A method for reciprocating equal channel angular pressing of a magnesium-zinc alloy

Abstract

The application provides a method for reciprocating equal-channel-angle-pressing strengthening of magnesium-zinc alloy, and belongs to the technical field of alloys. In the reciprocating ECAP process, high-temperature strain is used to activate the pyramidal <c+a> dislocation slip, so that a stronger deformation capacity is obtained, and dynamic recrystallization is induced, so that the generation of cracks in the material in the ECAP process is avoided, and multiple passes can be implemented to obtain a more fine and uniform microstructure and higher strength and plasticity. Meanwhile, in the high-temperature strain process, the uniform dynamic segregation of precipitated phases occurs at the grain boundaries, the migration of the grain boundaries is inhibited, and the recrystallized grains are uniformly refined. By controlling the angle of the equal-channel-angle-pressing die and the extrusion passes, the magnesium-zinc alloy can have finer grains and more stable grain boundaries, so that the strength and plasticity of the magnesium-zinc alloy are simultaneously improved, and therefore the magnesium-zinc alloy has better comprehensive mechanical properties.

Description

TECHNICAL FIELD

[0001] The present application relates to the alloy technical field, in particular to a kind of reciprocating equal channel angle extrusion reinforced magnesium-zinc alloy method. BACKGROUND

[0002] Magnesium alloy as the lightest metal structural material, with light, good thermal conductivity and electrical conductivity, damping vibration, electromagnetic shielding and other excellent performance, in transportation, communication, electrical and aerospace fields have broad application prospect.Mg as one of the constant elements in the human body, can be gradually corroded and degraded by body fluid in the body environment, and eventually absorbed and metabolized, so it has very excellent biological safety basis.Magnesium and magnesium alloy have good biocompatibility, bone induction, antibacterial and antitumor function, and have gradually become the mainstream research direction of new generation of medical degradable implant materials in the past decade, and show broad application prospect.However, magnesium alloy still has problems of low strength, poor plasticity and fast degradation in application process.Considering that its biological function and biological safety are easily affected by alloy composition, grain refinement is considered as one of the best methods to improve the mechanical properties of magnesium alloy, which can effectively improve the coordinated deformation ability of grain boundary in plastic deformation process without changing the original composition of the material, thereby improving the plasticity and toughness of the material.

[0003] The traditional magnesium alloy grain refinement method is severe plastic deformation (SPD), including equal channel angular extrusion (ECAP), high pressure torsion strain (HPT) and accumulative roll bonding technology (ARB) etc., wherein ECAP is widely concerned because it can prepare uniform and dense ultra-fine grained material with simple process implementation.The purpose of ECAP is to increase the dislocation density inside magnesium alloy by plastic deformation, induce recrystallization, and then refine the grain.However, the crystal structure of magnesium is close-packed hexagonal structure (hcp), and the independent slip system is single at room temperature, which is difficult to accumulate high dislocation density or form large-angle grain boundaries in three-dimensional space to induce nanocrystalline, and is prone to cracking during extrusion deformation.Therefore, it is difficult to obtain ultra-fine grained structure by using traditional severe plastic deformation method. SUMMARY

[0004] Therefore, the present application aims to provide a kind of reciprocating equal channel angle extrusion reinforced magnesium-zinc alloy method, the magnesium-zinc alloy reinforced by the present application has ultra-fine grained structure, and has good comprehensive mechanical properties.

[0005] In order to achieve the above-mentioned application purpose, the present application provides the following technical solutions:

[0006] The application provides a method for reciprocating equal-channel-angle extrusion of strengthened magnesium-zinc alloy, which comprises the following steps:

[0007] The magnesium-zinc alloy is placed in an equal-channel-angle extrusion die, and reciprocating equal-channel-angle extrusion is performed to obtain the strengthened magnesium-zinc alloy.

[0008] The initial temperature of the magnesium-zinc alloy is 300-450 DEG C.

[0009] The internal corner of the equal-channel-angle extrusion die is 90 DEG, and the external arc is 0-45 DEG.

[0010] The extrusion pass of the reciprocating equal-channel-angle extrusion is 10-20 passes.

[0011] Preferably, the zinc content in the magnesium-zinc alloy is 0-4 wt%.

[0012] Preferably, the temperature of the magnesium-zinc alloy is 300-450 DEG C. during the first pass of equal-channel-angle extrusion, and the magnesium-zinc alloy is not heated during the subsequent equal-channel-angle extrusion.

[0013] Preferably, the extrusion rate of the reciprocating equal-channel-angle extrusion is 5-20 mm / s.

[0014] Preferably, the strain of each pass of deformation of the reciprocating equal-channel-angle extrusion is 1.15 ～ 28.60.

[0015] Preferably, the equal-channel-angle extrusion die comprises a first port and a second port, and when odd-numbered pass equal-channel-angle extrusion is performed, the magnesium-zinc alloy is extruded from the first port to the second port; when even-numbered pass equal-channel-angle extrusion is performed, the magnesium-zinc alloy is extruded from the second port to the first port.

[0016] This invention provides a method for strengthening magnesium-zinc alloys by reciprocating equal channel angular pressing (ECAP), comprising the following steps: placing the magnesium-zinc alloy in an equal channel angular pressing die and performing reciprocating equal channel angular pressing to obtain the strengthened magnesium-zinc alloy; the initial temperature of the magnesium-zinc alloy is 300–450°; the inner rotation angle of the equal channel angular pressing die is 90°, and the outer curvature is 0–45°; the number of pressing passes in the reciprocating equal channel angular pressing is 10–20. This invention employs the reciprocating equal channel angular pressing (ECAP) method, utilizing the high-temperature strain during the reciprocating ECAP process to activate the conical surface.<c+a> Dislocation slip enables stronger deformation capacity and induces dynamic recrystallization, thereby preventing cracking during the ECAP process. This allows for multi-pass processing to achieve a finer, more uniform microstructure and higher strength and ductility. Compared to magnesium alloys, which are prone to cracking under traditional ECAP processes, magnesium-zinc alloys processed using this invention are less prone to cracking even after 10-20 extrusion passes. Simultaneously, during high-temperature strain, precipitates undergo uniform dynamic segregation at grain boundaries, inhibiting grain boundary migration and resulting in more uniform and refined recrystallized grains. By controlling the angle of the equal-channel angle extrusion die and the number of extrusion passes, this invention enables magnesium-zinc alloys to possess finer grains and more stable grain boundaries, simultaneously improving both strength and ductility, thus resulting in better overall mechanical properties.

[0017] The results of the examples show that the magnesium-zinc alloy strengthened by the method of the present invention has fine and uniform grains with an average grain size of less than 1 μm, a tensile strength of >250 MPa, and an elongation of >15%.

[0018] Meanwhile, the strengthening method provided by this invention is simple to operate. The sample does not need to be removed and rotated after a single extrusion, and no heating treatment is required during the intermediate extrusion deformation process. Therefore, the processing efficiency is higher, the cost is lower, and it is more suitable for industrial production. Attached Figure Description

[0019] Figure 1 This is a reciprocating, equal-channel-angle extrusion process;

[0020] Figure 2 The metallographic results of the strengthened magnesium-zinc alloys obtained in Examples 1-3 and Comparative Examples 1-4 are shown.

[0021] Figure 3 The tensile stress-strain curves of the reinforced magnesium-zinc alloys obtained in Examples 1-3 and Comparative Examples 1-4 are shown. Detailed Implementation

[0022] This invention provides a method for strengthening magnesium-zinc alloys by reciprocating equal channel angle extrusion, comprising the following steps:

[0023] Magnesium-zinc alloy is placed in an equal channel angle extrusion die and subjected to reciprocating equal channel angle extrusion to obtain a reinforced magnesium-zinc alloy.

[0024] In this invention, the zinc content in the magnesium-zinc alloy is preferably 0-4 wt%, more preferably 0.1-3.5 wt%, even more preferably 0.5-3 wt%, and even more preferably 1-2.5 wt%. This invention does not require a specific initial structure for the magnesium-zinc alloy material; it can be in either the cast or extruded state.

[0025] The present invention does not have special requirements for the size of the magnesium-zinc alloy, as long as it matches the size of the equal channel angle extrusion die.

[0026] In this invention, the equal channel angle extrusion die consists of a pressure head and two channels with identical cross-sections, whose axes intersect at a certain angle and are completely connected. The inner rotation angle of the two channels is φ, and the outer circumscribed arc is ψ.

[0027] In this invention, the inner rotation angle φ of the equal channel angle extrusion die is 90°, and the outer arc ψ is 0 to 45°, preferably 0 to 30°, and more preferably 0 to 15°.

[0028] In this 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 angle extrusion die is preferably 300–450°C, more preferably 350–400°C. In this invention, during the first pass of equal channel angle extrusion, the temperature of the magnesium-zinc alloy is 300–450°C; during subsequent passes of equal channel angle extrusion, neither the magnesium-zinc alloy nor the equal channel angle extrusion die is heated.

[0029] In this invention, the number of extrusion passes of the reciprocating equal channel angle extrusion is 10 to 20, preferably 10 to 12.

[0030] In this invention, the extrusion rate of the reciprocating equal channel angle extrusion is preferably 5 to 20 mm / s, more preferably 10 to 15 mm / s.

[0031] In this invention, the strain of each pass of the reciprocating equal channel angle extrusion is preferably 1.15. ～ 28.60. In this invention, the strain of each deformation is preferably calculated according to the Iwahashi theoretical formula: ε=(1 / √3)[2cot(φ / 2+ψ / 2)+ψcosec(φ / 2+ψ / 2)], where ε represents the strain of each deformation, φ represents the inner rotation angle of the equal channel angle extrusion die, and ψ represents the outer curvature of the equal channel angle extrusion die.

[0032] In this invention, the equal channel angle extrusion die includes a first port and a second port. When performing an odd-numbered pass equal channel angle extrusion, the magnesium-zinc alloy is extruded from the first port to the second port; when performing an even-numbered pass equal channel angle extrusion, the magnesium-zinc alloy is extruded from the second port to the first port. In this invention, the magnesium-zinc alloy is reciprocated along the internal path of the die between different passes, and the sample does not need to be removed during the extrusion process. In this invention, the extrusion process of the reciprocating equal channel angle extrusion is as follows: Figure 1 As shown.

[0033] This invention produces a magnesium-zinc alloy using a reciprocating equal-channel angular extrusion process. After multiple deformation passes, this alloy exhibits a uniform, ultrafine-grained structure, resulting in superior overall mechanical properties. This addresses the issues of low strength and poor plasticity in magnesium alloys used in medical applications. The method employed in this invention is relatively simple, eliminating the need for heating during the extrusion deformation process and thus reducing costs. Furthermore, the material is reciprocated along the die between single passes, eliminating the need for sample removal and improving process efficiency. This method is suitable for industrial production and represents a unique technological innovation. During the multi-pass extrusion deformation process, the alloy maintains good plasticity and flowability without cracking, promoting further uniform and refined grain size. In summary, this invention solves the problems of incompatible grain size, strength, plasticity, and cracking in magnesium alloys produced by equal-channel angular extrusion. It achieves the preparation of a uniformly structured, ultrafine-grained magnesium-zinc alloy using multi-pass reciprocating extrusion, improving its strength and plasticity, and resulting in superior overall performance.

[0034] The results of the examples show that the magnesium-zinc alloy strengthened by the method of the present invention has fine and uniform grains with an average grain size of less than 1 μm, a tensile strength of >250 MPa, and an elongation of >15%.

[0035] The following detailed description of the method for strengthening magnesium-zinc alloys by reciprocating equal channel angle extrusion provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1

[0037] The magnesium-zinc alloy material is in the as-cast state with Mg-2wt% Zn.

[0038] The alloy was subjected to 10 passes of equal-channel angular extrusion deformation, with sample dimensions of 15×15×50mm. The first pass of extrusion deformation was carried out at 400℃, followed by reciprocating extrusion at a rate of 12mm / s.

[0039] Example 2

[0040] The magnesium-zinc alloy material is in the as-cast state with Mg-2wt% Zn.

[0041] The alloy was subjected to 12 passes of equal-channel angular extrusion deformation, with sample dimensions of 15×15×50mm. The first pass of extrusion deformation was carried out at 380℃, followed by reciprocating extrusion at a rate of 10mm / s.

[0042] Example 3

[0043] The magnesium-zinc alloy material is in the as-cast state with Mg-0wt% Zn.

[0044] The alloy was subjected to 15 passes of equal-channel angular extrusion deformation, with sample dimensions of 15×15×50mm. The first pass of extrusion deformation was carried out at 400℃, followed by reciprocating extrusion at a rate of 10mm / s.

[0045] Comparative Example 1

[0046] The as-cast Mg-2wt%.Zn alloy was subjected to only one extrusion deformation, with an initial die temperature of 400°C, and the rest was the same as in Example 1.

[0047] Comparative Example 2

[0048] The as-cast Mg-2wt%.Zn alloy was subjected to two extrusion deformations with an initial die temperature of 400°C, and the rest was the same as in Example 1.

[0049] Comparative Example 3

[0050] The as-cast Mg-2wt%.Zn alloy was subjected to five extrusion deformations with an initial die temperature of 400°C. The rest of the process was the same as in Example 1.

[0051] Comparative Example 4

[0052] The as-cast Mg-2wt%.Zn alloy was subjected to 10 extrusion deformations. The initial die temperature was 400°C, the die rotation angle ψ = 300°, and the rest was the same as in Example 1.

[0053] Comparative Example 5

[0054] The as-cast Mg-2wt%.Zn alloy was subjected to single-pass extrusion deformation with a die temperature below 300°C, and the rest of the process was the same as in Example 1. Cracking occurred in the sample after three passes.

[0055] The metallographic results of the strengthened magnesium-zinc alloys obtained in Examples 1-3 and Comparative Examples 1-4 are as follows: Figure 2 As shown. Figure 2 In the middle (a), the cast Mg-2wt%.Zn alloy that underwent only one extrusion deformation (Comparative Example 1) shows that its metallographic structure exhibits typical deformation structure characteristics, namely, coarse grains, elongation deformation, and a large number of twins. Figure 2(b) shows the as-cast Mg-2wt% Zn alloy after two extrusion deformations (Comparative Example 2). It can be seen that, compared with Comparative Example 1, some grains undergo dynamic recrystallization, and the grain morphology is a refined equiaxed state. Figure 2 (c) shows the as-cast Mg-2wt% Zn alloy after 5 extrusion deformations (Comparative Example 3). It can be seen that after 5 deformations, the grains of the alloy are refined, but the microstructure is still uneven. Figure 2 In the figure (d), the as-cast Mg-2wt% Zn alloy (Example 1) underwent 10 extrusion deformations. It can be seen that after 10 deformations, the metallographic results show that ultrafine equiaxed crystals were obtained. Figure 2 In Example 2, (e) is a cast Mg-2wt% Zn alloy that has undergone 12 extrusion deformations. It can be seen that after 12 deformations, the metallographic results show that ultrafine equiaxed grains were obtained, and some grains grew compared to 10 deformations. Figure 2 In the figure (f), the cast Mg-2wt% Zn alloy (Comparative Example 4) is deformed by 10 extrusion passes when the die rotation angle ψ = 300°. It can be seen that the grain size is larger than that of Example 2, the grain size is not uniform, and the mechanical properties are reduced. Figure 2 In the example, (g) is the as-cast Mg-0wt%.Zn alloy after 15 extrusion deformations, i.e. pure Mg (Example 3). It can be seen that after 15 deformations, the grains of pure Mg also became uniformly refined.

[0056] Performance testing

[0057] The yield strength σ of the reinforced magnesium-zinc alloys obtained in the examples and comparative examples 0.2 Tensile strength σ b The elongation was tested according to GB / T228.1-2010, and the results are shown in Table 1. The stress-strain curves of the reinforced magnesium-zinc alloy tensile tests obtained in the examples and comparative examples are shown below. Figure 3 As shown.

[0058] Table 1. Mechanical properties of the reinforced magnesium-zinc alloys obtained in the examples and comparative examples.

[0059]

[0060]

[0061] From Table 1 and Figure 3 It can be seen that the magnesium-zinc alloy strengthened by this invention has good comprehensive mechanical properties.

[0062] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for reciprocating equal channel angular pressing (RECAP) of a magnesium-zinc alloy, comprising the steps of: placing a magnesium-zinc alloy in an equal channel angular pressing (ECAP) die, and performing RECAP on the magnesium-zinc alloy to obtain a strengthened magnesium-zinc alloy; the sample does not need to be taken out and rotated after single-pass extrusion; the initial temperature of the magnesium-zinc alloy is 380-450°C; the internal corner of the ECAP die is 90°, and the external arc is 0-45°; the extrusion pass of the RECAP is 10-20 passes; the zinc content in the magnesium-zinc alloy is 0-2 wt%; the extrusion rate of the RECAP is 10-15 mm / s; the temperature of the magnesium-zinc alloy during the first pass of the ECAP is 300-450°C; and the magnesium-zinc alloy is not heated during subsequent passes of the ECAP; the strain of each pass of the RECAP is 1.15-28.60; the ECAP die comprises a first port and a second port, the magnesium-zinc alloy is extruded from the first port to the second port when performing odd-numbered passes of the ECAP, and the magnesium-zinc alloy is extruded from the second port to the first port when performing even-numbered passes of the ECAP.

2. The method according to claim 1, wherein the magnesium-zinc alloy is a magnesium-zinc alloy with a zinc content of 0-2 wt%.

3. The method according to claim 1, wherein the extrusion rate of the RECAP is 10-15 mm / s.

4. The method according to claim 1, wherein the temperature of the magnesium-zinc alloy during the first pass of the ECAP is 300-450°C.

5. The method according to claim 1, wherein the strain of each pass of the RECAP is 1.15-28.

60.

6. The method according to claim 1, wherein the ECAP die comprises a first port and a second port, the magnesium-zinc alloy is extruded from the first port to the second port when performing odd-numbered passes of the ECAP, and the magnesium-zinc alloy is extruded from the second port to the first port when performing even-numbered passes of the ECAP. ​ 2. The method of claim 1, wherein, ​ 3. The method of claim 1, wherein, ​ 4. The method according to claim 1 or 2, characterized in that, ​

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