Non-metallic materials of metal casting raw materials: sand casting, in the whole process of pouring, because of the metal casting raw materials, the key is quartz (SiO2) into the metal material liquid, resulting in non-metallic materials mixed. Quartz sand and aluminum do not reflect, in metallographic analysis and observation of the complex corridor is clear square or irregular pattern of small blocks. Because of the high strength of quartz sand, the specimen is often embossed after grinding and polishing.  

Aluminum compound involvement: In the whole process of casting, because the air oxide skin of aluminum accompanies the metal material liquid into the metal mold casting, the compound involvement is generated in the casting. Metallographic analysis showed that the compounds were mixed with gray-black mass flocculent or bent flocculent, and the wheel corridor was not clear. Aluminum compounds can be found throughout the surface and interior of the cast, sometimes through the thickness of stainless steel flanges. Aluminum compound impurity caused by casting parts to produce cold insulation stainless steel flange surface compound impurity, the mechanism is loose and telescopic, shining light inspection luminescence, more serious when looking at the compound impurity inside the casting, X-ray perspective, usually can be found. Compound impurity can be found in low magnification, small magnification and fracture examination.  

Solution impurity: in stainless steel flange casting, because of the selection of a variety of refining agent, covering agent and mildew agent to solve the aluminum alloy water solution, not then, there will be this solution cleaning untidy, resulting in solution impurity.