Effect of Strain Induced Melt Activation Process on the Microstructure and Mechanical Properties of Al-5Ti-1B Treated Al-7Si Alloy

In this study, simultaneous effects of modified strain induced melt activation (M-SIMA) process and addition of Al-5Ti-1B chemical grain refiner on the casting defects, microstructural features, and mechanical properties of hypoeutectic Al-7Si alloys are investigated. The traditional melting and casting techniques were used to develop cast ingots of unrefined and grain refined structures of Al-7Si alloy. Addition of chemical refiner Al-5Ti-1B to Al-7Si melt could significantly change the secondary dendritic arm spacing and eutectic Si particle size to 31% and 28%, respectively. In the M-SIMA process, cast ingots were 60% warm deformed and heat-treated at mushy zone at temperature 585 °C for 30 min. Spherical morphology of α-Al grain and fine fibrous type eutectic Si are observed after M-SIMA process. Grain size of α-Al and eutectic Si are further reduced to 56% and 40% after M-SIMA process of grain refined Al-7Si alloy. Porosity and micro-cracks are also minimized after M-SIMA process. Microstructural features of cast and M-SIMA processed alloys were characterized through optical and scanning electron microscopy. X-ray diffraction techniques reveal the different phases present in the developed alloy. TEM analysis further confirms the presence of TiAl₃ and Ti₇Al₅Si₁₄ precipitates in grain refined Al-7Si alloy. A significant improvement of 132% in hardness (HV), 76% in yield strength, 120% in ultimate tensile strength, 125% in elongation to fracture, and 116% in specific ultimate tensile strength are obtained in M-SIMA processed grain refined Al-7Si alloy. Fractography analysis reveals the mixed mode of fracture in M-SIMA processed Al-7Si alloy with refined structure compared to brittle fracture of unrefined cast alloy.