I got a wheel of a land rover to weld once, the spokes that had cracked where soft and had cavities in the casting processThe metallurgy of aluminium can change dramatically through welding. Several times I have had a piece of perfectly machinable ally, done some welding on it then tried to machine it afterwards and it was all but impossible to work with. Went from nice chips/swarf to horrid gummy metal which tore up as it was being turned even pulling chunks out of the corners of features.
Find someone who can do it with confidence and experience is all I can suggest. Confidence on its own is not enough IMO any fool can be a confident fool.