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Understanding Porosity in Die Casting

What is Porosity, its types and how we can help you?

Die casting is a process involving the injection of liquid metal into a steel die to shape a die cast component. The filling and solidification happens rapidly under high pressure, and the part easily "freezes." The very design of this process of rapid cycling creates castings which contain some degree of porosity.

What is porosity?

The porosity in the die casting occurs when the air pocket is formed because the air or gas is trapped in the metal as it solidifies (gas porosity), or when the metal shrinks away from thick sections and into thin sections, leaving voids in the center (shrink porosity).

Gas Porosity

The formation of "bubbles" is a sign that the gas is trapped inside the die-cast part, which indicates the porosity of the gas. These pores may cause surface blisters to form when they are close to the surface of the casting. The die casting engineer will take a look at venting, gating, lubrication, an increase in time during the die, and other factors that may contribute to the defect.

Shrinkage Porosity

Such pores are larger and of an irregular nature, occurring in heavy die casting pieces. Shrinkage porosity reduces the integrity of the die-cast component, particularly when machining operations are located in close proximity to the pores. The die cast engineer must look at the possibility of removing thick walls and redesigning the portion where the porosity of the shrinkage occurs.

Porosity can be influenced by:

  • Part Design

  • Material cleanliness

  • Die Design

  • Metal & Die Temperatures

  • Die Casting Machine Pressure

  • Spray or Mold release

  • Shot Speed

  • Wall Thickness

  • Shrinkage

A simple knowledge of the die casting process is helpful to get a better understanding of porosity formation.

Die Casting 101

Die casting is a procedure involving the positioning of the molten metal within a shot cylinder. A piston uses a considerable amount of force and speed to inject the liquid metal into the die mounted on a machine. The system provides the power to inject the metal and keep the die shut down before solidification occurs which is assisted by the use of water or oil cooling in the die. The unit then opens the die and moves forward to force the component out of a set of ejector pins, built into the die.

For every die cast component, the process is repeated.

Exclusive Magnesium die casts all three of the most common alloy families; aluminium, magnesium , and Metal Matrix Composites. We employ state-of-the-art engineering systems to design the dies and to improve the process parameters to help reduce porosity. Request a callback or get a budgetary quote for your product by writing to us at

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