Glossary
Blisters — definition
Raised bumps in the surface caused by trapped gas expanding when the part is heated.
The gas trapped during die casting stays quiet as long as the part is at room temperature. Heat the part — in a solution treatment, during paint curing, or in service — and the gas expands and lifts the surface from within.
This is the concrete reason high pressure die castings are normally not heat treated, and it is also something to watch with powder coating, which cures at elevated temperature.
If a part will be both die cast and heated later, the temperatures it will see should be established early.