THE FORMATION OF ORDERED DELTA-'-PHASE IN AL-LI ALLOYS BY DIFFUSE AND SMALL-ANGLE NEUTRON-SCATTERING

The formation of the L12-ordered δ′ precipitates is investigated in AlLi alloys by neutron small angle scattering and by diffuse scattering techniques especially near the [100] ordering wave vector. A comparison of the results obtained gives no evidence for disordered Guinier-Preston zones at low temperatures, in contrast to recent suggestions in the literature. A scaling analysis was applied to the structure function characterizing the small angle scattering data. The results show that the scaled structure function for the higher concentrated Al-10.7 at.% Li alloy is narrower in Q-space than for the Al-8.0at.% Li system. The structure function therefore depends on the concentration but not on the annealing temperature, within the range investigated in this experiment. The narrowing of the structure function near the middle of the miscibility gap indicates the presence of correlations of longer range occurring for more symmetric alloys with respect to the phase diagram. © 1990.