Softening zone

The softening zone occurs in cold-worked or age-hardened aluminum alloys when the heat from welding changes the microstructure. This causes the material to lose strength at the weld, becoming softer and more prone to failure under load. This is especially critical for alloys that get their high strength from heat treatment. You need to keep the heat input during welding as low as possible to keep the zone small. If the parts will later bear high loads, it's often necessary to re-harden and age them after welding to restore the original strength.