What is Die Casting Porosity
Porosity refers to the holes or voids in cast metal parts that are originally solid. The size of the pores ranges from microscopic (micropores) to measurable cubic millimeters or larger pores. The cross-section of the hole is not always circular, but it can also take the form of irregular linear cracks.
There are two main reasons for porosity: solidification shrinkage and gas porosity. Let us examine the root causes of these two types more closely, and then we propose strategies to deal with them.
Die Casting Porosity Causes
- Design of molds and castings
- The purity of the metal or alloy used
- Pressure and spray speed of the machine
- Shrinkage of material wall thickness
- Too much lubricant in the mold
- Sharp corners in the mold
- Low metal temperature
- Air trapped in the metal
The most common way to check porosity is to perform an X-ray inspection of the material using computed tomography or by cutting and polishing sections and then analyzing them under a microscope.
Tips for Porosity Prevention
The severity of porosity varies. Sometimes it is acceptable, but in most cases, it is best to limit it as much as possible.
The most direct way to control porosity is to create an effective die casting process with your partners while ensuring the quality of the material. Process monitoring should focus on equipment maintenance and stability, which can help ensure uniform and adequate pressure throughout the casting.
Gas porosity is the bubbles formed inside the casting when it cools. This can be avoided by melting the material in a vacuum or a low solubility gas (including argon). The pores are created because the liquid can naturally remain in the dissolved gas. Sometimes it can be solved by exposing the molten material to another gas-the two gases react and pull each other out of the liquid.
If oxide formation is the cause of porosity, your material will also benefit from proper degassing after melting or filtering before using metal for aluminum pressure die casting or zinc pressure die casting.
Hot tears and hot spots are metallurgical defects that occur due to problems in the cooling process. If this happens, you first need to ensure that the casting is properly cooled in this local area of the part. If the hot spot still exists, you will need to adjust the cooling method by spraying more molds or adding more local cooling channels in the problem area.
