Which metal is lighter than aluminium and that should be highly corrosion resistant ?

Aluminium is lighter and that is camparatively corrosion resistant incase of aluminium alloy . Mg Is lighter than Aluminium but Highly corrosion supportive metal . I need to know some composite materials of my preference . Now -a-days the question which I put upon is the most problematic for Aeronautical Engineers . So try to find soln .