Influence of Al-Ti-B addition on the microstructure and mechanical properties of A356 alloys

The mechanical properties (σ _b, σ _0.2, and δ) and fracture behavior of tensile specimens of the refined A356 alloys were investigated as a function of the addition level of Al-Ti-B master alloy under both as-cast and T6 heat-treated conditions. The results show that as the addition level of Al-5Ti-1B master alloy increases from 0.1 wt.% to 5.0 wt.%, the mechanical properties of refined A356 alloys improve steadily and then decrease slightly under both as-cast and T6 heat-treated conditions. Also, they display excellent mechanical properties with σ _b = 231.30–258.30 MPa, σ _0.2 =134.00–155.50 MPa, and δ = 8.5%–11.75% at T6 heat-treated state. The excellent mechanical properties of refined A356 alloys are ascribed to the formation of α-Al equiaxed dendrites, the improvement of eutectic structure from needle/plate-like to short-lathy/block-shaped, and the Mg₂Si aging precipitation phase after T6 heat treatment. The fracture surface examined by SEM exhibits a mixed fracture mode of refined A356 alloys at as-cast state, while it reveals a ductile fracture mode after T6 heat treatment.