Abstract
The effect of Sb modification on the primary α-Al dendrite and eutectic Si in Al-7Si-0.35Mg alloy was investigated, and the Sb modification mechanism of eutectic Si was discussed. The effect of combined addition of B and Sb on microstructure and properties of Al–7Si–0.35Mg alloy was also studied. The results show that the secondary dendrite arm spacing (SDAS) of primary α-Al gradually decreased, and eutectic Si changed from coarse flake into fine lamellar with increase of Sb content. The SDAS decreased from 40.2 μm without modification to 20.8 μm with 0.6 wt% Sb modification, and eutectic Si had the minimum size. SDAS and eutectic Si size increased with an increase of Sb to 0.8 wt%. When Sb was introduced into Al melt, AlSb compounds formed and adsorbed on the growth front of eutectic Si, which reduced the growth temperature of eutectic Si, inhibited the growth of eutectic Si and refined eutectic Si. The primary α-Al changed from coarse dendrite of Sb modification to equiaxed grain when B was added to the melt modified with 0.6 wt% Sb. The primary α-Al of Al–7Si–0.35Mg alloy with combined addition of 0.1 wt% B + 0.6 wt% Sb had the minimum size of 321.8 μm. Its tensile strength, elongation and hardness were 192.8 MPa, 10.80% and 73 HV, which were increased by 16.7%, 117% and 21.6%, respectively, compared with the non-modified alloy. The tensile fracture of non-modified alloy was composed of tearing edges and cleavage planes, showing quasi-cleavage fracture. The alloy with 0.1 wt% B + 0.6 wt% Sb showed the micropore aggregation fracture, consisting of dimples, tearing edges and cleavage planes produced by Si phase.