There will be some defects when casting the die castings. Today, Longhua Die Casting Machine will take you to analyze the causes and solutions of the defects, and let us take a look.

Porosity and Bubble Analysis of Cast Aluminum Alloy Defects

Defect characteristics: The pores in the wall of the three castings are generally round or oval, with smooth surfaces, generally shiny oxide scales, and sometimes oil yellow. Surface pores and air bubbles can be found by sandblasting, internal pores can be found through X-ray fluoroscopy or mechanical processing. The air bubbles appear black on the X-ray film.

cause:

1. Casting alloy is not stable and is involved in gas

2. Type (core) sand mixed with organic impurities (such as coal dust, grass roots, horse dung, etc.)

3. Poor ventilation of molds and cores

4. Shrinkage on the surface of cold iron

5. Pouring system design for non-casting aluminum alloy defect analysis

Prevention method:

1. Correctly control the pouring speed and avoid being involved in gas.

2. Mould (core) sand must not be mixed with organic impurities to reduce the amount of gas generated by the modeling material

3. Improving the venting ability of (core) sand

4.Proper selection and handling of cold iron

5.Improved design of the pouring system

Defect features: Shrinkage of aluminum castings generally occurs in the thick parts of the riser root near the inner runner, the thickness of the wall, and the thin walls with large planes. In the as-cast state, the fracture is gray, and the light yellow is grayish white or yellowish or grayish black after heat treatment. It is cloud-like and severely filiform on the x-ray film, which can be found by X-ray, low-fluorescence fracture and other inspection methods.

cause:

1. Poor feeding effect of riser

2. Too much gas content in the charge

3.Overheating near the pouring gate

4.Excessive moisture in the sand mold, the core is not dried

5.Coarse alloy grains

6. Casting is not properly positioned in the mold

7. The pouring temperature is too high and the pouring speed is too fast

Prevention:

1. Refilling metal liquid from the riser to improve the design of the riser

2. The charge should be clean and non-corrosive.

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

4.Control sand moisture and core drying

5.Take measures to refine the granules

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

Defect characteristics:

1. Casting crack. It develops along the grain boundary, often accompanied by segregation. It is a crack formed at higher temperatures. Alloys with larger volume shrinkage and more complex shapes are prone to appear

2. Heat treatment crack: caused by heat treatment overheating or overheating. Often, alloys with large stresses and thermal expansion coefficients are cooled excessively. Or in the presence of other metallurgical defects

cause:

1. The structural design of the casting is unreasonable, there are sharp corners, and the thickness of the wall varies too much

2. Poor sand mold (core) concession

3. Local mold overheating

4. Pouring temperature is too high

5. Premature removal of castings from the mold

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

Prevention:

1. Improve the structural design of castings, avoid sharp corners, strive for uniform wall thickness, smooth transition

2. Take measures to increase the concession of the 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 pouring system

4. Reduce the pouring temperature properly

5. Control 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 quenching

The above is the solution to the defects that Longhua Technology has organized for you. I hope it will be helpful to you.