Preparation method of superfine crystal magnesium alloy bar

文档序号：112661 发布日期：2021-10-19 浏览：51次中文

阅读说明：本技术 一种超细晶镁合金棒材的制备方法 (Preparation method of superfine crystal magnesium alloy bar ) 是由郑瑞晓吕绍元肖文龙马朝利于 2021-03-22 设计创作，主要内容包括：本发明公开了一种超细晶镁合金棒材的制备方法,通过综合优化铸态镁合金的成分和改进热挤出处理的工艺,利用热挤出处理过程中的动态再结晶和纳米第二相的动态析出原理,发展一种工艺步骤简单的、可连续制备大尺寸低织构超细晶镁合金的短流程方法,进而实现高强高韧且力学性能各向同性镁合金的可控制备。上述制备方法工艺流程短,仅需要对镁合金进行一次热挤出处理即可获得超细晶组织,还可实现超细晶镁合金棒材的连续制备,生产效率高,适合大规模工业化生产。采用上述制备方法可以获得尺寸均匀的等轴超细晶组织,晶粒的再结晶程度高,织构强度低,合金的力学性能接近各向同性。(The invention discloses a preparation method of an ultrafine crystal magnesium alloy bar, which develops a short-flow method which has simple process steps and can continuously prepare large-size low-texture ultrafine crystal magnesium alloy by comprehensively optimizing the components of an as-cast magnesium alloy, improving the process of hot extrusion treatment and utilizing the principles of dynamic recrystallization and dynamic precipitation of a nanometer second phase in the hot extrusion treatment process so as to realize the controllable preparation of isotropic magnesium alloy with high strength, high toughness and mechanical properties. The preparation method has short process flow, can obtain the ultrafine grain structure only by carrying out one-time hot extrusion treatment on the magnesium alloy, can also realize the continuous preparation of the ultrafine grain magnesium alloy bar, has high production efficiency, and is suitable for large-scale industrial production. By adopting the preparation method, the equiaxial ultrafine crystal structure with uniform size can be obtained, the recrystallization degree of crystal grains is high, the texture strength is low, and the mechanical property of the alloy is close to isotropy.)

1. The preparation method of the superfine crystal magnesium alloy bar is characterized by comprising the following steps:

s1: melting pure magnesium and various magnesium intermediate alloys in an induction melting furnace, and then casting to obtain as-cast magnesium alloy; wherein the total mass content of rare earth elements in the as-cast magnesium alloy is 6-13%, the mass content of Zn elements is 0.2-1.5%, and the mass content of Zr elements is less than or equal to 0.5%;

s2: putting the as-cast magnesium alloy into a box-type resistance furnace, keeping the temperature at a first preset temperature for a preset time, taking out the magnesium alloy, and putting the magnesium alloy into water for cooling to obtain solid-solution magnesium alloy;

s3: and (2) carrying out hot extrusion treatment on the solid-solution magnesium alloy by adopting a horizontal extruder or a vertical extruder under the conditions that the extrusion temperature is 250-400 ℃, the extrusion rate is 0.1-1.0 mm/s and the extrusion ratio is 15: 1-50: 1, and cooling at room temperature to obtain the superfine crystal magnesium alloy bar.

2. The method for producing an ultrafine-crystal magnesium alloy rod according to claim 1, further comprising, after performing step S3, the steps of:

s4: and carrying out aging treatment on the superfine crystal magnesium alloy bar at a second preset temperature.

3. The method for preparing the ultra-fine grain magnesium alloy bar according to claim 1 or 2, wherein in step S2, the first preset temperature is 495 ℃ to 520 ℃.

4. The method for producing the ultrafine crystal magnesium alloy rod according to claim 1 or 2, wherein in step S2, the preset time period is 6 to 12 hours.

5. The method for preparing the ultra-fine grain magnesium alloy bar according to claim 2, wherein in step S4, the second preset temperature is 170 ℃ to 230 ℃.

Technical Field

The invention relates to the technical field of magnesium alloy manufacturing, in particular to a preparation method of an ultrafine crystal magnesium alloy bar.

Background

The magnesium alloy is a metal structure material with the lowest density in the current engineering application, and has wide application prospect in the fields of aerospace, transportation, electronic devices and the like with urgent weight reduction requirements.

Unlike common cubic metallic materials such as aluminum and iron, magnesium alloys have a typical Hexagonal Close Packed (HCP) crystal structure. The HCP structure has poor crystal symmetry and large difference in critical slitting stress between each potential slip system and twin system at room temperature, which makes the number of slip systems that can be actuated at room temperature insufficient (usually only basal plane slip), resulting in much lower room temperature strength and plasticity than common aluminum alloys. In general, the mechanical properties of as-cast metals can be improved by deformation processing, however, magnesium alloys are prone to form strong basal plane textures during deformation, which results in significant anisotropy of mechanical properties, which further limits their wide application as high-performance structural materials.

According to the classical Hall-Petch relation, the mechanical property of the metal material can be obviously improved through grain refinement, and particularly, when the grain size is refined to be in an ultra-fine grain category (d is less than 1 mu m), the strength of the material can be greatly improved. However, magnesium alloy has low melting point and difficult deformation processing, and the existing preparation technology of the ultra-fine crystal magnesium alloy mainly depends on methods such as severe plastic deformation, and the like, such as high-pressure torsion, equal channel angular extrusion, multidirectional forging and the like. For example, patent application No. CN201210516981.6 entitled "a method for processing an ultra-fine crystal magnesium alloy sheet with high yield" discloses a method for obtaining an ultra-fine crystal magnesium alloy sheet by rolling after channel extrusion of magnesium alloy and the like, but these processes are complex in preparation process, and usually require multiple passes of extrusion and rolling to achieve refinement of the structure, and the prepared sample is usually a short rod-like or sheet-like sample, and cannot achieve high-efficiency continuous preparation of large-size ultra-fine crystal magnesium alloy. The patent of application No. 201610589439.1, entitled "method for preparing bulk nanocrystalline magnesium alloy with small deformation" discloses a method for preparing nanocrystalline (40-100nm) Mg-Ag alloy by using room temperature cold rolling deformation and subsequent low-temperature short-time heat treatment process, the method is only suitable for specific alloy components, and the yield strength of the prepared material is lower and is only 120 MPa. Application No. 202010873447.5 entitled "A deformed magnesium alloy material of ultrafine grain and a process for producing the same" discloses a patent for producing a magnesium alloy of ultrafine grain with high rare earth content (rare earth content mass ratio > 13%) by a simple back extrusion method, the examples given mean grain sizes are all 5-6 μm, and are not an internationally widely recognized ultrafine grain structure (d < 1 μm).

Therefore, the development of a method which has a simple process flow and can continuously prepare the low-texture ultrafine-crystal magnesium alloy is urgently needed.

Disclosure of Invention

In view of this, the invention provides a method for preparing an ultrafine-crystal magnesium alloy bar, which is used for developing a method which has simple process flow and can continuously prepare low-texture ultrafine-crystal magnesium alloy.

The invention provides a preparation method of an ultrafine crystal magnesium alloy bar, which comprises the following steps:

In a possible implementation manner, in the method for preparing an ultrafine-crystal magnesium alloy bar provided by the present invention, after step S3 is executed, the method further includes the following steps:

s4: and carrying out aging treatment on the superfine crystal magnesium alloy bar at a second preset temperature.

In a possible implementation manner, in the preparation method of the ultrafine-crystal magnesium alloy bar provided by the invention, in step S2, the first preset temperature is 495 ℃ to 520 ℃.

In a possible implementation manner, in the preparation method of the ultrafine-crystal magnesium alloy bar provided by the invention, in step S2, the preset time period is 6h to 12 h.

In a possible implementation manner, in the preparation method of the ultrafine-crystal magnesium alloy bar provided by the invention, in step S4, the second preset temperature is 170 ℃ to 230 ℃.

According to the preparation method of the ultrafine-crystal magnesium alloy bar, the short-flow method which is simple in process steps and can be used for continuously preparing the large-size low-texture ultrafine-crystal magnesium alloy is developed by comprehensively optimizing the components of the as-cast magnesium alloy, improving the hot extrusion treatment process and utilizing the dynamic recrystallization and the dynamic precipitation principle of the nano second phase in the hot extrusion treatment process, so that the controllable preparation of the isotropic magnesium alloy with high strength, high toughness and mechanical properties is realized. The preparation method of the ultrafine-crystal magnesium alloy bar provided by the invention has the advantages that the process flow is short, the ultrafine-crystal structure can be obtained only by carrying out one-time hot extrusion treatment on the magnesium alloy, the continuous preparation of the ultrafine-crystal magnesium alloy bar can be realized, the production efficiency is high, and the preparation method is suitable for large-scale industrial production. By adopting the preparation method of the superfine crystal magnesium alloy bar, the equiaxial superfine crystal structure with uniform size can be obtained, the recrystallization degree of crystal grains is high, the texture strength is low, and the mechanical property of the alloy is close to isotropy.

Drawings

FIG. 1 is a flow chart of a method for preparing an ultra-fine crystal magnesium alloy bar provided by the invention;

FIG. 2 is a polar diagram of {0002} basal plane of an ultra-fine crystal magnesium alloy bar obtained in example 1 of the present invention;

FIG. 3 is a transmission electron micrograph of an ultra-fine grain magnesium alloy bar obtained in example 1 of the present invention;

FIG. 4 is a room temperature tensile and compressive stress-strain curve of an ultra-fine grain magnesium alloy bar obtained in example 1 of the present invention;

FIG. 5 is a polar view of {0002} basal plane of the magnesium alloy obtained in comparative example 1;

FIG. 6 is an electron back-scattered diffraction grain boundary diagram of the magnesium alloy obtained in comparative example 1.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only illustrative and are not intended to limit the present invention.

The invention provides a preparation method of an ultrafine crystal magnesium alloy bar, which comprises the following steps as shown in figure 1:

s1: melting pure magnesium and various magnesium intermediate alloys in an induction melting furnace, and then casting to obtain as-cast magnesium alloy; wherein, the total mass content of rare earth elements (Gd, Y, Sm and the like) in the cast magnesium alloy is 6 to 13 percent, the mass content of Zn element is 0.2 to 1.5 percent, and the mass content of Zr element is less than or equal to 0.5 percent;

the alloy melting method in step S1 is the same as the conventional magnesium alloy melting method, and is not described herein again; the as-cast magnesium alloy with the components obtained after smelting can form high-density nano second-phase particles (mainly LPSO, beta ', gamma' phases, and the like), which are very important for inhibiting the growth of crystal grains in the thermal deformation process;

s3: carrying out hot extrusion treatment on the solid-solution magnesium alloy by using a horizontal extruder or a vertical extruder under the conditions that the extrusion temperature is 250-400 ℃, the extrusion rate is 0.1-1.0 mm/s and the extrusion ratio is 15: 1-50: 1, and cooling at room temperature to obtain the superfine crystal magnesium alloy bar;

by designing the components of the as-cast magnesium alloy and the conditions of hot extrusion treatment, in the hot extrusion treatment process, the extrusion temperature is 250-400 ℃, the extrusion rate is 0.1-1.0 mm/s, and the extrusion ratio is 15: 1-50: 1, so that the original coarse grains can be dynamically recrystallized to obtain a completely recrystallized ultrafine grain structure close to random orientation; in addition, the grain boundary segregation of solid solution elements and the dynamic precipitation of high-density nanometer second-phase particles near the grain boundary are also accompanied in the hot extrusion treatment process, and the grain boundary segregation and the dynamic precipitation of the high-density nanometer second-phase particles can effectively pin the grain boundary, so that a dynamic recrystallization ultrafine-grained structure is reserved at high temperature; the proportion of recrystallized grains with the grain size less than 2 mu m in the obtained low-texture superfine crystal magnesium alloy bar is more than 80 percent, the average grain size is less than or equal to 1.5 mu m, the macro basal plane texture strength is less than or equal to 3.0mrd (random orientation distribution strength multiple), and the ratio of tensile and compressive yield strengths along the extrusion direction is in the range of 0.9-1.1.

Preferably, in order to further improve the strength of the low-texture ultrafine-crystal magnesium alloy bar, after step S3 in the method for preparing an ultrafine-crystal magnesium alloy bar provided by the invention is executed, the following steps may also be executed:

s4: carrying out aging treatment on the superfine crystal magnesium alloy bar at a second preset temperature; the strength of the low-texture superfine crystal magnesium alloy bar is further improved by the precipitation of the nanometer second phase.

In concrete implementation, when step S2 of the method for preparing an ultra-fine grain magnesium alloy bar provided by the invention is executed, the first preset temperature is preferably in the range of 495 ℃ to 520 ℃.

In concrete implementation, when the step S2 of the method for preparing the ultrafine-grain magnesium alloy bar provided by the invention is executed, the preset time is preferably in the range of 6h to 12 h.

In concrete implementation, when step S4 in the method for preparing an ultrafine-grain magnesium alloy bar provided by the invention is executed, the second preset temperature is preferably in the range of 170 ℃ to 230 ℃.

The following three specific examples and a comparative example are used to describe the specific implementation of the method for preparing the ultrafine-grained magnesium alloy bar and the microstructure and mechanical properties of the obtained magnesium alloy in detail.

Example 1:

the first step is as follows: alloy melting

The purchased pure magnesium and intermediate alloys of Mg-Y, Mg-Sm, Mg-Zn and Mg-Zr are melted at high temperature in a conventional magnesium alloy induction melting furnace and cast to obtain the as-cast magnesium alloy with the chemical components of Mg-6.5Y-4.5Sm-0.6Zn-0.3Zr (mass percentage).

The second step is that: solution treatment

And putting the cast magnesium alloy into a box-type resistance furnace at the temperature of 500 ℃, preserving the heat for 12 hours, taking out the cast magnesium alloy, and putting the cast magnesium alloy into water for rapid cooling to obtain the solid-solution magnesium alloy.

The third step: hot extrusion treatment

Processing solid solution magnesium alloy into a bar with the diameter of 50mm and the height of 150mm, putting the bar into a horizontal extruder for hot extrusion treatment, wherein the extrusion temperature is 350 ℃, the extrusion rate is 0.75mm/s, the extrusion ratio is 25:1, and after the hot extrusion treatment is finished, naturally cooling the bar in the air to obtain the low-texture superfine crystal magnesium alloy bar.

Fig. 2 is a polar diagram of the {0002} basal plane of the ultra-fine crystal magnesium alloy bar obtained in example 1, and the texture strength of the ultra-fine crystal magnesium alloy bar is 1.38 mrd. Fig. 3 is a transmission electron micrograph of an ultra-fine grain magnesium alloy bar obtained in example 1, all having recrystallized equiaxed grains of uniform size, and statistically measured to have an average grain size of 0.93 μm. Fig. 4 shows stress-strain curves (loading direction is parallel to extrusion direction) of room-temperature tensile (shown by solid line in fig. 4) and compressive (shown by dotted line in fig. 4) of the ultra-fine crystal magnesium alloy bar obtained in example 1, wherein room-temperature tensile yield strength and compressive yield strength are 378MPa and 363MPa respectively, tensile elongation at break is 12%, and tensile-compressive yield strength ratio is 1.04, and excellent toughness and mechanical property isotropy are exhibited.

Example 2:

the first step is as follows: alloy melting

The purchased pure magnesium and intermediate alloys of Mg-Y, Mg-Sm, Mg-Zn and Mg-Zr are melted at high temperature in a conventional magnesium alloy induction melting furnace and cast to obtain the cast magnesium alloy with the chemical components of Mg-5Y-3Sm-0.8Zn-0.5Zr (mass percentage).

The second step is that: solution treatment

The third step: hot extrusion treatment

Processing solid solution magnesium alloy into a bar with the diameter of 50mm and the height of 150mm, putting the bar into a horizontal extruder for hot extrusion treatment, wherein the extrusion temperature is 325 ℃, the extrusion rate is 0.50mm/s, the extrusion ratio is 25:1, and after the hot extrusion treatment is finished, naturally cooling the bar in the air to obtain the low-texture superfine crystal magnesium alloy bar.

The texture strength of the {0002} basal plane of the ultra-fine crystal magnesium alloy bar obtained in example 2 is 1.58, the average grain size is 0.88 μm, the room-temperature tensile strength and the yield strength are 348MPa and 341MPa respectively, and the tensile elongation at break is 10%. The ratio of tensile-compression yield strength is 1.02, and excellent toughness and isotropic mechanical properties are shown.

Example 3:

the first step is as follows: alloy melting

The purchased pure magnesium and Mg-Gd, Mg-Sm, Mg-Zn and Mg-Zr intermediate alloys are melted at high temperature in a conventional magnesium alloy induction melting furnace and cast to obtain the cast magnesium alloy with the chemical composition of Mg-6Gd-3Sm-0.5Zn-0.3Zr (mass percentage).

The second step is that: solution treatment

And putting the cast magnesium alloy into a box-type resistance furnace at the temperature of 510 ℃, preserving heat for 12h, taking out, putting into water, and rapidly cooling to obtain the solid-solution magnesium alloy.

The third step: hot extrusion treatment

Processing solid solution magnesium alloy into a bar with the diameter of 50mm and the height of 150mm, putting the bar into a horizontal extruder for hot extrusion treatment, wherein the extrusion temperature is 335 ℃, the extrusion rate is 0.65mm/s, the extrusion ratio is 25:1, and after the hot extrusion treatment is finished, naturally cooling the bar in the air to obtain the low-texture superfine crystal magnesium alloy bar.

The texture strength of the {0002} basal plane of the ultra-fine crystal magnesium alloy bar obtained in example 3 is 1.64, the average grain size is 0.98 μm, the room-temperature tensile strength and the yield strength are 377MPa and 350MPa respectively, and the tensile elongation at break is 10%. The ratio of tensile-compressive yield strength is 1.08, and excellent toughness and isotropic mechanical properties are shown.

Comparative example 1:

the first step is as follows: alloy melting

The second step is that: solution treatment

The third step: hot extrusion treatment

Processing the solid solution magnesium alloy into a bar with the diameter of 50mm and the height of 150mm, putting the bar into a horizontal extruder for hot extrusion treatment, wherein the extrusion temperature is 420 ℃, the extrusion rate is 3.0mm/s, the extrusion ratio is 25:1, and after the hot extrusion treatment is finished, naturally cooling the bar in the air to obtain a sample of the comparative example.

FIG. 5 is a polar diagram of the {0002} basal plane of the sample of this comparative example, in which the texture strength is 8.12mrd, FIG. 6 is an electron back scattering diffraction grain boundary diagram of the sample of this comparative example, the average grain size is 7.88 μm, the room temperature tensile and compressive yield strengths are 269MPa and 205MPa, respectively, the ratio of the tensile and compressive yield strengths is as high as 1.31, the strength is low, and the anisotropy of mechanical properties is significant.

The chemical components of the magnesium alloy obtained in the comparative example 1 are the same as those of the magnesium alloy obtained in the example 1, but the thermal extrusion process is the traditional high-temperature high-speed thermal extrusion, so that the magnesium alloy obtained in the comparative example 1 has a coarse grain structure and a strong basal texture, and is low in strength and obvious in mechanical property anisotropy. Therefore, the preparation method of the superfine crystal magnesium alloy bar provided by the invention can meet the requirements that the total mass content of rare earth elements (Gd, Y, Sm and the like) in the as-cast magnesium alloy is 6-13%, the mass content of Zn element is 0.2-1.5%, and the mass content of Zr element is less than or equal to 0.5% by optimizing the components of the as-cast magnesium alloy, and the hot extrusion treatment process is improved, and the conditions that the extrusion temperature is 250-400 ℃, the extrusion rate is 0.1-1.0 mm/s, and the extrusion ratio is 15: 1-50: 1 can be met, so that the low-texture superfine crystal magnesium alloy can be obtained.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

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