Causes and Solutions for the Air Holes in Aluminum Alloy Die Casting

Aluminum alloy die casting has some advantages that other castings can not compare, such as good looks, light weight, corrosion resistance, so that it is widely favored by users. But aluminum alloy die casting is prone to porosity and impurities, so how to solve this problem?

 

Firstly let’s see how does the air hole forms. During the process of forming and solidifying, the molten metal may have holes on the surface or inside of the casting due to gas intrusion.   Round holes can be formed by the intrusion of paint vapor. When the gas content of the alloy liquid is too high, it will produce round holes. In the solidification process of the metal liquid, shrinkage cavity will also be generated due to the shrinkage of the volume or the final solidification part. Due to the uneven thickness of the casting or local overheating, resulting in a slow solidification in a certain part, surface concave will be formed once the volume shrinks.

 

Due to the presence of porosity and shrinkage cavity in surface,  treatment of die casting is a big trouble. The water may enter into the hole, when painting and electroplating after baking, The gas in the hole expands by heat, or the water inside will become vapor with volume expansion at the same time which resulting in casting surface bubbles. So it’s necessary to use the appropriate methods to solve the causes of these defects in production.  

 

The key to avoid porosity is to reduce the amount of gas mixed into the casting. An ideal metal flow should be continuously accelerated by the nozzle through the diverging cone and runner into the cavity, forming a smooth and consistent direction of metal flow. In order to achieve this goal, the tapered runner design can be adopted, that is the pouring flow should be gradually reduced from the nozzle to the gate. A smooth liquid metal is conducive to gas entering into the overflow tank and exhaust tank from the gate and cavity , and at last going out of the mold.

 

Even heat dissipation and solidification at the same time for different parts during die casting process can avoid shrinkage cavity. And also reasonable nozzle design, gate thickness and position, mold design, mold temperature control and cooling are good solutions to eliminate shrinkage cavity of die casting.

 

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