Controlling the Particle Size, Spacing, Distribution, Volume Fraction, and Growth Rate of Intermetallic Particles in Binary Aluminum-Lithium Alloys by Thermal Processing and Composition Control

摘要

The thermal processing history and composition of a solution heat treated and artificially aged binary aluminum-lithium alloy containing 2.6wt.% lithium, and 0.09wt.% zirconium, was correlated to TEM microstructure. Quantitative measurements were made to determine precipitate size, distribution, spacing, morphology, and coarsening rate for both the δ' (Al_3Li) and for composite Al_3Li/Al_3Zr intermetallic precipitates. For all of the aging times studied the composite Al_3Li/Al_3Zr particles were much larger in size than the δ' Al_3Zr free particles. The particle coarsening rate, determined from the Lifshitz-Slyozov-Wagner coarsening rate theory, for the composite Al_3Li/Al_3Zr particles was more accelerated than that of the δ' Al_3Li precipitates. The presence of the Al_3Zr phase was found to accelerate the aging kinetics of the alloy. Therefore, the 0.09 wt.% of zirconium in the alloy resulted in a faster particle coarsening rate of the overall combined particle size distribution, and thus caused the demonstration alloy to precipitation age more rapidly than a pure binary Al-Li alloy. Increasing the aging time also resulted in a smaller percentage of δ' precipitates that deviated from an approximately spherical morphology.