the rest of Mg. The preparation method of the alloy comprises the following steps:

[0033] (1) The magnesium ingot is melted under the protection of argon gas or mixed gas of SF6 and CO2, and after refining, gas blowing and slag removal, the pure magnesium melt is obtained by standing at 690°C for 20 minutes. Then, pure Zn, pure Sn, Mg-20Sm intermediate alloy, and pure Ag are added, and after melting, stirring, refining and impurity removal, the magnesium alloy melt is obtained. After standing at 660°C for 20 minutes, the magnesium alloy melt is poured into a mold to obtain a magnesium alloy ingot;

[0034] (2) The magnesium alloy ingot obtained in step (1) is placed in an argon gas atmosphere protection heat treatment furnace for step-by-step solid solution treatment, and after standing at 350°C for 6 hours and heating to 440°C for 6 hours, the solid solution state magnesium alloy ingot is obtained after quenching;

[0035] (3) The solid solution state magnesium alloy ingot obtained in step (2) is subjected to differential temperature and differential speed rolling to obtain a magnesium alloy sheet. The differential temperature and differential speed rolling comprises a total of 6 passes, and the pass reduction of the first 4 passes is 40%, 35%, 35% and 30% respectively. Before each pass, the magnesium alloy ingot is heated in a heating box at 400°C for 20 minutes. The upper roller of the roller has a speed of 8 meters / minute and a temperature of 150°C, and the lower roller of the roller has a speed of 5 meters / minute and a temperature of 50°C. The pass reduction of the last 2 passes is 20% and 10% respectively. Before each pass, the magnesium alloy ingot is heated in a heating box at 175°C for 6 minutes. The upper roller of the roller has a speed of 10 meters / minute and a temperature of 50°C, and the lower roller of the roller has a speed of 15 meters / minute and a temperature of 100°C;

[0036] (4) The magnesium alloy sheet obtained in step (3) is placed in an argon gas atmosphere protection heat treatment furnace, and after standing at 250°C for 10 minutes, the high strength and toughness Mg-2.5Zn-2Sn-0.2Sm-0.1Ag alloy sheet is obtained after quenching.

[0037] The obtained high strength and toughness Mg-2.5Zn-2Sn-0.2Sm-0.1Ag alloy sheet has a basal plane texture component of 25% and a non-basal plane texture component of 75%. The yield strength and elongation at room temperature are 336 MPa and 26%, respectively. Example Three

[0038] The Mg-2Zn-2Sn-0.3Sm-0.1Sc-0.05Ca alloy is taken as an example, and the mass percentage of the alloy is as follows: Zn is 2%, Sn is 2%, Sm is 0.3%, Sc is 0.1%, Ca is 0.05%, and the rest is Mg. The preparation method of the alloy comprises the following steps:

[0039] (1) The magnesium ingot is melted under the protection of argon gas or mixed gas of SF6 and CO2, and after refining, gas blowing and slag removal treatment, the pure magnesium melt is obtained by standing at 690 °C for 30 minutes. Then, pure Zn, pure Sn and Mg-20Sm intermediate alloy are added, and then Mg-20Sc intermediate alloy and Mg-25Ca intermediate alloy are added in sequence. After melting, stirring, refining and impurity removal treatment, the magnesium alloy melt is obtained. After standing and heat preservation of the magnesium alloy melt at 670 °C for 20 minutes, the magnesium alloy ingot is obtained by pouring into a mold.

[0040] (2) The magnesium alloy ingot obtained in step (1) is placed in an argon gas atmosphere protection heat treatment furnace for step solid solution treatment, heat preservation at 380 °C for 3 hours, heat preservation at 480 °C for 6 hours, and then water quenching to obtain a solid solution state magnesium alloy ingot.

[0041] (3) The solid solution state magnesium alloy ingot obtained in step (2) is subjected to differential temperature and differential speed rolling to obtain a magnesium alloy sheet. The differential temperature and differential speed rolling comprises a total of 7 passes, and the pass reduction of the first 4 passes is 45%, 30%, 30% and 30% respectively. Before each pass, heat preservation is required in a heating box at 420 °C for 23 minutes. The rotating speed of the upper roller is 12 meters / minute, and the temperature is 200 °C. The rotating speed of the lower roller is 8 meters / minute, and the temperature is 70 °C. The pass reduction of the last 3 passes is 25%, 20% and 10% respectively. Before each pass, heat preservation is required in a heating box at 200 °C for 10 minutes. The rotating speed of the upper roller is 12 meters / minute, and the temperature is 70 °C. The rotating speed of the lower roller is 18 meters / minute, and the temperature is 120 °C.

[0042] (4) The magnesium alloy sheet obtained in step (3) is placed in an argon gas atmosphere protection heat treatment furnace, heat preservation at 300 °C for 20 minutes, and then water quenching to obtain a high strength and toughness Mg-2Zn-2Sn-0.3Sm-0.1Sc-0.05Ca alloy sheet.

[0043] The obtained high strength and toughness Mg-2Zn-2Sn-0.3Sm-0.1Sc-0.05Ca alloy sheet has a basal plane texture component of 40% and a non-basal plane texture component of 60%. The yield strength and elongation at room temperature are 330 MPa and 27% respectively. Example Four

[0044] The Mg-3Zn-3Sn-0.2Sm-0.15Sc-0.08Ca-0.05Ag alloy is taken as an example, and the preparation method of the alloy includes the following steps:

[0045] (1) The magnesium ingot is melted under the protection of argon gas or mixed gas of SF6 and CO2, and after refining, gas blowing and slag removal treatment, the pure magnesium melt is obtained by standing at 690 °C for 30 minutes. Then, pure Zn, pure Sn, Mg-20Sm intermediate alloy, Mg-20Sc intermediate alloy, Mg-25Ca intermediate alloy and pure Ag are added in sequence, and then the magnesium alloy melt is obtained after melting, stirring, refining and impurity removal treatment. After the magnesium alloy melt is placed at 665 °C for 27 minutes, it is poured into a mold to obtain a magnesium alloy ingot;

[0046] (2) The magnesium alloy ingot obtained in step (1) is placed in an argon gas atmosphere protection heat treatment furnace for step solid solution treatment, and is kept at 360 °C for 4 hours, and then is heated to 450 °C and kept for 8 hours. After quenching, a solid solution state magnesium alloy ingot is obtained;

[0047] (3) The solid solution state magnesium alloy ingot obtained in step (2) is subjected to differential temperature differential speed rolling to obtain a magnesium alloy sheet. The differential temperature differential speed rolling includes a total of 6 passes, and the pass reduction amount of the first 4 passes is 30%, 30%, 25% and 20% respectively. Before each pass, the magnesium alloy ingot needs to be kept in a heating box at 420 °C for 22 minutes. The rotating speed of the upper roller is 12 meters / minute, and the temperature is 220 °C. The rotating speed of the lower roller is 10 meters / minute, and the temperature is 80 °C. The pass reduction amount of the last 2 passes is 25% and 25% respectively. Before each pass, the magnesium alloy ingot needs to be kept in a heating box at 100 °C for 10 minutes. The rotating speed of the upper roller is 12 meters / minute, and the temperature is 50 °C. The rotating speed of the lower roller is 20 meters / minute, and the temperature is 120 °C;

[0048] (4) The magnesium alloy sheet obtained in step (3) is placed in an argon gas atmosphere protection heat treatment furnace, kept at 350 °C for 25 minutes, and quenched to obtain a high strength and toughness Mg-3Zn-3Sn-0.2Sm-0.15Sc-0.08Ca-0.05Ag alloy sheet.

[0049] The high strength and toughness Mg-3Zn-3Sn-0.2Sm-0.15Sc-0.08Ca-0.05Ag alloy sheet is obtained, in which the proportion of basal plane texture component is 33%, and the proportion of non-basal plane texture component is 67%. The yield strength and elongation at room temperature are 342 MPa and 28% respectively. Example Five

[0050] For example, the Mg-4Zn-3Sn-0.2Sm-0.1Ca alloy, in terms of mass percentage, contains 4% of Zn, 3% of Sn, 0.2% of Sm, 0.1% of Ca, and the rest of Mg. The preparation method of the alloy comprises the following steps:

[0051] (1) The magnesium ingot is melted under the protection of argon gas or mixed gas of SF6 and CO2, and after refining, gas blowing and slag removal treatment, the pure magnesium melt is obtained by standing and keeping at 690°C for 25 minutes. Then, pure Zn, pure Sn and Mg-20Sm intermediate alloy are added, and then Mg-25Ca intermediate alloy is added in sequence. After melting, stirring, refining and impurity removal treatment, the magnesium alloy melt is obtained. After standing and keeping at 670°C for 25 minutes, the magnesium alloy melt is poured into a mold to obtain a magnesium alloy ingot;

[0052] (2) The magnesium alloy ingot obtained in step (1) is placed in an argon gas atmosphere protection heat treatment furnace for step-by-step solid solution treatment, kept at 375°C for 5 hours, and then kept at 500°C for 10 hours. After quenching, the solid solution magnesium alloy ingot is obtained;

[0053] (3) The solid solution magnesium alloy ingot obtained in step (2) is subjected to differential temperature and differential speed rolling to obtain a magnesium alloy sheet. The differential temperature and differential speed rolling comprises a total of 6 passes, and the reduction of each pass is 40%, 40%, 30% and 30%. Before each pass, the magnesium alloy ingot is kept in a heating box at 430°C for 23 minutes. The upper roller rotates at a speed of 10 meters / minute and at a temperature of 200°C, and the lower roller rotates at a speed of 8 meters / minute and at a temperature of 70°C. The reduction of the last two passes is 25% and 15% respectively. Before each pass, the magnesium alloy ingot is kept in a heating box at 225°C for 8 minutes. The upper roller rotates at a speed of 10 meters / minute and at a temperature of 80°C, and the lower roller rotates at a speed of 25 meters / minute and at a temperature of 125°C;

[0054] (4) The magnesium alloy sheet obtained in step (3) is placed in an argon gas atmosphere protection heat treatment furnace, kept at 275°C for 20 minutes, and quenched to obtain a high strength and toughness Mg-4Zn-3Sn-0.2Sm-0.1Ca alloy sheet.

[0055] The high strength and toughness Mg-4Zn-3Sn-0.2Sm-0.1Ca alloy sheet is obtained, wherein the basal plane texture component accounts for 38%, and the non-basal plane texture component accounts for 62%. The yield strength and elongation at room temperature are 322 MPa and 31% respectively.

[0056] In the embodiments, the base texture component ratio and the non-base texture component ratio in the alloy are measured by EBSD testing (the EBSD testing is a conventional testing and characterization method of the alloy, and will not be described here), and the yield strength and the elongation are measured by room temperature tensile testing (the room temperature tensile testing is a conventional testing and characterization method of the alloy, and will not be described here).

[0057] The high-strength and high-toughness magnesium alloy sheet with the base texture component and the non-base texture component is prepared by alloy composition design and process parameter control according to the recrystallization mechanism of the magnesium alloy, and the magnesium alloy sheet with high strength and high plasticity is obtained.

[0058] To sum up, the above is only a preferred embodiment of the present application, and is not intended to limit the scope of the present application. Any equivalent changes and modifications made in the shape, structure, features and spirit of the present application within the scope of the claims of the present application should be included in the scope of the claims of the present application.

Claims

1. A high-strength and high-toughness Mg-Zn-Sn-Sm alloy, characterized in that: The Mg-Zn-Sn-Sm alloy comprises the following chemical components by mass percentage: Zn: 2-4%, Sn: 2-4%, Sm: 0.2-0.4%, with the remainder being magnesium and trace additives. The trace additives are one or more of Sc, Ca, and Ag, and the amount of each trace additive is 0.05-0.5%. The mass percentages of the added trace elements are Sc: 0.1-0.2%, Ca: 0.05-0.1%, and Ag: 0.05-0.1%. Its texture control method includes the following steps: Step 1: Alloy Melting Magnesium ingots are melted under an argon atmosphere or a mixture of SF6 and CO2. After refining, blowing, and slag removal, the melt is held at 650-750°C for 20-30 minutes to obtain pure magnesium melt. Pure Zn, pure Sn, and Mg-Sm master alloys are then added, followed by one or more of Mg-Sc master alloys, Mg-Ca master alloys, and pure Ag. After melting, stirring, refining, and impurity removal, magnesium alloy melt is obtained. The magnesium alloy melt is held at 660-670°C for 20-30 minutes and then poured into a mold to obtain magnesium alloy ingots. Step 2: Stepwise solution treatment The magnesium alloy ingot obtained in step one is placed in an argon atmosphere protected heat treatment furnace for step solution treatment. It is held at 350-400°C for 2-6 hours, then heated to 440-500°C and held for 6-10 hours. After quenching, a magnesium alloy ingot in solid solution state is obtained. Step 3: Differential Temperature and Differential Speed ​​Rolling The magnesium alloy ingot obtained in step two is subjected to differential temperature and speed rolling to obtain magnesium alloy sheet. The differential temperature and speed rolling is as follows: a total of 6-8 passes are required. The first 4 passes have a reduction of 30-48% per pass. Before each pass, the ingot is held at a heating box at 400-440°C for 20-25 minutes. The upper roll speed is 8-15 m / min and the temperature is 150-250°C. The lower roll speed is 5-10 m / min and the temperature is 50-100°C. The last 2-4 passes have a reduction of 10-25% per pass. Before each pass, the ingot is held at a heating box at 175-250°C for 6-12 minutes. The upper roll speed is 10-15 m / min and the temperature is 50-80°C. The lower roll speed is 15-25 m / min and the temperature is 100-150°C. Step 4: Recrystallization Annealing Treatment The magnesium alloy sheet obtained in step three is placed in an argon atmosphere protected heat treatment furnace and held at 250-400°C for 10-30 minutes, then quenched in water to obtain a high-strength and high-toughness Mg-Zn-Sn-Sm alloy sheet. The high-strength and high-toughness Mg-Zn-Sn-Sm alloy sheet in step four has a yield strength ≥320 MPa and an elongation ≥25%.

2. The high-strength and high-toughness Mg-Zn-Sn-Sm alloy and its texture control method according to claim 1, characterized in that: In step four, the high-strength and tough Mg-Zn-Sn-Sm alloy sheet comprises a base surface texture component with a deflection angle ≤25º between the base axis and the normal direction of the sheet, accounting for 25-40%; and a non-base surface texture component with a deflection angle ≥25º between the base axis and the normal direction of the sheet, accounting for 60-75%.