Skeletal distribution of silicon phase for high plasticity in hypoeutectic Al-Si alloy

Abstract

Phase selective recrystallization (PSR) has been proposed as an effective method to achieve ultra-high ductility of in as-cast Al-Si alloys. However, the intrinsic reasons for the exceptional ductility are still unclear. Here, the unique skeletal distribution of eutectic silicon phases in PSR-treated Al-Si alloys was investigated to reveal the relationship between the microstructure and mechanical property. The skeletal distribution of silicon phase is composed of three distinct microstructural configurations, silicon phase inside the grain (SIG), silicon phase at the grain boundary (SAG), and no silicon phase inside or outside the grain (NSG). Compared with the as-cast and fully recrystallized samples, the tensile elongation of PSR sample increased ∼18 % and 8 %, respectively. During deformation, SIG initially bears more deformation strain, with void nucleation occurring predominantly in this region until its strain-carrying capacity reaches its upper limit. In the middle and late deformation stages, strain location shifts towards SAG and NSG regions bear more strains, trigger more significant voids nucleation. The reduced strain level in SIG causes early-formed voids to grow slowly, delays the void coalescence and crack propagation. This work provides valuable insights for developing high-performance Al-Si alloys with concurrent strength and ductility enhancement.