Study On Non-destructive Testing Of Friction Stir Welded Joint Defects For Aluminum Alloy

Through continuous development, friction stir welding technology is widely used in the aerospace, ships, automobile manufacturing, high speed railway train manufacturing and other fields, especially for the requirements of light car body of high-speed train, and makes 7N01 aluminum alloy applied in railway vehicle manufacturing.Through the phased array ultrasonic system, this paper recognized weld defect for FSW weld defect detection of 9 mm and 4 mm thick 7N01 aluminium alloy, and analyzed the influence of the defects of the acoustic emission signal characteristic connecting with the stretching process of acoustic emission.The results show that, tunnel defects existed under the condition of the mixing head speed too low or too high, lack of penetration defects in the case of high speed welding, and S line defects under the condition of appropriate heat input.Through the analysis of different detection mode of phased array, we selected sector scan testing, and set excitation chip count 16, low pass high frequency 2.1 to 6.3 MHz ultrasound parameters such as, combined with the standard test block and artificial flaw detection test; With artificial defects detection for reference, 9 mm thickness was determined by one reflection wave detection, 4 mm adopted two reflection wave detection, and successfully detected tunnel defects, lack of penetration defects which can be implmented for positioning and quantitative analysis through A scan images, sector scan images and C scan images, the tunnel defect depth error is about 2%.FSW organization form had influence to detection, attenuation function is strong with the detection of weak signal for compact structure of weld along side; and we analyzed the influence of shape defects for ultrasonic signal at the same time, similar to the size of the tunnel type defects have scattering effect for ultrasonic with the multiple peak static waveform serrated, lack of penetration defects are only a single high crest; Other defect inspection is also affected for the angle of similar lack of penetration and the bottom..In the stretching process of acoustic emission, the existence of lack of penetration and S line defect made the acoustic emission signal increases with smooth tensile fracture organization, and the defects reduced the mechanical properties, deformation ability of the sample.