Aluminum casting defect characteristics

Feature

1.Casting crack

Development along grain boundaries, often accompanied by segregation, is a kind of cracks formed at higher temperatures, and alloys 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 through crystal cracks. Alloys that generate large stress and thermal expansion coefficients are often cooled. Or when there are other metallurgical defects

cause

1. The structural design of the casting 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. Remove the casting from the mold too early

6. Heat treatment overheating or overheating, cooling rate is too fast

Prevention method

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

2. Take measures to increase the sand type (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 the cooling time of the mold.

6. The heat correction method is adopted when the casting is deformed.

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

The problem is that the aluminum castings have loose structure and high porosity, and contain various metal and non-metal impurities. The anodic oxide film is easily stained with white spots, and the quality of the anodized film of the aluminum casting is difficult to ensure. In this regard, the relevant experts said that the following methods can be used to avoid this problem: First, the high voltage and high current density impact method is adopted. In the initial stage of anodizing, a high voltage and a large current impact are applied, and the "islands" of the size originally divided by the impurities are connected into a sheet by a large current impact. Second, the surface of the casting is polished. Grinding allows the ground aluminum to fill the pores of the casting and act as a bridge connecting the blocks "islands" separated by impurities. Third, the surface of the casting is shot peened. Before the peening method trial, the author used a round-head hammer to knock the method. The original intention was to make the gap of the "island" blocked by tapping and closing to achieve the purpose of connecting into pieces, and the result was remarkable. These methods can effectively avoid the appearance of white spots after dyeing of the anodized film of aluminum castings, thereby ensuring the quality.

Advantages of castings

1. It can produce parts with complex shapes, especially complex internal cavity blanks (such as heating)

2. Wide adaptability, metal materials commonly used in industry can be cast. A few grams ~ hundreds of tons.

3. A wide range of raw materials. The price is low. Scrap, scrap, chip

4. The shape and size of the casting are very close to the parts, reducing the amount of cutting, and there is little machining.