How to analysis the aluminum casting defects?

- Oct 29, 2019-

How to analysis the aluminum casting defects? (part two)

The finished product of casting machine not 100% perfect but have something problem as following(part two):

Three 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, the cloud-like severe filamentous shrinkage can be found by X-ray, fluorescent low-frequency fracture and other inspection methods.

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

Four crack

Defect characteristics:

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 sand (core) concession

3. 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