ABSTRACT
Ultrafine-grained Al samples were fabricated by spark plasma sintering (SPS) of a mechanically milled nanocrystalline powder. The effects of annealing and extrusion on the microstructure and tensile properties of the as-SPSed samples were investigated. Annealing removed the nanopores and caused significant coarsening of Al grains in the interparticle boundary (IPB) regions, leading to the formation of a heterogeneous structure consisting of coarse grains, ultrafine grains and Al4C3/Al2O3 nanoparticles. Hot extrusion also eliminated the nanopores and resulted in the formation of a heterogeneous structure containing enhanced volume fraction of ultrafine grains and finer nanoparticles. These microstructural changes rendered a much improved YS and UTS of 251 and 288 MPa, respectively, and excellent tensile ductility (elongation to fracture: 12.7%). The improvement in mechanical properties can be attributed to grain boundary and nanoparticle strengthening, strain delocalisation of the heterogeneous structure and improvement of the bonding strength of IPBs.
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Notes on contributors
Lei Cao
Lei Cao received a PhD degree in Materials Science and Engineering in 2020 from Shanghai Jiao Tong University.
Yuehuang Xie
Yuehuang Xie received a PhD degree in Materials Science and Engineering in 2020 from Shanghai Jiao Tong University.
Yifei Luo
Yifei Luo is currently a PhD candidate in Shanghai Jiao Tong University.
Jiamiao Liang
Jiamiao Liang is an engineer in School of Materials Science and Engineering, Shanghai Jiao Tong University.
Jun Wang
Jun Wang is a professor in School of Materials Science and Engineering, Northeastern University.
Deliang Zhang
Deliang Zhang is a distinguished professor in School of Materials Science and Engineering, Northeastern University.
Limin Wang
Limin Wang is a senior engineer in Wuhan Nanri Power Engineering Technology Equipment Co. Ltd.