Common Defects and Analysis of Aluminum Casting

ⅠOxidation slag

 Defect characteristics: Oxidized slag is mostly distributed on the upper surface of the casting, at the corners of the mold where no air flow. The fracture is mostly off-white or yellow, which can be found by X-ray fluoroscopy or mechanical processing. It can also be found during alkaline washing, pickling or anodization


  1. The charge is not clean, and the amount of back charge is too much

 2. Poor gating system design

 3. The slag in the alloy liquid is not cleaned

 4. Improper pouring operation brings in slag

 5. After refining and deterioration treatment, the standing time is not enough

Prevention method:

  1. The charge should be sand-blown, and the amount of charge used should be appropriately reduced
  2. Improve the design of the gating system to increase its slag retaining ability

 3. Use proper flux to remove slag

  1. When pouring, it should be stable and pay attention to slag retention

 5. After refining, the alloy liquid should stand for a certain time before pouring

Ⅱ stomata bubble

 Defect characteristics: The pores in the wall of the three Aluminum castings are generally round or oval, with a smooth surface, generally shiny oxide skin, sometimes oily yellow. Surface pores and bubbles can be found by sandblasting, and internal pores. Bubbles can be found by X-ray fluoroscopy or mechanical processing. Bubbles appear black on X-ray film


  1. The Aluminum Castings alloy is not stable, and gas is involved
  2. Type (core) sand mixed with organic impurities (such as coal cuttings, grass roots, horse manure, etc.)

 3. Poor ventilation of mold and sand core

 4. Shrinkage holes on the surface of cold iron

 5. Poor gating system design

Aluminum Castings Prevention method:

  1. Correctly control the pouring speed to avoid getting involved in gas.
  2. No organic impurities should be mixed in the mold (core) sand to reduce the amount of gas generated by the molding material

 3. Improve the exhaust ability of (core) sand

 4. Correct selection and treatment of cold iron

 5. Improve gating system design

Ⅲ Shrimatsu

 Defect characteristics: Aluminum castings generally produce shrinkage porosity at the root of the fly riser near the inner runner, the thick-thin wall transition part and the thin-walled part with a large plane. In the as-cast state, the fracture is gray, and the light yellow is gray after heat treatment, light yellow or gray black. On the X-ray film, it is cloudy and severely filiform. It can be found by X-ray, fluorescence, low-magnification, and other inspection methods.


  1. Poor feeder effect
  2. Too much gas in the charge

 3. Overheating near the sprue

 4. The sand mold has too much moisture and the sand core is not dried

 5. Coarse alloy grains

 6. Improper position of the casting in the mold

 7. Pouring temperature is too high, pouring speed is too fast

Prevention method:

  1. Replenish molten metal from the riser and improve the design of the riser
  2. The charge should be clean and free of corrosion

 3. A riser is set at the shrinkage porosity of the casting, and the cold iron or cold iron is placed in combination with the riser

 4. Control the moisture of molding sand and dry the sand core

 5. Take measures to refine the product

  1. Improve the position of the casting in the mold, reduce the pouring temperature and pouring speed

Aluminum Castings

Ⅳ Crack

 Defect characteristics:

  1. Casting cracks. It develops along the grain boundary and is often accompanied by segregation. It is a kind of cracks formed at a higher temperature that easily appear in alloys with larger volume shrinkage and castings with more complex shapes.
  2. Heat treatment cracks: due to heat treatment overburning or overheating, often appear transcrystalline cracks. The alloys with large thermal expansion coefficients and stresses are often cooled excessively. Or when there are other metallurgical defects


  1. The casting structure design is unreasonable, there are sharp corners, and the wall thickness changes too much.
  2. Poor concession of sand mold (core)

 3. Local overheating of the mold

 4. Pouring temperature is too high

 5. It is too early to take out the casting from the mold

 6. Heat treatment is overheated or burned, and the cooling rate is excessive

Prevention method:

  1. Improve the structural design of castings, avoid sharp corners, strive for uniform wall thickness and smooth transition
  2. Take measures to increase the concession of sand mold (core)

 3. Ensure that all parts of the casting are solidified at the same time or sequentially, and improve the design of the gating system

 4. Lower pouring temperature appropriately

 5. Control the mold cooling out time.

 6. The thermal correction method is used when the casting is deformed.

 7. Correctly control the heat treatment temperature and reduce the quenching cooling rate.



Eternal Bliss Alloy Casting & Forging Co, Ltd.



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