Hot plastic behavior of an ultrafine-grained aluminum alloy fabricated by laser powder bed fusion and equal channel angular pressing

Abstract. This research presents the microstructural evolution and mechanical properties of a hypoeutectic AlSi11Cu alloy obtained through laser powder bed fusion (L-PBF) and subsequent severe plastic deformation. The as-built alloy demonstrated a structure formed by an Al matrix surrounded by a Si-enriched cellular network. Tensile tests indicated a yield strength of 350 MPa and elongation to fracture lower than 5% for the as-built material. After subjecting the alloy to severe plastic deformation (SPD) using equal channel angular pressing (ECAP), superior mechanical properties such as an elongation almost twice as high as the as-built condition (12% compared to 6%) and a high tensile yield strength (320 MPa) were observed. ECAP produced average grain size reduction from 10 µm in the as-built state to 1 µm after six ECAP passes. Microstructural analyses highlight in particular the grain refinement of the microstructure after the ECAP process, changing from a microstructure composed of columnar grains to a heterogeneous microstructure characterized by ultra-fine (grain sizes between 200 nm - 500 nm) and elongated grains (grains between 5 µm – 10 µm). This finding supposes a huge improvement for the mechanical performance of this alloy breaking the strength-ductility paradox. The superplastic properties of the materials were characterized, depending on the variation of the temperature and strain rate parameters. This showed that the superplastic behavior was favored by low strain rates (here 0.001 s−1), and by increasing temperature (400 °C). Thus, elongations exceeding 70% were achieved with ECAP material.