Aluminum would be a bad choice for a lower radiator hose spring. In that small cross section it won't last. Stainless steel, particularly a 300 series alloy, would be a much better choice. The making of such a spring needs thought and care, you don't want it getting loose and working it's way into the water pump. Downside to the spring is it increases the turbulent flow effectively making the ID of the hose smaller.
Better would be to select a hose that has the spring molded into it rather than merely placed inside of it. I'm under the impression that some hoses are made this way, but I can't point to where I might have learned this so it may just be wishful thinking on my part.
