Effect of Prolonged Aging and Subsequent Swaging on the Microstructural Evolution and Mechanical Properties of AA6061 Alloy

In the present study, a processing strategy of AA6061 alloy to enhance mechanical properties (strength and ductility) by a combination of precipitation hardening to strain hardening has been proposed. In this study, AA6061 alloy rods that had undergone prolonged aging treatment (at 150 °C for 100 or 500 h) has been cold swaged to a 53% reduction in diameter (true strain ~ 1.5). The microstructure and mechanical properties (in terms of strength and hardness) in the processed samples have been investigated and correlated. The microstructures of as-aged rods of both conditions showed the evolution of similar kind of β″ precipitates (i.e., GP zones II). The obtained good combination of strength and ductility in the as-aged rods is attributed to the evolution of very fine and uniformly distributed β″ precipitates of optimum size and density. The microstructures of as-swaged samples of different conditions revealed that the interaction of β″ precipitates with dislocations played a very important role in the generation of complex dislocation structure which contributes to the strengthening of the deformed alloy. The overall microstructural evolution in samples during cold swaging also controlled by bigger second phase intermetallics/dispersoids. The role of β″ precipitates and bigger second phase intermetallics/dispersoids in microstructural evolution and mechanical properties during aging and subsequent cold swaging are discussed in detail.