A low density aluminum based alloy useful in aircraft structure for fuselage sheet or light-gauge plate applications which has high strength, high fracture toughness and high corrosion resistance, comprising 2.7 to 3.4 weight percent Cu, 0.8 to 1.4 weight percent Li, 0.1 to 0.8 weight percent Ag, 0.2 to 0.6 weight percent Mg and a grain refiner such as Zr, Mn, Cr, Sc, Hf, Ti or a combination thereof, the amount of which being 0.05 to 0.13 wt. % for Zr, 0.1 to 0.8 wt. % for Mn, 0.05 to 0.3 wt. % for Cr and Sc, 0.05 to 0.5 wt. % for Hf and 0.05 to 0.15 wt. % for Ti. The amount of Cu and Li preferably corresponds to the formula Cu(wt. %)+5/3 Li(wt. %)<5.2.