Oxidized slag
Defect characteristics: Oxidation slag is distributed on the upper surface of the casting at the corner where the mold is not ventilated. The fractures are mostly grayish white or yellow, which are found by x-ray or during machining, and can also be found during alkaline washing, pickling or anodizing.
Causes: 1. The furnace material is not clean, the amount of recycled material is too much; 2. The casting system is poorly designed; 3. The slag in the alloy liquid is not cleaned; 4. The pouring operation is improper, and the slag is brought into the slag; 5. Refining and deterioration The rest time after processing is not enough.
Prevention method: 1. The charge should be blown sand, and the amount of recycled material should be reduced appropriately; 2. Improve the design of the pouring system to improve its slag blocking capacity; 3. Use appropriate flux to remove slag; 4. It should be stable and should be noted when pouring. Slag blocking; 5. After the refining, the alloy solution should be allowed to stand for a certain period of time.
Two-hole bubble
Defect characteristics: The pores in the wall of the three castings are generally round or elliptical, with a smooth surface, generally shiny scale, sometimes oily yellow. Surface pores and bubbles can be found by sand blasting. The internal pores can be found by X-ray or machining, and the bubbles are black on the X-ray film.
Causes: 1. Casting alloy is not stable, entrapped in gas; 2. Type (core) sand mixed with organic impurities (such as coal chips, grass root horse manure, etc.); 3. Casting and sand core ventilation; 4. Cold iron The surface has shrinkage holes; 5. Pouring system design is poor.
Preventing methods: 1. Correctly control the casting speed and avoid entrapment of gas; 2. No organic impurities should be mixed into the type (core) sand to reduce the gas generation of the molding material; 3. Improve the exhaust capacity of the (core) sand; 4. Correct Selection and treatment of cold iron; 5. Improved casting system design.
Triple shrink
Defect characteristics: aluminum casting shrinkage generally occurs in the thick part of the root of the flying riser near the inner runner, the thick transition of the wall and the thin wall with a large plane. In the as-cast state, the fracture is gray, and the pale yellow is grayish-light yellow or gray-black after heat treatment. It is cloud-like on the x-ray film and is severely filamentous. Shrinkage can be found by inspection methods such as X-ray and fluorescent low-frequency fracture.
Causes: 1. The feeder has a poor feeding effect; 2. The furnace gas contains too much gas; 3. The furnace is overheated near the gate; 4. The sand type is too much, the sand core is not dried; 5. The alloy grain is coarse; The position of the casting in the mold is improper; 7. The pouring temperature is too high and the casting speed is too fast.
Prevention methods: 1. Fill the metal liquid from the riser to improve the design of the riser; 2. The charge should be clean and non-corrosive; 3. Set the riser at the shrinkage of the casting, and place the cold iron or cold iron with the riser; Control sand moisture, and sand core drying; 5. Take measures to refine the grain; 6. Improve the position of the casting in the mold to reduce the pouring temperature and casting speed.
Four crack
Defect features: 1. Cast cracks. Development along the grain boundary, often accompanied by segregation, is a kind of crack formed at higher temperature in the alloy with larger volume shrinkage and more complicated castings; 2. Heat treatment crack: due to heat treatment overheating or overheating, Often through the crystal crack. Alloys that generate large stress and thermal expansion coefficients are often cooled. Or when there are other metallurgical defects.
Causes: 1. The structural design of the casting is unreasonable, with sharp corners, the thickness of the wall is too disparate; 2. The sand type (core) has poor concession; 3. The mold is partially overheated; 4. The pouring temperature is too high; 5. Self-casting The casting is taken out too early; 6. The heat treatment is overheated or overheated, and the cooling rate is too high.
Prevention methods: 1. Improve the structural design of the casting, avoid sharp corners, strive for uniform wall thickness, and smooth transition; 2. Take measures to increase the retractability of sand (core); Ensure that all parts of the casting are solidified or sequentially solidified at the same time, improve the design of the casting system; 4. Reduce the pouring temperature appropriately; 5. Control the cooling time of the mold; 6. Use the heat correction method when casting the deformation; 7. Correctly control the heat treatment temperature, reduce Quenching cooling rate.
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