Concurrent enhancement of strength and ductility for Al-Si binary alloy by refining Si phase to nanoscale

The present study suggests a novel method of simultaneous improvement of strength and ductility for Al-7 wt% Si binary alloy by tailoring the precipitation of Si phase via high pressure solution treatment (HPST) and subsequent aging treatment. The coarse Si flakes are fully dissolved into Al matrix owing to highly enhanced solubility under HPST, and plenty of nanoscale Si particles re-precipitate during aging treatment. The massive spherical and plate-like Si precipitates effectively improve the yield strength as per Orowan mechanism, and then plastic relaxation including prismatic punching and particle rotation takes place. The prismatic punching near spherical precipitates results in rapid dislocation accumulation, while the rotation of plate-like precipitates leads to dislocation annihilation at interfaces. The dislocation density would be balanced when the proportion of two types of precipitates is reasonable, and then high uniform elongation is achieved. Therefore, introducing two different types of particles acting as dislocation sources and sinks into coarse-grained alloys is crucial to balance dislocation density and achieve excellent mechanical properties.