JPH05133820A - Method for measuring residual stress in surface of mg alloy - Google Patents

Abstract

PURPOSE:To measure a residual stress of a surface part of Mg alloy by performing X-ray diffraction by using CrKalpha as characteristic X rays and a surface with a large diffraction angle as a crystalline surface for measuring conditions of an X-ray diffraction device. CONSTITUTION:When X-ray diffraction of Mg alloy are performed by using CrKalpha as characteristic X rays and a surface with a large diffraction angle as a crystalline surface, an X-ray diffraction curve indicating a vivid diffraction line peak can be obtained. An X-ray diffraction angle (2theta) which is suited for the residual stress measurement is selected out of it and then a stress constant K and a residual stress deltakgf/mm<2> are calculated by an expression I using the diffraction angle and by an expression II, respectively. A diffraction angle of 140.1 degrees of a crystalline surface (202) and a diffraction angle of 152.7 degrees of a crystalline surface (104) are used for an Mg alloy AZ80A and Mg alloy ZK60A, respectively; expression I (K=-Ecottheta0Xpi/[2(1+gamma)X180], where E=4570kgf/mm<2>, gamma/0.35, theta0=70.05 deg. or 76.35 deg.), expression II (delta=K.(2theta)/(SIN<2>PSI), where PSI=X-rays incidence angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the residual stress on the surface of a Mg alloy by using the X-ray diffraction method.

[0002]

2. Description of the Related Art Since the X-ray diffraction method can detect the elastic strain of a minute portion of the surface of a polycrystalline material, it is generally possible to measure the residual stress in an arbitrary direction and is used for measuring the residual stress of many metal materials. It is well known that this is done.

However, although the elastic modulus E and the Poisson's ratio ν are known for Mg and Mg alloys, a method for measuring the residual stress σ using the X-ray diffraction method has not been established.

[0004]

As described above, as for Mg and Mg alloys, there is no established method for measuring residual stress using the X-ray diffraction method. However, when using a Mg alloy, it is necessary to know the residual stress of the surface portion for strength examination and the like. The present invention makes it possible to measure the residual stress with respect to the Mg alloy by establishing the measurement conditions necessary for measuring the residual stress of the surface portion by using the X-ray diffractometer in view of the current situation, and to provide a method therefor. To do.

[0005]

In order to achieve the above object, the present inventors have made various studies on measurement conditions for establishing measurement of residual stress of Mg and Mg alloy by X-ray diffraction method. That is, regarding the relationship between the X-ray diffractometer and the X-ray diffraction curve, measurement of residual stress, X-ray diffraction angle (2θ), stress constant, etc. Considered. As a result, they have found that the residual stress can be measured by performing X-ray diffraction under specific measurement conditions. The present invention has been completed based on the above findings.

The present invention utilizes an X-ray diffractometer and performs X-ray diffraction using CrKα as a characteristic X-ray and a face having a large diffraction angle as a crystal plane under the measurement conditions, and the surface portion of the Mg alloy is measured. This is a method of measuring residual stress.

Then, the Mg alloy AZ80A (JIS 4
The measurement conditions of the X-ray diffractometer for 203 MB3) are CrKα as the characteristic X-ray and (20) as the crystal plane.
The residual stress of the surface portion is measured using the diffraction angle of 140.1 degrees in 2).

In addition, Mg alloy ZK60A (JIS 42
The measurement conditions of the X-ray diffractometer for 03 MB6) are CrKα as the characteristic X-ray and (10) as the crystal plane.
4) The residual stress of the surface portion is measured using the diffraction angle of 152.7 degrees.

[0009]

The above-mentioned measurement conditions, that is, CrK as the characteristic X-ray
When the X-ray diffraction of the Mg alloy is performed using α as a crystal plane having a large diffraction angle, an X-ray diffraction curve showing a clear diffraction line peak can be obtained. Then, an X-ray diffraction angle (2θ) suitable for residual stress measurement is selected from them, and the stress constant K is calculated from the following equation (1) using the diffraction angle,
Further, the residual stress σKgf / mm ² is calculated from the equation (2). K = −Ecot θο × π / [2 (1 + ν) × 180] Equation (1) where E = 4570 Kgf / mm ² , ν = 0.3
5, θο = 70.05 ° (Example 1) or 76.35 ° (Example 2) σ = K · (2θ) / (sin ² Ψ) Equation (2) where Ψ: X-ray incident angle

The above equation (1) is an equation based on the relational expression (Bragg's equation: λ = 2d sin θ) between the diffraction angle 2θ and the diffraction plane spacing d when an X-ray of wavelength λ is incident. That is, when the interplanar spacing of the crystal on the sample surface changes from dο in the unstrained state to dο + Δd due to stress, when the formula is differentiated with the wavelength kept constant, Δθο = θ−θο = tan θ
ο (Δd / dο) =-εtan θο, and the change Δθ in the diffraction angle is measured, so t for lattice strain Δd / dο
anθο is the diffraction angle in the undistorted state, and the same Δd /
The larger tan θο is relative to dο, that is, θο is 9
The closer to 0 °, the larger the angle change and the higher the detection sensitivity.
Therefore, it is desirable that the X-ray diffraction angle (2θ) is large in terms of measurement accuracy.

[0011]

【Example】

Example 1 This invention was applied to the Mg alloy AZ80A (JIS 4203 M
The case of performing B6) will be described. Mg alloy (A
Z80A) A test piece having a size of 30 × 30 × 20 (mm) was cut out from a test material formed by heating and setting up an ingot, and the residual stress was measured by the X-ray diffraction method according to the present invention.

X-ray diffraction of AZ80A alloy by CrKα using an X-ray diffractometer (RAD-2C type manufactured by Rigaku Denki Co., Ltd.) having a strong X-ray source (tube voltage Max.60 KV, tube current Max.30 mA). The peak profile was examined. The result is shown in FIG. As a result, the diffraction angle (2
There are five types of Mg crystal planes in the range of θ) of 40 to 150 °, and clear diffraction line peaks are obtained for all of them. Of the five types of crystal planes, it was examined which crystal plane was suitable for the residual stress measurement. As mentioned above, X
Since the larger the line diffraction angle (2θ), the better, here
It was decided to use 140.1 ° of the (202) plane with the largest θ.

Under the measurement conditions shown in Table 1, using the above test piece, 140.1 ° obtained by investigating the diffraction angle at an X-ray incident angle of 0 ° was used, and the stress constant K was calculated by the above equation (1).
As a result of calculation, −10.72 Kgf / mm ² was obtained.

[0014]

[Table 1]

Then, the X-ray diffraction curve was measured under the measuring conditions shown in Table 1 for the surface residual stress, and the diffraction angle (2θ) was determined by using the half-value width midpoint method. The 2θ-sin ² Ψ diagram is shown in Table 2 and FIG. As a result, when the residual stress value σ was calculated using the equation (2), σ = −5.0K
It was gf / mm ² .

[0016]

[Table 2]

Further, as a result of calculating the 68.3% confidence limit by the equation (3), the confidence limit value Δσ = 1.3 Kgf / mm
A good value of ² was obtained. Δσ = K · ΔM Equation (3)

[0018]

[Equation 1]

[0019]

[Equation 2]

ΔM: 2θ-si due to variations in measured values
Confidence limit of gradient of n ² Ψ diagram t (α, n-2): t distribution of degrees of freedom (n-2), t distribution of confidence limit (1-α)

Calibration test of residual stress by bending test piece In order to carry out a calibration test with a stress value by a strain cage using a bending test piece, a standard 4-point bending test jig of the Japan Society of Materials is used to measure the dimensions. Has a width of 30 mm, a thickness of 3 mm, and a length of 1.
With a bending load applied to the 05 mm bending test piece, X-ray residual stress was measured under the measurement conditions shown in Table 1 using the X-ray diffractometer, and a strain gauge attached to the opposite surface of the bending test piece was used. A comparison with the stress value was made. The results are shown in Table 3 and FIG. From the results, it was confirmed that the difference between the residual stress value according to the present invention and the stress value due to the strain gauge was ± 1.3 Kgf / mm ² or less, and the residual stress of the Mg alloy could be measured by the X-ray diffraction method.

An electrolytic polishing method, which is indispensable for investigating the residual stress distribution in the depth direction on the surface of the test piece, was examined. That is, the electrolytic polishing applied to the residual stress measurement of phosphoric acid (3) + ethyl alcohol (5), which is an electrolytic polishing liquid of Mg alloy, and titanium alloy described in the X-ray stress measurement method edited by the Society of Materials Science, Japan. Using a liquid or the like, the electrolytic voltage and current were examined in the manner shown in FIG. 6, and the polishing rate (polishing depth per hour) was examined. In the apparatus of FIG. 6, 1 is a Mg alloy test piece, 2 is an electrode (stainless steel), 3 is a vinyl chloride cylinder placed on the test piece 1, and is attached with a beeswax 4 and a taping 5. The electrolytic polishing liquid 6 is contained in the cylinder 3.

As a result of the above examination, phosphoric acid (3) + ethyl alcohol (5) chemically react, but hardly react under the condition of electrolysis voltage of 10 to 30V. Perchloric acid (7) + butyl cellosolve (35) + methyl alcohol (59) has a weak reaction under the condition of electrolytic voltage of 20 V, but a current value of 1.6 to 1.3 A is obtained under the condition of 30 V, A polishing rate of 2 μm / 30 sec was obtained. The ammonium chloride saturated solution (70) + glycerin (30) has a current value of 0.4 to 0.8 A at an electrolysis voltage of 20 V, but a current value of 0.8 to 1.5 A is obtained under the condition of 30 V. A polishing rate of 10 μm / 30 sec was obtained. With a 10% sodium hydroxide solution, the electrolysis voltage is 20,
No reaction at 30V.

Example 2 Next, the present invention will be described with reference to Mg alloy ZK60A (JIS 420).
3 MB6) will be described. A test piece was prepared in the same manner as in Example 1, and the residual stress was measured using the same X-ray diffractometer. The result is shown in FIG. As can be seen from the figure, there are 15 types of Mg crystal planes in the range of 2θ of 30 to 110 °, and all have clear diffraction line peaks.
52.7 ° was used.

Under the measurement conditions shown in Table 3, the stress constant K was calculated by the above equation (1) using 152.7 ° obtained by investigating the diffraction angle at the X-ray incident angle of 0 ° using the above test piece.
As a result of calculation, −7.17 Kgf / mm ² was obtained.

[0026]

[Table 3]

Then, the X-ray diffraction curve was measured under the measuring conditions shown in Table 3 for the surface residual stress, and the diffraction angle (2θ) was determined by using the half-value width midpoint method. The 2θ-sin ² Ψ diagram is shown in Table 4 and FIG. As a result, when the residual stress value σ was calculated using the equation (2), σ = −1.2K
It was gf / mm ² .

[0028]

[Table 4]

Further, as a result of calculating the 68.3% confidence limit by the equation (3), the confidence limit value Δσ = 0.5 Kgf / mm
A good value of ² was obtained.

[0030]

According to the present invention, it is possible to establish a residual stress measuring method for Mg alloys using the X-ray diffraction method, and by utilizing the residual stress value in strength studies, various types of Mg alloys can be obtained. Useful for product design.

[Brief description of drawings]

FIG. 1 is a graph showing the results of X-ray diffraction curve investigation of AZ80A alloy in Example 1, where A: (101) in the figure.
Plane, B: (103) plane, C: (112) plane, D: (00
4) plane and E: (202) plane.

2 is 2θ-si of AZ80A alloy in Example 1. FIG.
It is a n < ² > (psi) diagram.

FIG. 3 is a graph showing the results of an X-ray diffraction curve investigation of the ZK60A alloy in Example 2, and the numbers on the diffraction peaks indicate the crystal planes.

4 is a 2θ-si of ZK60A alloy in Example 2. FIG.
It is a n < ² > (psi) diagram.

5 is a graph showing a calibration test result of X-ray residual stress measurement of the AZ80A alloy in Example 1. FIG.

FIG. 6 is an explanatory view of an electropolishing apparatus used for electropolishing a test piece in the present invention.

[Explanation of symbols]

 1 Test piece 2 Electrode 3 Vinyl chloride cylinder 4 Beeswax 5 Taping 6 Electrolyte

Claims (3)

[Claims] 1. An X-ray diffractometer is used, and the measurement conditions are as follows:
A method for measuring a residual stress in a surface portion of an Mg alloy, wherein X-ray diffraction of the Mg alloy is performed using CrKα as a characteristic X-ray and a surface having a large diffraction angle as a crystal plane. 2. The measurement conditions of an X-ray diffractometer are CrKα as a characteristic X-ray and a diffraction angle 14 of (202) as a crystal plane.
Mg alloy AZ80A (JIS420
3MB3) is subjected to X-ray diffraction to measure the residual stress. 3. The measurement conditions of an X-ray diffractometer are CrKα as a characteristic X-ray and a (104) diffraction angle of 15 as a crystal plane.
Mg alloy ZK60A (JIS420
3MB6) is subjected to X-ray diffraction to measure the residual stress.