Definition - What does Leafing mean?
Leafing is a term to describe a heavily corroded surface that is physically withering away due to build up and pressure along its grain boundary. Leafing is much more common in aluminum and copper-nickel alloyed metals.
Corrosionpedia explains Leafing
Leafing is a result of intergranular corrosion in which two or more grain boundaries interact in a high force and pressure manner, effectively clashing to expel granular surface microstructure. It often begins at grain-end locations such as edges, holes, and weld points. Material damage due to leafing occurs on a layer-by-layer basis.