Never weld alloy...it will take the stength down about 2/3rd's that of the original tempered material.

My first T boat I sailed on when I was a kid had a spliced mast. Dad put it together from two damaged sections laying around the SailCraft of Canada factory.

Had an internal sleeve section and an array of large (1/4"?) Monel rivets. That beast held together for decades. I believe the splice was beteween the hounds & spreaders.
Had to keep a low profile/avert eyes/ /etc. at a class meeting during the CORK regatta as a teenager one summer when they starting talking about a vote to ban "compound" masts that top guys were experimenting with to design in differenential flex charactistics between top & bottom sections...