Abstract: The creation of new materials of high resistance and low density is one of the main important concerns of metallurgists, in view of the aeronautic evolution. The aluminium alloys, with lithium, present a particular interest because they represent a gain of weight of 10-15% and offer a good rigidity and ameliorated characteristics. In different cases, the use of these alloys is better than composite materials or other alloys of other systems. Unfortunately, they gain technologic casting properties and consequently, they complicate their putting into form. In the first step, this work is a study of the influence of the addition of elements (Cu, Mg, Li), the modification agents (Ti, Zr, Sc) and impurities(Fe, Si, Ca, Na and other) on linear shrinkage, on the aptitude at the hot and the cold creek formation and the alloy structure of Al-Li-Mg and Al-Li-Cu systems. Then, the study optimizes the chemical composition of the alloys of the examined systems in the aim to increase the strength at the creek formation and the homogeneous wheat obtaining. The influence of the principal allied elements on the susceptibility at the creek formation and the linear shrinkage of the alloys of the Al-Li-Mg and Al-Li-Cu systems. The modification of the alloys of Al-Li-Mg by the addition of Zr and Sc is an efficient mean against the shrinkage on grain. Practically, a recommendation had been proposed on the optimization of the chemical composition of the alloys, according to their principal addition elements, modified by the additives and the impurities in the aim to diminish their fragility by the heat susceptible to the formation of the cold creek and the obtaining of fine grains of homogeneous structure. The application of this recommendation allows diminish or to eliminate totally the scandium grade uncertain alloys.