Defect characterization: There are raised small bubbles on the surface of the die-casting parts, which are discovered immediately after die-casting, exposed after polishing or processing, and appear after oil spraying or electroplating. Reason for occurrence: Mainly due to stomata and contraction mechanisms, stomata are often circular, while contraction is mostly irregular.

(1) Reason for shrinkage: During the solidification process of molten metal, shrinkage occurs due to volume reduction or the inability of the final solidification site to be filled by molten metal. Uneven thickness of castings or localized overheating of castings can cause slow solidification in a certain area, resulting in surface concavities when volume shrinks. Due to the presence of pores and shrinkage holes, during surface treatment of die-casting parts, the holes may enter water. When baking after painting and electroplating, the gas inside the holes expands due to heat; Or the water inside the hole will turn into steam, causing volume expansion and resulting in bubbling on the surface of the casting.

(2) Reason for porosity: The gas content in the A alloy liquid is too high, causing precipitation during solidification. When the gas in the mold cavity, the gas emitted by the coating, and the gas precipitated by the alloy solidification are poorly vented, they ultimately remain in the pores formed in precision casting. During the filling and solidification process of liquid metal, gas intrusion can cause the formation of pores on the surface or inside the casting. The gas emitted from the C coating invades. Precision castings