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Defect analysis of aluminum alloy die casting flow marks and cold watermarks


  If the surface layer of aluminum alloy wheels produced by gravity casting will have defects such as flow marks and cold watermarks if not handled properly, what measures should be taken to deal with it?

1. Flow mark defect:

Flow mark appearance characteristics: The flow mark defect of aluminum alloy die castings is also called streaks. It is characterized by the appearance of the surface of the castings in the same direction as the flow of the molten metal. Touching with the hand will notice the smooth texture of some depressions. This defect has no development direction and can be removed by polishing.

Causes of flow marks: two metal liquids are not traces caused by filling the cavity at the same time; when the mold temperature is relatively low, it is easy to cause such defects; the aluminum liquid fills the mold too fast; the amount of paint is too much.

Measures to solve the flow mark: adjust the cross-sectional area or orientation of the gate; adjust the temperature of the mold to increase the overflow groove; properly adjust the filling speed to change the flow state of the molten metal to fill the cavity; the coating should be thin and even.

Second, cold insulation defects:

Appearance characteristics of cold partitions: the appearance of die-casting parts has obvious, irregular, depressed linear textures (both penetrating and non-penetrating). The shape is small and narrow, and sometimes the edges are smooth, which may be developed under the action of external forces.

The reason for the cold partition: the temperature of two or more strands of molten soup is too low, and there are traces of overlapping. Metal bonding is very weak. Pouring temperature or mold temperature is low. The liquidity of the molten soup is poor. The sprue position is incorrect or the flow line is too long. Low filling speed and poor exhaust. Injection pressure is lower than pressure. The metal liquid does not flow smoothly in the cavity.

Solution for cold partition: Properly increase the pouring temperature, control it at 640°-680°C, and appropriately increase the mold temperature. Improve injection pressure and shorten filling time. During the debugging process of the die casting machine, the speed of the punch is appropriately increased, and the cross-sectional area of ​​the inner gate is increased at the same time. Improve exhaust gas filling conditions. Choose the appropriate alloy to improve the fluidity of the molten metal. Improve the smooth flow of metal liquid in the cavity. Check whether the wall thickness is too thin (design or manufacturing), the thinner area should be filled directly.

For the flow marks and cold watermark defects that occur during the aluminum alloy die casting process, measures must be taken to avoid affecting the quality and normal use of the die casting.

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