Common defects and analysis of the hottest aluminu

2022-08-05
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Common defects and analysis of aluminum castings

oxidation slag

defect characteristics: oxidation slag is mostly distributed on the upper surface of the casting, at the corner of the mold which is airtight. The fracture is mostly grayish white or yellow, which is found by X-ray fluoroscopy or during machining, and the causes of

can also be found during alkali washing, acid pickling or anodizing:

1. the furnace charge is not clean, and the use of recycled charge is too much

2 Poor design of gating system

3. the molten slag in the alloy liquid is not cleaned up

4. improper pouring operation leads to slag inclusion

5 Insufficient standing time after refining and metamorphism

prevention methods:

1. the furnace charge shall be blown sand, and the usage of the returned charge shall be appropriately reduced

2. the design of the gating system shall be improved to improve its slag retaining capacity

3 Proper flux shall be used to remove slag

4. casting shall be stable and attention shall be paid to slag blocking

5. after refining, the alloy liquid shall be kept still for a certain time before casting. Defect characteristics of two air holes and bubbles: the air holes in the wall of three castings are generally round or oval with smooth surface. Both of them may lead to the growth of the world high-tech biomaterial market to ≈ us. around 2030 More than 50000 billion yuan is usually shiny oxide skin, sometimes it is oil yellow. Surface blowholes and bubbles can be found by sand blasting, and internal blowholes and bubbles can be found by X-ray fluoroscopy or machining. The blowholes and bubbles are black on the X-ray film.

causes:

1. the casting alloy is unstable and involved in 1 When handling the hardness meter, the weight and indenter gas must be removed

2. organic impurities (such as coal scraps, grass root horse dung, etc.) are mixed in the mold (core) sand

3. poor ventilation of the mold and sand core

4. test methods for chilled iron ceramic tiles gb/t3810.1 ~ 16 ⑴ 999 shrinkage holes on the surface

5. poor design of the pouring system

prevention methods:

1. correctly master the pouring speed and avoid getting involved in gas

2. the mold (core) sand shall not be mixed with organic impurities to reduce the gas generation of molding materials

3. improve the exhaust capacity of (core) sand

4. correctly select and treat chilled iron

5. improve the design of gating system

three shrinkage porosity

defect characteristics: shrinkage porosity of aluminum castings generally occurs at the thick part of the root of the riser near the inner sprue, at the thickness transition of the wall and at the thin wall with a large plane. When as cast, the fracture surface is gray, light yellow. After heat treatment, it is gray white, light yellow or gray black. It is cloud like on the X-ray film. Serious filiform shrinkage porosity can be found through X-ray, fluorescent low magnification fracture and other inspection methods:

1. poor feeding effect of riser

2. too much air content in furnace charge

CISR has set up a South China Research Institute in Zhongji Zhigu. 3. overheating near the ingate

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

5. the alloy grain is coarse

6. the position of the casting in the mold is improper

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

prevention methods:

1. refill the molten metal from the riser and improve the riser design

2. the furnace charge should be clean and free of corrosion

3. set the riser at the shrinkage of the casting, place the chill or use the chill in conjunction with the riser

4. control the moisture of the molding sand, And sand core drying

5. take measures to refine the grain

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

four cracks

defect characteristics:

1. casting cracks. It develops along the grain boundary and is often accompanied by segregation. It is a kind of crack formed at higher temperature. Alloys with large volume shrinkage and castings with complex shapes are prone to

2. heat treatment crack: it is often a transgranular crack caused by over burning or overheating of heat treatment. It is often over cooled in alloys with high stress and thermal expansion coefficient. Or there are other metallurgical defects.

causes:

1. the casting structure design is unreasonable, there are sharp corners, and the thickness change of the wall is too great

2. the sand mold (core) has poor yielding

3. the mold is locally overheated

4. the pouring temperature is too high

5. the castings are taken out from the mold too early

6. the heat treatment is overheated or overburned, and the cooling speed is too high

prevention methods:

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 solidify at the same time or in sequence, and improve the design of gating system

4. appropriately reduce the pouring temperature

5. control the cooling time of the casting mold

6. thermal correction method shall be adopted for casting deformation

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

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