Aluminum Cast Alloy Microporosity
Microporosity in aluminum casting alloys arises from inadequate feeding and hydrogen solubility jump, leading to fine voids.
Physical-chemical mechanism of action
Aluminum casting alloys can develop microporosity during cooling. This is caused by insufficient feeding of oxygen and hydrogen, which get trapped in the aluminum crystals. If cooling is too fast or the moisture content in the mold is too high, these voids can form.
Metallurgical relevance & risks in welding
Microporosity can lead to weak spots in the weld, which can crack or form grooves under mechanical stress. It can also impair the permeability to water and other fluids, which is especially relevant in construction.
Workshop practice & action guidelines
To minimize microporosity, controlled cooling of the casting is essential. This can be achieved by slow cooling or by using feeding gases. Suppressing the hydrogen solubility jump is also important. During welding, temperatures and times should be selected so that no additional voids form. A typical goal is a t8/5 time of at least 10 seconds to achieve a homogeneous structure.