Gee whiz guys, I'm no expert on metallurgy but I do know that all those airplanes we fly on daily have aluminum wing spars and watch 'em flex while you ride. That is unless you fly an oldie with a spruce spar. ( my preference
Any airplanes ever built with steel wing spars? Fuselages, etc. yes (gas welded but that's another subject) but I don't think any wing spars that were successful.