Effects of annealing and extrusion on the microstructure and tensile properties of ultrafine-grained Al fabricated by spark plasma sintering

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.

KEYWORDS:

• Spark plasma sintering
• interparticle boundaries
• annealing
• hot extrusion
• heterogeneous structure
• mechanical properties

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work were supported by National Natural Science Foundation of China [Grant Number 51971143], SJTU Global Strategic Partnership Fund [Grant Number 2019 SJTU-UNSW] and State Grid Science and Technology Project of China [Grant Number SGLNDK00SPJS1800055].

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.