FCC lattice
The face-centered cubic lattice contains atoms at the corners and centers of all cube faces, enabling a high number of slip systems and excellent ductility.
FCC lattice, i.e. face-centered cubic, means: atoms sit at the corners and in the center of each cube face. This results in many slip planes, the material can be easily deformed and is tough – typical of aluminum or nickel.
When welding, you have to be careful not to ruin the structure. If you cool incorrectly, the material can become hard and brittle, and then it tends to crack hot. You have to control the cooling so the structure stays stable.
Don't let the weld cool too quickly, then the FCC structure is preserved. For aluminum and nickel, this means: let it cool calmly, no cold air blasts on it. If you control the cooling, you won't have problems with cracks.