Cast aluminum is a process in which molten aluminum is poured into a mold and cooled to form aluminum parts of the desired shape. Castings obtained by casting aluminum are called aluminum castings.
During the casting process of aluminum castings, defects such as internal loosening, shrinkage, and porosity are prone to occur. After these castings with defects are machined, the surface dense layer components are removed to expose the internal tissue defects.
The appearance of the defect:
1. Casting crack: It is a crack formed at a higher temperature. It is easy to appear when the volume shrinkage of the casting is large and the thermal expansion coefficient is large.
2. Heat treatment cracks: due to heat treatment overheating or overheating, often showing transcrystalline cracks.
Causes of cracks:
1. The structural design of the casting is unreasonable, with sharp corners, and the thickness of the wall changes too widely. If cracks occur in this case, the structural design of the casting should be improved to avoid sharp corners, and strive for uniform wall thickness and smooth transition.
2. Cracks can also occur in sand molds (cores) with poor yielding properties. Measures should be taken to increase the concession of the sand mold (core).
3. Local overheating of the casting mold will cause cracks. It should be ensured that all parts of the casting are solidified simultaneously or sequentially, and the design of the pouring system is improved.
4. If the pouring temperature is too high, cracks will also occur, and the pouring temperature should be appropriately reduced.
5. When the casting is taken out of the casting mold too early and the casting will be deformed, the thermal correction method should be used to control the cooling time of the casting mold.
6. The heat treatment is overheated, and the crack is generated after the cooling rate is excessively excited. The thermal correction method is used when the casting is deformed. Correctly control the heat treatment temperature and reduce the quenching cooling rate.