The Effect of Aging on the Microstructure and Precipitation Response of an Aluminum-Lithium Alloy

The consequence of thermal treatment on the precipitation response of intermetallic precipitates in the microstructure microstructure and subsequent mechanical properties of an Al-2.6wt.%Li-0.09wt.%Zr alloy was studied. The alloy was solution heat treated and artificially aged for a series of aging times and temperatures at various precipitation hardening conditions. The underaged, peak-aged and overaged microstructures of the alloy were analyzed. Quantitative particle size measurements were performed to determine the size, distribution, morphology and coarsening rate for both δ′(Al3Li) and δ′(Al3Li)/Al3Zr precipitates. The average particle size, distribution, spacing and volume fraction of the intermetallic precipitates were related to the heat treating process. For all of the aging times studied, the δ′(Al3Li)/Al3Zr particles were much larger in size than the δ′(Al3Li) and Al3Zr-free particles. The particle coarsening rate, determined from the Lifshitz, Slyozov and Wagner coarsening rate theory, was more accelerated for the δ′(Al3Li)/Al3Zr particles than for the δ′(Al3Li) precipitates. The presence of the Al3Zr phase was found to accelerate the aging kinetics of the alloy. Therefore, a small amount of zirconium in the alloy resulted in a faster particle coarsening rate of the overall combined particle size distribution and thus led to more rapid precipitation aging response.