Ultrasonic testing can also be used to inspect internal defects. It uses the sound beam with high-frequency sound energy to propagate inside the casting and finds defects when it encounters internal surfaces or defects and reflects. The magnitude of the reflected acoustic energy is a function of the directivity and nature of the interior surface or defect and the acoustic impedance of such a reflector, so the acoustic energy reflected from various defects or interior surfaces can be applied to detect the presence of defects, wall thickness or surface the depth of the defect. As a widely used non-destructive testing method, ultrasonic testing has the main advantages of high detection sensitivity, which can detect small cracks; large penetration ability, which can detect thick section castings. Its main limitations are: difficult to interpret reflection waveforms for discontinuous defects with complex contour dimensions and poor directivity; for undesired internal structures such as grain size, microstructure, porosity, inclusion content or fine dispersion Precipitates, etc., also hinder waveform interpretation; in addition, it is necessary to refer to standard test blocks during detection.
