1. Defect distribution characteristics
A total of 188 castings were produced, and the semi-finished products could not be identified by naked eyes. The defects were obvious after finishing, with a defect rate of 100%. The defects were all at the root of the installation surface, as shown in Figure 1. Through X-ray nondestructive testing, there is shadow at the defect position, as shown in Figure 2.
2. Defect analysis
Through the macroscopic characteristics, it is preliminarily judged that the defect is shrinkage porosity. After sampling and analyzing the defective parts and observing them under the scanning electron microscope, dendrite structure can be observed at the defective part, which is further enlarged to 500 times, and the dendrite structure is more obvious. As shown in Fig. 5, dendrite exists. According to the macro and micro comprehensive confirmation, this defect is shrinkage porosity.