Numerical and experimental studies on solidification of AZ80 magnesium alloy under out-of-phase pulsed magnetic field

For obtaining the finer grains of magnesium alloy, a novel combined pulsed magnetic field with different initial phases, also called out-of-phase pulsed magnetic field (OPPMF), was applied to study the solidification structure of AZ80 magnesium alloy. The numerical simulation was simultaneously conducted to investigate the refinement mechanisms. The experimental results showed that the macrostructure could be effectively refined by applying external magnetic field. Meanwhile, finer grains were obtained with the higher current intensity. However, the increase of current intensity could only refine the grains to about 0.5 mm. Furthermore, compared to a single pulsed magnetic field (PMF) and alternating series of OPPMF (Connection II), a finer structure was observed when the consecutive series of OPPMF (Connection I) was imposed. In contrast with a single PMF and Connection II, the numerical results showed that the greater axial Lorentz force was obtained under the Connection I, generating the stronger forced flow in the melt. It is believed that abundant nuclei could detach from the mold wall and move faster into the interior melt due to the stronger forced flow; besides, the lower superheat and greater temperature uniformity in bulk melt were realized, accounting for the finest structures under the Connection I.