Microstructure Refinement of Mg-Gd-Y-Zr Alloy Under Pulsed Magnetic Field

The effects of pulsed magnetic field on the solidified microstructure of Mg-Gd-Y-Zr alloy were investigated.Fine uniform equiaxed grains are acquired in the whole ingot by the pulsed magnetic field treatment,and the average grain size of the as-castφ50 mm and 100φmm ingots is refined to 37μm and 47μm with the pulsed magnetic field.The macrosegregation of solute elements of Mg-Gd-Y-Zr alloy is also reduced by the pulsed magnetic field treatment.Structure refinement is due to the electromagnetic undercooling zone in front of the solid/liquid interface by the magnetic pressure,and reduction of temperature gradient by the vibration of melt resulted from the pulsed magnetic field,which increases the nucleation rate and prohibits dendrite growth.In addition,primaryα-Mg dendrites break into fine crystals,resulting in a refined solidification structure of the magnesium alloys.The Joule heat effect induced in the melt also strengthens the grain refinement effect and the spheroidization of dendrite arms.