There appear to be too many variables for me to feel comfortable with welding an alloy wheel. Exact parent material constituents and finding a suitable filler rod being one of them along with proper pre heating of the rim etc. There is no doubt I'm sure that it can be done correctly but I don't think a lot of repairs are performed in this way and would likely be hugely expensive if they were. Not sure how your insurance company would look at a welded rim in event of an accident. Better to scrap it unless you are supremely confident in the ability of the repairer.