CN116099892A - A Method for Strengthening Magnesium-Zinc Alloy by Reciprocating Equal Channel Angular Extrusion - Google Patents

Abstract

The invention provides a method for reinforcing magnesium-zinc alloy by reciprocating equal channel angular extrusion, and belongs to the technical field of alloys. The invention utilizes high temperature strain in the process of reciprocating ECAP to activate dislocation slip of conical surface < c+a >, so as to obtain stronger deformability, and simultaneously induces dynamic recrystallization, thereby avoiding crack generation of materials in the process of ECAP, and realizing finer and uniform microstructure and higher strength and plasticity in multi-pass processing. Meanwhile, in the high-temperature strain process, the precipitated phase is uniformly and dynamically aggregated at the grain boundary to inhibit migration of the grain boundary, so that recrystallized grains are uniformly refined. According to the invention, by controlling the angle and the extrusion pass of the equal channel angle extrusion die, the magnesium-zinc alloy can have finer crystal grains and more stable crystal boundaries, so that the strength and the plasticity of the magnesium-zinc alloy are synchronously improved, and the magnesium-zinc alloy has better comprehensive mechanical properties.

Description

A Method for Strengthening Magnesium-Zinc Alloy by Reciprocating Equal Channel Angular Extrusion

technical field

The invention relates to the technical field of alloys, in particular to a method for strengthening magnesium-zinc alloys by reciprocating equal channel angular extrusion.

Background technique

As the lightest metal structural material, magnesium alloy has excellent properties such as light weight, good thermal and electrical conductivity, damping and shock absorption, and electromagnetic shielding. It has broad application prospects in the fields of transportation, communication, electrical appliances, and aerospace. As one of the constant elements in the human body, Mg can be gradually corroded and degraded by body fluids in the internal environment, and finally absorbed and metabolized, so it has a very good basis for biological safety. Magnesium and magnesium alloys have good biocompatibility, osteoinductivity, antibacterial and antitumor functions, and have gradually become the mainstream research direction of a new generation of medical degradable implant materials in the past decade, showing broad application prospects. However, magnesium alloys still have the problems of low strength, poor plasticity and rapid degradation in the application process. Considering that its biological functionality and biological safety are easily affected by the alloy composition, grain refinement is considered to be one of the best methods to improve the mechanical properties of magnesium alloys, which can effectively improve the mechanical properties of magnesium alloys without changing the original composition of the material. The coordinated deformation ability of grain boundaries during plastic deformation, thereby improving the plasticity and toughness of materials.

The traditional methods for grain refinement of magnesium alloys are severe plastic deformation (Severe Plastic Deformation, SPD), including equal channel angular pressing (ECAP), high pressure torsional strain (High Pressure and Torsion, HPT) and laminated rolling technology (Accumulative Roll Bonding, ARB), etc., among which ECAP has received extensive attention because of its simple process implementation and the ability to prepare ultra-fine-grained materials with uniform and dense structures. The purpose of ECAP is to increase the dislocation density inside the magnesium alloy through plastic deformation, induce recrystallization, and then refine the grains. However, the crystal structure of magnesium is a hexagonal close-packed structure (hcp), and the independent slip system is single at room temperature. It is difficult to accumulate high dislocation density or form large-angle grain boundaries in three-dimensional space to induce nanocrystals, and it is easy to Cracking occurs. Therefore, it is difficult to obtain ultra-fine-grained microstructures by traditional severe plastic deformation methods.

Contents of the invention

In view of this, the purpose of the present invention is to provide a method for strengthening magnesium-zinc alloy by reciprocating equal channel angular extrusion. The magnesium-zinc alloy strengthened by the present invention has an ultra-fine grain structure and good comprehensive mechanical properties.

In order to achieve the above-mentioned purpose of the invention, the present invention provides the following technical solutions:

The invention provides a method for strengthening magnesium-zinc alloy by reciprocating equal-channel angular extrusion, comprising the following steps:

The magnesium-zinc alloy is placed in an equal-channel angular extrusion die, and the reciprocating equal-channel angular extrusion is performed to obtain a strengthened magnesium-zinc alloy;

The initial temperature of the magnesium-zinc alloy is 300-450°C;

The inner turning angle of the equal channel angular extrusion die is 90°, and the outer radian is 0-45°;

The extrusion pass of the reciprocating equal channel angular extrusion is 10-20 passes.

Preferably, the zinc content in the magnesium-zinc alloy is 0-4wt%.

Preferably, during the first pass of equal channel angular extrusion, the temperature of the magnesium-zinc alloy is 300-450° C.; during subsequent passes of equal channel angular extrusion, the magnesium-zinc alloy is no longer heated.

Preferably, the extrusion rate of the reciprocating equal channel angular extrusion is 5-20 mm/s.

Preferably, the amount of strain per pass of the reciprocating equal channel angular extrusion is 1.15 _to 28.60.

Preferably, the equal-channel angular extrusion die includes a first port and a second port, and when an odd-numbered equal-channel angular extrusion is performed, the magnesium-zinc alloy is extruded from the first port to the second port; During even-numbered equal-channel angular extrusion, the magnesium-zinc alloy is extruded from the second port to the first port.

The invention provides a method for strengthening magnesium-zinc alloy by reciprocating equal-channel angular extrusion, comprising the following steps: placing the magnesium-zinc alloy in an equal-channel angular extrusion die, and performing reciprocating equal-channel angular extrusion to obtain a strengthened magnesium-zinc alloy The initial temperature of the magnesium-zinc alloy is 300-450°C; the inner rotation angle of the equal-channel angular extrusion die is 90°, and the outer radian is 0-45°; the extrusion path of the reciprocating equal-channel angular extrusion The times are 10-20 times. The invention adopts reciprocating Equal Channel Angular Pressing (EqualChannel Angular Pressing, ECAP) method, utilizes the high temperature strain in the process of reciprocating ECAP to activate the <c+a> dislocation slip of the conical surface, obtains strong deformation ability, and induces dynamic regeneration at the same time. Crystallization, so as to avoid the cracks of the ECAP process material, can achieve multi-pass processing to obtain a finer and more uniform microstructure as well as higher strength and plasticity. Compared with the phenomenon that the magnesium alloy is easy to crack under the traditional ECAP process, the magnesium-zinc alloy under the method of the present invention is not easy to crack even after 10-20 passes of extrusion. At the same time, during the high-temperature strain process, the precipitated phases segregate uniformly and dynamically at the grain boundaries, which inhibits the migration of the grain boundaries and makes the recrystallized grains uniformly refined. The invention can make the magnesium-zinc alloy have finer crystal grains and more stable grain boundaries by controlling the angle and extrusion passes of the equal-channel angular extrusion die, so that the strength and plasticity of the magnesium-zinc alloy can be simultaneously improved, so it has more Good comprehensive mechanical properties.

The results of the examples show that the magnesium-zinc alloy strengthened by the method of the present invention has fine and uniform grains, the average grain size is less than 1 μm, the tensile strength is >250 MPa, and the elongation is >15%.

At the same time, the strengthening method provided by the invention is easy to operate, the sample does not need to be taken out and rotated after a single extrusion pass, and no heat treatment is required during the extrusion deformation process of the intermediate pass, so the processing efficiency is higher, the cost is lower, and the Adapt to industrial production.

Description of drawings

Fig. 1 is the extrusion process of reciprocating equal channel angular extrusion;

Fig. 2 is the metallographic result of embodiment 1～3 and comparative example 1～4 gained strengthened magnesium-zinc alloy;

Fig. 3 is the tensile test stress-strain curve of the strengthened magnesium-zinc alloy obtained in Examples 1-3 and Comparative Examples 1-4.

Detailed ways

The invention provides a method for strengthening magnesium-zinc alloy by reciprocating equal-channel angular extrusion, comprising the following steps:

The magnesium-zinc alloy is placed in an equal-channel angular extrusion die for reciprocating equal-channel angular extrusion to obtain a strengthened magnesium-zinc alloy.

In the present invention, the zinc content in the magnesium-zinc alloy is preferably 0-4wt%, more preferably 0.1-3.5wt%, more preferably 0.5-3wt%, even more preferably 1-2.5wt%. The present invention does not require the initial structure of the magnesium-zinc alloy material, and it can be in a cast state or an extruded state.

The present invention has no special requirements on the size of the magnesium-zinc alloy, and only needs to match the size of the equal channel angular extrusion die.

In the present invention, the equal-channel angular extrusion die is composed of an indenter and two completely connected channels with identical cross-sections and intersecting axes at a certain angle. The inner turning angle of the two channels is φ, and the circumscribed arc is ψ.

In the present invention, the inner rotation angle φ of the equal channel angular extrusion die is 90°, and the outer radian ψ is 0-45°, preferably 0-30°, more preferably 0-15°.

In the present invention, the initial temperature of the magnesium-zinc alloy is preferably 300-450°C, more preferably 350-400°C; the initial temperature of the equal channel angular extrusion die is preferably 300-450°C, more preferably 350°C ~400°C. In the present invention, during the first pass of equal channel angular extrusion, the temperature of the magnesium-zinc alloy is 300-450°C; The die is heated.

In the present invention, the extrusion passes of the reciprocating equal channel angular extrusion are 10-20 passes, preferably 10-12 passes.

In the present invention, the extrusion rate of the reciprocating equal channel angular extrusion is preferably 5-20 mm/s, more preferably 10-15 mm/s.

In the present invention, the amount of strain per pass of the reciprocating equal channel angular pressing is preferably _1.15-28.60 . In the present invention, the strain amount of each pass deformation is preferably according to the Iwahashi theoretical formula: ε=(1/√3)[2cot(φ/2+ψ/2)+ψcosec(φ/2+ψ/2) ] calculated, where ε represents the strain amount of each pass deformation, φ represents the inner rotation angle of the ECA die, and ψ represents the outer radian of the ECA die.

In the present invention, the equal channel angular extrusion die includes a first port and a second port, and when an odd number of times of equal channel angular extrusion is performed, the magnesium-zinc alloy is extruded from the first port to the second port; When equal-channel angular extrusion is performed with even passes, the magnesium-zinc alloy is extruded from the second port to the first port. In the present invention, the magnesium-zinc alloy is reciprocally extruded along the inner path of the mold between different passes, and samples do not need to be taken out during the extrusion process. In the present invention, the extrusion process of the reciprocating equal channel angular extrusion is shown in FIG. 1 .

The magnesium-zinc alloy prepared by the reciprocating equal-channel angular extrusion process in the present invention has a uniform ultra-fine grain structure after multi-pass deformation, so it has better comprehensive mechanical properties and solves the problem of magnesium alloys in the medical field. The problem of low strength and poor plasticity. The steps of the method adopted by the invention are relatively simple, no heating means is used in the extrusion deformation process, and the cost is low. In a single pass, the material is reciprocally extruded along the mold, and the sample does not need to be taken out, which improves the process efficiency, is suitable for industrial production, and has unique technological innovations. During the multi-pass extrusion deformation process carried out by the invention, the alloy always has good plasticity and fluidity without cracking, which promotes the further uniform refinement of its crystal grains. In summary, the present invention solves the problems of incompatible grain size, strength, plasticity and cracking of magnesium alloys in the process of equal channel angular extrusion, and realizes the preparation of ultrafine Crystal magnesium zinc alloy, and improve its strength and plasticity, so that it has high comprehensive performance.

The results of the examples show that the magnesium-zinc alloy strengthened by the method of the present invention has fine and uniform grains, the average grain size is less than 1 μm, the tensile strength is >250 MPa, and the elongation is >15%.

The method for strengthening magnesium-zinc alloy by reciprocating equal channel angular extrusion provided by the present invention will be described in detail below in conjunction with the examples, but they should not be construed as limiting the protection scope of the present invention.

Example 1

The magnesium-zinc alloy material is cast Mg-2wt%.Zn.

The alloy was subjected to 10-pass equal channel angular extrusion deformation, and the sample size was 15×15×50mm. The extrusion deformation of the first pass was carried out at 400°C, and then the sample was subjected to reciprocating extrusion at a extrusion rate of 12mm/s.

Example 2

The magnesium-zinc alloy material is cast Mg-2wt%.Zn.

The alloy was subjected to 12-pass equal channel angular extrusion deformation, and the sample size was 15×15×50mm. The extrusion deformation of the first pass was carried out at 380°C, and then the sample was subjected to reciprocating extrusion at a extrusion rate of 10 mm/s.

Example 3

The magnesium-zinc alloy material is cast Mg-0wt%.Zn.

The alloy was subjected to 15 times of equal channel angular extrusion deformation, and the sample size was 15×15×50mm. The extrusion deformation of the first pass was carried out at 400°C, and then the sample was subjected to reciprocating extrusion at a extrusion rate of 10 mm/s.

Comparative example 1

The as-cast Mg-2wt%.Zn alloy is subjected to extrusion deformation only one pass, the initial mold temperature is 400° C., and the rest are the same as in Example 1.

Comparative example 2

The as-cast Mg-2wt%.Zn alloy was subjected to 2-pass extrusion deformation, the initial mold temperature was 400° C., and the rest were the same as in Example 1.

Comparative example 3

The as-cast Mg-2wt%.Zn alloy was subjected to extrusion deformation for 5 passes, the initial mold temperature was 400° C., and the rest were the same as in Example 1.

Comparative example 4

The as-cast Mg-2wt%.Zn alloy was subjected to extrusion deformation for 10 passes, the initial temperature of the mold was 400°C, and the arc of the mold rotation angle ψ=300°, and the rest were the same as in Example 1.

Comparative example 5

The as-cast Mg-2wt%.Zn alloy is subjected to single-pass extrusion deformation, and the mold temperature is lower than 300° C., and the rest is the same as that of Example 1. The sample cracked after 3 passes.

The metallographic results of the strengthened magnesium-zinc alloy obtained in Examples 1-3 and Comparative Examples 1-4 are shown in FIG. 2 . (a) in Fig. 2 is the as-cast Mg-2wt%.Zn alloy (comparative example 1) that undergoes only one pass of extrusion deformation. It can be seen that its metallographic structure presents typical deformation structure characteristics, that is, coarse grains , elongated deformation occurs, and a large number of twins exist. (b) in Fig. 2 is the as-cast Mg-2wt%.Zn alloy (comparative example 2) that undergoes 2-pass extrusion deformation. It can be seen that, compared with comparative example 1, dynamic recrystallization occurs in some grains, and the grain The particle morphology is a fine equiaxed state. (c) in Fig. 2 is the as-cast Mg-2wt%.Zn alloy (comparative example 3) that carries out extrusion deformation of 5 passes, it can be seen that after 5 passes of deformation, the crystal grains of the alloy are refined, but The tissue remains uneven. (d) in Fig. 2 is the as-cast Mg-2wt%.Zn alloy (embodiment 1) that carried out 10 passes of extrusion deformation, as can be seen, after 10 passes of deformation, the metallographic results show that now obtained Ultrafine equiaxed crystals. (e) in Fig. 2 is the as-cast Mg-2wt%.Zn alloy (embodiment 2) that carried out 12 passes of extrusion deformation, as can be seen, after 12 passes of deformation, the metallographic results show that now obtained Ultrafine equiaxed grains, compared with the 10th pass, some grains grow up. (f) in Fig. 2 is the as-cast Mg-2wt%.Zn alloy (comparative example 4) of 10 pass extrusion deformations when mold angle radian ψ=300 °, as can be seen, compared with embodiment 2 grain The size increases, the grain size is uneven, and the mechanical properties decrease. (g) in Fig. 2 is the as-cast Mg-0wt%.Zn alloy after carrying out 15 passes of extrusion deformation, i.e. pure Mg (embodiment 3), as can be seen, after 15 passes of deformation, the pure Mg The grains are also uniformly refined.

Performance Testing

The yield strength σ _0.2 , tensile strength σ _b , and elongation of the strengthened magnesium-zinc alloys obtained in the examples and comparative examples were tested. The test standards refer to GB/T228.1-2010. The results are shown in Table 1. The tensile test stress-strain curves of the strengthened magnesium-zinc alloy obtained in the examples and comparative examples are shown in FIG. 3 .

The mechanical properties of strengthened magnesium-zinc alloy obtained in table 1 embodiment and comparative examples

It can be seen from Table 1 and Figure 3 that the magnesium-zinc alloy strengthened by the present invention has good comprehensive mechanical properties.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (6)

1. A method for reinforcing magnesium-zinc alloy by reciprocating equal channel angular extrusion comprises the following steps:

placing the magnesium-zinc alloy in an equal channel angle extrusion die, and performing reciprocating equal channel angle extrusion to obtain the reinforced magnesium-zinc alloy;

the initial temperature of the magnesium-zinc alloy is 300-450 ℃;

the inner angle of the equal channel angle extrusion die is 90 degrees, and the outer radian is 0-45 degrees;

the extrusion pass of the reciprocating equal channel angular extrusion is 10-20.

2. The method according to claim 1, wherein the zinc content in the magnesium zinc alloy is 0 to 4wt%.

3. The method according to claim 1, wherein the temperature of the magnesium-zinc alloy is 300-450 ℃ during the first-pass equal channel angular extrusion; and in the subsequent pass of equal channel angular extrusion, the magnesium-zinc alloy is not heated any more.

4. A method according to claim 1 or 3, wherein the reciprocal equal channel angular extrusion has an extrusion rate of 5 to 20mm/s.

5. The method of claim 1, wherein the amount of strain per pass deformation of the reciprocating equal channel angular extrusion is 1.15 _～ 28.60。

6. A method according to claim 1 or 3, wherein the equal channel angle extrusion die comprises a first port and a second port, the magnesium zinc alloy being extruded from the first port to the second port when an odd pass equal channel angle extrusion is performed; when the even-pass equal channel angle extrusion is performed, the magnesium-zinc alloy is extruded from the second port to the first port.

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