Which type of porosity occurs when molten alloy is not allowed to fill in during cooling?

Shrinkage porosity occurs when molten alloy does not adequately fill the mold during the cooling process. As the alloy solidifies, it contracts, which can create voids or pores where the material has not filled in completely. This type of porosity is commonly associated with metal casting processes where the cooling and solidification cause the volume to decrease, resulting in an incomplete filling of the mold. The presence of shrinkage porosity can affect the mechanical properties and structural integrity of the final cast product.

In contrast, gas porosity is typically caused by trapped gases that are released during the solidification process. Contraction porosity may not accurately describe the specific phenomenon of incomplete filling due to voluntary withdrawal of material during cooling. Surface porosity refers to defects that appear on the surface of the cast material, often linked to issues like insufficient mold pressure or rapid cooling, but it does not specifically relate to the behavior during the cooling of molten alloy filling a mold. Thus, shrinkage porosity specifically addresses the scenario where incomplete filling of the mold occurs due to the contraction of the material as it transitions from liquid to solid.