Aluminum Parts Defects and Shrinkage

When aluminum alloy die-casting, the liquid metal contains a lot of gas, and if the smelting is not good at this time

---

[1] Reasons and control methods for the formation of porosity defects in aluminum castings

When aluminum alloy is die-casting, the liquid metal contains a lot of gas. If the smelting is not good at this time, it will lead to the crystallization of the foundation, resulting in the inability of the internal gas to be discharged and the problem of pores.

To control stomata defects, it should be handled strictly according to the process flow during production, the charge should be clean and dry, and even degassing agents should be used to assist exhaust. Attention should be paid to the exhaust link during die casting. Secondly, the die-casting process index should be selected accurately. If the index of the cast aluminum part is not selected accurately, the metal liquid is formed in the mold, or the liquid flow direction is not suitable, the gas in the mold will be difficult to discharge normally, so wrapping will occur. gas.

In order to avoid the formation of encapsulated gas, it is required to select an appropriate filling speed, and reduce the filling speed while forming a complete shape. Moreover, the range of the inner gate should be expanded, so that the flow rate of the metal liquid can be reduced and the occurrence of turbulence can be prevented.

It is also possible to reduce the casting temperature, speed and pressure, thus preventing the formation of entrapped gases. , The mold exhaust ability is not good. During casting, if the mold exhaust performance is poor, the gas will be cooled at the same time as the liquid, so that pores will be formed in the aluminum casting.

This phenomenon is not avoided, and the mold is required to have a good exhaust system to prevent multiple alloy flows from colliding and grinding in the grinding tool. The gate of the mold is the dominant flow state and should be convenient for exhaust to prevent the liquid metal from generating swirls. When planning the inner gate, a margin for mold repair should be left. Only in this way can the injection speed be managed and controlled during casting to reduce the probability of porosity formation.

[2]. Reasons and control methods of external shrinkage of aluminum castings

Reasons for the external shrinkage of aluminum castings: The shrinkage of the alloy is too large; the casting structure is not designed, and there is a hypertrophic position where the thickness and thickness of the cross-sectional area change; the cross-sectional area of ​​the inner gate is too small, or the flow direction of the aluminum liquid is very chaotic; the injection ratio is low ;

The mold exhaust performance is poor, and the air is compressed in the mold wall and castings.
Control method: replace the alloy with low shrinkage, or carry out metamorphic treatment on it, subdivide its grains, and reduce its shrinkage; optimize the design structure of the component, and try to prevent the thick and large positions of the two walls of the thick and thin sections from changing as much as possible. If it is unavoidable, it can be changed to a hollow structure and a block structure; reasonably expand the cross-sectional area of ​​the inner gate; properly increase the injection specific pressure; improve the exhaust performance of the aluminum casting mold, that is, add an exhaust groove, increase an overflow groove, etc.

Set the cooling device at the subsidence position and increase the amount of release agent applied at the position.

---

Previous: Magnesium machining Considerations  Next: Cylinder block casting aluminum casting process

---

Source: @cyanbat   Author: @Joe Li

---