Abstract
Equal-channel angular pressing (ECAP) is known to induce significant grain refinement and formation of tangled dislocations within the grains. These are induced to evolve to form low-angle boundaries (i.e., cell boundaries) and eventually high-angle boundaries (i.e., grain boundaries). On the other hand, the precipitation sequence of age hardening aluminum alloys can be significantly affected by pre-straining and severe plastic deformation. Thus, ECAP is expected to influence the T6 response of aluminum alloys. In this study, a complex Al-Cu-Mg-Li-Ag-Zr-Sc alloy was subjected to ECAP following different straining paths. The alloy was ECAP at 460 K via route A, C, and by forward-backward route A (FB-route A) up to four passes. That is, ECAP was carried out imposing billet rotation between passes (route A), billet rotation by +90° between passes (route C), and billet rotation by +90° and inversion upside down between passes (FB-route A). The alloy was also aged at 460 K for different durations after ECAP. TEM microstructure inspections showed a marked influence of the different shearing deformations induced by ECAP on the alloy aging response. The precipitation kinetics of the different hardening secondary phases were affected by shearing deformation and tangled dislocations. In particular, the T1-Al2CuLi phase was the one that mostly showed a precipitation sequence speed up induced by the tangled dislocations formed during ECAP. The T1 phase was found to grow with aging time according to the Lifshitz-Slyozov-Wagner low-power regime.
Highlights
Transmission electron microscopy (TEM) microstructure inspections showed a marked influence of the different shearing deformations induced by Equal-channel angular pressing (ECAP) on the alloy aging response
Boundary pinning β-(Al3 Zr) dispersoids characterized the T6 alloy microstructure. These hardening secondary-phase precipitates were observed by TEM inspections and Figure 2b,c shows representative bright-filed (BF)-TEM micrographs; in particular, Figure 2b,c are TEM micrographs showing the Al111 and Al002 planes, respectively
The TEM inspections and the quantitative analyses of the existing phases allowed to identify the role of the ECAP shearing and post-ECAP aging on the relative fraction of the hardening phases
Summary
Al-Cu-Li based alloys are recognized as important metallic materials for structural applications requiring a combination of high strength, low density, high fracture toughness, and good corrosion resistance [3,5,6,7,8]. All these mechanical and physical characteristics are relevant for aerospace applications [5,6,7]. Weight reduction is widely considered as a primary means to lower fuel cost in the aeronautics and aerospace industry [7].
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