Improvement of mechanical properties of Al-Si alloy with effective grain refinement by in-situ integrated Al2.2Ti1B-Mg refiner

Abstract

Abstract In order to improve the effectiveness and stability AlTiB grain refiners for cast Al-Si alloys, the present study investigated the grain refinement of cast Al-Si alloys using an in-situ integrated Al2.2Ti1B-Mg master alloy, which was synthesized through two-step chemical reaction to create TiB2 particles and magnesium aluminate (MgAl2O4) phase in the master alloy. Experimental results showed that the fine equiaxed grains were obtained for A356 alloy treated with Al2.2Ti1B-Mg master alloy. In comparison with the α-Al grain size at a level of 950 ± 135 μm and 620 ± 95 μm for A356 alloy without refinement and refined by conventional Al5Ti1B master alloy, the fine grain size of about 320 ± 50 μm could be obtained for A356 alloy refined by Al2.2Ti1B-Mg master alloy. The yield strength, ultimate tensile strength and elongation of the A356 alloy refined by Al2.2Ti1B-Mg was 257±5 MPa, 313±5 MPa and 7.8 ± 0.5% respectively, which was increased by 6% (14 MPa), 3% (8 MPa), and 13% (1.0%) in comparison with that obtained by Al5Ti1B. The improvement of mechanical properties of A356 alloy after treated by Al2.2Ti1B-Mg was attributed to the effective nucleation of α-Al phases. The formation of MgAl2O4 layer on the TiB2 surface was expected to reduce the misfits between TiB2 and Al and promote the nucleation of α-Al, and therefore improve the effectiveness of grain refinement.