Effect of stirring speed and temperature on the microstructure and mechanical properties of A356 alloy under vacuum

In this work, an effective method was proposed to purify aluminum alloy melt under stirring and vacuum. The formation mechanism of pore defects and their effects on the mechanical properties of A356 alloy were investigated. The results showed that compared with the untreated alloy, the mechanical properties of the purified A356 alloy were significantly improved. The purification parameters, including stirring speed and stirring temperature, had crucial effects on determining the size of dendrites and pores. The optimized stirring speed and stirring temperatures were 65 rpm and 730 °C, respectively. In this condition, grains with an average diameter of 279 μm and pores having an average diameter of 79.5 μm were obtained; the ultimate tensile strength, yield strength and elongation of the purified alloy reached 203.7 ± 4.3 MPa, 81.6 ± 3.3 MPa and 10.2 ± 0.5%, respectively. The variation in the microstructure and mechanical properties was associated with the bubble breakup mechanism, which accelerated the removal of bubbles in the melt during stirring in vacuum. Furthermore, the interaction between pore and solidified microstructure was also discussed.