JP2009107019A - Twist forward extrusion method and twist forward extrusion equipment - Google Patents

Abstract

Disclosed is a torsional forward extrusion method and a torsional forward extrusion apparatus suitable for creating a large-sized fine-grain bulk material that enables extrusion at a low pressure by a friction stir phenomenon and can refine crystal grains at once in a single continuous process.
After a billet B, which is a rod-shaped solid metal material, is loaded into a loading hole of a cylindrical container 1, the billet B is pressed by a pusher 3 toward a cylindrical die 2 disposed adjacent to the container 1. While rotating the die 2 and the billet B relative to each other around the extrusion axis P of the pusher 3, the pushing pressure of the pusher 3 and the rotational speed of the relative rotation are set so that one end of the billet B is attached to the inner surface of the die hole. The indentation pressure and the rotation speed are set so as to generate frictional force and frictional heat between one end of the billet B and the inner surface of the die hole by sliding while making contact, and to generate plastic flow at the one end. A torsional forward extrusion method characterized in that a torsional shear strain is applied while the flow is continued to the other end side of the billet B, and the billet B is twisted and extruded.
[Selection] Figure 1

Description

  The present invention relates to a torsional forward extrusion method and a torsional forward extrusion apparatus, and more particularly to a torsional forward extrusion method and method for applying a large processing strain to a solid metal material in order to produce a metal material having a fine microstructure. The present invention relates to a twist forward extrusion apparatus.

  The metal material is improved in strength at room temperature, toughness and workability at high temperature by refining crystal grains, and superplastic near-net molding is also possible for fine grain materials of several μm or less. However, regarding the production of fine-grained materials, productivity is poor in terms of man-hours, time, yield, etc., special equipment and high-power equipment are required, uniform miniaturization is difficult, and creation of large bulk materials is difficult Have various problems.

A twist extrusion method has been proposed as one method for refining crystal grains of a metal material (see, for example, Patent Documents 1 and 2).
In this torsion extrusion method, as shown in FIG. 5, a billet (workpiece) of a solid metal material and the die are extruded while being relatively rotated around the axis of the billet, thereby forming a billet in a single continuous process. A large torsional shear strain can be introduced efficiently. At this time, a high extrusion pressure (die surface pressure) is ensured by taking a large area reduction rate so that the workpiece is reliably twisted without slipping in the circumferential direction on the die surface.

Specifically, in Patent Document 1, a pure aluminum billet (φ8 mm × 20 mm) and a die (hole diameter φ3 mm), which are metal materials, are relatively rotated at a rotational speed of 20 to 40 rpm, and a pusher speed of 10 mm / min. By pushing the billet into the die, the outer peripheral portion is refined to an average crystal grain size of about 1 μm. Further, as shown in Patent Document 4, the center of the die, which is difficult to introduce strain due to torsion, is made almost uniform by making the axis of the die eccentric from the billet axis.
As shown in Non-Patent Documents 3 and 4, it was confirmed that various magnesium alloys can be processed without cracking even though the extrusion conditions are different, and can be applied to materials with poor ductility as well as the same refinement effect. Yes.

JP-A-2005-000990 JP-A-2005-000993 S. Mizunuma: "LARGE STRAINING BEHAVIOR AND MICROSTRUCTURE REFINEMENT OF METALS BY TORSION EXTRUSION PROCESS", MATER. SCI. FORUM, 503-504 (2006), 185-192. Kenji Kii, Masahide Takatsu, Masato Tsujikawa, Kenji Higashi, Satoshi Mizunuma, Satoshi Takahashi: “Refining and Superplasticity of Difficult-to-Work Magnesium Alloys by Torsional Extrusion (2nd Report)”, Proc. 2007), 9-10.

In recent years, there has been a strong demand for weight reduction of transportation equipment from the viewpoint of CO ₂ reduction, and a magnesium alloy (Mg alloy) having high specific strength and high rigidity has been attracting attention as a structural material for transportation equipment. Magnesium alloys can be hot forged by improving the ductility at high temperature by refining the crystal grains and obtaining a member with high productivity and high toughness. However, since it is difficult to refine a large bulk material required for forging of transportation equipment, it is currently produced by casting. Also in the torsion extrusion method of Patent Document 1, the reduction in area is increased (about 86%) so that a large extrusion pressure is generated so as to be surely twisted without causing circumferential slip on the die surface. Therefore, a large billet is required to obtain a large-diameter extruded material, and the apparatus is increased in size and requires extremely large power, which is not practically profitable.

  Therefore, in order to minimize the area reduction rate and the extrusion pressure, the inventors rotated the billet and the die at a relatively high speed instead of allowing circumferential slip on the die surface. The present invention provides the torsion forward extrusion method and the torsion forward extrusion apparatus that cause the friction stir phenomenon shown in Document 5. In the present invention, frictional force and frictional heat are generated on the contact surface of the workpiece with the die, and a torsional shear plastic flow is generated in the vicinity of the contact surface of the workpiece with the die. Furthermore, the fluidity of the material increases due to the heat generated by the plastic flow. In this case, the torsional speed generated in the workpiece is only about 1/10 to 1/30 of the relative rotational speed, but by increasing the relative rotational speed, the torsional shear strain equivalent to the torsional extrusion of Patent Document 1 is used. Can be introduced into the workpiece.

Thus, according to the present invention, after the billet, which is a rod-shaped solid metal material, is loaded into the loading hole of the cylindrical container, the billet is pressed by the pusher toward the cylindrical die disposed adjacent to the container. When the die and the billet are relatively rotated around the pusher extrusion shaft, the pushing pressure of the pusher and the rotational speed of the relative rotation are adjusted while bringing one end of the billet into contact with the inner surface of the die hole. The plastic flow is set to the indentation pressure and rotational speed so as to generate a frictional force and frictional heat between the one end of the billet and the inner surface of the die hole to generate a plastic flow at the one end. A torsion forward extrusion method is provided in which a billet is twisted and extruded by applying a torsional shear strain while continuing to the other end.
By this twist forward extrusion method, the relative rotation speed between the billet and the die is increased, and the friction stir phenomenon is used to refine the billet even in a state where the billet almost slides in the circumferential direction on the die surface. Sufficient torsional shear strain can be introduced.

  Further, according to another aspect of the present invention, there is provided a torsional front extrusion apparatus used in the torsional front extrusion method, wherein the container loaded with a billet, and the die disposed adjacent to the container, A torsional forward extrusion apparatus comprising: the pusher for pressing a billet in a container against the die; a rotating means for rotating the container or the die around the extrusion shaft; and a pressurizing means for moving the pusher in the direction of the extrusion axis. Provided.

In the torsional forward extrusion method of the present invention, by using the friction stir phenomenon, processing can be performed with a small area reduction rate and a low extrusion pressure (one order of magnitude lower than normal extrusion without twisting at the same area reduction rate). High-efficiency production of large, fine-grained bulk materials with high-spec equipment is expected.
In addition, unlike the conventional high-process refinement process, the torsion extrusion method of the present invention enables high-efficiency production in a single continuous process, is easy to apply to brittle materials, and enables relatively uniform refinement. It is.

(Explanation of twist forward extrusion method)
In the torsional forward extrusion method of the present invention, the workpiece is given a much larger torsional shear strain along with the vertical strain associated with the cross-sectional reduction at the die approach portion (the portion that causes the cross-sectional reduction in the workpiece). become. This leads to a significant reduction in the extrusion pressure from the strain increment theory, as shown in Patent Document 4. In order to make effective use of this effect, the torsional shear strain should be distributed over the widest possible range of the die approach portion where the cross-sectional area of the workpiece is reduced. An arc or an ellipse is desirable. On the other hand, when this shape is conical, torsional shear deformation concentrates near the boundary surface between the container and the die, and not only the extrusion pressure increases, but also twisting occurs due to the concentration of deformation.

The eccentricity of the die hole gives shear strain to the center as well, but in addition, the effect of suppressing slippage in the circumferential direction on the die surface of the workpiece is large, and the overall strain amount and strain rate are increased. To do. However, in the torsion extrusion method of the present invention having a large relative rotational speed, excessive eccentricity causes an excessive torsional shear strain rate and an excessive heat generation due to the processing, thereby causing thread breakage. The amount of eccentricity of the eccentric die can be, for example, about 0.2 to 0.4 mm for a billet of φ8 mm.
After all, the torsional speed of the workpiece determined by the relative rotation speed and the eccentricity ratio of the die hole (ratio of the eccentricity to the billet radius) and the ratio of the pushing speed to the indentation speed are factors that affect the temperature of the deformation site. It greatly affects the dynamic crystal grain size generated during extrusion.

  In the present invention, although the rotation speed depends on the type of the solid metal material, it is set to about 150 to 450 rpm, which is about an order of magnitude higher than the prior art, and the indentation pressure is drastically compared with the case where the rotation is not performed ( 1/10).

  The torsional forward extrusion method of the present invention generates a large amount of frictional heat, so it can be performed without heating with an AZ (Al, Zn) magnesium alloy, but tends to generate a large number of cavities of about 50 μm at low processing temperatures. It is in. This is because the billet's outer periphery preferentially flows out along the die surface at the beginning of the extrusion process, and there is a tensile stress field at the center of the billet during the transition to a steady state where the outer periphery and the center flow out uniformly. This is thought to occur.

This cavity defect can be eliminated by incorporating a heater in the container or die to raise the processing temperature, or chamfering the die side end face of the billet to mitigate a rapid change in metal flow. Since the dynamic recrystallization grain size increases as the processing temperature is raised, the latter method of chamfering the billet end face is desirable from the viewpoint of miniaturization, energy saving, and simplification of the apparatus. In this case, the range and angle to be chamfered are not particularly limited, but it is particularly effective to chamfer an area with a radius of 35 to 45% of the outer periphery of the one end on the die side of the billet at an angle of 40 to 50 °. It is desirable to chamfer an area with a radius of 40% at an angle of 45 °.
However, in consideration of the case where the cavity defect cannot be prevented by chamfering alone or application to a material that requires heating, the apparatus of the present invention enables the die to be heated up to about 270 ° C. In addition, although a container may be heated or a billet may be preheated, the local heating only of a deformation | transformation part is desirable from the point of thermal efficiency.

The solid metal material as a billet (workpiece) applied to the twist forward extrusion method of the present invention is not particularly limited, and examples thereof include the above-described magnesium alloy, aluminum, and aluminum alloy. Among these, magnesium alloys that are difficult to hot forge unless crystal grains are refined, and difficult-to-process magnesium alloys that have poor ductility and do not twist the extrusion process themselves (such as casting alloys AZ91 and Ca) The application of the torsional forward extrusion method of the present invention to a flame retardant alloy to which is added is particularly effective.
In addition, the A1100 alloy (industrial pure aluminum) can be extruded at an extremely low extrusion pressure of about 20 MPa.
It should be noted that application to a higher-strength metal material is not practical in terms of the durability of the tool and the capacity of a motor for rotating the billet and the die at a relatively high speed.

(Explanation of twist forward extrusion device)
The twist forward extrusion apparatus used in the twist forward extrusion method of the present invention includes the container loaded with a billet, the die placed adjacent to the container, and the pusher that presses the billet in the container to the die. And a rotating means for rotating the container or the die around the extrusion axis, and a pressurizing means for moving the pusher in the direction of the extrusion axis.

The cylindrical container is made of tool steel, and the cylindrical billet is dimensioned so that it can be easily loaded into the container. Even if there is a slight gap between the container and the billet, when the extrusion is started, the container and the billet are quickly deformed and brought into close contact with each other, and thereafter no relative rotation occurs.
The pusher is a push rod made of tool steel that moves in the direction of the extrusion axis in the loading hole of the container by the pressurizing means described later, and is formed in the maximum cross-sectional area that can be smoothly driven in the loading hole.

  The die is made of tool steel for hot forging, and has a bearing portion having a hole diameter smaller than the inner diameter of the container, an approach portion on the inlet side, and a relief portion on the outlet side. As described above, the shape of the approach part is a circular arc that is rounded to avoid torsional shear strain concentration near the interface between the container and the die, and to distribute the torsional shear strain as widely as possible. Or it is oval.

As described above, the rotation may be applied to the container or the die, but the rotation axis is the billet axis (in the case of the eccentric die, the axis of the hole is eccentric from the billet axis). When the container is rotated, as described above, the billet therein also rotates at the same speed as that of the container immediately after the start of extrusion, and the pusher is also rotated at the same speed as that of the container. Therefore, it is necessary to insert a thrust bearing having a large load resistance between the pusher and the pressure plate (non-rotating) of the pressure device.
Even when the container is rotating, the rotation speed of the container (= the rotation speed of the billet) is used as a reference (0), and the relative rotation speed of the die is R _D as R _D (> 0), R _D > R _M > 0, where R _M is the rotational speed of the part extruded from the workpiece die, and in an ideal state (the state where the extrusion pressure is minimized), the die is inserted from the front of the die hole entrance. The local rotational speed of the workpiece decreases in the hole.

  The rotating means includes, for example, a motor that applies a rotational force to the container or the die, a support part such as a frame, a holder, and a bearing that rotatably holds the container and the die, and the rotational force of the motor to the container or the die. A transmission mechanism such as a plurality of gears or chains for transmission and a motor controller for controlling the rotation speed of the motor can be provided.

  The pressurizing means includes, for example, a frame erected on a base on which the above-described rotating means, a support portion and the like are mounted, a hydraulic cylinder attached to the frame and having a shaft tip connected to a pusher, and hydraulic pressure applied to the hydraulic cylinder. An expansion / contraction drive unit that supplies and expands and contracts, a hydraulic control unit that controls the expansion / contraction drive unit so that a predetermined pressure is applied to the pusher, and the like can be provided. When the container side rotates, the pressure device pressure plate presses the pusher via the thrust bearing so that the pusher can also rotate as described above.

  The present torsional forward extrusion apparatus may further include a heating means for heating at least one of the die and the container so as to cope with the case where the billet (workpiece) is heated as described above. A heater (for example, a sheathed heater) can be used as the heating means. In this case, heating the die can efficiently heat the deformed portion of the billet.

Using the twist forward extrusion apparatus shown in FIG. 1, twist extrusion of aluminum billet, Mg—Al—Zn alloy (AZ31, AZ91) billet and Mg—Al—Zn—Ca alloy (AZX311, AZX911) billet was performed. The main chemical composition other than magnesium contained in the used AZ31 magnesium alloy is Al: 3.15 wt%, Zn: 0.78 wt%, Mn: 0.33 wt%, Fe: 0.002 wt%, Si: 0.009 wt%, Cu: 0.001 wt%, Ni: 0.001 wt%. In addition to magnesium contained in the used AZ91 magnesium alloy, Al: 8.9% by weight, Zn: 0.84% by weight, and Ca: 0.94% by weight are included.
As shown in FIG. 1, the twist forward extrusion apparatus includes a container 1 in which a billet B is loaded, a die 2 disposed adjacent to the bottom of the container 1, and a solid metal material B in the container 1 as a die 2. A pusher 3 that pushes the container 1 around, a rotation means 4 that rotates the container 1 around the billet axis P, a pressure means that is not shown that moves the pusher 3 in the direction of the extrusion axis P, and a sheathed heater that is not shown that heats the die 2. These are installed on a base 6 having a through hole 6a. Since the container and the die are both scratched with hardened tool steel, the container is slightly lifted by the lower thrust bearing.

  The cylindrical container 1 has a lower hole portion as a loading hole for loading the cylindrical billet B, and an upper portion of the hole portion as an insertion hole of a pusher root portion having a diameter larger than that of the loading hole. The loading hole has a hole diameter of 11 mm and a depth (length) of 20 mm. The reason why the base part of the pusher is made thick is to avoid buckling.

  The rotating means 4 includes an inverter motor M that applies a rotational force to the container 1, a cylindrical holder 43 that rotatably holds the container 1 with respect to the die 2 via bearings 41 and 42, and a rotational force of the motor M. Are provided with two gears 44 and 45 for transmitting the container and a motor control unit (not shown) for controlling the rotational speed of the motor M. A ring-shaped fixed leg 7 is fixed around the through hole 6 a of the base 5, and the lower end of the holder 43 is fixed on the fixed leg 7.

A cylindrical die holder 21 is detachably fixed to a lower portion of the hole portion of the holder 43, and the die 2 is detachably fixed in a recess formed at the upper end of the die holder 21.
The hole of the die holder 21 has a constant diameter substantially equal to the diameter of the lower end opening of the die hole.
Further, a cylindrical block 22 having a hole with a constant diameter substantially equal to the diameter of the hole of the die holder is fixed to the lower end surface of the die holder 21.

  The die 2 has a convex upper portion whose upper portion is formed in a circular convex shape, and the convex upper portion protrudes from the concave portion of the die holder 21 and is fitted in the concave portion at the lower end of the container 1. This minimizes biting (burr) of the solid metal material B into the gap between the container 1 and the die 2 and prevents runout during rotation of the container. Further, a ring member made of cast iron is fitted between the outer peripheral surface of the convex upper portion of the die 2 and the inner peripheral surface of the concave portion of the container 1 so that the shaft center of the container 1 and the die 2 is not shaken. At the same time, the tool steel is hardly worn.

Three types of dice 2 shown in FIGS. 2A to 2C were prepared. A die 2a shown in FIG. 2 (a) is formed in a tapered shape in which the upper end side (container side) of the inner surface of the die hole is reduced in diameter downward. A die 2b shown in FIG. 2 (b) and a die 2c shown in FIG. 2 (c) both have an approach portion of a die hole processed into an elliptical shape, and of these, the die 2c shown in FIG. 2 (c) The die hole axis D is an eccentric die eccentric with respect to the billet axis P.
More specifically, in the case of the die 2a (non-eccentric conical die) shown in FIG. 2A, the taper angle θ of the taper surface of the die hole is 60 °, the maximum diameter φ _a1 of the taper surface is 12 mm, and the depth of the taper surface. d _a1 is 3.5 mm. Further, the die hole has a hole diameter φ _a2 of 8 mm in a range where the depth φ _a2 is 1.5 mm from the tapered surface, and a hole diameter φ _a3 below the hole diameter φ _a3 is slightly larger 8.2 mm. In addition, the lower end opening edge of the inner surface of the die hole is formed in a taper shape whose diameter is expanded downward in order to smoothly feed the solid metal material that has been twisted and extruded.

Two types having different die hole sizes were prepared as the die 2b (non-eccentric arc die) in FIG.
The first of the two types of dies 2b has an R-processed arc surface R having a maximum diameter φ _b1 of 11 mm, a radius of curvature of the arc surface R of 2 mm, and a depth d _b1 of the arc surface R of 1.9 mm. Further, this die hole has a hole diameter φ _b2 of 8 mm in the range where the depth d _b2 is 4 mm from the arc surface R, and a hole diameter φ _b3 below the hole diameter φ _b3 is slightly larger 8.2 mm. In addition, the lower end opening edge of the inner surface of the die hole is similarly formed in a tapered shape whose diameter increases downward.
The second of the two types of dies 2b has a maximum diameter φ _b1 of 8 mm, a hole diameter φ _b2 of 5.0 mm, and a hole diameter φ _b3 of 5.5 mm, and the depth is almost the same as the first. It is.

Two types having different die hole sizes were prepared as the die 2c (eccentric arc die) in FIG.
The first of the two types of dies 2c has a maximum diameter φ _c1 of the R-processed arc surface R of 8 mm, a radius of curvature of the arc surface R of 2 mm, and a depth d _c1 of the arc surface R of 1.9 mm. Further, this die hole has a hole diameter φ _c2 of 5.2 mm in the range from the arc surface R to the depth d _c2 of 2.5 mm, and a hole diameter φ _c3 below the hole diameter φ _c3 is slightly larger 5.7 mm. The eccentric amount e of the die shaft with respect to the extrusion shaft is 0.2 mm. In addition, the lower end opening edge of the inner surface of the die hole is similarly formed in a tapered shape whose diameter increases downward.
The second of the two types of dies 2c is the same as the first die 2c except that the eccentricity e is 0.4 mm.

The pusher 3 is composed of an upper large-diameter portion and a lower small-diameter portion connected to the large-diameter portion, and a pressure plate of a pressurizing means (universal testing machine, not shown) via a thrust bearing 8 (including a guide). Is pressed.
The outer diameter of the large-diameter portion is matched with the diameter of the pusher insertion hole of the container 1, and the outer diameter of the small-diameter portion is matched with the diameter of the loading hole. The length of the small diameter portion is set to be substantially the same as the depth of the loading hole.

  Among the plurality of gears described above, the smaller gear 44 is fixed to the shaft tip of the motor M, and the larger gear 45 meshing with the small gear 44 is in a state where the center of the center hole coincides with the extrusion shaft P. It is fixed to the upper surface of the container 1. A cast iron cylinder member is provided between the large gear 45 and the large-diameter portion of the pusher 3 to reduce friction and wear with the gear 45 due to the vertical movement of the pusher 3, and the cylinder member is a gear. 45 is fixed to the inner peripheral surface of the center hole.

A hydraulic universal testing machine was used as the pressurizing means (not shown).
In addition, seed heaters (not shown) were respectively inserted into six vertical holes that penetrate the cylindrical block 22 and the die holder 21 and reach the vicinity of the die hole of the die 2.

(Comparative Example 1)
A commercially available pure aluminum material (A1100: diameter 12 mm, material crystal grain size about 80 μm) is cut to produce a pure aluminum solid material having a diameter of 11 mm × length of 25 mm, which is the non-eccentric cone shown in FIG. It set to the twist front extrusion apparatus of FIG. 1 using the die | dye 2a, the container rotational speed was set to 450 rpm and indentation pressure was set to 50 MPa, and the twist extrusion process was tried without the heating by a sheathed heater.
However, this Al solid material could not be twisted and extruded. This is considered to be because the plastic flow at the tip of the Al solid material did not occur.

(Comparative Example 2)
Except that the die 2a was heated at a die temperature of 260 ° C. with a sheathed heater, twist extrusion was attempted in the same manner as in Comparative Example 1, but seizure was likely to occur, and rotation stopped at the tip of the Al solid material frequently. . Along with this, the indentation pressure increased rapidly, and the Al solid material was cut off due to the concentration of the shear strain at the boundary between the die 2a and the container 1. Eventually, even if the rotational speed was lowered and the extrusion conditions were changed, it was possible to extrude only about several mm from the die hole outlet. In this case, the corner of the tip of the Al solid material slidably contacts the die hole surface, and this corner suddenly plastically flows to cause seizure, so that slippage deteriorates and plastic flow can be continued to the other end. As a result, it is considered that the rotation stopped.

(Example 1)
The same as Comparative Example 1 except that the non-eccentric arc die 2b (maximum diameter φ _b1 : 11 mm) shown in FIG. 2B was used and the die 2b was heated at a die temperature of 270 ° C. and the rotational speed was reduced to 150 rpm. When we tried to twist and extrude, we were able to extrude without twisting. The results are shown in Table 1.
Although the surface of the Al solid material after extrusion is rough and slightly seized, the indentation pressure is stable at a low pressure of about 20 MPa on average, the average extrusion speed is about 0.073 mm / s, and rotation at the tip of the Al solid material The deceleration is about 20 rpm, and when calculated from these, the estimated value of the equivalent strain introduced into the surface layer is about 34. The rotational speed of the tip of the Al solid material was measured by recording with a video camera installed below the die hole.
When the extruded Al solid material was cut in half in the axial direction and the cut surface was observed with an optical microscope, the average crystal grain size in the center was about 80 μm, which was not much different from that before extrusion, but it became finer as it went to the outer periphery. The thickness was about 10 μm at the ¼ position and about 4 μm at the outer periphery.

  In Example 1, as compared with Comparative Example 2, the container rotation speed is significantly reduced, and the die hole surface becomes a circular arc surface and the contact area with the Al solid material tip is increased. Since the frictional heat is not localized as compared with Comparative Example 1, the slip of the tip of the Al solid material is improved, and plastic flow is generated more slowly than Comparative Example 1, and as a result, the plastically flowed portions are sequentially formed in the die holes. It is thought that torsional shear strain was applied after introduction.

(Example 2)
Except that the die temperature was lowered to 250 ° C., the twist extrusion process was attempted in the same manner as in Example 1. As a result, it was possible to extrude without twisting. The results are shown in Table 1.
The result in Example 2 was almost the same as that in Example 1.

(Example 3)
An Mg-Al-Zn (AZ31) alloy material with a diameter of 16 mm (material particle size of 77 μm) is cut to produce a solid material of 11 mm in diameter and 25 mm in length. 2 (b) non-eccentric arc die 2b (maximum diameter φ _b1 : 11 mm) is set in the torsion forward extrusion device of FIG. When the die 2b was heated at 250 ° C. and a twist extrusion process was attempted, the die 2b was extruded without being broken. The results are shown in Table 1.
In AZ31, there was little seizure with respect to the die surface pressure, and even when the rotational speed was increased to 450 rpm, it was not broken. This is presumably because the deformation resistance is larger than the frictional resistance.

In AZ31, it is considered that only the outer peripheral portion in contact with the die hole surface was extruded in advance at the beginning of extrusion, and the center portion followed thereafter. The indentation pressure at the time when the central portion starts to follow reached the maximum of 170 MPa, and then gradually decreased to about 120 MPa. Moreover, the average extrusion speed was 0.044 mm / s.
When the AZ31 billet after extrusion was cut in half in the axial direction and the cut surface was observed with an optical microscope, the average crystal grain size at the center was not much different from 77 μm before extrusion, but partially at the 1/4 position. Dynamic recrystallization occurred and refined to about 25 μm, and the outer periphery was uniformly refined to about 10 μm.

  The Mg—Al—Zn alloy of Example 3 was less susceptible to seizure than aluminum, and as a result, threading was less likely to occur and the surface properties after extrusion were good.

(Examples 4 to 7 and Comparative Example 3)
In the same manner as in Example 1, Examples 4 to 7 and Comparative Example 3 were performed under the conditions shown in Table 1. The results are shown in Table 1.
Also in Examples 4 to 7 and Comparative Example 3, AZ31 was less likely to seize despite its large die surface pressure, and was not broken even at high speeds. However, Comparative Example 3 with a rotational speed of 0 required a very large extrusion pressure because the torsional shear strain was 0. In addition, “no defect” described in Tables 1 to 3 means that there is no cavity (pore) of about 50 μm.

(Example 8)
Except that the non-eccentric arc die 2b with the maximum diameter φ _b1 : 11 mm was replaced with the non-eccentric arc die 2b with the maximum diameter φ _b1 : 8 mm, and the die temperature, rotational speed and pushing speed were set to the conditions shown in Table 1. Example 8 was carried out in the same manner as Example 1. The results are shown in Table 1.
Also in Example 8, AZ31 had little seizure for the die surface pressure and was not broken even at high speed.

(Examples 9 to 18)
Except that the non-eccentric arc die 2b was replaced with an eccentric arc die 2c having an eccentric amount of 0.2 mm, and the materials, the die temperature, the rotation speed, and the pushing speed were set to the conditions shown in Table 2, and the same operation as in Example 1 was performed. Examples 9-18 were performed. The results are shown in Table 2.
Also in Examples 9 to 18, all of AZ31, AZX311 and AZX911 had little image sticking and were not broken even at high speed.
Further, from comparison between Examples 9 to 14 and Examples 3 to 8, there is a large difference in the ratio (area ratio) in which dynamic recrystallization occurs in the inner peripheral portion between the eccentric die and the non-eccentric die. This is particularly noticeable with a 0.4 mm eccentricity (Examples 19 and 20 described later).

(Examples 19 to 21)
Example except that the eccentric arc die 2c having an eccentric amount of 0.2 mm was replaced with an eccentric arc die 2c having an eccentric amount of 0.4 mm, and the conditions of the material, the die temperature, the rotational speed and the pushing speed were set to the conditions shown in Table 3. Examples 19 and 20 were carried out in the same manner as in Example 1. The results are shown in Table 3.
Furthermore, as Example 21, the material of Example 19 after twisted extrusion was annealed at 300 ° C. for 5 minutes, and the particle size of the material after annealing was measured.
In Examples 19 and 20, AZ31 was not seized or broken.
Further, from the comparison between Example 19 and Example 14, by increasing the amount of eccentricity of the eccentric arc die, the indentation pressure decreases, the dynamic recrystallization of the central part of AZ31 advances, and the residual portion of coarse grains It was found that it decreased considerably, and most of them were refined to about 3 μm.

3 (A1) and (A2) are photomicrographs showing the structure of the outer periphery and center of the billet after processing in Example 19, and FIGS. 3 (B1) and (B2) are those after processing in Example 20. It is a microscope picture which shows the structure | tissue of the outer peripheral part and center part of a billet. From these structural photographs, the relationship between the rotational speed, the indentation speed and the dynamic recrystallization grain size can be seen.
As shown in FIG. 3, from comparison between Example 19 and Example 20, when the rotational speed and the indentation speed are proportionally reduced to about 1/3, the extrusion pressure increases nearly four times. It was found that the crystal grain size can be reduced to about 1/3 of about 1/3.
Further, from the comparison between Example 19 and Example 21, the combination of static recrystallization by annealing after torsional extrusion significantly reduced the residual portion of coarse grains at the center of the AZ31 twisted extruded material, and it was also large at the center. It turned out that the crystal grain of a part refines | miniaturizes.

(Example 22)
FIG. 4A is a vertical cross-sectional photograph of the billet after processing of Example 19 processed using a normal billet (without chamfering), and FIG. 4B is processing of Example 22 processed using a chamfer billet. It is a longitudinal cross-sectional photograph of the latter billet.
In Example 19, it can be processed at room temperature and a low extrusion pressure, and it may be possible to achieve fairly uniform miniaturization up to the center, but as shown in FIG. Many spherical cavity defects having a diameter of about 50 μm are observed even in a considerably distant portion. The cause of this is considered to be the tensile stress field generated by a large change in the metal flow from the initial stage of extrusion to the steady state as described above.
Therefore, in Example 22, a billet whose tip was chamfered at 45 ° with C1.5 mm was used to reduce the change in the metal flow. Extrusion conditions excluding the billet shape are exactly the same as in Example 19. Looking at the longitudinal section of the bar after extrusion in these two examples, a number of cavity defects found in Example 19 were not recognized in Example 22 as shown in FIG. Although this cavity defect can be eliminated by heating the die to about 200 ° C., it is significant that the cavity defect can be eliminated by chamfering the billet in that a finer grain structure can be obtained without heating.

  The present invention is a highly refined process with excellent productivity that can refine a coarse crystal grain metal material such as an ingot to a grain size of several μm at a stroke in a single continuous process. Since it can be extruded with a surface area and low extrusion pressure, it is suitable for the creation of large fine-grain bulk materials. In particular, it is suitable for crystal refinement of a magnesium alloy that cannot be hot forged unless it is refined.

FIG. 1 is a structural explanatory view showing an example of a twist forward extrusion apparatus of the present invention. FIG. 2 is a partially enlarged cross-sectional view showing the shape of the die hole surface of various dies in the twist forward extrusion apparatus of the present invention. 3 (A1) and (A2) are photomicrographs showing the structure of the outer periphery and center of the billet after processing in Example 19, and FIGS. 3 (B1) and (B2) are those after processing in Example 20. It is a microscope picture which shows the structure | tissue of the outer peripheral part and center part of a billet. FIG. 4A is a vertical cross-sectional photograph of the billet after processing of Example 19 processed using a normal billet (without chamfering), and FIG. 4B is processing of Example 22 processed using a chamfer billet. It is a longitudinal cross-sectional photograph of the latter billet. FIG. 5 is a structural explanatory view showing an example of a conventional twisted forward extrusion apparatus.

Explanation of symbols

1 Container 2, 2a, 2b, 2c Dies 3 Pushers 4 Rotating means D Die shaft P Extrusion shaft

Claims (13)

  After loading the billet, which is a rod-shaped solid metal material, into the loading hole of the cylindrical container, the billet is pushed around the pusher push shaft toward the cylindrical die placed adjacent to the container, and the pusher pushes the billet around the pusher shaft. When the die and the billet are relatively rotated, the pushing pressure of the pusher and the rotational speed of the relative rotation are slid while contacting one end of the billet with the inner surface of the die hole, While setting the indentation pressure and the rotation speed so as to generate a frictional force and frictional heat with the inner surface of the die hole to generate plastic flow at the one end, while continuing the plastic flow to the other end side of the billet A torsional forward extrusion method characterized in that a billet is twisted and extruded by applying a torsional shear strain.   The twist forward extrusion method according to claim 1, wherein the billet is a magnesium alloy or aluminum.   The twist forward extrusion method according to claim 1 or 2, wherein the indentation pressure is 20 to 700 MPa, and the rotation speed is 150 to 450 rpm.   The twist forward extrusion method according to any one of claims 1 to 3, wherein a temperature of the die is set to room temperature to 270 ° C.   The twist forward extrusion method according to any one of claims 1 to 3, wherein a temperature of the die is set to 250 to 270 ° C.   The twist forward extrusion method according to any one of claims 1 to 5, wherein the axis of the die hole is eccentric with respect to the axis of the billet.   The torsion forward extrusion method according to any one of claims 1 to 6, wherein a region having a radius of 35 to 45% of the entire outer periphery of the one end of the billet on the die side is chamfered at an angle of 40 to 50 °.   A twist forward extrusion apparatus for use in the twist forward extrusion method according to any one of claims 1 to 7, wherein the container is loaded with a billet, and the die is disposed adjacent to the container. A torsional forward extrusion apparatus comprising: a pusher for pressing a billet in a container against the die; a rotating means for rotating the container or the die around the extrusion shaft; and a pressing means for moving the pusher in the direction of the extrusion axis. .   The torsional forward extrusion device according to claim 8, wherein the rotating means is configured to rotate the container, billet and pusher integrally.   The twist forward extrusion apparatus according to claim 8 or 9, further comprising heating means for heating at least one of the die and the container.   The twisting forward extrusion apparatus according to any one of claims 8 to 10, wherein the die has a container-side approach portion of the die hole having an arc or an elliptical roundness.   The twist forward extrusion apparatus according to any one of claims 8 to 11, wherein the die is an eccentric die in which an axis of a die hole is eccentric with respect to an axis of the billet.   The twist forward extrusion apparatus according to claim 12, wherein the eccentric amount of the eccentric die is 0.2 to 0.4 mm.