GRAIN-BOUNDARY PRECIPITATES WITH 5-FOLD DIFFRACTION SYMMETRY IN AN AL-LI-CU ALLOY

The note reports the presence of grain boundary precipitates exhibiting diffraction patterns with five-fold rotational symmetry in an alloy similar to that used by Ball and Lloyd but with no Mg. Care must be exercised when identifying the grain boundary precipitate in Al-Li-X alloys to avoid apparent confusion with the equilibrium AlLi ( delta ) precipitate. This particle is the primary grain boundary precipitates observed in this system under the conditions employed and its occurrence leads to a delta prime precipitate free zone.