Effect of Ti Addition on the Microstructure and Mechanical Properties of Hypo-Eutectic and Eutectic Al–Si Alloys

To study the effect of Ti–B content on the microstructure and mechanical properties of Al-7Si and Al-12.6Si alloys with Al-5Ti-1B content of 0% and 2%, respectively, were prepared through conventional melting and casting route. The microstructure and mechanical properties of as-cast alloys were investigated, and a correlation has been established between microstructural features (shape, size, and area of eutectic Si, SDAS of primary α-Al, inter-spacing between two nearby eutectic Si particles, and hardness) with strength and ductility of as-cast alloys. Results show that Ti content changes the morphology of primary α-Al grain from dendrite to rosette type in Al-7Si alloy and coarse dendrite to fine columnar dendrite in Al-12.6Si alloy. Eutectic Si particle’s shape and size also change with the addition of Ti to the melt. The thermally stable phase Al₃Ti is associated with Si and forms the Ti₇Al₅Si₁₄ phase. Lower SDAS values, finer dendrite α-Al grains, reduce thickness of eutectic Si particles, homogeneous structure, and minimization of casting defects in 2 wt.% Al-5Ti-1B added Al-12.6Si alloy plays a vital role in enhancing the hardness (71 HV), yield strength (YS, 126 MPa), ultimate tensile strength (UTS, 198 MPa).