Microstructures, Tensile Properties and Fatigue Crack Growth Behavior of the Zirconium Modified 2024 Alloys Processed by Liquid Dynamic Compaction

Abstract

In this study, Liquid Dynamic Compaction (LDC) was used to develop rapidly solidified 2024 aluminum alloys modified with small additions of zirconium. Three concentrations of zirconium (0.12, 0.28 and 0.53 wt%) were selected to examine the effect of zirconium on the microstructures, tensile properties and fatigue crack growth behavior of the modified 2024 alloys. The results show that all as-spray deposited materials have acceptable densities (91–95%) and fine equiaxed microstructures with uniform distribution of fine secondary phases, mainly Al₂Cu. Additions of zirconium (0.12 to 0.53 wt%) to the LDC 2024 alloy significantly refined the grain structures. The LDC-produced fine microstructures were retained during the subsequent hot rolling and T4 treatment when the Zr content was greater than about 0.28%. The increase in Zr concentration from 0.12 to 0.28 and 0.53 wt% significantly increased the tensile strength of the modified 2024 alloys. A small amount of Zr (< 0.3 wt%) also improved the ductility. The zirconium modified LDC 2024 alloys exhibited fatigue crack growth resistance superior to those for standard 2024-T3 and experimental LDC 7150-FS, a 7150 alloy with a relatively high concentration of Fe and Si. These beneficial effects are believed to come mainly from the additional precipitation of fine, stoichiometric Al₃Zr particles and refinement of microstructures.