INFLUENCE OF LITHIUM IN THE CHARACTERIZATION AND MECHANICAL PROPERTIES OF THE AL-LI-CU-MG ALLOYS OBTAINED WITH DIRECTIONAL SOLIDIFICATION AND IN THE "AS CAST" CONDITION

ALICIA ESTHER ARES; SERGIO FABIÁN GUEIJMAN; CARLOS ENRIQUE SCHVEZOV

Berlin, Alemania

Otro; THE TWELFT INTERNATIONAL SUMMER SCHOOL ON CRYSTAL GROWTH, ISSCG-12; 2004

The Institute of Crystal Growth (IKZ)

The Aluminum - Lithium Alloys are of important use in the auto and aerospace industry. It is generally accepted that good solidification structures are required for performance. In the present report the solidification structure of these alloys are studied experimentally. Alloys containing Al, Li and Cu were directionally solidified under different conditions of temperature gradients and velocities; the alloys also contained grain refiners. The alloys which were added with refiners were completely equiaxed. The dendritic structure was analyzed with scanning electron microscopy and image analyzer. The secondary dendritic space was measured and the results were compared and correlated with the models available in the literature. In addition, the influence of the lithium on the microhardness and ductility of an investment Al-Li-Cu-Mg alloy in the ?as cast? condition is study. The ductility of the alloy in this condition is of extreme importance, because if it is very low, cracks can occur during fabrication. The alloys were inductively melted down under protective atmosphere of argon, under a pressure of about 40 mbar and they were casted into a ceramic mould at 300°C, in order to obtain tensile specimens. The chemical composition was varied, ranging from 1,1 to 2,8% for Li, 1,0 to 3,6 for Cu, and 0,5 to 1,4 % for Mg (wt%). The alloys showed very poor results for the elongation obtained in the tensile tests. The grain size refinement with Al5Ti1B (5% Ti and 1 % B, wt%) was difficult due to the presence of Lithium, producing grain sizes in the range of 111 to 232 mm. These values seem to be too high for the improvement of the mechanical properties of these alloys.