Effect of hot extrusion on mechanical properties and microstructure of near eutectic Al–12.0%Si–0.2%Mg alloy

Effect of hot extrusion on microstructure and mechanical properties of near eutectic casting Al–12.0%Si–0.2%Mg alloy was investigated by mechanical properties testing and microstructure observation using OM (optical microscope), SEM, and TEM. Dynamical recrystallization of Al matrix, dynamical precipitation of deep sub-micron Si and Mg2Si particles and deformation-induced twinning of Si particle occur during extrusion. The mechanism of dynamical precipitation and recrystallization during hot extrusion for near eutectic Al–Si–Mg alloy is concluded according to microstructure observation. The dynamically precipitated particles are thought to play a Zener pinning role on the growth of recrystallized grains, resultantly leading to a much finer grain size of Al matrix. A good combination of tensile strength (256.3 MPa) and elongation (15.0%) when aged for 12 h after post-extrusion solution treatment is mainly due to fine aging precipitates and recrystallized fine grain structure. The negligible aging hardening effect of extruded samples is due to dynamical precipitation of sub-micron Si and Mg2Si particles.