AFAIK, anodizing is a current limited process, as the voltage rises over time, corresponding to the thickness of the layer. Hard anodize being the highest (around 100V I think?), and typical protective layers being 20-30V.
He would need a rectifier after that transformer, yes.
A welder rated for continuous duty (or cycles in the many minutes at least) would seem quite reasonable. In the 10kVA range, you'll be looking at 3 phase, certainly, which is fine for both an industrial grade machine like that, and for an industrial factory that's already got it available.
One plus: if you do it by transformer alone, you can use a six pulse rectifier to get continuous DC -- full wave rectified 3 phase draws a power factor somewhere around 0.8-0.9 (not unreasonable, though still runs afoul of .eu harmonics regs if that's a concern) and gives output ripple around 20% (who needs filter chokes / caps?).
Tim