Abstract
The dependence of strength and fatigue on microstructure of the Al-Cu-Mg alloy has been investigated. Various microstructures of the alloy were produced: the one with a coarse-grained (CG) structure after T6 heat treatment; the one with a homogeneous ultrafine-grained (UFG) structure and the one with a bimodal (mixed) structure, both processed by equal-channel angular pressing (ECAP). The mean grain size and morphology of precipitates were studied by transmission electron microscopy. The ultimate tensile strength and the fatigue endurance limit were determined using the tensile and fatigue tests of standard specimens. It is established that the formation of a homogeneous UFG structure and of a bimodal (mixed) structure alloy contributes to a significant increase in microhardness by 16% and 60%, and an increase of the ultimate tensile strength by 20 and 52%, respectively, as compared to the samples subjected to T6 heat treatment. Fatigue tests show that the alloy with a bimodal (mixed) structure has the highest fatigue endurance limit, 45% higher than in the sample subjected to T6 heat treatment. In contrast, the formation of a homogeneous UFG structure enables increasing the fatigue endurance limit by 15% only.
Highlights
Aluminum alloys of the Al-Cu-Mg system are widely used as structural materials
One of the ways to solve this task is the formation of an ultrafine-grained structure by severe plastic deformation (SPD) [1,2,3,4]
The structural features and mechanical properties of UFG aluminum alloys essentially depend on the regimes of severe plastic deformation and a material's chemical composition, determining the contributions of solidsolution strengthening and precipitation hardening
Summary
Aluminum alloys of the Al-Cu-Mg system are widely used as structural materials. Today, an important task is to enhance their strength and fatigue in order to expand their application areas in the aircraft industry and increase the service life of parts.One of the ways to solve this task is the formation of an ultrafine-grained structure by severe plastic deformation (SPD) [1,2,3,4].It is well known that grain refinement in various metals and alloys is accompanied by a significant enhancement in strength and a decrease in ductility [5,6,7,8]. The structural features and mechanical properties of UFG aluminum alloys essentially depend on the regimes of severe plastic deformation and a material's chemical composition, determining the contributions of solidsolution strengthening and precipitation hardening. UFG materials exhibit enhanced grain-boundary diffusion, which in the conditions of SPD may lead to a decrease in the aging temperature and time, required for the formation of precipitates [8, 9,10,11]. In their turn, the phase composition, volume fraction and size of precipitates may have an essential effect on the strength and fatigue of UFG aluminum alloys. Defining the UFG structure parameters that lead to the enhancement in the strength and fatigue properties of aluminum alloys is an important task
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