Development of Mixed-Flow Structure Graphite Rotor and Its Effect on Composition Homogeneity of A356 Alloy

Aiming at poor uniformity of composition in A356 alloy obtained by smelting with traditional radial-flow structure graphite rotor, a novel mixed-flow structure graphite rotor was developed. The flow field characteristics of the graphite rotor stirring the molten aluminum under different rotor rotation speeds (350, 450 r · min⁻¹) and different distances between the bottom of the rotor and of the melt pool (1/4, 1/2 of the axial-flow impeller diameter, which was 10, 20 mm) were studied by Fluent simulation method, and the optimal smelting process parameters were determined. A356 alloy castings were prepared with the mixed-flow structure graphite rotor. The uniformity of element distribution was analyzed by one-way variance statistical analysis, the microstructure was observed, and the element distribution and microstructure were compared with those of the alloy obtained by smelting with the traditional radial-flow structure graphite rotor. The results show that when the distance between the bottom of the rotor and the bottom of the melt pool was 20 mm and the rotor rotation speed was 350 r · min⁻¹, the vortices were generated in the molten aluminum, effectively eliminating the deposition of the molten aluminum at the bottom of the molten pool and forming a virtuous circulation flow in the molten pool. The content of each element between and within the specimens of aluminum alloy castings by smelting with the mixed-flow structure graphite rotor was at the significance level α=0.05 confidence interval, indicating no significant difference; the composition of the castings were uniform. the eutectic silicon in the microstructure was small in size, spheroidization was significant, no long strip eutectic silicon was observed, the eutectic silicon was well deteriorated, and the silicon phase was uniformly distributed at α-Al grain boundaries. The composition of the aluminum alloy castings obtained by smelting with traditional radial-flow structure graphite rotor was uneven; there was long strip eutectic silicon in the structure, the eutectic silicon was insufficiently deteriorated, and the silicon phase was uneven at α-Al grain boundaries.