JP5959260B2 - Processing method of magnesium alloy implant - Google Patents

Description

The present invention relates to a processing method of the magnesium alloy in-plant.

  Magnesium-magnesium alloys are lighter and stronger than other metals, and have been put into practical use in portable electronic devices and automobile parts. In addition, since magnesium has a characteristic of decomposing in vivo, application research as an absorbable stent or an absorbable osteosynthesis material is progressing (see, for example, Patent Document 1).

  Conventionally, a processing method of a magnesium alloy material that improves plastic workability by applying a load in a direction parallel to the extrusion direction of the extruded magnesium alloy material is known (for example, Patent Documents). 2).

JP 2009-178293 A Japanese Patent No. 4150219

  However, since the a-axis of the magnesium alloy crystal is arranged in the extrusion direction of the magnesium alloy, if a compressive force is applied in a direction parallel to this, plastic processing can be performed with a small force, while plastic workability is improved. The compressive force acts in a direction perpendicular to the c-axis of the metal crystal. In general, when a compressive force acts in a direction orthogonal to the c-axis, there is a disadvantage that a structural defect occurs in the crystal structure. In particular, when a magnesium alloy is used as a biodegradable material, the strength against a load in the thickness direction is weakened, which may cause material damage.

The present invention was made in view of the above circumstances, and its object is to provide a method for processing a magnesium alloy in plant which suppresses the occurrence of structural defects.

In order to achieve the above object, the present invention provides the following means.
One aspect of the present invention is an extrusion process for obtaining a plastically deformed magnesium alloy molding material by extruding a magnesium alloy, and the magnesium alloy molding material obtained by the extrusion process at 70 ° to 110 ° with respect to the extrusion direction. A method for processing a magnesium alloy implant comprising: a cutting step of cutting at an angle of °, and a compression step of applying a compressive force in a direction perpendicular to the extrusion direction to the massive magnesium alloy material obtained by the cutting step To do.

  According to this aspect, in the extrusion process, the magnesium alloy molding material whose composition is deformed by extruding the magnesium alloy so that the c-axis of the magnesium metal crystal is oriented in a direction of approximately 90 ° with respect to the extrusion direction. Is obtained. And a lump magnesium alloy material is obtained by cut | disconnecting a magnesium alloy molding material at an angle of 70 degrees-110 degrees with respect to an extrusion direction in a cutting process. Thereafter, in the compression step, a plastic processed product is manufactured by applying a compressive force in a direction orthogonal to the extrusion direction to the massive magnesium alloy material.

  In this case, since the compressive force is mainly applied in the c-axis direction, the compressive force acts in a direction orthogonal to the slip surface in the magnesium alloy metal crystal, and the compressive force is applied in the direction orthogonal to the c-axis. Compared to the case, the workability is lowered, but a plastic processed product with few structural defects can be manufactured. That is, a plastic processed product with high strength can be manufactured.

In the said aspect, the heating process which heats the said block magnesium alloy material may be included prior to the said compression process or in the said compression process.
By doing in this way, non-bottom slip can be generated and workability can be improved.

Moreover, in the said aspect, the said heating process may heat the said block magnesium alloy material at the temperature higher than 300 degreeC, More preferably, 350 degreeC or more and below melting | fusing point of a magnesium alloy.
By doing in this way, it is possible to plastically process a rare-earth alloy that is a typical medical magnesium alloy, more specifically, WE43 without causing cracks.

Moreover, in the said aspect, the said compression process may compress the said massive magnesium alloy material with a rolling reduction of 45% or more.
By doing in this way, the material particle diameter of a magnesium alloy can be refined | miniaturized and made uniform. That is, when a compressive force is applied to the massive magnesium alloy material, the recrystallized grain size almost reaches equilibrium at a rolling reduction of about 45%, so that the material grain size can be made uniform and the corrosion resistance can be improved. Here, the reduction ratio is
Reduction ratio = (Thickness before compression−Thickness after compression) / Thickness before compression × 100 (%)
Can be calculated.

Moreover, in the said aspect, the said compression process may apply a compressive force with the metal mold | die of the state which apply | coated the lubricant between the said block magnesium alloy materials.
By doing in this way, the pressure applied to a lump magnesium alloy material from a metal mold | die can be disperse | distributed with a lubricant, and it can approximate uniform deformation.

Moreover, in the said aspect, it is preferable that the said compression process repeats the application | coating of a lubrication agent between the said lump magnesium alloy material and the said metal mold | die, and application of a compression force at least twice.
By doing in this way, even if a new metal surface is generated by plastic working, it can be protected by a lubricant so that the new metal surface does not directly contact the mold and cause adhesion or seizure. As a result, it is possible to prevent the occurrence of defective products and the occurrence of damage to the mold.

Moreover, in the said aspect, the shearing process which cuts out a product from the compressed magnesium alloy material is included after the said compression process, and this shearing process may be performed at the reduction speed of 1.5 mm / sec or less.
By doing in this way, the magnesium alloy material compressed by the compression process is subjected to a shearing process to produce a plastic processed product. The shearing process is, for example, punching by a press device. In this case, along with the shearing process, a relatively smooth shearing part (shearing surface) and a fractured part (fracture surface) that instantaneously separates and presents a rough surface are generated on the cut surface. By carrying out at a reduction speed of 5 mm / sec or less, it is possible to produce a high-strength plastic processed product by suppressing the fractured portion on the cut surface to 50% or less and reducing the fracture region that causes stress concentration.

Moreover, one aspect as a reference example of the present invention provides a magnesium alloy implant in which the c-axis of a metal crystal is oriented in the main load direction.
As described above, deformation due to a compressive force parallel to the c-axis is less likely to be deformed than deformation due to a compressive force orthogonal to the c-axis, so that the strength can be improved by orienting the c-axis in the main load direction. it can.

In the said aspect, the average value of the shift | offset | difference angle of the perpendicular of the (0001) plane of a metal crystal with respect to the thickness direction may be 25 degrees or less.
By doing in this way, the c-axis of the metal crystal of the magnesium alloy can be oriented in the thickness direction, there are few structural defects, and the strength against the load in the thickness direction can be improved.

In the above aspect, the average deviation angle of the perpendicular line of the (0001) plane of the metal crystal with respect to the direction along the surface is 80 ° or more, and the deviation is 16 to 84% of the maximum deviation angle. The width of the cumulative distribution of corners may be 50 ° or less.
This also makes it possible to orient the c-axis of the metal crystal of the magnesium alloy substantially in the thickness direction, reduce structural defects, and improve the strength against loads in the thickness direction.

Moreover, in the said aspect, you may manufacture by a punching process.
In this case, it is preferable that the ratio of the shear plane in the plane along the thickness direction formed by punching is 50% or more with respect to the thickness.
By doing in this way, the fracture | rupture part which causes stress concentration can be decreased and the magnesium alloy implant with high intensity | strength can be provided.

  According to the present invention, it is possible to produce a magnesium alloy implant that suppresses the occurrence of structural defects and improves the material strength.

It is a flowchart which shows the processing method of the magnesium alloy implant which concerns on one Embodiment of this invention. It is a figure explaining the cutting process in the processing method of FIG. It is a figure explaining the compression process in the processing method of FIG. It is a figure explaining the direction of the compressive force which acts on a metal crystal in the compression process of FIG. (A) It is Example 1 of this invention, Comprising: The histogram of the shift | offset | difference angle with respect to the plate | board thickness direction of the normal line of the (0001) surface of the metal crystal of A material processed by the compression process of FIG. 3, (b) Comparative example FIG. 6 is a diagram showing a histogram of the deviation angle of the B material. (A) Histogram of deviation angle with respect to direction along product surface of normal line of (0001) plane of metal crystal of A material, (b) A diagram showing a histogram of deviation angle of B material as a comparative example. 4 is a graph showing the relationship between the true strain rate and the load when the processing conditions in the compression step of FIG. 3 are a heating temperature of 375 ° C. and a reduction speed of 0.05 mm, which is Example 2 of the present invention. 4 is a graph showing the relationship between the true strain rate and the load when the processing conditions in the compression step of FIG. 3 are a heating temperature of 375 ° C. and a reduction speed of 5 mm, which is Example 2 of the present invention. 4 is a graph showing the relationship between the true strain rate and the load when the processing conditions in the compression step of FIG. 3 are a heating temperature of 450 ° C. and a reduction speed of 0.05 mm, which is Example 2 of the present invention. 4 is a graph showing the relationship between the true strain rate and the load when the processing conditions in the compression step of FIG. 3 are a heating temperature of 450 ° C. and a reduction speed of 5 mm, which is Example 2 of the present invention. FIG. 4 is a graph showing the relationship between the true strain rate and the load when the processing conditions in the compression step of FIG. 3 are a heating temperature of 350 ° C. and a reduction speed of 1 mm, which is Example 2 of the present invention. 4 is a graph showing the relationship between the true strain rate and the load when the processing conditions in the compression step of FIG. 3 are a heating temperature of 350 ° C. and a reduction speed of 0.01 mm, according to Example 2 of the present invention. In the punching process of the processing method of FIG. 1, it is a figure which shows the relationship between the ratio of the torn surface part in the cut surface formed in the thickness direction, and reduction speed. It is a microscope picture of a cut surface which shows the case of (a) rolling speed 0.24mm / s, (b) rolling speed 1.44mm / s, and (c) rolling speed 1.92mm / s, respectively.

A magnesium alloy material processing method according to an embodiment of the present invention and a magnesium alloy implant manufactured by the processing method will be described below with reference to the drawings.
In the processing method according to the present embodiment, as shown in FIG. 1, an extrusion process (step S <b> 1) that obtains a plastically deformed magnesium alloy material by extruding a magnesium alloy material, and the extruded magnesium alloy material is cut. A cutting step (step S2), a compression step (step S3) for applying a compressive force to the cut bulk magnesium alloy material, and a punching step (step S4) for punching a product from the magnesium alloy material compressed in the compression step. I have.

  The extrusion step S1 is a step of plastically deforming the magnesium alloy material into a rod-like extrusion material 1 having a predetermined cross-sectional shape using a die. Depending on the extrusion conditions, the orientation of the metal crystals changes, and the (0001) plane of the metal crystals is oriented so as to be substantially parallel to the extrusion direction.

In the cutting step S2, as shown in FIG. 2, the extruded material 1 produced in the extruding step S1 is cut in a direction substantially orthogonal to the longitudinal direction, 70 ° to 110 °, and is a lump divided in the longitudinal direction. This is a step of obtaining the magnesium alloy material 2.
Actually, the orientation of the (0001) plane of the extruded material 1 is measured by pole figure measurement or the like, and is cut at an angle perpendicular to the plane in which the (0001) plane is remarkably oriented. It is preferable to obtain the material 2.

  In the compression step S3, as shown in FIG. 3, the compression force F is applied to the massive magnesium alloy material 2 obtained in the cutting step S2 from the reduction die in a direction perpendicular to the extrusion direction in the extrusion step S1. It is the process of adding and rolling to plate shape. Thereby, as shown in FIG. 4, a compressive force F is applied to the magnesium alloy metal crystal constituting the massive magnesium alloy material 2 substantially parallel to the c-axis orthogonal to the (0001) plane. It has become.

  In the compression step S3, the compression force F is applied while the massive magnesium alloy material 2 is heated. The temperature at the time of heating is preferably a temperature of 100 ° C. or higher that generates non-bottom slip, and in particular, when using WE43 which is a magnesium alloy material for medical use, it is higher than 300 ° C., more preferably 350 ° C. or higher. Preferably there is.

The compression step S3 is performed by applying a lubricant between the mold and the massive magnesium alloy material 2. As the lubricant, a solid lubricant, a fluid lubricant, or the like can be used.
In the compression step S3, the step of applying a lubricant and the step of reducing the massive magnesium alloy material 2 by a mold are repeated a plurality of times.

Furthermore, in the compression step S3, the massive magnesium alloy material 2 is compressed at a rolling reduction of 45% or more.
Here, the rolling reduction is expressed by the following equation.
Reduction ratio = (Thickness before compression−Thickness after compression) / Thickness before compression × 100 (%)

  The punching step S4 is a step of punching the plate-like magnesium alloy material obtained in the compression step S3 with a punching die. In this punching step S4, it is preferable to keep the die reduction speed of the magnesium alloy material to 1.5 mm / sec or less.

The operation of the magnesium alloy material processing method according to this embodiment configured as described above will be described below.
In order to plastically process the magnesium alloy material by the processing method according to the present embodiment, first, the rod-shaped extruded material 1 is obtained by extruding the magnesium alloy material in the extrusion step S1.

  In this extrusion step S1, the orientation of the metal crystal of the magnesium alloy material changes, and the (0001) plane of the metal crystal is oriented so as to be substantially parallel to the extrusion direction. Cutting process S2 is performed with respect to the extrusion material 1 obtained in this way. In cutting process S2, the extrusion material 1 is cut | disconnected by the cut surface orthogonal to the extrusion direction, and the several lump magnesium alloy material 2 is obtained. That is, the cut surface is arranged in a direction orthogonal to the (0001) plane of the metal crystal.

  Next, a compression step S3 is performed on each massive magnesium alloy material 2. In the compression step S3, a compression force F is applied to the massive magnesium alloy material 2 in a state heated to 100 ° C. or more in a direction orthogonal to the extrusion direction. The compressive force F is applied in a direction substantially parallel to the c-axis of the metal crystal oriented substantially in one direction at the position of the diameter where the degree of processing becomes the largest in the massive magnesium alloy material 2.

  In the compression step S3, the direction of the compression force F is a direction orthogonal to the slip surface of the metal crystal, and the ease of plastic working is reduced as compared with the case where the compression force F is applied parallel to the slip surface. There is an advantage that structural defects of the crystal hardly occur. That is, since the structural defect which generate | occur | produces in the magnesium alloy material after compression is suppressed, there exists an advantage that mechanical strength can be improved.

In this case, since the compressive force F is applied to the massive magnesium alloy material 2 heated to 100 ° C. or higher, the workability is improved by the occurrence of non-bottom slip as compared with the case where heating is not performed.
Further, in the compression step S3, since the compressive force F is applied in a state where the lubricant is applied between the mold and the massive magnesium alloy material 2, the compressive force F is applied to the massive magnesium alloy material by the action of the lubricant. 2 is distributed over the entire contact surface between the metal mold and the die, and a more uniform compressive force F can be applied to the entire bulk magnesium alloy material 2.

  When the compression force F is applied in the compression step S3, the magnesium alloy material becomes finer and the particle size becomes smaller. Assuming medical applications, it is known that there is a relationship between the homogeneity of the material particle size and the corrosion resistance of the material. When the material has corrosion resistance, it is desirable to make the material particle size uniform. Generally, when a compressive load is applied to a material, elastic deformation first occurs, and when the compressive load enters a plastic region, plastic deformation occurs with miniaturization. When a compressive load is further applied, the crystal grain size reaches an equilibrium state, and the material grain size becomes uniform.

  That is, it is desirable to apply a compression load until the material particle size is uniform. Specifically, compression is performed so that the rolling reduction is 45% or more, and the magnesium alloy material is refined to obtain a uniform particle size. When compressive force F is applied to the massive magnesium alloy material 2, the recrystallized grain size almost reaches equilibrium at a rolling reduction of about 45%, so that the material grain size can be made uniform. In particular, when the manufactured product is a product used for medical use such as a magnesium alloy implant, the homogeneity of the particle size can be achieved, whereby the corrosion resistance can be improved. is there.

  And punching process S4 is performed with respect to the plate-shaped magnesium alloy material obtained in compression process S3. The punching step S4 is a step of punching and removing unnecessary portions with a press machine in order to determine the product shape.

  Since the punching die is pressed in the plate thickness direction of the plate-like magnesium alloy material and punched by shearing, a cut surface is formed in the thickness direction, but by suppressing the reduction speed of the mold to 1.5 mm / sec or less The shearing surface portion in the cut surface can be made larger than the fracture surface portion. As a result, there is an advantage that the fracture surface portion is reduced, the cause of stress concentration is reduced, and the strength of the product, in particular, the magnesium alloy implant can be improved.

  Thus, according to the processing method of the magnesium alloy material which concerns on this embodiment, there exists an advantage that the structural defect after compression can be suppressed and a high-strength plastic processed product can be manufactured.

Next, examples of the present invention will be described below.
Example 1
Example 1 shows the relationship between the direction in which the compressive force F is applied to the massive magnesium alloy material 2 and the orientation of the metal crystals on the surface of the plate-like magnesium alloy material after compression.
In the case where the compression force F is applied to the direction perpendicular to the extrusion direction in the extrusion step S1 (A material) in FIG. 5 (a), similarly to the processing method according to the present embodiment, FIG. The orientation of the metal crystal on the surface of the plate-like magnesium alloy material when the compression force F is applied in a direction parallel to the extrusion direction (B material) is shown.

5 (a) and 5 (b) are histograms in which the horizontal axis represents the deviation angle of the normal line of the (0001) plane of the compressed metal crystal with respect to the plate thickness direction, and the vertical axis represents the frequency.
From these FIGS. 5 (a) and 5 (b), the average value of the deviation angle and the integrated width when compressed by each compression method are calculated as shown in Table 1.

  The accumulation width of the deviation angle refers to the width of the deviation angle in the range of 16% to 84% of the maximum value of the deviation angle in the cumulative distribution curves of FIGS.

  As shown in Table 1, the average value of the deviation angle of the A material is 16.8 °, whereas the average value of the deviation angle of the B material is 26.0 °, and the compression force F of the B material is It can be seen that the crystal orientation greatly changed by the action. Therefore, in the case of a product using a material having an average deviation angle of 25 ° or less, the compression force F is applied in a direction perpendicular to the extrusion direction, and there are few structural defects and the strength is improved. Can do.

  Moreover, as shown in Table 1, the accumulated width of the deviation angles of the A material is 17.6 °, whereas the average value of the deviation angles of the B material is 25.2 °. It can be seen that the orientation of the crystal is greatly changed by the action of the compressive force F. Therefore, in the case of a product using a material having a deviation angle accumulation width of 25 ° or less, the compression force F is applied in a direction perpendicular to the extrusion direction, and there are few structural defects and the strength is improved. Can do.

FIGS. 6A and 6B show histograms showing the relationship between the deviation angle of the normal line of the (0001) plane of the metal crystal of the A material and the B material with respect to the direction along the surface of the product and the frequency, respectively.
6A and 6B, the average value of the deviation angle and the accumulation width when compressed by each compression method are calculated as shown in Table 2.

  According to Table 2, the average deviation angle between the A material and the B material is equal to about 81 °, but it can be seen that there is a large difference in the integration width. In the case of A material, it is 17.0 °, while in the case of B material, it is 53 °. Therefore, when the average deviation angle of the normal line of the (0001) plane of the metal crystal with respect to the direction along the surface is 80 ° or more and the accumulated width of the deviation angle is 50 ° or less on the surface of the product Moreover, it turns out that it was manufactured by the processing method in this embodiment.

(Example 2)
Example 2 was performed by changing the compression conditions when applying the compression force F to the massive magnesium alloy material 2 (WE43) suitable for medical applications.
As a sample, a lump magnesium alloy material 2 having a diameter of 8 mm and a length of 12 mm is used, the heating temperature in the compression step S3 is changed to 300 ° C., 375 ° C., and 450 ° C., and the reduction speed during compression is 5 mm / sec. The results of changing to 5 mm / sec and 0.05 mm / sec are shown in Table 3. Further, the heating temperature is changed to 350 ° C., 400 ° C., and 450 ° C., and the reduction speed during compression is 1 mm / sec, 0.1 mm / sec. Table 4 shows the results obtained by changing the sec and 0.01 mm / sec.

From Tables 3 and 4, the heating temperature of the massive magnesium alloy material 2 during compression is higher than 300 ° C, more preferably 350 ° C or higher.
7 shows a heating temperature of 375 ° C. and a reduction speed of 0.05 mm, FIG. 8 shows a heating temperature of 375 ° C. and a reduction speed of 5 mm / sec, and FIG. 9 shows a heating temperature of 450 ° C. and a reduction speed of 0.05 mm / sec. FIG. 10 shows a heating temperature of 450 ° C. and a reduction speed of 5 mm / sec, FIG. 11 shows a heating temperature of 350 ° C. and a reduction speed of 1 mm / sec, and FIG. 12 shows a heating temperature of 350 ° C. and a reduction speed of 0.01 mm / sec. In this case, the relationship between the true strain rate ε and the load σ is shown.
Here, the reduction ratio is
Reduction ratio = (Thickness before compression−Thickness after compression) / Thickness before compression × 100 (%)
It can be expressed as.

  7 to 12, it is understood that when the compressive force F is applied to the massive magnesium alloy material 2, the recrystallized grain size almost reaches equilibrium with a true strain rate ε of about 0.6. When the compression ratio is calculated from here, it can be seen that the reduction ratio is about 45%. Since the recrystallized grain size almost reaches equilibrium at a rolling reduction of about 45%, it can be seen that compression at a rolling reduction of 45% or more can make the material grain size uniform and improve the corrosion resistance. In this embodiment, the WE43 is considered, but a magnesium alloy other than the WE43 may be used.

Example 3
A case where a shearing force is applied by changing the rolling speed while the plate-like magnesium alloy material (WE43) 2 having a thickness of 1 mm is heated to 350 ° C. will be described with reference to FIGS.
FIG. 13 shows the relationship between the ratio of the fracture surface portion (fracture surface ratio) in the cut surface formed in the thickness direction and the reduction speed in the punching step S4. FIG. 14 is a photomicrograph of the cut surface when the rolling speed is changed, (a) rolling speed 0.24 mm / sec, (b) rolling speed 1.44 mm / sec, (c) rolling speed. The case of 1.92 mm / sec is shown respectively. According to these figures, it is shown that the fracture surface ratio increases as the rolling speed increases, and it was found that the fracture surface ratio and the rolling speed are in a substantially proportional relationship.

  Therefore, according to FIG. 13, by setting the reduction speed to 1.5 mm / sec or less, the fracture surface portion in the cut surface in the thickness direction can be suppressed to 50% or less. As a result, there is an advantage that the fracture surface portion can be reduced, the cause of stress concentration can be reduced, and the strength of the product can be improved. In this embodiment, the WE43 is considered, but a magnesium alloy other than the WE43 may be used.

F Compression force 1 Extruded material (magnesium alloy molding material)
2 Bulk Magnesium Alloy Material S1 Extrusion Process S2 Cutting Process S3 Compression Process S4 Punching Process (Shearing Process)

Claims (8)

An extrusion process for obtaining a plastically deformed magnesium alloy molding material by extruding the magnesium alloy;
A cutting step of cutting the magnesium alloy molding material obtained by the extrusion step at an angle of 70 ° to 110 ° with respect to the extrusion direction;
And a compression step of applying a compression force in a direction perpendicular to the extrusion direction to the massive magnesium alloy material obtained by the cutting step.   The processing method of the magnesium alloy implant of Claim 1 including the heating process which heats the said block magnesium alloy material prior to the said compression process or in the said compression process.   The processing method of the magnesium alloy implant according to claim 2, wherein the heating step heats the massive magnesium alloy material at a temperature higher than 300 ° C. and not higher than a melting point of the magnesium alloy.   The processing method of the magnesium alloy implant according to claim 2, wherein the heating step heats the massive magnesium alloy material at a temperature of 350 ° C. or higher and lower than the melting point of the magnesium alloy.   The processing method of the magnesium alloy implant according to claim 2 or 3, wherein the compression step compresses the massive magnesium alloy material at a rolling reduction of 45% or more.   The processing method of the magnesium alloy implant according to any one of claims 1 to 4, wherein in the compression step, a compression force is applied by a mold in a state where a lubricant is applied to the massive magnesium alloy material.   The processing method of the magnesium alloy implant according to claim 5, wherein the compression step repeats at least twice the application of a lubricant between the metal mold and the massive magnesium alloy material and the application of a compression force. After the compression step, including a shearing step of cutting the product from the compressed magnesium alloy material;
The processing method of the magnesium alloy implant according to any one of claims 1 to 7, wherein the shearing step is performed at a reduction speed of 1.5 mm / sec or less.

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