Inspection device and inspection method for friction stir welding unit

Abstract

To provide a nondestructive inspection technique using ultrasonic waves that can evaluate the bonding strength of a friction stir welding unit.SOLUTION: An inspection device 10 comprises: a transmission unit 20 that causes an ultrasonic wave to propagate internally through an inspection object 15 subjected to friction stir welding; a receiving unit 30 that receives the internally propagated ultrasonic wave 13; a signal processing unit 40 that extracts a frequency component 53 having a wavelength of 0.05 mm to 0.5 mm in a detection signal 43 of the detected ultrasonic wave 13; and a calculation unit 50 that calculates a signal intensity 55 of the extracted frequency component 53.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a non-destructive inspection technique for a friction stir welded portion using ultrasonic waves. [Background technology]

[0002] Ultrasonic testing (UT) is a non-destructive technique for inspecting the surface and internal integrity of structural materials, and is an essential inspection method in a variety of fields. Various methods have also been proposed for imaging the inside of inspection targets, depending on the application.

[0003] Known ultrasonic flaw detection testing methods widely used in industrial applications include a method in which a single piezoelectric element is brought into contact with the test object to transmit and receive ultrasonic waves, and a phased array ultrasonic test (PAUT) method in which multiple small piezoelectric elements are arranged in contact with the test object and emit ultrasonic waves with different timing (delay times).

[0004] Another type of flaw detection testing known as laser ultrasonic testing (LUT) involves irradiating the test object with a pulsed laser to excite ultrasonic waves, and then detecting minute vibrations on the surface using another laser and a laser interferometer. LUT utilizes the advantages of using a laser, making it useful for inspecting narrow or high-temperature areas. As such, it can be applied not only to post-manufacture inspections of products, but also to inspections during manufacturing and inspections of drive parts. Furthermore, laser ultrasonic testing, which has the advantage of being able to inspect without contact, can also be applied to metal materials during welding.

[0005] Friction stir welding is a technique in which materials that have been softened by frictional heat are joined while being stirred. Friction stir welding is generally used to join metals of the same type, but it can also be used to join dissimilar metals, and there are also examples of it being used to join metals and non-metals. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5651533 [Patent Document 2] Japanese Patent Application Publication No. 2022-44319 Summary of the Invention [Problem to be solved by the invention]

[0007] The strength of friction stir welds is generally evaluated comprehensively by combining visual observation, microstructural observation, mechanical strength testing, and non-destructive testing. Ultrasonic testing and X-ray testing, which are commonly used as non-destructive testing, can distinguish between bonded and non-bonded areas, but they have difficulty evaluating bond strength.

[0008] The embodiments of the present invention have been made in consideration of the above circumstances, and have an object to provide a non-destructive inspection technique using ultrasonic waves that can evaluate the joining strength of a friction stir welded joint. [Means for solving the problem]

[0009] The inspection device for friction stir welded portions according to the embodiment includes a transmitting unit that transmits ultrasonic waves internally to a friction stir welded inspection object, a receiving unit that receives the ultrasonic waves that have propagated internally, a signal processing unit that extracts frequency components with wavelengths of 0.05 mm to 0.5 mm from the detection signal of the detected ultrasonic waves, and a calculation unit that calculates the signal strength of the extracted frequency components. [Effects of the Invention]

[0010] According to an embodiment of the present invention, a non-destructive inspection technique using ultrasonic waves is provided that is capable of evaluating the joining strength of a friction stir welded joint. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram showing an inspection device for a friction stir welded portion according to a first embodiment of the present invention. [Figure 2](A) Cross-sectional view of the test object showing the detection position of ultrasonic waves that propagate long distances internally in the bonded area. (B) Cross-sectional view of the test object showing the detection position of ultrasonic waves that propagate short distances internally in the bonded area. [Figure 3] (A) Graph showing the time change in signal strength of frequency components extracted from the ultrasonic detection signal at the detection position in Figure 2(A), (B) Graph showing the time change in signal strength of frequency components extracted from the ultrasonic detection signal at the detection position in Figure 2(B). [Figure 4] An image in which the signal strength of the ultrasonic detection position is associated with the in-plane coordinates of the object being inspected. [Figure 5] FIG. 1 is a plan view of an object to be inspected showing a welded region that was friction stir welded using a rotary tool. [Figure 6] FIG. 2 is a perspective view showing a scanning unit that scans the detection position of ultrasonic waves with a laser scanner. [Figure 7] FIG. 2 is a perspective view showing a scanning unit that scans the detection position of ultrasonic waves using a uniaxial stage. [Figure 8] FIG. 2 is a perspective view showing a scanning unit that scans the detection position of ultrasonic waves using a two-axis stage. [Figure 9] FIG. 1 is an explanatory diagram of a method for inspecting friction stir welding that is carried out simultaneously with construction. [Figure 10] FIG. 10 is a block diagram of an inspection device for a friction stir welded portion, showing a modified example of the first embodiment. [Figure 11] FIG. 6 is a block diagram showing an inspection device for a friction stir welded portion according to a second embodiment of the present invention. [Figure 12] FIG. 10 is a block diagram of an inspection device for a friction stir welded portion, showing a modified example of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] (First embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a block diagram showing an inspection device 10A (10) (hereinafter simply referred to as "inspection device 10A") for a friction stir welded portion according to a first embodiment of the present invention. This inspection device 10A uses a laser ultrasonic method.

[0013] As described above, the inspection device 10A includes a transmitting unit 20 that transmits ultrasonic waves 13 (FIG. 2) internally to the friction stir welded inspection object 15, a receiving unit 30 that receives the internally propagated ultrasonic waves 13, a signal processing unit 40 that extracts frequency components 53 having wavelengths of 0.05 mm to 0.5 mm from the detection signal 43 of the detected ultrasonic waves 13, and a calculation unit 50 that calculates the signal intensity 55 of the extracted frequency components 53.

[0014] In friction stir welding, a cylindrical rotating tool 18 is rotated while its tip is pressed against the surface of an inspection object 15. The inspection object 15 is generally made of the same metal, but it may be made of a combination of dissimilar metals or a combination of a metal and a non-metal.

[0015] Then, the frictional heat generated at the tip of the rotating tool 18 softens the base material region 17 of the test object 15, and the rotational force causes the base material region 17 to plastically flow and mix. This allows the test object 15, which is made up of separated components, to be integrated in the joining region 16. In the illustration, the separated components are shown with their main surfaces overlapping, but they may also be shown with their ends butted together.

[0016] The laser ultrasonic method uses a laser (first laser 21) for transmitting ultrasonic waves to irradiate the test object 15 with ultrasonic waves 13 excited therein, and then detects the ultrasonic waves using a laser (second laser 22) for receiving the ultrasonic waves. This makes it possible to perform remote, non-contact, non-destructive testing to evaluate the joining strength of the friction stir welded joint region 16 of the test object 15.

[0017] The transmitting section 20 of the inspection device 10A is composed of a first light source 11 that emits a first laser 21, a transmission path 26 for the first laser 21 that is composed of an optical fiber or the like, and a transmitting probe 27 that transmits this first laser 21 to the object to be inspected 15.

[0018] The first light source 11 may be, but is not limited to, a laser that can oscillate, for example, an Nd:YAG laser, a CO2 laser, an Er:YAG laser, a titanium sapphire laser, an alexandrite laser, a ruby laser, a dye (dye) laser, or an excimer laser as the first laser 21. The same applies to the second light source 12.

[0019] The first laser 21 uses a pulse wave to excite high-intensity ultrasonic waves 13 with a wavelength of 0.05 mm to 0.5 mm in the inspection object 15. The second laser 22 generally uses a continuous wave (CW) wave, but a pulse wave can also be used.

[0020] The receiving unit 30 of the inspection device 10A also has a second light source 12 that emits a second laser 22 that is irradiated to receive the ultrasonic waves 13 that have propagated internally, and an interferometer 39 that outputs the reflected wave 35 of the second laser 22 reflected from the object of inspection 15 as a detection signal 43.

[0021] The second laser 22 oscillated by the second light source 12 is transmitted through a transmission path 26 formed of an optical fiber or the like and is irradiated onto the inspection object 15 from a receiving probe 37. Of the second laser 22 reflected from the surface of the inspection object 15, a reflected wave 35 that reaches the receiving probe 37 is transmitted through a transmission path 38 and input to an interferometer 39.

[0022] Examples of the interferometer 39 include, but are not limited to, a Michelson interferometer, a homodyne interferometer, a heterodyne interferometer, a Fizeau interferometer, a Mach-Zehnder interferometer, a Fabry-Perot interferometer, and a photorefractive interferometer.

[0023] Fig. 2(A) is a cross-sectional view of the inspection target 15 showing the detection position 14a (14) of the ultrasonic wave 13 where the internal propagation becomes long distance in the bonding region 16. Fig. 3(A) is a graph showing the time change of the signal intensity 55a of the frequency component 53 (Fig. 1) extracted from the detection signal 43 (Fig. 1) of the ultrasonic wave 13 at the detection position 14a in Fig. 2(A).

[0024] 2(B) is a cross-sectional view of the inspection target 15 showing the detection position 14b (14) of the ultrasonic wave 13 where the internal propagation distance is short in the bonded region 16. FIG. 3(B) is a graph showing the time change in signal strength 55b of the frequency component 53 (FIG. 1) extracted from the detection signal 43 (FIG. 1) of the ultrasonic wave 13 at the detection position 14b in FIG. 2(B).

[0025] The minute area on the surface of the inspection object 15 irradiated by the first laser 21 from the transmitter 20 is instantaneously heated, and ultrasonic waves 13 are excited by thermal stress or evaporation reaction force. These ultrasonic waves 13 propagate along the surface of the inspection object 15 and further propagate into the interior of the inspection object 15. The ultrasonic waves 13 that have propagated inside the inspection object 15 are reflected by the rear surface and cause the surface of the inspection object 15 to vibrate minutely with a displacement on the order of nanometers.

[0026] As shown in Figure 1, the second laser 22 emitted by the second light source 12 is transmitted through a transmission path 36 composed of an optical fiber or the like, and is irradiated from a transmitting probe 27 toward a detection position 14 (14a, 14b) (Figure 2). When the second laser 22 is irradiated onto the surface of the test object 15, which is vibrating slightly, a reflected wave 35 with a shifted wavelength due to an optical frequency shift (Doppler shift) is reflected.

[0027] Interferometer 39 detects the Doppler shift of input reflected wave 35 and outputs a detection signal 43 to signal processing unit 40. Signal processing unit 40 has an AD conversion unit 45 that converts detection signal 43 from an analog signal to a digital signal, and a frequency extraction unit 46 that extracts frequency components 53 from detection signal 43 that have wavelengths of 0.05 mm to 0.5 mm.

[0028] Here, the AD conversion unit 45 has a sampling number that allows it to record the frequency band of the ultrasonic wave 13 from the detection signal 43. The frequency extraction unit 46 has a function of extracting, by filtering, a desired frequency component 53 (here, a wavelength of 0.05 mm to 0.5 mm) from the recorded frequency band of the detection signal 43 converted into a digital signal.

[0029] The calculation unit 50 calculates the signal intensity 55 at time intervals that are sufficiently shorter than the period of the frequency component 53. Comparing Fig. 3(A) with Fig. 3(B), it can be seen that the signal intensity 55 (55a, 55b) of the time waveform differs depending on the detection position 14 (14a, 14b) shown in Fig. 2. This is thought to be because, when the ultrasonic waves 13 propagating inside the inspection object 15 contain wavelengths of 0.05 mm to 0.5 mm, a difference occurs in the attenuation rate when passing between the joint region 16 and the base material region 17.

[0030] Alternatively, it is thought that the signal intensity of the ultrasonic waves 13 with a wavelength of 0.05 mm to 0.5 mm propagating inside is highly sensitively affected depending on the distribution and uniformity of the physical properties inside the inspection object 15. Note that for frequency components 53 with wavelengths longer than 0.5 mm, no difference is observed in the signal intensity 55 (55a, 55b) at the detection position 14 (14a, 14b), but for frequency components with wavelengths shorter than 0.05 mm, the accuracy decreases due to the influence of noise components.

[0031] Let us consider the sampling interval for digital conversion in the AD conversion unit 45 (FIG. 1). Assume that the speed of sound in the inspection object 15 is 5000 m / s. In this case, the wavelength of the excited ultrasonic wave 13 reaches the upper limit of the range, 0.5 mm, when the frequency is 10 MHz, and the wavelength reaches the lower limit of the range, 0.05 mm, when the frequency is 100 MHz. In the following, an example of a sound speed of 5000 m / s will be explained, substituting the specified ultrasonic wavelength of 0.05 mm to 0.5 mm with the corresponding frequency of 10 MHz to 100 MHz.

[0032] In this case, the AD conversion unit 45 only needs to have the performance to acquire waveform data information of frequency components 53 between 10 MHz and 100 MHz. For example, when acquiring waveform data information at the lower limit of 10 MHz, at least five sampling points, preferably 10 or more sampling points, are required per waveform. Therefore, the sampling frequency of the AD conversion unit 45 is at least 50 MHz, preferably 100 MHz or higher. When acquiring waveform data information at the upper limit of 100 MHz, the sampling frequency is 10 times that, or 500 MHz, preferably 1 GHz or higher. The sampling frequency of the AD conversion unit 45 is changed according to the speed of sound in the test object 15.

[0033] FIG. 4 shows a screen of the display unit 60 (FIG. 1) displaying an image in which the signal intensities 55 (55a, 55b) of the detection positions 14 (14a, 14b) of the ultrasound 13 are associated with the in-plane coordinates of the object of inspection 15. Such an image can be mapped by scanning the first laser 21 and the second laser 22 or the object of inspection 15 and displacing the detection positions 14. The display unit 60 expresses the signal intensities 55 calculated at each detection position 14 as brightness and displays the image in association with the in-plane coordinates of the object of inspection 15. This makes it possible to distinguish differences in the physical properties inside the object of inspection 15 from the brightness distribution of the image. The display unit 60 can be a general PC monitor or television screen, but it can also be a device with a control function, such as a touch panel.

[0034] 5 is a plan view of the inspection object 15 showing the welded region 16 friction stir welded by the rotary tool 18. In this way, within the welded region 16 in the plan view of the inspection object 15, a first circumstantial line 41 of the first region 31 stirred by the protrusion 49 of the rotary tool 18 is defined. Then, a second circumstantial line 42 of the second region 32 stirred by the main body 48 of the rotary tool 18 is defined. Furthermore, a reference line 44 is set that divides the region sandwiched between the first circumstantial line 41 and the second circumstantial line 42 into half.

[0035] The calculation unit 50 (FIG. 1) further calculates the ratio of signal intensities 55 (55a, 55b) (FIG. 3) of two ultrasonic waves propagated internally at detection positions 14a, 14b inside and outside the reference line 44. Note that each of the detection positions 14a, 14b is defined as the center position of an ultrasonic wave irradiation surface having a certain area. In this way, the display unit 60 (FIG. 1) may display the image shown in FIG. 4.

[0036] Although the rotary tool 18 having the protrusion 49 has been exemplified so far, the reference line 44 can also be defined for a rotary tool 18 that does not have the protrusion 49. In this case, a protrusion 49 with a radius of 0 is assumed, and the locus of the center point of the main body 48 of the rotary tool 18 is defined as the first circumtangent 41.

[0037] 4, it is necessary to acquire detection signals 43 at a plurality of detection positions 14 at different in-plane coordinates of the inspection object 15. Various methods are conceivable, broadly divided into a method of scanning the first laser 21 and the second laser 22 using an optical system mechanism, and a method of moving the inspection object 15. A combination of both methods is also conceivable.

[0038] FIG. 6 is a perspective view showing a scanning unit 65 that uses a laser scanner 65a to scan the detection positions 14 of the ultrasonic waves 13. A galvanometer scanner or the like that controls the irradiation direction using an optical mechanism and scans a laser beam is suitable as this laser scanner 65a. The first laser 21 (21a, 21c, 21d) and the second laser 22 (22a, 22b, 22c) scan along the width and length directions of the bonding area 16 so that the detection positions 14 (14a, 14b, 14c) are spaced at a predetermined pitch. This allows two-dimensional mapping as shown in FIG. 4 to be performed.

[0039] Fig. 7 is a perspective view showing a scanning unit 65 that uses a uniaxial stage 65b to scan the detection position 14 of the ultrasonic wave 13. In Fig. 7, the object to be inspected 15 is moved linearly along the longitudinal direction of the bonding region 16 while the irradiation of the first laser 21 and the second laser 22 is fixed.

[0040] Fig. 8 is a perspective view showing a scanning unit 65 that scans the detection position 14 of the ultrasonic wave 13 using a two-axis stage 65c. In Fig. 7, the object 15 to be inspected is moved two-dimensionally in the width direction and the length direction of the bonding region 16 while the irradiation of the first laser 21 and the second laser 22 is fixed. This makes it possible to perform two-dimensional mapping as shown in Fig. 4.

[0041] 9 is an explanatory diagram of a method for inspecting friction stir welding that is carried out simultaneously with welding. In this embodiment, the inspection device 10A includes a scanning unit 65 that scans the detection position 14 of the ultrasonic wave 13 using a housing 65d that integrates the transmitting unit 20 and the receiving unit 30. Alternatively, the rotation drive unit of the rotary tool 18 and the housing 65d may be fixed, and the inspection object 15 may be moved.

[0042] This allows the housing 65d to follow the movement of the rotary tool 18 that performs friction stir welding. The physical properties of the welded region 16 that has been welded by friction stir welding with the rotary tool 18 can be monitored on the spot immediately after welding.

[0043] FIG. 10 is a block diagram of an inspection device 10B (10) (hereinafter simply referred to as "inspection device 10B") for a friction stir welded portion, which is a modified example of the first embodiment. In the inspection device 10A shown in FIG. 1, the transmitter 20 and the receiver 30 are arranged on one side of the inspection object 15. In contrast, in the inspection device 10B, the transmitter 20 and the receiver 30 are arranged so as to sandwich the inspection object 15. Except for the above differences, the inspection device 10A shown in FIG. 1 and the inspection device 10B shown in FIG. 10 have common configurations and functions, and corresponding components are denoted by the same reference numerals, and redundant explanations will be omitted.

[0044] (Second embodiment) Next, a second embodiment of the present invention will be described with reference to Fig. 11 and Fig. 12. Fig. 11 is a block diagram showing an inspection device 10C (10) for a friction stir welded portion according to a second embodiment of the present invention (hereinafter simply referred to as "inspection device 10C"). Fig. 12 is a block diagram of an inspection device 10D (10) for a friction stir welded portion (hereinafter simply referred to as "inspection device 10D") showing a modification of the second embodiment. These inspection devices 10C and 10D use ultrasonic sensors of piezoelectric elements.

[0045] In the inspection device 10C shown in Fig. 11, the transmitting unit 20 and the receiving unit 30 are arranged on one side of the inspection object 15. In contrast, in the inspection device 10D, the transmitting unit 20 and the receiving unit 30 are arranged so as to sandwich the inspection object 15. Except for the above differences, the inspection device 10C shown in Fig. 11 and the inspection device 10D shown in Fig. 12 have common configurations and functions, and corresponding components are denoted by the same reference numerals, and redundant explanations will be omitted.

[0046] As described above, the inspection devices 10C and 10D according to the second embodiment include a transmitting unit 20 that transmits ultrasonic waves 13 internally to the friction stir welded inspection object 15, a receiving unit 30 that receives the internally propagated ultrasonic waves 13, a signal processing unit 40 that extracts frequency components 53 having wavelengths of 0.05 mm to 0.5 mm from the detection signal 43 of the detected ultrasonic waves 13, and a calculation unit 50 that calculates the signal intensity 55 of the extracted frequency components 53.

[0047] In the inspection device 10C, the transmitter 20 transmits an excitation signal 29 to a transducer 28 (28a) that comes into contact with the inspection object 15 and outputs ultrasonic waves 13. The receiver 30 receives a detection signal 43 from a transducer 28 (28b) that comes into contact with the inspection object 15 and receives the ultrasonic waves 13 that have propagated inside the transducer 28 (28b).

[0048] Here, the transducers 28 (28a, 28b) may be piezoelectric elements commonly used in contact ultrasonic methods, but are not limited to these and may be electromagnetic ultrasonic probes or other devices capable of transmitting and receiving ultrasonic waves. The transducers 28 do not need to oscillate ultrasonic waves 13 covering the entire wavelength range of 0.05 mm to 0.5 mm, but only need to be able to set the center frequency within or near that range.

[0049] In the above explanation, the positional relationship of the transmitter 20 and receiver 30 with respect to the processing surface and the opposite surface of the rotary tool 18 in the joining region 16 is shown in a limited manner, but there is no limitation to this positional relationship.

[0050] According to at least one of the embodiments of the inspection device for friction stir welded portions described above, a non-destructive ultrasonic inspection technology is provided that can evaluate the welding strength of friction stir welded portions by extracting frequency components with wavelengths of 0.05 mm to 0.5 mm from the detected ultrasonic detection signal.

[0051] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as the inventions described in the claims and their equivalents. [Explanation of symbols]

[0052] 10 (10A, 10B, 10C, 10D)...friction stir welding inspection device, 11...first light source, 12...second light source, 13...ultrasound, 14 (14a, 14b)...detection position, 15...inspection object, 16...joining area, 17...base material area, 18...rotating tool, 20...transmitting unit, 21...first laser, 22...second laser, 26...transmission path, 27...transmitting probe, 28...oscillator, 29...excitation signal, 30...receiving unit, 31...first area, 32...second area, 35...reflected wave, 36...transmission path, 3 7...receiving probe, 38...transmission path, 39...interferometer, 40...signal processing unit, 41...first circumferential line, 42...second circumferential line, 43...detection signal, 44...reference line, 45...AD conversion unit, 46...frequency extraction unit, 50...calculation unit, 53...frequency component, 55 (55a, 55b)...signal strength, 60...display unit, 65a (65)...laser scanner (scanning unit), 65b (65)...uniaxial stage (scanning unit), 65c (65)...biaxial stage (scanning unit), 65d (65)...housing (scanning unit).

Claims

1. a transmitter for transmitting ultrasonic waves to the interior of the friction stir welded inspection object; a receiving unit that receives the ultrasonic waves that have propagated inside; a signal processing unit that extracts frequency components having a wavelength of 0.05 mm to 0.5 mm from the detected ultrasonic wave detection signal; and a calculation unit that calculates the signal intensity of the extracted frequency component.

2. The inspection device for a friction stir welded portion according to claim 1, The signal processing unit an AD converter having a sampling number capable of recording the frequency band of the ultrasonic wave and converting the detection signal from an analog signal to a digital signal; and a frequency extraction unit that filters the detection signal converted into the digital signal to extract the frequency component.

3. The inspection device for a friction stir welded portion according to claim 1, defining a first circumstantial line of a first region stirred by a protrusion of a rotary tool in a welding region in a plan view of the inspection object; defining a second circumscribing line of a second region stirred by the body of the rotary tool; a reference line that divides an area sandwiched between the first circumferential line and the second circumferential line into halves; The friction stir weld inspection device further calculates a ratio of the signal intensities of the two ultrasonic waves propagated internally at detection positions inside and outside the reference line.

4. The inspection device for a friction stir welded portion according to claim 1, The transmission unit a first light source that oscillates a first laser that is irradiated to excite the ultrasonic wave in the inspection object; The receiving unit a second light source that oscillates a second laser that is irradiated to receive the ultrasonic waves that have propagated inside; an interferometer that outputs the reflected wave of the second laser reflected from the object to be inspected as the detection signal.

5. The inspection device for a friction stir welded portion according to claim 1, the transmitting unit transmits an excitation signal to a transducer that contacts the test object and outputs the ultrasonic wave; The receiving unit receives the detection signal from a vibrator that has come into contact with the object to be inspected and inputs the ultrasonic waves that have propagated inside the object.

6. The inspection device for a friction stir welded portion according to any one of claims 1 to 5, a scanning unit that scans the detection position of the ultrasonic waves that have propagated inside; a display unit that displays the signal strength calculated at each of the detection positions displaced during the scanning in association with the in-plane coordinates of the object to be inspected.

7. The inspection device for a friction stir welded portion according to any one of claims 1 to 5, The apparatus for inspecting a friction stir welded portion is such that the transmitting unit and the receiving unit are arranged to sandwich the inspection object or to one side of the inspection object.

8. Propagating ultrasonic waves inside a friction stir welded test object; receiving the internally propagated ultrasonic waves; extracting frequency components having a wavelength of 0.05 mm to 0.5 mm from the detected ultrasonic wave detection signal; and calculating the signal intensity of the extracted frequency component.

9. 9. The method for inspecting a friction stir welded portion according to claim 8, wherein the ultrasonic waves are propagated inside the friction stir welded portion in accordance with the movement of a rotary tool.

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