The alkali you used will remove the aluminium residues but not the iron\ nickel \ chrome oxides.
I suggest you try either phosphoric acid or if that does not take it off, muriatic acid should do the trick.
Both are used and commercially available for preparation of metal surfaces (oxide layer removal) for painting.
Note well the precauations stated on the label.
In particular always add acid to water, not the other way round if you dilute the stuff.