For the shrinkage porosity defect, it is opened at the defect position, as shown in the figure. It is found that the shrinkage porosity defects are distributed on the side far away from the cold iron in the thickness direction, and the depth is about 12mm.
Due to the chilling effect of cold iron, in the solidification process of alloy liquid, the side close to the cold iron first solidifies, and the side far away from the cold iron finally solidifies. In the solidification process, the feeding channel becomes narrower and narrower, and higher feeding pressure is required to realize feeding. Shrinkage porosity is easy to appear in the case of insufficient feeding pressure. When the pressure maintaining and boosting value is sufficient, feeding can be realized. When the feeding pressure is constant, increasing the thickness of cold iron or decreasing the thickness of casting will reduce the feeding channel and increase the tendency of defect formation.
Therefore, the casting thickness, chill thickness and packing pressure have mutual influence on the formation of casting defects, which should be considered comprehensively. At the same time, there is no cold iron in the qualified development of flat parts, which is obviously different from the qualified development of aluminum alloy cabin, bracket and other structural castings.