EFFECTS OF NEW GRAIN REFINER ALCRNITI ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Al-7Si-BASED ALLOY

In this work, the changes of microstructure and strength of Al-7Si alloys after introducing trace multicomponent AlCrNiTi alloy were studied. The addition contents of AlCrNiTi alloys to the Al-7Si-based alloy were 0.3, 0.6, 0.9 and 1.2 wt% (marked as S1, S2, S3, S4, S5 alloy), respectively. According to the results, the microstructure of Al-7Si alloy was obviously refined with the increase of adding AlCrNiTi concentration. When the introduction concentration of AlCrNiTi alloy was 0.9 wt%, the alpha-Al was significantly refined from coarse dendrites to equiaxed crystals, and its grain size and secondary dendrite arm spacing (SDAS) were reduced by 72.4% and 33.8%, respectively. Additionally, the size of Si phases was also decreased sharply and the roundness was increased from 0.29 to 0.45. Moreover, it was observed that the nano-sized Si phases with the size of 370 nm, bulk Al3Ni phase and AlCrNiTi particles precipitated during solidification. With the addition of AlCrNiTi modifier, the nucleation under-cooling of Si and alpha-Al phases of Al-7Si alloys was decreased by 2.5 degrees C and 5.3 degrees C, respectively. With the modification and refinement of the microstructure in Al-7Si alloy, the mechanical properties have been significantly improved. Compared with the modifier-free S1 alloy, the elongation value (El) of S4 alloy enhanced by 36.7% from similar to 7.9 to similar to 10.8%, and the ultimate tensile strength (UTS) is increased by 12.1% from similar to 173 to similar to 194 MPa.