The increase of weight efficiency and flight-technical characteristics of the aircraft engineering is presently the actual task, requiring the constant search for new materials. The aluminum alloys low density (< 2500 kg/m(3)) based on Al-Mg-Li system developed allowed to solve the problem of creating the pressurized sections of the aircraft airframe, where the basic semiproduct are die forgings 1420 alloy. The tensile mechanical properties, low cycle fatigue at axial loading (LCF), the critical stress intensity factor under plain strain (K-1C), fatigue crack growth (FCGR) were determined in forgings of 1420 alloy and its weldments.