Shrinkage Porosity in Al Castings

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Major factors affecting shrinkage porosity:

1. Cooling Rate: Rapid cooling of the molten aluminum can lead to premature solidification and create voids as the metal shrinks during solidification.

2. Geometry and Wall Thickness: Parts with irregular or thick sections are more prone to shrinkage porosity as they cool unevenly.

3. Alloy Composition: The choice of aluminum alloy can impact porosity. Some alloys are more susceptible to shrinkage issues than others.

4. Feeding Systems: Poor design or inadequate feeding systems may not supply enough molten metal to compensate for shrinkage, leading to porosity.

5. Molding and Gating Design: Inadequate gating and riser designs can restrict the flow of metal and exacerbate porosity.

6. Gas Entrapment: Trapped gases, such as hydrogen or air, can create voids in the casting as they try to escape during solidification.

7. Pouring Temperature: The pouring temperature must be carefully controlled to avoid premature solidification.

8. Mold Quality: The quality of the mold and the presence of contaminants can affect the formation of porosity.

The above image shows the dendritic structure in shrinkage porosity with primary and secondary dendritic arms clearly visible.