JP5889698B2 - Cu-Zn alloy plate excellent in stress relaxation resistance and method for producing the same - Google Patents

Description

The present invention relates to a Cu—Zn alloy plate excellent in stress relaxation resistance and suitable for a small female terminal having, for example, a spring leaf-shaped contact, and a method for producing the same .

A Cu—Zn alloy (brass) plate used for the fitting type terminal is often used with an average crystal grain size of around 5 μm in consideration of strength and bending workability. However, when the operating temperature increases, the contact pressure of the brass terminal decreases due to stress relaxation, and electrical reliability cannot be maintained. For this reason, the use environment of a brass terminal has been normally limited to 120 ° C. or less.
On the other hand, with the miniaturization of electronic components, the terminals constituting the components are also miniaturized. Along with this movement, the terminal material is required to be thin and high in strength. Further, the shape of the contact portion of the fitting type terminal is increased from the faston type which has been frequently used, and the leaf spring type having a movable spring piece is increased, and the stress relaxation resistance is further required. However, Cu-Zn alloy plates have a problem of low stress relaxation resistance, and have not been applied to small terminal shapes.

Patent Document 1 proposes a brass for terminals which is excellent in stress corrosion resistance and stress relaxation resistance. However, since this brass is added with Mg to improve the stress relaxation rate, Mg is oxidized and melted into the ingot at the time of melting, so that the copper alloy plate has wrinkles, and bending cracks occur during terminal molding. Cause it to occur. In addition, the measurement conditions for stress relaxation resistance do not meet current strict requirements.
Patent Document 2 proposes a lead frame and a Cu—Zn alloy for terminals that are excellent in strength, electrical conductivity, bending workability, stress relaxation resistance, and stress corrosion cracking resistance. However, a relatively large amount of Sn, Fe, P is added to this Cu—Zn alloy in order to obtain the desired characteristics, and it is considered that the conductivity is low.

  Patent Document 3 proposes a brass for a terminal that has high strength and excellent bending workability, and Patent Document 4 discloses a terminal that has excellent strength, electrical conductivity, bending workability, and stress relaxation resistance. Cu-Zn alloys for use have been proposed. However, in Patent Documents 3 and 4, since the final stage of hot rolling is performed at a low temperature of 600 ° C. or less, the structure of the Cu—Zn alloy after hot rolling tends to be mixed grains. Thereafter, even if cold rolling and heat treatment are repeated, this effect remains, and the structure of the final product tends to be mixed grains. Therefore, the Cu-Zn alloy described in Patent Documents 3 and 4 has stable bending workability and stress resistance. It is considered difficult to obtain relaxation characteristics.

Japanese Patent Application Laid-Open No. 06-041659 JP 2000-178670 A JP 2006-188722 A JP 2009-185341 A

  The present invention was made in view of the above-mentioned problems of the conventional Cu-Zn alloy (brass). By optimizing the crystal structure, the present invention has high strength and excellent bending workability, and at the same time excellent stress relaxation characteristics. It aims at obtaining a Cu-Zn alloy.

  Generally, the stress relaxation resistance of a Cu—Zn alloy (brass) can be improved as the crystal grain size is larger. On the other hand, if the crystal grain size becomes too large, the bending workability is lowered. In contrast, the present inventors investigated the relationship between the stress relaxation resistance and bending workability of Cu-Zn alloy and the crystal structure, and appropriately set the average crystal grain size, standard deviation of crystal grain size, and aspect ratio. It has been found that by controlling, the stress relaxation resistance can be improved, and at the same time, bending workability and strength characteristics can be secured.

That is, the Cu-Zn alloy plate according to the present invention contains Zn: 15 to 37% by mass, the balance is made of Cu and inevitable impurities, and is parallel to the rolling direction in a cross section perpendicular to the plate surface and parallel to the rolling direction. The average crystal grain size in the direction is 7 to 15 μm, the standard deviations of the crystal grain sizes in the direction parallel to and perpendicular to the rolling direction are both 1.5 μm or less, and the average crystal grain size in the direction parallel to the rolling direction is The aspect ratio a / b is 1.6 ≦ a / b ≦ 2.6, where b is the average crystal grain size in the direction perpendicular to the rolling direction. In the present invention, the term “plate” is used to include a strip.
The Cu—Zn alloy sheet is a cold-rolled material obtained by finish cold rolling after recrystallization annealing, or a tempered material obtained by further low-temperature annealing.

  According to the present invention, in a Cu-Zn alloy (brass) having a composition within the JIS standard range, excellent bending workability and high strength can be ensured simultaneously with high stress relaxation resistance. As a result, the Cu—Zn alloy according to the present invention is suitable for manufacturing mainly small-sized fitting-type terminals that require the above characteristics, in addition to female terminals having spring-leaf shaped contacts.

The stress relaxation phenomenon is a phenomenon in which defects (dislocations and vacancies) inside the material introduced by processing move plastically in the direction of the stress load even though the stress load is within the elastic range. . This behavior is promoted at higher temperatures. In the present invention, on the premise of use in a high temperature environment, the objective was to obtain a stress relaxation rate of 55% or less in a stress relaxation rate measurement test described later.
The terminal is pressed so as to be continuous with the longitudinal direction of the Cu—Zn alloy plate (strip). For this reason, for example, a spring (leaf spring) of a female terminal having a spring leaf type contact has a longitudinal direction of T.P. D. Direction (direction perpendicular to the rolling direction). Therefore, the mechanical characteristics required for the spring of the female terminal are mainly T.P. D. The stress relaxation resistance is also a characteristic of T.W. D. It is required to be excellent in direction.

The bending workability of a material is generally shown by the relationship between the plate thickness t and the minimum bending radius R at which no cracking occurs during bending, and the smaller the R / t, the better the bending workability. When a Cu—Zn alloy plate is actually processed into a female terminal, the most severe bending is a 90 ° bending that forms a box shape. W. Bending (bending axis is perpendicular to the rolling direction) is important. As a bending workability of a material necessary to withstand this box-shaped bending, G.G. W. The aim was to have a bending R / t of 0.5 or less.
In view of the present situation that the strength of the Cu-Zn alloy is required to be thin and high strength, T.W. D. Direction (direction perpendicular to the rolling direction) and L. D. Direction (parallel to the rolling direction direction) together, a tensile strength of 500 N / mm ² or more, a 0.2% proof stress was targeted 450 N / mm ² or more.

In the present invention, the crystal structure and alloy composition of the Cu-Sn alloy plate are defined so that the above mechanical characteristics can be obtained. Hereinafter, the crystal structure and alloy composition of the Cu—Sn alloy plate according to the present invention and the production method will be specifically described.
[Crystal structure]
(Average grain size in the direction parallel to the rolling direction; 7 to 15 μm)
In the cross section perpendicular to the plate surface and parallel to the rolling direction, if the average crystal grain size in the direction parallel to the rolling direction is less than 7 μm, the stress relaxation resistance decreases. On the other hand, if the average crystal grain size exceeds 15 μm, excellent bending workability cannot be secured. In the cross section, when the average crystal grain size is 7 to 15 μm, both excellent stress relaxation resistance and bending workability can be achieved. Therefore, the average crystal grain size is 7 to 15 μm, preferably 8 to 13 μm. In the present invention, the twin interface is regarded as a grain boundary.

(Standard deviation of crystal grain size: 1.5 μm or less)
If the crystal grain size of the Cu-Sn alloy plate is non-uniform and the standard deviation is large, the strain introduced into the material at the time of bending becomes non-uniform, the surface of the bending tends to be rough and cracked, and the bending workability decreases. . Further, even when a stress within the range of elastic deformation is applied, the strain distribution inside the material becomes non-uniform and the stress relaxation resistance is reduced. For this reason, it is desirable that the standard deviation of the crystal grain size is as small as possible. In the present invention, in the cross section perpendicular to the plate surface and parallel to the rolling direction, the standard deviation of the crystal grain size in both the parallel direction and the perpendicular direction to the rolling direction is 1 .5 μm or less. Preferably both are 1.4 μm or less.

(Aspect ratio a / b; 1.6 to 2.6)
The Cu—Zn alloy plate according to the present invention is a cold rolled finished material obtained by cold rolling after finishing recrystallization annealing or a tempered material obtained by further low-temperature annealing the cold rolled finished material. The recrystallized grains after the recrystallization annealing of the Cu—Zn alloy plate are entirely equiaxed crystals. When this is cold-rolled, the recrystallized grains expand in the rolling direction and shrink in the thickness direction, and the aspect ratio a / B (in a cross section perpendicular to the plate surface and parallel to the rolling direction, the average crystal grain size in the direction parallel to the rolling direction is a and the average crystal grain size in the direction perpendicular to the rolling direction is b) is greater than 1. This aspect ratio does not change with low temperature annealing.
The aspect ratio a / b increases as the cold rolling processing rate increases, and the strength of the Cu—Zn alloy sheet is improved accordingly. Therefore, the aspect ratio a / b can also be said to be a parameter linked to the cold rolling processing rate after recrystallization annealing.
If the aspect ratio a / b is less than 1.6, the cold rolling ratio is low and the strength of the Cu—Zn alloy sheet is insufficient. On the other hand, if the aspect ratio a / b exceeds 2.6, bending workability and stress relaxation resistance are deteriorated. . Therefore, the aspect ratio a / b is set to 1.6 to 2.6. The value of the aspect ratio a / b is substantially equivalent to a cold rolling ratio of more than 30% to 60%. The value of aspect ratio a / b is preferably 2.0 to 2.5.

[Alloy composition]
(Zn content; 15 to 37% by mass)
When the Zn content exceeds 37% by mass, the β layer comes to exist, so that the hardness increases rapidly, the elongation decreases, and the conductivity decreases greatly. In addition, the stress corrosion cracking resistance is reduced, and the Zn-free corrosion is likely to occur. On the other hand, when the Zn content is less than 15% by mass, the strength is insufficient, and bending workability and stress relaxation characteristics are deteriorated. Therefore, Zn content shall be 15-37 mass%. The amount is desirably 25 to 35% by mass, and more desirably 28 to 32% by mass.

In the Cu—Zn alloy according to the present invention, elements other than Zn such as S, Ni, Sn, Fe, P, Al, and Mg are included as inevitable impurities as described below, or added as necessary.
(S; 40 mass ppm or less)
When the S concentration increases, the number of S and Zn compounds that become the starting point of cracking during bending increases, and particularly when the content exceeds 40 mass ppm, bending workability deteriorates rapidly. Therefore, the S content is restricted to 40 ppm or less. Desirably, it is 30 ppm or less.

(Ni; 0.1 mass% or less)
Ni has a function of improving the stress relaxation resistance and strength by dissolving in a Cu-Zn alloy, and is added as necessary. However, Ni lowers the electrical conductivity, delays recovery and recrystallization, suppresses crystal grain growth during annealing, and makes it difficult to obtain the above-mentioned recrystallized structure after recrystallization annealing. Therefore, the content is 0.1% by mass or less. When added, the content is in the range of 0.01 to 0.1% by mass, preferably in the range of 0.01 to 0.05%.
(Sn; 0.1 mass% or less)
Sn is dissolved in Cu-Zn alloy and has a larger atomic radius than Cu. Therefore, heat resistance is improved by size effect, stress relaxation resistance is improved, and work hardening is achieved by rolling. Since it has the effect | action which improves intensity | strength, it is added as needed. However, Sn decreases the conductivity, so the content is 0.1% by mass or less. When added, the content is in the range of 0.01 to 0.1% by mass, desirably in the range of 0.01 to 0.05% by mass.

(Fe; 0.05 mass% or less)
Fe dissolves or precipitates in the Cu—Zn alloy, has the effect of increasing the softening temperature, and is added as necessary when heat resistance is required. However, Fe lowers the electrical conductivity, delays recovery and recrystallization, suppresses crystal grain growth during annealing, and makes it difficult to obtain the above-mentioned recrystallized structure after recrystallization annealing. Therefore, the Fe content is 0.05% by mass or less. When adding, it is set as the range of 0.001-0.05 mass%, It is desirably set as the range of 0.001-0.02 mass%.

(P; 0.01% by mass or less)
P is dissolved in the Cu—Zn alloy or precipitated as Ni—P, Fe—P, and has an effect of improving heat resistance, and is added as necessary. However, P lowers the electrical conductivity and lowers the stress relaxation characteristics, so the content is made 0.01% by mass or less. When added, the content is in the range of 0.001 to 0.01% by mass, preferably in the range of 0.001 to 0.005%.
(Al; 0.1 mass% or less)
Al dissolves in the Cu-Zn alloy and has the effect of improving the strength by work hardening. It is added as necessary, but its content is 0.1% by mass or less in order to reduce the electrical conductivity. When added, the content is in the range of 0.01 to 0.1% by mass, preferably in the range of 0.01 to 0.02%.

(Mg; 0.01% by mass or less)
Mg is an element having a large effect of improving the stress relaxation resistance. Moreover, the strength of the Cu—Zn alloy plate is improved by dissolving in the Cu matrix. However, Mg is oxidized at the time of dissolution, and the oxidized Mg is easily caught in the ingot, thereby causing problems such as plate wrinkling and cracking during bending. For this reason, when adding Mg, it is 0.01 mass% or less.

[Method for producing Cu-Zn alloy sheet]
The Cu-Zn alloy plate according to the present invention is obtained by subjecting an ingot having a predetermined alloy composition to a roughing condition after performing homogenization treatment, hot rolling, rapid cooling after hot rolling, and both face chamfering under normal conditions. It can manufacture by performing cold rolling, recrystallization annealing, and finish cold rolling, and also performing low temperature annealing as needed. Hereinafter, rough cold rolling, recrystallization annealing, finish cold rolling, and low temperature annealing will be described more specifically.

(Rough cold rolling)
Rough cold rolling needs to be performed at a high processing rate in order to obtain equiaxed recrystallized grains with a small standard deviation in the subsequent recrystallization annealing. Specifically, if the processing rate is 80% or more, the dislocations can be distributed at high density and evenly within the material regardless of the crystal grain size and strain state of the material before the rough cold rolling, It is possible to prevent only some of the recrystallized grains from becoming coarse during recrystallization annealing, and to obtain equiaxed recrystallized grains with a small standard deviation.

(Recrystallization annealing)
In the recrystallization annealing, since the recrystallization of the material is surely completed and the crystal grain size of the recrystallization annealing material is slightly larger as a whole (the average crystal grain size after finish cold rolling is 7 to 15 μm), The recrystallization annealing temperature (450 to 550 ° C.) is higher than that. Specifically, when continuous annealing is assumed, the ultimate temperature is 570 to 700 ° C., desirably 590 to 650 ° C., and more desirably 600 to 625 ° C. The holding time may be selected within a range of about 10 to 60 seconds.
If recrystallization is incomplete in recrystallization annealing, or if only some of the recrystallized grains are coarsened by secondary recrystallization, the crystal structure of the recrystallized annealing material is non-uniform and the aspect ratio of the grains is large, or / And the standard deviation of the crystal grain size increases. The non-uniform crystal structure is inherited by the crystal structure after finish cold rolling, and as a result, a product (Cu-Zn alloy plate according to the present invention) having a crystal structure with a predetermined aspect ratio and standard deviation is obtained. I can't. Therefore, the crystal structure of the recrystallized annealing material is, for example, an equiaxed crystal having an aspect ratio of 0.9 to 1.2, a standard deviation of crystal grain size of 1.5 μm or less, and a uniform structure of 1.2 μm or less. It is desirable to do. This crystal structure can be achieved under the rough cold rolling processing rate and recrystallization annealing conditions.

(Finish cold rolling)
As the processing rate of finish cold rolling increases, the strength of the Cu—Zn alloy plate improves, and conversely, the bending workability decreases. Moreover, if the processing rate is large, the movable dislocation density in the material increases, which leads to an increase in the stress relaxation rate. Therefore, the processing rate of finish cold rolling is selected within the range in which the above-described target strength, bending workability, and stress relaxation resistance can be obtained, and its numerical value is preferably more than 30% to 60%, which is desirable. Is 35-55%.
As the processing rate of finish cold rolling is larger within the above range, the average crystal grain size and aspect ratio (a / b) in the rolling parallel direction in the cross section perpendicular to the sheet thickness direction and parallel to the rolling direction increase. Note that, in the region where the processing rate of finish cold rolling is large, the standard deviation of the crystal grain size tends to be slightly larger than that of the recrystallized annealing material.

(Low temperature annealing)
By performing low temperature annealing after finish cold rolling, the dislocations introduced by finish cold rolling can be rearranged to improve the stress relaxation resistance. However, if the temperature of the low-temperature annealing is too low, dislocation rearrangement does not occur, strain abnormality occurs, and the stress relaxation resistance does not improve. On the other hand, if the annealing temperature is too high, the transition density decreases and softens. In order to improve the stress relaxation characteristics while maintaining the strength, when continuous annealing is assumed, 300 to 400 ° C. × 10 to 60 seconds is appropriate in a glass stone furnace. In the case of batch annealing, it is appropriate that the temperature is 150 to 300 ° C. × 0.5 to 2 hours.

A Cu—Zn alloy having a composition shown in Table 1 was melted to prepare an ingot having a thickness of 45 mm. After soaking at 850 ° C. for 3 hours, hot rolling was performed to obtain a thickness of 15 mm. The hot rolling was finished at a temperature exceeding 600 ° C. and immediately quenched. However, no. When No. 22 was rolled to a thickness of about 16 mm, it was heated to 850 ° C. for 30 minutes and hot-rolled to a thickness of 3.25 mm. The end temperature exceeded 600 ° C., and was quenched immediately after the end of hot rolling.
The surface of this hot-rolled material was chamfered 1 mm on each side to remove the oxide scale and scratches on the surface, and then subjected to rough cold rolling to a thickness of 0.31 to 0.83 mm.
Subsequently, no. Nos. 1 to 20 and 22 are crystallization annealing at 570 to 650 ° C. × 20 seconds, No. 21 was subjected to recrystallization annealing at 500 ° C. for 20 seconds, followed by finish cold rolling at various processing rates to obtain a Cu—Zn alloy plate having a thickness of 0.25 mm. No. No. 4 was further subjected to low-temperature annealing at 340 ° C. for 20 seconds. Table 1 shows the processing rate of finish cold rolling.

Using the obtained Cu-Zn alloy plate as a test material, observe the crystal structure as follows, mechanical properties (tensile properties, spring limit values), Vickers hardness, bending workability, stress relaxation properties, and electrical conductivity Was measured. The results are shown in Table 2.
(Crystal structure)
Observe a cross-section perpendicular to the plate surface and parallel to the rolling direction, and obtain an average crystal grain size a parallel to the rolling direction and an average crystal grain size b perpendicular to the rolling direction by a cutting method. a / b was calculated. Further, the standard deviation (σa) of the crystal grain size parallel to the rolling direction is obtained from the cutting length of each crystal grain completely cut by the line parallel to the rolling direction, and the line segment perpendicular to the rolling direction is obtained. The standard deviation (σb) of the crystal grain size in the direction perpendicular to the rolling direction was determined from the cutting length of each crystal grain completely cut by the above. In measuring the average crystal grain size a, b and the standard deviation (σa, σb) of the crystal grain size, the length of the line segment was constant in each test material. The number of crystal grains completely cut by the line segment was 10-30. The twin interface was regarded as a grain boundary.

(Tensile properties)
JIS No. 5 tensile test specimens were collected from each specimen so that the longitudinal direction was the rolling direction (LD) and the vertical direction (TD), and a tensile test was performed in accordance with JIS-Z2241. The tensile strength and 0.2% proof stress were measured.
(Spring limit value)
A test piece having a width of 10 mm and a length of 200 mm was taken from each specimen so that the longitudinal direction was the rolling direction (LD) and the vertical direction (TD), and the JIS-H3130 repeated deflection test was performed. Measured according to
(Vickers hardness)
Based on JIS-Z2244, the test force was set to 0.49N and the Vickers hardness was measured.

(Bending workability)
From each of the test materials, L.P. 10 mm wide × 30 mm long. D. A bending test piece (longitudinal direction parallel to the rolling direction) was collected and G.B. W. Bending (bending process in which the bending axis is perpendicular to the rolling direction) was performed. The surface of the bent portion is visually observed with a 100 × optical microscope to obtain a minimum bending radius R at which no crack is generated, and a value obtained by dividing the minimum bending radius R by a plate thickness t (t = 0.25 mm) R / t Was used as an index of bending workability.

(Stress relaxation characteristics)
From each sample material, a strip-shaped T.P. D. A specimen (length direction is perpendicular to the rolling direction) was taken, and the stress relaxation rate was measured by a cantilever method. One end of the test piece is fixed to a rigid test stand, the distance between the ratings from the fixed end is calculated so that surface stress equivalent to 80% of the proof stress is applied to the fixed end, and a deflection amount d of 10 mm is given to that portion. It was. The test piece in this state is taken out after being held in an oven at 180 ° C. for 30 hours, and the permanent strain δ when the deflection amount d is removed is measured, and the stress relaxation rate SRR is calculated by SRR = (δ / d) × 100. did. Note that the holding at 180 ° C. × 30 hr corresponds to the holding at about 150 ° C. × 1000 hr when calculated with the Larson-Miller parameter.
(conductivity)
The conductivity was measured by a four-terminal method using a double bridge in accordance with a nonferrous metal material conductivity measurement method defined in JIS-H0505.

As shown in Table 2, No. 1 satisfying the composition and crystal structure defined in the present invention. 1-10 are L. D. Direction and T. D. Both direction, a tensile strength of 500 N / mm ² or more, 0.2% proof stress has a 450 N / mm ² or more high strength, R / t is excellent in bending workability in 0.5 or less, the stress relaxation ratio Less than 55%, excellent stress relaxation resistance and higher T.I. D. Has directional spring limit and relatively high conductivity.
On the other hand, no. 11 to 22 are inferior in any of strength, bending workability, stress relaxation resistance, and electrical conductivity.

Looking individually, no. No. 11 has a large average crystal grain size and is inferior in bending workability.
No. No. 12 has a small aspect ratio a / b and a low strength.
No. No. 13 has a large aspect ratio a / b, inferior bending workability and stress relaxation resistance, and a high finish cold work rate, so that the conductivity is also lowered.
No. No. 14 has low Zn content and low strength. Also, bending workability and stress relaxation resistance are inferior.
No. No. 15, since the Ni content is large, the growth of recrystallized grains is suppressed, the average crystal grain size a in the direction parallel to the rolling direction is small, the aspect ratio a / b is small, and the standard deviation σa of the crystal grain size is large, The stress relaxation resistance was inferior and the conductivity was also lowered.
No. Since No. 16 had much Sn content, electrical conductivity fell.
No. No. 17, since the Fe content is large, the growth of recrystallized grains is suppressed, the average crystal grain size a in the direction parallel to the rolling direction is small, the aspect ratio a / b is small, and the standard deviation σa of the crystal grain size is large, Bending workability was lowered, the stress relaxation resistance was inferior, and the conductivity was also lowered.
No. No. 18 has a high P content, resulting in a decrease in electrical conductivity and poor stress relaxation characteristics.
No. No. 19 had a low Al conductivity because of its high Al content.
No. No. 20 is inferior in bending workability because of its large S content.
No. No. 21 is obtained by performing recrystallization annealing under the conventional conditions, the average crystal grain size a in the direction parallel to the rolling direction is small, and the stress relaxation resistance is inferior.
No. No. 22 was obtained by rough cold rolling at 60%, the cold working rate was low, and the density of dislocations accumulated in the material was insufficient. Workability is inferior.

Claims (6)

Zn: 15 to 37% by mass, the balance is made of Cu and inevitable impurities, S content of the inevitable impurities is 40 ppm by mass or less, and in the cross section perpendicular to the plate surface and parallel to the rolling direction. The average crystal grain size in the parallel direction is 7 to 15 μm, the standard deviations of the crystal grain sizes in the parallel direction and the vertical direction in the rolling direction are both 1.5 μm or less. Cu, an aspect ratio a / b where the average crystal grain size in the direction perpendicular to the rolling direction is b is 1.6 ≦ a / b ≦ 2.6. Zn alloy plate. Ni content is 0.1 mass% or less, Sn content is 0.1 mass% or less, Fe content is 0.05 mass% or less, P content is 0.01 mass% or less, and Al content is 0.00. The Cu-Zn alloy plate having excellent stress relaxation resistance according to claim 1, wherein the Cu-Zn alloy sheet is limited to 1 mass% or less and the Mg content is limited to 0.01 mass% or less. A female terminal made of the Cu-Zn alloy plate according to claim 1 and having a spring leaf-shaped contact. Zn: 15 to 37% by mass, with the balance being Cu and unavoidable impurities, and ingot of Cu-Zn alloy with an S content of 40 mass ppm or less among the unavoidable impurities, homogenization treatment, hot rolling In addition, rapid cooling after hot rolling and both face milling, rough cold rolling, recrystallization annealing and finish rolling are performed . At that time, the rough cold rolling is performed at a processing rate of 80% or more, and the recrystallization annealing is performed. Continuous annealing is performed, the ultimate temperature is 570 to 700 ° C., the holding time is within the range of 10 to 60 seconds, and the finish rolling is performed at a processing rate of more than 30% to 60%, which is perpendicular to the plate surface and parallel to the rolling direction. In the cross section, the average crystal grain size in the direction parallel to the rolling direction is 7 to 15 μm, and the standard deviations of the crystal grain sizes in the parallel direction and the perpendicular direction to the rolling direction are both 1.5 μm or less. The average grain size of a is perpendicular to the rolling direction Excellent stress relaxation characteristics characterized by producing a Cu—Zn alloy plate having an aspect ratio a / b of 1.6 ≦ a / b ≦ 2.6 when the average crystal grain size in the direction is b A method for producing a Cu-Zn alloy plate. 5. The method for producing a Cu—Zn alloy sheet having excellent stress relaxation resistance according to claim 4, further comprising annealing at a low temperature after finish rolling. In the Cu-Zn alloy, the Ni content is 0.1 mass% or less, the Sn content is 0.1 mass% or less, the Fe content is 0.05 mass% or less, and the P content is 0.01 mass% or less. Cu-Zn excellent in stress relaxation resistance according to claim 4 or 5, characterized in that the Al content is limited to 0.1 mass% or less and the Mg content is limited to 0.01 mass% or less. Manufacturing method of alloy plate .