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Achieving high strength and large ductility of an ultrafine‑grained 211ZX aluminium alloy processed by improved thermomechanical processing

Luo Tao, Lei Lei, Feng Ke, Yang Ming, Jiang Yun

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 2

art. no. e127, 2023

Simultaneously achieving high strength and ductility has been a long-standing goal in aluminum alloys, while the increase in strength usually leads to ductility loss. In this study, a novel thermomechanical treatment (TMT) method, i.e., pre-existing precipitation in coarse grain (CG) and cryogenic rolling plus warm rolling followed by peak aging, is developed to achieve high strength and good ductility in 211ZX aluminum alloy. As a result, a composite nanostructure including ultrafine-grained (UFG) and nanoprecipitation is obtained. Compared to a conventional T6 sample, the multi-step TMT sample has a finer grain (205 nm), while numerous GP zones and θ" phases are dispersed inside the grain. The precipitation characteristics are similar to the T6 sample. The yield strength (635 MPa) and ultimate tensile strength (690 MPa) are about 81% and 53% higher than the T6 sample, respectively, with only a slight decrease in plasticity. Microstructural characterization and thermodynamic analysis confirmed that pre-existing precipitates and cryogenic temperatures facilitate the formation of the composite nanostructure. Quantitatively strengthening calculations demonstrate that the high strength is attributed to the ultra-fine grain strengthening and precipitation strengthening, while the high plasticity is mainly due to the reduction of dislocation density caused by recovery and recrystallization during the aging process as well as the massive production of nano-GIPs (interior grain precipitates).

Grain refinement in aluminium and the aluminium Al-Cu-Mg-Mn alloy by hydrostatic extrusion

Lewandowska M., Garbacz H., Pachla W., Mazur A., Kurzydłowski K. J.

Materials Science Poland

2005

Vol. 23, No. 1

279--286

Hydrostatic extrusion was used as a method for grain refinement in technically pure aluminium andin an aluminium alloy. Both materials were deformed up to a true strain of ~4. Such a deformation resulted in substantial grain size refinement to below 1 žm in aluminium and below 100 nm in the aluminium alloy. In pure aluminium, microstructure evolution proceeds by a continuous increase in the grain boundary misorientation, without changing the grain size. In the aluminium alloy, which has lower stacking fault energy, grains continuously decrease in size, down to the nanometre scale. As a consequence of such microstructure evolutions, the mechanical properties of pure aluminium remain almost constant within a wide range of strains, whereas the mechanical properties of the aluminium alloy are significantly improved. From the present study, one can conclude that hydrostatic extrusion can offer an alternative way to produce nano-metallic elements made of aluminium alloys for light-weight applications.