Effect of Si content on the transformation of Sc-containing phases and mechanical properties in Al-xSi-Mg-Sc-Zr-Ti alloys

To investigate the influence of Si content on the transition Sc-containing phases in Al Si alloys. Al-xSi-Mg-Sc-Zr-Ti alloys with varying Si contents (0–6.0 wt%) were prepared. The results demonstrate that a minor Si addition (0.5 wt%) promotes an increase in the number density of granular (Al, Si) 3 (Sc, Zr, Ti) precipitates within the Al matrix. Concurrently, the transformation of granular (Al, Si) 3 (Sc, Zr, Ti) particles into needle-shaped AlSi 2 (Sc, Zr, Ti) 2 phases initiates at this composition and is completed upon the addition of 1.0 wt% Si. With further increasing Si content, the growth of the needle-shaped AlSi 2 (Sc, Zr, Ti) 2 precipitates is markedly suppressed, resulting in a gradual reduction in their average size from ∼7.6 μm (1 wt% Si) to ∼2.7 μm (6.0 wt% Si). For mechanical property, as the Si content increases from 0 to 6.0 wt%, the ultimate tensile strength of the alloys significantly improves from 156 MPa to 423 MPa, the elongation decreases from 17.3 % to 7.4 %. This study reveals that Si additions not only facilitate the phase transformation of Sc-containing precipitates but also effectively enhance the mechanical strength of the alloys. • Si content drives the phase transformation of Sc-containing precipitates from granular to needle-like. • The transformation initiates at 0.5 wt% Si and completes at 1.0 wt% Si. • Increasing Si content limits the size of the needle-like AlSi 2 (Sc, Zr, Ti) 2 .