Cause of formation
During the casting solidification process, the aggregation of certain elements is caused by the selection of crystallization and diffusion, resulting in uneven chemical composition. According to the different positions of the distribution, it can be divided into ingot type, center and point segregation.
On the acid immersion sample, when the segregation is an erodible substance or a gas inclusion, the color is dark and the shape is irregular, slightly depressed, the bottom is flat, and there are many dense micropore spots. If the resist element is aggregated, it is a slightly convex, irregularly shaped, relatively smooth micro-convex spot.