As an alloy solidifies, the first metal to freeze is purer than the liquid left behind. This causes chemical gradients across individual dendrites and grains, leaving the grain boundaries richer in solute. It weakens the metal and creates localized spots vulnerable to corrosion, but can often be reversed with a homogenization heat treatment.
Heard on the job
The microsegregation in this casting is severe enough that we need to bump the homogenization time up by two hours.
Insider tip
Cooling a casting rapidly minimizes microsegregation by trapping the elements in place before they have time to diffuse away from the freezing front.
Do not mix it up with
- Macrosegregation: Microsegregation happens within single microscopic grains, while macrosegregation spans large sections of an ingot or casting.