JP7512932B2 - Material evaluation method and manufacturing method for metal member - Google Patents

Description

This disclosure relates to a material evaluation method and a manufacturing method for metal components.

When manufacturing metal components such as electrical connection terminals by processing metal sheets that involves bending, the material used is selected so that the metal material will not suffer damage due to shear deformation, such as cracks or wrinkles, when it is bent as specified. As a basis for selecting an appropriate material, it is important to understand through testing the relationship between the stress applied to the material and the occurrence of damage. For this reason, tests are conducted to determine the level of damage that will occur when a certain level of stress is applied to the metal material.

The method of such a test is, for example, specified in the standard "JBMA T307:1999" of the Japan Copper and Brass Association, which is published in the following non-patent document 1. In this standard, as shown in FIG. 7A, a jig 90 is used that includes an upper die 91 having two convex portions 92, 92 and a lower die 95 having two concave portions 96, 96 that can accommodate the convex portions 92, 92, to bend a test material S' configured as a metal plate material. That is, as shown in FIG. 7B, the test material S' is sandwiched between the upper die 91 and the lower die 95 and bent into a W shape. Then, the bent portion S'1 of the test material S' that has become a mountain due to bending is observed with an optical microscope, and the degree of the "wrinkles" and "cracks" formed is evaluated. Here, "wrinkles" are defined as "a state in which a step-like depression or streak that appears due to bending can be observed," and "cracks" are defined as "a state in which the bottom of the crack cannot be observed from directly above and the crack is cracked along the shear band." The test material S' is classified into five levels: "no wrinkles," "small wrinkles," "large wrinkles," "small cracks," and "large cracks."

"Japan Copper and Brass Association Technical Standard: Material Evaluation Method for Copper and Copper Alloy Thin Sheet Strips, JBMA T307:1999" Japan Copper and Brass Association, Standardization Committee for Copper Alloys for Electronic Components, 1999 Kunio MIYAUCHI, "A Proposal of a Planar Simple Shear Test in Sheet Metals", Scientific Papers of the Institute of Physical and Chemical Research, 1972, Vol. 78, No. 3, pp. 27-40

In the case of evaluating the effect of shear stress generated when bending a metal sheet material, as in the standard published in Non-Patent Document 1, when the degree of cracking and wrinkles is evaluated by observing the bent part with a microscope, the evaluation index is qualitative. This makes it difficult to quantitatively compare the bending workability between different materials. The evaluation results may vary depending on the tester. In addition, in order to compare the bending workability between different materials, it is necessary to evaluate a large number of test materials S' while changing the ratio R/t of the radius of curvature R of the curved shape at the top of the convex parts 92, 92 of the upper die 91 of the jig 90 and the top of the joint part 97 between the two concave parts 96, 96 of the lower die 95 to the sheet thickness t of the test material S', which requires a lot of testing effort.

In addition, the strain that occurs during bending of metal components may depend on the dimensions of the components, particularly the width dimension that intersects with the bending direction, even if the target material type is the same. For example, the standard published in Non-Patent Document 1 specifies the width of the test material as 10 mm, but in electrical connection terminals, the width of the spring part formed by bending is often much smaller than 10 mm, and the evaluation method of the standard published in Non-Patent Document 1 may not be able to properly evaluate the effect of strain during bending. In this case, in addition to the above ratio R/t, the width of the test material must also be considered as a variable parameter, which further increases the effort required to evaluate the material. In addition, interpretation may also be complicated.

Therefore, the objective of the present invention is to provide a material evaluation method that can quantitatively evaluate the bending workability when bending metal plate material, and a manufacturing method for metal parts that can quantitatively evaluate bending workability and select raw materials.

The material evaluation method disclosed herein involves performing a shear test on a test material configured as a metal plate, obtaining a shear stress curve in which shear stress is recorded as a function of shear strain, defining the 0.2% yield strength obtained from the shear stress curve as shear yield stress _τs , and defining the tensile yield stress obtained as 0.2% yield strength by a tensile test of the test material as _σs , and determining that the larger the yield stress ratio calculated as _τs / _σs , the less likely the test material is to develop wrinkles when bent. Alternatively, a shear test is performed on a test material configured as a metal plate to obtain a shear stress curve in which the shear stress is recorded as a function of shear strain, and in the shear stress curve, the shear stress at which the test material breaks is defined as the maximum shear stress τ _max , and the tensile strength obtained by a tensile test of the test material is defined as σ _max . The larger the maximum stress ratio calculated as τ _max /σ _max , the less likely the test material is to crack when bent.

The manufacturing method of the metal component disclosed herein uses a metal material selected as a raw material after evaluation using the material evaluation method, and manufactures the metal component by bending the metal material.

The material evaluation method disclosed herein can quantitatively evaluate the bending workability when bending a metal plate. Furthermore, the manufacturing method for metal components disclosed herein can quantitatively evaluate bending workability and select raw materials.

FIG. 1 is a side view illustrating a method of shear testing by mechanical measurement. 2A and 2B are plan views showing the test material used in the shear test, with Fig. 2A being an overall view and Fig. 2B being an enlarged view showing the vicinity of the tip of the slit. FIG. 3 is an example of a shear stress curve obtained by a shear test using mechanical measurement. 4A and 4B are images illustrating a shear test using an image correlation method, where Fig. 4A shows the state before load application and Fig. 4B shows the state during load application. 5A and 5B are examples of shear stress curves obtained in a shear test using an image correlation method, where Fig. 5A is an overall view and Fig. 5B is an enlarged view showing a low strain region. Fig. 6A is a diagram for explaining the direction of stress generated during bending deformation of a metal material, and Fig. 6B is a diagram for explaining a σ _xx -σ _zx yield surface. 7A and 7B are diagrams for explaining a conventional material evaluation method, in which Fig. 7A shows the state before bending and Fig. 7B shows the state after bending.

[Description of the embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described.

The material evaluation method according to the first embodiment of the present disclosure involves performing a shear test on a test material configured as a metal plate, obtaining a shear stress curve in which shear stress is recorded as a function of shear strain, and defining the 0.2% yield strength obtained from the shear stress curve as shear yield stress _τs and the tensile yield stress obtained as 0.2% yield strength by a tensile test of the test material as _σs.The larger the yield stress ratio calculated as _τs / _σs , the less likely the test material is to develop wrinkles when bent.

In the above-mentioned material evaluation method, a shear stress curve is obtained by a shear test, and then the yield stress ratio τ _s /σ _s is quantitatively determined from the shear yield stress τ _s obtained from the shear stress curve and the tensile yield stress σ _s obtained by a tensile test. The value of this yield stress ratio τ _s /σ _s is an index that reflects the resistance to wrinkles during bending, that is, wrinkle resistance. Therefore, by using the yield stress ratio as an index and judging that a material with a larger value is less likely to wrinkle when bending, the possibility of wrinkles occurring during bending can be quantitatively evaluated.

Here, when the yield stress ratio _τs / _σs is equal to or greater than a predetermined yield stress ratio threshold, it is possible to determine that the test material has sufficient wrinkle resistance. Then, materials that have high wrinkle resistance and are unlikely to wrinkle even when subjected to bending can be distinguished based on a quantitative index and selected as the raw material to be subjected to bending or other processes.

In this case, when the test material is copper or a copper alloy and a shear test is performed within the plane of the test material, the yield stress ratio threshold value should be set to 0.48. This makes it possible to distinguish copper or copper alloys with high wrinkle resistance with high accuracy.

A material evaluation method according to a second embodiment of the present disclosure involves performing a shear test on a test material configured as a metal plate to obtain a shear stress curve in which shear stress is recorded as a function of shear strain, and determining that the shear stress at which the test material breaks in the shear stress curve is the maximum shear stress τ _max and that the tensile strength obtained by a tensile test of the test material is σ _max , and that the larger the maximum stress ratio calculated as τ _max /σ _max , the less likely the test material is to crack when bent.

In the above-mentioned material evaluation method, a shear stress curve is obtained by a shear test, and then the maximum stress ratio τ _max /σ _max is quantitatively calculated from _the maximum shear stress τ _max obtained from the shear test curve and the tensile strength σ max obtained by a tensile test. The value of this maximum stress ratio τ _max /σ _max is an index that reflects the resistance to cracking during bending, that is, crack resistance. Therefore, by using the maximum stress ratio as an index and judging that a material with a larger value is less likely to crack when bending, the possibility of cracking during bending can be quantitatively evaluated.

Here, when the maximum stress ratio τ _max /σ _max is equal to or greater than a predetermined maximum stress ratio threshold, it is possible to determine that the test material has sufficient crack resistance. Then, materials that have high crack resistance and are unlikely to crack even when subjected to bending can be distinguished based on a quantitative index and selected as the raw material to be subjected to bending or other processes.

In this case, when the test material is copper or a copper alloy and a shear test is performed within the plane of the test material, the maximum stress ratio threshold value should be set to 0.60. This makes it possible to distinguish copper or copper alloys with high crack resistance with high accuracy.

When obtaining the shear stress curve, it is preferable to evaluate the shear strain by an image correlation method based on an image of the test material. In this case, the magnitude of the shear strain is evaluated by image analysis, so that the obtained shear stress curve is less likely to have non-essential contributions due to the influence of the members used in the shear test, such as a jig. For example, when applying shear stress to the test material through a jig and evaluating the magnitude of the shear strain based on the amount of movement of the jig, the magnitude of the shear strain may not be accurately estimated due to the influence of deformation or deviation of the jig. If the image correlation method can estimate the relationship between shear strain and shear stress while reducing non-essential influences, it becomes easier to accurately evaluate the bending workability of the material. In particular, the accuracy of the measurement of shear strain in the low strain region is increased, making it easier to accurately evaluate the shear yield stress.

The test material is a rectangular plate material with two sets of slits extending from a pair of opposing sides, and the areas outside the two sets of slits along the pair of sides are defined as end regions, and the area between the two sets of slits is defined as an inner region. In the shear test, shear forces are applied in opposite directions to the two end regions and the inner region within the plane of the test material to obtain the shear stress curve for the shear deformation within the plane of the test material. Then, shear deformation occurs symmetrically at the two deformation parts corresponding to the points between each set of slits, so that the effect of rotation in the shear direction is reduced and a highly accurate shear stress curve can be obtained.

In this case, in the test material, the distance between the slits constituting each set is a, the width at the tip of each of the slits is b, the plate thickness of the test material is t, the Young's modulus of the test material is E, and the 0.2% yield strength in tension is _σy , and it is preferable that 2t≦b≦(E/ _σy ) ^0.5 ·t and 3mm≦a≦(E/ _σy )·( ^t2 /b) are satisfied. This makes it easier to further improve the measurement accuracy of the shear strain.

The method for manufacturing a metal component according to an embodiment of the present disclosure uses a metal material selected as a raw material after evaluation using the material evaluation method, and manufactures the metal component by bending the metal material.

When manufacturing metal parts through bending, if damage due to shear such as cracks occurs at the bent area, it becomes difficult to manufacture metal parts with the specified performance and strength. Therefore, by using the above-mentioned material evaluation method to evaluate the bending workability of the raw metal material based on the shear stress curve obtained from the shear test, raw materials with high bending workability can be selected based on a quantitative index. As a result, it becomes possible to manufacture metal parts with the specified strength and performance with high reliability through bending, etc. Since the bending workability can be quantitatively evaluated and then used as an index for manufacturing metal parts, it is not necessary to test a large number of test materials or manufacture a large number of prototypes, even when manufacturing multiple types of metal parts with different dimensions and shapes.

Here, it is advisable to select as the raw material a metal material that is determined to have sufficient wrinkle resistance in the material evaluation method. This makes it possible to manufacture metal components while suppressing the occurrence of wrinkles during bending.

Alternatively, a metal material that is determined to have sufficient crack resistance in the material evaluation method can be selected as the raw material. This makes it possible to manufacture metal components while suppressing the occurrence of cracks during bending.

The metal member may be an electrical connection terminal. Electrical connection terminals are manufactured by processing metal plate material into a predetermined shape through bending and other processes. Bending at a steep angle is often performed. If damage such as cracks or wrinkles occurs during bending, this may affect the mechanical strength and electrical characteristics of the electrical connection terminal. Therefore, by manufacturing electrical connection terminals using raw materials that are determined to have sufficient bending workability by the above-mentioned material evaluation method, it is possible to manufacture electrical connection terminals with desired characteristics and strength with high productivity.

[Details of the embodiment of the present disclosure]
Hereinafter, the material evaluation method and the manufacturing method of the metal member according to the embodiment of the present disclosure will be described in detail with reference to the drawings. Based on the results of the evaluation by the material evaluation method according to the present disclosure, the manufacturing method of the metal member according to the present disclosure can be carried out. Hereinafter, in this specification, various measurements are measured at room temperature and in the atmosphere unless otherwise specified. In addition, the concepts of in-plane, out-of-plane, vertical, etc., which represent the shape and arrangement of the member, and the dimensional values, include not only geometrically strict concepts, but also deviations within the range allowed in the evaluation of metal plate materials.

<Outline of material evaluation method>
A material evaluation method according to an embodiment of the present disclosure will be described. In the material evaluation method according to the present embodiment, a shear test is performed on a test material configured as a metal plate material, a shear stress curve is obtained in which the shear stress is recorded as a function of shear strain, and the bending workability of the metal material is evaluated using the shear stress curve. Here, bending workability indicates the degree to which damage such as cracks and wrinkles occurs at the bending point when bending a metal material, and the less likely such damage occurs, the higher the bending workability is considered to be. The shear test may be performed on the in-plane shear deformation of the test material configured as a metal plate material, or on the out-of-plane shear deformation.

The inventors' research has revealed that when crystal orientation is analyzed by electron backscatter diffraction (EBSD) at the point where metal material such as copper alloy is bent, cracks and wrinkles due to bending occur with the formation of shear bands. Furthermore, it has been confirmed that shear deformation occurs during bending deformation, and as the shear deformation progresses, a group of crystal grains with a specific orientation is generated within the crystal structure. Therefore, the shear stress curve obtained by the material evaluation method can be associated with the susceptibility of cracks and wrinkles occurring during bending.

In particular, the maximum shear stress τ _max and the shear yield stress τ _s can be suitably used as representative values of stress obtained in the shear stress curve as indicators of the resistance of the material to shear deformation. The maximum shear stress τ _max corresponds to the stress at which the test material breaks, and as shown in the following examples, has a high correlation with the occurrence of cracks in the test material. Therefore, it can be said that the larger the value of the maximum shear stress τ _max , the less likely the material is to crack due to shear deformation. On the other hand, the shear yield stress τ _s corresponds to the stress at which shear bands begin to occur in the test material, and is related to the occurrence of wrinkles in the test material, as shown in the following examples. Therefore, it can be said that the larger the value of the shear yield stress τ _s , the less likely the material is to wrinkle due to shear deformation.

In this way, the maximum shear stress τ _max obtained as the shear stress when the test material breaks in the shear test can be associated with the degree of cracking during bending. The larger the maximum shear stress τ _max , the less likely it is to crack during bending. The maximum shear stress τ _max may be compared directly between different materials, but the bending workability of the material can be more accurately evaluated by dividing the maximum shear stress τ _max by the tensile strength σ _max of the material to obtain the maximum stress ratio τ _max /σ _max . The larger the value of the maximum stress ratio τ _max /σ _max , the less likely it is to crack during bending, that is, the higher the crack resistance can be evaluated.

Furthermore, the shear yield stress τ _s obtained in the shear test can be associated with the degree of wrinkles occurring during bending. It can be considered that the larger the shear yield stress τ _s , the less likely wrinkles will occur during bending. Here, the value of 0.2% proof stress obtained in the shear test can be used as the shear yield stress τ _s . The values of the shear yield stress τ _s may be directly compared between different materials, but the bending workability of the material can be more accurately evaluated by dividing the shear yield stress τ _s by the tensile yield stress σ _s of the material to obtain the yield stress ratio τ _s /σ _s . The larger the value of the yield stress ratio τ _s /σ _s , the less likely wrinkles will occur during bending, that is, the higher the wrinkle resistance can be evaluated.

Here, the tensile strength σ _max of a material is the tensile stress applied to a sample when the material is pulled to break, and can be evaluated, for example, by a tensile test in accordance with JIS Z 2241. The tensile yield stress σ _s of the material can be obtained as the 0.2% proof stress in the tensile test.

The deformation of metal materials caused by bending may progress with both plane strain and shear strain, but it is considered that plane strain is related to tensile stress and shear strain is related to shear stress. As mentioned above, shear strain can cause cracks and wrinkles during bending, but plane strain is unlikely to cause cracks or wrinkles. Therefore, if the tensile strength σ _max or tensile yield stress σ _s of a material is small and it is easy to bend with plane strain, it can be said that even a material with a relatively small shear stress is unlikely to cause cracks or wrinkles due to shear strain when bending. Therefore, rather than associating the values of the maximum shear stress τ _max and the shear yield stress τ _s themselves with bending workability, the maximum stress ratio τ _max /σ _max and the yield stress ratio τ _s /σ _s , which are values obtained by dividing the maximum shear stress τ _max and the shear yield stress τ _s by the tensile strength σ max and the tensile yield stress σ s, respectively, can be used as indexes to more accurately evaluate whether cracks or wrinkles are likely to occur during bending.

By comparing the maximum stress ratio τ _max /σ _max and the yield stress ratio τ _s /σ _s between different materials, the crack resistance and wrinkle resistance can be compared between the materials. In addition, the maximum stress ratio τ _max /σ _max and the yield stress ratio τ _s /σ _s may be estimated as thresholds above which cracks and wrinkles do not occur in the material. The thresholds may be estimated, for example, by comparing the results of a preliminary test in which the degree of cracks and wrinkles caused by bending is estimated by microscopic observation with the results of a shear test. Then, if the maximum stress ratio τ _max /σ _max of the material to be evaluated is equal to or greater than a predetermined maximum stress ratio threshold, the material may be evaluated as having sufficient crack resistance. Furthermore, if the yield stress ratio τ _s /σ _s is equal to or greater than a predetermined yield stress ratio threshold, the material may be evaluated as having sufficient wrinkle resistance.

When evaluating the bending workability of a metal material, as described in Non-Patent Document 1, if the actual bent portion is observed under a microscope to determine the presence or absence of cracks or wrinkles, it is difficult to quantitatively evaluate the bending workability and use it for comparison between materials. However, in the material evaluation method according to the present embodiment, a shear test is performed, and the maximum shear stress τ _max and the shear yield stress τ _s are measured as numerical values, and then the bending workability can be quantitatively evaluated by comparing them with threshold values. Therefore, the influence of qualitative evaluation, such as the variation between evaluators, can be eliminated, and the bending workability can be estimated as an objective numerical value, and quantitative comparison between different materials can also be easily performed.

<Shear test>
In the above material evaluation method, a shear test for obtaining a shear stress curve will be described. In the shear test, a shear stress is applied to a test material, and the shear stress is recorded as a function of shear strain to obtain a shear stress curve. In the shear test, the method of applying the shear stress and the method of evaluating the shear strain are not particularly limited. For example, a shear test using mechanical measurement or a shear test using image analysis, as exemplified below, can be used. The shear test may be performed on the in-plane shear deformation of a test material made of a metal plate material, or on the out-of-plane shear deformation, but the in-plane shear test will be described below.

Here, we will explain the shape of the test material that can be suitably used for the in-plane shear test. Figure 2A shows the shape of the test material S. The test material S is formed as a plate material having a rectangular outer shape. Here, the outer shape of the test material S is a square. Two pairs of slits S1, S1 extending opposite each other are provided from a pair of opposing sides S3, S3 of the test material S, that is, a total of four slits S1. All four slits S1 have the same shape and dimensions. Along the side S3, the test material S is divided into three regions, the region sandwiched between the two pairs of slits S1 is the inner region R1, and the regions outside the two pairs of slits S1 are the end regions R2, R2, respectively.

In the shear test, loads F1 and F2 are applied to the test material S within the plane of the test material S. At this time, load F2 is applied in the same direction to the two end regions R2 and R2, and load F1 is applied to the inner region R1 between them in the opposite direction to the end regions R2 and R2. By applying these loads F1 and F2, shear stress is applied to the deformed parts R3 and R3, which are the regions between each pair of slits S1 and S1, and shear deformation occurs. As shown by the arrows in the deformed parts R3 and R3 in Figure 2A, shear stress acts symmetrically on the two deformed parts R3 and R3, so the rotational moment generated in the deformed parts R3 and R3 is reduced. Therefore, the relationship between shear stress and shear strain can be evaluated by reducing the effect of the rotational moment.

The test material having a shape divided into three regions by four slits is also adopted in the shear test disclosed in Non-Patent Document 2, but in the test material S preferably used in the material evaluation method according to this embodiment, the dimensions of the slit S1 are different from those disclosed in Non-Patent Document 2. In this embodiment, as shown in the enlarged view in FIG. 2B, the distance between the slits S1, S1 constituting each set, that is, the length of the deformed portion R3, is a. Also, the width at the tip S2 of each slit S1, that is, the width of the deformed portion R3, is b. In the illustrated embodiment, a rounded shape (corner R shape) is formed at the corner of the tip of the slit S1, and the inner dimension of these rounded shapes is b. The plate thickness of the test material S is t, the Young's modulus is E, and the 0.2% proof stress in tension is σ _y . Note that σ _y refers to the same as the above tensile yield stress σ _s . In this case, the dimensions a and b are expressed by the following formulas (1) and (2).

By setting the dimensions a and b in this way, the effect of suppressing compressive buckling is superior even in test pieces with a very thin plate thickness t of 0.25 mm or less, or 0.15 mm or less, compared to the form in Non-Patent Document 2. Furthermore, in order to increase the accuracy in measuring the shear strain, it is preferable to determine a and b so as to satisfy the following formulas (3) and (4).
b ≧ 2t (3)
a ≧ 3 mm (4)

The width b' of the slit S1 as a whole is not particularly limited, but it is preferable to determine the width b' so as to replace b with b' and satisfy the above formulas (1) and (3). When the test material S is made of copper or a copper alloy and the plate thickness t is 0.15 to 0.25 mm, it is preferable to determine the dimensions of each part as follows, for example.
・Outer dimensions of test material S: 30 mm x 30 mm
Length a of the deformed portion R3: 5.0 mm
Width b of the deformed portion R3: an arbitrary width determined by formulas (1) and (3) Overall width b' of the slit S1: 0.4 mm

<Shear test by mechanical measurement>
Next, an in-plane shear test by mechanical measurement will be described as a specific method for applying a shear load to the above-mentioned test material S and obtaining a shear stress curve. Figure 1 shows a schematic side view of a test device that can be used for the shear test.

The test device 1 has a support frame 10 and a holder 20. The holder 20 has a pair of fixed jigs 21, 21, and a movable jig 22 between them. These jigs 21, 22 are each divided into two blocks in the front-to-back direction (perpendicular to the paper surface), and the plate surface of the test material S can be sandwiched between them. Here, the two end regions R2, R2 of the test material S are sandwiched between the fixed jigs 21, and the inner region R1 is sandwiched between the movable jig 22. With the test material S sandwiched, the holder 20 can hold the test material S by tightening the screws 24 that pass through the two blocks and are positioned outside the test material S.

The holder 20 holding the test material S is housed and held in the support frame 10. At this time, the holder 20 is placed with the plate surface of the test material S standing vertically so that the slit S1 is vertical. The fixed jig 21 of the holder 20 is placed on and supported by the support frame 10, but the movable jig 22 does not contact the support frame 10. In this state, the pressing member 31 of the pressing tool 30 is placed in contact with the movable jig 22, and then the pressing member 31 is moved downward. As the pressing member 31 moves, the test material S held by the holder 20 is sandwiched between the pressing tool 30 and the support frame 10, so that a downward load F1 is applied to the inner region R1 of the test material S, and an upward load F2 is applied to the end regions R2, R2 on both sides.

A load cell (not shown) is attached to the pressing tool 30, and the magnitude of the load F1 applied to the test material S by the pressing member 31 can be measured. The relationship between the displacement of the pressing member 31 and the load F1 can then be recorded. Pressing by the pressing member 31 can be performed using a known material testing machine capable of performing tensile tests, compression tests, etc. on metal materials as a device capable of measuring and recording the displacement while applying the load F1. A shear stress curve can be obtained by converting the displacement of the pressing member 31 into strain and plotting it on the horizontal axis, and plotting the load F1 applied by the pressing member 31 as shear stress on the vertical axis.

In this way, the load F1 is applied to the test material S to generate shear stress, and the material evaluation method according to this embodiment is performed based on the shear stress curve obtained from the relationship between the shear strain measured by mechanical means and the shear stress, and the bending workability can be evaluated from the perspective of crack resistance and wrinkle resistance. However, since the shear strain is evaluated by a mechanical parameter, namely the movement amount of the pressing member 31, there is a possibility that the evaluation of the relationship between the shear strain and the shear stress may be inaccurate. Specifically, the load F1 applied from the pressing member 31 may cause a displacement other than the shear deformation of the test material S. For example, deformation may occur in the components of the test device 1, such as the support frame 10 and each jig 21, 22, or a shift may occur in the clearance between these components. These deformations and shifts cause a displacement to the pressing member 31 in addition to the shear deformation of the test material S. In this case, if the shear strain is obtained based on the amount of movement of the pressing member 31 and used as a shear stress curve, the contribution of phenomena that are not essential to shear deformation will be mixed into the shear stress curve.

The contribution of deformation and displacement of the components of the test device 1 is unlikely to cause significant problems in the region where the shear strain is large. Therefore, when estimating the maximum shear stress τ _max corresponding to the shear stress when the test material S breaks by shearing, it is possible to estimate it with a certain degree of accuracy even by using the shear stress curve obtained by the mechanical method as described above. Based on the maximum shear stress τ _max , the maximum stress ratio τ _max /σ _max can be calculated and used to evaluate the crack resistance of the material by comparing it with the maximum stress ratio threshold value, etc.

However, the contribution of the deformation and displacement of the components of the test device 1 is particularly significant in the region where the shear strain is small. For example, FIG. 3 illustrates a shear stress curve obtained based on the relationship between the movement amount of the pressing member 31 and the load F1 applied by the pressing member 31 as described above. Here, the horizontal axis is the stroke (movement amount) of the pressing member 31. In the curve of FIG. 3, as shown by the dashed line, a curve that is significantly convex downward is seen in the region where the shear strain is small. In a metal material, in the elastic region where the strain is small, the relationship between the strain and the load should be linearly approximated, and the downward convex curve of FIG. 3 cannot be said to accurately reflect the behavior of the metal material in the shear deformation. This is because the contribution of the deformation and displacement of the components of the test device 1 is superimposed on the movement amount of the pressing member 31 in addition to the deformation of the test material S, and the displacement amount is estimated to be larger than the actual deformation of the test material S. In this way, when non-essential contributions are superimposed on the shear stress curve in the low strain region, the shear yield stress _τs , which is a quantity estimated based on information in the low strain region, may not be accurately evaluated. Therefore, the next method to be used is a shear test using image analysis, which is easier to accurately evaluate the relationship between shear stress and shear strain in the low strain region than a shear test using mechanical measurement.

<Shear test using image analysis>
When image analysis is used, the measurement of the shear strain when a shear load is applied to the test material S is performed by image analysis of an image of the test material S, rather than the amount of movement of the components of the test apparatus 1. In this form of shear test, the test apparatus 1 shown in FIG. 1 is used to apply a load F1 by the pressing member 31, and shear stress is generated in the test material S. At this time, the magnitude of the shear stress is evaluated from the load F1 measured by the load cell attached to the pressing member 31, but the magnitude of the shear strain is evaluated based on the image of the test material S, rather than the amount of movement of the pressing member 31. Then, a shear stress curve is obtained as the relationship between the shear stress and the shear strain.

Specifically, a camera capable of photographing the surface of the test material S is provided on the front side of the test device 1 (the side facing the page), and the surface of the test material S is photographed continuously or intermittently before and during the shear test. The surface of the test material S may be photographed using a microscope as appropriate. Note that most of the surface of the test material S is sandwiched between the jigs 21 and 22 and cannot be seen from the outside, so the camera photographs the area in the gap 25 between the adjacent fixed and movable jigs 21 and 22.

As the test material S, a metal plate material with slits S1 as shown in FIG. 2A may be used as it is, but it is preferable to provide an irregular pattern on the surface of the test material S so that the shear deformation can be easily recognized in the image of the surface. Then, when the test material S undergoes shear deformation, the deformation or displacement of the pattern can be used as an index to easily and accurately estimate the amount of deformation. By scattering a powder material having a different color from the surface of the metal material and/or spraying paint, a pattern in which a large number of dot-like or island-like regions are distributed can be easily formed. By forming a pattern using materials of multiple different colors, it becomes even easier to recognize the deformation of the test material S. As shown in the image of the surface in FIG. 4A, a suitable example of a form in which a pattern is formed by spraying white paint and scattering graphite powder can be exemplified.

When quantitatively evaluating the shear deformation of the test material S based on the image of the test material S undergoing the shear test, the image before the test material S is changed by the application of the load F1 is compared with the image during the application of the load F1, or multiple images during the application of the load F1, and the amount of displacement of each part of the surface of the test material S is estimated using the surface pattern as an index. In this case, a (digital) image correlation method can be preferably used as a specific method of image analysis. Figures 4A and 4B explain the analysis of displacement using the image correlation method. Figure 4A is an image of the surface of the test material S in the initial state before the load is applied, and a dark pattern of graphite powder and a white pattern of white paint are mixed. Figure 4B shows an image of the test material S during the application of the load F1 in the vertical direction of the image. Here, the shape and position of the surface pattern have changed compared to the initial state of Figure 4A.

In the image correlation method, an image in an initial state is divided into minute regions, and a region having the same luminance distribution as the minute region is searched from the entire image during load application. Then, the amount of displacement is estimated based on the change in the coordinates of the corresponding minute region. In FIG. 4A, the regions having the centers of gravity at coordinates ( _x1 , _y1 ), ( _x2 , _y2 ), and ( _x3 , y3), respectively shown as rectangles 1, 2, and ₃ , are deformed into parallelograms 1', 2', and 3' in FIG. 4B, respectively, and the coordinates of the centers of gravity are displaced to ( _x'1 , _y'1 ), ( _x'2 , _y'2 ), and ( _x'3 , _y'3 ). In this way, the shear strain in the test material S can be estimated from the displacement of the coordinates in the image.

When evaluating the shear strain of the test material S based on image analysis, unlike the case where the mechanical measurement described above is used, the deformation amount of the test material S is estimated without contact. Therefore, in the test device 1 that applies the load F1 in contact with the test material S, even if deformation or displacement of the constituent members occurs due to the application of the load F1, the shear strain of the test material S can be estimated without being affected by such deformation or displacement. Therefore, the relationship between shear stress and shear strain can be evaluated with high accuracy from the low strain region.

Figures 5A and 5B show shear stress curves obtained by a shear test using the image correlation method. Figure 5A is an overall view, and Figure 5B is an enlarged view showing the region where the shear strain is small. The figure shows the shear stress curve for the "Cu-Mg alloy" used in the following examples. In the figure, the measurement results in the direction parallel to the rolling direction of the metal material (GW) are displayed in black, and the measurement results in the direction perpendicular to the rolling direction (BW) are displayed in gray. As shown in Figure 5A surrounded by a dashed line and clearly seen in the enlarged view of Figure 5B, in the region where the shear strain is small, approximately 0.004 or less, the shear stress and strain are almost proportional. The solid line shows an approximation line. This linear behavior is significantly different from the shear stress curve obtained by the shear test by mechanical measurement in Figure 3, where the curve was downwardly convex in the low strain region, and matches the ideal behavior in the elastic region. This is because the measured value of shear strain does not include the contribution of non-essential factors other than shear strain, such as deformation or shifting of the components of the test device 1.

Since the behavior of the linear elastic region is obtained, the 0.2% yield strength can be estimated with high accuracy as the shear yield stress τ _s . That is, as shown in FIG. 5B, the approximation line (shown by the solid line of each color) passing through the origin approximating the elastic region of the shear stress curve is translated to the point of shear strain 0.002 (shown by the dashed line of each color), and the value of the shear stress at the intersection with the shear stress curve is taken as the 0.2% yield strength, that is, the shear yield stress τ _s . Based on the shear yield stress τ _s , the yield stress ratio τ _s /σ _s can be calculated and used to evaluate the wrinkle resistance of the material by comparison with the yield stress ratio threshold value, etc.

By using the image correlation method, a highly accurate shear stress curve can be obtained in the low strain region, so that in addition to the shear yield stress τ _s , physical properties obtained based on the behavior in the low strain region can be estimated with high accuracy. For example, the slope of the straight line (solid line in FIG. 5B) that approximates the elastic region can be used as the rigidity modulus. Furthermore, after displaying the shear stress curve in double logarithmic scale (not shown), the region after switching to the plastic region can be linearly approximated, and the slope of the approximated straight line can be used as the work hardening exponent (n value).

From the viewpoint of obtaining a highly accurate shear stress curve, the shear strain can be evaluated by image analysis in the entire range from the low strain region to the high strain region. However, the image analysis and the mechanical measurement described above may be used in combination to estimate the shear strain and obtain the shear stress curve. As described above, in the region of large shear strain, the shear strain can be evaluated with a certain degree of accuracy even when mechanical measurement is used. Therefore, for example, the evaluation in the low strain region including the elastic region may be performed by image analysis, and the evaluation in the high strain region may be performed by mechanical measurement.

<In-plane shear test and bending workability>
As described above, by performing a shear test to obtain the maximum shear stress τ _max and the shear yield stress τ _s , and then comparing the maximum stress ratio τ _max /σ _max and the yield stress ratio τ _s /σ _s between different materials, the crack resistance and wrinkle resistance between materials can be quantitatively compared. In addition, by setting threshold values for the maximum stress ratio τ _max /σ _max and the yield stress ratio τ _s /σ _s and making these values equal to or greater than the threshold values, the metal material can be made to have high crack resistance and wrinkle resistance.

Here, as explained above, the maximum shear stress τ _max and shear yield stress τ _s obtained by performing an in-plane shear test on a metal material can be used as an index of bending workability, which is out-of-plane deformation. In many metal materials, the relationship between shear stress and shear strain is similar between in-plane shear deformation and out-of-plane shear deformation, and materials with large in-plane shear strain tend to have large out-of-plane shear strain as well. In other words, when the maximum stress ratio τ _max /σ _max and the yield stress ratio τ _s /σ _s obtained by the in-plane shear test are large, the crack resistance and wrinkle resistance in in-plane deformation are high, but at the same time, the crack resistance and wrinkle resistance in out-of-plane deformation such as bending deformation are also likely to be high. In addition, when anisotropy exists between the in-plane shear stress and the out-of-plane shear stress, the correlation between the maximum stress ratio τ _max /σ _max and the yield stress ratio τ _s /σ _s estimated by the in-plane shear test and the crack resistance and wrinkle resistance in the out-of-plane deformation may be low. In such a case, it is advisable to set the maximum stress ratio threshold and the yield stress ratio threshold to large values so that materials that exhibit high crack resistance and wrinkle resistance in the out-of-plane deformation can be distinguished even if they are affected by the low correlation.

The specific maximum stress ratio threshold and the yield stress ratio threshold can be set according to the main component of the alloy, the type of material, the application, etc. For example, in the case of copper or copper alloy used as a material for an electrical connection terminal, etc., if the maximum stress ratio threshold applied to the maximum stress ratio τ _max /σ _max obtained in the in-plane shear test is set to 0.60 as shown in the following examples, a material that is less likely to crack during bending can be selected. It is more preferable to set the maximum stress threshold to 0.65. In addition, if the yield stress ratio threshold applied to the yield stress ratio τ _s /σ _s obtained in the in-plane shear test is set to 0.48, a material that is less likely to wrinkle during bending can be selected. It is more preferable to set the yield stress ratio threshold to 0.51.

As explained above, by dividing the maximum shear stress τ _max and the shear yield stress τ _s by the tensile strength σ _max and the tensile yield stress σ _s , and evaluating the bending workability using the maximum stress ratio τ _max /σ _max and the yield stress ratio τ _s /σ _s as indicators, it is possible to take into account not only the small shear strain but also the high bending workability due to the large contribution ratio of plane strain. Here, the significance of evaluating the out-of-plane bending workability using the yield stress ratio τ _s /σ _s obtained by dividing the shear yield stress τ _s obtained by the in-plane shear test by the tensile yield stress σ _s can be explained in more detail based on the relationship between the yield curve and the strain. As shown in FIG. 6A, when a plate material having a plate surface on the xy plane is bent and deformed, if the amount of bending becomes large to a certain extent, a stress σ _zx in the out-of-plane direction is generated. At this time, as shown in FIG. 6B, a strain occurs in a direction perpendicular to the σ _xx -σ _zx yield surface (dε). The component of this strain in the σ _zx direction is the shear strain. In such a yield surface, the larger the inclination of the σ _zx side (the angle between the σ _zx axis and the yield surface; the same applies below when referred to as inclination), the larger the shear strain becomes, and the more likely shear bands are to be formed. Here, the yield stress τ _s obtained by the above shear test can be associated with the in-plane shear stress σ _xy , and the tensile yield stress σ _s obtained by the tensile test can be associated with the normal stress σ _xx , but if there is no anisotropy in the shear yield surface, then σ _zx =σ _xy . In this case, the slope of the σ _xx -σ _zx yield curve can be roughly associated with the yield stress ratio τ _s /σ _s , which is the ratio of the tensile yield stress σ _s to the in-plane shear yield stress τ _s . In other words, the smaller the yield stress ratio τ _s /σ _s , the larger the slope of the σ _xx -σ _zx yield curve, and the more likely shear deformation will progress. Therefore, the yield stress ratio τ _s /σ _s is calculated based on the shear yield stress τ _s evaluated by the in-plane shear test, and the yield stress ratio τ _s /σ _s is increased, which can be adopted as a guideline for reducing the strain generated in the out-of-plane direction when the plate material is bent out-of-plane.

In the above, the bending workability of the metal material was evaluated based on the results of the in-plane shear test, but it can also be evaluated based on the results of the out-of-plane shear test. In this case, for example, the test material S is prepared as a rectangular plate material, and the test material S is sandwiched from above and below in the thickness direction by each of the jigs 21, 21, and 22 of the test device 1 in FIG. 1, and a load F1 is applied perpendicularly to the plate surface by the pressing member 31. Then, a shear stress curve is obtained in the same manner as above, and the bending workability is evaluated based on the maximum shear stress τ _max and the shear yield stress τ _s . When estimating the strain by image analysis, a pattern is formed on the end surface in the thickness direction of the test material S, and the end surface is photographed by a camera. As in the case of the in-plane shear test, it can be evaluated that the larger the maximum stress ratio τ _max /σ _max , the higher the crack resistance during bending, and the larger the yield stress ratio τ _s /σ _s , the higher the wrinkle resistance during bending.

<Metal member manufacturing method>
Finally, a method for manufacturing a metal component according to an embodiment of the present disclosure will be described. Here, a plate-shaped metal material is used as a raw material, and a metal component having a predetermined shape is manufactured through bending. In this case, when selecting a metal material to be used as the raw material, the material evaluation method according to the embodiment of the present disclosure described above is applied.

That is, the metal material to be processed is evaluated by the material evaluation method described above. For example, if a candidate metal material has a maximum stress ratio τ _max /σ _max equal to or greater than a predetermined maximum stress ratio threshold value, and is therefore evaluated to have sufficient crack resistance, the metal material can be used as a processed raw material that is less likely to crack. If a candidate metal material has a yield stress ratio τ _s /σ _s equal to or greater than a predetermined yield stress ratio threshold value, and is therefore evaluated to have sufficient wrinkle resistance, the metal material can be used as a processed raw material that is less likely to wrinkle. Alternatively, a plurality of candidates can be compared, and a metal material that exhibits a large maximum stress ratio τ _max /σ _max and a large yield stress ratio τ _s /σ _s can be selected as a raw material for processing.

The type of metal member to be manufactured is not particularly limited, but an electrical connection terminal is a suitable example. Electrical connection terminals are manufactured by punching out a metal plate, typically copper or a copper alloy, into a predetermined shape and then bending it. This often involves bending at a steep angle, such as 180°. If damage such as cracks or wrinkles occurs in the plate during bending, the electrical connection terminal manufactured may not be able to ensure the specified electrical characteristics and mechanical strength. By quantitatively evaluating the bending workability of the material using the above material evaluation method and selecting a material with sufficiently high crack resistance and wrinkle resistance as the raw material, electrical connection terminals with the specified electrical characteristics and mechanical strength can be manufactured with high productivity.

Examples are shown below. Note that the present invention is not limited to these examples. Here, in-plane shear tests were performed on various copper alloy materials to obtain shear stress curves, and representative values were compared with bending test results. Each evaluation below was performed at room temperature (25°C) in the atmosphere.

[Test method]
(Sample Preparation)
As samples, the following copper alloy sheets were prepared.
Cu-Mg alloy Corson alloy 1, 2: The contents of the component elements are different from each other.
・Cu-Ni-Sn alloy ・7-3 brass ・High strength brass

(Obtaining shear stress curve)
Using a test apparatus having the structure shown in FIG. 1, an in-plane shear test using the image correlation method described above was performed to obtain a shear stress curve. A material testing machine (Shimadzu Corporation "Autograph AG-10") was used for the applied load. The displacement rate was 2 mm/min. In estimating the strain, the image correlation method was applied to an image of the plate surface of the test material taken through a microscope. For the analysis using the image correlation method, GOM-Correlate was used as software. From the obtained shear stress curve, the shear stress at break was read and taken as the maximum shear stress τ _max , and the 0.2% proof stress was read and taken as the shear yield stress τ _s .

The test material used had the shape shown in Fig. 2A. The dimensions of each part were as follows:
・Outline of test material: 30 mm x 30 mm square ・Length of deformed part a = 5.0 mm
・Width of the deformation part b = 0.4 mm
Slit width b' = 0.5 mm
・Thickness t = 0.15 mm
For the shear test, both GW tests were performed on the test pieces with slits parallel to the roll marks formed during rolling, and BW tests were performed on the test pieces with slits perpendicular to the roll marks. A pattern was formed on the surface of the test pieces by spraying white paint and scattering graphite powder.

(Tensile test)
A tensile test was performed on each sample in accordance with JIS Z 2241 to measure the tensile strength σ _max and the tensile yield stress σ _s . The measurements were performed by processing a plate-shaped sample with a thickness of 0.15 mm into a dumbbell shape according to JIS 13B, and applying a tensile load in each of the GW and BW directions. A material testing machine (Shimadzu Corporation's "Autograph AG-10") was used for the test, with a test speed of 2 mm/min and a gauge length of 25 mm.

(Bending evaluation test)
Each sample was subjected to bending processing to evaluate bending workability. Specifically, a sample with a thickness of 0.15 mm and a width of 1.5 mm was bent in two directions, GW and BW. At this time, the sample was bent 180° so that the radius of curvature (inner R) on the inside of the bend was 0.3 mm. Thereafter, the part on the outside of the bend was observed with an optical microscope to observe the presence or absence of cracks and wrinkles. At this time, as in the standard described in Non-Patent Document 1, "cracks" were judged as "a state in which the bottom of the crack cannot be observed from directly above and the crack is cracked along the shear band," and "wrinkles" were judged as "a state in which a step-like depression or streak that appeared due to bending can be observed." Regarding the formation of "wrinkles," when the width of the wrinkles in the bending direction was less than 10 μm, it was evaluated as "small," when it was 10 μm or more and less than 50 μm, it was evaluated as "medium," and when it was 50 μm or more, it was evaluated as "large."

[Test results]
Figure 5A shows the shear stress curve obtained for the "Cu-Mg alloy". The black area indicates the GW measurement result, and the gray area indicates the BW measurement result. As explained above, the shear stress curve shows behavior that can be approximated to a straight line from the very low strain region enclosed by the dashed line, and it can be said that the behavior in the elastic region can be accurately evaluated. In this way, by using the image correlation method to estimate the strain, the relationship between shear stress and strain can be accurately evaluated.

Table 1 below summarizes the measurements obtained from the shear test and tensile test, as well as the bending evaluation results.

According to Table 1, it is generally seen that the maximum stress ratio τ _max /σ _max tends to be larger when no cracks occur compared to when cracks occur in the bending evaluation test. And, if the maximum stress ratio τ _max /σ _max is 0.60 or more, no cracks occur. From this, it is shown that there is a correlation between the maximum shear stress τ _s and the occurrence of cracks, and by making the maximum shear stress ratio τ _max /σ _max sufficiently large, the occurrence of cracks can be avoided. By setting a threshold value of 0.60 for the maximum stress ratio τ _max /σ _max and selecting materials having a maximum stress ratio τ _max /σ _max equal to or greater than the threshold value, the occurrence of cracks can be avoided during bending. The same value can be applied as the threshold value regardless of the test direction (GW or BW).

Furthermore, when focusing on the occurrence of wrinkles, if the yield stress ratio τ _s /σ _s is 0.48 or more, serious wrinkles evaluated as "large" do not occur. This shows that there is a correlation between the shear yield stress τ _s and the occurrence of wrinkles, and that the occurrence of serious wrinkles can be avoided by making the yield stress ratio τ _s /σ _s sufficiently large. By setting a threshold value of 0.48 for the yield stress ratio τ _s /σ _s and selecting materials having a yield stress ratio τ _s /σ _s equal to or greater than the threshold value, the occurrence of serious wrinkles can be avoided during bending. Furthermore, if the threshold value is set to 0.51, the occurrence of even moderate wrinkles evaluated as "medium" can be avoided. Note that there are some data points where the correlation between the maximum stress ratio τ _max /σ _max and the presence or absence of cracks, and between the yield stress ratio τ _s /σ _s and the degree of wrinkles is low, but this is thought to be due to the presence of anisotropy between the in-plane stress and the out-of-plane stress.

The above describes the embodiments of the present disclosure in detail, but the present invention is not limited to the above embodiments, and various modifications are possible without departing from the gist of the present invention.

Reference Signs List 1 Testing apparatus 10 Support frame 20 Holder 21 Fixed jig 22 Movable jig 24 Screw 25 Gap 30 Pressing tool 31 Pressing member 90 Conventional jig for bending workability testing 91 Upper die 92 Convex portion 95 Lower die 96 Concave portion 97 Joint portion a Length of deformed portion b Width of deformed portion b' Width of slit F1, F2 Load R1 Central region R2 End region R3 Deformed portion S, S' Test material S1 Slit S2 Tip portion S3 of slit Side S'1 on which slit is provided Bending portion t Plate thickness

Claims (13)

performing a shear test on a test material configured as a metal plate to obtain a shear stress curve recording shear stress as a function of shear strain;
The 0.2% proof stress obtained from the shear stress curve is defined as the shear yield stress τ _s ,
The tensile yield stress obtained as 0.2% proof stress by the tensile test of the test material is defined as σ _s ,
A material evaluation method, in which the test material is judged to be less prone to wrinkles during bending as the yield stress ratio calculated as τ _s /σ _s increases. The material evaluation method according to claim 1 , wherein the test material is determined to have sufficient wrinkle resistance when the yield stress ratio τ _s /σ _s is equal to or greater than a predetermined yield stress ratio threshold value. The material evaluation method according to claim 2, wherein the test material is copper or a copper alloy, and the yield stress ratio threshold is set to 0.48 when performing an in-plane shear test on the test material. In the shear stress curve, the shear stress at which the test material breaks is defined as a maximum shear stress τ _max ,
The tensile strength obtained by the tensile test of the test material is defined as σ _max ,
4. The material evaluation method according to claim 1 , wherein the test material is determined to be less susceptible to cracking during bending as the maximum stress ratio calculated as τ _max /σ _max is larger. 5. The material evaluation method according to claim 4, wherein the test material is determined to have sufficient crack resistance when the maximum stress ratio τ _max /σ _max is equal to or greater than a predetermined maximum stress ratio threshold value. The material evaluation method according to claim 5, wherein the test material is copper or a copper alloy, and the maximum stress ratio threshold is set to 0.60 when performing an in-plane shear test on the test material. The material evaluation method according to any one of claims 1 to 6, in which the shear strain is evaluated by an image correlation method based on an image of the test material when obtaining the shear stress curve. As the test material, a rectangular plate material having two sets of slits extending from a pair of opposing sides of the plate material was used.
Along the pair of sides, the regions outside the two sets of slits are defined as end regions, and the region between the two sets of slits is defined as an inner region,
A material evaluation method according to any one of claims 1 to 7, wherein in the shear test, shear forces are applied in mutually opposite directions within the plane of the test material at the two end regions and the internal region, and the shear stress curve is obtained for shear deformation within the plane of the test material. In the test material, the distance between the slits constituting each set is a, and the width of each of the slits at its tip is b;
The plate thickness of the test material is t, the Young's modulus of the test material is E, and the 0.2% yield strength in tension is _σy .
2t≦b≦(E/ _σy ) ^0.5 ·t, and 3mm≦a≦(E/ _σy )·( ^t2 /b)
The material evaluation method according to claim 8 , A metal material selected as a raw material through evaluation by the material evaluation method according to any one of claims 1 to 9 is used,
A method for manufacturing a metal member, comprising the steps of: manufacturing a metal member through bending the metal material. The method for manufacturing a metal component according to claim 10, in which a metal material determined to have sufficient wrinkle resistance in the material evaluation method according to claim 2 or claim 3 is selected as the raw material. The method for manufacturing a metal component according to claim 10 or 11, in which a metal material determined to have sufficient crack resistance in the material evaluation method according to claim 5 or 6 is selected as the raw material. The method for manufacturing a metal member according to any one of claims 10 to 12, wherein the metal member is an electrical connection terminal.

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