The difficulty is making a weld that doesn't weaken or anneal the parent metal through heat induced material changes. Welding thick to thin is nontrivial becau

The difficulty is making a weld that doesn't weaken or anneal the parent metal through heat induced material changes. Welding thick to thin is nontrivial because of the different heat input required in each substrate. You tend to burn through the thin part. Patching may be possible but thick patches don't make things any easier.