What defects aluminum alloy casting may appear?

aluminum alloy casting defect

aluminum alloy casting defect

1: 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. cause:
1. The charge is not clean, and the amount of recycled material is too much.
2. Pouring gypsum system design
3. The slag in the alloy liquid is not cleaned
4. Improper pouring operation, bring in slag
5. After the refining treatment, the rest time is not enough
Prevention method:
1. The charge should be blown and the amount of recycled material should be reduced appropriately.
2. Improve the design of the gating system and improve its slag blocking capacity
3. Use appropriate flux to remove slag
4. It should be smooth when pouring and should pay attention to slag
5. The alloy solution should be allowed to stand for a certain period of time before refining. delete

2. Pores, bubbles
Defect characteristics: The pores in the wall 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, and internal pores can be found by X-ray or machining. The pores are black on the X-ray film.
cause:
1. Casting alloy is not stable, and it is involved in gas
2. Type (core) sand mixed with organic impurities (such as coal chips, grass roots, etc.)
3. Poor mold and sand core ventilation
4. Cold iron surface has shrinkage holes
5. Poorly designed gating system
Prevention method:
1. Correctly control the pouring speed to avoid getting in the gas.
2. No organic impurities may be mixed into the type (core) sand to reduce the amount of gas generated by the molding material.
3. Improve the exhaust capacity of (core) sand
4. Correct selection and handling of cold iron
5. Improved casting system design removal

3: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. On the x-ray film, a cloud-like severe filamentous shrinkage can be found by X-ray, fluorescence low-fold fracture and the like.
cause:
1. Poor feeder shrinkage
2. The charge contains too much gas
3. Overheating near the gate
4. Sand type is too much moisture, sand core is not dried
5. Alloy grain coarse
6. Improper position of the casting in the mold
7. Pouring temperature is too high, casting speed is too fast
Prevention method:
1. Replenishing molten metal from the riser and improving the riser design
2. The charge should be clean and free of corrosion
3. Set the riser at the shrinkage of the casting, and place the cold iron or cold iron with the riser.
4. 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.

4, crack:
1. Casting 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 complex castings are prone to appear
2. Heat treatment crack: Due to heat treatment over-burning or overheating, it is often a transgranular crack. Alloys that generate large stress and thermal expansion coefficients are often cooled. Or when there are other metallurgical defects
cause:
1. The design of the casting structure is unreasonable, with sharp corners, and the thickness of the wall changes too much.
2. Sand type (core) poor concession
3. Local overheating of the mold
4. Pouring temperature is too high
5. Premature removal of the casting from the mold
6. Heat treatment overheated or overheated, cooling rate is too fast
Prevention method:
1. Improve the structural design of the casting to avoid sharp corners, uniform wall thickness, smooth transition
2. Take measures to increase the sand (core) concession. Ensure that all parts of the casting are solidified or sequentially solidified at the same time to improve the design of the casting system
4. Properly reduce the pouring temperature
5. Control mold cooling time
6. Thermal correction method for casting deformation
7. Correct control of heat treatment temperature and reduction of quenching cooling rate
Porosity analysis: Among the defects in die castings, the most common ones are the pores.
Stomata characteristics. It has a smooth surface and is round or oval in shape. The form of expression can be on the surface of the casting, or under the needle hole, or inside the casting.

 

Those are some summary about abluminum alloy casting defects, welcome more friends together to rich experiences, and making aluminum alloy castings goes better. 🙂