The peculiarities of the influences of superplastic strain-heat treatment (SPSHT) on the mechanical properties, especially crack resistance, have been established for the aluminum alloy 1420 (Al-Mg-Li). SPSHT of coarse-crystalline (CC) blanks leads to the formation of microcrystalline (MC) structure in them, while a conventional treatment (isothermal forging) produces preferably unrecrystallized structure. The influence of grain refinement and SPSHT is directly manifested in the difficulty of static cracks initiation and in facilitating their growth. Blanks with MC structure and those obtained by superplastic deformation are recommended for the production of the principle parts whose service life is limited by the first crack appearance. When it is necessary to ensure the exploitation of parts with cracks the use of CC blanks manufactured by conventional hot isothermal forming is preferable.