Processing method for improving creep property of magnesium alloy

Abstract

The invention discloses a processing method for improving creep property of a magnesium alloy, which is characterized in that the magnesium alloy comprises the following components in percentage by mass: 0.5-0.8% of Bi; 0.5 to 0.8 percent of Ca; 0 to 0.8 percent of Zn; 0 to 0.8 percent of Mn; and the balance of Mg and inevitable impurities. By regulating and controlling elements of magnesium and alloy thereof, the magnesium alloy generates creep dynamic precipitation in the high-temperature creep process, and the creep dynamic precipitation phase improves the stability of the material, refines the grain structure, weakens the texture of the Mg-Bi alloy, improves the structure of the magnesium alloy, improves the tensile yield strength and corrosion resistance, so that the magnesium alloy has excellent ductility; and the creep resistance of the material is improved, the material has more excellent mechanical performance and production efficiency under an Mg-Bi matrix, the operation is simplified, and the economic cost is saved.

Description

Technical Field

[0001] The invention relates to a processing method for improving the creep performance of a magnesium alloy, and belongs to the technical field of processing of magnesium alloys. Background Art

[0002] The density of magnesium and its alloys is small, only 64% of aluminum and 25% of steel, with a density of 1.8g / m 3 It has high specific strength, large specific elastic modulus, good heat dissipation performance, good shock absorption, better impact load bearing capacity than aluminum alloy, and good resistance to organic and alkali corrosion. The main alloying elements are aluminum, manganese, zinc, cerium, thorium and a small amount of zirconium or cadmium. Magnesium alloy resources are relatively abundant, low density, high specific strength and specific stiffness, strong damping, vibration reduction and noise reduction capabilities, ability to shield electromagnetic radiation and easy recycling. It has been applied to certain industries such as automobiles, aerospace, 3C, etc. With the progress of society and the development of related industries, higher requirements are put forward for the performance of magnesium alloys. The development of thermal conductive and high creep performance magnesium alloys has become the focus of current research.

[0003] Traditional magnesium alloys show a relatively poor balance between strength and plasticity, and the crystal creep performance of precipitation at high temperatures is poor, which limits the application of magnesium alloys. Therefore, how to improve the processing composition of magnesium alloys is a problem that needs to be overcome in order to improve its creep performance at high temperatures and expand its application area. Summary of the invention

[0004] The present invention provides a processing method for improving the creep performance of a magnesium alloy, characterized in that the magnesium alloy comprises the following components in mass percentage:

[0005] Bi: 0.5~0.8%;

[0006] Ca: 0.5-0.8%;

[0007] Zn: 0-0.8%;

[0008] Mn: 0-0.8%;

[0009] The rest is Mg and unavoidable impurities;

[0010] The processing method is as follows:

[0011] 1) Performing solid solution treatment on magnesium alloy;

[0012] 2) Extrusion in the solid solution state, the extrusion temperature is 225℃~250℃, the extrusion rate is 0.02mm / s, and the extrusion ratio is 25:1;

[0013] 3) The extruded magnesium alloy is subjected to compression deformation, the compression direction is parallel to the extrusion direction, the compression temperature is 20°C to 100°C, the compressive stress is 0.01 to 0.02, the strain rate is 1×10-4-2×10-4s, and the compression is 5 to 10 minutes.

[0014] Preferably, the mass percentages of the magnesium alloy are Bi: 0.5%, Ca: 0.8%, Zn: 0.8%, Mn: 0.8%, and the rest are magnesium and impurities that cannot be removed.

[0015] Preferably, the magnesium alloy melting temperature is 720°C;

[0016] Preferably, after smelting, 420°C solution heat treatment is used for 2 hours, and 500°C solution heat treatment is used for 3 hours;

[0017] Preferably, water quenching is performed after solid solution;

[0018] Preferably, the extrusion temperature is 225° C., the extrusion rate is 0.02 mm / s, and the extrusion ratio is 25:1.

[0019] In summary, the beneficial effects of the present invention are:

[0020] 1. The alloying in the invention can improve the structure of magnesium alloy, enhance the strength of alloy and improve the corrosion resistance. As a thermally stable Mg-Bi based alloy with excellent mechanical properties and high production efficiency, it has great potential in developing rare earth-free Mg alloys with excellent synthetic mechanical properties.

[0021] 2. The invention described above obtains a structure with excellent ductility by extrusion. In the extruded state, a large amount of Mg 3 Bi 2 phase, without causing plastic loss, with high tensile yield strength, the compression temperature control cannot be too high to prevent the aging effect during compression deformation, which provides sufficient and ideal microscopic observation.

[0022] 3. The Invention When Bi is added in an amount of 0.5 wt.%, the alloy exhibits excellent ductility.

[0023] 4. The invention adds Ca and Zn. The addition of Ca can significantly affect the grain refinement process, weaken and change the texture of the Mg-Bi alloy, thereby maintaining excellent ductility. Moreover, the addition of Ca will not affect the extrusion efficiency of the alloy. After comparing the creep resistance, the alloy with the best creep resistance is determined.

[0024] 5. The magnesium alloy of the invention has low production cost, simple experimental steps, high efficiency, and further improves the creep performance of the magnesium alloy.

[0025] The improvement of creep properties of magnesium alloys is of great significance to development. The creep properties of experimental magnesium alloys and the comparison of corresponding alloys are illustrated by the following figures:

[0026] Figure 1 It is the creep strain-time curve of BXZ011 alloy at 150℃;

[0027] Figure 2 It is the creep rate-time curve of BXZ011 alloy at 150℃;

[0028] Figure 3 It is the creep strain-time curve of BXM011 alloy at 150℃;

[0029] Figure 4 It is the creep rate-time curve of BXM011 alloy at 150℃;

[0030] Figure 5 It is a creep strain-time curve diagram of Example 1 and Comparative Example 2 at a temperature of 175°C;

[0031] Figure 6 It is a creep rate-time curve diagram of Example 1 and Comparative Example 2 at a temperature of 175°C;

[0032] Figure 7 It is the stable creep strain curve of Example 1 and Comparative Examples 1 and 2 at a temperature of 175°C. Specific implementation plan

[0033] The following will clearly and completely describe the concept and technical effects of the present invention in combination with the embodiments, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of invention protection.

[0034] Example 1

[0035] This embodiment 1 adopts a processing method to improve the creep performance of magnesium alloy, and the specific process is as follows:

[0036] The Mg-0.5Bi-0.8Ca-0.8Zn alloy named BXZ011 was prepared by water-cooled semi-continuous casting. The alloy ingot was made of commercial pure Mg (99.9wt.%), Mg10Bi (wt.%), Mg-30Ca (wt.%)-2.5Zn (wt.%) intermediate alloy to obtain a magnesium alloy cast material, wherein the mass percentage of the magnesium alloy is Bi: 0.5%, Ca: 0.8%, Zn: 0.8%, and the rest is magnesium and impurities that cannot be removed.

[0037] The alloy castings in Example 1 were heated in a resistance furnace with CO 2 and SF 6 The mixed gas (gas ratio is 1:99) is melted at 720°C for 20 minutes and then the solid structure is subjected to solution treatment at 420°C for 2 hours and at 500°C for 3 hours.

[0038] In Example 1, the solid solution was water quenched and then extruded at 225°C, with an extrusion speed of 0.02 mm / s and an extrusion ratio of 25:1 to obtain an extruded rod with a diameter of 12 mm. The extruded rod was cut with a cutting machine to obtain an "I-shaped" specimen, and a creep experiment was performed. The creep performance test was performed at a creep temperature of 150°C and pressures of 50, 60, and 70 MPa, respectively. The test results are shown in FIG. Figure 1 , two As shown, with the increase of pressure and temperature, the strength of the alloy decreases. Due to the influence of tensile strength, the creep rate of the alloy (6.0E-0.7) changes dramatically and drops to a stable rate (0.01E+0).

[0039] Comparative Example 1

[0040] In Comparative Example 1, a Mg-0.5Bi-0.8Ca-0.8Mn alloy named BXM011 was prepared by a water-cooled semi-continuous casting method. The alloy ingot was made of commercial pure Mg (99.9wt.%), Mg10Bi (wt.%), and Mg-30Ca (wt.%)-2.5Mn (wt%) intermediate alloy to obtain a magnesium alloy cast material, wherein the mass percentage of the magnesium alloy is Bi: 0.5%, Ca: 0.8%, Mn: 0.8%, and the rest is magnesium and impurities that cannot be removed.

[0041] After the extruded rods are made, they are cut by a cutting machine to obtain "I-shaped" specimens for creep tests. The creep performance tests are carried out at a creep temperature of 150°C and pressures of 50, 60, and 70 MPa. The test results are as follows: Figure 3 , Four As shown, with the increase of creep time and pressure, the creep rate changes significantly, and the creep performance decreases significantly under a pressure of 60 MPa. The creep rate first decreases and then increases sharply. In Table 1, Example 1 and Comparative Example 1 are compared and analyzed, as shown in the following table:

[0042]

[0043]

[0044] It can be seen from the data in Table 1 that the creep performance of Example 1 is better than that of the sample of Comparative Example 1, and the preparation of the magnesium alloy casting is relatively successful.

[0045] Comparative Example 2

[0046] In comparative example 2, Mg-0.5Bi-0.8Ca alloy and Mg-0.8Ca-0.8Zn were prepared by water-cooled semi-continuous casting, which were named BX10 and XZ11 respectively. The alloy ingots were made of commercial pure Mg (99.9wt.%), Mg10Bi (wt.%), Mg-30Ca (wt.%)-2.5Mn (wt.%), and Mg-30Ca (wt.%) intermediate alloy to obtain magnesium alloy cast materials, wherein the mass percentage of BX10 magnesium alloy is Bi: 0.5%, Ca: 0.8%, and the rest is magnesium and impurities that cannot be removed, and the mass percentage of XZ11 magnesium alloy is Ca: 0.8%, Zn: 0.8%, and the rest is magnesium and impurities that cannot be removed.

[0047] After the extruded rods are made, they are cut by a cutting machine to obtain "I-shaped" specimens for creep experiments. The creep performance tests are carried out at a creep temperature of 175°C and pressures of 50, 60, and 70 MPa, respectively. The creep performance curves are as follows: Figure 5 , 6 As shown, by comparing Example 1 with Comparative Example 2, it can be found that the creep performance of BXZ011 is more stable and the creep change rate is also smaller.

[0048] The creep strain curves and n values ​​of Example 1 and Comparative Examples 1-2 are as follows: Figure 7 As shown, at the same temperature, the larger the n value, the higher the stress sensitivity. When the n value is greater than 8, the constraint law is no longer applicable. It can be seen that BXZ011 has the lowest strain sensitivity, and the creep performance of Example 1 is higher than that of the samples of Comparative Examples 1 and 2.

[0049] The above is only a specific implementation of the invention, but the protection scope of the invention is not limited to it. Any changes or substitutions that are not conceived through creative work should be included in the protection scope of the invention. Therefore, the protection scope of the invention should be based on the protection scope defined in the claims.

Claims

1. A processing method for improving the creep performance of magnesium alloy, characterized in that : The mass percentage of magnesium alloy is, including the following components: Bi: 0.5~0.8%; Ca: 0.5-0.8%; Zn: 0-0.8%; Mn: 0-0.8%; The rest is Mg and unavoidable impurities; The processing steps are as follows: 1) Solution treatment of magnesium alloy; 2) Extruding the solid solution magnesium alloy at a temperature of 225°C to 250°C, an extrusion rate of 0.02 mm / s, and an extrusion ratio of 25:1; 3) The extruded magnesium alloy is subjected to compression deformation, the compression direction is parallel to the extrusion direction, the compression temperature is 20°C to 100°C, the compressive stress is 0.01 to 0.02, the strain rate is 1×10-4-2×10-4s, and the compression is 5 to 10 minutes.

2. The method for improving creep properties of magnesium alloy according to claim 1, characterized in that The mass percentages of the magnesium alloy are Bi: 0.5%, Ca: 0.8%, Zn: 0.8%, Mn: 0.8%, and the rest are magnesium and impurity elements that cannot be removed.

3. The method for improving creep properties of magnesium alloy according to claim 1, characterized in that: The melting temperature of the magnesium alloy is 720°C, and the solid solution temperature after melting is 420°C and 500°C. The solid solution temperature is 420°C for 2 hours and the solid solution temperature is 500°C for 3 hours.

4. A processing method for improving creep properties of magnesium alloy according to claim 1, characterized in that The extrusion temperature is 225° C., the extrusion rate is 0.02 mm / s, and the extrusion ratio is 25:1.

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