The (usually) unseen problem is that the existing metal is now stretched. There is physically more area; just as a curved line between two points is longer than a straight line between the same two points. To bring the mast back to its original strength, the metal must be shrunk.

When working with ferrous alloys, like a car body, this can be accomplished by heating and then striking or quenching. I don't know if aluminum has the same property.