采用自行研制的超声换能器和透声楔块,对99mm厚奥氏体焊缝进行了超声扫描成像检测.为消除透声楔块中超声的散射噪声,将检测信号与楔块中的信号进行了相消处理.利用基于匹配追踪和小波分析的信号处理方法,有效消除了焊缝中粗大晶粒造成的材料噪声信号,提高了厚壁焊缝超声检测的信噪比.基于经过信号预处理的超声扫描信号,生成了焊缝的超声扫描图像,并对图像分辨率、缺陷定位精度进行了分析.结果表明:该方法可检测到焊缝试块中φ2人工横孔,实现了奥氏体厚壁焊缝缺陷的超声检测成像.%Ultrasonic scanning imaging was carried out on a 99mm-thick austenitic weld block with self-developed ultrasonic transducers and acoustically transparent wedge. To eliminate the scattering noise from the wedge, testing signals were processed by deducting a signal that is only relative to the wedge. A signal processing method combining matching pursuit and wavelet analysis was proposed to remove the material noise caused by coarse grain. It is proved that the method could effectively enhance the signal-to-noise ratio. Ultrasonic scanning image of the weld block was generated with the preprocessed ultrasonic scanning signals, the resolution of ultrasonic imaging and defect positioning accuracy were analyzed. The results show that the method could find the 2mm-diameter artificial cross-drilled holes in the weld block and construct ultrasonic scanning imaging of the weld.
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