Intergranular Attack
This is a view of 6061 - T6 in cross-section. The corrosion was lab induced for this specific photo. The interesting thing about intergranular attack (IGA) or intergranular corrosion (ICG) is why the corrosion attacks this way. The grain itself is resistant to the attack, yet the percipients along the grain boundaries are allowing this solution to attack it. This corrosion was induced with a salt water solution for about 6 hours with the use of a catalyst.