Abstract
Aluminum alloy die-cast plates (ADC12) were subjected to scanning acoustic microcopy measurement for developing a nondestructive method to detect cold flakes in the die-cast. Acoustic images inside the aluminum die-cast specimen were obtained at 0.1mm interval from 0.5mm to 2mm depth, and compared with optical micrographs of cross-sections at the same depth as the acoustic images. The acoustic images of the cold flakes were good agreement with those observed in micrograph. Then the crack appearance inside the specimen was observed through ultrasonic microscopy during the bending test. The crack can easily start from the surface oxide layer or near the surface (0.1mm〜0.3mm inside), when the oxide layer is perpendicular to the applied stress. But no major effect of the oxide layer parallel to the applied stress on the crack initiation even in the near surface. A crack did not initiate from the inside cold flakes.
