Aluminum alloy casting porosity deviation causes.

1. Refinement in addition to the poor quality of gas produced by the air holes.

In the aluminum alloy casting production process, molten aluminum pouring environment temperature is generally 610 ~ 660 ℃. Under such conditions, many vapors (usually radon gas) melted in lithium bromide solution. Aluminum alloy profile hydrogen solubility and aluminum alloy material environment temperature is closely related. 660 ℃ about liquid aluminum liquid is about 0.69cm3/100g, 660 ℃ about solid aluminum alloy profile is only 0.036cm3/100g. Therefore, when the aluminum alloy profile condensation, aluminum alloy casting is a lot of hydrogen deposition of the way of the vapour bubble.

Reduce the air content in the aluminum liquid, to avoid the aluminum alloy profile condensation of many vapor deposition caused by air holes, is the aluminum alloy profile smelting process in the refining in addition to the effect of gas. If the air content in the aluminum liquid is reduced, the amount of gas accumulated in the condensation will also be reduced, so the bubble will be significantly reduced. Therefore, aluminum alloy profile refining is a crucial processing technology, refining cost-effective, less air holes, refining quality is not good, more air holes. The initiative to protect the quality of refining is to choose a good refining agent. A good refining agent can also be reflected in the 660 ℃ up and down to cause bubbles, the resulting bubbles are not too strong, but is proportional to continue to cause bubbles. According to the physical adsorption, this bubble and aluminum liquid completely touch, suction in the aluminum liquid radon gas, get it out of the liquid level meter. Therefore, the bubble length is not suitable for too short, generally need to have 6~8min bubble length.

Aluminum alloy profile refrigeration to 300 ℃, hydrogen in the aluminum alloy profile solubility is only 0.001cm3/100g or less, this is only after the liquid 1/700. this kind of condensation of hydrogen deposition produced by the out of the gas hole decentralization, pinhole is small, unaffected by the leakage of steam and production of the surface layer, basically invisible to the human eye.

Sand casting aluminum castings aluminum liquid condensation, radon gas deposition produced by the bubble is also larger, mainly in the liquid aluminum last condensation heart. Although they are also decentralized, but these bubbles often cause leakage, the more serious cases often cause product damage.

2. Exhaust pipe is not good caused by the air holes.

In aluminum alloy casting, because the mold exhaust safety channel is blocked, mold exhaust design principle is not good, aluminum die casting link in the concave mold gas can not be completely successful exhaust out, cause some fixed position of the goods occurred porosity. This kind of formed by the mold core of the steam body out of the hole size is not the same, out of the hole cavity is aluminum and oxidation of the air oxidation color. Unlike the air vent produced by radon deposition, the inner cavity of the air vent produced by radon deposition is not as clean as the air vent and has no air oxidation color, but is a light gray inner cavity. To the exhaust pipe is not good caused by the air hole, should improve the mold exhaust pipe safety channel, timely processing mold exhaust safety channel on the residual embossed aluminum plate.

3. Aluminum die casting main parameter unreasonable caused by the air hole.

Aluminum die casting production process aluminum die casting main parameter selection is unreasonable, aluminum liquid aluminum die casting filling rate is too fast, so that the vapor in the die cavity can not be completely immediately successful extrusion concave mold, and the flow of aluminum liquid rolled into the aluminum liquid. Because the aluminum alloy profile surface layer cooling fast, wrapped in the condensation of aluminum alloy shell, can not be discharged, resulting in a relatively large porosity. This kind of air hole is usually in the following workpiece surface, aluminum liquid inlet than the last one connected to the less, pear-shaped or oval, the last condensation and more and more big. For this matter out of the air holes should be adjusted filling rate, so that the aluminum alloy profiles flow liquid stability to promote, will not produce rapid movement and roll gas.

4. Aluminum alloy material shrinks out of the air holes.

Like other materials, aluminum alloy profiles need to be closed in the condensation process. The higher the forging temperature of the aluminum alloy material, the more it closes. Individual holes caused by volumetric consolidation are present in the final condensed portion of the alloy, and are irregular in appearance or, in severe cases, web-like. Usually in the product, it and the solidification process of radon accumulation of holes used together, radon deposition holes or roll out of the gas hole near the shrinkage of the gas hole, near the bubble has reached the outside of the flocculent or mesh structure of the holes.

For this kind of air holes, need to start from the forging environment temperature, in the casting process allows, as far as possible to reduce the liquid aluminum forging environment temperature. That can reduce the volume of casting pieces to close, reduce shrinkage holes and casting defects. If such holes are often in the heating position, you can choose to enhance the core or straight pouring channel, change the final condensation position, to deal with the shortcomings of the leakage.