A magnesium alloy extrusion die and an extrusion method

Abstract

The present invention discloses a magnesium alloy extrusion die and an extrusion method, including a die body. An extrusion channel is provided in the die body. The extrusion channel from the feed inlet to the discharge outlet is successively: an inlet section, a tapered transition section, and an outlet section. The large-diameter end of the tapered transition section is connected to the inlet section, and the small-diameter end of the tapered transition section is connected to the outlet section. A plurality of protrusions are annularly arranged on the inner side wall of the tapered transition section. It can effectively improve the texture strength of the extruded magnesium alloy bars, and improve the performance and yield rate of the magnesium alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloy forming, and particularly to a magnesium alloy extrusion die and an extrusion method. Background Art

[0002] Magnesium alloys have many excellent properties, such as extremely high specific strength, specific stiffness, good biocompatibility, damping property, machinability, thermal conductivity, electromagnetic shielding property, etc. In addition, magnesium alloys also have the advantages of good machining performance, dimensional stability, and recyclability. Therefore, magnesium alloys have been widely used in the automotive industry, 3C digital electronics industry, aerospace and other fields. It is very necessary to develop this energy-saving and environment-friendly green metal material of magnesium alloy. Research, development, and expansion of the applications of magnesium alloys can effectively help China alleviate the shortage of resources and dependence on traditional energy-consuming materials, and promote the sustainable development of China.

[0003] From the perspective of the forming process, magnesium alloy castings generally have defects caused by the casting process, such as: coarse grains, dendritic segregation in the structure, and more impurities. Compared with as-cast magnesium alloys, the microstructure and properties of magnesium alloys manufactured by plastic deformation can be significantly improved. The plastic processing method not only does not cause environmental pollution, but also can produce materials with excellent microstructure and mechanical properties. Among them, the extrusion process is widely used in the entire field of magnesium alloy plastic forming, with an extremely large proportion. Extrusion is an advanced plastic processing technology with little or no waste. Extrusion forming is a process developed on the basis of traditional plastic processing technology. The greatest advantage of extrusion processing is that the stress state of the billet in the extrusion cylinder is a strong triaxial compressive stress; in this stress state, the maximum plasticity of the material can be stimulated. Research has found that most magnesium alloys can activate very few slip systems at room temperature, and even if more slip systems are activated after the temperature rises, their plastic deformation ability is still very limited. Therefore, the triaxial compressive stress can well improve the disadvantage of poor plastic forming ability of magnesium alloys, and this deformation method of extrusion should be preferred.

[0004] Although a large number of alloy extrusion plastic deformation technologies have emerged at present, for example, an asymmetric extrusion device and its extrusion method disclosed in CN108188191A, which is an asymmetric extrusion method; the preparation process of aluminum-magnesium alloy products disclosed in CN114141402A, which is an equal-channel angular extrusion method. They change the structure and refine the grains by increasing the shear strain during the deformation process, reducing the flow velocity difference between the core and the surface, and finally can be used to weaken the texture of magnesium alloys. These processes are indeed beneficial to improving the performance of magnesium alloys, but there are also obvious deficiencies. The equal-channel extrusion technology requires the manufacture of special equal-channel molds, which are expensive and costly, and are only suitable for producing relatively large-sized magnesium alloy blocks to a large extent, and it is difficult to apply to more practical magnesium alloy bars. The asymmetric extrusion process requires additional traction and straightening for the extruded materials, and the equipment is large, the components are complex, and it is difficult to maintain. Summary of the Invention

[0005] In order to solve the deficiencies of the prior art, the present invention provides a magnesium alloy extrusion die and an extrusion method, which can effectively improve the texture strength of the extruded magnesium alloy bars, and improve the performance and yield rate of magnesium alloys.

[0006] The magnesium alloy extrusion die of the present invention includes a die body, and an extrusion channel is arranged in the die body. The extrusion channel from the feed port to the discharge port is successively: an inlet section, a tapered transition section, and an outlet section. The large-diameter end of the tapered transition section is connected to the inlet section, and the small-diameter end of the tapered transition section is connected to the outlet section; several protrusions are annularly arranged on the inner side wall of the tapered transition section.

[0007] Further, the number of the protrusions is two.

[0008] Further, the cross section of the protrusion is semi-circular.

[0009] Further, the diameter of the cross section of the protrusion is 1 / 8 - 1 / 6 of the radius of the inlet section.

[0010] Further, both the inlet section and the outlet section are equal-diameter channels, and the inner diameter of the inlet section > the inner diameter of the outlet section.

[0011] Further, the cone angle of the tapered transition section is 45°.

[0012] Further, the die body is symmetric about the axis of the extrusion channel.

[0013] A magnesium alloy extrusion method uses the magnesium alloy extrusion die of the present invention to extrude a magnesium alloy bar-shaped blank to be extruded, and includes the following steps:

[0014] S1, processing the outer diameter of the bar-shaped blank to be the same as the inner diameter of the inlet section of the extrusion channel;

[0015] S2. Preheat the rod blank and the die body;

[0016] S3. Place the preheated rod blank at the inlet section and install the ejector rod;

[0017] S4. Under the action of thrust, the ejector rod extrudes the rod blank along the extrusion axis. The rod blank flows into the outlet section through the conical transition section under the action of extrusion force, and a magnesium alloy rod with a set diameter is extruded.

[0018] Furthermore, when extruding the rod blank in S4, continuously heat the die body so that the die body is maintained at a set temperature.

[0019] Furthermore, the preheating temperature in S2 and the set temperature of the die body during the extrusion process in S4 are reasonably limited according to the material of the magnesium alloy rod blank to be extruded.

[0020] The present invention has the following beneficial effects compared with the prior art.

[0021] 1. In the present invention, a number of protrusions are annularly arranged on the inner side wall of the conical transition section. When the rod blank passes through the conical transition section under the action of extrusion force, the setting of the protrusions will strongly change the forming state of the surface of the rod blank and the flow path of the blank, causing the maximum principal strain along the extrusion direction to shift, thereby weakening the texture strength in the extrusion direction and improving the performance of the extruded magnesium alloy rod.

[0022] 2. The present invention makes less modification to the die body. Therefore, the die body can be directly installed on a general support, and pressure is applied to the ejector rod by using a common horizontal extrusion press to realize the extrusion process. It does not require the high cost like equal-channel angular extrusion, and also omits the straightening equipment required for asymmetric extrusion. It has low cost and a simple process flow, and is suitable for large-scale popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic structural diagram of the die body of the present invention;

[0024] Figure 2 is a schematic cross-sectional diagram of the die body of the present invention;

[0025] Figure 3 is a schematic diagram of the state of the rod blank inside the die body before the start of extrusion;

[0026] Figure 4 is a schematic diagram of the extrusion process;

[0027] Figure 5 is a schematic diagram of the simulation of the metal streamline in the material during the existing extrusion process;

[0028] Figure 6It is a schematic diagram of the simulation of the metal streamline in the material during the extrusion process of the present invention;

[0029] Figure 7 It is the extrusion temperature distribution diagram from the core to the surface of the magnesium alloy bar at the extrusion outlet;

[0030] Figure 8 It is the equivalent strain distribution diagram from the core to the surface of the magnesium alloy bar at the extrusion outlet;

[0031] Figure 9 It is the flow velocity distribution diagram from the core to the surface of the magnesium alloy bar at the extrusion outlet.

[0032] 1 - Die body, 2 - Extrusion channel, 3 - Inlet section, 4 - Conical transition section, 5 - Outlet section, 6 - Protrusion, 7 - Bar blank, 8 - Ejector rod. Specific embodiments

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0034] See Figure 1 And Figure 2 As shown in [relevant figures], the magnesium alloy extrusion die includes a die body 1, and an extrusion channel 2 is provided inside the die body 1. The die body 1 is symmetric about the axis of the extrusion channel 2. The extrusion channel 2 successively includes an inlet section 3, a conical transition section 4, and an outlet section 5 from the inlet to the outlet. The large-diameter end of the conical transition section 4 is connected to the inlet section 3, and the small-diameter end of the conical transition section 4 is connected to the outlet section 5; both the inlet section 3 and the outlet section 5 are equal-diameter channels, and the inner diameter of the inlet section 3 > the inner diameter of the outlet section 5; the cone angle of the conical transition section 4 is 45°, and there is no need to additionally set a flow guiding groove. A number of protrusions 6 are annularly arranged on the inner side wall of the conical transition section 4. The setting of the protrusions 6 will strongly change the forming state and the flow path of the bar-shaped blank 7 on the surface, causing the maximum principal strain along the extrusion direction to shift, thereby weakening the texture strength in the extrusion direction and improving the performance of the extruded magnesium alloy bar.

[0035] Preferably, the number of the protrusions 6 is two. If the number is too small, the influence on the forming state and the flow path of the bar-shaped blank 7 on the surface is small, and thus the weakening effect of the texture strength is limited. If the number is too large, the resistance to the bar-shaped blank will increase, affecting the smoothness of the extrusion flow.

[0036] In order to improve the smooth flow of the rod-shaped blank during extrusion, the cross-section of the protrusion is set to be semi-circular, and the diameter of the cross-section of the protrusion is 1 / 8 of the radius of the inlet section.

[0037] A magnesium alloy extrusion method, using the magnesium alloy extrusion die of the present invention to extrude the magnesium alloy rod-shaped blank to be extruded, includes the following steps:

[0038] S1, Extrude the ZK60 magnesium alloy ingot into a rod with a diameter of 450 mm, and then continue to extrude it at a low temperature to a rod with a diameter of 100 mm, and finally extrude it into a rod-shaped blank 7 with a diameter of 78 mm for subsequent extrusion experiments, that is, process the outer diameter of the rod-shaped blank 7 to be the same as the inner diameter of the inlet section 3 of the extrusion channel 2.

[0039] S2, Preheat the rod-shaped blank 7 and the die body 1, the preheating temperature is 300 °C, and the preheating time is 1 h.

[0040] S3, Refer to Figure 3 , Use a specific fixture to place the preheated rod-shaped blank 7 in the inlet section 3 of the die body 1, and then immediately install the ejector rod 8. There is a certain gap between the rod-shaped blank 7 and the inner wall of the inlet section 3, and the ejector rod 8 is in close contact with the inner wall of the inlet section 3.

[0041] S4, The ejector rod 8 extrudes the rod-shaped blank 7 along the extrusion axis under the thrust of a horizontal extruder with a thrust of more than 800 tons. During the extrusion process, the die body 1 is continuously heated to keep the temperature of the die body at about 300 °C. The rod-shaped blank 7 flows through the tapered transition section 3 into the outlet section 4 under the action of the extrusion force. The extrusion speed is about 1 mm / s, the extrusion method is forward extrusion, and the extrusion ratio is set to 12.56. The magnesium alloy bar of the set diameter is extruded. After extrusion, the magnesium alloy bar is pulled.

[0042] Refer to Figure 4 , The rod-shaped blank 7 has to go through four stages from being placed in the die body 1: the initial state, filling the cavity, entering the sizing zone, and the end of non-steady extrusion. The initial state is that the rod-shaped blank 7 is placed in the inlet section 3 of the die body 1, and then the ejector rod 8 is immediately installed. There is a certain gap between the rod-shaped blank 7 and the inner wall of the inlet section 3, and the ejector rod 8 is in close contact with the inner wall of the inlet section 3.

[0043] The cavity filling stage is that the rod-shaped blank 7 fills the entire die cavity of the extrusion part, that is, the inlet section 3 and the tapered transition section 4. The stage of entering the sizing zone is that the rod-shaped blank 7 flows into the inlet end of the sizing zone, that is, the outlet section 5, under the action of the extrusion force, and then extrudes the magnesium alloy bar of a specific caliber. There may be a section of non-steady extrusion at the beginning of the extrusion. In this embodiment, the length of the non-steady extrusion part is about 66 mm, which should be cut off after extrusion. Subsequently, it is the end stage of non-steady extrusion.

[0044] See Figure 5 and Figure 6 , it can be seen from the comparison of simulation results that during the extrusion process of the magnesium alloy rod blank, when the outer surface passes through the protrusion 6, compared with the conventional 45° conical transition section die, the setting of the protrusion 6 will cause the material on the outer surface to be subjected to greater resistance, that is, the setting of the protrusion 6 will strongly change the forming state of the surface of the rod blank 7 and the flow path of the blank.

[0045] Perform performance testing on the magnesium alloy rod at the extrusion outlet, see Figures 7 to 9 , compared with the conventional 45° conical transition section die, the setting of the protrusion 6 will cause the material on the outer surface to be subjected to greater resistance, reduce the surface flow velocity, generate greater equivalent strain and equivalent stress, and the presence of the annular protrusion will also change the direction of the maximum principal strain of the material points on the surface of the magnesium alloy rod, causing the maximum principal strain originally along the extrusion direction to shift, thereby weakening the texture strength in the extrusion direction and improving the performance of the magnesium alloy rod.

[0046] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A magnesium alloy extrusion die, comprising a die body, wherein an extrusion channel is provided in the die body, and it is characterized in that: The extrusion channel is successively from the feed inlet to the discharge outlet: an inlet section, a tapered transition section, and an outlet section. The large-diameter end of the tapered transition section is connected to the inlet section, and the small-diameter end of the tapered transition section is connected to the outlet section; Both the inlet section and the outlet section are equal-diameter channels, and the inner diameter of the inlet section > the inner diameter of the outlet section; Two protrusions are annularly arranged on the inner side wall of the tapered transition section. The cross-section of the protrusion is semi-circular, and the diameter of the cross-section of the protrusion is 1 / 8 - 1 / 6 of the radius of the inlet section.

2. The magnesium alloy extrusion die according to claim 1, characterized in that: The cone angle of the tapered transition section is 45°.

3. The magnesium alloy extrusion die according to claim 1, characterized in that: The die body is symmetric about the axis of the extrusion channel.

4. A magnesium alloy extrusion method, characterized in that, Using the magnesium alloy extrusion die according to any one of claims 1 - 3 to extrude the magnesium alloy rod-shaped blank to be extruded, the following steps are included: S1, machining the outer diameter of the rod-shaped blank to be the same as the inner diameter of the inlet section of the extrusion channel; S2, preheating the rod-shaped blank and the die body; S3, placing the preheated rod-shaped blank in the inlet section and installing the ejector rod; S4, the ejector rod extrudes the rod-shaped blank along the extrusion axis under the action of thrust. The rod-shaped blank flows into the outlet section through the tapered transition section under the action of the extrusion force, and a magnesium alloy rod with a set diameter is extruded.

5. The magnesium alloy extrusion method according to claim 4, characterized in that: During the extrusion of the rod-shaped blank in S4, the die body is continuously heated so that the die body is maintained at the set temperature.

6. The magnesium alloy extrusion method according to claim 5, characterized in that: The preheating temperature in S2 and the set temperature of the die body during the extrusion process in S4 are reasonably limited according to the material of the magnesium alloy rod-shaped blank to be extruded.

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